the Creative Commons Attribution 4.0 License.
the Creative Commons Attribution 4.0 License.
| 25 Mar 2026
The Northernmost Mountain Belt on Earth: Birth and Death of the Eurekan Orogen in North Greenland
Abstract. The >1000 km long Eurekan Belt is the northernmost mountain belt on Earth and formed as an intraplate orogen in response to Cenozoic plate reorganization of the North Atlantic–Arctic region. Eurekan deformation is well documented on Ellesmere Island, North Greenland and Svalbard. In North Greenland, the general orientation of the Eurekan Belt changes. The kinematic and temporal relationships between the differently trending fault systems of North Greenland remain poorly constrained. This study aims to explore the relationship between the major fault systems of North Greenland by providing a temporal framework for their kinematics. We present new low-temperature thermochronological data, including the first apatite (U-Th)/He ages from North Greenland, complemented by apatite fission track analyses and apatite U–Pb dating of mafic dykes. Thermal history models indicate a short-lived heating period during the latest Cretaceous (~70–65 Ma), with temperatures exceeding 120 °C, likely associated with a Late Cretaceous basin along the margin of North Greenland. The models imply repeated reactivation of the Kap Cannon Thrust Zone, the Harder Fjord Fault Zone and the Trolle Land Fault System during the Palaeocene, early and mid-Eocene, and Oligocene. The differently oriented fault systems constitute a coherent system, interpreted as part of the De Geer Fracture Zone, that was repeatedly reactivated under changing stress fields. The exhumation episodes of North Greenland were synchronous with those of adjacent regions of the Eurekan Belt. Oligocene exhumation of North Greenland can be linked to tectonic reorganization of the northern North Atlantic and the opening of the Proto-Fram Strait, which likely developed along pre-existing structural weaknesses. Together, these findings highlight the role of structural inheritance, thermal weakening, and fault reactivation in intraplate orogeny and provide temporal constraints on the tectonic and topographic evolution of the Arctic relevant to paleogeographic and high-latitude environmental reconstructions.
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Status: open (until 31 May 2026)
- CC1: 'Comment on egusphere-2026-1389', Jaroslaw Majka, 01 Apr 2026 reply
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CC2: 'Comment on egusphere-2026-1389', Christian Schiffer, 02 Apr 2026
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Very comprehensive paper, which I will read great interest.
There is some pioneering geophysical work on the crustal structure of Ellesmere Island that I noticed has not been considered. This is, of course, not North Greenland, but the only(?) crustal-scale geophysical data across the Eurekan, so highly relevant for an overview of the Eurekan Orogen. There are several more publications, but I think at least the following two should be discussed:
An integrated geological-geophysical cross-section (Stephenson, R., Piepjohn, K., Schiffer, C., Von Gosen, W., Oakey, G.N. and Anudu, G., 2018. Integrated crustal–geological cross-section of Ellesmere Island).
There is earlier work by Oakey and Stephenson that should be integrated (Oakey, G.N. and Stephenson, R., 2008. Crustal structure of the Innuitian region of Arctic Canada and Greenland from gravity modelling: implications for the Palaeogene Eurekan orogen. Geophysical Journal International, 173(3), pp.1039-1063.)
Citation: https://doi.org/10.5194/egusphere-2026-1389-CC2 -
RC1: 'Comment on egusphere-2026-1389', Jean-Baptiste Koehl, 09 Apr 2026
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Review of Meier et al. (2026)
Dear Sir, Madam,
thank you very much for inviting me to review this interesting work. Here are my suggestions to the authors to help improve the manuscript. Please do not hesitate to contact me, shall some comments be unclear. I look very much forward to receiving the response from the authors and, should it be needed, discussing further suggestions in (a) potential subsequent review round(s).
Sincerely,
Jean-Baptiste Koehl
Summary
I see great potential for the interesting data presented here. However, it is underexploited in its current form, especially in the Discussion chapter, which focuses on fitting the obtained dataset into one specific model (e.g., Piepjohn et al., 2016 their figs. 7 and 9). This model includes one paleo transform fault now well-known to be erroneous (Wegener Fault) and another highly doubtful (De Geer Zone). Models proposed by other research groups not part of Dr. Piepjohn’s network need to be discussed systematically especially recent studies in Arctic Canada, Svalbard, and the Barents Sea, to balance the Discussion and present an objective perspective. A major question I have to the lead author of the present manuscript is “What do you think?”. Despite my numerous comments, which only reflect my interest in this work, and the suggested major revisions, especially for the Discussion and Conclusions chapters, I strongly believe that the data presented could provide a fresh perspective on the Eurekan episode in northern Greenland and open new research avenues. Thus, I look very much forward to reading a revised version of the manuscript and hope that the authors of the present manuscript find my comments helpful and constructive. Many thanks to the journal editors and authors for their trust in allowing me to review this manuscript.
Comments by the reviewer
Comment 1: Line 1: Uninformative and simply flashy. It is recommended to delete this part and refine the title (e.g., drawing on the fission track method), e.g.:
-Constraining the timing of Eurekan contraction in northern Greenland using apatite fission track and U–Pb geochronology.
-Apatite fission track and U–Pb geochronological constraints on Eurekan tectonism in northern Greenland (: implications for the northernmost mountain belt on Earth).
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Comment 2: Line 13: Be consistent in using (or not using in the present case) the Oxford comma, which is the optional comma before prepositions like "and" or "or" at the end of a three-or-more-item list. For example, use either "apple, banana, and orange" or "apple, banana and orange". In the present case, there is no Oxford comma, whereas an Oxford comma is used, e.g., line 21 ("Palaeocene, early and mid-Eocene, and Oligocene").
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Comment 3: Line 13: How so? As it is now, this sentence is uninformative. Either specify how the belt changes (strike, geometry, other change? e.g., "the belt bends from a NE–SW in Ellesmere Island to N–S in Svalbard") or delete the sentence.
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Comment 4: Lines 14–16: Redundant. Merge these two sentences or shorten or delete the second one, e.g., "This study aims to explore the relationship between the, thus far, poorly-understood temporal and kinematic relationships between major fault systems in North Greenland using apatite fission track and U–Pb geochronology" or similar. It is also possible to partly merge with the next sentence.
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Comment 5: Line 17: Use en-dash character instead of hyphen (because the meaning is "U to Th"). Be consistent in the use of hyphen vs en dash in the whole manuscript. En-dash should typically be used for geochronological systems (element U decaying into element Pb = “U–Pb”), structural strikes (e.g., northeast to southwest = NE–SW), and any other phrasing implying “to”, e.g., “early to mid Eocene” = early–mid Eocene, “gentle to moderate dip” = gentle–moderate dip. Use hyphen mostly for composite adjectives (e.g., “NE–SW-striking foliation”, “gently–moderately-dipping surface”).
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Comment 6: Line 21: Be consistent in using British vs American English. Here British English is used, whereas line 169 American English is used ("Paleogene"). Either use "Palaeocene" and "Palaeogene" or "Paleocene" and "Paleogene". Check for other British vs American English inconsistencies.
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Comment 7: Line 21: This has already been mentioned a couple of times but the respective strikes are still not mentioned, leaving the reader wondering whether the strike difference is relevant or not (e.g., < 30 degrees, i.e., minor or > 60 degrees, i.e., significant). Either specify each fault system's strike (and dip direction?) in the previous sentence (e.g., "the steeply-SSW-dipping Kap Cannon Thrust Zone" or appropriate strike and dip or dip direction) or delete the various occurrences of "differently oriented" in the abstract.
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Comment 8: Line 22: The official name of this overall structure is “De Geer Zone” (De Geer, 1926; Holtedahl, 1936; du Toit, 1937; Wegmann, 1948; Harland, 1961; Harland, 1967; Harland, 1969; Horsfield & Maton, 1970; Faleide et al., 1993; Faleide et al., 2008). If the discussed structure is distinct from the De Geer Zone, specify how (also in a map if possible).
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Comment 9: Line 26: Do you mean "in intraplate orogens" or "during intraplate orogenesis"?
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Comment 10: Line 31: Perhaps more appropriate to use "fold-and-thrust belt"?
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Comment 11: Line 32: Do you mean "continental crust in the Arctic Ocean"? If so, specify accordingly.
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Comment 12: Line 35: Greenland was and is still part of Laurentia/North American plate. See also comment line 46 about the Wegener Fault. Delete "Greenland".
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Comment 13: Line 36: Replace by "orogenesis", which is the process. "Orogeny" refers to the episode (i.e., time-related).
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Comment 14: Line 38: Replace by "and".
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Comment 15: Line 40: A separation of contractional deformation at ca. 66–60 Ma into a “pre-Eurekan” event/stage, i.e., not part of the Eurekan Orogeny like the Eurekan I and II stages, is not logical and does not make sense. Either avoid splitting deformation into various stages/pulses since this practice is outdated and often incorrect (e.g., Fossen, 2020), especially in areas like northern Greenland where clear geochronological constraints on individual structures are lacking. Alternatively, rename these stages to create a logical and less confusing nomenclature (e.g., Eurekan I, II, and III; see also comment lines 632–633).
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Comment 16: Line 41: Replace by "seafloor spreading".
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Comment 17: Line 41: Replace by “in”.
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Comment 18: Line 41: Replace by "and".
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Comment 19: Line 42: Replace by en dash (i.e., meaning "Norwegian to Greenland sea").
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Comment 20: Line 43: Add "potentially" to reflect the uncertainty around the existence of a major plate boundary in the Nares Strait (see comment about the Wegener Fault line 46).
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Comment 21: Line 46: The authors of the present do not include mention of the large body of evidence suggesting that the Wegener Fault does not exist. The authors of the present manuscript need to go back to the origin of the Wegener Fault hypothesis. Taylor (1910) first postulated the presence of a strike-slip fault along Nares Strait based on the physiographic morphology of the area (i.e., linear geometry of the Nares Strait sound) and presumed lateral offset of rock units on either side of the strait, an offset that is now known not to exist as demonstrated by detailed geophysical and geological field mapping across the Nares Strait (e.g., Oakey and Chalmers, 2012; Oakey and Damaske, 2006; Oakey and Stephenson, 2008; Rasmussen and Dawes, 2011). For example, the E–W-striking Neoproterozoic intrusions such as the Kap Leiper dyke, which crops out in northwestern Greenland and was dated to ca. 627 Ma (Dawes et al., 1982), were traced across the Nares Strait in magnetic data with no lateral offset (Damaske and Oakey, 2006; Rasmussen and Dawes, 2011). This is further supported by gravimetric data, which show that the Nares Strait gravimetric low runs parallel to the Eurekan fold-and-thrust belt, i.e., oblique to the Wegener Fault, and displays no sign of offset. The initially postulated offset is therefore inexistant. Furthermore, physiographic morphology and topography cannot be used as sole arguments to infer fault zones since erosion may localize along various types of geological features, e.g., fold axes, fold axial cleavage, and weak rock units/layers (e.g., sedimentary beds). The authors of the present manuscript may very well mention models involving the Wegener Fault, but should balance these with alternatives involving no Cenozoic strike-slip fault in the Nares Strait.
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Comment 22: Lines 47–48: Similarly to the comment about the Wegener Fault line 46, mention should be made of the large body of evidence against any Cenozoic lateral movement along the De Geer Zone and related fault zones in seismic data (e.g., Austegard et al., 1988; Riis & Vollset, 1988; Gabrielsen et al., 1990; Eiken, 1994; Lasabuda et al., 2018; Koehl, 2025) and the continuation of oblique Neoproterozoic thrust systems across the presumed location of the De Geer Zone (Koehl, 2025), i.e., conflicting with the possibility of Cenozoic dextral offset along the De Geer Zone. Unlike the studies from which the De Geer Zone was postulated, the herein-mentioned studies show actual data supporting their claim and should, thus, to keep the manuscript balanced and objective.
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Comment 23: Line 48: Do you mean "SE-directed contraction"? If so, rewrite as such.
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Comment 24: Line 50: Replace hyphen by en dash.
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Comment 25: Line 50: Replace by "seafloor spreading in the Labrador Sea and Baffin Bay".
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Comment 26: Lines 51–52: Too simplistic and outdated. No plate/crustal block on Earth moves independently from the other plates/blocks. Moving one block in a specific direction implies both vertical and horizontal motions by adjacent blocks to accommodate and respond to these movements (e.g., thickening of the crust and escape tectonics in Eurasian plate in response to northward movement of Indian plate). Similarly, crustal thinning during rifting and extension necessarily results in contraction and/or subduction some distance away from the spreading center due to space constraints. Crustal blocks/tectonic plates may move in different directions, but sometimes are still connected with adjacent blocks (e.g., North American and Eurasia plates moving away from one another in the northeastern Atlantic and Arctic oceans despite being partly linked (i.e., no discrete plate boundary) via continental crustal blocks in the Laptev Sea, Lomonosov Ridge, and Alpha–Mendeleev Ridge, and Greenland with North America during the Eurekan episode; cf. comment about the Wegener Fault line 46). Rephrase or delete this part of the sentence.
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Comment 27: Lines 52–53: What about the present-day transform faults in the Fram Strait, the Molloy and Spitsbergen fault zones? No mention is made of these actual fault zones along which up to 200 km lateral offset/stepping of the mid-ocean ridge is observed, from the Knipovich Ridge to the Molloy Ridge and the Lena Trough (e.g., Johnson & Eckhoff, 1966; Crane et al., 1982; Myhre & Thiede, 1995; Thiede et al., 1990). This clearly needs updating both here, in the Discussion chapter, and the figures and proposed tectonic models/reconstructions. How do these transform faults fit in the proposed models? How much of the total displacement did they accommodate? When did they initiate? What is their relationship with onshore fault zones described in the present work (e.g., Harder Fjord Fault Zone)? This is a major shortcoming of the manuscript at present and needs to be addressed.
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Comment 28: Line 56: Replace hyphen by en dash.
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Comment 29: Line 59: Replace by "in".
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Comment 30: Line 61: Improper use. Also confusing with erosional dissection in geomorphology. Replace by "thinning and break up" or similar, or delete the last part of the sentence.
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Comment 31: Line 63: Replace colon by period. Alternatively uncapitalize because middle of the sentence.
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Comment 32: Line 63: Be consistent and mention the northern end first (i.e., NE–SW-striking). Also replace hyphen by en dash.
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Comment 33: Line 68: Cannot apply to "cross-cutting relationships". A potential way to rephrase the sentence is as follows: "Cross-cutting relationships between these two regional structural trends are difficult to interpret and co-occurrence of both fault systems in outcrop are scarce".
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Comment 34: Line 70: Two inconsistencies here. First, "north-west" is hyphenated, which is not consistently done for orientations in the manuscript, e.g., line 681 ("northwest-southeast"). Second, orientations must be either abbreviated or spelled out consistently, i.e., either use "NW" and "SE" or "northwest" and "southeast" (or "north-west" and "south-east"), e.g., line 48 ("SE contraction").
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Comment 35: Lines 71–73: There seem to be a major cause for concern here. The authors seem to fully rely on crosscutting relationships to infer the relative timing of fault activity, which is known to be biased (e.g., Dyer, 1988; Moir et al., 2010; Nortje et al., 2011; Hansen and Bergh, 2012). Thus, the fact that the Harder Fjord Fault Zone truncates the Trolle Land Fault Zone (if it is indeed what is meant by this sentence; see comment line 71) does not consistute a definitive evidence of relative timing. The use of crosscutting relationships in the present manuscript should therefore be assisted by geochronological constraints where available or toned down (i.e., specify that the timing is uncertain because of the lack of geochronological constraints and large uncertainties attached to crosscutting relationships).
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Comment 36: Line 72: Uninformative. To intersect means "to share an intersection with", i.e., it does not inform about crosscutting relationships. Do you mean "truncates", "crosscuts", "offsets", other? Specify.
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Comment 37: Line 72: Repetition of "also". A potential solution is to rephrase as follows: "Von Gosen and Piepjohn (2003) consider both successive and simultaneous activity". However, this comment may no longer be relevant after correction related to the comment lines 71 to 73.
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Comment 38: Line 80: "temporal"?
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Comment 39: Line 80–82: Redundant with previous sentence. Rewrite, e.g., by merging both sentences?
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Comment 40: Line 84: Although this is probably done in a subsequent chapter of the manuscript, it would be relevant to specify why these dykes were dated (e.g., potentially syn-kinematic dykes intruded along a shear zone? pre- or post-kinematic dykes providing indirect time-constraints on fault activity? other? and for which fault they are relevant).
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Comment 41: Line 87: Be consistent. Use of en dash before "the Eocene" and hyphen after. Use en dash for both or parentheses.
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Comment 42: Line 87: Not exactly in line with the conclusions of the manuscript. Be consistent.
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Comment 43: Line 87: Replace by ", which" to smoothen the flow of the sentence.
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Comment 44: Line 88: Do you mean at the same time as in the Antarctic? If so, add “at the same time” or “simultaneously” or similar.
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Comment 45: Line 92: Be consistent. Either use a comma or not, but do it consistently: "e.g.," or "e.g.". Here, there is no comma after “e.g.”, whereas a comma is used lines 37 and 107.
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Comment 46: Line 95: How about Eurekan deformation in Billefjorden and Andrée Land in central and northern Spitsbergen (e.g., Koehl, 2021; Koehl et al., 2022). Simply add these zones to figure 1a.
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Comment 47: Line 97: An alternative and/or updated model is necessary here. Either update the present model to, at the very least, showing the impact of the actual present-day transform faults in the Fram Strait (Molloy and Spitsbergen fault zones). Alternatively, add an additional alternative model reflecting the tectonic evolution of Arctic regions based on geophysical evidence (i.e., without the Wegener Fault and De Geer Zone; e.g., Koehl, 2025).
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Comment 48: Line 98: Figure 1c: temperatures: “decrease from 5–13 to 12–8 °C” should be reworded into “change from 5–13 to 12–8 °C” since it might as well represent a temperature increase. Also Do you mean -12–8°C, if so the minus sign is missing. If not, be consistent and update into “8–12°C”. What about environmental/climatic conditions in Svalbard in the Paleocene–Eocene (e.g., Smyrak-Sikora et al., 2025 their sub-chapters 4.5.2 to 4.5.4). These would be worth mentioning because Svalbard was also located relatively close to northern Greenland in the Eocene, although probably not as close as depicted in the present manuscript’s figure 1b (cf. comment about the De Geer Zone lines 47–48).
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Comment 49: Line 109: What about the M'Clintock Orogen in the Pearya Terrane? If the Caledonian Orogeny is relevant to the present study, why would the coeval M'Clintock Orogeny not be (e.g., Powell and Schneider, 2022)? If not, specify why not.
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Comment 50: Line 114: There are several issues with the figure references:
1) Fig. 3 (line 302) is first referred to after Figs. 4, 5, 6, and 7 (line 114). This needs to be corrected (e.g., turn Fig. 3 into Fig. 7?).
2) Fig. 7b (line 508) is first referred to after Fig. 7c (line 340).
3) Figure insets are found both capitalized (e.g., “Fig. 2A” lines 117 and 130) and uncapitalized (e.g., “Fig. 5a” line 130) and separated by a comma or (inappropriately) by an hyphen (e.g., “Fig. 3b-d” line 340 and “Fig. 7a,b” line 508). Be consistent. Choose one format (capitalized or not and separated by an en-dash character or a comma) and stick to it in the entire manuscript.
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Comment 51: Line 116: "Wandel Sea basin" or "Wandel Sea Basin". Be consistent. "Wandel Sea Basin" is used here and "Wandel Sea basin" is used in the caption of Fig. 2 line 169.
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Comment 52: Line 116: Do you mean "Upper Cretaceous"?
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Comment 53: Line 117: Do you mean "Upper Cretaceous"? Double this in the entire manuscript.
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Comment 54: Line 119: Delete hyphen.
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Comment 55: Line 123: This took some time to figure out. If guessed correctly, "Fig. 2-1" actually means "point/stratigraphic relationship 1 in Fig. 2". If so, rewrite it as such for every stratigraphic section in the entire manuscript. "Fig. 2A-3" coupled with the recurrent misuse of hyphen versus en dash in the manuscript could suggest "Fig. 2A to Fig. 3".
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Comment 56: Line 124: Either "north–south-, northwest–southeast-, and east–west-trending dykes" or "N–S-, NW–SE-, and E–W-trending dykes", or "These dykes strike north–south, northwest–southeast, and east–west and yield" or similar. Adapt accordingly to your decision on the Oxford comma and capitalizing or not orientations.
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Comment 57: Lines 124–125: Replace by "Ar–Ar and U–Pb".
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Comment 58: Line 127: Replace by "east–west-trending" or "east–west-striking". Correct consistently in the whole manuscript.
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Comment 59: Lines 128–129: Do you mean that the faults formed during N–S-oriented compression? If so, rewrite accordingly.
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Comment 60: Line 134: Replace by "Mylonites" or "Similar mylonites".
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Comment 61: Line 134: Replace by "northeastern continuation".
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Comment 62: Lines 138–139: This is a questionable assumption. This hypothesis should be further tested, e.g., via geochronological analysis of fault rocks. Brittle and ductile deformation may very well occur simulateously and at the same depth, e.g., in rock units with different rheological properties (e.g., competent basaltic lavas are more likely to deform by brittle faulting, whereas layered (meta-) sedimentary sequences with significant internal rheological property contrasts have an increased probability of deforming into ductile structures). It is suggested to rephrase into “Unlike the southern block, they are mostly affected by brittle deformation associated with NNW-directed thrusting. These variations in deformation style were postulated to reflect diachronous events, i.e., later deformation at a shallower crustal level in the central block (von Gosen and Piepjohn, 1999)” or simply omit the last phrase: “Unlike the southern block, they are mostly affected by brittle deformation associated with NNW-directed thrusting (von Gosen and Piepjohn, 1999).”.
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Comment 63: Line 141: Do you mean a fault that was not identified previously and that was observed in outcrop? Or do you mean a fault that could not be observed in outcrop, but which was inferred based on other arguments/data?
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Comment 64: Line 147: Perhaps change to "Wandel Sea Basin" for the sake of consistency?
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Comment 65: Line 149: "Late" or "latest"?
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Comment 66: Line 149: Delete.
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Comment 67: Line 150: Not sure where this is. Please add the location to one of the relevant figures (e.g., Fig. 2b? but this would require enlarging Fig. 2's insets a to e, which are too small at the moment to clearly distinguish stratigraphy and add local place names).
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Comment 68: Line 150: Were these dated by geochronological studies? Or do you mean "Upper Cretaceous"?
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Comment 69: Lines 151–153: In its current state, it is not possible to distinguish any purple-colored greenstone unit (or the sandstone-dominated deposits) in Fig. 2b, which would need to be further enlarged and detailed. All insets in Fig. 2 would benefit from being enlarged (to at least a width of half a page).
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Comment 70: Lines 154–155: It would be great if these relationships were plotted in Fig. 2b.
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Comment 71: Line 162: Replace by "flat-lying".
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Comment 72: Line 167: This is an excellent and important figure, which deserves more space. Consider enlarging all inset maps (a) to (e) to a half-page width.
The red arrows are not included in the legend and their meaning might not be clear to non specialists.
"Basement" is an adjective and cannot stand alone. Replace by "Basement rocks" or similar.
Do you mean "Late Cretaceous dykes"?
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Comment 73: Line 171: Add a comma.
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Comment 74: Line 172: Delete unnecessary parenthesis.
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Comment 75: Line 175: Not necessarily. Thrust faults and normal faults also show linear geometries depending on scale and subsequent reworking. Conversely, major strike-slip faults (e.g., San Andreas fault, North Anatolian fault) are not linear. Is this fault subvertical? If so, such a geometrical characteristic might (if made in conjunction with other critical observations) suggest strike-slip kinematics.
If you absolutely want to keep this, it is suggested to rephrase into something like "Strike-slip kinematics have been postulated (Piepjohn et al., 2015; Soper and Higgins, 1991)".
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Comment 76: Line 179: After reviewing Piepjohn and von Gosen (2001) and Soper and Higgins (1987), it becomes clear that the Harder Fjord Fault Zone shows no clear indicator of strike-slip movements at all. On the one hand, Piepjohn and von Gosen (2001) show that the only evidence of strike-slip faulting along the Harder Fjord Fault Zone are minor faults with meter-scale offsets, which strike orthogonal to the Harder Fjord Fault Zone (in their words: "strike-slip transfer planes resulting from N–S to NE–SW compression"). On the other hand, the presumed 20 km offset of stratigraphic boundaries and Ellesmerian folds in Nansen Land from Soper and Higgins (1987) is highly questionable because (1) the said stratigraphic contacts in Nansen Land were covered by an ice sheet (as shown in their fig. 2) and (2) the fault and said stratigraphic contacts are subparallel (10 to 15 degrees oblique to one another), thus suggesting that there may be no lateral offset at all and that the Harder Fjord Fault Zone may simply have locally localized along the folded stratigraphic contact (some bedding-parallel faulting/movement is not unusual in fold-and-thrust belts). Furthermore, Higgins et al. (1981) stated that on Moa Island (i.e., next to the postulated 20 km dextral offset): "At one point on Moa Ø, Paradisfjeld Group carbonates to the north are juxtaposed against Frigg Fjord mudstones to the south, indicating a throw approximately equivalent to the thickness of the Polkorridoren Group- perhaps 1500 to 2000 m if due allowance is made for the uncertainties arising from the intense folding. The fault plane of the northernmost fault is well exposed in the eastern cliffs of Hazen Land, where it dips steeply southwards at about 65°. No significant strike-slip displacement can be demonstrated", which strongly suggests that the Harder Fjord Fault Zone did not accommodate much (if any) strike-slip movement. Thus, this phrase is not necessary. It is recommended to delete it or to rephrase into something like ", which is consistent with the occurrence of minor conjugate strike-slip faults orthogonal to the Harder Fjord Fault Zone in the east." or similar.
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Comment 77: Line 184: Perhaps add reference to Piepjohn and von Gosen (2001), Higgins et al. (1981), Soper and Higgins (1987), and any other relevant works?
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Comment 78: Lines 217–218: Please rephrase into "von Gosen and Piepjohn (2003) postulated/speculated continuity of the two fault systems, with faults of the Trolle Land Fault System possibly bending into an E–W strike, i.e., parallel to the Harder Fjord Fault Zone". The main argument in turning this into an assumption/speculation/hypothesis is that the traces of these faults are highly speculative. For example, the main fault splay/segment of the Trolle Land Fault System, the Trolle Land Fault Zone, is a speculated fault, which has not been observed anywhere in the field according to von Gosen and Piepjohn (2003). If these authors have observed this fault in the field, it is then not clearly indicated in their study. Notably, their fig. 3 shows that the Trolle Land Fault Zone is speculated everywhere except in easternmost Peary Land (i.e., within the frame of their fig. 5). Their fig. 5 shows that the fault does not represent a major boundary of any rock unit (e.g., Silurian to Permian rock units crosscut by the fault are found on both sides of the fault). This is also the case in their fig. 12a, which zooms in a section of the Trolle Land Fault Zone and nearby faults. Further inspecting their fig. 12a shows that the Trolle Land Fault Zone in the area is dashed, i.e., inferred but not observed. Thus, the Trolle Land Fault Zone is only a speculated structure, i.e., a hypothesis.
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Comment 79: Line 229: Unnecessary. Delete.
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Comment 80: Line 231: Add missing space.
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Comment 81: Lines 243–244: Probably from a template. Delete?
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Comment 82: Line 244: Replace by “to obtain”?
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Comment 83: Line 247: Replace by "to test".
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Comment 84: Line 248: Delete unnecessary space.
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Comment 85: Line 275: Questionable assumption. What about folding and erosion and bedding-parallel faulting/décollement (i.e., with limited displacement)? Were these considered in relevant places? If not, why not? The temperature ranges during ductile deformation (300–400°C) are well within the temperature required to reset any of the used systems (e.g., bulging and subgrain rotation during quartz recrystallization; Stipp et al., 2002a, 2002b).
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Comment 86: Lines 289–290: Do you mean "time to temperature paths"? If so, replace hyphen by en dash.
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Comment 87: Line 317: Replace by "age-elevation".
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Comment 88: Line 330: Which fault is that? It does seem located far from any major fault in fig. 2. Specify or delete.
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Comment 89: Line 353: "Cretaceous Period" is capitalized.
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Comment 90: Line 354: Do you mean of the Mohns Ridge or the Norwegian–Greenland Sea or other? Specify.
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Comment 91: Lines 355–358: This belongs more to the Introduction chapter. Consider moving it there.
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Comment 92: Lines 358–359: The colon structure is inappropriate to a Discussion chapter. Either delete this unnecessary phrase or end it with a period.
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Comment 93: Lines 365–367: Some of the conclusions of Meier et al. (2024) and the present manuscript are circular reasoning:
-It is assumed that the De Geer Zone exists (which is unlikely; Koehl, 2025 and references therein).
-It is assumed that tectonic movements along the De Geer Zone are responsible for thermal weakening and the distinct thermal history of the Nakkehoved area/terrane, which yielded older AHe ages than nearby areas.
-The discrete thermal history of the Nakkehoved area is used to infer an origin as an allochthonous terrane transported laterally c. 100–200 km to its present position. Contrasting thermal evolution may have various implications other than large-scale strike-slip fault movements and simply imply a different exhumation history. This could be related to various factors including but not limited to vertical fault movements, folding, erosion rates, climate. None of these are discussed in Meier et al. (2024) and the present study. These factors need to be discussed.
-These fault movements are concluded to have caused further crustal weakening, thus allowing the opening of the Fram Strait.
-These lines of evidence are used to further support the existence of the De Geer Zone.
This critical issue needs to be addressed before the manuscript can pass peer review.
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Comment 94: Line 377: Replace by "70–65 Ma".
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Comment 95: Line 386: Delete or replace by "their".
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Comment 96: Line 390: Replace by "had".
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Comment 97: Line 390: Unnecessarily wordy. Delete to improve the sentence flow.
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Comment 98: Lines 394–397: Could this event be fully or partly related to Late/latest Cretaceous, early-Eurekan ductile deformation (e.g., folding, shearing, metamorphism)? If not, state relevant arguments.
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Comment 99: Line 401: Consider replacing by "fluvial" to be consistent with lines 157 and 194?
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Comment 100: Line 402: Replace by "relatively".
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Comment 101: Lines 408–410: This is an interesting correlation. If Upper Cretaceous sedimentary rocks in Kilen are indeed correlative of the Kveite Formation, which deposited during tectonic quiescence or minor/moderate (early Eurekan?) contraction as suggested by the lack of Late Cretaceous normal faults and related syn-tectonic deposits and by contractional salt diapirism in the Late Cretaceous to Paleocene in the Tromsø Basin (Rowan and Lindsø, 2017; Kairanov et al., 2021), then it follows that Upper Cretaceous sedimentary deposits in Kilen and the Nakkehoved area can neither have deposited in pull-apart basins, nor in fault-controlled segmented sub-basins in a larger basin, but must rather have deposited over a broad (shallow to deep) marine domain (as suggested by Piepjohn and von Gosen, 2001), possibly (but not necessarily) affected by early Eurekan contraction in the Late or latest Cretaceous. This is supported by the occurrence of Upper Cretaceous deposits on either side of major fault strands of the Trolle Land Fault System (i.e., not deposited in fault-bounded basins; e.g., Svennevig et al., 2017). This should be discussed here.
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Comment 102: Lines 417–419: Split into a separate sentence to remove a pair of parentheses and smoothen the flow of the text.
Also delete the unnecessary comma before "respectively".
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Comment 103: Line 420: Not in line with the correlation with the Kveite Formation in the Barents Sea and the Late Cretaceous tectonic setting there (quiescence to minor contraction with no fault-bounded Upper Cretaceous deposits; see comment lines 408 to 410).
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Comment 104: Line 425: The extent of the proposed Late Cretaceous basin does not coincide exactly with major faults and does not encompass the Late Cretaceous dykes south of Frigg Fjord. What is/are the main reason(s) behind these discrepancies? This should be specified in the main text. It is argued that this proposed Late Cretaceous basin is bounded by faults, but its proposed extent goes beyond presumed major faults in the area. Why is that? It is proposed that the basin is related to the intrusion of the Late Cretaceous dykes. Thus, could the proposed basin also extend south of Frigg Fjord (e.g., yielding an overall three-arm/triple-junction-like geometry)? The criteria used (and those not used) to infer the basin extent should be further discussed in the present section.
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Comment 105: Lines 430–431: See comments lines 275, 365–367, and 394–397.
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Comment 106: Lines 440–454: Exhumation of the central block earlier to lower temperature is not surprising since (1) the central-block sample was taken in a structural syncline consisting of younger rock units and (2) away from major fault zones, and (3) Eurekan deformation appears to have localized in Cambrian rocks in the southern block as a broad zone of mylonites (rather than in younger Upper Cretaceous units in the central block) and along major faults in the northern block where these faults (Kap Christiansen Thrust and Kap Christiansen Fault) seem to have (partly) used existing discontinuities (e.g., stratigraphic contacts and rheological contrasts). Thus, "tectonic heating" is to be expected to have persisted in the southern and northern blocks, while the central block cooled rapidly despite its topographically lower position/higher burial depth (i.e., in a syncline). If this is what was suggested, then perhaps rephrase to make it clearer to the reader. If this is not what was proposed, this should be discussed here.
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Comment 107: Line 440: Replace by "had"?
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Comment 108: Line 456: The legend reads "Upper Cretaceous dykes". In the text, "Late Cretaceous dykes" was used. Be consistent. Were these dykes dated via geochronological analysis or were they not and are simply confined to Upper Cretaceous sedimentary units?
The color shades of green used in (a) are challenging to segregate, even for non-colorblind individuals. It is suggested to use shades and/or colors with higher contrast.
In its present state, it is impossible to check the relationship of the Kap Christiansen Thrust and Kap Christiansen Fault in map view because the area of Kap Christiansen is crowded with many symbols. Perhaps zoom in further so that it becomes more obvious how they interesect and which units they truncate or not, e.g., by adding an extra inset zoomed in Lockwood Island or the Kap Christiansen area.
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Comment 109: Line 461: With respect to the comment lines 440 to 454, this figure should reflect that this is only one possible interpretation, which assumes a direct relationship between cooling and exhumation with no regards for "tectonic heating". If taking the later into account together with the overall anticline, syncline, and anticline position of the northern, central, and southern blocks respectively, it follows that another possibility involves continuous exhumation of the southern block from the pre-Eurekan to Eurekan II events/periods, thus, in agreement with the Paleocene Ar–Ar ages from Lyberis and Manby (2001) for the mylonites in the southern block (and possible exhumation of the northern blocksince the pre-Eurekan).
Another factor that is, at present, not discussed is differential erosion of old (metamorphosed?) Cambrian rocks and young (potentially weaker?) Cretaceous volcanosedimentary deposits. Could this have played any role in cooling/exhuming the central block more rapidly? This should be discussed in the main text.
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Comment 110: Lines 466–471: This belongs to the Methods chapter. Consider moving it there.
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Comment 111: Line 471: Inappropriate. This is the Discussion chapter, not the Conclusion. In the present chapter, potential interpretations of the data should be presented and discussed against existing data and interpretations from the literature. It is recommended to delete this phrase or at least to rephrase it (e.g., remove the term "conclusions" and amend the colon structure).
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Comment 112: Line 472: Delete.
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Comment 113: Line 476: How shallow? Specify to help the reader follow your reasoning.
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Comment 114: Lines 476–477: Why could this be? Could this mean that Eurekan contraction in this block resulted mostly in horizontal top-north movements, i.e., related to a décollement/detachment, which is was proposed in the area (e.g., Soper and Higgins, 1987)?
Could the cooling to c. 50°C prior to the Cenozoic be related to previous tectonic (and erosional) episodes, e.g., Carboniferous to earliest Permian rifting and erosion as documented in Svalbard and northern Norway (e.g., Smyrak-Sikora et al., 2018; Koehl et al., 2018), which is potentially supported by the AFT ages for samples SE39 and SE141, and renewed rifting in the Jurassic, e.g., in eastern Greenland (Salomon et al., 2020) supported by the earliest Jurassic AFT age for sample MZ18-58 (though with a large error extending from the Permian rifting episode to the to Early Cretaceous, which also was a period marked by extension)?
These should be discussed here.
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Comment 115: Line 480: Not quite obvious from fig. 6a. Instead, the only faults extending along the edges of both blocks strike E–W (i.e., parallel to the Harder Fjord Fault Zone).
In addition, the thermochronological data obtained (suggesting shallow, cool conditions for the Harder Fjord Fault Zone core in the south and cooling and possible exhumation of the Greenstone block in the pre-Eurekan event in the north; fig. 6b) are difficult to reconcile with tectonic movements along segments of the Harder Fjord Fault Zone, since these faults clearly are top-north reverse faults (e.g., Piepjohn and von Gosen, 2001; Soper and Higgins, 1987). Thus, exhumation of the southern block (i.e., Harder Fjord Fault Zone core) should have occurred, which differs from the thermochronological record presented here. Furthermore, should strike-slip kinematics be proposed for the faults involved, it remains unclear how they would have contributed to significantly and rapidly exhume one or the other block mostly through lateral movements. This needs to be further addressed.
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Comment 116: Lines 480–481: It is actually more probable that the said faults were active in the Paleocene, since cooling (which was almost complete in the Greenstone block by 55 Ma; fig. 6b) would have occurred coeval and/or continued after thrusting and erosion were completed.
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Comment 117: Line 481: Do you mean “Paleocene”? The early Eocene is (together with the Paleocene) part of the Paleogene.
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Comment 118: Lines 482–486: What about later exhumation due to location farther within the core of the orogen? Why was this alternative not considered? Faulting may have occurred synchronously everywhere, but erosion would have taken more time to exhume areas within the core of the orogen, thus possibly explaining the observed younger age for MZ18-55. In addition, AFT data typically yield faster exhumation rates for orogenic cores, which is the case for MZ18-55 cooling down rapidly during the Eurekan II event while MZ18-54, 56, and 57 cooled down to comparable temperatures from the Eurekan I event.
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Comment 119: Line 498: After reaching this point, the Ar–Ar, AFT, and AHe ages obtained along the Harder Fjord Fault Zone and Kap Cannon Thrust Zone and related faults no longer appear random. Some areas may be grouped together based on their similar position within the structural setting of the area:
-Western basement and southern basement blocks cooled during the Eurekan II and post-Eurekan events.
-Old core cooled prior to the Eurekan Orogeny up to the pre-Eurekan event.
-Greenstone block cooled during the pre-Eurekan event and Eurekan I event.
-MZ18-55 and triangle blocks cooled during the Eurekan II to post-Eurekan events.
-Northern basement block in Johannes V Jensen Land and southern block in Lockwood Island cooled during the Eurekan I to Eurekan II (and possibly up to the post-Eurekan event).
-Central block in Lockwood Island cooled during the pre-Eurekan and Eurekan I events.
-Northern block in Lockwood Island cooled during the Eurekan II to post-Eurekan events.
These various blocks may be discussed against the décollement/detachment level from Soper and Higgins (1987) as part of a c. 50 km-wide system of in- and out-of-sequence, top-north thrust imbricate (see attached figure), which is consistent with outcrop-scale imbricate geometries along the Harder Fjord Fault Zone (e.g., Piepjohn and von Gosen, 2001; Lyberis and Manby, 2001 their fig. 8). Eurekan top-north thrusting may have initiated during the Late or latest Cretaceous along the Harder Fjord Fault Zone, possibly including the initiation of horizontal, décollement- to detachment-related movements (thereby explaining the lack of cooling and possibly exhumation recorded by samples within the Harder Fjord Fault Zone core; see (a) in attached figure). Thrusting then possibly proceeded with a series of in-sequence thrusts between 66 Ma and 48 Ma (Pre-Eurekan and Eurekan I events/periods), including the Kap Cannon Thrust Zone and Kap Christiansen Fault Zone ((b) and (c) in attached figure). A couple of out-of-sequence thrusts may then have formed in the hanging wall of the Harder Fjord Fault Zone and Kap Cannon Thrust Zone between 44 Ma to 38 Ma (Eurekan II event/period; see (d) in attached figure), and thrusting may have remained active along a majority of the thrust faults up to 26 Ma (Post-Eurekan event/period; (e) in attached figure). This model or a similar type of model should be discussed.
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Comment 120: Line 500: The color of the "old core" in the legend does not match that used in the map. Line 500: What are the arguments supporting a potential NE–SW-striking fault in northeasternmost Frederick E. Hyde Fjord? According to geological maps (e.g., Higgins et al., 1981), rocks of the Paradisfjeld Group are found on either side of the fjord without any apparent vertical or lateral offset. It is suggested to either state clearly your arguments supporting the presence of a potential fault there, or to delete this fault. The presence of an elongated fjord does not constitute a sufficient piece of evidence to infer the existence of a fault zone since (glacial) erosion may exploit other weaknesses (e.g., foliation surfaces, fold axes, bedding surfaces, cleavage, rheological contrasts, etc.). Please apply this logic to all inferred fault lines in the entire study area. Note that it is this type of mistakes (i.e., assumptions gradually turned into pseudofacts; "type 1 error") that has led entire communities along erroneous paths sometimes for decades or centuries, e.g., hypotheses of the Wegener Fault and De Geer Zone initially postulated by Taylor (1910) and De Geer (1926) and Holtedahl (1936) respectively solely based on the topography (i.e., linear geometry of the Nares Strait fjord and linear geometry of the western Svalbard–Barents Sea margin). These hypotheses were gradually turned into facts despite conflicting or lack of further evidence. The growing body of evidence against the presence of a fault in Nares Strait is now overwhelming and can no longer be ignored (e.g., Oakey and Chalmers, 2012; Oakey and Damaske, 2006; Oakey and Stephenson, 2008; Rasmussen and Dawes, 2011). Similarly, evidence supporting large-scale (400 km) dextral movements along the De Geer Zone are highly improbable (Koehl, 2025 and references therein) since this hypothesis notably disregards the actual two active major transform faults in the Fram Strait (Molloy and Spitsbergen fault zones), both of which accommodated transform movements or rift steps in the order of 200 km. Note that if the North Atlantic rift stepped in the Fram Strait rather than having been offset, then even less lateral fault movement is needed in reconstructions. Even without considering the offshore seismic evidence in the Fram Strait, Occam's Razor suggests that the simplest hypothesis is the more likely, i.e., no large-scale movements along the De Geer Zone, which was recently proposed to be an inverted Caledonian thrust system based on regional onshore–offshore fault and basin geometries (Koehl, 2025).
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Comment 121: Line 504: Here, the exhumation pattern suggests a relationship to fold structures, which include N–S- to NNW–SSE-striking and E–W-striking folds (e.g., Higgins et al. 1981 their fig. 15 and Soper and Higgins, 1987 their fig. 2). This should be discussed in the Discussion chapter.
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Comment 122: Lines 511–512: Not necessarily. The data presented suggest that Eurekan-related cooling (and, thus, exhumation) did not affect the area southwest of the Trolle Land Fault System. This, however, does not mean that Eurekan deformation did not occur in this area since deformation does not necessarily imply exhumation (e.g., strike-slip faulting or décollement faulting). Consider deleting this phrase or rephrasing into something like "thus potentially supporting previous observations that most of Eurekan deformation was restricted to the Trolle Land Fault System".
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Comment 123: Line 519: Do you mean "upper Paleocene to lower–middle Eocene"?
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Comment 124: Line 519: Who and what suggested this? Is this a conclusion derived from observations/data presented in the present study? if so, what are these? Lyck and Stemmerik (2000) did not suggest this. It is suggested that the arguments supporting such a claim and/or the source reference(s) it was taken from should be stated here. Alternatively delete "in pull-apart basins".
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Comment 125: Lines 529–533: Regardless of whether the Nakkehoved area is an allochthnous terrane or not, it remains unclear how strike-slip faults may explain significant exhumation and the marked differences in the timing of cooling (exhumation?) in blocks supposedly bounded by the same faults. This should be clarified. Else, it should be clearly stated whether fault movements (and what type of fault kinematics) are supported or not by the data.
Furthermore, according to Meier et al. (2024 their fig. 5), the Nakkehoved area/terrane was located relatively close to Herluf Trolle Land, thus conflicting with the claim herein by the authors of the present manuscript that the "Nakkehoved [...] cooling history may not be representative for the Trolle Land Fault System". If the Nakkehoved terrane was indeed located close to the Herluf Trolle Land area and Block V there, then why should the thermal evolution of the Nakkehoved terrane differ so much? If the Nakkehoved terrane was indeed located near Herluf Trolle Land, which is used as a representative area for the Trolle Land Fault System, then why would the Nakkehoved area not be representative of the Trolle Land Fault System too? This inconsistencies need to be clarifed and further discussed. Focus should be on evidence of vertical (fault/fold) movements along the Trolle Land Fault System, which are more likely to explain the exhumation and cooling history of the studied samples and potential discrepancies from one block to the other. A model of imbricate and/or in- and out-of-sequence thrusts (i.e., similar to that proposed in comment line 498 and in the attached figure) or simply folding and erosion should be discussed. A model of E–W-striking thrust imbricates is consistent with field observations of such structures in the Kilen area by von Gosen and Piepjohn (2003 their paragraph 52).
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Comment 126: Line 539: Here is a major issue which concerns the entire discussion about the Trolle Land Fault System and the redrawn cross section from Pedersen and Håkansson (2001). The issue sparks from the model proposed by Pedersen and Håkansson (2001). In their study, they report dominantly E–W- to WNW–ESE-striking thrust faults and folds, both in Kilen and St. Nord (their Kilen and Ingebord terranes). They propose that these E–W- to WNW–ESE-striking folds and thrusts formed as en-echelon structures along a major dextral, NW–SE- to NNW–SSE-striking fault system, the Trolle Land Fault System, whose fault segments represent major terrane boundaries, although none of these fault segments were actually observed. This model is based on the assumption that the De Geer Zone exists (see their Introduction and Discussion chapters). Again, circular reasoning. Note that Guarnieri (2015) interpreted the NNW–SSE-striking fault segment of the Trolle Land Fault System bounding the Ingebord terrane to the southwest as a thrust based on paleostress analysis and vitrinite reflectance.
Moreover, Pedersen and Håkansson (2001) constructed the highly unlikely NE–SW-trending cross section reproduced here using two areas (St Nord and Kilen) crosscut exclusively by E–W-striking thrusts and folds and separated by large distances covered by an icesheet. Instead, their N–S-striking local cross sections (their figs. 3, 7, and 9) are much more robust and realistic (largely because based on actual observations and data). Furthermore, their fig. 10 and associated data (including vitrinite reflectance and palynomorph color index) clearly show an E–W to WNW–ESE trend in Kronprins Christian Land, i.e., parallel to the Harder Fjord Fault Zone. Such a trend is also reflected by the data presented in the present study, which shows pre-Cenozoic cooling for the Amdrup Land samples in the south. A possible model similar to that proposed in the comment line 498 and the attached figure could thus involve in- and out-of-sequence thrusting along E–W- to WNW–ESE-striking thrusts separating the Kilen, Nakkehoved, and Herluf Trolle Land blocks IV and V, without the need for large-scale strike-slip displacement along postulated NNW–SSE-striking fault segments of the Trolle Land Fault System (whose existence and kinematics should, just like those of the De Geer Zone, be thoroughly reviewed and questioned) and without the need for allochthnous terranes.
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Comment 127: Lines 546–547: Do you mean that since the Tibetan frontal thrust and the San Andreas fault are active contemporaneously, they are connected? Rephrase into "their contemporaneous movements suggest they potentially interacted with one another" or similar.
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Comment 128: Line 549: Inappropriate. Replace by a period.
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Comment 129: Lines 550–551: Not at all clear from the data presented. It is suggested to delete this sentence.
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Comment 130: Line 552: Consistency. You used "oriented" in the rest of the manuscript (e.g., line 548).
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Comment 131: Lines 552–553: Do you mean that "the north–south-oriented Eurekan stress caused top-north thrusting along the Kap Cannon Thrust Zone"? If so, rephrase as such or similar.
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Comment 132: Lines 554–555: Not sure how this is derived from Guarnieri (2015) and Lyberis and Manby (2001) who:
-interpreted the possible fault bounding the Ingebord terrane in the southwest as a thrust (Fiskehalen thrust; Guarnieri, 2015);
-interpreted all the fault segments of the Trolle Land Fault System as thrust faults (Lyberis and Manby, 2001 their figs. 9 and 10) and clearly stated that "A strike-slip origin for the Wandel Sea Basin margin deformation pattern might be taken to imply a partitioning between the
observed compressional structures and a hypothetical (offshore?) major strike-slip fault. The proposed dextral strike-slip movement should, however, have been of Late Palaeocene
Eocene age but the compressional deformation of the Wandel Sea Basin margin was concluded by this time", thus further illustrating the circular reasoning behind the major dextral transform movements along the De Geer Zone. The De Geer Zone must exist because Svalbard and northern Greenland must have been adjacent prior to the opening of the Fram Strait (which is only an assumption/hypothesis based on the linear geometry/topography of these margins; De Geer, 1926; Holtedahl, 1936). However, the structures observed and interpreted in the area (e.g., Kronprins Christian Land) are all thrust faults. Thus, the De Geer Zone transform must be located offshore. This assumption is clearly biased and speculative.
In addition, the interpretation of von Gosen and Piepjohn (2003) of dextral movements along NW–SE-striking faults in Kronprins Christian Land and Peary Land is tentative since they mostly observed E–W-striking folds and thrusts and, in places, minor apparent lateral offsets along faults with relatively small (tens of meter) extent (their figs. 7b–c, 9a–b, 12a–b, 14, , 16a–c, and 17a–c). As illustrated by their fig. 11a–b, presumed major NNW–SSW-striking fault segments of the Trolle Land Fault System, e.g., Parish Bjerg Fault, are not exposed and some of them (e.g., main fault line not exposed in their fig. 11b) could instead reflect fold axes as suggested by oppositely dipping bedding surfaces and the same rock unit on either side of the inferred fault, i.e., a synform that would be parallel to the folds mapped c. 100–300 m to the northeast (their fig. 11b; Occam’s Razor again). Furthermore, the apparent lenses observed on extensively eroded outcrops along the inferred Parish Bjerg Fault (their figs. 7a and 8) could also reflect sedimentary processes. More evidence is needed to support a potential tectonic origin (e.g., outcrop-scale photographs of sheared lenses).
These uncertainties and inconsistencies must be clearly stated and the model proposed revised accordingly.
Svalbard and northern Greenland do not need to have been located significantly closer to one another than their present-day position if the rift stepped across the Fram Strait. It is of course possible that, instead of stepping, the rift was offset by 200 km offset along the actual transform faults in the Fram Strait, the NW–SE-striking Spitsbergen and Molloy fault zones, which parallel the Harder Fjord Fault Zone, Kap Cannon Thrust Zone, and related thrusts, as well as now-well-documented late Neoproterozoic Timanian thrusts across the entire Barents Sea and Svalbard (Klitzke et al., 2019; Koehl et al., 2022; Koehl et al., 2023; Koehl, 2025; Koehl and Stokmo, 2025; Koehl and Mottram, 2025). Regardless, large-scale strike-slip movements along the Trolle Land Fault System are highly unlikely, just like they are along the De Geer Zone and Billefjorden Fault Zone (Koehl, 2021; Koehl and Allaart, 2021; Koehl et al., 2022; Koehl, 2025).
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Comment 133: Lines 556–557: Delete. The Harder Fjord Fault Zone cannot be a conjugate strike-slip of the Trolle Land Fault Zone, simply because Piepjohn and von Gosen (2001) and Soper and Higgins (1987) have demonstrated that the Harder Fjord Fault Zone is a thrust and does not show any major lateral offset (see previous comments line 179).
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Comment 134: Lines 558–559: Von Gosen and Piepjohn (2003) did not "observe" this anywhere. They postulated it in various places (e.g., Kilen and potential intersection of Trolle Land Fault System and Harder Fjord Fault Zone; their figs. 3, 18, and 19), but definitely did not show any such outcrop relationship.
The work by Zinck-Jørgensen (1994b; and 1994a) is not published and any claim therein, thus, cannot be assessed.
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Comment 135: Lines 560–562: Here is another example of assumptions turned into pseudofact. Pedersen and Håkansson (2001) most definitely did not "observe" that the Trolle Land Fault Zone merged into the Harder Fjord Fault Zone but postulated it, stating " the NW-SE strike-slip displacements along the WHSSMB have conceivably been transmitted into bended wrench fault movements along the E-W trending Harder Fjord Fault Zone".
Stijl and Mosher (1998) focused on mineral deposits and their paper includes a simple review of the Harder Fjord Fault Zone and Trolle Land Fault System based on speculations from previous studies. Reference to their work should therefore be deleted as it is misleading and contributes to turn hypotheses/assumptions into pseudofacts. About the Trolle Land Fault System, they notably state that " The fault zone appears in the Citronen Fjord area as a prominent lineament that on aerial photographs can be traced in a west to north-west direction". Lineaments on aerial photographs could correspond to anything from glacial erosion along fold axes, to bedding surfaces, rhealogical contrasts, or magmatic intrusions, i.e., not necessarily reflecting the presence of faults. Stijl and Mosher (1998) then proceed by suggesting that " the structure [i.e., the topographic lineament interpreted to be the Trolle Land Fault Zone] continues until it eventually merges with the Harder Fjord Fault Zone at a point north of Frigg Fjord (Pedersen 1980; Fig. 22). This suggests that the Trolle Land Fault Zone originally developed as a splay of the Harder Fjord Fault Zone". According to Stijl and Mosher (1998), the existence of the Trolle Land Fault Zone is thus largely speculative and its formation as a splay of the Harder Fjord Fault Zone an assumption pending that the first assumption (i.e., the existence of the Trolle Land Fault Zone) is correct.
This sentence should be reworked or deleted since it is misleading as it is.
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Comment 136: Lines 564–565: Based on previous comments (e.g., lines 498, 539, 554–555, 556–557, 560–562), this sentence should be reworked or deleted, since most structures in northern Greenland (including Lockwood Island, Peary Land, and Kronprins Christian Land) strike E–W to WNW–ESE, i.e., oblique to the Wandel Hav Mobile Belt and related speculative faults (e.g., Trolle Land Fault System). It is recommended to consider the Wandel Hav Mobile Belt as a part of a repeatedly reworked, E–W- to WNW–ESE-striking fold-and-thrust belt, just like its northern continuation in Peary Land and its counterpart in Svalbard (i.e., reworked during the late Neoproterozoic Timanian, early to mid Paleozoic Caledonian, and early Cenozoic Eurekan orogenies; e.g., Koehl, 2025).
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Comment 137: Lines 567–568: How could the Kap Cannon Thrust Zone and the Harder Fjord Fault Zone, which have been demonstrated (see references in present study) to have accommodated mostly reverse movement and limited to no lateral movement be part of a transform fault system? In addition, the main fault segment of the Trolle Land Fault System (Trolle Land Fault Zone) has not been observed anywhere and was simply inferred, though not sure on what arguments (see comment lines 217–218; von Gosen and Piepjohn, 2003).
This is another illustration of weak circular reasoning: the Kap Cannon Thrust Zone and Harder Fjord Fault Zone are erroneously assumed to be part of an existing major transform system (De Geer Zone) despite showing no clear evidence of significant lateral movement, and a postulated fault (Trolle Land Fault Zone) is believed to be part of this transform fault system too, thus supporting the existence of this speculative fault system (De Geer Zone).
This needs reworking or to be deleted.
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Comment 138: Lines 569–570: The De Geer Zone strikes NNW–SSE to N–S whereas the Spitsbergen fault zone strikes NW–SE. These are two dicrete structures, which was not taken into account by Håkansson and Pedersen (1982) and their claim is, indeed as stated, a speculation. Nevertheless, it should be noted that they note about the Trolle Land Fault System that " Deformation consisted of reverse movements in the pre-existing system of steep, parallel faults defining the zone", i.e., in line with Guarnieri (2015) and Lyberis and Manby (2001), but not with major strike-slip movements. Delete "already".
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Comment 139: Lines 570–573: Damaske and Estrada's (2006; potentially update the publication year) interpretation of magnetic anomalies as pull-apart basins along the Wegener Fault can be dismissed since this fault was later demonstrated not to exist by the same lead author (e.g., Oakey and Damaske, 2006; Oakey and Stephenson, 2008; Rasmussen and Dawes, 2011; Oakey and Chalmers, 2012). Aeromagnetic data can reflect a wide range of structures (e.g., folds, faults, basins) and rock units (e.g., highly magnetic sedimentary beds, magmatic intrusions) and, used alone, are insufficient to confidently determine the nature of the subsurface.
The high-velocity ridges evidenced on refraction data off northern Greenland by Brotzer et al. (2022) and west of Svalbard by Ritzmann et al. (2002), Ritzmann et al. (2004), and Czuba et al. (2004) have been demonstrated (using high-resolution seismic reflection data) to reflect major west-dipping Caledonian thrust systems, which were inverted during post-Caledonian extension and accommodated mostly (if not exclusively) vertical (i.e., reverse and normal) movements (Koehl, 2025). This is consistent with Caledonian thrust systems in outcrops onshore western Svalbard (see references in Koehl, 2025). Since Caledonian-aged contraction also occurred in northern Greenland (M'Clintock Orogeny), it is probable that the high-velocity feature off northern Greenland, which parallels those west of Spitsbergen, corresponds to the rifted northwards continuation of Caledonian thrusts in Svalbard. Moreover, the seismic reflection line used to infer the presence of a tentative strike-slip fault off northern Greenland is of low quality and the related interpretation is therefore highly doubtful.
Considering Døssing et al. (2010), magnetic and gravimetric anomaly data (e.g., their figs. 5 and 7) show clear undulating anomalies off the coast of northern Greenland, which were interpreted as early Cenozoic Eurekan structures. The undulating geometries of these features suggests that they correspond to folds. Should any major, late Cenozoic transform/strike-slip fault be recorded in these datasets, it should either show offset of older anomalies or a linear anomaly of its own, none of which is the case. The data of Døssing et al. (2010) thus do not support the presence of the De Geer Zone off northern Greenland.
Jokat et al. (2016) do not mention the De Geer Zone and do not make any speculative inference about onshore to offshore structural correlation in the Fram Strait. They simply mention the NW–SE-striking Spitsbergen fault zone, i.e., an actual transform fault with ongoing seismicity.
The present sentence must therefore be amended, e.g., by replacing "Wandel Hav Mobile Belt or the De Geer Fracture Zone" by "preexisting Caledonian thrusts or Cenozoic to present-day transform faults such as the Spitsbergen fault zone (e.g., Jokat et al., 2016; Koehl, 2025)". It should be specified that the magnetic and gravimetric data of Døssing et al. (2010) do not support the presence of a major strike-slip or transform fault offshore northern Greenland.
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Comment 140: Line 573–574: Specify whether you refer to the De Geer Zone or the Spitsbetgen and Molloy fault zones.
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Comment 141: Line 575: Delete. This work refers to the De Geer Zone only once (in their conclusion; paragraph 23) and refers to Engen et al. (2008; already cited here). This reference is therefore irrelevant. Alternatively, specify why it is relevant and should be cited.
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Comment 142: Line 575: Replace by semicolon.
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Comment 143: Line 577: Perhaps shorten into "Tectonic evolution of North Greenland" since "tectonic" already implies regional scale.
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Comment 144: Line 578: Perhaps rephrase into "Latest Cretaceous (~70–66 Ma) heating and burial".
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Comment 145: Line 579: Add "Zone" for consistency.
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Comment 146: Line 593: Overall good paragraph. However, what about evidence of Late Cretaceous contraction on the conjugate western Barents Sea margin (e.g., Tromsø Basin, Veslemøy High, and Sørvestnaget Basin; Knutsen and Larsen, 1997; Kristensen et al., 2017; Rowan and Lindsø, 2017; Kairanov et al., 2021). Could a similar setting (i.e., early Eurekan contraction) be possible in northern Greenland? If not, why?
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Comment 147: Line 604: Rephrase into "Pre-Eurekan (~66–60 Ma) extension or convergence".
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Comment 148: Lines 605–607: This is not consistent with AFT data from the Harder Fjord Fault Zone core (Old core block), which had already cooled below 50 degrees prior to Eurekan contraction. How is this discrepancy explained? What would have needed to happen to cool this block down to 50 degrees in the Carboniferous–Early Cretaceous and avoid eroding it too much and keep the dated samples close to the surface (e.g., what type of fault movements, e.g., normal or reverse, along the Harder Fjord Fault Zone? Movements along other (un)related faults? other factors?)?
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Comment 149: Lines 607–609: One-sided argumentation citing only studies from one research group. What about the 40Ar–39Ar and (U–Th)/He geochronological constraints on Eurekan contraction in northern Ellesmere Island by Powell and Schneider (2022)? This data should be discussed here and mentioned in the Geological setting chapter.
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Comment 150: Line 611: How about adding mention time constraints on the Eurekan Orogeny in Svalbard, which was dated via 40Ar–39Ar, K–Ar, U–Pb, and U–(Th)–Pb geochronology to ca. 67–44 Ma (Barnes & Schneider, 2018; Blythe & Kleinspehn, 1998; Charles et al., 2011; Haaland et al., 2024; Jones et al., 2017; Koehl and Mottram, 2025; Schaaf et al., 2020; Schneider et al., 2018; Tessensohn et al., 2001). These constraints could instead/also be mentioned in the Geological setting chapter.
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Comment 151: Line 614: How is this reconciled with the data and model by Jones et al. (2016, 2017)? Their data and model suggest that the Kap Washington magmatic center is the source of 61 Ma tephra layers in the Central Tertiary Basin in Svalbard, which was (presumably) located near Kap Washington at the time and was already experiencing Eurekan contraction, e.g., 40Ar–39Ar, K–Ar, U–Pb, and U–(Th)–Pb geochronological ages of ca. 67–44 Ma (Barnes & Schneider, 2018; Blythe & Kleinspehn, 1998; Charles et al., 2011; Haaland et al., 2024; Jones et al., 2017; Koehl and Mottram, 2025; Schaaf et al., 2020; Schneider et al., 2018; Tessensohn et al., 2001). These ages largely overlap with the 71–61 Ma ages of the Kap Washington Group, not to mention that the AFT data of Dörr et al. (2012) suggested an even earlier onset of Eurekan contraction in Svalbard at ca. 82–80 Ma. These conclusions need to be included to balance the potential interpretation of geochemical data by Thórarinsson et al. (2011b).
In addition, silicic metaluminous magmatism does not exclusively originate in rift settings (e.g., I-type granites, which reflect subduction or collision, i.e., thrusting).
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Comment 152: Lines 621–624: Not in agreement with Powell and Schneider (2022). It is suggested to rework this sentence into "Early Palaeocene convergence presumably originated from the opening of Baffin Bay and the Labrador Sea, thus causing Greenland to move to the northeast (Fig. 1b). Coeval nearby rifting in Baffin Bay may have generated extension and exhumation by crustal thinning in Ellesmere Island (e.g., Vamvaka et al., 2019). However, the more proximal location of Eurekan thrusts in Ellesmere Island and new geochronological studies suggest ubiquitous contraction (Powell and Schneider, 2022)." or similar.
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Comment 153: Line 625: Rephrase this as "Rise of the Eurekan Belt during the Eurekan I (~55–48 Ma) and Eurekan II (~44–38 Ma) events" or "Onset of the Eurekan Orogeny during the Eurekan I (~55–48 Ma) and Eurekan II (~44–38 Ma) events" or similar.
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Comment 154: Lines 626–633: This belongs to the Geological setting chapter.
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Comment 155: Line 626: Replace by "the "Eurekan Orogeny"".
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Comment 156: Line 627: Replace by "and".
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Comment 157: Line 628: Replace by "i.e.,".
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Comment 158: Line 630: Not really. The actual data of each study can directly be compared by leaving out the interpretation the author(s) made of them. This needs to be done more systematically in the present manuscript (e.g., comment lines 607–609, 614, and 621–624).
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Comment 159: Line 631: Split this sentence into two here.
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Comment 160: Lines 632–633: The Eurekan Orogeny should include the entirety of the period with contractional movements in Arctic Canada, northern Greenland, Svalbard, and the Barents Sea. It is of course possible to define specific events/stages during the orogeny, although this practice is old-fashionned and inappropriate in areas with insufficient geochronological constraints (e.g., Fossen, 2020). Thus, while the segregation of several tectonic pulses/events during the Eurekan Orogeny is acceptable, the definition of Eurekan Orogeny as only one part of the period during which orogenesis occurred is inappropriate because misleading and confusing, especially when using the term "Pre-Eurekan" (event) for a period that is clearly part of the Eurekan Orogeny. Please update this definition and, if possible, rename Eurekan tectonic stages/events/pulses/phases into Eurekan I, II, and III (or Eurekan 0, 1, and 2) or similar.
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Comment 161: Line 636: Replace by "during".
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Comment 162: Line 636: Replace by "assuming".
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Comment 163: Line 637: Add "in the Central Tertiary Basin in Svalbard and" to better reflect the interpretation of Flowerdew et al. (2023).
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Comment 164: Lines 642–645: Why should it be different if western Spitsbergen was located adjacent to northern Greenland? This needs to be clarified.
In addition, it seems here that Vamvaka et al. (2019) is used to argue for subsidence and basin formation, but not extension. This is not consistent with the previous section in which the same study is used to suggest extension-related exhumation in Ellesmere Island during at the same time as Eurekan contraction in Svalbard and northern Greenland. Clarify or delete both sentences.
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Comment 165: Line 646: Do you mean that Paleogene orogenic basins stopped subsiding and started to exhume? If so, rephrase as such, since "tectonic inversion" refers to reversal of tectonic movements, e.g., from reverse to normal or normal to reverse, along related faults.
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Comment 166: Line 648: Also add the initial study by Wilson (1976)?.
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Comment 167: Line 649: Why is that? According to Wilson (1976) and Piepjohn et al. (2013), sedimentary rocks of the Eureka Sound Group are Maastrichian to Paleocene and according to Lyck and Stemmerik (2000), sedimentary deposits of the Thyra Øya Formation are late Paleocene (to earliest Eocene), i.e., no younger than 55 Ma, which coincides with the onset of your Eurekan I event. Could deformation have initiated during the Eurekan I event? If not, specify why.
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Comment 168: Lines 649–650: In what way and why? Do you mean that coeval deformation of Eureka Sound Group and Thyra Øya Formation deposits in northern Greenland and Ellesmere Island suggest homogeneous exhumation? If so, not necessarily since the extent of deposits of the Thyra Øya Formation is restricted to a narrow area. Further clarify this statement.
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Comment 169: Line 654: Which areas do you suggest should be targeted in future studies?
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Comment 170: Lines 657–658: What about the Eurekan-related topography had already been deeply eroded and sedimentary deposition started waning? Could this have contributed? If not, why not?
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Comment 171: Line 667: Possibly rephrase into "Post-Eurekan (~34–26 Ma) opening of the proto Fram Strait".
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Comment 172: Line 681: Be consistent. Either use fully spelled (like here) or abbreviated orientations (e.g., E–W and NW–SE).
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Comment 173: Line 683: What about transtensional reactivation inherited E–W- to WNW–ESE-striking faults parallel to the Molloy and Spitsbergen (transform) fault zones in the Fram Strait, e.g., late Neoproterozoic Timanian thrust systems in Svalbard (Koehl, 2025; Koehl and Mottram, 2025) and northern Greenland (Rosa et al., 2016; Estrada et al., 2018)?
This should be discussed against the hypothesis of the De Geer Zone.
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Comment 174: Line 685: This is supported by structural and geochronological studies in Svalbard (Barnes and Schneider, 2018; Haaland et al., 2024; Koehl and Mottram, 2025). Add reference to these works here.
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Comment 175: Line 687: Replace by "Baffin Bay and the Labrador Sea".
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Comment 176: Line 692: Also add reference to Koehl (2025).
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Comment 177: Lines 692–693: Alternative interpretations have been made and need to be discussed too, e.g., exhumation as a core complex (Schaaf et al., 2020) and contribution of Eurekan contraction to exhuming Prins Karls Forland and related basement highs (Gabrielsen et al., 1992; Kleinspehn & Teyssier, 1992; Kleinspehn & Teyssier, 2016; Lepvrier, 1990; Koehl, 2025).
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Comment 178: Lines 693–694: Replace by "normal faulting along N–S- to NNW–SSE-striking faults and normal-sinistral reactivation of inherited WNW–ESE-striking Timanian thrust systems onshore–offshore Spitsbergen (Haaland et al., 2024; Koehl, 2025; Koehl and Mottram, 2025)".
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Comment 179: Lines 694–695: Rephrase into "Danskøya and Sjubrebanken basins north and northwest of Svalbard (Ritzmann and Jokat, 2003; Koehl, 2025)" or similar.
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Comment 180: Lines 697–699: Why should exhumation always be related to tectonic processes and changes in plate kinematics? Could a decrease in exhumation rate not simply be related to the absence of continental mass to erode in nearby areas and, e.g., because breakup has been been achieved in the Fram Strait, which was proposed to have occurred at ca. 24 Ma; Engen et al., 2008? The model proposed in Koehl (2025) shows that plate kinematic changes upon breakup are not required and unlikely in the Fram Strait. This needs to be discussed here.
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Comment 181: Lines 699–700: Replace by "divergence of".
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Comment 182: Lines 700–702: Do you simply mean that the continental crust was sufficiently thinned to achieve breakup and, thus, that exhumation stopped? If so, write so in simpler terms. The current sentence is too long and loaded with unnecessary technical jargon.
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Comment 183: Line 707: Add reference to Prestvik (1978) and Amundsen et al. (1987).
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Comment 184: Lines 708–709: What does this mean? Renewed rifting/extension or rift-shoulder uplift and erosion or other? Specify.
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Comment 185: Lines 714–715: Do you have any evidence for active rifting in the Late Cretaceous in this area (e.g., geochronological data for fault-rock along normal faults? Syn-tectonic sedimentary deposits? Other?). If so, mention these. In addition, this conclusion is inconsistent with, among others, Dörr et al. (2012) and Powell and Schneider (2022) whose studies suggest a Late to latest Cretaceous onset for Eurekan contraction in Svalbard and Arctic Canada. Make sure their lines of evidence are discussed in the Discussion and update this conclusion accordingly.
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Comment 186: Line 717: It is stated lines 453 to 454 that "The limited resolution of the model from the southern block does not allow inferences for post-Eurekan fault movement on the Kap Cannon Thrust". This sentence or the statement line 453 to 454 must thus be amended.
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Comment 187: Line 718: Outdated approach to split orogenies/contractional episodes into discrete tectonic stages, especially based on partial/incomplete geochronological data (e.g., Fossen, 2020). If you still want to proceed with these discrete stages/pulses, update the name of these events as suggested in comment lines 632–633.
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Comment 188: Lines 718–721: Revise according to previous comments, especially related to the highly doubtful character of the Trolle Land Fault System, where E–W-striking thrusts and folds dominate, whereas NNW–SSE-striking faults parallel to the postulated De Geer Zone and Trolle Land Fault System are inferred but never observed.
It is however agreed that all the system of E–W- to WNW–ESE-striking thrusts and folds in Arctic Canada (Eurekan thrusts; Powell and Schneider, 2022), Svalbard (e.g., inherited Timanian thrusts reactivated as Eurekan thrusts and mid–late Cenozoic strike-slip faults; Koehl, 2025; Koehl and Mottram, 2025), Fram Strait (Molloy and Spitsbergen fault zone), and northern Greenland (including those in Kronprins Christian Land and Herluf Trolle Land, the Harder Fjord Fault Zone, Kap Cannon Thrust Zone, Kap Christiansen Fault, Kap Christiansen Thrust, and the potential in- and out-of-sequence thrusts proposed in the figure attached to comment line 498) form a coherent fold-and-thrust belt.
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Comment 189: Line 722: Replace by "orogenesis"?
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Comment 190: Line 723: Specify that you mean "Eurekan contractional deformation".
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Comment 191: Line 724: Adjective needing to be supplemented by a noun, e.g., "Eurekan episode", "Eurekan orogeny", or similar.
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Comment 192: Line 726: Topography can either be positive (e.g., mountain ranges) or negative (e.g., troughs). Specify what kind of topography was developed.
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Comment 193: Line 728: Update according to comment lines 697–699.
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Comment 194: Lines 733–737: Uninformative and unspecific. Move to (the end of the) Introduction chapter? alternatively delete completely.
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Comment 195: Line 741: UnFAIR (meant in reference to the FAIR research principles: Findable, Accessible, Interoperable, and Re-usable). Make sure that the Digital Object Identifyer is included here (and in the Method chapter) and that the relevant dataset(s) are submitted, accepted, and published on the specified online Open Access data repository.
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CC3: 'Comment on egusphere-2026-1389', Paul. Green, 16 Apr 2026
reply
Comment on Meier et al. 2026-1389 ”The Northernmost Mountain Belt on Earth: Birth and Death of the Eurekan Orogen in North Greenland” EGUsphere
Under Review for Solid Earth April 2026
Paul Green1, James Chalmers2, Peter Japsen2
1 Geotrack International, 1/11 Tullarmine Park Road, Tullamarine, Victoria 3043, Australia
2 Geological Survey of Denmark and Greenland (GEUS), Øster Voldgade, 10, 1354 Copenhagen, Denmark
Meier et al. present apatite fission track (AFT) and apatite helium (AHe) thermochronology data on samples from North Greenland and discuss the resulting thermal history interpretations within the plate tectonic context surrounding the Eurekan Orogeny. Their study in many ways parallels our own work in the region (Japsen et al., 2021, 2023), so we consider ourselves well placed to offer the following comments on their work.
Our comments are focussed on two aspects of their work, the plate tectonic framework of the region and the way that thermal histories have been extracted from AFT and AHe data.
Plate-tectonic framework Maastrichtian
Meier et al. (Line 18) interpret a ’short-lived heating period during the latest Cretaceous (~70–65 Ma), with temperatures exceeding 120°C, likely associated with a Late Cretaceous basin along the margin of North Greenland’. They attribute this event to ‘increased and locally highly variable geothermal gradient and enhanced heat transfer along faults’ (Line 581) and claim that this interpretation is ‘…in marked contradiction to Japsen’s et al. (2023) assumption of “regional Maastrichtian exhumation” which “possibly reflects doming above the rising Iceland Plume”’. (Lines 585-587), Meier et al. ‘..consider both Maastrichtian exhumation and Cretaceous movements associated with the Iceland Plume unlikely’ (Lines 587-588).
In contrast to this statement by Meier et al., Japsen et al. (2023) presented several lines of evidence pointing to Maastrichtian uplift across the Arctic. Latest Cretaceous uplift was widespread in the North American Arctic (Rickets; 1994), and sedimentation in the Sverdrup and Beaufort-MacKenzie Basins was interrupted at 68 Ma by an unconformity (Embry and Beachamp, 2019). Unconformities of the same age are found on- and off-shore West Greenland (Dam et al., 2009; Gregersen, et al., 2022), and in the Wandel Sea Basin of North Greenland a significant hiatus separates sediments of Santonian age from upper Paleocene deposits (Lyck and Stemmerik, 2000; Hovikoski et al., 2018. AFTA data from Svalbard record Maastrichtian exhumation (Japsen et al., 2023) which led to the formation of the Albian – mid-Paleocene hiatus in the Central Tertiary Basin. And Japsen et al. (2023) discussed evidence from AFT studies in Arctic Canada for Maastrichtian exhumation in that area. We also suggest that the Maastrichtian – mid-Paleocene hiatus across the south-western Barents Shelf also represents this episode (Henriksen et al., 2011; Jones et al., 2017). An unconformity of Maastrichtian age is also present off central and southern west Norway (Vergara et al., 2001; Sømme et al., 2019).
AFTA data from North Greenland presented by Japsen et al. (2021, 2023) do not resolve definite evidence of Maastrichtian cooling, possibly because any such effects were overprinted by the high temperatures during subsequent paleo-thermal episodes.
Japsen et al. (2023) suggested that this latest Cretaceous unconformity documented across vast parts of the Arctic reflects the doming above the rising Iceland plume head upon its arrival in the upper mantle, prior to its impact at the base of the lithosphere. The picritic volcanism in West Greenland was the surface expression of the impact of the Iceland plume on the lithosphere (Pedersen et al., 2017) at the same time (62.5 Ma) as sea-floor spreading started in the Labrador Sea (see below).
Paleocene
Meier et al. (Lines 40-42) write ’Formation of the Eurekan Belt was strongly episodic (Fig. 1b). First movements, here referred to as the pre-Eurekan stage, occurred during the Late Cretaceous to Palaeocene, when rifting and spreading of the Labrador Sea/Baffin Bay initiated (Oakey and Chalmers, 2012; Roest and Srivastava, 1989)."
The onset of spreading in Labrador Sea (and possibly Baffin Bay) can be dated accurately to mid-Paleocene time, because the first sea-floor spreading magnetic anomaly is 27N (Chalmers and Laursen, 1995), which lasted from 62.53 to 62.278 Ma (Vandenberghe, et al., 2012), not ’during the Late Cretaceous to Palaeocene’ as Meier et al. write (above). This phase of sea-floor spreading caused Greenland to move towards Svalbard, causing E–W- to ENE–WSW-oriented compression on Svalbard, the West Spitsbergen Fold Belt (Japsen et al., 2023 and references therein, Manby and Lyberis, 1996; Bergh et al., 1997). This phase of movement also caused compression in northern Greenland at the same time, reflected in the Paleocene (~60 Ma) cooling recorded by Japsen et al. (2021, 2023). The movement was dextral relative to Ellesmere Island and, at least in the northeast, was probably along the Wegener Fault. Further southwest, there appears to have been no single boundary and the dextral movement was distributed across an area up to 500 km wide (Harrison, 2004; Japsen et al., 2013; Oakey and Chalmers, 2014; Oakey and Damaske, 2006). Japsen et al. (2023) suggested the onset of the Eurekan Orogeny therefore coincides with the mid-Paleocene onset of sea-floor spreading in the Labrador Sea.
Eocene
Greenland continued to move NE relative to North America until sea-floor spreading started between Greenland and Eurasia at 57 Ma (early Eocene) (Gaina et al., 2017), causing Greenland to move north relative to North America and southward verging thrusting began in eastern Ellesmere Island. These movements represent the main stage of the Eurekan Orogeny (Harrison, 2004; Piepjohn et al., 2016; Japsen et al., 2023).
Post-Eurekan
Movement between Greenland and North America ceased at 35 Ma (Kristofferson & Talwani, 1977) and the Eurekan Orogeny came to an end. Any movements "between ~34–26 Ma for the post-Eurekan, with intermittent periods of slow exhumation (Fig. 1c)" (Meier et al. Lines 56-57) cannot, therefore, be due to the northward movement of Greenland relative to the Canadian archipelago.
It is also worth noting that many of the thermal histories shown by Meier et al. in their Supporting Information Fig. S4 show a distinct Miocene cooling phase Meier et al. do not discuss this aspect of their results but it is consistent with cooling around 10 Ma reported by Japsen et al. (2023).
Directions of plate movements
The directions of movement shown in Figure 1b of Meier et al. do not agree with the known times and/or directions of plate movements. There was a little, very slow extension in Labrador Sea and Baffin Bay prior to 62 Ma, but the timing of this movement is not known and may have taken place during the early- to mid-Cretaceous extension events documented on both sides of the Labrador Sea (Balkwill, 1987; Gregersen et al., 2022). There is thus no direct evidence for the pre-Eurekan sinistral movement between Greenland and Ellesmere Island prior to 62 Ma shown in Meier et al (Figure 1b Pre-Eurekan).
Greenland moved SW to NE from 62 Ma to 57 Ma as documented by Oakey & Chalmers (2012). The spreading directions shown in Meier et al (Figure 1b Eurekan I) are inaccurate. There is also no evidence for spreading between Eurasia and Greenland at this time. At 57 Ma, Greenland moved almost directly northwards relative to Ellesmere Island (Oakey & Chalmers, 2012), so the spreading directions in Meier et al. (Fig 1b Eurekan II) are very inaccurate.
Thermochronology
Meier et al. state " Exhumation associated with the different stages of Eurekan deformation was dated by low-temperature thermochronology on northern Ellesmere Island (Vamvaka et al., 2019). These data revealed rapid exhumation between ~66-60 Ma for the pre-Eurekan, between 55-48 Ma and 44-38 Ma for Eurekan I and II, and between ~34–26 Ma for the post-Eurekan, with intermittent periods of slow exhumation (Fig. 1c)."
Inappropriate constraints on thermal histories
Japsen et al. (2023) expressed doubts about the thermal history solutions derived by Vamvaka et al. (2019) on the grounds that they were based on a restricted set of AHe ages with no independent control on selection, and that they were governed largely by artificial and partly undeclared constraints on allowed histories.
The thermal history solutions presented by Meier et al. are also dominated by external constraints on viable histories, as displayed in their Figure S4 from the Supporting Information file. Constraint boxes defining depositional ages are straightforward and necessary, but additional constraint boxes are placed in each of the intervals regarded by Meier as defining stages of the Eurekan Orogeny, as listed above. Meier et al. explain this as a means of testing if “the cooling histories … (were) in agreement with exhumation phases (defined by) Vamvaka et al., (2019)”. However, for many samples, Meier et al. placed two constraint boxes within the same interval, and since allowed paths must pass through each box, this has the result that the thermal history solutions pass from the higher temperature constraint box to the lower temperature box, producing a cooling event controlled solely by these artificial constraints. In all samples the apparent cooling episodes shown by the thermal history solutions are governed by these artificial constraints. Given the wide range of temperature-time conditions within the cooling paths, we consider that the data cannot be regarded as providing definitive constraints on the timing of major cooling episodes.
Problems with AHe methods
Meier et al. note that their AHe ages show no systematic relationship with either equivalent uranium content or grain radius, as would be expected according to the diffusion models used in their interpretation (Farley, 2000; Flowers et al., 2009). This observation is not restricted to the study by Meier et al. but is a common feature of almost all studies using AHe methods. This can now be understood as a result of ramp-heating experiments on He loss from apatite (e.g. McDannell et al., 2018; Guo et al., 2021) which show that in many apatites the loss of He during heating is not governed by thermally activated diffusive loss but by other processes which are yet to be fully defined. These key observations explain why AHe ages often show a high degree of dispersion. Because of this, thermal history solutions derived from AHe ages using thermally activated diffusion models such as those employed by Meier et al. cannot be regarded with any confidence. We should emphasise that such problems are by no means the sole province of Meier et al. but apply to all studies in which AHe data have been used in this way.
AFTA data from Japsen et al. (2021, 2023)
Meier et al. state that they reassessed previous AFT data in the region from Japsen et al. (2021, 2023) but were unable to extract thermal histories because “data were originally modelled without clear descriptions and justifications of the included constraints” and due to “insufficient documentation of key parameters” (Lines 280-283). We find these comments difficult to understand, as all aspects of the data and treatment were reported by Japsen et al. (2021, 2023) in Supplementary Data files.
Meier et al. add (Line 281) that the thermal histories from Japsen et al. (2012, 2023) were “using an unpublished and inaccessible annealing algorithm”. The methods adopted by Japsen et al have been extensively described in numerous publications over the last 40 years and reviewed in detail e.g. by Green and Duddy (2012, 2020) and Green et al., 2013, 2022). We have written that thermal histories are extracted using a kinetic annealing model consisting of a series of fanning Arrhenius plot models, with constants that vary systematically with wt% Cl. While specific constants are undeclared, we have stated that the treatment is very similar to the model of Ketcham et al. (2007), and similar results should be obtained using that model. Assessing our data in this way should have been a straightforward task for Meier et al.
It is disappointing that Meier et al. should focus on this aspect of our work when their treatment is based on inapplicable models for the AHe system (above), when they use Dpar as a kinetic parameter even though this was shown many years ago to be a very poor indicator of the variability of fission track annealing kinetics in different apatite species (Green et al., 2005), and when their thermal histories are largely the artefactual product of their methods (above).
Meier et al. claim (Lines 341-342) that “the evaluation of the cooling phases of the individual samples from Japsen et al. (2021, 2023) are broadly consistent with the cooling phases supported by our thermal history models”. We do not agree with this suggestion (see below). Japsen et al. (2021, 2023) found that the Cenozoic uplift history of the region was dominated by Paleocene, end-Eocene and Miocene exhumation episodes, but found no evidence of cooling during phases Eurekan I and II (55–38 Ma) claimed by Meier et al. and Vamvaka et al. (2019). As above, we suggest that evidence for these cooling episodes is an artefact resulting from inappropriate constraints on viable thermal history models.
Results from Amdrup Land
Meier et al. state (Lines 346-347): “In contrast to Japsen et al. (2021, 2023) our thermal history models support Palaeogene cooling in Amdrup Land”. But the thermal history solutions shown in the Supplementary Information file for samples CXX-14 and CXX-25 (the only samples from Amdrup Land shown therein) do not show any Paleocene cooling, but are dominated by earlier events, in agreement with Japsen et al. (2021, 2023).
Differing chronologies of exhumation – Why?
Meier et al., following previous work (Piepjohn et al, 2016; Vamvaka et al., 2019), propose that the Eurekan orogeny was defined by four episodes of exhumation, viz:
1: Pre-Eurekan (Late Cretaceous-Paleocene),
2: Eurekan I (55-45 Ma),
3: Eurekan II (45-34 Ma)
4: post Eurekan (34-26 Ma).
In contrast, our results from North Greenland and Svalbard, together with published work reviewed by Japsen et al. (2023), suggest a different exhumation chronology:
1: Regional Maastrichtian exhumation, possibly reflecting the rise of the Iceland Plume (c. 68 Ma).
2: Paleocene exhumation due to inversion of fault zones linked to the onset of sea-floor spreading west of Greenland (c. 60 Ma).
3: Regional end-Eocene exhumation post-dating sea-floor spreading west of Greenland (c. 35 Ma).
4: Regional, late Miocene exhumation (c. 10 Ma).
We suggest that evidence presented by Meier et al. and Vamvaka et al. (2019) for their Eurekan I, Eurekan II and post-Eurekan episodes arises in large part from artificial constraints imposed on cooling histories derived from their thermochronology data.
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Citation: https://doi.org/10.5194/egusphere-2026-1389-CC3
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This is an interesting paper indeed. However, it omits some key petrological and geochronological works from Prins Karls Forland, Svalbard. The paper by Branes & Schneider (2019) is referenced in the text, but the paper by Schneider et al. (2019; same volume as the aforementioned paper) is not. The latter is of the utmost importance because it reports, to my knowledge, the only modern Ar-Ar data, yielding the timing of the Eurekan event in Svalbard. Moreover, Kośmińska et al. (202, JMetGeol) provide evidence for the upper greenschist/lower amphibolite facies conditions for this event in the very same section of the Pinkie unit in Prins Karls Forland. I believe that this information should be mentioned in the presented manuscript and discussed in relation to the deeper parts of the Eurekan-reworked rock complexes in N Greenland.