the Creative Commons Attribution 4.0 License.
the Creative Commons Attribution 4.0 License.
| 25 Sep 2024
Emplacement Age of the Sevier Gravity Slide, Utah, USA
Abstract. The Marysvale volcanic field in southwestern Utah hosts three large volume gravity slides: the Sevier (SGS), the Markagunt (MGS), and the Black Mountains (BGS). The gravity slides are composed of lahar deposits, lava flows, and ash-flow tuffs erupted from former stratovolcanoes and other vents during the Oligocene and Miocene. The ash-flow tuffs are prime targets for dating to constrain the age of the gravity slides because some ash-flow tuffs are deformed within the slides, whereas others are undeformed and cap the slides. Furthermore, the gravity slides produced pseudotachylyte during slide motion, a direct indicator for the timing of each slide. This work provides new 40Ar/39Ar dates for several ash-flow tuffs and pseudotachylyte for the SGS, along with U/Pb zircon dates for one deformed tuff and overlying alluvium at the slide plane. Results show that the slide was emplaced at 25.25 ± 0.05 Ma and was immediately followed by the eruption of the Antimony Tuff at 25.19 ± 0.02 Ma. The model presented here suggests that the intrusion of magma related to the Antimony Tuff acted as a triggering mechanism for the slide, and that slide movement itself led to decompression melting and eruption of the Antimony Tuff. This sequence of events occurred on a geologically rapid timescale and may have been virtually instantaneous.
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RC1: 'Comment on egusphere-2024-2899', Martha Papadopoulou, 06 Nov 2024
Comments on the submitted pre-print “ Emplacement age of the Sevier Gravity Slide, Utah, USA” by T. Rivera, et al.
Reviewer: Martha Papadopoulou
General comments: the study is looking into the association between gravity slides, their cause of origin (e.g. new injected magma into a magma chamber) and their consequences on the volcanism of an active volcanic region (e.g. decompression melting due to displacement) using age constraints from different crucial layers of the studied formation. The studied area is the Sevier Gravity Slide, and their results are compared with other studies. The manuscript reads well, giving insights on the geological history of the area, the work that has been done so far, and how this study connects with previous works on the area. There is an overall good understanding of the associations between the different layers and a good understanding of the methods used and their limitations. I really enjoy how the works builds upon previous results and refines them, adding to the knowledge of the volcanic history of the region, and to the poorly understood causes of a gravity slide as well as their consequences to an area.
Specific comments: the few comments provided here on specific issues identified are meant in order to improve the quality of the manuscript and help a reader with no previous knowledge of the studied area to gain a better understanding. It is upon the authors to decide if they will act on them or not, but hopefully they will be taken into account on a revised version.
- Section 2 provides a lot of information about the geological background of the area, referring to a lot of features, such as plateaus, calderas etc.. I believe the section (and consequently the reader) would benefit from an extra map (or set of maps if too complicated) showing the location and association between these features. For example, maybe a map showing the extent of the Colorado Plateau and the Basin & Range province, with the Marysvale VF and the Marysvale gravity slide complex depicted on it; the location of the three calderas mentioned in the text; and the relative location of the Markagunt and Black Mountains gravity slides compared to the Sevier gravity slide.
- At the beginning of section 3 different units are described as deformed if within the SGS or undeformed if above it. However, towards the end of the section the Osiris tuff, which is marked as an undeformed unit, is described to be deformed but not from the SGS. I feel this is a bit contradictory. Maybe an additional sentence at the beginning (or somewhere else) of the section clarifying that all units deformed by an event other than the SGS will be seen (for the purposes of this study) as undeformed might be more appropriate.
- What units does the Mount Dutton Formation comprises of? From the stratigraphic column in Fig. 1 I had the impression that Mount Dutton Formation includes all the various units depicted in there, then I got confused from Fig. 5, where Kingston Canyon Tuff and Mount Dutton Alluvium where described as belonging to separate formations? Could you add to the stratigraphic column the various formations and their extent?
Technical comments:
- Not sure it’s only on my computer, but rows 44-46 (first three sentences in the introduction part) have a different format to the rest of the text. Please format accordingly
- Rows 50-51 “…a friction induced… in sliding”: references needed
- Row 54: could you define the word “gigantic”? E.g. average area extent
- Rows 61&64: you have performed 40Ar/39Ar dating, why is there suddenly a * to the 40Ar? It’s not consistent with further down the text
- Rows 81-82 “The breakaway regions… volcanic activity”: references needed
- Row 84 “…the breakaway of the… batholith”: references needed
- Row 86: for consistency with the rest of the text provide first the older then the younger age constraint of the volcanic activity (32-23 Ma)
- Row 86: please re-write to “Peak volcanic activity (32-23 Ma)…”
- Row 117: Fig. 2a-c
- Row 118: “…and biotite (Fig. 2c)”
- Row 118: “…igneous rocks (Fig. 2b)”
- Row 120: Fig. 2d-f
- Row 121: “…1-3 cm long (Fig. 2e)”
- Row 122: Fig. 2i
- Row 131: Fig. 2g-h
- Row 221: ages 23.0 and 25.4 presented as advised in comment 7
- Row 225: show the Buckskin Breccia the stratigraphic column of Fig. 1
Citation: https://doi.org/10.5194/egusphere-2024-2899-RC1 -
AC1: 'Reply on RC1', Tiffany Rivera, 27 Nov 2024
Dear Martha, Thank you for the comments on the preprint. Your suggestions are much appreciated. Below you will find responses to each of your comments, both specific and technical.
Specific comments:
- In regards to comment 1, yes, I agree that a map with the regional geology and the features discussed would be helpful to a reader that is unfamiliar with the location. I will include additional maps in the revision.
- In regards to comment 2, thank you for pointing out the confusion. The Osiris Tuff is undeformed by the SGS (which is 25 Ma), but in another location it is deformed by the younger MGS (23 Ma). I will clarify this in the text.
- In regards to comment 3, the Mount Dutton formation consists of lahar flows and welded ash-flow tuffs, including both the Kingston Canyon tuff and the alluvium that was sampled directly above the tuff. I’m unsure where the confusion comes in as the caption to figure 5 indicates that both the tuff and alluvium are of the Mount Dutton Formation. Is there a place that I could better clarify?
Technical comments
- I have added references, corrected fonts, and specified the individual panels of figures.
- In regards to the comment for the use of * in 40Ar/39Ar, the * indicates that it is radiogenic, so for instance, 70%Ar* indicates the amount of radiogenic Ar produced from the K decay. According to Schaen et al (2020), the most common usage for dates is 40Ar/39Ar, which I will revise to consistently use throughout the paper. However, the * must be included in describing the amount of radiogenic argon present, as in the results section 4.1.
- In regards to the comment about showing the placement of the Buckskin Breccia on the strat column of figure 1, I would like to decline this figure modification suggestion. I would like to keep the units in figure 1 restricted to those for which we provide new dates for in this publication.
Citation: https://doi.org/10.5194/egusphere-2024-2899-AC1
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RC2: 'Comment on egusphere-2024-2899_Emplacement age of the Sevier Gravity Slide, Utah, USA Rivera et al. 2024', Bryant Ware, 14 Nov 2024
General Comments:
The study presented in this manuscript utilised structurally constrained samples and multiple geochronometers to tightly constrain the emplacement age of the Sevier Gravity Slide. Utilising this approach the authors contribute to the ongoing debate around the causality of gravity slides. The manuscript is structured well, the data is presented logically and clearly, with sufficient consideration and use of previous data/studies results, and connects these localised results well to the ‘outstanding questions’ of the origin and connections between gravity slides and igneous activity. I thought the approach of the study is well informed of and builds upon previous work to then have a targeted approach of what techniques and samples are best to address the hypothesis. The understanding of the geochronology data within the context of the structural relations of the gravity flow deposits provides a cool approach to provide such tight constraints in timing between these various units.
Specific Comments:
- As the study area is quite a local study, additions to the map figure would be much appreciated by a reader such as myself without much knowledge of the geology of the area/region. If there is the ability to have more panel slightly zoomed out further than the presented zoom (still including this panel though) would benefit the readers who are not familiar with the local geology, as well as providing easier ability for the readers to follow the large number of features presented in the ‘Introduction’ and ‘Geologic background’ sections.
- I would like to see just a little more detail added to the analytical sections 3.1 and 3.2. As a few different analytical techniques were conducted for the Ar-Ar geochronology (some of the samples (the ash flow tuffs) are weighted means of many single grain analyses, then the lava and pseudotachylyte are step heated), the section would benefit from the added information of how the grains were selected. Were the sanidine and the plagioclase also hand-picked prior to the analyses like the pseudotachyle glass? Where these selections made under a binocular scope? Were the two step heating experiments on populations? Although some of this may be known/be able to be inferred by readers with an Argon geochronology background, having this information detailed would help the interpretations/understanding the interpretations being made of the data. Just about the same request of added detail to the U-Pb analytical section as well; were the zircon grains picked after being separated via panning, heavy liquid, and magnetic, or is this more of a dump mount after the various separation techniques? This information will provide more clarity on the assessing the interpretations being made of the U-Pb data (hand picking can provide some bias, therefore good to note particularly as multiple fractions (with significant peaks) are observed in the Kingston Canyon Tuff (images of the analysed grains in the supplementary material would be great as well).
Technical Corrections:
Line 61: The asterisk is not represented in every instance, could the ‘*’ after 40Ar be defined… and if required, the writing of 40Ar*/39Ar (instead of 40Ar/39Ar) be standardised throughout the text. Those that are not as familiar with the argon system may not immediately understand the use of the asterisk as a radiogenic Ar notation.
Line 99: The Markagunt gravity slide and the Sevier gravity slide have already been defined as MGS and SGS, respectively, in the ‘Abstract’ as well as lines 54 and 55 in the ‘Introduction’. No need to define them again here.
Line 195: Same comment as above regarding the use of the asterisk after 206Pb.
Figure 5 Caption: IsoPlotR should be IsoplotR. The two references in the caption are not in the bibliography; Galbraith and Laslett (1993) and Vermeesch (2021).
Figure S2 Caption: A space needs to be added after ‘(b)’.
Supplementary Material Tables 2-5: The Taylor (1982) and the Min et al. (2000) references are not included in the bibliography.
Supplementary Material Tables 6-7: Could a ‘caption’ for the U-Pb tables be added that denotes the uncertainties (e.g. are the isotopic ratio data 1 sigma %, 2 sigma % or 1 standard error %).
Citation: https://doi.org/10.5194/egusphere-2024-2899-RC2 -
AC2: 'Reply on RC2', Tiffany Rivera, 27 Nov 2024
Dear Bryant, Thank you for the comments on the preprint. Your suggestions are much appreciated. Below you will find responses to each of your comments, both specific and technical.
Specific:
- In regards to comment 1, yes, I agree that a map with the regional geology and the features discussed would be helpful to a reader that is unfamiliar with the location. I will include additional maps in the revision.
- Thank you for the suggestion in comment 2. I will add the additional methodology to the argon and U/Pb sections. For your reference, though, yes, feldspars were handpicked under a binocular scope. The step-heating experiments were conducted on purified bulk samples (that is, not on individual glass shards or groundmass fragments). Zircon grains were separated with magnetic and heavy liquid techniques prior to mounting. CL images of the grains will be provided in the supplement.
Technical:
- The * indicates that it is radiogenic, so for instance, 70%Ar* indicates the amount of radiogenic Ar produced from the K decay. According to Schaen et al (2020), the most common usage for dates is 40Ar/39Ar, which I will revise to consistently use throughout the paper. However, the * must be included in describing the amount of radiogenic argon present, as in the results section 4.1. For Pb, the text has been updated to reflect the convention used in Condon et al. (2024) which excludes the ‘*’.
- The text has been updated for typos.
- Full citations are provided for references in the supplement.
- Clarifications have been made to the uncertainties in the U-Pb data tables.
Citation: https://doi.org/10.5194/egusphere-2024-2899-AC2
-
EC1: 'Comment on egusphere-2024-2899', Fred Jourdan, 20 Nov 2024
Dear Dr Rivera,
I have now received recommendations from two reviewers. Both reviewers agree that the data and the main question you attempt to address is interesting and they are both supportive of publication in GChron pending some minor revisions. You will also find my own flash review below which require minor revisions as well.
The two reviewers and myself altogether made a list of comments that should help you improve some aspects of your manuscripts.
Therefore I am recommending the equivalent of minor revisions and request that you first provide responses to the reviewers and myself on how you will address those points (aka a rebuttal letter). Should you disagree with any of the reviewer’s comments you would need to justify your choices in your responses.
Note that the Peer-review process in GChron is different than standard journals in that, only after I have read your responses / rebuttal letters, I will either invite you to submit a revised manuscript or directly reject the manuscript in the (unlikely) case that your responses are not satisfying. That being said, nothing prevent you to work on the manuscript as you elaborate your answer in the anticipation of a positive outcome.
Fred
------
Flash review by AE – F. Jourdan
Interesting contribution.
L167. Those ages are very precise for plagioclase crystals. Either your machine ability is of the chart (good for you!), or they are huge crystals… or they are not plagioclase, but anorthoclase. Now, that does not change the results and their interpretation in anyway, but I would still like to see more information on what has been dated. The information about grain sizse, K/Ca ratios to show it is indeed plagioclase, etc …
L167. MSWD is an important piece of information, but frankly, it requires the reader to make some calculation to know if good or not based on the degree of freedom. Easy when at 1.3, but what about at 1.67 – is that a single population or not? therefore I’m asking you to report the P-value with all the MSWD value in the text and on the graph. The advantage is that the reader has no math to do to know if it passes the test (>0.05 or not).
L172. That would be great to add the step heating figures for the lava and especially the pseudotachylite. They are both important results for your interpretation so should not be relegated to the supplemental material. In plus, they look good, so should be shared with the reader.
L172 &180. Please, provide stats values (MSWD and P) for the step heated glass and plagioclase samples. Those values should be both on the data figures each time an age is mentioned.
L.180 – I might have missed it, but this age (lava flow – 24.68 ± 0.32 Ma) is never mentioned anywhere after. Every age obtained as to be somehow part of the discussion otherwise there is no point reporting it. I suggest you elaborate on its significance somewhere in the discussion, even if it to say it was not part of the sequence or something like that. If you did already and I missed it, please make it clearer by quoting the age.
Citation: https://doi.org/10.5194/egusphere-2024-2899-EC1 -
AC3: 'Reply on EC1', Tiffany Rivera, 30 Nov 2024
Dear Editor Jourdan,
Thank you for providing editorial assistance on this manuscript. I have read through the reviews and made responses to the reviewer comments. In most cases, I accepted the suggestions for manuscript improvement. Below I respond to your comments. I have made the appropriate changes within the manuscript document and await your decision regarding the submission of a revised manuscript.
Best,
Tiffany Rivera
- In response to comment for L167: The information regarding the K/Ca ratio is provided in supplementary tables 2 through 5. For grain size, the samples were sieved at the 180-350 µm fraction. This detail will be added to the methods section.
- In response to comment for L167: P-values will be added to the manuscript text and figures.
- In response to comment for L172: These step-heating diagrams will be moved from the supplement and added to the main text. They will be referenced accordingly.
- In response to comment for L172 & 180: Yes, I have added these statistics to the plateau diagrams and in the text.
- In response to comment for L180: Thank you for this comment. Because the age is so much younger than the units bracketing the pseudotachylyte, it was omitted from further discussion. I will be sure to include this note in the revised manuscript.
Citation: https://doi.org/10.5194/egusphere-2024-2899-AC3
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AC3: 'Reply on EC1', Tiffany Rivera, 30 Nov 2024
Status: closed
-
RC1: 'Comment on egusphere-2024-2899', Martha Papadopoulou, 06 Nov 2024
Comments on the submitted pre-print “ Emplacement age of the Sevier Gravity Slide, Utah, USA” by T. Rivera, et al.
Reviewer: Martha Papadopoulou
General comments: the study is looking into the association between gravity slides, their cause of origin (e.g. new injected magma into a magma chamber) and their consequences on the volcanism of an active volcanic region (e.g. decompression melting due to displacement) using age constraints from different crucial layers of the studied formation. The studied area is the Sevier Gravity Slide, and their results are compared with other studies. The manuscript reads well, giving insights on the geological history of the area, the work that has been done so far, and how this study connects with previous works on the area. There is an overall good understanding of the associations between the different layers and a good understanding of the methods used and their limitations. I really enjoy how the works builds upon previous results and refines them, adding to the knowledge of the volcanic history of the region, and to the poorly understood causes of a gravity slide as well as their consequences to an area.
Specific comments: the few comments provided here on specific issues identified are meant in order to improve the quality of the manuscript and help a reader with no previous knowledge of the studied area to gain a better understanding. It is upon the authors to decide if they will act on them or not, but hopefully they will be taken into account on a revised version.
- Section 2 provides a lot of information about the geological background of the area, referring to a lot of features, such as plateaus, calderas etc.. I believe the section (and consequently the reader) would benefit from an extra map (or set of maps if too complicated) showing the location and association between these features. For example, maybe a map showing the extent of the Colorado Plateau and the Basin & Range province, with the Marysvale VF and the Marysvale gravity slide complex depicted on it; the location of the three calderas mentioned in the text; and the relative location of the Markagunt and Black Mountains gravity slides compared to the Sevier gravity slide.
- At the beginning of section 3 different units are described as deformed if within the SGS or undeformed if above it. However, towards the end of the section the Osiris tuff, which is marked as an undeformed unit, is described to be deformed but not from the SGS. I feel this is a bit contradictory. Maybe an additional sentence at the beginning (or somewhere else) of the section clarifying that all units deformed by an event other than the SGS will be seen (for the purposes of this study) as undeformed might be more appropriate.
- What units does the Mount Dutton Formation comprises of? From the stratigraphic column in Fig. 1 I had the impression that Mount Dutton Formation includes all the various units depicted in there, then I got confused from Fig. 5, where Kingston Canyon Tuff and Mount Dutton Alluvium where described as belonging to separate formations? Could you add to the stratigraphic column the various formations and their extent?
Technical comments:
- Not sure it’s only on my computer, but rows 44-46 (first three sentences in the introduction part) have a different format to the rest of the text. Please format accordingly
- Rows 50-51 “…a friction induced… in sliding”: references needed
- Row 54: could you define the word “gigantic”? E.g. average area extent
- Rows 61&64: you have performed 40Ar/39Ar dating, why is there suddenly a * to the 40Ar? It’s not consistent with further down the text
- Rows 81-82 “The breakaway regions… volcanic activity”: references needed
- Row 84 “…the breakaway of the… batholith”: references needed
- Row 86: for consistency with the rest of the text provide first the older then the younger age constraint of the volcanic activity (32-23 Ma)
- Row 86: please re-write to “Peak volcanic activity (32-23 Ma)…”
- Row 117: Fig. 2a-c
- Row 118: “…and biotite (Fig. 2c)”
- Row 118: “…igneous rocks (Fig. 2b)”
- Row 120: Fig. 2d-f
- Row 121: “…1-3 cm long (Fig. 2e)”
- Row 122: Fig. 2i
- Row 131: Fig. 2g-h
- Row 221: ages 23.0 and 25.4 presented as advised in comment 7
- Row 225: show the Buckskin Breccia the stratigraphic column of Fig. 1
Citation: https://doi.org/10.5194/egusphere-2024-2899-RC1 -
AC1: 'Reply on RC1', Tiffany Rivera, 27 Nov 2024
Dear Martha, Thank you for the comments on the preprint. Your suggestions are much appreciated. Below you will find responses to each of your comments, both specific and technical.
Specific comments:
- In regards to comment 1, yes, I agree that a map with the regional geology and the features discussed would be helpful to a reader that is unfamiliar with the location. I will include additional maps in the revision.
- In regards to comment 2, thank you for pointing out the confusion. The Osiris Tuff is undeformed by the SGS (which is 25 Ma), but in another location it is deformed by the younger MGS (23 Ma). I will clarify this in the text.
- In regards to comment 3, the Mount Dutton formation consists of lahar flows and welded ash-flow tuffs, including both the Kingston Canyon tuff and the alluvium that was sampled directly above the tuff. I’m unsure where the confusion comes in as the caption to figure 5 indicates that both the tuff and alluvium are of the Mount Dutton Formation. Is there a place that I could better clarify?
Technical comments
- I have added references, corrected fonts, and specified the individual panels of figures.
- In regards to the comment for the use of * in 40Ar/39Ar, the * indicates that it is radiogenic, so for instance, 70%Ar* indicates the amount of radiogenic Ar produced from the K decay. According to Schaen et al (2020), the most common usage for dates is 40Ar/39Ar, which I will revise to consistently use throughout the paper. However, the * must be included in describing the amount of radiogenic argon present, as in the results section 4.1.
- In regards to the comment about showing the placement of the Buckskin Breccia on the strat column of figure 1, I would like to decline this figure modification suggestion. I would like to keep the units in figure 1 restricted to those for which we provide new dates for in this publication.
Citation: https://doi.org/10.5194/egusphere-2024-2899-AC1
-
RC2: 'Comment on egusphere-2024-2899_Emplacement age of the Sevier Gravity Slide, Utah, USA Rivera et al. 2024', Bryant Ware, 14 Nov 2024
General Comments:
The study presented in this manuscript utilised structurally constrained samples and multiple geochronometers to tightly constrain the emplacement age of the Sevier Gravity Slide. Utilising this approach the authors contribute to the ongoing debate around the causality of gravity slides. The manuscript is structured well, the data is presented logically and clearly, with sufficient consideration and use of previous data/studies results, and connects these localised results well to the ‘outstanding questions’ of the origin and connections between gravity slides and igneous activity. I thought the approach of the study is well informed of and builds upon previous work to then have a targeted approach of what techniques and samples are best to address the hypothesis. The understanding of the geochronology data within the context of the structural relations of the gravity flow deposits provides a cool approach to provide such tight constraints in timing between these various units.
Specific Comments:
- As the study area is quite a local study, additions to the map figure would be much appreciated by a reader such as myself without much knowledge of the geology of the area/region. If there is the ability to have more panel slightly zoomed out further than the presented zoom (still including this panel though) would benefit the readers who are not familiar with the local geology, as well as providing easier ability for the readers to follow the large number of features presented in the ‘Introduction’ and ‘Geologic background’ sections.
- I would like to see just a little more detail added to the analytical sections 3.1 and 3.2. As a few different analytical techniques were conducted for the Ar-Ar geochronology (some of the samples (the ash flow tuffs) are weighted means of many single grain analyses, then the lava and pseudotachylyte are step heated), the section would benefit from the added information of how the grains were selected. Were the sanidine and the plagioclase also hand-picked prior to the analyses like the pseudotachyle glass? Where these selections made under a binocular scope? Were the two step heating experiments on populations? Although some of this may be known/be able to be inferred by readers with an Argon geochronology background, having this information detailed would help the interpretations/understanding the interpretations being made of the data. Just about the same request of added detail to the U-Pb analytical section as well; were the zircon grains picked after being separated via panning, heavy liquid, and magnetic, or is this more of a dump mount after the various separation techniques? This information will provide more clarity on the assessing the interpretations being made of the U-Pb data (hand picking can provide some bias, therefore good to note particularly as multiple fractions (with significant peaks) are observed in the Kingston Canyon Tuff (images of the analysed grains in the supplementary material would be great as well).
Technical Corrections:
Line 61: The asterisk is not represented in every instance, could the ‘*’ after 40Ar be defined… and if required, the writing of 40Ar*/39Ar (instead of 40Ar/39Ar) be standardised throughout the text. Those that are not as familiar with the argon system may not immediately understand the use of the asterisk as a radiogenic Ar notation.
Line 99: The Markagunt gravity slide and the Sevier gravity slide have already been defined as MGS and SGS, respectively, in the ‘Abstract’ as well as lines 54 and 55 in the ‘Introduction’. No need to define them again here.
Line 195: Same comment as above regarding the use of the asterisk after 206Pb.
Figure 5 Caption: IsoPlotR should be IsoplotR. The two references in the caption are not in the bibliography; Galbraith and Laslett (1993) and Vermeesch (2021).
Figure S2 Caption: A space needs to be added after ‘(b)’.
Supplementary Material Tables 2-5: The Taylor (1982) and the Min et al. (2000) references are not included in the bibliography.
Supplementary Material Tables 6-7: Could a ‘caption’ for the U-Pb tables be added that denotes the uncertainties (e.g. are the isotopic ratio data 1 sigma %, 2 sigma % or 1 standard error %).
Citation: https://doi.org/10.5194/egusphere-2024-2899-RC2 -
AC2: 'Reply on RC2', Tiffany Rivera, 27 Nov 2024
Dear Bryant, Thank you for the comments on the preprint. Your suggestions are much appreciated. Below you will find responses to each of your comments, both specific and technical.
Specific:
- In regards to comment 1, yes, I agree that a map with the regional geology and the features discussed would be helpful to a reader that is unfamiliar with the location. I will include additional maps in the revision.
- Thank you for the suggestion in comment 2. I will add the additional methodology to the argon and U/Pb sections. For your reference, though, yes, feldspars were handpicked under a binocular scope. The step-heating experiments were conducted on purified bulk samples (that is, not on individual glass shards or groundmass fragments). Zircon grains were separated with magnetic and heavy liquid techniques prior to mounting. CL images of the grains will be provided in the supplement.
Technical:
- The * indicates that it is radiogenic, so for instance, 70%Ar* indicates the amount of radiogenic Ar produced from the K decay. According to Schaen et al (2020), the most common usage for dates is 40Ar/39Ar, which I will revise to consistently use throughout the paper. However, the * must be included in describing the amount of radiogenic argon present, as in the results section 4.1. For Pb, the text has been updated to reflect the convention used in Condon et al. (2024) which excludes the ‘*’.
- The text has been updated for typos.
- Full citations are provided for references in the supplement.
- Clarifications have been made to the uncertainties in the U-Pb data tables.
Citation: https://doi.org/10.5194/egusphere-2024-2899-AC2
-
EC1: 'Comment on egusphere-2024-2899', Fred Jourdan, 20 Nov 2024
Dear Dr Rivera,
I have now received recommendations from two reviewers. Both reviewers agree that the data and the main question you attempt to address is interesting and they are both supportive of publication in GChron pending some minor revisions. You will also find my own flash review below which require minor revisions as well.
The two reviewers and myself altogether made a list of comments that should help you improve some aspects of your manuscripts.
Therefore I am recommending the equivalent of minor revisions and request that you first provide responses to the reviewers and myself on how you will address those points (aka a rebuttal letter). Should you disagree with any of the reviewer’s comments you would need to justify your choices in your responses.
Note that the Peer-review process in GChron is different than standard journals in that, only after I have read your responses / rebuttal letters, I will either invite you to submit a revised manuscript or directly reject the manuscript in the (unlikely) case that your responses are not satisfying. That being said, nothing prevent you to work on the manuscript as you elaborate your answer in the anticipation of a positive outcome.
Fred
------
Flash review by AE – F. Jourdan
Interesting contribution.
L167. Those ages are very precise for plagioclase crystals. Either your machine ability is of the chart (good for you!), or they are huge crystals… or they are not plagioclase, but anorthoclase. Now, that does not change the results and their interpretation in anyway, but I would still like to see more information on what has been dated. The information about grain sizse, K/Ca ratios to show it is indeed plagioclase, etc …
L167. MSWD is an important piece of information, but frankly, it requires the reader to make some calculation to know if good or not based on the degree of freedom. Easy when at 1.3, but what about at 1.67 – is that a single population or not? therefore I’m asking you to report the P-value with all the MSWD value in the text and on the graph. The advantage is that the reader has no math to do to know if it passes the test (>0.05 or not).
L172. That would be great to add the step heating figures for the lava and especially the pseudotachylite. They are both important results for your interpretation so should not be relegated to the supplemental material. In plus, they look good, so should be shared with the reader.
L172 &180. Please, provide stats values (MSWD and P) for the step heated glass and plagioclase samples. Those values should be both on the data figures each time an age is mentioned.
L.180 – I might have missed it, but this age (lava flow – 24.68 ± 0.32 Ma) is never mentioned anywhere after. Every age obtained as to be somehow part of the discussion otherwise there is no point reporting it. I suggest you elaborate on its significance somewhere in the discussion, even if it to say it was not part of the sequence or something like that. If you did already and I missed it, please make it clearer by quoting the age.
Citation: https://doi.org/10.5194/egusphere-2024-2899-EC1 -
AC3: 'Reply on EC1', Tiffany Rivera, 30 Nov 2024
Dear Editor Jourdan,
Thank you for providing editorial assistance on this manuscript. I have read through the reviews and made responses to the reviewer comments. In most cases, I accepted the suggestions for manuscript improvement. Below I respond to your comments. I have made the appropriate changes within the manuscript document and await your decision regarding the submission of a revised manuscript.
Best,
Tiffany Rivera
- In response to comment for L167: The information regarding the K/Ca ratio is provided in supplementary tables 2 through 5. For grain size, the samples were sieved at the 180-350 µm fraction. This detail will be added to the methods section.
- In response to comment for L167: P-values will be added to the manuscript text and figures.
- In response to comment for L172: These step-heating diagrams will be moved from the supplement and added to the main text. They will be referenced accordingly.
- In response to comment for L172 & 180: Yes, I have added these statistics to the plateau diagrams and in the text.
- In response to comment for L180: Thank you for this comment. Because the age is so much younger than the units bracketing the pseudotachylyte, it was omitted from further discussion. I will be sure to include this note in the revised manuscript.
Citation: https://doi.org/10.5194/egusphere-2024-2899-AC3
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AC3: 'Reply on EC1', Tiffany Rivera, 30 Nov 2024
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