the Creative Commons Attribution 4.0 License.
the Creative Commons Attribution 4.0 License.
| 27 Sep 2023
Extensional exhumation of cratons: insights from the Early Cretaceous Rio Negro-Juruena belt (Amazonian Craton, Colombia)
Abstract. This study presents results from apatite fission track (AFT) thermochronology to investigate the thermal history and exhumation dynamics of the Rio Negro-Juruena basement, situated within the western Guiana Shield of the Amazonian Craton. AFT dating and associated thermal history modelling in South America has largely been restricted to the plate’s margins (e.g. Andean active margin, Brazilian passive margin and others). Our paper reports on low-temperature thermochronological data from the internal part of the western Guiana Shield for the first time. This area is part of a vast cratonic lithosphere that is generally thought to be stable and little influenced by Mesozoic and Cenozoic tectonics. Our data however show AFT central ages ranging from 79.1 ± 3.2 Ma to 177.1 ± 14.8 Ma with mean confined track lengths of ca. 12 µm. Contrary to what might be expected of stable cratonic shields, inverse thermal history modeling indicates a rapid basement cooling event in the early Cretaceous. This cooling is interpreted as a significant exhumation event of the basement that was likely driven by the coeval extensional tectonics associated with back-arc rifts in the Llanos and Putumayo-Oriente-Maranon basins. The extensional tectonics facilitated both basement uplift and subsidence of the adjoining basins, increasing erosional dynamics and consequent exhumation of the basement rocks. The tectonic setting shifted in the late Cretaceous from extensional to contractional, resulting in reduced subsidence of the basins and consequential diminishing cooling rates of the Guiana Shield basement. Throughout the Cenozoic, only gradual, slow subsidence occurred in the study area due to regional flexure linked to the Andean orogeny. Comparative analysis with low-temperature thermochronology data from other West Gondwana cratonic segments highlights that exhumation episodes are highly controlled by tectonic inheritance, lithospheric strength, and proximity to rift zones. This study underscores the complex interplay between tectonic events and the response of cratonic lithosphere over geological time scales and highlights extensional settings as an important geological context for craton exhumation.
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Notice on discussion status
The requested preprint has a corresponding peer-reviewed final revised paper. You are encouraged to refer to the final revised version.
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Preprint
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The requested preprint has a corresponding peer-reviewed final revised paper. You are encouraged to refer to the final revised version.
- Preprint
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Supplement
(3351 KB) - BibTeX
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- Final revised paper
Journal article(s) based on this preprint
Interactive discussion
Status: closed
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RC1: 'Comment on egusphere-2023-2113', Paul. Green, 23 Oct 2023
Publisher’s note: the supplement to this comment was edited on 23 October 2023. The adjustments were minor without effect on the scientific meaning.
I am submitting a Review plus annotated copies of ms and Supplementary File.
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AC2: 'Reply on RC1', Ana Carolina Fonseca, 12 Dec 2023
Dear reviewers,
Thank you for your comments on our manuscript. The comments are encouraging and appear to share our judgement that this study and its results are original and important for the regional geological context with broader implications for similar setting worldwide. All of the comments were very helpful for revising and improving our paper. We have studied these comments carefully and have made corresponding corrections that we hope will meet with your approval. The responses to both reviewers’ comments are provided in the attached file. We have been able to incorporate changes to reflect most of the suggestions. If you have any further question, please do not hesitate to contact us. We appreciate the time and effort that both of you, Paul Green and Chiara Amadori, have dedicated to providing your valuable feedback on our manuscript.
Kind regards,
Ana Carolina Liberal Fonseca on behalf of all co-authors
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AC2: 'Reply on RC1', Ana Carolina Fonseca, 12 Dec 2023
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RC2: 'Comment on egusphere-2023-2113', Chiara Amadori, 30 Oct 2023
Manuscript by Ana Fonseca, Simon Nachtergaele, Amed Bonilla, Stijn Dewaele, Johan De Grave
https://doi.org/10.5194/egusphere-2023-2113 Preprint. Discussion started: 27 September 2023
Dear Editor and authors,
first, I really thank the Editor for choosing me to review the manuscript by Fonseca et al. I really enjoyed reading it and I also admit I learned a lot.
Please, see my comments for this manuscript are provided in two files. Here, you find a formal summary of my major comments and concerns, and a marked-up version of the manuscript sent to me for review (PDF document). Both files contain similar comments/questions/suggestions. Still, comments on figures and some text corrections are better explained in the PDF document, so please ensure that both are reviewed during revisions.
General comments
The manuscript objectives are well defined but sometimes I believe the reader needs some more information or better displayed. In the reviewed PDF I have noted a few times the need to add more references. In these comments, I suggest some papers that might be included in the manuscript.
Figure 1
In general, this figure is too crowded with information. I strongly suggest to divide it in three.
1A: DEM + Geological and geographical elements. Basins are not well highlighted if shown only with isobaths. For example, the lines behind Tukutu (or Takutu?) Basins are barely visible. If you divide this figure in two you have a cleaner DEM to put geological information on.
1B: DEM at the same scale as 1A but with only geochronological provinces, perhaps shown with polygons in different colours.
1C: geological profile. Check carefully that the geology in the profile and in the map match 100%.
In the Geological Setting you have a long description based on just two references. I believe you can integrate more bibliography. Also, you always cite fig. 1 but in that figure, it is not possible to unravel all the history you are describing.
In the main text, you cite Fig. 3 before Fig. 2. Switch the order of the figures If you need to.
Figure 2
What is the basement you have sampled? You show stars for ZUPb but your study is actually focused on AFT samples, thus they need to be put on this figure too.
Figure 4
This image is really confusing to understand... Why don't you use colour shades to show the subsidence values along the basin? Also, creating a bigger block diagram including the study area would help the reader a lot.
Figure 5
I do not fully agree with that. Your Fig. 5 shows a high peak around 1 Ga in the Neogene units. However, if you do not show the values on the y-axis you cannot compare the relative contributions from different histograms, thus your sentence here cannot be supported.
Figure 6
These pie charts need to be larger because they show the data you discuss, so they are the most important thing in the figure. This figure is essentially a paleogeography, it is important to write – at least in the caption – the geological time the map refers to.
The modelling chapter is an important part of this paper. You also use an uncommon and interesting approach which deserves to be better illustrated. I suggest moving some figures from the supplemental material to the main manuscript to help the reader visualize the differences among the models’ results. Reading only their descriptions can be confusing.
I see your Dpar measurements are values and sometimes very low. Do you think the differences in AFT ages and lengths are only due to the differences in thermal history and may not be influenced by the nature of the apatite itself? Perhaps you should detail this a little more.
I appreciate you were careful to not stress any conclusions for T< 60 and Cenozoic geological history.
However, more and more scientists agree on the fact that one thermochron. system only can lead to a partial T-t history, and the use of two dating methods is always advised. Do you think you can use data from published works?
Also, you report ages from 97 to 177 Ma, but you are confident in describing the area with a homogeneous rock cooling history. I guess you need to explain this a little deeper.
In the discussion section, I would also mention that cooling ages may also depend on the volcanic activity at the plate margin. Many passive margins are volcanic and offshore they show very interesting - and poorly constrained - Seaward Dipping Reflectors which are the product of onshore volcanic complexes today completely eroded. This means that we constantly underestimate the geothermal gradient (and its variation) and the possible reheating cycles of the margins which involves an additional complication to the T-t paths.
I still strongly support the work by Fonseca and coauthors. Their findings are needful for the scientific community working on Paleozoic paleogeography. I hope the authors will consider my comments as constructive suggestions; my notes have the only purpose of improving the manuscript to be more appealing to a larger audience.
Sincerely,
Chiara Amadori, PhD
Research Fellow
University of Pavia, Italy
-
AC1: 'Reply on RC2', Ana Carolina Fonseca, 12 Dec 2023
Dear reviewers,
Thank you for your comments on our manuscript. The comments are encouraging and appear to share our judgement that this study and its results are original and important for the regional geological context with broader implications for similar setting worldwide. All of the comments were very helpful for revising and improving our paper. We have studied these comments carefully and have made corresponding corrections that we hope will meet with your approval. The responses to both reviewers’ comments are provided in the attached file. We have been able to incorporate changes to reflect most of the suggestions. If you have any further question, please do not hesitate to contact us. We appreciate the time and effort that both of you, Paul Green and Chiara Amadori, have dedicated to providing your valuable feedback on our manuscript.
Kind regards,
Ana Carolina Liberal Fonseca on behalf of all co-authors
-
AC1: 'Reply on RC2', Ana Carolina Fonseca, 12 Dec 2023
Interactive discussion
Status: closed
-
RC1: 'Comment on egusphere-2023-2113', Paul. Green, 23 Oct 2023
Publisher’s note: the supplement to this comment was edited on 23 October 2023. The adjustments were minor without effect on the scientific meaning.
I am submitting a Review plus annotated copies of ms and Supplementary File.
-
AC2: 'Reply on RC1', Ana Carolina Fonseca, 12 Dec 2023
Dear reviewers,
Thank you for your comments on our manuscript. The comments are encouraging and appear to share our judgement that this study and its results are original and important for the regional geological context with broader implications for similar setting worldwide. All of the comments were very helpful for revising and improving our paper. We have studied these comments carefully and have made corresponding corrections that we hope will meet with your approval. The responses to both reviewers’ comments are provided in the attached file. We have been able to incorporate changes to reflect most of the suggestions. If you have any further question, please do not hesitate to contact us. We appreciate the time and effort that both of you, Paul Green and Chiara Amadori, have dedicated to providing your valuable feedback on our manuscript.
Kind regards,
Ana Carolina Liberal Fonseca on behalf of all co-authors
-
AC2: 'Reply on RC1', Ana Carolina Fonseca, 12 Dec 2023
-
RC2: 'Comment on egusphere-2023-2113', Chiara Amadori, 30 Oct 2023
Manuscript by Ana Fonseca, Simon Nachtergaele, Amed Bonilla, Stijn Dewaele, Johan De Grave
https://doi.org/10.5194/egusphere-2023-2113 Preprint. Discussion started: 27 September 2023
Dear Editor and authors,
first, I really thank the Editor for choosing me to review the manuscript by Fonseca et al. I really enjoyed reading it and I also admit I learned a lot.
Please, see my comments for this manuscript are provided in two files. Here, you find a formal summary of my major comments and concerns, and a marked-up version of the manuscript sent to me for review (PDF document). Both files contain similar comments/questions/suggestions. Still, comments on figures and some text corrections are better explained in the PDF document, so please ensure that both are reviewed during revisions.
General comments
The manuscript objectives are well defined but sometimes I believe the reader needs some more information or better displayed. In the reviewed PDF I have noted a few times the need to add more references. In these comments, I suggest some papers that might be included in the manuscript.
Figure 1
In general, this figure is too crowded with information. I strongly suggest to divide it in three.
1A: DEM + Geological and geographical elements. Basins are not well highlighted if shown only with isobaths. For example, the lines behind Tukutu (or Takutu?) Basins are barely visible. If you divide this figure in two you have a cleaner DEM to put geological information on.
1B: DEM at the same scale as 1A but with only geochronological provinces, perhaps shown with polygons in different colours.
1C: geological profile. Check carefully that the geology in the profile and in the map match 100%.
In the Geological Setting you have a long description based on just two references. I believe you can integrate more bibliography. Also, you always cite fig. 1 but in that figure, it is not possible to unravel all the history you are describing.
In the main text, you cite Fig. 3 before Fig. 2. Switch the order of the figures If you need to.
Figure 2
What is the basement you have sampled? You show stars for ZUPb but your study is actually focused on AFT samples, thus they need to be put on this figure too.
Figure 4
This image is really confusing to understand... Why don't you use colour shades to show the subsidence values along the basin? Also, creating a bigger block diagram including the study area would help the reader a lot.
Figure 5
I do not fully agree with that. Your Fig. 5 shows a high peak around 1 Ga in the Neogene units. However, if you do not show the values on the y-axis you cannot compare the relative contributions from different histograms, thus your sentence here cannot be supported.
Figure 6
These pie charts need to be larger because they show the data you discuss, so they are the most important thing in the figure. This figure is essentially a paleogeography, it is important to write – at least in the caption – the geological time the map refers to.
The modelling chapter is an important part of this paper. You also use an uncommon and interesting approach which deserves to be better illustrated. I suggest moving some figures from the supplemental material to the main manuscript to help the reader visualize the differences among the models’ results. Reading only their descriptions can be confusing.
I see your Dpar measurements are values and sometimes very low. Do you think the differences in AFT ages and lengths are only due to the differences in thermal history and may not be influenced by the nature of the apatite itself? Perhaps you should detail this a little more.
I appreciate you were careful to not stress any conclusions for T< 60 and Cenozoic geological history.
However, more and more scientists agree on the fact that one thermochron. system only can lead to a partial T-t history, and the use of two dating methods is always advised. Do you think you can use data from published works?
Also, you report ages from 97 to 177 Ma, but you are confident in describing the area with a homogeneous rock cooling history. I guess you need to explain this a little deeper.
In the discussion section, I would also mention that cooling ages may also depend on the volcanic activity at the plate margin. Many passive margins are volcanic and offshore they show very interesting - and poorly constrained - Seaward Dipping Reflectors which are the product of onshore volcanic complexes today completely eroded. This means that we constantly underestimate the geothermal gradient (and its variation) and the possible reheating cycles of the margins which involves an additional complication to the T-t paths.
I still strongly support the work by Fonseca and coauthors. Their findings are needful for the scientific community working on Paleozoic paleogeography. I hope the authors will consider my comments as constructive suggestions; my notes have the only purpose of improving the manuscript to be more appealing to a larger audience.
Sincerely,
Chiara Amadori, PhD
Research Fellow
University of Pavia, Italy
-
AC1: 'Reply on RC2', Ana Carolina Fonseca, 12 Dec 2023
Dear reviewers,
Thank you for your comments on our manuscript. The comments are encouraging and appear to share our judgement that this study and its results are original and important for the regional geological context with broader implications for similar setting worldwide. All of the comments were very helpful for revising and improving our paper. We have studied these comments carefully and have made corresponding corrections that we hope will meet with your approval. The responses to both reviewers’ comments are provided in the attached file. We have been able to incorporate changes to reflect most of the suggestions. If you have any further question, please do not hesitate to contact us. We appreciate the time and effort that both of you, Paul Green and Chiara Amadori, have dedicated to providing your valuable feedback on our manuscript.
Kind regards,
Ana Carolina Liberal Fonseca on behalf of all co-authors
-
AC1: 'Reply on RC2', Ana Carolina Fonseca, 12 Dec 2023
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Ana Fonseca
Simon Nachtergaele
Amed Bonilla
Stijn Dewaele
Johan De Grave
The requested preprint has a corresponding peer-reviewed final revised paper. You are encouraged to refer to the final revised version.
- Preprint
(2600 KB) - Metadata XML
-
Supplement
(3351 KB) - BibTeX
- EndNote
- Final revised paper