Nanoscale earthquake records preserved in plagioclase microfractures from the lower continental crust

Petley-Ragan, Arianne J.; Plümper, Oliver; Ildefonse, Benoit; Jamtveit, Bjørn

doi:https://doi.org/10.5194/se-12-959-2021

Articles | Volume 12, issue 4

https://doi.org/10.5194/se-12-959-2021

© Author(s) 2021. This work is distributed under
the Creative Commons Attribution 4.0 License.

https://doi.org/10.5194/se-12-959-2021

© Author(s) 2021. This work is distributed under
the Creative Commons Attribution 4.0 License.

Articles | Volume 12, issue 4

Research article

|

23 Apr 2021

Research article |

| 23 Apr 2021

Nanoscale earthquake records preserved in plagioclase microfractures from the lower continental crust

Arianne J. Petley-Ragan, Oliver Plümper, Benoit Ildefonse, and Bjørn Jamtveit

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Final revised paper (published on 23 Apr 2021)
Preprint (discussion started on 28 Sep 2020)

Interactive discussion

Status: closed

AC: Author comment | RC: Referee comment | SC: Short comment | EC: Editor comment

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RC1: 'Review of the manuscript SE-2020-146', Anonymous Referee #1, 08 Oct 2020
- AC1: 'Reply on RC1', Arianne Petley-Ragan, 18 Jan 2021
RC2: 'Review of “Nano-scale earthquake record preserved in plagioclase microfractures from the lower continental crust”', Mark Pearce, 08 Dec 2020
- AC2: 'Reply on RC2', Arianne Petley-Ragan, 18 Jan 2021

Peer-review completion

AR: Author's response | RR: Referee report | ED: Editor decision

AR by Arianne Petley-Ragan on behalf of the Authors (04 Feb 2021) Author's response Author's tracked changes Manuscript

ED: Publish subject to technical corrections (08 Feb 2021) by David Healy

ED: Referee Nomination & Report Request started (15 Feb 2021) by David Healy

RR by Anonymous Referee #1 (12 Mar 2021)

Suggestions for revision or reasons for rejection

The new manuscript incorporates significant changes that respond the the previous reviewer’s comments as also detailed in the author’s responses. I find that this new version much improved compared with the original submission. The manuscript is a neat, well-written and represents a novel/well documented contribution for the understanding the role of coseismic fluid infiltration in lower crustal dry rocks. This process determine a radical change in rock rheology determining an abrupt transition of dry, strong, brittle rocks to hydrous counterparts capable of ductile flow.
I believe that the manuscript is now suitable for acceptance for publication in SE.
I have just some very minor points that I hope the authors may want to consider before the submission of the final version.

Line 14-15 – “Dislocation-free plagioclase and Kfeldspar aggregates fill the microfractures”
Comment: It is a very minor point, but for sake of clarity, considering that the authors discuss the fluid infiltration along the coseismic microfractures associated with eartquake propagation, the term “filling” may be misleading. The authors interpret the fracture “filling” as the result of the modification and repolymerization of the pseudoamorphous cataclastic material formed along the cracks derived from the host-rock feldspars. I suggest to use the term “occur” (“Dislocation-free plagioclase and Kfeldspar aggregates occur along the microfractures). In fact, across the manuscript the authors never use any more the term “filling” for the feldspar within the microfractures.

Lines 39-41 – “Furthermore, for ambient lower crustal temperatures in the range 600-700°C, the transient temperature following an earthquake may exceed 1000°C within 1 cm of the slip surface (Bestmann et al., 2012; Clerc et al., 2018). Such conditions, although short-lived, are expected to drive irreversible processes within the rock record.”
Comments:
A) This part is a little “out of order”. The authors first discuss the dynamic stress field, then the thermally induced stress and finally go back to the dynamic stress. I suggest to re-order this part
B) In addition, the authors refer to the “irreversible processes” caused by the the thermal pulse associated with the frictional heating. These include thermal fracturing in addition with the annealing processes dealt with in this paper and in Bestmann et al. (2012). The authors can provide specific references to thermal shock fracturing.
C) “°C” is a unit measurement symbol. Here, and across the whole text, the authors should put a space between in front of this symbol, e.g. change 1000°C to 1000 °C.

Line 50 – “…. to a lower crustal pseudotachylyte”
Suggested editing: “ …. from a pseudotachylyte vein formed under lower crustal conditions”

Lines 72-74 – “University of Oslo’s Department of Geoscience.”
Suggested editing: “Department of Geoscience at the University of Oslo” (consistently to how the other Institutions are reported in the manuscript)

Line 111 – “At distances less than the half thickness of the pseudotachylyte (x), …”
Comment: The parameter “a” in the formula (the pseudotachylyte half vein thickness) is not defined. Please add this information.

Lines 121-22, 123-124 “…. with a mean grain size of 1.73 µm2” and “) with a mean grain size of 2.14 µm2”
Comment: as written it is not clear if the grainsize refers to the grains in the microfractures ofr to the pseudotachylyte grainseize. Please clarify.

Congratulations to the authors for such a nice piece of work

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ED: Publish subject to technical corrections (15 Mar 2021) by David Healy

ED: Publish subject to technical corrections (15 Mar 2021) by Federico Rossetti (Executive editor)

AR by Arianne Petley-Ragan on behalf of the Authors (18 Mar 2021) Author's response Manuscript

Short summary

Earthquakes cause rapid deformation that has long-term effects on the Earth's crust. We studied the most abundant mineral, feldspar, in the vicinity of an earthquake to unravel its deformation history. With microscopy, we found internal nm-scale structures that indicate a history of high stress and destruction of atomic structure. This was quickly followed by high temperature and fluid introduction within seconds. Our findings illustrate the intense conditions imposed on rocks by earthquakes.