the Creative Commons Attribution 4.0 License.
the Creative Commons Attribution 4.0 License.
| 04 Jul 2024
Earthquake swarms frozen in an exhumed hydrothermal system (Bolfin Fault Zone, Chile)
Abstract. Earthquake swarms commonly occur in upper-crustal hydrothermal-magmatic systems and activate mesh-like fault networks. How these networks develop through space and time along seismic faults is poorly constrained in the geological record. Here, we describe a spatially dense array of small-displacement (< 1.5 m) epidote-rich fault-veins within granitoids, occurring at the intersections of subsidiary faults with the exhumed seismogenic Bolfin Fault Zone (Atacama Fault System, Northern Chile). Epidote faulting and veining occurred at 3–7 km depth and 200–300 °C ambient temperature. At distance ≤ 1 cm to fault-veins, the magmatic quartz of the wall-rock shows (i) thin (< 10-µm-thick) interlaced deformation lamellae, and (ii) crosscutting quartz-filled veinlets. The epidote-rich fault-veins (i) include clasts of deformed magmatic quartz, with deformation lamellae and quartz-filled veinlets, and (ii) record cyclic events of extensional-to-hybrid veining and either aseismic or seismic shearing. Deformation of the wall-rock quartz is interpreted to record the large stress perturbations associated with the rupture propagation of small earthquakes. In contrast, dilation and shearing forming the epidote-rich fault-veins are interpreted to record the later development of a mature and hydraulically-connected fault-fracture system. In this latter stage, the fault-fracture system cyclically ruptured due to fluid pressure fluctuations, possibly correlated with swarm-like earthquake sequences.
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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.
Journal article(s) based on this preprint
Interactive discussion
Status: closed
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RC1: 'Comment on egusphere-2024-1841', Anonymous Referee #1, 04 Aug 2024
The manuscript “Earthquake swarms frozen in an exhumed hydrothermal system (Bolfin Fault Zone, Chile)” submitted by Masoch et al. describes microstructures from epidote-prehnite sealed hybrid veins within granitoids from the Bolfin Fault Zone, Chile. Magmatic quartz clasts in the veins contain various deformation microstructures: (1) deformation lamellae characterized by an undulating, lamellar change in extinction position in transmitted polarized light and darker CL, (2) healed microcracks characterized by fluid inclusion trails in single quartz grains and dark CL as well as (3) fractures in quartz sealed with feldspar and quartz (veinlets). These deformation microstructures occur in association with shear zones related to the Bolfin Fault Zone. Together with the observation that veins contain fragments of former veins, the quartz deformation microstructures are taken to record cyclic cataclasis and sealing and is interpreted as an ancient seismogenic hydrothermal system. The topic is timely and of significant interest to the readers of Solid Earth.
However, from my point of view, the presentation, interpretation and discussion of the deformation lamellae, healed microcracks and veinlets in magmatic quartz, where especially the deformation lamellae are taken as one important argument for transient high stresses, should be improved before publication. The specific comments are as follows:
- A better presentation and correlation/distinction between deformation lamellae, healed microcracks and veinlets in the magmatic quartz would be necessary, as the microstructures record different processes. Especially, a correlation of the lamellar change in extinction position (i.e. “deformation lamellae”) in polarized light micrographs with the marked change in CL shown in the impressive Figures 4 d, f, h, would be important. The lamellar change in extinction position is shown from four quartz grains in the images Fig. 3d, e, S1a, b and S2, which are of relatively low magnification. The correlation with the CL images is, however, only shown for the quartz grains in Figs. S1a, b, d and S2/Fig. 6j, where the deformation lamellae are not that well visible, as the thin sections are 100µm thick. Furthermore, Fig. 3d shows fluid inclusion trails in a quartz grain, thus interpreted as healed microcracks. It would be good to also show a CL image of this grain, to see the difference in CL related to the healed microcracks and to the deformation lamellae. As both, healed microcracks and deformation lamellae, appear to be characterized by darker CL in relation to the host, a distinction from CL images alone is not possible. The BSE images Fig. 4 a, c, g, e, are not helpful, as they show no contrast. Maybe BSE images at higher magnification and better contrast would help to show at least the “veinlets” sealed also with feldspar, as described in the text (e.g. line 155-160) with reference to the Figures 4f, 6i, 6j, S1, which however, are not really helpful to distinguish the veinlets from the healed microcracks, as no other phases are indicated. Maybe some confusion arises also because the text does not distinguish between epitaxially healed microcracks in quartz, e.g. characterized by “fluid inclusion trails” in a quartz grain with one main extinction position as shown in Fig. 3d, and “quartz-healed” veinlets with other phases like albite and K-Fsp (e.g. line 155-160). It would be good to present also data of the other phases in the veinlets, I did not find a figure showing these?
- The EBSD data presented in Figure 5 are not suited to characterize the slight oscillatory change in crystallographic orientation, which would be expected across the deformation lamellae. The misorientation profiles are not very specific and could also represent the usual “noise” of deformed quartz with internal misorientation/undulatory extinction. The gradual increase in misorientation angle to the reference orientation in profile 1 (blue line) is probably not related to the deformation lamellae. A correlation of the misorientation profiles with GROD, GOS or relative misorientation maps would be necessary to relate the slight changes in orientation across the lamellae. Were more EBSD measurements performed then those from Fig. 5? Are the observed deformation lamellae generally of (sub)basal orientation and what is the angle to the basal plane? This information would be important for the discussion.
- The discussion on the deformation lamellae in Chapter 5.1 is misleading: The two planar shock effects in quartz, Planar Fracturs (PFs) and Planar deformation features (PDFs), from meteorite impactites are very different from deformation lamellae. PFs are cleavage cracks in quartz and are typically not associated with a change in extinction position, as deformation lamellae are. PDFs are very straight, following specific crystallographic planes (they can be curved but only if the grain orientation is changing respectively), very fine lamellar (typically without a change in extinction position, i.e. without misorientation along the lamellae) and occur in sets of different orientations. Basal PDFS in quartz are mechanical Brazil twins (only resolvable by TEM) and rhombohedral PDFs are characterized by localized transformations from/to diaplectic glass. A comparison to the undulating dark lamellae in CL observed here appears very distracting and misleading from my point of view. Instead, a much more specific and careful discussion of (sub)basal deformation lamellae, short wave length undulatory extinction and fine extinction bands in quartz, the indication of the respective formation processes (relevance of dislocation glide, pile up of dislocations, influence of microcracking (!) etc.) as well as a discussion on the deformation conditions (transient high stresses?) would be very important and relevant here.
Further comments:
- Line 30-32: I think that also Nüchter and Stöckhert, 2007, 2008 (references see below) are very relevant studies on the topic of transient permeability and fluid flow related to seismic activity recorded by quartz veins, which should be discussed here.
- Line 78, please rephrase, as this might be mistakeable. I assume that here the initiation of the fault system is meant and not the nucleation of an earthquake.
- Line 135, Fig. 2a) the hybrid extensional-shear veins and alteration halos are not well visible in the figure
- Line 153-170 please rewrite this paragraph and describe the microstructures more specifically: e.g., I recommend to not use “planar features” which is very unspecific and maybe mistakeable by the very specific term “planar deformation features” in shocked quartz from meteorite impactites. This is especially as the microstructures shown in Fig. 3e and 4 are not really planar except maybe of the healed microcracks in Fig. 3d, see specific comment 1 above. Usually the term “deformation lamellae” is referring to lamellar undulatory extinction with the lamellae subparallel to the basal plane, i.e. the plane at high angle to , as described here. The term short wave length undulatory extinction is referring to wavy, lamellar undulatory extinction also subparallel to other crystallographic planes (m, r, z).
- Line 155-160: I strongly recommend to distinguish fractures in quartz sealed also with other phases (i.e. veins, or if you wish veinlets) from epitaxially healed microcracks in quartz (Fig. 3d)
- line 165: are all observed deformation lamellae of (sub)basal orientation? What is the angle of the lamellae to the basal plane?
- Line 169-170: the epitaxy of the healed microcracks is better to see in Fig. 3d, by the same extinction position of the grain (but please label the healed microcracks, see below). Where is the veinlet in Fig. 5a, which is corresponding to the grain in Fig. 4d, please indicate the veinlet in both images. In the BSE image also no veinlet is visible, which should indicate the presence of different phases, as feldspar. Again, an optical micrograph could be much more helpful…
- 3 d, e: Please indicate also the healed microcracks in Fig. 3d. It would be very interesting to see the CL images of these two grains, especially Fig. 3d, to see the difference in CL related to the healed microcracks and to the deformation lamellae.
- 4: The undulating lamellae dark in CL are very impressive. Yet, the figure does not allow to distinguish between deformation lamellae, veinlets or healed microcracks, as all three microstructures are obviously characterized by the wavy lamellae of dark CL and in BSE all three microstructures do not show up. I would expect that at least the different phases and grains in veinlets should be visible in BSE, but for that a better contrast/resolution would help. Also, in optical micrographs, all three microstructures should easily be distinguishable. Thus, I strongly recommend to exchange the BSE images with meaningful optical micrographs.
- Line 185 caption to Fig. 4: what do you expect from BSE image? The z-contrast can show other phases, e.g. in your veinlets, but no veinlets filled with albit/K-Fsp are shown? The orientation contrast may show deformation microstructures, but not in this resolution…, see also specific comment 1 above.
- Line 195/EBSD data, see specific comment 2 above
- Line 216: fig. 5h? fig. 6h?
- 6 b: the idiomorphic zoned epidote does not really show up in the figure?
- 6e S-C foliation?
- 6g) idiomorphic crystals? Triple junctions, of course there are triple junctions in a 2D picture of a polyphase aggregate, what is the relevance?
- 6 i, j where are the veinlets, as referenced in line 219, there are wavy dark lamellae in the CL images, but whether these are deformation lamellae, healed microcracks or veinlets with other phases does not get clear from these two images.
- Lines 260-285 please rewrite this paragraph, see specific comment 3 above
- line 397, where are the quartz-healed veinlets in S1?
- Figure S1, 2: the deformation lamellae are hard to be resolved in the micrographs of the 100µm-thick thin sections.
Recommended references:
Nüchter, J.‐A., and B. Stöckhert (2007), Vein quartz microfabrics indicating progressive evolution of fractures into cavities during postseismic creep in the middle crust, J. Struct. Geol., 29, 1445–1462.
Nüchter, J.‐A., and B. Stöckhert (2008), Coupled stress and pore fluid pressure changes in the middle crust: Vein record of coseismic loading and postseismic stress relaxation, Tectonics, 27, TC1007, doi:10.1029/2007TC002180.
Citation: https://doi.org/10.5194/egusphere-2024-1841-RC1 - AC1: 'Reply on RC1', Simone Masoch, 06 Oct 2024
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RC2: 'Comment on egusphere-2024-1841', Anonymous Referee #2, 08 Aug 2024
The manuscript by Masoch et al deals with the microstructures from a fault zone in northern Chile related with tectono-magmatic and hydrothermal activity. The authors claim that the deformation modes recorded therein could be representative of processes at stake in active swarm systems. Even though the idea of relating the features visible in this fault zone is not totally new and already proposed in the previous papers from the same group on this locality, I found the study well conducted, adequately documented and rather convincing. There are probably several ways of interpreting the finite structures recorded in this fault zone. Future work will tell if those are indeed swarms -or not-. The discussion and the genetic model is mostly supported by the observations even though some re-wording and clarification is needed in places (see below). I also believe that the microstructures should perhaps be described with greater care. Overall I recommend publication after moderate revisions.
- I think that the authors should better explain the part on the internal versus external fluid infiltration, and locate the epidote-bearing domains in their figure 8. Because epidote formation requires the incoming of large amounts of calcium, I believe that a better discussion of this aspect would bring water to their mill when it comes to discussing fluid infiltration after the first fracturing event. Have similar epidote-rich veins been described elsewhere in Northern Chile (or elsewhere) as a consequence of deeper emplacement/cooling of a plutonic body? Can you discard the possibility that the fluid source comes from the currently downgoing subducting plate?
- The interpretation of fault zone structures in terms of slip velocity is hazardous. It is currently impossible to tell whether breccias or cataclasites result from slip at seismic strain rates in the absence of pseudotachylytes. I suggest a more careful writing.
Detailed points:
L.14: fault-veins / epidote faulting: what do you mean? Please clarify. Not clear enough for an abstract.
L.17-21: the abstract lacks material that enables understanding how you came to these conclusions.
L.65: linkage zone? What do you mean?
L.129: replace by ‘EBSD data was processed using the MTEX…’
L.132: why such a low (6 nA) current?
L.135: you mean alkali devolatilization? (instead of migration)
L.202: (Al-rich; light: Fe-rich) there is something missing here
L.211: show the pores!
L.216: there is no figure 5h! check again the figure calls. Do you mean 6h?
L.267: ‘high stresses’: how high?
L.269: how slow?
L.282: ‘the latter hypothesis’: clarify to which hypothesis you are referring to
L.295-298: It is not clear to me how high stresses can be reached here in hybrid veins, since mode ii veins by definition require higher fluid pressures than pure shear veins
L.305: rephrase: too long and not clear
L.314-317: Yes, but this study deals with dissolution precipitation of the host metasediments towards the host. In this study you suggest permeability increments associated with fluid advection.
L.326: any evidence for pressure-solution at this stage that could account for elemental redistribution?
L.351: see Angiboust et al. (2015, G-cubed) for another example where an epidote-rich cataclazed fault system is described, forming as a consequence of transients increase in pore fluid pressure in a sheared system. See also Oncken et al. (2021, geosphere) for further evidence of foliated cataclasites as a key fault zone material in deep plate boundary systems. See also Muñoz-Montecinos et al. (EPSL, 2021).
L.353: foliated, fluidized cataclasites and breccias may also form at sub-seismic strain rates (see Oncken et al., 2021). I would be more careful in the writing here.
L.370: check syntax in this sentence (perhaps you mean ‘by an increase of the rate of fluid pressure…’)
L.372: which type of deformation events?
L.384: coexist (no ‘s’)
L.430: the presence of suspended clasts within cataclasite should not be viewed alone as a solid evidence for seismic slip
Bird & Spieler (2004, rev. Min. Geochem) could be a useful reference when it comes to demonstrating that your veins were once part of a supra-plutonic environment.
Figure 1: how do you define the ‘weakly fractured unit’? is there a statistical criterion or is it purely arbitrary? Also, explain better your difference between chloritized/Fractured and chlorite-rich cataclastic: foliated and massive, in the caption of the map.
Figure 3: better label minerals and features as explained in the caption
Figure 4: what are the analytical conditions used for obtaining these CL images?
Figure 5b: how many points considered for this pole figure? figure 5a: why not showing the misorientation map instead? It would be more useful here. What is the Y direction and what is the reference frame?
Figure 8: part (a) title: propagation (not progation). The three lines (crystal plasticity, dynamic fracturing …) are not well positioned and not very easy to understand in the frame of this sketch.
Figure 9: ok but this figure does not consider the reactivation of the fault
Citation: https://doi.org/10.5194/egusphere-2024-1841-RC2 - AC2: 'Reply on RC2', Simone Masoch, 06 Oct 2024
Interactive discussion
Status: closed
-
RC1: 'Comment on egusphere-2024-1841', Anonymous Referee #1, 04 Aug 2024
The manuscript “Earthquake swarms frozen in an exhumed hydrothermal system (Bolfin Fault Zone, Chile)” submitted by Masoch et al. describes microstructures from epidote-prehnite sealed hybrid veins within granitoids from the Bolfin Fault Zone, Chile. Magmatic quartz clasts in the veins contain various deformation microstructures: (1) deformation lamellae characterized by an undulating, lamellar change in extinction position in transmitted polarized light and darker CL, (2) healed microcracks characterized by fluid inclusion trails in single quartz grains and dark CL as well as (3) fractures in quartz sealed with feldspar and quartz (veinlets). These deformation microstructures occur in association with shear zones related to the Bolfin Fault Zone. Together with the observation that veins contain fragments of former veins, the quartz deformation microstructures are taken to record cyclic cataclasis and sealing and is interpreted as an ancient seismogenic hydrothermal system. The topic is timely and of significant interest to the readers of Solid Earth.
However, from my point of view, the presentation, interpretation and discussion of the deformation lamellae, healed microcracks and veinlets in magmatic quartz, where especially the deformation lamellae are taken as one important argument for transient high stresses, should be improved before publication. The specific comments are as follows:
- A better presentation and correlation/distinction between deformation lamellae, healed microcracks and veinlets in the magmatic quartz would be necessary, as the microstructures record different processes. Especially, a correlation of the lamellar change in extinction position (i.e. “deformation lamellae”) in polarized light micrographs with the marked change in CL shown in the impressive Figures 4 d, f, h, would be important. The lamellar change in extinction position is shown from four quartz grains in the images Fig. 3d, e, S1a, b and S2, which are of relatively low magnification. The correlation with the CL images is, however, only shown for the quartz grains in Figs. S1a, b, d and S2/Fig. 6j, where the deformation lamellae are not that well visible, as the thin sections are 100µm thick. Furthermore, Fig. 3d shows fluid inclusion trails in a quartz grain, thus interpreted as healed microcracks. It would be good to also show a CL image of this grain, to see the difference in CL related to the healed microcracks and to the deformation lamellae. As both, healed microcracks and deformation lamellae, appear to be characterized by darker CL in relation to the host, a distinction from CL images alone is not possible. The BSE images Fig. 4 a, c, g, e, are not helpful, as they show no contrast. Maybe BSE images at higher magnification and better contrast would help to show at least the “veinlets” sealed also with feldspar, as described in the text (e.g. line 155-160) with reference to the Figures 4f, 6i, 6j, S1, which however, are not really helpful to distinguish the veinlets from the healed microcracks, as no other phases are indicated. Maybe some confusion arises also because the text does not distinguish between epitaxially healed microcracks in quartz, e.g. characterized by “fluid inclusion trails” in a quartz grain with one main extinction position as shown in Fig. 3d, and “quartz-healed” veinlets with other phases like albite and K-Fsp (e.g. line 155-160). It would be good to present also data of the other phases in the veinlets, I did not find a figure showing these?
- The EBSD data presented in Figure 5 are not suited to characterize the slight oscillatory change in crystallographic orientation, which would be expected across the deformation lamellae. The misorientation profiles are not very specific and could also represent the usual “noise” of deformed quartz with internal misorientation/undulatory extinction. The gradual increase in misorientation angle to the reference orientation in profile 1 (blue line) is probably not related to the deformation lamellae. A correlation of the misorientation profiles with GROD, GOS or relative misorientation maps would be necessary to relate the slight changes in orientation across the lamellae. Were more EBSD measurements performed then those from Fig. 5? Are the observed deformation lamellae generally of (sub)basal orientation and what is the angle to the basal plane? This information would be important for the discussion.
- The discussion on the deformation lamellae in Chapter 5.1 is misleading: The two planar shock effects in quartz, Planar Fracturs (PFs) and Planar deformation features (PDFs), from meteorite impactites are very different from deformation lamellae. PFs are cleavage cracks in quartz and are typically not associated with a change in extinction position, as deformation lamellae are. PDFs are very straight, following specific crystallographic planes (they can be curved but only if the grain orientation is changing respectively), very fine lamellar (typically without a change in extinction position, i.e. without misorientation along the lamellae) and occur in sets of different orientations. Basal PDFS in quartz are mechanical Brazil twins (only resolvable by TEM) and rhombohedral PDFs are characterized by localized transformations from/to diaplectic glass. A comparison to the undulating dark lamellae in CL observed here appears very distracting and misleading from my point of view. Instead, a much more specific and careful discussion of (sub)basal deformation lamellae, short wave length undulatory extinction and fine extinction bands in quartz, the indication of the respective formation processes (relevance of dislocation glide, pile up of dislocations, influence of microcracking (!) etc.) as well as a discussion on the deformation conditions (transient high stresses?) would be very important and relevant here.
Further comments:
- Line 30-32: I think that also Nüchter and Stöckhert, 2007, 2008 (references see below) are very relevant studies on the topic of transient permeability and fluid flow related to seismic activity recorded by quartz veins, which should be discussed here.
- Line 78, please rephrase, as this might be mistakeable. I assume that here the initiation of the fault system is meant and not the nucleation of an earthquake.
- Line 135, Fig. 2a) the hybrid extensional-shear veins and alteration halos are not well visible in the figure
- Line 153-170 please rewrite this paragraph and describe the microstructures more specifically: e.g., I recommend to not use “planar features” which is very unspecific and maybe mistakeable by the very specific term “planar deformation features” in shocked quartz from meteorite impactites. This is especially as the microstructures shown in Fig. 3e and 4 are not really planar except maybe of the healed microcracks in Fig. 3d, see specific comment 1 above. Usually the term “deformation lamellae” is referring to lamellar undulatory extinction with the lamellae subparallel to the basal plane, i.e. the plane at high angle to , as described here. The term short wave length undulatory extinction is referring to wavy, lamellar undulatory extinction also subparallel to other crystallographic planes (m, r, z).
- Line 155-160: I strongly recommend to distinguish fractures in quartz sealed also with other phases (i.e. veins, or if you wish veinlets) from epitaxially healed microcracks in quartz (Fig. 3d)
- line 165: are all observed deformation lamellae of (sub)basal orientation? What is the angle of the lamellae to the basal plane?
- Line 169-170: the epitaxy of the healed microcracks is better to see in Fig. 3d, by the same extinction position of the grain (but please label the healed microcracks, see below). Where is the veinlet in Fig. 5a, which is corresponding to the grain in Fig. 4d, please indicate the veinlet in both images. In the BSE image also no veinlet is visible, which should indicate the presence of different phases, as feldspar. Again, an optical micrograph could be much more helpful…
- 3 d, e: Please indicate also the healed microcracks in Fig. 3d. It would be very interesting to see the CL images of these two grains, especially Fig. 3d, to see the difference in CL related to the healed microcracks and to the deformation lamellae.
- 4: The undulating lamellae dark in CL are very impressive. Yet, the figure does not allow to distinguish between deformation lamellae, veinlets or healed microcracks, as all three microstructures are obviously characterized by the wavy lamellae of dark CL and in BSE all three microstructures do not show up. I would expect that at least the different phases and grains in veinlets should be visible in BSE, but for that a better contrast/resolution would help. Also, in optical micrographs, all three microstructures should easily be distinguishable. Thus, I strongly recommend to exchange the BSE images with meaningful optical micrographs.
- Line 185 caption to Fig. 4: what do you expect from BSE image? The z-contrast can show other phases, e.g. in your veinlets, but no veinlets filled with albit/K-Fsp are shown? The orientation contrast may show deformation microstructures, but not in this resolution…, see also specific comment 1 above.
- Line 195/EBSD data, see specific comment 2 above
- Line 216: fig. 5h? fig. 6h?
- 6 b: the idiomorphic zoned epidote does not really show up in the figure?
- 6e S-C foliation?
- 6g) idiomorphic crystals? Triple junctions, of course there are triple junctions in a 2D picture of a polyphase aggregate, what is the relevance?
- 6 i, j where are the veinlets, as referenced in line 219, there are wavy dark lamellae in the CL images, but whether these are deformation lamellae, healed microcracks or veinlets with other phases does not get clear from these two images.
- Lines 260-285 please rewrite this paragraph, see specific comment 3 above
- line 397, where are the quartz-healed veinlets in S1?
- Figure S1, 2: the deformation lamellae are hard to be resolved in the micrographs of the 100µm-thick thin sections.
Recommended references:
Nüchter, J.‐A., and B. Stöckhert (2007), Vein quartz microfabrics indicating progressive evolution of fractures into cavities during postseismic creep in the middle crust, J. Struct. Geol., 29, 1445–1462.
Nüchter, J.‐A., and B. Stöckhert (2008), Coupled stress and pore fluid pressure changes in the middle crust: Vein record of coseismic loading and postseismic stress relaxation, Tectonics, 27, TC1007, doi:10.1029/2007TC002180.
Citation: https://doi.org/10.5194/egusphere-2024-1841-RC1 - AC1: 'Reply on RC1', Simone Masoch, 06 Oct 2024
-
RC2: 'Comment on egusphere-2024-1841', Anonymous Referee #2, 08 Aug 2024
The manuscript by Masoch et al deals with the microstructures from a fault zone in northern Chile related with tectono-magmatic and hydrothermal activity. The authors claim that the deformation modes recorded therein could be representative of processes at stake in active swarm systems. Even though the idea of relating the features visible in this fault zone is not totally new and already proposed in the previous papers from the same group on this locality, I found the study well conducted, adequately documented and rather convincing. There are probably several ways of interpreting the finite structures recorded in this fault zone. Future work will tell if those are indeed swarms -or not-. The discussion and the genetic model is mostly supported by the observations even though some re-wording and clarification is needed in places (see below). I also believe that the microstructures should perhaps be described with greater care. Overall I recommend publication after moderate revisions.
- I think that the authors should better explain the part on the internal versus external fluid infiltration, and locate the epidote-bearing domains in their figure 8. Because epidote formation requires the incoming of large amounts of calcium, I believe that a better discussion of this aspect would bring water to their mill when it comes to discussing fluid infiltration after the first fracturing event. Have similar epidote-rich veins been described elsewhere in Northern Chile (or elsewhere) as a consequence of deeper emplacement/cooling of a plutonic body? Can you discard the possibility that the fluid source comes from the currently downgoing subducting plate?
- The interpretation of fault zone structures in terms of slip velocity is hazardous. It is currently impossible to tell whether breccias or cataclasites result from slip at seismic strain rates in the absence of pseudotachylytes. I suggest a more careful writing.
Detailed points:
L.14: fault-veins / epidote faulting: what do you mean? Please clarify. Not clear enough for an abstract.
L.17-21: the abstract lacks material that enables understanding how you came to these conclusions.
L.65: linkage zone? What do you mean?
L.129: replace by ‘EBSD data was processed using the MTEX…’
L.132: why such a low (6 nA) current?
L.135: you mean alkali devolatilization? (instead of migration)
L.202: (Al-rich; light: Fe-rich) there is something missing here
L.211: show the pores!
L.216: there is no figure 5h! check again the figure calls. Do you mean 6h?
L.267: ‘high stresses’: how high?
L.269: how slow?
L.282: ‘the latter hypothesis’: clarify to which hypothesis you are referring to
L.295-298: It is not clear to me how high stresses can be reached here in hybrid veins, since mode ii veins by definition require higher fluid pressures than pure shear veins
L.305: rephrase: too long and not clear
L.314-317: Yes, but this study deals with dissolution precipitation of the host metasediments towards the host. In this study you suggest permeability increments associated with fluid advection.
L.326: any evidence for pressure-solution at this stage that could account for elemental redistribution?
L.351: see Angiboust et al. (2015, G-cubed) for another example where an epidote-rich cataclazed fault system is described, forming as a consequence of transients increase in pore fluid pressure in a sheared system. See also Oncken et al. (2021, geosphere) for further evidence of foliated cataclasites as a key fault zone material in deep plate boundary systems. See also Muñoz-Montecinos et al. (EPSL, 2021).
L.353: foliated, fluidized cataclasites and breccias may also form at sub-seismic strain rates (see Oncken et al., 2021). I would be more careful in the writing here.
L.370: check syntax in this sentence (perhaps you mean ‘by an increase of the rate of fluid pressure…’)
L.372: which type of deformation events?
L.384: coexist (no ‘s’)
L.430: the presence of suspended clasts within cataclasite should not be viewed alone as a solid evidence for seismic slip
Bird & Spieler (2004, rev. Min. Geochem) could be a useful reference when it comes to demonstrating that your veins were once part of a supra-plutonic environment.
Figure 1: how do you define the ‘weakly fractured unit’? is there a statistical criterion or is it purely arbitrary? Also, explain better your difference between chloritized/Fractured and chlorite-rich cataclastic: foliated and massive, in the caption of the map.
Figure 3: better label minerals and features as explained in the caption
Figure 4: what are the analytical conditions used for obtaining these CL images?
Figure 5b: how many points considered for this pole figure? figure 5a: why not showing the misorientation map instead? It would be more useful here. What is the Y direction and what is the reference frame?
Figure 8: part (a) title: propagation (not progation). The three lines (crystal plasticity, dynamic fracturing …) are not well positioned and not very easy to understand in the frame of this sketch.
Figure 9: ok but this figure does not consider the reactivation of the fault
Citation: https://doi.org/10.5194/egusphere-2024-1841-RC2 - AC2: 'Reply on RC2', Simone Masoch, 06 Oct 2024
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Giorgio Pennacchioni
Michele Fondriest
Rodrigo Gomila
Piero Poli
José Cembrano
Giulio Di Toro
The requested preprint has a corresponding peer-reviewed final revised paper. You are encouraged to refer to the final revised version.