Publication Date:
2024-04-25
Description:
〈title xmlns:mml="http://www.w3.org/1998/Math/MathML"〉Abstract〈/title〉〈p xmlns:mml="http://www.w3.org/1998/Math/MathML" xml:lang="en"〉To evaluate how the presence of pseudotachylytes affects the strength of crustal rocks, deformed pseudotachylytes and their relationship with pristine pseudotachylytes at the base of the Silvretta nappe are analyzed. Pseudotachylytes formed associated with high‐stress crystal plasticity (〈italic〉σ〈/italic〉〈sub〉〈italic〉d〈/italic〉〈/sub〉 > 400 MPa), as indicated by twinned amphiboles in gneisses. Mylonitic quartz clasts enclosed within deformed pseudotachylytes and mylonitic vein‐quartz, hosting folded pseudotachylyte injection veins, reflect creep at lower stresses (ca. 100 MPa) after seismic rupturing. Deformed pseudotachylytes can be crosscut by pristine pseudotachylytes, indicating a second, independent stage of coseismic rupturing after creep. The evidence of dynamic dislocation creep of quartz and the presence of stilpnomelane and epidote associated with all fault rocks indicate similar ambient greenschist facies conditions during all deformation stages. Whereas the intermediate stage of creep is interpreted to represent deformation at large distance to the propagating thrust tip, the pristine pseudotachylytes represent the last stage of rupturing eventually leading to nappe decoupling from its basement. Gneiss clasts in an ultramylonitic matrix (i.e., deformed pseudotachylyte) reveal that pseudotachylytes have a lower strength during creep in relation to the hosting gneisses. In contrast, during coseismic high‐stress crystal plasticity, the coarse gneisses accumulate a higher amount of strain. This strength‐relationship explains that only those rocks rupture, which have not been previously deformed before. The study demonstrates the importance of different strengths of crustal rocks at specific stress‐ and strain‐rate conditions in dependence on the distance to the propagating fault tip.〈/p〉
Description:
Key Points:
〈list list-type="bullet"〉
〈list-item〉
〈p xml:lang="en"〉Ultramylonites (deformed pseudotachylytes) and mylonites represent creep at large distance to the propagating thrust tip〈/p〉〈/list-item〉
〈list-item〉
〈p xml:lang="en"〉Pristine pseudotachylytes represent final deformation at the tip of the propagating thrust fault associated with nappe decoupling〈/p〉〈/list-item〉
〈list-item〉
〈p xml:lang="en"〉Pseudotachylytes are weak during aseismic creep and strong during coseismic high‐stress plasticity〈/p〉〈/list-item〉
〈/list〉
〈/p〉
Description:
Deutsche Forschungsgemeinschaft
http://dx.doi.org/10.13039/501100001659
Description:
https://doi.org/10.17632/xhh2ktks9g.4
Description:
https://nano.oxinst.com/products/aztec/
Description:
https://www.horiba.com/aut/scientific/products/detail/action/show/Product/labspec-6-spectroscopy-suite-software-1843/
Keywords:
ddc:551.8
;
(deformed) pseudotachylytes
;
(ultra‐)mylonites
;
creep
;
multiple high‐stress events
;
seismic cycle
;
nappe decoupling
Language:
English
Type:
doc-type:article
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