Low effective fault strength due to frictional-viscous flow in phyllonites, Karakoram Fault Zone, NW India
Phyllosilicate-rich fault rocks are common in large-scale fault zones and can dramatically impact fault rheology. Experimental evidence suggests that multi-mechanism frictional-viscous flow (FVF) may operate in such lithologies, potentially significantly weakening mature fault cores. We report micro...
| Main Authors: | , , , , |
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| Format: | Journal article |
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Elsevier
2015
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| _version_ | 1826276298319724544 |
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| author | Wallis, D Lloyd, G Phillips, R Parsons, A Walshaw, R |
| author_facet | Wallis, D Lloyd, G Phillips, R Parsons, A Walshaw, R |
| author_sort | Wallis, D |
| collection | OXFORD |
| description | Phyllosilicate-rich fault rocks are common in large-scale fault zones and can dramatically impact fault rheology. Experimental evidence suggests that multi-mechanism frictional-viscous flow (FVF) may operate in such lithologies, potentially significantly weakening mature fault cores. We report microstructures indicative of FVF in exhumed phyllonites of the Karakoram Fault Zone (KFZ), NW India. These include interconnected muscovite foliae, lack of quartz/feldspar crystal preferred orientations, and sutured grains and overgrowths indicative of fluid-assisted diffusive mass transfer. FVF microphysical modelling, using microstructural observations from the natural fault rock and experimentally-derived friction and diffusion coefficients, predicts low peak shear strengths of <20 MPa within the frictional-viscous transition zone. Chlorite geothermometry indicates that synkinematic chlorites grew at 351 ± 34 °C (c. 10 km depth) during FVF, immediately above the transition to quartz crystal plasticity. The deformation processes and interpreted low shear strength of the exhumed KFZ fault rocks provide analogues for processes operating currently at depth in active faults of similar scale. If similar lithologies are present at depth, then the Quaternary seismic characteristics of the KFZ support faults with phyllonitic cores being able to accommodate large seismic ruptures. The results also provide rare rheological constraints for mechanical models of the India-Asia collision zone. |
| first_indexed | 2024-03-06T23:11:51Z |
| format | Journal article |
| id | oxford-uuid:65c063cb-a26a-4001-ac73-89128c730675 |
| institution | University of Oxford |
| last_indexed | 2024-03-06T23:11:51Z |
| publishDate | 2015 |
| publisher | Elsevier |
| record_format | dspace |
| spelling | oxford-uuid:65c063cb-a26a-4001-ac73-89128c7306752022-03-26T18:27:33ZLow effective fault strength due to frictional-viscous flow in phyllonites, Karakoram Fault Zone, NW IndiaJournal articlehttp://purl.org/coar/resource_type/c_dcae04bcuuid:65c063cb-a26a-4001-ac73-89128c730675Symplectic Elements at OxfordElsevier2015Wallis, DLloyd, GPhillips, RParsons, AWalshaw, RPhyllosilicate-rich fault rocks are common in large-scale fault zones and can dramatically impact fault rheology. Experimental evidence suggests that multi-mechanism frictional-viscous flow (FVF) may operate in such lithologies, potentially significantly weakening mature fault cores. We report microstructures indicative of FVF in exhumed phyllonites of the Karakoram Fault Zone (KFZ), NW India. These include interconnected muscovite foliae, lack of quartz/feldspar crystal preferred orientations, and sutured grains and overgrowths indicative of fluid-assisted diffusive mass transfer. FVF microphysical modelling, using microstructural observations from the natural fault rock and experimentally-derived friction and diffusion coefficients, predicts low peak shear strengths of <20 MPa within the frictional-viscous transition zone. Chlorite geothermometry indicates that synkinematic chlorites grew at 351 ± 34 °C (c. 10 km depth) during FVF, immediately above the transition to quartz crystal plasticity. The deformation processes and interpreted low shear strength of the exhumed KFZ fault rocks provide analogues for processes operating currently at depth in active faults of similar scale. If similar lithologies are present at depth, then the Quaternary seismic characteristics of the KFZ support faults with phyllonitic cores being able to accommodate large seismic ruptures. The results also provide rare rheological constraints for mechanical models of the India-Asia collision zone. |
| spellingShingle | Wallis, D Lloyd, G Phillips, R Parsons, A Walshaw, R Low effective fault strength due to frictional-viscous flow in phyllonites, Karakoram Fault Zone, NW India |
| title | Low effective fault strength due to frictional-viscous flow in phyllonites, Karakoram Fault Zone, NW India |
| title_full | Low effective fault strength due to frictional-viscous flow in phyllonites, Karakoram Fault Zone, NW India |
| title_fullStr | Low effective fault strength due to frictional-viscous flow in phyllonites, Karakoram Fault Zone, NW India |
| title_full_unstemmed | Low effective fault strength due to frictional-viscous flow in phyllonites, Karakoram Fault Zone, NW India |
| title_short | Low effective fault strength due to frictional-viscous flow in phyllonites, Karakoram Fault Zone, NW India |
| title_sort | low effective fault strength due to frictional viscous flow in phyllonites karakoram fault zone nw india |
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