Generation of amorphous carbon and crystallographic texture during low-temperature subseismic slip in calcite fault gouge

Claudio Delle Piane,William D.A Rickard,Martin Saunders,M Ben Clennell,Charlie Kong,Michael Verrall,Sandra Piazolo,Julien Bourdet,Ausama Giwelli,Nicholas E Timms,Vladimir Luzin

doi:10.1130/g39584.1

Claudio Delle Piane, William D.A Rickard + Show 9 more

Open Access

PDF Available

https://doi.org/10.1130/g39584.1

Copy DOI

Export

Save

Cite

Abstract
Highlights/Summary
Full-Text PDF
Similar Papers

Abstract

Listen

Identification of the nano-scale to micro-scale mechanochemical processes occurring during fault slip is of fundamental importance to understand earthquake nucleation and propagation. Here we explore the micromechanical processes occurring during fault nucleation and slip at subseismic rates (∼3 × 10−6 m s–1) in carbonate rocks. We experimentally sheared calcite-rich travertine blocks at simulated upper crustal conditions, producing a nano-grained fault gouge. Strain in the gouge is accommodated by cataclastic comminution of calcite grains and concurrent crystal-plastic deformation through twinning and dislocation glide, producing a crystallographic preferred orientation (CPO). Continued wear of fine-grained gouge particles results in the mechanical decomposition of calcite and production of amorphous carbon. We show that CPO and the production of amorphous carbon, previously attributed to frictional heating and weakening during seismic slip, can be produced at low temperature during stable slip at subseismic rates without slip weakening.

Highlights

Carbonate rocks in the upper crust host hypocenters of medium to large earthquakes worldwide and studies conducted on exhumed carbonatehosted faults indicate that coseismic slip is accommodated within highly localized slip zones a few millimeters thick, filled with fault gouge
Elucidating the conditions and nano-scale to micro-scale deformation mechanisms that control the occurrence of these microstructural features and how they relate to the frictional behavior of the fault gouge during seismic and subseismic slip is crucial for understanding the processes leading to earthquake slip in carbonate rocks
Our results show that deformation at subseismic slip rates is accommodated by a combination of cataclastic grain comminution, crystal-plastic deformation by twinning and dislocation glide, and mechanically activated dissociation of calcite leading to generation of amorphous carbon, simultaneously occurring without changes in bulk frictional properties of the fault zone

Summary

INTRODUCTION

Carbonate rocks in the upper crust host hypocenters of medium to large earthquakes worldwide and studies conducted on exhumed carbonatehosted faults indicate that coseismic slip is accommodated within highly localized slip zones a few millimeters thick, filled with fault gouge. These slip zones are characterized by the presence of nano-scale grains (SimanTov et al, 2013), the occurrence of decarbonation products and amorphous phases linked to frictional heating (Collettini et al, 2014), and crystallographic preferred orientation (CPO) (Smith et al, 2013). We monitor the frictional response of the rock as a function of shear displacement during direct shear experiments and use a range of microanalytical techniques including

METHODS

DISCUSSION