T77 Deformation Zones in Time and Space I: A Celebration of the Career of Steven Wojtal

Monday, 10 October 2022
8:00 AM - 12:00 PM
207

PRIMED TO SLIDE: THE ROLE OF CLAY NANOCOATINGS IN THE DEVELOPMENT OF SCALY FAULT FABRICS

Paper number: T77-5
Program: Technical Sessions
Time: 8:55 AM – 9:10 AM

Authors

Abstract

Scaly fabrics, composed of elongate phacoids, often host distributed slip in fault zones when deformation is not concentrated along a single slip surface. Scaly fabrics can develop in a wide range of host rocks. Here, we examine the development of scaly fabrics from the terrane-bounding, strike-slip Minas fault zone (Nova Scotia, Canada). In the low temperature (~150 ºC) domain of deformation, shear strain is localized into a phyllite-hosted fault strand ~7 m wide which contains phacoids ranging from 1 mm to 15 cm in length. Phacoid edges show slickenlines with a range of rakes, but with a dominant sub-horizontal orientation consistent with strike-slip kinematics. Between phacoids are angular fragments of wallrock and rounded spheres (~5 cm in diameter) of quartz coated in a black layer of chlorite with pervasive slickenlines. Transmission electron microscopy images of phacoids display evidence for dissolution and re-precipitation of framework silicates. However, framework silicates are coated in nm-scale layers of chlorite which indent into the framework silicates. We hypothesize that early deformation in the fault strand was accommodated by dissolution-precipitation creep followed by a switch in deformation mechanism to frictional sliding through the development of chlorite nanocoatings. Nanocoatings of clay can dramatically alter deformation over the lifetime of a fault.

Geological Society of America Abstracts with Programs. Vol. 54, No. 6

doi: 10.1130/abs/2022AM-381945

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