Abstract

The Neoarchean Cundimurra Pluton (Yilgarn Craton, Western Australia) was emplaced incrementally along the transpressional Cundimurra Shear Zone. During syndeformational cooling, discrete networks of cataclasites and ultramylonites developed in the narrowest segment of the shear zone, showing the same kinematics as the earlier synmagmatic structures. Lithological boundaries between aplite/pegmatite veins and host granitic gneiss show more intense pre-cataclasite fabrics than homogeneous material, and these boundaries later became the preferred sites of shear rupture and cataclasite nucleation. Transient ductile instabilities established along lithological boundaries culminated in shear rupture at relatively high temperature (~500–600 °C). Here, tensile fractures at high angles from the fault plane formed asymmetrically on one side of the fault, indicating development during seismic rupture, establishing the oldest documented earthquake on Earth. Tourmaline veins were emplaced during brittle shearing, but fluid pressure probably played a minor role in brittle failure, as cataclasites are in places tourmaline-free. Subsequent ductile deformation localized in the rheologically weak tourmaline-rich aggregates, forming ultramylonites that deformed by grain-size sensitive creep. The shape and width of the pluton/shear zone and the regime of strain partitioning, induced by melt-present deformation and established during pluton emplacement, played a key role in controlling the local distribution of brittle and then ductile subsolidus structures.

DOI

10.1016/j.jsg.2018.02.001

Publication Date

2018-05-01

Publication Title

Journal of Structural Geology

Volume

110

Publisher

Elsevier

ISSN

0191-8141

Embargo Period

2024-11-25

Keywords

Cataclasite, Mylonite, Rupture, Strain partitioning, Tourmaline, Transpression

First Page

1

Last Page

23

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