Geochemical and microstructural evidence for interseismic changes in fault zone permeability and strength, Alpine Fault, New Zealand

Boulton, C.; Menzies, C.D; Toy, V.G.; Townend, J.; Sutherland, R.

Abstract

Oblique dextral motion on the central Alpine Fault in the last circa 5 Ma has exhumed garnetoligoclase facies mylonitic fault rocks from 35 km depth. During exhumation, deformation, accompanied by fluid infiltration, has generated complex lithological variations in fault-related rocks retrieved during Deep Fault Drilling Project (DFDP-1) drilling at Gaunt Creek, South Island, New Zealand. Lithological, geochemical, and mineralogical results reveal that the fault comprises a core of highly comminuted cataclasites and fault gouges bounded by a damage zone containing cataclasites, protocataclasites, and fractured mylonites. The fault core-alteration zone extends 20–30 m from the principal slip zone (PSZ) and is characterized by alteration of primary phases to phyllosilicate minerals. Alteration associated with distinct mineral phases occurred proximal the brittle-to-plastic transition (T300–4008C, 6–10 km depth) and at shallow depths (T520–1508C, 0–3 km depth). Within the fault core-alteration zone, fractures have been sealed by precipitation of calcite and phyllosilicates. This sealing has decreased fault normal permeability and increased rock mass competency, potentially promoting interseismic strain buildup.

Citation

Boulton, C., Menzies, C., Toy, V., Townend, J., & Sutherland, R. (2017). Geochemical and microstructural evidence for interseismic changes in fault zone permeability and strength, Alpine Fault, New Zealand. Geochemistry, Geophysics, Geosystems, 18(1), 238-265. https://doi.org/10.1002/2016gc006588

• Journal Article Type: Article
• Acceptance Date: Dec 12, 2016
• Online Publication Date: Jan 25, 2017
• Publication Date: Jan 31, 2017
• Deposit Date: Oct 2, 2019
• Publicly Available Date: Nov 22, 2019
• Journal: Geochemistry, Geophysics, Geosystems
• Electronic ISSN: 1525-2027
• Publisher: American Geophysical Union
• Peer Reviewed: Peer Reviewed
• Volume: 18
• Issue: 1
• Pages: 238-265
• DOI: https://doi.org/10.1002/2016gc006588
• Public URL: https://durham-repository.worktribe.com/output/1290020