Open AccessGeochemical and microstructural evidence for interseismic changes in fault zone permeability and strength, A lpine F ault, N ew Z ealand
Author(s) -
Boulton Carolyn,
Menzies Catriona D.,
Toy Virginia G.,
Townend John,
Sutherland Rupert
Publication year - 2017
Publication title -
geochemistry, geophysics, geosystems
Language(s) - English
Resource type - Journals
SCImago Journal Rank - 1.928
H-Index - 136
ISSN - 1525-2027
DOI - 10.1002/2016gc006588
Subject(s) - geology , mylonite , fault (geology) , detachment fault , petrology , geochemistry , fault gouge , shear zone , seismology , tectonics , extensional definition
Oblique dextral motion on the central Alpine Fault in the last circa 5 Ma has exhumed garnet‐oligoclase 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 (T ≤ 300–400°C, 6–10 km depth) and at shallow depths (T = 20–150°C, 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.