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

Geochemical and microstructural evidence for interseismic changes in fault zone permeability and strength, Alpine Fault, New Zealand
Geochemical and microstructural evidence for interseismic changes in fault zone permeability and strength, Alpine Fault, New Zealand
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.
238-265
Boulton, Carolyn
b4c9d954-1708-4eac-8501-ee6e19084693
Menzies, Catriona
04bc2a62-064d-4911-9c45-17b47f3005de
Toy, Virginia G.
fc903111-1385-4cf6-a398-86d1d0e904c1
Townend, John
60be76ed-47bd-4c9a-92e1-2cba6fdad2e4
Rupert, Sutherland
e1194f14-af6c-4982-9276-599e56dd4b6b
Boulton, Carolyn
b4c9d954-1708-4eac-8501-ee6e19084693
Menzies, Catriona
04bc2a62-064d-4911-9c45-17b47f3005de
Toy, Virginia G.
fc903111-1385-4cf6-a398-86d1d0e904c1
Townend, John
60be76ed-47bd-4c9a-92e1-2cba6fdad2e4
Rupert, Sutherland
e1194f14-af6c-4982-9276-599e56dd4b6b

Boulton, Carolyn, Menzies, Catriona, Toy, Virginia G., Townend, John and Rupert, Sutherland (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. (doi:10.1002/2016GC006588).

Record type: Article

Abstract

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.

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Boulton et al 2017 G3 accepted - Accepted Manuscript
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Boulton_et_al-2017-Geochemistry,_Geophysics,_Geosystems - Version of Record
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Accepted/In Press date: 12 December 2016
e-pub ahead of print date: 25 January 2017
Published date: 25 January 2017
Organisations: Geochemistry

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Local EPrints ID: 406453
URI: https://eprints.soton.ac.uk/id/eprint/406453
PURE UUID: a4e1f5e8-cc02-495c-a324-913e1d4af867

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Date deposited: 10 Mar 2017 10:47
Last modified: 15 Aug 2019 05:03

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