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Quartz vein formation by local dehydration embrittlement along the deep, tremorgenic subduction thrust interface

Fagereng, Ake, Diener, Johann, Meneghini, Francesca, Harris, Chris and Kvadsheim, Ada 2017. Quartz vein formation by local dehydration embrittlement along the deep, tremorgenic subduction thrust interface. Geology 46 (1) , pp. 67-70. 10.1130/G39649.1

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Abstract

Hydrothermal quartz veins are ubiquitous in exhumed accretionary complexes, including the Namibian Damara belt. Here, subduction-related deformation occurred at temperatures ≤550 °C, and vein geometry is consistent with plate interface shear, low effective normal stresses, and mixed-mode deformation. Quartz vein δ18O values relative to Standard Mean Ocean Water (SMOW) range from 9.4‰ to 17.9‰ (n = 30), consistent with precipitation from metamorphic fluids. A dominant subset of quartz veins away from long-lived high-strain zones and basaltic slivers have δ18O values in a smaller range of 14.9‰ ± 1‰, requiring precipitation from a fluid with δ18O of 12‰ ± 1‰ at 470–550 °C. This uniform fluid isotope value is consistent with progressive local breakdown of chlorite allowing extensive hydrofracture at temperatures typical of the plastic regime. In active subduction zones, brittle deformation within the plastic regime is inferred from observations of tectonic tremor, a noise-like seismic signal including overlapping low- and very low-frequency earthquakes, which occurs below the seismogenic zone. Both tremor and hydrothermal veins correlate with zones of inferred high fluid pressure, could represent a mixture of shear and dilatant failure, and may therefore be controlled by episodic hydrofracturing within a dominantly plastic and aseismic regime.

Item Type: Article
Date Type: Publication
Status: Published
Schools: Earth and Ocean Sciences
Subjects: Q Science > QE Geology
Publisher: Geological Society of America
ISSN: 0091-7613
Funders: European Research Council, Claude Leon Foundation, University of Cape Town
Date of First Compliant Deposit: 1 December 2017
Date of Acceptance: 23 August 2017
Last Modified: 24 Sep 2019 08:49
URI: http://orca-mwe.cf.ac.uk/id/eprint/107191

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