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Evidence of hydrothermal fluid circulation driving elemental mass redistribution in an active fault zone

Dorsey, MT; Rockwell, TK; Girty, GH; Ostermeijer, GA; Browning, J; Mitchell, TM; Fletcher, JM; (2021) Evidence of hydrothermal fluid circulation driving elemental mass redistribution in an active fault zone. Journal of Structural Geology , 144 , Article 104269. 10.1016/j.jsg.2020.104269. Green open access

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Abstract

Important fault zone processes can be discerned from the characterization of fracture damage and chemical transformations associated with active seismic sources. To characterize the 2010 M7.2 El Mayor-Cucapah rupture zone, continuous samples of fault core and 23 samples of damaged rock were collected perpendicular to strike of the Borrego fault. Samples were analyzed for clay mineralogy, bulk geochemistry, and bulk and grain density from which porosities and volumetric strains were derived. Prior to the Borrego fault forming, the tonalitic protolith, containing chlorite, epidote, and titanite, was subjected to temperatures of ∼330–340 °C during deuteric alteration. Rocks within the damage zone are partially pulverized and contain abundant cataclastic seams. Porosity and volumetric strain peak in zones 1.5 m–10.5 m from the core. Within these zones, losses in Ca and P mass, increases in Mg and Na mass, along with the conservation of Fe and Si mass are consistent with oxidizing acidic conditions at < 200 °C. Gains in LOI are attributed to increases in clay content. The above data support a model of Mg- and Na-rich oxidizing fluid circulation within the damage zone of the Borrego fault.

Type: Article
Title: Evidence of hydrothermal fluid circulation driving elemental mass redistribution in an active fault zone
Open access status: An open access version is available from UCL Discovery
DOI: 10.1016/j.jsg.2020.104269
Publisher version: https://doi.org/10.1016/j.jsg.2020.104269
Language: English
Additional information: © 2020 The Author(s). Published by Elsevier Ltd. This is an open access article under the CC BY license (http://creativecommons.org/licenses/by/4.0/).
Keywords: Hydrothermal alteration, Elemental mass redistribution, Fault zone architecture, Damage zone
UCL classification: UCL
UCL > Provost and Vice Provost Offices
UCL > Provost and Vice Provost Offices > UCL BEAMS
UCL > Provost and Vice Provost Offices > UCL BEAMS > Faculty of Maths and Physical Sciences
UCL > Provost and Vice Provost Offices > UCL BEAMS > Faculty of Maths and Physical Sciences > Dept of Earth Sciences
URI: https://discovery.ucl.ac.uk/id/eprint/10124317
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