The University of Southampton
University of Southampton Institutional Repository

The hydrothermal plumbing of a serpentinite-hosted detachment: evidence from the West Iberia non-volcanic rifted continental margin

The hydrothermal plumbing of a serpentinite-hosted detachment: evidence from the West Iberia non-volcanic rifted continental margin
The hydrothermal plumbing of a serpentinite-hosted detachment: evidence from the West Iberia non-volcanic rifted continental margin
This study documents the critical role of structurally-induced fluid flow during the evolution of the footwall succession to a major low-angle normal (detachment) fault, drilled by the Ocean Drilling Program leg 173, Site 1068 beneath the Southern Iberia Abyssal Plain. The fault zone comprises (carbonate-altered, rodingitized, and albitized) metabasite-rich sedimentary breccias and serpentinized mantle peridotites. The brittle infrastructure of the detachment consists of mineralized high dilation breccias, and meshes of mineralized extensional and shear veins, that root into chlorite and serpentine cataclasite, and gouge. The fault rocks are underlain by cohesive serpentinite that shows kernel textures, indicative of volume expansion accompanying serpentinization of peridotite. The texture is disrupted and offset by small-scale fractures and faults. The distribution of serpentine polytypes, carbonates, Fe^Ni alloys, sulfides, oxides, and other silicate phases, varies across the fault zone in patterns consistent with mineralization, and replacement, from solutions derived from two end member components: seawater, and CH4-bearing calciumhydroxide enriched hydrothermal solutions. The latter form when heated seawater reacts with peridotite to form serpentinite at low water to rock ratios. Serpentine mineral chemistries indicate that fracture-controlled serpentinite recrystallization and replacement occurred at various fO2, aSiO2 and Ca2þ conditions. In places this also involved mild prograde thermal events. The serpentinite also hosts tochilinite-valleriite group minerals and aragonite, both are interpreted as indicators of sea water incursions into the upper reaches of the detachment. To account for the evidence of coeval hydrothermal mineralization and displacements across the detachment we relate hydrothermal discharge to the buffering of high pore fluid pressures by fault slip. Localized sources of high fluid pressures at depth are attributed to serpentinization of peridotite around the fault that promotes changes to solution mass density, exothermic reactions and swelling pressures. Sealing of the fault between the serpentinization front and the top of the detachment results from hydrothermal mineralization, alteration, and serpentine gouges. Hydrothermal discharges from the detachment accompanying shear failure allow for variable mixing between the hydrothermal solutions and seawater, and post-slip convective draw down of seawater into the detachment. It is suggested that the latter may have been limited in duration by ongoing mineralization leading to the restoration of the fault seal. Concomitant serpentinization around the detachment at depth provides scope for cyclic hydrothermal discharges and fault slip.
serpentinite, serpentinization, hydrothermal mineralization, detachment, overpressure
0025-3227
301-315
Hopkinson, L.
bd4c65de-14e5-4e90-8ca5-4c6986dc87f3
Beard, J.S.
85cd87e2-f07f-4e50-bf28-0851d9155ba8
Boulter, C.
dc0aded9-dc21-4c37-8cce-0eeff62e1dec
Hopkinson, L.
bd4c65de-14e5-4e90-8ca5-4c6986dc87f3
Beard, J.S.
85cd87e2-f07f-4e50-bf28-0851d9155ba8
Boulter, C.
dc0aded9-dc21-4c37-8cce-0eeff62e1dec

Hopkinson, L., Beard, J.S. and Boulter, C. (2004) The hydrothermal plumbing of a serpentinite-hosted detachment: evidence from the West Iberia non-volcanic rifted continental margin. Marine Geology, 204 (3-4), 301-315. (doi:10.1016/S0025-3227(03)00374-8).

Record type: Article

Abstract

This study documents the critical role of structurally-induced fluid flow during the evolution of the footwall succession to a major low-angle normal (detachment) fault, drilled by the Ocean Drilling Program leg 173, Site 1068 beneath the Southern Iberia Abyssal Plain. The fault zone comprises (carbonate-altered, rodingitized, and albitized) metabasite-rich sedimentary breccias and serpentinized mantle peridotites. The brittle infrastructure of the detachment consists of mineralized high dilation breccias, and meshes of mineralized extensional and shear veins, that root into chlorite and serpentine cataclasite, and gouge. The fault rocks are underlain by cohesive serpentinite that shows kernel textures, indicative of volume expansion accompanying serpentinization of peridotite. The texture is disrupted and offset by small-scale fractures and faults. The distribution of serpentine polytypes, carbonates, Fe^Ni alloys, sulfides, oxides, and other silicate phases, varies across the fault zone in patterns consistent with mineralization, and replacement, from solutions derived from two end member components: seawater, and CH4-bearing calciumhydroxide enriched hydrothermal solutions. The latter form when heated seawater reacts with peridotite to form serpentinite at low water to rock ratios. Serpentine mineral chemistries indicate that fracture-controlled serpentinite recrystallization and replacement occurred at various fO2, aSiO2 and Ca2þ conditions. In places this also involved mild prograde thermal events. The serpentinite also hosts tochilinite-valleriite group minerals and aragonite, both are interpreted as indicators of sea water incursions into the upper reaches of the detachment. To account for the evidence of coeval hydrothermal mineralization and displacements across the detachment we relate hydrothermal discharge to the buffering of high pore fluid pressures by fault slip. Localized sources of high fluid pressures at depth are attributed to serpentinization of peridotite around the fault that promotes changes to solution mass density, exothermic reactions and swelling pressures. Sealing of the fault between the serpentinization front and the top of the detachment results from hydrothermal mineralization, alteration, and serpentine gouges. Hydrothermal discharges from the detachment accompanying shear failure allow for variable mixing between the hydrothermal solutions and seawater, and post-slip convective draw down of seawater into the detachment. It is suggested that the latter may have been limited in duration by ongoing mineralization leading to the restoration of the fault seal. Concomitant serpentinization around the detachment at depth provides scope for cyclic hydrothermal discharges and fault slip.

This record has no associated files available for download.

More information

Published date: 2004
Keywords: serpentinite, serpentinization, hydrothermal mineralization, detachment, overpressure

Identifiers

Local EPrints ID: 9821
URI: http://eprints.soton.ac.uk/id/eprint/9821
ISSN: 0025-3227
PURE UUID: 2da96cdd-a404-4fdf-afe7-692912c0e35b

Catalogue record

Date deposited: 13 Oct 2004
Last modified: 15 Mar 2024 04:57

Export record

Altmetrics

Contributors

Author: L. Hopkinson
Author: J.S. Beard
Author: C. Boulter

Download statistics

Downloads from ePrints over the past year. Other digital versions may also be available to download e.g. from the publisher's website.

View more statistics

Atom RSS 1.0 RSS 2.0

Contact ePrints Soton: eprints@soton.ac.uk

ePrints Soton supports OAI 2.0 with a base URL of http://eprints.soton.ac.uk/cgi/oai2

This repository has been built using EPrints software, developed at the University of Southampton, but available to everyone to use.

We use cookies to ensure that we give you the best experience on our website. If you continue without changing your settings, we will assume that you are happy to receive cookies on the University of Southampton website.

×