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

Hopkinson, L., Beard, J.S. and Boulter, C.A. (2004) The hydrothermal plumbing of a serpentinite-hosted detachment: evidence from the West Iberia non-volcanic rifted continental margin Marine Geology, 204 (3-4). pp. 301-315. ISSN 0025-3227

Full text not available from this repository.

Official URL: http://www.sciencedirect.com/science/article/pii/S...

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 calcium-hydroxide 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 Ca2+ 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.

Item Type:Journal article
Uncontrolled Keywords:serpentinite; serpentinization; hydrothermal mineralization; detachment; overpressure
Subjects:F000 Physical Sciences > F800 Physical Geography and Environmental Sciences > F850 Environmental Sciences
F000 Physical Sciences > F600 Geology
DOI (a stable link to the resource):10.1016/S0025-3227(03)00374-8
Faculties:Faculty of Science and Engineering > School of Environment and Technology > Applied Geosciences
Faculty of Science and Engineering > School of Environment and Technology > Ecology, Landscape and Pollution Management
Faculty of Science and Engineering > School of Environment and Technology
ID Code:831
Deposited By:editor environment
Deposited On:23 Nov 2006
Last Modified:10 Jun 2013 10:56

Repository Staff Only: item control page