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Moving reactive interfaces and fractal carbonate replacement patterns in serpentinites: evidence from the southern Iberia Abyssal Plain

Published online by Cambridge University Press:  05 July 2018

L. J. Hopkinson ,
S. Dee  and
C. A. Boulter
L. J. Hopkinson
Affiliation:
School of Ocean and Earth Science, University of Southampton, Southampton Oceanography Centre, Empress Dock, European Way, Southampton, SO14 3ZH, UK
S. Dee
Affiliation:
Alastair Beach Associates Ltd, 11 Royal Exchange Square, Glasgow G1 3AJ, UK
C. A. Boulter*
Affiliation:
School of Ocean and Earth Science, University of Southampton, Southampton Oceanography Centre, Empress Dock, European Way, Southampton, SO14 3ZH, UK
*
*E-mail: c.boulter@soc.soton.ac.uk
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Abstract

Serpentinized ultramafic rocks recovered from beneath the southern Iberia Abyssal Plain (Ocean Drilling Programme Leg 173) provide the first record of fractal carbonate replacement patterns in a serpentinite. The patterns are expressed as microscopic branching aggregates (clusters) of aragonite disseminated throughout the serpentinites. Aragonite growth was the final mineralization event. The aragonite diminishes rapidly in quantity from an essential to a trace component of the serpentinite over a distance of ∼40 m from a normal fault. Decreasing abundance of aragonite away from the normal fault links the growth of the carbonate to the multistage hydrothermal mineralization associated with the fault.

Aragonite clusters are concentrated in picrolite, where they are interwoven with colloid-sized chrysotile, and show fractal growth habits. Areas adjacent to the clusters are sites of Mg enrichment of the serpentine medium relative to aragonite-free picrolite. It is interpreted that the aragonite clusters result from incursions of reactive seawater solutions through fine-scale pore structures in and around the fault in response to pressure gradients emanating from active tectonism. Cluster growth is interpreted to be a percolation phenomenon and provides a novel source of information on the nature of fine-scale reactive fluid flow, pore-space connectivity, and carbonate replacement processes in serpentinites.

Keywords

serpentinitefractal growth patternsviscous fingersaragonite
Type
Research Article
Information
Mineralogical Magazine , Volume 64 , Issue 5 , October 2000 , pp. 791 - 800
Copyright
Copyright © The Mineralogical Society of Great Britain and Ireland 2000

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Footnotes

†

Current address: Department of Earth Sciences, College of Science, Sultan Qaboos University, PO Box 50, Al-Khod 123, Muscat, Sultanate of Oman

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