Harvey, J orcid.org/0000-0002-0390-3438, Savov, IP orcid.org/0000-0003-4218-4365, Agostini, S et al. (2 more authors) (2014) Si-metasomatism in serpentinized peridotite: The effects of talc-alteration on strontium and boron isotopes in abyssal serpentinites from Hole 1268a, ODP Leg 209. Geochimica et Cosmochimica Acta, 126. pp. 30-48. ISSN 0016-7037
Abstract
Ultramafic rocks recovered from Hole 1268a, Ocean Drilling Program Leg 209, to the south of the 15°20′N Fracture Zone on the Mid-Atlantic ridge have experienced a complex history of melt depletion and subsequent interaction with a series of fluids under varying temperature and pH conditions. After intense melt depletion, varying degrees of serpentinization at 100–200 °C took place, initially under seawater-like pH conditions. Subsequently, interaction with a higher temperature (300–350 °C) fluid with low (4–5) pH and low MgO/SiO2 resulted in the heterogeneous alteration of these serpentinites to talc-bearing ultramafic lithologies. The proximity of the currently active, high temperature Logatchev hydrothermal field, located on the opposite flank of the Mid-Atlantic ridge, suggests that unlike more distal localities sampled during ODP Leg 209, Hole 1268a has experienced Si-metasomatism (i.e. talc-alteration) by a Logatchev-like hydrothermal fluid. Serpentinite strontium isotope ratios were not materially shifted by interaction with the subsequent high-T fluid, despite the likelihood that this fluid had locally interacted with mid-ocean ridge gabbro. 87Sr/86Sr in the ultramafic lithologies of Hole 1268a are close to that of seawater (c.0.709) and even acid leached serpentinites retain 87Sr/86Sr in excess of 0.707, indistinguishable from Logatchev hydrothermal fluid. On the other hand, boron isotope ratios appear to have been shifted from seawater-like values in the serpentinites (δ11B = c.+40‰) to much lighter values in talc-altered serpentinites (δ11B = +9 to +20‰). This is likely a consequence of the effects of changing ambient pH and temperature during the mineralogical transition from serpentine to talc. Heterogeneous boron isotope systematics have consequences for the composition of ultramafic portions of the lithosphere returned to the convecting mantle by subduction. Inhomogeneities in δ11B, [B] and mineralogy introduce significant uncertainties in the prediction of the composition of slab fluids released during the early- to mid-stages of subduction.
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Item Type: | Article |
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Authors/Creators: |
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Copyright, Publisher and Additional Information: | (c) 2013 Elsevier Ltd. All rights reserved. Uploaded in accordance with the publisher's self-archiving policy. NOTICE: this is the author’s version of a work that was accepted for publication in Geochimica et Cosmochimica Acta. Changes resulting from the publishing process, such as peer review, editing, corrections, structural formatting, and other quality control mechanisms may not be reflected in this document. Changes may have been made to this work since it was submitted for publication. A definitive version was subsequently published in Geochimica et Cosmochimica Acta, 126, (2014) DOI 10.1016/j.gca.2013.10.035 |
Dates: |
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Institution: | The University of Leeds |
Academic Units: | The University of Leeds > Faculty of Environment (Leeds) > School of Earth and Environment (Leeds) > Inst of Geophysics and Tectonics (IGT) (Leeds) |
Depositing User: | Symplectic Publications |
Date Deposited: | 03 Oct 2014 15:25 |
Last Modified: | 30 Oct 2020 12:56 |
Published Version: | http://dx.doi.org/10.1016/j.gca.2013.10.035 |
Status: | Published |
Publisher: | Elsevier |
Identification Number: | 10.1016/j.gca.2013.10.035 |
Open Archives Initiative ID (OAI ID): | oai:eprints.whiterose.ac.uk:80450 |