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Petrogenesis of crustal wehrlites in the Oman ophiolite: Experiments and natural rocks

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Koepke, J and Schoenborn, S and Oelze, M and Wittmann, H and Feig, ST and Hellebrand, E and Boudier, F and Schoenberg, R (2009) Petrogenesis of crustal wehrlites in the Oman ophiolite: Experiments and natural rocks. Geochemistry Geophysics Geosystems, 10 (10). pp. 1-26. ISSN 1525-2027

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Abstract

In the Wadi Haymiliyah of the Oman ophiolite (Haylayn block), discordant wehrlite bodies ranging in size from tens to hundreds of meters intrude the lower crust at different levels. We combined investigations on natural wehrlites from the Wadi Haymiliyah section with an experimental study on the phase relations in a wehrlitic system in order to constrain the petrogenesis of the crustal wehrlites of the Oman ophiolite. Secondary ion mass spectrometry analyses of clinopyroxenes from different wehrlite bodies imply that the clinopyroxenes were crystallized from tholeiitic, mid-ocean ridge (MORB)–type melts. The presence of primary magmatic amphiboles in some wehrlites suggests a formation under hydrous conditions. Significantly enhanced 87Sr/86Sr isotope ratios of separates from these amphiboles imply that the source of the corresponding magmatic fluids was either seawater or subduction zone–related. The experiments revealed that under wet conditions at relatively low temperatures, a MORB magma has the potential to produce wehrlite in the ocean crust by accumulation of early olivine and clinopyroxene. These show typically high Mg# which is a consequence of the oxidizing effect of the prevailing high aH2O. First plagioclases crystallizing after clinopyroxene under wet conditions are high in An content, in contrast to the corresponding dry system. Trace element compositions of clinopyroxenes of those wehrlites from the Moho transition zone are too depleted in HREE to be in equilibrium with present-day MORB, implying a genetic relation to the V2 lavas of the Oman ophiolite, which are interpreted to be the result of fluidenhanced melting of previously depleted mantle. We present a model on the petrogenesis of the crustal wehrlites in an upper mantle wedge above an initial, shallow subduction zone at the beginning of the intraoceanic thrusting.

Item Type: Article
Keywords: wehrlites; Oman ophiolite; oceanic crust; experimental petrology; hydrous magmatism
Journal or Publication Title: Geochemistry Geophysics Geosystems
Page Range: pp. 1-26
ISSN: 1525-2027
Identification Number - DOI: 10.1029/2009GC002488
Additional Information: Copyright 2009 by the American Geophysical Union
Date Deposited: 09 Mar 2010 02:23
Last Modified: 18 Nov 2014 04:09
URI: http://eprints.utas.edu.au/id/eprint/9665
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