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Chrome-spinel geochemistry of the northern Oman-United Arab Emirates ophiolite

Dare, Sarah Anne Sophia 2007. Chrome-spinel geochemistry of the northern Oman-United Arab Emirates ophiolite. PhD Thesis, Cardiff University.

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The Oman ophiolite is the largest and best preserved ophiolite in the world and records a switch from mid-ocean ridge (MOR) to supra-subduction zone (SSZ) setting. This study investigates the geochemical variability of chrome-spinel in the mantle sequence of the poorly known United Arab Emirates (U.A.E.) part of the northern Oman-U.A.E. ophiolite. Extensive field work was carried out and 260 samples collected for petrogenetic studies and geochemical mapping of the U.A.E. mantle. Chrome-spinel geochemistry provides valuable information on bom the residual mantle and on the nature and extent of melt-rock reaction. In particular, it is used to fingerprint the compositions of the magmas that interacted with the mantle lithosphere. This study also develops a new method to analyse gallium in chrome-spinel by Laser Ablation-ICP-MS, and successfully uses it to improve the tectonic discrimination of chrome-spinel. The results show that the U.A.E. mantle lithosphere formed at a MOR-type setting and was modified by melt-rock reaction with MORB-type and SSZ-type melts. This history of melt infiltration strongly resembles the magmatic history of the crustal sequence in each of the Aswad and Khawr Fakkan Blocks. Geochemical mapping illustrates a strong spatial control on the pattern of melt infiltration in the mantle and constrains the proximity of each mantle domain with respect to the subduction zone. The Khawr Fakkan mantle extensively interacted with boninitic melts during subduction initiation. Thus, it was closer to the subduction zone than the Aswad mantle which predominantly interacted with island-arc tholeiite melts. Importantly, this work demonstrates for the first time that the Dibba Zone peridotites originate from pre-existing 'true' MOR mantle lithosphere between the trench and the main body of the ophiolite. A further important conclusion is that the mantle lithosphere of the northern Oman-U.A.E. ophiolite was not the source region for the SSZ magmatism. Previous workers proposed that the plane of detachment and the subduction zone were the same, which implies that the mantle of the ophiolite was the source of the SSZ magmatism. Instead, this study proposes that detachment of the ophiolite took place at a shallower level than the plane of the subduction zone and thus provides strong evidence for a subduction zone at a still deeper level. During detachment, the ophiolite incorporated slices of ultramafic rock near the trench (i.e. the Dibba Zone peridotites) as it bulldozed its way over the underlying plate and onto the continental margin of Arabia.

Item Type: Thesis (PhD)
Status: Unpublished
Schools: Earth and Ocean Sciences
Subjects: Q Science > QE Geology
ISBN: 9781303213502
Date of First Compliant Deposit: 30 March 2016
Last Modified: 08 Oct 2014 08:25

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