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Suprasubduction-zone origin of the podiform chromitites of the Bir Tuluhah ophiolite, Saudi Arabia, during Neoproterozoic assembly of the Arabian Shield

Abuamarah, Bassam A. and Asimow, Paul D. and Azer, Mokhles K. and Ghrefat, Habes (2020) Suprasubduction-zone origin of the podiform chromitites of the Bir Tuluhah ophiolite, Saudi Arabia, during Neoproterozoic assembly of the Arabian Shield. Lithos, 360-361 . Art. No. 105439. ISSN 0024-4937. https://resolver.caltech.edu/CaltechAUTHORS:20200220-092957322

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Abstract

The ultramafic section of a dismembered ophiolite is exposed at Bir Tuluhah, in the north-central part of the Arabian Shield. It is penetratively serpentinized and locally carbonate-altered to talc‑carbonate and quartz‑carbonate rocks (listvenite) along shear zones and fault planes. Despite the high degree of mineral replacement, preserved mesh and bastite textures and fresh relics of primary Cr-spinel and olivine show that the protoliths were mainly harzburgite with minor dunite, with sparse massive chromitite bodies of various forms and sizes. Olivine inclusions in the chromitite lenses have higher forsterite content and NiO concentrations than fresh olivine relics in the host harzburgites and dunites, due to subsolidus re-equilibration. Cr-spinels in the chromitites have higher Cr# (0.74–0.82) than those hosted in dunite (0.72–0.76) or harzburgite (0.55–0.66). The scarce Cr-spinel crystals in harzburgite that have Cr# < 0.6 are interpreted to represent the population least affected by melt-rock interaction. The chromitite bodies are interpreted to have formed just below the contact between the oceanic crust and mantle sections (i.e., the petrologic Moho). The primary olivine (high Fo and Ni content) and Cr-spinel core compositions (high Cr# and low TiO2 content) of the Bir Tuluhah serpentinized peridotite are typical of modern supra-subduction zone (SSZ) fore-arc peridotites and consistent with crystallization from boninitic magma. The multistage petrogenesis leading to the chromitite bodies begins with moderate to high degrees of melt extraction from the protoliths of the serpentinized harzburgites, followed by reaction with melt compositions that evolved from tholeiite to boninite and left dunite residues. The massive Cr-rich chromitites in the Bir Tuluhah ophiolite are most probably the residues of such interaction between depleted harzburgite and ascending melts; mixtures of the reacted melts formed boninites, which became saturated with chrome-rich spinel and crystallized chromite pods before ascending past the Moho. We offer a novel thermodynamic model of this mixing and reaction process that quantifies the yield of Cr-spinel.


Item Type:Article
Related URLs:
URLURL TypeDescription
https://doi.org/10.1016/j.lithos.2020.105439DOIArticle
ORCID:
AuthorORCID
Asimow, Paul D.0000-0001-6025-8925
Azer, Mokhles K.0000-0002-3711-8630
Additional Information:© 2020 Published by Elsevier B.V. Received 10 January 2020, Revised 16 February 2020, Accepted 17 February 2020, Available online 20 February 2020. The authors would like to extend their appreciation and gratitude to the King Saud University for funding and supporting this work through Researchers Supporting Project number (RSP-2019/151), King Saud University, Riyadh, Saudi Arabia. PDA is supported by the US NSF award EAR-1826310. In addition, the authors highly appreciate thoughtful reviews by Prof. Hilmy E. Moussa and an anonymous reviewer. The authors are also indebted to the editor (Prof. Michael Roden) for his efforts and numerous helpful comments. Declaration of Competing Interest: None.
Funders:
Funding AgencyGrant Number
King Saud UniversityRSP-2019/151
NSFEAR-1826310
Subject Keywords:Arabian Shield; Bir Tuluhah; Cr-rich chromitite; Fore-arc; Melt-rock reaction; Supra-subduction zone
Record Number:CaltechAUTHORS:20200220-092957322
Persistent URL:https://resolver.caltech.edu/CaltechAUTHORS:20200220-092957322
Official Citation:Bassam A. Abuamarah, Paul D. Asimow, Mokhles K. Azer, Habes Ghrefat, Suprasubduction-zone origin of the podiform chromitites of the Bir Tuluhah ophiolite, Saudi Arabia, during Neoproterozoic assembly of the Arabian Shield, Lithos, Volumes 360–361, 2020, 105439, ISSN 0024-4937, https://doi.org/10.1016/j.lithos.2020.105439. (http://www.sciencedirect.com/science/article/pii/S0024493720300761)
Usage Policy:No commercial reproduction, distribution, display or performance rights in this work are provided.
ID Code:101416
Collection:CaltechAUTHORS
Deposited By: Tony Diaz
Deposited On:20 Feb 2020 18:57
Last Modified:09 Mar 2020 16:20

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