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Petrological characteristics of the Neoproterozoic Ess ophiolite mantle section, Arabian Shield, Saudi Arabia: a mineral chemistry perspective

Gahlan, Hisham A. and Azer, Mokhles K. and Asimow, Paul D. and Mubarak, Heba S. and Al-Kahtany, Khalid M. (2020) Petrological characteristics of the Neoproterozoic Ess ophiolite mantle section, Arabian Shield, Saudi Arabia: a mineral chemistry perspective. International Journal of Earth Sciences, 109 (1). pp. 239-251. ISSN 1437-3254. https://resolver.caltech.edu/CaltechAUTHORS:20191203-153418375

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Abstract

The Ess ophiolite, one of the most important ophiolitic massifs of the Arabian Shield, consists of a lower succession of serpentinized mantle rocks overlain by an ultramafic cumulate sequence, layered and isotropic gabbros, sheeted dykes, pillow lavas and pelagic sediments. The Ess mantle section is composed mainly of serpentinized peridotites with chromitite pods, dunite, wehrlite and pyroxenite. Extensive metasomatism and alteration has transformed the ultramafic rocks to talc-carbonates, magnesite deposits and listvenite, especially along shear zones and fault planes. Nevertheless, relics of primary chromian spinel, olivine and pyroxenes are observed. Both primary and metamorphic olivines can be recognized in dunite; the latter is marked by very high forsterite content (97–98), low NiO content (< 0.2 wt%) and wide variations in MnO content (0.03–1.3 wt%). The mesh and bastite textures of the serpentine suggest that protoliths were mainly harzburgite with minor dunite. Some fresh cores of Cr-spinel are rimmed by ferritchromite and Cr-magnetite, indicating prograde metamorphism at lower amphibolite facies under oxidizing conditions. The high Cr# (> 0.6) and low TiO2 content (< 0.14 wt%) of fresh Cr-spinel and the high forsterite (0.90–0.93) and NiO contents (0.4–0.5 wt%) of fresh olivine are all consistent with residual mantle rocks that experienced high degrees of partial melt extraction. Orthopyroxene and clinopyroxene in the Ess peridotites have low CaO, Al₂O₃ and TiO₂ contents resembling those typically found in depleted harzburgites from fore-arcs. Consequently, we propose that the Ess mantle peridotites formed in a forearc setting during subduction initiation that developed as a result of northwest subduction due to the convergence between East and West Gondwana, leading eventually to closure of the Mozambique Ocean during the Pan-African orogeny.


Item Type:Article
Related URLs:
URLURL TypeDescription
https://doi.org/10.1007/s00531-019-01799-3DOIArticle
ORCID:
AuthorORCID
Azer, Mokhles K.0000-0002-3711-8630
Asimow, Paul D.0000-0001-6025-8925
Additional Information:© 2019 Geologische Vereinigung e.V. (GV). Received 16 May 2019; Accepted 23 November 2019; First Online 03 December 2019. Special thanks are conveyed to King Saud University, Deanship of Scientific Research, Research Group No. RG-1436-036, for their support. PDA acknowledges support from the US NSF, award OCE-1826310. Comments by Prof. John Shervais (Utah State University, USA) and Ingo Braun improved the present version of the manuscript. Prof. Wolf-Christian Dullo (Editor-in-Chief) is acknowledged for editorial handling.
Funders:
Funding AgencyGrant Number
King Saud UniversityRG-1436-036
NSFOCE-1826310
Subject Keywords:Ess ophiolite; Serpentinized peridotite; Fore-arc; Supra-subduction zone; Arabian shield
Issue or Number:1
Record Number:CaltechAUTHORS:20191203-153418375
Persistent URL:https://resolver.caltech.edu/CaltechAUTHORS:20191203-153418375
Official Citation:Gahlan, H.A., Azer, M.K., Asimow, P.D. et al. Int J Earth Sci (Geol Rundsch) (2020) 109: 239. https://doi.org/10.1007/s00531-019-01799-3
Usage Policy:No commercial reproduction, distribution, display or performance rights in this work are provided.
ID Code:100170
Collection:CaltechAUTHORS
Deposited By: Tony Diaz
Deposited On:04 Dec 2019 18:05
Last Modified:12 Feb 2020 17:43

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