Chemical homogeneity of high-Cr chromitites as indicator for widespread invasion of boninitic melt in mantle peridotite of Bir Tuluha ophiolite,Northern Arabian Shield,Saudi Arabia |
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| Institution: | 1. Faculty of Earth Sciences, King Abdulaziz University, Jeddah, Saudi Arabia;2. Geology Department, Faculty of Science, Helwan University, Cairo, Egypt;3. Department of Earth Sciences, Kanazawa University, Kanazawa 920-1192, Japan;1. Department of Geological Sciences, Jadavpur University, Kolkata 700032, India;2. School of Geosciences, University of the Witwatersrand, Johannesburg 2001, South Africa;1. Department of Geological Sciences, Jadavpur University, Kolkata 700032, India;2. School of Petroleum Technology, Pandit Deendayal Petroleum University, Gandhinagar 382007, India;1. Geology Department, Faculty of Science, Tanta University, Tanta, Egypt;2. Norwegian Polar Institute, Hjalmar Johansens gt. 14, NO-9296 Tromsø, Norway;3. Egyptian Institute of Geodynamic, Cairo, Egypt;1. Instituto de Geociências, Universidade Federal do Rio Grande do Sul, Av. Bento Gonçalves 9500, Prédio 43129, Porto Alegre, RS CEP 91501-970, Brazil;2. Companhia de Ferro Ligas da Bahia – FERBASA, Pojuca, BA, Brazil;3. Instituto de Geociências – Universidade de Brasília, Brazil;1. School of Geosciences, University of the Witwatersrand, Johannesburg 2050, South Africa;2. Impala Platinum Mines, Rustenburg, South Africa;1. Department of Earth Sciences, Manipur University, Canchipur, Imphal 795003, India;2. Australian Research Council Centre of Excellence for Core to Crust Fluid Systems and Department of Earth & Planetary Sciences, Macquarie University, Sydney, NSW 2109, Australia;3. Steinman Institut für Geologie, Mineralogie und Paläontologie, Poppelsdorfer Schloss, 53115 Bonn, Germany;4. Physical Research Laboratory, Ahmedabad 380009, India |
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| Abstract: | The Bir Tuluha ophiolite is one of the most famous chromitite-bearing occurrences in the Arabian Shield of Saudi Arabia, where chromitite bodies are widely distributed as lensoidal pods of variable sizes surrounded by dunite envelopes, and are both enclosed within the harzburgite host. The bulk-rock geochemistry of harzburgites and dunites is predominately characterized by extreme depletion in compatible trace elements that are not fluid mobile (e.g., Sr, Nb, Ta, Hf, Zr and heavy REE), but variable enrichment in the fluid-mobile elements (Rb and Ba). Harzburgites and dunites are also enriched in elements that have strong affinity for Mg and Cr such as Ni, Co and V. Chromian spinels in all the studied chromitite pods are of high-Cr variety; Cr-ratio (Cr/(Cr + Al) atomic ratio) show restricted range between 0.73 and 0.81. Chromian spinels of the dunite envelopes also show high Cr-ratio, but slightly lower than those in the chromitite pods (0.73–0.78). Chromian spinels in the harzburgite host show fairly lower Cr-ratio (0.49–0.57) than those in dunites and chromitites. Platinum-group elements (PGE) in chromitite pods generally exhibit steep negative slopes of typical ophiolitic chromitite PGE patterns; showing enrichment in IPGE (Os, Ir and Ru), over PPGE (Rh, Pt and Pd). The Bir Tuluha ophiolite is a unimodal type in terms of the presence of Ru-rich laurite, as the sole primary platinum-group minerals (PGM) in chromitite pods. These petrological features indicates that the Bir Tuluha ophiolite was initially generated from a mid-ocean ridge environment that produced the moderately refractory harzburgite, thereafter covered by a widespread homogeneous boninitic melt above supra-subduction zone setting, that produced the high-Cr chromitites and associated dunite envelopes. The Bir Tuluha ophiolite belt is mostly similar to the mantle section of the Proterozoic and Phanerozoic ophiolites, but it is a “unimodal” type in terms of high-Cr chromitites and PGE-PGM distribution. |
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| Keywords: | Podiform chromitites Chemical homogeneity Chromian spinel PGE-PGM Bir Tuluha Arabian Shield Saudi Arabia |
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