Geochemistry of metacherts associated with continental margin volcanic seamount hydrothermal activity: metamorphic sole
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ORIGINAL PAPER
Geochemistry of metacherts associated with continental margin volcanic seamount hydrothermal activity: metamorphic sole rocks of the UAE Abdel-Rahman Fowler 1 & Mohamed El-Tokhi 1,2 & Bahaa Eldin Mahmoud Amin 1 Received: 31 May 2020 / Accepted: 2 September 2020 # Saudi Society for Geosciences 2020
Abstract The metacherts of the Asima Window, in northeastern U.A.E. at the southeastern corner of the Arabian Peninsula, are the dominant metamorphic sole lithologies of the Semail ophiolite that was obducted onto the Arabian continental margin at the end of the Cretaceous. There have been no previous geochemical studies of these metacherts. The Asima metachert samples of this study form four groups based on geochemistry, petrography and field association: (1) black hematitic, (2) green epidotechlorite rich, (3) pink piedmontite-bearing and (4) grey micaceous metacherts. A continental margin setting for the parent cherts is indicated geochemically by Al2O3 to Fe2O3 and SiO2 ratios, low ΣREE, low La, moderate positive Ce/Ce* and Lan/Cen ~ 1. A significant terrigenous fraction was composed of illite, chlorite and Fe hydroxides. A hydrothermal component can be recognized in all of the metachert groups but is particularly evident in the black and green metacherts by low Al/(Al + Fe + Mn), high (Fe + Mn)/Ti, high Ba and Ba/Sr ratios, positive Eu/Eu* and left-leaning REE profiles. Most silica was biogenic. A hydrogenous component included REE’s, Cu, Ni, Zn, V, Ba and Co that were adsorbed onto clays, Fe hydroxide and Mn oxide particles. The Asima cherts were deposited in a marine basin adjacent to but separated from the continental margin by seamounts of the Al Hala Volcanics. These volcanics provided Fe,Mn-rich hydrothermal fluids that mixed with the oxygenated seawaters, leading to rapid hematite deposition (black metacherts) and slow Mn oxidation to form Mn oxide particles that accumulated in the pink metacherts. Grey metacherts were deposited farther from the vents. Green metacherts have similarities to the hydrothermal black metacherts. Keywords Metachert environment . Hydrothermal components . Continental margin seamounts . Asima Window . United Arab Emirates
Introduction The growing research interest in the geochemistry of cherts has advanced considerably the understanding of chertforming events and, at the same time, has created a tool for deep ocean environmental studies. Geochemical studies of chert clarify the factors and processes that control the concentration of chemical elements in deep seawaters and associated Responsible Editor: Domenico M. Doronzo * Bahaa Eldin Mahmoud Amin [email protected] 1
Geology Department, United Arab Emirates University, Al-Ain, Abu Dhabi, UAE
2
Geology Department, Damietta University, Damietta, Egypt
marine sediments. Such studies have successfully developed criteria for recognizing the constituents of cherts (terrigenous, biogenic, hydrothermal and hydrogenous components) and have also provided semi-quantitative estimates of distance of the chert-forming
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