Asian Journal of Applied Science and Technology (AJAST) (Open Access Quarterly International Journal) Volume 2, Issue 2, Pages 10-20, 2018 10 | P age Online ISSN: 2456-883X Impact Factor: 1.805 Website: www.ajast.net Petrographical and Geochemical Studies of Amphibolites Rocks (Metamorphic Sole) At Masafi Area, UAE Mohamed El Tokhi 1 , Bahaa Eldin Mahmoud Amin 2 , Ahmed B. O. Abdelwahed 3 , Amr A. Abdelsamad 4 , Ali A. M. Bustanji 5 and Muhammad R. Khairunnas 6 1,2,3,4,5,6 UAE University, College of Science, Geology Department, Al Ain, United Arab Emirates. Article Received: 24 December 2017 Article Accepted: 27 February 2018 Article Published: 02 April 2018 1. INTRODUCTION In the Asimah tectonic window of the northeast UAE the amphibolites form a <100 m thick sheet of highly metamorphosed rocks in the upper most part of a much thicker metamorphic sole (~2000 m thick) dominated by greenschist facies quartz rich gneisses and meta carbonate rocks. The sole was attached to the base of the Semail Ophiolite, a 10 - 20 km thick piece of oceanic crust and upper mantle lithosphere of Cretaceous age that was thrusted over the ancient Arabian continental margin during the closure of the Tethys Ocean with obduction completed as 75 million years ago. The amphibolites and other metamorphic rocks at the base of the Semail are exposed in a complexly arched section of the ophiolite that was cut by erosion to expose the underlying metamorphic rocks in its core. This exposure is a long southward tapering area called the Asimah Window (Fig. 1). Ophiolite represented slices of the upper mantle and oceanic crust lithosphere that have been thrusted onto the continent during tectonic convergence. The ophiolite usually, but not necessarily, indicates supra subduction zone rifting and spreading [19] and represents the formation of a fresh oceanic crust. The ophiolite lithology is complicated and is divided by some geologists into: a mantle sequence and a crustal sequence. The Semail mantle sequence in the UAE- Oman (at the bottom) includes peridotites (tectonized, foliated and serpentinized) with dunitic layers and lenses increasing upward, as well as chromititic pods. Overlying this is the crustal sequence, which consists of gabbros (cumulus, layered and massive), diabase (dolerite) sheeted dikes enclosing small intrusions of plagiogranites that may sit between the gabbro and sheeted dikes, and extrusive pillow lavas covered by deep seated pelagic sediments. The transition or boundary between the mantle and crustal sequences in the ophiolite complex is termed the Petrological Moho. ABSTRACT Metamorphic rocks occur in several locations in the UAE, including the Masafi-Asimah area and the area around bordering Bulaydeh. Both have previously been interpreted as forming part of the metamorphic sole of the Oman-UAE ophiolite. The age of these metamorphosed by hornbland dating is around 90-95 Ma Late Cretaceous (Cenomanian to Turonian). In the Masafi area, ortho- and para-amphibolites exist within sheared rocks as bands, lenses, and linear bodies up to 100m thick. The amphibolites are composed of amphibole and plagioclase commonly secondary epidote and garnet. In some outcrops, parallel-sided plagioclase-rich veins cut across the amphibolites and in other areas, migmatitic segregations within the amphibolite were observed. Whole-rock analyses confirm that the amphibolites were originally tholeiitic basalts. A comparison of trace element suggests that the protoliths were not equivalent to the Haybi alkaline and transitional tholeiites found in the underlying structural slice, or to the Semail ophiolite volcanic rocks, which lie structurally higher in the sequence. Structurally, the amphibolites lie within the metamorphic sheet: greenschist facies metasedimentary rocks, including quartzites and marbles and interbanded with metamafic rocks. It is suggested that the sedimentary and volcanic protoliths were metamorphosed in a subduction zone environment during underthrusting initial ophiolite displacement. The amphibolites were incorporated into the ophiolitic rocks after they were metamorphosed as part of a metamorphic sole at the base of peridotites during the northward subduction of a branch of Neotethys. Keywords: Masafi, Asimah, Amphibolites, UAE.