Petrology, geochemistry and remote sensing data of island arc assemblage along Wadi Abu Marawat, Central Eastern Desert,
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ORIGINAL PAPER
Petrology, geochemistry and remote sensing data of island arc assemblage along Wadi Abu Marawat, Central Eastern Desert, Egypt A. M. Asran & R. Kh. Bekir & E. Abdel Rahman & A. Abdel El-Rashed
Received: 8 September 2011 / Accepted: 26 December 2011 / Published online: 2 February 2012 # Saudi Society for Geosciences 2012
Abstract The basement rocks of Abu Marawat area comprise serpentinites (oldest), metavolcanics and their equivalent pyroclastics, intrusive metagabbro–diorite complex, synkinematic granitoids, Hammamat sediments and basic intrusion (youngest). Remote sensing ETM+ data of Abu Marawat area were analyzed, and band ratios technique was applied to discriminate between different varieties of these basement rocks. Serpentinites are represented by lensoidal bodies tectonically incorporated in the metavolcanics. On band ratio 5/7 image, they are characterized by very bright image signature. The metavolcanics comprise basalts, andesite and subordinate dacites together with their equivalent pyroclastics. They were regionally metamorphosed up to the greenschist facies and exhibit dark grey image signatures on band ratio 5/7 image. The metagabbro–diorite complex is made up of metagabbros, diorites and quartz diorites, whereas the synkinematic granitoids are formed of tonalites and granodiorites. The band ratio 5/7 image illustrates tonalites with dark image signature, whereas metagabbro–diorites and granodiorites exhibit grey image signature. The metavolcanic suites are of island arc setting, where metabasalts are of tholeiitic affinity, while the meta-andesites and metadacites are of calc-alkaline character. The metagabbroic and granitoid rocks are of I-type, calc-alkaline affinity and were formed in arc tectonic setting. They are enriched in LIL elements and depleted in Nb and HFS elements, a A. M. Asran : R. K. Bekir : A. Abdel El-Rashed Geology Department, Faculty of Science, Sohag University, Sohag, Egypt E. Abdel Rahman (*) Geology Department, Faculty of Science (Aswan), South Valley University, Qena, Egypt e-mail: [email protected]
characteristic feature of subduction-related magmatism. The regular variation trends among the major and trace elements as well as the coincidence of the plotted samples favor the assumption that they are comagmatic and formed by processes such as fractional crystallization. Keywords Abu Marawat . Island arc . Remote sensing data . Geochemistry . Petrology . Egypt
Introduction The area under consideration represents part of the Arabian– Nubian Shield (ANS). The association of ophiolite sequence and the calc-alkaline volcanic rocks with island arc affinity had led to several models being proposed for the structure and evolution of the Pan-African belt in the ANS. The first group of models suggests one or more island arcs accreted together to a passive continental margin (Shackelton et al. 1980; Gass 1977; Ries et al. 1983; El-Ramly et al. 1984). The ANS collided with pre-Neoproterozoic continental blocks to the east and west at ~750–650 Ma Kroner et al. (19
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