The petrogenesis of late Neoproterozoic gabbro/diorite intrusion at Sheikh El-Arab area, central Sinai, Egypt
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ORIGINAL PAPER
The petrogenesis of late Neoproterozoic gabbro/diorite intrusion at Sheikh El-Arab area, central Sinai, Egypt Michael Dawood Samuel & Doris Sadek Ghabrial & Hilmy Essa Moussa & Mohamed Wahbi Ali-Bik
Received: 23 April 2014 / Accepted: 22 September 2014 # Saudi Society for Geosciences 2014
Abstract The late Neoproterozoic gabbro/diorite intrusion (~11.7 km2) at Sheikh El-Arab area represents the only mafic exposure in the basement rocks of Katharina province of central Sinai largely occupied by granitoids and their volcanic equivalents. The field relations indicate that the intrusion is younger than the lower unit (630–615 Ma) of the volcanics and clastics of the Rutig Formation, and older than the surrounding granodiorites of Sheikh El-Arab and Rahaba (~610 Ma) plutons. It is not affected by regional metamorphism or ductile deformation, but recorded petrographic uralitization/amphibolitization signature. It is composed chiefly of pyroxene-hornblende gabbro, diorite, and quartz diorite. The chemical composition of the mafic minerals indicated that the suite was derived from calc-alkaline magma. Geochemically, the studied rocks are characterized by enrichment of LILE relative to HFSE and LREE relative to HREE. The gabbros are notably low in total REE (38–56 ppm) with (La/Yb)n =2.7–4.8, while the dioritic rocks are high in ΣREE (142–161 ppm) with high (La/Yb)n values (12.5–15.8); both are characterized by the absence of Eu anomaly, their Eu/Eu* ratios are close to unity (0.93–1.11). The studied intrusion evolved from mafic mantle magma into different types by assimilation fractional crystallization process (AFC) and/or gradual decrease in oxygen fugacity. The initial magma corresponds, most probably, to pyroxene-hornblende gabbro and the crystallization of hornblende was ascribed by slight H2O increase in magma after crystallization of near-liquidus clinopyroxene with high Ca content (Wo42–52) and Ca-rich plagioclase (An80–83). The intrusion is related to the later calcalkaline substage of post-collisional tectonic setting. M. D. Samuel : D. Sadek Ghabrial (*) : H. E. Moussa : M. W. Ali-Bik Geological Sciences Department, National Research Centre, 12662, Dokki Cairo, Egypt e-mail: [email protected]
Keywords Neoproterozoic . Sinai . Arabian-Nubian shield . Gabbro/diorite intrusion . Post-collisional setting
Introduction The basement rocks of Sinai are located in the northernmost outcrops of the Arabian-Nubian Shield (ANS) (Fig. 1). The Shield is a prominent example of juvenile crustal province of Neoproterozoic age (1000–540 Ma) (e.g. Bentor 1985; Stern 1994; Johnson and Woldehaimanot 2003). It is the northern part of the East African Orogen, which is viewed as a collage of island arc complexes accreted during the closure of the Mozambique Ocean between East and West Gondwana (Kröner 1985; Stern 1994; Meert 2003; Jarrar et al. 2003; Stoeser and Frost 2006). In Sinai, the ANS juvenile crust comprises the island arc complexes (IAC) of pre-collisional stage (~820–740 Ma) and formed of metamorphosed v
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