Pan-African (intraplate and subduction-related?) metasomatism in the Fawakhir ophiolitic serpentinites, Central Eastern Desert of Egypt: mineralogical and geochemical evidences

Abstract

Fawakhir serpentinites are the most western ophiolitic ultramafics relative to the Pan-African collision suture at the Qift-Quseir road in the Central Eastern Desert of Egypt. Their location is the basis for their selection in examining the possible contribution of the westerly dipping subducted oceanic slab-related melt/fluid with the intraplate granitic intrusion-related melt/fluid in the metasomatism of the Neoproterozoic ophiolitic serpentinites in the Eastern Desert. Non-residual mineralogy and geochemistry of serpentinites (SF1) far from the post-collision A2-type Fawakhir granitoids and those of serpentinites (SF2) in the vicinity of the granitoid pluton were investigated. The Fawakhir serpentinites are harzburgitic in composition and the Cr# (0.66-0.80) and Mg# (0.32-0.50) of their unaltered spinel cores are indicators for their forearc setting, where they were formed in the oceanic mantle wedge. Based on the spinel Cr# and the whole rock Yb-V bivariate, the melt extraction from the primitive mantle is in excess of 18% up to 24%. The HREE pattern of the SF1 serpentinites refers to the fractional type of melting. The formation of nonresidual mineral phases particularly in SF2 samples (amphibole, biotite, apatite thorite, and monazite) and the enrichment of all serpentinites in trace incompatible elements refer to these two serpentinite groups having underwent modal metasomatism. It is suggested that viscous fluid/melt related to the Fawakhir granitoid emplacement metasomatized the SF2 serpentinites, causing a strong enrichment in LREE (display concave LREE; La N /Sm N = 3.32-6.25 and U-type HREE; Gd N /Yb N =1.14-2.69) and a slight enrichment in Zr (12-16.62 ppm). All serpentinites are enriched in fluid-mobile elements by aqueous fluids, but the SF2 are more enriched in these elements. The spiked B compared to the other fluid-mobile elements respectively) suggests that these elements were added to the obducted ophiolitic Fawakhir serpentinites by the percolation of subduction-related fluids at shallow depths. The contribution of B from shallow continental crust-related fluids is debated. Hosting the Fawakhir serpentinites for the gold deposit at Fawakhir Mine implies a possible genetic relation between gold mineralizations hosted in the ultramafic rocks of the ANS and the processes of recycling of the subducted oceanic slab and the interaction with the mantle. Detailed stable and radiogenic isotopic analyses of the mineralization zones are required to address this question.

Multiple Stages of Carbonation and Element Redistribution during Formation of Ultramafic-Hosted Magnesite in Neoproterozoic Ophiolites of the Arabian-Nubian Shield, Egypt

“…Thus, although Zimmer et al (1995) inferred an open-ocean mid-ocean ridge tectonic setting for the Gerf ophiolites in the south Eastern Desert of Egypt, the past two decades have seen the development of a mounting consensus that all the ophiolitic rocks of Eastern Desert of Egypt formed in subduction-related settings (e.g., El Sayed et al 1999;Ahmed et al 2001;Farahat et al 2004;Azer and Khalil 2005;Azer and Stern 2007). At a finer level of detail, while the majority of recent studies of serpentinites throughout the Eastern Desert have assigned their origin to forearc settings (e.g., Azer and Stern 2007;Khalil and Azer 2007;Abd El-Rahman et al 2009;Azer et al 2013;Hamdy et al 2013;Khedr and Arai 2013;Khalil et al 2014;Gahlan et al 2015;Obeid et al 2016), a few ophiolitic outcrops continue to be assigned to backarc settings on the basis of the transitional geochemical character of their volcanic sequences, between those of island arcs and mid-ocean ridges (e.g., El Sayed et al 1999;Farahat et al 2004;Abd El-Rahman et al 2009;Basta et al 2011).…”

Petrological studies of neoproterozoic serpentinized ultramafics of the nubian shield: spinel compositions as evidence of the tectonic evolution of egyptian ophiolites

“…El Sayed et al 1999;Farahat et al 2004;Abd El-Rahman et al 2009;Basta et al 2011). A fore-arc setting has rarely been considered for the ophiolites (Azer and Stern 2007;Khalil and Azer 2007;Abd El-Rahman et al 2009;Hamdy et al 2013;Khedr and Arai 2013;Azer et al 2013).…”

“…In the past, studies of the Egyptian ophiolites have focused on volcanic rocks for evaluating their tectonic setting and petrogenesis. The ophiolitic peridotites have been largely ignored until recently (Azer and Khalil 2005;Azer and Stern 2007;Farahat 2008;Hamdy et al 2013;Khedr and Arai 2013), although the mantle peridotites provide complementary information about the petrogenesis and tectonic setting of the ophiolitic rocks.…”

Petrology and Geochemistry of Some Ophiolitic Metaperidotites from the Eastern Desert of Egypt: Insights into Geodynamic Evolution and Metasomatic Processes

“…In this case, the LREEs (La, Ce, Pr and Nd) were most probably carried to the studied mantle peridotites during hydrothermal alteration at the subduction zone (e.g. Paulick et al, 2006;Kodolá nyi et al, 2012;Hamdy et al, 2013;Khedr et al, 2014).…”