Late Neoproterozoic Dokhan Volcanics, North Eastern Desert, Egypt: geochemistry and petrogenesis

HA Eliwa, JI Kimura, T Itaya - Precambrian Research, 2006 - Elsevier
HA Eliwa, JI Kimura, T Itaya
Precambrian Research, 2006Elsevier
Origin and tectonic setting of the late Neoproterozoic Dokhan Volcanics (ca. 610–560Ma by
whole rock Rb–Sr and ca. 600–590Ma by SHRIMP U–Pb zircon) in the Egyptian Eastern
Desert is debated. Debate concerns the tectonic setting they formed in, during transition
between convergent to extensional, during or after collision of E and W Gondwana∼
600Ma. In order to solve this problem, we studied the geology and analyzed major and trace
elements of lavas from Wadi Um Sidra and Um Asmer in the northern Eastern Desert. These …
Origin and tectonic setting of the late Neoproterozoic Dokhan Volcanics (ca. 610–560Ma by whole rock Rb–Sr and ca. 600–590Ma by SHRIMP U–Pb zircon) in the Egyptian Eastern Desert is debated. Debate concerns the tectonic setting they formed in, during transition between convergent to extensional, during or after collision of E and W Gondwana ∼600Ma. In order to solve this problem, we studied the geology and analyzed major and trace elements of lavas from Wadi Um Sidra and Um Asmer in the northern Eastern Desert. These range from medium- to high-K basalt to rhyolite. They comprise voluminous medium- to high-K calc-alkaline lavas, subordinate adakitic lavas, and minor alkali basalt. Adakitic lavas contain very low Y (<18ppm) and heavy REE (HREE) (Yb≤1ppm) contents, with high Sr (>767ppm) and Sr/Y (>40). They also have high Cr and Ni and low Nb, Rb, and Zr contents compared to coexisting calc-alkaline lavas. The adakitic lavas exhibit a fractionated rare earth element (REE) patterns with HREE depletion (LaN/LuN=11.1–14.4), while calc-alkaline rocks have less fractionated REE patterns (LaN/LuN=6.3–9.4). REE patterns of the alkali basalt are also similar to that of adakitic lavas. These alkali basalt, calc-alkaline, and adakitic lavas all show enrichment in large ion lithophile elements (LILEs) and show negative Nb–Ta anomalies with high Th/Zr, which suggest involvement of subducted slab melts in their petrogenesis. Our proposal is subduction of hot oceanic ridge before collision and later melting of the hot oceanic slab beneath Dokhan even after collision event.
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