Petrological, mineralogical and geochemical studies of Late Ediacaran A-type Volcanics, North Arabian Shield, Saudi Arabia

Document Type : Original Article

Authors

1 Geology department, faculty of Science, Zagazig university

2 Geology Department, Faulty of Science, Zagazig University, Zagazig , Egypt.

3 Geology Department, faculty of Science, Tanta university, Tanta, Egypt

4 Geology Department, Faculty of science, ZAGAZIG UNIVERSITY, Zagazig University, Zagazig, Egypt.

5 The Ministry of Education, Kuwait

6 Geology Department, Faculty of Science Zagazig University

Abstract

The Late Ediacaran A-type alkaline Jabal Asfar Thwelil volcanics (JATV) represent the ultimate episode in the Precambrian growth of the Arabian Shield. This episode is characterized by switching the geodynamic regime from subduction-related to post-collision and intra-plate extension. JATV are exclusively subaerial and unmetamorphosed volcanics that are represented by porphyritic rhyolite, aphyric rhyolite and deposition of pyroclastics and ignimbrites. The fall out pyroclastics include fine (ash) tuffs, banded tuffs, crystal tuffs and lithic tuffs. Geochemically, JATV are highly evolved alkaline volcanics of comenditic rhyolitic composition. They are mainly metaluminous to slightly peralkaline domains similar to the trend of Pan-African peralkaline granites. JATV are belonging to A-type ferroan alkaline magma, which were emplaced during an anorogenic stage during extensional stresses and intraplate rifting. The porphyritic rhyolite and aphyric rhyolite are cogenetic. The present data suggests the generation of parental magma through partial melting of asthenospheric mantle sources, which subsequent followed by extensive fractional crystallization. The main fractionated phases were feldspars, apatite and Fe-Ti oxide. The suggested source of JATV was low oxygen fugacity hot-dry- reduced magma of asthenospheric mantle source. This source was garnet-free and spinel-rich source and comprising a crustal component. This crustal component may either recycled component from pre-collision event or a recycled component in the source.

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