Geochemistry and petrogenesis of the Ediacaran post-collisional Jabal Al-Hassir ring complex, Southern Arabian Shield, Saudi Arabia

The Jabal Al-Hassir ring complex is located between latitudes 19°21' and 19°42'N, and longitudes 42°55' and 4312'E, Southern Arabian Shield. It is an alkaline to highly fractionated calc-alkaline granite complex consisting of an inner core of biotite granite followed outward by porphyritic sodic-calcic amphibole (ferrobarroisite) granite. U-Pb zircon geochronology indicates that the Jabal Al-Hassir ring complex was emplaced at ca. 620Ma. The granites display highly fractionated geochemical features (i.e., Eu/Eu*=0.05-0.35; enrichment of K, Rb, Th, U, Zr, Hf, Y and REE; depletion of Ta, Nb, Ba, Sr, P, Eu, and Ti). Jabal Al-Hassir granites are post-collisional plutonic rocks and contain abundant microcline perthite and sodic-calcic amphibole, sharing the petrological and chemical features of A₂-type granites. Sr_i values range from 0.70241 to 0.70424, are similar to those expected for magmas extracted from a Neoproterozoic depleted source and much lower than what would be expected, if there was minor involvement of pre-Neoproterozoic continental crust. The geochemical characteristics indicate that their magma was most plausibly represented by partial melting of juvenile lower crust following the collision between East and West Gondwana at the final stage of the Arabian Shield evolution. The data presented in this study are therefore consistent with an intraplate, post-collisional magmatism formed at the beginning of a transition from convergent to extensional tectonics.