Single zircon Hf-O isotope constraints on the origin of A-type granites from the Jabal Al-Hassir ring complex, Saudi Arabia

The Jabal Al-Hassir ring complex in the southern Arabian Shield is an alkaline granite complex comprising an inner core of biotite granite that outwardly becomes a porphyritic sodic-calcic amphibole (ferrobarroisite-katophorite) granite. A combined study of mineral chemistry and single zircon Hf-O zircon isotope analyses was carried out to infer the magma sources of the Neoproterozoic post-collisional A-type granitoids in Saudi Arabia. The granitic rocks show high positive initial epsilon Hf(t) values of +7.0 to +10.3 and delta O-18 values of +5.8 parts per thousand to +7.4 parts per thousand that are consistent with melting of a juvenile crustal protolith that was formed during the Neoproterozoic assembly of the Arabian-Nubian Shield (ANS). Crustal-model ages (Hf-t(NC)) of 0.71-0.94 Ga indicate minor contribution from an older continental crust in the formation of the Jabal Al-Hassir granitic rocks (crystallization age = 620 +/- 3 Ma), but any such component is likely to be Neoproterozoic in age. Temperature and oxygen fugacity (fO(2)) estimates suggested that the Jabal Al-Hassir A-type granite magma was generated at high temperature (820-1050 degrees C) and low fO(2). Geochemical characteristics (e.g., low fO(2)), geochronological data, and Hf and O isotope compositions, indicate that the magmas of the Neoproterozoic A-type granites of the Jabal Al-Hassir ring complex were likely generated by crustal partial melting of a juvenile Neoproterozoic lower crustal tholeiitic rocks, following collision between East and West Gondwana in the final stages of the evolution of the Arabian Shield. (C) 2014 Elsevier B.V. All rights reserved.