Geochemistry and petrogenesis of south Qorveh A-type granitoids (northwest of Sanandaj- Sirjan zone): An evidence for active continental margin tensional tectonic

• Published in: Pitruluzhī (Online) 2020-12, Vol.11 (3), p.85-110
• Main Authors: Majid Shirmohammadi, Ali Asghar Sepahi Gerow, Mohammad Maanijou, Ashraf Tourkian
• Format: Article
• Language: per
• Subjects: a-type granites; charnokite; neo-tethys; sanandaj-sirjan zone
• ISSN: 2228-5210; 2322-2182
• DOI: 10.22108/ijp.2020.123500.1186

The studied area (Galali- Varmaqan) located at the northern part of the Sanandaj- Sirjan zone, south of the Qorveh city. The granitic rocks are dominated by quartz, alkali- feldspar and plagioclase. Amphibole and biotite are the most important mafic minerals, apatite, sphene, zircon and Fe- oxides are the accessories. The Galai- Varmaqan granitoids show geochemical characteristics of metaluminous A-type granites with mainly shoshonitic and high- K calc- alkaline affinity. Based on geotectonic diagrams, these rocks are mostly clusterred at the volcanic arc granites (VAG) and within plate granites (WPG) fields which points to their formation in a post- orogenic magmatic system. LILEs and HFSEs enrichment indicates the existence of a crustal source for the studied granites and formation of the parent magma at the stability field of plagioclase in the lack of garnet. In this study, we suggest that the A-type granites have been formed by partial melting of lower crust charnokitic rocks. The A-type granites are related to extensional magmatism of the Neo- Tethys oceanic crust beneath the Central Iranian microcontinent, due to roll- back of subducting slab. Thus, change of tectonic regime from compressional to tensional in the late- Jurassic to early- Cretaceous time (probably in a pull-apart basin tectonic setting), is suggested for the formation of A-type granites in this region of the Sanandaj- Sirjan zone.