Document Type : Original Research Paper
Authors
1
Department of Earth Sciences, SR.C., Islamic Azad University, Tehran, Iran
2
Department of Geology, Ma.C., Islamic Azad University, Mashhad, Iran
3
Department of Geology, Kah.C., Islamic Azad University, Kahnooj, Iran
4
Department of Geology, Zah.C., Islamic Azad University, Zahedan, Iran
10.22071/gsj.2026.588448.2259
Abstract
The intrusive body northwest of Torbat-e-Jam in the Central Iran Zone comprises four stocks of biotite granite, granodiorite, gneiss, diorite, and gabbro, whose tectono-magmatic evolution requires precise explanation. Investigations show that the calc-alkaline granitoids of the region, characterized by enrichment in LILEs and depletion in HFSEs, are peraluminous S-type. These rocks are the product of the partial melting of immature volcanogenic greywackes, which is further supported by surmicaceous enclaves and reverse zircon geochemistry. The presence of andalusite–sillimanite paragenesis and pseudo tachylytes indicates syn-kinematic melting, seismic ascent of the magma, and rapid exhumation under a thermal-extensional regime caused by subducting slab rollback; where the injection of mafic magma in the Neoproterozoic was the main trigger for crustal melting. The lithospheric evolution model of the region within the framework of a Wilson cycle involves three phases: 1) initiation of subduction and deep deformation (630 to 650 Ma),2) slab rollback and generation of S-type granitoids in the late Ediacaran, and3) severe crustal thinning and injection of tholeiitic mafic pulses during the rifting stage (around 471 Ma). This coherent framework well explains previous contradictions regarding the simultaneous evidence of S- and I-type granitoids by defining them as successive phases of a single evolutionary cycle.
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