Mineral chemistry, petrogenesis and tectonic setting of Band-e-Hezarchahgranitoids (SE Shahrood)

The Band-e-Hezarchah granitoids mainly include alkali granite and granite. that intruded in Late Neoproterozoic metamorphic rocks. Orthoclase, microcline, plagioclase, quartz and biotite are the main rock-forming minerals. Plagioclase is mostly albite and oligoclase with Si = 2.57-2.7 a.p.f.u. and An0.4–12.6. Biotite is mostly siderophyllite, with Si = 4.30-6.22 a.p.f.u. and XMg= 0.025 - 0.859. Chlorite with Si = 4-5.53 a.p.f.u. and XFe= 0.84-0.91 is mostly daphnite and pseudothuringite. Field and geochemical evidences show the BHG is S type and their magmas seem to have originated from melting meta-pelitic and metagraywacky metamorphic rocks in the active continental marginal above a subduction zone. These rocks are thought to be formed in acontinental arc setting, related to the oblique subduction of Proto-Tethys oceanic lithosphere beneath the northern margin of Gondwanan supercontinent during Ediacaran- Early Cambrian time.