Geochemistry and petrogenesis of the Gasht peraluminous granite, western Alborz Mountains, Iran

Abstract

The Gasht leucogranite consists of plagioclase, alkali feldspar, quartz, muscovite, tourma- line and apatite, but lacks biotite. This leucogranite is peraluminous having SiO 2 contents of 70.1-75.7 wt%. The TiO2 content is less than 0.06 wt%. Chondrite-normalized REE patterns show overall low REE concentrations with relatively higher light rare earth elements (LREE), and small negative Eu anomalies. Geochemical studies of the Gasht pluton suggest an origin by low degree partial melting of a muscovite-rich metapelite under a low aH 2 O. Partial melting occurred in the mid-levels of the continental crust of the Alborz Range during deformation, shearing and subsequent collapse of the previously thickened crust. The Alborz collision zone of northern Iran is a result of northward sub- duction and consumption of the Paleotethys and subsequent collision between the Gondwana-derived central Iranian block and the Eurasian plate.