Petrography, geochemistry and petrogenesis of Alvand batholith leucocratic granites

The leucocratic granite emplaced as small masses and dykes in the Alvand batholith. The leucocratic granite consists of tourmaline alkali granite, biotite alkali granite, arfvedsonite alkali granite, rutil alkali granite, and biotite- muscovite granites with alkaline and peraluminous affinities. They show enrichments of LREEs relative to HREEs and LILE relative to HFSE with negative anomalies in Nb, Ta and Ti, in normalized trace element diagrams. The leucocratic granite of the Alvand batholith resemble A-type and can be further classified in two of A and A' types granite. The trace elements content of A-type is much higher than A'-type granite. Based on geochemical data, it seems that A- and A'-type granites were generated from partial melting of mantle source. As mantle magma ascends, fractionate and empalce into the crust, A-type leucocratic are formed with minimal contamination and A'-type leucocratic with significant contaminant with continent crust are formed. Field and geochronology data suggest that the leucocratic granite were generated in the late Jurassic, which is contemporaneous with the subduction of the Neo-Tethys oceanic crust beneath the central Iran. It seems that the leucocratic granites were emplaced during a local extensional phase as dykes and small bodies in the Alvand batholith.