منشاء پتروژنزه و سن سنجي راديومتري باتوليت پيچاقچي (شمال باختر ايران )

Origin, Petrogenesis and Radiometric Age Dating of Pichagchi Batholite (North West Iran)

Pichagchi batholith, located in 35 km southeast of Shahin Dezh, northwest of Iran, is situated in Central Iran , cutting Paleozoic rocks. Absolute age determination for this batholith by K-Ar radiorneteric method gives 74.20 Ma, indicating Late Cretaceous - Paleocene time Corresponding to Laramide orogeny. This batholith consists of quartz diorite, tonalite, granodiorite and quartz monzodiorite in which main mafic minerals are biotite and amphibole. Enclaves are micaschist and fine graind quartz diorite in various sizes. Sieve texture and zonation observed in Plagioclase minerals indicate that the original magma has been produced by magma mixing of lower crust and upper mantle. Geochemistry study of the main elements shows that the batholite is cafe-alkaline and metaluminous and A12O3, Na2O, K2O, FeO values are high where as MgO, CaO, MnO, P2O5, TiO2 are low. In additon, genetic parameters for this batholith is compatible with I- Type granites (Caledonian). Rare earth elements plotted in spider diagrams show that the average slope of the curves is from K towards Cr (left to right), indicating partial melting. Depletion of compatible elements such as Ni, Cu, V and enrichment of incompatible elements imply that magma was not original and not initiated from mantle. Furthermores trough of Nb could be interpreted by magma mixing with crustal materials or by subduction. Also trough of Ti and crest of Y elements show that the origin of the magma is I-type. Finally, Pichagchi batholith is orogenic and its tectonic setting is compatible with continental arc granitoids (VAG).