Scientific Quarterly Journal of Geosciences

Scientific Quarterly Journal of Geosciences

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

Document Type : Original Research Paper

Authors
Mohammad Hosein Kholghi 1
Mansour Vossoughi Abedini 2
1 Geological Survey of Iran , Tehran, Iran
2 Earth Science Faculty, Shahid Beheshti University, Tehran, Iran
Abstract
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 radiometeric 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 grained 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 calc-alkaline and metaluminous and Al2O3, Na2O, K2O, FeO values are high whereas MgO, CaO, MnO, P2O5, TiO2 are low. In addition, genetic parameters for this batholith are 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. Furthermore, 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 (V AG).
Keywords
Pichagchi
Iran
I-Type granite
Cretaceous granodiorite
fine grain dark enclaves
biotite
amphibole
Partial melting
magma mixing
calc - alkaline
metaluminous
radiometric age dating

Subjects

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Scientific Quarterly Journal of Geosciences
Volume 13, 49-50
Autumn & Winter 2004, Vol. 13, No. 49-50
Winter 2004
Pages 78-89