Rb/Sr biotite–whole rock dating from Kashmar granitoid, NE Iran

Category Petrology
Group GSI.IR
Location The 25 Symposium of Geosciences
Author Abolfazl Soltani
Holding Date 02 July 2007



The Kashmar granitoid is a major plutonic suite occurring in North Doruneh Fault Magmatic Belt. It intrudes into Early Eocene volcanic rocks and crops out by extensive I-type plutons of mainly granite and granodiorite in composition. These plutons show characteristics of low temperature and low pressure granites which formed in sub–volcanic environment. Rb/Sr dating on biotite–whole rock pairs from granite, granodiorite and alkali feldspar granite yield isotopic ages ranging from ۴۳.۵ to ۴۲.۴±۰.۴ Ma which indicate Middle Eocene times (Lutetian) and a short time interval for emplacement of the Kashmar granitoid. The Sr and Nd isotopes represent low initial ۸۷Sr/۸۶Sr, intermediate initial ۱۴۳Nd/۱۴۴Nd and low and negative εNd values for all analyses of the Kashmar granitoid. Isotopic and petrological studies show that the Kashmar granitoid originated from partial melting of quartzofeldspathic rocks of lower continental crust (infra-crustal) and evolved dominantly through the fractionation of restite.