Geochemistry of enclaves and host granitoids from the kashan granitoid complex, central iran: Implications for enclave generation by interaction of cogenetic magmas

Abstract

The major and trace elements and Sr-Nd-Pb isotopes of Miocene host granitoid rocks and their mafic microgranular enclaves (MMEs) were studied to understand the petrogenesis of MMEs in the Kashan complex, which is part of the Urumieh-Dokhtar magmatic belt (Iran). The host rocks consist of quartz-diorite and tonalite associated with a dioritic intrusion. The enclaves show microgranular texture and the same mineralogy as their respective host with plagioclase, quartz and biotite. MMEs have a diorite to quartz-diorite composition and show geochemical characteristics mostly between their granitoid host and the diorite intrusion. Chondrite-normalized REE patterns of all samples are moderately fractionated [(La/Yb)N=2.1 to 12.9]. The MMEs display in part small negative Eu anomalies (Eu/Eu*=0.54 to 0.99), with enrichment of LILE and depletion of HFSE. The enclaves show emplacement depth of ~4 to 6 km which is comparable with the host rocks. Moreover, the Hornblende-plagioclase equilibrium temprature of MMEs yields average temperatures of 795°C which is slightly higher than the host ones. Identical mineral compositions and Nd-Sr-Pb isotopic features of MME-host granitoid pairs indicate interactions and parallel evolution of MME and enclosing granitoid in the Kashan plutons. Additionally, the geochemical and isotopic investigations of host and dioritic intrusions suggest a common source for their genesis. A thermal anomaly induced by underplated basic magma into a hot crust would have caused partial melting in the lower crust to generate Kashan granitoid rocks.