Document Type : Original Research Paper
Author
Assistant Professor, Department of Geology, University of Urmia, Urmia, Iran.
Abstract
A barrovian-type metamorphism occurred in the mafic rocks from the Qori complex (South Sanandaj - Sirjan zone), because of a regional arc-related metamorphism with a peak metamorphic condition of 700 °C and 8.5 kbar at 147 million years ago. As a result of the process, the rocks changed to migmatite. Trondhjemitic granitoids were formed as the dike form because parts of the melts can be extracted from the migmatites. Decreasing and increasing trace and rare earth elements in the amphibolites and trondhjemites were resulted of stability or instability in the metamorphic minerals during peak of the metamorphism, which caused migmatization and also formation of trondhjemite. Based on the partition coefficients of elements in different minerals, light rare earth elements (LREE) were mostly controlled by hornblende and garnet and apatite (but not a lot) during the partial melting of the amphibolites. Related to the LREE, heavy rare earth elements (HREE) and Y were controlled by apatite and garnet. Elements with high field strength (HFS), such as Zr, Nb, Ta and Th were controlled and distributed by hornblende and ilmenite. Large ionic lithophile elements (LILE) such as Sr, Ba and Rb showed that plagioclase and biotite were main minerals to control and distribute the elements. The evidence suggests that the Qori trondhjemitic granitoids are similar to the Al-poor trondhjemites, which are the result of partial melting of the garnet-hornblende from the amphibolitic protolith in presence of calcic plagioclase as stable phase.
Keywords
References
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