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The purpose of the present study is to investigate the petrogenesis of some basic intrusives, with the same relative age (Upper Jarassic), in Sanandaj-Sirjan metamorphic belt. For this purpose, Almogholagh, Cheshmeh Qassaban, Serkan and Bouin-Miandasht basic intrusives have been selected, for out studies.
These are small bodies with a limitted outcrops accompaynig by granitoidic bodies of Almogholagh, Alvand, and Bouin-Miandasht.
petrographically, these basic intrusives show different compossitions from olivine-gabbro to diorite pegmatoid and they are intersected with few microgabbroic and mirodioritic dykes. Radiometric age determination and chronostratigraphic studies indicate that the basic intrusives have intruded into older regional metamorphic rocks, during Upper Jurassic which conseqerntly lead to a high-grade contact metamorphism in ablite-epidote to pyroxene hornfels facies.
These masses have tholeiitic nature and lack any lithologic, mineralogic or geochemical continuum with their neighboring granitoids. The mechanism responsible for their generation is independent of the proceses compared to their accompanied granitoids. These basic intrusives with such chracteristics can be considerd as “precursor gabbros”.
The basic intrusives has been disturbed and intersected by the latter emplacement of granitodic masses in Sanandaj-Sirjan metamorpic belt (in Upper Cretaceous-Lower Paleocene).
The basic rocks have been undergone a considerable metasomatism indicated by the observable evidences of biotitization and tourmalinization.