Mineral chemistry and thermobarometry of migmatitic rocks of Boroujerd area (north of Sanandaj-Sirjan zone)


1 Department of Geology, Faculty of Sciences, Lorestan University, Khorramabad, Iran

2 دانشگاه لرستان، دانشکده علوم پایه، گروه زمین شناسی


Migmatites have formed an important part of high-grade metamorphism in the Boroujerd area aureole (north of Sanandaj-Sirjan zone). Migmatitic complex including: migmatites, schist migmatites and hornfelse migmatites with a different range of structural and mineralogical compositions. These rocks are observed as light (leucosome), dark (melanosome) and dark and light (mesosome). Leucosomes mainly composed from quartz, plagioclase, K-feldspar, biotite and muscovite and also have perthite, poikiloblastic, granoblastic, graphic and myrmekite textures. Melanosomes formed from minerals such as biotite, garnet, andalusite, tourmaline and sillimanite have lepidobalastic, porphyrolepidoblastic and lepidoporphyrobalastic textures. Mesosomes formed from dark and light minerals and show porphyroblastic, lepidoblastic and granoblastic textures. According to petrographic studies and whole rock chemical analyses for these rocks revealed that dominant protolith is pelitic rocks. The thermobarometry results showed temperature range of of 568°C to 662 °C and pressure of 2.8 to 3.3 kbars. According to the calculated temperature and pressure, the geothermal gradient of schist migmatites and hornfels migmatites determined 48 °C/km and 60 °C/km, respectively. Heat release of the Bourojerd pluton, mafic magmatism in area (that enclaves of them can be seen in the granitoids) and subduction fluid causes migmatites that it shows the main factor increasing geothermal gradient is the presence of hot igneous plutons and enter intrusion fluid in the magmatic arcs.