origin and significance of tourmaline-bearing rocks in boroujerd region, sanandaj-sirjan zone, western iran

Tourmaline minerals are a main petrogenetic tool because of their refractory nature, chemical variability, and extensive occurrence invarious geological settings. the middle-jurassic boroujerd igneous rocks are one of the largest bodies that located in the middle partin the sanandaj-sirjan magmatic arc (ssma) that introduced into regional metamorphic rocks. they are mostly composed ofgranitoids (granodiorite, quartz-diorite, and monzogranite) and contain apatite, zircon and tourmaline as abounadant accessoryminerals. tourmalines occur in varying types of mineral assemblages, chemical compositions and individual forms includingtourmalinite, quartz-tourmaline vein, as accessory mineral in the more evolved granitoids, and schists. tourmaline crystal sizes in theserocks varies from very fine to coarse-grained. the colour is brown to black and some crystals displaying a finescale chemical zonation.tourmaline crystals commonly exhibit cellular features. based on electron probe microanalysis (epma) analyses, schorl is the mostabundant type of tourmaline in granitoids but foitite and dravite are common compositions in the pegmatite and schist, respectively.presence of several tourmaline generations and their compositional trend may indicate time-varying relatively acidic boron-bearingfluids and reflects an anatexic melts influence in their crystallization.