THE M-TYPE SIAH KUH GRANITE BATHOLITH SE OF KERMAN/IRAN: EVIDENCE FOR INITIATION OF NEOTETHYS SUBDUCTION IN TRIASSIC TIME

The upper Triassic granite batholith of Siah Kuh, which lies in the Paleozoic Sanandaj-Sirjan metamorphic belt in south-central Iran, is intruded into the greenschist rocks of the upper Devonian-lower Carboniferous. The Paleozoic Sanandaj-Sirjan zone consists of various lithological units including low to high grade greenschist facies, gabbro and few scattered granitoid plutons, tholeiitic lava flows, and unmetmorphosed continental shelf sediments, quartz diorite, and diorite with minor syenite and monzonitic rocks. The contact of the complex with the metamorphic rocks is marked by a thin layer of recrystallized amphibole.

These granitoid rocks show low LIL and HFS element abundances. The low Rb/Zr ratio reflects the lack of crustal contamination. Geochemical data, multi-element and various trace elment discrimination diagrams, the presence of K-feldspar, interstitial micrographic texure along with lower Ta, Nb, Hf and Y abundances indicate that the Siah Kuh granitic rocks have characteristics of tholeiitic, meta-aluminous, M-type granites of primitive island arc settings and are probably formed during a pre-plate collision by the onset of subduction of Neotethys oceanic crust beneath Central Iran in Triassic time and from a parental magma which derived directly from the partial melting of mantle or subduction of an oceanic crust beneath the island arc.