Triassic Paleo-Tethys subduction in the center of the Alpine- Himalayan Orogen: Evidence from Dehnow I-type granitoids (NE Iran)

摘要

The granitoids of Dehnow in NE Iran are part of a calc-alkaline plutonic series (diorite-tonalite- granodiorite) that intruded the remnants of the Paleo-Tethys oceanic crust during the Triassic. New major and trace element data together with isotopic compositions elucidate their I-type nature and a deep magma origin. P-T calculations based on amphibole and plagioclase suggest crystallization stages in the upper lithosphere at an approximate pressure of 6.4 kbar and temperature of 708 ℃. The Dehnow granitoids are characterized by high concentrations of LILE, LREE, HFSE and low concentrations of HREE, similar to some worldwide I-type granites, including examples from Harsit (along the Alpine-Himalayan suture zone), Iberia and the Martins Pereira plutons. The new geochemical data in combination with mineral parageneses and field observations suggest that the origin of the low temperature, Caledonian-type, arc-related granitoids of Dehnow resulted from the subduction of the Paleo-Tethys oceanic slab beneath the Turan block (along the Alpine-Himalayan suture zone) and involved the contribution of lower crust and mantle melts in this collisional setting.