Petrogenetic modeling of rock variety in the Khalkhab–Neshveh pluton,NW of Saveh,Iran     

MEHDI REZAEI‐KAHKHAEI  DARIUSH ESMAEILY  FERNANDO CORFU 《Island Arc》2011,20(3):329-345

The Khalkhab–Neshveh (KN) pluton is a part of Urumieh–Dokhtar Magmatic Arc and was intruded into a covering of basalt and andesite of Eocene to early Miocene age. It is a medium to high‐K, metaluminous and I‐type pluton ranging in composition from quartz monzogabbro, through quartz monzodiorite, granodiorite, and granite. The KN rocks show subtle differentiation trends strongly controlled by clinopyroxene, plagioclase, hornblende, apatite, and titanite, where most major elements (except K₂O) are negatively correlated with SiO₂; and Al₂O₃, Na₂O, Sr, Eu, and Y define curvilinear trends. Considering three processes of magmatic differentiation including mixing and/or mingling between basaltic and dacitic magmas, gravitational fractional crystallization and in situ crystallization revealed that the latter is the most likely process for the evolution of KN magma. This is supported by the occurrence of all rock types at the same level, the lack of mafic enclaves in the granitoid rocks, the curvilinear trends of Na₂O, Sr, and Eu, and the constant ratios of (⁸⁷Sr/⁸⁶Sr)_i from quartz monzodiorite to granite (0.70475 and 0.70471, respectively). In situ crystallization took place via accumulation of plagioclase and clinopyroxene phenocrysts and concentration of these phases in the quartz monzogabbro and quartz monzodiorite at the margins of the intrusion at T ≥ 1050°C, and by filter pressing and fractionation of hornblende, plagioclase, and later biotite in the granitoids at T = ～880°C.  相似文献