شیمی کانی گابروهای همسانگرد افیولیت کرمانشاه، شواهدی بر خاستگاه زمین‌ساختی

Isotropic gabbros of Kermanshah ophiolite include olivine gabbro, gabbro, gabbronorite, olivine gabbronorite and troctolite. The isotropic gabbros are medium to fine grained with euhedral to subhedral orthopyroxenes, clinopyroxenes and subhedral plagioclase, olivine together with rare amphiboles. Mineral chemistry of isotropic gabbros reveal that the clinopyroxenes are diopsidic to augitic in composition within the compositional ranges of En(50.91–45.79), Fs(7.41–3.64), and Wo(48.5–43.81). They are Ca-rich and Na poor (Na2O < 0.54 wt%) characterized by high-Mg (Mg# 85.62–89.35) and low-Ti (TiO2 < 0.28 wt%) contents. Plagioclases are bytownite in compositions (An(70.51–90.15), Ab(9.62-29.02) and Or (0/00-0.63), orthopyroxene are mostly enstatites within the compositional ranges of En(78.27-84.94), Fs(13.0-20.07) and Wo(1.43-3.36), olivine, forstrite and amphiboles are Mg-rich (tremolite, actinolite to actinohornblendes) with Mg# (64.35-84/86). The presence of highly magnesian olivines (Fo 80.07–84.82), clinopyroxenes (Mg# 85.62–89.35), and orthopyroxenes (Mg# 79.59–85.72) as well as highly calcic plagioclases (An 70.51–90.15) and amphiboles in the isotropic gabbros indicates a subduction-related tectonic environment. The tectonic discrimination plots of clinopyroxene data indicate island arc signature of the source magma. The results of studies confirm that the Kermanshah ophiolite formed in a suprasubduction zone environment in the southern branch of Neotethys