Geochemistry and mineral chemistry of the armoor granitoids,eastern dharwar craton: implications for the redox conditions and tectono-magmatic environment  

作　　者：A.Ajay Kumar Ch.Ashok 

机构地区：[1]Department of Geology,Osmania University,Hyderabad 500007,India [2]CSIR-National Geophysical Research Institute,Uppal,Hyderabad 500007,India

出　　处：《Acta Geochimica》2024年第1期110-133,共24页地球化学学报（英文）

摘　　要：The mineralogical and geochemical characteristics of the K-rich granites from the Armoor granitic rocks in the northeastern portion of the Eastern Dharwar Craton(EDC) are presented.In order to understand its physicochemical conditions,the petrogenesis of the granitoid was explained from biotite chemistry and geochemical systematics.Studies of mineral chemistry expose that compositionally,K-feldspar and plagioclase in Armoor granite rocks range from An0,Ab_(3-5.9),Or_(94-96.9) and An_(5-29,-Ab71.9-94.9),Or_(0-1.5),respectively.The mineral chemistry of biotite crystals exhibits composition that varies from primary to re-equilibrated primary biotites.Although biotites from the Armoor granites generally exhibit an I-type trend,with calc-alkaline parental magma in a subduction setting.Biotite chemistry of granites displays magnetite(oxidized)series nature,which has oxygen fugacity(fO_(2))=-15.1 to-16.7(log_(10) bar),under high oxidizing conditions.Temperature and pressure estimates for the crystallization of Armoor granites based on biotite composition are T=612-716 ℃ and 1.0-0.4 kbar,respectively.Geochemically,these rocks are metaluminous to slightly peraluminous and magnesian,with calc-alkaline potassiumrich granite.On the chondrite normalized REE diagram,the granites have positive europium anomalies;rich Sr/Y,(Dy/Yb)_(N) ratios and reduced Mg#,Rb/Sr,Rb,Sr indicate that the melting of earlier rocks,crystal accumulation and residual garnet source formed at high pressures.The examined granites show that they are produced from the melting of crustal sources.Thus,the extensive analyses of the described Armoor granite suggest that they were produced by crust sources and developed under oxidizing conditions in subduction setting.

关 键 词：Armoor granites Oxygen fugacity Crystal accumulation REMELTING SUBDUCTION 

分 类 号：P588.121[天文地球—岩石学] P542[天文地球—地质学]