内蒙古西乌旗沙尔哈达晚侏罗世A型花岗岩:地球化学特征、岩石成因与动力学背景

Late Jurassic A-type granite in Sharhada,West Ujimqin,Inner Mongolia:geochemical characteristics,petrogenesis and geodynamic setting

内蒙古西乌旗沙尔哈达花岗岩侵入于贺根山缝合带蛇绿岩中。LA-ICP-MS锆石测年指示,沙尔哈达花岗岩岩株于晚侏罗世(154.6±1.2 Ma)侵位,矿物组合以石英、碱性长石和斜长石为主,富SiO_(2)(74.86%~75.97%)、K_(2)O(4.4%~4.95%),贫MgO(0.044%~0.22%)、CaO(0.38%~0.77%)、TiO_(2)(0.046%~0.18%)和P_(2)O_(5)(0.007%~0.042%),A/CNK=1.03~1.09,小于1.1,强烈亏损Ba、Sr、Eu、P、Ti,具有典型的右倾“海鸥型”稀土元素分配模式,表现出典型的铝质A型花岗岩的矿物组合及地球化学特征。沙尔哈达A型花岗岩具有低的(^(87)Sr/^(86)Sr)i值(0.7014~0.70374)、低正ε_(Nd)(t)值(+3.96~+4.31)、高的ε_(Hf)(t)值(+10.54~+14.72)。同位素地球化学特征指示,沙尔哈达花岗岩可能源于新生的中基性地壳物质部分熔融及其后的结晶分异作用。沙尔哈达A型花岗岩为晚侏罗世蒙古-鄂霍茨克洋闭合后造山伸展作用的产物,和蒙古-华北北部地块散布的其他A型花岗岩共同指示中晚侏罗世广泛的中下地壳伸展。

The Sharhada granite in West Ujimqin,Inner Mongolia intruded into ophiolite in Hegenshan suture.LA-ICP-MS zircon dating indicates that the Sharhada granite was emplaced in the Late Jurassic(154.6±1.2 Ma).The mineral assemblage of the Shardaha granite is mainly composed of quartz,alkali feldspar and plagioclase.The granite is characterized by high SiO_(2)(74.86%~75.97%),K_(2)O(4.4%~4.95%),low MgO(0.044%~0.22%),CaO(0.38%~0.77%),TiO_(2)(0.046%~0.18%)and P_(2)O_(5)(0.007%~0.042%),A/CNK=1.03~1.09<1.1.It is strongly depleted in Ba,Sr,Eu,P and Ti,with a typical right dipping"Seagull-type"REE distribution pattern,showing the geochemical characteristics of typical aluminous A-type granite.The Sharhada A-type granite has low(^(87)Sr/^(86)Sr)i(0.7014~0.70374),positiveεNd(t)values(+3.96~+4.31)and highεHf(t)(+10.54~+14.72),which may due to the partial melting of the newly formed intermediate/basic crustal materials and the subsequent crystallization differentiation.Furthermore,together with other A-type granites scattered in the Mongolia-Northern North China block,the Sharhada A-type granite is recognized as the product of the post-orogenic extension of the Mongolian-Okhotsk tectonic domain in the Late Jurassic,which indicates the extensive middle-lower crust extension in the Middle-Late Jurassic.