新疆阿勒泰红柱石-矽线石型递增变质带特征及其PT条件研究

FEATURES AND PT CONDITION STUDY OF THE ADNALUSITE-SILLIMANITE TYPE PROGRESSIVE METAMORPHIC BELT IN ALETAI,XINJIANG

新疆阿勒泰地区发育了红柱石-矽线石型递增变质带,由绿泥石-黑云母带、黑云母-石榴石带、石榴石-十字石带、十字石-红柱石带和矽线石带组成,根据石榴石成分环带、变质与变形关系、矿物共生组合演化等特征,将变质作用分为峰前期、峰期和峰后期3个演化阶段。峰前期、峰期为连续的递增变质过程,形成典型的中-低压过渡型递增变质带,峰后期属于退变质过程。据石榴石-斜长石-黑云母-白云母-石英组合内部一致地质温压计估算出峰期温度-压力:T=580℃～670℃,P=0.4GPa～0.5GPa。变质作用演化具有顺时针的PTt轨迹,代表陆壳有一定程度的构造增厚,但幅度不大,没有大规模的陆壳俯冲或拆沉作用,这种增厚可能以陆壳的构造叠置机制为主。总体相当于地体间斜向走滑兼有一定垂直分量的拼合过程的地球动力学机制。

Andalusite-sillimanite type progressive metamorphic belt composed of chlorite-biotite zone,biotite-garnet zone,garnet- staurolite zone,staurolite-andalusite zone and sillimanite zone in Aletai Xinjiang is studied. According to the component zoning of the garnets,the relationship between metamorphism and deformation,and the paragenetic association evolution of the minerals, etc,the metamorphism is divided into three evolution stages： the stage before peak metamorphism,the peak metamorphism stage and the stage after peak metamorphism. The stage before peak metamorphism and the peak metamorphicsm stage are continuous progressive metamorphic process, and form typical mid-to-low pressure intermediate type progressive metamorphic belt. However,the stage after the peak metamorphism was a retrograde metamorphic process. According to the consistent geothermometer and manometer of the assemblage of garnet-plagioclase-biotite-muscovite-quartz,thepeak temperature and pressure are estimated as：T=580 ℃-670 ℃,P =0.4 GPa-0. 5 GPa. The PT） paths of the metamorphism evolution is clockwise. Therefore,it is considered that the crust of this area underwent certain degree tectonic thickenning without large scale subduction of continental crust. The geodynamic mechanism is characterized by the matching process of different terranes with oblique slip and certain amount of vertical movement.