东昆仑诺木洪地区白沙河岩组岩石学、地球化学及年代学特征

金水口岩群上部的白沙河岩组作为东昆仑的基底变质岩系之一，对研究东昆仑造山带的形成与演化具有重要的地质意义.选择青海省诺木洪地区出露的白沙河岩组作为研究对象，对其开展野外地质调查、岩石学、岩石地球化学、锆石U-Pb同位素年代学等相关研究.通过调查将该地区白沙河岩组划分为上中下3个岩性段，从中识别出矽线石、石榴子石、单斜辉石、白云石等特征变质矿物组合，表明该岩组经历了高角闪岩相-低麻粒岩相变质作用.对识别出的泥质变质岩利用石榴子石-黑云母温度计和石榴子石-黑云母-斜长石-石英压力计所恢复的视峰期变质温度为660~683℃，压力为3.9~4.2 kbar；对基性变质岩使用角闪石-斜长石温度计与角闪石-斜长石-石英压力计，恢复其变质温度为723~772℃，压力为3.4~4.9 kbar.对其中的长英质副变质岩进行碎屑锆石年代学研究，频数峰值集中在1 300 Ma，其原岩沉积年龄应晚于中元古代.白沙河岩组中变质基性岩原岩为形成于板内伸展环境的拉斑玄武岩；长英质变质岩原岩为泥质-砂质陆缘碎屑岩.白沙河岩组原岩建造为陆缘碎屑岩夹基性火山岩系列，上部为碳酸盐岩沉积，其可能形成于由伸展向挤压转换的构造条件下的大陆裂谷晚期. 

Petrology,Geochemistry and Chronology of the Baishahe Formation in Numohong Area of Eastern Kunlun Orogenic Belt

The Baishahe Formation in the lower part of the Jinshuikou Group is one of the basement metamorphic rock series in the East Kunlun,which has essential geological significance for studying the formation and evolution of the East Kunlun orogenic belt. In this paper,the Baishahe Formation exposed in the Nuomuhong area of Qinghai Province was selected as the object of study,which was investigated by geological field survey,petrology,whole-rock geochemistry,zircon U-Pb chronology,etc. The Baishahe rock group in the area was divided into three lithologic sections through investigation. Characteristic metamorphic mineral combinations such as sillimanite,garnet,monoclinic pyroxene,and dolomite were identified. This indicats that the rock group had experienced high amphibolite facies-low granulite facies metamorphism. For the identified argillaceous metamorphic rocks,the apparent peak metamorphic temperature and pressure recovered by the garnet-biotite thermometer and garnet-biotite-plagioclase-quartz manometer are 660-683 ℃,and 3.9-4.2 kbar,respectively. For basic metamorphic rocks,the metamorphic temperature and temperature recovered using hornblende-plagioclase thermometer and hornblende-plagioclase-quartz manometer are 723-772 ℃ and 3.4-4.9 kbar,respectively. The paragneiss was studied using clastic zircon chronology. Results show that the frequency peak concentrated at 1 300 Ma,and the original rock sedimentation age should be later than the Mesoproterozoic. The original rocks were recovered using rock geochemical data. The original rocks of the basic metamorphic rock in the Baishahe Formation were determined to be tholeiitic basalt formed in the extensional environment within the plate; the original rocks of the felsic metamorphic rock were identified as muddy-sand continental marginal clastic rock. The original rocks of the Baishahe Formation are constructed of continental marginal clastic rocks with basic volcanic rocks,with carbonate deposits in the upper part. It may have been formed in the late stage of continental rifting and under the tectonic environments from extension to compression.