北澜沧江花岗岩地球化学特征及其构造意义  

Geochemical characters of the granites in the North Lancangjiang granitic belt and its tectonic implication

作　　者：张圣听 王世锋[1] 王淇 宋立才 Zhang Shengting;Wang Shifeng;Wang Qi;Song Licai(Institute of Geomechanics,Chinese Academy of Geological Sciences,Beijing 100081;School of Earth and Space Sciences,Peking University,Beijing 100871;Institute of Disaster Prevention,Sanhe,Hebei 065201)

机构地区：[1]中国地质科学院地质力学研究所,北京100081 [2]北京大学地球与空间科学学院,北京100871 [3]防灾科技学院,河北三河065201

出　　处：《地质科学》2024年第5期1361-1373,共13页Chinese Journal of Geology(Scientia Geologica Sinica)

基　　金：科技部专项(编号:2021YFB2301401-01);西藏自治区重大科技专项(编号:XZ202101ZD0001G-01-01-I)资助。

摘　　要：藏东地区广泛发育古特提斯花岗岩,如与金沙江缝合带相关的江达—维西花岗岩带和与甘孜—理塘缝合带相关的义敦花岗岩带。但是与龙木错—双湖(碧土)古特提斯主缝合带相关的北澜沧江花岗岩带并没有得到普遍认可。本文选取北澜沧江花岗岩带南端的碧罗雪山花岗岩展开研究,揭示其岩石学、年代学和地球化学特征,并进一步揭示其构造意义。岩石样品中锆石具有明显的岩浆岩振荡环带,年龄数据聚集在在217±1 Ma左右,ε_(Hf)(t)均值为-13.5,ε_(Nd)(t)值为-12.0,Sr-Nd-Hf同位素二阶段模式年龄均在2.0 Ga左右;岩石显微观察及地化特征表明岩石为花岗岩类,样品的岩浆来自具有古老地壳重熔成因的中上地壳酸性岩,构造判别图显示岩石为陆陆碰撞阶段花岗岩特征,这与主特提斯洋向东俯冲于兰坪—思茅地块之下以及随后发生陆陆碰撞的构造演化模型相契合。岩石地化特征和其构造位置支持碧罗雪山花岗岩带是北澜沧江花岗岩带的南端。由此,藏东地区存在一条长达700 km的花岗岩带,该花岗岩带从类乌齐、昌都吉塘、左贡东大山、芒康盐井、德钦梅里雪山延伸到维西碧罗雪山。碧罗雪山花岗岩的岩石年代学、地球化学数据为龙木措—双湖缝合带与昌宁—孟连缝合带的对接提供了详细的证据。Paleotethyan granites are well developed in eastern Tibet,such as the Jiangda-Weixi granitic belt related to the Jinshajiang suture,the Yidun granitic belt related to the Ganzi-Litang suture belt.But as part of the main Paleotethyan suture,the North Lancangjiang granitic belt is not well studied.Here we provide petrologic and geochemical feathers of the rocks in this belt to disclose its tectonic implication.The zircon ages of the granite rocks are clustered around 217±1 Ma;meanεHf(t)value is around-13.5 with mean TDM2 age around 2.1 Ga;and meanεNd(t)value is around-12.0 with mean TDM2 age around 2.0 Ga.Isotope and geochemical data show that the rocks are derived from middle or upper crust with ancient lower crustal material contamination,and emplaced in continental collision environment.The case suggests eastward subduction of the oceanic lithosphere beneath the Lanping-Simao massif and subsequence collision during the paleo-Tethyan evolution.The discovery of the granite in Weixi area further suggests the North Lancangjiang granitic belt spans over 700 km in eastern Tibet.The granitic belt from Leiwuqi country,through Jitang and Yanjing towns in Changdu City,then passing Meili Snow Mountain,finally reached the Biluo Snow Mountain of Weixi Country.The petrologic,geochronological and geochemical data in this paper provide new data for the correlation between Longmu co-Shuanghu suture belt and Changning-Menglian suture belt.

关 键 词：北澜沧江花岗岩带 碧罗雪山花岗岩 古特提斯缝合带 地球化学特征 S型花岗岩 

分 类 号：P588.12[天文地球—岩石学] P59[天文地球—地质学]