西藏拉萨地块松多榴辉岩的锆石Lu／Hf同位素研究及LA-ICPMS U-Pb定年  

Study of Lu-Hf geochemical tracing and LA-ICPMS U-Pb isotopic dating of the Sumdo eclogite from the Lhasa block,Tibet.

作　　者：陈松永[1,2] 杨经绥[1,2] 徐向珍[1,2] 李化启[1,2] 杨岳衡[3] 

机构地区：[1]中国地质科学院地质研究所 国土资源部大陆动力学重点实验室,北京100037 [2]中国地质科学院青藏高原大陆动力学研究中心,北京100037 [3]中国科学院地质与地球物理研究所,北京100029

出　　处：《岩石学报》2008年第7期1528-1538,共11页Acta Petrologica Sinica

基　　金：中国地质调查局地质调查项目(编号:1212010610107和1212010610105);国家自然科学基金项目(编号:40610098)的部分成果

摘　　要：最近在青藏高原拉萨地块中发现一条榴辉岩带。榴辉岩带位于拉萨北东近200km 处的松多乡一带,呈近东西方向延伸,至少长60km,宽2km～3km。锆石样品选自新鲜的榴辉岩样品,共测了39个数据点,其中前19个数据点仅做 Lu-Hf同位素分析,后20个数据点既做了锆石原位 Lu-Hf 同位素分析,同时也做了锆石原位 LA-MC-ICPMS U-Pb 定年。结果表明,松多榴辉岩锆石 Hf 同位素组成比较均一,具有高^(176)Hf/^(177)Hf 和低^(176)Lu/^(177)Hf 特征,^(76)Hf/^(177)Hf 和^(176)Lu/^(177)Hf 值分别变化在0.2829651～0.2830295和0.000002～0.000008之间,其可能代表全岩体系在变质作用发生时的平均 Hf 同位素组成。松多榴辉岩的高^(176)Hf/^(177)Hf 和低^(176)Lu/^(177)Hf 组成特征可能跟其高压变质作用以及在变质作用过程中形成石榴子石矿物有关。ε_(Hf)(0)变化于6.8～10.0,表明在其变质过程中,变质流体有亏损地幔物质的加入。LA-ICPMS 锆石 U-Pb 定年,所获得加权平均年龄260Ma±16Ma,为变质年龄。从而进一步确定了松多榴辉岩变质事件发生在二叠纪。An at least 60km long and 2km - 3km wide eclogite belt was recently discovered in the Lhasa block, which is located near Sumdo village about 200km east of the Lhasa city, Tibet. The Lu-Hf geochemical tracing and isotopic dating of zircons from the Sumdo eclogite gave a very even Lu-Hf isotopic composition and uniform age. All the zircons have the similar composition with higher ^176 Hf/^177 Hf （0. 2829651 - 0. 2830295 ） and lower ^176 Lu/^177 Hf （0. 000002 - 0. 000008 ）, which is probably related to its metamorphism and the formation of garnet during the metamorphism. The value of δHf（0） is between 6. 8 and 10. 0, which indicates that there is a significant input from the depleted mantle during the metamorphism. LA-ICPMS U-Pb dating of zircons from the eclogite yielded an average metamorphic age of 260 ± 16Ma, indicating that there exist Permian HP/UHP（？） metamorphic belt in the Lhasa terrane.

关 键 词：松多榴辉岩 拉萨地块 Lu—Hf LA—ICPMS U—Pb定年 

分 类 号：P588.348[天文地球—岩石学] P597.3[天文地球—地质学]