青藏高原北部风火山花岗斑岩锆石U-Pb同位素测年及其地质意义  

U-Pb Isotopic Dating of Zircons from Porphyry Granite of the Fenghuoshan Mts.,Northern Tibetan Plateau and Its Geological Significance

作　　者：吴珍汉[1] 叶培盛[1] 胡道功[1] 张维[2] 周春景[1] 

机构地区：[1]中国地质科学院地质力学研究所 [2]北京离子探针中心

出　　处：《现代地质》2007年第3期435-442,共8页Geoscience

基　　金：科技部国际合作项目(2006DFB211330);中国地质调查局青藏高原综合研究与INDEPTH-IV项目

摘　　要：青藏高原北部风火山花岗斑岩与逆冲推覆构造存在密切关系,岩浆侵位发生在区域地质构造演化的重要历史时期。对风火山北麓花岗斑岩及暗色包体,在显微观测和矿物鉴定的基础上,通过单颗粒锆石离子探针U-Pb同位素测年,获得高精度的测年资料。测得早期岩浆锆石结晶平均年龄为(34.5±1.4)Ma,对应于岩浆源区地壳局部熔融时代;晚期岩浆锆石结晶平均年龄为(27.6±0.5)M a,对应于岩浆向上侵入雅西错群的岩浆侵位时代。风火山北麓花岗斑岩属青藏高原北部出露的最年轻花岗岩,岩体内部不同类型锆石的U-Pb同位素测年为区域地层、区域构造和高原隆升的研究提供了重要的年代学约束。Porphyry granites were genetically related to regional thrusting in the Fenghuoshan Mts. , northern Tibetan Plateau. Both the granite emplacement and thrusting occurred in Oligoeene, a key period of regional tectonic evolution according to field geological data. The porphyry granite and dark xenolith within the granite were sampled in northern Fenghuoshan Mts. , and minerals of the samples were identified in detail by using microscope. SHRIMP U-Pb isotopic dating of zoned zircons from magmatie crystallization of the samples gives two groups of ages. Mean age of one group of U-Pb isotopic ages is （34. 5 ± 1.4） Ma, representing time of partial melting of the crust and formation of granitic magma. Mean age of another group of U-Pb isotopic ages is （27.6 ± 0. 5 ） Ma, representing time of granitic magma emplacement into the Yaxieuo group. Porphyry granite intruded in 27.6 Ma in northern Fenghuoshan Mts. belongs to the youngest granite complex outcropped in north Tibetan Plateau. U-Pb isotopic dating of the porphyry granite and its xenolith provides important time constrains for Cenozoic stratigraphie system, regional thrusting and plateau uplift.

关 键 词：风火山花岗斑岩 锆石U-Pb同位素测年 离子探针 逆冲推覆构造 青藏高原北部 

分 类 号：P588.1[天文地球—岩石学]