川西义敦岛弧稻城花岗岩体和海子山花岗岩体锆石U-Pb年代学、Hf同位素特征及地质意义  

Zircon U-Pb Geochronology and Hf Isotopic Characteristics of the Daocheng Granite and Haizishan Granite in the Yidun Arc,Western Sichuan,and Their Geological Significance

作　　者：王楠[1,2,3] 吴才来[1] 秦海鹏[1] 雷敏[1] 郭文峰[1] 张昕[1] 陈红杰[1] 

机构地区：[1]中国地质科学院地质研究所中国地质调查局大陆动力学研究中心,北京100037 [2]中国地质大学地球科学学院地质过程与矿产资源国家重点实验室,武汉430074 [3]中国地质科学院矿产资源研究所国土资源部成矿作用与资源评价重点实验室,北京100037

出　　处：《地质学报》2016年第11期3227-3245,共19页Acta Geologica Sinica

基　　金：中国地质调查局项目(编号12120114061701;121201102000150005-06和12120115027001)联合资助成果

摘　　要：义敦岛弧形成于晚三叠世大规模俯冲造山作用过程中,位于松潘-甘孜褶皱带和羌塘地体之间。稻城岩体和海子山岩体分别为义敦岛弧上出露的晚三叠世和白垩纪花岗质岩体。结合野外考察,本文对上述岩体进行岩相学、锆石U-Pb年代学和Hf同位素的研究,结果表明,1稻城岩体和海子山岩体主要矿物为斜长石、钾长石、石英和黑云母,副矿物为锆石、榍石、磁铁矿和磷灰石等;钠质斜长石颗粒,以及钾长石和石英不连续出现,表明二者均属于低熔线花岗岩,是含水条件下,在与造山事件有关的环境中形成。2稻城岩体的侵位年龄为217.4Ma,属晚三叠世花岗岩侵入体,εHf(t)为-7.1^-0.1,二阶段模式年龄(tDM2)为1.26~1.7Ga,表明在中元古代与扬子克拉通经历了共同的地壳演化历史;海子山岩体的形成时代为98.3 Ma,为白垩纪时期产物,εHf(t)变化于-12.1^+2.5,二阶段模式年龄(tDM2)变化于1.0~1.93Ga。3结合前人研究成果,本文认为稻城岩体源岩可能是与扬子克拉通有关的中元古代的下地壳物质,在甘孜-理塘洋俯冲闭合后的同碰撞造山阶段,因地幔岩浆底侵作用而发生了部分熔融,同时伴有少量的亏损地幔成分加入,之后上升侵位于中—上地壳,并且侵位后经历了快速的冷却过程。海子山岩体是与俯冲有关的造山后伸展环境下形成的A2型花岗岩,源岩主要为中元古代地壳物质,同样有少量地幔物质加入,在白垩纪时侵位于地壳较浅部位,之后亦同样经历了快速的冷却过程。Yidun Arc, located between Songpan-Garzê Fold Belt and Qiangtang Block, southwestern China was the result of Late Triassic large-scale subduction orogenic process. Daocheng granite and Haizishan granite are the two outcropped granites in the Yidun Arc during the Late Triassic and Cretaceous, respectively. On the basis of field investigation, this study carried out the analysis of petrology and zircon U-Pb ages for these two plutons. The results show rock-forming minerals of the two granitic plutons are mainly composed of plagioclase, K-feldspar, quartz and biotite, and the accessory minerals include zircon, sphene, magnetite and apatite. Sodic plagioclase grains and occasionally present K-feldspar and quartz indicate that the two granitic plutons belong to subsolvus granite and the formation of two plutons was related to orogenic event under water-bearing condition. The Daocheng granite has emplacement age of 217.4 Ma （Late Triassic）, with εHf（t）ranging from -7.1 to -0.1, and two-stage model age（tDM2）of 1.26~1.7 Ga, indicating that the Yidun Arc and Yangtze Block may experience the same evolutionary history of continental crust during the Mesoproterozoic time. The Haizishan granite has an emplacement age of 98.3 Ma （Cretaceous） , with εHf（t）ranging from -12.1 to ＋2.5, and a tDM2 age of 1.0~1.93 Ga. In combination with previous studies about magmatism in the Yidun Arc, it can be concluded that the source rocks of Daocheng granite was probably derived from partial melting of the Mesoproterozoic lower crust material related to Yangtze Craton with addition of minor depleted mantle-derived magma, which was triggered by the underplating of large-scale mantle-derived magma under the syn-collisional tectonic setting following the westward subduction and closure of the Garzê-Litang paleo-ocean. The Haizishan granite was an A2-type granitic pluton resulting from post-collisional extensional tectonic setting related to arc-continent collision during Early Cretaceous. Its source rocks

关 键 词：义敦岛弧 稻城花岗岩体 海子山花岗岩体 矿物学 U—Pb年代学 HF同位素 地质意义 

分 类 号：P597.3[天文地球—地球化学] P588.121[天文地球—地质学]