云南香格里拉浪丁岩体锆石 U-Pb 年龄及地球化学特征

Zircon U-Pb age and geochemical characteristics of Langding intrusion of Shangri-La,Yunnan Province

香格里拉地区广泛分布印支期中-中酸性浅成-超浅成岩体,位于西斑岩带的浪丁岩体主要由角闪闪长玢岩、石英闪长玢岩、含辉石角闪闪长玢岩组成。锆石U-Pb年龄显示岩体侵位于206.4±3.9 Ma。其地球化学特征与埃达克岩相似:SiO 2含量为56.66%~64.84%,平均60.42%;Eu异常不明显(Eu/Eu*为0.90~1.23,平均为1.08);富集轻稀土元素和大离子亲石元素,亏损重稀土元素,贫高场强元素;高Sr(490~1165×10^-6,平均842×10^-6)、Sr/Y(37.4~77.2,平均56.9)、La/Yb(21.7~28.4,平均25.6),低Y(13.1×10^-6~17.4×10^-6,平均14.6×10^-6)、Yb(1.20×10^-6~1.56×10^-6,平均1.37×10^-6)。年代学和地球化学研究结果显示,浪丁岩体形成于岛弧环境下,其形成与晚三叠世甘孜理塘洋壳板片的部分熔融有关,该地区的甘孜-理塘洋壳向西俯冲时,可能以较低的角度进入中咱地块之下。

The west porphyry belt and east porphyry belt in Shangri-La are mainly composed of Indosinian intermediate-acidic intrusive complex rocks.In the western porphyry belt,there are Luanitang porphyry,Xuejiping porphyry,Chundu porphyry,Are porphyry and Langding porphyry from north to south.In the eastern porphyry belt,there are Disuga porphyry,Songnuo porphyry,Pulang porphyry and Lanzhong porphyry from north to south.The Langding porphyry is mainly composed of hornblende diorite porphyrite,quartz diorite porphyrite and pyroxene diorite porphyrite.The zircon U-Pb age indicates that the intrusive rock has an age of 206.4±3.9 Ma.Geochemical characteristics of the Langding porphyry are similar to those of adakite,whose SiO 2 is higher than 56.66,averaging 60.42%,and whoseδEu is not distinct(0.90~1.23,averaging 1.08).Chondrite-normalized REE patterns show right-inclined feature,and are characterized by enrichment of LREE and LILE,heavy depletion of HREE,high Sr(490×10^-6~1165×10^-6,averaging 842×10^-6),Sr/Y(37.4~77.2,averaging 56.9)and La/Yb(21.7~28.4,averaging 25.6),but low Y(13.1×10^-6~17.4×10^-6,averaging 14.6×10^-6)and Yb(1.20×10^-6~1.61×10^-6,averaging 1.37×10^-6).The results of the studies of major oxides,REEs,trace elements and zircon U-Pb age show that the Langding rock body was formed in an island arc environment,and its formation was related to the partial melting of the low-angle subduction of Garze-Litang oceanic crust slab.