塔什库尔干地区位于青藏高原西北缘,帕米尔高原东北部,是中国境内唯一属于帕米尔弧形构造带的地区.然而,对于东北帕米尔地区新生代岩浆作用的研究相对青藏高原主体的研究薄弱得多.我们对东北帕米尔塔什库尔干地区新生代岩浆岩的锆石U-Pb年代学、地球化学及锆石Hf同位素组成进行了研究.结果表明:塔什库尔干新生代岩体中锆石U-Pb年龄约为10 Ma.所有样品显示高钾、碱性特征:K20(4.39％ ～ 11.86％)、AR值为3.07 ～ 6.36及A/CNK为0.57～0.81,为高钾碱性岩.塔什库尔新生代高钾碱性岩相对亏损Nb、Ta、Zr、Hf、Ti等高场强元素.岩石具有高的Sr/Y比值,Eu异常不明显.富集LREE,(La/Yb)N=40.26～ 287.59.这些地球化学特征指示了塔什库尔干高钾碱性岩可能来源于榴辉岩相加厚下地壳.岩石的εHf (t)为-0.83～-8.90,范围较大,说明其源岩物质主要来自地壳.推测新生代印度—亚洲大陆碰撞后,印度板块持续向北推进引起帕米尔地壳快速增厚,由于地壳增厚不均以及喀喇昆仑断裂的向北扩展作用,在中新世中期塔什库尔干地区局部范围内岩石圈重力失稳并发生垮塌,下地壳发生部分熔融形成高钾碱性岩浆.%Objectives:The Tashkorgan region is located on the northwestern margin of the Xizang (Tibet) plateau and northeastern part of the Pamir plateau.It is the only place in China belonging to the Pamir syntax.Compared with other areas of the Xizang (Tibet) plateau,studies on Cenozoic magmatism in Tashkorgan region are much dificient.Methods:Here we present new zircon U-Pb ages,whole-rock geochemical data and Hf isotope data for the Cenozoic rocks in Tashkorgan region.Results:Zircon U-Pb dating results of the rocks yield ages of 10.1 ～ 10.3 Ma.All samples are of high K contents and alkaline,with K2O =4.39％ ～ 11.86％,A/CNK =0.57 ～0.81 and AR =3.07 ～6.36.The Tashkorgan high K alkaline rocks are deplete in Nb,Ta,Zr,Hf and Ti,P,high Sr,low Nd content,high Sr/Y,insignificant Eu anomalies,and rich in LREE with (La/Yb)N varing from 40.26 to 287.59.All these characteristics suggest that the Tashkorgan high K alkaline rocks most likely derived from eclogitic thickened lower crust.Conclusions:We propose that continuous northward movement of the India craton after the Indian—Asian plate collision event led to rapid thickening of the Miocene northeastern Pamir crust.Due to the imbalance of the new thickened northeastern Pamir crust and northward extention of Karakorum Fault,the northeastern Pamir lithosphere collapsed in Middle Miocene,then the lower crust was partially melted and the high K and alkaline magma formed.
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