阿尔金索尔库里地区石英闪长玢岩锆石U-Pb年龄、地球化学特征及其地质意义

为了明确阿尔金索尔库里地区石英闪长玢岩脉的成因及形成时代，对该类岩脉进行了全岩主微量、稀土元素及LA-ICP-MS锆石U-Pb定年。锆石U-Pb同位素测年结果显示，石英闪长玢岩脉形成于（375.7±2.2）Ma。地球化学资料显示岩脉具有较高的硅含量（SiO2=61.41%~69.93%），富铝（Al2O3=13.48%~15.57%），贫铁（TFeO=3.47%~4.53%）、镁（MgO=0.66%~1.83%）、钙（CaO=2.81%~4.21%）的特征，归类为钙碱性I型花岗岩；稀土元素总量较高，稀土元素分馏较显著，（La/Yb）N为6.25~8.51，无明显Eu异常；微量元素以富集Rb、Pb、Th、U等大离子亲石元素（LILE），亏损Nb、Ta、Ti等高场强元素（HFSE）为特征。上述地球化学特征指示，石英闪长玢岩脉为幔源岩浆底侵作用引发下地壳基性岩部分熔融形成的母岩浆，经过分离结晶而形成。结合区域地质资料及同期岩浆岩活动，认为索尔库里地区石英闪长玢岩脉形成于造山后伸展构造环境，与阿尔金断裂晚泥盆世的走滑活动相关。

Zircon U-Pb Ages and Geochemical Characteristics of Quartz Diorite Porphyrite from Suoerkuli Area in Altyn Tagh and their Geological Significance

In order to confirm the genesis and formation age of quartz diorite porphyrite from Suoerkuli area in Altyn Tagh, its geochemical characteristics and LA-ICP-MS zircon U-Pb age have been studied in this paper. The LA-ICP-MS zircon U-Pb dating indicates that these quartz diorite porphyrites was formed at (375.7±2.2) Ma. The geochemical data show that these rocks are relatively rich in SiO2 (61.41%~69.93%) and Al2O3 (13.48%~15.57%) contents, but low in TFeO (3.47%~4.53%), MgO (0.66%~1.83%) and CaO (2.81%~4.21%) contents, showing the features of calc-alkaline I-type granites. These rocks have relative high total REE concentration (∑REE=129.32×10-6~253.63×10-6), with fractionated REE[(La/Yb)N=6.25~8.51] and no remarkable Eu anomalies. Furthermore, they are enriched in LILE (e.g. Rb, Pb, Th and U), but depleted in HFSE (e.g. Nb, Ta and Ti). The geochemical characteristics suggest that these quartz diorite porphyrites were generated by the partial melting of basic rocks in lower crust and formed by the fractional crystallization, and the parental magma was caused by the underplating of mantle-derived materials. Based on the regional geological investigations and the spatial-temporal distribution of the coeval igneous rocks, it's considered that the quartz diorite porphyrite was emplaced in a post-orogenic extensional environment, which is related with the strike slip of Altyn Tagh Fault.