东昆仑拉陵高里河沟脑地区晚三叠世花岗闪长斑岩年代学、岩石地球化学及Hf同位素特征

U-Pb age, geochemical and Hf isotopic characteristics of Late Triassicgranodiorite porphyry in Gounao area of Lalinggaoli River,Eastern Kunlun Mountains

笔者等对东昆仑拉陵高里河沟脑花岗闪长斑岩开展详细的全岩地球化学、LA-ICP-MS锆石U-Pb年代学、锆石Hf同位素研究,确定其形成时代,并探讨其岩石成因及成岩构造背景。结果显示,花岗闪长斑岩LA-ICP-MS锆石U-Pb年龄为231.1±1.2 Ma,指示其侵位于晚三叠世早期。全岩K2O/Na2O值为0.69~0.71,Mg#值为40.5~41.6,里特曼指数σ为1.90~2.09,A/CNK=1.01~1.03,属弱过铝质中—高钾钙碱性岩石系列。岩石的轻重稀土元素分异明显,(La/Yb)N值为19.54~25.52,具弱负Eu异常(δEu为0.96~0.97),富集大离子亲石元素K、Rb、Ba、Th,亏损高场强元素Nb、Ta、Ti等,具有高的Sr含量(606.0×10^(-6)~647.9×10^(-6))和Sr/Y值(60.38~62.99),较低的Y(9.62×10^(-6)~10.66×10^(-6))和Yb(0.86-6~0.92×10^(-6))含量,显示Adakite(高锶低钇中酸性岩)的地球化学特征。锆石Hf同位素εHf(t)值介于-6.93~-2.94,地壳模式年龄(TDm^(2))范围为1.45~1.70 Ga。综合分析表明,拉陵高里河沟脑花岗闪长斑岩形成于东昆仑洋壳俯冲末期至局部碰撞的转换阶段,岩浆源于高压条件下的加厚下地壳部分熔融。

Objectives: Through the study of granodiorite porphyry in Lalinggaoli River, East Kunlun, it provides animportant basis for the subduction collision orogenic process of the Paleotethys Ocean, and also provides furtherbasic data support for the next prospecting work in this area.Methods: Detailed petrogeochemistry, LA-ICP-MS zircon U-Pb geochronology and zircon Hf isotope studies ofgranodiorite porphyry in Gounao area of Lalinggaoli River, are carried out to determine its formation age, anddiscuss the petrogenesis and diagenetic tectonic setting.Results: The zircon U-Pb age of granodiorite porphyry is (231. 1 ± 1. 2) Ma, which indicated that theemplacement occurred in the early Late Triassic. The K2O/ Na2O values of the whole-rock were 0. 69~0. 71, Mg#values were 45. 3 ~ 46. 02, σ values were 1. 90 ~ 2. 09, and A/ CNK 1. 01 ~ 1. 03, which belong to weakperaluminous medium-high potassium calc-alkaline rock series. The samples have obvious differentiation of lightand heavy REE elements (La/ Yb)N values of 19. 54 ~ 25. 52, slight negative Eu anomaly (δEu 0. 96 ~ 0. 97),enriched in large ion lithophile elements K, Rb, Ba, Th, and depleted high field strength elements Nb, Ta, Ti.The samples have high Sr content (606. 0×10^(-6) ~647. 9×10-6) and Sr/ Y value (60. 38~62. 99), low Y (9. 62×10^(-6) ~10. 66×10-6) and Yb (0. 8610^(-6) ~0. 92×10-6), showing an adakitic geochemical characteristics. Zircon Hfisotope εHf(t) values ranged from -6. 93 to -2. 94, corresponding to the distribution range of crustal model age(TDM2) from 1. 70 to 1. 45 Ga.Conclusions: Comprehensive analyses show that granodiorite porphyry was formed in the transition setting fromthe subduction of Eastern Kunlun oceanic crust to local collision, and was sourced in the partial melting ofthickened lower crust under high pressure.