柴北缘胜利口东地区白云母二长花岗岩锆石U-Pb年代学、地球化学及Hf同位素

张金明; 王秉璋; 薛万文; 付彦文; 田成秀; 雷晓清

doi:10.12029/gc20220218

柴北缘胜利口东地区白云母二长花岗岩锆石U-Pb年代学、地球化学及Hf同位素

Zircon U-Pb geochronology, geochemistry and Hf isotopes of Shenglikou muscovite monzogranite in northern margin of Qaidam Basin

摘要

摘要:
研究目的 柴北缘地区分布着大量早古生代花岗岩，是否存在与大陆深俯冲和早期碰撞阶段的岩浆活动，截至目前研究资料较少，制约了对柴北缘地区大地构造背景演化的认识。
研究方法 本文对胜利口东地区白云母二长花岗岩进行锆石U-Pb年代学、岩石地球化学及Hf同位素研究。
研究结果 通过LA-ICP-MS锆石U-Pb同位素测年，获得白云母二长花岗岩的年龄为（433±1.6）Ma（MSWD=0.026），属中志留世岩浆活动的产物。岩石地球化学特征显示岩石具富硅(SiO₂=76.33%~76.99%)和碱(K₂O+Na₂O=7.28%~8.19%)，高K₂O的特征，K₂O/Na₂O＞1，低镁(MgO=0.21%~0.29%)和Mg^#值(Mg^#=23.29~30.17)，A/CNK介于1.12~1.19，属强过铝质钙碱性岩石系列。岩石相对富集Rb、Th、U等大离子亲石元素，亏损Nb、Ta、Ti、P等高场强元素及Ba、Sr等部分大离子亲石元素。稀土元素配分曲线呈右倾型，显示明显的负Eu异常(δEu=0.32~0.63)。锆石Hf同位素ε_Hf(t)比值为-5.2~-16.0，对应的Hf同位素地壳模式年龄T_DM2为1.86~2.20 Ga。
结论综合岩石地球化学及同位素的研究表明，胜利口东白云母二长花岗岩为S型花岗岩，源于古元古代地壳物质的重熔再造。在综合对比白云母二长花岗岩形成年龄与区域高压—超高压变质时代的基础上，结合岩石地球化学及同位素的研究认为，胜利口东白云母二长花岗岩形成于柴北缘高压—超高压变质带碰撞阶段。

Abstract:
This paper is the result of geological survey engineering.
Objective There are a large number of early Paleozoic granites distributed in the northern margin of Qaidam Basin. However, there are few research data on the existence of magmatic activities in the stage of deep subduction and early collision with the continent, which restricts the understanding of the tectonic background evolution in the northern margin of Qaidam Basin.
Methods Zircon U-Pb geochronology, petrochemistry and Hf isotope of muscovite monzogranite in the east of Shenglikou are studied.
Results LA-ICP-MS zircon U-Pb dating shows that the age of muscovite monzogranite is (433 ± 6) Ma (MSWD = 0. 026), which is the product of middle Silurian magmatism. Geochemical characteristics show that the rocks are rich in silicon (SiO₂=76.33%-76.99%) and alkali (K₂O+Na₂O=7.28%-8.19%), high K₂O, K₂O / Na₂O>1, low Mg (MgO=0.21%-0.29%) and Mg ^# (Mg ^#=23.29-30.17), A/CNK(1.12-1.19), belonging to the strongly peraluminous calc alkaline rock series. The rocks are relatively enriched in Rb, Th, U and other large ion lithophile elements, and depleted in Nb, Ta, Ti, P and some Ba, Sr and other large ion lithophile elements (LILE). The REE distribution curve is right dipping, showing obvious negative Eu anomaly(δEu=0.32-0.63). Hf isotope of zircon ε_Hf(t)=–5.2-–16.0, and the corresponding Hf isotopic crustal model ages T_DM2=1.86-2.20 Ga.
Conclusions The study of geochemistry and isotope shows that the muscovite monzogranite is S-type granite, which originated from the remelting and reconstruction of Paleoproterozoic crust. Based on the comprehensive comparison of the formation age of muscovite monzogranite and the regional high-pressure ultra-high pressure metamorphic age, combined with the study of petrochemistry and isotope, it is considered that the muscovite monzogranite in the east of Shenglikou was formed in the collision stage of the high-pressure ultra-high pressure metamorphic belt in the northern margin of Qaidam Basin.

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