西藏狮泉河地区渐新世钾质火山岩成因及其地质意义  

Petrogenesis and geological implications of Oligocene potassic volcanic rocks in the Shiquanhe area,Tibet

作　　者：俞嘉嘉 陈伟[1] 唐菊兴[1] 李阳 YU JiaJia;CHEN Wei;TANG JuXing;LI Yang(Institute of Mineral Resources,Chinese Academy of Geological Sciences,Beijing 100037,China;School of Earth Science and Resource,China University of Geosciences(Beijing),Beijing 100083,China)

机构地区：[1]中国地质科学院矿产资源研究所,北京100037 [2]中国地质大学(北京)地球科学与资源学院,北京100083

出　　处：《岩石学报》2025年第1期151-166,共16页Acta Petrologica Sinica

基　　金：中国地质调查项目(DD20230054、DD20230359)资助.

摘　　要：新生代钾质-超钾质火山岩与南北向裂谷关系密切,是认识青藏高原隆升过程的重要途径。本次工作在中拉萨地块狮泉河左左区识别出一套钾质粗面岩,为探讨其成因及构造背景指示,本文对其进行了年代学、岩石地球化学以及Lu-Hf同位素研究。锆石U-Pb年龄确定该套火山岩形成于24.2Ma和22.3Ma,从而将原属于则弄群朗久组的火山岩重新厘定为渐新世。地球化学分析表明其具有高硅(64.6%<SiO_(2)<67.0%)、高钾(6.22%<K_(2)O<6.53%,1.8<K_(2)O/Na_(2)O<2.2)特征,与拉萨地块西部地区南北向裂谷出露的钾质岩具有相似的构造背景,以及类似埃达克质岩的地球化学特征,如富集LREEs和LILEs,亏损HFSEs,高Sr低Y和高La低Yb等特征。较低的ε_(Hf)(t)值(-11.3~-9.48),指示其可能起源于后碰撞环境下拉萨地块增厚下地壳富钾物质的部分熔融。狮泉河左左区24~22Ma钾质岩的发现,为亚热裂谷西部的狮泉河地区是否还存在一条“狮泉河南北向裂谷”提供了依据,且有待进一步深入研究。The Cenozoic potassic-ultrapotassic volcanic rocks are closely related to the formation of the north-south rifts in Tibetan Plateau,which are important objects to study the uplift process of the plateau.We identified a suite of potassic trachyte in the Zuozuoqu of the Shiquanhe in the middle Lhasa subterrane.In order to explore the petrogenesis and tectonic indications of the potassic volcanic rocks,we present detailed chronological,petrographic geochemical and Lu-Hf isotopic geochemistry studies on them.The zircon U-Pb ages of the volcanic rocks are 24.2Ma and 22.3Ma,indicating that the volcanic rocks originally thought to be the Langjiu Formation,Zenong Group should be reclassified as Oligocene.The geochemical characteristics show they have high silicon(64.6%<SiO_(2)<67.0%)and potassium(6.22%<K_(2)O<6.53%,1.8<K_(2)O/Na_(2)O<2.2)contents.They have characteristics of a similar tectonic environment with the potassic rocks exposed in the north-south rifts in the western part of Lhasa terrane,together with adakitic geochemical characteristics such as enrichment of LREEs and LILEs,depletion of HFSEs,high Sr and low Y,high La and low Yb.The lowε_(Hf)(t)values(-11.3~-9.48)suggest that it may have originated from the partial melting of the potassium-rich material in the thickened lower crust of the Lhasa terrane in the post-collisional environment.The identification of the potassic rocks in the Zuozuoqu of Shiquanhe(24~22Ma)provides a basis for the existence of a‘Shiquanhe north-south rift’in the Shiquanhe area in the western Yare Rift,which needs to be further investigated.

关 键 词：钾质-超钾质火山岩 粗面岩 南北向裂谷 狮泉河地区 

分 类 号：P588.143[天文地球—岩石学] P597.3[天文地球—地质学]