地质学报2025，Vol.99Issue(5)：1632-1655,24.DOI:10.19762/j.cnki.dizhixuebao.2023082
西藏羌塘南缘热那错地区埃达克质英安岩的成因及构造启示:锆石U-Pb年龄、岩石地球化学和Sr-Nd-Hf同位素证据
Petrogenesis and tectonic implications of the dacites in the Rena-Co area,southern margin of Qiangtang,Tibetan Plateau:Evidence from zircon U-Pb dating,petrogeochemistry and Sr-Nd-Hf isotopes
摘要
Abstract
This study investigates the petrogenesis of Mesozoic igneous rocks along the Bangong-Nujiang suture zone in Tibet,which is crucial for understanding the tectonic evolution of the Bangong-Nujiang Ocean.We focus on dacites from the Rena-Co area in the southern margin of Qiangtang,using zircon LA-ICP-MS U-Pb dating,Lu-Hf isotopic analysis,and comprehensive geochemical assessments.Our key findings are:① The Rena-Co dacites were formed approximately 109.6～109.5 Ma,as determined by LA-ICP-MS zircon U-Pb dating.② Geochemically,these rocks display medium-K calc-alkaline affinities with adakite-like characteristics.They exhibit high SiO2(64.79％～70.37％),Al2 O3(13.81％～16.13％),and Sr(517 ×10-6～598 × 10-6),coupled with low Y(8.45×10-6～10.7×10-6)and MgO(0.68％～0.88％),with Mg# values ranging from 23.83 to 29.65 and Sr/Y ratios from 53.0 to 70.8.③ The dacites show strong enrichment in light rare earth elements and large ion lithophile elements(e.g.,Rb,U,Th,K,and Pb),but are depleted in heavy rare earth and high field strength elements(e.g.,Nb,Ta,and Ti),consistent with arc-type magmas generated in subduction zones.④ Isotopically,they present initial 87Sr/86Sr ratios of 0.705119～0.705491,εNd(t)values from-0.28 to+1.25,and Nd model ages of 931～806 Ma.Their zircon εHf(t)values range from+3.9 to+13.1,indicating a young Hf-depleted mantle age of 924～332 Ma.The combined geochemical and isotopic data suggest the dacites likely originated from juvenile,thickened mafic lower continental crust,potentially incorporating partial melts of metasomatized peridotite and subduction-related fluids.Considering these findings and previous research,we suggest that the closure of the Bangong-Nujiang Ocean occurred post-early Cretaceous.关键词
英安岩/岩石成因/早白垩世/新生下地壳/羌塘南缘Key words
dacite/petrogenesis/Early Cretaceous/Juvenile thickened lower continental crust/southern margin of Qiangtang引用本文复制引用
韦少港,白云,唐菊兴,宋扬,李宝龙,刘治博,董玉杰,白羽彤,相硕,刘思..西藏羌塘南缘热那错地区埃达克质英安岩的成因及构造启示:锆石U-Pb年龄、岩石地球化学和Sr-Nd-Hf同位素证据[J].地质学报,2025,99(5):1632-1655,24.基金项目
本文为中国地质调查局项目(编号DD20230286,DD20230033,DD20221684)、国家自然科学基金项目(编号42172100)、中央科研院所基本科研业务专项(编号KK2107)、国家重点研发计划项目(编号2022YFF0800404)和常熟理工学院科研启动专项(编号KYZ2022017Q)联合资助的成果. （编号DD20230286,DD20230033,DD20221684）
