成都理工大学学报（自然科学版）2026，Vol.53Issue(1)：152-168,17.DOI:10.12474/cdlgzrkx.2024061901
北拉萨地块东段早白垩世麦巴岩体成因及构造背景
Petrogenesis and tectonic setting of the early Cretaceous Maiba pluton in the eastern section of the northern Lhasa block:constraints from zircon U-Pb geochronology and geochemistry
摘要
Abstract
Early Cretaceous magmatic rocks are widely exposed in the northern Lhasa block,but the deep geodynamic setting in which they formed is still debated.In this paper,we study the granodiorite and tonalite from the Maiba pluton in the Zuogong area,located in the eastern section of the northern Lhasa block.We focus on the petrography,geochronology,geochemical characteristics,and zircon Hf isotopes in the rocks.LA-ICP-MS dating of the granodiorite and tonalite yields crystallization ages of 130.2～127.0 Ma and 121.8 Ma,respectively,suggesting that the Maiba pluton formed during the early Cretaceous.The granodiorite has an SiO2 content of 63.09%～69.28%,an all-alkali content(Na2O+K2O)of 5.13%～7.79%,an Al2O3 content of 13.27%～15.96%,and an aluminum saturation index(A/CNK)of 0.84～1.04;the corresponding values for tonalite are 60.92%～62.79%,4.50%～5.77%,15.45%～17.32%,and 0.81～1.00.These geochemical characteristics indicate that granodiorite and tonalite are metaluminous to weakly peraluminous high-K calc-alkaline I-type granite.Both granodiorite and tonalite are relatively enriched in light rare earth elements and large ion lithophile elements(Rb,Th,U,and K),but depleted in heavy rare earth elements and high field strength elements(Ta,Nb,and Ti).They exhibit high Mg#values(42～65)and show significant variation in zircon Hf isotopic compositions[εHf(t)=-11.65 to-5.74],indicating that their parental magmas originated from a mixed source of ancient lower crust and mantle.Combined with previous research findings,it is suggested that the Maiba pluton formed at the end of the southward subduction of the Bangong-Nujiang Ocean.The rollback of the subducting slab caused asthenospheric upwelling,which triggered partial melting of the ancient lower crust,and its subsequent mixing with mantle-derived melts formed the parental magma of the Maiba pluton.关键词
早白垩世/北拉萨地块/班公湖—怒江洋/板片回转/闪长岩Key words
early Cretaceous/northern Lhasa block/Bangong-Nujiang Ocean/slab rollback/diorite分类
天文与地球科学引用本文复制引用
扎西平措,王旭辉,解鸿儒,邵锐,杜秋,吴强,普琼,德央,向巴次成..北拉萨地块东段早白垩世麦巴岩体成因及构造背景[J].成都理工大学学报（自然科学版）,2026,53(1):152-168,17.基金项目
西藏自治区科技计划项目(XZ202401YD0006) （XZ202401YD0006）
中国地质调查局西南三江有色金属资源基地调查项目(121201010000150007-02,DD20160016-20) （121201010000150007-02,DD20160016-20）
国家重点研发计划(2022YFC2905000). （2022YFC2905000）
