The Lhasa terrane records voluminous magmatism related to the subduction of the Neo-Tethyan oceanic lithosphere,the study of which constrains the tectonomagmatic evolution of the region.We report zircon U-Pb ages,whole-rock compositions and Sr-Nd isotopic data from volcanic rocks in the Bangba district within the central Lhasa subterrane to constrain their magmatic source and petro-genesis.Zircon U-Pb dating of two volcanic rock samples yields End Cretaceous ages of 70.0±0.8 and 74.3±1.2 Ma.The rocks have high SiO2(65.41 wt.％-68.45 wt.％),Al2O3(16.16 wt.％-16.59 wt.％)and K2O(5.00 wt.％-6.73 wt.％)contents,and low TFe2O3(2.33 wt.％-2.79 wt.％),MgO(0.64 wt.％-1.44 wt.％)and TiO2(0.61 wt.％-0.65 wt.％)contents,with aluminium saturation indices(A/CNK)of 0.99-1.06.The major-and trace-element compositions of the rocks show they are metaluminous to slightly peraluminous high-K calc-alkaline trachydacite.The relatively high SiO2 and Sr-Nd isotopic composi-tions((87Sr/86Sr),=0.722 654,0.722 038 and 0.725 787 and εNd(t)=-12.27,-12.36 and-6.09,respectively)indicate that the trachydacites formed by partial melting of crustal material.The trachydacites are rela-tively enriched in light rare earth elements,depleted in heavy rare earth elements,have high(La/Yb)N and(Gd/Yb)N ratios(＞61 and＞6,respectively),and low Y(＜18 ppm)and Yb(＜18 ppm)contents,indi-cating they most likely formed from partial melting of lower crust in the garnet stability field.Consider-ing the geodynamic setting of the region during this period,partial melting of the ancient Lhasa crust was likely triggered by underplating mafic magmas during rollback of the Neo-Tethyan slab.

Yan Cao;Zhiqiang Kang;Feng Yang;Tong Zhou;Dongmei Liu;Rui Wang

State Key Laboratory of Geological Processes and Mineral Resources,China University of Geosciences(Beijing),Beijing 100083,China;College of Earth Sciences,Collaborative Innovation Center for Exploration of Hidden Nonferrous Metal Deposits and Development of New Materials in Guangxi,Guilin University of Technology,Guilin 541004,China

地球科学学刊（英文版）

[1]Yan Cao;Zhiqiang Kang;Feng Yang;Tong Zhou;Dongmei Liu;Rui Wang-.Geochronology,Geochemistry and Geological Significance of Volcanic Rocks of the Bangba District,Western Segment of the Central Lhasa Subterrane)[J].地球科学学刊（英文版）,2022(03):681-695

Bangba,Subterrane,tectonomagmatic,subterrane,trachydacite,trachydacites

Geochronology,Geochemistry,Geological,Significance,Volcanic,Rocks,District,Segment,Central,Lhasa,records,voluminous,magmatism,related,subduction,Neo,Tethyan,oceanic,lithosphere,study,which,constrains,evolution,region,report,zircon,Pb,ages,whole,compositions,Nd,isotopic,data,from,volcanic,rocks,district,within,central,their,source,petro,genesis,Zircon,dating,two,samples,yields,End,Cretaceous,Ma,have,high,SiO2,wt,Al2O3,K2O,contents,TFe2O3,MgO,TiO2,aluminium,saturation,indices,CNK,major,trace,show,they,metaluminous,slightly,peraluminous,calc,alkaline,relatively,87Sr,86Sr,respectively,indicate,that,formed,by,partial,melting,crustal,material,enriched,rare,earth,elements,depleted,heavy,La,Yb,Gd,ratios,ppm,cating,most,likely,lower,garnet,stability,field,Consider,geodynamic,setting,during,this,period,ancient,was,triggered,underplating,mafic,magmas,rollback,slab

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