Late Cambrian Magmatic Events in SW Yunnan and Implications for the Tectonic Reconstruction of Northern Gondwana  

作　　者：Guichun Liu Jianwei Zi Xiaomei Nie M.Santosh Cai Zhu Wei Wang Tianyu Zhao Guangyan Chen Qinglai Feng 

机构地区：[1]Yunnan Institute of Geological Sciences,Kunming 650216,China [2]School of Earth Sciences,China University of Geosciences,Wuhan 430074,China [3]State Key Lab of Geological Processes and Mineral Resources,China University of Geosciences,Wuhan 430074,China [4]John de Laeter Centre State Key,Curtin University,Bentley 6102,Australia [5]School of Earth Sciences and Resources,China University of Geosciences,Beijing 100083,China [6]Department of Earth Science,University of Adelaide,Adelaide SA5005,Australia [7]Yunnan Geotechnical Engineering Survey and Design Institute,Kunming 650214,China [8]Yunnan Exploration Institute of Geology and Mineral Resources,Kunming 650051,China

出　　处：《Journal of Earth Science》2024年第5期1407-1425,共19页地球科学学刊（英文版）

基　　金：supported by projects from the“Xingdian Talent”Youth Talent Program in Yunnan Province(No.XDYCQNRC-2022-0041);the National Natural Science Foundation of China(Nos.42162020,41873062,92055314)。

摘　　要：In this study,we investigated Early Paleozoic magmatic rocks of the Manlai Formation exposed along the eastern margin of the Lancang terrane to better understand the tectonic history of the Proto-Tethys.We present petrological,geochemical and whole-rock Sr-Nd and zircon Hf isotopic data for basalts and gabbros sampled from the Qianmai mélange.Zircon grains from six basaltic and gabbroic samples yielded U-Pb ages of 495-482 Ma.These rocks are characterized by tholeiitic and Nbenriched compositions,with Nb/La ratios in the range of 0.38-1.38,similar to the typical Nb-enriched basalts.All the mafic rocks show slightly negative to positiveε_(Nd)(t)(-1.67 to+4.32)and zirconε_(Hf)(t)values(-7.3 to+3.8).Elemental and isotopic data suggest that the Qianmai Nb-enriched mafic rocks were mainly derived from the mixing of an OIB-like source with a subduction-modified mantle wedge source.Together with magmatic and sedimentary records of similar ages in the Lancang terrane and the Baoshan Block,our results reveal Early Paleozoic magmatic and sedimentary sequences along an active margin of the Proto-Tethys.Taking into account the recently identified Early Paleozoic ophiolitic mélange in the Yunxian-Menghai belt,we consider the Qianmai magmatic rocks to represent the products of early-stage subduction-related magmatism within a primitive island arc or fore-arc setting associated with the southward subduction of the Proto-Tethys.We infer that prolonged south-dipping subduction on the northern margin of Gondwana persisted from the Cambrian to the Late Ordovician.

关 键 词：Qianmai melange Nb-enriched basalts island arc Proto-Tethys northern margin of Gondwana SW Yunnan tectonics geochemistry 

分 类 号：P534.41[天文地球—古生物学与地层学] P588.11[天文地球—地质学] P542