地球学报2024，Vol.45Issue(4)：450-464,15.DOI:10.3975/cagsb.2024.051701
滇西陇川地区早古生代火山岩年代学、地球化学特征及其对原特提斯洋俯冲的指示
Chronology and Geochemical Characteristics of the Early Paleozoic Volcanic Rocks in Longchuan Area,Western Yunnan Province,and Their Significance to the Proto-Thehyan Ocean Subduction
摘要
Abstract
To explore the structural evolution characteristics of the Proto-Tethyan in western Yunnan,we selected a rock combination consisting of hornblende plagioclase granulite and monzonite leptite,identified from the Gaoligongshan Group in the Longchuan area of western Yunnan,for research.The protolith of the hornblende plagioclase granulite was basaltic andesite,while that of the monzonite leptite was rhyolite.Using LA-ICP-MS zircon U-Pb dating,we determined the zircon U-Pb ages of the hornblende plagioclase granulite and monzonite leptite to be(486.8±4.5)Ma and(486.6±4.2)Ma,respectively,indicating that the rocks formed in the early Ordovician period.The hornblende plagioclase granulite exhibits characteristics of low alkali(alk=2.75%-4.58%),high potassium(Na2O/K2O=2.32-4.79),and low titanium(TiO2=0.70%-1.12%).Chondrite-normalized REE patterns of the hornblende plagioclase granulite resemble those of MORB.Trace elements show enrichment in Rb,Th,K,Nd,and light rare earth elements,and depletion in Nb,Sr,P,and Ti.Sr-Nd-Pb isotopic characteristics indicate that the rocks originated from EMⅡ mantle,suggesting that hornblende plagioclase granulite(basaltic andesite)is a product of ocean crust subduction.The La-La/Nb diagram suggests that the hornblende plagioclase granulite exhibits geochemical features of island-arc basalts.The monzonite leptite has the characteristics of medium alkali(alk=6.09%-7.59%),high natrium(Na2O/K2O=0.4-0.9),and low titanium(TiO2=0.10%-0.21%).Chondrite-normalized REE patterns are inclined to the right.Trace elements show enrichment in Rb,Th,K,Nd,and light rare earth elements,heavy depletion in Sr,P,and Ti,and low depletion in Ba,U,Nb,and Ta,similar to the characteristics of island-arc granite.The Rb/30-Hf-3Ta diagram indicates that the monzonite leptite exhibits geochemical features of island-arc granite.The monzonite leptite(rhyolite)is formed by the intrusion of basic magma into the crust,providing sufficient heat to partially melt it.Geochemical characteristics indicate that the tectonic setting of the Early Paleozoic volcanic rocks in Longchuan area was an active continental margin.Early Paleozoic volcanic rocks were products of Proto-Tethyan ocean crust subduction to the northern margin of Gondwana.关键词
早古生代火山岩/地球化学/Sr-Nd-Pb同位素/陇川地区/原特提斯洋Key words
Early Paleozoic volcanic rock/geochemistry/Sr-Nd-Pb isotopic/Longchuan area/Proto-Tethyan分类
天文与地球科学引用本文复制引用
吴嘉林,浦涛,柏杨,刘军平,何世军,李序贵,何兆荣..滇西陇川地区早古生代火山岩年代学、地球化学特征及其对原特提斯洋俯冲的指示[J].地球学报,2024,45(4):450-464,15.基金项目
本文由云南省科技计划项目(编号:202305AD160031 （）
202401AT070012)、云南省自然资源厅基金项目"云南省 1:5 万铜壁关幅弄璋街幅芒东幅平山幅陇川幅清平街幅区域地质调查"(编号:D2017015)和"云南省 1:5 万驾车湾幅菱角塘幅功山幅寻甸县幅区域地质调查"(编号:SJ[2024]QD002)联合资助. This paper was supported by Science and Tech-nology Plan Project of Yunnan Province(Nos.202305AD160031 and 202401AT070012),and Department of Natural Resources of Yunnan Province(Nos.D2017015 and SJ[2024]QD002). （编号:D2017015）
