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
投稿时间:2024-03-19  修订日期:2024-05-07  点此下载全文
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作者单位邮编
吴嘉林 云南省地质调查院
自然资源部三江成矿作用及资源勘查利用重点实验室
云南大学地球科学学院 
650216
浦涛 云南省地质调查院
自然资源部三江成矿作用及资源勘查利用重点实验室 
柏杨 四川省第十二地质大队 
刘军平* 云南省地质调查院
自然资源部三江成矿作用及资源勘查利用重点实验室
中国地质大学地球科学与资源学院 
何世军 中国冶金地质总局第二地质勘查院 
李序贵 云南省地质调查院
自然资源部三江成矿作用及资源勘查利用重点实验室 
何兆荣 云南省地质调查院 
中文摘要:通过1:5万区域地质调查及典型剖面研究,在滇西陇川地区高黎贡山岩群中识别出一套角闪斜长变粒岩夹二长浅粒岩的岩石组合,其原岩恢复分别为玄武安山岩和流纹岩,为典型的双峰式火山岩组合。对其进行年代学研究,分别获得486±4.5Ma和486.6±4.2Ma的锆石U-Pb年龄,喷发时代为早奥陶世。角闪斜长变粒岩具全碱含量低(alk=2.75%~4.58%)、富钠(Na2O/K2O=2.32~4.79)、低钛(TiO2=0.70~1.12)的特点,稀土配分曲线显示具MORB稀土地球化学特征,相对富集大离子亲石元素Rb、Ba、Th、K、Nd和轻稀土元素,相对亏损Nb、Sr、P、Ti,Sr-Nd-Pb同位素特征显示角闪斜长变粒岩具有EMII地幔特征,在La-La/Nb图解中具有岛弧玄武岩特征,地球化学和同位素特征表明角闪斜长变粒岩(安山玄武岩)是由洋壳俯冲析出流体交代的富集地幔楔部分熔融形成。二长浅粒岩具有全碱含量中等(alk=6.09%~7.59%)、富钾(Na2O/ K2O=0.4~0.9)、低钛(TiO2=0.10~0.21)的特点,稀土配分曲线为右倾型,相对富集大离子亲石元素Rb、Th、K、Nd和轻稀土元素,强烈亏损Sr、P、Ti,轻微亏损Ba、U、Nb、Ta,类似于岛弧花岗岩特征,在Rb/30-Hf-3Ta图解中具有火山弧特征,地球化学特征表明,二长浅粒岩(流纹岩)是由来源于地幔的玄武质岩浆侵入下地壳,为下地壳提供足够热量使其部分熔融形成。综合研究认为本次发现的双峰式火山岩组合形成的构造背景为活动大陆边缘,是由原特提斯洋向冈瓦纳大陆北缘俯冲的产物。
中文关键词:双峰式火山岩  早古生代  地球化学  Sr-Nd-Pb同位素  陇川地区  原特提斯洋
 
Chronology and Geochemistry Characteristics of Early Paleozoic bimodal volcanic rocks in Longchuan aera,western Yunnan Province and its Significance to the Proto-Thehyan Ocean subduction
Abstract:Through 1∶50000 regional Geological survey and typical section study, a set of hornblende plagioclase ganulite and monzonite leptite has been identified from Gaoligongshan Group in Longchuan aera,western Yunnan Province. The protolith of hornblende plagioclase ganulite was basaltic andesite and that of monzonite leptite was rhyolite, composed of bimodal volcanic rocks.The zircon U-Pb ages of hornblende plagioclase ganulite and monzonite leptite were obtained to be 486±4.5Ma and 486.6±4.2Ma respectively by LA-ICP-MS zircon U-Pb dating, indicating that the rocks formed in early ordovician. The SiO2 content of the hornblende plagioclase ganulite is between49.98% and 52.99%,alk=2.75%~4.58%,Na2O/K2O=2.32~4.79,TiO2=0.70~1.12,with the characteristics of low alkali,high potassium,low titanium. Chondrite-normalized REE patterns of hornblende plagioclase ganulite like MORB. The trace elements were enriched in large ion lithophile elements(Rb、Th、K、Nd)and light rare earth elements ,while depletd in Nb、Sr、P、Ti. The Sr-Nd-Pb isotopic characteristics of hornblende plagioclase ganulite indicate that the rocks was orginated from EMⅡ mantle, hornblende plagioclase ganulite(basaltic andesite)is product of ocean crust subduction. The La-La/Nb diagram indicate hornblende plagioclase ganulite has geochemical features of island-arc basalts. The SiO2 content of the monzonite leptite is between76.74% and 77.61%,alk=6.09%~7.59%,Na2O/K2O=0.4~0.9,TiO2=0.10-0.21,with the characteristics of medium alkali,high natrium,low titanium. Chondrite-normalized REE patterns of the monzonite leptite are inclined to right, the trace elements were enriched in large ion lithophile elements(Rb、Th、K、Nd)and light rare earth elements , heavily depletd in Sr、P、Ti, slightly depletd in Ba、U、Nb、Ta, similar to the characteristics of island-arc granite. The Rb/30-Hf-3Ta diagram indicate the monzonite leptite has geochemical features of island-arc granite. The monzonite leptite (rhyolite) is formed by the intrusion of basic magma into the lower crust, providing sufficient heat to partially melt it.Geochemistry characteristics indicate that the tectonic setting of bimodal volcanic rocks in Longchuan aera is active continental margin, the bimodal volcanic rocks were products of Proto-Tethyan ocean crust subduction to the northern margin of Gondwana.
keywords:Bimodal volcanic rock  Early Paleozoic  Geochemistry  Sr-Nd-Pb isotopic  Longchuan aera  Proto-Tethyan
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