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赵枫,李龚健,张鹏飞,王传斌,孙载波,唐鑫. 2018. 西南三江临沧花岗岩基成因与构造启示:元素地球化学、锆石U-Pb年代学及Hf同位素约束. 岩石学报, 34(5): 1397-1412
西南三江临沧花岗岩基成因与构造启示:元素地球化学、锆石U-Pb年代学及Hf同位素约束
作者单位
赵枫 中国地质大学地质过程与矿产资源国家重点实验室, 北京 100083 
李龚健 中国地质大学地质过程与矿产资源国家重点实验室, 北京 100083 
张鹏飞 中国地质大学地质过程与矿产资源国家重点实验室, 北京 100083 
王传斌 中国地质大学地质过程与矿产资源国家重点实验室, 北京 100083 
孙载波 云南省地质调查院, 昆明 650216 
唐鑫 中国地质大学地质过程与矿产资源国家重点实验室, 北京 100083 
基金项目:本文受国家重点基础研究发展计划"973"项目(2015CB452606)、国家重点研发计划(2016YFC0600307)和国家自然科学青年基金项目(41602090)联合资助.
摘要:
      昌宁-孟连缝合带系中国西南三江特提斯造山带一条重要的古特提斯主洋残余,在洋盆消减过程中发生了强烈岩浆作用,形成了以临沧花岗岩基为代表的平行缝合带的大规模物质-热活动产物。其为理解古特提斯洋俯冲和闭合过程提供了良好窗口。本文对出露于临沧岩基中部临沧地区的花岗岩类进行了全岩元素地球化学、锆石U-Pb年代学和Hf同位素组成研究。实验样品锆石206Pb/238U加权年龄为215.5±0.4Ma(MSWD=2.8,n=23),反映岩浆岩侵位于晚三叠世。花岗岩主要属于高钾钙碱性系列,岩性为花岗闪长岩和二长花岗岩,高铝饱和指数(A/CNK=1.09~1.17)和刚玉分子数(>1%)显示了过铝质特征。样品富集轻稀土元素(LREE/HREE=6.29~17.01,(La/Yb)N=6.36~33.5)和大离子亲石元素,亏损Nb、Ta等高场强元素。锆石Hf同位素分布集中,εHft)均为负值(-15.9~-9.08),Hf地壳模式年龄较老(1.6~1.9Ga),全岩Zr饱和温度(734~779℃)较低,指示了临沧花岗岩主体系古老地壳基底部分熔融产物,无明显地幔物质加入。S型花岗岩源区包括泥质岩和硬砂质岩两种,本文研究临沧花岗岩源区主要为硬砂质岩。明显Eu负异常(δEu=0.19~0.58)和较低分异指数(DI=73~82),反映源区存在斜长石和角闪石等的残留。文章进一步总结并分析了前人岩石地球化学和同位素数据,结果表明临沧岩基花岗岩类岩石成因类型复杂多变。由晚二叠世到晚三叠世(260~200Ma),古特提斯洋由俯冲到闭合过程中,依次演化发育S型、I型和A型多种类型花岗岩。综合临沧岩基两侧与之平行的高压变质岩类和双峰式火山岩地质特征,认为临沧花岗岩类主体形成于古特提斯洋同碰撞造山(250~237Ma)和后碰撞伸展(235~203Ma)两种构造环境,早期存在少量与洋盆俯冲作用相关的岩浆岩(~252Ma)。
英文摘要:
      The Changning-Menglian suture zone locating in the Sanjiang orogenic belt of SW China has widely been accepted as a vital remnant of the main Paleo-Tethys. Abundant magmatic rocks were induced by the oceanic subdution and closure. The most spectacular result was indicated by the gaint N-S trending Lincang granitic pluton exposed alongside the eastern margin of the suture, which provided us good oppotunity for understanding the tectonic evolution of the Paleo-Tethys. In this paper, the whole rock element geochemistry, zircon U-Pb chronology and Hf isotopic compositions were studied in the granites that were exposed in the Lincang area in the central part of Lincang rock basement. The zircon 206Pb/238U weighted average age of the experimental samples is 215.5±0.4Ma (MSWD=2.8, n=23), indicating that the magmatic rocks intruded in the Late Triassic. Granites belong to the high-K calc-alkaline series with lithology of granodiorite and monzogranite. The high aluminum saturation index (A/CNK=1.09~1.17) and the number of corundum molecules (>1%) with aluminum feature. Samples were enriched in light rare earth elements (LREE/HREE=6.29~17.01, (La/Yb)N=6.36~33.5), large ion lithophile and depleted Nb, Ta and other high field strength elements. The Hf isotopes of zircons are concentrated, the values of εHf(t) are negative (-15.9~-9.08), Hf crustal age is older (1.6~1.9Ga), the whole rock Zr saturation temperature (734~779℃) indicated part of Lincang granite main crust base melting products, no significant mantle material added. S-type granite source area includes two types of meta-pelite and meta-greywacke, the study of Lincang granite source area is mainly meta-greywacke. Significant Eu negative anomalies (δEu=0.19~0.58) and lower dissimilarity index (DI=73~82), indicating the presence of plagioclase and hornblende residues in the source area. The paper further summarizes and analyzes the geochemistry and isotope data of the predecessors. The results show that the genetic types of the granites in the Lincang rock basement are complex and changeable. From Late Permian to Late Triassic (260~200Ma), the paleo-Tethys Ocean evolves successively from subduction to closure, and successively evolves various types of granites such as S-type, I-type and A-type. Based on the geological features of high-pressure metamorphic rocks and bimodal volcanic rocks parallel to the two sides of Lincang rock basement, it is considered that the main body of Lincang granite was formed in the syn-orogenic collision (250~237Ma) and post-orogenic collision (235~203Ma), there were also a few magmatic rocks (~252Ma) associated with subduction of oceanic basins in the early stage.
关键词:临沧花岗岩  古特提斯洋  岩石和地球化学特征  后碰撞
投稿时间:2017-12-08  修订日期:2018-03-30
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主办单位:中国矿物岩石地球化学学会
印刷版(Print): ISSN 1000-0569 网络版(Online): ISSN 2095-8927
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