• 首页|本刊简介|在线投稿|过刊浏览|高级检索|专家风采|学习园地|期刊论坛|联系我们
青藏高原凯蒙蛇绿混杂岩中碱性火山岩的发现及意义
The discovery of alkaline volcanic rocks in the Kaimeng ophiolite mélange, Tibet, and its implications
投稿时间:2019-09-06  修订日期:2019-10-13
中文关键词:橄榄粗安岩  碱性火山岩  班公湖-怒江洋  凯蒙  青藏高原
英文关键词:mugearite  alkaline volcanic rocks  Bangong Co-Nujiang Ocean  Kaimeng  Tibetan Plateau
基金项目:国家自然科学基金资助项目(41672054,41972052)
作者单位E-mail
潘政 中国科学院 青藏高原研究所 大陆碰撞与高原隆升实验室, 北京 100101
中国科学院大学, 北京 100049 
 
史仁灯 中国科学院 青藏高原研究所 大陆碰撞与高原隆升实验室, 北京 100101
中国科学院 青藏高原地球科学卓越创新中心, 北京 100101 
shirendeng@itpcas.ac.cn 
黄启帅 中国科学院 青藏高原研究所 大陆碰撞与高原隆升实验室, 北京 100101  
陈生生 中国科学院 青藏高原研究所 大陆碰撞与高原隆升实验室, 北京 100101  
龚小晗 中国地质大学, 北京 100083  
吴钪 中国科学院 青藏高原研究所 大陆碰撞与高原隆升实验室, 北京 100101
中国科学院大学, 北京 100049 
 
杨可 中国地质大学, 北京 100083  
摘要点击次数: 124
全文下载次数: 118
中文摘要:
      班公湖-怒江洋的关闭时间直接制约青藏高原早期构造演化的认识。最近,在班公湖-怒江缝合带南侧凯蒙蛇绿混杂岩中发现一碱性火山岩,岩性主要是橄榄粗安岩,具粗面结构,斑晶主要是更长石和少量普通辉石,基质主要由更长石、普通辉石和少量填隙的碱性长石组成,有的具辉绿结构。岩石化学成分较一致,SiO2含量介于51.34%~53.91%之间,TiO2含量为1.02%~1.55%,具有高Al2O3(17.06%~18.46%)和Na2O (4.90%~6.36%)、低K2O (0.05%~0.88%)含量特点,大多数Mg#大于60,最高68.62,里特曼指数(σ)介于3.65~4.47之间,为碱性系列火山岩;富集Sr、Rb、Ba等大离子亲石元素,亏损Nb、Y、Yb等高场强元素,相对富集Zr、Ti,Nb/U、Zr/Nb、La/Yb等比值稳定,分别为7.45~8.51、15.92~17.26和7.26~8.06;(87Sr/86Sr)i值变化范围较小,介于0.706~0.707之间,(143Nd/144Nd)t值在0.512 368~0.512 548之间,说明源区较为一致,结合Ce/Pb-SiO2图解判断结果,认为凯蒙碱性火山岩具有原始地幔、陆壳和深海沉积物源区混合特征。锆石U-Pb同位素定年结果表明该火山岩年龄为101.8±1.1 Ma,可能形成于洋壳俯冲阶段末期,由大陆边缘陆壳与俯冲洋壳板片断离导致软流圈地幔上涌诱发部分熔融所致,推测班公湖-怒江洋大约在早白垩世晚期关闭。
英文摘要:
      The closure time of the Bangong Co-Nujiang Tethys Ocean (BNTO) between Lhasa terrane and Qiangtang terrane directly constrains the early tectonic evolution of the Tibetan Plateau. Recently, alkaline volcanic rocks have been recognized from the Kaimeng ophiolitic mélange, a southern sector of Bangong Co-Nujiang suture zone. These rocks are mainly fresh mugearite with trachytic structure. The phenocrysts are mainly oligoclase with minor augite, and the groundmass is mainly composed of oligoclase, pyroxene and trace alkaline feldspar filling other minerals. The chemical compositions of the mugearite are fairly uniform, with the abundances of SiO2 and TiO2 ranging from 51.34% to 53.91% and from 1.02% to 1.55%, respectively, suggesting alkaline series volcanic rocks with high Na2O content (4.90%~6.36%), low K2O content (0.05%~0.88%) and intermediat Rittman index (σ=3.65~4.47). The most of Mg# values are higher than 60, even up to 68.62. The trace elements of the mugearite are characterized by relative enrichment of large ion lithophile elements (LILE) Sr, Rb, Ba, Th and U and depletion of high field strength elements (HFSE), with negative Nb and Ta anomalies. The stable Nb/U, Zr/Nb and La/Yb ratios (7.45~8.51, 15.92~17.26 and 7.26~8.06, respectively), the initial 87Sr/86Sr ratios(0.706~0.707)and the (143Nd/144Nd)t ratios (0.512 368~0.512 548) as well as the Ce/Pb-SiO2 diagram suggest that the source of the mugearite was probably mixed primitive mantle (PM) and lower continental crust and abyssal sediments. The zircon U-Pb isotopic dating shows that the age of the mugearite is 101.8±1.1 Ma, indicating that it was likely produced by the partial melting of asthenospheric mantle upwelled by the slab break-off at the end of oceanic crust subduction, which implies that the BNTO was closed at the late stage of early Cretaceous period.
潘政,史仁灯,黄启帅,陈生生,龚小晗,吴钪,杨可,2020,青藏高原凯蒙蛇绿混杂岩中碱性火山岩的发现及意义[J].岩石矿物学杂志,(1):18~34.
查看全文  查看/发表评论  下载PDF阅读器
关闭
您是本站第 6658885位访问者  京ICP备05032737号-8
版权所有:《岩石矿物学杂志》编辑部
主管:中国科学技术协会 主办:中国地质学会岩石学专业委员会 中国地质学会矿物学专业委员会 中国地质科学院地质研究所
技术支持:北京勤云科技发展有限公司

京公网安备 11010202007772号