| 青藏高原凯蒙蛇绿混杂岩中碱性火山岩的发现及意义 |
| |
| 引用本文： | 潘政,史仁灯,黄启帅,陈生生,龚小晗,吴钪,杨可.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,2020,39(1):18-34. |
| |
| 作者姓名： | 潘政 史仁灯 黄启帅 陈生生 龚小晗 吴钪 杨可 |
| |
| 作者单位： | 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,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,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 青藏高原研究所 大陆碰撞与高原隆升实验室, 北京 100101,中国地质大学, 北京 100083,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,中国地质大学, 北京 100083 |
| |
| 基金项目： | 国家自然科学基金资助项目（41672054，41972052） |
| |
| 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,Si O2含量介于51.34%~53.91%之间,Ti O2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-Si O2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。
|
| 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 |
| 收稿时间： | 2019/9/6 0:00:00 |
| 修稿时间： | 2019/10/13 0:00:00 |
The discovery of alkaline volcanic rocks in the Kaimeng ophiolite mélange, Tibet, and its implications |
| |
| PAN Zheng,SHI Ren-deng,HUANG Qi-shuai,CHEN Sheng-sheng,GONG Xiao-han,WU Kang and YANG Ke.The discovery of alkaline volcanic rocks in the Kaimeng ophiolite mélange, Tibet, and its implications[J].Acta Petrologica Et Mineralogica,2020,39(1):18-34. |
| |
| Authors: | PAN Zheng SHI Ren-deng HUANG Qi-shuai CHEN Sheng-sheng GONG Xiao-han WU Kang and YANG Ke |
| |
| Institution: | Key Laboratory of Continental Collision and Plateau Uplift, Institute of Tibetan Plateau Research, Chinese Academy of Sciences, Beijing 100101, China;University of Chinese Academy of Sciences, Beijing 100049, China,Key Laboratory of Continental Collision and Plateau Uplift, Institute of Tibetan Plateau Research, Chinese Academy of Sciences, Beijing 100101, China;GAS Center for Excellence in Tibetan Plateau Earth Sciences, Beijing 100101,Key Laboratory of Continental Collision and Plateau Uplift, Institute of Tibetan Plateau Research, Chinese Academy of Sciences, Beijing 100101, China,Key Laboratory of Continental Collision and Plateau Uplift, Institute of Tibetan Plateau Research, Chinese Academy of Sciences, Beijing 100101, China,China University of Geosciences, Beijing 100083, China,Key Laboratory of Continental Collision and Plateau Uplift, Institute of Tibetan Plateau Research, Chinese Academy of Sciences, Beijing 100101, China;University of Chinese Academy of Sciences, Beijing 100049, China and China University of Geosciences, Beijing 100083, China |
| |
| Abstract: | 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. |
| |
| Keywords: | mugearite alkaline volcanic rocks Bangong Co-Nujiang Ocean Kaimeng Tibetan Plateau |
| 本文献已被 CNKI 维普 等数据库收录！ |
| 点击此处可从《岩石矿物学杂志》浏览原始摘要信息 |
| 点击此处可从《岩石矿物学杂志》下载免费的PDF全文 |
|
