|
|||||
|
|
| 哀牢山构造岩浆带晚二叠世-早三叠世火山岩特征及其构造环境 | |
| 引用本文： | 刘翠,邓晋福,刘俊来,石耀霖.哀牢山构造岩浆带晚二叠世-早三叠世火山岩特征及其构造环境[J].岩石学报,2011,27(12):3590-3602. |
| 作者姓名： | 刘翠 邓晋福 刘俊来 石耀霖 |
| 作者单位： | 1. 中国科学院研究生院,北京100049;中国地质大学,北京100083 2. 中国地质大学,北京,100083 3. 中国科学院研究生院,北京,100049 |
| 基金项目： | 本文受国家自然科学青年基金项目(40802020)、中国地质调查局项目(1212010661311、1212011121075、1212010911028)和973专题 (2009CB421002、2009CB421008)联合资助. |
| 摘 要： | 本文对中国云南哀牢山构造岩浆带内的雅轩桥、帽盒山、绿春火山岩等开展了相关研究.雅轩桥附近的火山岩为晚二叠世,岩性主要为橄榄粗安岩-玄武岩(少量安山岩),在TAS图上既有碱性又有亚碱性.钾含量较低(＜1.19％),为低钾钙碱-中钾钙碱性,Peacock碱钙指数以钙碱性为主.与MORB相比,其痕量元素蛛网图亏损Nb、Ta,而富集Pb,从Zr-V曲线呈平坦型,并且整体比MORB亏损.稀土元素配分模式与MORB相近,但略显轻稀土元素富集和重稀土元素亏损.在构造环境判别图上均位于火山弧环境.他郎河边(雅轩桥地区)火山岩为英安岩,属亚碱性,中钾钙碱性,Peacock指数为钙性.痕量元素蛛网图、REE模式图以及大地构造环境判别图,均表明其属于弧的构造环境.由上推测雅轩桥火山岩在晚二叠世属于弧火山岩.帽盒山玄武岩的锆石SHRIMP U-Pb测年结果为249±1.6Ma,为早三叠世.岩性为亚碱性钠长玄武岩,低钾钙碱性系列,Peacock碱钙指数以钙性为主.痕量元素蛛网图和REE配分模式图与MORB相比,LREE略微富集.在构造环境判别图中位于从E-MORB向岛弧过渡的构造环境.绿春地区流纹岩的锆石SHRIMP U-Pb年龄为247.3±1.8Ma,为早三叠世,属亚碱性,钾玄岩系列,Peacock碱钙指数为碱钙性.痕量元素蛛网图、REE配分模式图及大地构造环境判别图显示其为成熟岛弧向陆陆碰撞的过渡环境.结合前人研究,推测哀牢山洋在晚泥盆世形成,可能在石炭世-早二叠世(?)处于洋的扩张期.晚二叠世时,在哀牢山洋的西侧出现了雅轩桥的初始孤火山岩,预示着至少在这一时期,哀牢山洋已经开始俯冲.到三叠世早期(249±1.6Ma),在哀牢山洋的东侧出现了具有弧和MORB的双重特性的帽盒山玄武岩,可能指示此时哀牢山洋盆已经变小,或已转化为孤间或弧后盆地,洋的演化进入了晚期阶段,并且在局部地段,如绿春地区,此时(247.3±1.8Ma)已经进入到成熟岛弧向陆陆碰撞的过渡阶段.因此支持哀牢山洋在晚三叠世闭合的结论,亦符合上三叠统一碗水组不整合在哀牢山蛇绿混杂岩之上的事实. |
| 关 键 词： | 雅轩桥-帽盒山-绿春火山岩 锆石SHRIMP U-Pb定年 晚二叠世-早三叠世 构造环境 哀牢山构造岩浆带 |
| 收稿时间： | 2011/5/31 0:00:00 |
| 修稿时间： | 2011/8/23 0:00:00 |
Characteristics of volcanic rocks from Late Permian to Early Traissic in Ailaoshan tectono-magmatic belt and implications for tectonic settings |
|
| LIU Cui,DENG JinFu,LIU JunLai and SHI YaoLin.Characteristics of volcanic rocks from Late Permian to Early Traissic in Ailaoshan tectono-magmatic belt and implications for tectonic settings[J].Acta Petrologica Sinica,2011,27(12):3590-3602. | |
| Authors: | LIU Cui DENG JinFu LIU JunLai and SHI YaoLin |
| Institution: | Graduate University of Chinese Academy of Sciences, Beijing 100049, China;China University of Geosciences, Beijing 100083, China;China University of Geosciences, Beijing 100083, China;China University of Geosciences, Beijing 100083, China;Graduate University of Chinese Academy of Sciences, Beijing 100049, China |
| Abstract: | This paper studies the volcanic rocks of Yaxuanqiao, Maoheshan and Lvchun in Ailaoshan tectono-magmatic belt, Yunnan Province, SW China. Yaxuanqiao volcanic rocks mainly composed of Mugearite-basalts with minor andesites formed in Late Permian. In TAS diagram, they are plotted in both alkaline and sub-alkaline areas. These rocks are low-in K2O (<1.19%) and belong to low-potassic to middle-potassic calc-alkaline series. They are mainly calc-alkaline in terms of Peacock's index. Their spider diagrams of trace elements show enrichment in Pb and depletion in Nb and Ta. The trace element spider diagrams from Zr to V are flat and overall lower compared with those of MORB. The REE patterns are similar to those of MORB, but slightly enriched in LREE and depleted in HREE. These rocks are all plotted in arc settings in tectonic discrimination diagrams. The volcanic rocks in Talanghebian of Yaxuanqiao area are sub-alkaline dacites and belong to middle-potassic calc-alkaline series. Besides, it is mainly calsic in terms of Peacock's index. The features of spider diagrams of trace elements, REE distribution pattern and tectonic discrimination diagrams indicate that they formed in an arc tectonic setting. Thus it is suggested that Yaxuanqiao igneous rocks belong to arc-type igneous rocks in Late Permian. Zircon SHRIMP U-Pb dating of Maoheshan basalt gave an age of 249±1.6Ma, i.e., Early Triassic. These rocks are sub-alkaline albite basalts, belonging to low-potassic calc-alkaline series. It is mainly calsic in terms of Peacock's index. Compared with MORB, the trace element spider diagrams and REE patterns show slightly enriched in LREE. In the diagrams for discrimination of tectonic settings, they are plotted in the transition area from E-MORB to island-arc. Zircon SHRIMP U-Pb dating of Lvchun rhyolite yielded an age of 247.3±1.8Ma, i.e., Early Traissic. Rhyolites are sub-alkaline, shoshonite series. It is alkaline-calsic in terms of Peacock's index. Trace elements spider diagrams, REE patterns and plots of tectonic setting discrimination all indicate the Lvchun rhyolites occur in a transition setting from matured arc to continent-continent collision. Combined with previous studies, the paper suggests that Ailaoshan Ocean had opened since Late Devonian and probably been spreading between Carboniferous and Early Permian(?). But in Late Permian the Ailaoshan ocean had begun to subduct to form initial arc of Yaxuanqiao to the west of the Ailaoshan. In Early Triassic (249±1.6Ma), Maoheshan basalts, characterized by both arc and MORB, formed as a part of Ailaoshan ophiolites. It may suggest that the Ailaoshan ocean basin had been shrunk, or converted to intra-arc or back-arc basins of supra-subduction zones. Thus the evolution of the Ailaoshan ocean went into the late stage, and in some area, such as Lvchun area, it became a transitional setting from matured arc to continent-continent collision (247.3±1.8Ma). All those mentioned above support the conclusion that the Ailaoshan ocean had closed in Late Triassic, which also coincides with the fact that Yiwanshui Group of Late Triassic unconformably overlied the Ailaoshan Shuanggou ophiolites. |
| Keywords: | Volcanic rocks of Yaxuanqiao Maoheshan and Lvchun SHRIMP U-Pb dating of zircon Late Permian-Early Triassic Tectonic setting Ailaoshan tectono-magmatic belt |
| 本文献已被 CNKI 万方数据 等数据库收录！ | |
| 点击此处可从《岩石学报》浏览原始摘要信息 | |
| 点击此处可从《岩石学报》下载免费的PDF全文 | |