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| 缅甸密支那地区发现侏罗纪的SSZ型蛇绿岩 | |
| 引用本文： | 杨经绥,许志琴,段向东,李静,熊发挥,刘钊,蔡志慧,李化启.缅甸密支那地区发现侏罗纪的SSZ型蛇绿岩[J].岩石学报,2012,28(6):1710-1730. |
| 作者姓名： | 杨经绥 许志琴 段向东 李静 熊发挥 刘钊 蔡志慧 李化启 |
| 作者单位： | 1. 大陆构造与动力学国家重点实验室,中国地质科学院地质研究所,北京100037 2. 云南省地质调查院,昆明,651000 3. 中国地质大学,北京,100083 |
| 基金项目： | 本文受国家自然科学基金重点项目(40930313)、国家自然科学基金创新群体项目(40921001)、国家行业专项(SinoProbe-05-02)、中国地质调查局工作项目(1212011121263、1212011121272)和国土资源部行业基金 (200911943-07)联合资助. |
| 摘 要： | 本文报道了在缅甸的密支那地区发现的一套侏罗纪SSZ型蛇绿岩和有关的岩石单元。蛇绿岩由地幔橄榄岩、安山玄武岩、淡色辉长岩和辉长岩类、橄榄辉石岩和含长辉石岩类、以及斜长花岗岩组成。锆石的U-Pb定年获得安山玄武岩的形成年龄为166±3Ma、淡色辉长岩177±1Ma、橄榄辉石岩171±2Ma,和斜长花岗岩176±1Ma。安山玄武岩以低K2O(平均0.21%)和中TiO2(0.8%～1.2%)为特征,熔岩的球粒陨石标准化属于近平坦和LREE轻微富集型〔(La/Yb)N变化于1～1.3之间〕。微量元素MORB标准化蛛网图显示,熔岩和其他基性岩的大离子亲石元素Sr,K,Rb和Ba含量明显富集,而高场强元素Nb、Th、Ta、Zr、Ti明显亏损,为典型的SSZ构造背景成因的熔岩特征。87Sr/86Sr(i)比值为0.70367～0.70397,以及εNd(t)为正值(4～5.3),均表明它们的岩浆源区为亏损地幔源区。从空间展布看,密支那蛇绿岩与缅甸东带蛇绿岩应属同一条蛇绿岩带,与我国西藏的雅鲁藏布江缝合带相连。但不同的是,雅鲁藏布江缝合带侏罗纪时(约170Ma)为MOR型蛇绿岩,但密支那侏罗纪出现的是SSZ型蛇绿岩。两者时间如此相近,我们认为用洋内俯冲来解释较为合适。但值得注意的是,也有人将缅甸东带蛇绿岩与西藏北带的班公湖-怒江缝合带相连,并且后者在侏罗纪时也已经出现SSZ型蛇绿岩。因此,有必要进一步开展对密支那蛇绿岩构造背景的研究。 |
| 关 键 词： | 蛇绿岩 SSZ型 堆晶岩 密支那 缅甸 |
| 收稿时间： | 2012/2/10 0:00:00 |
| 修稿时间： | 5/7/2012 12:00:00 AM |
Discovery of a Jurassic SSZ ophiolite in the Myitkyina region of Myanmar |
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| YANG JingSui,XU ZhiQin,DUAN XiangDong,LI Jing,XIONG FaHui,LIU Zhao,CAI ZhiHui and LI HuaQi.Discovery of a Jurassic SSZ ophiolite in the Myitkyina region of Myanmar[J].Acta Petrologica Sinica,2012,28(6):1710-1730. | |
| Authors: | YANG JingSui XU ZhiQin DUAN XiangDong LI Jing XIONG FaHui LIU Zhao CAI ZhiHui and LI HuaQi |
| Institution: | State Key Laboratory for Continental Tectonics and Dynamics, Institute of Geology, Chinese Academy of Geological Sciences, Beijing 100037, China;State Key Laboratory for Continental Tectonics and Dynamics, Institute of Geology, Chinese Academy of Geological Sciences, Beijing 100037, China;Yunan Institute of Geological Survey, Kunming 651000, China;Yunan Institute of Geological Survey, Kunming 651000, China;State Key Laboratory for Continental Tectonics and Dynamics, Institute of Geology, Chinese Academy of Geological Sciences, Beijing 100037, China;China University of Geosciences, Beijing 100083, China;State Key Laboratory for Continental Tectonics and Dynamics, Institute of Geology, Chinese Academy of Geological Sciences, Beijing 100037, China;State Key Laboratory for Continental Tectonics and Dynamics, Institute of Geology, Chinese Academy of Geological Sciences, Beijing 100037, China |
| Abstract: | A Jurassic SSZ-type ophiolite and related rock units have been recognized in the Myitkyina region of Myanmar. The ophiolite consists of mantle peridotite,andesite-basalt,leucogabbro and gabbro,olivine pyroxenite and plagioclase-bearing pyroxenite,and plagiogranite. U-Pb dates on zircon yield ages of 166 ± 3 Ma for the andesite-basalt,177 ± 1 Ma for the leucogabbro,171 ± 2 Ma for the olivine pyroxenite,and 176 ± 1 Ma for the plagiogranite. The andesite-basalts are characterized by low K2O ( average 0. 21% ) andmedium TiO2( 0. 8% ～1. 2%) ,and have flat to slightly LREE-enriched chondrite-normalized REE patterns ( La/Yb)N= 1 ～ 1. 3].In MORB-normalized spider diagrams,the lavas are enriched in Sr,K,Rb and Ba,and depleted in Nb,Th,Ta,Zr and Ti. They have low 87Sr /86Sr( i),ranging from 0. 70367 to 0. 70397 and εNd( t) of +4 to +5. 3,indicating a depleted mantle source. However,the enrichment in LILE and depletion in Nb and Ta suggest formation in a subduction-related ( SSZ) tectonic setting,such as a forearc or backarc basin. Based on the regional geology,the Myitkyina ophiolite can be part of the East Ophiolite of Myanmar,and lies in an eastward extension of the southern Tibet Yarlung Zangbo suture zone. However,during the Jurassic the Neotethyan ophiolites along thissuture were being formed in a MOR setting,and therefore,an intra-oceanic subduction model is probably suited for the Myitkyina ophiolite. We also notice that the East Ophiolite Belt of Myanmar has been connected to the Jurassic Mesotethyan ophiolites along the Bangong-Nujiang suture of central Tibet,which were being formed in a SSZ setting. Thus,further study is needed to determine its specific tectonic setting. |
| Keywords: | Ophiolite SSZ type Cumulates Myitkyina Myanmar |
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