滇西云龙县漕涧地区中三叠世流纹岩的厘定及其对古特斯构造体制转化的约束  

Determination of Middle Triassic rhyolite in Caojian area,Yunlong County of western Yunnan,and its constraints on the Paleo-Tethys tectonic system transition

作　　者：熊波 黄亮 王晓林 朱勋早 王晓峰 浦涛 宋冬虎 方雄 杨仕潘 XIONG Bo;HUANG Liang;WANG Xiaolin;ZHU Xunzao;WANG Xiaofeng;PU Tao;SONG Donghu;FANG Xiong;YANG Shipan(Yunnan Institute of Geological Survey,Kunming 650216,Yunnan,China;MNR Key Laboratory of Sanjiang Metallogeny and Resources Exploration and Utilization,Kunming 650051,Yunnan,China)

机构地区：[1]云南省地质调查院,云南昆明650216 [2]自然资源部三江成矿作用及资源勘查利用重点实验室,云南昆明650051

出　　处：《地质通报》2021年第7期1094-1105,共12页Geological Bulletin of China

基　　金：中国地质调查局项目《全国陆域及海区地质图件更新与共享》子项目《云南省系列地质图件数据处理与洋板块地质研究》(编号:DD20190370)、《云南1∶5万归州、宝丰、漕涧、功果街幅区域地质调查》(编号:1212010000150007-26)、《云南省1∶5万撒马基幅因民幅贵城幅舒姑幅4幅区域地质调查》(编号:D201905)

摘　　要：1∶5万区域地质调查表明,在滇西澜沧江断裂带与保山地块之间断续出露一套中-晚三叠世中酸性-酸性火山岩、火山碎屑岩、火山-沉积岩,主要出露于云南云龙县漕涧、昌宁县珠山、凤庆县大四甲、双江县勐库、勐海县曼养等地,属弧间盆地内的火山-沉积岩系。对云龙县漕涧一带出露的流纹岩进行了地球化学和锆石U-Pb测年。结果表明,其A/CNK=1.05~2.44,为一套过铝质的高钾钙碱性-钾玄岩系列,LA-ICP-MS锆石U-Pb年龄为235.8±4.9 Ma、235.2±5.6 Ma,属中三叠世。在地球化学特征上,该套火山岩以显著富集Nb、Ta、Th、Zr、Hf、Y等高场强元素(HFSE),亏损Sr、Ba等大离子亲石元素及P、Ti等高场强元素为特征,属中-上部地壳变质沉积岩低压角闪岩相条件下的低程度部分熔融物,是碰撞造山作用结束后,区域性地壳松弛过程中,深部地幔物质上涌引起的加热增温与隆升减压熔融联合作用的结果。往南至凤庆县、双江县等地,该套火山岩逐渐向准铝质-过铝质的高钾钙碱性-钙碱性系列过渡;微量元素蛛网图显示明显的"T-N-T"的负异常,指示在隆升减压条件下,受俯冲流体交代的中-下地壳物质在高压角闪岩相-麻粒岩相条件下发生了较高程度的部分熔融作用。这套三叠纪火山岩虽然在岩浆源区、部分熔融程度、岩浆形成的温-压条件等方面存在差异,但都是古特提斯洋关闭后,大洋构造体制向大陆构造体制转化的深部过程在地表的反映。In recent years,1∶50 000 regional geological survey reveals that a set of intermediate-acid and acid volcanic rocks,pyroclastic rocks and volcanic-sedimentary rocks of the Middle-Late Triassic are intermittently outcropped between the Lancang River fault in western Yunnan and Baoshan block.They are mainly outcropped in Caojian,Yunlong County,Zhushan,Changning County,Dasijia,Fengqing County,Mengku,Shuangjiang County,Manyan,Menghai County and other places,belonging to the volcanic-sedimentary rock series in the interarc basin.The study focuses on the rhyolite outcropped in Caojian of Yunlong County.Its A/CNK value of 1.05-2.44 indicates a peraluminous high-potassium calc-alkaline-potassic series.The zircon LA-ICP-MS U-Pb ages of 235.8±4.9 Ma and 235.2±5. 6 Ma implies Middle Triassic. This set of volcanic rocks is chemically characterized by significant enrichment of high field strength elements such as Nb,Ta,Th,Zr,Hf and Y,depletion of large ionic elements such as Sr and Ba,and high field strength elements such as P and Ti.It is a low-grade partial melt under the condition of low-pressure amphibolite facies of metamorphic sedimentary rocks in the middle-upper crust.It is the result of the combined heating,warming,uplifting,decompression and melting caused by upwelling of deep mantle materials in the process of regional crustal relaxation after collision orogeny.Southward to Fengqing County,Shuangjiang County and other places,this set of volcanic rocks gradually transit to a quasi-aluminum-peraluminous series of high potassium calcalkaline-calc-alkaline.The cobweb diagram of trace element ratio shows obvious negative anomaly of "T-N-T",which indicates a high degree of partial melting under the conditions of high-pressure amphibolite facies-granulite facies of the middle-lower crust metasomatized by subduction fluid under the conditions of uplift and decompression.Although there are some differences in magma source,partial melting degree and temperature-pressure conditions for magma formation, these Triassic volc

关 键 词：中三叠世流纹岩 隆升减压熔融 弧间盆地 构造体制转换 滇西 

分 类 号：P534.42[天文地球—古生物学与地层学] P588.121[天文地球—地质学]