滇中峨山地区中元古界昆阳群黑山头组火山岩锆石U-Pb年龄及其地质意义
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摘要
滇中玉溪—昆阳一带广泛出露的中元古界昆阳群是一套与晋宁运动密切相关的浅变质火山-沉积岩系,其形成时代、沉积充填序列及大地构造属性一直存在争议。出露于峨山县美党地区的昆阳群黑山头组富良棚段发育有厚近百米的安山质熔结凝灰岩、晶屑凝灰岩、玄武岩及岩屑凝灰岩。对样品D0121-1及D0121-2进行同位素年代学研究,分别获得LA-ICP-MS锆石U-Pb年龄加权平均值为1007±13Ma和1005±18Ma;同时,样品D0121-2中还获较多的2200±15Ma继承性锆石,推测滇中地区应存在古元古代的地质体。2件样品锆石的Th/U值均大于0.3,均具清晰的振荡环带结构,均为岩浆成因的锆石,表明黑山头组富良棚段形成于中元古代晚期,属于与造山作用相关的火山岩系,可能是罗迪尼亚超大陆事件在扬子陆块的响应,是全球格林维尔期造山过程的组成部分。
Mesoproterozoic Kunyang Group,which is widely exposed in Yuxi-Kunyang area in central Yunnan Province, consists of metamorphic volcanic sedimentary rocks that are closely related to the Jinning movement. The chronology, sedimentary filling series and geotectonic features of Kunyang Group are problems of long controversy. There are andesitic ignimbrite, crystal tuff, basalt and lithic tuff several hundred meters in thickness in Fuliangpeng member of Heishantou Formation within Kunyang Group exposed in Meidang area, Eshan County. Two samples of D0121-1 and D0121-2 were used for isotopic dating. The weighted average ages of U-Pb zircon LA-ICP-MS obtained from sample D0121-1 and D0121-2 are 1007±13 Ma and 1005±18 Ma respectively. In addition, ancient inherited zircon 2200±15 Ma was found in sample D0121-2. It is inferred that there is a Paleproterozoic geological bodyin central Yunnan Province. The Th/U ratios of zircon obtained from both samples are higher than 0.3, suggesting magmatic zircon.It is considered that Fuliangpeng member of Heishantou Formation was formed in the Late Mesoproterozoic period and belonged to the volcanic rock series related to orogeny, which was probably the response of the Rodinia Supercontinent Events in Yangtze continental block, being a part of the global Greenville orogenic process.
Mesoproterozoic Kunyang Group,which is widely exposed in Yuxi-Kunyang area in central Yunnan Province, consists of metamorphic volcanic sedimentary rocks that are closely related to the Jinning movement. The chronology, sedimentary filling series and geotectonic features of Kunyang Group are problems of long controversy. There are andesitic ignimbrite, crystal tuff, basalt and lithic tuff several hundred meters in thickness in Fuliangpeng member of Heishantou Formation within Kunyang Group exposed in Meidang area, Eshan County. Two samples of D0121-1 and D0121-2 were used for isotopic dating. The weighted average ages of U-Pb zircon LA-ICP-MS obtained from sample D0121-1 and D0121-2 are 1007±13 Ma and 1005±18 Ma respectively. In addition, ancient inherited zircon 2200±15 Ma was found in sample D0121-2. It is inferred that there is a Paleproterozoic geological bodyin central Yunnan Province. The Th/U ratios of zircon obtained from both samples are higher than 0.3, suggesting magmatic zircon.It is considered that Fuliangpeng member of Heishantou Formation was formed in the Late Mesoproterozoic period and belonged to the volcanic rock series related to orogeny, which was probably the response of the Rodinia Supercontinent Events in Yangtze continental block, being a part of the global Greenville orogenic process.
引文
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[20]高林志,尹崇玉,张恒,等.云南晋宁地区柳坝塘组凝灰岩SHRIMP锆石U-Pb年龄及其对晋宁运动的制约[J].地质通报,2015,34(9):1595-1604.
[2]李希勣,吴懋德,段锦荪.昆阳群层序及顶底问题[J].地质论评,1984,30(5):399-408.
[3]李复汉,王福星,申玉连,等.康滇地区的前震旦系[M].重庆:重庆出版社,1988:1-214.
[4]戴恒贵.康滇地区昆阳群和会理群地层、构造及找矿靶区研究[J].云南地质,1997,16(1):1-39.
[5]吕世琨,戴恒贵.康滇地区建立昆阳群(会理群)层序的回顾和重要赋矿层位的发现[J].云南地质,2001,20(1):1-24.
[6]Gill J B. Orogenic Andesites and Plate Tectonics[M]. Berlin:Springer-Verlag, 1981:1-90.
[7]牟传龙,林仕良,余谦.四川会理-会东及邻区中元古界昆阳群沉积特征及演化[J].沉积与特提斯地质,2000,20(1):44-51.
[8]周朝宪,魏春生,李朝阳.扬子地块西南缘下震旦系火成岩系研究[J].矿物学报,1998,18(4):405-41.
[9]孙传敏.川西元古代蛇绿岩与扬子板块西缘元古代造山带[J].成都理工学院学报,1994,21(4):11-18.
[10]张立生.论凤山铜矿床的再生成因[J].矿产与地质,1992,6(6):431-439.
[11]张立生.云南易门狮山铜矿床的喷气沉积成因[J].南京地质矿产研究所所刊,1989,10(4):52-71.
[12]高建国.易门铜矿三家厂矿田成矿元素特征分析[J].昆明工学院学报,1991,16(4):10-22.
[13]杜远生,张传恒,韩欣,等.滇中中元古代昆阳群的地震事件沉积及其地质意义[J].中国科学(D辑),2001,31(4):283-288.
[14]张传恒,高林志,武振杰,等.滇中昆阳群凝灰岩锆石SHRIMP U-Pb年龄华南格林威尔期造山的证据[J].科学通报,2007,52(7):818-824.
[15]孙志明,尹福光,关俊雷,等.云南东川地区昆阳群黑山组凝灰岩锆石SHRIMP U-Pb年龄及其地层学意义[J].地质通报,2009,28(7):898-900.
[16]Hu Z,Gao S,Liu Y,et al. Signal enhancement in laser ablation ICP-MS by addition of nitrogen in the central channel gas[J]. Journal of Analytical Atomic Spectrometry,2008,23(8):1093-1101.
[17]Hu Z,Liu Y,Gao S,et al. A“wire”signal smoothing device for laser ablation inductively coupled plasma mass spectrometry analysis[J].Spectrochimica Acta Part B Atomic Spectroscopy, 2012,78(78):50-57.
[18]Ludwig K R. Isoplot 3.00:A Geochronological Toolkit for Microsoft Excel[M]. Berkelery:Ber keley Geochronology Center,California 39,2003.
[19]王海然,赵红格,乔建新,等.锆石U-Pb同位素测年原理及应用[J].地质与资源,2013,22(3):229-242.
[20]高林志,尹崇玉,张恒,等.云南晋宁地区柳坝塘组凝灰岩SHRIMP锆石U-Pb年龄及其对晋宁运动的制约[J].地质通报,2015,34(9):1595-1604.
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