扬子西缘会理地区通安组角闪岩锆石U-Pb定年及其地质意义
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摘要
在会理地区进行前寒武纪地质调查过程中,于会理县通安镇皎平渡一带发现通安组片岩中分布少量高绿片岩相-角闪岩相岩石组合,其中典型的岩石类型为角闪岩,经过室内薄片鉴定和利用地球化学进行原岩恢复,角闪岩原岩为基性火山岩(玄武质岩)。研究采用LA-ICP-MS方法,对角闪岩进行锆石微区U-Pb同位素测年,获得了1 720Ma±7Ma(MSWD=0.47,N=23)的原岩成岩年龄。结合通安组的年龄资料和区域大地构造演化背景,认为1 720Ma±7Ma代表了通安组早期年龄,限定了通安组一段顶部的沉积时限,而以角闪岩为代表的这套变基性火山岩形成于古元古代晚期古老基底扩展环境,是全球哥伦比亚超大陆裂解事件在扬子西缘的地质记录。
During the process of the Precambrian geological survey in Huili area,high greenschist-amphibolite facies rocks with the typical rock of amphibolite has been found in Jiaopingdu region.The identification and original rock recovery revealed that the original rock of amphibolite belong the metamorphosed mafic volcanic rocks.U-Pb isotope of zircons from amphibolite are determined by the LA-ICP-MS method,and yielded a concordia age of 1 720Ma±7Ma(MSWD=0.47,N=23).It represents the age of the lower part of Tongan Formation and implied that the mafic volcanic rocks formed in the continental extension environment at the late Paleoproterozoic of the ancient basement.Also,it reflects the breakup event of Columbia supercontinent in the western margin of the Yangtze Block.
During the process of the Precambrian geological survey in Huili area,high greenschist-amphibolite facies rocks with the typical rock of amphibolite has been found in Jiaopingdu region.The identification and original rock recovery revealed that the original rock of amphibolite belong the metamorphosed mafic volcanic rocks.U-Pb isotope of zircons from amphibolite are determined by the LA-ICP-MS method,and yielded a concordia age of 1 720Ma±7Ma(MSWD=0.47,N=23).It represents the age of the lower part of Tongan Formation and implied that the mafic volcanic rocks formed in the continental extension environment at the late Paleoproterozoic of the ancient basement.Also,it reflects the breakup event of Columbia supercontinent in the western margin of the Yangtze Block.
引文
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[3]耿元生,柳永清,高林志,等.扬子克拉通西南缘中元古代通安组的形成时代[J].地质学报,2012,86(9):1 479-1 490.
[4]尹福光,孙志明,张璋.会理-东川地区中元古代地层-构造格架[J].地质论评,2011,57(6):770-778.
[5]尹福光,孙志明,任光明,等.上扬子陆块西南缘早-中元古代造山运动的地质记录[J].地质学报,2012,86(12):1 917-1 932.
[6]牟传龙,林仕良,余谦.四川会理—会东及邻区中元古代昆阳群沉积特征及演化[J].沉积与特提斯地质,2000,20(1):44-50.
[7]Greentree M R,Li Z X,Li X H,et al.Late Mesoproterozoic to earlist NeoProterozoic basin record of the Sibao orrgenesis in western South China and relationship to the assembly of Rodinia[J].Precambrian Research,2006,151:79-100.
[8]Sun W H,Zhou M F,Gao J F,et al.Detrital zircon U-Pb geochronological and Lu-Hf isotopic constraints on the Precambrian magmatic and crustal evolution of the western Yangtze Block,SW China[J].Precambrian Research,2009,172:99-126.
[9]阚泽忠,乔正福.四川会理-河口地区褶皱基底的双层结构[J].四川地质学报,1999,19(3):204-209.
[10]王冬兵,尹福光,孙志明,等.扬子陆块西缘古元古代基性侵入岩LA-ICP-MS锆石U-Pb年龄和Hf同位素及其地质意义[J].地质通报,2013,32(4):617-630.
[11]Fan HP,Zhu WG,Li Z X,et al.Ca.1.5Ga mafic magmatism in South China during the break-up of the supercontinent Nuna/Columbia:The Zhuqing Fe-Ti-V oxide ore-bearing mafic intrusions in westernYangtze Block[J].Lithos,2013,168-169:85-98.
[12]宋彪,张玉海,万渝生,等.锆石SHRIMP样品靶制作、年龄测定及有关现象讨论[J].地质论评,2002,48:26-30.
[13]Nasdala L,Hofmeister W,Norberg N,et al.Zircon M257-A homogeneous natural reference material for the ion microprobe U-Pb analysis of zircon[J].Geostandards and Geoanalytical Research,2008,32:247-265.
[14]Liu Y S,Gao S,Hu Z C,et al.Continental and oceanic crust recycling-induced melt-peridotite interactions in the Trans-North China Orogen:U-Pb dating,Hf isotopes and trace elements in zircons from mantle xenoliths[J].Journal Petrology,2010,51:537-571.
[15]Andersen T.Correction of common lead in U-Pb analyses that do not report R204Pb[J].Chemical geology,2002,192:59-79.
[16]侯可军,李延河,田有荣.LA-MC-ICP-MS锆石微区原位U-Pb定年技术[J].矿床地质,2009,28(4):481-492.
[17]Sláma J,Kosler J,Condon D J,et al.Plesovice zircon-A new natural reference material for U-Pb and Hf isotopic microanalysis[J].Chemical Geology,2008,249:1-35.
[18]吴元保,郑永飞.锆石成因矿物学研究及其对U-Pb年龄解释的制约[J].科学通报,2004,49(16):1 589-1 604.
[19]Zhao X F,Zhou M F,Li J W,et al.Late Paleoproterozoic to early Mesoproterozoic Dongchuan Group in Yunnan,SW China:Implications for tectonic evolution of the Yangtze Block[J].Precambrian Research,2010,182:57-69.
[20]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.
[21]王冬兵,孙志明,尹福光,等.扬子陆块西缘河口群的时代:来自火山岩LA-ICP-MS U-Pb年龄的证据[J].地层学杂志,2012,36(3):630-635.
[22]杨红,刘福来,杜利林,等.扬子地块西南缘大红山群老厂组变质火山岩的锆石U-Pb定年及其地质意义[J].岩石学报,2012,28(9):2 994-3 014.
[23]尹福光,王冬兵,孙志明,等.哥伦比亚超大陆在扬子陆块西缘的探秘[J].沉积与特提斯地质,2012,32(3):31-40.
①四川省地质局第一区域地质测量队.1∶20×104会理幅区域地质调查报告[R].1970.
②王伟生,蒋小芳,廖震文,等.扬子地台西缘基底成矿作用及找矿方向研究报告[R].2011.
③李雁龙,周雪梅,岳昌桐,等.1∶25×104东川幅建造构造图及说明书[R].2011.
④杨忠华,周信国,胡炎基,等.1∶5×104小街幅区域地质调查报告[R].1984.