湖南宁乡钾镁煌斑岩及相关岩石重砂锆石地球化学特征、U-Pb年龄及其地质意义
摘要
对湖南宁乡等地多个含有金刚石的钾镁煌斑岩及相关岩石的重砂矿物进行了分离,利用电子探针、阴极发光图像及LA-ICPMS等对其中的锆石进行了主微量元素成分、内部结构及U-Pb同位素年龄的分析。结果表明,不同地点钾镁煌斑岩重砂锆石的地球化学特征具有一定相似性;与钾镁煌斑岩有关锆石的U-Pb年龄显示研究区的岩浆活动具有多期次的特点,其中宁乡Ⅰ号及Ⅲ号岩管钾镁煌斑岩4颗重砂锆石的206Pb/238U加权平均年龄为(101.6±5.1)Ma,显示出较为年轻的特点,但石门上五通地区白垩系红层中也发现具有207Pb/206Pb谐和年龄为(2 008±29)Ma古老岩浆结晶锆石的存在,证实该地和金刚石有关火山物质的来源具有复杂性。
Heavy mineral zircons were separated from diamondiferous lamproites and their associated rocks in Ningxiang and nearby area,Hunan province,and their main and trace element compositions,interior structure and the U-Pb isotopic ages were obtained with EPMA,cathodoluminescence microscope and LA-ICPMS measurement.The zircons in lamproites from different locations generally have similar geochemical characteristics.The U-Pb dating of zircons suggests that the lamproites were probably formed during multi-stages.A young age of(101.6±5.1)Ma was obtained on four zircon samples from No.1 and No.3 pipe lamproites.The zircon collected from the Cretaceous red strata in Shangwutong area has a concordant 207Pb/ 206Pb age of(2 008±29)Ma.These results cannot specifically determine the source rocks of diamond in the study area.
Heavy mineral zircons were separated from diamondiferous lamproites and their associated rocks in Ningxiang and nearby area,Hunan province,and their main and trace element compositions,interior structure and the U-Pb isotopic ages were obtained with EPMA,cathodoluminescence microscope and LA-ICPMS measurement.The zircons in lamproites from different locations generally have similar geochemical characteristics.The U-Pb dating of zircons suggests that the lamproites were probably formed during multi-stages.A young age of(101.6±5.1)Ma was obtained on four zircon samples from No.1 and No.3 pipe lamproites.The zircon collected from the Cretaceous red strata in Shangwutong area has a concordant 207Pb/ 206Pb age of(2 008±29)Ma.These results cannot specifically determine the source rocks of diamond in the study area.
引文
[1]罗会文,杨光树.贵州省镇远地区钾镁煌斑岩岩石特征[J].岩石矿物学杂志,1989,(2):97-109.
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[14]汪相.锆石形态的定量描述及其动力学分析[J].中国科学D辑,1998,28(3):232-238.
[15]VAVRAG.Aguide to quantitative morphology of acces-sory zircon[J].Chem Geol,1993,93:15-28
[16]CROFU F,HANCHAR J M,HOSKIN P W O,et al.Atlas of zircon textures[J].Reviews in Mineralogy andGeochemistry,2003,53:469-495
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[18]银剑钊.初论金刚石原生矿床成矿系列[J].地球科学-中国地质大学学报,2000,25(4):380-383.
[19]钟玉芳,马昌前.含U副矿物的地质年代学研究综述[J],地球科学进展,2006,21(4):372-382.
[20]TAYLOR S R,McLENNAN S M.The continental crust:Itscomposition and evolution[M].USA:Blackwell Sci-entific Publications,1985
[21]LI S,XIAO Y,LIU D,et al.Collision of the north Chinaand Yangtse blocks and formation of coesite-bearingeclogites:Timing and processes[J].Chem Geol,1993,109:89-111.
[22]赖冬梅.锆石U_Pb年龄不一致原因浅析[J].四川有色金属,2004,(2):12-18.
[23]湖南省413地质队.湖南金刚石原生矿预测研究报告[R],1990.
[24]舒良树,周新民,邓平,等.中国东南部中新生代盆地特征与构造演化[J].地质通报,2004,23(9-10):876-884.
[25]LI X H,McCULLOCH M T.Geochemica1 characteris-tics of Cretaceous mafic dikes from northern Guangdong,SE China:Age,origin and tectonic significance[J].Geo-dynamics,1998,27:405-419
[26]谢桂青,毛景文;胡瑞忠,等.中国东南部中—新生代地球动力学背景若干问题的探讨[J].地质论评,2005,51(6):613-619
[27]范蔚茗,王岳军,郭峰,等.湘赣地区中生代镁铁质岩浆作用与岩石圈伸展[J].地学前缘,2003,10(3):159-169.
[2]刘观亮,汪雄武,吕学淼.湖北大洪山地区钾镁煌斑岩岩石学、矿物学特征及含矿性研究[M].北京:地质出版社,1993.
[3]李子云,马文运.宁乡县云影窝含金刚石镁煌斑岩地质特征[J].湖南地质,1993,12(4):221-225.
[4]ZHENG J P,GRIFFIN W L,O’REILLY S Y,et al.Widespread Archean basement beneath the Yangtze craton[J].Geology,2006,7:417-420.
[5]谢桂青,胡瑞忠,蒋国豪,等.锆石的成因和U_Pb同位素定年的某些进展[J].地质地球化学,2001,29(4):64-70.
[6]LEE J,WILLIAMS L,ELLIS D.Pb,Uand Th diffusionin nature zircon[J].Nature,1997,390(13):159-162.
[7]CHERNIAK D J,WATSON E B.Pb diffusion in zircon[J].Chemical Geology,2000,172:5-24.
[8]GRIFFIN W L,PEARSON N J,BELOUSOVA E A,etal.The Hf isotope composition of cratonic mantle:LAM-MC-ICPMS analysis of zircon megacrysts in kimberlites[J].Geochim Cosmochim Acta,2000,64:133-147.
[9]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):1589-1604.
[10]钟玉芳,马昌前,佘振兵.锆石地球化学特征及地质应用研究综述[J].地质科技情报,2006,25(1):27-40.
[11]BELOUSOVA E A,GRIFFIN W L,O’REILLY S Y,etal.Igneous zircon:trace element composition as an in-dicator of source rock type[J].Contribution to Mineral-ogy and Petrology,2002,143(5):602-622.
[12]饶家荣.湖南原生金刚石矿深部构造地质背景及成矿预测[J].湖南地质,1999,18(1):21-28.
[13]刘观亮,张自超,李志昌等.湖南宁乡钾镁煌斑岩中火山微球粒的初步研究[J].岩石矿物学杂志,1995,14(3):242-251.
[14]汪相.锆石形态的定量描述及其动力学分析[J].中国科学D辑,1998,28(3):232-238.
[15]VAVRAG.Aguide to quantitative morphology of acces-sory zircon[J].Chem Geol,1993,93:15-28
[16]CROFU F,HANCHAR J M,HOSKIN P W O,et al.Atlas of zircon textures[J].Reviews in Mineralogy andGeochemistry,2003,53:469-495
[17]丘志力,龚盛玮,于庆媛,等.福建明溪锆石巨晶中的斜锆石、锆石矿物包裹体及其成因启示[J].中山大学学报:自然科学版,2004,43(6):135-139.
[18]银剑钊.初论金刚石原生矿床成矿系列[J].地球科学-中国地质大学学报,2000,25(4):380-383.
[19]钟玉芳,马昌前.含U副矿物的地质年代学研究综述[J],地球科学进展,2006,21(4):372-382.
[20]TAYLOR S R,McLENNAN S M.The continental crust:Itscomposition and evolution[M].USA:Blackwell Sci-entific Publications,1985
[21]LI S,XIAO Y,LIU D,et al.Collision of the north Chinaand Yangtse blocks and formation of coesite-bearingeclogites:Timing and processes[J].Chem Geol,1993,109:89-111.
[22]赖冬梅.锆石U_Pb年龄不一致原因浅析[J].四川有色金属,2004,(2):12-18.
[23]湖南省413地质队.湖南金刚石原生矿预测研究报告[R],1990.
[24]舒良树,周新民,邓平,等.中国东南部中新生代盆地特征与构造演化[J].地质通报,2004,23(9-10):876-884.
[25]LI X H,McCULLOCH M T.Geochemica1 characteris-tics of Cretaceous mafic dikes from northern Guangdong,SE China:Age,origin and tectonic significance[J].Geo-dynamics,1998,27:405-419
[26]谢桂青,毛景文;胡瑞忠,等.中国东南部中—新生代地球动力学背景若干问题的探讨[J].地质论评,2005,51(6):613-619
[27]范蔚茗,王岳军,郭峰,等.湘赣地区中生代镁铁质岩浆作用与岩石圈伸展[J].地学前缘,2003,10(3):159-169.
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