滇东—黔西地区峨眉山玄武岩富Nb榍石矿物学特征
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摘要
滇东—黔西地区广泛发育一套Nb-Ga-REE多金属矿化富集层,其底板为峨眉山玄武岩。为了探讨底板玄武岩对该矿化层的贡献,本文系统开展了玄武岩的微区矿物学及地球化学研究,尤其利用电子探针对玄武岩中的榍石进行了深入的研究和系统的面扫分析。结果发现研究区玄武岩主要为高钛玄武岩,以富榍石为特征。高钛玄武岩中含有多种形态的榍石,主要有自形榍石、半自形榍石、信封状榍石、晶粒状榍石、云雾状榍石、片状榍石、十字形榍石、团块状榍石和蚀变榍石等。榍石中微量元素除富含Nb外,还有一定量的Zr、Y、Ce,结合该地区玄武岩地球化学特征,认为研究区榍石可能有2种成因:其一主要形成于岩浆活动晚期,可能是原始基性岩浆的产物;其二是由岩浆早、中期析出的钛铁矿、晶粒状榍石、含钛辉石在岩浆后期蚀变阶段的水化作用和氧化作用下形成。另外,高钛玄武岩中榍石的表生风化蚀变作用可能是研究区发生铌矿化的主要原因,榍石为上覆的矿层提供了Nb、Zr、Y和Ce等成矿元素。
A set of enriched Nb-Ga-REE polymetallic layer is widely developed in the eastern Yunnan-western Guizhou area, with its footwall of the Emeishan basalts. In this paper, microscopic mineralogy and geochemistry of the Emeishan basalts, especially the intensive analyses and systematic elemental scanning of sphene grains in the Emeishan basalts by using the electron probe microanalysis(EPMA), have been systematically studied to explore the contribution of footwall basalts to the Nb-Ga-REE polymetallic mineralization layer. The results show that most of basalts in the study area belong to the Ti-rich basalt type featured by the sphene enrichment. The Ti-rich basalt contains various morphological sphenes including euhedral, semi-euhedral, enveloped, grain shaped, cloudy, flaky, cross-shaped, crumby, and altered sphenes.Besides the enriched Nb,sphene contains a certain amount of Zr, Y and Ce. Combining with geochemical characteristics of the Emeishan basalts, sphene could be either as a product of primitive basic magma formed mainly in late stage of magmatism or generated from the hydration and oxidation of minerals, including ilmenite, grain sphene, and Ti-rich pyroxene, formed in the early and middle stages of magmatism. In addition, the surface weathering of sphane hosted in the Ti-rich basalt could be the main reason of Nb-mineralization in the research area as the weathered sphane could have provided ore-forming elements such as Nb, Zr, Y, and Ce for the overlying ore layer.
A set of enriched Nb-Ga-REE polymetallic layer is widely developed in the eastern Yunnan-western Guizhou area, with its footwall of the Emeishan basalts. In this paper, microscopic mineralogy and geochemistry of the Emeishan basalts, especially the intensive analyses and systematic elemental scanning of sphene grains in the Emeishan basalts by using the electron probe microanalysis(EPMA), have been systematically studied to explore the contribution of footwall basalts to the Nb-Ga-REE polymetallic mineralization layer. The results show that most of basalts in the study area belong to the Ti-rich basalt type featured by the sphene enrichment. The Ti-rich basalt contains various morphological sphenes including euhedral, semi-euhedral, enveloped, grain shaped, cloudy, flaky, cross-shaped, crumby, and altered sphenes.Besides the enriched Nb,sphene contains a certain amount of Zr, Y and Ce. Combining with geochemical characteristics of the Emeishan basalts, sphene could be either as a product of primitive basic magma formed mainly in late stage of magmatism or generated from the hydration and oxidation of minerals, including ilmenite, grain sphene, and Ti-rich pyroxene, formed in the early and middle stages of magmatism. In addition, the surface weathering of sphane hosted in the Ti-rich basalt could be the main reason of Nb-mineralization in the research area as the weathered sphane could have provided ore-forming elements such as Nb, Zr, Y, and Ce for the overlying ore layer.
引文
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[16]汪云亮,李巨初,王旺章.微量元素丰度模式与峨眉山玄武岩成因[J].矿物岩石,1989,9(4):100-105.
[17]Davies GF,Richards MA.Mantle convection[J].Journal Geology,1992,100:151-206.
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[19]张鸿翔,徐志方,马英军,等.大陆溢流玄武岩的地球化学特征及起源[J].地球科学,2004,26(3):261-268.
[20]张招崇,郝艳丽,王福生.大火成岩省中苦橄岩的研究意义[J].地学前缘,2003,10(3):105-114.
[21]张招崇,王福生,范蔚茗,等.峨眉山玄武岩研究中的一些问题的讨论[J].岩石矿物学杂志,2001,20(3):239-246.
[22]Campbell IH,Griffiths RW.The evolution of mantle's chemicalstructure[J].Lithos,1993,30:389-399.
[23]Chung SL,Jahn BM.Plume-lithosphere interaction in generation of the Emeishan flood basalts at the Permian-Triassic boundary[J].Geology,1995,23(10):889-892.
[24]Mecdonald R,Roges NW,Fitton JG.Plume-lithosphere interactions in the generation of the basalts of the Kenya Rift,East Africa[J].Journal of Petrology,2001,42(5):877-900.
[25]王登红.地幔柱的概念、分类、演化与大规模成矿-对中国西南部的探讨[J].地学前缘,2001,8(3):67-72.
[26]徐义刚,钟孙霖.峨眉山大火成岩省:地幔柱活动的证据及其熔融条件[J].地球化学,2001,30(1):1-9.
[27]张招崇.关于峨眉山大火成岩省一些重要问题的讨论[J].中国地质,2009,36(3):634-646.
[28]郝艳丽,张招崇,王福生,等.峨眉山大火成岩省“高钛玄武岩”和“低钛玄武岩”成因探讨[J].地质评论,2004,50(6):587-592.
[29]严再飞,黄智龙,许成,等.峨眉山二滩玄武岩地球化学特征[J].矿物岩石,2006,26(3):77-84.
[30]严再飞,黄智龙,程礼军,等.峨眉山高钛玄武岩物源的不均一性研究[J].矿物岩石,2007,27(4):60-65.
[31]侯明才,邓敏,张本健,等.峨眉山高钛玄武岩中主要的赋钛矿物-榍石的产状、特征及成因[J].岩石学报,2011,27(8):2487-2499.
[32]徐义刚,何斌,罗震宇,等.我国大火成岩省和地幔柱研究进展与展望[J].矿物岩石地球化学通报,2013,32(1):25-39.
[33]赵利信.滇东北晚二叠世煤型铌矿床的元素富集成矿机理[D].北京:中国矿业大学(北京),2016.
[34]王正瑛,李秀华,王文才,等.峨眉龙门洞地区峨眉山玄武岩顶部古风化壳[J].矿物岩石,1982,(3):56-64.
[35]侯明才,王文楷,张本健,等.四川周公山-汉王场地区峨眉山玄武岩中流体类型及活动期次[J].岩石学报,2013,29(8):2709-2718.
[36]Xu YG,Chung SL,Jahn BM,et al.Petrologic and geochemical constraints on the petrogenesis of Permo-Triassic Emeishan flood basalts in southwestern China[J].Lithos,2001,58(3):145-168.
[37]Xiao L,Xu YG,Mei HJ,et al.Distinct mantle sources of low-Ti and high-Ti basalts from the western Emeishan large igneous province,SW China:implications for plume-lithosphere interaction[J].Earth and Planetary Science Letters,2004,228(3/4):525-546.
[38]Zhang ZC,Wang FS.Geochemistry of two types of basalts in the Emeishan Basaltic Province:evidence for mantle plume-lithosphere interaction[J].Acta Geologica Sinica,2002,76:229-237.
[39]Song XY,Zhou MF,Reid R Keays,et al.Geochemistry of the Emeishan flood basalts at Yangliuping,Sichuan,SW China:implications for sulfide segregation[J].Contrib Mineral Petro,2006,152(1):53-74.
[40]Song XY,Qi HW,Robinson PT,et al.Melting of the subcontinental lithospheric mantle by the Emeishan mantle plume;evidence from the basal alkaline basalts in Dongchuan,Yunnan,Southwestern China[J].Lithos,2008,100(1-4):93-111.
[41]袁见齐.矿床学.北京:地质出版社,1985.
[2]Courtillot V,Jaupart C,Manighetti I,et al.On causal links between flood basalts and continental breakup[J].Earthand Planetary Science Letters,1999,166(3/4):177-195.
[3]Wignall PB.Large igneous provinces and mass extinctions[J].Earth-Science Reviews,2001,53(1/2):1-33.
[4]He B,Xu YG,Chung SL,et al.Sedimentaryevidence for a rapid,kilometer-scale crustal doming prior to theeruption of the Emeishan flood basalts[J].Earth and Planetary Science Letters,2003,213(3/4):391-405.
[5]He B,Xu Y,Wang Y,et al.Sedimentation and lithofacies paleogeography in Southwestern China before and after the Emeishan flood volcanism:New insights into surface response to mantle plume activity[J].Journal of Geology,2006,114(1):117-132.
[6]姜寒冰,姜常义,钱壮志,等.云南峨眉山高钛和低钛玄武岩的岩石成因[J].岩石学报,2009,25(5):1117-1134.
[7]孟昌忠,陈旸,张莹华,等.峨眉山大火成岩省去顶作用与黔西铁-多金属矿床成因:锆石U-Pb同位素年代学约束[J].中国科学:地球科学,2015,45(10):1469-1480.
[8]Boven A,Pasteels P,Punzalan LE,et al.40Ar/39Ar geochronological constraints on the age and evolution of the Permo-Triassic Emeishan Volcanic Province,Southwest China[J].Journal of Asian Earth Sciences,2002,20(2):157-175.
[9]侯增谦,陈文,卢记仁.四川峨眉大火成岩省259Ma大陆溢流玄武岩喷发事件:来自激光40Ar/39Ar测年证据[J].地质学报,2006,80(8):1130.
[10]宋谢炎,侯增谦,曹志敏,等峨眉大火成岩省的岩石地球化学特征及时限[J].地质学报,2001,75(4):498-506.
[11]林建英.峨眉山玄武岩系的岩石组合及其地质特征[J].中国地质科学院成都地质矿产研究所所刊,1987,8:109-122.
[12]侯增谦,卢记仁,汪云亮,等.峨眉火成岩省:结构、成因与特色[J].地质论评,1999,45(7):885-891.
[13]肖龙,徐义刚,何斌.峨眉地幔柱-岩石圈的相互作用:来自低钛和高钛玄武岩的Sr-Nd和O同位素证据[J].高校地质学报,2003,9(2):207-217.
[14]何斌,徐义刚,肖龙,等.峨眉山大火成岩省的形成机制及空间展布:来自沉积地层学的新证据[J].地质学报,2003,7(2):194-202.
[15]汪云亮,Hughes SS,童纯菡,等.峨眉山玄武岩地球化学和大陆地慢演化[J].成都地质学院学报,1987,14(3):59-74.
[16]汪云亮,李巨初,王旺章.微量元素丰度模式与峨眉山玄武岩成因[J].矿物岩石,1989,9(4):100-105.
[17]Davies GF,Richards MA.Mantle convection[J].Journal Geology,1992,100:151-206.
[18]张招崇,王福生.峨眉山大陆溢流玄武岩省苦橄质岩石的高镁橄榄石和高铬尖晶石及其意义[J].自然科学进展,2004,14(1):70-74.
[19]张鸿翔,徐志方,马英军,等.大陆溢流玄武岩的地球化学特征及起源[J].地球科学,2004,26(3):261-268.
[20]张招崇,郝艳丽,王福生.大火成岩省中苦橄岩的研究意义[J].地学前缘,2003,10(3):105-114.
[21]张招崇,王福生,范蔚茗,等.峨眉山玄武岩研究中的一些问题的讨论[J].岩石矿物学杂志,2001,20(3):239-246.
[22]Campbell IH,Griffiths RW.The evolution of mantle's chemicalstructure[J].Lithos,1993,30:389-399.
[23]Chung SL,Jahn BM.Plume-lithosphere interaction in generation of the Emeishan flood basalts at the Permian-Triassic boundary[J].Geology,1995,23(10):889-892.
[24]Mecdonald R,Roges NW,Fitton JG.Plume-lithosphere interactions in the generation of the basalts of the Kenya Rift,East Africa[J].Journal of Petrology,2001,42(5):877-900.
[25]王登红.地幔柱的概念、分类、演化与大规模成矿-对中国西南部的探讨[J].地学前缘,2001,8(3):67-72.
[26]徐义刚,钟孙霖.峨眉山大火成岩省:地幔柱活动的证据及其熔融条件[J].地球化学,2001,30(1):1-9.
[27]张招崇.关于峨眉山大火成岩省一些重要问题的讨论[J].中国地质,2009,36(3):634-646.
[28]郝艳丽,张招崇,王福生,等.峨眉山大火成岩省“高钛玄武岩”和“低钛玄武岩”成因探讨[J].地质评论,2004,50(6):587-592.
[29]严再飞,黄智龙,许成,等.峨眉山二滩玄武岩地球化学特征[J].矿物岩石,2006,26(3):77-84.
[30]严再飞,黄智龙,程礼军,等.峨眉山高钛玄武岩物源的不均一性研究[J].矿物岩石,2007,27(4):60-65.
[31]侯明才,邓敏,张本健,等.峨眉山高钛玄武岩中主要的赋钛矿物-榍石的产状、特征及成因[J].岩石学报,2011,27(8):2487-2499.
[32]徐义刚,何斌,罗震宇,等.我国大火成岩省和地幔柱研究进展与展望[J].矿物岩石地球化学通报,2013,32(1):25-39.
[33]赵利信.滇东北晚二叠世煤型铌矿床的元素富集成矿机理[D].北京:中国矿业大学(北京),2016.
[34]王正瑛,李秀华,王文才,等.峨眉龙门洞地区峨眉山玄武岩顶部古风化壳[J].矿物岩石,1982,(3):56-64.
[35]侯明才,王文楷,张本健,等.四川周公山-汉王场地区峨眉山玄武岩中流体类型及活动期次[J].岩石学报,2013,29(8):2709-2718.
[36]Xu YG,Chung SL,Jahn BM,et al.Petrologic and geochemical constraints on the petrogenesis of Permo-Triassic Emeishan flood basalts in southwestern China[J].Lithos,2001,58(3):145-168.
[37]Xiao L,Xu YG,Mei HJ,et al.Distinct mantle sources of low-Ti and high-Ti basalts from the western Emeishan large igneous province,SW China:implications for plume-lithosphere interaction[J].Earth and Planetary Science Letters,2004,228(3/4):525-546.
[38]Zhang ZC,Wang FS.Geochemistry of two types of basalts in the Emeishan Basaltic Province:evidence for mantle plume-lithosphere interaction[J].Acta Geologica Sinica,2002,76:229-237.
[39]Song XY,Zhou MF,Reid R Keays,et al.Geochemistry of the Emeishan flood basalts at Yangliuping,Sichuan,SW China:implications for sulfide segregation[J].Contrib Mineral Petro,2006,152(1):53-74.
[40]Song XY,Qi HW,Robinson PT,et al.Melting of the subcontinental lithospheric mantle by the Emeishan mantle plume;evidence from the basal alkaline basalts in Dongchuan,Yunnan,Southwestern China[J].Lithos,2008,100(1-4):93-111.
[41]袁见齐.矿床学.北京:地质出版社,1985.
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