贵州省黔西县大寨地区中三叠统关岭组绿豆岩锆石U-Pb年代学、地球化学特征及地质意义
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摘要
针对贵州省黔西县大寨地区中三叠统关岭组底部绿豆岩,利用LA-ICPMS锆石U-Pb测年手段,明确贵州黔西县大寨地区早—中三叠世界线年龄。对贵州省黔西县大寨地区中三叠统关岭组底部绿豆岩1件U-Pb年龄样品、 8件地球化学样品的测试分析,结果表明,锆石U-Pb加权年龄为248.6 Ma±2.7 Ma,谐和年龄为248.7 Ma±1.1 Ma;绿豆岩属于高硅(w_(SiO2)均值为62.40%)、铝(w_(Al2)O_3均值为14.61%)、钾(w_(K2)O均值为7.22%),低铁(w_(Fe2)O_3均值为0.94%,w_(FeO)均值为0.51%)、钛(w_(TiO2)均值为0.24%)的中酸性火山物质,具有稀土元素总量相对较低、相对富集轻稀土元素和轻重稀土元素分馏程度低的特征,负Eu异常显著,δEu=0.17～0.22。综合分析,该绿豆岩是由火山活动喷发的火山灰经风化、搬运、沉积改造而形成,为下三叠统嘉陵江组与中三叠统关岭组松子坎段界线岩性标志,同时为测区早—中三叠世界线年龄提供了准确的年代学证据。
Zircon U-Pb LA-ICP-MS dating and geochemical analysis on the mung bean rocks occurred on the bottom of middle Triassic Guanling Formation in Qianxi County,Guizhou Province are carried out with one geochronology sample and 7 geochemical samples.It shows that mung the bean rock has weighted mean age of 248.6 Ma±2.7 Ma and concordant age of 248.7 Ma±1.1 Ma.Geochemically,the mung bean rocks are rich in Si,Al,K(the average value of w_(SiO2) is 62.40%,w_(Al2)O_3 is 14.61% and w_(K2)O is 7.22%) and depleting in Fe,Ti(the average value of w_(Fe2)O_3 is 0.94%,w_(FeO) is 0.51% and w_(TiO2) is 0.24%),characteristic of moderate-acidic volcanic material.Total amount REE of the mung bean rocks is low,LREE is relatively rich and the REE fractionation is low with obvious negative Eu anomaly(δEu of 0.17～0.22).Comprehensive analysis indicates that the mung bean rocks are formed by volcanic ash which is subsequently experienced the processes of weathering,transporting and deposition.The mung bean rock is the demarcation marker layer for the lower Triassic Jialingjiang Formation and middle Triassic Guanling Formation.The zircon U-Pb LA-ICP-MS dating age of mung the bean rock provides geochronologcal evidence for the demarcation of early-middle Triassic boundary.
Zircon U-Pb LA-ICP-MS dating and geochemical analysis on the mung bean rocks occurred on the bottom of middle Triassic Guanling Formation in Qianxi County,Guizhou Province are carried out with one geochronology sample and 7 geochemical samples.It shows that mung the bean rock has weighted mean age of 248.6 Ma±2.7 Ma and concordant age of 248.7 Ma±1.1 Ma.Geochemically,the mung bean rocks are rich in Si,Al,K(the average value of w_(SiO2) is 62.40%,w_(Al2)O_3 is 14.61% and w_(K2)O is 7.22%) and depleting in Fe,Ti(the average value of w_(Fe2)O_3 is 0.94%,w_(FeO) is 0.51% and w_(TiO2) is 0.24%),characteristic of moderate-acidic volcanic material.Total amount REE of the mung bean rocks is low,LREE is relatively rich and the REE fractionation is low with obvious negative Eu anomaly(δEu of 0.17～0.22).Comprehensive analysis indicates that the mung bean rocks are formed by volcanic ash which is subsequently experienced the processes of weathering,transporting and deposition.The mung bean rock is the demarcation marker layer for the lower Triassic Jialingjiang Formation and middle Triassic Guanling Formation.The zircon U-Pb LA-ICP-MS dating age of mung the bean rock provides geochronologcal evidence for the demarcation of early-middle Triassic boundary.
引文
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[19] 孙艳,王登红,高允,等.重庆铜梁地区富锂绿豆岩地球化学特征[J].岩石矿物学杂志,2018,37(3):445-453.
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[22] 陈好寿.同位素地球化学研究[M].杭州:浙江大学出版社,1994:330-333.
[23] Liu Yan,Hou Zengqian.A synthesis of mineralization styles with an integrated genetic model of carbonatite-syenite-hosted REE deposits in the Cenozoic Mianning-Dechang REE metallogenic belt,the eastern Tibetan Plateau,southwestern China[J].Journal of Asian Earth Sciences,2017,137:35-79.
[24] 冯宝华.酸性火-沉粘土岩的微量元素地球化学研究[J].矿物岩石地球化学通报,1993,12(1):3-6.
①贵州省地质矿产局.《息烽幅》、《毕节县福》(1∶25×104)区域地质测量报告[R].贵州,2004.
[2] 朱立军.贵州早中三叠世间绿豆岩黏土矿物学研究[J].贵州工学院学报,1994,23(5):19-24.
[3] 朱立军.贵州绿豆岩中黏土矿物特征及其成因探讨[J].矿物学报,1995,15(1):75-81.
[4] 刘宝珺.沉积岩石学[M].北京:地质出版社,1981,145-155.
[5] 王彦斌,刘敦一,姚建新,等.黔西南下-中三叠统界线年龄[J].地质学报,2004,78(5):586-591.
[6] 殷鸿福,杨遵仪,童金南.国际三叠系研究现状[J].地层学杂志,2000,24(2):109-113.
[7] 殷鸿福,童金南.关于中国的海相三叠系建阶及下三叠统分阶界线[J].地球科学,2002,27(5):490-497.
[8] 秦典夕,颜承锡,熊剑飞.黔中三叠纪牙形类生物地层研究的新进展[J].贵州地质,1993,10(2):120-128.
[9] 王志浩,钟端.滇东、黔西和桂北不同相区的三叠纪牙形刺生物地层[J].地层学杂志,1990,14(1):15-35.
[10] Retallack G L,Renne P R,Kimbrough D L.New radiometric ages for Triassic floras of Southeast Gondwana.In:Lucas S G,M orales M,eds.The nonmarine Triassic[J].New M exicaM useum of Natural Histo ry and Science Bulletin,1993,3:415-418.
[11] 彭元桥,殷鸿福,杨逢清.陆相二叠系-三叠系界线研究进展[J].地球科学进展, 2001,16( 6):769- 776.
[12] 胡世玲,李曰俊.贵州绿豆岩激光质谱40Ar-39Ar年龄[J].岩石学报,1996,12(3):409-414.
[13] 郑连弟,姚建新,仝亚博,等.贵州南部地区安尼阶底界锆石SHRIMP年龄结果[J].地质学报,2010,84(8):1 112-1 117.
[14] Lehrmann D J,Ramezani J,Bowring,S A, et al.Timing of recovery from the End-Permian extinction:geochronologic and biostratigraphic constraints from South China[J].Geology,2006,34(12):1 053-1 056.doi:10,1130/G22827A.1.
[15] 黄虎,杨江海,杜远生,等.右江盆地上二叠统-中三叠统凝灰岩年龄及其地质意义[J].地球科学-中国地质大学学报,2012,37(1):125-138.
[16] 曾广乾,何良伦,杨坤光.黔西普安辉绿岩的年代学、地球化学特征及其地质意义[J].矿物岩石,2014,34(4):61-70.
[17] 贵州省地质矿产局.贵州省区域地质志[M].北京:地质出版社,2013.
[18] 王银喜,张明生,周建新,等.云南前寒武系-寒武系界线锆石激光拉曼光谱研究及意义[J].地质论评,2007,53(1):22-103.
[19] 孙艳,王登红,高允,等.重庆铜梁地区富锂绿豆岩地球化学特征[J].岩石矿物学杂志,2018,37(3):445-453.
[20] Sun S S,Mcdonough W F.Chemical and isotopic systematics of oceanic basalts:Implications for mantle composition and processe[J].Geological Society London Special Publications,1989,42:313-345.
[21] 路风香,桑隆康.岩石学[M].北京:地质出版社,2012:43-53.
[22] 陈好寿.同位素地球化学研究[M].杭州:浙江大学出版社,1994:330-333.
[23] Liu Yan,Hou Zengqian.A synthesis of mineralization styles with an integrated genetic model of carbonatite-syenite-hosted REE deposits in the Cenozoic Mianning-Dechang REE metallogenic belt,the eastern Tibetan Plateau,southwestern China[J].Journal of Asian Earth Sciences,2017,137:35-79.
[24] 冯宝华.酸性火-沉粘土岩的微量元素地球化学研究[J].矿物岩石地球化学通报,1993,12(1):3-6.
①贵州省地质矿产局.《息烽幅》、《毕节县福》(1∶25×104)区域地质测量报告[R].贵州,2004.
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