甘肃省文县刘家坪蓟县系变基性火山岩地球化学特征及构造环境
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摘要
详细的野外地质调查显示,甘肃省刘家坪蓟县系为一套变基性火山岩,岩石以变玄武岩为主。岩石地球化学特征表明:A/CNK平均值为0. 59%,具有铝不饱和特征; Na2O/K2O值为47. 00～144. 00,表现为钠质;在TAS图解中,显示原岩为亚碱性系列;在AFM图解中,样品点均落入拉斑玄武岩系列;稀土元素含量∑REE为58. 22×10-6～95. 59×10-6,平均为67. 81×10-6;δEu=0. 83～1. 17,δCe=0. 88～0. 95,稀土配分模式为平坦型;微量元素中,高场强元素Zr、P、Y、Yb相对亏损,Th、Hf、Nb相对富集,低场强元素K亏损明显,Rb、Ba相对富集,且Zr/Y值为2. 38～3. 91,Ti/Zr值为92. 30～147. 23,Th/Ta值为1. 77～2. 21,大于1. 60。Sm-Nd同位素测试结果表明,变玄武岩等时线年龄为(1 387±32) Ma。根据地球化学构造环境判别图,结合区域地质背景,认为刘家坪蓟县系变基性火山岩主要形成于与岛弧相关的构造环境,这一认识对研究碧口地块的构造演化具有重要意义。
Detailed field geological survey suggested that the Jixian Group volcanic rocks in Liujiaping are mainly meta-basalts. Geochemical analysis showed that the rocks are aluminum unsaturated( average A/CNK =0. 59%) and sodic( Na2 O/K2 O = 47. 00-144. 00). In the TAS diagram,the basalts are sub-alkaline. In the AFM diagram,the samples fall into the tholeiitic basalt field. The total REE contents( ∑REE) vary in the range of 58. 22 × 10-6-95. 59 × 10-6( average 67. 81 × 10-6). The rocks show anomalies of Eu( δEu = 0. 83-1. 17) and Ce( δCe = 0. 88-0. 95),with flat chondrite-normalized REE distribution pattern. The trace element geochemistry is characterized by distinct depletions of Zr,P,Y and Yb,and relative enrichments of Th,Hf and Nb. There is also strong depletion in K and relative enrichments in Rb and Ba. The values of Zr/Y are2. 38-3. 91; Ti/Zr are 92. 30-147. 23; and Th/Ta are 1. 77-2. 21,more than 1. 60. The meta-basalt yiel-ded a whole-rock Sm-Nd isochron age of( 1,387 ± 32) Ma. Based on geochemical tectonic discrimination and regional geological background,it is considered that the Jixian Group meta-basalts in Liujiaping were formed in an island arc setting,which is important to the tectonic evolution study of the Bikou terrane.
Detailed field geological survey suggested that the Jixian Group volcanic rocks in Liujiaping are mainly meta-basalts. Geochemical analysis showed that the rocks are aluminum unsaturated( average A/CNK =0. 59%) and sodic( Na2 O/K2 O = 47. 00-144. 00). In the TAS diagram,the basalts are sub-alkaline. In the AFM diagram,the samples fall into the tholeiitic basalt field. The total REE contents( ∑REE) vary in the range of 58. 22 × 10-6-95. 59 × 10-6( average 67. 81 × 10-6). The rocks show anomalies of Eu( δEu = 0. 83-1. 17) and Ce( δCe = 0. 88-0. 95),with flat chondrite-normalized REE distribution pattern. The trace element geochemistry is characterized by distinct depletions of Zr,P,Y and Yb,and relative enrichments of Th,Hf and Nb. There is also strong depletion in K and relative enrichments in Rb and Ba. The values of Zr/Y are2. 38-3. 91; Ti/Zr are 92. 30-147. 23; and Th/Ta are 1. 77-2. 21,more than 1. 60. The meta-basalt yiel-ded a whole-rock Sm-Nd isochron age of( 1,387 ± 32) Ma. Based on geochemical tectonic discrimination and regional geological background,it is considered that the Jixian Group meta-basalts in Liujiaping were formed in an island arc setting,which is important to the tectonic evolution study of the Bikou terrane.
引文
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[7]闫全人,王宗起,闫臻,等.碧口群火山岩的时代——SHRIMP锆石U-Pb测年结果[J].地质通报,2003,22(6):456-458.
[8]赖绍聪,李永飞,秦江锋.碧口群西段董家河蛇绿岩地球化学及LA-ICP-MS锆石U-Pb定年[J].中国科学D辑,2007,37(增刊):262-270.
[9]胡安新,孙丰月,王英德,等.川陕交界地区刘家坪花岗岩年代学、地球化学特征及构造意义[J].西北地质,2014,47(2):30-40.
[10]左国朝.西秦岭泥盆纪构造建造及其地壳演化[J].甘肃地质,1984(2):99-110.
[11]秦克令,金浩甲,赵东宏.碧口群古岛弧带构造演化与成矿[J].河南地质,1994,12(4):304-317.
[12]刘铁庚,叶霖.碧口群形成的地质构造环境探讨[J].矿物学报,1999,19(4):446-452.
[13]王宗起,闫全人,闫臻,等.秦岭造山带主要大地构造单元的新划分[J].地质学报,2009,83(11):1527-1546.
[14]夏林圻,夏祖春,徐学义.南秦岭中-晚元古代火山岩性质与前寒武纪大陆裂解[J].中国科学D辑,1996,26(3):237-243.
[15]徐学义,夏祖春,夏林圻.碧口群火山旋回及其地质构造意义[J].地质通报,2002,21(8/9):478-485.
[16]夏林圻,夏祖春,徐学义,等.碧口群火山岩岩石成因研究[J].地学前缘,2007,14(3):84-101.
[17]董广法,王富国,刘继顺.勉略宁地区东沟坝组火山岩的成因浅析[J].大地构造与成矿学,1998,22(2):163-169.
[18]裴先治.南秦岭碧口群岩石组合特征及其构造意义[J].西安地质学院学报,1989,11(2):46-56.
[19]张国伟,程顺有,郭安林,等.秦岭—大别中央造山系南缘勉略古缝合带的再认识——兼论中国大陆主体的拼合[J].地质通报,2004,23(9/10):846-853.
[20] XIAO L,ZHANG H F,CLEMENS J D,et al. Late Triassic granitoids of the eastern margin of the Tibetan Plateau:Geochronology,petrogenesis and implications for tectonic evolution[J].Lithos,2007,96:436-452.
[21]李佐臣,裴先治,李瑞宝,等.扬子地块西北缘刘家坪地区大滩花岗岩体年代学、地球化学及其构造环境[J].地质论评,2013,59(5):869-884.
[22]杨根生,陈彦文,胡晓隆.西秦岭丹凤群变质火山岩的地球化学特征及其成矿环境初探[J].现代地质,2004,18(4):518-523.
[23] LANGMUIR C H,BENDER J F,BEBCE A E,et al. Petrogenesis of basalts from the famous area:Mid-Atlantic ridge[J].Earth and Planetary Science Letters,1977,36:133-156.
[24] CONDIE K C. Geochemical changes in basalts and andesites across the Archaean-Proterozoic boundary:identification and significance[J]. Lithos,1989,23:1-18.
[25] LE BAS M J,LE MAITRE R W,STRECKEISEN A,et al.Chemical classification of volcanic rocks based on the total alkalisilica diagram[J]. Journal of Petrology,1986,27(3):745-750.
[26] IRVINE T N,BARAGER W R A. A guide to the chemical classification of the common volcanic rocks[J]. Canadian Journal of Earth Sciences,1971,8:523-548.
[27] SUN S S,MCDONOUGH W F. Chemical and isotopic systematics of oceanic basalts:implication for mantle composition and processes[M]//SAUMDERS A D,NORRY M J. Magmatism in Ocean Basins. London:Geological Society of London,1989:313-345.
[28]汪晓伟,裴先治,李瑞保,等.南秦岭勉略构造带中堂沟火山岩地球化学特征及其地质意义[J].中国地质,2014,41(2):361-377.
[29] WILON M. Igneous Petrogenesis:a Global Tectonic Approach[M]. London:Chapman and Hall,1989:1-466.
[30] PEARCE J A. The role of sub-continental lithosphere in magma genesis at destructive plate margins[M]//HAWKESWORTH C J, NORRY M J. Continental Basalts Mantle Xenoliths.Nantwich:Shiva Publishing Ltd,1983:230-249.
[31]李昌年.火成岩微量元素岩石学[M].武汉:中国地质大学出版社,1992:1-195.
[32]黄建国,李虎杰,李文杰,等.贵州戈塘金矿萤石微量元素特征及衫-钕测年[J].地球科学进展,2012,27(10):1043-1050.
[33]杨杰东,王银喜,王宗哲.吉林大阳岔寒武系/奥陶系界线地层化石中Sm-Nd同位素的研究[J].科学通报,1988,36(16):1247-1249.
[34]张宗清,吴家善,叶笑江.阜平群下部太古代变质岩的REE、Rb-Sr和Sm-Nd年龄及意义[J].地球化学,1991,20(2):118-127.
[35]陈岳龙,王忠,罗照华,等.康定杂岩Rb-Sr、Sm-Nd同位素系统及其意义[J].现代地质,2008,22(5):707-714.
[36] FAURE G. Principle of Isotope Geology[M]. New York:John Wiley and Sons Inc,1986:1-207.
[37] PEARCE J A. Statistical analysis of major element patterns in basalts[J]. Journal of Petrology,1976,17:15-43.
[38] PEARCE J A,NORRY M J. Petrogenetic implications of Ti,Zr,Y,and Nb variations in volcanic rocks[J]. Contributions to Mineralogy and Petrology,1979,69:33-47.
[39] MULLEN E D. MnO/TiO 2/P2O5:a minor element discriminant for basaltic rocks of oceanic environments and its implications for petrogenesis[J]. Earth and Planetary Science Letters,1983,62:53-62.
(1)甘肃地矿局第三地质矿产勘查院. 1∶50 000刘家坪幅、三河幅、楚家坝幅区调报告. 2010.
[2]张国伟,张本仁,袁学诚,等.秦岭造山带与大陆动力学[M].北京:科学出版社,2001:1-855.
[3]张国伟,郭安林,姚安平.中国大陆构造中的西秦岭—松潘大陆构造结[J].地学前缘,2004,11(3):23-32.
[4]魏春景.陕甘川交界区碧口群的变质作用及其地质意义[J].地质学报,1994,68(3):241-254.
[5]秦克令,邹湘华,何世平.陕、甘、川交界处摩天岭区碧口群层序及时代划分[J].中国地质科学院西安地质矿产研究所所刊,1990,30:1-60.
[6]李耀敏.甘肃省陇南地区碧口群的时代、层序及含矿性探讨[J].甘肃地质,1991(12):38-69.
[7]闫全人,王宗起,闫臻,等.碧口群火山岩的时代——SHRIMP锆石U-Pb测年结果[J].地质通报,2003,22(6):456-458.
[8]赖绍聪,李永飞,秦江锋.碧口群西段董家河蛇绿岩地球化学及LA-ICP-MS锆石U-Pb定年[J].中国科学D辑,2007,37(增刊):262-270.
[9]胡安新,孙丰月,王英德,等.川陕交界地区刘家坪花岗岩年代学、地球化学特征及构造意义[J].西北地质,2014,47(2):30-40.
[10]左国朝.西秦岭泥盆纪构造建造及其地壳演化[J].甘肃地质,1984(2):99-110.
[11]秦克令,金浩甲,赵东宏.碧口群古岛弧带构造演化与成矿[J].河南地质,1994,12(4):304-317.
[12]刘铁庚,叶霖.碧口群形成的地质构造环境探讨[J].矿物学报,1999,19(4):446-452.
[13]王宗起,闫全人,闫臻,等.秦岭造山带主要大地构造单元的新划分[J].地质学报,2009,83(11):1527-1546.
[14]夏林圻,夏祖春,徐学义.南秦岭中-晚元古代火山岩性质与前寒武纪大陆裂解[J].中国科学D辑,1996,26(3):237-243.
[15]徐学义,夏祖春,夏林圻.碧口群火山旋回及其地质构造意义[J].地质通报,2002,21(8/9):478-485.
[16]夏林圻,夏祖春,徐学义,等.碧口群火山岩岩石成因研究[J].地学前缘,2007,14(3):84-101.
[17]董广法,王富国,刘继顺.勉略宁地区东沟坝组火山岩的成因浅析[J].大地构造与成矿学,1998,22(2):163-169.
[18]裴先治.南秦岭碧口群岩石组合特征及其构造意义[J].西安地质学院学报,1989,11(2):46-56.
[19]张国伟,程顺有,郭安林,等.秦岭—大别中央造山系南缘勉略古缝合带的再认识——兼论中国大陆主体的拼合[J].地质通报,2004,23(9/10):846-853.
[20] XIAO L,ZHANG H F,CLEMENS J D,et al. Late Triassic granitoids of the eastern margin of the Tibetan Plateau:Geochronology,petrogenesis and implications for tectonic evolution[J].Lithos,2007,96:436-452.
[21]李佐臣,裴先治,李瑞宝,等.扬子地块西北缘刘家坪地区大滩花岗岩体年代学、地球化学及其构造环境[J].地质论评,2013,59(5):869-884.
[22]杨根生,陈彦文,胡晓隆.西秦岭丹凤群变质火山岩的地球化学特征及其成矿环境初探[J].现代地质,2004,18(4):518-523.
[23] LANGMUIR C H,BENDER J F,BEBCE A E,et al. Petrogenesis of basalts from the famous area:Mid-Atlantic ridge[J].Earth and Planetary Science Letters,1977,36:133-156.
[24] CONDIE K C. Geochemical changes in basalts and andesites across the Archaean-Proterozoic boundary:identification and significance[J]. Lithos,1989,23:1-18.
[25] LE BAS M J,LE MAITRE R W,STRECKEISEN A,et al.Chemical classification of volcanic rocks based on the total alkalisilica diagram[J]. Journal of Petrology,1986,27(3):745-750.
[26] IRVINE T N,BARAGER W R A. A guide to the chemical classification of the common volcanic rocks[J]. Canadian Journal of Earth Sciences,1971,8:523-548.
[27] SUN S S,MCDONOUGH W F. Chemical and isotopic systematics of oceanic basalts:implication for mantle composition and processes[M]//SAUMDERS A D,NORRY M J. Magmatism in Ocean Basins. London:Geological Society of London,1989:313-345.
[28]汪晓伟,裴先治,李瑞保,等.南秦岭勉略构造带中堂沟火山岩地球化学特征及其地质意义[J].中国地质,2014,41(2):361-377.
[29] WILON M. Igneous Petrogenesis:a Global Tectonic Approach[M]. London:Chapman and Hall,1989:1-466.
[30] PEARCE J A. The role of sub-continental lithosphere in magma genesis at destructive plate margins[M]//HAWKESWORTH C J, NORRY M J. Continental Basalts Mantle Xenoliths.Nantwich:Shiva Publishing Ltd,1983:230-249.
[31]李昌年.火成岩微量元素岩石学[M].武汉:中国地质大学出版社,1992:1-195.
[32]黄建国,李虎杰,李文杰,等.贵州戈塘金矿萤石微量元素特征及衫-钕测年[J].地球科学进展,2012,27(10):1043-1050.
[33]杨杰东,王银喜,王宗哲.吉林大阳岔寒武系/奥陶系界线地层化石中Sm-Nd同位素的研究[J].科学通报,1988,36(16):1247-1249.
[34]张宗清,吴家善,叶笑江.阜平群下部太古代变质岩的REE、Rb-Sr和Sm-Nd年龄及意义[J].地球化学,1991,20(2):118-127.
[35]陈岳龙,王忠,罗照华,等.康定杂岩Rb-Sr、Sm-Nd同位素系统及其意义[J].现代地质,2008,22(5):707-714.
[36] FAURE G. Principle of Isotope Geology[M]. New York:John Wiley and Sons Inc,1986:1-207.
[37] PEARCE J A. Statistical analysis of major element patterns in basalts[J]. Journal of Petrology,1976,17:15-43.
[38] PEARCE J A,NORRY M J. Petrogenetic implications of Ti,Zr,Y,and Nb variations in volcanic rocks[J]. Contributions to Mineralogy and Petrology,1979,69:33-47.
[39] MULLEN E D. MnO/TiO 2/P2O5:a minor element discriminant for basaltic rocks of oceanic environments and its implications for petrogenesis[J]. Earth and Planetary Science Letters,1983,62:53-62.
(1)甘肃地矿局第三地质矿产勘查院. 1∶50 000刘家坪幅、三河幅、楚家坝幅区调报告. 2010.