湖南江永回龙圩煌斑岩特征——兼论华夏地块西部煌斑岩类岩石成因和构造意义
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摘要
利用锆石U-Pb年代学、矿物化学、全岩元素和同位素地球化学等方法,结合前人的研究成果,探讨了华夏地块西部煌斑岩类岩石成因和构造意义。回龙圩云煌岩形成时代为172 Ma,斑晶为金云母,全岩主要化学成分SiO_2 47.84%～48.91%、 Al_2O_311.42%～12.35%、 CaO 10.91%～13.14%、 K_2O 2.34%～3.65%, Mg~#为64～71,为钾玄质碱性基性岩。云煌岩稀土元素总量较低(∑REE=171～187),轻稀土元素富集重稀土元素亏损(LREE/HREE=10～11),δEu=0.85～0.87,类似洋岛玄武岩的稀土元素分配模式;微量元素Rb、 Ba、 K等大离子亲石元素富集, Nb、 Ta、 Ti等高场强元素亏损。云煌岩(~(87)Sr/~(86)Sr)_i为0.705 930～0.706 170,(~(143)Nd/~(144)Nd)_i为0.512 334～0.512 379,ε_(Nd)(t)值为-0.74～-1.61;全岩δ~(18)O_(V-SMOW)值为9.7‰。全岩主量元素、微量元素和Sr-Nd-O同位素地球化学特征表明,回龙圩云煌岩为受富集组分交代的岩石圈地幔发生部分熔融的产物,富集组分为来自软流圈的含上地壳或俯冲洋壳沉积物的流体。华夏地块西部沿祁东至罗城一带分布的晚三叠世、中侏罗世和早白垩世的煌斑岩类和碱性玄武岩表明,区域上在这3个阶段有深大断裂活动,意味着华夏地块西部地区从晚三叠世以来就转换为岩石圈伸展的构造背景,该背景激活了长期存在的薄弱地带,华夏地块西部有煌斑岩类和碱性玄武岩分布的祁东至罗城一线可能是华夏地块西缘与扬子地块的分界线。
Petrogenesis and tectonic significance of lamprophyres in western Cathaysia Block are discussed using zircon U-Pb geochronological, mineral chemical, bulk-rock elemental and isotopic methods, combined with previous studies. Our study shows that emplacement age of minette in Huilongxu is 172 Ma, phenocryst of the minette is phlogopite, the major elements contents of minette include SiO_2(47.84%-48.91%), Al_2O_3(11.42%-12.35%), CaO(10.91%-13.14%), K_2O(2.34%-3.65%), Mg~#=64-71, which belong to shoshonitic alkaline basic rock. The minette has lower total REE content(ΣREE=171-187). Chondrite-normalised rare-earth elements(REE) patterns show light rare-earth element enrichment and heavy rare-earth element depletion(LREE/HREE=10-11), δEu=0.85-0.87, like OIB rare-earth elements patterns. Primitive mantle normalised trace-element patterns show that the minette is enriched with large ion lithophile elements(such as Rb, Ba, K) and depleted in high field strength elements(such as Nb, Ta, Ti). The minette has initial(~(87)Sr/~(86)Sr)_i values of 0.705 930 to 0.706 170, initial(~(143)Nd/~(144)Nd)_i values of 0.512 334 to 0.512 379, and ε_(Nd)(t) ranges from-0.74 to-1.61, with oxygen isotopic value(δ~(18)O_(V-SMOW)) of 9.7‰. Bulk-rock major, trace elemental and Sr-Nd-O isotopic geochemical characteristics indicate that the minette is the melting product from lithosphere mantle which was metasomatized by fluids enriched with upper crustal materials or marine sediments from asthenosphere. Lamprophyres and alkaline basalts from Qidong-Luocheng belt in western Cathaysia Block prove that Late Triassic, Middle Jurassic and early Cretaceous deep-faults were moved, implying tectonic setting of the western Cathaysia Block transformed into lithospheric extension since the Late Triassic. The extension setting reactivated long-lived lithospheric zones of weakness, indicating that Qidong-Luocheng belt with lamprophyres and alkaline basalts could be the suture between Yangtze Block and Cathaysia Block.
Petrogenesis and tectonic significance of lamprophyres in western Cathaysia Block are discussed using zircon U-Pb geochronological, mineral chemical, bulk-rock elemental and isotopic methods, combined with previous studies. Our study shows that emplacement age of minette in Huilongxu is 172 Ma, phenocryst of the minette is phlogopite, the major elements contents of minette include SiO_2(47.84%-48.91%), Al_2O_3(11.42%-12.35%), CaO(10.91%-13.14%), K_2O(2.34%-3.65%), Mg~#=64-71, which belong to shoshonitic alkaline basic rock. The minette has lower total REE content(ΣREE=171-187). Chondrite-normalised rare-earth elements(REE) patterns show light rare-earth element enrichment and heavy rare-earth element depletion(LREE/HREE=10-11), δEu=0.85-0.87, like OIB rare-earth elements patterns. Primitive mantle normalised trace-element patterns show that the minette is enriched with large ion lithophile elements(such as Rb, Ba, K) and depleted in high field strength elements(such as Nb, Ta, Ti). The minette has initial(~(87)Sr/~(86)Sr)_i values of 0.705 930 to 0.706 170, initial(~(143)Nd/~(144)Nd)_i values of 0.512 334 to 0.512 379, and ε_(Nd)(t) ranges from-0.74 to-1.61, with oxygen isotopic value(δ~(18)O_(V-SMOW)) of 9.7‰. Bulk-rock major, trace elemental and Sr-Nd-O isotopic geochemical characteristics indicate that the minette is the melting product from lithosphere mantle which was metasomatized by fluids enriched with upper crustal materials or marine sediments from asthenosphere. Lamprophyres and alkaline basalts from Qidong-Luocheng belt in western Cathaysia Block prove that Late Triassic, Middle Jurassic and early Cretaceous deep-faults were moved, implying tectonic setting of the western Cathaysia Block transformed into lithospheric extension since the Late Triassic. The extension setting reactivated long-lived lithospheric zones of weakness, indicating that Qidong-Luocheng belt with lamprophyres and alkaline basalts could be the suture between Yangtze Block and Cathaysia Block.
引文
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[10]Liu C Z,Liu Z C,Wu F Y,et al.Mesozoic accretion of juvenile sub-continental lithospheric mantle beneath South China and its implications:geochemical and Re-Os isotopic results from Ningyuan mantle xenoliths[J].Chemical Geology,2012,291:186-198.
[11]郭锋,范蔚茗,林舸.湘南中生代玄武岩浆成因与岩石圈—软流圈相互作用[J].矿物岩石地球化学通报,1998,17(1):1-4.
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[14]Zhao Z H,Bao Z W,Zhang B Y.Geochemistry of the Mesozoic basaltic rocks in southern Hunan Province[J].Science in China (Series D),1998,41(S):102-112.
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[16]王磊,金鑫镖,王新宇,等.桂北罗城垒洞煌斑岩形成过程:地球化学、年代学和Sr-Nd-Pb同位素约束[J].地质科技情报,2015,34(1):10-19.
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[18]梁恩云,陈迪,邹光均,等.湖南江永回龙圩煌斑岩地球化学特征及其构造意义[J].桂林理工大学学报,2018,38(4):640-646.
[19]Le Maitre R W.Igneous rocks:a classification and glossary of terms,recommendations of the international union of geological sciences subcommission on the systematics of igneous rocks[M].Cambridge:Cambridge University Press,2002.
[20]Foley S F,Venturelli G,Green D H,et al.The ultrapotassic rocks:characteristics,classification and constraints for petrogenetic models[J].Earth-Science Reviews,1987,24:81-134.
[21]Wilson M.Igneous petrogenesis[M].Netherlands:Springer,1989.
[22]朱介寿,蔡学林,曹家敏,等.中国华南及东海地区岩石圈三维结构及演化[M].北京:地质出版社,2005.
[23]宋彪,张玉梅,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 (S):26-30.
[24]Song S G,Su L,Li X H,et al.Tracing the 850-Ma continental flood basalts from a piece of subducted continental crust in the North Qaidam UHPM belt,NW China[J].Precambrian Research,2010,183:805-816.
[25]Gao S,Liu X M,Yuan H L,et al.Determination of forty two major and trace elements in USGS and NIST SRM glasses by laser ablation-inductively coupled plasma-mass spectrometry[J].Geostandards Newsletter,2002,26(2):181-196.
[26]Rudnick R L,Gao S,Ling W L,et al.Petrology and geochemistry of spinel peridotite xenoliths from Hannuoba and Qixia,North China craton[J].Lithos,2004,77:609-637.
[27]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 of Petrology,2010,51:537-571.
[28]Liu Y S,Hu Z C,Zong K Q,et al.Reappraisement and refinement of zircon U-Pb isotope and trace element analyses by LA-ICP-MS[J].Chinese Science Bulletin,2010,55 (15):1535-1546.
[29]Blichert-Toft J,Chauvel C,Albarède F.Separation of Hf and Lu for high-precision isotope analysis of rock samples by magnetic sector-multiple collector ICP-MS[J].Contributions to Mineralogy and Petrology,1997,127:248-260.
[30]Hu Z C,Liu Y S,Gao S,et al.Improved in situ Hf isotope ratio analysis of zircon using newly designed X skimmer cone and jet sample cone in combination with the addition of nitrogen by laser ablation multiple collector ICP-MS[J].Journal of Analytical Atomic Spectrometry,2012,27:1391-1399.
[31]Hoskin P W O,Schaltegger U.The composition of zircon and igneous and metamorphic petrogenesis[J].Reviews in Mineralogy and Geochemistry,2003,53 (1):27-62.
[32]Rock N M S.Lamprophyres[M].New York:Blackie and Son Ltd.,1991.
[33]Miyashiro A.Nature of alkalic volcanic rock series[J].Contributions to Mineralogy and Petrology,1978,66:91-104.
[34]Sun S -s,McDonough W F.Chemical and isotopic systematics of oceanic basalts:implications for mantle composition and processes[M]//Saunders A D,Norry M J.Magmatism in the ocean basins.London:Geological Society Special Publication,1989,42:313-345.
[35]Prelevic D,Foley S F,Romer R,et al.Mediterranean Tertiary lamproites derived from multiple source components in postcollisional geodynamics[J].Geochimica et Cosmochimica Acta,2008,72:2125-2156.
[36]Zhao Z D,Mo X X,Dilek Y,et al.Geochemical and Sr-Nd-Pb-O isotopic compositions of the post-collisional ultrapotassic magmatism in SW Tibet:petrogenesis and implications for India intra-continental subduction beneath southern Tibet[J].Lithos,2009,113:190-212.
[37]Gao Y F,Hou Z Q,Kamber B S,et al.Lamproitic rocks from a continental collision zone:evidence for recycling of subducted Tethyan oceanic sediments in the mantle beneath southern Tibet[J].Journal of Petrology,2007,48(4):729-752.
[38]Lee M J,Lee J I,Choe W H,et al.Trace element and isotopic evidence for temporal changes of the mantle sources in the South Shetland Islands,Antarctica[J].Geochemical Journal,2008,42:207-219.
[39]Jahn B M,Wu F Y,Lo C H,et al.Crust-mantle interaction induced by deep subduction of the continental crust:geochemical and Sr-Nd isotopic evidence from post-collisional mafic-ultramafic intrusions of the northern Dabie complex,central China[J].Chemical Geology,1999,157:119-146.
[40]郭智超,时毓,王新宇,等.桂北罗城垒洞煌斑岩LA-ICP-MS锆石U-Pb定年及其地质意义[J].桂林理工大学学报,2018,38 (2):208-216.
[41]James D E.The combined use of oxygen and radiogenic isotopes as indicators of crustal contamination[J].Annual Review of Earth and Planetary Sciences,1981,9:311-344.
[42]Taylor S R,McLennan S M.The continental crust:its composition and evolution[M].Palo Alto,Canada:Blackwell Scientific Publications,1985.
[43]Yang J B,Zhao Z D,Hou Q Y,et al.Petrogenesis of Cretaceous (133-84 Ma) intermediate dykes and host granites in southeastern China:implications for lithospheric extension,continental crustal growth,and geodynamics of Palaeo-Pacific subduction[J].Lithos,2018,296-299:195-211.
[44]Liu L,Xu X S,Zou H B.Episodic eruptions of the Late Mesozoic volcanic sequences in southeastern Zhejiang,SE China:petrogenesis and implications for the geodynamics of paleo-Pacific subduction[J].Lithos,2012,154:166-180.
[2]Li Z X,Li X H,Chung S L,et al.Magmatic switch-on and switch-off along the South China continental margin since the Permian:transition from an Andean-type to a Western Pacific-type plate boundary[J].Tectonophysics,2012,532-535:271-290.
[3]Chung S L,Cheng H,Jahn B M,et al.Major and trace element,and Sr-Nd isotope constraints on the origin of Paleogene volcanism in South China prior to the South China Sea opening[J].Lithos,1997,40:203-220.
[4]Huang J,Li S G,Xiao Y L,et al.Origin of low δ26Mg Cenozoic basalts from South China Block and their geodynamic implications[J].Geochimica et Cosmochimica Acta,2015,164:298-317.
[5]Li Y Q,Ma C Q,Robinson P T,et al.Recycling of oceanic crust from a stagnant slab in the mantle transition zone:evidence from Cenozoic continental basalts in Zhejiang Province,SE China[J].Lithos,2015,230:146-165.
[6]Zou H B,Zindler A,Xu X S,et al.Major,trace element,and Nd,Sr and Pb isotope studies of Cenozoic basalts in SE China:mantle sources,regional variations,and tectonic significance[J].Chemical Geology,2000,171:33-47.
[7]Wang Y J,Fan W M,Zhang G W,et al.Phanerozoic tectonics of the South China Block:key observations and controversies[J].Gondwana Research,2013,23:1273-1305.
[8]Zheng J P,O’ Reilly S Y,Griffin W L,et al.Nature and evolution of Mesozoic-Cenozoic lithospheric mantle beneath the Cathaysia block,SE China[J].Lithos,2004,74:41-65.
[9]Li X Y,Zheng J P,Sun M,et al.The Cenozoic lithospheric mantle beneath the interior of South China Block:constraints from mantle xenoliths in Guangxi Province[J].Lithos,2014,210-211:14-26.
[10]Liu C Z,Liu Z C,Wu F Y,et al.Mesozoic accretion of juvenile sub-continental lithospheric mantle beneath South China and its implications:geochemical and Re-Os isotopic results from Ningyuan mantle xenoliths[J].Chemical Geology,2012,291:186-198.
[11]郭锋,范蔚茗,林舸.湘南中生代玄武岩浆成因与岩石圈—软流圈相互作用[J].矿物岩石地球化学通报,1998,17(1):1-4.
[12]Jiang Y H,Jiang S Y,Dai B Z,et al.Middle to late Jurassic felsic and mafic magmatism in southern Hunan province,southeast China:implications for a continental arc to rifting[J].Lithos,2009,107:185-204.
[13]杨金豹,赵志丹,莫宣学,等.湖南道县虎子岩碱性玄武岩及其基性捕虏体成因和地质意义[J].岩石学报,2015,31 (5):1421-1432.
[14]Zhao Z H,Bao Z W,Zhang B Y.Geochemistry of the Mesozoic basaltic rocks in southern Hunan Province[J].Science in China (Series D),1998,41(S):102-112.
[15]梁新权,范蔚茗,王岳军.湖南中生代陆内构造变形的深部过程:煌斑岩地球化学示踪[J].地球学报,2003,24 (6):603-610.
[16]王磊,金鑫镖,王新宇,等.桂北罗城垒洞煌斑岩形成过程:地球化学、年代学和Sr-Nd-Pb同位素约束[J].地质科技情报,2015,34(1):10-19.
[17]Su H M,Jiang S Y,Zhang D Y,et al.Partial melting of subducted sediments produced Early Mesozoic calc-alkaline lamprophyres from northern Guangxi Province,South China[J].Scientific Reports,2017(7):4864.DOI:10.1038/s41598-017-05228-w.
[18]梁恩云,陈迪,邹光均,等.湖南江永回龙圩煌斑岩地球化学特征及其构造意义[J].桂林理工大学学报,2018,38(4):640-646.
[19]Le Maitre R W.Igneous rocks:a classification and glossary of terms,recommendations of the international union of geological sciences subcommission on the systematics of igneous rocks[M].Cambridge:Cambridge University Press,2002.
[20]Foley S F,Venturelli G,Green D H,et al.The ultrapotassic rocks:characteristics,classification and constraints for petrogenetic models[J].Earth-Science Reviews,1987,24:81-134.
[21]Wilson M.Igneous petrogenesis[M].Netherlands:Springer,1989.
[22]朱介寿,蔡学林,曹家敏,等.中国华南及东海地区岩石圈三维结构及演化[M].北京:地质出版社,2005.
[23]宋彪,张玉梅,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 (S):26-30.
[24]Song S G,Su L,Li X H,et al.Tracing the 850-Ma continental flood basalts from a piece of subducted continental crust in the North Qaidam UHPM belt,NW China[J].Precambrian Research,2010,183:805-816.
[25]Gao S,Liu X M,Yuan H L,et al.Determination of forty two major and trace elements in USGS and NIST SRM glasses by laser ablation-inductively coupled plasma-mass spectrometry[J].Geostandards Newsletter,2002,26(2):181-196.
[26]Rudnick R L,Gao S,Ling W L,et al.Petrology and geochemistry of spinel peridotite xenoliths from Hannuoba and Qixia,North China craton[J].Lithos,2004,77:609-637.
[27]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 of Petrology,2010,51:537-571.
[28]Liu Y S,Hu Z C,Zong K Q,et al.Reappraisement and refinement of zircon U-Pb isotope and trace element analyses by LA-ICP-MS[J].Chinese Science Bulletin,2010,55 (15):1535-1546.
[29]Blichert-Toft J,Chauvel C,Albarède F.Separation of Hf and Lu for high-precision isotope analysis of rock samples by magnetic sector-multiple collector ICP-MS[J].Contributions to Mineralogy and Petrology,1997,127:248-260.
[30]Hu Z C,Liu Y S,Gao S,et al.Improved in situ Hf isotope ratio analysis of zircon using newly designed X skimmer cone and jet sample cone in combination with the addition of nitrogen by laser ablation multiple collector ICP-MS[J].Journal of Analytical Atomic Spectrometry,2012,27:1391-1399.
[31]Hoskin P W O,Schaltegger U.The composition of zircon and igneous and metamorphic petrogenesis[J].Reviews in Mineralogy and Geochemistry,2003,53 (1):27-62.
[32]Rock N M S.Lamprophyres[M].New York:Blackie and Son Ltd.,1991.
[33]Miyashiro A.Nature of alkalic volcanic rock series[J].Contributions to Mineralogy and Petrology,1978,66:91-104.
[34]Sun S -s,McDonough W F.Chemical and isotopic systematics of oceanic basalts:implications for mantle composition and processes[M]//Saunders A D,Norry M J.Magmatism in the ocean basins.London:Geological Society Special Publication,1989,42:313-345.
[35]Prelevic D,Foley S F,Romer R,et al.Mediterranean Tertiary lamproites derived from multiple source components in postcollisional geodynamics[J].Geochimica et Cosmochimica Acta,2008,72:2125-2156.
[36]Zhao Z D,Mo X X,Dilek Y,et al.Geochemical and Sr-Nd-Pb-O isotopic compositions of the post-collisional ultrapotassic magmatism in SW Tibet:petrogenesis and implications for India intra-continental subduction beneath southern Tibet[J].Lithos,2009,113:190-212.
[37]Gao Y F,Hou Z Q,Kamber B S,et al.Lamproitic rocks from a continental collision zone:evidence for recycling of subducted Tethyan oceanic sediments in the mantle beneath southern Tibet[J].Journal of Petrology,2007,48(4):729-752.
[38]Lee M J,Lee J I,Choe W H,et al.Trace element and isotopic evidence for temporal changes of the mantle sources in the South Shetland Islands,Antarctica[J].Geochemical Journal,2008,42:207-219.
[39]Jahn B M,Wu F Y,Lo C H,et al.Crust-mantle interaction induced by deep subduction of the continental crust:geochemical and Sr-Nd isotopic evidence from post-collisional mafic-ultramafic intrusions of the northern Dabie complex,central China[J].Chemical Geology,1999,157:119-146.
[40]郭智超,时毓,王新宇,等.桂北罗城垒洞煌斑岩LA-ICP-MS锆石U-Pb定年及其地质意义[J].桂林理工大学学报,2018,38 (2):208-216.
[41]James D E.The combined use of oxygen and radiogenic isotopes as indicators of crustal contamination[J].Annual Review of Earth and Planetary Sciences,1981,9:311-344.
[42]Taylor S R,McLennan S M.The continental crust:its composition and evolution[M].Palo Alto,Canada:Blackwell Scientific Publications,1985.
[43]Yang J B,Zhao Z D,Hou Q Y,et al.Petrogenesis of Cretaceous (133-84 Ma) intermediate dykes and host granites in southeastern China:implications for lithospheric extension,continental crustal growth,and geodynamics of Palaeo-Pacific subduction[J].Lithos,2018,296-299:195-211.
[44]Liu L,Xu X S,Zou H B.Episodic eruptions of the Late Mesozoic volcanic sequences in southeastern Zhejiang,SE China:petrogenesis and implications for the geodynamics of paleo-Pacific subduction[J].Lithos,2012,154:166-180.