应用大地热流和地下流体氦同位素组成资料计算中国大陆地壳生热元素丰度
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摘要
根据能量守恒原理和中国大陆实测热流数据,给出中国大陆地壳生热率上限值为1.3μWm-3。根据热流值和地下流体氦同位素组成资料,估算出中国大陆地壳生热率为0.58～1.12μWm-3,中位数为0.85μWm-3,相应的铀、钍、钾丰度范围分别是0.83～1.76μg/g、3.16～6.69μg/g和1.0%～2.12%。中国陆壳铀、钍、钾元素整体丰度值明显高于太古宇地壳,反映中国陆壳成分演化程度较高。同时,中国大陆地壳成分具有明显的横向非均匀性特征:东部地壳相对西北部富集铀、钍、钾等强不相容元素,褶皱带相对克拉通地区富集铀、钍、钾元素。基于大陆地壳SiO2含量与地壳生热率之间的正相关关系推断,中国东部地壳较西部富长英质组分,褶皱带地壳成分较克拉通富长英质组分。此区域性变化特征与基于地震波速资料推断的结果相符。基于中国大陆地壳生热率变化范围以及地震波速低于全球平均值的特征,推断Rudnick和Fountain(1995)、Rudnick和Gao(2003)、Weaver和Tarney(1984)、Shaw等(1986)以及Wedepohl(1995)的全球陆壳成分模型均高估了铀、钍、钾等强不相容元素丰度。
Based on the law of conservation of energy and heat flow data in continental China, the upper limit of heat production for the crust beneath continental China is determined as 1.3μWm-3. Then, using the data of the heat flow and helium isotopic composition of underground fluids, the heat productions of various tectonic units in the crust of continental China are estimated to be in the range of 0.58-1.12μWm-3 with a median of 0.85μWm-3, and the corresponding U, Th and K abundances are in the ranges of 0.83-1.76μg/g, 3.16-6.69μg/g and 1.0%-2.12% respectively. These data indicate that the abundances of the radioactive elements U, Th and K in continental crust of China are notably higher than those in the Archean crust, suggesting that the components of continental crust of China are highly evolved. In addition, the crustal composition of continental China exhibits significant lateral heterogeneity. The crust beneath eastern China is enriched in highly incompatible elements such as U, Th and K relative to that beneath western China, and the crust beneath fold belts is enriched in U, Th and K relative to that beneath cratonic areas. It is inferred on the basis of a positive correlation between the SiO2 content and heat production of continental crust that the crust beneath eastern China and fold belts are more felsic than beneath western China and cratons. This regional variation is consistent with the results of inference from the seismic wave velocity data in China. According to the fact that the seismic wave velocity and heat production range of the crust of continental China are lower than the global average values, combined with a comparison with the global crustal composition models published by previous studies, it is deduced that the abundances of highly incompatible elements such as U, Th and K in continental crust are overestimated in the average composition models of global continent crust constructed by Rudnick and Fountain (1995), Rudnick and Gao (2003), Weaver and Tarney (1984), Shaw et al. (1986) and Wedepohl (1995).
Based on the law of conservation of energy and heat flow data in continental China, the upper limit of heat production for the crust beneath continental China is determined as 1.3μWm-3. Then, using the data of the heat flow and helium isotopic composition of underground fluids, the heat productions of various tectonic units in the crust of continental China are estimated to be in the range of 0.58-1.12μWm-3 with a median of 0.85μWm-3, and the corresponding U, Th and K abundances are in the ranges of 0.83-1.76μg/g, 3.16-6.69μg/g and 1.0%-2.12% respectively. These data indicate that the abundances of the radioactive elements U, Th and K in continental crust of China are notably higher than those in the Archean crust, suggesting that the components of continental crust of China are highly evolved. In addition, the crustal composition of continental China exhibits significant lateral heterogeneity. The crust beneath eastern China is enriched in highly incompatible elements such as U, Th and K relative to that beneath western China, and the crust beneath fold belts is enriched in U, Th and K relative to that beneath cratonic areas. It is inferred on the basis of a positive correlation between the SiO2 content and heat production of continental crust that the crust beneath eastern China and fold belts are more felsic than beneath western China and cratons. This regional variation is consistent with the results of inference from the seismic wave velocity data in China. According to the fact that the seismic wave velocity and heat production range of the crust of continental China are lower than the global average values, combined with a comparison with the global crustal composition models published by previous studies, it is deduced that the abundances of highly incompatible elements such as U, Th and K in continental crust are overestimated in the average composition models of global continent crust constructed by Rudnick and Fountain (1995), Rudnick and Gao (2003), Weaver and Tarney (1984), Shaw et al. (1986) and Wedepohl (1995).
引文
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[18]汪洋.利用地下流体氦同位素比值估算大陆壳幔热流比例[J].地球物理学报,2000,43(6):762～770.W ang Yang.Estim ations of the ratio of crust/m antle heat flow using helium isotope ratio ofunderground fluid[J].C hinese Journal of G eophysics,2000,43(6):762～770(in C hinese w ith English abstract).
[19]W ang Y ang,W ang Jiyang,D eng Jingfu.G eotherm alcharacteristics and geological im plications of m ajor tectonic units in C hina[J].Journal of C hina U niversity of G eosciences(English Edition),2000,11(3):346～351.
[20]W ang Y ang,W ang Jiyang,X iong Liangping.H eatflow pattern in the m ainland of C hina and its geodynam ic significance[J].Acta G eologica Sinica(English Edition),2000,74:375～380.
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[25]赵平,汪集,汪缉安,等.中国东南地区岩石生热率分布特征[J].岩石学报,1995,11(3):292～305.Zhao Ping,W ang Jiyang,W ang Jian,et al.C haracteristics of heat production distribution in SE C hina[J].Acta Petrologica Sinica,1995,11(3):292～305(in C hinese w ith English abstract).
[26]吴澄宇,万渝生.稀土元素地球化学与花岗质岩石的成因-应用与问题[A].见:张炳熹等主编.岩石圈研究的现代方法[C].北京:原子能出版社,1997.201～214.W u C engyu,W an Y usheng.R are elem ent geochem istry and petrogenesisofgranitoid rocks—Applicationsand problem s[A].In:Zhang Bingxi,et al(ed.).M odern M ethods in the Lithospheric R esearch[C].Beijing:Atom ic Energy Press,1997.201～214(in C hinese).
[27]汪洋.对“新疆北部地区岩石生热率分布特征”一文的商榷[J].中国科技大学学报,2000,30(5):627～632.W ang Y ang.C om m ents on“Characteristics of heat production distribution in northern X injiang”[J].Journal of U niversity of Science and Technology ofChina,2000,30(5):627～632(in C hinese w ith English abstract).
[28]黎彤.中国陆壳及其沉积层和上地壳的化学元素丰度[J].地球化学,1994,23:140～145.LiTong.Elem entabundance ofcontinentalcrust,sedim entary layer and upper crust of C hina[J].G eochim ica,1994,23:140～145(in C hinese w ith English abstract).
[29]黎彤,倪守斌.塔里木—华北板块的地壳和岩石圈元素丰度[J].地质与勘探,1998,34:20～24.Li Tong,N i Soubin.Elem ent abundance of crust and lithosphere of Tarim-N orth C hina plate[J].G eology and Prospecting,1998,34:20～24(in C hinese w ith English abstract).
[30]倪守斌,满发胜,王兆荣,等.新疆北部地区岩石生热率分布特征[J].中国科技大学学报,1999,29(4):408～414.N iSoubin,M an Fasheng,W ang Zaorong,et al.C haracteristics of heat production distribution in northern X injiang[J].Journal of U niversity ofScience and Technology ofC hina,1999,29(4):408～414(in C hinese w ith English abstract).
[31]谢学锦.中国东部与全球大陆化学成分的比较[J].地质通报,2004,23(11):1057～1058.X ie X uejin.The com parison of chem ical com position of crust betw een the eastern C hina and global continent[J].G eological Bulletin ofC hina,2004,23(11):1057～1058(in C hinesew ith English abstract).
[32]LiS,M ooney W D.C rustalstructure ofC hina from deep seism ic sounding profiles[J].Tectonophysics,1998,288:105～113.
[33]G ao S,Zhang BR,Jin ZM,et al.H ow m afic is the low er continentalcrust[J].Earth PlanetSciLett,1998b,161:101～117.
[34]赵俊猛,刘国栋,卢造勋.天山造山带与准噶尔盆地岩石圈结构及其动力学模型[A].见:邓乃恭等主编.大陆构造及陆内变形暨第六届全国地质力学学术讨论会论文集[C].北京:地震出版社,1999.85～88.Zhao Junm eng,Liu G uodong,Lu Zaoxun.Lithospheric structure and dynam ic m odel of Tianshan orogenic belt and Junggar basin[A].In:D eng N aigong,et al(eds.).C ontinental Tectonics and Intra-plate D eform ation—The C ollected Papers of the6th N ationalSym posium on G eom echanics[C].Beijing:Seism ological Press,1999.85～88(in C hinese).
[35]R udnick R L,M cD onough W F,O'C onnell R J.Therm al structure,thickness and com position of continental lithosphere[J].C hem icalG eology,1998,145:395～411.
[36]M organ P.C rustal radiogeneic heat production and the selective survival of continentalcrust[J].J G eophys R es,1985,90:C561～C570.
[37]Lenardic A.O n the heat flow variation from Archean craton to Proterozoic m obile belts[J].JG eophysR es,1997,102:709～721.
[2]TaylorS R,M cLennan S M.The continentalcrust:Itscom position and evolution[M].C am bridge,M ass.:Blackw ell,1985,312.
[3]Taylor S R,M cLennan S M.The geochem ical evolution of the continentalcrust[J].R ev G eophys.1995,33:241～265.
[4]Shaw D M,C ram er J J,H iggins M D,et al.C om position of the C anadian Precam brian shield and the continentalcrust of the earth[A].In:D aw son J B,et al(eds).The nature of the Low er C ontinentalC rust.G eolSoc Spec Publ,1986,24:275～282.
[5]R udnick R L.M aking continentalcrust[J].N ature,1995,378:571～578.
[6]R udnick R L,Fountain D M.N ature and com position of the continental crust:A low er crustal perspective[J].R ev G eophys,1995,33:267～309.
[7]W edepohl K H.The com position of the continental crust[J].G eochim C osm ochim Acta,1995,59:1217～1232.
[8]鄢明才,迟清华.中国东部地壳与岩石的化学组成[M].北京:科学出版社,1997.1～292.Y an M ingcai,C hi Q inghua.C hem ical C om position of C rust and R ocksin Eastern China[M].Beijing:Science Press,1997.1～292(in C hinese).
[9]G ao S,Luo T C,Zhang B R,et al.C hem icalcom position ofthe continental crust as revealed by studies in East C hina[J].G eochim ica etC osm ochim ica Acta,1998,62:1959～1975.
[10]高山,骆庭川,张本仁,等.中国东部地壳的结构和组成[J].中国科学D辑,1999,29:204～213.G ao San,Luo Tingchuan,Zhang Benren,et al.C rustal structure and com position ofeastern C hina[J].Science in C hina(Series D),1999,29:204～213(in C hinese).
[11]R udnick R L,G ao S.The com position of continentalcrust[A].In:R udnick R L(eds.).Treatise on G eochem istry,Vol.3,The C rust[C].O xford:Elsevier,2003,1～64.
[12]M cLennan S M,Taylor S R.H eat flow and the chem ical com position ofcontinentalcrust[J].JG eol,1996,104:369～377.
[13]R ybach L.D eterm ination ofheatproduction rate[A].In:H aenel R,R ybach L,Stegena L(eds).H andbook ofTerrestrialH eat-Flow D ensity D eterm ination[C].D ordrecht:Kluw erA cadem ic Publishers,1988.125～142.
[14]H ofm ann A W.C hem ical differentiation of the Earth:The relationship betw een m antle,continentalcrustand oceanic crust[J].Earth PlanetSciLett,1988,90:297～314.
[15]C hristensen N I,M ooney W D.Seism ic velocity structure and com position ofthe continentalcrust:A globalview[J].JG eophys R es,1995,100:9761～9788.
[16]赵伦山,张本仁.地球化学[M].北京:地质出版社,1988.1～404.Zhao Lunsan,Zhang Benren.G eochem istry[M].Beijing:G eologicalPublishing H ouse,1988.1～404(in C hinese).
[17]Jaupart C,M areschal J C,G uillou-Frottier L,D availle A.H eat flow and thicknessofthe lithosphere in the C anadian Shield[J].J G eophysR es,1998,103:15269～15286.
[18]汪洋.利用地下流体氦同位素比值估算大陆壳幔热流比例[J].地球物理学报,2000,43(6):762～770.W ang Yang.Estim ations of the ratio of crust/m antle heat flow using helium isotope ratio ofunderground fluid[J].C hinese Journal of G eophysics,2000,43(6):762～770(in C hinese w ith English abstract).
[19]W ang Y ang,W ang Jiyang,D eng Jingfu.G eotherm alcharacteristics and geological im plications of m ajor tectonic units in C hina[J].Journal of C hina U niversity of G eosciences(English Edition),2000,11(3):346～351.
[20]W ang Y ang,W ang Jiyang,X iong Liangping.H eatflow pattern in the m ainland of C hina and its geodynam ic significance[J].Acta G eologica Sinica(English Edition),2000,74:375～380.
[21]任继舜.中国及邻区大地构造图(1:5000000)[M].北京:地质出版社,1999.R en Jishun.G eotectonic m ap of C hina and its adjacent area(1:5000000)[M].Beijing:G eologicalPublishing H ouse,1999.
[22]Y uan X uecheng.Atlas of G eophysics in C hina,Publication N o.201of the International Lithosphere Program[M].Beijing:G eologicalPublishing H ouse,1996.1～217.
[23]W illiam s C F,Anderson R N.Therm ophysicalproperities of the Earth's crust:In situ m easurem ents from continental and ocean drilling[J].JG eophysR es,1990,95:9209～9236.
[24]赵平.中国东南地区岩石生热率研究[D].北京:中国科学院地质研究所,1993,1～96.Zhao Ping.H eatprodution rate ofrocksin southeastern C hina(Ph.D.thesis,Institute ofG eology)[D].C hinese Academ y ofSciences,Beijing:1993,1～96(in C hinese w ith English abstract).
[25]赵平,汪集,汪缉安,等.中国东南地区岩石生热率分布特征[J].岩石学报,1995,11(3):292～305.Zhao Ping,W ang Jiyang,W ang Jian,et al.C haracteristics of heat production distribution in SE C hina[J].Acta Petrologica Sinica,1995,11(3):292～305(in C hinese w ith English abstract).
[26]吴澄宇,万渝生.稀土元素地球化学与花岗质岩石的成因-应用与问题[A].见:张炳熹等主编.岩石圈研究的现代方法[C].北京:原子能出版社,1997.201～214.W u C engyu,W an Y usheng.R are elem ent geochem istry and petrogenesisofgranitoid rocks—Applicationsand problem s[A].In:Zhang Bingxi,et al(ed.).M odern M ethods in the Lithospheric R esearch[C].Beijing:Atom ic Energy Press,1997.201～214(in C hinese).
[27]汪洋.对“新疆北部地区岩石生热率分布特征”一文的商榷[J].中国科技大学学报,2000,30(5):627～632.W ang Y ang.C om m ents on“Characteristics of heat production distribution in northern X injiang”[J].Journal of U niversity of Science and Technology ofChina,2000,30(5):627～632(in C hinese w ith English abstract).
[28]黎彤.中国陆壳及其沉积层和上地壳的化学元素丰度[J].地球化学,1994,23:140～145.LiTong.Elem entabundance ofcontinentalcrust,sedim entary layer and upper crust of C hina[J].G eochim ica,1994,23:140～145(in C hinese w ith English abstract).
[29]黎彤,倪守斌.塔里木—华北板块的地壳和岩石圈元素丰度[J].地质与勘探,1998,34:20～24.Li Tong,N i Soubin.Elem ent abundance of crust and lithosphere of Tarim-N orth C hina plate[J].G eology and Prospecting,1998,34:20～24(in C hinese w ith English abstract).
[30]倪守斌,满发胜,王兆荣,等.新疆北部地区岩石生热率分布特征[J].中国科技大学学报,1999,29(4):408～414.N iSoubin,M an Fasheng,W ang Zaorong,et al.C haracteristics of heat production distribution in northern X injiang[J].Journal of U niversity ofScience and Technology ofC hina,1999,29(4):408～414(in C hinese w ith English abstract).
[31]谢学锦.中国东部与全球大陆化学成分的比较[J].地质通报,2004,23(11):1057～1058.X ie X uejin.The com parison of chem ical com position of crust betw een the eastern C hina and global continent[J].G eological Bulletin ofC hina,2004,23(11):1057～1058(in C hinesew ith English abstract).
[32]LiS,M ooney W D.C rustalstructure ofC hina from deep seism ic sounding profiles[J].Tectonophysics,1998,288:105～113.
[33]G ao S,Zhang BR,Jin ZM,et al.H ow m afic is the low er continentalcrust[J].Earth PlanetSciLett,1998b,161:101～117.
[34]赵俊猛,刘国栋,卢造勋.天山造山带与准噶尔盆地岩石圈结构及其动力学模型[A].见:邓乃恭等主编.大陆构造及陆内变形暨第六届全国地质力学学术讨论会论文集[C].北京:地震出版社,1999.85～88.Zhao Junm eng,Liu G uodong,Lu Zaoxun.Lithospheric structure and dynam ic m odel of Tianshan orogenic belt and Junggar basin[A].In:D eng N aigong,et al(eds.).C ontinental Tectonics and Intra-plate D eform ation—The C ollected Papers of the6th N ationalSym posium on G eom echanics[C].Beijing:Seism ological Press,1999.85～88(in C hinese).
[35]R udnick R L,M cD onough W F,O'C onnell R J.Therm al structure,thickness and com position of continental lithosphere[J].C hem icalG eology,1998,145:395～411.
[36]M organ P.C rustal radiogeneic heat production and the selective survival of continentalcrust[J].J G eophys R es,1985,90:C561～C570.
[37]Lenardic A.O n the heat flow variation from Archean craton to Proterozoic m obile belts[J].JG eophysR es,1997,102:709～721.
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