扬子板块北缘光雾山地区钾长花岗岩年代学、地球化学特征及构造意义
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摘要
为了限定扬子板块北缘地区新元古代岩浆活动事件的准确时间及和探讨岩石成因,本文对出露于四川省南江县光雾山钾长花岗岩进行了LA-ICP-MS锆石U-Pb定年和岩石地球化学研究。结果表明光雾山地区钾长花岗岩锆石U-Pb年龄为836.3 Ma±8.3 Ma,属于新元古代花岗岩。岩石具有高w(SiO_2)(72.68%～78.10%),w(K_2O)(4.26%～5.32%),w(Na_2O)(1.68%～3.38%),相对富钾(K_2O/Na_2O=1.12～2.54),高碱(w(Na_2O+K_2O)=7.64%～8.99%),低P_2O_5含量等特征,铝饱和指数A/CNK=0.99～1.49,光雾山花岗岩属于过铝质高钾钙碱性花岗岩。岩石具有轻稀土元素相对富集,重稀土元素亏损的特征,具有明显Eu负异常,δEu为0.48～0.73。光雾山花岗岩微量元素表现出Rb,Th,K,Nd,Sm元素富集,Ba,Nb,Ta,Sr,P,Ti元素亏损的特点。地球化学研究表明,光雾山钾长花岗岩主要以粘土岩部分熔融为主及少部分含粘土的变质杂砂岩部分熔融形成的。岩浆可能来源于本区结晶基底新太古界—古元古界后河岩群和褶皱基底中—新元古界火地亚群中深变质岩为代表的地壳物质的部分熔融产物,为壳源成因类型,具有岛弧型花岗岩特征,形成于岛弧构造环境。光雾山钾长花岗岩的形成是新元古界时期扬子板块与华北板块之间的俯冲碰撞、岛弧形成构造演化过程中使区域地壳不断加厚和地壳深融作用的响应。扬子陆块北缘南江地区约836 Ma同碰撞岛弧型钾长花岗岩的发现,表明该地区在约836 Ma时为Rodinia超大陆汇聚形成阶段,此时期该区Rodinia超大陆尚未进入大陆裂解阶段。
The chronology and geochemistry of Guangwushan K-feldspar granites in the northern margin of the Yangtze block are studied by means of LA-ICP-MS zircon U-Pb dating and geochemical analysis techniques so as to constrain the precise emplacement time and genesis of the Neoproterozoic igneous rocks in the Nanjiang County of Sichuan Province. The zircon LA-ICP-MS dating reveals that the Guangwushan K-feldspar granites were formed in the Neoproterozoic period with an emplacement age of 836.3 Ma±8.3 Ma. Geochemical analyses show that the Guangwushan K-feldspar granites have medium content of w(SiO_2)(72.68%～78.10%),high K(K_2/Na_2O=1.12～2.54) and peraluminous ratio(A/CNK)=0.99～1.49) and belong to k black to high-K calc-alkaline peraluminous S-type granites, similar to calc-alkaline rocks of island arc or active continental margin. The ΣREE of granites ranges from 158.85×10~(-6) to 304.26×10~(-6) with rightward incline pattern and obvious negative Eu abnormity(δEu=0.48～0.73).Rb,Th,K,Nd and Sm are enriched and Ba,Nb,Ta,Sr,P and Ti depleted,also similar to calc-alkaline rocks in island arc or active continental margin. It is proposed that the original rocks of the granites are greywacke and mudstone and the magma source is probably derived from partial melting of the Neo Archean Houhe Rock Group and Paleoproterozoic to mid-Proterozoic Huodeya Group metamorphosed basement.Based on the geochemical characteristics,it is considered that the Neoproterozoic K-feldspar granites were in an island arc and syn-collision environment and formed in a transitional tectonic setting from the compression system to the island arc system.The tectonic-magmatic movement in northern margin of Yangtze block is intimately related to the subduction and collision between the Yangtze plate and North China plate,and the granites were resulted from the thickening and deep melting of the regional crust in the geological process.
The chronology and geochemistry of Guangwushan K-feldspar granites in the northern margin of the Yangtze block are studied by means of LA-ICP-MS zircon U-Pb dating and geochemical analysis techniques so as to constrain the precise emplacement time and genesis of the Neoproterozoic igneous rocks in the Nanjiang County of Sichuan Province. The zircon LA-ICP-MS dating reveals that the Guangwushan K-feldspar granites were formed in the Neoproterozoic period with an emplacement age of 836.3 Ma±8.3 Ma. Geochemical analyses show that the Guangwushan K-feldspar granites have medium content of w(SiO_2)(72.68%～78.10%),high K(K_2/Na_2O=1.12～2.54) and peraluminous ratio(A/CNK)=0.99～1.49) and belong to k black to high-K calc-alkaline peraluminous S-type granites, similar to calc-alkaline rocks of island arc or active continental margin. The ΣREE of granites ranges from 158.85×10~(-6) to 304.26×10~(-6) with rightward incline pattern and obvious negative Eu abnormity(δEu=0.48～0.73).Rb,Th,K,Nd and Sm are enriched and Ba,Nb,Ta,Sr,P and Ti depleted,also similar to calc-alkaline rocks in island arc or active continental margin. It is proposed that the original rocks of the granites are greywacke and mudstone and the magma source is probably derived from partial melting of the Neo Archean Houhe Rock Group and Paleoproterozoic to mid-Proterozoic Huodeya Group metamorphosed basement.Based on the geochemical characteristics,it is considered that the Neoproterozoic K-feldspar granites were in an island arc and syn-collision environment and formed in a transitional tectonic setting from the compression system to the island arc system.The tectonic-magmatic movement in northern margin of Yangtze block is intimately related to the subduction and collision between the Yangtze plate and North China plate,and the granites were resulted from the thickening and deep melting of the regional crust in the geological process.
引文
[1] 四川省地质矿产局.四川省区域地质志[M].北京:地质出版社,1991.
[2] 魏显贵,杜思清,何政伟,等.米仓山地区构造演化[J].矿物岩石,1997,17(增刊):107-113.
[3] 肖渊甫,马润则,何政伟,等.米仓山碱性杂岩单元特征及构造环境分析[J].矿物岩石,1997,17(增刊):59-66.
[4] 肖渊甫,马润则,魏显贵,等.米仓山澄江期基性侵入杂岩特征及其成因探讨[J].成都理工学院报,1998,25(4):537-542.
[5] 马润则,肖渊甫,魏显贵,等.米仓山地区岩浆活动与构造演化[J].矿物岩石,1997,17(增刊):76-82.
[6] 马润泽,肖渊甫.米仓山地区晋宁期基性超基性侵入岩中造岩矿物研究[J].成都理工学院学报,2001,28(1):34-39.
[7] 裴先治,李佐臣,丁仨平,等.扬子陆块西北缘轿子顶新元古代过铝质花岗岩:锆石SHRIMP U-Pb年龄和岩石地球化学及其构造意义[J].地学前缘,2009,16(3):231-249.
[8] Zhou Meifu,Kennedy A K,Sun M,et al.Neo-proterozoic arc-related mafic intrusions in the northern margin of South China:Implications for accretion of Rodina[J].Geology,2002a,110:611-618.
[9] Zhao Junhong,Zhou Meifu.Secular evolution of the Neoproterozoic lithospheric mante underneath the northern margin of the Yangtze B1ock,South China[J].Lithos,2009,107:152-168.
[10] Dong Yunpeng,Liu Xiaoming,Santosh M,et al.Neoproterozoic subduction tectonics of the Yangtze Block in South China:Constrains from zircon U-Pb geochronology and geochemistry of mafic intrusions in the Harman Massif[J].Precambrian Research,2011a,189(1):66-90.
[11] 敖文昊,张宇昆,张瑞英,等.新元古代扬子北缘地壳增生事件:来自汉南祖师店奥长花岗岩地球化学、锆石 LA-ICP-MS U-Pb 年代学和 Hf 同位素证据[J].地质论评,2014,60(6):1 393-1 408.
[12] 凌文黎,王欲华,程建萍.扬子北缘晋宁期望江山基性岩体的地球化学特征及其构造背景[J].矿物岩石地球化学通报,2001,20(4):218-222.
[13] 赖绍聪,李三忠,张国伟.陕西西乡群火山沉积岩系形成的构造环境:火山岩地球化学约束[J].岩石学报,2003,19(1):143-152.
[14] 徐学义,李婷,陈隽璐,等.扬子地台北缘檬子地区侵入岩年代格架和岩石成因研究[J].岩石学报,2011,27(3):699-720.
[15] Liu Yongsheng,Hu Zhaochu,Gao Shan,et al.In situanalysis of major and trace elements of anhydrous minerais by LA-ICP-MS without applying an internal standard[J].Chem Geol,2008,257:34-43.
[16] Liu Yongsheng,Hu Zhaochu,Zong Keqing,et al.Reappraisement and refinement of zircon U-Pb isotope and trace element analyses by LA-ICP-MS[J].Chin Sci Bull,2010,55:1535-1546.
[17] Ludwig K R.User′s Manual for a Geochronological Toolkit for Microsoft Excel[J].Berkeley:Berkeley Geochronology Center,Specpubl,2003,4:1-30.
[18] Middlemost E A K.Naming materials in the magma/igneous rock system[J].Earth-Sci Rev,1994,37:215-224.
[19] Maniar P D,Piccolli P M.Tectonic discrimination of granitoids[J].Geol Soc Am Bull,1989,101(5):635-643.
[20] Rickwood P C.Boundary lines within petrologic diagrams which use oxides of major and minor elements[J].Lithos,1989,22(4):247-263.
[21] Sun S S,McDonough W F.Chemical and isotopic systematics of oceanic basalts:implications for mantle composition and processes[J].Geol Soc London Spec Pub,1989,42:313-345.
[22] Anderson T.Correction of common lead in U-Pb analyses that do not report 204Pb[J].Chemical Geology,2002,192:59-79.
[23] Chappell B W,White A JR.Two contrasting granite types[J].Pacific Geology,1974,8(2):173-174.
[24] 王德滋,刘昌实,沈渭洲,等.桐庐 I 型和相山 S 型两类碎斑熔岩对比[J].岩石学报,1993,9(1):44-53.
[25] Altherr R,Holl A,Hegner E.High-potassium,calc-alkaline plutonism in the European Variscides:northern Vosges (France) and northern Schwarzwald (Germany)[J].Lithos,2000,50:51-73.
[26] Sylvester P J.Post-collisional strongly peraluminous granites[J].Lithos,1998,45:29-44.
[27] Frey F A,Green D H,Roy S D.Integrated models of basalt petrogenesis:a study of quartit holeites to olivine melilities from south eastern Australia utilizing geochemical and experimental petrological data[J].J petrol,1978,19:463-513.
[28] Hawkesworth C J,Kemp A I S.The differentiation and rates of generation of the continental crust[J].Chemical Geology,2006,226,134-143.
[29] Pearce J A.Sources and setting of granitic rocks[J].Episodes,1996,19(4):120-125.
[30] Harris NBW,Pearce J A,Tindle AG.Geochemica characteristics of collision-zone magmatism.In:Coward M P,Reis AC eds.Collision tectonics[C].Geological Society of London,Special Publication,1986,19:67-81.
①成都理工学院南江区调队.1∶5×104关坝乡幅区域地质调查报告[R].1995.
②陕西省地质调查院.1∶25×104南江县幅区域地质调查报告[R].2008.
[2] 魏显贵,杜思清,何政伟,等.米仓山地区构造演化[J].矿物岩石,1997,17(增刊):107-113.
[3] 肖渊甫,马润则,何政伟,等.米仓山碱性杂岩单元特征及构造环境分析[J].矿物岩石,1997,17(增刊):59-66.
[4] 肖渊甫,马润则,魏显贵,等.米仓山澄江期基性侵入杂岩特征及其成因探讨[J].成都理工学院报,1998,25(4):537-542.
[5] 马润则,肖渊甫,魏显贵,等.米仓山地区岩浆活动与构造演化[J].矿物岩石,1997,17(增刊):76-82.
[6] 马润泽,肖渊甫.米仓山地区晋宁期基性超基性侵入岩中造岩矿物研究[J].成都理工学院学报,2001,28(1):34-39.
[7] 裴先治,李佐臣,丁仨平,等.扬子陆块西北缘轿子顶新元古代过铝质花岗岩:锆石SHRIMP U-Pb年龄和岩石地球化学及其构造意义[J].地学前缘,2009,16(3):231-249.
[8] Zhou Meifu,Kennedy A K,Sun M,et al.Neo-proterozoic arc-related mafic intrusions in the northern margin of South China:Implications for accretion of Rodina[J].Geology,2002a,110:611-618.
[9] Zhao Junhong,Zhou Meifu.Secular evolution of the Neoproterozoic lithospheric mante underneath the northern margin of the Yangtze B1ock,South China[J].Lithos,2009,107:152-168.
[10] Dong Yunpeng,Liu Xiaoming,Santosh M,et al.Neoproterozoic subduction tectonics of the Yangtze Block in South China:Constrains from zircon U-Pb geochronology and geochemistry of mafic intrusions in the Harman Massif[J].Precambrian Research,2011a,189(1):66-90.
[11] 敖文昊,张宇昆,张瑞英,等.新元古代扬子北缘地壳增生事件:来自汉南祖师店奥长花岗岩地球化学、锆石 LA-ICP-MS U-Pb 年代学和 Hf 同位素证据[J].地质论评,2014,60(6):1 393-1 408.
[12] 凌文黎,王欲华,程建萍.扬子北缘晋宁期望江山基性岩体的地球化学特征及其构造背景[J].矿物岩石地球化学通报,2001,20(4):218-222.
[13] 赖绍聪,李三忠,张国伟.陕西西乡群火山沉积岩系形成的构造环境:火山岩地球化学约束[J].岩石学报,2003,19(1):143-152.
[14] 徐学义,李婷,陈隽璐,等.扬子地台北缘檬子地区侵入岩年代格架和岩石成因研究[J].岩石学报,2011,27(3):699-720.
[15] Liu Yongsheng,Hu Zhaochu,Gao Shan,et al.In situanalysis of major and trace elements of anhydrous minerais by LA-ICP-MS without applying an internal standard[J].Chem Geol,2008,257:34-43.
[16] Liu Yongsheng,Hu Zhaochu,Zong Keqing,et al.Reappraisement and refinement of zircon U-Pb isotope and trace element analyses by LA-ICP-MS[J].Chin Sci Bull,2010,55:1535-1546.
[17] Ludwig K R.User′s Manual for a Geochronological Toolkit for Microsoft Excel[J].Berkeley:Berkeley Geochronology Center,Specpubl,2003,4:1-30.
[18] Middlemost E A K.Naming materials in the magma/igneous rock system[J].Earth-Sci Rev,1994,37:215-224.
[19] Maniar P D,Piccolli P M.Tectonic discrimination of granitoids[J].Geol Soc Am Bull,1989,101(5):635-643.
[20] Rickwood P C.Boundary lines within petrologic diagrams which use oxides of major and minor elements[J].Lithos,1989,22(4):247-263.
[21] Sun S S,McDonough W F.Chemical and isotopic systematics of oceanic basalts:implications for mantle composition and processes[J].Geol Soc London Spec Pub,1989,42:313-345.
[22] Anderson T.Correction of common lead in U-Pb analyses that do not report 204Pb[J].Chemical Geology,2002,192:59-79.
[23] Chappell B W,White A JR.Two contrasting granite types[J].Pacific Geology,1974,8(2):173-174.
[24] 王德滋,刘昌实,沈渭洲,等.桐庐 I 型和相山 S 型两类碎斑熔岩对比[J].岩石学报,1993,9(1):44-53.
[25] Altherr R,Holl A,Hegner E.High-potassium,calc-alkaline plutonism in the European Variscides:northern Vosges (France) and northern Schwarzwald (Germany)[J].Lithos,2000,50:51-73.
[26] Sylvester P J.Post-collisional strongly peraluminous granites[J].Lithos,1998,45:29-44.
[27] Frey F A,Green D H,Roy S D.Integrated models of basalt petrogenesis:a study of quartit holeites to olivine melilities from south eastern Australia utilizing geochemical and experimental petrological data[J].J petrol,1978,19:463-513.
[28] Hawkesworth C J,Kemp A I S.The differentiation and rates of generation of the continental crust[J].Chemical Geology,2006,226,134-143.
[29] Pearce J A.Sources and setting of granitic rocks[J].Episodes,1996,19(4):120-125.
[30] Harris NBW,Pearce J A,Tindle AG.Geochemica characteristics of collision-zone magmatism.In:Coward M P,Reis AC eds.Collision tectonics[C].Geological Society of London,Special Publication,1986,19:67-81.
①成都理工学院南江区调队.1∶5×104关坝乡幅区域地质调查报告[R].1995.
②陕西省地质调查院.1∶25×104南江县幅区域地质调查报告[R].2008.