滇西南勐海布朗山奥陶纪花岗岩锆石U-Pb年龄、Hf同位素组成特征及其构造意义
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摘要
对滇西南勐海布朗山花岗岩进行LA-ICP-MS锆石U-Pb年龄测试,获得该花岗岩的~(206)Pb/~(238)U年龄加权平均值为458.5±3.0Ma(n=21,MSWD=2.3),属中—晚奥陶世的产物。样品锆石的ε_(Hf)(t)变化范围为-2.4～0.9之间,平均值为-0.9;亏损地壳模式年龄tDMC变化范围为1.41～1.58Ga,加权平均值为1.49Ga。岩石地球化学特征表明,该花岗岩具有高SiO_2(75.79%～77.56%)、富碱(K_2O+Na_2O=7.39%~8.42%)、中-高钾(K_2O/Na_2O=1.23～1.95)、低MgO(0.14%～0.27%)、低CaO(0.05%～0.64%)的特征。铝过饱和指数A/CNK值介于1.02～1.27之间,岩石属高钾钙碱性强过铝S型花岗岩。岩石稀土元素总体表现为由轻稀土元素富集型向平坦的"海鸥"型过渡,具强烈负Eu异常,δEu值为0.03～0.14;在原始地幔标准化微量元素蛛网图上,明显富集Rb、Th、Nd、Ta等元素,具有明显的Ba、Sr、P、Ti亏损。结合区域地质资料分析,该岩体的形成可能与原特提斯洋俯冲,以及古特提斯洋扩张成盆时,该区处于强烈挤压状态,持续的俯冲使澜沧陆壳残片地壳不断加厚并导致区域重力均衡隆升,引起深部地壳物质在加热后抬升减压发生部分熔融有关。
The LA-ICP-MS U-Pb dating of the zircon from the Bulangshan granite in the Menghai area of Yunnan Province was carried out. The weighted average age of the granite~(206)Pb/~(238)U was 458.5±3.0 Ma(n=21, MSWD=2.3), suggesting that the Bulangshan granite was not formed in Late Yanshanian period as originally thought, but was produced in Middle-Late Ordovician. The zircon εHf(t)of the samples range from-2.4 to 0.9 with an average of-0.9. The tDMCof the crustal model vary from 1.41 Ga to 1.58 Ga with a weighted average of 1.49 Ga. It is inferred that the original rock was probably the second cloud(quartz) schist. The geochemi-cal characteristics of the rock indicate that the granite has high SiO_2(75.79%～77.56%), high alkali(K_2O+Na_2O=7.39%～8.42%), medium-high potassium(K_2O/Na_2O=1.23~1.95), and low MgO(0.14%～0.27%) and CaO(0.05%～0.64%). Aluminum supersaturated index A/CNK values range from 1.02 to 1.27, and the rock is a high-potassium-calcium-alkali-strong over-aluminum S-type granite. The total amount of rare earth elements in the rocks appears to be transition from LREE enrichment to a flat"gull"type,with a strong negative Eu anomaly and δEu values ranging from 0.03 to 0.14. There exists significant enrichment of elements such as Rb, Th, Nd, and Ta and significant loss of Ba, Sr, P, and Ti in the original mantle standard trace element spider pattern. Combined with regional geological data, the authors hold that the formation of the rock mass may be related to the following factors:the subduction of the original Tethys Ocean and the Paleo-Tethys Ocean expanded into basins, the area was under the condition of intense compression, and the continued intracontinental subduction and collision would continuously increase the regional crust and led to regional equilibrium gravity uplift, which caused deep crust materials to migrate upward after heating and decompression and partial melting.
The LA-ICP-MS U-Pb dating of the zircon from the Bulangshan granite in the Menghai area of Yunnan Province was carried out. The weighted average age of the granite~(206)Pb/~(238)U was 458.5±3.0 Ma(n=21, MSWD=2.3), suggesting that the Bulangshan granite was not formed in Late Yanshanian period as originally thought, but was produced in Middle-Late Ordovician. The zircon εHf(t)of the samples range from-2.4 to 0.9 with an average of-0.9. The tDMCof the crustal model vary from 1.41 Ga to 1.58 Ga with a weighted average of 1.49 Ga. It is inferred that the original rock was probably the second cloud(quartz) schist. The geochemi-cal characteristics of the rock indicate that the granite has high SiO_2(75.79%～77.56%), high alkali(K_2O+Na_2O=7.39%～8.42%), medium-high potassium(K_2O/Na_2O=1.23~1.95), and low MgO(0.14%～0.27%) and CaO(0.05%～0.64%). Aluminum supersaturated index A/CNK values range from 1.02 to 1.27, and the rock is a high-potassium-calcium-alkali-strong over-aluminum S-type granite. The total amount of rare earth elements in the rocks appears to be transition from LREE enrichment to a flat"gull"type,with a strong negative Eu anomaly and δEu values ranging from 0.03 to 0.14. There exists significant enrichment of elements such as Rb, Th, Nd, and Ta and significant loss of Ba, Sr, P, and Ti in the original mantle standard trace element spider pattern. Combined with regional geological data, the authors hold that the formation of the rock mass may be related to the following factors:the subduction of the original Tethys Ocean and the Paleo-Tethys Ocean expanded into basins, the area was under the condition of intense compression, and the continued intracontinental subduction and collision would continuously increase the regional crust and led to regional equilibrium gravity uplift, which caused deep crust materials to migrate upward after heating and decompression and partial melting.
引文
[1]莫宣学,沈上越,朱勤文,等.三江中南段火山岩-蛇绿岩与成矿[M]北京:地质出版社,1998:123-132.
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[3]彭头平,王岳军,范蔚名,等.澜沧江南段早中生代酸性火成岩SHRIMP锆石U-Pb定年及构造意义[J].中国科学(D辑),2006,36(2):123-132.
[4]廖世勇,尹福光,王冬兵,等.滇西“三江”地区临沧花岗岩基中三叠世碱长花岗岩的发现及其意义[J].岩石矿物学杂志,2013,33(1):1-12.
[5]刘德利,刘继顺,张彩华,等.滇西南澜沧江结合带北段云县花岗岩的地质特征及形成环境[J].岩石矿物学杂志,2008,27(1):23-31.
[6]秦元季.滇西临沧花岗岩基的基本特征和构造侵位机制[D].中国科学院地质与地球物理研究所博士学位论文,1991.
[7]李兴林.临沧复式花岗岩基的基本特征及形成环境的研究[J].云南地质,1996,15(1):1-18.
[8]陈吉琛.滇西花岗岩类形成的构造环境及岩石特征[J].云南地质,1989,8(3/4):205-212.
[9]刘昌实,朱金初,徐夕生.滇西临沧复式岩基特征研究[J].云南地质,1989,8(3/4):189-204.
[10]吕伯西,王增,张德能,等.三江地区花岗岩类及其成矿专属性[M].成都:四川科技出版社,1993:1-133.
[11]王舫,刘福来,刘平华,等.澜沧江南段临沧花岗岩的锆石U-Pb年龄及构造意义[J].岩石学报,2014,30(10):3034-3050.
[12]Hennig D,Lehmanneh B D,Frei D,et al.Early Permian seafloor to continental arc magmatism in the eastern Paleo-Tethys:U-Pb age and Nd-Sr isotope data from the southern Lancangjiang zone,Yunnan China[J].Lithos,2009,113(3):408-422.
[13]孔会磊,董国臣,莫宣学,等.滇西三江地区临沧花岗岩的岩石成因--地球化学、锆石U-Pb年代学及Hf同位素约束[J].岩石学报,2012,28(5):1438-1452.
[14]Liu Y S,Hu Z C,Gao S,et al.In situ analysis of major and trace elements of anhydrous minerals by LA-ICP-MS without applying an internal standard[J].Chemical Geology,2008,257:34-43.
[15]Zong K Q,Klemd R,Yuan Y,et al.The assembly of Rodinia:The correlation of early Neoproterozoic(ca.900Ma)high-grade metamorphism and continental arc formation in the southern Beishan Orogen,southern Central Asian Orogenic Belt(CAOB)[J].Precambrian Research,2017,290:32-48.
[16]Hu Z C,Zhang W,Liu Y S,et al.“Wave”signal smoothing and mercury removing device for laser ablation quadrupole and multiple collector ICP-MS analysis:application to lead isotope analysis[J].Analytical Chemistry,2015,87:1152-1157.
[17]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 of mantle xenoliths[J].Journal of Petrology,2010,51:537-571.
[18]Lin J,Liu Y S,Yang Y H,et al.Calibration and correction of LA-ICP-MS and LA-MC-ICP-MS analyses for element contens and isotopic ratios[J].Solid Earth Science,2016,1:5-27.
[19]Ludwig K R.Isoplot 3.00:A Geochronological Toolkit for Microsoft Excel[M].Berkeley Geochronology Center,California,Berkeley,2003.
[20]耿建珍,李怀坤,张健,等.锆石Hf同位素组成的LA-ICP-MS测定[J].地质通报,2011,30(10):1508-1513.
[21]Taylor S R,Mclennan S M.The continental crust:Its composition and evolution[M].Oxford:Blackell Scientific Publications,198554-372.
[22]刘振声,王洁民.青藏高原南部花岗岩地质地球化学特征[M].成都:四川科技出版社,1994:1-133.
[23]Alther 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.
[24]Zhou X M,Li W X.Origin of Late Mesozoic igneous rocks in South eastern China:Implications for lithosphere subduction and underplating of mafic magmas[J].Tectonophysics,2000,326(3/4)269-287.
[25]吴福元,李献华,郑永飞,等.Lu-Hf同位素体系及其岩石学应用[J].岩石学报,2007,23(2):185-220.
[26]Amelin Y,Lee D C,Halliday A N.Early-middle Archaean crusta evolution deduced from Lu-Hf and U-Pb isotopic studies of single zircon grains[J].Geochimical et Cosmochimica Acta,2000(64):4205-4225.
[27]Vervoort J D,Pachelt P J,Gehrels G E,et al.Constraints on early Earth differentiation from hafnium and neodymium isotopes[J].Nature,1996,(379):624-627.
[28]Sylvester P J.Post-collisional strongly peraluminous granites[J].Lithos,1998,(45):29-44.
[29]Patino D A E,Johnson A D.Phase equilibrium and melting productivity in the politic system:Implication for the origin of peraluminous granitoids and aluminous guanulites[J].Contributions to Mineralogy and Petrology,1991,(107):202-218.
[30]Vielzeuf D,Montel J M.Partial melting of metagreywackes.PartⅠ:Fluid-absent experiments and phase relationships[J].Contributions to Mineralogy and Petrology,1994,117:375-393.
[31]Peter D K,Roland M.Lu-Hf and Sm-Nd isotope systems in zircon[J].Reviews in Mineralogy and Geochemistry,2003,53(1):327-341.
[32]Barbarin B.Genesis of the two main types of peraluminous granitoids[J].Geology,1996,24(3):295-298.
(1)云南省地质调查院.1:25万景洪、勐腊幅区域地质矿产调查报告.2013.
(2)云南省地质调查院.1:25万澜沧、勐海幅区域地质矿产调查报告.2013.
(3)云南省地质局.1:20万勐海幅区域地质报告.1980.
[2]Sone M,Metcalfe I.Parallel Tethyan sutures in mainland Southeast Asia:New insights for Paleo-Tethys closure and implications for the Indosinian orogeny[J].Comptes Rendus eosciences,2008,340(2/3):166-179.
[3]彭头平,王岳军,范蔚名,等.澜沧江南段早中生代酸性火成岩SHRIMP锆石U-Pb定年及构造意义[J].中国科学(D辑),2006,36(2):123-132.
[4]廖世勇,尹福光,王冬兵,等.滇西“三江”地区临沧花岗岩基中三叠世碱长花岗岩的发现及其意义[J].岩石矿物学杂志,2013,33(1):1-12.
[5]刘德利,刘继顺,张彩华,等.滇西南澜沧江结合带北段云县花岗岩的地质特征及形成环境[J].岩石矿物学杂志,2008,27(1):23-31.
[6]秦元季.滇西临沧花岗岩基的基本特征和构造侵位机制[D].中国科学院地质与地球物理研究所博士学位论文,1991.
[7]李兴林.临沧复式花岗岩基的基本特征及形成环境的研究[J].云南地质,1996,15(1):1-18.
[8]陈吉琛.滇西花岗岩类形成的构造环境及岩石特征[J].云南地质,1989,8(3/4):205-212.
[9]刘昌实,朱金初,徐夕生.滇西临沧复式岩基特征研究[J].云南地质,1989,8(3/4):189-204.
[10]吕伯西,王增,张德能,等.三江地区花岗岩类及其成矿专属性[M].成都:四川科技出版社,1993:1-133.
[11]王舫,刘福来,刘平华,等.澜沧江南段临沧花岗岩的锆石U-Pb年龄及构造意义[J].岩石学报,2014,30(10):3034-3050.
[12]Hennig D,Lehmanneh B D,Frei D,et al.Early Permian seafloor to continental arc magmatism in the eastern Paleo-Tethys:U-Pb age and Nd-Sr isotope data from the southern Lancangjiang zone,Yunnan China[J].Lithos,2009,113(3):408-422.
[13]孔会磊,董国臣,莫宣学,等.滇西三江地区临沧花岗岩的岩石成因--地球化学、锆石U-Pb年代学及Hf同位素约束[J].岩石学报,2012,28(5):1438-1452.
[14]Liu Y S,Hu Z C,Gao S,et al.In situ analysis of major and trace elements of anhydrous minerals by LA-ICP-MS without applying an internal standard[J].Chemical Geology,2008,257:34-43.
[15]Zong K Q,Klemd R,Yuan Y,et al.The assembly of Rodinia:The correlation of early Neoproterozoic(ca.900Ma)high-grade metamorphism and continental arc formation in the southern Beishan Orogen,southern Central Asian Orogenic Belt(CAOB)[J].Precambrian Research,2017,290:32-48.
[16]Hu Z C,Zhang W,Liu Y S,et al.“Wave”signal smoothing and mercury removing device for laser ablation quadrupole and multiple collector ICP-MS analysis:application to lead isotope analysis[J].Analytical Chemistry,2015,87:1152-1157.
[17]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 of mantle xenoliths[J].Journal of Petrology,2010,51:537-571.
[18]Lin J,Liu Y S,Yang Y H,et al.Calibration and correction of LA-ICP-MS and LA-MC-ICP-MS analyses for element contens and isotopic ratios[J].Solid Earth Science,2016,1:5-27.
[19]Ludwig K R.Isoplot 3.00:A Geochronological Toolkit for Microsoft Excel[M].Berkeley Geochronology Center,California,Berkeley,2003.
[20]耿建珍,李怀坤,张健,等.锆石Hf同位素组成的LA-ICP-MS测定[J].地质通报,2011,30(10):1508-1513.
[21]Taylor S R,Mclennan S M.The continental crust:Its composition and evolution[M].Oxford:Blackell Scientific Publications,198554-372.
[22]刘振声,王洁民.青藏高原南部花岗岩地质地球化学特征[M].成都:四川科技出版社,1994:1-133.
[23]Alther 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.
[24]Zhou X M,Li W X.Origin of Late Mesozoic igneous rocks in South eastern China:Implications for lithosphere subduction and underplating of mafic magmas[J].Tectonophysics,2000,326(3/4)269-287.
[25]吴福元,李献华,郑永飞,等.Lu-Hf同位素体系及其岩石学应用[J].岩石学报,2007,23(2):185-220.
[26]Amelin Y,Lee D C,Halliday A N.Early-middle Archaean crusta evolution deduced from Lu-Hf and U-Pb isotopic studies of single zircon grains[J].Geochimical et Cosmochimica Acta,2000(64):4205-4225.
[27]Vervoort J D,Pachelt P J,Gehrels G E,et al.Constraints on early Earth differentiation from hafnium and neodymium isotopes[J].Nature,1996,(379):624-627.
[28]Sylvester P J.Post-collisional strongly peraluminous granites[J].Lithos,1998,(45):29-44.
[29]Patino D A E,Johnson A D.Phase equilibrium and melting productivity in the politic system:Implication for the origin of peraluminous granitoids and aluminous guanulites[J].Contributions to Mineralogy and Petrology,1991,(107):202-218.
[30]Vielzeuf D,Montel J M.Partial melting of metagreywackes.PartⅠ:Fluid-absent experiments and phase relationships[J].Contributions to Mineralogy and Petrology,1994,117:375-393.
[31]Peter D K,Roland M.Lu-Hf and Sm-Nd isotope systems in zircon[J].Reviews in Mineralogy and Geochemistry,2003,53(1):327-341.
[32]Barbarin B.Genesis of the two main types of peraluminous granitoids[J].Geology,1996,24(3):295-298.
(1)云南省地质调查院.1:25万景洪、勐腊幅区域地质矿产调查报告.2013.
(2)云南省地质调查院.1:25万澜沧、勐海幅区域地质矿产调查报告.2013.
(3)云南省地质局.1:20万勐海幅区域地质报告.1980.
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