西藏冈底斯带阿索构造混杂岩南侧亚布努马花岗斑岩地球化学特征及锆石U-Pb年龄
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摘要
西藏中冈底斯北部尼玛县阿索乡亚布努马地区东侧出露一处花岗斑岩岩脉,LA-ICP-MS锆石U-Pb测年结果显示,该花岗斑岩的形成时代为晚侏罗世(161.2±5.9Ma)。全岩地球化学数据显示其高硅、富碱、富铝的特征,属于碱性准铝质花岗斑岩;富集轻稀土元素,轻、重稀土元素分异明显,具有明显的负Eu异常,富集Rb、Pb等大离子亲石元素,亏损Ba、Sr元素及Nb、Ta、Ti、U等高场强元素,形成于岛弧环境。其源区可能为来自俯冲带增厚下地壳的深熔作用,结合区域上同时代的岩浆事件,亚布努马花岗斑岩应该形成于以班公湖-怒江洋南向俯冲为动力背景的陆缘弧环境。
The granite porphyry vein in the Yabunuma area is located in Asuo and Nyima area of northern Central Gangdise. LAICP-MS zircon U-Pb age of 161.2±5.9 Ma indicates emplacement during the Late Jurassic. The bulk rock geochemical analyses indicate the characteristics of high silica,rich alkali and Al,suggesting alkali metaluminous granite porphyry. The granite porphyry samples are rich in LREE, the fractionation between LREE and HREE is strong and shows obvious negative Eu anomalies, with the characteristics of enrichment of Rb and Pb, depletion of Ba, Sr, Nb, Ta, Ti and U,suggesting an island-arc setting. The granite porphyry is likely to root in anatexis of thickened lower crust. Considering coeval magma event in the vicinity, the authors hold that granite porphyry from Yabunuma region should have formed in an active epicontinental environment on the background of the southern subduction of Bangong Co-Nujiang Tethyan Ocean crust.
The granite porphyry vein in the Yabunuma area is located in Asuo and Nyima area of northern Central Gangdise. LAICP-MS zircon U-Pb age of 161.2±5.9 Ma indicates emplacement during the Late Jurassic. The bulk rock geochemical analyses indicate the characteristics of high silica,rich alkali and Al,suggesting alkali metaluminous granite porphyry. The granite porphyry samples are rich in LREE, the fractionation between LREE and HREE is strong and shows obvious negative Eu anomalies, with the characteristics of enrichment of Rb and Pb, depletion of Ba, Sr, Nb, Ta, Ti and U,suggesting an island-arc setting. The granite porphyry is likely to root in anatexis of thickened lower crust. Considering coeval magma event in the vicinity, the authors hold that granite porphyry from Yabunuma region should have formed in an active epicontinental environment on the background of the southern subduction of Bangong Co-Nujiang Tethyan Ocean crust.
引文
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[26]Marchev P,Georgiev S,Zajacz Z,et al.High-K ankaramitic melt inclusions and lavas in the Upper Cretaceous Eastern Srednogorie continental arc,Bulgaria:Implications for the genesis of arc shoshonites[J].Lithos,2009,113(1/2):228-245.
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[28]闫晶晶.西藏中拉萨地块许如错岩体年代学和地球化学[D].中国地质大学(北京)硕士学位论文,2016.
[29]Pearce J A,Harris N B W,Tindle A G.Trace element discrimination diagrams for the tectonic interpretation of granitic rocks[J].Journal of Petrology,1984,25(4):956-983.
[2]朱弟成,潘桂棠,莫宣学,等.冈底斯中北部晚侏罗世—早白垩世地球动力学环境:火山岩约束[J].岩石学报,2006,22(3):534-546.
[3]朱弟成,潘桂棠,王立全,等.西藏冈底斯带中生代岩浆岩的时空分布和相关问题的讨论[J].地质通报,2008,27(9):1535-1536.
[4]莫宣学,董国臣,赵志丹,等.西藏冈底斯带花岗岩的时空分布特征及地壳生长演化信息[J].高校地质学报,2005,11(3):281-290.
[5]Zhu D C,Pan G T,Chung S L,et al.SHRIMP zircon age and geochemical constraints on the origin of Lower Jurassic volcanic rocks from the Yeba Formation,southern Gangdese,South Tibet[J].International Geology Review,2008,50(5):442-471.
[6]Govindaraju K.Compilation of working values and sample description for 383 geostandards[J].Geostandards and Geoanalytical Research,1994,18:1-158.
[7]于红.陕西商南松树沟橄榄岩矿物地球化学特征及成因机理示踪[D].中国地质大学(北京)硕士学位论文,2011.
[8]Wiedenbeck M,Alle P,Corfu F,et al.Three natural zircon standards for U-Th-Pb,Lu-Hf,trace element and REE analyses[J].Geostandards and Geoanalytical Research,1995,19(1):1-23.
[9]Peccerillo A,Taylor S R.Geochemistry of eocene calc-alkaline volcanic rocks from the Kastamonu area,Northern Turkey[J].Contributions to Mineralogy&Petrology,1976,58(1):63-81.
[10]Middlemost E A K.Naming materials in the magma/igneous rock system[J].Earth-Science Reviews,1994,37(3/4):215-224.
[11]Maniar P D.Tectonic discrimination of granitoids[J].Geol.soc.am.bull.,1989,101(5):635-643.
[12]Sun S S,Mc Donough W F.Chemical and isotopic systematics of oceanic basalts:implications for mantle composition and processes[J].Geological Society,London,Special Publications,1989,42(1):313-345.
[13]Chappell B W.Aluminium saturation in I-and S-type granites and the characterization of fractionated haplogranites[J].Lithos,1999,46(3):535-551.
[14]King P L,White A J R,Chappell B W,et al.Characterization and origin of aluminous A-type granites from the Lachlan Fold belt,southeastern Australia[J].Journal of Petrology,1997,38(3):371-391.
[15]王强,赵振华,熊小林.桐柏-大别造山带燕山晚期A型花岗岩的厘定[J].岩石矿物学杂志,2000,19(4):297-306.
[16]Watson E B,Harrison T M.Zircon saturation revisited:temperature and composition effects in a variety of crustal magma types[J].Earth&Planetary Science Letters,1983,64(2):295-304.
[17]刘昌实,陈小明,陈培荣,等.A型岩套的分类、判别标志和成因[J].高校地质学报,2003,9(4):573-591.
[18]Whalen J B,Currie K L,Chappell B W.A-type granites:geochemical characteristics,discrimination and petrogenesis[J].Contributions to Mineralogy&Petrology,1987,95(4):407-419.
[19]Richards J P.Magmatic to hydrothermal metal fluxes in convergent and collided margins[J].Ore Geology Reviews,2011,40(1):1-26.
[20]Wang X S,Bi X W,Leng C B,et al.Geochronology and geochemistry of Late Cretaceous igneous intrusions and Mo-Cu-(W)mineralization in the southern Yidun Arc,SW China:Implications for metallogenesis and geodynamic setting[J].Ore Geology Reviews,2014,61(8):73-95.
[21]Wu F Y,Jahn B M,Wilde S A,et al.Highly fractionated I-type granites in NE China(Ⅱ):isotopic geochemistry and implications for crustal growth in the Phanerozoic[J].Lithos,2003,67(3):191-204.
[22]邱检生,肖娥,胡建,等.福建北东沿海高分异Ⅰ型花岗岩的成因:锆石U-Pb年代学、地球化学和Nd-Hf同位素制约[J].岩石学报,2008,24(11):2468-2484.
[23]Joplin G A.Some chemical data on members of the shoshonite association[J].Mineralogical Magazine,1972,(300):936-945.
[24]Meen J K.Formation of shoshonites from calcalkaline basalt magmas:geochemical and experimental constraints from the type locality[J].Contributions to Mineralogy&Petrology,1987,97(3):333-351.
[25]Meen J K.Elevation of potassium content of basaltic magma by fractional crystallization:the effect of pressure[J].Contributions to Mineralogy&Petrology,1990,104(3):309-331.
[26]Marchev P,Georgiev S,Zajacz Z,et al.High-K ankaramitic melt inclusions and lavas in the Upper Cretaceous Eastern Srednogorie continental arc,Bulgaria:Implications for the genesis of arc shoshonites[J].Lithos,2009,113(1/2):228-245.
[27]Roberts M P.Origin of high-potassium,calc-alkaline,I-type granitoids[J].Geology,1993,21(9):825.
[28]闫晶晶.西藏中拉萨地块许如错岩体年代学和地球化学[D].中国地质大学(北京)硕士学位论文,2016.
[29]Pearce J A,Harris N B W,Tindle A G.Trace element discrimination diagrams for the tectonic interpretation of granitic rocks[J].Journal of Petrology,1984,25(4):956-983.