坦桑尼亚维多利亚湖绿岩带变质火山岩地球化学特征及成岩机制
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摘要
坦桑尼亚维多利亚湖绿岩带位于坦桑尼亚太古宙克拉通西北部,是重要的金成矿带。火山岩类型主要为变质镁铁质火山岩和变质长英质火山岩,具有双峰式火山岩特征。文章通过对维多利亚湖地区变质火山岩主量元素、微量元素及稀土元素的研究,了解了坦桑尼亚绿岩带构造演化环境和成岩机制。岩石地球化学特征表明:变质镁铁质火山岩属于钙性岩系列,源岩为亏损洋脊玄武岩幔源(DMM)物质和俯冲消减物质(SDC)的混合物;变质长英质火山岩呈高Na_2O/K_2O比值和高Al_2O_3含量,强烈的负Nb异常,重稀土元素含量低(Yb为0.24×10~(-6)~0.68×10~(-6))并有较强的分异作用,这些特征与典型的太古宙TTG岩套相似。该区熔岩具有洋中脊玄武岩和岛弧玄武岩地球化学亲和性特征,具有聚敛边缘构造背景,形成于太古宙弧后盆地。
The Victoria Lake greenstone belt in NW Archacan craton in Tanzania is an important gold-forming belt. The volcanic rocks mainly consist of metamorphic mafic volcanic rocks and felsic rocks,showing the characteristics of bimodal volcanic rocks.This paper presents a study of the volcanics from the Victoria Lake area on its major and trace elements to further understand the tectonic evolution.Petrogeochemical characteristics show that metamorphic mafic volcanic rocks represent a calcic rock series,which are a result of the interaction between DDM and SDC sources; metamorphic felsic rocks are characteristed by high Na2 O/K2 O ratios and Al2 O3,large negative Nb anomalies and low HREE contents leading to highly fractionated REE patterns.These characteristics are similar to typical of Archaean TGG suits ﹒ The lavas in this area show the mixture of MORB and arc-like geochemical affinities,presenting a convergent margin tectonic setting,which are formed in an Archaean back arc basin.
The Victoria Lake greenstone belt in NW Archacan craton in Tanzania is an important gold-forming belt. The volcanic rocks mainly consist of metamorphic mafic volcanic rocks and felsic rocks,showing the characteristics of bimodal volcanic rocks.This paper presents a study of the volcanics from the Victoria Lake area on its major and trace elements to further understand the tectonic evolution.Petrogeochemical characteristics show that metamorphic mafic volcanic rocks represent a calcic rock series,which are a result of the interaction between DDM and SDC sources; metamorphic felsic rocks are characteristed by high Na2 O/K2 O ratios and Al2 O3,large negative Nb anomalies and low HREE contents leading to highly fractionated REE patterns.These characteristics are similar to typical of Archaean TGG suits ﹒ The lavas in this area show the mixture of MORB and arc-like geochemical affinities,presenting a convergent margin tectonic setting,which are formed in an Archaean back arc basin.
引文
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Shukrani Manya.2008.Geochemistry and geochronology of Neoarchaean volcanic rocks of the Iramba-Sekenke greenstone belt,central Tanzania[J].Science Direct,11(3):265-278.
Smithies R H.2000.The Archaean tonalite-trondhjemite-granodiorite(TTG)series is not an analogue of Cenozoic adakite[J].Earth and Planetary Science Letters,77(5):115-125.
Sun S S,Mc Donough W F.1989.Chemical and isotopic systematics of oceanic basalts:implication for mantle composition and progress[J].Geological Society of London Special Publication,37(2):313-345.
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曹建辉,袁万明,郝娜娜,冯云磊,陈小宁,段宏伟,程学芹.2015.东昆仑沟里地区花岗岩年代学、岩石地球化学及其地球动力学意义[J].地质科技与情报,34(2):42-51.
曾键年,许继峰.2008.埃达克质岩与成矿:困惑与探索[J].地学前缘,15(6):278-292.
崔小军,彭俊,李水平,孟有杰,毛金彪,司建涛.2015.坦桑尼亚绿岩带构造蚀变岩型金矿床找矿方法[J].物探与化探,39(4):722-727.
陆顺富,李锦伟,曾键年,龚鹏飞,吴亚飞,李小芬,余冯力.2014.铜陵地区狮子山矿田侵入岩地球化学特征及成岩机制探讨[J].地质科技与情报,33(5):43-52.
Borg G,Krogh T.1999.Isotopic age data of single zircons from the Archaean Sukumaland Greenstone Belt,Tanzania[J].Journal of African Earth Sciences,29(2):301-312.
Borg G,Shackleton R M.1997.The Tanzania and NE Zaire cratons[J].Clarendon Press,5(4):608-619.
Borg G.1992.New aspects of lithostratigraphy and evolution of the Siga Hills,an Archaean granite-greenstone terrain in NW Tanzania[J].Journal of Geology,38(3):89-93.
Cann J R.1970.Rb,Sr,Y,Zr and Nb in some ocean floor basalt rocks[J].Earth Planetary Science Letters 10,12(3):7-11.
Clifford J R.1970.The structural framework of Africa[J].Oliver and boyd,3(4):1-26.
Condie K C.1997.Contrasting sources for upper and lower continental crust:the greenstone connection[J].Journal of Geology,105(1):729-736.
Condie K C.1997.Contrasting sources for upper and lower continental crust:the greenstone connection[J].Journal of Geology,63(1):729-736.
Corcoran P L,Dostal J.2001.Development of an ancient back arc basin overlying continental crust:The Archaean Peltier Formation,Northwest Territories,Canada[J].Journal of Geology,109(2):329-348.
Hawkins J W,Lonsdale P F,Macdougall J D.1990.Petrology of the axial ridge of the Mariana Trough back arc spreading center[J].Rarth and Planetary Science Letters,55(3):226-250.
Manya S.2004.Geochemistry and petrogenesis of volcanic rocks of the Neoarchaean Sukumaland Greenstone Belt,Northwestern Tanzania[J].Science Direct,51(4):269-279.
Polat A,Kerrich R,Wyman D A.1998.The late Archaean SchreiberHemlo and White-River greenstone belts,Superior Province:collages of oceanic plateaus,oceanic arcs,and subduction accretion complexes[J].Tectonophysics,289(1):295-326.
Saunders A D,Norry M J.1988.Origin of MORB and chemically depleted mantle reservoirs:trace element constraints[J].Journal of Petrology Special Lithosphere Issue,42(4):415-445.
Shukrani Manya.2008.Geochemistry and geochronology of Neoarchaean volcanic rocks of the Iramba-Sekenke greenstone belt,central Tanzania[J].Science Direct,11(3):265-278.
Smithies R H.2000.The Archaean tonalite-trondhjemite-granodiorite(TTG)series is not an analogue of Cenozoic adakite[J].Earth and Planetary Science Letters,77(5):115-125.
Sun S S,Mc Donough W F.1989.Chemical and isotopic systematics of oceanic basalts:implication for mantle composition and progress[J].Geological Society of London Special Publication,37(2):313-345.
Winchester J A,Floyd P A.1977.Geochemical discrimination of different magma series and their differentiation products using immobile elements[J].Chemical Geology,20(4):325-343.
曹建辉,袁万明,郝娜娜,冯云磊,陈小宁,段宏伟,程学芹.2015.东昆仑沟里地区花岗岩年代学、岩石地球化学及其地球动力学意义[J].地质科技与情报,34(2):42-51.
曾键年,许继峰.2008.埃达克质岩与成矿:困惑与探索[J].地学前缘,15(6):278-292.
崔小军,彭俊,李水平,孟有杰,毛金彪,司建涛.2015.坦桑尼亚绿岩带构造蚀变岩型金矿床找矿方法[J].物探与化探,39(4):722-727.
陆顺富,李锦伟,曾键年,龚鹏飞,吴亚飞,李小芬,余冯力.2014.铜陵地区狮子山矿田侵入岩地球化学特征及成岩机制探讨[J].地质科技与情报,33(5):43-52.