西藏羌塘南缘查格隆去申拉组火山岩锆石U-Pb年龄、地球化学特征——对班公湖-怒江洋盆演化时限的制约
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摘要
针对西藏羌塘南缘查格隆地区发现的白垩纪去申拉组火山岩(K1q)做了精确的定年和地球化学研究。本次工作采集1个年龄样和10个地球化学样品进行分析。去申拉组火山岩主要包括低钾-中钾钙碱性的玄武岩、玄武安山岩和安山岩,主量元素富集w(Al2O3)(平均为15.43%)、贫w(MgO)(平均为3.18%);稀土元素总量较高,稀土元素配分图显示为轻稀土富集右倾型,存在弱Eu负异常。地球化学分析表明,改则查格隆去申拉组陆相火山沉积建造说明火山岩并非典型岛弧火山岩类型,其构造环境整体属于大陆板内裂谷,其岩浆源区很可能为较厚陆壳背景下的相对地幔楔源区的部分熔融,与新特提斯班公湖-怒江洋的北向俯冲有关。锆石206Pb/238 U加权平均年龄为107 Ma±0.4 Ma,说明至少在107 Ma拉萨地块和羌塘地块已经开始碰撞。
Aimed at Cretaceous the Qushengla Formation(K1 q)volcanic rock,which was found at the Chagelong area settled in south edge of Qiangtang,Tibet,this paper does researches on precise zircon dating and geochemistry aspect.This work collected 1 age samples and 10 geochemical samples for analysis.The volcanic rocks of the Qushenla Formation mainly consist of low-kaliumcalc-alkaline basalts,basaltic andesite and andesites,with the major elements enriched in w(Al_2O_3)(15.43% on average)and w(MgO)poor(3.18% on average).The gross amount of REE(rare earth element)is relatively high.REE distribution pattern show the characteristics of the rocks are enriched in LREE,with weak negative Eu anomalies.According to the regional geological data,the volcanic rock in continental volcanic sedimentary deposit of Qushengla Formation in Chagelong,Gaize is not the typical island arc volcanic type.The total tectonic environment belongs to the intraplate continental rift,which means that magma source region is likely to be partial melting of the mantle wedge-source region under thick continental crust.This is related with the northward subduction of the Neo-Tethys Bangonghu-Nujiang Ocean.Weighted-average age of zircon ~(206)Pb/~(238)U is 107 Ma±0.4 Ma.It indicates that Lhasa block and Qiangtang massif had started crustal collision since 107 Ma.
Aimed at Cretaceous the Qushengla Formation(K1 q)volcanic rock,which was found at the Chagelong area settled in south edge of Qiangtang,Tibet,this paper does researches on precise zircon dating and geochemistry aspect.This work collected 1 age samples and 10 geochemical samples for analysis.The volcanic rocks of the Qushenla Formation mainly consist of low-kaliumcalc-alkaline basalts,basaltic andesite and andesites,with the major elements enriched in w(Al_2O_3)(15.43% on average)and w(MgO)poor(3.18% on average).The gross amount of REE(rare earth element)is relatively high.REE distribution pattern show the characteristics of the rocks are enriched in LREE,with weak negative Eu anomalies.According to the regional geological data,the volcanic rock in continental volcanic sedimentary deposit of Qushengla Formation in Chagelong,Gaize is not the typical island arc volcanic type.The total tectonic environment belongs to the intraplate continental rift,which means that magma source region is likely to be partial melting of the mantle wedge-source region under thick continental crust.This is related with the northward subduction of the Neo-Tethys Bangonghu-Nujiang Ocean.Weighted-average age of zircon ~(206)Pb/~(238)U is 107 Ma±0.4 Ma.It indicates that Lhasa block and Qiangtang massif had started crustal collision since 107 Ma.
引文
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[18]陶刚,李智武,朱利东,等.羌塘地体南缘改则格列戈阿尔辉长岩锆石U-Pb年代学、地球化学及地质意义[J].地质论评,2016,62(5):1 149-1 165.
[19]Liu Y,Hu Z,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(1):34-43.
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[21]左祖发,罗春林,王会敏,等.赣南横市地区基性岩墙LA-ICP-MS锆石U-Pb年龄、地球化学特征及其地质意义[J].地质论评,2015,61(6):1 417-1 428.
[22]金性春.板块构造学基础[M].上海科学技术出版社,1984.
[23]康志强,许继峰,董彦辉,等.拉萨地块中北部白至纪则弄群火山岩:Slainajap洋南向俯冲的产物?[J].岩石学报,2008,24(2):303-314.
[24]马国林,岳雅慧.西藏拉萨地块北部白垩纪火山岩及其对冈底斯岛弧构造演化的制约[J].岩石矿物学杂志,2010,29(5):525-538.
[25]Green D H.Experimental testing of equilibrium partial melting of peridotite under water-saturated,high pressure conditions[J].Canadian Mineralogist,1976,14(3):255-268.
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[28]常青松.西藏羌塘地块南缘热那错火山岩的岩石学、年代学和地球化学[D].北京:中国地质大学,2012.
[29]Pearce J A,Norry M J.Petrogenetic implications of Ti,Zr,Y,and Nb variations in volcanic rocks[J].Contributions to mineralogy and petrology,1979,69(1):33-47.
[30]Peyret R,Taylor T D.Computational methods for fluid flow[J].Physics Today,1986,39(7):70-71.
[31]Yunliang W,Juchu L,Wenxi H,et al.The principles for discrimination of the source composition of mantle-derived igneous rocks and the nature of the mantle source region of the emeishan basalt[J].Acta Geological Sinica,1993,6(3):315-328.
[32]Zhang Y X,Zhang K J,Li B,et al.Zircon SHRIMP U-Pb geochronology and petrogenesis of the plagiogranites from the Lagkor Lake ophiolite,Gerze,Tibet,China[J].Chinese Science Bulletin,2007,52(5):651-659.
[33]谢国刚,莫宣学,赵志丹,等.西藏班公湖地区侏罗纪—白垩纪沉积及古海洋盆地的演化[J].地学前缘,2009,16(4):31-39.
[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]陈玉禄,江元生.西藏班戈-切里错地区早白垩世火山岩的时代确定及意义[J].地质力学学报,2002,8(1):43-49.
[4]康志强,许继峰,王保弟,等.拉萨地块北部去申拉组火山岩:班公湖-怒江特提斯洋南向俯冲的产物?[J].岩石学报,2010,26(10):3 106-3 116.
[5]Liu S,Hu R,Gao S,et al.U-Pb zircon age,geochemical and Sr-Nd isotopic data as constraints on the petrogenesis and emplacement time of andesites from Gerze,southern Qiangtang Block,northern Tibet[J].Journal of Asian Earth Sciences,2012,45(2):150-161.
[6]吴浩,李才,胡培远,等.西藏尼玛县塔色普勒地区去申拉组火山岩的发现及其地质意义[J].地质通报,2013,32(7):1 014-1 026.
[7]李伟.西藏改则地区去申拉组火山岩地球化学特征及锆石年代学制约[D].北京:中国地质大学,2012.
[8]黄启帅,史仁灯,丁炳华,等.班公湖MOR型蛇绿岩Re-Os同位素特征对班公湖-怒江特提斯洋裂解时间的制约[J].岩石矿物学杂志,2012,31(4):465-478.
[9]Shi R,Griffin W L,O′Reilly S Y,et al.Melt/mantle mixing produces podiform chromite deposits in ophiolites:Implications of Re-Os systematics in the Dongqiao Neo-tethyan ophiolite,northern Tibet[J].Gondwana Research,2012,21(1):194-206.
[10]潘桂棠,莫宣学,侯增谦,等.冈底斯造山带的时空结构及演化[J].岩石学报,2006,22(3):521-533.
[11]和钟铧,杨德明,郑常青,等.冈底斯带门巴花岗岩同位素测年及其对新特提斯洋俯冲时代的约束[J].地质论评,2006,52(1):100-106.
[12]李才,王天武,李惠民,等.冈底斯地区发现印支期巨斑花岗闪长岩-古冈底斯造山的存在证据[J].地质通报,2003,22(5):364-366.
[13]耿全如,潘桂棠,王立全,等.西藏冈底斯带叶巴组火山岩同位素地质年代[J].沉积与特提斯地质,2006,26(1):1-7.
[14]Zhang Y X,Li Z W,Zhu L D,et al.Newly discovered eclogites from the Bangong MesoaTethyan suture zone(Gaize,central Tibet,western China):mineralogy,geochemistry,geochronology,and tectonic implications[J].International Geology Review,2016,58(5):574-587.
[15]张玉修.班—怒带中西段构造演化[D].北京:中国科学院研究生院,2007.
[16]朱弟成,莫宣学,赵志丹,等.西藏冈底斯带措勤地区则弄群火山岩锆石U-Pb年代学格架及构造意义[J].岩石学报,2008,24(3):401-412.
[17]曲晓明,辛洪波.藏西班公湖斑岩铜矿带的形成时代与成矿构造环境[J].地质通报,2006,25(7):792-799.
[18]陶刚,李智武,朱利东,等.羌塘地体南缘改则格列戈阿尔辉长岩锆石U-Pb年代学、地球化学及地质意义[J].地质论评,2016,62(5):1 149-1 165.
[19]Liu Y,Hu Z,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(1):34-43.
[20]刘颖,刘海臣.用ICPMS准确测定岩石样品中的40余种微量元素[J].地球化学,1996,25(6):552-558.
[21]左祖发,罗春林,王会敏,等.赣南横市地区基性岩墙LA-ICP-MS锆石U-Pb年龄、地球化学特征及其地质意义[J].地质论评,2015,61(6):1 417-1 428.
[22]金性春.板块构造学基础[M].上海科学技术出版社,1984.
[23]康志强,许继峰,董彦辉,等.拉萨地块中北部白至纪则弄群火山岩:Slainajap洋南向俯冲的产物?[J].岩石学报,2008,24(2):303-314.
[24]马国林,岳雅慧.西藏拉萨地块北部白垩纪火山岩及其对冈底斯岛弧构造演化的制约[J].岩石矿物学杂志,2010,29(5):525-538.
[25]Green D H.Experimental testing of equilibrium partial melting of peridotite under water-saturated,high pressure conditions[J].Canadian Mineralogist,1976,14(3):255-268.
[26]Atherton M P,Petford N.Generation of sodium-rich magmas from newly underplated basaltic crust[J].Nature,1993,362(6416):144-146.
[27]康志强,许继峰,王保弟,等.拉萨地块北部白垩纪多尼组火山岩的地球化学:形成的构造环境[J].地球科学(中国地质大学学报),2009,4(1):89-104.
[28]常青松.西藏羌塘地块南缘热那错火山岩的岩石学、年代学和地球化学[D].北京:中国地质大学,2012.
[29]Pearce J A,Norry M J.Petrogenetic implications of Ti,Zr,Y,and Nb variations in volcanic rocks[J].Contributions to mineralogy and petrology,1979,69(1):33-47.
[30]Peyret R,Taylor T D.Computational methods for fluid flow[J].Physics Today,1986,39(7):70-71.
[31]Yunliang W,Juchu L,Wenxi H,et al.The principles for discrimination of the source composition of mantle-derived igneous rocks and the nature of the mantle source region of the emeishan basalt[J].Acta Geological Sinica,1993,6(3):315-328.
[32]Zhang Y X,Zhang K J,Li B,et al.Zircon SHRIMP U-Pb geochronology and petrogenesis of the plagiogranites from the Lagkor Lake ophiolite,Gerze,Tibet,China[J].Chinese Science Bulletin,2007,52(5):651-659.
[33]谢国刚,莫宣学,赵志丹,等.西藏班公湖地区侏罗纪—白垩纪沉积及古海洋盆地的演化[J].地学前缘,2009,16(4):31-39.