西藏切穷地区早白垩世花岗岩年代学和地球化学特征及其构造环境
|
摘要
西藏谢通门县切穷地区发育面积较广的早白垩世花岗岩岩体。为了进一步查明花岗岩的特征、侵入时代及其形成环境,对其进行了地质学、岩石地球化学及年代学研究。岩体LA-ICP-MS锆石U-Pb定年结果表明,研究区花岗岩岩体侵位年龄主要集中于(129. 3±0. 8)～(130. 5±0. 9) Ma,属早白垩世。从岩石地球化学特征来看,研究区花岗岩岩体具有高SiO_2(73. 19%～76. 7%)、富碱(K_2O+Na_2O=7. 81%～8. 41%)特征,铝饱和指数(A/CNK)介于0. 93～1. 12之间,为强过铝质花岗岩;贫CaO(0. 32%～7. 31%)、MgO(0. 01%～1. 76%),显示明显的负铕(δEu=0. 11～1. 25)异常,富集Rb、Th、Nd元素,亏损Nb、Sr、P、Ti、K元素。从形成环境来看,研究区花岗岩具有明显的大陆碰撞环境的特征。研究认为,西藏切穷地区早白垩世花岗岩形成于同碰撞环境,但在后碰撞过程中地壳缩短增厚发生拆沉作用,玄武质岩浆岩底侵,经过中下地壳发生改造重熔形成的。
A wide range of Early Cretaceous granitic intrusions were formed in the Qieqiong area in Tibet. To better understand the geological characteristics,intrusion age and petrogenetic environment,we have studied the geology,geochemistry and geochronology of intermediate granite rocks from the area. LA-ICP-MS zircon U-Pb dating shows that the granitoids were emplaced in the Early Cretaceous,from( 129. 3 ± 0. 8) Ma to( 130. 5 ±0. 9) Ma. Geochemical analyses show that the granitoids are high in SiO_2( 73. 19%-76. 7%),alkali( K_2 O +Na_2 O = 7. 81%-8. 41%),with A/CNK = 0. 93 to 1. 12,displaying strong peraluminous characteristics. The rocks have low CaO( 0. 32%-7. 31%) and MgO( 0. 01%-1. 76%),and distinct negative Eu anomalies( δEu = 0. 11-1. 25). Primitive-mantle normalized multi-element spider diagram displays apparent enrichments in Rb,Th and Nd,and marked depletions in Nb,Sr,P,Ti and K. These intermediate granitoids show continental collision geochemical affinities. Considering the regional tectonic setting and published information,we infer that the granites at Qieqiong were formed in the a post-collisionalsetting,when crustal thickening and delamination occurred. The magmas were sourced by basaltic magma underplating and the subsequent partial melting of the middle-lower crust.
A wide range of Early Cretaceous granitic intrusions were formed in the Qieqiong area in Tibet. To better understand the geological characteristics,intrusion age and petrogenetic environment,we have studied the geology,geochemistry and geochronology of intermediate granite rocks from the area. LA-ICP-MS zircon U-Pb dating shows that the granitoids were emplaced in the Early Cretaceous,from( 129. 3 ± 0. 8) Ma to( 130. 5 ±0. 9) Ma. Geochemical analyses show that the granitoids are high in SiO_2( 73. 19%-76. 7%),alkali( K_2 O +Na_2 O = 7. 81%-8. 41%),with A/CNK = 0. 93 to 1. 12,displaying strong peraluminous characteristics. The rocks have low CaO( 0. 32%-7. 31%) and MgO( 0. 01%-1. 76%),and distinct negative Eu anomalies( δEu = 0. 11-1. 25). Primitive-mantle normalized multi-element spider diagram displays apparent enrichments in Rb,Th and Nd,and marked depletions in Nb,Sr,P,Ti and K. These intermediate granitoids show continental collision geochemical affinities. Considering the regional tectonic setting and published information,we infer that the granites at Qieqiong were formed in the a post-collisionalsetting,when crustal thickening and delamination occurred. The magmas were sourced by basaltic magma underplating and the subsequent partial melting of the middle-lower crust.
引文
[1]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.
[2]黄圭成,李志昌,邱瑞照,等.西藏冈底斯西段狮多地区火山岩的地质地球化学特征[J].现代地质,2004,18(4):511-517.
[3]王立全,李定谋,潘桂棠,等.青藏高原矿产及成矿背景图及说明书[M].成都:成都地图出版社,2014:94-96.
[4]王程,魏启荣,刘小念,等.冈底斯印支晚期后碰撞花岗岩锆石U-Pb年代学及岩石地球化学证据[J].地球科学,2014,39(9):1278-1300.
[5]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.
[6]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俯冲时代的约束[J].地质论评,2006,52(1):100-106.
[7]王立全,朱弟成,潘桂棠.青藏高原1∶25万区域地质调查主要成果和进展综述(南区)[J].地质通报,2004,23(5):414-420.
[8]潘桂棠,王立全,张万平,等.青藏高原及邻区大地构造图及说明书[M].北京:地质出版社,2013:98-99.
[9]吴新国,贾建称,崔邢涛.雅鲁藏布江缝合带开合演化模式的探讨[J].现代地质,2005,19(4):489-484.
[10]莫宣学,赵志丹,喻学惠,等.青藏高原新生代碰撞-后碰撞火成岩[M].北京:地质出版社,2009:1-5.
[11] ANDERSON T. Correction of common lead in U-Pb analyses that do not report204Pb[J]. Chemical Geology,2002,192:59-79.
[12]吴元保,郑永飞.锆石成因矿物学研究及其对U-Pb年龄解释的制约[J].科学通报,2004,49(16):1589-1602.
[13] RUTATTO D. Zircon trace element geochemistry:Partitioningwithgarnet and the link between U-Pb ages and metamorphism[J]. Chemical Geology,2002,184:123-138.
[14] MIDDLEMOSTE A K. Naming materials in the magma/igneous rock system[J]. Earth Science-Reviews,1994,37(3/4):215-224.
[15] MIDDLEMOSTE A K. Magmas and Magmatic Rocks[M].London:Longman,1985:1-266.
[16] MANIAR P D,PICCOLI P M. Tectonic discrimination of granitoids[J]. Geological Society of America Bulletin,1989,101(5):635-643.
[17] WRIGHT J B. A simple alkalinity ratio and its application to questions of non-orogenic granite genesis[J]. Geological Magazine,1969,106(4):370-384.
[18] SUN S S,MCDONOUGH W F. Chemical and isotopic systematics of oceanic basalts:Implications for mantle composition and processes[J]. Geological Society,London,Special Publication,1989,42(2):313-345.
[19] TAYLOR S R,MCLENANN S M. The Continental Crust:Its Composition and Evolution[M]. London:Oxford Press,1985:1-312.
[20] MANIAP D,PICCOLI P M.. Tectonic discrimination of granitoids[J]. Geological Society of America Bulletin,1989,101(5):635-643.
[21]肖庆辉,邱瑞照,邢作云,等.花岗岩成因研究前沿的认识[J].地质论评,2007,53(增刊):18-27.
[22] BHATIA M R. Rare earth element geochemistry of Australian Paleozoic graywackes and mudrocks provinces and tectonic control[J]. Sedimentary Geology,1985,45(3):97-113.
[23]肖庆辉,邓晋福,马大铨,等.花岗岩研究思维与方法[M].北京:地质出版社,2002:41-55.
[24]张旗,潘国强,李承东,等.花岗岩构造环境问题:关于花岗岩研究的思考之三[J].岩石学报,2007,23(11):2683-2698.
[25] BATCHELOR R A,BOWDEN P. Petrogenetic interpretation of granitoid rock series usingmulticationicparameters[J]. Chemical Geology,1985,11:43-45.
[26] 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.
[27] LIEGEOIS J P,NAVES J,HERTOGEN J,et al. Contrasting origin of post-collisional high-K calc-alkaline and shoshonitic versus alkaline and peralkaline granitoids[J]. Lithos,1998,45:1-28.
[28]翟庆国,李才,李惠民,等.西藏冈底斯中部淡色花岗岩锆石U-Pb年龄及其地质意义[J].地质通报,2005,24(4):350-353.
[2]黄圭成,李志昌,邱瑞照,等.西藏冈底斯西段狮多地区火山岩的地质地球化学特征[J].现代地质,2004,18(4):511-517.
[3]王立全,李定谋,潘桂棠,等.青藏高原矿产及成矿背景图及说明书[M].成都:成都地图出版社,2014:94-96.
[4]王程,魏启荣,刘小念,等.冈底斯印支晚期后碰撞花岗岩锆石U-Pb年代学及岩石地球化学证据[J].地球科学,2014,39(9):1278-1300.
[5]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.
[6]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俯冲时代的约束[J].地质论评,2006,52(1):100-106.
[7]王立全,朱弟成,潘桂棠.青藏高原1∶25万区域地质调查主要成果和进展综述(南区)[J].地质通报,2004,23(5):414-420.
[8]潘桂棠,王立全,张万平,等.青藏高原及邻区大地构造图及说明书[M].北京:地质出版社,2013:98-99.
[9]吴新国,贾建称,崔邢涛.雅鲁藏布江缝合带开合演化模式的探讨[J].现代地质,2005,19(4):489-484.
[10]莫宣学,赵志丹,喻学惠,等.青藏高原新生代碰撞-后碰撞火成岩[M].北京:地质出版社,2009:1-5.
[11] ANDERSON T. Correction of common lead in U-Pb analyses that do not report204Pb[J]. Chemical Geology,2002,192:59-79.
[12]吴元保,郑永飞.锆石成因矿物学研究及其对U-Pb年龄解释的制约[J].科学通报,2004,49(16):1589-1602.
[13] RUTATTO D. Zircon trace element geochemistry:Partitioningwithgarnet and the link between U-Pb ages and metamorphism[J]. Chemical Geology,2002,184:123-138.
[14] MIDDLEMOSTE A K. Naming materials in the magma/igneous rock system[J]. Earth Science-Reviews,1994,37(3/4):215-224.
[15] MIDDLEMOSTE A K. Magmas and Magmatic Rocks[M].London:Longman,1985:1-266.
[16] MANIAR P D,PICCOLI P M. Tectonic discrimination of granitoids[J]. Geological Society of America Bulletin,1989,101(5):635-643.
[17] WRIGHT J B. A simple alkalinity ratio and its application to questions of non-orogenic granite genesis[J]. Geological Magazine,1969,106(4):370-384.
[18] SUN S S,MCDONOUGH W F. Chemical and isotopic systematics of oceanic basalts:Implications for mantle composition and processes[J]. Geological Society,London,Special Publication,1989,42(2):313-345.
[19] TAYLOR S R,MCLENANN S M. The Continental Crust:Its Composition and Evolution[M]. London:Oxford Press,1985:1-312.
[20] MANIAP D,PICCOLI P M.. Tectonic discrimination of granitoids[J]. Geological Society of America Bulletin,1989,101(5):635-643.
[21]肖庆辉,邱瑞照,邢作云,等.花岗岩成因研究前沿的认识[J].地质论评,2007,53(增刊):18-27.
[22] BHATIA M R. Rare earth element geochemistry of Australian Paleozoic graywackes and mudrocks provinces and tectonic control[J]. Sedimentary Geology,1985,45(3):97-113.
[23]肖庆辉,邓晋福,马大铨,等.花岗岩研究思维与方法[M].北京:地质出版社,2002:41-55.
[24]张旗,潘国强,李承东,等.花岗岩构造环境问题:关于花岗岩研究的思考之三[J].岩石学报,2007,23(11):2683-2698.
[25] BATCHELOR R A,BOWDEN P. Petrogenetic interpretation of granitoid rock series usingmulticationicparameters[J]. Chemical Geology,1985,11:43-45.
[26] 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.
[27] LIEGEOIS J P,NAVES J,HERTOGEN J,et al. Contrasting origin of post-collisional high-K calc-alkaline and shoshonitic versus alkaline and peralkaline granitoids[J]. Lithos,1998,45:1-28.
[28]翟庆国,李才,李惠民,等.西藏冈底斯中部淡色花岗岩锆石U-Pb年龄及其地质意义[J].地质通报,2005,24(4):350-353.