帕米尔地区穆尔尕布辉长岩-闪长岩的成因:锆石U-Pb年龄、Hf同位素及岩石地球化学证据
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摘要
穆尔尕布岩体位于塔吉克斯坦帕米尔地区中部,中帕米尔和南帕米尔之间的Rushan-Pshart缝合带中,岩石类型主要由辉长岩和少量闪长岩组成,呈岩株状侵入于新元古代(?)萨雷吉尔加组浅变质碎屑岩中。根据LA-ICPMS锆石U-Pb定年结果,穆尔尕布岩体中辉长岩的年龄为(232.0±1.5)Ma,闪长岩的年龄为(231.5±1.9)Ma,两者在误差范围内一致,代表了该岩体的形成时代。辉长岩和闪长岩中锆石的εHf(t)值变化范围分别为4.8~12.1、6.4~10,加权平均值为8.1±1.5(MSWD=6.5)和7.9±0.8(MSWD=2.4),显示其原岩来源于地幔物质,其单阶段Hf模式年龄TDM1分别为477~621 Ma,391~672 Ma,指示其原岩为寒武纪—前寒武纪基底。岩石地球化学研究表明,辉长岩类具有贫碱、低Al、富Mg特征,属于低钾(拉斑)系列,闪长岩类则显示富Si、Al,贫Mg、低Ti的特征,属于钙碱性-高钾钙碱性系列;两者的稀土和微量元素特征相似,稀土总量高,呈轻稀土富集的右倾型配分型式,无Eu异常或轻微正Eu异常,微量元素富集大离子亲石元素,亏损高场强元素,指示穆尔尕布岩体可能形成于岛弧环境。综合区域地质资料,认为在晚三叠世Rushan洋陆俯冲尚未结束,表明洋盆闭合时限晚于232 Ma。
Located in the central part of Pamir, Tajikistan, near the Rushan-Pshart suture zone, the Murgab pluton separates the middle Pamir from southern Pamir. Petrologically, the pluton consists of gabrro and diorite which intruded into the epimetamorphicdetrital rocks of late Proterozoic(?). LA-ICP-MS zircon U-Pb dating shows that the age of gabbro and that of diorite is 232±1.5 Ma and 231.5 ± 1.9 Ma respectively, which represents the formation age of this pluton. The εHf(t) values of the zircon are in the range of 4.8-12.1 and 6.4-10, with a weighted average of 8.1±1.5(MSWD =6.5) and 7.9±0.8(MSWD = 2.4), suggesting that its original rock was derived from mantle materials. The one-stage Hf model ages(TDM1) are 477-621 Ma, 391-672 Ma respectively indicating an original rock of Cambrian-Precambrian basement. The lithogeochemical data shows that gabbros are characterized by rich Mg and, poor Al and alkali, thus belonging to low-potassium rocks, whereas the diorites are rich in Si, Al and poor in Mg, Ti,hence belonging to calc-alkaline to high K calc-alkaline rocks. The gabbros and diorites share similar REE and trace elements features, which are characterized by high total REE content and rich LREE with slight normal Eu anomaly. The trace elements are characterized by rich LILEs and poor HFES. Based on geochemical characteristics, the authors infer that the pluton formed in an island-arc environment. The subduction was continuing during late Triassic, which indicates that the Rushan Ocean basin was closed at least later than 232 Ma.
Located in the central part of Pamir, Tajikistan, near the Rushan-Pshart suture zone, the Murgab pluton separates the middle Pamir from southern Pamir. Petrologically, the pluton consists of gabrro and diorite which intruded into the epimetamorphicdetrital rocks of late Proterozoic(?). LA-ICP-MS zircon U-Pb dating shows that the age of gabbro and that of diorite is 232±1.5 Ma and 231.5 ± 1.9 Ma respectively, which represents the formation age of this pluton. The εHf(t) values of the zircon are in the range of 4.8-12.1 and 6.4-10, with a weighted average of 8.1±1.5(MSWD =6.5) and 7.9±0.8(MSWD = 2.4), suggesting that its original rock was derived from mantle materials. The one-stage Hf model ages(TDM1) are 477-621 Ma, 391-672 Ma respectively indicating an original rock of Cambrian-Precambrian basement. The lithogeochemical data shows that gabbros are characterized by rich Mg and, poor Al and alkali, thus belonging to low-potassium rocks, whereas the diorites are rich in Si, Al and poor in Mg, Ti,hence belonging to calc-alkaline to high K calc-alkaline rocks. The gabbros and diorites share similar REE and trace elements features, which are characterized by high total REE content and rich LREE with slight normal Eu anomaly. The trace elements are characterized by rich LILEs and poor HFES. Based on geochemical characteristics, the authors infer that the pluton formed in an island-arc environment. The subduction was continuing during late Triassic, which indicates that the Rushan Ocean basin was closed at least later than 232 Ma.
引文
Angiolini L,Zanchi A,Zanchetta S,Nicora A,Vezzoli G.2013.The Cimmerian geopuzzle:New data from South Pamir[J].Terra Nova25,352-360.
Arculus R J.1994.Aspects of magma genesis in arcs[J].Lithos,33:189-208.
Ballard J R,Palin J M,Williams I S.2001.Two ages of porphyry intrusion resolved for the super-giant Chuquicamata copper deposit of northern Chile by LA-ICP-MS and SHRIMP[J].Geology,9:383-386.
Blichert-Toft J and Albarede F.1997.The Lu-Hf isotope geochemistry of chondrites and the evolution of the mantle-crust system[J].Earth Planet.Sci.Lett.,148:243-258.
Burtman V S and P Molnar.1993.Geological and geophysical evidence for deep subduction of continental crust beneath the Pamir[J].Geol.Soc.Am.Spec.Pap,281,1-76.
Davies J H,Stevenson D J.1992.Physical model of source region of subduction zone volcanics[J].Journal of Geophysical Research,97:2037-2070.
Ducea M N,Lutkov V,Minaev V T,Hacker B,Luffi P,Metcalf J.2003.Building the Pamirs:the view from the underside[J].Geological Society of America,31(10):849-852.
Eiler J M,Grawford A J,Elliott T R,Farley K A,Valley J W,Stolper E M.2000.Oxygen isotope geochemistry of oceanic arc lavas[J].Journal of Petrology,41:229-256.
Frey F A,Prinz M.1978.Ultramafic inclusions from San Carlos,Arizona:petrologic and geochemical data bearing on their petrogenesis[J].Earth and Planetary Science Letters,38(1):129-176.
Griffin W L,Pearson N J,Belousova E,Jackson S E,Achterbergh EV.2000.The Hf isotope composition of cratonic mantle:LAM-MC-ICPMS analysis of zircon megacrysts in kimberlites[J].Geochimica et Cosmochimica Acta,64:133-147.
Grove T L,Elkins Tanton L T,Parman S W,Chatterjee N,Müntener O,Gaetani G A.2003.Fractional crystallization and mantle melting controls on calk-alkaline differentiation trends[J].Contributions to Mineralogy and Petrology,145(5):515-533.
Hong Jun,Ji Wenhua,Zhang Huishan,Yao Wenguang,Meng Guanglu,Wang Bin,Lv Pengrui,Yang Bo.2014.Zircon SHRIMP U-Pb dating,geochemistry and tectonic implications of the Qieshijiebie gabbro on the northern margin of South Pamir[J].Geological Bulletin of China,33(6):820-829(in Chinese with English abstract).
Hong Jun,Ji Wenhua,Zhang Huishan,Yao Wenguang,Fan Baocheng,Liu Mingyi,Luo Yanjun.2015.LA-ICP-MS zircon U-Pb dating,geochemistry and tectonic implications of the Dugeli Alkali-rich porphyries on the eastern margin of Pamir[J].Acta Geologica Sinica,89(9):1463-1654(in Chinese with English abstract).
Horn I,Rudnick R L,Mcdonough W F.2000.Precise element and isotope ratio determination by simultaneous solution nebulization and LA-ICP-MS:Application to U-Pb geochronology[J]Chemical Geology,167:405-425.
Kosler J,Fonneland H,Sylvester P.2002.U-Pb dating of detrita zircons for sediment provenance studies-acomparison of LA-ICP-MS and SIMS techniques[J].Chemical Geology,182:605-618.
Leven E Y.1995.Permian and Triassic of the Rushan-Pshart zone(Pamir)[J].Riv.Ital.Paleontol.Stratigr.101,3-16.
Ludwing K R.2003.Isoplot 3.0-A geochronological toolkit for Microsoft Excel[J].Berkeley Geochronological Center,Spec.Pub.(4):1-70.
Lukens C E,Carrapa B,Singer B S,Gehrels G E.2012.Miocene exhumation of the Pamir revealed by detrital geothermochronology of Tajikstan rivers[J].Tectonics 31,12.
Matte P,Tapponnier P,Arnaud N,Bourjot L,Avouac J P,Vidal P,Liu Q,Pan Y,Wang Y.1996.Tectonics of Western Tibet,between the Tarim and the Indus[J].Earth Planet.Sci.Lett.142,311-330.
Pashkov B R,Budanov V I.1990.The tectonics of the zone of intersection between the Southeastern and southwestern Pamir[J]Geotectonics 24,246-253(in Russian).
Pashkov B R,Shvol'man V A.1979.Rift margins of Tethys in the Pamirs[J].Geotectonics 13,447-456.
Pearce J A.1984.Trace element discrimination diagram for tectonic interpretation of granitic rocks[J].Petrology,25:656-682.
Robinson A C,Yin An,Manning C E,Harrison T M,Zhang S H,Wang X F.2004.Tectonic evolution of the northeastern Pamir constraints from the northern portion of the Cenozoic Kongur Shan extensional system[J].Geol.Soc.Am.Bull,116:953-974.
Robinson A C,Yin An,Manning C E,Harrison T M,Zhang S H,Wang X F.2007.Cenozoic evolution of the eastern Pamir:implications for strain accommodation mechanisms at the western end of the Himalayan-Tibetan orogen[J].Geol.Soc.Am.Bull.119,882-896.
Robinson A C,Ducea M,Lapen T J,2012.Detrital zircon and isotopic constraints on the crustal architecture and tectonic evolution of the northeastern Pamir[J].Tectonics 31,TC2016.
Scherer E,Munker C and Mezger K,2001,Calibration of the lutetiumhafnium clock[J].Science,293:683-687.
Schwab M,Ratschbacher L,Siebel W,Mc Williams M,Minaev VLutkov V,Chen F,Stanek K,Nelson B,Frisch W,Wooden JL.2004.Assembly of the Pamirs:Age and origin of magmatic belts from the southern Tienshan to the southern Pamirs and their relation to Tibet[J].Tectonics 23,TC4002.
Sun Shuqin,Wang Yunliang,Zhang Chengjiang.2003.Discrimination of the tectonic settings of Basalts by Th,Nb,and Zr[J].Geologica Review,49(1):40-47.
Sun S S,Mc Donough W F.1989.Chemical and isotopic systematic of oceanic basalts:Implications for mantle composition and processes[C]//Saunders A D,Norry M J(eds.).Magmatsm in the Ocean Basins[J].Geological Society Special Publication,42:313-345.
Taylor S R and Mc Lennan S.1995.The geochemical composition of the continental crust[J].Reviews of Geophysics,33:241-265.
Vavra G,Gebauer D,Schmid R.1996.Multiple zircon growth and recrystallization during polyphase Late Carboniferous to Triassic metamorphism in granulites of the Ivrea Zone:Anion microprobe study[J].Contrib.Mineral.Petrol.,122:337-358.
Wang Yunliang,Zhang Chengjiang,Xiu Shuzhi.2001.Th/Hf-Ta/Hf identification of tectonic setting of basalts[J].Acta Petrologica Sinica,17(3):413-421(in Chinese with English abstract).
Wu Yuanbao and Zheng Yongfei.2004.Genesis of zircon and its const raints on inter pretation of U-Pb age[J].Chinese Science Bulletin,49(15):1554-1569(in Chinese with English abstract).
Yin An,Harrison T M.2000.Geologic evolution of the HimalayanTibetan orogen[J].Annu.Rev.Earth Planet.Sci.,28,211-280.
Yan Jun,Chen Jiangfeng,Xu Xisheng.2008.Geochemistry of Cretaceous mafic rocks from the Lower Yangtze region,eastern China:characteristics and evolution of the lithospheric mantle[J].Journal of Asian Earth Sciences,33:177-193.
Yan Yi,Lin Ke,Li Zi'an.2003.Provenance tracing of sediments by means of synthetic study of shape,composition and chronology of zircon[J].Geotectonica et Metallogenia,27(2):184-190.
Yuan H L,Gao S,Liu X M et al.2004.Accurate U-Pb age and trace element determinations of zircon by laser ablation-inductively coupled plasma mass spectrometry[J].Geostandards and Geoanalytical Reaerch,28(3):353-370.
洪俊,计文化,张辉善,姚文光,孟广路,王斌,吕鹏瑞,杨博.2014.南帕米尔北缘切实界别辉长岩LA-ICP-MS锆石U-Pb定年、地球化学特征及其地质意义[J].地质通报,33(6):820-829.
洪俊,计文化,张辉善,姚文光,范堡程,刘明义,罗彦军.2015.帕米尔东缘杜格里富碱斑岩锆石U-Pb定年、地球化学特征及构造意义[J].地质学报,89(9):1463-1654.
孙书勤,汪云亮,张成江.2003.玄武岩类岩石大地构造环境的Th、Nb、Zr判别[J].地质论评,49(1):40-47.
汪云亮,张成江,修淑芝.2001.玄武岩类形成的大地构造环境的Th/Hf-Ta/Hf图解判别[J].岩石学报,17(3):413-421.
吴元保,郑永飞.2004.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,49(16):1589-1604.
闫义,林柯,李自安.2003.利用锆石形态、成分组成及年龄分析进行沉积物源区示踪的综合研究[J].大地构造与成矿学,27(2):184-190.
(1)苏联国家地质委员会.1956.苏联1:20万区域地质图,图幅号J43-XXI.
Arculus R J.1994.Aspects of magma genesis in arcs[J].Lithos,33:189-208.
Ballard J R,Palin J M,Williams I S.2001.Two ages of porphyry intrusion resolved for the super-giant Chuquicamata copper deposit of northern Chile by LA-ICP-MS and SHRIMP[J].Geology,9:383-386.
Blichert-Toft J and Albarede F.1997.The Lu-Hf isotope geochemistry of chondrites and the evolution of the mantle-crust system[J].Earth Planet.Sci.Lett.,148:243-258.
Burtman V S and P Molnar.1993.Geological and geophysical evidence for deep subduction of continental crust beneath the Pamir[J].Geol.Soc.Am.Spec.Pap,281,1-76.
Davies J H,Stevenson D J.1992.Physical model of source region of subduction zone volcanics[J].Journal of Geophysical Research,97:2037-2070.
Ducea M N,Lutkov V,Minaev V T,Hacker B,Luffi P,Metcalf J.2003.Building the Pamirs:the view from the underside[J].Geological Society of America,31(10):849-852.
Eiler J M,Grawford A J,Elliott T R,Farley K A,Valley J W,Stolper E M.2000.Oxygen isotope geochemistry of oceanic arc lavas[J].Journal of Petrology,41:229-256.
Frey F A,Prinz M.1978.Ultramafic inclusions from San Carlos,Arizona:petrologic and geochemical data bearing on their petrogenesis[J].Earth and Planetary Science Letters,38(1):129-176.
Griffin W L,Pearson N J,Belousova E,Jackson S E,Achterbergh EV.2000.The Hf isotope composition of cratonic mantle:LAM-MC-ICPMS analysis of zircon megacrysts in kimberlites[J].Geochimica et Cosmochimica Acta,64:133-147.
Grove T L,Elkins Tanton L T,Parman S W,Chatterjee N,Müntener O,Gaetani G A.2003.Fractional crystallization and mantle melting controls on calk-alkaline differentiation trends[J].Contributions to Mineralogy and Petrology,145(5):515-533.
Hong Jun,Ji Wenhua,Zhang Huishan,Yao Wenguang,Meng Guanglu,Wang Bin,Lv Pengrui,Yang Bo.2014.Zircon SHRIMP U-Pb dating,geochemistry and tectonic implications of the Qieshijiebie gabbro on the northern margin of South Pamir[J].Geological Bulletin of China,33(6):820-829(in Chinese with English abstract).
Hong Jun,Ji Wenhua,Zhang Huishan,Yao Wenguang,Fan Baocheng,Liu Mingyi,Luo Yanjun.2015.LA-ICP-MS zircon U-Pb dating,geochemistry and tectonic implications of the Dugeli Alkali-rich porphyries on the eastern margin of Pamir[J].Acta Geologica Sinica,89(9):1463-1654(in Chinese with English abstract).
Horn I,Rudnick R L,Mcdonough W F.2000.Precise element and isotope ratio determination by simultaneous solution nebulization and LA-ICP-MS:Application to U-Pb geochronology[J]Chemical Geology,167:405-425.
Kosler J,Fonneland H,Sylvester P.2002.U-Pb dating of detrita zircons for sediment provenance studies-acomparison of LA-ICP-MS and SIMS techniques[J].Chemical Geology,182:605-618.
Leven E Y.1995.Permian and Triassic of the Rushan-Pshart zone(Pamir)[J].Riv.Ital.Paleontol.Stratigr.101,3-16.
Ludwing K R.2003.Isoplot 3.0-A geochronological toolkit for Microsoft Excel[J].Berkeley Geochronological Center,Spec.Pub.(4):1-70.
Lukens C E,Carrapa B,Singer B S,Gehrels G E.2012.Miocene exhumation of the Pamir revealed by detrital geothermochronology of Tajikstan rivers[J].Tectonics 31,12.
Matte P,Tapponnier P,Arnaud N,Bourjot L,Avouac J P,Vidal P,Liu Q,Pan Y,Wang Y.1996.Tectonics of Western Tibet,between the Tarim and the Indus[J].Earth Planet.Sci.Lett.142,311-330.
Pashkov B R,Budanov V I.1990.The tectonics of the zone of intersection between the Southeastern and southwestern Pamir[J]Geotectonics 24,246-253(in Russian).
Pashkov B R,Shvol'man V A.1979.Rift margins of Tethys in the Pamirs[J].Geotectonics 13,447-456.
Pearce J A.1984.Trace element discrimination diagram for tectonic interpretation of granitic rocks[J].Petrology,25:656-682.
Robinson A C,Yin An,Manning C E,Harrison T M,Zhang S H,Wang X F.2004.Tectonic evolution of the northeastern Pamir constraints from the northern portion of the Cenozoic Kongur Shan extensional system[J].Geol.Soc.Am.Bull,116:953-974.
Robinson A C,Yin An,Manning C E,Harrison T M,Zhang S H,Wang X F.2007.Cenozoic evolution of the eastern Pamir:implications for strain accommodation mechanisms at the western end of the Himalayan-Tibetan orogen[J].Geol.Soc.Am.Bull.119,882-896.
Robinson A C,Ducea M,Lapen T J,2012.Detrital zircon and isotopic constraints on the crustal architecture and tectonic evolution of the northeastern Pamir[J].Tectonics 31,TC2016.
Scherer E,Munker C and Mezger K,2001,Calibration of the lutetiumhafnium clock[J].Science,293:683-687.
Schwab M,Ratschbacher L,Siebel W,Mc Williams M,Minaev VLutkov V,Chen F,Stanek K,Nelson B,Frisch W,Wooden JL.2004.Assembly of the Pamirs:Age and origin of magmatic belts from the southern Tienshan to the southern Pamirs and their relation to Tibet[J].Tectonics 23,TC4002.
Sun Shuqin,Wang Yunliang,Zhang Chengjiang.2003.Discrimination of the tectonic settings of Basalts by Th,Nb,and Zr[J].Geologica Review,49(1):40-47.
Sun S S,Mc Donough W F.1989.Chemical and isotopic systematic of oceanic basalts:Implications for mantle composition and processes[C]//Saunders A D,Norry M J(eds.).Magmatsm in the Ocean Basins[J].Geological Society Special Publication,42:313-345.
Taylor S R and Mc Lennan S.1995.The geochemical composition of the continental crust[J].Reviews of Geophysics,33:241-265.
Vavra G,Gebauer D,Schmid R.1996.Multiple zircon growth and recrystallization during polyphase Late Carboniferous to Triassic metamorphism in granulites of the Ivrea Zone:Anion microprobe study[J].Contrib.Mineral.Petrol.,122:337-358.
Wang Yunliang,Zhang Chengjiang,Xiu Shuzhi.2001.Th/Hf-Ta/Hf identification of tectonic setting of basalts[J].Acta Petrologica Sinica,17(3):413-421(in Chinese with English abstract).
Wu Yuanbao and Zheng Yongfei.2004.Genesis of zircon and its const raints on inter pretation of U-Pb age[J].Chinese Science Bulletin,49(15):1554-1569(in Chinese with English abstract).
Yin An,Harrison T M.2000.Geologic evolution of the HimalayanTibetan orogen[J].Annu.Rev.Earth Planet.Sci.,28,211-280.
Yan Jun,Chen Jiangfeng,Xu Xisheng.2008.Geochemistry of Cretaceous mafic rocks from the Lower Yangtze region,eastern China:characteristics and evolution of the lithospheric mantle[J].Journal of Asian Earth Sciences,33:177-193.
Yan Yi,Lin Ke,Li Zi'an.2003.Provenance tracing of sediments by means of synthetic study of shape,composition and chronology of zircon[J].Geotectonica et Metallogenia,27(2):184-190.
Yuan H L,Gao S,Liu X M et al.2004.Accurate U-Pb age and trace element determinations of zircon by laser ablation-inductively coupled plasma mass spectrometry[J].Geostandards and Geoanalytical Reaerch,28(3):353-370.
洪俊,计文化,张辉善,姚文光,孟广路,王斌,吕鹏瑞,杨博.2014.南帕米尔北缘切实界别辉长岩LA-ICP-MS锆石U-Pb定年、地球化学特征及其地质意义[J].地质通报,33(6):820-829.
洪俊,计文化,张辉善,姚文光,范堡程,刘明义,罗彦军.2015.帕米尔东缘杜格里富碱斑岩锆石U-Pb定年、地球化学特征及构造意义[J].地质学报,89(9):1463-1654.
孙书勤,汪云亮,张成江.2003.玄武岩类岩石大地构造环境的Th、Nb、Zr判别[J].地质论评,49(1):40-47.
汪云亮,张成江,修淑芝.2001.玄武岩类形成的大地构造环境的Th/Hf-Ta/Hf图解判别[J].岩石学报,17(3):413-421.
吴元保,郑永飞.2004.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,49(16):1589-1604.
闫义,林柯,李自安.2003.利用锆石形态、成分组成及年龄分析进行沉积物源区示踪的综合研究[J].大地构造与成矿学,27(2):184-190.
(1)苏联国家地质委员会.1956.苏联1:20万区域地质图,图幅号J43-XXI.