高喜马拉雅晚新生代富铁火山岩的发现及其构造意义
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摘要
本文首次报道了在藏南高喜马拉雅变质带新发现的一种特殊的晚新生代超基性富铁火山岩,主要由铁橄榄石、氧化铁、及富钾玻璃基质组成,铁橄榄石中含有少量自形铁尖晶石,玻璃基质中含有少量铁石榴石雏晶。岩石具玻基斑状结构,气孔构造发育,具有典型鬣刺构造。全岩成分具有强烈硅不饱和(全岩SiO_2含量为18.8%~29.7%)和极端富铁(全岩Fe2OT3含量为56.2%~74.2%)的特征。地球化学分析表明其大离子亲石元素Th和U等强烈富集,高场强元素Nb和Ta及Ti元素相对亏损,Sr元素具有明显的负异常,显示与板块消减俯冲有关的地球化学特征。该火山岩切割区域片麻理,说明其形成于碰撞后的陆内伸展环境,而其富铁和硅极不饱和的特征表示其有可能属于不混溶作用的产物,也可能属于后期热液蚀变作用,以及由富铁原岩在深部发生熔融并在伸展环境沿裂隙喷发而形成。该火山岩的K/Ar年龄介于4.76~7.25Ma,被熔浆包裹的围岩的磷灰石裂变径迹(AFT)分析结果是2.04±0.21Ma,指示该火山岩可能是上新世-更新世喷发的(2～4Ma)。这些超基性富铁火山岩首次提供了高喜马拉雅构造带在新生代经历碰撞后发生伸展作用的火山岩证据,为认识青藏高原南部大地构造格局及其形成演化过程提供了新的依据。
Late Cenozoic ultra-mafic magnetite-rich volcanic rocks in the High Himalaya metamorphic belt,southern Tibet,are firstly reported in this study. The rocks are mainly composed of Fe-olivine,Fe oxides,Fe-garnet and potassic-rich glasses. A few euhedral Fe-spinel inclusions are discovered in the Fe-olivine grains. Vesicular structure,vitro basic porphyritic texture and typical spinifex texture are normally observed in the rocks. The bulk rock composition of the rock has a feature of strong Si-unsaturation( 18. 8% ~ 29. 7% SiO_2) and extreme Fe-richness( 56. 2% ~ 74. 2% Fe2 O3 T). Geochemical analyses show that it is strong rich in LILE of Th and U,relative depletion in high field strong elements such as Nb,Ta and Ti,and obvious negative anomalies for Sr element,indicating a geochemical process related to subduction. The volcanic lava cuts across the regional gneissic foliation,implying that it was probably formed in a post-collisional intracontinental extensional environment. Further,the Fe-rich and Si-unsaturated feature also indicates that it might be formed as a result of eruption along extentional fault and melting of Fe-rich protolith from a deep source. The volcano probably erupted during Pliocene-Pleistocene( 2 ~ 4 Ma),based on its K/Ar ages between 4. 76 ~ 7. 25 Ma,and surrounding rocks wrapped by lava with an apatite fission track( AFT) age of 2. 04 ± 0. 21 Ma. Generally,the volcanic rock provides first volcanic evidence for post-collisional extension in the High Himalaya tectonic belt during Late Cenozoic,which is critical to further understand the tectonic framework of the southern Tibet Plateau and its evolutionary processes.
Late Cenozoic ultra-mafic magnetite-rich volcanic rocks in the High Himalaya metamorphic belt,southern Tibet,are firstly reported in this study. The rocks are mainly composed of Fe-olivine,Fe oxides,Fe-garnet and potassic-rich glasses. A few euhedral Fe-spinel inclusions are discovered in the Fe-olivine grains. Vesicular structure,vitro basic porphyritic texture and typical spinifex texture are normally observed in the rocks. The bulk rock composition of the rock has a feature of strong Si-unsaturation( 18. 8% ~ 29. 7% SiO_2) and extreme Fe-richness( 56. 2% ~ 74. 2% Fe2 O3 T). Geochemical analyses show that it is strong rich in LILE of Th and U,relative depletion in high field strong elements such as Nb,Ta and Ti,and obvious negative anomalies for Sr element,indicating a geochemical process related to subduction. The volcanic lava cuts across the regional gneissic foliation,implying that it was probably formed in a post-collisional intracontinental extensional environment. Further,the Fe-rich and Si-unsaturated feature also indicates that it might be formed as a result of eruption along extentional fault and melting of Fe-rich protolith from a deep source. The volcano probably erupted during Pliocene-Pleistocene( 2 ~ 4 Ma),based on its K/Ar ages between 4. 76 ~ 7. 25 Ma,and surrounding rocks wrapped by lava with an apatite fission track( AFT) age of 2. 04 ± 0. 21 Ma. Generally,the volcanic rock provides first volcanic evidence for post-collisional extension in the High Himalaya tectonic belt during Late Cenozoic,which is critical to further understand the tectonic framework of the southern Tibet Plateau and its evolutionary processes.
引文
Chen SS,Shi RD,Gong XH,Liu DL,Huang QS,Yi GD,Wu K and Zou HB.2015.A syn-collisional model for Early Cretaceous magmatism in the northern and central Lhasa subterranes.Gondwana Research,doi:org/10.1016/j.gr.2015.04.008
Dare SAS,Barnes SJ and Beaudoin G.2014a.Did the massive magnetite“lava flows”of El Laco(Chile)form by magmatic or hydrothermal processes?New constraints from magnetite composition by LA-ICP-MS.Mineralium Deposita,doi:10.1007/s00126-014-0560-1
Dare SAS,Barnes SJ,Beaudoin G,Méric J,Boutroy E and PotvinDoucet C.2014b.Trace elements in magnetite as petrogenetic indicators.Mineralium Deposita,49:785-796
Ding ZG,Tong LX,Liu X,Liu Z and Zhou X.2018.Metamorphic P-Tpath of high-pressure mafic granulite(retrograded eclogite)from Dingye of Tibet and its tectonic implication.Earth Science,43(1):220-235(in Chinese with English abstract)
Ferreira VP,Sial AN,Pimental MM,Armstrong R,Guimaraes IP,da Silva Filho AF,de Lima MMC and da Silva TR.2015.Reworked old crust-derived shoshonitic magma:The Guarany pluton,Northeastern Brazil.Lithos,232:150-161
Galbraith RF.1981.On statistical models for fission track counts.Math Geology,13:471-483
Gleadow A,Harrison M,Kohn B,Lugo-Zazueta R and Phillips D.2015.The Fish Canyon Tuff:A new look at an old low-temperature thermochronology standard.Earth and Planetary Science Letters,424:95-108
Hasebe N,Barberand J,Jarvis K,Carter A and Hurford AJ.2004.Apatite fission-track chronometry using laser ablation ICP-MS.Chemical Geology,207:135-145
Hildebrand RS.1986.Kiruna-type deposits;their origin and relationship to intermediate subvolcanic plutons in the Great Bear magmatic zone,Northwest Canada.Economic Geology,81:640-659
Hou T,Charlier B,Namur O,Philip S,Schwarz-Schampera U,Zhang ZC and Holtz F,2017.Experimental study of liquid immiscibility in the Kiruna-type Vergenoeg iron-fluorine deposit,South Africa.Geochimica et Cosmochimica Acta,203:303-322
Hou T,Charlier B,Holtz F,Veksler I,Zhang ZC,Thomas R and Namur O.2018.Immiscible hydrous Fe-Ca-P melt and the origin of iron oxide-apatite ore deposits.Nature Communications,doi:10.1038/s41467-018-03761-4
Jaffey AH,Flynn KF,Glendenin LE,Bentley WC and Essling AM.1971.Precision measurement of the half-lives and specific activities of235U and238U.Physical Review,4:1889-1906
Li DW,Liao QA,Yuan YM,Wan YS,Liu DM,Zhang XH,Yi SH,Cao SZ and Xie DF.2003.Zircon U-Pb chronology of Rimana granulite in central section of Hymalaya orogenic belt.Chinese Science Bulletin,48(20):2176-2179(in Chinese)
Liu SW,Zhang JJ,Shu GM and Li QG.2005.Mineral chemistry-PTt path and exhumation process of Dingye mafic granulites in southern Tibet.Science in China(Series D),35(9):810-820(in Chinese)
Liu XH,Hsu KJ,Ju YT,Li GW,Liu XB,Wei LJ,Zhou XJ and Zhang XG.2012.New interpretation of tectonic model in South Tibet.Journal of Asian Earth Sciences,56(29):147-159
Liu Y and Liu H.1996.Simutaneous and precise determination of 40trace elements in rock samples using ICP-MS.Geochimica,6:552-558(in Chinese with English abstract)
Naranjo JA,Henríquez F and Nystr9m JO.2010.Subvolcanic contact meta-somatism at El Laco Volcanic Complex,Central Andes.Andean Geology,37:110-120
Nystr9m J and Henríquez F.1994.Magmatic features of iron ores of the Kiruna type in Chile and Sweden:Ore textures and magnetite geochemistry.Economic Geology,89:820-839
Park CF.1961.A magnetite“flow”in northern Chile.Economic Geology,56:431-441
Rojas PA,Barra F,Deditius A,Reich M and Rojo M.2018.New contribution to the understanding of Kiruna-type iron oxide-apatite deposits revealed by magnetite ore and gangue mineral geochemistry at the El Romeral deposit,Chile.Ore Geology Reviews,93:413-435
Pearce JA.1982.Trace element characteristics of lavas from destructive plate boundaries.In:Thorpe RS(ed.).Andesites:Orogenic Andesites and Related Rocks.John Wiley&Sons,Chichester,525-548
Ruiz C,Aguirre L,Corvalan J,Klohn C,Klohn E and Levi B.1965.Geologia y yacimientos metal feros de Chile.Santiago:Instituto de Investigaciones,Geologicas,305
Ruiz C,Ortiz F,Moraga A and Aguilar A.1968.Genesis of the Chilean iron ore deposits of Mesozoic age.Prague,23rdInternational Geological Congress,7:323-338
Sillitoe RH and Burrows DR.2002.New field evidence bearing on the origin of the El Laco magnetite deposit,northern Chile.Economic Geology,97:1101-1109
Sarah AS,Dare SAS,Sarah-Jane B and Georges B.2014.Did the massive magnetite“lava flows”of El Laco(Chile)form by magmatic or hydrothermal processes?New constraints from magnetite composition by LA-ICP-MS.Mineralium Deposita,doi:10.1007/s00126-014-0560-1
Sun SS and Mc Donough WF.1989.Chemical and isotopic systematics of oceanic basalts:Implications for mantle composition and processes.In:Saunders AD and Norry MJ(eds.).Magmatism in the Ocean Basins.Geological Society of London,Special Publication,42(1):313-345
Wang Y,Zhang L,Zhang J and Wei C.2015.The youngest eclogite in central Himalaa:P-T path,U-Pb zircon age and its tectonic implication.Gondwana Research,doi:10.1016/j.gr.2015.10.013
Xie CF,Zhu JC,Ding SJ,Zhang YM,Fu TA and Li ZH.2006.Determination of Hercynian shoshonitic intrusions in central Hainan Island and tectonic implications.Chinese Science Bulletin,51(16):1944-1954(in Chinese)
丁自耕,仝来喜,刘小汉,刘兆,周学君.2018.西藏定结高压基性麻粒岩(退变榴辉岩)的变质P-T轨迹及构造意义.地球科学,43(1):220-235
李德威,廖群安,袁晏明,万渝生,刘德民,张雄华,易顺华,曹树钊,谢德凡.2003.喜马拉雅造山带中段日玛那麻粒岩锆石U-Pb年代学.科学通报,48(20):2176-2179
刘树文,张进江,舒桂明,李秋根.2005.藏南定结镁铁质麻粒岩矿物化学-PTt轨迹和折返过程.中国科学(D辑),35(9):810-820
刘颖,刘海臣.1996.用ICP-MS准确测定岩石样品40余种微量元素.地球化学,25(6):552-558
谢才富,朱金初,丁式江,张业明,付太安,李志宏.2006.琼中海西期钾玄质侵入岩的厘定及其构造意义.科学通报,51(16):1944-1954
(1)李德威,张雄华,廖群安等.2003.1∶250000定结幅、陈塘区幅区域地质调查报告
Dare SAS,Barnes SJ and Beaudoin G.2014a.Did the massive magnetite“lava flows”of El Laco(Chile)form by magmatic or hydrothermal processes?New constraints from magnetite composition by LA-ICP-MS.Mineralium Deposita,doi:10.1007/s00126-014-0560-1
Dare SAS,Barnes SJ,Beaudoin G,Méric J,Boutroy E and PotvinDoucet C.2014b.Trace elements in magnetite as petrogenetic indicators.Mineralium Deposita,49:785-796
Ding ZG,Tong LX,Liu X,Liu Z and Zhou X.2018.Metamorphic P-Tpath of high-pressure mafic granulite(retrograded eclogite)from Dingye of Tibet and its tectonic implication.Earth Science,43(1):220-235(in Chinese with English abstract)
Ferreira VP,Sial AN,Pimental MM,Armstrong R,Guimaraes IP,da Silva Filho AF,de Lima MMC and da Silva TR.2015.Reworked old crust-derived shoshonitic magma:The Guarany pluton,Northeastern Brazil.Lithos,232:150-161
Galbraith RF.1981.On statistical models for fission track counts.Math Geology,13:471-483
Gleadow A,Harrison M,Kohn B,Lugo-Zazueta R and Phillips D.2015.The Fish Canyon Tuff:A new look at an old low-temperature thermochronology standard.Earth and Planetary Science Letters,424:95-108
Hasebe N,Barberand J,Jarvis K,Carter A and Hurford AJ.2004.Apatite fission-track chronometry using laser ablation ICP-MS.Chemical Geology,207:135-145
Hildebrand RS.1986.Kiruna-type deposits;their origin and relationship to intermediate subvolcanic plutons in the Great Bear magmatic zone,Northwest Canada.Economic Geology,81:640-659
Hou T,Charlier B,Namur O,Philip S,Schwarz-Schampera U,Zhang ZC and Holtz F,2017.Experimental study of liquid immiscibility in the Kiruna-type Vergenoeg iron-fluorine deposit,South Africa.Geochimica et Cosmochimica Acta,203:303-322
Hou T,Charlier B,Holtz F,Veksler I,Zhang ZC,Thomas R and Namur O.2018.Immiscible hydrous Fe-Ca-P melt and the origin of iron oxide-apatite ore deposits.Nature Communications,doi:10.1038/s41467-018-03761-4
Jaffey AH,Flynn KF,Glendenin LE,Bentley WC and Essling AM.1971.Precision measurement of the half-lives and specific activities of235U and238U.Physical Review,4:1889-1906
Li DW,Liao QA,Yuan YM,Wan YS,Liu DM,Zhang XH,Yi SH,Cao SZ and Xie DF.2003.Zircon U-Pb chronology of Rimana granulite in central section of Hymalaya orogenic belt.Chinese Science Bulletin,48(20):2176-2179(in Chinese)
Liu SW,Zhang JJ,Shu GM and Li QG.2005.Mineral chemistry-PTt path and exhumation process of Dingye mafic granulites in southern Tibet.Science in China(Series D),35(9):810-820(in Chinese)
Liu XH,Hsu KJ,Ju YT,Li GW,Liu XB,Wei LJ,Zhou XJ and Zhang XG.2012.New interpretation of tectonic model in South Tibet.Journal of Asian Earth Sciences,56(29):147-159
Liu Y and Liu H.1996.Simutaneous and precise determination of 40trace elements in rock samples using ICP-MS.Geochimica,6:552-558(in Chinese with English abstract)
Naranjo JA,Henríquez F and Nystr9m JO.2010.Subvolcanic contact meta-somatism at El Laco Volcanic Complex,Central Andes.Andean Geology,37:110-120
Nystr9m J and Henríquez F.1994.Magmatic features of iron ores of the Kiruna type in Chile and Sweden:Ore textures and magnetite geochemistry.Economic Geology,89:820-839
Park CF.1961.A magnetite“flow”in northern Chile.Economic Geology,56:431-441
Rojas PA,Barra F,Deditius A,Reich M and Rojo M.2018.New contribution to the understanding of Kiruna-type iron oxide-apatite deposits revealed by magnetite ore and gangue mineral geochemistry at the El Romeral deposit,Chile.Ore Geology Reviews,93:413-435
Pearce JA.1982.Trace element characteristics of lavas from destructive plate boundaries.In:Thorpe RS(ed.).Andesites:Orogenic Andesites and Related Rocks.John Wiley&Sons,Chichester,525-548
Ruiz C,Aguirre L,Corvalan J,Klohn C,Klohn E and Levi B.1965.Geologia y yacimientos metal feros de Chile.Santiago:Instituto de Investigaciones,Geologicas,305
Ruiz C,Ortiz F,Moraga A and Aguilar A.1968.Genesis of the Chilean iron ore deposits of Mesozoic age.Prague,23rdInternational Geological Congress,7:323-338
Sillitoe RH and Burrows DR.2002.New field evidence bearing on the origin of the El Laco magnetite deposit,northern Chile.Economic Geology,97:1101-1109
Sarah AS,Dare SAS,Sarah-Jane B and Georges B.2014.Did the massive magnetite“lava flows”of El Laco(Chile)form by magmatic or hydrothermal processes?New constraints from magnetite composition by LA-ICP-MS.Mineralium Deposita,doi:10.1007/s00126-014-0560-1
Sun SS and Mc Donough WF.1989.Chemical and isotopic systematics of oceanic basalts:Implications for mantle composition and processes.In:Saunders AD and Norry MJ(eds.).Magmatism in the Ocean Basins.Geological Society of London,Special Publication,42(1):313-345
Wang Y,Zhang L,Zhang J and Wei C.2015.The youngest eclogite in central Himalaa:P-T path,U-Pb zircon age and its tectonic implication.Gondwana Research,doi:10.1016/j.gr.2015.10.013
Xie CF,Zhu JC,Ding SJ,Zhang YM,Fu TA and Li ZH.2006.Determination of Hercynian shoshonitic intrusions in central Hainan Island and tectonic implications.Chinese Science Bulletin,51(16):1944-1954(in Chinese)
丁自耕,仝来喜,刘小汉,刘兆,周学君.2018.西藏定结高压基性麻粒岩(退变榴辉岩)的变质P-T轨迹及构造意义.地球科学,43(1):220-235
李德威,廖群安,袁晏明,万渝生,刘德民,张雄华,易顺华,曹树钊,谢德凡.2003.喜马拉雅造山带中段日玛那麻粒岩锆石U-Pb年代学.科学通报,48(20):2176-2179
刘树文,张进江,舒桂明,李秋根.2005.藏南定结镁铁质麻粒岩矿物化学-PTt轨迹和折返过程.中国科学(D辑),35(9):810-820
刘颖,刘海臣.1996.用ICP-MS准确测定岩石样品40余种微量元素.地球化学,25(6):552-558
谢才富,朱金初,丁式江,张业明,付太安,李志宏.2006.琼中海西期钾玄质侵入岩的厘定及其构造意义.科学通报,51(16):1944-1954
(1)李德威,张雄华,廖群安等.2003.1∶250000定结幅、陈塘区幅区域地质调查报告