拉萨地块西段尼雄地区早白垩世晚期花岗闪长岩的成因及构造意义
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摘要
青藏高原拉萨地体中西部广泛发育白垩纪岩浆岩,为探讨青藏高原新生代之前的地质演化历史提供了重要线索。然而其成因及构造背景还存在不同的认识,严重阻碍了青藏高原演化历程的反演工作。本文对藏西措勤县尼雄地区的一套花岗闪长岩进行了详细的年代学和全岩地球化学分析,结果表明,尼雄花岗闪长岩的SiO2含量为65.24%～67.61%,Na2O/K2O为0.91～3.93,铝饱和指数(A/CNK)为0.94～1.14,属I型钙碱性岩石。它们富集轻稀土元素(LREEs)和大离子亲石元素(LILEs,如Rb、Th等),亏损重稀土元素(HREEs)和高场强元素(HFSEs,如Nb、Ta等),轻重稀土分馏明显[(La/Yb)N=7.6～12.2],具有弱-中等的负Eu异常(δEu为0.6～0.9)。两个花岗闪长岩样品中获得的岩浆锆石U-Pb定年结果分别为119.7 Ma和120.5 Ma,代表了尼雄地区的花岗闪长岩为早白垩世晚期岩浆活动的产物。综合研究表明,这套花岗闪长岩主要来源于古老下地壳物质的重熔,并伴有同期幔源岩浆的加入和混合。它们可能是雅鲁藏布江新特提斯洋壳岩石圈北向俯冲的产物。
The Cretaceous magmatic rocks widely exposed in the central and western Lhasa block,Xizang may provide important clues to the study of the pre Cretaceous evolutionary history of the Qinghai Xizang Plateau.However,there is still considerable debate concerning the petrogenesis and tectonic significance of the Cretaceous magmatic rocks in the restoration of the evolutionary processes of the Plateau. The emphasis in this study is placed upon the late Early Cretaceous granodiorites in the Nyixung area,western Lhasa block,Xizang. The petrographic and whole rock geochemical studies have disclosed that these rocks have SiO_2 contents from 65. 24% to 67. 61%,Na_2O/K_2O ratios of 0. 91 to 3. 93,and aluminium saturation index(A/CNK)values of 0. 94 to 1. 14%,indicative of I type calc alkaline granitic rocks. The Nyixung granodiorites are enriched in LREEs and LILEs(e. g. Rb and Th)and depleted in HREEs and HFSEs(e. g. Nb and Ta),with remarked LREE and HREE fractionation[(La/Yb)N = 7. 6-12. 2]and slightly to moderately negative Eu anomalies(δEu = 0. 6 0. 9). The measured two granodiorite samples give the LA-ICP-MS zircon U-Pb ages of 119. 7 Ma and 120. 5 Ma,respectively,which are dated at the late Early Cretaceous. The results of research in this study have reflected that the granodiorites were derived from the partial remelting of ancient lower crust,and associated with the mingling and mixing of the contemporaneous mantle derived magmas. It is inferred that the granodiorites may be the products of the northward subduction of the Yarlung Zangbo Neo tethyan oceanic crust.
The Cretaceous magmatic rocks widely exposed in the central and western Lhasa block,Xizang may provide important clues to the study of the pre Cretaceous evolutionary history of the Qinghai Xizang Plateau.However,there is still considerable debate concerning the petrogenesis and tectonic significance of the Cretaceous magmatic rocks in the restoration of the evolutionary processes of the Plateau. The emphasis in this study is placed upon the late Early Cretaceous granodiorites in the Nyixung area,western Lhasa block,Xizang. The petrographic and whole rock geochemical studies have disclosed that these rocks have SiO_2 contents from 65. 24% to 67. 61%,Na_2O/K_2O ratios of 0. 91 to 3. 93,and aluminium saturation index(A/CNK)values of 0. 94 to 1. 14%,indicative of I type calc alkaline granitic rocks. The Nyixung granodiorites are enriched in LREEs and LILEs(e. g. Rb and Th)and depleted in HREEs and HFSEs(e. g. Nb and Ta),with remarked LREE and HREE fractionation[(La/Yb)N = 7. 6-12. 2]and slightly to moderately negative Eu anomalies(δEu = 0. 6 0. 9). The measured two granodiorite samples give the LA-ICP-MS zircon U-Pb ages of 119. 7 Ma and 120. 5 Ma,respectively,which are dated at the late Early Cretaceous. The results of research in this study have reflected that the granodiorites were derived from the partial remelting of ancient lower crust,and associated with the mingling and mixing of the contemporaneous mantle derived magmas. It is inferred that the granodiorites may be the products of the northward subduction of the Yarlung Zangbo Neo tethyan oceanic crust.
引文
[1]Yin A,Harrison T M. Geologic evolution of the Himalayan-Tibetan orogeny[J]. Annual Review of Earth and Planetary Sciences,2000,28:211-280.
[2]曹圣华,邓世权,肖志坚,等.班公湖-怒江结合带西段中特提斯多岛弧构造演化[J].沉积与特提斯地质,2006,36(4):25-32.
[3]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.
[4]Zhu D C,Pan G T,Zhao Z D,et al. Early Cretaceous subduction-related adakite-like rocks in the Gangdese,south Tibet:products of slab melting and subsequent melt-peridotite interaction[J]?Journal of Asian Earth Sciences,2009,34(3):298-309.
[5]Zhu D C,Zhao Z D,Niu Y L,et al. The Lhasa Terrane:Record of a microcontinent and its histories of drift and growth[J]. Earth and Planetary Science Letters,2011,301(1/2):241-255.
[6]常承法,郑锡澜.中国西藏南部珠穆朗玛地区地质构造特征及其青藏高原东西向诸山系形成的探讨[J].中国科学(D辑),1973,2:190-201.
[7]管琪,朱弟成,赵志丹,等.西藏南部冈底斯带东段晚白垩世埃达克岩:新特提斯洋脊俯冲的产物[J]?岩石学报,2010,26(7):2165-2179.
[8]张亮亮,朱弟成,赵志丹,等.西藏北冈底斯巴尔达地区岩浆作用的成因:地球化学、年代学及Sr-Nd-Hf同位素约束[J].岩石学报,2010,26(6):1871-1888.
[9]于玉帅,高原,杨竹森,等.西藏措勤尼雄矿田滚纠铁矿侵入岩LA-ICP-MS锆石U-Pb年龄与地球化学特征[J].岩石学报,2011,27(7):1949-1960.
[10]王力圆,郑有业,高顺宝,等.中部拉萨地体南侧吉瓦地区早白垩世则弄群火山岩的发现及意义[J].岩石学报,2016,32(5):1543-1555.
[11]Zhang K J,Zhang Y X,Tang X C,et al. Late Mesozoic tectonic evolution and growth of the Tibetan plateau prior to the Indo-Asian collision[J]. Earth-Science Reviews,2012,114(3-4),236-249.
[12]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,(3):521-533.
[13]Meng F Y,Zhao Z D,Zhu D C,et al. Late Cretaceous magmatism in Mamba area,central Lhasa subterrane:products of backarc extension of Neo-Tethyan Ocean[J]?Gondwana Research,2014,26(2):505-520.
[14]Pan G T,Ding J,Yao D S. Guidebook of 1:1500000 geologic map of the Qinghai-Xizang(Tibet)plateau and adjacent areas[J]. Chengdu:Chengdu Cartographic Publishing House,2004,1-48.
[15]Lin Y H,Zhang Z M,Dong X,et al. Precambrian evolution of the Lhasa terrane,Tibet:constraint from the zircon U-Pb geochronology of the gneisses[J]. Precambrian Research,2013,237:64-77.
[16]Mo X X,Niu Y L,Dong G C,et al. Contribution of syn-collisional silicic magmatism to continental crust growth:a case study of the Paleogene Linzizong volcanic Succession in southern Tibet[J]. Chemical Geology,2008,250(1-4):49-67.
[17]Liu Y S,Hu Z C,Zong K Q,et al. Reappraisement and refinement of zircon U-Pb isotope and trace element analyses by LA-ICP-MS[J]. Chinese Science Bulletin,2010,55(15):1535-1546.
[18]Ludwig,K. R. Isoplot/Ex Version 3. 00:A Geochronological Toolkit for Microsoft Excel[J]. Special Publication,No. 4.Berkeley Geochronology Center,2003. 1-73.
[19]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):1589-1604.
[20]Whalen J B,Currie K L,Chappell B W. A-type granites:geochemical characteristics,discrimination and petrogenesis[J].Contributions to Mineralogy and Petrology,1987,95:407-419.
[21]Baker M B,Hischmann M M,Ghiorso M S,et al. Compositions of near-solidus predictive melts from experiments and thermodynamic calculations[J]. Nature,1995,375:308-311.
[22]Harris N B W,Inger S,Xu R. Cretaceous plutonism in Central Tibet:an example of post-collision magmatism[J]?Journal of Volcanology and Geothermal Research,1990,44:21-32.
[23]Rudnick R L,Gao S. Composition of the continental crust[A].Rudnick RL(Ed.). The Crust:Treaties on Geochemistry[C].Oxford:Elsevier Pergamon,2003,1-64.
[24]Barth M G,McDonough W F,Rudnick R L. Tracking the budget of Nb and Ta in the continental crust[J]. Chemical Geology,2000,165(3-4):197-213.
[25]张晓倩,朱弟成,赵志丹,等.西藏措勤尼雄岩体的岩石成因及其对富Fe成矿作用的潜在意义[J].岩石学报,2010,26(6):1793-1804.
[26]丁慧霞,张泽明,向华,等.青藏高原拉萨地体北部早白垩世火山岩的成因及意义[J].岩石学报,2015,31(5):1247-1267.
[27]Kapp P,Yin A,Harrison T M,et al. Cretaceous-Tertiary shortening,basin development,and volcanism in central Tibet[J]. Geological Society of America Bulletin,2005,117(7):865-878.
[28]Pearce J A,Mei H. Volcanic rocks of the 1985 Tibet Geotraverse Lhasa to Golmud[C]. Philosophical Transactions of the Royal Societyof London,Series A,Mathematical and Physical Sciences,1988,327(1594):169-201.
[29]曹圣华,陈毓川,楼法生.西藏措勤县尼雄矽卡岩型铁(铜)矿田特征与找矿远景分析[J].矿床地质,2010,29(S1):65-66.
[30]曲晓明,辛洪波,杜德道,等.西藏班公湖-怒江缝合带中段碰撞后A型花岗岩的时代及其对洋盆闭合时间的约束[J].地球化学,2012,41(1):1-14.
[31]曲晓明,辛洪波,杜德道,等.西藏班公湖-怒江缝合带中段A-型花岗岩的岩浆源区与板片断离[J].地质学报,2013,87(6):759-772.
[32]隋清霖.西藏拉萨地块盐湖地区早白垩世岩浆岩年代学、岩石成因及构造意义[D].北京:中国地质大学(北京). 2014
[33]Garzanti E,Le Fort P,Sciunnach D. First report of Lower Permian basalts in South Tibet:tholeiitic magmatism during break-up andincipient opening of Neo-Tethys[J]. Journal of Asian Earth Sciences,1999,17:533-546.
[34]Yin J R,Grant-Mackie J A. Late Tiassic-Jurassic Bivalves from volcanic sediments of the Lhasa Block,Tibet. New Zealand Journal of Geology and Geophysics,48(3):555-577.
[35]邹洁琼,余红霞,王保弟,等.南拉萨地块中部早白垩世仁钦则花岗闪长岩成因及地质意义[J].地球化学,2018,43(8):2795-2810.
[36]De La,Roche H,Leterrier J,Grandclaude P,et al. A classification of volcanic and plutonic rocks using R1-R2diagrams and major element analysis-its relationships and current nomenclature[J]. Chemical Geology,1980,29:183-210.
[37]Irvine T N,Baragar W R A. A guide to chemical classification of the common volcanic rock[J]. Canadian Journal of Earth Sciences,1971,8,523-548.
[38]Frost B R,Arculus R J,Barnes C G,et al. A geochemical classification of granitic rocks[J]. Journal of Petrology,2001,42(1):2033-2048.
[39]Maniar P D,Piccoli P M. Tectonic discrimination of granitoids[J]. Geological Society of America Bulletin,1989,101(5):635-643.
[40]Sun S S,McDonough W F. Chemical and isotopic systematics of oceanic basalts:implication for mantle composition and process[A]. Saunders AD. Magmatism in Ocean Basins[C].Geological Society Publication,1989. 313-345.
[41]Collins W,Beams S,White A,et al. Nature and Origin of A-type Granites with Particular Reference to Southeastern Australia[J]. Contributions to Mineralogy and Petrology,1982,80(2):189-200.
[42]Setsuya N,Masaki T. Regional variationin chemistry of the Miocene intermediate to felsic magmas in the Outer Zone and the Setouchi Province of Southwest Japan[J]. The Geological Society of Japan,1979,85(9):571-582.
[43]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,1984,25:956-983.
[2]曹圣华,邓世权,肖志坚,等.班公湖-怒江结合带西段中特提斯多岛弧构造演化[J].沉积与特提斯地质,2006,36(4):25-32.
[3]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.
[4]Zhu D C,Pan G T,Zhao Z D,et al. Early Cretaceous subduction-related adakite-like rocks in the Gangdese,south Tibet:products of slab melting and subsequent melt-peridotite interaction[J]?Journal of Asian Earth Sciences,2009,34(3):298-309.
[5]Zhu D C,Zhao Z D,Niu Y L,et al. The Lhasa Terrane:Record of a microcontinent and its histories of drift and growth[J]. Earth and Planetary Science Letters,2011,301(1/2):241-255.
[6]常承法,郑锡澜.中国西藏南部珠穆朗玛地区地质构造特征及其青藏高原东西向诸山系形成的探讨[J].中国科学(D辑),1973,2:190-201.
[7]管琪,朱弟成,赵志丹,等.西藏南部冈底斯带东段晚白垩世埃达克岩:新特提斯洋脊俯冲的产物[J]?岩石学报,2010,26(7):2165-2179.
[8]张亮亮,朱弟成,赵志丹,等.西藏北冈底斯巴尔达地区岩浆作用的成因:地球化学、年代学及Sr-Nd-Hf同位素约束[J].岩石学报,2010,26(6):1871-1888.
[9]于玉帅,高原,杨竹森,等.西藏措勤尼雄矿田滚纠铁矿侵入岩LA-ICP-MS锆石U-Pb年龄与地球化学特征[J].岩石学报,2011,27(7):1949-1960.
[10]王力圆,郑有业,高顺宝,等.中部拉萨地体南侧吉瓦地区早白垩世则弄群火山岩的发现及意义[J].岩石学报,2016,32(5):1543-1555.
[11]Zhang K J,Zhang Y X,Tang X C,et al. Late Mesozoic tectonic evolution and growth of the Tibetan plateau prior to the Indo-Asian collision[J]. Earth-Science Reviews,2012,114(3-4),236-249.
[12]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,(3):521-533.
[13]Meng F Y,Zhao Z D,Zhu D C,et al. Late Cretaceous magmatism in Mamba area,central Lhasa subterrane:products of backarc extension of Neo-Tethyan Ocean[J]?Gondwana Research,2014,26(2):505-520.
[14]Pan G T,Ding J,Yao D S. Guidebook of 1:1500000 geologic map of the Qinghai-Xizang(Tibet)plateau and adjacent areas[J]. Chengdu:Chengdu Cartographic Publishing House,2004,1-48.
[15]Lin Y H,Zhang Z M,Dong X,et al. Precambrian evolution of the Lhasa terrane,Tibet:constraint from the zircon U-Pb geochronology of the gneisses[J]. Precambrian Research,2013,237:64-77.
[16]Mo X X,Niu Y L,Dong G C,et al. Contribution of syn-collisional silicic magmatism to continental crust growth:a case study of the Paleogene Linzizong volcanic Succession in southern Tibet[J]. Chemical Geology,2008,250(1-4):49-67.
[17]Liu Y S,Hu Z C,Zong K Q,et al. Reappraisement and refinement of zircon U-Pb isotope and trace element analyses by LA-ICP-MS[J]. Chinese Science Bulletin,2010,55(15):1535-1546.
[18]Ludwig,K. R. Isoplot/Ex Version 3. 00:A Geochronological Toolkit for Microsoft Excel[J]. Special Publication,No. 4.Berkeley Geochronology Center,2003. 1-73.
[19]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):1589-1604.
[20]Whalen J B,Currie K L,Chappell B W. A-type granites:geochemical characteristics,discrimination and petrogenesis[J].Contributions to Mineralogy and Petrology,1987,95:407-419.
[21]Baker M B,Hischmann M M,Ghiorso M S,et al. Compositions of near-solidus predictive melts from experiments and thermodynamic calculations[J]. Nature,1995,375:308-311.
[22]Harris N B W,Inger S,Xu R. Cretaceous plutonism in Central Tibet:an example of post-collision magmatism[J]?Journal of Volcanology and Geothermal Research,1990,44:21-32.
[23]Rudnick R L,Gao S. Composition of the continental crust[A].Rudnick RL(Ed.). The Crust:Treaties on Geochemistry[C].Oxford:Elsevier Pergamon,2003,1-64.
[24]Barth M G,McDonough W F,Rudnick R L. Tracking the budget of Nb and Ta in the continental crust[J]. Chemical Geology,2000,165(3-4):197-213.
[25]张晓倩,朱弟成,赵志丹,等.西藏措勤尼雄岩体的岩石成因及其对富Fe成矿作用的潜在意义[J].岩石学报,2010,26(6):1793-1804.
[26]丁慧霞,张泽明,向华,等.青藏高原拉萨地体北部早白垩世火山岩的成因及意义[J].岩石学报,2015,31(5):1247-1267.
[27]Kapp P,Yin A,Harrison T M,et al. Cretaceous-Tertiary shortening,basin development,and volcanism in central Tibet[J]. Geological Society of America Bulletin,2005,117(7):865-878.
[28]Pearce J A,Mei H. Volcanic rocks of the 1985 Tibet Geotraverse Lhasa to Golmud[C]. Philosophical Transactions of the Royal Societyof London,Series A,Mathematical and Physical Sciences,1988,327(1594):169-201.
[29]曹圣华,陈毓川,楼法生.西藏措勤县尼雄矽卡岩型铁(铜)矿田特征与找矿远景分析[J].矿床地质,2010,29(S1):65-66.
[30]曲晓明,辛洪波,杜德道,等.西藏班公湖-怒江缝合带中段碰撞后A型花岗岩的时代及其对洋盆闭合时间的约束[J].地球化学,2012,41(1):1-14.
[31]曲晓明,辛洪波,杜德道,等.西藏班公湖-怒江缝合带中段A-型花岗岩的岩浆源区与板片断离[J].地质学报,2013,87(6):759-772.
[32]隋清霖.西藏拉萨地块盐湖地区早白垩世岩浆岩年代学、岩石成因及构造意义[D].北京:中国地质大学(北京). 2014
[33]Garzanti E,Le Fort P,Sciunnach D. First report of Lower Permian basalts in South Tibet:tholeiitic magmatism during break-up andincipient opening of Neo-Tethys[J]. Journal of Asian Earth Sciences,1999,17:533-546.
[34]Yin J R,Grant-Mackie J A. Late Tiassic-Jurassic Bivalves from volcanic sediments of the Lhasa Block,Tibet. New Zealand Journal of Geology and Geophysics,48(3):555-577.
[35]邹洁琼,余红霞,王保弟,等.南拉萨地块中部早白垩世仁钦则花岗闪长岩成因及地质意义[J].地球化学,2018,43(8):2795-2810.
[36]De La,Roche H,Leterrier J,Grandclaude P,et al. A classification of volcanic and plutonic rocks using R1-R2diagrams and major element analysis-its relationships and current nomenclature[J]. Chemical Geology,1980,29:183-210.
[37]Irvine T N,Baragar W R A. A guide to chemical classification of the common volcanic rock[J]. Canadian Journal of Earth Sciences,1971,8,523-548.
[38]Frost B R,Arculus R J,Barnes C G,et al. A geochemical classification of granitic rocks[J]. Journal of Petrology,2001,42(1):2033-2048.
[39]Maniar P D,Piccoli P M. Tectonic discrimination of granitoids[J]. Geological Society of America Bulletin,1989,101(5):635-643.
[40]Sun S S,McDonough W F. Chemical and isotopic systematics of oceanic basalts:implication for mantle composition and process[A]. Saunders AD. Magmatism in Ocean Basins[C].Geological Society Publication,1989. 313-345.
[41]Collins W,Beams S,White A,et al. Nature and Origin of A-type Granites with Particular Reference to Southeastern Australia[J]. Contributions to Mineralogy and Petrology,1982,80(2):189-200.
[42]Setsuya N,Masaki T. Regional variationin chemistry of the Miocene intermediate to felsic magmas in the Outer Zone and the Setouchi Province of Southwest Japan[J]. The Geological Society of Japan,1979,85(9):571-582.
[43]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,1984,25:956-983.