Petrogenesis and Geochemistry of Meso-Cenozoic Granitic Rocks and Implication of Crustal Structure Changes in Shannan Area, Southern Tibet
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摘要: 西藏拉萨地块南部发育大规模东西带状展布的花岗质岩石，记录了新特提斯洋壳俯冲晚期及随后印度-欧亚大陆碰撞、后碰撞过程的重要信息，受到了学者的广泛关注.对拉萨地块南部山南地区采集的6件花岗质岩石样品进行了LA-ICP-MS锆石U-Pb年代学、Hf同位素及全岩主微量元素和Sr-Nd同位素地球化学分析，获得了~90 Ma、65 Ma及23 Ma三阶段的锆石年龄，显示区域内发育了三期岩浆活动事件.三个时代的岩石样品均为亚碱性系列，具类似埃达克质岩特征，富集高场强元素并亏损大离子亲石元素，稀土元素分布图呈右倾型，具有弧岩浆的地球化学特征.本文所有样品的锆石εHf(t)均为正值(+5.6~+14.6)，暗示它们可能来源于新生下地壳物质的部分熔融.结合前人已有数据，采用花岗质岩石的La/Yb比值定量还原了山南地区100 Ma以来的地壳厚度演化历史.从晚中生代开始，区域内地壳厚度由厚减薄，到新生代早期达到最薄，此后逐渐增厚.这与中新生代以来新特提斯洋俯冲至印度-欧亚大陆碰撞-后碰撞过程引起地壳结构变化较好地契合.Abstract: In the southern part of the Lhasa block in southern Tibet, large-scale zonal distribution of granitic rocks is developed, where the important information on the late subduction of the Neo-Tethys oceanic crust and subsequent collisions and post-collision processes in the Indian-Eurasia continent is recorded. In this paper, LA-ICP-MS zircon U-Pb geochronology, Hf isotope and total trace elements and Sr-Nd isotope geochemical analysis of six granitic rock samples collected in the southern Shannan area of the Lhasa block were obtained. The three-stage zircon ages of~90 Ma, 65 Ma and 23 Ma show that three phases of magmatic activity occurred in the area. The rock samples of the three eras are all subalkalic series, with similar adakite characteristics, enriched with high field strength elements and depleted with large ion lithophile elements. The distribution of rare earth elements is right-dip, geochemical with the feature of arc magma. The zircon εHf(t) of all samples in this paper are positive (+5.6-+14.6), suggesting that they may be derived from the partial melting of the new lower crust. Based on the previous data, the La/Yb ratio of granitic rocks is used to quantitatively show the evolution of crustal thickness in the Shannan area for 100 Ma. From the late Mesozoic, the thickness of the crust in the area was thinned from thick to thin in the Early Cenozoic, and gradually thickened thereafter. This is in line with the changes in the crustal structure caused by the subduction of the Neo-Tethys and the Indian-Eurasia collision-postcollision process since Mesozoic to Cenozoic.
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Key words:
- South Lhasa block /
- crustal thickness /
- quantitative calculation /
- La/Yb ratio /
- intermediate-acid magma /
- petrology
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图 1 青藏高原南部岩浆-构造分布简图及山南地区结巴乡地质图和样品情况
修改自Chung et al.(2009)；Jiang et al.(2014)；MBT.主边界逆冲断层；MCT.主中央逆冲断层；STDS：藏南拆离断层系；Kf.钾长石；Hb.角闪石；Q.石英
Fig. 1. Sketch map of southern Tibetan Plateau showing major blocks and temporal spatial distribution of magmatic rocks and geological map and photos of granitic rocks of Jieba Village in Shannan area
图 2 山南地区花岗质岩石锆石U-Pb年龄谐和图
Fig. 2. Zircon U-Pb concordia diagrams of the granitic rocks in Shannan area
图 3 山南地区花岗质岩石锆石年龄与εHf(t)图解
Fig. 3. Plot of εHf(t) versus age for the granitic rocks in Shannan area
图 4 山南地区花岗质岩石TAS图解
Fig. 4. Plot of total alkali versus SiO2 of the granitic rocks in Shannan area
图 5 山南地区花岗质岩石(La/Yb)N-(Yb)N图解
Fig. 5. Plot of (La/Yb)N versus (Yb)N of the granitic rocks in Shannan area
图 6 山南地区花岗质岩石全岩原始地幔标准化微量元素蛛网图和球粒陨石均一化稀土分配图
Fig. 6. Primitive mantle-normalized trace element patterns and chondrite-normalized rare earth element (REE) patterns of the granitic rocks in Shannan area
图 7 山南地区花岗质岩石Sr-Nd同位素组成图解
数据底图据Jiang et al.(2014)
Fig. 7. Plot of εHf(t) vs. (87Sr/86Sr)i of the granitic rocks in Shannan area
图 8 山南地区晚白垩世-中新世地壳厚度演化
Fig. 8. Crustal thickness evolution of Shannan area from Late Cretaceous to Miocene
表 1 山南地区花岗质岩石岩石Sr-Nd同位素分析结果
Table 1. Sr-Nd isotope analysis results of the granitic rocks in Shannan area
样品编号 87Rb/86Sr 87Sr/86Sr 2σ 87Sr/86Sri 147Sm/144Nd 143Nd/144Nd 1σ εHf(t) fSm/Nd tDM(Ma) tDM2(Ma) 13JBX-01 0.428 5 0.705 49 5 0.705 35 0.092 86 0.512 55 7 -1.1 -0.53 753 945 13JBX-02 0.263 8 0.704 38 5 0.704 03 0.099 98 0.512 77 8 4.8 -0.49 517 598 13JBX-03 2.431 3 0.706 13 5 0.703 88 0.102 98 0.512 75 9 3.7 -0.48 557 635 13JBX-04 1.558 1 0.705 06 5 0.703 03 0.092 52 0.512 76 6 4.8 -0.53 487 592 13JBX-05 0.816 4 0.704 90 6 0.703 86 0.095 62 0.512 76 8 4.7 -0.51 503 600 13JBX-06 0.638 1 0.705 18 6 0.704 39 0.101 09 0.512 74 10 4.1 -0.49 559 642 
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[1] Belousova, E.A., Griffin, W.L., O'Reilly, S.Y., et al., 2002.Ig-neous Zircon:Trace Element Composition as an Indica-tor of Source Rock Type. Contributions to Mineralogy and Petrology, 143(5):602-622. doi: 10.1007/s00410-002-0364-7 [2] Chapman, J. B., Ducea, M. N., DeCelles, P. G., et al., 2015.Tracking Changes in Crustal Thickness during Orogenic Evolution with Sr/Y:An Example from the North Amer-ican Cordillera.Geology, 43(10):919-922. doi: 10.1130/G36996.1 [3] Chen, J. L., Xu, J. F., Zhao, W. X., et al., 2011. Geochemical Variations in Miocene Adakitic Rocks from the Western and Eastern Lhasa Terrane:Implications for Lower Crustal Flow beneath the Southern Tibetan Plateau.Lith-os, 125(3-4):928-939. https://doi.org/10.1016/j.lith-os.2011.05.006 [4] Chiaradia, M., 2015. Crustal Thickness Control on Sr/Y Sig-natures of Recent Arc Magmas:An Earth Scale Perspec-tive. Scientific Reports, 5:8115. https://doi.org/10.1038/srep08115 [5] Chung, S.L., Chu, M.F., Ji, J.Q., et al., 2009.The Nature and Timing of Crustal Thickening in Southern Tibet:Geo-chemical and Zircon Hf Isotopic Constraints from Post-collisional Adakites. Tectonophysics, 477(1-2):36-48. https://doi.org/10.1016/j.tecto.2009.08.008 [6] Dai, Z. W., Li, G. M., Ding, J., et al., 2018. Late Cretaceous Adakite in Nuri Area, Tibet:Products of Ridge Subduc-tion. Earth Science, 43(8):2727-2741(in Chinese with English abstract). [7] Defant, M. J., Drummond, M. S., 1990. Derivation of Some Modern Arc Magmas by Melting of Young Subducted Lithosphere.Nature, 347:662-665. doi: 10.1038/347662a0 [8] Hou, Z.Q., Duan, L.F., Lu, Y.J., et al., 2015.Lithospheric Ar-chitecture of the Lhasa Terrane and Its Control on Ore Deposits in the Himalayan-Tibetan Orogen. Economic Geology, 110(6):1541-1575. https://doi.org/10.2113/econgeo.110.6.1541 [9] Hu, F. Y., Ducea, M. N., Liu, S. W., et al., 2017. Quantifying Crustal Thickness in Continental Collisional Belts:Global Perspective and a Geologic Application.Scientific Re-ports, 7:7058. [10] Huang, F., Xu, J. F., Chen, J. L., et al., 2016. Two Cenozoic Tectonic Events of N-S and E-W Extension in the Lhasa Terrane:Evidence from Geology and Geochronology.Lithos, 245:118-132. https://doi.org/10.1016/j.lith-os.2015.08.014 [11] Huang, F., Xu, J.F., Zeng, Y.C., et al., 2017.Slab Breakoff of the Neo-Tethys Ocean in the Lhasa Terrane Inferred from Contemporaneous Melting of the Mantle and Crust. Geochemistry, Geophysics, Geosystems, 18(11):4074-4095. https://doi.org/10.1002/2017gc007039 [12] Ji, W.Q., Wu, F.Y., Chung, S.L., et al., 2009a.Zircon U-Pb Geochronology and Hf Isotopic Constraints on Petrogen-esis of the Gangdese Batholith, Southern Tibet. Chemi-cal Geology, 262(3-4):229-245. doi: 10.1016/j.chemgeo.2009.01.020 [13] Ji, W. Q., Wu, F. Y., Liu, C. Z., et al., 2009b. Geochronology and Petrogenesis of Granitic Rocks in Gangdese Batho-lith, Southern Tibet. Science in China (Series D), 52(9):1240-1261. doi: 10.1007/s11430-009-0131-y [14] Jiang, Z.Q., Wang, Q., Wyman, D., et al., 2011.Origin of~30 Ma Chongmuda Adakitic Intrusive Rocks in the Southern Gangdese Region, Southern Tibet:Partial Melting of the Northward Subducted Indian Continent Crust? Geochimica, 40(2):126-146(in Chinese with English abstract). [15] Jiang, Z.Q., Wang, Q., Wyman, D.A., et al., 2014.Transition from Oceanic to Continental Lithosphere Subduction in Southern Tibet:Evidence from the Late Cretaceous-Early Oligocene (~91-30 Ma) Intrusive Rocks in the Chanang-Zedong Area, Southern Gangdese. Lithos, 196-197:213-231. doi: 10.1016/j.lithos.2014.03.001 [16] Kang, Z.Q., Xu, J.F., Wilde, S.A., et al., 2014.Geochronology and Geochemistry of the Sangri Group Volcanic Rocks, Southern Lhasa Terrane:Implications for the Early Sub-duction History of the Neo-Tethys and Gangdese Mag-matic Arc. Lithos, 200-201:157-168. https://doi.org/10.1016/j.lithos.2014.04.019 [17] Li, X. W., Mo, X. X., Scheltens, M., et al., 2016. Mineral Chemistry and Crystallization Conditions of the Late Cretaceous Mamba Pluton from the Eastern Gangdese, Southern Tibetan Plateau.Journal of Earth Science, 27(4):545-570. https://doi.org/10.1007/s12583-016-0713-5 [18] Ma, L., Wang, Q., Wyman, D. A., et al., 2013. Late Creta-ceous Crustal Growth in the Gangdese Area, Southern Tibet:Petrological and Sr-Nd-Hf-O Isotopic Evidence from Zhengga Diorite-Gabbro.Chemical Geology, 349-350:54-70 doi: 10.1016/j.chemgeo.2013.04.005 [19] Ma, L., Wang, Q., Wyman, D. A., et al., 2015. Late Creta-ceous Back-Arc Extension and Arc System Evolution in the Gangdese Area, Southern Tibet:Geochronological, Petrological, and Sr-Nd-Hf-O Isotopic Evidence from Dagze Diabases. Journal of Geophysical Research:Solid Earth, 120(9):6159-6181. doi: 10.1002/2015JB011966 [20] Mantle, G.W., Collins, W.J., 2008.Quantifying Crustal Thick-ness Variations in Evolving Orogens:Correlation be-tween Arc Basalt Composition and Moho Depth.Geolo-gy, 36(1):87. https://doi.org/10.1130/g24095a.1 [21] McDonough, W. F., Sun, S. S., 1995. The Composition of the Earth. Chemical Geology, 120(3-4):223-253. https://doi.org/10.1016/0009-2541(94)00140-4 [22] Mo, X.X., Hou, Z.Q., Niu, Y.L., et al., 2007.Mantle Contribu-tions to Crustal Thickening during Continental Collision:Evidence from Cenozoic Igneous Rocks in Southern Ti-bet.Lithos, 96(1-2):225-242. https://doi.org/10.1016/j.lithos.2006.10.005 [23] Owens, T.J., Zandt, G., 1997.Implications of Crustal Property Variations for Models of Tibetan Plateau Evolution.Na-ture, 387:37-43. [24] Profeta, L., Ducea, M.N., Chapman, J.B., et al., 2016.Quanti-fying Crustal Thickness over Time in Magmatic Arcs.Scientific Reports, 5:17786. https://doi.org/10.1038/srep17786 [25] Rapp, R.P., Watson, E.B., 1995.Dehydration Melting of Me-tabasalt at 8-32 kbar:Implications for Continental Growth and Crust-Mantle Recycling.Journal of Petrolo-gy, 36(4):891-931. doi: 10.1093/petrology/36.4.891 [26] Wang, B.D., Wang, L.Q., Chung, S.L., et al., 2016.Evolution of the Bangong-Nujiang Tethyan Ocean:Insights from the Geochronology and Geochemistry of Mafic Rocks within Ophiolites. Lithos, 245:18-33. https://doi.org/10.1016/j.lithos.2015.07.016 [27] Wang, Q., McDermott, F., Xu, J.F., et al., 2005.Cenozoic K-Rich Adakitic Volcanic Rocks in the Hohxil Area, North-ern Tibet:Lower-Crustal Melting in an Intracontinental Setting. Geology, 33(6):465. https://doi.org/10.1130/g21522.1 [28] Wen, D., Liu, D., Chung, S., et al., 2008.Zircon SHRIMP U-Pb Ages of the Gangdese Batholith and Implications for Neotethyan Subduction in Southern Tibet.Chemical Ge-ology, 252(3-4):191-201. https://doi.org/10.1016/j.chemgeo.2008.03.003 [29] Xu, B., Griffin, W. L., Xiong, Q., et al., 2017. Ultrapotassic Rocks and Xenoliths from South Tibet:Contrasting Styles of Interaction between Lithospheric Mantle and Asthenosphere during Continental Collision.Geology, 45(1):51-54. https://doi.org/10.1130/g38466.1 [30] Yin, A., Harrison, T.M., 2000.Geologic Evolution of the Hi-malayan-Tibetan Orogen. Annual Review of Earth and Planetary Sciences, 28(1):211-280. doi: 10.1146/annurev.earth.28.1.211 [31] Zhang, Z.M., Zhao, G.C., Santosh, M., et al., 2010.Late Creta-ceous Charnockite with Adakitic Affinities from the Gangdese Batholith, Southeastern Tibet:Evidence for Neo-Tethyan Mid-Ocean Ridge Subduction? Gondwana Research, 17(4):615-631. doi: 10.1016/j.gr.2009.10.007 [32] Zhu, D. C., Wang, Q., Cawood, P. A., et al., 2017. Raising the Gangdese Mountains in Southern Tibet.Journal of Geophysical Research:Solid Earth, 122(1):214-223. doi: 10.1002/2016JB013508 [33] Zhu, D.C., Zhao, Z.D., Niu, Y.L., et al., 2011.The Lhasa Ter-rane:Record of a Microcontinent and Its Histories of Drift and Growth.Earth and Planetary Science Letters, 301(1-2):241-255. https://doi.org/10.1016/j.epsl.2010.11.005 [34] Zhu, D.C., Zhao, Z.D., Niu, Y.L., et al., 2013.The Origin and Pre-Cenozoic Evolution of the Tibetan Plateau.Gondwa-na Research, 23(4):1429-1454. https://doi.org/10.1016/j.gr.2012.02.002 [35] Zou, J. Q., Yu, H. X., Wang, B. D., et al., 2018. Petrogenesis and Geological Implications of Early Jurassic Granodio-rites in Renqinze Area, Central Part of Southern Lhasa Subterrane. Earth Science, 43(8):2795-2810(in Chinese with English abstract). [36] 代作文, 李光明, 丁俊, 等, 2018.西藏努日晚白垩世埃达克岩:洋脊俯冲的产物.地球科学, 43(8):2727-2741. http://earth-science.net/WebPage/Article.aspx?id=3908 [37] 姜子琦, 王强, Wyman, D.A., 等, 2011.西藏冈底斯南缘冲木达约30 Ma埃达克质侵入岩的成因:向北俯冲的印度陆壳的熔融?地球化学, 40(2):126-146. [38] 邹洁琼, 余红霞, 王保弟, 等, 2018.南拉萨地块中部早侏罗世仁钦则花岗闪长岩成因及其地质意义.地球科学, 43(8):2795-2810. http://earth-science.net/WebPage/Article.aspx?id=3913 -
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