Early Cretaceous high Mg# and high Sr/Y clinopyroxene-bearing diorite in the southeast Gangdese batholith, Southern Tibet
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摘要:
野外地质调查和SHRIMP锆石U-Pb定年表明，在冈底斯南缘朗县北部发育一套年龄为121.8±1.5Ma的闪长岩，侵入到一套年龄为360.8±3.5Ma弱片麻理化的花岗闪长岩中。除了典型的闪长岩矿物组合外，这套早白垩世闪长岩不仅含岩浆型绿帘石，而且含单斜辉石。朗县早白垩世闪长岩具有以下地球化学特征：(1) 较低的SiO2(54.9%~55.4%) 和较高的Al2O3(17.7%~17.9%) 和Mg# (65.3~66.1)；(2) 较高的Na2O/K2O比值(＞2.5)，显示富钠的特征；(3) 富集LREE，亏损HREE，从Ho到Lu稀土分布样式比较平坦((Ho/Yb)N=0.93~1.07)，具有微弱的Eu负异常(Eu/Eu*=0.88~0.91)；(4) 富集Sr (488×10-6~500×10-6) 和Ba (176×10-6~181×10-6)，较高的Sr/Y比值(37.5~41.7) 和较低的La/Yb比值(7.6~9.8)；(5) 锆石εHf(t) 值相对较高，为+3.4~+6.9；(6) 亏损高场强元素，富集石榴石相容元素(Sc、Y和HREE) 和地幔相容元素(Cr、Ni、Co)，这些地球化学特征和矿物组合表明这个岩体为富水的岩体，是新特提斯洋北向俯冲过程中俯冲板片释放的流体所交代的地幔楔的部分熔融的产物。通过铝在角闪石的压力计，确定了该套早白垩世闪长岩的侵位深度大约为13km，而早石炭世花岗闪长岩的侵位深度大约为21km，表明在早白垩世岩浆作用时，拉萨地块南缘经历了长期平均速率最小为~0.04mm/yr的剥露作用。
Abstract:Field investigations and SHRIMP zircon U-Pb dating indicate that a suite diorite that intruded into gneisses of granodioritic composition north of Langxian of the southern Gangdese belt, formed at 121.8±1.5Ma. This Early Cretaceous suite contains magmatic epidote and clinopyroxene. Whole rock geochemical data and zircon Hf isotope data of this suite of diorite show the following characteristics: (1) low SiO2(54.9%~55.4%), high Al2O3(17.7%~17.9%) and high Mg# (65.3~66.1); (2) relatively high Na2O/K2O ( > 2.5), indicating that they were of granite rich in sodium; (3) enriched in LREE, depleted in HREE, nearly flat distribution patterns for elements from Ho to Yb with (Ho/Yb)N=0.93~1.07, and weak negative Eu anomalies with Eu/Eu*=0.88~0.91; (4) relatively high Sr (488×10-6~500×10-6) and Ba (176×10-6~181×10-6), high Sr/Y (37.5~41.7) and low La/Yb (7.6~9.8); (5) relatively high zircon εHf(t) values (+3.4~+6.9); and (6) depleted in the HFSE, but relatively enriched in garnet compatible elements (Sc, Y and HREE) as well as mantle compatible elements (Cr, Ni and Co). These geochemical features and mineral assemblages indicate that they were hydrous magma derived from the partial melting of fluid metasomatised mantle wedge during the northward subduction of the Neo-Tethyan slab. Emplace depths for the Early Cretaceous diorite as well as the Early Carboniferous granodiorite estimated by Al-in-hornblende geobarometer indicate that they were emplaced at~13km and~21km, respectively, which in turn yields a long term exhumation rate of~0.04mm/yr.
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Key words:
- Gangdese batholith /
- Diorite /
- Zircon U-Pb dating /
- Zircon Hf isotope geochemistry /
- Emplacement depth
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图 1
藏南朗县地区地质图及采样位置
Figure 1.
Simplified geological map in the Langxian region, Southern Tibet, and showing map locations
图 2
朗县早白垩世闪长岩(a-d) 与早石炭世花岗闪长岩(e-h) 的显微照片
Figure 2.
Microphotographs showing the typical texture and mineral assemblages of Early Cretaceous diorite and Early Carboniferous granodiorite in Langxian
图 3
朗县早白垩世闪长岩中角闪石和单斜辉石的BSE图像
Figure 3.
BSE images showing the texture of hornblende and clinopyroxene in Langxian Early Cretaceous diorite
图 4
朗县早白垩世闪长岩和早石炭世花岗闪长岩的主量元素地球化学特征
Figure 4.
Covariation diagram of selected major oxides of CaO (a), Al2O3 (b), Na2O/K2O (c) and MgO (d) versus SiO2 in Langxian Early Cretaceous diorite and Early Carboniferous granodiorite
图 5
朗县早白垩世闪长岩和早石炭世花岗闪长岩的微量元素地球化学特征(标准化值据Sun and McDonough, 1989)
Figure 5.
Trace element distribution diagram of Langxian Early Cretaceous diorite and Early Carboniferous granodiorite (normalization values after Sun and McDonough, 1989)
图 6
朗县早白垩世闪长岩和早石炭世花岗闪长岩的稀土元素地球化学特征(标准化值据Sun and McDonough, 1989)
Figure 6.
Rare earth element distribution diagram for Langxian Early Cretaceous diorite and Early Carboniferous granodiorite (normalization values after Sun and McDonough, 1989)
图 7
朗县早白垩世闪长岩的锆石阴极发光图像(CL) 和U-Pb定年结果锆石上的点为Hf同位素所打点
Figure 7.
Cathodoluminescence (CL) images showing the texture and respective spots for SHRIMP U-Pb analysis on zircon grains from Langxian Early Cretaceous diorite
图 8
朗县早白垩世闪长岩的SHRIMP锆石U-Pb谐和图(a) 和年龄分布图(b)
Figure 8.
U-Pb concordia (a) and age distribution (b) diagrams for SHRIMP zircon U-Pb analytical results of Langxian Early Cretaceous diorite
图 9
朗县早石炭世花岗闪长岩的锆石阴极发光图像(CL) 和U-Pb定年结果
Figure 9.
Cathodoluminescence (CL) images showing the texture and respective spots for SHRIMP U-Pb analysis on zircon grains from Langxian Early Carboniferous granodiorite
图 10
朗县早石炭世花岗闪长岩的SHRIMP锆石U-Pb谐和图(a) 和年龄分布图(b)
Figure 10.
U-Pb Concordia (a) and age distribution (b) diagrams for SHRIMP zircon U-Pb analytical results of Langxian Early Carboniferous granodiorite
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Anderson JL and Smith DR. 1995. The effects of temperature and fO2 on the Al-in-hornblende geobarometer. American Mineralogist, 80(5-6): 549-559
Atherton MP and Sanderson LM. 1985. The chemical variation and evolution of the super-units of the segmented Coastal Batholith. In: Pitcher WS, Atherton MP, Cobbing EJ and Beckensale RD (eds.). Magmatism at a Plate Edge: The Peruvian Andes. Glasgow: Blackie, 208-227
Atherton MP and Petford N. 1993. Generation of sodium-rich magmas from newly underplated basaltic crust. Nature, 362(6416): 144-146
Brandon AD, Creaser RA and Chacko T. 1996. Constraints on rates of granitic magma transport from epidote dissolution kinetics. Science, 271(5257): 1845-1848
Cherniak DJ and Watson EB. 2003. Diffusion in zircon. In: Hanchar JM and Hoskin PWO (eds.). Zircon. Zircon Reviews in Mineralogy and Geochemistry, 53(1): 113-143
Chung SL, Liu DY, Ji JQ, Chu MF, Lee HY, Wen DJ, Lo CH, Lee TY, Qian Q and Zhang Q. 2003. Adakites from continental collision zones: Melting of thickened lower crust beneath southern Tibet. Geology, 31(11): 1021-1024
Coulon C, Maluski H, Bollinger C and Wang S. 1986. Mesozoic and Cenozoic volcanic rocks from central and southern Tibet: 39Ar/40Ar dating, petrological characteristics and geodynamical significance. Earth and Planetary Science Letters, 79(3-4): 281-302
Defant MJ and Drummond MS. 1990. Derivation of some modern arc magmas by melting of young subducted lithosphere. Nature, 347(6294): 662-665
Defant MJ, Jackson TE, Drummond MS, De Boer JZ, Bellon H, Feigenson MD, Maury RC and Stewart RH. 1992. The geochemistry of young volcanism throughout western Panama and southeastern Costa Rica: An overview. Journal of the Geological Society, 149(4): 569-579
Ding L, Kapp P, Zhong DL et al. 2003. Cenozoic volcanism in Tibet: Evidence for a transition from oceanic to continental subduction. Journal of Petrology, 44(10): 1833-1865
Dong X, Zhang ZM, Geng GS, Liu F, Wang W and Yu F. 2010. Devonian magmatism from the southern Lhasa terrane, Tibetan Plateau. Acta Petrologica Sinica, 26(7): 2226-2232 (in Chinese with English abstract)
Dupuy C, Dostal J, Marcelot G, Bougault H, Joron JL and Treuil M. 1982. Geochemistry of basalts from central and southern New Hebrides arc: Implication for their source rock composition. Earth and Planetary Science Letters, 60(2): 207-225
Guan Q, Zhu DC, Zhao ZD, Zhang LL, Liu M, Li XW, Yu F and Mo XX. 2010. Late Cretaceous adakites in the eastern segment of the Gangdese belt, southern Tibet: Products of Neo-Tethyan ridge subduction? Acta Petrologica Sinica, 26(7): 2165-2179(in Chinese with English abstract)
Guan Q, Zhu DC, Zhao ZD, Dong GC, Zhang LL, Li XW, Liu M, Mo XX, Liu YS and Yuan HL. 2011. Crustal thickening prior to 38Ma in southern Tibet: Evidence from lower crust-derived adakitic magmatism in the Gangdese Batholith. Gondwana Research, 21(1): 88-99
Guo ZF, Wilson M and Liu JQ. 2007. Post-collisional adakites in south Tibet: Products of partial melting of subduction-modified lower crust. Lithos, 96(1-2): 205-224
Gutscher MA, Maury R, Eissen JP and Bourdon E. 2000. Can slab melting be caused by flat subduction? Geology, 28(6): 535-538
Hammarstrom JM and Zen EA. 1986. Aluminum in hornblende: An empirical igneous geobarometer. American Mineralogist, 71(11-12): 1297-1313
Hawkesworth CJ, Hergt JM, Ellam RM and McDermott F. 1991. Element fluxes associated with subduction related magmatism. Philosophical Transactions of the Royal Society, London. Series A, 335(1638): 393-405
Hollister LS, Grissom GC, Peters EK, Stowell HH and Sisson VB. 1987. Confirmation of the empirical correlation of Al-in hornblende with pressure of solidification of calc-alkaline plutons. American Mineralogist, 72(3-4): 231-239
Hou KJ, Li YH, Zou TR, Qu XM, Shi YR and Xie GQ. 2007. Laser ablation-MC-ICP-MS technique for Hf isotope microanalysis of zircon and its geological applications. Acta Petrologica Sinica, 23(10): 2595-2604 (in Chinese with English abstract)
Hou ZQ, Gao YF, Qu XM, Rui ZY and Mo XX. 2004. Origin of adakitic intrusives generated during Mid-Miocene east-west extension in South Tibet. Earth and Planetary Science Letters, 220(1-2): 139-155
Ji WQ, Wu FY, Chung SL, Li JX and Liu CZ. 2009. Zircon U-Pb geochronology and Hf isotopic constraints on the petrogenesis of the Gangdese batholith, southern Tibet. Chemical Geology, 262(3-4): 229-245
Ji WQ, Wu FY, Liu CZ and Chung SL. 2009. Geochronology and petrogenesis of granitic rocks in Gangdese batholith, southern Tibet. Science in China (Series D), 52(9): 1240-1261
Ji WQ, Wu FY, Chung SL and Liu CZ. 2012a. Identification of Early Carboniferous granitoids from southern Tibet and implications for terrane assembly related to the Paleo-Tethyan evolution. The Journal of Geology, 120(5): 531-541
Ji WQ, Wu FY, Liu CZ and Chung SL. 2012b. Early Eocene crustal thickening in southern Tibet: New age and geochemical constraints from the Gangdese batholith. Journal of Asian Earth Sciences, 53: 82-95
Johnson MC and Rutherford MJ. 1989. Experimental calibration of the aluminum-in-hornblende geobarometer with application to Long Valley caldera (California) volcanic rocks. Geology, 17(9): 837-841
Kapp P, DeCelles PG, Gehrels GE, Heizler M and Ding L. 2007. Geological records of the Lhasa-Qiangtang and Indo-Asian collisions in the Nima area of central Tibet. Geological Society of America Bulletin, 119(7-8): 917-932
Kay SM, Ramos VA and Marquez M. 1993. Evidence in Cerro Pampa volcanic rocks for slab-melting prior to ridge-trench collision in southern South America. The Journal of Geology, 101(6): 703-714
Le Fort P and Cronin VS. 1988. Granites in the tectonic evolution of the Himalaya, Karakoram and southern Tibet. Philosophical Transactions of the Royal Society, London, Series A. 326(1589): 281-299
Ludwig K. 2003. User’s manual for Isoplot 3.00: A geochronological toolkit for Microsoft Excel. Berkeley Geochronology Center Special Publication, (4): 1-70
Martin H, Smithies RH, Rapp RP, Moyen JF and Champion DC. 2005. An overview of adakite, tonalite-trondhjemite-granodiorite (TTG) and sanukitoid: Relationships and some implications for crustal evolution. Lithos, 79(1-2): 1-24
McCulloch MT and Perfit MR. 1981. 143Nd/144Nd, 87Sr/86Sr and trace element constraints on the petrogenesis of Aleutian island arc magmas. Earth and Planetary Science Letters, 56: 167-179
Mo XX, Hou ZQ, Niu YL, Dong GC, Qu XM, Zhao ZD and Yang ZM. 2007. Mantle contributions to crustal thickening during continental collision: Evidence from Cenozoic igneous rocks in southern Tibet. Lithos, 96(1-2): 225-242
Morel MLA, Nebel O, Nebel-Jacobsen YJ et al. 2008. Hafnium isotope characterization of the GJ-1 zircon reference material by solution and laser-ablation MC-ICPMS. Chemical Geology, 255(1-2): 231-235
Patchett PJ. 1983. Importance of the Lu-Hf isotopic system in studies of planetary chronology and chemical evolution. Geochimica et Cosmochimica Acta, 47(1): 81-91
Pearce JA and Mei HJ. 1988. Volcanic rocks of the 1985 Tibet Geotraverse: Lhasa to Golmud. Philosophical Transaer U and Allègre CJ. 1985. Magmatism and metamorphism in the Lhasa block (Tibet): A geochronological study. Journal of Geology, 93(1): 41-57
Zen EA and Hammastrom JM. 1984. Magmatic epidote and its petrologic significances. Geology, 12(9): 515-518
Zen EA. 1985. Implications of magmatic epidote-bearing plutons on crystal evolution in the accreted terranes of northwestern North America. Geology, 13(4): 266-269
Zen EA. 1989. Plumbing the depths of batholiths. American Journal of Science, 289(10): 1137-1157
Zeng LS, Gao LE, Xie KJ and Jing LZ. 2011. Mid-Eocene high Sr/Y granites in the Northern Himalayan Gneiss Domes: Melting thickened lower continental crust. Earth and Planetary Science Letters, 303(3-4): 251-266
Zhang HF, Xu WC, Guo JQ, Zong KQ, Cai HM and Yuan HL. 2007. Zircon U-Pb and Hf isotopic composition of deformed granite in the southern margin of the Gangdise belt, Tibet: Evidence for Early Jurassic subduction of Neo-Tethyan oceanic slab. Acta Petrologica Sinica, 23(6): 1347-1353 (in Chinese with English abstract)
Zhang KJ, Xia BD, Wang GM, Li YT and Ye HF. 2004. Early Cretaceous stratigraphy, depositional environments, sandstone provenance, and tectonic setting of central Tibet, western China. Geological Society of America Bulletin, 116(9): 1202-1222
Zhang ZM, Zhao GC, Santosh M, Wang JL, Dong X and Shen K. 2010. Late Cretaceous charnockite with adakitic affinities from the Gangdese batholith, southeastern Tibet: Evidence for Neo-Tethyan mid-ocean ridge subduction? Gondwana Research, 17(4): 615-631
Zhang ZM, Dong X, Liu F, Lin YH, Yan R and Santosh M. 2012. Tectonic evolution of the Amdo Terrane, central Tibet: Petrochemistry and zircon U-Pb geochronology. The Journal of Geology, 120(4): 431-451
Zhu DC, Zhao ZD, Pan GT, Lee HY, Kang ZD, Liao ZL, Wang LQ, Li GM, Dong GC and Liu B. 2009a. Early Cretaceous subduction-related adakite-like rocks of the Gangdese Belt, southern Tibet: Products of slab melting and subsequent melt-peridotite interaction? Journal of Asian Earth Sciences, 34(3): 298-309
Zhu?DC, Mo XX, Niu YL, Zhao ZD, Wang LQ, Liu YS and Wu FY. 2009b. Geochemical investigation of Early Cretaceous igneous rocks along an east-west traverse throughout the central Lhasa Terrane, Tibet. Chemical Geology, 268(3-4): 298-312
Zhu DC, Zhao ZD, Niu YL, Mo XX, Chung SL, Hou ZQ, Wang LQ and Wu FY. 2011. The Lhasa Terrane: Record of a microcontinent and its histories of drift and growth. Earth and Planetary Science Letters, 301(1-2): 241-255
Zhu DC, Zhao ZD, Niu YL, Dilek Y, Wang Q, Ji WH, Dong GC, Sui QL, Liu YS, Yuan HL and Mo XX. 2012. Cambrian bimodal volcanism in the Lhasa Terrane, southern Tibet: Record of an Early Paleozoic Andean-type magmatic arc in the Australian proto-Tethyan margin. Chemical Geology, 328: 290-308tra-oceanic arc system in Southern Tibet: Geochemistry and tectonic implications. Acta Petrologica Sinica, 28(6): 1741-1754 (in Chinese with English abstract)
Wang Q, McDermott F, Xu JF, Bellon H and Zhu YT. 2005. Cenozoic K-rich adakitic volcanic rocks in the Hohxil area, northern Tibet: Lower-crustal melting in an intracontinental setting. Geology, 33(6): 465-468
Wen DR, Chung SL, Song B, Iizuka Y, Yang HJ, Ji JQ, Liu DY and Gallet S. 2008a. Late Cretaceous Gangdese intrusions of adakitic geochemical characteristics, SE Tibet: Petrogenesis and tectonic implications. Lithos, 105(1-2): 1-11
Wen DR, Liu DY, Chung SL, Chu MF, Ji JQ, Zhang Q, Song B, Lee TY, Yeh MW and Lo CH. 2008b. Zircon SHRIMP U-Pb ages of the Gangdese Batholith and implications for Neotethyan subduction in southern Tibet. Chemical Geology, 252(3-4): 191-201
Wu FY, Ji WQ, Liu CZ and Chung SL. 2010. Detrital zircon U-Pb and Hf isotopic data from the Xigaze fore-arc basin: Constraints on Transhimalayan magmatic evolution in southern Tibet. Chemical Geology, 271(1-2): 13-25
Xu JF, Shinjo R, Defant MJ, Wang Q and Rapp RP. 2002. Origin of Mesozoic adakitic intrusive rocks in the Ningzhen area of East China: Partial melting of delaminated lower continental crust? Geology, 30(12): 1111-1114
Xu RH, Schr
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