Abstract
This paper reports geochemical and Pb-Sr-Nd isotopic compositions of the Indosinian Yangba (215 Ma), Nanyili (225 Ma) and Mopi granitoids from the Bikou block of the northwestern margin of the Yangtze plate. These granitoids are enriched in Al (Al2O3: 14.56%–16.48%) and Sr (352 μg/g–1047 μg/g), and depleted in Y (<16 μg/g) and HREE (e.g. Yb<1.61 μg/g), resulting in high Sr/Y (36.3–150) and (La/Yb)N (7.8–36.3) ratios and strongly fractionationed REE patterns. The Indosinian granotoids show initial Sr isotopic ratios (I Sr) from 0.70419 to 70752, ε Nd(t) values from −3.1 to −8.5, and initial Pb isotopic ratios 206Pb/204Pb=17.891−18.250, 207Pb/204Pb=15.494−15.575, and 208Pb/204Pb=37.788−38.335. Their geochemical signatures indicate that the granitoids are adakitic. However, they are distinct from some adakites, generated by partial melting of subducted oceanic slab and/or underplated basaltic lower crust, because they have high K (K2O: 1.49%–3.84%) and evolved Nd isotopic compositions, with older Nd isotopic model ages (T DM=1.06–1.83 Ga). Geochemical and Sr-Nd isotopic compositions suggest that the magmas of the Insoninian adakitic rocks in the Bikou block were derived from partial melting of thickened basaltic lower crust. Combined with regional analyses, a lithospheric delamination model after collision between the North China and South China plates can account for the Indosinian adakitic magma generation. On the other hand, based on the Pb-Sr-Nd isotopic probing to the magma sources of the adakitic rocks, it is suggested that there is an unexposed continent-type basement under the exposed Bikou Group volcanic rocks. This can constrain on the Bikou Group volcanic rocks not to be MORB-or OIB-type.
Similar content being viewed by others
References
Yan Q R, Hanson A D, Wang Z Q, et al. Geochemical and tectonic setting of the Bikou volcanic terrane on the northern margin of the Yangtze plate. Acta Petrol Mineral (in Chinese with English abstract), 2004, 23: 1–11
Kemp A I S, Hawkesworth C J. Granitic perspectives on the generation and secular evolution of the continental crust. Treatise Geochem, 2003, 3: 349–410
Qin J F, Lai S C, Li Y F. Petrogenesis and geological significance of Yangba granodiorites from Bikou area, northern margin of Yangtze plate. Acta Petrol Sinica (in Chinese with English abstract), 2005, 21: 697–710
Zhang Z Q, Zhang G W, Tang S H, et al. Isotopic Chronology of South Qinling Metamorphic Rock-Group (in Chinese). Beijing: Geological Publishing House, 2002. 1–256
Yan Q R, Wang Z Q, Yan Z, et al. SHRIMP U-Pb zircon dating constraints on formation time of the Bikou Group volcanic rocks. Geol Bull Chin (in Chinese with English abstract), 2003, 22: 456–459
Tao H X, He H Y, Wang Q Q, et al. Tectonic Evolution of the Northern Margin of the Yangtze Plate. Xi’an: Northwest University Press, 1993. 1–141
Yan Q R, Wang Z Q, Hanson A D, et al. The Hengdan turbidite terrane: fillings in a late Paleozoic forearc basin developed on the passive margin of the Yangtze plate. Geol Bull Chin (in Chinese with English abstract), 2002, 21: 495–500
Sun S S, McDonough W F. Chemical and isotopic systematics of oceanic basalts: implications for mantle composition and processes. In: Saunders A D, Norry M J, eds. Magmatism in the Ocean Basins. Geol Soc Spec Publ, London, United Kingdom, 1989, 313–345
Taylor S R, McLennan S M. The Continental Crust: Its Composition and Evolution. Oxford: Blackwell Scientific Publication, 1985. 1–312
Defant M J, Drummond M S. Derivation of some modern arc magmas by melting of young subducted lithosphere. Nature, 1990, 34: 662–665
Zhang L G. Block-Geology of Eastern Asia Lithosphere-Isotope Geochemistry and Dynamics of Upper Mantle, Basement and Granite (in Chinese with English abstract). Beijing: Science Press, 1995. 1–252
Peacock S M, Rusher T, Thompson A B. Partial melting of subducting oceanic crust. Earth Planet Sci Lett, 1994, 121: 224–227
Drummond M S, Defant M J. Kepezhinskas P K. Petrogenesis of slab-derived trondhjemite-tonalite-dacite/adakite magmas. Trans R Soc Edinburgh Earth Sci, 1996, 87: 205–215
Sajona F G, Maury R C, Pubellier M. Magmatic source enrichment by slab-derived melts in a young post-collision setting, central Mindanao (Philippines). Lithos, 2000, 54: 173–206
Gutscher M A, Maury R, Eissen J P, et al. Can slab melting be caused by flat subduction? Geology, 2000, 28: 535–538
Beate B, Monzier M, Spikings R, et al. Mio-Pliocene adakite generation related to flat subduction in southern Ecuador: the Quimsacocha volcanic center. Earth Planet Sci Lett, 2001, 192: 561–570
Atherton M P, Petord N. Generation of sodium-rich magmas from newly underplated basaltic crust. Nature, 1993, 362: 144–146
Muir R G, Weaver S D, Bradshaw J D, et al. Geochemistry of the Cretaceous Separation Point batholiths, New Zealand: granitoid magmas formed by melting of mafic lithosphere. J Geol Soc, 1995, 152: 689–701
Barnes C G, Petersen S W, Kistler R W, et al. Source and tectonic implications of tonalite-trondhjemite magmatism in the Klamath Mountain. Contrib Mineral Petrol, 1996, 123: 40–60
Petford N, Atherton M. Na-rich partial melts from newly underplated basaltic crust: the Cordillera Blanca batholith. Peru J Petrol, 1996, 37: 1491–1521
Xu J F, Wang Q. Tracing the thickening process of continental crust through studying adakitic rocks: evidence from volcanic rocks in the north Tibet. Earth Sci Front (in Chinese with English abstract), 2003, 10: 401–406
Hou Z Q, Gao Y F, Qu X M, et al. Origin of adakitic intrusives generated during mid-Miocene east-west extension in southern Tibet. Earth Planet Sci Lett, 2004, 220: 139–155
Chung S L, Liu D Y, Ji J Q, et al. Adakites from continental collision zones: Melting of thickened lower crust beneath southern Tibet. Geology, 2003, 31: 1021–1024
Wang Q, McDermott F, Xu J F, et al. Cenozoic K-rich adakitic volcanics in the Hohxil area, northern Tibet: lower crustal melting in an intracontinental setting. Geology, 2005, 33: 464–468
Xu J F, Shinjo R, Defant M J, et al. Origin of Mesozoic adakitic intrusive rocks in the Ningzhen area of east China: partial melting of delaminated lower continental crust? Geology, 2002, 30: 1111–1114
Gao S, Rudnick R L, Yuan H L, et al. Recycling lower continental crust in the North China craton. Nature, 2004, 432: 892–897
Wang Q, Xu J F, Jian P, et al. Petrogenesis of adakitic porphyries in an extensional tectonic setting, Dexing, South China: implications for the genesis of porphyry copper mineralization. J Petrol, 2006, 47: 119–144
Wang Q, Xu J F, Zhao Z H. The summary and comment on research on a new kind of igneous rock — adakite. Adv Earth Sci (in Chinese), 2001, 16: 201–208
Zhang Q, Wang Y, Qian Q, et al. The characteristics and tectonic-metallogenic significances of the adakites in Yanshan period from eastern China. Acta Petrol Sinica (in Chinese with English abstract), 2001, 17: 236–244
Sen C, Dunnt T. Dehydration melting of a basaltic composition amphibolite at 1.5 and 2.0 GPa: Implication for the origin of adakites. Contrib Mineral Petrol, 1994, 117: 394–409
Rapp R P, Watson E B. Dehydration melting of metabasalt at 8–32 kbar: Implications for continental growth and crust-mantle recycling. J Petrol, 1995, 36: 891–931
Zhang G W, Zhang B R, Yuan X C, et al. Qinling Orogenic Belt and Continental Dynamics (in Chinese with English abstract). Beijing: Science Press, 2000. 1–855
Zhang H F, Ouyan J P, Lin W L, et al. Pb, Sr and Nd isotope composition of Ningshan granitoids, South Qinling and their deep geological implication. Acta Petrol Mineral (in Chinese with English abstract), 1997, 16: 20–32
Zhu M X, Luo T C, Zhang H F, et al. Pb, Sr and Nd isotopic geochemical characteristics of Dongjiankou plutons in South Qinling constraints on their magma source. Geology-Geochemistry (in Chinese with English abstract), 1998, (1): 30–36
Zhang H F, Jin L L, Zhang L, et al. Geochemical and Pb-Sr-Nd isotopic compositions of granitoids from western Qinling belt: Constraints on basement nature and tectonic affinity. Sci China Ser D-Earth Sci, 2007, 50(2):184–196
Zhang H F, Gao S, Zhang B R, et al. Pb isotopes of granitoids suggest Devonian accretion of Yangtze (South China) craton to North China craton. Geology, 1997, 25: 1015–1018
Sisson T W, Ratajeski K, Hankins W B, et al. Voluminous granitic magmas from common basaltic sources. Contrib Mineral Petrol, 2005, 148: 635–661
Pearce J A, Harris N B W, Tindle A G. Trace element discrimination diagrams for the tectonic interpretation of granitic rocks. J Petrol, 1984, 25: 956–983
Ames L, Tilton G R, Zhou G. Timing of collision of the Sino-Korea and Yangtze cratons: U-Pb dating of coesite-bearing eclogites. Geology, 1993, 21, 339–342
Li S G, Xiao Y L, Liou D L. Collision of the North China and Yangtze blocks and formation of coesite-bearing eclogites: Timing and processes. Chem Geol, 1993, 109: 89–111
Li S G, Sun W D, Zhang G W, et al. Chronology and geochemistry of metavolcanic rocks from Heigouxia Valley in Mianlue tectonic arc, South Qinling: Observation for a Paleozoic oceanic basin and its close time. Sci China Ser D-Earth Sci, 1996, 39: 300–310
Hacker B R, Wang X, Eide E A, et al. The Qinling-Dabie ultra-high-pressure collisional orogen, In: Yin A, Harriso T M, eds. The Tectonics of Asia. Cambridge: Cambridge University Press. 1996, 345–370
Lu X X, Xiao Q H, Dong Y, et al. Granitoid Tectonic Map of Qinling Belt (in Chinese). Beijing: Geological Publishing House, 2000
Sun W D, Li S G, Chen Y D, et al. Timing of synorogenic granotoids in south Qinling, central China: Constraints on the evolution of the Qinling-Dabie Orogenic Belt. J Geology, 2002, 110: 457–468
Wang X X, Wang T, Lu X X, et al. Petrographic evidence of hybirdization of magmas of the Laojunshan and Qinlingliang rapakivi-textured granites in the north Qinling and its significance. Geol Bull Chin (in Chinese with English abstract), 2002, 21: 525–529
Lu X X, Wei X D, Xiao Q H, et al. Geochronological studies of rapakivi granites in Qinling and its geological implications. Geol J Chin Univ (in Chinese with English abstract), 1999, 15:372–377
Yin A, Harrison T M. Geologic evolution of the Himalayan-Tibetan orogen. Annu Rev Earth Planet Sci, 2000, 28: 211–280.
Harrison T M, Lovera O M, Grove M. New insights into the origin of two contrasting Himalayan granite belts. Geology, 1997, 25: 899–902
Harris N, Massey J. Decompression and anatexis of Himalayan metapelites. Tectonics, 1994, 13: 1537–1546
Zhang G W, Cheng S Y, Guo A L, et al. Mianlue paleo-suture on the southern margin of central orogenic system in Qinling-Dabie: A discussion of the assembly of the main part of the continent. Geol Bull Chin (in Chinese with English abstract), 2004, 23: 846–853
Roger F, Malavieille J, Leloup Ph H, et al. Timing of granite emplacement and cooling in the Songpan-Garze fold belt (eastern Tibetan Plateau) with tectonic implications. J Asian Earth Sci, 2004, 22: 465–481
Gao S, Zhang B R, Jin Z M, et al. Lower crustal delamination in Qinling-Dabie Orogenic Belt. Sci Chin Ser D-Earth Sci, 1999, 42: 423–433
Author information
Authors and Affiliations
Corresponding author
Additional information
Supported by the National Natural Science Foundation of China (Grant Nos. 40234052 and 40521001) and the Program for Changjiang Scholars and Innovative Research Team in University (Grant No. IRT0441)
Rights and permissions
About this article
Cite this article
Zhang, H., Xiao, L., Zhang, L. et al. Geochemical and Pb-Sr-Nd isotopic compositions of Indosinian granitoids from the Bikou block, northwest of the Yangtze plate: Constraints on petrogenesis, nature of deep crust and geodynamics. SCI CHINA SER D 50, 972–983 (2007). https://doi.org/10.1007/s11430-007-0014-z
Received:
Accepted:
Issue Date:
DOI: https://doi.org/10.1007/s11430-007-0014-z