Science in China Series D: Earth Sciences

, Volume 46, Issue 3, pp 200–209 | Cite as

U-Pb isotopic compositions of the ultrahigh pressure metamorphic (UHPM) rocks from Shuanghe and gneisses from Northern Dabie zone in the Dabie Mountains, central China: Constraint on the exhumation mechanism of UHPM rocks

  • Li Shuguang 
  • Huang Fang 
  • Zhou Hongying 
  • Li Huimin 
Article

Abstract

The U-Pb isotopic study of the ultrahigh pressure metamorphic (UHPM) rocks and gneisses from the Dabie Mountains shows that the UHPM rocks exposed in the Southern Dabie zone have relatively low Pb contents (most > 4×10−6), high U/Pb ratios (most < 0.1), and a large variation of Pb isotopic ratios with relatively high radiogenic Pb (206Pb/204Pb = 17.026–20.781). Their low Pb contents could be the result of Pb loss caused by fluid expulsion during continental subduction, while their high radiogenic Pb values can be explained by the mixing of the upper crust Pb and the mantle Pb. In contrast, the gneisses exposed in the Northern Dabie zone have higher Pb contents (most < 4× 10−6), lower U/Pb ratios (> 0.07), and lower Pb isotopic ratios (206Pb/204Pb = 15.799–17.204), which are similar to those of the Mesozoic granites developed in both Northern and Southern Dabie zones. It is suggested that the Northern Dabie zone may have experienced a smaller fluid expulsion and Pb loss during the continental subduction, and their Pb isotopic compositions could be explained by the mixing of the lower crust Pb and the mantle Pb. Their initial Pb isotope ratios at 230 Ma suggest that the U/Pb ratios of the UHPM rocks in the Southern Dabie zone are higher than those of the gneisses in the Northern Dabie zone in a long period of time before the continental subduction. The above observations suggest that the protoliths of the UHPM rocks in the Southern Dabie zone are upper crustal rocks in the subducted continental crust, while the gneisses in the Northern Dabie zone have the middle-lower crust features. Based on these observations, a model for the exhumation of UHPM rocks is proposed, i.e. the detachment between the upper crust and lower crust in the subducted continental crust could have occurred during subduction, thus the subducted upper crust was uplifted by buoyancy and moved southward along the thrust.

Keywords

ultrahigh pressure metamorphic rocks Dabie Mountains U-Pb isotopic geochemistry 

Preview

Unable to display preview. Download preview PDF.

Unable to display preview. Download preview PDF.

References

  1. 1.
    Smith, D. C., Coesite in clinopyroxene in the Caledonides and its implications for geodynamics, Nature, 1984, 310: 641–644.CrossRefGoogle Scholar
  2. 2.
    Chopin, C., Coesite and pure pyrope in high-grade blueschists of the Western Alps: A first record and some consequences, Contrib. Mineral. Petrol., 1984, 86: 107–118.CrossRefGoogle Scholar
  3. 3.
    Sobolev, N. V., Shatsky, V. S., Diamond inclusions in garnets from metamorphic rocks, Nature, 1990, 343: 742–746.CrossRefGoogle Scholar
  4. 4.
    Wang, X., Liou, J. G., Mao, H. G., Coesite-bearing eclogites from the Dabie Mountains in central China, Geology, 1989, 17: 1085–1088.CrossRefGoogle Scholar
  5. 5.
    Okay, A. I., Xu, S., Sengör, A. M. C., Coesite from the Dabie Shan eclogites, central China, Eur. Jour. Mineral., 1989, 1: 595–598.Google Scholar
  6. 6.
    Xu, S., Okay, A. I., Ji, S. et al., Diamond from the Dabie Shan metamorphic rocks and its implication from tectonic setting, Science, 1992, 256: 80–82.CrossRefGoogle Scholar
  7. 7.
    Li, S., Liu, D., Chen, Y. et al., Neodymium isotopic compositions of continental crust in the northern margin of Yangtze Block and its tectonic implications, Geochimica (in Chinese with English abstract), 1994, 23(Suppl): 10–17.Google Scholar
  8. 8.
    Xie, Z., Chen, J., Zhang, X., Nd isotopic compositions of metamorphic and granitic rocks from the Dabie orogen and their geological significance, Acta Petr. Sinica (in Chinese with English abstract), 1996, 12(3): 401–408.Google Scholar
  9. 9.
    Li, S., Huang, F., Nie, Y. et al., Geochemical and geochronological constraints on the suture location between the North and South China Blocks in the Dabie orogen, central China, Physics and Chemistry of the Earth (A), 2001, 26: 655–672.CrossRefGoogle Scholar
  10. 10.
    Doe, B. R., Zartman, R. E., Plumbotectonic—The model, Tectonophysics, 1981, 75: 135–162.CrossRefGoogle Scholar
  11. 11.
    Xu, S., Liu, Y., Sun, W. et al., Discovery of the eclogite and its petrography in the northern Dabie Mountains, Chinese Sci. Bull., 2000, 45(3): 273–278.CrossRefGoogle Scholar
  12. 12.
    Liu, Y., Li, S., Xu, S. et al., U-Pb ages and multi-growth of zircons from eclogite and tonolitic gneiss in the northern Dabie Mountains, Geol. J. China Univ. (in Chinese with English abstract), 2000, 6(3): 417–423.Google Scholar
  13. 13.
    Liu, Y., Li, S., Xu, S. et al., Sm-Nd isotopic age of eclogite from the North Dabie zone and its geological implications, Geochimica (in Chinese with English abstract), 2001, 30(1): 79–87.Google Scholar
  14. 14.
    Xue, F., Rowley, D. B., Tucker, R. D. et al., U/Pb zircon ages of Granitois rocks in the North Dabie complex, eastern Dabie Shan, China, J of Geology, 1997, 105: 744–753.CrossRefGoogle Scholar
  15. 15.
    Zhang, R. -Y., Liou, J. G., Tsai, C. -H., Petrogenesis of a high-temperature metamorphic belt: A new tectonic interpretation for the northern Dabieshan, central China, J. Meta. Geol., 1996, 14: 319–333.CrossRefGoogle Scholar
  16. 16.
    Chen, N. -S., Sun, M., You, Z. -D. et al., Well-preserved garnet zoning in granulite from the Dabie Mountains, central China, J. Metamorphic Geol., 1998, 16: 213–222.CrossRefGoogle Scholar
  17. 17.
    Carswell, D. A., Wilson, R. N., Zhai, M., The enigma of eclogite-gneiss relationship in the ultra-high pressure terrane of Dabie Shan, central China, Inter. Workshop on UHP Metamorphism and Exhumation at Stanford Univ., 1998, A-40–44.Google Scholar
  18. 18.
    Ye, K., Yao, Y. -P., Katayama, I. et al., Large area extent of ultrahigh-pressure metamorphism in the Sulu ultrahigh-pressure terrane of East China: New implications from coesite and omphacite inclusions in zircon of granitic gneiss, Lithos., 2000, 52: 157–164.CrossRefGoogle Scholar
  19. 19.
    Zhang, L., Block-geology of Eastern Asia Lithosphere (in Chinese), Beijing: Science Press, 1995, 53–62.Google Scholar
  20. 20.
    Taylor, S. R., McLennan, S. M., The continental crust: Its composition and Evolution, Oxford: Blackwell, 1985, 46–92.Google Scholar
  21. 21.
    Kogiso, T., Tatsumi, Y., Nakono, S., Trace element transport during dehydration processes in the subducted oceanic crust: 1. Experiments and implications for the origin of ocean island basalts, Earth Planet. Sci. Lett., 1997, 148: 193–205.CrossRefGoogle Scholar
  22. 22.
    Zindler, A., Hart, S., Chemical geodynamics, Ann. Rev. Earth Planet Sci., 1986, 14: 493–571.CrossRefGoogle Scholar
  23. 23.
    Hofmann, A. W., Mantle geochemistry from oceanic volcanism, Nature, 1997, 385: 219–228.CrossRefGoogle Scholar
  24. 24.
    Li, S., Jagoutz, E., Xiao, Y. et al., Geochronology of ultrahigh pressure metamorphic rocks from the Dabie-Sulu belt (I) —Sm-Nd isotopic system, Sci. in China, Ser. D, 1996, 39(6): 597–609.Google Scholar
  25. 25.
    Li, S., Li, H., Chen, Y. et al., Geochronology of ultrahigh pressure metamorphic rocks from the Dabie-Sulu belt (II)— Zircon U-Pb system, Sci. in China, Ser. D (in Chinese), 1997, 27(3): 200–206.Google Scholar
  26. 26.
    Zheng, Y. -F., Fu., B., Gong, B. et al., U-Pb dating of marble associated with eclogite from the Dabie Mountains, East China, Chinese J. Geochemistry, 1997, 16(3): 193–201.CrossRefGoogle Scholar
  27. 27.
    Zheng, Y. -F., Fu, B., Li, Y. et al., Oxygen and hydrogen isotope geochemistry of ultra high-pressure eclogites from the Dabie Mountains and the Sulu terrane, Earth Planet. Sci. Letters, 1998, 155: 113–129.CrossRefGoogle Scholar
  28. 28.
    Fu, B., Zheng, Y. -F., Wang, Z. et al., Oxygen and hydrogen isotope geochemistry of gneisses associated with ultrahigh pressure eclogites at Shuanghe in the Dabie Mountains, Contrib. Mineral. Petrol., 1999, 134: 52–66.CrossRefGoogle Scholar
  29. 29.
    Chemenda, A. I., Mattauer, M., Malavieille, J. et al., A mechanism for syn-collisional rock exhumation and associated normal faulting: Results from physical modeling, Earth Planet. Sci. Lett., 1995, 132: 225–232.CrossRefGoogle Scholar
  30. 30.
    Okay, A., Sengör, A. M. C., Evidence for intracontinental thrust-related exhumation of the ultra-high-pressure rocks in China, Geology, 1992, 20: 411–414.CrossRefGoogle Scholar
  31. 31.
    Webb, L. E., Hacker, B. R., Ratschacher, L. et al., Thermochronologic constrains on deformation and cooling history of high- and ultrahigh-pressure rocks in the Qinling-Dabie orogen, eastern China, Tectonics, 1999, 18(4): 621–638.CrossRefGoogle Scholar

Copyright information

© Science in China Press 2003

Authors and Affiliations

  • Li Shuguang 
    • 1
  • Huang Fang 
    • 1
  • Zhou Hongying 
    • 2
  • Li Huimin 
    • 2
  1. 1.Department of Earth and Space SciencesUniversity of Science and Technology of ChinaHefeiChina
  2. 2.Tianjin Institute of Geology and Mineral ResourcesTianjinChina

Personalised recommendations