Journal of Petrology Advance Access originally published online on August 22, 2006
Journal of Petrology 2006 47(11):2233-2256; doi:10.1093/petrology/egl042
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Mineral Chemistry of Peridotites from Paleozoic, Mesozoic and Cenozoic Lithosphere: Constraints on Mantle Evolution beneath Eastern China
1 STATE KEY LABORATORY OF GEOLOGICAL PROCESSES AND MINERAL RESOURCES, FACULTY OF EARTH SCIENCES, CHINA UNIVERSITY OF GEOSCIENCES WUHAN 430074, P.R. CHINA
2 GEMOC ARC NATIONAL KEY CENTRE, DEPARTMENT OF EARTH AND PLANETARY SCIENCES, MACQUARIE UNIVERSITY NSW 2109, AUSTRALIA
3 KEY LABORATORY OF ISOTOPE GEOCHRONOLOGY AND GEOCHEMISTRY, GUANGZHOU INSTITUTE OF GEOCHEMISTRY, CHINESE ACADEMY OF SCIENCES GUANGZHOU 510640, P.R. CHINA
4 INSTITUTE OF GEOLOGY, CHINESE ACADEMY OF GEOLOGICAL SCIENCES BAIWANZHUANG ROAD 26, BEIJING 100037, P.R. CHINA
5 DEPARTMENT OF GEOLOGICAL AND ENVIRONMENTAL SCIENCES, STANFORD UNIVERSITY CA 94305, USA
RECEIVED NOVEMBER 4, 2005; ACCEPTED AUGUST 1, 2006
Major- and trace-element data on the constituent minerals of garnet peridotite xenoliths hosted in early Paleozoic (457–500 Ma) kimberlites and Neogene (16–18 Ma) volcanic rocks within the North China Craton are compared with those from the pre-pilot hole of the Chinese Continental Scientific Drilling Project (CCSD-PP1) in the tectonically exhumed Triassic (
220 Ma) Sulu ultrahigh-pressure (UHP) terrane along its southern margin. P–T estimates for the Paleozoic and Neogene peridotite xenoliths reflect different model geotherms corresponding to surface heat flows of 40 mW/m2 (Paleozoic) and 80 mW/m2 (Neogene). Garnet peridotite xenoliths or xenocrysts from the Paleozoic kimberlites are strongly depleted, similar to peridotites from other areas of cratonic mantle, with magnesium olivine (mean Fo92.7), Cr-rich garnet and clinopyroxene with high La/Yb. Garnet (and spinel) peridotite xenoliths hosted in Neogene basalts are derived from fertile mantle; they have high Al2O3 and TiO2 contents, low-Mg-number olivine (mean Fo89.5), low-Cr garnet and diopside with flat rare earth element (REE) patterns. The differences between the Paleozoic and Neogene xenoliths suggest that a buoyant refractory lithospheric keel present beneath the eastern North China Craton in Paleozoic times was at least partly replaced by younger, hotter and more fertile lithospheric mantle during Mesozoic–Cenozoic times. Garnet peridotites from the Sulu UHP terrane have less magnesian olivine (Fo91.5), and lower-Cr garnet than the Paleozoic xenoliths. The diopsides have low heavy REE (HREE) contents and sinusoidal to light REE (LREE)-enriched REE patterns. These features, and their high Mg/Si and low CaO and Al2O3 contents, indicate that the CCSD-PP1 peridotites represent a moderately refractory mantle protolith. Details of mineral chemistry indicate that this protolith experienced complex metasomatism by asthenosphere-derived melts or fluids in Mesoproterozoic, and subsolidus re-equilibration involving fluids/melts derived from the subducted Yangtze continental crust during UHP metamorphism in the early Mesozoic. Tectonic extension of the subcontinental lithospheric mantle of the North China Craton and exhumation of the Sulu UHP rocks in the early Mesozoic induced upwelling of the asthenosphere. Peridotites sampled by the Neogene basalts represent newly formed lithosphere derived by cooling of the upwelling asthenospheric mantle in Jurassic–Cretaceous and Paleogene time.
KEY WORDS: garnet peridotite xenoliths; North China Craton; lithospheric thinning; Sulu UHP terrane; UHP lithosphere evolution; mantle replacement
*Corresponding author. Fax: +86 27 6788 3873. E-mail: jpzheng{at}cug.edu.cn and jpzheng2003{at}yahoo.com
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