Re-Os evidence for the age and origin of peridotites from the Dabie-Sulu ultrahigh pressure metamorphic belt, China

Serpentinized garnet peridotites from the Xugou peridotite body of the Sulu ultrahigh-pressure (UHP) metamorphic terrane, central eastern China, are refractory (olivines have Fo(91.7-93.1)), indicating their origin as residual mantle. Negative correlations between whole-rock MgO and TiO2, Al2O3, total Fe2O3 and CaO (r=-0.90 to -0.95) and positive correlations between wholerock Al2O3 and CaO and incompatible elements [Li, V, Cu, Ga, Sr, Y, Zr, heavy rare earth elements (HREEs), Hf, Ph and U] (r=0.69 to 0.98) likely reflect melt depletion trends. Four highly refractory samples were selected for Re-Os isotopic analysis. Although they show evidence of variable enrichment of incompatible elements during serpentinization/metasomatism, no correlations exist between Re-187/Os-188 or (OS)-O-187/(OS)-O-188 with either La or Re (r=0.00 to 0.17). These results indicate that any Re addition was fairly recent and did not affect the Os isotopic composition significantly. The correlation between Os-187/Os-188 and Re-187/Os-188 ratios thus, most likely reflects an ancient melt extraction event. The T-RD, T-MA and errorchron ages of the Xugou peridotites are all similar, suggesting that these peridotites formed around 2.0 Ga ago. This age is similar to Os model ages of mantle peridotites from the Dabie terrane, but contrasts markedly with the Archean ages of the continental lithospheric mantle (CLM) beneath the eastern block of the North China craton (NCC). If we assume that the Dabie-Sulu belt formed by the Triassic collision of the Yangtze craton with the eastern block of NCC and that the Archean aged CLM of the latter persisted until the Triassic, the Paleoproterozoic ages suggest derivation of these Dabie-Sulu mantle peridotites from the Yangtze craton. A Yangtze craton origin is consistent with the existing tectonic model of the Dabie-Sulu UHP belt. Our results support the hypothesis that the crust and underlying lithospheric mantle of the Yangtze craton were subducted to depths of > 180-200 km to form the world's largest UHP belt. (c) 2006 Elsevier B.V. All rights reserved.