Sr-Nd-Pb isotopic constraints on multiple mantle domains for Mesozoic mafic rocks beneath the South China Block hinterland

The Si-Nd and Pb isotopic compositions of middle Jurrasic to late Cretaceous mafic rocks across the Chenzhou-Linwu Fault Within the South China Block are presented to constrain the characteristics and evolution of Mesozoic mantle Source. These data, in combination with geochronological results, can be divided into four groups. Group 1 (similar to 175-170 Ma) occurs on either side of the Chenzhou-Linwu Fault and has moderately depleted Sr-Nd and radiogenic Pb isotopes. akin to a FOZO-like source and is inferred to have originated from deep asthenospheric mantle with delaminated lower crustal signatures. Group 2 (similar to 175-145 Ma) is restricted to the west of file fault and shows a significant Dupal anomaly and a binary mixing array between a component from an enriched mantle source (EM 1) with low, epsilon(Nd(t)) values and (206)pb/Ph-204, and intermediate Sr-87/Sr-86 ratios and a FOZO-like component characterized by Group) 1. Group 3 (similar to 175-125 Ma) occurs to the east of the fault and exhibits low epsilon(Nd(t)) values and high Sr-Pb isotopic ratios, similar to EM2 component with minor DMM component. The Sr-Nd-Pb isotopic systematics for Group 4 (-93-80 Ma) resembles those of SE China Cenozoic basilts, Suggestive of DMM-EM2 reservoir in response to the uppermost asthenospheric mantle Source. These temporal and spatial variations, together with other geologic and paleomagnetic data, suggest that (1) the Multiple mantle reservoirs include FOZO-, DMM-, EM1- and EM2-like components beneath file South China Block; (2) DMM-EM2 sources have dominated the mantle domains beneath SE Asia since late Cretaceous: (3) the Chenzhou-Linwu Fault corresponds with the early Mesozoic lithospheric boundary between the Yangtze and Cathaysia blocks Within the South China Block. The Mesozoic mafic rocks within the South China Block developed in an active rift setting in response to the delamination of partially over-thickened lithospheric keel and upwelling of asthenosphere rather than a supra-subduction environment. (C) 2008 Elsevier B.V. All rights reserved.