Petrogenesis and significance of the Mesozoic North Taihang complex: Major and trace element evidence

The Mesozoic North Taihang complex consists mainly of intermediate rocks and leucogranites as well as minor, synplutonic enriched-mantle derived mafic rocks. The intermediate rocks show high-K calc-alkaline affinity, and high Sr (and Ba) and La/Yb ratios with negligible Eu anomalies, but are low in Y; these signatures are shared by the mafic rocks. The intermediate rocks were probably produced by magma mixing between the evolved enriched-mantle derived mafic magma and a crustal granitic magma, followed by fractional crystallization. The leucogranites show high SiO2 and low ferromagnesian contents; they probably represent residual melts produced from fractional crystallization of the intermediate rocks. Therefore, the North Taihang complex represents significant addition of juvenile crust in the Mesozoic. Mobilized by an upwelling asthenosphere, enriched portions of subcontinental lithospheric mantle experienced partial melting and were consumed significantly, resulting in the intensive magmatism within the North China Craton (NCC). This process is possibly an important mechanism responsible for the lithosphere thinning beneath the NCC. Although the Taihang (and the whole eastern China) granites display rare earth patterns similar to adakites, they appear to have no genetic link with the latter. The model of "eastern plateau" proposed by some authors is not supported by our new data for the Taihang rocks.