Source characteristics and temporal-spatial evolution of Mesozoic and Cenozoic basaltic magmatism in the Taihang Mountains

A summary of elemental and isotopic compositions of the Mesozoic gabbros and Cenozoic basalts from the Taihang Mountains shows a remarkable difference in their mantle sources. Cenozoic basalts are mainly alkaline basalts with minor olivine tholeiites and originated from partial melting of asthenosphere with some involvements of old subcontinental lithospheric mantle. In contrast, the Mesozoic gabbros are high in SiO2 content, enriched in LREE and LILE (Ba, Th, U) and depleted in HFSE (Nb, Ta, Zr and Ti). They are also enriched in Sr-Nd isotopes (most Sr-87/Sr-86(i) > 0.705, Nd-143/(144) Nd-i < 0.512) and depletion in Ph isotopes (Pb-206/Pb-204 < 17.5, Pb-207/Pb-204 < 15.5, Pb-208/Pb-204(i) < 38.0). These geochemical features indicate that these Mesozoic gabbros were generated from enriched old lithospheric mantle, which was greatly modified by silicate melt. Such a modification might be related to the Proterozoic subduction/collision during the formation of the Trans-North China Orogen. The old and isotopically enriched lithospheric mantle is existent till the Cenozoic, as recorded in mantle peridotitic xenoliths from Cenozoic basalts of the region.