Asthenosphere-litho spheric mantle interaction in an extensional regime: Implication from the geochemistry of Cenozoic basalts from Taihang Mountains, North China Craton

摘要

Compositions of Cenozoic basalts from the Fansi (26.3-24.3 Ma), Xiyang-Pingding (7.9-7.3 Ma) and Zuoquan (similar to 5.6 Ma) volcanic fields in the Taihang Mountains provide insight into the nature of their mantle sources and evidence for asthenosphere-lithospheric mantle interaction beneath the North China Craton. These basalts are mainly alkaline (SiO2 = 44-50 wt.%, Na2O+ K2O = 3.9-6.0 wt.%) and have OIB-like characteristics, as shown in trace element distribution patterns, incompatible elemental (Ba/Nb = 6-22, La/Nb = 0.5-1.0, Ce/Pb = 15-30, Nb/U = 29-50) and isotopic ratios (Sr-87/Sr-86 = 0.7038-0.7054, Nd-143/Nd-144 = 0.5124-0.5129). Based on TiO2 contents, the Fansi lavas can be classified into two groups: high-Ti and low-Ti. The Fansi high-Ti and Xiyang-Pingding basalts were dominantly derived from an asthenospheric source, while the Zuoquan and Fansi low-Ti basalts show isotopic imprints (higher Sr-87/Sr-86 and lower Nd-143/Nd-144 ratios) compatible with some contributions of subcontinental lithospheric mantle. The variation in geochemical compositions of these basalts resulted from the low degree partial melting of asthenosphere and the interaction of asthenosphere-derived magma with old heterogeneous lithospheric mantle in an extensional regime, possibly related to the far effect of the India-Eurasia collision. (c) 2006 Elsevier B.V. All rights reserved.