The geochemistry of late Mesozoic volcanic rocks from the North China Craton and temporal and spatial constraints on the lithosphere thinning

Abstract

The Yuanjiazhuang and Bainaobao volcanic rock suites are of late Mesozoic age located respectively in the east and west of the Daxing'anling-Taihangshan gravity gradient zone. These volcanic rocks display similar characteristics in incompatible trace elements and radiogenic isotopes. They are highly fractionated in rare earth elements (REE) with a high LREEs/HREEs ratio, enriched in large ion lithophile elements (such as Rb, Ba, Th, U, K), relatively depleted in high field strength elements (HFSE: Nb, Ta, Zr, Hf, Ti), high ( 87Sr/86Sr)i and low εNd(t) and εHf(t). All these data suggest that the sources for the two volcanic rock suites are similar and their parental melts must have derived from partial melting of ancient metasomatized mantle lithosphere. Combined with the data in the literature, we propose that the lithospheric thinning beneath the North China Craton happened not only in the east but also to the west of the gradient zone in the late Mesozoic.