Continental Thermal Blanketing Explains the Compositional Dichotomy of the Diffuse Basaltic Province Across Central-Eastern Asia

A diffuse magmatic province covering central-eastern Asia continent displays a compositional transition at 120-100 Ma and probably reflects melting initiation in isotopically enriched lithospheric mantle, followed by melting of the asthenosphere. However, the cause for the transition across such a vast landmass remains poorly constrained. Here, analyses of newly found Chaoge basalts (similar to 95 Ma, central Asia) and compiled data from across the basaltic province are combined to reveal the factors controlling the basalt dichotomy. The Chaoge basalts are considered to originate from a hot pyroxenite-bearing asthenosphere with potential temperatures of similar to 1,450 degrees C, overlapping the source thermochemical conditions for most post-transition basaltic rocks. The asthenosphere in 120-100 Ma is suggested to be hotter and to have controlled the compositional transition in the studied basaltic province. We suggest that asthenospheric warming resulted from prolonged continental thermal blanketing and can account for other diffuse igneous provinces with similar compositional variations and tectonic histories. A diffuse magmatic province covering central-eastern Asia continent occupies a time span from Late Mesozoic to the present and consists of many basaltic fields, each including numerous small-volume monogenic basaltic extrusions. The spatially and temporally dispersed basaltic rocks show a concurrent compositional transition at 120-100 Ma but the related causes remain unclear. Here, the newly found Chaoge basalts (similar to 95 Ma, central Asia) and a data synthesis of the Cretaceous-Cenozoic basaltic province reveal the factors controlling the basalt dichotomy. The Chaoge basalts and other post-transition equivalents are shown to be derived from hot pyroxenite-bearing asthenospheric domains with potential temperatures higher than the ambient mantle. Such overheated asthenosphere is inferred to have existed at 120-100 Ma and controlled the basalt dichotomy. That is, the melting initiated in strongly metasomatized lithospheric mantle to produce the pre-transition basalts under a normal thermal mantle state, followed by a magmatic hiatus due to the drainage of the fusible components; later melting occurred in the overheated asthenosphere to produce the post-transition basaltic rocks. We suggest that this overheating-driven basaltic dichotomy is a natural outcome of prolonged thermal blanketing of large continental lithosphere and should have general relevance.