Seismic evidence for craton reworking at Ordos block

The North China Craton (NCC) is one of the best documented Archean cratons that has experienced lithospheric reworking. It is commonly accepted that the SCLM beneath the Eastern NCC was largely destroyed and removed. In contrast, cratonic keel of the Ordos block, nuclei of the Western NCC, is believed to be largely preserved during the Mesozoic craton destruction. However, our recent studies, including tomographic images and seismic anisotropy, suggest that warm asthenospheric materials surrounding the Ordos block may penetrate into its northeastern, southeastern, and southwestern margins. In particular, Beneath the Datong volcanoes (DTV), to the northeast Ordos, a low velocity anomaly dips westward with depth and closely follows the slope of the lithosphere beneath the Ordos. This low velocity is connected with the low velocities beneath the northern Ordos, which is further connected with the low velocities beneath the northeastern Tibetan plateau (NET). We propose an on-going lithospheric mantle reworking at the boundaries of the Ordos block due to complicated mantle flow surrounding the Ordos block in response to the continuous convergence of the Indian-Eurasian plates. The eastward asthenospheric flow breaks into two branches, with one branch around the southern corner of the block, along the Weihe graben and the Qinling-Dabie orogeny; another one flows towards the northern Ordos lithosphere and then the asthenosphere flows upward following the eastward thinning lithosphere, which leads to decompression partial melting and feeds the DTV.