A global comparison of V p , V s , and V p / V s structures of the mantle lithosphere beneath major cratons

Cratons formed due to the specific melting regime of the primitive mantle with elevated mantle temperature during Archean. However, each craton has undergone a distinct evolution history, and some have lost their stability. To investigate to what degree cratons in comparison with one another have been modified from their analogous initial form, we employed Sn-Pn differential (PSn) traveltimes to derive V p / V s ratio, which is thought to be related to Mg# of the uppermantle. We assessed Pn, Sn, and PSn data using three datasets based on epicentral distance: (1) 2°–12°, (2) 2°–7°, and (3) 7°–12°. The results suggest that most cratons show comparable seismic properties with high velocities and low V p / V s ratio, implying a highly depleted uppermost mantle that resembles the original residue from the partial melt extraction of the primitive mantle during the Archean. Conversely, the Eastern North China Craton (ENCC) displays the lowest P- and S-wave velocities, and noticeable high V p / V s ratios in all datasets, implying a systematic difference with other cratons. This observation suggests a scenario of total removal of the depleted Archean mantle lithosphere beneath the ENCC. In contrast, the Ordos Block located at the western part of the North China Craton (WNCC) shows velocities and V p / V s ratio comparable with those of the typical cratons, suggesting that it has still maintained its Archean mantle lithosphere. The Wyoming Craton has a high V p / V s ratio similar to that of the ENCC and a high P-wave velocity comparable to that of the typical cratons. These features suggest that the Archean mantle lithosphere has been significantly modified rather than totally removed and replaced by a younger fertile mantle. The Indian Craton presents a low V p / V s ratio and comparatively high velocities at shallow parts of the mantle lithosphere but a high V p / V s ratio at deeper parts similar to that of the ENCC, suggesting a partial modification of the Indian Craton at deeper parts.