| Abstract: | Margins of old continental lithosphere are likely prone to ongoing modification processes. Therefore, constraining detailed structures beneath the margin can be essential in understanding the evolution of the continental lithosphere. The eastern margin of the Eurasian plate is a natural laboratory that allows us to study the strong effects from multiple episodes of continental collision and subduction of different oceanic plates since their formation. To reveal the detailed evolution of cratons at their margins, we describe, for the first time, the upper mantle structures beneath the southern Korean Peninsula (SKP) based strictly on teleseismic relative arrival time data from densely deployed local seismic arrays, which allows us to constrain the details of the lithospheric structures beneath the Archean-Proterozoic basement. We imaged a thick (~150 km) high-velocity anomaly mainly beneath the Proterozoic Yeongnam Massif with large velocity contrasts (dlnVp ≈ 4.0% and dlnVs ≈ 6.0%) at its boundaries, suggesting the presence of a long-lasting cratonic root in the southwestern SKP. On the other hand, low-velocity anomalies were found beneath the Proterozoic Gyeonggi Massif, Gyeongsang arc-back-arc basin, and along the eastern margin of the SKP, indicating significantly modified regions. The possible existence of a remnant cratonic root beneath the SKP and contrasting lithospheric structures across the different Precambrian massifs suggests the highly heterogeneous modification of cratonic lithosphere at the eastern Eurasian plate margin. Strong velocity reductions, which indicate a thermally elevated upper mantle potentially with partial melts, correspond to areas of Cenozoic basalts, high surface heat flow, and high topography along the eastern KP margin. We interpret this coincidence as a result of recent reactivation of a craton margin, which is controlled by intense interaction between the convective upper mantle and heterogeneous continental lithosphere. |
