Heterogeneous Modification and Ongoing Reactivation of Craton Margin beneath Northeast Asia Continental Margin: Insight from Teleseismic Traveltime Tomography of the Korean Peninsula

Abstract:

Continental lithosphere at the eastern margin of the Eurasian plate experienced multiple episodes of continental collision and subduction of different oceanic plates since its formation. The Korean Peninsula (KP) is known to consist of Archean–Proterozoic massifs (e.g., Gyeonggi, Yeongnam Massif) located at the forefront in northeast Asia, where current dynamics in the upper mantle and effects due to nearby subducting slabs are the most significant.

We present 3-D velocity structure of KP by teleseismic body wave traveltime tomography. Detailed P-wave and S-wave images of the crust and upper mantle were formed by approximately 5 years of data from dense arrays of seismometers. We found a thick high-velocity body beneath the southwestern KP with a thickness of ~150 km, which represents a fragment of lithospheric root beneath the Proterozoic Yeongnam Massif. Also, we found low velocities beneath the Gyeonggi Massif, eastern KP margin, and Gyeongsang continental arc-back-arc system with significant velocity contrasts (dlnVp of ~4.5% and dlnVs of ~7.0%) with the high-velocity structure. Joint analysis of P- and S-wave data suggests distinct contrasts in mantle Vp/Vs ratios between the lithospheric root and its margin, indicating modified continental margins. There was a clear correlation of the upper mantle low-velocity anomalies and areas characterized by Cenozoic basaltic eruptions, high heat flow, and high topography, which suggest possible links between mantle dynamics and recent tectonic reactivation.

The presence of a remnant cratonic root beneath the KP and contrasting lithospheric structures across the different Precambrian massifs suggests heterogeneous modification along the Sino-Korean craton margin. The structural heterogeneity of craton margin is likely sharp in scale and thickness within a confined area. Intense interaction of upper mantle dynamics and inherent structural heterogeneities of a craton margin played an important role in shaping the current marginal lithosphere structure and Cenozoic tectonic evolution of Proterozoic lithosphere in northeast Asia.