Shear-wave splitting beneath southern Korea and its tectonic implication

Relation between mantle shear zone deformation and metasomatism in spinel peridotite xenoliths of Jeju Island (South Korea): Evidence from olivine CPO and trace elements

“…Therefore, the studied xenoliths do not show extreme seismic anisotropies, probably as a result of their weak olivine CPO. Delay times of 1.05 and 1.15 s were reported for shear-wave splitting at Jeju Island by Kang and Shin (2009) (Fig. 1(a)).…”

“…Dashed yellow lines depict the major tectonic boundaries of the Korean Peninsula (after Chough et al, 2000). Results of SKS-wave splitting measurements are compiled after Fouch and Fischer (1996), Fischer et al (1998), Long and van der Hilst (2006), Salah et al (2008), Wirth and Long (2008), Chang et al (2009), Kang andShin (2009), Salah et al (2009), where solid bars indicate the fast polarization direction and red circles are scaled to denote the delay time. Satellite image downloaded from GoogleEarth.…”

“…The bulk fast direction of the mantle rocks is mainly affected by the preferred orientation of olivine, giving rise to bulk anisotropy (Savage, 1999). Kang and Shin (2009) investigated seismic anisotropy beneath the southern Korean Peninsula based on the SKS waves of deepfocused earthquakes ( Fig. 1(a)).…”

“…Variations of the splitting directions suggest that a single asthenospheric flow event since at least the late Cenozoic cannot solely explain the seismic anisotropy beneath the region. It is more plausible that the shallow lithospheric mantle beneath the southern Korean Peninsula retains some Paleozoic fossil anisotropy, which was not completely relaxed by subsequent orogenic events during the late Paleozoic and Mesozoic (Kang and Shin, 2009). From the late Mesozoic to the Cenozoic, the lower part of the lithospheric mantle of the eastern margin of the Eurasian continent is thought to have been widely deformed as a result of either thermal erosion Table 4 Calculated J-index (after Bunge, 1982) and seismic properties of the selected peridotites of the Jeju Island.…”

“…(Chen et al, 2003) or delamination (Gao et al, 2004). Therefore, if the mantle anisotropy in the region represents a pre-Mesozoic fossil anisotropy, its source is not asthenospheric flow, but rather the shallow lithospheric mantle relatively unaffected by later deformation (Kang and Shin, 2009). Based on the CPO data and modal compositions, seismic anisotropy values for the studied peridotite xenoliths were calculated using the softwares of Mainprice (2005d,a).…”