Mineral chemistry of spinel peridotite xenoliths from Baengnyeong Island, South Korea, and its implications for the paleogeotherm of the uppermost mantle

Abstract   The mantle-derived xenoliths entrained in the Pliocene basanite from Baengnyeong Island, South Korea, are spinel lherzolites and spinel harzburgites. The overall compositional range of the Baengnyeong xenoliths matches that of the post-Archean xenoliths of lithospheric mantle origin from eastern China, but without any compositional evidence for a refractory Archean mantle root. Mineral compositions of the xenoliths have been used to estimate the equilibrium temperatures and pressures, and to construct a paleogeothermal gradient of the source region. The xenolith-derived paleogeotherm is constrained from about 820°C at 7.3 kbar to 1000°C at 20.6 kbar. Like those from the post-Archean Chinese xenoliths of lithospheric mantle origin, the Baengnyeong geotherm is considerably elevated relative to the conductive models at the depth of the crust–mantle boundary, reflecting a thermal perturbation probably related to lithospheric thinning. There is no significant P / T difference between harzburgite and lherzolite, which suggests that the harzburgites are interlayered with lherzolites within the depth interval beneath Baengnyeong Island.     

Crust and upper mantle structure of the Ailao Shan-Red River fault zone and adjacent regions

Using arrival data of the body waves recorded by seismic stations, we reconstructed the velocity structure of the crust and upper mantle beneath the southeastern edge of the Tibetan Plateau and the northwestern continental margin of the South China Sea through a travel time tomography technique. The result revealed the apparent tectonic variation along the Ailao Shan-Red River fault zone and its adjacent regions. High velocities are observed in the upper and middle crust beneath the Ailao Shan-Red River fault zone and they reflect the character of the fast uplifting and cooling of the metamorphic belt after the ductile shearing of the fault zone, while low velocities in the lower crust and near the Moho imply a relatively active crust-mantle boundary beneath the fault zone. On the west of the fault zone, the large-scale low velocities in the uppermost mantle beneath western Yunnan prove the influence of the mantle heat flow on volcano, hot spring and magma activities, however, the upper mantle on the eas     

Passive Seismic Experiment Mosaic - A Pilot Study of Mantle Lithosphere Anisotropy of the Bohemian Massif

We present results of an array study of seismic anisotropy beneath the Bohemian Massif (BM) showing distinct lateral and directional variations of the fast shear-wave polarization and split-delay time consistent with variations in the P-residual spheres, in which directional means of relative residuals are subtracted. Our analysis of the S- and P-wave anisotropy suggests that the mantle lithosphere of the BM consists of at least three large domains with different orientation of the large-scale fabric separated by sutures cutting most likely the whole lithosphere. Boundaries of the units are characterised by a null or small shear-wave splitting, as well as by smaller values in the P-residual spheres. We present self-consistent 3D anisotropic models of the lithosphere domains of the BM resulting from joint inversion of anisotropic parameters searching for a 3D orientation of mantle fabric. While in the Saxothuringian and Sudetes parts of the BM the (a, c) foliations dip prevailingly to the N-NW, they dip to the S and SW in the southern and eastern parts of the Moldanubian.