Multidisciplinary Surveys for the Crustal Structure of the Lützow-Holm Complex, Enderby Land, East Antarctica: SEAL-2000, -2002

Lithospheric evolution of the East Antarctic shield is one of the keystones for understanding continental growth process during the Earth's evolution. Architecture of the East Antarctic craton and the surrounding areas would be characterized by a comparison with lithospheric structure of the other Precambrian terrains by deep seismic surveys. A geoscience program named "Structure and Evolution of the East Antarctic Lithosphere (SEAL)" is carrying out since 1997 austral summer as part of the Japanese Antarctic Research Expedition (JARE). Several geological and geophysical surveys were conducted including a deep seismic refraction / wide-angle reflection and gravimetric surveys in the Lützow-Holm Complex (LHC), Western Enderby Land, East Antarctica. The LHC had been experienced a high-grade metamorphism during the Pan-African orogenic event, where is considered to be the collision zones in the last stage of the formation of Gondwana. In the austral summer in 2000, and 2002, two big seismic surveys were carried out on the continental ice sheet of the Mizuho Plateau in the LHC by SEAL program. In both surveys, more than 170 geophones were installed on the plateau totally 190 km in length. A total of 8,300 kg dynamite charges at the fourteen seismic shot points on the ice sheet gave enough information concerning the deep structure of a continental margin of the LHC. The gravity measurements were conducted by a SCINTREX (CG-3M) gravity meter at about 1 km-interval along the seismic survey lines. These surveys had revealed that the Moho depth was more than 40 km with the velocities of the surface layer, the middle crust, the lower crust and the mantle, about 6.2, 6.4, 6.7 and 7.9 km/s. Moreover, the clear reflected waves from the lower crust and the Moho were observed on all the record sections. In this presentation, we review the subsurface structure of the LHC by several geophysical approaches, such as the seismic first arrival and wide-angle analyses, gravity measurements, GPS positioning and also the radio-echo soundings to detect the precise bedrock elevation around the seismic traverse routes. Then the multidisciplinary crustal model of the LHC will be presented including geological evidence to estimate the evolution process around the coastal outcrops.