Lithoepheric Structure And Tectonics Derived From Active And Passive Seismic Studies In The Early-Paleozoic Lutzow-Holm Complex, Eastern Dronning Maud Land, East Antarctica

Lithospheric structure beneath the Lutzow-Holm Complex (LHC), Eastern Dronning Maud Land, East Antarctica, were studied using both the active and passive seismic sources. LHC is considered to be one of the collision zones between East- and West- Gondwana during the formation of a paleo-supercontintnt in Pan-African orogeny. Seismic velocities and reflection structure beneath LHC were obtained by deep explorations on continental ice sheet of Mizuho Plateau in LHC, in 1999-2000 and 2001-2002 austral summers by Japanese Antarctic Expedition. Travel-time analyses for wide-angle reflection and refraction data revealed the Moho depths ranging in 38-42 km from the coast to 200 km inland, with the averaged velocities of upper, middle, lower crust and uppermost mantle, as 6.1, 6.4, 6.5 and 8.0 km/s, respectively. Velocities in the topmost crust have a variation in 5.9-6.2 km/s along the NE-SW direction profile (parallel with coast), which corresponds to metamorphic grade of surface geology from amphibolite to granulite facies. These crustal velocities have almost coincident with those derived from the receiver functions analyses by applying non-linear Genetic Algorithm (GA) waveform inversion for the Broadband-Array data of outcrops along the coast in LHC. Second, reflection section derived from the total 12 explosions revealed several reflections around crust-mantle boundary; which can be traced at 13-14 s of TWT. These Moho reflections consist from several horizontally lying segments partially duplicated architecture in NE-SW profile: on the contrary, fairly flat and smooth signature in NW-SE (perpendicular to the coast). Inner crustal reflectors, moreover, are found around lower crustal depths at 9-10 s of TWT. Layered structure around the Moho can also be supported by spectral ratio analyses for PmP phases against refracted P phases in the near-field records. The above heterogeneous structure from lower crust to crust-mantle boundary may be originated from the ancient tectonic setting, such as Pan-African metamorphism associated with the continent-continent collision between East- and West Gondwana, followed by the breakup of LHC with India and Sri Lanka in mid Mesozoic. In presentation, we also introduce the characteristic waves originated from natural sources recorded on the exploration, such as of deep teleseismic and regional events around Antarctic together with local icequakes. For instance, frequency contents of 2.0 Hz in the waveforms show discordances around the stations at where just above the valley topographic interface between ice sheet and topmost crust.