**Author details**

stress during Pan-African and the conversion stage between East and West Gondwana terrains at the age. In these concerns, it was proposed that the mantle anisotropy had been originated by lithologic orientation of the mantle minerals during amalgamation process of Gondwana rather than the current asthenospheric flow which parallel to the absolute plate motion.

The lattice-preferred orientation (LPO) induced mechanical anisotropy developed along the direction of preexisting lithospheric structure during continental rifting [33]. The origin of anisotropy beneath Western Dronning Maud Land was pointed out as the ancient lithospheric structure modified by rifting processes during breakup [34]. Since the spreading direction off the Enderby Land was NW-SE initial stage of breakup [35], a strike of the rift was generally parallel to the continental margin of LHB. The fast polarization directions of the upper layer ("lithosphere") in the SKS analysis were roughly parallel to the continental margin. In this regard, it was plausible that the breakup process affected the formation of anisotropy in the lithosphere. The preexisting lithospheric structure might also influence the formation of

Passive seismic source investigations using teleseismic data revealed heterogeneous structure in LHB. Depth variations of the upper mantle discontinuities (both for 410 and 660 km) were derived by long-period receiver functions by using local array network at the area. Shallow depths in topography of upper mantle discontinuity were identified at the continental back azimuth beneath the ice sheet. The evidence reflected the effect by paleo-upwelling flow associating the mantle plume with regard to the Gondwana breakup. Lithospheric mantle anisotropy derived by the SKS splitting was supposed to be formed by "fossil" anisotropy caused by the past tectonics in NE-SW orientation. The origin of the mantle anisotropy was assumed by the LPO involving the process of supercontinent assembly rather than present asthenospheric flow which parallel with the absolute plate motion on the Earth's surface. In addition, several results from deep seismic surveys by using active seismic sources which were carried out on the continental ice sheet provided clear information on crust-mantle boundary, in addition to the inner lithospheric mantle seismic reflections. After processing of deep seismic reflections, the extracted lithospheric cross section implied tectonic influence of compressive

The authors would like to express their appreciation to the involved JARE members for their great efforts to conduct seismic deployments around the LHB. The authors would also like to express sincere thanks to the geosciences staffs of NIPR, led by Prof. K. Shiraishi, the Director General, for their useful discussion. They would like to express their thankfulness to the reviewers, for their critical checks and useful comments. The authors would like to appreciate editors of this book series on "tectonics" as well as the editorial office of InTech Publisher.

anisotropy in the succeeding breakup process.

8 Tectonics - Problems of Regional Settings

**4. Summary**

stress during Pan-African age.

**Acknowledgements**

Masaki Kanao1 \* and Vladimir D. Suvorov<sup>2</sup>

\*Address all correspondence to: kanao@nipr.ac.jp

1 National Institute of Polar Research, Research (NIPR), Organization of Information and Systems (ROIS), Tokyo, Japan

2 Trofimuk Institute of Petroleum Geology and Geophysics of Siberian Branch, Russian Academy of Sciences, Novosibirsk, Russia
