**Seismological Implication to the Tectonic Evolution of the Lützow-Holm Bay Region (East Antarctica) the Lützow-Holm Bay Region (East Antarctica)**

**Seismological Implication to the Tectonic Evolution of** 

DOI: 10.5772/intechopen.71972

Masaki Kanao and Vladimir D. Suvorov Masaki Kanao and Vladimir D. Suvorov Additional information is available at the end of the chapter

Additional information is available at the end of the chapter

http://dx.doi.org/10.5772/intechopen.71972

#### **Abstract**

Passive source studies using teleseismic events demonstrated heterogeneous structure in the Lützow-Holm Bay (LHB) region, East Antarctica. Depth variations of upper mantle discontinuities (410 and 660 km) were derived from long-period receiver functions by local array stations. Shallow depths in topography of upper mantle discontinuity were cleared beneath the continental ice sheet back azimuth. These results reflect a paleoupwelling of the mantle plume associated with Gondwana breakup. Lithospheric mantle anisotropy derived by shear waves' (SKS) splitting anticipated a relationship between "fossil" anisotropy and the past tectonics in NE-SW orientation. Origin of mantle anisotropy was assumed to be caused by supercontinent assembly rather than present asthenospheric flow parallel with absolute plate motion. The deep seismic surveys by active sources, moreover, were carried out over continental ice sheet and provided clear information on crust-mantle boundary, together with inner lithospheric mantle reflections. The extracted lithospheric cross-sectional images by seismic reflection analyses implied tectonic influence of compressive stress during Pan-African age.

**Keywords:** upper mantle structure, Lützow-Holm Bay region, East Antarctica, Gondwana supercontinent, tectonic evolution

## **1. Introduction**

East Antarctic continent consists of several geological terrains as resultant of amalgamation and breakup of Rodinia and Gondwana [1, 2]. In wide areas of Western Enderby Land-Eastern Dronning Maud Land, inside the East Antarctica, several geological complexes are adjacent to each other from East to West: the Napier (Archaean), the Rayner (late Proterozoic), the Lützow-Holm (early Paleozoic), and the Yamato-Belgica (early Paleozoic) (**Figure 1**) [3–5]. Combined with other Gondwana component continents such as Africa, India, and Australia,

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© 2016 The Author(s). Licensee InTech. This chapter is distributed under the terms of the Creative Commons

order to provide comprehensive understanding in formation of the upper mantle structure and dynamics beneath LHB, associated with evolving process of supercontinents in southern

Seismological Implication to the Tectonic Evolution of the Lützow-Holm Bay Region (East…

http://dx.doi.org/10.5772/intechopen.71972

3

Seismological investigations in LHB demonstrated sufficient images of the structure and dynamics in the upper mantle underneath the Antarctic continent. The investigations by using passive seismic sources such as teleseismic events occurring over the globe had demonstrated strong heterogeneity existing in the upper mantle depths. Depth variations of the upper mantle discontinuities (410 and 660 km depths, respectively) were derived from longperiod receiver function analysis (0.2 Hz low-pass filtered), which indicated shallow depths in the 660 km seismic discontinuity beneath continental back azimuths in LHB (**Figure 2**) [16]. The depth distributions of P-S conversion points were also revealed in particular for the 660 km discontinuity. The shallow depths in topography for the 660 km discontinuity were identified beneath the continental azimuths over the ice sheet. These results could provide an evidence of upwelling flow associated with mantle plume in terms of Gondwana breakup

hemisphere during the Earth history.

SYO

Lützow-Holm Bay

270 90

0

180

are circled by the light-green open squares.

P-S conversion points for 660 km discontinuity

continental ice sheet

**Figure 2.** Back azimuth distribution of the depth variation in the upper mantle seismic discontinuities by receiver function analyses of broadband seismic data in LHB (modified after [16]). (Left) Location of the strong heterogeneous azimuths in LHB. The area for strong depth variations in upper mantle discontinuities is represented by the light-green open squares, which are almost parallel with the coastal line. Symbolic notation for the P-S conversion points at the mantle discontinuities around 660 km in depth. (Right) Color images represent the smoothed amplitudes of the longperiod receiver functions. Two dashed lines are traced for the maximum amplitudes of both 410 km and 660 km depth discontinuities, respectively. Two back azimuth groups for strong depth variations in the upper mantle discontinuities

**2. Seismic investigations of the upper mantle**

**Figure 1.** Gondwana reconstruction at 480 Ma, centered on East Antarctica (modified after [5]) showing the geologic ages of major exposed coastal outcrops [2]. The areas corresponding "undifferentiated Precambrian" terrains belonging to each continental blocks of Gondwanaland (Australia, Africa, South America, and Antarctica) are distinguished by different colors (yellow dot, green dot, brown dot, and light-blue dot), respectively. Abbreviations are as follows: SYO, Syowa Station; LHB, Lützow-Holm Bay; SR, Shackleton range; SPCM, Southern Prince Charles Mountains; LT, Lambert Terrane; EG, Eastern Ghats; PB, Prydz Bay; DG, Denman Glacier; OH, Obruchev Hills; P. Or, Pinjarra Orogeny; TA. Cr, Terre Adélie Craton; G. Cr, Gawler Craton; MR, Miller Range; GSM, Gamburtsev Subglacial Mountains.

the crust and lithospheric mantle architecture with relevant tectonic history of East Antarctica provide evidence of amalgamation and separation of the past supercontinents [6, 7]. The Lützow-Holm Bay (LHB) region, where the Japanese Syowa Station (SYO, 69S, 39E) is located, has been experiencing regional metamorphic events in early Paleozoic [8]. The metamorphic grade increases from amphibolite facies in eastern LHB to granulite facies in the western. During the Pan-African metamorphism, LHB was deformed under compression stress perpendicular to the thermal axis [9].

Seismological evidence with respect to the structure and tectonics of the upper mantle beneath LHB has been derived in the last few decades by both the computer modeling and field observations by the Japanese Antarctic Research Expedition (JARE). Teleseismic data detected at seismic stations in LHB have sufficient signal-to-noise quality for various kinds of analyses so as to clarify local seismicity, heterogeneities of the lithospheric structure, as well as deep interiors of the Earth [10–13]. Several studies had aimed at deriving static structure, tectonics, and dynamics within the crust and mantle depths, associated with geological evolution of the region [14, 15]. In this chapter, by taking into account the tectonic evolution around the Lützow-Holm Bay (LHB) region, passive and active seismic source studies were reviewed in order to provide comprehensive understanding in formation of the upper mantle structure and dynamics beneath LHB, associated with evolving process of supercontinents in southern hemisphere during the Earth history.
