17:15 〜 19:15
[SMP26-P01] Tectonic evolution of the Pan-African mobile belt estimated from deep seismic explorations in the Lützow-Holm Complex, East Antarctica
キーワード：Tectonic evolution、Pan-African mobile belt、seismic explorations、Lützow-Holm Complex、East Antarctica
Active seismic surveys for elucidating structure of crust and lithospheric mantle were conducted on the continental ice sheet in the Lützow-Holm Complex (LHC) by SEAL (Structure and Evolution of the Antarctic Lithosphere) project in 2000 - 2002. Detailed velocity structures were derived through refraction and wide-angle reflection methods using large-energy explosive sources (Miyamachi et al., 2003; Yoshii et al., 2004). The architecture of seismic reflective layers around the Moho discontinuity was clearly imaged in terms of conversion tectonics when forming the LHC (Tsutsui et al., 2001; Yamashita et al., 2006). The obtained lithospheric structures were integrated with surface geology and geophysical dataset to evaluate anisotropic patterns that contain rock deformation and flow mechanism associate with past plate motion. This integration also revealed deep-seated tectonic heterogeneities within lithosphere of the LHC relating to formation and breakup of the Gondwanaland (Ishikawa and Kanao, 2002; Kanao et al., 2011). Furthermore, density models were obtained based on gravity measurements along the survey lines (Toda et al., 2013, 2014). During the metamorphic event in early-Paleozoic age as a part of Pan-African orogens, the LHC was deformed under compressional stress perpendicular to the thermal axis (almost parallel to the coast).
In coastal area in LHC, shallow reflection surveys were also conducted in the outcrop of East Ongul Island in 2007 and 2010, to reveal geological structure and upper crustal boundaries. These surveys contributed to understanding the layered structure of the gneiss that makes the surface layer of LHC, as well as to estimating the position of faults and fracture zones near the Ongul Strait (Kanao et al., 2014). However, these surveys did not achieve detailed imaging of geological structures because of coarse interval between observation points and low number of stackings (repetition of signals) which resulted in low seismic source energy. In this regard, it is planned in future by dense stations using portable high-energy active sources (PASS; Tsuji et al., 2021).
In this presentation, the seismic structure of the crust and lithospheric mantle derived from active and passive sources are demonstrated involving tectonic evolution of the LHC. The Dronning Maud Land, located to the west of LHC, was once connected to the Kaapvaal Craton (Nkosi et al., 2022) during the Gondwana era. Investigating and comparing the crustal structures and evolutionary processes around these cratons is crucial for studying the formation and breakup processes of the supercontinent that once spanned the southern hemisphere in Earth's history (Brown et al., 2001). Based on the findings from previous geological surveys and large-scale deep seismics, we may discuss in detail the evolutionary processes of the upper crust of LHC in relation to the formation of supercontinent.
In coastal area in LHC, shallow reflection surveys were also conducted in the outcrop of East Ongul Island in 2007 and 2010, to reveal geological structure and upper crustal boundaries. These surveys contributed to understanding the layered structure of the gneiss that makes the surface layer of LHC, as well as to estimating the position of faults and fracture zones near the Ongul Strait (Kanao et al., 2014). However, these surveys did not achieve detailed imaging of geological structures because of coarse interval between observation points and low number of stackings (repetition of signals) which resulted in low seismic source energy. In this regard, it is planned in future by dense stations using portable high-energy active sources (PASS; Tsuji et al., 2021).
In this presentation, the seismic structure of the crust and lithospheric mantle derived from active and passive sources are demonstrated involving tectonic evolution of the LHC. The Dronning Maud Land, located to the west of LHC, was once connected to the Kaapvaal Craton (Nkosi et al., 2022) during the Gondwana era. Investigating and comparing the crustal structures and evolutionary processes around these cratons is crucial for studying the formation and breakup processes of the supercontinent that once spanned the southern hemisphere in Earth's history (Brown et al., 2001). Based on the findings from previous geological surveys and large-scale deep seismics, we may discuss in detail the evolutionary processes of the upper crust of LHC in relation to the formation of supercontinent.