Introduction to the special issue on tectonic environment and seabed resources of the southern Okinawa Trough

Abstract

Okinawa Trough (OT) is a back-arc basin behind the Ryukyu arc-trench system and located along the eastern margin of the Eurasian continent. It extends from the southwest Kyushu Island to the Ilan Plain of Taiwan (Fig. 1). The width and water depth vary from about 230 km and 200 m in its north to 60 - 100 km and 2300 m in its south (Sibuet et al. 1998). Based on geophysical and geological studies, the Okinawa Trough is considered to be in the rifting stage (Lee et al. 1980; Letouzey and Kimura 1986; Sibuet et al. 1987, 1998; Uyeda 1987; Kimura et al. 1988). Such a tectonic setting is characterized by active normal faulting in its upper crust and numerous intrusions of magma. Hence, the OT is expected to have a favorable environment for the development of a hydrothermal system. Recently, diverse microbial communities and other hydrothermal minerals have been discovered in the middle and northern Okinawa Trough (Uyeda 1987; Kimura et al. 1988; Halbach et al. 1989; Sakai et al. 1990; Glasby and Notsu 2003; Lüders and Niedermann 2010; Ishibashi et al. 2014; Toki et al. 2016; Minami and Ohara 2017). The southern OT is close to Taiwan and topographically has the lowermost trough throughout the Okinawa Trough (Fig. 1), suggesting a pronounced back-arc basin. However, restricted by the limited sampling and sequencing studies, our understanding of its marine environment and hydrothermal potential is poor. Supported by Central Geological Survey (CGS), Ministry of Economic Affairs (MOEA) of Taiwan, a 4-year program entitled “Geological Investigation of Mineral Resource Potential in the Offshore Area of Northeastern Taiwan” was launched in 2016. Significant contributions have been made in understanding the origin, distribution, and characteristics of hydrothermal deposits in the southern Okinawa Trough. Integration of geological, geophysical, geochemical and seafloor observation studies of the background environment is very helpful for understanding the hydrothermal mineral deposits in the southern OT.