Because of extreme environmental conditions, deep sea subsurface sediments were traditionally regarded as a huge ‘desert’ unable to support any kind of life-form. However, 30 years’ investigation by the successive DSDP and ODP deep drilling projects indicated that microbes are extensively distributed in the deeply buried sediments and some shallow oceanic crusts in the world oceans. The subseafloor deep biosphere has huge microbial biomass and great biological and molecular diversity, and carries out a series of complicated and diverse physio-ecological functions. Study of the deep subseafloor biosphere microorganisms became the foci of studies on life’s origin and evolution, earth system evolution and transformation, global climate change, biotechnological development and exploitation of marine life and subseafloor natural energy resources. This review discusses the significances of the subseafloor deep biosphere microbial study and summarizes the progresses newly made in this field, in order to promote the initiation and development of related researches in our country for the active engagement in global marine resource exploitation and in international cooperation in tackling profound scientific issues in the new millennium.
The Okinawa Trough (OT) is a new moon-like back-arc rifting basin, intense tectonic activity and drastic magmatism are main characteristics for it and adjacent areas.In this paper,according to major,trace elements, Sr-Nd isotopic and age data of volcanic rocks, volcanic properties and distribution as well as their link with geological background and evolution were discussed in order to understand the development of magmatism and tectonics on the OT and adjacent areas,deeply. The main conclusions are as follow:(1)Geochemic data show that volcanic rocks from the basin-arc system belong to cal-alkali rock groups, including basalts, basaltic andesites, and rhyolites. The magmatism is bimodal.(2)Rock compositions are different in different parts of the study area. Depth variation of magma source can be thought as a major factor to lead these differences. In middle and northern study area, volcanic rocks are mostly andesites and ryolites.The former mainly located in middle and northern trough,and was juvenile rocks(<1 Ma);The latter outcropped in the arc and formed during Miocene.Volcanic rocks in southern study area mostly contain basalts and basaltic andesites.From old to young,they located at Ryukyu arc (RA,6～18 Ma),Northern Taiwan Volcanic Zone(NTVZ,from 3 Ma-present),and central grabens(Quaternary).(3)Ryukyu volcanic arc (including the southern arc) have been formed since middle and late Miocene (8～6 Ma). The continental extension behind RA caused the Northern and middle OT opening about 6Ma ago, but the collision between Luson Arc and Eurasian plate changed geodynamical conditions in this region about 12Ma ago and led that southern OT opening was later than middle and northern OT. This kinetic change hasn’t effected on middle and northern OT, because Kerama Gap stopped the affect of the event. In addition, southern OT should belong to the back-arc basin, because southern RA has been formed about 13Ma ago.
Ferromanganese crusts are some of the most potentially valuable mineral resources under seawater,and are rich in metal elements,such as Mn、Fe、Cu、Co、Ni、Pt.Due to their abundance ,high potentially economic value,low exploitation venture,and low exploitation influence on the environment,they have become notable internationally.The most favorable environments for crusts to form are underwater seamounts far away from active tectonic zone formed by volcanoes and have subsided many times.Their formation and distribution are related to volcanic action,seamount structure,types of basement rocks,and their weathering degree,etc.Seamounts furnish favorable environments for ferromanganese crusts to form and develop;volcanic action and weathering of basement rocks furnish rich materials for ferromanganese crust formation and microbial action catalyzes and accelerates the process.The influene of seamount structure,volcanic action and basement rocks,etc.on the formation and distribution of ferromanganese crusts,material source and formation mechanism of ferromanganese crusts are still not known perfectly.We think that the above fertilize grounds for research.Resolutions of these problems are helpful for developing the theory of methallic enrichment and metallogenic environment of ferromanganese crusts.At the same time,the development of high precision microscope and the advance of dating technology with isotopes will promote the development of these studies.
