A series of paleogeographic maps of the Japanese Islands, from their birth at ca 750–700 Ma to the present, is newly compiled from the viewpoint of plate tectonics. This series consists of 20 maps that cover all of the major events in the geotectonic evolution of Japan. These include the birth of Japan at the rifted continental margin of the Yangtze craton (ca 750‐700 Ma), the tectonic inversion of the continental margin from passive to active (ca 500 Ma), the Paleozoic accretionary growth incorporating fragments from seamounts and oceanic plateaux (ca 480‐250 Ma), the collision between Sino‐Korea and Yangtze (250–210 Ma), the Mesozoic to Cenozoic accretionary growth (210 Ma‐present) including the formation of the Cretaceous paired metamorphic belts (90 Ma), and the Miocene back‐arc opening of the Japan Sea that separated Japan as an island arc (25‐15 Ma).

Pelagic cherts of Japan and British Columbia, Canada, recorded a long-term and worldwide deep-sea anoxic (oxygen-depleted) event across the Permo-Triassic (or Paleozoic and Mesozoic) boundary (251 ± 2 million years ago). The symmetry in lithostratigraphy and redox condition of the boundary sections suggest that the superocean Panthalassa became totally stratified for nearly 20 million years across the boundary. The timing of onset, climax, and termination of the oceanic stratification correspond to global biotic events including the end-Guadalupian decline, the end-Permian extinction, and mid-Triassic recovery.

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Methanogenic microbes may be one of the most primitive organisms, although it is uncertain when methanogens first appeared on Earth. During the Archaean era (before 2.5 Gyr ago), methanogens may have been important in regulating climate, because they could have provided sufficient amounts of the greenhouse gas methane to mitigate a severely frozen condition that could have resulted from lower solar luminosity during these times. Nevertheless, no direct geological evidence has hitherto been available in support of the existence of methanogens in the Archaean period, although circumstantial evidence is available in the form of approximately 2.8-Gyr-old carbon-isotope-depleted kerogen. Here we report crushing extraction and carbon isotope analysis of methane-bearing fluid inclusions in approximately 3.5-Gyr-old hydrothermal precipitates from Pilbara craton, Australia. Our results indicate that the extracted fluids contain microbial methane with carbon isotopic compositions of less than -56 per thousand included within original precipitates. This provides the oldest evidence of methanogen (> 3.46 Gyr ago), pre-dating previous geochemical evidence by about 700 million years.

The Phanerozoic &cum-Pacific erogenic belts contain numerous ocean-derived materials accreted through plate converging processes. Japanese Islands, in particular, display various kinds of oceanic materials of different origins including fragments of seamounts, oceanic reef limestone, MORB-like rocks and oceanic mantle, and pelagic sediments. The compilation of these rocks in many subduction complexes of Late Permian to the present, led to following conclusions.Accretion processes work effectively only for materials primarily composing the upper portion of subducting oceanic crust, i.e. Layer 1 and Layer 2. Many fragments of seamount with alkali basalt (600), hot-spot seamount (26), oceanic reef limestone (291), MORB-like basalt (200), and numerous cherts (more than 1000) are recognized as ancient oceanic materials accreted to the Japanese Islands. However, gabbros and mantle materials of Layer 3 and lower parts of the oceanic lithosphere, scarcely occur in subduction-accretion complexes except for a few examples of back-arc basin or fore-arc origin. Accretion occurs episodically. In Southwest Japan, oceanic materials were accreted intermittently in (a) end-Permian, (b) Middle-Late Jurassic, (c) Late Cretaceous times, (d) at ea. 50 Ma, and (e) in Miocene times, while in Northeast Japan and Hokkaido this ocwrred in (b) Middle-Late Jurassic, (cf Late Cretaceous, and (f) Early Cretaceous times.In wntrast to the general belief on accretion of younger oceanic plates, the majority of Japanese subduction-accretion complexes were formed during the subduction of plates, up to 160 Ma old. The accretionary events in end-Permian and Middle-Late Jurassic times coincide with northward collision of ancient island arcs, oceanic rises or seamount chains (of hot-spot origin) with the Asian continent. Accretion relevant to subduction of older plates may be controlled by the collision-subduction process of these topographic reliefs on an oceanic plate. In addition, the chronological coincidence with the continent collision-amalgamation between the Sino-Korean and Siberian platforms and between the Sino-Korean and Yangtze blocks, also implies collision-induced voluminous supply of elastics from back-arc regions and its contribution to the formation of huge accretionary complexes.Accreted fragments of ancient seamounts are much smaller than the average size of modem seamounts. This impties that most parts of a colliding seamount are not accreted but subducted together with the underlying oceanic crust to much deeper levels.With respect to the metamorphic grades for Japanese subduction complexes, oceanic materials have less than 1 vol.% in the zeolite facies, 15-20% in the prehnite-pumpellyite metagraywacke facies, and ca. 30% in the greenschist/glaucophane schist facies and albite-epidote amphibolite facies. This relationship indicates that the major process for landward accretion of oceanic materials is not off-scraping or sedimentary mixing at the trench, but underplating (subcretion) at much deeper levels of a subduction zone.