【正文】 ing quantitative, . economic importance, will be discussed first. The midplate continental margin is the setting of shelf deposits, whereas the cratonic and rift valley settings refer to the interior of consolidated areas. 3 Coalfields Situated Near Convergent Plate Edges The relationships between tectonic setting and coal content of a region inferred from Tables and suggest that coal can form more frequently in geological environments capable of offering a larger number and variety of crustal movements per unit time than less mobile areas. As mentioned above, this is a reature of foredeeps, which have been prolific coal producers in the pat. Mountain chains consisting of folded and often metamorphosed rocks are formed as linear and often arcuate welts along the edges of convergingplates by a number of tectonic and magmatic events, all of which appear to be primarily related to the process of subduction. However, not all former subduction zones have led to the formation of coalfields, which is a problem related to the nature of the converging plates, . whether they consist of oceanic or continental crust. According to Figs. and , there are three scenarios: 1. Subduction of oceanic crust beneatn oceanic crust (Fig. ). It is unlikely that this situation will lead to significant coalfield formation because of the considerable water cover of the sea floor. Oceanic crust emerges above water only where it has been thickened by magmatic injection and may then produce isolated small coal occurrences. However, as long as only oceanic crust is involved, the lack of a strong nearby sediment source leaves the adjacent ocean basin starved and too deep for peat accumulation. Conversely, posite arc systems, in which several subduction zones are operating simultaneously in opposite directions and/or in which allochthonous crustal fragments (terranes) have been accreted to the arc system, may provide suitable conditions for coal formation. An example are the Japanese islands, which contain coalfields of Tertiary age in both fore and backarc positions (Aihara 1986). Forearc basins elsewhere are not known to be significant coal producers due to the tectonic instability during the basin stage and the subsequent destruction by tectonism. The occurrence of a 3000mthick Palaeogene succession of folded and faulted coal measures in the Hidaka Basin of central Hokkaido, described by Aihara (1986), is therefore a paratively rare case of a thick coal measure sequence formed and preserved in a forearc setting. 2. Subduction of oceanic crust underneath continental crust (). There are several past and present examples of extensive coal formation associated with this type of plate convergence. The main coalfields formed in the process occupy retroarc basins (Dickinson 1974) filled with thick sedimentary successions. The beginning of sedimentation is probably related to extensional tectonics in the backarc area, at a time when subduction is still in process. However, during and following the accretion of allochthonous terranes the retroarc basin is subjected to a pressional stress regime which causes it to subside under the weight of overriding thrust wedges. 3. Partial subduction of continental crust beneath continental crust (). This type represents an example of continental collision. Because of its thickness and low density, continental crust can only partially be subducted which leads to tectonic stacking and overlap of the two plate margins. The conditions of coal formations in a retroarc basin are the same as in (2) for the overriding plate. In addition, at least two loci of potential peat accumulation are contributed by the consumed plate, one (usually destroyed by subsequent orogenesis and metamorphism) in the form of the continental shelf margin which was formed before collision occurred, and the other in the form of a peripheral basin (Dickinson 1974) formed at the foot of the collision belt. Retroarc and peripheral basins share the same basic foredeep architecture (Beaumont 1981), because both are the products of flexural downwarping of the underlying crust following loading by overriding thruet sheets. AC. Three possibilities of plate convergence. Continental crust。 Laubscher 1978。CoalProducing Tectonic Environments This final chapter in the investigation of coal sedimentation is concerned with depositional aspects of the highest order of magnitude, namely, the influence of the crustal setting on peat accumulation. This is a broad and plex field which draws on information, gathered from many different disciplines of the earth sciences. Some of these are currently evolving quite rapidly, while others re in a “mopping up” stage, insensu Kuhn (1970) and Walker (1973), following recent scientific revolutions. An example of the latter is the replacement of the geosynclinal hypothesis in the early 1970s by the concept of plate tectonics. Even after a life span of 20 years, this new paradigm is still in the process of being refined and fitted out with conceptual subsets, as shown by the current emphasis on terrane analysis. It is therefore not possible at this stage to make a definitive statement on the chosen subject, but merely to outline the principle on which a modern geotectonic classification of coalfields can be established. Even this modest goal is fraught with difficulty, because the change from the predominantly static geosynclinal view of global tectonics to its modern, largely mobilistic interpretation has plicated the tectonic classification of some coalfields. While the tectonic status of many coalfields, . those in foredeeps or foreland basins has changed relatively little, the setting of coals found in inter and intramontane troughs, . within orogenic