Uyeda

Uyeda and Kanamori (1979) divided mode of subduction into two types Mariana-type characterized steep subduction and Chilean-type characterized by gentle subduction estimated from the dip of Benioff-Wadati zones (Fig. 1.161). The geological phenomena associated with these subductions are shown in Fig. 1.162. It is inferred that the change in mode of subduction from Mariana-type to Chilean-type occurred at ca. 5 Ma in Northeast Honshu. Kuroko deposits are associated with Mariana-type, whereas epithermal vein-type deposits (particularly Au-Ag deposits) with Chilean-type. 

Uyeda, S. (1983) Hydrothermal circulation in the Mariana trough, Kuroko and the mode of subduction. Mining Geology Special Issue, 11, 37-53 (in Japanese with English abst.). 

Uyeda, S. and Nishiwaki, C. (1980) Stress field, metallogenesis, and mode of subduction. Geol. Soc. Canada, Special Paper, 20, 323-339. 

Yamano, M., Uyeda, S., Foucher, J.P. and Sibuet, J.C. (1981) Heat flow anomaly in the middle Okinawa Trough. Tectonophy.sic.s, 159, 307-318. 

Sugimura, A. and Uyeda, S. (1973) Island Arcs Japan and Its Environs. Amsterdam Elsevier. 

Ozawa, 1963 Sugimura and Uyeda, 1973). For example, Sugimura and Uyeda (1973) summarized volcanic rocks, degree of deformation of sediments, structural trends of sediments deposited, and amount of uplift and subsidence since Miocene. 

Sugi, N., Chinzei, K. and Uyeda, S. (1983) Vertical crustal movements of the northeast Japan since middle Miocene. Geodynamic Sen, 11, Amer. Geophys. Union/Geology. Soc. Am., 317-329. 

Figure 1.161. Dip of Benioff-Wadati zones (Uyeda and Kanamori, 1979).

Figure 1.162. Two kinds of subduction boundaries (Uyeda and Kanamori, 1979).

Otsuki, K. and Ehiro, M. (1978) Major strike slip faults and spreading of the Japan sea (Uyeda, S., Morphy, R.W. and Kobayashi, K., eds.). J. Phys, Earth Suppl. Issue, 26, 537-555. 

The origin of the back-arc basins has been investigated considerably (Karig, 1971 Sleep and Tok.soz, 1971 Uyeda and Kanamori, 1979 Tamaki and Honza, 1991 Uyeda, 1991 Tamaki, 1995) and various explanations for the origin have been proposed. 

In any model, back-arc basins form under the extensional stress regime and are associated by Mariana-type subduction by Uyeda and Kanamori (1979) rather than Chilean-type subduction. 

These different sites of hydrothermal and ore-forming activity may have resulted from the mode of subduction of the Pacific Plate. Mariana-type subduction (characterized by a steep angle of subduction and back-arc basin formation Uyeda and Kanamori, 1979) during middle Miocene caused WNW-ESE extension, submarine hydrothermal activity, thick accumulation of bimodal (basaltic and dacitic) volcanic activity (Green tuff) and Kuroko-type formation (Shikazono and Shimizu, 1993). Plio-Pleistocene Chilean-type subduction (shallow-dipping subduction zone, E-W compression Uyeda and Kanamori, 1979) and oblique subduction of the Pacific Plate beneath the North American Plate led to uplift and expansion of land area, subaerial hydrothermal activity accompanied by meteoric water circulation, subaerial andesitic volcanic activity and formation of vein-type deposits. 

During Miocene age most of this province was in a submarine environment. Violent submarine volcanism (bimodal and basic type) took place at Miocene age in this province. This geologic environment may be related to an extensional stress regime (Uyeda and Kanamori, 1979). The Kuroko deposits have been formed related to this tectonic situation. 

Several different hypotheses on the tectonic setting of the Kuroko mine area have been proposed. They include volcanic front of island arc (T. Sato, 1974 Horikoshi, 1975a), rifting of island arc (Cathles, 1983a), back-arc depression (Fujioka, 1983 Uyeda, 1983), and back-arc basin. 

Possibility (1) was proposed by Shikazono (1987b) who considered that the lower values of sulfide sulfur than base-metal vein-type deposits and Kuroko deposits can be explained by the leaching of sulfide sulfur from volcanic rocks with lower values (0%o to -t-5%o) (Uyeda and Sakai, 1984). 

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