Report on DELP 1985 Cruises in the Japan Sea : Part 1 : General Outline

In the summer of 1985, as a part of the Japanese Development and Dynamics of Lithosphere Program (DELP), geophysical and geological research cruise (DELP-85 WAKASHIO cruise) was made in the Yamato Basin and the Japan Basin of the Japan Sea. These basins are believed to have been formed as a result of back-arc spreading during a short period of time (15-21Ma) and their crust show an intermediate character between continental and normal oceanic crusts. There were other cruises for similar program closely related to the present survey and run by several institutions, i.e. Geological Survey of Japan, Ocean Research Institute (Univ. Tokyo) as well as Japan Marine Science and Technology Center in the fiscal years 1985 and 1986. This report describes mainly the results of the research DELP-85 WAKASHIO cruise in the Yamato and Japan Basin. Some of the results still remain in a preliminary stage of analysis. Data and interpretations obtained by other cruises related to the resent program are also referred to in this report. The ship used for this cruise was the WAKASHIO-MARU chartered from the Nippon Salvage Co. Ltd. Scientists from six universities and the Geological Survey of Japan participated in the program. The scientific objectives, surveyed area, cruise periods, terms of observation, filing of data base, name of participants and areas covered by other cruises related to the present program are listed below. Some results obtained prior to the present survey are also included in the concluding discussion (8. Main Results) of this part.1985年度を中心とする日本海海底探査研究航海のうち,DELP研究グループが主催ないしは関連した部分について得られた固体地球科学的成果について述べる.日本海の中で大和海盆と日本海盆は主要部分を占める.これら海盆の成因・年代・構造については主として,Back-arc spreadingの機構で説明されるものと考えられてきた.今回の総合的研究によって日本海生成の古環境についてより評細な知見が得られ,日本海の拡大は複雑な過程を経て行われ,海といえどもかなりの部分に陸的性質の混在を許している事が分かってきた