Studies in East Asia Tectonics and Resources (SEATAR) 



An international group of scientists are performing a large- 

 scale, comprehensive investigation of the interplay between the 

 regional tectonics and the occurrences of metals and hydro- 

 carbons in East Asia. Projects are listed in table 13. This proj- 

 ect, based on recommendations of a workshop held in Bangkok 

 in 1973, made significant progress in 1977. Major operations, 

 both marine and land, were conducted along the Sunda Arc 

 and Banda Arc and the Philippine Sea. In addition, work on a 

 geophysical atlas of the area has been completed and accepted 

 for publication as part of the Geological Society of America 

 map series. A bathymetric map was published in 1977. The 

 final product, scheduled to be issued later this year, will include 

 gravity, magnetic anomaly, total sediment isopach (based on 

 seismic reflection velocities), crustal structure (seismic refraction 

 velocity distribution), tectonics, and heat flow. A seismotectonic 

 map covering a more limited area (115° E to 130° E and 

 5° S to 20° N) has been partially completed. A report on the 

 Banda Sea area is in press, and the area of the Moluccas 

 and Philippines is near completion. Two more segments are 

 scheduled: Taiwan-Ryukyu Trench and the Mariana-Philippine 

 Sea. The heat flow cited above was based on existing data. 

 Additional surveys have been made on the island of Sumatra 

 by V. Vacquier (SIO) and in Thailand, Malaysia, and the 

 Philippines by S. Uyeda (Tokyo U). A geothermal gradient map 

 was published in 1977 by the Southeast Asia Petroleum Explo- 

 ration (SEAPEX) Society using data from oil exploration wells. 

 The result of all these efforts will be the most comprehensive 

 survey of temperature data for an active island arc system. 



Curray and Shor (SIO) and Karig (Cornell) completed four 

 legs of a cruise in the area of the Andaman Sea, Java Sea, and 

 Banda Sea. The Scripps multichannel seismic system operated 

 successfully on its first field experience. In this region of thick 

 sediments, the multichannel data provided diagnostic evidence 

 of the interplay between basement tectonics, sea level, and sedi- 

 ment supply. In the Sunda Arc, where the India plate is sub- 

 ducting the China plate, reflection data are obtained from the 

 deep structure of the descending slab and deep structure and 



sediments in the fore-arc basin. In cooperation with Indonesian 

 scientists, seismic refraction data from two ships were obtained 

 from oceanic crust and mantle. Karig and associates made 

 detailed investigations of the fore-arc sections on the islands 

 offshore of Sumatra. The Scripps group obtained additional 

 geophysical data and geological samples in the Banda Sea to 

 refine the interpretation based on the 1976 cruise. The several 

 participants in this cruise will work together on the analysis of 

 this broad spectrum of data. British, German, and Japanese 

 geologists working on land in Sumatra and field geologists from 

 the oil companies working in Southeast Asia are generously 

 cooperating in a broad effort to unravel the problems of plate 

 tectonics in this area. 



On another leg of the Scripps cruise, Eli Silver (UCSD) and 

 R. Raitt (SIO) collected data on seismic reflection and gravity, 

 and extensive bottom samples from the Molucca Sea, which lies 

 north of the Banda Arc and south of Mindanao. Preliminary 

 results indicate that this is a zone of arc-arc collision. Seismic 

 reflection data trace the parallel thrusts and, in combination 

 with bottom samples, confirm the melange nature of the sedi- 

 mentary section. 



The RV Valdivia (Federal Republic of Germany) carried 

 out a broad-scale program of geophysical measurements (includ- 

 ing multichannel seismic data) and geological sampling, extend- 

 ing from the Malacca Strait to the Philippines and including the 

 northwest continental margin of Australia, Strait of Makassar, 

 Island of Celebes, Sulu Sea, and Philippine Sea. Lamont com- 

 pleted a geophysical survey of the West Philippine Basin and 

 Luzon margin using 24-channel common depth point (CDP) 

 seismic reflection techniques and complementary geophysical 

 measurements. These large-scale data gathering efforts were 

 made jointly in support of the SEATAR and IPOD site surveys. 



In 1978, IDOE will support a major program to study the 

 tectonics and evolutionary history of the marginal basins and 

 the island-arc-trench systems along the Mariana-Philippine 

 Transect. The areas of focus are the Mariana Trough and 

 arc-Trench plus selected portions of the Parece Vela and west 

 Philippine Basins. Both shipboard field work and land-based 

 programs in selected portions of the Marianas are scheduled. 



Okm- 



Generalized E-W crustal section across Mariana Island Arc subduction zone at latitude 18°N, including locations of drilling sites 

 from DSDP Leg 60. Bathymetry drawn by W. Coulbourn based on data from Hawaii Institute of Geophysics (HIG) 1976 cruise. 

 Crustal structure generalized by D. Hussong from HIG seismic refraction, reflection, and gravity data collected in 1976 and 

 1977. 



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