RV SONNE. Cruise report SO138 - GINCO-2: Geoscientific investigations on the active convergence zone between the east Eurasian and Australian plates along Indonesia, Jakarta - Jakarta, 29.12.1998 - 28.01.1990. FS SONNE. Fahrtbericht SO138

The main goal of RV SONNE cruise SO138 - GINCO II (Geoscientific investigations on the active convergence zone between the east Eurasian and Australian plates along Indonesia) from 29th December 1998 to 28th January 1999 was to investigate the large scale structure of the offshore parts of the continental margins of Sumatera and Java and within Sunda Strait. Along 9 profiles with a total length of 1860 km, ocean bottom hydrophones (OBH) and seismometers (OBS) were deployed at 111 positions. All of them except one were safely recovered. Single channel seismic data were also recorded along the seismic profiles. All seismic data were preprocessed and displayed onboard for quality assurance, archiving and preliminary interpretation. Continuous recordings of gravity and hydroacoustic soundings were made throughout the entire cruise. Magnetic measurements using a state-of-the-art gradient magnetometer were carried out along 2700 km of trackline. Together with the data from the previous cruise SO137, a good coverage of bathymetric, magnetic and gravity data is obtained along the Sunda trench, which is especially dense in the three working areas of cruise SO138. Off Sumatera, an area landward of the trench has been fully covered. A detailed bathymetric map was produced for Sunda Strait. A first analysis of the data was accomplished onboard. Although the results are preliminary, some key observations can already be made. Off Sumatera, a pronounced thickening of the oceanic crust immediately seaward of the trench is found. From the data collected during the cruise it cannot be deduced if this crustal thickening extends furthe or is only a local anomaly. The accretionary complex, which is up to 12 km thick, is characterized by high seismic velocities. The Mentawai fault separates the accreationary complex from a deep forearc basin, which contains up to 5 km of young infill and is underlain by continental crust, with the Moho found at 24 km depth. The accretionary front shows a chaotic topography with many small ridges and numerous slides. Further landward, larger bathymetric units are visible such as elongated ridges and basins. There is also a pronounced retreat of the accretionary wedge of about 10 km, for which no obvious explanation is known. (orig.)Summary in GermanSIGLEAvailable from TIB Hannover: RR 1846(81) / FIZ - Fachinformationszzentrum Karlsruhe / TIB - Technische InformationsbibliothekDEGerman