Active Margins, Part 3—Java Trench, Profiles P-7 and N-508
P. Lehner, H. Doust, G. Bakker, P. Allenbach, J. Gueneau, 1983. "Active Margins, Part 3—Java Trench, Profiles P-7 and N-508", Seismic Expression of Structural Styles: A Picture and Work Atlas. Volume 1–The Layered Earth, Volume 2–Tectonics Of Extensional Provinces, & Volume 3–Tectonics Of Compressional Provinces, A. W. Bally
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Along the southern rim of the Sunda arc, between India and Australia, the oceanic basement of the Indian Ocean plunges below the continental masses of southeast Asia. The associated Benioff zone of earthquake epicenters dips away from the Java trench to a depth of about 500 km (310 mi) below the Java Sea. To illustrate the structure of this subduction zone, two profiles across the Java trench were selected. These profiles are "classical" in the sense that they represented, in 1972, the first seismic confirmation of the subduction model postulated by plate theory.
The oceanic basement of the Indian Ocean, which descends into the Java trench, is of Late Jurassic to Early Cretaceous age. JOIDES corehole 271 in the Wharton basin, some 150 km (93 mi) to the south of the trench, encountered about 500 m (1,640 ft) of deep-sea clay with radiolarian and nannoplankton oozes, ranging in age from Early Cretaceous to Quaternary, and resting on oceanic basement.
Reflection seismic across the Java trench shows the downward plunge of the oceanic basement below a highly imbricated accretionary wedge of sediments, which forms its landward slope. The uppermost portion of the oceanic basement, which probably consists of bedded pillow basalts, is structurally deformed and partly imbricated. The accretionary prism forms a ridge parallel to the trench. The internal structure of the ridge is difficult to resolve from seismic, but sporadic reflections indicate its imbricated nature. The thrusts appear to become steeper away from the trench as would be expected for mechanical reasons. There is evidence on the migrated seismic profile that individual imbrications bend over toward the trench in their uppermost portion in adjustment to the slope topography. This process probably triggers submarine slides and turbidity flows.The sediment fill of the fore-arc basins of Java ranges in age from late Oligocene/early Miocene to Recent. Onshore western Java, folded paralic sediments of Eocene age with limestones and coals are unconformably overlain by Oligocene volcanics. Offshore wells in the fore-arc basin encountered Oligocene volcaniclastics below the base Miocene unconformity. The presence of reefs on the unconformity surface indicates that the fore-arc basin subsided to its present depth after an Oligocene orogenic pulse.