STRUCTURAL MECHANISMS LIKELY RESPONSIBLE FOR SOUTH-WESTERN JAVA'S GEOMORPHOLOGY

Closely spaced east-west lineaments in the Southern Mountains of Western Java are of unknown origin. Profile analyses of north-south streams cutting across the lineaments reveals a series of laterally continuous knickpoints with offsets up to 100 m. Because most of the lithology the streams are cutting is homogeneous, these knickpoints most likely relate to tectonic deformation. Beneath the lineaments, thrust fault plane solutions show a south-dipping low-angle nodal plane at a depth of 30-50 km, which is interpreted as part of a landward (north) dipping thrust system moving the proximal forearc over the southern edge of the volcanic arc. This deformation is possibly associated with strong coupling of the subduction zone interface from underthrusting and duplexing of the Christmas Island seamount chain. An elevation profile parallel to the forearc basin under which these seamounts pass, shows shallow depths. The most likely mechanism responsible for the lineaments is strong coupling between the lower and upper plate causing neutral surface extension or uplifted marine terraces or both.