ABSTRACT: Tectonics of the Parece Vela Basin (the Philippine Sea)
Alexander Ivanovich Khanchuk
Recently, different institutions of the Far Eastern Branch of the USSR Academy of Sciences carried out a great number of geoscience researches in the Parece Vela basin. The topography of the seafloor was defined significantly.
Principally, the sedimentary cover is lacking in the Parece Vela basin. A clear asymmetry in the seafloor structure was observed. The eastern part of the basin is a plain with low hills, the western part is dissected by northeast-trending en echelon troughs.
A submeridional rift was supposed in the axial part. The studies showed, however, a chain of isometric local basins 6300-7200 m deep with a deepening of about 2000 m relative to the basin floor (exceeding the thickness of the first and second layers of the crust) instead of deep linear basins. The distance between these diamond-shaped basins is 70 to 90 km.
In addition to ultramafics, gabbros, and basalts, common for the oceanic crust, younger gabbros and basalts with increased Ti and Fe contents were dredged in the local basins. Sediments comprise tectonic breccias.
The analysis of the basin morphostructure suggests that the Yap Fracture, about 1000 km long, is a right-lateral strike-slip fault, the movement along which took place after spreading (i.e., younger than 17 Ma) and probably along its axis. In local tension zones, caused by strike-slip movements, magmatic activity finished later, and tholeiitic magma was more intensely differentiated.
AAPG Search and Discovery Article #90097©1990 Fifth Circum-Pacific Energy and Mineral Resources Conference, Honolulu, Hawaii, July 29-August 3, 1990