SEGMENTATION OF ISLAND ARCS AND APPLICATION TO PETROLEUM GEOLOGY†

Abstract

Island arcs are commonly depicted as smoothly curved or sinuous structures. This presentation almost certainly is incorrect. Most island arcs, perhaps all, are composed of more or less straight segments whose trend changes direction suddenly at specific hinge or boundary zones; these zones seem to consist of multiple transverse faults. Each straight segment itself is cut by transverse faults. The presence of the transverse structural systems is evident from geological and geophysical data.Examples of segmentation include island arcs in Indonesia, the Philippines, Solomons, New Hebrides, Kuril‐Kamchatka, Lesser Antilles, Central America, Mexico, Tonga, Alaska, Japan, Chile, Andaman‐Nicobar Islands, New Britain, Marianas, Greece, and the Himalayas. The fracture system may be related to structural, morphological, or movement aspects of an underthrusting slab, or it may be the result of movement in the backdeep or of the overthrusting sheet in general. Some of the transverse faults may be old ones that have been rejuvenated within the island‐arc area.Transverse structural systems seem to have had a pronounced effect on the petroleum accumulations of island‐arc regions, both from a stratigraphic and structural viewpoint; they therefore affect petroleum‐exploration procedures. Such systems are also likely to be found in ancient basins that went through an island‐arc stage. Knowledge of the segmentation of island arcs should aid future exploration.