ABSTRACT: Transtensional Structures Along a Transform Fault

Philip A. Jarvis, John Hughes-Clark, Loren Kroenke, Donald Tiffin

Recently acquired side-scan imagery and single-channel seismic profiles along the Fiji transform fault reveal the structures produced by its sinistral motion. The fault extends from Peggy Ridge in the northern Lau basin into the central North Fiji basin, at least as far as the Viwa spreading ridge near Viti Levu, Fiji. A change in character of the fault along its length is evident in the imagery. Adjacent to the Fiji platform, the fault is clearly defined. Deformation and seismicity are confined to a narrow linear band which is offset by two left-stepping relay zones. Farther to the west in the north Fiji basin, however, the fault is not well defined. A series of ridges and basins occurs in a complicated region between 174°E and 177°E. These are produced by inte action of the fault with the nearby spreading centers. Interpretations differ as to the fault and spreading center geometry in this area.

The arrangement of the tectonic elements has controlled the formation of the observed structures. The intersection of the fault with the Viwa spreading ridge has features typical of ridge-transform insections. Within the complicated area between 174°E and 177°E, the ridges and basins are postulated to be a consequence of the fault's shearing motion.

AAPG Search and Discovery Article #91003©1990 AAPG Annual Convention, San Francisco, California, June 3-6, 1990