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ABSTRACT: Tectonic Fabric of Northern North Fiji and Lau Basins from GLORIA Sidescan

D. L. Tiffin, J. E. H. Clarke, P. Jarvis, D. Johnson, P. Hill, Q. Huggett, L. Pearson, R. Price

GLORIA mosaics, Seabeam, and seismic data over parts of the backarc New Hebrides arc, northwest and central North Fiji basin, Fiji Fracture Zone north of Fiji, Peggy Ridge, northeast Lau basin, northern Tonga arc, northwestern Tonga Trench, and Western Samoa reveal a complex tectonic framework for the region. Two triple junctions and several rifts are clearly delineated by outcrops and ridges of neo-volcanic rocks. Backarc troughs in the New Hebrides Arc are commonly floored by volcanic rocks with little sediment cover. The locus of major faults are well defined in places by volcanic ridges and scarps. On the Fiji Fracture Zone north of Fiji, scarps indicate the trace, but west of Fiji it disappears for about 100 km, becoming well pronounced again near the central North F ji basin triple junction. At Peggy Ridge a very extensive area of sheet-like volcanics indicates activity extends northeast from Peggy Ridge toward the western extension of the Tonga Trench passing west of Niuafo'ou Island, possibly marking a fault-to-trench transition. East of Niuafo'ou Island, backarc spreading close to the Tofua Arc is seen at a nascent triple junction, its northern arm approaching close to the western Tonga Trench. Long linear fault scarps in the trench result from bending of the crust. Only a few areas, including the seafloor north of Samoa, are mainly sediment covered.

Two known hydrothermal deposits near the two triple junctions have been imaged, but other mapped areas of extensive neo-volcanics in the vicinity of propagators and pull-apart basins suggest sites for further investigation. The prevalence of ridge propagators and extensional basins suggests their significant role in the development of the region.

AAPG Search and Discovery Article #90097©1990 Fifth Circum-Pacific Energy and Mineral Resources Conference, Honolulu, Hawaii, July 29-August 3, 1990