Magnetic and Tectonic Fabric of the North Fiji Basin and Lau Basin
Detailed airborne and shipboard magnetic studies conducted over the eastern marginal basins of the southwest Pacific between New Zealand and the Solomon Islands suggest that seafloor spreading in the North Fiji Basin, which began in the latest Miocene, continues today. The North Fiji Basin is marked by at least two triple junctions, located in the central (16°50’S, 173°45’E) and northeastern (14°S, 179°30’E) parts of the basin. Both were apparently formed during the past five million years in response to continuing adjustments in the strike of the active spreading centers in the North Fiji Basin. Two additional contemporary spreading centers appear to have formed within the last one million years to the north and immediately to the west of Viti Levu. Although magnetic anomalies from 1 to 3 (0–5 Ma) are seen to form a clearly defined lineation pattern over the North Fiji Basin, earthquake foci suggest that only portions of the present North Fiji/Lau Basin spreading center system are currently active.
Analysis of the magnetic anomalies suggests that spreading began in the North Fiji Basin about 8 Ma (shortly before anomaly 4). At about 6 Ma (shortly before anomaly 3), the New Hebrides/Fiji island arc began to fragment through the development of an active spreading center (calculated half-spreading rate of 3.5 cm/yr) located between the New Hebrides and Fiji portions of the island arc. Subsequently, portions of the northeastern sector of the South Fiji Basin Plain were subducted beneath the North Fiji Basin. Between 4.5 Ma and 3.5 Ma (anomalies 3 and 2’), spreading in the North Fiji Basin extended into the Lau Basin and Havre Trough, thus separating the Tonga and Lau ridges. As a result, a distinct series of active spreading centers developed southward along the axis of the Havre Trough/Lau Basin.
The continuum of spreading centers from the North Fiji Basin into the Lau Basin and Havre Trough has been accomplished through the formation of triple junctions located in the North Fiji and northern Lau basins and propagating southward rifts in the southern Lau Basin.
KeywordsConvection Petroleum Cretaceous Miocene Subduction
Unable to display preview. Download preview PDF.
- Chase, C.G., 1971, Tectonic history of the Fiji Plateau: Geological Society of America Bulletin, v. 82, p. 2087–2110.Google Scholar
- Cherkis, N.Z., 1980, Aeromagnetic investigations and seafloor spreading history in the Lau Basin and Northern Fiji Plateau, in Proceedings, Petroleum Potential in Island Arcs, Small Ocean Basins, Submerged Margins and Related Areas Symposium, UN ESCAP, CCOP/SOPAC Technical Bulletin 3, p. 37.Google Scholar
- Cherkis, N.Z., A. Malahoff, and J.M. Brozena, 1978, Magnetic lineations over the Fiji Plateau, EOS, Transactions, American Geophysical Union, 59, p. 266 (abstract).Google Scholar
- Cherkis, N.Z., Malahoff, A., and Brozena, J.M., 1980, An aeromagnetic investigation of the Lau Basin and the North Fiji Plateau, Abstracts w/ Program 12, Geological Society America, Northeastearn section, 15th Annual Meeting (abstract).Google Scholar
- Hamburger, M.W., and B.L. Isacks, Shallow seismicity in the North Fiji Basin: this volume.Google Scholar
- Kroenke, L.W., J.V. Eade, C.Y. Yan, and R. Smith, Sediment dis- tribution in the north central North Fiji Basin: this volume.Google Scholar
- Sinton, J.M., R.C. Price, K.M. Johnson, H. Staudigel, and A. Zindler, Petrology and geochemistry of submarine lavas from the Lau and North Fiji back-arc basins: this volume.Google Scholar
- Watanabe, T., M.G. Langseth, and R.N. Anderson, 1977, Heat flow in back-arc basins of the western Pacific, in M. Talwani, and W.C. Pitman (eds.), Island Arcs, Deep Sea Trenches, and Back-arc Basins; Maurice Ewing Series, v. 1, p. 137–161, American Geophysical Union.Google Scholar
- Watts, A.B., J.K. Weissel, and F.J. Davey, 1977a, Tectonic evolution of the south Fiji marginal basin, in M. Talwani, and W.C. Pitman (eds.), Island Arcs, Deep Sea Trenches, and Back-arc Basins; Maurice Ewing Series, v. 1, p. 419–427, American Geophysical Union.Google Scholar
- Weissel, J.K., 1977, Evolution of the Lau Basin by the growth of small plates, in M. Talwani, and W.C. Pitman (eds.), Island Arcs, Deep Sea Trenches, and Back-arc Basins; Maurice Ewing Series, v. 1, p. 429–436, American Geophysical Union.Google Scholar