Morphotectonics of the Lau Basin Seafloor-Implications for the Opening History of Backarc Basins

Abstract

A new bathymetric chart has been compiled from conventional wide-beam echo-sounder profiles and recently acquired swath bathymetric data for the Lau Basin between 18°30' to 21°S and 175°30' and 178°W. Long-range sidescan sonar data has been interpreted for the same area, and together the two data sets provide powerful imagery revealing the morphological and textural setting for the Ocean Drilling Program Sites 834 through 839. Our interpretation of these data suggests that the Lau Basin may be subdivided into two principal morphotectonic domains on the basis of significantly different topography and structure. The recognition of a fundamental contrast in the crustal character between the earliest formed basin and the most recently formed (1 Ma) seafloor has far-reaching implications for understanding the early geological evolution of all marginal basins, particularly those in backarc settings.Major bathymetric compilations of the Lau Basin have been made by a number of workers, including Hawkins (1974) and Chase (1985); modifications to these base maps have been incorporated into other published reviews of the morphology and geology of the region, the most notable among them being Kroenke (1984). The principal source of data used in the preparation of these charts has been single-track, echo-sounder profiles acquired by survey vessels. The seafloor topography between these lines of primary data has then been interpolated using the subjective skill and judgment of the compiler. Most recently, cruises by French, German, and American survey vessels fitted with multibeam bathymetric swath mapping (SeaBeam) systems have accelerated the capacity to produce more detailed and accurate bathymetric charts, and these latter data are in various stages of publication. The SEAPSO program (Foucher and Shipboard Party, 1986) covered the southern portion of the backarc axis on and near the Valu Fa Ridge, between 20° and 23°S. These data were followed by published results from the Sonne 35 and 48 cruises (von Stackleberg, 1990), who in addition surveyed some of the central Lau Basin. Scripps Institution of Oceanography PAPATUA expedition Leg 04 (Hawkins, 1988) and Leg 05 (Craig and Pareda, 1987) surveyed extensively throughout the area, and ROUNDABOUT expeditions Legs 14 and 15 (Hawkins, 1989) provided additional coverage between 15° and 19°S. Almost all of these data have been acquired since the last major bathymetric revision, and we present here the first major compilation of bathymetry to include all of these new data.As well as including all of the data recorded using swath multibeam bathymetric techniques, we have included the most recent soundings acquired by conventional echo-sounding methods. These include data accessed by means of the National Geophysical Data Center (NGDC), Boulder, CO. The chart presented as Figure 1 (back-pocket foldout) forms a small subset of a regional compilation of the bathymetry of the Lau Basin made at a scale 1:375000, which is in the final stages of preparation (Parson et al., unpu...

A three‐plate kinematic model for Lau Basin opening

“…We compiled HMR1 side scan sonar imagery from MW9603 with MMAJ9507 Hydrosweep amplitude data and published GLORIA imagery from two cruises (HMAS Cook cruise CK8915 [ Hughes Clarke et al , 1993; Parson and Tiffin , 1993; Hill and Tiffin , 1993] and RRS Charles Darwin cruise CD3388 [ Parson et al , 1990, 1992]). The digital acoustic imagery varies in quality as a function of the sonar frequency, resolution, and dynamic range of the three systems.…”

Tectonics and Sedimentation in the Lau Basin (Southwest Pacific)

“…The west face of the arc shoal depicted in Figure 6B drops down to the floor of an approximately north-south rift valley deepening to more than 2775 mbsl, illustrated in Figure 6C. This area of the western Lau Basin was insonified by GLORIA long-range sidescan sonar survey in 1988 (Parson et al, 1989). These data reveal brightly backscattering seafloor occurring in a broad band, flanked by linear targets that are thought to represent fault scarps.…”

“…Because no downhole logging was undertaken at Site 837, no dipmeter data are available. The only constraint on the sedimentary bedding orientation comes from shipboard multishot data of unknown reliability, which suggest a broad spread of dip directions scattered over the northeastern and southeastern quadrants (Parson, Hawkins, Allan, et al, 1992).…”

“…The sedimentary succession at Site 839 is 214 m thick (with a further thin sediment interbed between lava flows at -260 mbsf); as at Site 838, the lower volcaniclastic interval is extremely thick (180-200 m), with the upper clay nannofossil ooze unit very much thinner. Sedimentation rates were extremely high: Parson, Hawkins, Allan, et al (1992) estimate an average rate of -880 mm/k.y. below approximately 60 mbsf.…”

Volcaniclastic gravity flow sedimentation on a frontal arc platform: The Miocene of Tonga

“…1) have been studied previously using seismic reflection profiling, dredge sampling, and by the Ocean Drilling Program (Scholl & Vallier 1985;Parson et al 1991;Hawkins et al 1994;Stevenson et al 1994;Clift et al 1998). An overview of the geology and structure of the Tonga Ridge and its tectonic evolution is in Tappin (1993).…”