Bouguer anomaly map of Viti Levu, Fiji

Abstract

The Bouguer anomaly map of Viti Levu in the Fiji Group consists essentially of a gravity "low" surrounded by gravity "highs". The "low" can be explained partly by the effect of the younger rocks which have a specific gravity 0·4 g/cm' less than the older rocks (Lower Tertiary), and partly by a relative thickening of the crust by about 10 km. The average crustal thickness is about 30 km which supports the geological evidence that the Fiji islands are continental.

The geology of New Caledonia

“…The latter suggests that on the Lord Howe rise the crust is of the order of 20-25 km thick, but the calculation of 30 km for the crust in Fiji (Robertson, 1967) suggests a notable thickness also for New Caledonia although a figure of only 15 km is tentatively quoted by Coleman (1966) for the Solomon Islands. As yet no :figure is given for New Caledonia, but we may guess it is likely to be about 25-30 km.…”

A crustal model for Zealandia and Fiji

“…Geophysical surveys of Fiji and the surrounding region have led to varying interpretations of crustal thickness. Estimates based on gravity measurements are 30 km (Robertson 1967), 19–24 km (Solomon & Biehler 1969) and 18–20 km (Worthington 1973, as cited in Hamburger et al (1990). The long baseline refraction experiments of Shor et al (1971) gave a thickness of only 12–15 km beneath the Fiji Platform.…”

“…Woolnough 1903;Crook 1963;Rodda 1967). Geophysical determinations of thick crust, together with the geological evidence led Robertson (1967) and Chase (1971) to affirm that the crust of the Fiji Platform was continental. In contrast, Dickinson (1967) and Hamburger et al (1990) explicitly considered and rejected models of rifted continental crust, pointing out that many other arcs have similarly thick crust.…”