Kinematics of active spreading in the central North Fiji Basin (Southwest Pacific)

Abstract

Based on a synthesis of magnetic and bathymetric data, we re-evaluate the kinematics of the recent opening of the central part of the North Fiji Basin (NFB). The westward motion of the Pacific plate along the left-lateral North Fiji Fracture Zone (NFFZ) results in the opening of two N-S trending spreading ridges, located at 173°30′E and 176°E. Both ridges show complex features such as propagating rifts, ridge jumps and overlapping spreading centres. Their spreading rates are similar: 7.6 to 4 cm yr −1 across the western ridge, 5.5 cm yr −1 across the eastern one. While the NFFZ is purely strike-slip to the east of the eastern ridge, it becomes more complex to the west: it changes from transpressional to transtensional, then to purely transform and finally joins the western N-S ridge in a RRR-type triple junction. Our kinematic analysis shows that most of the left-lateral motion along the NFFZ is transferred to the eastern ridge at the RTF-type 176°E triple junction. It suggests that the western N-S ridge is probably connected to the north with another left-lateral transform, possibly the South Pandora “ridge”.