800-KM-LONG N-S SPREADING SYSTEM OF THE NORTH FIJI BASIN

The 800-km-long N-S spreading system in the North Fiji Basin consists of six contiguous fan-shaped rift segments each 100-200 km long with various structural styles, such as structural overprinting, triple junction, rift-propagation, voluminous magmatism, and transform or strike-slip fault influence. Deformation of the plate boundary system within the young, hot, weak lithosphere occurred under local stress conditions resulting in a unique rift segmentation distinct from that of mid-oceanic ridges. Spreading across a series of short and variably oriented segments produces series of fanning spreading centers whose rotation pole is located at the end of each segment. The surrounding seafloor basement has adjusted to this setting with non-rigid deformation or with fragmentation. Furthermore. the changing tectonic framework caused by the arc rotation probably makes it difficult to keep the same stress condition for a long period. Small-scale fan-shaped sea-floor spreading is short-lived and results in a rapidly evolving plate boundary geometry. This suggests a more complicated tectonic style for marginal basins than mid-ocean ridge spreading centers.