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 v arious structural styles, such as structural overprinting, triple junc tion, 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 condition s resulting in a unique rift segmentation distinct from that of mid-oc eanic 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 b asement has adjusted to this setting with non-rigid deformation or wit h fragmentation. Furthermore. the changing tectonic framework caused b y the arc rotation probably makes it difficult to keep the same stress condition for a long period. Small-scale fan-shaped sea-floor spreadi ng is short-lived and results in a rapidly evolving plate boundary geo metry. This suggests a more complicated tectonic style for marginal ba sins than mid-ocean ridge spreading centers.