Literature REFERENCES for Fiji GEOLOGY are scant, indicating that UPLIFT BEGAN in the LATE EOCENE, with VULCANISM in the Oligocene; this agrees with my calculations- which find near 30 m.y. for several NEARBY ROTATIONS. I'll use a TIDAL MOVEMENT RATE of 30 mm/yr TEMPORARILY, until finding a more accurate value from CASE HISTORIES. The Tonga TRENCH has been estimated as moving 30 cm/yr.
This TRENCH is currently being investigated by geologists, and can be expected to follow the PLATE DOGMA. Google earth will divulge the MECHANISM, and we just have to follow the CLUES!