Radiometric age data on rocks from Viti Levu, Fiji

Abstract

Results of age determinations made on rocks from Viti Levu are discussed in relation to ages determined paleontologically. Rocks of the Tholo Plutonic Suite appear to have been emplaced in at least two distinct episodes, one possibly ranging from 50 to 30 million years (m.y.), the other accompanying the folding of the Wainimala Group rocks at about 10 m.y. Evidence is given that the Tertiary ƒ stage (Indonesian scale) may have continued to less than 10 m.y. ago in the Fiji region. Two samples from the Tavua volcanic centre (Mba Basaltic Group) suggest that volcanic activity began there before 10 m.y.; products were mostly basaltic but trachyandesite was also produced. The last activity, ranging from eruption of basalt and trachybasalt to intrusion of trachyandesite and monzonite, took place 4 to 5 m.y. ago. A suggested relationship between the products of this volcano and rocks of the Koroimavua Andesitic Group dated at about 5 m.y. is illustrated. The large monzonite sill in the interior of Viti Levu was dated at 4.7 m.y.