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ABSTRACT: Provenance Analysis of Navosa and Nadi Sedimentary Groups: Viti Levu, Fiji

Dale A. Kramer

Two late Miocene marine basins of southwest Viti Levu island, Fiji, were filled with volcaniclastic sediments resulting from interaction between the Indo-Australian and Pacific plates. Subduction, transcurrent, and divergent plate margins were proximal to these basins.

The laterally adjacent Nadi basin and the Navosa (Sovi) trough were filled during the complex evolution of the Melanesian Borderlands. Sedimentation in the Sovi trough was controlled by a dextral, transcurrent fault that is now partially concealed by Pliocene volcanics. The northeast-trending Sovi fault that bounds the trough represents this former plate margin.

Determining provenance (through petrography) of these voluminous, largely mass-flow deposits is constrained by basin morphology and diagenetic overprinting. Major diagenetic features include albitization and zeolitization of plagioclase and K-feldspar, dissolution of rock fragments, replacement of plagioclase by calcite and quartz, and growth of clay minerals. These diagenetic features occur in both basins indicating similar burial histories.

Q-F-L plots of normalized point counts of Sovi trough sandstones average Q:27, F:19, L:54; and in the Nadi basin, Q:15, F:39, L:46. This corresponds to a transitional arc tectonic setting. The source of sediment for these transitional arc basins was extra-basinal andesitic volcanics and intra-basinal basaltic volcanics.

AAPG Search and Discovery Article #90097©1990 Fifth Circum-Pacific Energy and Mineral Resources Conference, Honolulu, Hawaii, July 29-August 3, 1990