ABSTRACT: An Intra-Arc Basin as a Potential Hydrocarbon Prospect--Recent Results of Ocean Drilling Project Leg 134 Drilling in the North Aoba Basin, Vanuatu
GREENE, H. GARY, U.S. Geological Survey, Menlo Park, CA, and Moss Landing Marine Labs, Moss Landing, CA, JEAN-YVES COLLOT, ORSTROM, Villefranche, France, LAURA B. STOKKING, ODP, College Station, TX, and SHIPBOARD SCIENTIFIC PARTY, Leg 134
The North Aoba basin (NAB) is one of two major, deep (~3-km water depth) intra-arc basins situated along the summit platform of the central New Hebrides Island Arc. The other basin is the South Aoba basin (SAB), which is separated from the NAB by an active transcurrent, arc-transverse fracture zone along which the active volcanic Island of Aoba has formed. Both basins are filled with more than 5 km of sediment and appear to have been one continuous basin before the formation of the Aoba Fracture Zone. Neogene tectonic activity, consisting of possible subduction polarity reversal and ridge-arc collision, is responsible for the formation of these unusual intra-arc basins.
The New Hebrides Island Arc was part of the Miocene and older continuous outer Melanesian Arc, composed of part of Papua New Guinea (PNG), the Solomon Islands, Fiji, and Tonga, as well as the New Hebrides. Because hydrocarbons have been detected in PNG and Tonga, reconnaissance surveys were undertaken to evaluate the hydrocarbon potential of the central New Hebrides Island Arc. Before Ocean Drilling Project (ODP) drilling in the Central Basins area (Vanuatu), small, yet potential traps consisting of anticlines and faults were mapped along the shallow margins of the intra-arc basins, and onshore source-rock analyses indicating a potential for gas generation were made. However, migration pathways, heat flow, and submarine source-rock potential are unknown.
Although the ODP is a scientific drilling program and drillsites are selected in areas where hydrocarbon concentrations are believed to be absent, many drilling data are useful in appraising regional hydrocarbon potential. Two sites (Sites 832 and 833), drilled deeper than 1 km, were sampled in the NAB. In the central part of the NAB (Site 832), an early(?) Miocene to Holocene section was drilled. Generally, high porosities and permeabilities indicate good migration pathways. Along the eastern margin of the NAB, a thicker Pliocene section was penetrated, consisting of basaltic lavas that intruded Pliocene sediment as sills. Measured heat flows here were high. Initial hydrocarbon analyses on the recovered cores from both sites in the NAB indicate less than 0.5 wt.% organic carbon.
AAPG Search and Discovery Article #91015©1992 AAPG International Conference, Sydney, N.S.W., Australia, August 2-5, 1992 (2009)