Stratigraphic and Radiometric Evidence for the Oligocene Emergence of the Southern Lesser Antilles Volcanic Arc Between the Grenada and Tobago Basins

Author(s): Jacob Miller (presenter), Paul Mann, The University of Houston

Using a single, 645-km long, deep-penetration seismic and OBS-refraction line, Aitken et al. (2011) proposed that the southern segment of the Lesser Antilles volcanic arc migrated 220 km to the east to its present location in the southern Lesser Antilles from its late Cretaceous location along the Aves Ridge. We use a grid of 9,320-km 2D industry seismic data, satellite gravity data, and a compilation of radiometric ages to better define the Oligocene emergence of the southern Lesser Antilles volcanic arc (LAVA) into a broad, forearc basin setting. The study area spans a 400-km-wide transect across the Lesser Antilles subduction system that includes from east to west: Tobago forearc basin (TFB), LAVA; Grenada back-arc basin (GBAB); and Aves remnant arc (ARA). To test the Aitken et al. hypothesis, we: 1) improved seismic stratigraphic correlations of the three major sequences filling the 12-km-thick TFB and 14-km-thick GBAB that flank the LAVA; 2) mapped tilted late Eocene and older sedimentary units adjacent to both sides of the LAVA that are onlapped by Oligocene to recent sections that include mass transport complexes. These stratigraphic results for Oligocene emplacement of the southern Lesser Antilles arc are consistent with: 1) radiometric age dates on the oldest volcanic units in the southern Lesser Antilles (37-25 Ma); and 2) emplacement of Middle Eocene forearc-related, oceanic crust along with the intruding volcanic arc (Speed and Walker 1993). Stratigraphic control of the GBAB and TB were improved by direct ties to Venezuelan offshore wells and include: Sequence 1: chaotic to semi-continuous and wedge-shaped reflectors of Middle Eocene to Late Eocene age that were deposited prior to arc emergence; Sequence 2: continuous reflectors of Oligocene to middle Miocene age that onlap sequence 1 in the GBAB and TB and post-date arc emergence; and Sequence 3: Late Miocene to Recent chaotic to semi-continuous reflectors in the Grenada basin and semi-continuous in the Tobago basin that reflect the presence of the Lesser Antilles arc separating the two basins.