HR: 1340h
AN: T33B-1367    [Abstracts]
TI: Aruba and Curacao: Remnants of a Collided Pacific Oceanic Plateau? Initial Geologic Results from the BOLIVAR Project
AU: * Wright, J E
EM: jwright@gly.uga.edu
AF: Department of Geology, University of Georgia, Athens, Ga 30602
AB: The oldest rocks exposed on Aruba are amygdaloidal pillow basalts and lesser basaltic sandstone. The pillow lavas are geochemically similar to MORB and OIT. Locally, there is a distinctive unit of pebbly mudstone, argillite and basaltic tuff interstratified with the pillow lavas. Turonian(?) ammonites have been recovered from argillites. Both the pillow lava unit and argillaceous sediments were then intruded by a diabase complex. The intrusive rocks are geochemically indistinguishable from the pillow lavas. White and others (1999) interpret the lavas and diabase as having been formed in an ocean plateau. Following emplacement of the diabase unit, Aruba became emergent. There is abundant evidence for weathering and erosion of the pillow lavas and diabase unit. Basaltic magmatism continued as witnessed by the accumulation of accretionary lapilli tuff. Accretionary lapilli only form in a subaerial environment. The accretionary lapilli tuff was shortly thereafter reworked by local stream(s) which produced a coarse conglomerate composed entirely of clasts of basalt, diabase and lesser amounts of accretionary lapilli. The acreetionary lapilli and conglomerate units are almost always found together and are interpreted to have been deposited in a paleo-valley. Following this, the entire sequence underwent low grade regional metamorphism accompanied by folding and cleavage formation. Available data constrain this event to be post Turonian (93.5 $\pm$ 4 Ma) but pre emplacement of the Aruba batholith at 89 $\pm$ 1 Ma (SHRIMP-RG U-Pb zircon date). Thus, Aruba went from being emergent to undergoing regional metamorphism and batholith emplacement in a very short time period. We suggest that the pre-batholithic rocks were partially subducted prior to batholith emplacement. The metamorphic complex and batholith were exhumed and exposed by at least the Eocene/Miocene as they are overlain by shallow marine limestone of that age. On Curacao, the Curacao lava formation is geochemically similar to and broadly correlative with pre-batholithic basalts and diabase on Aruba (e.g. White and others, 1999). Following accumulation of the Curacao lava formation the area became emergent as there is widespread evidence for weathering and erosion of the basalts (Beets, 1972). Thus, both Curacao and Aruba became emergent in the Late Cretaceous. However, the subsequent geologic history of Curacao is distinct from Aruba, as it was not affected by Turonian/Coniacian deformation and metamorphism, but instead subsided and developed as a sedimentary basin, leading to the accumulation of extensive deposits of Late Cretaceous (Santonian-Maastrichtian) to Early Paloecene age. Late Cretaceous turbidites on Curacao contain a significant population of euhedral zircons in the range of 70-87 Ma (older Cretaceous grains in the range of 103-125 Ma are also present) along with angular hornblende and plagioclase mineral fragments. These arc derived grains are accompanied by older Mesozoic, Paleozoic and Precambrian zircon and undated coarse detrital muscovite, all presumably derived from the South American continental margin. Deformation (folding) on Curacao occurred between the Danian and middle Eocene (Beets, 1972) presumably during accretion to the Venezuelan continental margin. These data complicate models which interpret Aruba and Curacao to represent remnants of a Pacific oceanic plateau whose collision with a west-facing island arc produced subduction polarity reversal in the Late Cretaceous. Alternatively, we suggest that Aruba and Curacao formed on the subducting plate of an already east-facing arc system. Preliminary work on the island of Bonaire suggests a similar overall tectonic setting.
DE: 8102 Continental contractional orogenic belts
DE: 8105 Continental margins and sedimentary basins
DE: 8110 Continental tectonics--general (0905)
DE: 8158 Plate motions--present and recent (3040)
SC: Tectonophysics [T]
MN: 2004 AGU Fall Meeting