SHALLOW LEVEL EXHUMATION HISTORY OF THE LEEWARD ANTILLES, OFFSHORE VENEZUELA: EVIDENCE FROM FLUID INCLUSION ANALYSIS

The Leeward Antilles have been exhumed and rotated along the diffuse South American-Caribbean plate boundary since the Late Cretaceous. The Leeward Antilles include from west to east - Aruba, Curaçao, Bonaire, La Blanquilla and Los Testigos, all located offshore Venezuela. Fluid inclusions in quartz-calcite veins in volcanics and in quartz in plutonic rocks were analyzed to determine the regional exhumation history. The vein orientations vary from northeast to north to northwest, and are associated with 3 phases of diachronous deformation and clockwise rotation. Overall, the inclusions indicate a minimum of three pressure-temperature trapping conditions during exhumation of the islands. Aruba and Bonaire had a maximum burial depth of approximately 6 kilometers while Curaçao remained at relatively shallow depths near the surface. Each of the three P-T environments can be correlated with different vein orientations.

A range of fluid inclusion melting temperatures suggests several fluid origins. For example, some fluids trapped in the Aruba quartz veins are meteoric water. Bonaire quartz vein inclusions contain low salinity fluids, likely seawater. Plutonic fluid inclusion samples from La Blanquilla, Los Testigos, and Aruba are also low salinity. The plutonic textures indicate they are shallow intrusives that trapped seawater and magmatic fluids with mixing during cooling.

Overall, microthermometry suggests at least three phases of exhumation since the Late Cretaceous, ~90 Ma, which coincides with regional deformation at the obliquely convergent South American-Caribbean plate boundary. Apatite fission track dating indicates Maastrichtian uplift of La Blanquilla at approximately 67 +/- 7.5 Ma. The age date supports diachronous deformation from west to east along the Leeward Antilles island chain. Along the WNW-ESE trending island chain, Aruba and Bonaire were relatively deep while Curaçao, La Blanquilla, and Los Testigos remained shallow. Consequently, fluid inclusion analysis indicates a complex evolution in terms of relative exhumation along the margin.