A. Beardsley, H. G. Avé Lallemant, and the BOLIVAR Study Group
Rice University, Houston, TX
As part of the BOLIVAR project, we performed structural analysis of the brittle deformation features on the Netherlands Leeward Antilles island arc. The arc is located offshore Venezuela and from west to east includes Aruba, Curaçao, and Bonaire (ABCs). The ABCs trend approximately WNW-ESE parallel to the obliquely convergent Caribbean and South American plate boundary zone. The goal of the research project is to characterize deformation structures in relation to plate motions to improve understanding of regional tectonic history.
Structural analysis of faults, joints, veins, and bedding planes has identified several deformation events on the ABCs. The oldest (D1) structures are megascopic folds that trend WNW-ESE. Some of these folds display a weak axial plane cleavage. Thrust faults trend NW and are thought to be related to the D1 event. These structures are crosscut by NE-SW trending joints, veins, and normal faults (D2). Dextral strike-slip faults (D3) trend WNW-ESE to NE-SW. Normal faults trending WNW may be the youngest structures (D4). Newly acquired MCS lines are interpreted; megascopic structures in these lines are compared to the mesoscopic structural data on the islands.
We attribute all of these features to two deformation mechanisms: 1) oblique plate convergence accompanied by displacement partitioning and 2) escape tectonics of the Maracaibo block. The D1 - D4 structures result from displacement partitioning and can be separated into three components. The arc-normal component of the plate convergence vector is accommodated with margin parallel folds and thrusts. Joints and veins correspond to the arc-parallel stretching component. The parallel component is characterized by dextral strike-slip faults. The tectonic escape of the Maracaibo block is associated with the clockwise rotation of the ABCs from EW to WNW. These are preliminary results and future study includes zircon and apatite fission-track dating and fluid inclusion analysis to determine the relationship between uplift of the ABCs and plate boundary dynamics.