FAULT SLIP AND PALEOMAGNETIC ANALYSIS OF THE TECTONICS OF TOBAGO, WEST INDIES

We present in-progress results from a multi-disciplinary study of the tectonic history of Tobago, West Indies. Tobago is an accreted arc-forearc terrane in the currently dextral transform Caribbean-South American plate boundary zone. Fault slip inversions using data collected from 23 sites with rock ages ranging from Cretaceous (Albian) to Quaternary indicate four principal phases of deformation. In current (unrotated) coordinates they are (from youngest to oldest): 1) Quaternary-Pliocene N-S extension, 2) NNW-SSE compression associated with strike-slip and reverse faults, 3) pervasive NE-SW extension that was tilted by phase 2 faults, and 4) a NE-SW compression associated with tilting and rocks containing a metamorphic foliation. Published paleomagnetic results from the Cretaceous Tobago Volcanic Group rocks indicate a 90° bulk clockwise rotation of Tobago. We are beginning work to determine a step-wise (incremental) rotation history using NRM analyses on a suite of rock samples from the Tobago metamorphics, Tobago Intrusive Group (gabbro-diorites and dikes; dike paleo-declination = 360-354°), Pliocene Rockly Bay Formation (magnetic moment = 1.038 x 10^-4 to 8.283 x 10^-5 emu; results from oriented samples forthcoming), and Quaternary carbonate cap rocks (results forthcoming). We present our preliminary paleomagnetic results. We are building and will use a more robust suite of paleomagnetic results to rotate fault-slip paleostress axes into palinspastic orientations to better interpret the tectonic history and evolution of Trinidad and Tobago.