PALEOMAGNETISM OF THE TAMANA, CHAUDIERE, AND POINT-A-PIERRE FORMATIONS, CENTRAL RANGE FAULT ZONE, TRINIDAD

Trinidad, an island off the northeast coast of Venezuela, is located on the Caribbean-South American plate boundary. Previous studies using GPS data show the Caribbean plate moving eastward at 20 mm/yr with respect to a fixed South American plate. The Central Range fault zone in central Trinidad is accommodating 12 ± 3 mm/yr of this movement. The folding and faulting in the Central Range can be accounted for by Miocene collision and/or modern transpression. Paleomagnetic data were collected to constrain the amount of block rotation in the Central Range since the Miocene. An understanding of the total amount of strain may give insight into how much deformation is due to neotectonic activity vs. Miocene contraction.

Paleomagnetic samples were collected from the Tamana, Chaudiere, and Point-a-Pierre Formations across the Central Range fault zone. Due to poor outcrop most sites were collected in quarries where continuous stratigraphic sections were clearly visible. Five to ten cores were collected at each site and were analyzed using the alternating field demagnetization process. In most samples demagnetization revealed a weak, single component magnetization. Paleomagnetic results in the Tamana formation show 23+/-17 degrees of counterclockwise vertical axis rotation in the Central Range, a value tentatively supported by preliminary data from the Point-a-Pierre Formation. This degree of rotation is based on a sample subset that passes a tilt test, however the tilt test is not very robust because all sample sites were located on the same limb of a fold. A conglomerate test in the Chaudiere formation, which is stratigraphicly below the Tamana and Pointe-a-Pierre formations also supports that the rocks have not been magnetically altered since deposition. The counterclockwise rotation noted by there data are interesting because modern kinematics in the Central Range are dextral, which implies clockwise block rotation. Counterclockwise rotation recorded in the Tamana formation suggesting that the block rotation in the Central Range fault zone occurred in the Miocene. This interpretation requires the modern dextral transpression regime to be a very young system that has not accumulated enough strain to overprint any pre-existing counterclockwise rotations.