A PRELIMINARY PALEOMAGNETIC POLE FOR MIDCRETACEOUS ROCKS FROM TOBAGO - FURTHER EVIDENCE FOR LARGE CLOCKWISE ROTATIONS IN THE CARIBBEAN SOUTH-AMERICAN PLATE BOUNDARY ZONE

The island of Tobago occupies the eastern end of the central (igneous) belt of the Caribbean-South American plate boundary zone. Volcaniclas tic sediment of the Albian (similar to 100 Ma) Tobago Volcanic Group a nd dikes of similar age within it were sampled in two homoclinal secti ons with different attitudes. The mean of virtual geomagnetic poles fo r 12 sites (25.4 degrees N, 24.1 degrees E, A(95) = 4.2 degrees) is we ll defined, pre-tilting and apparently reliable, yet is far removed fr om a similar age reference pole for South America. Five other paleomag netic studies of Cretaceous rocks from widely separated localities far ther west in the plate boundary zone yield pole positions that are rem arkably similar to the Tobago pole. Poles obtained from the Guajira Pe ninsula of Colombia, the islands of Aruba and Bonaire, and the Caribbe an Mountains of Venezuela are among those that agree with the Tobago r esult. The paleolatitudes for study areas within the plate boundary zo ne are consistent with an origin on or near South America, yet the pol es throughout the zone are rotated roughly 90 degrees. Dextral relativ e motion between the Caribbean and South American plates was probably responsible for the rotation.