Ocean Drilling Program, United States

We used paleomagnetic results from Sites 998, 999, 1000, and 1001 to estimate the paleolatitude of the Caribbean region over the past 80 m.y. The data include remanence measurements of split-core sections (typically 1.5 m long) and discrete samples (6-12 cm (super 3) in volume) from volcanic and sedimentary rocks. From these, we computed 15 new paleolatitude estimates for Sites 999 and 1001 on the Caribbean plate and three new paleolatitude estimates for Site 998 on the Cayman Rise, currently on the southern North American plate. One estimate from Site 1001 is based on 230 measurements made along split-core sections of basalt after demagnetization of 20-25 mT. The other 17 estimates are based on principal component analysis of demagnetization data from 438 discrete paleomagnetic samples from sedimentary units. Where necessary, the 18 new paleolatitude estimates are corrected for a polarity ambiguity bias that occurs when averaging paleomagnetic data from drill cores that have shallow inclinations and are not azimuthally oriented. We also investigated the contribution of additional biases that may arise from a compaction-related inclination error, which could affect the sedimentary units, though not the basalt units. Several lines of evidence, including the lack of a correlation between porosity (or water content) and inclination, indicate that the inclination error is small, if present at all. The results from Sites 999 and 1001 indicate that the Caribbean plate was 5 degrees -15 degrees south of its current position at approximately 80 Ma, possibly placing it directly over the equator in the Late Cretaceous. Although the data do not preclude changes in the rate of northward motion over the past 80 m.y., they are consistent with a constant northward progression at a rate of 18 km/m.y. Given the uncertainties in the data, rates of northward motion could be as low as 8 km/m.y. or as high as 22 km/m.y. These results are compatible with several existing models for the evolution of the Caribbean plate, including those that have the Caribbean plate originating in the Pacific Ocean west of subduction zones active in the Central American region during the Cretaceous, and those that have the Caribbean plate originating within the Central American region, though more than 1000 km west of its current position relative to North and South America.