Palaeomagnetism of Cretaceous Dikes from Jamaica

Abstract

Summary In order to contribute to resolution of hypotheses involving the tectonic history of the central Caribbean, a palaeomagnetic survey has been carried out on a series of Cretaceous dikes from the Central Inlier of Jamaica. The magnetic properties of the dikes, which are basalt, andesite, trachyandesite, and hornblende-andesite in composition, are variable but are generally dominated by low oxidation state titanomagnetites. This has caused some difficulty in defining a stable direction of magnetization. Nevertheless, two distinct palaeomagnetic groups are recognized: eleven dikes possess virtual geomagnetic poles (VGP) which when averaged are indistinguishable from the previously-defined North American Cretaceous pole position, and four other dikes recorded closely-grouped equatorial VGP. Both groups contain polarity differences. The favoured interpretation is that Jamaica has not rotated significantly about a vertical axis since the Cretaceous, and for a limited period the regional geomagnetic field behaviour resulted in low latitude virtual geomagnetic poles, similar to previously described geomagnetic activity detected in Tertiary lavas of Hawaii, Alaska, Oregon, and Iceland.