Paleomagnetic and geochemical constraints on the timing and duration of the CAMP activity in northeastern Brazil

Abstract

The northeastern border of the Maranhao basin (NE Brazil) is dominated by low-Ti tholeiites which show strong geochemical affinity with the low-Ti Early Jurassic Mosquito Formation from the western side of the basin. The low-Ti tholeiitic flows (Early Jurassic) from Lavras basin, and the low-Ti dikes outcropping in the Ceara State are also comparable to the Mosquito tholeiites. Compositional similarity also exists between the Early Cretaceous Sardinha intrusives (eastern Maranhao basin), the high-Ti dikes from the Ceara State, and the high-Ti rocks of the Rio Ceara-Mirim dike swarm (mainly subswarms I and III) easterwards. The high-Ti and low-Ti rocks show paleomagnetic remanences that allow the discrimination of the two groups. However, the characteristic remanent magnetization from the Rio Ceara-Mirim subswarm II differs significantly from the other two groups; these rocks can be also distinguished from the other high-Ti rocks by slight different chemical characteristics. On paleomagnetic basis, three age groups were identified: Early Cretaceous (Sardinha Formation, high-Ti Ceara dikes, and Ceara-Mirim subswarms I, III, and V), Early Jurassic (Mosquito Formation, low-Ti Ceara dikes, Lavras basin flow, and Ceara-Mirim subswarm IV), and Late Triassic (Ceara-Mirim subswarm II), and corresponding paleomagnetic poles were calculated. The Early Jurassic pole fits well with other CAMP poles from South America, extending easterwards the area in northern South America affected by that magmatic event. The Late Triassic age might represent a magmatic manifestation preceding by about 20-30 My the CAMP activity in NE Brazil.