The Mesozoic Equatorial Atlantic Magmatic Province (EQUAMP)

Abstract

Mafic dike swarms and sills intruding, respectively, the Precambrian Borborema and Paleozoic Parnaiba provinces (NE Brazil) constitute two major magmatic events related to the continental break-up that formed the Equatorial Atlantic. Available whole rock K–Ar determinations and a few plagioclase 40Ar/39Ar ages suggest that these events occurred approximately between 135 and 120 Ma. Airborne magnetic data indicates that the main dike swarm, the Rio Ceara-Mirim swarm, can be traced for about 1,000 km along an arcuate trajectory between the Cretaceous Potiguar rift near the Atlantic coastline, and the northern margin of the Sao Francisco craton. The dikes of the such a giant swarm form isolated (often en-echelon) segments that can reach up to 40 km in length and have a mean width of about 70 m. The sills, known as Sardinha magmatism, are intercalated between the Paleozoic sedimentary strata of the Parnaiba basin having major expression in subsurface rather than on surface. Geochemical data indicate that the parental tholeiitic magmas of dikes and sills would largely derive from melting of subcontinental lithospheric sources. However, a subordinate OIB-type component identified in some dikes would indicate contribution of a mantle plume as a melt source. In this paper we propose that the Sardinha and Rio Ceara-Mirim magmatic products, which are found over an area of about 700,000 km2, all together represent a newly recognized Cretaceous LIP in South America here named Equatorial Atlantic Magmatic Province (EQUAMP).