The equatorial Atlantic Magmatic Province (EQUAMP):a geochemical and geochronological approach

Abstract

This proposal intends to study magmatic events exposed in the northeastern Brazil that were related to the evolution of the Atlantic continental margin during the Cretaceous and therefore to the break-up of the West Gondwana. These events are represented by: (1) a continental-scale arcuate mafic (dolerites) dike swarm that crosscuts a major Precambrian basement block named the Borborema Province, and (2) a sill province intruding the Paleozoic sedimentary succession of the Parnaíba basin. The mafic dikes were until recently restrict to be a 350 km-long E-trending swarm consisting mainly of high-Ti tholeiitic dolerites closely related to the Atlantic Ocean opening. It has been known as Rio Ceará-Mirim Dike Swarm. Recent high-resolution airborne magnetic surveys carried out on the Borborema Province have shown its continuation to SW extending about 1,000 km in length across the province, thus representing a giant dike swarm as defined in the classical work of Ernst and Buchan (1997) [AGU Geophysical Monograph, 100: 297-333]. The sill province is, in turn, located immediately west of the exposure area of the swarm, and is mostly represented by high-Ti coarse-grained basalts to basaltic andesites. They have been named as Sardinha sills. The very close spatial relationship between the dike swarm and the sills, together with existence of Early Cretaceous K-Ar ages in the literature allow us to test the hypothesis that they are part of a major continental magmatic province. In this proposal, we collectively refer them as the Equatorial Atlantic Magmatic Province (EQUAMP), and intend to formally characterize it as a new Gondwanan Large Igneous Province (LIP) in South America. In order to have success in our initiative we will follow some of the recommendations of the LIP Commission and firstly examine the CMDS and Sardinha sills based on geochemistry and geochronology. We will focus on gathering (1) textural, geochemical and Sr-Nd-Pb isotope data and (2) 40Ar/39Ar ages to understand the geochemical evolution of the EQUAMP magmas and establish timing and duration of their emplacement. With these results we will examine the dynamics of the lithospheric mantle and asthenosphere, as well as crust, during the evolution of the Equatorial Atlantic margin in the Cretaceous, as result of the Gondwana disruption. In order to have success in our initiative we will follow some of the recommendations of the LIP Commission and examine the CMDS and Sardinha sills based on geochemistry and geochronology. We will focus on gathering (1) elemental and Sr-Nd-Pb isotope data and (2) 40Ar/39Ar ages to understand the geochemical evolution of the EQUAMP magmas and establish timing and duration of their emplacement. With these results we will examine the dynamics of the lithospheric mantle and asthenosphere, as well as crust, during the evolution of the Equatorial Atlantic margin in the Cretaceous as result of the Gondwana disruption. In a wider perspective, our data will be added to the data pool of international bibliography in order to extend the existing knowledge on modern plate tectonics and, consequently, how supercontinents have broken up. (AU)