Unraveling the tectonic setting and crystallization history of the Equatorial Atlantic Magmatic Province

In NE Brazil, Early Cretaceous mafic dikes and sills intrude the Precambrian Borborema Province and the Paleozoic Parnaiba basin, where they form the Equatorial Atlantic Magmatic Province. The Rio Cear ' a-Mirim dike swarm (RCM) is a giant arcuate structure ca. 1100 km in length composed of sets of dikes ranging from E-W to NE-SW. There are two additional giant swarms with WNW and NE-SW orientations spanning 380 km and 355 km, respectively, in the NW and SE regions of the Borborema Province. We investigated the tectonic setting and crystallization history of the mafic magmatism through orientation, dimensions (960 dikes), and 32 represen-tative samples of plagioclase crystal size distributions (CSD) to shed light on the connection between the dikes and sills. Plagioclase compositions in EQUAMP intrusions indicate normal crystallization trends with the magma becoming more evolved towards the final stages of crystallization. CSD data suggests that residence times are similar for dikes and sills (<= 1.5 yrs), although some dikes display higher residence times (3.6-1.8 yrs) in agreement with a longer crystallization history. These results suggest a deeper crystallization setting for the dikes in agreement with a plumbing system in that dikes penetrate the stiffer basement units to feed upward the sills accommodated between sedimentary layers with contrasted rheologies. The regional distribution of the mafic magmatism resulted from a bulk NW-trending extensional deformation, where the brittle (re)activation and control of pre-existing structures allowed the nucleation of the arcuate giant dike system and other satellite swarms. We also examine connections between tholeiitic igneous events in NE South America and tectono-magmatic episodes affecting the Pangea and West Gondwana landscapes in the Mesozoic Era.

Automated summary

In NE Brazil, mafic dikes and sills intrude the Borborema Province and Parnaiba basin, forming the Equatorial Atlantic Magmatic Province. The Rio Cear ' a-Mirim dike swarm is a huge arcuate structure composed of dikes. Other giant swarms are also found in different orientations in the Borborema Province. Through analyzing crystal size distributions, it is found that the dikes and sills have similar crystallization histories, with the dikes crystallizing at a deeper setting.