New volcanological, 40Ar/39Ar dating and paleomagnetic record from Trindade Island and stratigraphic implications

Abstract

Unrevealing the stratigraphy of volcanic systems is fundamental to understanding their eruptive history and requires a multiproxy approach for the accurate correlation and interpretation of deposits. We present new volcanological, 40Ar/39Ar ages and paleomagnetic data from the volcanic rocks of Trindade Island, located at ∼1.260 km from the Brazilian coast in the South Atlantic Ocean. The reconstruction of the volcanic history of Trindade Island is important because it is the youngest volcanic terrain in Brazil and part of a submarine chain that represents the most recent plume-induced alkaline manifestation beneath the South American plate. Our results suggest Trindade Island underwent two main phases of volcanism. The first phase (3.9–1.5 Ma) formed the Trindade Complex and Desejado Formation, with eruptive styles ranging from phreatomagmatic/Surtseyan to Vulcanian and of dominant phonolitic composition. The second phase (1.0–0.06 Ma) formed the nephelinitic monogenetic centers Morro Vermelho, Valado and Paredão Volcano Formations through dominant Hawaiian and Strombolian styles. The new ages imply a revised stratigraphy for the youngest units of Trindade Island, with partial overlap between them. The revised chronology integrated to the paleomagnetic directional data evidence that Trindade Complex formed during Gauss normal chron (D = 355.4°; I = −49.6°), Valado and Paredão Volcano during Brunhes normal chron (D = 14°; I = −42.3° and D = 9.2°; I = −35.2°, respectively), while Morro Vermelho records the late Matuyama-early Brunhes chron (D = 36.5°; I = −19.8°), with site-level mean paleodirections of normal and transitional polarity within the reverse Matuyama interval.