Architecture and Tectono-magmatic evolution of the Campos Rifted Margin: Control of OCT structure by basement inheritance

Abstract

Abstract The formation of rifted margins involves the deformation of pre-existing lithosphere whose rheological and mechanical behavior during extension is complex since it is the product of numerous earlier tectonic events. In this work we investigate the Campos Rifted Margin (CRM) architecture, with the aim of exploring the role of basement inheritance and early magmatism on margin evolution. We present a new compilation of high resolution aeromagnetic data, integrated with seismic interpretation and crustal thickness from 3D gravity inversion, to resolve margin architecture, ocean-continent transition (OCT) structure and the oceanward extent of continental basement. We examine the lateral variation of crustal rheology, necking geometry and rift segmentation, revealing striking spatial heterogeneities that separate three distinct sectors along the Campos margin. The basement of the Campos Rifted Margin consists of Precambrian/Eo-Paleozoic Ribeira Belt (RB) and the easternmost Cabo Frio Tectonic Domain (CFTD) whose Neoproterozoic-Cambrian nappes and thrusts are well preserved offshore and give a rheologically layered crust. This pre-rift basement configuration, along with the Mesozoic magmatism, has resulted in different crustal responses to extension which vary from north to south. It influenced the temporal and spatial distribution of deformation, and as a consequence, the necking geometry, subsidence and sedimentary evolution of the margin. We show that the Campos basin evolution was controlled by crustal inheritance corresponding to that observed in onshore basement terranes. The more massive basement of the northern Campos basin can be correlated with the post-collisional Cambro-Ordovician magmatic province of the Aracuai belt that partially obliterated the earlier orogenic structures. The lack of a structured crust localized the strain generating the observed narrow necking zone. In addition, its more mafic composition resulted in a competent crust which also influenced the rifting processes. In contrast the basement of the central and southern Campos margin, represented by the Cabo Frio Tectonic Domain, is structurally and petrologically distinct from the Aracuai Belt and has layered orogenic crust which responded differently to rifting stresses forming the observed wide necking zone. We propose that the Campos Rifted Margin evolved from a pre-rift complex inherited rheology which dominated the first stages of rifting. However once the crust was highly extended, the deformation was nearly synchronous regionally, leading to giant salt basin formation and breakup.