Pre-rift tectonic scenario of the Eo-Cretaceous Gondwana break-up along SE Brazil–SW Africa: insights from tholeiitic mafic dyke swarms

Abstract

This chapter presents a synthesis of the pre-break-up plate tectonics of western Gondwana and the pre- and syn-rift magmatism in the SW South Atlantic margin (Brazil, Uruguay and Argentina) and the conjugate African continental margin (Angola, Namibia and South Africa). An updated database of the geographical locations of the primary available radiometric ages is also included in this work. A systematic analysis of the K–Ar and Ar/Ar ages from outcrops and boreholes shows a marked Mid to Late Jurassic peak in the southernmost segment of the South Atlantic, related to the emplacement of the Karoo volcanics in South Africa and in Argentina (including the Falkland Islands), and an important Early Cretaceous peak with age distributions that are related to the Gondwana break-up and formation of rift basins along the incipient continental margins. In both the southern Brazilian and Argentinian margins, as well as in the conjugate Namibian and South African margins, several igneous centres and basaltic lava flows are suggestive of the influence of mantle plumes in the Early Cretaceous, which were heralded by mafic dyke swarms in Argentina, Brazil, South Africa and Namibia.Supplementary material:A complete table with Radiometric ages of Jurassic–Early Cretaceous magmatism in the southern portion of West Gondwana is available at: www.geolsoc.org.uk/SUP18589

Some remarks on the earthquakes of Fennoscandia: A conceptual seismological model drawn from the perspective of hyperextension

“…Topographic profile A-A' made with DEM data from Smith & Sandwell (1997). Vector decomposition describing initial stretching direction prior to breakup from Zalán & Oliveira (2005) and Almeida et al (2013). unknown depth -in effect, at the TB. Our results indicate that the TB functions as a permanently weakened zone that responds seismically if stress relaxation cannot keep pace with the incoming sedimentary load.…”

(U-Th)/He Ages from the Fuorite Mineralization of the Tanguá Alkaline Intrusion Idades

“…These magmatic manifestations are associated with two large events which affected the South American platform and according to Mota & Geraldes ( 2006) may be classified in the following way: early Cretaceous tholeiitic magmatism of the Paraná-Etendeka magmatic event, associated with the break-up of Gondwana and with the opening of the South Atlantic Ocean; and later alkaline magmatism linked to Cenozoic uplift of the Serra do Mar and with the development of the Continental Rift of Southeastern Brazil and associated basins. Published geochronogical data indicates that the earlier tholeiitic magmatism peaked at 132 Ma with ages concentrated between 119 and 139 Ma (Almeida et al, 2013). This tholeiitic magmatism has been linked to the early evolution of southeastern Brazil's offshore basins.…”

Conjugate divergent margins: an introduction

“…This was associated with a massive volcanic and magmatic episode in the onshore Palaeozoic basins and also along the incipient margins. Some of these features are discussed by Almeida et al (2013)'s paper, which focuses on the pre-and syn-rift volcanism that heralded the formation of the continental margins. Important volcanic and magmatic features are also recorded in the drift phase of the plates, and the paper by Geraldes et al (2013) analyses some of the mechanisms responsible for developing intraplate igneous structures.…”