0000000000224762
AUTHOR
Riccardo Petrini
Basalt magmatism along the passive continental margin of SE Brazil (Campos basin)
The SE-Brazil passive continental margin is characterized by tholeiitic magmatism that is particularly widespread in the marginal Campos basin, facing the inland flood basalts of the adjacent Parana basin. Campos magmatism is represented by Early Cretaceous (EC; 134–122 Ma) flood basalts and minor Upper Cretaceous-Early Tertiary basalt flows and intrusives, which were emplaced in a basin with attenuated crustal thickness (20 km). Petrography, mineral chemistry, wholerock geochemistry and Sr−Nd isotope composition emphasize that the EC-Campos basalts have suffered extensive seawater interaction which caused enrichment in MgO, FeO total, K2O, Rb and Ba, and depletion in SiO2 and CaO, while Zr…
Evidence of magmatic activity related to Middle Jurassic and Lower Cretaceous rifting from northeastern Brazil (Ceará-Mirim): K/Ar age, palaeomagnetism, petrology and Sr/1bNd isotope characteristics
The Mesozoic magmatic activity in the easternmost part of NE Brazil (Ceara-Mirim) is mainly represented by two-pyroxene tholeiitic dykes; only few dykes have alkaline character. K/Ar ages and palaeomagnetism data indicate that Ceara-Mirim dykes are of Middle Jurassic (175-160 Ma) and Early Cretaceous (140-130 Ma) age. Both Middle Jurassic and Lower Cretaceous dykes have high incompatible-element concentrations and TiO2 with the lower contents generally confined to the Middle Jurassic dykes; rare tholeiitic dykes low in TiO2 and incompatible elements are present. Sr/1bNd isotopic and other chemical data do not support appreciable crustal contamination and in a 87Sr86Sr vs. 143Nd144Nd diagram…
Lower Cretaceous tholeiitic dyke swarms from the Ponta Grossa Arch (southeast Brazil): Petrology, Sr-Nd isotopes and genetic relationships with the Paraná flood volcanics
The Lower Cretaceous dykes of the Ponta Grossa Arch, the most important dyke swarms in Brazil, are associated with the flood basalts and rare acid flows of the northern Parana basin. The Ponta Grossa (PG) dykes are formed by two-pyroxene tholeiites and rare acid rocks. The basaltic dykes may be distinguished into two main groups: a dominant, high-TiO2 (> 2 wt.%; HTi) group and a subordinate, low-TiO2 (< 2 wt.%; LTi) group, characterized, for similar MgO content, by high and low incompatible-element contents, respectively. Most PG dykes do not show chemical and isotope evidence supporting important crustal contamination. PG dykes with (87Sr86Sr)0 < 0.7060 plot in the mantle array (ϵSr ≈ + 17…
A NEW AREA OF ALKALINE ROCKS IN EASTERN PARAGUAY
Alkaline rocks can be found in three major areas (northern, northeastern and central-eastern) of Eastern Paraguay. On die basis of geographic distribution and tectonic association, Livieres & Quade (1987) proposed inclu- sion of these outcrop areas different alkaline provinces: Alto Paraguay, Amambay and Central, respectively (Fig. 1). Presently, only the Central Province, clustering the largest number of occurrences, is the subject of systematic investigation. Available information on the Alto Paraguay and Amambay rocks is still scarce.