Original paper

Geochemical Distribution Patterns of Magmatites from the Archipelago of Fernando de Noronha

Schwab, Roland Gottlieb; Bloch, Wolfgang

Abstract

Fifty-six samples of igneous rocks were taken from the archipelago of Fernando de Noronha to study their major and trace element distribution. The research work was undertaken to gain a more detailed view of the two main rock series which the island consists of: the Remédios and the Quixaba Formation. Although these rock series differ in the time of their eruption, the geochemical distribution patterns prove that they originate from the same magma, where they were separated by a process of differentiation. With the help of variation diagrams a continuous geochemical evolution can be demonstrated: the lighter and later differentiates were erupted first, forming the Remédios Formation, followed by the heavier differentiates of the Quixaba Formation.

Kurzfassung

Aus dem Archipel Fernando de Noronha standen 56 Proben zur Haupt- und Spurenelementanalyse zur Verfügung. Die Probennahme erfolgte unter Berücksichtigung sowohl der zeitlichen als auch der räumlichen Verteilung beider größerer Gesteinsserien, der Remédios-Formation und der Quixaba-Formation. Die Untersuchungen zeigen, daß diese Gesteinsserien zwar zeitlich getrennt, geochemisch aber als durch einen Differentiationsprozeß aus einem Urmagma entstandene vulkanische Einheit zu sehen sind. Entsprechende Korrelations-Diagramme veranschaulichen diese kontinuierliche Entwicklung, wobei die leichteren Differentiate als Remédios-Formation, die schwereren Differentiate als Quixaba-Formation später eruptierten.

Abstract

56 amostras de rochas do Arquipélago de Fernando de Noronha foram analisadas para seus elementos maiores e traços. Para a amostragem foramções consideradas as distribuições no tempo e no espaço das duas maiores séries de rochas, a saber, as formações Remédios e Quixaba. As pesquisas mostraram que, embora essas séries sejam separadas no tempo, pela geoquímica devem ser vistas como uma única unidade vulcânica, derivada de um processo de diferencição de um magma inicial. Em diagramas apropriados é mostrado um continuo desenvolvimento onde os diferenciados leves da Formao Remédios entraram em erupcao primeiro, seguidos pelos diferenciados pesados da Formação Quixaba.

Keywords

magmatitesBrazilArchipelago of Fernando de Noronha