Dyke Swarms of the Paraná Triple Junction, Southern Brazil

• Main Author: José Moacyr Vianna Coutinho
• Format: Article
• Language: English
• Published: Universidade de São Paulo 2008-10-01
• Series: Geologia USP. Série Científica
• Subjects: Enxame de diques; Ocorrências no Sudeste brasileiro; Petrografia; Quimismo; Geocronologia.
• Online Access: http://ppegeo-local.igc.usp.br/pdf/guspsc/v8n2/03.pdf

This work intends primarily to survey the field, mineralogical and petrographic characters of the mafic dykes which occuron a stretch of 650 km along the Southeastern coast of Brazil, between the city of São Sebastião, and the island of SantaCatarina. New chemical and geochronological data are also presented. The coastal dyke swarms are envisaged as the northernand southern arms of a plume-generated triple junction system centered on the Paraná State coast, and related to the initialopening of the South Atlantic. Mafic magma intruded as dyke swarms along three directions: N-S (the southern arm, along theParaná-Santa Catarina coast), NW-SE (Ponta Grossa arch) and NE-SW (the northern arm along the São Paulo coast). Fiftytwo dykes, almost all tholeiitic diabases, were mapped and sampled along the south arm coast. The Ponta Grossa arch dykes are chiefly composed of tholeiitic diabases and lesser intrusions of andesitic to rhyolitic composition. Over 240 dykes were sampled and identified along the north arm west of São Sebastião. Lamprophyres are here abundant, followed by diabases, microdiorite porphyries and lesser amounts of trachy-andesite, carbonatite and Precambrian dykes. Special attention was given to the study of lamprophyres, their field appearance relative abundance, mineral and chemical composition, enclaves and relations to neighboring alkaline intrusions.