The Late Triassic-Early Jurassic Voicanism of Morocco and Portugal in the geodynamic framework of the opening of the Central Atlantic Ocean

Nasrrddine Youbi, Linia Tavares Martins , Jose Manuel Munhi, Hassan lbouh, Jose Madeira , El Houssaine Ait Chayeb, and Adelmajid El Boukhari A.

1 Department of Geology, Faculty of Sciences-Semlalia, Cadi Ayyad University. P.O. Box. 2390, Prince Moulay Abdellah Avenue, Marrakech 40000, Morocco. Youbi@ucam.ac.ma
2 Centro de Geologia, Departamento de Geologia da Faculdade de Ciencias da Universidade de Lisboa, Edif. C2 50 piso, 1749-016 Lisboa, Portugal. Itm@fc.ul.pt; jmunha@fc.ul.pt
3 Department of Geology, Faculty of Sciences and Technics-Gubliz, Cadi Ayyad University. P.O. Box.618, Marrakech 40000, Morocco.
4 LATTEX, Departamento de Geologia da Faculdade de Cidncias da Universidade de Lisboa, Edit C2 50 piso, 1749?016 Lisboa, Portugal. jose.madeira@fc.ul.pt

Abstract

An overview on the Late Triassic-Early Jurassic Magmatic Province of Morocco and Portugal (TJMPMP) is presented.  It comprises clastic rocks sequences interbedded with extrusive basalts, preserved in elongated rift basins, and their feeder dikes and sills.  Paleontologic data indicates ages that range from Upper Ladinian-Lower Carnian to the Sinemurian for the sediments, while available 40Ar/39Ar analysis yield a mean age of 200±1,6 Ma for the volcanics.  The volcanologic characteristics of the TJMPMP are those of confinental basaltic successions.  It comprises subaerial lava flows and pyroclastic deposits, sometimes deposited in lacustrine environments, and feeder dikes, constituting an interesting volcanic sub-province of the Central Atlantic Magmatic Province (CAMP) as most outcrops are preserved as extrusive volcanics.  These rocks correspond to low-Ti, quartz normative, tholeiites displaying very uniform chemical and isotopic characteristics, showing variable upper crustal contamination.  The most primitive non-contaminated rocks represent a mantle source localised in continental lithospheric mantle.  The nucleation of the rifting process may have started at two different triple junctions: an RRR junction near Florida, and a RRT between Africa-lberia-America.