Cuppone, Tiberio (2009) Camp Volcanism: age, volcanic stratigraphy and origin of the magmas. Cases studies from Morocco and the U.S.A. [Tesi di dottorato]
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During Triassic time, in the proto-North Atlantic area, the late Palaeozoic fracture system, inherited from the building of Pangea supercontinent, was reactivated. Rifting and breakup of Pangea, initiated during the early Triassic, continued and intensified at the beginning of the Norian. After few million years later, a massive magmatic event, namely CAMP (Central Atlantic Magmatic Province), occurred in the rifted and inside the cratonic areas, covering more than 10 millions kilometers square, leaving its products on 4 continents: North and South America, southwest Europe and west Africa. The main magmatic event occurred at ca 199-200 Ma near the Triassic-Jurassic boundary (Tr-J) with two minor secondary pulses al ca. 195 Ma and 192 Ma. The time spanned by the main magmatic event is very short, probably less than 1 Ma (ca. 610 Ka based on Milankovitch cyclostratigraphy), and the tight occurrence with one of great extinctions events in the Phanerozoic time and the climatic crisis and biotic turnover demarcating the Tr-J, led to the intriguing hypothesis that CAMP magmatism triggered these global events. At present the CAMP magmatism is represented by tholeiitic dikes, sills and minor amounts of lava flows, deeply eroded and in few places well preserved, being due to the subtropical palaeogeographic position of the basaltic outcrops which led to heavy weathering. Most of the CAMP basalts throughout circum-Atlantic domain have quite homogeneous compositions, with low-Ti (TiO<2wt.%) except for high-Ti dyke storms documented in Liberia, French Guyana and northern Brazil, strong Nb-Ta(PM) negative anomaly, enriched in light earth rare elements (LREE) and large ion lithophile elements (LILE) respect to the common normal mid-ocean ridge basalts. The purpose of this work is to describe and correlate 6 CAMP volcanic sequences in three different Morocco regions (three in the Central High Atlas, two in the Middle Atlas and one in the Western Meseta) on the base of a petrographic-mineralogic-geochemical-magneto-stratigraphic study in order to highlight similarities between the four basaltic units which made up the lava piles. Phase relationships, their major, minor and trace element compositions will be investigated to constrain crystallization order and conditions (T, P, H2O content and fO2) of basalts while the accurate chemo-magneto-stratigraphic correlation of five lava sequence allow to do new suppositions about feeding system of the Moroccan CAMP basalts. Finally new and accurate 40Ar/39Ar dating on plagioclase and biotite separates from 10 basaltic sample of the Eastern North America (Newark and Culpeper basins) will be presented, discussed and compared to both previous dating of the same province and a overall CAMP ages dataset.
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