Petrology of mafic and ultramafic intrusions from the Portneuf-Mauricie Domain, Grenville Province, Canada

The Portneuf-Mauricie Domain (PMD), located in the south-central part of the Grenville Province, comprises several mafic and ultramafic intrusions hosting Ni-Cu ± platinum-group element (PGE) prospects and a former small mining operation (Lac Édouard mine). These meter- to kilometer-scale, sulfide-bearing intrusions display diverse forms, such as layered and tabular bodies with no particular internal structure, and zoned plutons. They were injected ~ 1.40 Ga into a mature oceanic arc, before and during accretion of the arc to the Laurentian margin. The pressure-temperature conditions of the magmas at the beginning of their emplacement were 3 kbar and 1319-1200 °C (according to the petrologic modeling results from this study). The PMD mineralized intrusions are interpreted to represent former magma chambers or magma conduits in the roots of the oceanic arc. The parent magmas of the mineralized intrusions resulted mainly from the partial melting of a mantle source composed of spinel-bearing lherzolite. Petrologic modeling and the occurrence of primary amphibole in the plutonic rocks indicate that these parent melts were basaltic and hydrous. In addition, fractional crystallization modeling and Mg/Fe ratios suggest that most of the intrusions may have formed from evolved magmas, with Mg# = 60, resulting from the fractionation of more primitive magmas (primary magmas, with Mg# = 68). Petrologic modeling demonstrates that 30% fractional crystallization resulted in the primitive to evolved characteristics of the studied intrusive rocks (as indicated by the crystallization sequences and mineral chemistry). Exceptions are the Réservoir Blanc, Boivin, and Rochette West parent magmas, which may have undergone more extensive fractional crystallization, since these intrusions contain pyroxenes that are more iron rich and have lower Mg numbers than pyroxenes in the other PMD intrusions. The PMD mafic and ultramafic intrusions were intruded into an island arc located offshore from the Laurentian continent. Thus, their presence confirms the existence of a well-developed magmatic network (responsible of the fractionation processes) beneath the Proterozoic arc, which resulted in the wide range of compositions observed in the various plutons.

Distribution of euphausiids (Crustacea) at the Great Meteor seamount, Atlantic Ocean

In the course of the voyages 9a and 9c (1967) and 19 (1970) of the RV "Meteor" samples of plankton and neuston have been taken in the area of the Great Meteor Seamount. The euphausiids of this material have been examined quantitatively as well as qualitatively in order to study the influence of the Great and Small Meteor Seamount on a vertically migrating group of plankton. 20 species could be identified. All stem from the surrounding deep water and belong to the tropical and subtropical fauna. On the plateau of the Great Meteor Seamount no indigenous species have been encountered and also the typical neritic species from the west coast off Africa are lacking. As for the euphausiids no relationships exist between the Great Meteor Seamount and the shelf area of West Africa. The dominant species around the Meteor Seamount were Euphausia brevii, Stylocheiron suhmii, E. hemigibba, S. longicorne and Thysanopoda subaequalis. Using the index of diversity (Simpson) distinct differences in the composition of species could be shown to exist between the plateau area of the Meteor Seamount and the surrounding sea. On the plateau of the Great Meteor Seamount the number of species was only 7, E. brevis and S. suhmii dominated. None of the species occurred in great numbers and none is adapted to the specific environmental conditions of the plateau of the Meteor Seamount. The fauna of the plateau is a depauperate one as compared with that of the surrounding sea. This can be explained by the fact that adult euphausiids require for their existence greater water depths than are found above the plateau of the Meteor Seamount.

Calcareous dinoflagellate cysts analysis of sediment cores from the Equatorial South Atlantic Ocean

An overview is presented of the current state of knowledge on paleo-ecological aspects of calcareous dinoflagellate resting cysts. Apart from literature-based information, a discussion of new results is also provided from Equatorial Atlantic surface plankton samples, surface sediment samples and Late Quaternary sediments from two gravity cores. With the aid of redundancy analysis statistics, variations in the calcareous cyst content of both cores are correlated to variations in total organic carbon (TOC). On a global scale, the calcareous cyst distribution in bottom sediments varies with latitude and inshore-offshore gradients. In the Equatorial Atlantic Ocean, enhanced calcareous cyst production can be observed in regions and time intervals with stratified, oligotrophic conditions in the upper water masses.