Abstract
The Morin Plutonic Complex, in the southern part of the Grenville tectonic province (Canadian Shield) consists of a rock suite ranging from troctolite to farsundite. The centre of the complex is a large domical anorthosite body. Twenty-six chemical analyses have been carried out in order to compare the Morin Complex with similar complexes in the Grenville and Nain provinces. Variation diagrams constructed by plotting the major oxides vs. the differentiation index Al2O3+CaO+MgO show a gap between troctolite and anorthosite in the Morin Complex whereas this gap is absent in the anorogenic complexes of Labrador (Nain province). It is inferred that this gap is the result of intrusion, from the same magma chamber, of two distinct pulses separated by an intervening period of crustal uplift. A second gap occurs between anorthosites and farsundites in all complexes as yet investigated. This gap is an argument for an independent, possibly anatectic, origin of the farsundites. Mineral assemblages in the Morin Complex are compatible with cooling in the lower crust, at a depth of approximately 30 km.
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