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Russian Geology and Geophysics

2004 year, number 11

INITIAL MAGMAS OF PROTEROZOICTROCTOLITE-ANORTHOSITE MASSIFS OF NORTH AMERICAAND EVOLUTIONARY TREND OF TIME-DEPENDENT VARIABILITYOF COMPOSITION OF PERIDOTITE-GABBRO MASSIFS

P.A. Balykin and T.E. Petrova
Institute of Geology, Siberian Branch of the RAS, 3 prosp. Akad. Koptyuga, Novosibirsk, 630090, Russia
Keywords: Troctolite-anorthosite massifs, initial magma, numerical modeling, depth of melting, physicochemical conditions of crystallization, formational type, evolutionary trend
Pages: 1274-1285

Abstract

Compositions of initial magmas for some well-explored troctolite-anorthosite massifs of North America were estimated and numerically modeled using the COMAGMAT-3.3 program. The objects of study were the Kiglapait, Michikamau, and Harp Lake massifs of the Nain plutonic series of the Labrador Peninsula (Canada), the Adirondack massif of the Grenville orogen of Proterozoic age (New York, USA), and the Duluth massif of the North American rift (Minnesota, USA). These massifs have been characterized in short, with petrochemistry of their rock components estimated statistically. It has been established that in norm composition the initial magma corresponded to olivine-orthopyroxene-bearing basalts for the Harp Lake massif, and to olivine basalts, for the other massifs. On the basis of the Albarede regression equations, it has been shown that the magmas were extracted by melting at pressures of 9-13 kbar (Harp Lake, Michikamau, and Kiglapait massifs) to 19-22 kbar (Duluth and Adirondack massifs) and at temperatures of 1200 to 1400