Abstract
In southern Nova Scotia, tonalite, trondhjemite, granodiorite and granite intruded metasedimentary rocks of the Appalachian belt during the Acadian orogeny. The mineral assemblages of these metasedimentary rocks define the staurolite-in (or staurolite + cordierite-in) isograd of the amphibolite facies of the low-pressure, intermediate-type of regional metamorphism. The chemical compositions of these tonalitic to granitic rocks indicate that the magmas before and possibly during crystallization were under relatively high pressures (3.5–6.5 kbar) and at temperatures above ‘minimum melt’ temperatures, possibly in the range 670–730°C, with exception of the tonalitic magma for which a higher temperature of formation is required. These rocks show many geochemical affinities such as relatively high Na/K ratios and similar K/Rb ratios and REE abundances. The REE patterns are moderately fractionated, with a negative Eu anomaly. An origin by partial melting of the metasedimentary rocks of the orogenic belt is postulated for these rocks in the light of the geochemical evidence. This hypothesis has been tested by application of a quantitative model of equilibrium between granitic melts and probable residual material.
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