Ž . Lithos 44 1998 117–140 Geochemical evolution of peraluminous plutons in southern Nova Scotia, Canada—a pegmatite-poor suite K.L. Currie a, ) , J.B. Whalen a,1 , W.J. Davis a,2 , F.J. Longstaffe b,3 , B.L. Cousens c,4 a Geological SurÕey of Canada, 601 Booth Street, Ottawa ON, Canada K1A 0E8 b Department of Earth Sciences, The UniÕersity of Western Ontario, London ON, Canada N6A 5B7 c Department of Earth Sciences, Carleton UniÕersity, Ottawa ON, Canada K1S 5B6 Received 27 March 1998; accepted 19 August 1998 Abstract Three southern Nova Scotia plutons crystallized rapidly at ;375 Ma from magma containing both mantle and crustal components. Isotopic and chemical data suggest that the crustal contribution included both lower crustal material and Cambro-Ordovician turbidites of the host Meguma Group. Despite local evidence of mixing and mingling of magmas, the bulk of the plutons evolved by assimilation and fractional crystallisation. Evolved portions of the plutons have compositions appropriate for development of rare-metal pegmatite fields, but pegmatites are relatively rare and little differentiated. Like parental plutons, pegmatites fall into biotite qplagioclase and muscovite qpotassium feldspar assemblages. The latter locally contain Mn-rich garnet qbiotite, giving calculated P– T conditions of pegmatite crystallisation of ;6208C, 0.44 GPa under water-saturated conditions. Host rocks at the time of emplacement experienced P– T conditions varying from -5008 to ;6208C at 0.44 GPa. Beryl-bearing pegmatites occur only where host rocks were below sillimanite-grade, and pegmatites of any kind are scarce in sillimanite-grade host rocks. Rarity of pegmatites can be ascribed to a combination of insufficient amounts of F, Li, and B in the magma with rapid cooling which prevented extensive fractionation and undercooling. Our data suggest rather that peraluminous suites, produced by rapid heating due to incursions of lithospheric mantle into supracrustal rocks, and typified by biotite-rich, cordierite-bearing plutons, are not favorable locales for major rare-metal-enriched pegmatite fields. Such fields appear to require relatively prolonged anatexis resulting from crustal thickening, or an areally extensive mafic underplate, q 1998 Elsevier Science B.V. All rights reserved. Keywords: Granitic composition; Plutons; Pegmatite; Geochemistry; Absolute age ) Corresponding author. Tel.: q1-613-995-1208; Fax: q1-613- 995-7997; E-mail: kcurrie@nrcan.gc.ca 1 E-mail: jwhalen@nrcan.gc.ca. 2 E-mail: bidavis@nrcan.gc.ca. 3 E-mail: flongsta@julian.uwo.ca. 4 E-mail: bcousens@ccs.carleton.ca. 1. Introduction Rare-element-enriched pegmatites consistently oc- cur associated with highly fractionated peraluminous Ž . granites Martin and Cerny, 1992 , although peg- matites may be spatially separated from the parental body. However not all highly fractionated peralumi- 0024-4937r98r$ - see front matter q 1998 Elsevier Science B.V. All rights reserved. Ž . PII: S0024-4937 98 00051-6