Plutonic rocks make up about one quarter of the exposed Canadian Appalachians, occuring in all tectonostrati- graphic zones. Plutons range in age from Middle Protero- zoic to Cretaceous, but ages of plutons in particular zones are restricted to small parts of this range. Compositions range from ultramafie to high-silica granites. Overall there is a noticeable deficiency of mafic compositions (dioritic and more mafic) compared to other well-studied orogenic belts such as the Cordillera. Late Precambrian, early Paleozoic, and Mesozoic magmatism produced mafic dyke swarms of major dimensions, and significant amounts of mafic plu- tonic rocks. Most other periods of magmatism produced few dykes, and mafic plutonic rocks are either subordinate to salic phases or virtually absent.
Despite their large area, plutonic rocks received rela- tively little attention prior to 1965 because of the strati- graphic and structural focus of much of the early geological work in this region. Interest in the plutonic rocks increased markedly with the realization that they hold important clues to the tectonic history of the region, and may contain significant mineral deposits. The pioneering compilation of Neale and Pajari (1972) served as a prototype for provincial compilations (Strong, 1980; Clarke et al., 1980; Fyffe et al., 1981) and stimulated studies of individual plutons. During the past decade, mainly under the sponsorship of provincial and federal governments, a great deal of work has been undertaken on plutonic rocks of the Canadian Appalachian region. The general outlines and petrography of most plutons are now known, and bulk rock
Figures & Tables
This volume focuses on the highly populated Canadian Appalachian region. The chapter on the East Greenland Caledonides stands alone and there is no attempt to integrate the geological accounts of the two far removed regions. Rocks of the Canadian Appalachian region are described under four broad temporal divisions: lower Paleozoic and older, middle Paleozoic, upper Paleozoic, and Mesozoic. The rocks of these temporal divisions define geographic zones, belts, basins, and graben, respectively. The area is of special interest because so many modern concepts of mountain building are based on Appalachian rocks and structures.