The first metamorphic sodic amphibole identified from the Newfoundland Appalachians—its occurrence, composition and possible tectonic implications

Abstract

MODELS for the emplacement of the western Newfoundland ophiolite suites include obduction over an eastward-dipping subduction zone1, but no blueschist facies assemblages, considered to form in response to the high P/T gradients associated with subduction, have yet been identified in this area. Magnesioriebeckite and crossite which occur in metavolcanics from the vicinity of Croque, northwestern Newfoundland, provide the first indication that these conditions may have been approached. This report deals with the petrographic relations, composition and probable conditions of formation of the Newfoundland sodic amphiboles, the latest in a series of occurrences described from Vermont2,3, Quebec4 and New Brunswick5,6 (Fig. 1).