Fracture control of late Archean pluton emplacement in the northern Slave Province, Canada

Abstract

The structural and geophysical characteristics of 2590–2580 Ma leucogranites in the northern Slave Province have been studied to determine the role and conditions of late Archean regional deformation during their emplacement. The irregularly shaped, straight sided, c. 10 km long Ulu pluton is located in the southern part of the High Lake greenstone belt, northern Slave Province. Fabrics in the pluton and its wall rocks indicate that it was emplaced at mid- to upper crustal levels during regional E–W late Archean compression. A gravity survey and resulting three-dimensional gravity model of the pluton show that it has several linear, deep (>6 km) root zones, which feed a relatively thin (<2 km) tabular body. The orientations of the major root zone, along the pluton's western side, and three subsidiary roots correspond to those of the pluton contacts to within 5°. Landsat TM data reveal several sets of lineaments, interpreted to represent fractures formed during the early assembly of the Slave Province, which cut both the greenstone belt and the younger plutons. Analysis of these lineaments defines several maxima whose orientations correspond with those of both the feeder zones and the contacts of the Ulu pluton. The pluton therefore appears to have been emplaced via an intersecting set of vertical fractures. Magma was arrested by and spread along an unknown horizontal structure. Subsequent inflation of the pluton was also facilitated by vertical translation on pre-existing fractures.