FRACTURE CONTROL OF LATE ARCHEAN PLUTON EMPLACEMENT IN THE NORTHERN SLAVE PROVINCE, CANADA

The structural and geophysical characteristics of 2590-2580 Ma leucogr anites in the northern Slave Province have been studied to determine t he role and conditions of late Archean regional deformation during the ir 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 roc ks indicate that it was emplaced at mid- to upper crustal levels durin g regional E-W late Archean compression. A gravity survey and resultin g three-dimensional gravity model of the pluton show that it has sever al linear, deep (>6 km) root zones, which feed a relatively thin (<2 k m) tabular body. The orientations of the major root zone, along the pl uton's western side, and three subsidiary roots correspond to those of the pluton contacts to within 5 degrees. Landsat TM data reveal sever al sets of lineaments, interpreted to represent fractures formed durin g the early assembly of the Slave Province, which cut both the greenst one belt and the younger plutons. Analysis of these lineaments defines several maxima whose orientations correspond with those of both the f eeder zones and the contacts of the Ulu pluton. The pluton therefore a ppears to have been emplaced via an intersecting set of vertical fract ures. Magma was arrested by and spread along an unknown horizontal str ucture. Subsequent inflation of the pluton was also facilitated by ver tical translation on pre-existing fractures. (C) 1998 Elsevier Science Ltd. All rights reserved.