Petrology, geochemistry, geochronology and tectonic history of Nicola Horst, British Columbia

The Nicola Horst (NH), in the southern part of Intermontane Belt of British Columbia, is separated from surrounding volcaniclastic rocks of the Late Triassic Nicola Group by Tertiary faults. The Horst includes two types of units: stratified rocks and intrusive rocks. The stratified rocks, highly deformed and intruded by a variety of plutonic units, include (a) Metaconglomerates accompanied by black graphitic mica schist, (b) Meta-Nicola rocks consisting of amphibolite and biotite-amphibole schists and (c) Intermediate metavolcanic rocks, mainly metavolcaniclastic (probably ignimbrites) and intrusive porphyries. The metasedimentary (a) and metavolcanic (c) units have been grouped under the Bob Lake Assemblage. The bulk of the NH is intrusive rocks, which are medium to coarse-grained plutonic rocks, predominantly granodiorite but ranging from biotite granite, hornblende biotite tonalite to gabbro. These rocks are of three distinct ages: Late Triassic metatonalite and metadiorite; Jurassic Lejeune and Bush Lake granodiorite; and Paleocene Rocky Gulch granite-granodiorite, Frogmoore granodiorite and leucogranite.; From thin sections and hand specimen, there is textural and mineral evidence of one peak amphibolite grade syn-kinetic metamorphism throughout the horst, which probably took place during Paleocene, before the emplacement of Rocky Gulch and Frogmoore granodiorites, which were not affected by it. The local presence of high-grade minerals like sillimanite in the southeast of Bob Lake, bordering the Paleocene Rocky Gulch granodiorite can be attributed to contact metamorphism. (Abstract shortened by UMI.)...