GEOCHEMISTRY, GEOCHRONOLOGIC AND TECTONIC HISTORY OF THE NICOLA HORST, BRITISH COLUMBIA, CANADA

The Nicola Horst, in the western part of the Intermontane Belt of British Columbia, Canada, is a mini metamorphic core complex and is separated from surrounding volcaniclastic rocks of the Late Triassic Nicola Group by steep brittle Tertiary normal faults. It includes metavolcanic units correlative with the Nicola Group and quartzite metaconglomerate and graphitic metapelite that are probably older, intruded by mafic and granitic rocks ranging in age from Paleocene to latest Triassic. Supracrustal rocks and early metatonalite are strained, metamorphosed to amphibolite facies and truncated by less deformed plutonic units. The horst provides a ‘window’ into the middle crust and perhaps below the base of the Nicola Group. The metavolcanics in the horst have more or less similar geochemical trends with the surrounding Nicola Group rocks. Geothermobarometric studies on the metapelites have revealed a pressure – temperature of 3000-4500 bars and 475-500C. Stable oxygen isotope studies have revealed a temperature of 525 C at the southern end of Horst. The upliftment of the horst is tilted with the northern end coming up faster than the southern end and western end coming up faster than the eastern end. The average upliftment rate calculated is 0.21 mm/yr.