Abstract

A metamorphic high, the Selkirk-Monashee-Cariboo complex (SMC) is a 200 km × 60 km area cored by K-feldspar-sillimanite rocks. In the Mica Creek area, there appear to be no discontinuities in metamorphic isograds, structural trends, or the Late Precambrian stratigraphic units. U-Pb dates suggested that the continuities may only be apparent. In this paper, we report 40Ar/39Ar dates on muscovite, biotite, and hornblende from some of the same samples dated by U-Pb and samples that crop out very close to the dated samples. The goal was to set constraints on the alternative interpretations of the metamorphic-structural history. These interpretations are as follows: (1) U-Pb ages record different times of metamorphic crystallization and deformation, and there are significant tectonic displacements; the mappable continuities are only apparent. (2) The structural and stratigraphic continuity is real, and the range is due to localized heating and deformation events spanning ∼100 Ma; the relative uniformity of the 40Ar/39Ar dates over a distance of ∼45 km suggests that the area behaved as a coherent cooling unit.

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