Journal Article

40 Ar/ 39 Ar dates on hornblende, muscovite, and biotite from the Mica Creek area, British Columbia: regional metamorphic and tectonic implications

Ghent, Edward, Villeneuve, Michael

2006

Overview

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 40 Ar/ 39 Ar 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 40 Ar/ 39 Ar dates over a distance of ~45 km suggests that the area behaved as a coherent cooling unit.