Metamorphism and structure of the Soards Creek area, British Columbia
Abstract
Garnet amphibolite layers up to 300 metres thick occur with metasediments of the rlaydrian Horsethief Creek Group in the upper ampnibolite facies near Mica Creek, B.C .. Since the sillimanite isograd projects through the study area, it was possible to study both metapelitic and metabasic rocks under well characterized conditons. The contacts between the metabasites and metapelites are sharp and conformable to both the regional foliation and bedding. Due to mineralogy, thickness and phase chemistry data, the metabasites are inferred to be orthoamphibolites of basaltic composition. The sillimanite isograd was mapped in the metapelites by the first appearance of coarse grained sillimanite. Garnet-biotite temperatures, using Thompson's (1976) calibration, along the isograd range from 600° to 625°C. Pressures range from 6.0 kb to 6.7 kb. The range in pressures can be explained by the plunge of the third phase of deformation structures. PH0 approximately equals Ptotal in the sillimanite zone. The partitioning of iron and magnesium in the octahedral site in hornblende and the dodecahedral site in garnet is calibrated with to temperature in the metabasites. respect lnK~b-g = lnK;b-g The expression: 1979.5 T( K) and T. Oo71, best characterizes the relationship between The reaction: tr + 7/2an = 1213 py + 11/6 gr+ 9/2 qtz + H2 0, may account for the varying Ca-amphibole compositions encountered in the amphibolite facies o The reaction: tr + 3/4an = 23/4 diop + 3/4 py + 1314 qtz + H2 0, may account for the formation of clinopyroxene in the upper amphibolite facies in metabasic rocks, and is a reaction or isograd that could be easily mapped in the field. The study area has undergone three phases of deformation in superimposition. Phase 1 and 2 folds tend to be isoclinal with sharp narrow hinge zones. They have a style that is approximately similar. Phase 3 folds dominate the map pattern on Soards Ridge. These are minor folds that occur along the S.W. flank of the Mica Dam Antiform, a major third phase structure. The metamorphic culmination occurred after the cessation of the second phase of deformation, o2. The metamorphic grade dropped off to approximately biotite grade prior to o3. The sillimanite isogradic surface was deformed and folded during o3.
Description
Bibliography: p. 142-148.
Keywords
Citation
Knitter, C. C. (1979). Metamorphism and structure of the Soards Creek area, British Columbia (Master's thesis, University of Calgary, Calgary, Canada). Retrieved from https://prism.ucalgary.ca. doi:10.11575/PRISM/12360