Meso and Micro-scale Analysis of Foliated Rocks of the Southern Coast Belt: A Transect from Whistler to Lillooet, British Columbia
MESO AND MICRO-SCALE ANALYSIS OF FOLIATED
ROCKS OF THE SOUTHERN COAST BELT:
A TRANSECT FROM WHISTLER TO LILLOOET, BRITISH COLUMBIA
Erich Victor Zorn, M.S.
University of Pittsburgh, 2005
Between Whistler and Lillooet, British Columbia within the Coast Belt rocks of Gambier Group, Cadwallader Group, Chism Creek Schist, Cayoosh Assemblage, Bridge River Complex/Schist, and the Brew Group, penetrative deformation is commonly recorded. Along this 110 km transect foliation generally dips 30ºNE to vertical and strikes northwest. Down-dip lineation is common in these rocks. Although they are commonly re-crystallized, locally developed microstructures preserve shear-sense indicators in sections cut parallel to dip and perpendicular to foliation. Differences among ductile structures indicate at least five episodes of deformation. 1) Foliation of Oligocene-Miocene (~25-14 Ma) age which strikes northeast and dips steeply is present in Early Cretaceous plutonic rocks east of Whistler. 2) Sub-horizontal penetrative foliation and shear bands in the Brew Group record NW-SE extension that is interpreted to record structural exhumation of the Brew in the footwall of the Cayoosh Creek Fault. 3) Steeply dipping mylonite and L-tectonite with distinct sub-horizontal mineral lineation is present along the dextral, Eocene Marshall Creek Fault. The penetrative deformation overprints microstructures that record left and right lateral shear sense indicators. 4) Pre-85 Ma: Mineral lineations and meso-scale asymmetric folds that give a sense of oblique left-slip and pure shear are recorded in the Chism Creek Schist and Cayoosh Assemblage close to the Bralorne and Downton Creek fault systems. 5) Post-113 Ma: Near Whistler, outcrops of very fine grained volcanic rocks and meta-sediments of the Gambier Group have mylonitic foliation and show strong mineral lineation parallel to the dip direction. Meso-scale kink folds and asymmetric tails in thin section are interpreted to record extension whereas symmetric tails record flattening during pure shear. Late Jurassic intrusive rocks nearby to the west and east of this belt of meta-volcanics are ductily deformed.
Advisor:Charles Jones; William Harbert; Thomas Anderson
School:University of Pittsburgh
School Location:USA - Pennsylvania
Source Type:Master's Thesis
Keywords:geology and planetary science
Date of Publication:10/18/2005