SEARCHING FOR SHEAR ZONES IN THE SOUTHERN COAST MOUNTAINS, BRITISH COLUMBIA
Author:
Jessica GrenaderMentor:
Margaret Rusmore, Professor of Geology, Occidental CollegeAnalysis of the structural development of the Coast Mountains gives possible evidence that the mid-Cretaceous thrust belt continues the length of the Coast Mountains batholith, signaling the final amalgamation of the orogen of the eastern and western arcs by 100 Ma. Recent work in the northern batholith shows these were welded together during the mid-Cretaceous deformation and shortening, however whether this deformation and shortening seen in the north also continues into the southern portion of the Coast Mountains is unknown. To test my hypothesis I analyzed unpublished data collected on the Coast Mountains project led by Jim Roddick with Glenn Woodsworth, and converted by Glenn Woodsworth from original punch card data collected in the field. Then compared the orientation and distribution of foliation and bedding to what we would expect in a thrust belt. A variety of NW-trending fabrics are present: many plutons are NW, bedding is oriented NW, shearing strikes NW-SE, and successive metamorphic breaks are NW-trending. The thickest dikes generally strike east-west and form a NW-trending zone. These patterns correspond with that expected in NW-trending contractional belt and are suggestive of NW-striking faults and likely a shear zone continuing the length of the batholith.