TESTING THE CORRELATION OF ROCKS EAST AND WEST OF THE HARRISON LAKE SHEAR ZONE USING DETRITAL ZIRCON GEOCHRONOLOGY

Located in southwest British Columbia the Harrison Lake Shear Zone (HLSZ) is a steeply-dipping oblique reverse fault zone with northeast-side-up dextral motion, and proposed affinities to the Fire Creek-Ascent Creek-Breakenridge Fault complex; being along strike and exhibiting the same ages and structure. The HLSZ is part of the West Coast Belt foreland within the Coast Belt Thrust System (CBTS), a west-verging contractional belt that developed along the inboard margin of the Insular superterrane during the late Cretaceous. East of the HLSZ the Central Coast Belt detachment (CCBD) is a ductile shear zone and main locality of displacement for deep crustal rocks within the CBTS. Currently the CCBD is interpreted to be the boundary between West and Central Coast belt domains, and represents the eastern margin of the Insular superterrane. The HLSZ is not considered an inter-terrane suture as rocks west and east of the HLSZ have been correlated based on comparable faunal successions, similarity of protoliths, and overlapping U/Pb isotopic ages of igneous zircon in metadacites and metadiorites east of Harrison Lake. To test these correlations, we conducted geochronological studies of rocks on both sides of the HLSZ. Detrital zircon measurements were conducted on 2 polymict conglomerate and 3 arkosic arenite samples within the Gambier and Harrison Lake assemblages west of the HLSZ. These were compared to 2 metasedimentary Slollicum Schist samples taken east of the HLSZ. The Gambier and Harrison Lake assemblages yield detrital zircon populations from late Devonian to late Cretaceous. The Slollicum Schist yields detrital zircon populations from late Triassic to early Cretaceous. Comparison of maximum depositional ages from detrital zircons suggest a wider range from early to late Cretaceous west of the HLSZ, which contrasts with early Cretaceous ages consistently identified east of the HLSZ. The dissimilarity of detrital zircon populations and maximum depositional ages suggests these deposits may not correlate and that the HLSZ may be a more fundamental structural and stratigraphic break in the Coast Belt Thrust System then previously interpreted.