LATEST CRETACEOUS TO EARLY TERTIARY DEXTRAL STRIKE-SLIP FAULTING ON THE SOUTHEASTERN YALAKOM FAULT SYSTEM, SOUTHEASTERN COAST BELT, BRITISH-COLUMBIA

Citation
Pj. Umhoefer et P. Schiarizza, LATEST CRETACEOUS TO EARLY TERTIARY DEXTRAL STRIKE-SLIP FAULTING ON THE SOUTHEASTERN YALAKOM FAULT SYSTEM, SOUTHEASTERN COAST BELT, BRITISH-COLUMBIA, Geological Society of America bulletin, 108(7), 1996, pp. 768-785
Citations number
84
Language
INGLESE
art.tipo
Article
Categorie Soggetti
Geosciences, Interdisciplinary
ISSN journal
0016-7606
Volume
108
Issue
7
Year of publication
1996
Pages
768 - 785
Database
ISI
SICI code
0016-7606(1996)108:7<768:LCTETD>2.0.ZU;2-L
Abstract
The Yalakom fault system cuts the Cadwallader, Bridge River, and Metho w terranes for 300 km along the northeast side of the Coast Belt in so uthwestern British Columbia. The fault system had major dextral slip a fter middle Cretaceous contractional deformation and early Late Cretac eous volcanism, which ceased by late Eocene time. At discrete times, t he Yalakom fault system had major changes in the configuration of acti ve faulting, which resulted in four stages of faulting over approximat e to 40 m.y. The latest Cretaceous dextral slip occurred on the associ ated Castle Pass-Downton Creek fault zone and possibly the Yalakom fau lt. Strike slip recurred on the Yalakom fault during the Paleocene(?)- middle Eocene, and there is an associated series of left-stepping faul ts with zones of contraction and uplift in the stepovers. This associa ted deformation included early to middle Eocene dextral shear, and sou th-vergent thrusting within the Shulaps metamorphic belt on the southw est side of the Yalakom fault. The Marshall Creek fault became an impo rtant component of the system during middle Eocene time, and this led to tectonic unroofing of the Shulaps belt along normal faults localize d in the right-stepping transfer zone linking the Marshall Creek and Y alakom faults. Magmatism was widespread but minor during faulting and was commonly localized along faults. Magmatism may have aided uplift o f the Shulaps belt. No basinal deposition accompanied the strike-slip faulting. An estimate of 115 km dextral, strike-slip displacement on t he Yalakom fault is based on offset of a unique three-part structural succession of the Methow, Cadwallader, and Bridge River terranes. Abou t 5 km of dextral slip occurred on subsidiary faults that do not merge with the Yalakom fault; therefore, 120 km of dextral offset is estima ted for the Yalakom fault system. All but approximate to 10 km of dext ral offset occurred in the Eocene (and Paleocene?). Thus our interpret ations preclude the Yalakom fault from being a major contributor to la rge-scale northward translation of the northwestern Cordillera (the Ba ja British Columbia hypothesis) interpreted from paleomagnetic data to have occurred largely before Eocene time. On the basis of our correla tions across the Yalakom fault, such large faults must lie east of the Methow terrane. The Yalakom fault system probably was linked to the H ozameen and Boss Lake faults (now exposed more than 100 km to the sout h on the east side of the Fraser and Straight Creek faults). An intern ally consistent regional model of strike-slip faulting based on offset of geologic units and timing on faults suggests greater than or equal to 250 km of dextral displacement between ca. 80 and 35 Ma within the southeast Coast Belt. This model resolves the apparent conflict in fa ult data from Washington and British Columbia and gives a template for comparison of pre-Late Cretaceous geology.