Brittle faulting in the Thor–Odin culmination, Monashee complex, southern Canadian Cordillera: constraints on geometry and kinematics

Abstract

Regionally recognized dextral strike-slip faulting is present in the Monashee complex of the southern Canadian Cordillera but is overprinted and partially obscured by subsequent extension. Eocene brittle faults and fractures within the Thor-Odin culmination of the Monashee complex are divisible into three distinct sets. Initial 340°-010°t rending strike-slip faults (set 1) were locally overprinted and reactivated by normal faults with a 325°-020°trend (set 2). A third set of 255°-275°trending fractures (set 3) are interpreted as conjugates to set 1, reactivated as transfer faults to the set 2 normal faults. Large regional faults weather recessively, forming topographic lineaments that transect the Monashee complex. The Victor Creek Fault defines one such lineament. Detailed mapping within the northern Thor-Odin culmination reveals piercement points (fold hinges) on the east side of the fault that are not readily matched on the west side. The minimum displacement required on the Victor Creek Fault to down-drop the fold hinge below the level of exposure on the west side is 1370 m, assuming normal down-to-the-west displacement. The geometry of the fault is consistent with a set 1 dextral strike-slip fault, however. Matching the piercement points in the study area with possible equivalents to the north indicates 55-60 km of dextral strike-slip displacement.Résumé : Des failles de décrochement dextre sont reconnues à l'échelle régionale dans le complexe de Monashee de la partie sud de la Cordillère canadienne, mais elles sont surimprimées et partiellement masquées par des extensions subséquentes. Les failles et les fractures fragiles Èocène à l'intérieur de la culmination Thor-Odin du complexe de Monashee (Éocène) ont été divisées en trois ensembles distincts. Les failles décrochantes initiales, dont la direction tend surtout 340º-010º (Ensemble 1), ont été localement surimprimées et réactivées par des failles normales, dont la direction tend surtout 325º-020º (Ensemble 2). Un troisième ensemble de fractures à tendance 255º-275º (Ensemble 3) représenterait des failles conjuguées à l'Ensemble 1, réactivées en tant que failles de transfert à l'ensemble des failles normales de l'Ensemble 2. De grandes failles régionales s'altèrent de manière récessive formant des linéations topographiques qui recoupent le complexe de Monashee. La faille de Victor Creek définit une telle linéation. La cartographie détaillée à l'intérieur de la culmination nord Thor-Odin révèle des points de percement (charnières de plis) sur le côté est de la faille qui n'ont pas de concordance facile sur le côté ouest. Le déplacement minimum requis le long de la faille Victor Creek pour abaisser la charnière sous le niveau affleurant sur le côté ouest est de 1370 m, en supposant un abaissement normal vers l'ouest. Toutefois, la géométrie de la faille concorde avec une faille décrochante dextre de l'Ensemble 1. La correspondance des points de percement de la région à l'étude avec des équivalents possibles au nord indique un déplacement de décrochement dex...

Age and provenance of a Paleoproterozoic to Devonian Canadian Cordilleran sequence of metasedimentary rocks, Thor-Odin dome, southeastern British Columbia

“…Group 3 metasedimentary units appear to be present only west of major Eocene brittle faults. Our own samples are consistently located west of the Eocene Victor Creek fault, which displays up to ~60 km dextral displacement (Kruse and Williams, 2005;Figs. 1 and 2).…”

“…1.30-1.00 Ga age group. This sample occurs west of the Ratchford Creek-Perry River normal fault (Kruse and Williams, 2005; Fig. 1), while all samples in Frenchman Cap that do not yield Mesoproterozoic zircon grains occur east of it.…”

Mineralogy and Geochemistry of Pegmatites on Mount Begbie, British Columbia

“…The largest pegmatite (GRANITE) has a thickness of ~10 m near its center and a length in excess of 500 m. Nearly all of the pegmatites strike between 295° and 330° with a subvertical dip (Table 1). These orientations appear to be controlled by exhumation-related shear zones that were previously mapped by Craig (1966) and Kruse (2007) (Fig. 2).…”

“…2. Map of pegmatites and related bodies within the study area, modified after and Kruse (2006Kruse ( , 2007:…”

“…Brief notes on the pegmatites are primarily found within the numerous articles covering the regional geology and tectonic history of the region (e.g., Craig 1966, Johnston et al 2000, Kruse 2007). The pegmatites were reported to have an S-type composition; in some cases black tourmaline may comprise up to 5% of the pegmatite volume and be up to 10 cm long, aplitic portions contain more abundant tourmaline, and one geochemical sample contained 13 ppm Li (Craig 1966, Reesor & Moore 1971, Mulligan 1972.…”