Eocene sedimentation and volcanism in the Fig Lake Graben, southwestern British Columbia

Abstract

The Fig Lake Graben is a narrow, complex Eocene basin that developed along part of the Coldwater fault system in southwestern British Columbia. Its origin as a pull-apart basin is probably related to dextral wrench faulting along the Fraser Fault and low-angle normal faulting of the Okanagan shear zone. Within the graben are Kamloops Group volcanic and sedimentary rocks, the thickness of which implies that one fault block has been downthrown at least 4.5 km. Geochemical interpretation of previously published analyses of Kamloops Group volcanic rocks indicates that magma production was genetically related to both extension and subduction.Le graben du Fig Lake est un bassin complexe Ctroit, d'Lge CocBne, dkvelopp6 le long d'un segment du systkme de failles de Coldwater, dans le sud-ouest de la Colombie-Britannique. L'origine du graben, en tant que bassin d'extension, est probablement relik 2 un dkcrochement dextre le long de la faille du Fraser et au mouvement d'une faille normale subhorizontale dans la zone de cisaillement d'okanagan. Les roches volcaniques et sdimentaires du Groupe de Kamloops gisent dans le graben, et leur Cpaisseur est telle qu'un bloc de faille a dfi &re affaissC d'au moins 4,5 krn. L'interpr6tation gkochimique des analyses dCji publiCes des roches volcaniques du Groupe de Kamloops r6vBle que le magma produit Ctait relie gCnCtiquement aux stades d'extension et de subduction.[Traduit par la revue]Can.

Life and death of the Resurrection plate: Evidence for its existence and subduction in the northeastern Pacific in Paleocene–Eocene time

“…Calc-alkalic affinities initially led workers to relate these rocks to subduction (e.g., Lipman et al, 1972). Trace element, rare earth element, and isotopic studies demonstrate crustal, mantle, and mixed sources (Ewing, 1980;Thorkelson, 1989;Dudás, 1991;Norman and Mertzman, 1991;Morris and Creaser, 1998;Morris et al, 2000). 40 Ar/ 39 Ar and U-Pb geochronology limits the ages of these rocks to between 53 and 45 Ma (Berger and Snee, 1992;Wooden and Box, 1996;Ispolatov et al, 1996;Janecke et al, 1997;Grainger et al, 2001;Breitsprecher, 2002).…”

“…Metamorphic core complexes (Parrish et al, 1988;Friedman and Armstrong, 1988;Doughty and Price, 1995) and/ or extensional faulting occurred synchronously with, or around the same time as, volcanism in almost all areas. In southern British Columbia, the volcanic rocks show alkalinity trends and geochemistry typical of arc volcanic sequences (Ewing, 1980;Thorkelson, 1989). However, in the northwestern United States, the magmatism may not be arc related, because alkalinity does not increase with distance from the subduction zone and because the magmatism was compositionally varied, spatially and temporally discontinuous, and coeval at different distances from the continental margin (Dudás, 1991;Norman and Mertzman, 1991;Morris et al, 2000).…”

Eocene paleo-physiography and drainage directions, southern Interior Plateau, British Columbia

“…Near Churn Creek along the Fraser River, conglomerates with provenance to the west and south indicate a north-flowing stream in Paleogene time ( (Fig. 2, site 15; Thorkelson 1989).…”

Generation of Eocene volcanic rocks from the Cordilleran arc of south‐central British Columbia (Canada) during subduction of the Farallon and Resurrection plates and Yellowstone oceanic plateau

“…The Savona rocks with SiO 2 < 60 wt.% have relatively high Mg# varying between 0.61 and 0.50. All these rocks resemble other suites of volcanic rocks from the Challis–Kamloops belts (e.g., Breitsprecher, ; Dostal et al, , , ; Ewing, ; Thorkelson, ) although they differ from the alkali rocks of the Penticton Group which have higher contents of alkalis, particularly of potassium (Church, ; Dostal, Breitsprecher, Church, Thorkelson, & Hamilton, ).…”