Kettle dome and related structures of northeastern Washington

The Grand Forks complex, in the southern Omineca belt of British Columbia, is a fault-bounded tectonic window exposing Proterozoic sediments and associated mafic rocks metamorphosed to upper amphibolite to granulite facies. Its western margin is marked by the Granby fault, an Eocene west-dipping, low-angle, normal fault characterized by brittle deformation. The metasediments of the Grand Forks complex consist of migmatitic paragneiss containing a peak metamorphic assemblage of garnet + cordierite + sillimanite + K-feldspar ± biotite + quartz. Pressure-temperature conditions for this assemblage are 800 ± 35°C and 5.8 ± 0.6 kbar (1 kbar = 100 MPa). Resorption of garnet to cordierite ± spinel suggests nearly isothermal decompression of about 2 kbar from peak conditions, interpreted to have occurred prior to normal displacement on the Granby fault. Laser ablation U-Pb dating of monazite from the metasediments suggests a dominant episode of Late Cretaceous metamorphism at 84 ± 3 Ma, with evidence for earlier episodes of Cretaceous metamorphism at 119 ± 3 and 104 ± 3 Ma. Early Tertiary recrystallization at 51 ± 2 Ma is coeval with the emplacement of the nearby Coryell plutonic suite. In the hanging wall of the Granby fault, allochthonous sedimentary and volcanic rocks of Quesnel terrane contain mineral assemblages indicative of the upper greenschist to lower amphibolite facies. Pressure-temperature conditions are estimated at 425 ± 40°C and 2.3 ± 0.7 kbar. The throw (vertical displacement) on the Eocene Granby fault is estimated to be on the order of 5 km. While significant, the fault cannot account for the entire amount of tectonic uplift of the core complex.Résumé : Le complexe métamorphique de Grand Forks est une fenêtre tectonique, bordée de failles normales, qui expose des roches de la croûte moyenne dans la ceinture d'Omineca, en Colombie-Britannique. Sur sa marge occidentale, la faille éocène de Granby est une faille cassante à pendage modéré vers l'ouest. Le complexe métamorphique expose des migmatites au faciès des granulites, localement caractérisés par l'assemblage minéralogique grenat + cordiérite + sillimanite + feldspath potassique ± biotite + quartz, dérivées de sédiments protérozo|que. Les conditions de pression-température maximum sont estimées à 800 ± 35°C et 5,8 ± 0,6 kbar (1 kbar = 100 MPa). Une texture de résorption du grenat en cordiérite suggère un épisode de décompression quasi-isothermique, précédant le déplacement sur la faille de Granby. La datation U-Pb par ablation au laser sur monazite démontre une période de métamorphisme régional au Crétacé tardif à 84 ± 3 Ma. Des évènements métamorphiques sont aussi datés à 119 ± 3 et 104 ± 3 Ma. Une recrystallisation éocene de la monazite (51 ± 2 Ma) est concomitante avec l'intrusion du batholithe de Coryell. Dans le toit de la faille de Granby, les roches sédimentaires et volcaniques allochtones du terrane de Quesnel contiennent des assemblages minéralogiques caractéristiques de la transition entre le faciès supérieur des schistes verts au faciès infé...

Section: Regional Geologymentioning

confidence: 99%

“…1). In Washington State the continuation of the complex is known as the Kettle Dome (Cheney 1980;Rhodes and Cheney 1981). The GFC is centrally located within the Shuswap culmination of the southern Omineca belt, a region of high-grade metamorphic rocks in the hinterland of the Cordilleran orogen.…”

Section: Introductionmentioning

confidence: 99%

Geology of the western margin of the Grand Forks complex, southern British Columbia: high-grade Cretaceous metamorphism followed by early Tertiary extension on the Granby fault

Laberge¹,

Pattison²

2007

“…Kettle, Okanogan, Priest River, Bitterroot, Pioneer, Albion Armstrong ( ), Fox et al (1977, Chase et al (1978), metamorphic core complexes, Republic graben Cheney (1980), Hyndman (1980), Miller (1980), Rhodes and Cheney (1981), Harms and Price (1983) …”

mentioning

confidence: 97%

Paleogeographic evolution of the United States Pacific Northwest during Paleogene time

Heller¹,

Tabor²,

Suczek³

1987

Paleogeographic reconstructions for Oregon and Washington during Paleogene time illustrate a major transition from a dominantly compressional (prior to middle Eocene time) to an extensional tectonic regime. This transition resulted in the development of three phases of Paleogene basin evolution in the United States Pacific Northwest. During the initial phase, basins formed along the continental margin during collision of oceanic islands. Sediments in these basins were derived from nearby orogenic highlands. The second phase of basin development began in middle Eocene time and consisted of rapid subsidence of individual basins that formed within a broad forearc region. Nonmarine basins that formed during this phase were caused by extension possibly associated with transcurrent faulting. Rapid sedimentation in both marine and nonmarine basins during this time consisted dominantly of sandstone derived from Cretaceous plutonic sources far to the east. The final stage of basin development was the modification of previous basin configurations by the growth of the Cascade volcanic arc, which was initiated in early Oligocene time. The rising Cascade Range diverted streams canying eastem-derived material, thereby reducing overall sedimentation rates in the coastal basins and providing a local source of volcanic detritus.Dans les Ctats de l'Or6gon et de Washington, les reconstitutions palBogCographiques durant le PalCogbne illustrent une pCriode de transition majeure d'un regime de compression tectonique dominante (anterieur i 1'Eocbne moyen) B un rCgime de distension tectonique. Trois phases de 1'Cvolution du bassin palkogbne dans le nord-ouest Pacifique des Etats-Unis sont dues h cette transition. Au cours de la phase initiale, des bassins se formbrent le long de la marge continentale lors de la collision des iles ockaniques. Les saiments dans yes bassins provenaient des hautes terres des monts avoisinants. La seconde phase de dtveloppement du bassin dCbuta i 1'Eocttne moyen, et elle correspond B une subsidence rapide des bassins individuels qui s'ktaient formCs au coeur d'une grande region d'arc frontal. Les bassins continentaux qui se developpbrent durant cette phase doivent leur origine B une extension qui accompagnait probablement un dkcrochement. La sedimentation rapide dans les bassins marins et continentaux i cette Cpoque Ctait dominee par des g k s dCrivCs des &ions nourricsres plutoniques cr6tacCes situCes plus i l'est. L'Ctape final du dCveloppement des bassins fut la modification des configurations des bassins dCjB exitants provoquke par la croissance de l'arc volcanique des Cascades, lequel arc est apparu au dCbut de I'Oligocbne. Le soulbvement de la chaine des Cascades a modifiC la direction d'ecoulement des cours d'eau qui transportaient des matkriaux provenant de l'est, de ce fait rkduisant les taux de sedimentation moyens dans les bassins c6tiers et foumissant une source locale de detritus volcanique.[Traduit par la revue]Can.

“…The high-grade metamorphic core complexes in southern British Columbia and northeastern Washington have been shown to be bounded by shallowly dipping brittle-ductile mylonite zones that were the locus of significant extension (Cheney 1980;Rhodes and Cheney 1981;Harms 1982;Harms and Price 1983;Corbett and Simony 1984;Tempelman-Kluit and Parkinson 1986;Can-et al 1987;Parrish et al 1988). Extension is tightly constrained to Eocene time by intrusive cross-cutting relations with the mylonites and by dates of the mylonites (Rhodes and Cheney 1981;Harms 1982;Harms and Price 1983;Corbett and Simony 1984;Tempelman-Kluit and Parkinson 1986;Carr et al 1987;Parrish et al 1988).…”

Section: Discussionmentioning

confidence: 95%

Fission-track evidence for Cenozoic uplift of the Nelson batholith, southeastern British Columbia

Sweetkind¹,

Duncan²

1989

Apatite and zircon fission-track data from the Nelson batholith in southeastern British Columbia reveal that a significant amount of uplift has occurred since Paleocene time, including an episode of rapid uplift during Eocene time. Age versus elevation curves for apatite and zircon, combined with a calculated present depth to the 105°C apatite-annealing isotherm, suggest that some 6 km of apparent uplift has occurred in the vicinity of the Nelson batholith since Paleocene time. A period of rapid cooling and uplift occurred from 59 to 45 Ma, when the bounding faults of the adjacent Valhalla gneiss dome, the Valkyr shear zone, and the Slocan Lake fault zone were active. The rapid uplift is interpreted as being related to Eocene extension and the rise of the adjacent Valhalla gneiss dome during Eocene time.