East-derived strata in the Methow basin record rapid mid-Cretaceous uplift of the southern Coast Mountains batholith

Abstract

Abstract:The Jurassic-Cretaceous Methow basin of northern Washington State and southern British Columbia forms an overlap sequence linking several small tectonostratigraphic terranes. Sandstone petrography, sandstone and mudrock geochemistry, and detrital zircon U-Pb age and Hf analysis of mid-Cretaceous, east-derived Methow strata together document a remarkably uniform provenance signature that suggests proximal, abundant, and unchanging sediment sources throughout deposition. The eastern belt of the Coast Mountains batholith, intruded into Stikine and related inboard terranes of the Intermontane superterrane, along with Jurassic and Cretaceous plutons of the westernmost Okanogan Range, provide the best match to the provenance signature of east-derived sediment in the Methow basin during the mid-Cretaceous. Furthermore, the Cretaceous and Jurassic plutons of the eastern Coast Mountains batholith and western Okanogan Range were rapidly uplifted to provide the substantial thickness of sediment in the Methow basin, and they must have acted as a topographic barrier that effectively prevented sediment derived from the continental interior from reaching the basin. This uplift of a proximal eastern source occurred during regional late Early Cretaceous sinistral transpression and resulted in subsidence of the Methow trough and rapid deposition of east-derived strata in the Methow basin. Because Methow sediment sources apparently did not include the North American interior, the extent of post-depositional large-scale translation relative to the North American craton of the Methow basin with its proximal, eastern sources cannot be unequivocally determined.Résumé : Le bassin de Methow (Jurassique-Crétacé) du nord de l'État de Washington et du sud de la Colombie-Britannique forme une séquence de chevauchement reliant plusieurs petits terranes tectonostratigraphiques. La pétrographie des grès, la géochimie des grès et des pélites ainsi que les âges déterminés par U-Pb sur des zircons détritiques et des analyses Hf des strates de Methow provenant de l'est (Crétacé moyen) documentent ensemble une signature de provenance remarquablement uniforme, suggérant des sédiments de sources proximales, abondantes et inchangées durant toute la déposition. La ceinture est du batholite de la Chaîne côtière, introduite dans le terrane de Stikine et d'autres terranes intérieurs reliés du superterrane intermontagneux, et les plutons datant du Jurassique et du Crétacé de la partie la plus à l'ouest du chaînon Okanogan, fournissent la meilleure concordance pour une signature de provenance de sédiments de l'est vers le bassin de Methow au Crétacé moyen. De plus, les plutons datant du Crétacé et du Jurassique du batholite de l'est de la chaîne Côtière et de l'ouest du chaînon Okanagan ont été soulevés rapidement, fournissant l'importante épaisseur de sédiments dans le bassin de Methow, et ils ont dû agir de barrière topographique qui a effectivement empêché les sédiments provenant de l'intérieur du continent d'atteindre le bassin. Ce soulèvement ...

Evolution of the Jura-Cretaceous North American Cordilleran margin: Insights from detrital-zircon U-Pb and Hf isotopes of sedimentary units of the North Cascades Range, Washington

“…The Methow terrane (Barksdale, 1975), the northwest Cascades thrust system (Misch, 1966;Brandon et al, 1988;Brown and Gehrels, 2007), the western mélange belt (Frizzell et al, 1987;Tabor et al, 1993), and the Nanaimo Group mainly contain volcanic and plutonic sedimentary detritus (Jett and Heller, 1988;Mustard, 1994;DeGraaff-Surpless et al, 2003;Brown and Gehrels, 2007;Brown, 2012;Surpless et al, 2014). The NWCS and WMB were amalgamated with the Insular superterrane by the Late Cretaceous (Misch, 1966;Brown, 1987;Brandon et al, 1988), whereas the Methow terrane lies between the plutonic rocks of the Coast Plutonic Complex-North Cascades and Intermontane the east (Fig.…”

“…3; Coates, 1974;Garver, 1992;Garver and Brandon, 1994;Kiessling and Mahoney, 1997;DeGraaffSurpless et al, 2003;Miller et al, 2006;Surpless et al, 2014). DeGraaff-Surpless et al (2003) and Surpless et al (2014) interpret that the Jackass Mountain and Pasayten Groups were derived from proximal sources located to the east of the basin based on detrital-zircon peaks of ca. 160-150 and 120-110 Ma with very minimal (<1%) input from inboard cratonic or recycled sedimentary sources.…”

“…Possible sources of these zircons include the eastern belt of the Coast Plutonic Complex and/or the Okanogan Range, a ca. 120-110 Ma plutonic complex located to the east (Surpless et al, 2014).…”

“…An arkosic sandstone was collected from the Upper Winthrop Formation within the mid to Upper Cretaceous Pasayten Group located stratigraphically above the Twisp Formation to complement the extensive detrital-zircon data set of DeGraaff- Surpless et al (2003) and Surpless et al (2014) (Fig. 3).…”

“…Jurassic to Eocene convergence along the western margin of the North American continent resulted in the accretion of multiple oceanic-arc terranes, intrusion of arc plutons, and formation of large sedimentary basins (e.g., Saleeby and Busby-Spera, 1992;Dickinson, 2004). The U-Pb age spectra of detrital zircons from western North American Cor dilleran sedimentary rocks have been used to help understand episodic high-flux magmatism (Paterson and Ducea, 2015), the timing at which sediment sources were uplifted and when basins subsided (e.g., DeGraaff-Surpless et al, 2003;Laskowski et al, 2013;Surpless et al, 2014), paleogeography, and terrane mobility (e.g., Gehrels et al, 1995;Housen and Beck, 1999;Barbeau et al, 2005). Hafnium-isotope analyses of detrital zircons are used as an additional fingerprint of sedimentary provenance (e.g., Gehrels and Pecha, 2014;Surpless et al, 2014;Holland et al, 2015) by comparing to zircon Hf-isotope compositions of potential source rocks (e.g., Goodge and Vervoort, 2006;Gaschnig et al, 2011;Lackey et al, 2012;Shaw et al, 2014).…”