Geometry and sequence of thrusting, McKnight and Kelmbeck Canyons, Tendoy Range, southwestern Montana

Williams, Nancy S.; Bartley, John M.

doi:10.1130/mem171-p307

Cited by 6 publications

(9 citation statements)

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“…By late Campanian time, much of the Beaverhead Group was sourced from more proximal thrust sheets in the Sevier thrust belt to the west (MC and RB on Figure 9b). (Skipp, 1988;Williams & Bartley, 1988).…”

Section: Propagation Of Sevier Fold-thrust Belt During the Late Cretamentioning

confidence: 99%

Provenance of Synorogenic Foreland Basin Strata in Southwestern Montana Requires Revision of Existing Models for Laramide Tectonism: North American Cordillera

2020

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The Laramide province is characterized by foreland basin partitioning through the growth of basement arches. Although variable along the western U.S. margin, the general consensus is initiation of this structural style by the early Campanian (~80 Ma). This has been linked to flat-slab subduction beneath western North America, but the extent and cause for a flat slab remain debated, invoking the need for better constraints on the regional variations in timing of Laramide deformation. We present new conglomerate clast composition, sandstone petrographic, and detrital zircon U-Pb geochronologic data from the Upper Cretaceous Beaverhead Group in southwestern Montana that suggest a pre-Campanian history of basement-involved deformation. During the early stages of deposition (~88-83 Ma), two separate depositional systems derived sediment from the Lemhi subbasin and distal thrust sheets to the west as well as Paleozoic strata eroding off the exhuming Blacktail-Snowcrest arch to the east. Our data provide the first conclusive evidence for the longitudinal transport of gravel via Cordilleran paleorivers connecting sediment sources in east central Idaho to depocenters in southwestern Montana and northwestern Wyoming. Furthermore, erosion of Paleozoic strata by this time requires that the Blacktail-Snowcrest arch was exhuming prior to~88 Ma in order to remove the Mesozoic overburden. Later (~73-66 Ma) sediment flux was entirely from the foreland-propagating fold-thrust belt to the west. These results suggest that Laramide-style deformation in southwestern Montana preceded initiation elsewhere along the margin, requiring revision of existing models for Laramide tectonism.

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Section: Propagation Of Sevier Fold-thrust Belt During the Late Cretamentioning

confidence: 99%

Provenance of Synorogenic Foreland Basin Strata in Southwestern Montana Requires Revision of Existing Models for Laramide Tectonism: North American Cordillera

2020

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“…Williams and Bartley, 1988;Schmitt et al, 1995), which is interpreted to have been active by late Campanian to early Maastrichtian time (Perry et al, 1988). Our findings support Wardlaw and Pecora, 1985;Williams and Bartley, 1988). Given the DZ Mix results, most of the sandstone clasts are likely from the Quadrant Formation.…”

Section: Previous Researchers Have Interpreted Conglomerate Clasts Insupporting

confidence: 80%

“…Mississippian limestone from the composite McKenzie Canyon-Four Eyes Canyon composite thrust (e.g. Williams and Bartley, 1988;Schmitt et al, 1995), which is interpreted to have been active by late Campanian to early Maastrichtian time (Perry et al, 1988). Our findings support Wardlaw and Pecora, 1985;Williams and Bartley, 1988).…”

Section: Previous Researchers Have Interpreted Conglomerate Clasts Insupporting

confidence: 78%

“…Haley, 1985;Skipp, 1988;Haley and Perry, 1991). However, it is important to consider the possibility that other (Skipp, 1988;Williams and Bartley, 1988). The Ashbough Canyon limestone conglomerate is at least partially sourced from the Hawley Creek due to the presence of zircons unique to the Beaverhead Plutons (Lund et al, 2010).…”

Section: 2: Implications For Timing Of Local Deformation and Local mentioning

confidence: 99%

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A multi-proxy provenance approach and depositional age constraints for the Upper Cretaceous Beaverhead Group, Southwest Montana

Garber¹

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I owe much gratitude to my colleague and friend, Justin Rosenblume, who worked his hardest this past summer to help me with my field work in Montana, around-the-clock sample processing, and analysis in Arizona. The many hours of discussion and working together tirelessly on this project are something I will always be grateful for. Thanks also to Berkley Grimm for his help with sample processing and analysis, and to the staff at the Arizona LaserChron Center for their attentiveness. I have much appreciation for the many great friends I have made here these past couple years and their emotional support and friendship, namely the very small group I arrived in Iowa City with last Fall (Justin, Tanner, Larkin, and Reuben). Many thanks to my undergraduate advisor, Dr. David Malone, for the continued support and for helping me realize how powerful detrital zircons are. Thanks to my wonderful parents, Dana Garber and Lola Arnett, for the unconditional love and support that got me where I am today. Finally, thank you to Scott Grube, who has been my rock (pun intended) through all the good and bad during my time as a graduate student and supportive and loving every step of the way.

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“…This depth is consistent with illite crystallinity analysis of the Scott Peak Formation (Mississippian limestone) in the Lost River Range, which indicates peak metamorphic temperatures of 220°C (Kübler indices average 0.20°2) during Sevier deformation, as well as rare textural evidence (deformation lamellae, subgrains) indicative of dislocation creep in calcite which is thought to require temperatures of ϳ300°C (Rutter, 1976). In contrast, emergent thrusting and fan delta development along the southwest Montana thrust front suggests deformation near the synorogenic ground surface (Perry and Sando, 1983;Perry and others, 1988;Kulik and Perry, 1988;Williams and Bartley, 1988;Skip and Link, 1992;Schmitt and others, 1995;Anastasio and others, 2002). Vitrinite reflectance and conodont color alteration index Influenced by Oliver (1986), Garven (1989) and Hutcheon and others (2000).…”

Section: Idaho-montana Thrust Belt-stratigraphy and Deformation Condimentioning

confidence: 89%

Extra-basinal fluid infiltration, mass transfer, and volume strain during folding: Insights from the Idaho-Montana thrust belt

Anastasio

Bebout

Holl

2004

American Journal of Science

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Finite strain and geochemical variations along strain gradients were used to study cleavage development in carbonates in the Lost River Range, Idaho. Deformation accommodating layer-parallel shear was partitioned into thin deformation zones during folding of Willow Creek anticline. Cleavage intensity is strong to very strong in deformation zones and weak in surrounding rocks. Strain magnitudes range from e s ‫23.0؍‬ (1.15:0.93:0.73; x, y, z, principal axes of strain) outside, to e s ‫46.0؍‬ (1.29:0.80:0.52) inside, deformation zones. We found a positive linear correlation between strain, cleavage development, and negative dilation. Volume loss, at a cubic centimeter scale, ranges from 12 percent to 49 percent. Cleavage selvages are depleted in Ca and 18 O and enriched in other elements relative to microlithons and less deformed protolith carbonates. Mass-balance considerations indicate that cleavage was formed by incongruent pressure solution leading to a passive concentration of less soluble components during Ca loss and metasomatic additions of Si, Al, and K to produce authigenic clay minerals in selvages. Data for the Willow Creek locality and elsewhere in the Lost River Range (Davidson and others, 1998), Pioneer Mountains, and the Tendoy Range (Bebout and others, 2001), show that across the Sevier orogen, fluid infiltration was heterogeneous at centimeter-kilometer scales and resulted from positive feedback between deformation and far-traveled surficial fluids. Metasomatic strain softening enhanced deformation zone development, which generated increased permeability as the thrust belt evolved from a porosity-based closed system to a discontinuity-based open system. Increased fluid infiltration and isotopic exchange was associated with volume loss, increasingly prolate strains, and crystallization of clays, to produce the cleavage selvages. Mass transfer was accommodated by diffusion early and advection later in the deformation history. Mesoscopic structures (deformation zones, faults, veins) focused fluid flow and were kinematically related to larger-scale structures (faults, faultrelated folds). The inferred addition of surficial fluids to depths of >7 kilometers in the thrust belt implies a fluid regime involving significant topographically driven recharge. Deformed whole-rocks and microsamples are lower in ␦ 18 O than undeformed samples which have O-and C-isotope compositions similar to those of marine carbonates. Veins are even lower in ␦ 18 O V-SMOW , with minimum values of ϳ؉5 permil reflecting penetration of the crust by ocean-derived precipitation with ␦ 18 O near to somewhat lower than 0 permil (range of ؊7.5 to ؉2.5‰ calculated for H 2 O in equilibrium with these veins). The inferred penetration, into the thrust belt, of nearshore meteoric waters is consistent with proximity to the reconstructed Western Interior Seaway. Later fluid infiltration locally lowered the ␦ 18 O of carbonates even further, based on the O-isotope compositions of veins related to younger compressional deformation and to the o...

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Geometry and sequence of thrusting, McKnight and Kelmbeck Canyons, Tendoy Range, southwestern Montana

Cited by 6 publications

References 0 publications

Provenance of Synorogenic Foreland Basin Strata in Southwestern Montana Requires Revision of Existing Models for Laramide Tectonism: North American Cordillera

Provenance of Synorogenic Foreland Basin Strata in Southwestern Montana Requires Revision of Existing Models for Laramide Tectonism: North American Cordillera

A multi-proxy provenance approach and depositional age constraints for the Upper Cretaceous Beaverhead Group, Southwest Montana

Extra-basinal fluid infiltration, mass transfer, and volume strain during folding: Insights from the Idaho-Montana thrust belt

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