Thermotectonic History of the Kluane Ranges and Evolution of the Eastern Denali Fault Zone in Southwestern Yukon, Canada

Exhumation and landscape evolution along strike‐slip fault systems reflect tectonic processes that accommodate and partition deformation in orogenic settings. We present 17 new apatite (U‐Th)/He (He), zircon He, apatite fission‐track (FT), and zircon FT dates from the eastern Denali fault zone (EDFZ) that bounds the Kluane Ranges in Yukon, Canada. The dates elucidate patterns of deformation along the EDFZ. Mean apatite He, apatite FT, zircon He, and zircon FT sample dates range within ~26–4, ~110–12, ~94–28, and ~137–83 Ma, respectively. A new zircon U‐Pb date of 113.9 ± 1.7 Ma (2σ) complements existing geochronology and aids in interpretation of low‐temperature thermochronometry data patterns. Samples ≤2 km southwest of the EDFZ trace yield the youngest thermochronometry dates. Multimethod thermochronometry, zircon He date‐effective U patterns, and thermal history modeling reveal rapid cooling ~95–75 Ma, slow cooling ~75–30 Ma, and renewed rapid cooling ~30 Ma to present. The magnitude of net surface uplift constrained by published paleobotanical data, exhumation, and total surface uplift from ~30 Ma to present are ~1, ~2–6, and ~1–7 km, respectively. Exhumation is highest closest to the EDFZ trace but substantially lower than reported for the central Denali fault zone. We infer exhumation and elevation changes associated with ~95–75 Ma terrane accretion and EDFZ activity, relief degradation from ~75–30 Ma, and ~30 Ma to present exhumation and surface uplift as a response to flat‐slab subduction and transpressional deformation. Integrated results reveal new constraints on landscape evolution within the Kluane Ranges directly tied to the EDFZ during the last ~100 Myr

Variation in postoperative outcomes of patients with intracranial tumors: insights from a prospective international cohort study during the COVID-19 pandemic

Background: This study assessed the international variation in surgical neuro-oncology practice and 30-day outcomes of patients who had surgery for an intracranial tumor during the COVID-19 pandemic. Methods: We prospectively included adults aged ≥18 years who underwent surgery for a malignant or benign intracranial tumor across 55 international hospitals from 26 countries. Each participating hospital recorded cases for 3 consecutive months from the start of the pandemic. We categorized patients’ location by World Bank income groups (high [HIC], upper-middle [UMIC], and low- and lower-middle [LLMIC]). Main outcomes were a change from routine management, SARS-CoV-2 infection, and 30-day mortality. We used a Bayesian multilevel logistic regression stratified by hospitals and adjusted for key confounders to estimate the association between income groups and mortality. Results: Among 1016 patients, the number of patients in each income group was 765 (75.3%) in HIC, 142 (14.0%) in UMIC, and 109 (10.7%) in LLMIC. The management of 200 (19.8%) patients changed from usual care, most commonly delayed surgery. Within 30 days after surgery, 14 (1.4%) patients had a COVID-19 diagnosis and 39 (3.8%) patients died. In the multivariable model, LLMIC was associated with increased mortality (odds ratio 2.83, 95% credible interval 1.37–5.74) compared to HIC. Conclusions: The first wave of the pandemic had a significant impact on surgical decision-making. While the incidence of SARS-CoV-2 infection within 30 days after surgery was low, there was a disparity in mortality between countries and this warrants further examination to identify any modifiable factors

The Stratigraphy and sedimentology of siliciclastic rocks, west-central Yukon, and their tectonic implications

Bibliography: p. 311-329.Siliciclastic strata between Carmacks and Dawson in west-central Yukon were previously interpreted as Eocene or younger in age and fluvial/continental in origin. Detailed stratigraphic and sedimentologic investigations in the Indian River and Sixtyrnile River areas indicate that some of the strata are much older and were deposited in a paralic environment. The Indian River Formation (new) is at least 500 m thick and consists of interbedded sandstone, shale, conglomerate dinoflagellates and minor indicate coal. that the Spores, formation pollen and is Middle Albian in age and was deposited in a hitherto unrecognized marginal marine basin by a southward prograding fan-delta complex. The Sixtyrnile Formation (new) is approximately 200 m thick and consists of interbedded conglomerate, sandstone, shale and minor limestone and tuff, and intercalated basalt flows. the close association of Palynomorphs, fossil leaves and volcanic rocks indicate the formation is Late Cretaceous-Paleocene in age, possibly Maastrichtian, and is assigned to the lower part of the Carmacks Group. The formation was deposited in a restricted, nonmarine basin by a northward flowing braided-meandering river system and a southward prograding alluvial fan complex. Previous paleogeographic reconstructions indicate that Whitehorse Trough, a Late Triassic to Middle Jurassic backarc or forearc basin {Lewes River and Laberge groups, basalt flows, carbonate reefs and flysch), evolved into a series of restricted, nonmarine basins by Late Jurassic to Early Cretaceous time {Tantalus Formation, alluvial plain). This study proposes that the Trough evolved from a Late Triassic to Middle Jurassic backarc or forearc basin into a successor basin by Late Jurassic to Early Cretaceous time {Tantalus and Indian River formations), which subsequently evolved into a series of restricted, nonmarine basins by Late Cretaceous to Paleogene time {Sixtymile Formation and unnamed strata). Late Mesozoic-Paleogene siliciclastic strata in west-central Yukon reflect the collision, suturing and emplacement of allochthonous with autochthonous terranes and are interpreted as part of the "successor basin" molasse facies of the Canadian Cordillera

Depositional themes in a turbitide succession, Dezadeash Formation (Jura-Cretaceous), Yukon

Bibliography: p. 103-106