Thermal and exhumation history of the Eocene Chumstick Basin, Washington State, USA

Abstract

This study investigates the Cenozoic evolution of the Cascades Mountains, USA, by means of reconstructing the thermal history of the Chumstick Basin deposits that are located on the eastern flank of the orogen. We present new detrital apatite (U-Th-Sm)/He and detrital apatite fission-track ages from the middle Eocene (~48-37 Ma) Chumstick Formation and modern river detritus. These data are integrated with the published thermochronometric ages of the adjoining Cascade Mountains basement. The new thermochronometer results are combined with existing vitrinite reflectance data for modeling of the basin's thermal history. Results suggest constant temperatures throughout the late Oligocene to early Miocene followed by rapid cooling since 17-10 Ma. Results indicate that the middle to late Miocene uplift of the Cascades resulted in reactivation of the fault zones bounding the Chumstick Basin. The structural reactivation and the weaker lithology of the basin strata in comparison to the harder and more resistant basement rocks of the Cascades resulted in significant basin exhumation. This interpretation is determined from younger apatite (U-Th-Sm)/He cooling ages observed in the reset detrital bedrock of the Chumstick Formation than in the adjoining basement rocks. These observations suggest a structural and lithological control on exhumation magnitudes in this region.

Eocene‐Oligocene proto‐Cascades topography revealed by clumped (Δ47) and oxygen isotope (δ18O) geochemistry (Chumstick Basin, WA, USA)

“…Similarly, our T (Δ 47 ) data are consistent with low‐temperature thermochronology [ Enkelmann et al ., ]. Thermal history modeling suggests burial temperatures of 100–140°C for Phase 1 and 60–80°C for the overlying Phase 3 deposits [ Enkelmann et al ., ].…”

“…Similarly, our T (Δ 47 ) data are consistent with low‐temperature thermochronology [ Enkelmann et al ., ]. Thermal history modeling suggests burial temperatures of 100–140°C for Phase 1 and 60–80°C for the overlying Phase 3 deposits [ Enkelmann et al ., ]. Discordance between zircon and apatite fission track ages indicates that the sediments were heated to temperatures between the annealing temperature of apatite (100–120°C) and zircon (230–250°C) [ Gresens et al ., ; Evans , ; Enkelmann et al ., ].…”

“…Magmatic activity in the surrounding region resulted in the syndepositional emplacement of several plutonic complexes northeast of the Chumstick basin, such as the Duncan Hill, Cooper Mountain, or Railroad Creek plutons [e.g., Tabor et al ., ; Paterson et al ., ]. The assumption that heating is mostly due to burial, however, is supported by detrital bedrock apatite fission track ages that increase from stratigraphically older (Phase 1) to younger (Phase 3) Chumstick sediments [ Enkelmann et al ., ]. The distribution of Δ 47 temperatures suggests that the Chumstick sediments were not thermally overprinted by the Columbia River flood basalts.…”

“…This indicates that the thermal input of the basalts was too low to reset clumped isotope systematics. In addition, low‐ T thermometry data show no resetting associated with basalt emplacement [ Enkelmann et al ., ].…”

“…Here we provide a δ 18 O record of groundwater of meteoric origin (δ 18 O water ) as preserved in terrestrial sedimentary sequences of the Eocene Chumstick basin, which today is located in the rain shadow of the northern Washington Cascades. Combining information on the basin burial history [ Evans , , ; Enkelmann et al ., ], we use clumped isotope (Δ 47 ) thermometry to reconstruct δ 18 O values of Eocene groundwater in the Chumstick basin. Our Δ 47 thermometry ( T (Δ 47 )) results indicate that the Chumstick basin sediments experienced carbonate growth at temperatures between 70°C and 110°C depending on burial depth, a result in accord with thermochronological and vitrinite reflectance data.…”