INTERCALIBRATION OF THERMOCHRONOMETERS AND A MAGNETIC GEOTHERMOMETER TO QUANTIFY THE CONDITIONS AND DURATION OF MAGMA FLOW THROUGH A COLUMBIA RIVER FLOOD BASALT DIKE

Temperature (T) sensitive tools such as thermochronometers are useful for studying geologically-short heat pulses associated with dike emplacement. Our group recently developed a conductive heating and chemical diffusion code that predicts the resetting of zircon and apatite (U-Th)/He (AHe, ZHe) ages in the wallrocks next to dikes as a function of ambient wallrock T, melt-fraction T relationships, and a parameterization of magma flow. In an inverse modeling framework, this code was previously used to fit a spatial pattern of reset AHe and ZHe ages and paleomagnetic inclination in the wallrock next to a Columbia River flood basalt (CRB) dike and quantify that magma flowed through the dike for 1-6 years. Here, we ask: (1) Does our method produce similar predictions using a variety of T-sensitive tools? (2) Do tools that are sensitive to high vs. low T constrain other key parameters, including ambient T, thermal conductivity, and thermochronometer kinetics? We studied a 9 m wide, ca. 16 Ma dike segment that was shallowly emplaced into a ca. 130 Ma pluton in NE Oregon and fed part of the main eruptive phase of the CRB. We generated AHe, ZHe, apatite and zircon fission-track (AFT, ZFT), and biotite ⁴⁰Ar/³⁹Ar (BtAr) ages along a 215 m transect away from the dike-wallrock contact; along this transect we also used the distance to unreset paleomagnetic inclination as a magnetic geothermometer (MGT). To test the intercalibration of these T-sensitive tools, we modeled four different combinations of data. All inversion results constrained the magma flow duration to 2.2-11.3 years. This reproducibility suggests that any combination of T-sensitive tools can quantify the duration of magma flow through a dike; models that use low- and high-T tools together best resolve the ambient T of the wallrocks (62-76°C). Thermal conductivity was consistently unconstrained, which may have implications for hydrothermal systems active during dike emplacement. AFT resistance to annealing was constrained to 0.842-0.869, but kinetics for AHe, ZHe, or BtAr were not resolved. We conclude that our approach to quantifying the conditions into which dikes were emplaced, as well as the duration of magma flow, offers a robust toolkit for investigating the consequences of flood basalt eruptions on the Earth system and the kinetic behavior of thermochronometers.