Multi-sample thermal history inversion in HeFTy along a structural profile using time-depth modeling: application to the Argentine Frontal Cordillera (29–33°S)

Abstract:

Application of multiple thermochronometers to a single sample provides valuable information about the thermal and geological history of the rock, including the time/temperature of peak heating, timing and magnitude of erosional episodes, and sample cooling rates. Multi-sample approaches to thermal history inverse modelling further leverage these datasets to provide spatial constraints on regional cooling and geologic events. We present a new extension to the HeFTy thermal history modeling software that implements time-depth modeling, which in turn allows multiple, multi-chronometer samples along a structural or topographic profile to be inverted simultaneously. An integrated 1D thermal model simulates burial and unroofing, accounting for the lag between deformation and heat conduction. In the context of a multi-sample application, this allows HeFTy to better approximate transient effects such as isotherm compression during rapid exhumation, and transition from geothermal to elevation gradients. The software also allows for a change in relative depth position among samples (e.g., tilting, folding) during the history within user-defined constraints, allowing the thermochronological data to help ascertain the timing of deformation. We also discuss the recommended workflow for HeFTy multi-sample modeling, and HeFTy modeling in general. We apply this new functionality to a thermochronological modeling dataset of 22 igneous samples from the Argentine Frontal Cordillera (29–33°S) to extract the spatio-temporal record of rock cooling during Paleogene subduction and Neogene flattening of the Nazca oceanic plate. Thermal history inverse modeling of apatite and zircon (U-Th)/He results from five structural transects records regionally coeval middle Miocene cooling and features a major shift in the geometry of the eastern (retroarc) Frontal Cordillera, from an orogen-scale fault-bend fold anticline at 29–31°S to west-dipping hanging wall panels exhumed along emergent faults at roughly 31–33°S. Multi-sample modeling considerably improves the time-temperature results obtained from single-sample approaches and allows us to probe the relative influence of subducted slab dip vs. upper-crustal processes on regional patterns of deformation and unroofing.