Context matters: Modeling thermochronologic data in geologic frameworks using the Great Unconformity as a case study

Abstract

The critical importance of sample context and geologic information for interpreting geochronologic data has long been fundamental to the Earth sciences. However, the lack of quantitative uncertainties associated with contextual, observational information means that much geologic data cannot be statistically treated in computational models using the same approaches as quantitative datasets. This challenge is showcased by the current debate over whether and how geologic data should be used when modeling thermochronologic results, which has important implications for deriving time-temperature (tT) paths from which burial and exhumation histories are interpreted. Holistically leveraging observational data to test hypotheses and determine the set of geologically reasonable thermal histories that can explain thermochronologic results has a longstanding history, but some recent studies have criticized this approach as one that arbitrarily limits tT solutions. Here, a geologic context approach to thermal history modeling, in which observational and thermochronologic datasets are combined to design geologically valid models and reach the most geologically likely interpretation, is illustrated using an example of constraining Great Unconformity exhumation in Colorado where this modeling philosophy has been questioned. Although the quality of geologic data and their applicability to modeled samples can vary and be debated, this does not mean that all geologic data are inherently unreliable and therefore discardable. Exploring models with varying or minimal constraints can be useful to test different hypotheses and determine the resolving power of the data, but using an endmember context-blind approach to interpret thermochronologic results can produce outcomes that violate fundamental aspects of the geology. The strategy outlined here is not the only valid approach to modeling thermochronologic data, but if the purpose of the modeling is to derive meaningful interpretations about sample tT paths in order to better illuminate the geologic history, then critical thinking about the sample context, first order geologic observations, and primary relationships should be integral components of the modeling process.