A Multiple Chronometer approach to the Deep-Time Thermochronology of Cratons

William Guenthner, University of Illinois Urbana-Champaign
,
,
,
,
,
,
,

Abstract

Deep-time thermochronology is a method to resolve the thermal histories of rocks that span billions of years and provide insights into mid- to upper-crustal geological processes occurring at temperatures below 350 degrees C. This approach has seen renewed interest in the last decade with applications in Precambrian geologic settings. Most prominently, the deep-time approach has been used to investigate the erosional origin of the Great Unconformity surface, a continent-scale nonconformity that separates lowermost Paleozoic strata from underlying Precambrian basement, and how cratonic interiors—regions not subject to metamorphism and fabric development—record distinct thermal events associated with tectonism subsequent to cratonization. In this talk, I will present results from a study of the deep-time thermal history of basement rocks in the US Upper Midwest cratonic interior. Here, we have further investigated the origin of the Great Unconformity surface, and the long-term (in)stability of the Laurentian craton. I will discuss the geologic implications of these results, but will also use them as a vehicle to prompt group discussions about: 1) how best to design and interrogate deep-time thermochronology datasets, 2) the continuing viability of the deep-time approach, and 3) lingering questions that need to be resolved to ensure this viability. In order to further frame this last topic, I will briefly touch upon ongoing work by our group to improve our understanding of the kinetics of one particular deep-time thermochronometer, the zircon (U-Th)/He system, with a multiple pathway approach to modeling He diffusion in zircon.

Session

Rates and dates