Heterogeneous Exhumation of the Mount Isa Orogen in NE Australia After 1.6 Ga Nuna Assembly: New High‐Precision 40Ar/39Ar Thermochronological Constraints

The circa 1.60 Ga Isan Orogeny in NE Australia has been ascribed to the collision of Australia and Laurentia (North America), marking the final assembly of the Proterozoic supercontinent Nuna. However, details regarding the tectonic evolution of the orogen remain poorly constrained. To investigate the late orogenic to postorogenic thermal evolution and exhumation history, 40Ar/39Ar dating on hornblende, muscovite, and biotite was conducted in the Mount Isa Inlier, NE Australia, where intense crustal imbrication occurred during the Proterozoic continental collision. Published thermochronological results were recalculated using the current decay constant. Petrological examination and calculation of sample‐specific 40Ar/39Ar closure temperatures and cooling rates were used to reconstruct the pressure‐temperature evolution of individual structural domains. Diachronous cooling histories are revealed between western, central, and eastern belts through ~525–330°C, mainly between 1.53 and 1.48 Ga. Contrasting cooling across postmetamorphic fault zones records the reactivation of inherited normal (i.e., early basinal) and reverse (i.e., orogenic) faults. Estimated exhumation rates are generally low (