THERMAL AND STRUCTURAL EVOLUTION OF THE INTRACRATONIC ARLTUNGA-NAPPE COMPLEX, CENTRAL AUSTRALIA

The thermal and structural evolution of a Paleozoic thrust system in central Australia, the Arltunga Nappe Complex, has been examined through field mapping, pentrographic, microstructural and chemical analyses, K/Ar and 40Ar/39Ar thermochronology, and multi-diffusion-domain (time-temperature) modeling of K-feldspar 40Ar/39Ar data. The Arltunga Nappe Complex contains three distinct tectonic units, bounded by regional faults and shear zones, that have undergone contrasting deformational and metamorphic histories. The cooling history of the three tectonic units has been constrained by K/Ar and 40Ar/39Ar isotopic age data from K-feldspars, micas, and amphiboles. Results are consistent with a piggyback history of crustal imbrication spanning over 100 m.y., with the hottest rocks uplifted and cooled first and with imbrication acting progressively toward the foreland. Implications for the intracratonic Paleozoic tectonics of central Australia are (1) uplift within the structurally highest tectonic unit was initiated before 400 Ma; (2) continued piggyback imbrication, footwall failure, and uplift and exhumation of the crust resulted in duplexing in the lowest structural unit at approximately 325-300 Ma; (3) the contrast in thermal history between the tectonic units indicates that once widely separated crustal segments were juxtaposed during thrusting above a hinterland dipping megathrust, resulting in similar to 85 km of crustal shortening.