GSA Annual Meeting in Phoenix, Arizona, USA - 2019

Paper No. 280-7
Presentation Time: 9:00 AM-6:30 PM


DAIGLE, Lane W., Department of Geological Sciences, University of Colorado Boulder, 2200 Colorado Ave, Boulder, CO 80309, JOHNSON, Benjamin W., School of Earth and Ocean Sciences, University of Victoria, Victoria, BC V8P 5C2, Canada, METCALF, James R., Arizona State Univ, Tempe, AZ 85281-1404 and FLOWERS, Rebecca M., Department of Geological Sciences, University of Colorado Boulder, Boulder, CO 80309

The Pilbara Craton of Western Australia is an Archean craton that has provided key insights into the Early Earth, including continental formation, emergence, and early evolution of life. However, its younger history of Phanerozoic burial, exhumation, and uplift is poorly understood due to its considerable age and scarcity of published regional low temperature thermochronology data. Here, we present new zircon and apatite (U-Th)/He (ZHe and AHe, respectively) data gathered from multiple Archean granitic intrusions across the Eastern Pilbara Craton. The samples cover an area of 12,000 km2, and include intrusions emplaced between 3500 and 2900 Ma, and range in composition from true granites to granodiorites and one dolerite. Our preliminary findings suggest that the ~2940 Ma Chillerina granite, which unconformably underlies the Jurassic-Cretaceous Callawa Formation, underwent a period of rapid cooling (from about >190 °C to <70 °C) between 425-370 Ma. This implies the Chillerina has been at its current depth since at least the Silurian, and must have been exposed at the surface during the Mesozoic and the deposition of the Callawa formation. Previous apatite fission-track studies, from about 200 km south of the Chillerina, suggests that cooling of that region occurred around 320 Ma (Weber et al. 2005). This comparison implies that the Pilbara Craton had a dynamic and protracted Paleozoic exhumation history. We are continuing analysis of several other granites (Fig Tree, Mt. Edgar dome) to understand the regional thermal history will help develop an improved model on the complexity of uplift/exhumation events throughout the Pilbara.