Use of40Ar/39Ar K‐feldspar thermochronology in basin thermal history reconstruction: an example from the Big Lake Suite granites, Warburton Basin, South Australia

Abstract

ABSTRACTThe potential use of40Ar/39Ar thermochronologic data from K‐feldspars in reconstructing basin thermal history has been evaluated using the example of the Warburton/Cooper/Eromanga Basin, Australia's largest onshore oil‐ and gas‐producing basin. Results from40Ar/39Ar step‐heating experiments reveal details of the evolution of the basin system, including the following: (1) the operation of high geothermal gradient regimes during the earliest basin evolution, suggesting that basin formation was active rather than passive; (2) slow cooling from a Permo‐Triassic temperature peak of at least 250–300°C; (3) a rise in thermal gradients to contemporary bottom hole temperatures in the last 5–10 Myr; and (4) spatially variable recrystallization events between 100 and 50 Ma and at around 20 Ma. Initial microstructural observations serve as a useful predictor of the quality and nature of the obtainable age information. Data from ‘pristine’ K‐feldspars may constrain the peak temperature conditions experienced in the basin, the basin's early thermal history and also any recent changes in thermal gradient. Contrasting data from texturally modified K‐feldspars may constrain times of thermal transients and/or fluid flow, with the preferred interpretation that K‐feldspars recrystallize in response to such events. The Warburton/Cooper/Eromanga Basin example suggests that the40Ar/39Ar technique may serve as a useful adjunct to apatite and zircon fission track analysis and conventional organic maturation indices in basin thermal history analysis.