Thermal History of Drummond Basin, Queensland (Australia) from Apatite and Zircon (U-Th)/He Thermochronology

Abstract:

The thermal history of the Drummond Basin in central Queensland (Australia) has only been partly investigated. Inverse thermal modeling of apatite and zircon (U-Th)/He data can reveal the complex thermal history of sedimentary basins. We performed (U-Th)/He dating for detrital apatite and zircon grains extracted from five sandstone samples from the Campaspe DDH-1 drill hole. Mean apatite helium ages generally increase from 65.9 Ma (depth = 538 m) to 83.8 Ma (depth = 263 m). The deeper four samples yielded mean zircon helium (ZHe) ages of 289.7 - 278.2 Ma, with a systematic increase of the ZHe ages from deep to shallow samples. The shallowest sample (depth = 117 m) yielded a mean ZHe age of 263.6 Ma. Our inverse thermal modeling suggests five thermal events since burial: (1) rapid heating to the maximum temperature of 180~380 ^oC during ~320-290 Ma, (2) rapid cooling from ~260 ^oC to ~80 ^oC during ~290-240 Ma, (3) subdued cooling from ~80 ^oC to ~30 ^oC during ~240-200 Ma, (4) slow heating from ~30 ^oC to ~80 ^oC during ~200-80 Ma, followed by (5) rapid cooling from ~80 ^oC to ~35 ^oC at ~80 Ma. The timing and temperature conditions of the initial thermal event are consistent with K/Ar ages and temperatures deduced from illite. This period was characterized by voluminous regional magmatism and crustal extension preceding opening of the overlying Bowen Basin. Rapid cooling during ~290-240 Ma identified by our inverse thermal modeling roughly coincides with the thermal relaxation phase and foreland basin phase of the overlying Bowen Basin. This rapid cooling was probably a result of cessation of extension and subsequent contractional events to the east of Bowen Basin. Cooling slowed down during ~240-200 Ma. The Drummond Basin probably underwent serious erosion during this period, coeval with the peneplanation phase of the Bowen Basin. As is delineated by our modeling, the Drummond Basin was slowly heated from ~20 ^oC to ~90 ^oC during ~200-80 Ma, synchronous with development of the Eromanga Basin and slow subsidence of the Surat Basin . The final episode of rapid cooling at ~80 Ma identified from our modeling is consistent with regional-scale uplift, denudation and cooling in the nearby Eromanga Basin during Late Cretaceous.