Deep basement cores from petroleum and stratigraphic drill holes through central and southwest Queensland show that the subsurface Thomson Orogen is dominated by monotonous metasedimentary units but also includes scattered felsic volcanic rocks and more abundant (locally batholithic-scale) intrusions. These igneous rocks and small granitoid exposures along the Eulo Ridge provide means of probing the deeper crustal composition and the geological evolution of this vast area that is mostly covered by deep sedimentary basins.

The Neoproterozoic to Palaeozoic Thomson Orogen occupies a large portion of eastern Australia but is poorly known due to extensive cover. Currently, models for the tectonic evolution of the Thomson Orogen and its relationship to surrounding elements largely focus on the exposed areas. The long and complex structural and thermal history interpreted from these outcropping rocks raises many questions as to the age and origin of rocks in the vast undercover portion of the Thomson Orogen. Glimpses of the undercover Thomson Orogen are revealed in basement intersections of petroleum drill cores throughout central and south-western Queensland. These are dominated by low grade metasedimentary rocks (dominantly turbidites) with minor volcanic rocks and granites. New in-situ zircon analysis for U-Pb (SHRIMP) and Lu-Hf (Laser ablation multi-collector ICP-MS) isotopes are presented here and provide new temporal and provenance information for the rocks occurring beneath cover. Two distinct detrital zircon signatures are identified. A 'Pre-Gondwana' signature is identified in two drill holes on the north-western margin of the Thomson Orogen, adjacent to the North Australian Craton (GSQ Machattie 1, HPP Goleburra 1). These samples both have near-unimodal zircon age peaks at ~1180 Ma. -Hf (900-1300Ma) values from HPP Goleburra 1 display a range of -Hf(t) between 0 and 9 representing a moderately juvenile source. These sediments were possibly derived from the Musgrave Province in central Australia during the Cambrian Petermann Orogeny. Comparable detrital zircon age spectra from the Amadeus and Officer Basins suggests that the Thomson Orogen was connected and formed part of the greater Centralian Superbasin during this period. The second detrital zircon signature is identified extensively throughout the Thomson Orogen in basement drill cores (GSQ Eromanga 1, AAO Beryl 1, GSQ Maneroo 1, DIO Naryilco 1, DIO Betoota 1) and the outcropping Puddler Creek Formation and Les Jumelles Beds. This signature is remarkably consistent and characterised by a dominant age peak at ~570 Ma, a lesser population between ~1300-900 Ma and maximum depositional ages of ~495 Ma. This pattern is termed the 'Pacific Gondwana' detrital zircon signature and is widely recognised in eastern and central Australia and Antarctica. -Hf(500-700) data for Thomson Orogen rocks with this signature is highly variable with -Hf(t) values between -20 and 8 suggesting input from multiple source regions. Our isotopic work suggests connectivity between the Centralian Superbasin and the Thomson Orogen during and after the ~570-530 Ma, Petermann Orogeny. Parts of the uplifted Musgrave Province remained the dominant source of sediments until at least the late Cambrian when the Pacific Gondwana signature became dominant in the Thomson Orogen and central Australian basins.

During May-June 1973, a deep crustal seismic refraction survey was undertaken in the Bowen Basin, Queensland. Blasts from open-cut coal mines in the Basin were used as sources of seismic energy, and recordings were made at twenty-two sites on a 375 km-long line along the axis of the Basin between Goonyella in the north and Moura in the south. A four-layer crust was interpreted from the seismic data, with P-wave velocities of 4.00 ± .22, 5.33 ± .08, 6.39 ± .07 and 7.07 ± .02 km/ s respectively. The total thickness of the 4.00 and 5.53 km/s layers is about 6 km under Goonyella, and slightly more under Dingo 130 km north of Moura. Earlier magnetic and gravity work indicates that these two layers thin southwards towards Moura. They comprise folded Permian-Triassic sediments and possibly also Early to Middle Palaeozoic rocks. The 6.39 km/s layer probably represents the igneous or granitised basement. A lower crustal layer with a velocity of 7.07 km/s and thickness ranging between 5 and 6 km has been interpreted. The total crustal thickness at the centre of the traverse is 36 km, and the upper mantle P-wave velocity is 8.10 ± .11 km/s. A southward-dipping Moho may be interpreted, with the crustal thickness increasing from 35 km, 30 km south of Peak Downs, to 37 km near Dingo. The gravity field calculated from the model conflicts with the observed gravity, suggesting a more complex model than that defined by the seismic refraction data alone.

In northern Queensland there are several old land surfaces which are related to previous periods of erosional and depositional activity. The surfaces are of two main types - buried and exhumed unconformity surfaces formed during periods of active erosion and deposition; and terminal planation surfaces of both erosional and depositional origin which formed as stability returned at the end of each cycle of erosional activity. These terminal surfaces have generally been deeply weathered or duricrusted. The oldest landforms are exhumed unconformity surfaces of Cambrian and Mesozoic age which formed the base of the Georgina and Carpentaria Basins respectively. Three sets of unconformity and terminal surfaces are related to cycles of activity within the Cainozoic Karumba Basin. They have been correlated with surfaces elsewhere in Queensland and the Northern Territory. There are also subsidiary depositional surfaces of the current cycle, and a suite of arid landforms which has previously been treated as a surface.

Survey conducted by the Commonwealth Government or State/Territory Geological Survey (or equivalent) collecting airborne geophysical data