QLD
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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.
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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.
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This report presents new Sensitive High Resolution Ion Microprobe (SHRIMP) U-Pb zircon results for eighteen samples from the Thomson Orogen, Mossman Orogen, New England Orogen and Mount Isa Inlier. Also reported are the SHRIMP U-Pb monazite results for a gneiss from the New England Orogen. Nine samples from the Thomson Orogen are from basement cores. Eight of these are metasediments where SHRIMP U-Pb detrital zircon geochronology was undertaken and a further sample is a volcanic rock. Detrital zircon geochronology was also undertaken on four sedimentary outcrop samples from the Hodgkinson Province (Mossman Orogen). Samples from the New England Orogen are from the Connors Subprovince and comprise three granites, a volcanic and a gneiss.
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Total magnetic intensity (TMI) data measures variations in the intensity of the Earth's magnetic field caused by the contrasting content of rock-forming minerals in the Earth crust. Magnetic anomalies can be either positive (field stronger than normal) or negative (field weaker) depending on the susceptibility of the rock. The data are processed via standard methods to ensure the response recorded is that due only to the rocks in the ground. The results produce datasets that can be interpreted to reveal the geological structure of the sub-surface. The processed data is checked for quality by GA geophysicists to ensure that the final data released by GA are fit-for-purpose. These line dataset from the Weipa, Qld, 1985 survey were acquired in 1985 by the QLD Government, and consisted of 14704 line-kilometres of data at 3000m line spacing and 500m terrain clearance. To constrain long wavelengths in the data, an independent data set, the Australia-wide Airborne Geophysical Survey (AWAGS) airborne magnetic data, was used to control the base levels of the survey data. This survey data is essentially levelled to AWAGS.
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Total magnetic intensity (TMI) data measures variations in the intensity of the Earth's magnetic field caused by the contrasting content of rock-forming minerals in the Earth crust. Magnetic anomalies can be either positive (field stronger than normal) or negative (field weaker) depending on the susceptibility of the rock. The data are processed via standard methods to ensure the response recorded is that due only to the rocks in the ground. The results produce datasets that can be interpreted to reveal the geological structure of the sub-surface. The processed data is checked for quality by GA geophysicists to ensure that the final data released by GA are fit-for-purpose. These line dataset from the Clarence-Moreton (Chinchilla), QLD, 1986 survey were acquired in 1986 by the QLD Government, and consisted of 14192 line-kilometres of data at 1500m line spacing and 150m terrain clearance. To constrain long wavelengths in the data, an independent data set, the Australia-wide Airborne Geophysical Survey (AWAGS) airborne magnetic data, was used to control the base levels of the survey data. This survey data is essentially levelled to AWAGS.
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Total magnetic intensity (TMI) data measures variations in the intensity of the Earth's magnetic field caused by the contrasting content of rock-forming minerals in the Earth crust. Magnetic anomalies can be either positive (field stronger than normal) or negative (field weaker) depending on the susceptibility of the rock. The data are processed via standard methods to ensure the response recorded is that due only to the rocks in the ground. The results produce datasets that can be interpreted to reveal the geological structure of the sub-surface. The processed data is checked for quality by GA geophysicists to ensure that the final data released by GA are fit-for-purpose. These line dataset from the Clarence-Moreton (Dalby, Ipswich, Brisbane), QLD, 1986 survey were acquired in 1986 by the QLD Government, and consisted of 35525 line-kilometres of data at 1500m line spacing and 150m terrain clearance. To constrain long wavelengths in the data, an independent data set, the Australia-wide Airborne Geophysical Survey (AWAGS) airborne magnetic data, was used to control the base levels of the survey data. This survey data is essentially levelled to AWAGS.
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Total magnetic intensity (TMI) data measures variations in the intensity of the Earth's magnetic field caused by the contrasting content of rock-forming minerals in the Earth crust. Magnetic anomalies can be either positive (field stronger than normal) or negative (field weaker) depending on the susceptibility of the rock. The data are processed via standard methods to ensure the response recorded is that due only to the rocks in the ground. The results produce datasets that can be interpreted to reveal the geological structure of the sub-surface. The processed data is checked for quality by GA geophysicists to ensure that the final data released by GA are fit-for-purpose. These line dataset from the Cape York (Aurukun, Coen), QLD, 1986 survey were acquired in 1986 by the QLD Government, and consisted of 25998 line-kilometres of data at 1500m line spacing and 150m terrain clearance. To constrain long wavelengths in the data, an independent data set, the Australia-wide Airborne Geophysical Survey (AWAGS) airborne magnetic data, was used to control the base levels of the survey data. This survey data is essentially levelled to AWAGS.
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Gravity data measures small changes in gravity due to changes in the density of rocks beneath the Earth's surface. The data collected are processed via standard methods to ensure the response recorded is that due only to the rocks in the ground. The results produce datasets that can be interpreted to reveal the geological structure of the sub-surface. The processed data is checked for quality by GA geophysicists to ensure that the final data released by GA are fit-for-purpose. This Buchanan Gravity (P199130) contains a total of 410 point data values acquired at a spacing between 1000 and 5000 metres. The data is located in QLD and were acquired in 1991, under project No. 199130 for Bureau of Mineral Resources (BMR); Department of Natural Resources, Mines and Energy (Queensland).
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Gravity data measures small changes in gravity due to changes in the density of rocks beneath the Earth's surface. The data collected are processed via standard methods to ensure the response recorded is that due only to the rocks in the ground. The results produce datasets that can be interpreted to reveal the geological structure of the sub-surface. The processed data is checked for quality by GA geophysicists to ensure that the final data released by GA are fit-for-purpose. This Eumundi Gravity Data (P199140) contains a total of 259 point data values acquired at a spacing between 250 and 2500 metres. The data is located in QLD and were acquired in 1991, under project No. 199140 for None.
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Gravity data measures small changes in gravity due to changes in the density of rocks beneath the Earth's surface. The data collected are processed via standard methods to ensure the response recorded is that due only to the rocks in the ground. The results produce datasets that can be interpreted to reveal the geological structure of the sub-surface. The processed data is checked for quality by GA geophysicists to ensure that the final data released by GA are fit-for-purpose. This Westmoreland Traverse Gravity Survey, Qld 1991 - EPM8182, CR24150 (P199144) contains a total of 71 point data values acquired at a spacing of 200 metres. The data is located in QLD and were acquired in 1991, under project No. 199144 for Western Mining Corporation Ltd.