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The crustal architecture as well as the kinematic evolution of the Thomson Orogen in Queensland is poorly resolved because the region is concealed under thick Phanerozoic sedimentary basins and the basement geology is known from limited drill holes. Combined potential field and seismic interpretation indicates that the Thomson Orogen is characterized by prominent regional NE- and NW-trending structural grain defined by long wavelength and low amplitude geophysical anomalies. The ‘smooth’ magnetic signature is interpreted to reflect deeply buried source bodies in the mid- to lower crust. Short wavelength positive magnetic features that correlate with negative gravity anomalies are interpreted to represent shallower granitic intrusions. They appear to be focused along major fault zones that might have controlled the locus for magmatism. The eastern Thomson Orogen is characterized by a prominent NE structural grain and orthogonal faults and fold interference patterns resulting in a series of troughs and highs. The western Thomson Orogen consists of a series of NW-trending structures interpreted to reflect reverse faults. Sedimentation and basin development are interpreted to have initiated in the Neoproterozoic to Early Cambrian during E–W- to ENE–WSW extension, possibly related to the Rodinia break-up. This extensional event was followed by Late Cambrian shortening recorded in the Maneroo Platform and the Diamantina River Domain which possibly correlates with the Delamerian Orogeny. Renewed deposition and volcanism occurred during the Ordovician and may have continued until Late Silurian, resulting in thinned Proterozoic basement crust and extensive basin systems that formed in a distal continental back-arc environment. Our interpretation places the Thomson Orogen to the west of the Neoproterozoic passive margin preserved in the Anakie Inlier. The region is likely to represent the internal extensional architecture during the Rodinia break-up that has been subsequently extensively modified by multiple extensional basin forming events and transient episodes of crustal shortening and basin inversion. [ABSTRACT FROM AUTHOR]

Abstract: This review synthesizes the Proterozoic and early Paleozoic geology of Tasmania, Bass Strait and western and central Victoria. We examine the many different conflicting hypotheses that have been proposed to solve the paradoxical relationships between Tasmanian geology and that of mainland Australia, most notably the prevalence of Proterozoic basement of western and central Tasmania, while immediately across Bass Strait evidence of Proterozoic rocks is much more cryptic. We conclude that the Selwyn block model is the most satisfactory hypothesis to date, since it fits best with the obvious patterns in the magnetic and gravity data. This model proposes that the central Victorian Melbourne Zone is underlain by the northern extension of thin Tasmanian Proterozoic and Cambrian crust under Bass Strait, and that the Silurian to Middle Devonian Melbourne Zone was shortened along a décollement during the Tabberabberan Orogeny. The Ordovician rocks of eastern Tasmania correlate more closely with the Tabberabbera Zone than the Melbourne Zone in Victoria; however the Silurian and Devonian correlations are less certain. Major unresolved issues are the origins of the Proterozoic and Early Cambrian lithostratigraphic packages, tectonic models for their assembly during the Tyennan Orogeny, and how these models fit with those for mainland Australia. [Copyright &y& Elsevier]

Abstract: Structural mapping of poorly exposed shear zone outcrops is integrated with the analysis of aeromagnetic and Bouguer gravity data to develop a multi-scale kinematic and relative overprinting chronology for the Palaeoproterozoic Tallacootra Shear Zone, Australia. D2 mylonitic fabrics at outcrop record Kimban-aged (ca. 1730–1690Ma) N–S shortening and correlate with SZ1 movements. Overprinting D3 sinistral shear zones record the partitioning of near-ideal simple shear and initiated Riedel to regional-scale SZ2 strike-slip on the Tallacootra Shear Zone (SZ2). Previously undocumented NE–SW extension led to the emplacement of aplite dykes into the shear zone and can be correlated to the (ca. 1595–1575Ma) Hiltaba magmatic event. D4 dextral transpression during the (ca. 1470–1450Ma) Coorabie Orogeny reactivated the Tallacootra Shear Zone (SZ2–R4) exhuming lower crust of the northwestern Fowler Domain within a positive flower structure. This latest shear zone movement is related to a system of west-dipping shear zones that penetrate the crust and sole into a lithospheric detachment indicating wholesale crustal shortening. These methods demonstrate the value of integrating multi-scale structural analyses for the study of shear zones with limited exposure. [Copyright &y& Elsevier]

The basement rocks in central Queensland are largely obscured by the Phanerozoic sedimentary succession and direct information comes only from sparse geological data. 2.5D forward modelling of regional aeromagnetic and Bouguer gravity data has been undertaken to unveil the crustal architecture at the junction of the Proterozoic Mount Isa terrane and the Phanerozoic Thomson Orogen in Queensland. The most prominent geophysical character is represented by the abrupt termination of positive NNW-trending geophysical anomalies of the Mount Isa terrane against NE-trending, low amplitude gravity and magnetic anomalies of the Diamantina River Domain of the Thomson Orogen. Potential field forward modelling indicates that the lower basement crust of the Thomson Orogen is petrophysically indistinguishable from the crust of the Proterozoic Mount Isa terrane. We interpret that the prominent gradients associated with the Cork Fault represent the displacement and burial of the Mount Isa terrane crust under the Thomson Orogen. In this context, the Cork Fault is inferred to represent a fundamental crustal discontinuity but does not represent the eastern margin of Rodinia because the Thomson Orogen is floored by Precambrian continental crust. Initiation of the Cork Fault might have occurred as early as the Mesoproterozoic. At that time, the Cork Fault was a major structure that developed during the separation of the Mount Isa terrane and the Curnamona Province. It is inferred that this break-up occurred during initial N-S to NNW-SSE extension. The Cork Fault formed part of a network of major north- and south-dipping normal faults active at that time. The Cork Fault was repeatedly reactivated during the Neoproterozoic Rodinia break-up and during the Phanerozoic evolution of the Tasmanides. We suggest that the segment of the inferred ‘Tasman Line’ along the southern termination of the Mount Isa terrane should be regarded as a set of structures offsetting the Proterozoic crust rather than a simple lineament dividing the Proterozoic and the Phanerozoic Australian continent. [ABSTRACT FROM AUTHOR]

Abstract: The Archaean to Mesoproterozoic basement of northern South Australia is almost completely overlain by thick Neoproterozoic and younger basins (≪1% outcrop), yet is likely to preserve an important record of the interactions between the Archean-Proterozoic Gawler Craton and the Proterozoic Musgrave Province during the amalgamation of Australia in the Proterozoic. However, constraints on the location and geometry of the boundary between these provinces are poor. We use potential field data to determine the 3D basement architecture and so constrain where this Palaeo-Mesoproterozoic boundary may be located beneath the Eastern Officer Basin. We establish the geometry and properties of the overlying basins and explicitly include them during forward and inverse modelling of potential field data to highlight the structure of the underlying basement. Our analysis identifies three crustal domains. (1) Southeast of the steep northeast–southwest Middle Bore Fault, positive gravity and magnetic anomalies are co-located and sourced from bodies in the upper crust, these bodies overlie middle to lower crust that is apparently uniform. (2) Between the Middle Bore Fault and the southern edge of the Munyarai Trough, the highest amplitude gravity and magnetic anomalies are not co-located and are sourced from large northwest dipping bodies. (3) To the northwest, the crust underlying the Munyarai Trough has similar properties to the Musgrave Province, suggesting that the Musgrave Province extends at least 50km beneath the Eastern Officer Basin. Although details of the geology in the second (central) domain are poorly constrained, the domain preserves large crustal-scale Precambrian structures and is interpreted to mark the boundary between the Gawler Craton and the Musgrave Province. In particular, the multiply reactivated Middle Bore Fault forms a major crustal boundary and is interpreted to mark the northern limit of the Gawler Craton. The Middle Bore Fault may have formed as early as the Kimban Orogeny (∼1.7Ga), although substantial reactivation and modification of the crustal architecture could have occurred between the Kimban Orogeny and intrusion of the cross-cutting Gairdner Dolerite Dykes (827Ma). [Copyright &y& Elsevier]

Abstract: High resolution gravity and magnetic data have been acquired across Lake Coragulac, a Quaternary maar volcano located in the Newer Volcanics Province of south-eastern Australia. A gravity low is observed across the maar crater, with several local gravity highs identified in the centre of the crater, often with corresponding magnetic anomalies. Geophysical data has been integrated with geologic observations and subjected to 2D forward and 3D inverse potential field modelling. Modelling has revealed a complex subsurface maar structure with four coalesced diatremes and several intrusive dykes identified. The modelled diatremes are shallow (maximum of 290m deep) with the margins having a similar density to the host rock, while the diatreme centre is often denser, indicating that higher volumes of volcanic debris are present. Deposits of the maar rim sequence show frequent transitions between phreatomagmatic and magmatic fragmentation styles, a result of fluctuations in magma rise rate and interactions with external water. The complex nature of the underlying maar-diatreme suggests that the maar formed from at least four vents which migrated laterally during the eruption. [Copyright &y& Elsevier]