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The Diamantina River ring feature, Winton region, western Queensland
Abstract
The Diamantina ∼120 km-diameter ring feature, a unique feature in western Queensland, is manifested by a near-360° circular drainage pattern, radial creeks and a coincident radiometric K–Th–U pattern. The structure has been studied in the context of an investigation of the nature and origin of Australian circular structures. Geophysical signatures, including total magnetic intensity (TMI), gravity and seismic reflection transect data from the region of the ring feature are examined to help test the origin of the structure. A western subdued TMI arc with a ∼110 km diameter is offset by ∼30 km eastward from the western rim of the drainage ring. Bouguer anomaly data show a gravity low near the centre of the ring structure, but no outer circular pattern. Two recent seismic transects indicate a moderately reflective to weakly reflective crust below flat lying strata of the Jurassic–Cretaceous Eromanga and Permian–Triassic Galilee basins, and above a usually well-defined ∼39–45 km-deep Moho. An approximately ∼100 km-wide seismically non-reflective to weakly reflective zone overlapping the Diamantina ring feature separates crust of different seismic reflection character to either side. The nature of the seismic non-reflective crust is unknown. A potential interpretation of the ring structure in terms of asteroid impact cannot be confirmed or rejected given the present state of knowledge, owing to (1) the near-30 km depth of the seismically non-reflective zone along the transects; and (2) the shift of the TMI part ring zone relative to the geomorphic expression of the Diamantina ring feature. A test of the nature and origin of the Diamantina ring feature requires a cored drill hole near the centre of the TMI ring structure.
... The lack of strong reflectivity through this zone (labelled D in Figures 8 and 11a) may be a result of local signal attenuation by overlying cover basins (a relatively thick package of Eromanga Basin sediments and Galilee Basin coal measures) or loss of resolution due to unknown changes in the recording environment. Alternatively, Glikson et al. (2016) speculate that the feature results from an asteroid impact in the latest Carboniferous, now reflected at the surface by circular drainage features in the region. However, this timing seems unlikely, as the apparent loss of resolution occurs throughout the whole stratigraphic section, in rocks both older and younger than the Carboniferous (see Figure 8). ...
The report provides an interpretation of the stratigraphic detail and structural architecture revealed by the deep seismic profile 14GA-CF1 which traverses the subsurface extent of the eastern Mount Isa Inlier, as well as imaging its abrupt termination at the southern edge of the North Australian Craton along the Cork Fault. The interpretation includes some discussion of other closely associated seismic and magnetotelluric datasets traversing Northwest Queensland, and discusses inferences that can be drawn on the location of the deeply buried eastern Mount Isa continental margin (the Gidyea Suture).
... According to the global impact crater database, there are eight unconfirmed and unnamed impact craters in Australia. Among them, the Winton crater located in the northeast of Australia, which was first presented by Glikson et al. (2016). The other unconfirmed and unnamed impact craters can be accessed by the world list of unnamed terrestrial craters via Wikiwand (n.d). ...
Remote sensing (RS) can certainly provide deep insights about detecting the terrestrial structure of unknown origin. In this paper, we also detected impact crater of unknown origin in northeast Australia by RS techniques, specifically to enhance the credibility of scientific database on the possible impact craters in the continent of Australia. Following the RS procedures, a circular-shaped unnamed crater, hereafter the Winton crater, was detected with a diameter of approximately 130-km. Furthermore, the topographical parameter was obtained from RS data, which showed that the area, depth and volume of the crater are ~100-m2, ~130-m and ~99.8-m3, respectively. The geological data revealed that inside the crater, the outcrops are mainly consisted of sedimentary and low grade metamorphic rock, specifically included the mixed sediments and conglomerates, limestone and siltstone of the Craterous period. However, the exterior of the circular shaped in the southern part is consisted of unconsolidated deposits of the Tertiary period. The positive value of gravity anomaly for the major part of the crater is 3000 mGal and Bouguer gravity onshore grid has an anomaly of 900 mGal over the impact crater. It showed that the Winton crater could not be the due to any volcanic or karstic processes. On the other hand, a detailed field and petrology investigation should need to distinguish the origin of the crater of old and fossil travertine or an impact crater.
The transition between the North Australian Craton and the Thomson Orogen in the area south of the Mount Isa terrane lies under cover and is a critical element in interpretation of the nature of the Tasmanides. The location of the boundary between these domains is controlled by potential field results; the gravity and magnetic signatures are most sensitive to shallow structure, and so there is little information on structure at depth. Full-crustal reflection profiling crosses the boundary in a few locations but does not provide areal coverage. A deployment of 79 passive seismic stations spanning from southern Queensland into the Mount Isa terrane (AQT experiment) is exploited to examine the variations in crustal thickness and the nature of crustal structure across an area with no prior sampling. The analysis exploits the autocorrelation of the seismic signals that extracts the reflection response from the transmitted signals recorded at the surface, which can be migrated to provide an image of structure at depth. The combination of the active and passive seismic results and other geophysical data indicates that the structure of the northern and central Thomson Orogen is relatively homogeneous with a highly reflective, and magnetic, lower crust suggesting a common substrate across the region. The crust thickens and changes character in the North Australian Craton with variations under cover that can be linked to the areas of exposure. There is a zone approximately 100 km wide that separates the characteristic seismic signatures of the two domains indicating reworking at the craton margin.
• KEY POINTS
• A combination of passive and active seismic imaging sheds light on the transition from the Thomson Orogen to the North Australian Craton.
• The north central Thomson Orogen shows a consistent reflection character with a strong band of lower crustal reflectivity.
• The North Australian Craton shows seismic domains with varying character of reflectivity and crustal thickness.
• A transition zone about 100 km wide separates the distinctive styles of crustal architecture.
The 14-GA-CF1seismic transect adds new detail to previous understandings of the subsurface linkages between the Mount Isa and Georgetown Provinces, including new detail of the longitudinal extent of the Mesoproterozoic? Millungera Basin. The transect also provides the first full crustal image of the continent scale Diamantina Lineament which abruptly terminates the Mount Isa Province at its southern extremity. The latter is revealed as a crustal scale south dipping fault penetrating the MOHO, forming the northern margin of a northeast trending rift-like basin controlling deposition of the earliest Thomson Orogen successions. The northern segment of the seismic profile images the eastern margin of the Mount Isa Inlier as a southeast dipping extensional fault system (displaying some later Isan Orogeny inversion) facilitating development of the (now subsurface) Julia Creek Basin during the latest Paleoproterozoic. The basin extends to a depth of ~6.5secs TWt (~20 kms) and is inferred to comprise mainly of moderately to poorly reflective metasediments, mafic lavas and sills of the Soldiers Cap Group, underlain by a basal relatively non-reflective sequence of uncertain affinity. By comparison with the intersecting 07-GA-IG1 seismic profile, the Julia Creek Basin section is here recognised as being contiguous with the Kowanyama Seismic Province of Korsch & others (2012), while the underlying more reflective lower crustal section is recognised as a continuation of the Numil Seismic Province defined by Korsch & others (2012) from the 07-GA-IG1profile. The now deeply buried Numil crustal layer forming basement to the Julia Creek Basin displays a segmented, block faulted character in the 14-GA-CF1 profile, probably reflecting its fragmentation during basin development prior to its eventual foundering and burial by the Julia Creek Basin succession. An upper more reflective section of the Numil Province crust has also been delineated in the 14-GA-CF1 profile, and has also been recognised in
the orthogonal 07-GA-IG1 deep seismic profile.
A zone running the length of the eastern margin of the Mount Isa Inlier has been identified where discrete Numil-Isa seismic and conductivity contrasts occur. However, no feature similar in character to the Gidyea Suture Zone defining the eastern margin of the Mount Isa Inlier on the 07-GA-IG1 seismic profile has been identified from the 14-GA-CF1
profile crossing the Mount Isa margin further to the northeast. Moreover, the Numil-Isa
basement contrast is not evident at depth across this segment of the Mount Isa margin, where the Isa basement displays more Numil-style characteristics. These features point to a more complex history for the eastern Mount Isa margin than previously proposed, and highlight the need for further careful integration of existing and new geophysical, geological and isotopic datasets to resolve the origin, timing and significance of crustal scale structures underpinning the region.
Circular drainage patterns, round lakes and oval depressions may provide hints of possible underlying ring or dome structures, requiring field tests or drilling where no outcrop occurs (Grieve RAF, Pilkington M, Aust Geol Surv J Aust Geol Geophys 16:399–420, 1996; Glikson AY, Uysal IT, Earth-Sci Rev 125:114–122, 2013). Structural domes and near-circular fold structures may initially be mistaken for impact structures, as are basins of approximately circular or slightly elongate pattern and plutonic domes such as oval granite intrusions, laccoliths and gabbro plugs. In orogenic belts, domes may be produced by compression and associated folding, including folding fold sets with different trends producing domes at the culminations of crossing anticlines. Diapirs are cored by relatively low-density rocks or magma, an example being granite domes rising in response to the gravity instability of the granitic magma relative to the denser country rocks. Circular drainage patterns, round lakes and oval depressions may provide hints of possible underlying ring or dome structures, requiring field tests or drilling where no outcrop occurs (Grieve RAF, Pilkington M, Aust Geol Surv J Aust Geol Geophys 16:399–420, 1996; Glikson AY, Uysal IT, Earth-Sci Rev 125:114–122, 2013). Structural domes and near-circular fold structures may initially be mistaken for impact structures, as are basins of approximately circular or slightly elongate pattern and plutonic domes such as oval granite intrusions, laccoliths and gabbro plugs. In orogenic belts domes may be produced by compression and associated folding, including folding fold sets with different trends producing domes at the culminations of crossing anticlines. Diapirs are cored by relatively low-density rocks or magma, an example being granite domes rising in response to the gravity instability of the granitic magma relative to the denser country rocks.
Deep seismic reflection surveys in north Queensland that were collected in 2006 and 2007 discovered a previously unknown sedimentary basin, now named the Millungera Basin, which is completely covered by a thin succession of sediments of the Jurassic–Cretaceous, Eromanga-Carpentaria Basin. Interpretation of regional aeromagnetic data suggests that the basin could have areal dimensions of up to 280 km by 95 km. Apart from regional geophysical data, virtually no confirmed geological information exists on the basin. To complement the seismic data, new magnetotelluric data have been acquired on several lines across the basin. An angular unconformity between the Eromanga and Millungera basins indicates that the upper part of the Millungera Basin was eroded prior to deposition of the Eromanga-Carpentaria Basin. Both the western and eastern margins of the Millungera Basin are truncated by thrust faults, with well-developed hangingwall anticlines occurring above the thrusts at the eastern margin. The basin thickens slightly to the east, to a maximum preserved subsurface depth of ˜3,370 m. Using sequence stratigraphic principles, three discrete sequences have been mapped. The geometry of the stratigraphic sequences, the post-depositional thrust margins, and the erosional unconformity at the top of the succession all indicate that the original succession across much of the basin was thicker–by up to at least 1,500 m–than preserved today. The age of the Millungera Basin is unknown, but petroleum systems modelling has been carried out using two scenarios, that is, that the sediment fill is equivalent in age to (1) the Neoproterozoic-Devonian Georgina Basin, or (2) the Permian–Triassic Lovelle Depression of the Galilee Basin. Using the Georgina Basin analogue, potential Cambrian source rocks are likely to be mature over most of the Millungera Basin, with significant generation and expulsion of hydrocarbons occurring in two phases, in response to Ordovician and Cretaceous sediment loading. For the Galilee Basin analogue, potential Permian source rocks are likely to be oil mature in the central Millungera Basin, but immature on the basin margins. Significant oil generation and expulsion probably occurred during the Triassic, in response to late Permian to Early Triassic sediment loading. Based on the seismic and potential field data, several granites are interpreted to occur immediately below the Millungera Basin, raising the possibility of hot rock geothermal plays. Depending on its composition, the Millungera Basin could provide a thermal blanket to trap any heat which is generated. 3D inversion of potential field data suggests that the inferred granites range from being magnetic to nonmagnetic, and felsic (less dense) to more mafic. They may be part of the Williams Supersuite, which is enriched in uranium, thorium and potassium, and exposed just to the west, in the Mount Isa Province. 3D gravity modelling suggests that the inferred granites have a possible maximum thickness of up to 5.5 km. Therefore, if granites with the composition of the Williams Supersuite occur beneath the Millungera Basin, in the volumes indicated by gravity inversions, then, based on the forward temperature modelling, there is a good probability that the basin is prospective for geothermal energy.
The high level of endogenic geological activity makes the terrestrial record of impact difficult to read. In their largely uneroded states, terrestrial impact structures have the basic so-called simple and complex forms observed on other planetary bodies, but few of them have morphometric parameters, such as apparent and true depth and stratigraphic uplift, that can be defined. Erosion severely affects such parameters, and can even result in a positive topographic form due to differential erosion. The principal criterion for the recognition of terrestrial impact structures is, therefore, not their form, but the occurrence of shock-metamorphic effects. In addition to a characteristic geological signature, terrestrial impact structures have characteristic geophysical signatures. The most common is a Bouguer gravity low, which extends out to the rim. The magnetic signature can be more varied but generally corresponds to a subdued low. The geophysical, geological, and morphological characteristics at terrestrial impact structures are summarised in tabular form as an aid to the recognition of additional structures.
The Tasmanides of eastern Australia record the break-up of Rodinia, followed by the growth of orogenic belts along the eastern margin of Gondwana. Spatially, the Tasmanides comprise five orogenic belts, with an internal Permian-Triassic rift-foreland basin system. Temporally, the Tasmanides comprise three (super)cycles, each encompassing relatively long periods of sedimentation and igneous activity, terminated by short deformational events. The Neoproterozoic-earliest Ordovician Delamerian cycle began by rifting, followed by convergent margin tectonism and accretion of island-arc forearc crust and ?island arcs in the Middle-Late Cambrian. The Ordovician-Carboniferous convergent margin Lachlan supercycle consists of three separate cycles, each ending in major deformation. The Ordovician Benambran cycle includes convergent (island-arc) and transform margin activity terminated by terrane accretion in the latest Ordovician-earliest Silurian. The Silurian-Middle Devonian Tabberabberan cycle reflects development of a large back-arc basin system, marked by rift basins and granite batholiths, behind intra-oceanic arcs and an Ordovician-Early Devonian terrane that were accreted in the Middle Devonian. The Middle Devonian to Carboniferous Kanimblan cycle began by rifting, followed by continental sedimentation inboard of a major convergent margin system that forms the early part of the Late Devonian-Triassic Hunter Bowen supercycle. This supercycle comprises a Late Devonian-Carboniferous continental arc, forearc basin and outboard accreted terranes and subduction complexes intruded by the roots of a Permian-Triassic continental margin arc. Complex deformation ended with accretion of an intra-oceanic arc in the Early Triassic. Key features of the Tasmanides are: continuity of cycles across and along its length, precluding growth by simple eastwards accretion; development of a segmented plate margin in the Late Cambrian, reflected by major rollback of the proto-Pacific plate opposite the southern part of the Tasmanides; rifting of parts of the Delamerian margin oceanwards, to form substrate to outboard parts of the Tasmanides; the presence of five major Ordovician terranes in the Lachlan Orogen; and the generation of deformations either by the accretion of arcs, the largely orogen-parallel 'transpressive' accretion of Ordovician turbidite terranes (in the Lachlan Orogen), or by changes in plate coupling.
The Proterozoic Mount Isa terrain records the effects of four periods of intraplate tectonism. The c. 1870 Ma Barramundi Orogeny was characterized by a massive felsic magmatic event, and global correlations suggest a physical link between Australia and Laurentia at this time. Thereafter, the terrain underwent an extensional history spanning 200 Ma involving repeated episoded of rifting, post-rift subsidence and associated depositional and magmatic phases. This protracted rifting history resulted in a cumulative stratigraphic thickness of up to 25km above attenuated continental crust. Rifting was interrupted prior to the formation of ocean crust by the compressional Isan Orogeny (1590-1500 Ma). The Isan Orogeny was synchronous with low-pressure high-temperature metamorphism and widespread metasomatism. In the waning stages of shortening, the Mount Isa terrain evolved into a wrench system characterized by an extensive network of strike-slip faults. The current level of exposure in this terrain provides spectacular examples of superimposed rifts, basin inversion, and wrench geometries developed at middle to upper crustal levels.
New insights into the 3D structure, composition and origin of the Mt Ashmore dome, west Bonaparte Basin, Timor Sea, are enabled by reprocessed seismic-reflection data and by optical microscopic, X-ray diffraction (XRD), scanning electron microscopy (SEM)/energy dispersive spectrometry (EDS) and transmission electron microscopy (TEM) analyses of drill cuttings. The structural dome, located below a major pre-Oligocene post-Late Eocene unconformity and above a ∼6 km-deep-seated basement high indicated by marked gravity and magnetic anomalies, displays chaotic deformation at its core and a centripetal kinematic deformation pattern. A study of drill cuttings of Lower Oligocene to Lower Jurassic sedimentary rocks intersected by the Mt Ashmore 1B petroleum-exploration well reveals microbrecciation and extreme comminution and flow-textured fluidisation of altered sedimentary material. The microbreccia is dominated by aggregates of poorly diffracting micrometre to tens of micrometres-scale to sub-millimetre particles, including relic subplanar fractured quartz grains, carbonate, barite, apatite and K-feldspar. A similar assemblage occurs in fragments in basal Oligocene sediments, probably derived from the eroded top section of the dome, which protrudes above the unconformity. SEM coupled with EDS show the micrometre to tens of micrometres-scale particles are characterised by very low totals and non-stoichiometric compositions, including particles dominated by Si, Al–Si, Si–Ca–Al, Si–Al–Ca, Si–Mg, Fe–Mg–Ca, Fe–Mg and carbonate. XRD analysis identifies a high proportion of amorphous poorly diffracting material. TEM indicates internally heterogeneous, fragmented and recrystallised structure of the amorphous grains, which accounts for the low totals in terms of the high-volatile and porous nature of the particles. Another factor for the low totals is the uneven thin-section surfaces which affect the totals. No volcanic material or evaporites were encountered in the drillcore, militating against interpretations of the structure in terms of magmatic intrusion or salt diapirism. Such models are also inconsistent with the strong gravity and magnetic anomalies, which signify a basement high below the dome. An interpretation of the dome in terms of a central rebound uplift of an impact structure can not be proven due to the lack of shock metamorphic effects such as planar deformation features, impact melt or coesite. However, an impact model is consistent with the chaotic structure of the domal core, centripetal sense of deformation, microbrecciation, comminution and fluidisation of the Triassic to Eocene rocks. In this respect, an analogy can be drawn between the Mt Ashmore structural dome and likely but unproven impact structures formed in volatile (H2O, CO2)-rich sediments where shock is attenuated by high volatile pressure, such as Upheaval Dome, Utah. In terms of an impact hypothesis the Mt Ashmore dome is contemporaneous with a Late Eocene impact cluster (Popigai: D = 100 km, 35.7 ± 0.2 Ma; Chesapeake Bay: D = 85 km, 35.3 ± 0.1 Ma).
By virtue of its large area of exposure of different crustal levels, and preservation of a protracted (400 million years) Palaeoproterozoic to Mesoproterozoic tectonic evolution, the Mt Isa Inlier is an excellent natural laboratory to study Proterozoic tectonic processes. The inlier preserves evidence of intracontinental basin development, plutonism, low-pressure metamorphism, orogenesis at different crustal levels, and crustal-scale metasomatism. In addition, the Mt Isa Inlier is endowed with a variety of ore deposits, including the Mt Isa Pb – Zn – Ag and Cu deposits, Century Zn – Pb – Ag deposit, Cannington Ag – Pb – Zn deposit, and the Osborne and Ernest Henry iron oxide Cu – Au deposits. Basement rocks were deformed and metamorphosed during the ca 1900 – 1870 Ma Barramundi Orogeny and intruded by the granitic rocks of the ca 1850 Ma Kalkadoon and Ewen Batholiths and their coeval Leichhardt Volcanics. Three stacked and superimposed superbasins evolved between ca 1800 and ca 1595 Ma. These basins evolved in an environment characterised by elevated heat flow and transient episodes of magmatism and basin inversion in an inferred continental backarc setting. The ca 1600 – 1500 Ma Isan Orogeny probably records two phases of orogenesis. The first phase (ca 1600 – 1570 Ma) involved approximately north – south to northwest – southeast shortening in which a northwest-vergent fold-thrust belt evolved in the Eastern Fold Belt and localised basin inversion occurred in the Western Fold Belt. The second phase (ca 1550 – 1500) involved thick-skinned deformation in the Eastern and Western Fold Belts, characterised by upright folding, reverse faulting, and dextral wrenching. Voluminous granites were emplaced throughout the Eastern Fold Belt between ca 1550 and 1500 Ma. Exhumation and cooling of the crustal pile following the Isan Orogeny were related to crustal extension and widespread erosion in eastern and southern Australia. Subtle reactivation of faults within the inlier following the Isan Orogeny records the distal effects of Mesoproterozoic to Neoproterozoic breakup events and orogenesis in central Australia.
The Shoemaker impact structure, on the southern margin of the Palaeoproterozoic Earaheedy Basin, with an outer diameter of similar to ~30 km, consists of two well-defined concentric ring structures surrounding a granitoid basement uplift. The concentric structures, including a ring syncline and a ring anticline, formed in sedimentary rocks of the Earaheedy Group. In addition, aeromagnetic and geological field observations suggest that Shoemaker is a deeply eroded structure. The central 12 km-diameter uplift consists of fractured Archaean basement granitoids of syenitic composition (Teague Granite). Shock-metamorphic features include shatter cones in sedimentary rocks and planar deformation features in quartz crystals of the Teague Granite. Universal-stage analysis of 51 sets of planar deformation features in 18 quartz grains indicate dominance of sets parallel to omega (10 (1) over bar3}, but absence of sets parallel to pi (10 (1) over bar2}, implying peak shock pressures in the range of 10-20 GPa for the analysed sample. Geophysical characteristics of the structure include a -100 mus(-2) gravity anomaly coincident with the central uplift and positive circular trends in both magnetic and gravity correlating with the inner ring syncline and outer ring anticline. The Teague Granite is dominated by albite-quartz-K-feldspar with subordinate amounts of alkali pyroxene. The alkali-rich syenitic composition suggests it could either represent a member of the Late Archaean plutonic suite or the product of alkali metasomatism related to impact-generated hydrothermal activity. In places, the Teague Granite exhibits partial to pervasive silicification and contains hydrothermal minerals, including amphibole, garnet, sericite and prehnite. Recent isotopic age studies of the Teague Granite suggest an older age limit of ca 1300 Ma (Ar-Ar on K-feldspar) and a younger age limit of ca 568 Ma (K-Ar on illite-smectite). The significance of the K-Ar age of 568 Ma is not clear, and it might represent either hydrothermal activity triggered by impact-related energy or a possible resetting by tectonothermal events in the region.
Abundant evidence now shows that the buried Chicxulub structure in northern Yucatan, Mexico, is indeed the intensely sought-after source of the ejecta found world-wide at the Cretaceous-Tertiary (K/T) boundary. In addition to large-scale concentric patterns in gravity and magnetic data over the structure, recent analyses of drill-core samples reveal a lithological assemblage similar to that observed at other terrestrial craters. This assemblage comprises suevite breccias, ejecta deposit breccias (Bunte Breccia equivalents), fine-grained impact melt rocks, and melt-matrix breccias. All these impact-produced lithologies contain diagnostic evidence of shock metamorphism, including planar deformation features in quartz, feldspar, and zircons; diaplectic glasses of quartz and feldspar; and fused mineral melts and whole-rock melts. In addition, elevated concentrations of Ir, Re, and Os, in meteoritic relative proportions, have been detected in some melt-rock samples from the center of the structure. Isotopic analyses, magnetization of melt-rock samples, and local stratigraphic constraints identify this crater as the source of K/T boundary deposits.
There is now a comprehensive coverage of magnetic and gravity potential-field datasets for the Australian region. Onshore government regional airborne magnetic surveys and ground gravity surveys commenced about fifty years ago, and these datasets now cover the whole continent. Marine magnetic and gravity data have been acquired over the same period, and recently these data have been combined with the onshore data to provide single coherent compilations for much of the Australian region. Digital processing, enhancement and display of these datasets provide geoscientists with an unparalleled opportunity to unravel the tectonic framework of the Australian Plate, particularly in areas obscured by recent cover material. The datasets are being used extensively in the minerals, petroleum, coal, groundwater, environmental and educational industries. This paper discusses several enhancements of the national magnetic and gravity datasets in comparison to the geophysical interpretation published as the Australian Crustal Elements map. A detailed example, the Tasman Line in the Broken Hill region, shows how these datasets can be used to interpret geology under cover.
The basement rocks of the southern Mount Isa terrane are concealed under younger sedimentary units and its crustal architecture is understood using constrained regional potential field analysis. Prominent N-S- to NNW-trending geophysical anomalies extend for ∼250 km south of the exposed Mount Isa Inlier and are abruptly terminated by the NE-trending Cork Fault. Palaeoproterozoic basinal successions and major Palaeo- to Mesoproterozoic structures recorded in the Mount Isa Inlier are interpreted to continue southward under the Palaeozoic cover. The intensely positive geophysical signature of the region is mostly attributed to shallowing of the Barramundi-aged basement and distribution of metamorphosed sedimentary and volcanic rocks deposited during the formation of the ca. 1790–1730 Ma Leichhardt Superbasin. Regional low magnetic and low gravity responses may reflect basinal sequences deposited during the formation of the ca. 1725–1690 Ma Calvert Superbasin and the ca. 1675–1595 Ma Isa Superbasin. Short wavelength magnetic anomalies and co-located low intensity Bouguer gravity anomalies are interpreted to represent shallow and variously magnetized granitic intrusions.
For over 35 years, deep seismic reflection profiles have been acquired routinely across Australia to better understand the crustal architecture and geodynamic evolution of key geological provinces and basins. Major crustal-scale breaks have been interpreted in some of the profiles, and are often inferred to be relict sutures between different crustal blocks, as well as sometimes being important conduits for mineralising fluids to reach the upper crust. The widespread coverage of the seismic profiles now allows the construction of a new map of major crustal boundaries across Australia, which will better define the architecture of the crustal blocks in three dimensions. It also enables a better understanding of how the Australian continent was constructed from the Mesoarchean through to the Phanerozoic, and how this evolution and these boundaries have controlled metallogenesis. Starting with the locations in 3D of the crustal breaks identified in the seismic profiles, geological (e.g. outcrop mapping, drill hole, geochronology, isotope) and geophysical (e.g. gravity, aeromagnetic, magnetotelluric) data are used to map the crustal boundaries, in plan view, away from the seismic profiles. For some of these boundaries, a high level of confidence can be placed on the location, whereas the location of other boundaries can only be considered to have medium or low confidence. In other areas, especially in regions covered by thick sedimentary successions, the locations of some crustal boundaries are essentially unconstrained, unless they have been imaged by a seismic profile. From the Mesoarchean to the Phanerozoic, the continent formed by the amalgamation of many smaller crustal blocks over a period of nearly 3 billion years. The identification of crustal boundaries in Australia, and the construction of an Australia-wide GIS dataset and map, will help to constrain tectonic models and plate reconstructions for the geological evolution of Australia, and will provide constraints on the three dimensional architecture of Australia. Deep crustal-penetrating structures, particularly major crustal boundaries, are important conduits to transport mineralising fluids from the mantle and lower crust into the upper crust. There are several greenfields regions across Australia where deep crustal-penetrating structures have been imaged in seismic sections, and have potential as possible areas for future mineral systems exploration.
The diameter of the Woodleigh impact structure within the Gascoyne Platform, on the Southern Carnarvon Basin in Western Australia, is estimated at 120 km from gravity and magnetic data, making it the largest impact structure discovered on the Australian continent. The structure has its centre at 26°03'25"S and 114°39'50"E, about 50 km east of Hamelin Pool. The structure is evident only from geophysical data because it is buried by up to 600 m of Jurassic–Tertiary sedimentary rock. The age of the impact is best constrained between the
Middle Devonian and Early Jurassic by the regional stratigraphy.
Gravity data indicate a multi-ring feature with an inner ring anomaly about 25 km in diameter, which is interpreted as the central uplift of a complex impact structure. There is good coincidence between the concentric annular gravity lows and highs and the troughs and ridges on seismic data. The outermost diameter corresponds to the abrupt truncation of the northerly trending Wandagee and Ajana Ridges. The eastern margin of the structure is defined by an arcuate magnetic anomaly, coincident with a drainage divide, implying recent reactivation
along a bounding ring fault. The southeast–northwest asymmetry of gravity anomalies within the structure is interpreted as the combined effect of different rock types within the impact site and post-impact tectonism during the Early Cretaceous. The latter reactivated faults along the Wandagee–Ajana Ridges,
producing a regional tilt to the northwest and probably allowing the southeastern side of the structure to be eroded.
A ground magnetic survey over the centre of the structure detected a magnetic dipole anomaly sourced from a shallow part of the central uplift. Modelling of this anomaly is too poorly constrained to provide an independent age for the structure. Seismic data show intense deformation up to 25 km from the centre and only minor deformation to the outer rim — a pattern of deformation consistent with other impact structures in which the inner third to one half has undergone intense deformation.
The discovery of large asteroid impact structures, likely and possible impact structures, onshore and offshore the Australian continent (Woodleigh [120 km; similar to 360 Ma], Gnargoo [75 km; Lower Permian - upper Cretaceous], Tookoonooka [55-65 km; similar to 125 Ma], Talundilly [similar to 84 km; similar to 125 Ma], Mount Ashmore [>100 km; end-Eocene] and Warburton twin structures [>400km; pre-end Carboniferous]) requires re-examination of the diagnostic criteria used for their identification. Bouguer anomalies of established impact structures (Chicxulub [170 km; 64.98 +/- 0.05 Ma], Woodleigh impact structure and Gnargoo probable impact structure display a unique structural architecture where pre-impact structural ridges are intersected and truncated by the outer ring of the circular structure. Seismic reflection data outline circular central uplift domes, basement plugs and rim synclines. Sharp circular seismic tomography anomalies indicate low velocity columns under both the Woodleigh impact structure and Warburton probable impact, hinting at deep crustal fracturing. Deformed, curved and clouded intra-crystalline planar deformation features in quartz (Qz/PDFs), displaying Miller indices ({10-11}, {10-12}, {10-13}) diagnostic of shock metamorphism, abound around exposed established impact structures (Vredefort [298 km; 2023 +/- 4 Ma], Sudbury [similar to 250 km; 1850 +/- 3 Ma], Charlevoix [54 km; 342 +/- 15 Ma], Manicouagan [100 km; 214 +/- 1 Ma]), Tookoonooka and Talundilly). Deformed Qz/PDFs allow recognition of shock metamorphism in buried impact structures, where original Qz/PDFs were bent, recrystallized and/or clouded during formation of the central uplift and hydrothermal activity triggered by the impact. Planar deformation in quartz can also occur in explosive pyroclastic units but are limited to Boehm lamella (Brazil twins) with single lamella sets {0001}. It has been suggested that a class of microstructures in quartz, referred to as metamorphic deformation lamella (Qz/MDL), occur in endogenic tectonic-metamorphic terrains. However, no type locality has been established for Qz/MDL of non-impact origin.
This paper reports geophysical anomalies and intra-crystalline quartz lamellae in drill cores from the Warburton West Basin overlapping the border of South Australia and the Northern Territory. The pre-Upper Carboniferous ~ 450x300 km-large Warburton Basin, north-eastern South Australia, is marked by distinct eastern and western magnetic, gravity and low-velocity seismic tomography anomalies. Quartz grains from arenite core samples contain intra-crystalline lamellae in carbonate-quartz veins and in clastic grains, similar to those reported earlier from arenites, volcanic rocks and granites from the Warburton East Basin. Universal stage measurements of quartz lamellae in both sub-basins define Miller-Bravais indices of {10-12} and {10-13}. In-situ quartz lamellae occur only in pre-late Carboniferous rocks whereas lamellae-bearing clastic quartz grains occur in both pre-late Carboniferous and post –late Carboniferous rocks – the latter likely redeposited from the pre-late Carboniferous basement. Quartz lamellae in clastic quartz grains are mostly curved and bent either due to tectonic deformation or to re-deformation of impact-generated planar features during crustal rebound or/and post-impact tectonic deformation. Seismic tomography low-velocity anomalies in both West and East Warburton Basin suggest fracturing of the crust to depths of more than 20 km. Geophysical modelling of the Cooper Basin, which overlies the eastern Warburton East Basin, suggests existence of a body of high-density (~ 2.9-3.0 gr/cm3) and high magnetic susceptibility (SI ~ 0.012-0.037) at depth of ~ 6-10 km at the centre of the anomalies. In the Warburton West Basin a large magnetic body of SI = 0.030 is modelled below ~ 10 km, with a large positive gravity anomaly offset to the north of the magnetic anomaly. In both the Warburton East and Warburton West the deep crustal fracturing suggested by the low velocity seismic tomography complicates interpretations of the gravity data. Universal Stage measurements of quartz lamellae suggest presence of both planar deformation features of shock metamorphic derivation and deformed planar lamella. The latter may be attributed either to re-deformation of impact-generated lamella, impact rebound deformation or/and post impact tectonic deformation. The magnetic anomalies in the Warburton East and West sub-basins are interpreted in terms of (1) presence of deep seated central mafic bodies; (2) deep crustal fracturing and (3) removal of Devonian and Carboniferous strata associated with rebound of a central uplift consequent on large asteroid impact. Further tests of the Warburton structures require deep crustal seismic transects.
The Eastern Warburton Basin, Northeast South Australia, features major geophysical anomalies, including a magnetic high of near-200 nT centred on a ~ 25 km-wide magnetic low (< 100 nT), interpreted in terms of a magmatic body below 6 km depth. A distinct seismic tomographic low velocity anomaly may reflect its thick (9.5 km) sedimentary section, high temperatures and possible deep fracturing. Scanning electron microscope (SEM) analyses of granites resolves microbreccia veins consisting of micron-scale particles injected into resorbed quartz grains. Planar and sub-planar elements in quartz grains (Qz/PE) occur in granites, volcanics and sediments of the > 30,000 km-large Eastern Warburton Basin. The Qz/PE include multiple intersecting planar to curved sub-planar elements with relic lamellae less than 2 μm wide with spacing of 4–5 μm. Qz/PE are commonly re-deformed, displaying bent and wavy patterns accompanied with fluid inclusions. U-stage measurements of a total of 243 planar sets in 157 quartz grains indicate dominance of ∏{10–12}, ω{10–13} and subsidiary §{11–22}, {22–41}, m{10–11} and x{51–61} planes. Transmission Electron Microscopy (TEM) analysis displays relic narrow ≤ 1 μm-wide lamellae and relic non-sub grain boundaries where crystal segments maintain optical continuity. Extensive sericite alteration of feldspar suggests hydrothermal alteration to a depth of ~ 500 m below the unconformity which overlies the Qz/PE-bearing Warburton Basin terrain. The data are discussed in terms of (A) Tectonic–metamorphic deformation and (B) impact shock metamorphism producing planar deformation features (Qz/PDF). Deformed Qz/PE are compared to re-deformed Qz/PDFs in the Sudbury, Vredefort, Manicouagan and Charlevoix impact structures. A 4–5 km uplift of the Big Lake Granite Suite during ~ 298–295 Ma is consistent with missing of upper Ordovician to Devonian strata and possible impact rebound. The occurrence of circular seismic tomography anomalies below the east Warburton Basin, the Poolowana Basin and the Woodleigh impact structure signifies a potential diagnostic nature of circular tomographic anomalies.
A deep crustal seismic reflection and magnetotelluric survey, conducted in 2007, established the architecture and geodynamic framework of north Queensland, Australia. Results based on the interpretation of the deep seismic data include the discovery of a major, west-dipping, Paleoproterozoic (or older) crustal boundary, considered to be an ancient suture zone, separating relatively nonreflective, thick crust of the Mount Isa Province from thinner, two layered crust to the east. Farther to the east, a second major crustal boundary also dips west or southwest, offsetting the Moho and extending below it, and is interpreted as a fossil subduction zone. Across the region, the lower crust is mostly highly reflective and is subdivided into three mappable seismic provinces, but they have not been tracked to the surface. In the east, the Greenvale and Charters Towers Provinces, part of the Thomson Orogen, have been mapped on the surface as two discrete provinces, but the seismic interpretation raises the possibility that these two provinces are continuous in the subsurface, and also extend northwards to beneath the Hodgkinson Province, originally forming part of an extensive Neoproterozoic–Cambrian passive margin. Continuation of the Thomson Orogen at depth beneath the Hodgkinson and Broken River Provinces suggests that these provinces (which formed in an oceanic environment, possibly as an accretionary wedge at a convergent margin) have been thrust westwards onto the older continental passive margin. The Tasman Line, originally defined to represent the eastern limit of Precambrian rocks in Australia, has a complicated geometry in three dimensions, which is related to regional deformational events during the Paleozoic. Overall, the seismic data show evidence for a continental margin with a long history (Paleoproterozoic to early Mesozoic) but showing only limited outward growth by crustal accretion, because of a repeated history of overthrust shortening during repeated phases of orogenesis.
The Talundilly Structure, southwestern Queensland, Australia, is represented on 2D seismic reflection transects as a major seismic anomaly disrupting the consistent ‘C’ seismic–stratigraphic horizon above the early Cretaceous Bulldog Wallumbilla Formation throughout the Eromanga Basin. The seismic anomalous zone, estimated at 84 km in diameter from the maximum extent of horizon disruption, coincides with a prominent aeromagnetic (TMI) high which is centrally located within a near-circular seismic anomaly of the ‘C’ horizon. The structure consists of a raised central area, with radial faults extending from the central high, an annular synform with disrupted seismic elements dipping at low angles towards the central uplift, and an outer faulted rim. Cuttings from the Talundilly-1 well, drilled ∼30 km northwest from the central high, contain quartz grains with planar deformation features (PDF) indicative of shock metamorphism. The age of the structure, as determined from seismic correlation and sparse palynology, post-dates the ‘C’ seismic horizon and is determined as approximately 125 Ma, coinciding with a marine transgression. Correlation of seismic profiles suggest that the Talundilly impact structure is a possible twin of the Tookoonooka impact structure, dated as 125 ± 1 Ma and located 328 km to the south.
The Gnargoo structure is located on the Gascoyne Platform, Southern Carnarvon Basin, Western Australia, and is buried beneath about 500 m of Cretaceous and younger strata. The structure is interpreted as being of possible impact origin from major geophysical and morphometric signatures, characteristic of impact deformation, and its remarkable similarities with the proven Woodleigh impact structure, about 275 km to the south on the Gascoyne Platform. These similarities include: a circular Bouguer anomaly (slightly less well-defined at Gnargoo than at Woodleigh); a central structurally uplifted area comprising a buried dome with a central uplifted plug; and the lack of a significant magnetic anomaly. Gnargoo shows a weakly defined inner 10 km-diameter circular Bouguer anomaly surrounded by a broadly circular zone, ∼75 km in diameter. The north–south Bouguer anomaly lineament of the Giralia Range (a regional topographic and structural feature) terminates abruptly against the outer circular zone which is, in turn, intersected on the eastern flank by the Wandagee Fault. A Keywords: Gnargoo; Southern Carnarvon Basin; gravity anomalies; impact structure; magnetic anomalies; seismic-reflection surveys Document Type: Research Article DOI: http://dx.doi.org/10.1080/08120090500170377 Affiliations: Department of Earth and Marine Sciences, Australian National University, Canberra, ACT, 0200, Australia Publication date: January 1, 2005 $(document).ready(function() { var shortdescription = $(".originaldescription").text().replace(/\\&/g, '&').replace(/\\, '<').replace(/\\>/g, '>').replace(/\\t/g, ' ').replace(/\\n/g, ''); if (shortdescription.length > 350){ shortdescription = "" + shortdescription.substring(0,250) + "... more"; } $(".descriptionitem").prepend(shortdescription); $(".shortdescription a").click(function() { $(".shortdescription").hide(); $(".originaldescription").slideDown(); return false; }); }); Related content In this: publication By this: publisher By this author: Iasky, R. P. ; Glikson, A. Y. GA_googleFillSlot("Horizontal_banner_bottom");
Geoscience Australia and the Australian State and Territory Geological Surveys have systematically surveyed most of the Australian continent over the past 40 years using airborne gamma-ray spectrometry to map potassium, uranium and thorium elemental concentrations at the Earth's surface. However, the individual surveys that comprise the national gamma-ray spectrometric radioelement database are not all registered to the same datum. This limits the usefulness of the database as it is not possible to easily combine surveys into regional compilations or make accurate comparisons between radiometric signatures in different survey areas. To solve these problems, Geoscience Australia has undertaken an Australia-Wide Airborne Geophysical Survey (AWAGS), funded under the Australian Government's Onshore Energy Security Program, to serve as a radioelement baseline for all current and future airborne gamma-ray spectrometric surveys in Australia. The AWAGS survey has been back-calibrated to the International Atomic Energy Agency's (IAEA) radioelement datum. We have used the AWAGS data to level the national radioelement database by estimating survey correction factors that, once applied, minimise both the differences in radioelement estimates between surveys (where these surveys overlap) and the differences between the surveys and the AWAGS traverses. The database is thus effectively levelled to the IAEA datum. The levelled database has been used to produce the first `Radiometric Map of Australia' - levelled and merged composite potassium (% K), uranium (ppm eU) and thorium (ppm eTh) grids over Australia at 100m resolution. Interpreters can use the map to reliably compare the radiometric signatures observed over different parts of Australia. This enables the assessment of key mineralogical and geochemical properties of bedrock and regolith materials from different geological provinces and regions with contrasting landscape histories.
Terrestrial impact craters are examined in terms of their geophysical characteristics which can be used to identify additional impact craters. The geophysical signatures examined include the circular gravity low which is modeled for the cases of bowl-shaped and complex craters. The size of the gravity anomaly for both types of craters is established and modeled with known morphometric parameters of impact structures. The gravity anomaly varies directly with crater diameter and reaches a maximum at about 20-30 mGal at diameters of 20-30 km. The magnetic signatures of the craters are found to vary primarily according to the reduction in susceptibility, and crater structures with diameters of more than 40 km show central high-amplitude anomalies. Seismic techniques such as reflection surveys demonstrate that the subsurface structures of the craters are dominated by brecciation and fracturing. The criteria developed in this study can be employed to evaluate the possibilities that various geophysical anomalies are due to impact.
The discovery of the Woodleigh impact structure, first identified by R. P. lasky, bears a number of parallels with that of the Chlcxulub impact structure of K-T boundary age, underpinning complications inherent in the study of buried impact structures by geophysical techniques and drilling. Questions raised in connection with the diameter of the Woodleigh impact structure reflect uncertainties in criteria used to define original crater sizes in eroded and buried impact structures as well as limits on the geological controls at Woodleigh. The truncation of the regional Ajona - Wandagee gravity ridges by the outer aureole of the Woodleigh structure, a superposed arcuate magnetic anomaly along the eastern part of the structure, seismic-reflection data indicating a central > 37 km-diameter dome, correlation of fault patterns between Woodleigh and less-deeply eroded impact structures (Ries crater, Chesapeake Bay), and morphometric estimates all indicate a final diameter of 120 km. At Woodleigh, pre-hydrothermal shock-induced melting and diaplectic transformations are heavily masked by pervasive alteration of the shocked gneisses to montmorillonite-dominated clays, accounting for the high MgO and low K(2)O of cryptocrystalline components. The possible contamination of sub-crater levels of the Woodlelgh impact structure by meteoritic components, suggested by high Ni, Co, Cr, Ni/ Co and Ni/Cr ratios, requires further siderophile element analyses of vein materials. Although stratigraphic age constraints on the impact event are broad (post-Middle Devonian to pre-Early Jurassic) high-temperature (200-250 degrees C) pervasive hydrothermal activity dated by K-Ar isotopes of illite - smectite indicates an age of 359 +/- 4 Ma. To date neither Late Devonian crater fill, nor impact ejecta fallout units have been identified, although metallic meteoritic ablation spherules of a similar age have been found in the Conning Basin.
During the Permian and Triassic, eastern Australia was part of an active Gondwanaland convergent plate margin. The Bowen and Gunnedah Basins formed in a backarc setting, which was initially extensional, but switched to contractional in the mid-Permian, leading to the development of a major west-directed retroforeland thrust belt in the New England Orogen, and the formation of a major foreland basin phase to the west in the Bowen and Gunnedah Basins. The contractional deformational style is asymmetric, changing from the eastern side of the basins, adjacent to the thrust belt, to the western side of the basins which was not physically affected by the retrothrust belt. In the east, new thrusts are hard-linked to the growing thrust wedge further to the east, which propagated westwards and cannibalised the eastern part of the basin system. In the western part of the basin, however, the transmission of far-field compressional stresses led to the inversion of Early Permian extensional faults as thrusts, along with the development of new thrusts and backthrusts, which are not hard-linked to the retrothrust belt in the east. During the sustained period of rapid subsidence and sedimentation driven by thrust loading in the Bowen and Gunnedah Basins in the Late Permian to Late Triassic, there are several short periods of non-deposition and contraction. The contractional events were usually short-lived, less than a few million years each in duration, in an overall period of subsidence that lasted for 30–35 Ma. It is suggested that shallow to flat subduction over much of this period produced strong coupling across the plate boundary, which allowed the transmission of compressive far-field stresses well into the distal part of the foreland, possibly during times of global plate boundary reorganisation. A final contractional event in the early Late Cretaceous corresponds with the cessation of sedimentation in the Surat Basin, uplift and reactivation of earlier structures.
This handbook of Shock-Metamorphic Effects in Terrestrial Meteorite Impact Structures emphasizes terrestrial impact structures, field geology, and particularly the recognition and petrographic study of shock-metamorphic effects in terrestrial rocks. Individual chapters include: 1) Landscapes with Craters: Meteorite Impacts, Earth, and the Solar System; 2) Target Earth: Present, Past and Future; 3) Formation of Impact Craters; 4) Shock-Metamorphic Effects in Rocks and Minerals; 5) Shock-Metamorphosed Rocks (Impactities) in Impact Structures; 6) Impact Melts; 7) How to Find Impact Structures; and 8) What Next? Current Problems and Future Investigations.
Preliminary results of recent deep seismic and MT surveys and new proposed projects for Northwest Queensland. Queensland Geological Record
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