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Geological interpretation of the deep seismic reflection and magnetotelluric line 08GA-OM1: Gawler Craton-Officer Basin-Musgrave Province-Amadeus Basin (GOMA), South Australia and Northern Territory

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In 2008, as part of its Onshore Energy Security Program, Geoscience Australia, in conjunction with AuScope, Primary Industries and Resources South Australia (PIRSA) and the Northern Territory Geological Survey, acquired 634 km of vibroseis-source, deep seismic reflection data and gravity data along a single traverse from about 25 km southeast of Erldunda in the southern Northern Territory to near Tarcoola in central South Australia. This traverse, 08GA-OM1, followed the Adelaide to Alice Springs railway line, utilising the railway access road, and is referred to as GOMA as it traversed the northern Gawler Craton, eastern Officer Basin, eastern Musgrave Province and the southern Amadeus Basin (Figures 1 to 3). Crustal-scale, magnetotelluric data were also collected along the southern part of the seismic route. Here, we report the results of an initial geological interpretation of the seismic and magnetotelluric data, with the geodynamic implications being discussed by Korsch et al. (2010).
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... A common approach to interpretation of crustal seismic reflection profiles relies on subjective identification of faults, which in most cases are identified as discrete and narrow zones of deformation along which crustal movement was accommodated. However, examples of co-located magnetotelluric and seismic reflection profiles in Australia show that particularly in the mid to lower crust sub-vertical zones of high conductivity cross-cut crustal-scale faults interpreted from seismic sections (Korsch et al., 2010;Thiel et al., , 2015Johnson and Thorne, 2011). There is therefore a need to determine whether or not the results of both techniques can be related to the same geodynamic process (Cook and Jones, 1995), and inform on how different types of inter pretation may better link the two data types. ...
... Structural interpretation of seismic reflectors is carried out in a similar fashion to structural mapping of surface geology, with discrete structures being marked at offsets, terminations or change in direction of reflectors . Lithostratigraphic units are interpreted based on seismic character and named when found outcropping or in drillhole intersections, whilst seismic provinces are termed for interpreted packages with no known surface expression or drillhole intersection, and are generally reserved for mid-lower crustal units (Korsch et al., 2010). Typically, interpretations in the style described above (e.g. ...
... Typically, interpretations in the style described above (e.g. Fraser et al., 2010a;Korsch et al., 2010) are appropriate for brittle deformation styles, whilst only limited attention has been paid to ductile deformation in the lower crust (Torvela et al., 2013), pervasive mass transfer or broad scale alteration processes. Drummond et al. (2006) and more recent studies endorse modification of reflectivity as a key characteristic enabling interpretation of post-formational processes such as magma transfer, hydrothermal alteration or ductile shear fabric development Wise et al., 2015c;Dutch et al., 2016). ...
Article
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Over the last two decades, co-located seismic and magnetotelluric (MT) profiles provided fundamental geophysical data sets to image the Australian crust. Despite their complimentary nature, the data are processed and often interpreted separately without common processes in mind. We here qualitatively compare 2D resistivity inversion models derived from MT and seismic reflection profiles across a region of Archean–Proterozoic Australia to address the causes of variations in seismic response and anomalous conductivity in the crust. We find that there exists a spatial association between regions of low reflectivity in seismic sections and low resistivity in co-located 2D MT modelled sections. These relationships elucidate possible signatures of past magmatic and fluid-related events. Depending on their diffuse or discrete character, we hypothesize these signatures signify fossil melting of the crust due to mafic underplating, magma movement or hydrothermal fluid flow through the crust. The approach discussed herein is a process-oriented approach to interpretation of geophysical images and a significant extension to traditional geophysical methods which are primarily sensitive to a singular bulk rock property or state.
... From west to east, these are the Nawa, Christie and Wilgena Domains. The eastern end of seismic line 13GA-EG1 is at Tarcoola, which intersects the southern end of the north-south 08GA-OM1 seismic line (Korsch et al., 2010). ...
... The interpretation of the western Gawler Craton part of the seismic line showed an overall westward dipping architecture of the main shear zones (Dutch et al., 2015b). The Moho showed deepening in two places from about 42 km in the east to about 53 km depth under the Nawa and Christie Domains (Kennett and Chopping, 2015). In general, the crust shows three layers: a reflective lower crust; a discontinuous, weakly reflective middle crust; and a moderately reflective upper crust . ...
... The Nawa Domain contains a series of northeast-trending shears that dip to the northwest. Further to the northeast in the Nawa Domain, these structures trend east-west with dips to the north (Korsch et al., 2010;Baines et al., 2011). A series of contrasting magnetic signatures, which range from the very high to the very low, appear to wrap around in a large-scale, tight fold at the southwestern end of the Nawa Domain. ...
Article
This paper highlights the complimentary potential field studies that have been done in parallel to the interpretation of the 13GA-EG1 Eucla-Gawler deep crustal reflection seismic line. Gravity and magnetic images have been interpreted and potential field data has been modelled using edge detection, forward modelling and inversions to pick out the main domains and structures. Seismic, MT and drill core analysis has been progressing in parallel to the potential field investigations. The different approach taken here was to allow more freedom and independence in the interpretations originating from the potential field studies, rather than constraining them with a predefined architecture from the seismic interpretation. Initial results show gravity and magnetic worms correlating with interpreted structures and domain boundaries. Inversions show the 3D distribution of magnetic susceptibility and densities associated with major features such as the Mundrabilla Shear Zone and folded feature seen in the Nawa Domain. This paper summarises the main findings from the potential field studies, which, in conjunction with the parallel studies, allows for a more robust understanding of the crustal architecture and assessment of the mineral potential of the region.
... These metasedimentary and meta-igenous rocks are interpreted to overlie or intrude an older basement (Daly et al., 1998), which comprises c. 1920 Ma and c. 2460 Ma orthogneiss (Fanning et al., 2007; Howard et al., 2011b; Reid et al., 2014a). Geophysical data reveal that rocks of the Nawa Domain are deformed by a series of north-east trending structures that are predominantly north-dipping (Korsch et al., 2010; Baines et al., 2011). At least some of the north-dipping structures likely formed during development of the Paleoproterozoic basin, with these basin-bounding structures being reactivated during the Kimban and Kararan orogenic events (Daly et al., 1998; Payne et al., 2008; Betts et al., 2010; Fraser et al., 2012; Cutts et al., 2013), and again during the reworking associated with shear zone reactivation at c. 1450 Ma (Fraser and Lyons, 2006). ...
... At least some of the north-dipping structures likely formed during development of the Paleoproterozoic basin, with these basin-bounding structures being reactivated during the Kimban and Kararan orogenic events (Daly et al., 1998; Payne et al., 2008; Betts et al., 2010; Fraser et al., 2012; Cutts et al., 2013), and again during the reworking associated with shear zone reactivation at c. 1450 Ma (Fraser and Lyons, 2006). The Coober Pedy Ridge Domain is also present in the northern Gawler Craton and is located between the Karari Shear Zone and the Horse Camp Fault (Fig. 1) and represents a pop-up structure formed during deformation on these crustal scale shear zones (Korsch et al., 2010). The Coober Pedy Ridge Domain comprises metasedimentary and meta-igneous rocks with virtually identical characteristics to similar rocks of the Nawa and Fowler domains (Daly et al., 1998), being dominantly clastic sediments formed at c. 1750 Ma and intruded by c. 1730 Ma mafic and felsic igneous rocks (Fanning et al., 2007). ...
... The Karari Shear Zone (KSZ) is a major north-east orientated shear zone in the northern Gawler Craton (Figs. 1 & 2) that is sub-vertical in the western Gawler Craton (Rankin et al., 1989). Based on deep crustal reflection seismic data, Korsch et al. (2010) concluded that the KSZ dips to the north to northwest along the southern margin of the Coober Pedy Ridge, with the northern margin of the Coober Pedy Ridge being defined by a splay from the KSZ, called the Horse Camp Fault (Fig. 2). The exact location of the KSZ to the east of the Coober Pedy Ridge is poorly defined as the structure appears to splay into several subsidiary structures and becomes more deeply buried by younger sediment (Rankin et al., 1989;Fraser et al., 2012). ...
Article
The formation of major Palaeoproterozoic and Mesoproterozoic (Cu)-Au deposits at the metal-rich margins of the Gawler Craton, South Australia, has received a lot of attention, however, the relationship between metal occurrences, the exhumation level of the crust and the structural architecture of the craton margins is less clear. Here, we present results from apatite fission track thermochronology applied to basement rocks at the northern margin of the Gawler Craton, revealing a differential cooling history with respect to the Karari shear zone (KSZ). The KSZ is a major shear zone that extends to the Moho in reflection seismic images and has a prolonged history of high-temperature activity during the Paleoproterozoic and Mesoproterozoic. New apatite fission track data show that samples taken to the north of the KSZ record a significant pulse of Carboniferous cooling, in contrast to the Phanerozoic monotonic slow cooling history documented for the area just south of the KSZ. This Carboniferous cooling signal coincides with a sedimentary hiatus between the Neoproterozoic – Devonian Officer Basin and the late Carboniferous to Early Permian Arckaringa Basin, to the north of the KSZ. Therefore, Carboniferous cooling can be linked with exhumation and fault reactivation of the KSZ at that time, which is interpreted to be associated with far-field compression caused by the Alice Springs Orogeny (~450–300 Ma) of central Australia. Following Carboniferous exhumation, a localized thermal overprint was observed in locations associated with Palaeogene palaeochannels. The extent of Phanerozoic exhumation shows a spatial relation with the location of Au (and/or Cu, Fe) mineralization in the northern Gawler Craton. Areas that were significantly modified by Mesoproterozoic mineralizing events, such as the Olympic IOCG province and the Central Gawler Gold Province, record post-Silurian exhumation histories related to the Alice Springs Orogeny. To the west of these two major mineral provinces, Archaean – early Palaeoproterozoic terranes in the northwestern Gawler Craton with abundant Au (and Cu, Fe) mineral occurrences were not affected by Phanerozoic exhumation and denudation. These relations suggest that the Mesoproterozoic mineralized terranes were more susceptible to Phanerozoic deformation compared to the Archaean – Palaeoproterozoic terranes within the stronger parts of the Gawler Craton. Hence, understanding the timing of fault reactivation and the associated relative exhumation level may provide valuable constraints for ore deposit preservation and mineral exploration within the Gawler Craton.
Article
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Previous thermochronology studies of the northern Gawler Craton have interpreted cooling from mid-crustal temperatures in two phases; either cooling subsequent to a c. 1610–1580 Ma event or over the interval c. 1460–1440 Ma, however the extent and the significance of these ages has been uncertain. We have obtained nine new ⁴⁰Ar/³⁹Ar thermochronological dates on igneous and metamorphic rocks from drill hole samples across the region. The new data show that different fault-bound blocks have different thermal histories, and that cooling to below biotite closure to argon diffusion over the interval c. 1460–1415 Ma was widespread across the region. Arrhenius data from step heating experiments in this study yield closure temperature estimates for biotite samples that range from 436 to 310 °C. Cooling rates ranging from 3 to 5 °C/Myr are widespread across the region, with one block having slightly faster cooling, up to 14 °C/Myr. These rates suggest a combination of cooling related to thermal relaxation and modest erosion rates, with faster cooled zones likely resulting from moderate degrees of active exhumation along shear zone systems. This cooling may be linked to early stages of break-up of the Nuna supercontinent as c. 1460–1415 Ma tectonic activity is also documented across many terranes of the Nuna supercontinent including the Terre Adelie Craton in Antarctica and terranes of Laurentia.
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Craton margins are known to host many major deposit styles across the globe, and constraining the spatial and temporal relation between permissive geometries and thermal drivers for alteration processes are key for identifying prospective terranes. Orthogonal deep crustal reflection seismic profiles provide insight into the three-dimensional crustal architecture of the north-western Gawler Craton, South Australia. Correlating between north-south seismic line 08GA-OM1 and east-west seismic line 13GA-EG1, has enabled the interpretation of a major crustal boundary separating the core of the Gawler Craton from re-worked crustal provinces to the west and north. We use seismic character, potential fields and magnetotellurics to locate and constrain the geometry of this major boundary, and isotopic signatures from sparse drillholes to characterize the crustal age and composition either side of the interpreted boundary. In recent years, isotopic evidence has been used to infer the presence of early Palaeoproterozoic oceanic crust having existed between the Gawler and Yilgarn Cratons. We present a new model for the north-western Gawler Craton, locating a transitional region between a cratonic core and this oceanic crust, and suggest that the craton margin was ~100 km inboard of current interpretations.
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Apatite U–Pb thermochronology was applied to granitoid basement samples across the northern Gawler Craton to unravel the Proterozoic, post-orogenic, cooling history and to examine the role of major fault zones during cooling. Our observations indicate that cooling following the ∼2500 Ma Sleaford Orogeny and ∼1700 Ma Kimban Orogeny is restricted to the Christie and Wilgena Domains of the central northern Gawler Craton. The northern Gawler Craton mainly records post-Hiltaba Event (∼1590 Ma) U–Pb cooling ages. Cooling following the ∼1560 Ma Kararan Orogeny is preserved within the Coober Pedy Ridge, Nawa Domain and along major shear zones within the south-western Fowler Domain. The Nawa Domain samples preserve U–Pb cooling ages that are >150 Ma younger than the samples within the Coober Pedy Ridge and Fowler Domain, indicating that later (∼1300 Ma) fault movement within the Nawa Domain facilitated cooling of these samples, caused by arc collision in the Madura Province of eastern Western Australia. When compared to ⁴⁰Ar/³⁹Ar from muscovite, biotite and hornblende, our new apatite U–Pb ages correlate well, particularly in regions of higher data density. Our data also preserve a progressive younging of U–Pb ages from the nucleus of the craton to the periphery with a stark contrast in U–Pb ages across major structures such as the Karari Shear Zone and the Southern Overthrust, which indicates the timing of reactivation of these major crustal structures. Although this interpolation was based solely on thermochronological data and did not take into account structural or other geological data, these maps are consistent with the structural architecture of the Gawler Craton and reveal the thermal footprint of known tectonic and magmatic events in the Gawler Craton.
Thesis
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This thesis is directed at exploiting information in the coda of seismic phases and the ambient noise field to provide new constraints on the structure of the Australian Continent. ¶ The exploitation of the immediate coda following the onset of P waves from a distant earthquake using radial receiver functions is now a well established method. The 40 sec interval following P contains reverberations and conversions, by deconvolving the radial component trace with the vertical components, the conversions are emphasized by canceling the part of the response that are common to both components. A member of different styles of such deconvolution, are investigated and a variant of the multitaper method is adopted for subsequent applications. ... ¶ The second part of the thesis is directed at the exploitation of ambient noise or seismic coda to gain information on the Green's function between seismic stations. ¶ ...
Chapter
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Geophysical anomalies are normally attributed to variations in surface petrology. However, corrections are required for variations in the geothermal gradient. In particular, seismic velocities and magnetic anomalies are sensitive to temperature. Consequently, additional geothermal data are required prior to constructing more detailed models of crustal evolution. Heat flow can be correlated with seismic travel time residuals and heat production can be determined using seismic velocities. Magnetic anomalies may be directly related to the Curie Depth but lateral contacts are complicated by geological noise and province boundaries may be obscured.
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