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Isotropic three-dimensional (3-D) inversion has become a standard tool in the interpretation of magnetotelluric (MT) data. 3-D anisotropic inversion codes are under development, yet the number of unknowns increases by a factor of 6 rendering the problem extremely ill-posed. The presence of anisotropy is usually inferred from (i) spurious sequences of conductive and resistive bodies or (ii) comparison with two-dimensional anisotropic modelling approaches. Here, we investigate the 3-D structure of the Gawler Craton down to ∼250 km depth using 282 sites of the AusLAMP array located in the southern half of South Australia. Inversions of the MT impedance as phase tensors and real and imaginary parts result in diverging structures at depths > 70 km. We demonstrate that a unifying model that explains all data types similarly well is suggestive of an anisotropic resistivity structure at the base of the Gawler Craton lithosphere at depths of 120–210 km. Depth location and orientation of the anisotropy agree well with results from the analysis of seismic receiver functions. We suggest that electric anisotropy in the Gawler Craton is a result of lattice-preferred orientation of olivine crystals and metasomatic processes with macroscopic preferential orientation. Our results illustrate that inversion of phase tensor data is superior for the direct imaging of anisotropic resistivity contrasts in otherwise isotropic resistivity models; inversion models obtained with impedances may miss such structures. "Comparable" overall RMS misfits are often meaningless when comparing inversion results for various data types since sensitivities differ between data types. Reliable inversion results consistent with the entire data set can only be recovered if data fits are assessed systematically for all data representations. We also discuss the influence of error settings for phase tensors on the inversion. Our study also revealed that, if persistent across large areas, (i) parallel orientation of phase tensor major axes, (ii) constantly high phase tensor maximum phases or (iii) diverging directions of phase tensor major axes and induction arrows are suggestive of anisotropic structures and corresponding hypotheses should be evaluated. [ABSTRACT FROM AUTHOR]

Mabel Creek Ridge, in the northern Gawler Craton, is a granulite‐facies domain recording early Mesoproterozoic metamorphism, flanked by less metamorphosed rocks and dissected by crustal‐scale divergent structures. The nature of early Mesoproterozoic events is poorly understood due to the lack of basement outcrop. Calculated metamorphic phase diagrams and geochronology are used to decipher the tectonic regime of a potential gneiss dome. Pressure–temperature (P–T) modelling of metapelites from five drill holes across Mabel Creek Ridge suggests it has experienced conditions of ~6.4–7.4 kbar and 800–850°C and the growth of suprasolidus cordierite after garnet indicates subsequent decompression. In situ U–Pb monazite and Lu–Hf garnet geochronology constrains the granulite‐facies metamorphism of Mabel Creek Ridge to ca. 1600–1560 Ma. In contrast, drill hole GOMA DH4 located to the north of Mabel Creek Ridge records conditions of 2.2–5.4 kbar and 710–740°C at ca. 1520 Ma, with no evidence for 1600–1560 Ma metamorphism. Our new P–T pseudosection results and geochronology data from Mabel Creek Ridge and adjacent crust, coupled with the regional seismic and airborne magnetic data, reveal that Mabel Creek Ridge represents a record of early Mesoproterozoic extension in the Gawler Craton, during which thermally perturbed lower crustal rocks were exhumed within a gneiss dome. Early Mesoproterozoic extension took place within a complex geodynamic regime resulting from the interplay between final Nuna convergence along the margin of northeast Australia at ca. 1600 Ma and subduction to the southwest at ca. 1630–1610 Ma. [ABSTRACT FROM AUTHOR]

[Display omitted] • The AusArray SA and Lake Eyre Basin arrays expand seismic coverage in South Australia. • We develop a shear wave model of southern Australia crustal structure to 20 km depth. • We interpret variations in uppermost to mid crustal seismic structure. The rocks of southern Australia record over three billion years of Earth's evolution, but the basement geology is veiled by sediment. Geophysical data are needed to unveil the geology. The 2018–2022 Lake Eyre Basin and 2020–2022 AusArray SA seismic arrays expand seismic coverage in South Australia. In conjunction with permanent and preceding temporary arrays, we extracted Rayleigh wave dispersion data from ambient noise recordings at a total of 501 seismic stations spanning the transition from Precambrian to Phanerozoic Australia. These data were used to develop Rayleigh wave phase velocity maps of southern Australia at periods 3–20 s, and in turn, a shear wave velocity model to 20 km depth. At upper-crustal depths, low velocity structure tracks Phanerozoic sedimentary accumulations. The Moyston Fault, regarded as the boundary between the Delamerian and Lachlan Orogens, has an intermittent expression in the shear velocity model: it has no obvious expression at depths shallower than ∼ 10 km, but in the mid-crust is marked by a velocity contrast in southern Victoria and a velocity contrast tracing the southern edge of the Darling Basin in western New South Wales. An arcuate velocity contrast characterising the western edge of deep, sediment-filled troughs of the Darling Basin is a candidate for the transition from Precambrian to Phanerozoic crust. Fluid derived from neotectonic metamorphic devolatilization and/or remnant hydrated mantle is our preferred hypothesis for explaining seismicity and coincident seismic and conductivity anomalies in the mid-to-lower crust beneath the Ikara–Flinders Ranges. Our model suggests that the Olympic Dam and Carrapateena IOCG deposits reside above the margin of a mid-crustal low seismic velocity zone. We surmise that this might reflect past metalliferous fluid movement associated with the Olympic Cu-Au Province, akin to low reflectivity and low resistivity zones evident in 2D reflection seismic and magnetotelluric profiles, respectively. [ABSTRACT FROM AUTHOR]

Rapid plate motion, alongside pronounced variations in age and thickness of the Australian continental lithosphere, makes it an excellent location to assess the relationship between seismic anisotropy and lithosphere‐asthenosphere dynamics. In this study, SKS and PKS shear‐wave splitting is conducted for 176 stations covering the transition from the South Australian Craton to eastern Phanerozoic Australia. Comparisons are made with models of lithospheric thickness as well as numerical simulations of mantle flow. Splitting results show uniform ENE‐WSW aligned fast directions over the Gawler Craton and broader South Australian Craton, similar to the orientation of crustal structures generated during an episode of NW‐SE directed compression and volcanism ∼1.6 billion years ago. We propose that heat from volcanism weakened the lithosphere, aiding widespread lithospheric deformation, which has since been preserved in the form of frozen‐in anisotropy. Conversely, over eastern Phanerozoic Australia, fast directions show strong alignment with the NNE absolute plate motion. Overall, our results suggest that when the lithosphere is thin (<125 km), lithospheric contributions are minimal and contributions from asthenospheric anisotropy dominate, reflecting shear of the underlying mantle by Australia's rapid plate motion above. Further insights from geodynamical simulations of the regional mantle flow field, which incorporate Australian and adjacent upper mantle structure, predict that asthenospheric material would be drawn in from the south and east toward the fast‐moving continental keel. Such a mechanism, alongside interactions between the flow field and lithospheric structure, provides a plausible explanation for smaller‐scale anomalous splitting patterns beneath eastern Australia that do not align with plate motion. Plain Language Summary: The Australian continent is moving rapidly northward at around 7–8 cm per year. As the continent moves, it is expected to shear or deform the warmer and weaker layer of the Earth below, called the mantle. The actual pattern of deformation within the mantle can be investigated by studying how seismic waves are polarized as they pass through this material. Results show that for one of the geologically oldest regions in Australia, an area in South Australia, the deeper part of the continent here was substantially deformed 1.6 billion years ago. This deformation was likely aided by volcanism that occurred at the same time that would have warmed and weakened the material, making it easier to deform. This material has since cooled and strengthened over time, freezing in the ancient pattern of deformation. Meanwhile in eastern Australia, the continental material here has a much younger geological age (<550 million years old). The results from this region instead show agreement with the present‐day direction of shear due to the fast northward motion of the Australian continent, as initially expected. Key Points: Fossilized anisotropy dominates where lithosphere is old and thick, with deformation of the Gawler Craton from ∼1.6 Ga preservedAsthenospheric shear relating to Australia's fast plate motion dominates where lithosphere is young and thinLithospheric thickness variations likely induce further deviations in mantle flow [ABSTRACT FROM AUTHOR]

Abstract Rapid plate motion, alongside pronounced variations in age and thickness of the Australian continental lithosphere, makes it an excellent location to assess the relationship between seismic anisotropy and lithosphere‐asthenosphere dynamics. In this study, SKS and PKS shear‐wave splitting is conducted for 176 stations covering the transition from the South Australian Craton to eastern Phanerozoic Australia. Comparisons are made with models of lithospheric thickness as well as numerical simulations of mantle flow. Splitting results show uniform ENE‐WSW aligned fast directions over the Gawler Craton and broader South Australian Craton, similar to the orientation of crustal structures generated during an episode of NW‐SE directed compression and volcanism ∼1.6 billion years ago. We propose that heat from volcanism weakened the lithosphere, aiding widespread lithospheric deformation, which has since been preserved in the form of frozen‐in anisotropy. Conversely, over eastern Phanerozoic Australia, fast directions show strong alignment with the NNE absolute plate motion. Overall, our results suggest that when the lithosphere is thin (

The central portion of the Kalinjala Shear Zone, in the Port Neill region, South Australia, is recognised as a northeast-trending anomalously magnetic corridor coinciding with a sub-vertical transpressional dextral shear zone. This shear zone is a primary lithospheric structure, separating the nucleus of the Archean Gawler Craton from a suite of Paleoproterozoic granites (ca 1850 Ma) and earlier paragneiss. At Port Neill, there is an apparent 17 km dextral offset of a pre-existing Bouguer gravity anomaly by the Kalinjala Shear Zone. This is attributed to Kimban-aged (ca 1740–1690 Ma) deformation that is accompanied by peak granulite facies metamorphic conditions reaching pressures of ∼1.0 GPa and temperatures of ∼800 °C. This is consistent with the presence of leucosomes, within the sheared fabric, in the axial surface of mylonitic folds and in mafic gneisses. Strain has been localised within and adjacent to mafic dykes, predominantly hosted in the granitic rocks, with the highest strained areas having the greatest evidence of leucosome extraction. The local orientation of stretching lineations in this shear zone do not necessarily correlate with the transport direction but may reflect along- and across-strike variations in finite shear strain into alternating zones dominated by either constrictional or a superimposed flattening strain. Overprinting the dominant dextral movement are sinistral shears, with horizontal strike-slip movements, which post-date the peak metamorphic assemblages and are generally confined to sites containing late K-feldspar-rich pegmatites. The major movement recorded in the Kalinjala Shear Zone was both horizontal and vertical, occurring in response to regional exhumation of the Cornian-aged (ca 1850 Ma) sequences in the east, during the Kimban Orogeny, and was basically controlled by the nature of lithospheric plate convergence during accretion of a continental backarc onto the Gawler Craton. Dextral transpression with late-sinistral along-strike extension and east-up exhumation is associated with 17 km of horizontal offset along the central section of the Kalinjala Shear Zone. Deformation is dominated by three major Kimban-aged (ca 1730–1690 Ma) events, which overprint older ensialic backarc metasedimentary rocks, orthogneiss and granites of the Donington Suite. Granulite facies metamorphic conditions control the nature of deformation and strain distribution within the shear zone. The Kimban events record the collision of the Gawler Craton nucleus with the southern margin of the North Australian Craton. [ABSTRACT FROM AUTHOR]

Crystallographic preferred orientations of quartz aggregates in mylonitic orthogneisses from the highest strained central region of the Kalinjala Shear Zone, Port Neill South Australia, are products of a combination of constrictional and flattening strains. These rocks were deformed under granulite facies peak metamorphic conditions, reaching pressures of ∼1.0 GPa and temperatures of ∼800 ± 50 °C. Neutron diffraction textural and fabric analysis methods reveal a dominant single c-axis maximum parallel to the Y-strain axis. This is accompanied by a symmetric orthorhombic pattern, where the c-axis fabrics and corresponding pole figure densities of {a}, {m}, {r} and {z} planes are arranged around the XY foliation plane. These fabrics from coexisting adjacent layers suggest that the activation of prism- slip is characteristic for these high-temperature deformation conditions. A small asymmetry in the [c], {a} and {m} pole figures suggests a minor component of dextral shearing. The c-axis pattern is weakened where the foliation is dominated by secondary phases, such as concentrations of biotite mica. The opening angles obtained from cross-girdle c-axis patterns produce temperature estimates that are ∼100 °C lower than the peak metamorphic temperature of ∼800 ± 50 °C, but closer to temperatures related to a component of flattening strain. These c-axis patterns are consistent with other structural characteristics and can be related to the late-stage flattening strains during the Kimban Orogeny. Mylonitic orthogneisses are deformed under granulite facies conditions. Quartz fabrics were measured by bulk neutron diffraction and optical methods. Mylonite c-axis fabrics can be related to the high-temperature deformation and activation of the prism-< a > slip system. Crystal preferred orientations indicate a large component of flattening strain superimposed on the dextral shearing observed in the Kalinjala Shear Zone. [ABSTRACT FROM AUTHOR]

To improve the understanding of the formation and evolution of the sub‐continental lithospheric mantle (SCLM) underlying the South Australian Craton we have conducted a detailed petrological study on >3,000 mantle xenocrysts from 13 kimberlites emplaced across the craton. Pressure (P) and temperature (T) estimates on Cr diopside and garnet have been coupled with their chemical concentrations to constrain lithospheric thickness and chemo‐lithostratigraphy. We show that lithospheric thickness is greatest beneath the Gawler Craton, whereas thinner lithosphere occurs beneath the Adelaide Fold Belt. Mineral compositions highlight two litho‐chemical domains within the shallow and deep SCLM that are separated by a mid‐lithosphere discontinuity (MLD). The shallow SCLM (60–130 km) comprises low Cr2O3 lherzolite and wehrlite. Shallow SCLM xenocrysts record depleted and refertilized compositions enriched in light rare earth elements related to metasomatism by kimberlite or related melts. The mid‐lithosphere (130–160 km) is depleted in garnet and Cr diopside which may relate to a layer of pargasite lherzolite. The deep SCLM (>160 km) comprises high Cr2O3 lherzolite with elevated TiO2 and FeO. We interpret the litho‐chemical stratification of the SCLM to reflect a multi‐stage top‐down growth. The shallow SCLM reflects an amalgamation of Precambrian cratonic nuclei characterized by heterogeneity in geochemical enrichment and depletion. Interaction of the shallow SCLM with mantle plumes accreted melts along the paleo‐lithosphere‐asthenosphere boundary, which now occurs as a MLD. The deep SCLM represents depleted mantle residue formed during mantle plume impingement and thickened during orogenesis. This domain has been metasomatized and refertilized by high‐T melts from the asthenosphere. Key Points: The South Australian Craton comprises three litho‐chemical layers within the shallow, middle and deep lithospheric mantleXenocrysts define a heterogeneously depleted‐kimberlite melt metasomatized shallow sub‐continental lithospheric mantle (SCLM) and fertile‐melt metasomatized deep SCLMThe mid‐lithosphere is a seismic and geochemical discontinuity marked by negative Vp and lower modal proportions of garnet and diopside [ABSTRACT FROM AUTHOR]

Abstract To improve the understanding of the formation and evolution of the sub‐continental lithospheric mantle (SCLM) underlying the South Australian Craton we have conducted a detailed petrological study on >3,000 mantle xenocrysts from 13 kimberlites emplaced across the craton. Pressure (P) and temperature (T) estimates on Cr diopside and garnet have been coupled with their chemical concentrations to constrain lithospheric thickness and chemo‐lithostratigraphy. We show that lithospheric thickness is greatest beneath the Gawler Craton, whereas thinner lithosphere occurs beneath the Adelaide Fold Belt. Mineral compositions highlight two litho‐chemical domains within the shallow and deep SCLM that are separated by a mid‐lithosphere discontinuity (MLD). The shallow SCLM (60–130 km) comprises low Cr2O3 lherzolite and wehrlite. Shallow SCLM xenocrysts record depleted and refertilized compositions enriched in light rare earth elements related to metasomatism by kimberlite or related melts. The mid‐lithosphere (130–160 km) is depleted in garnet and Cr diopside which may relate to a layer of pargasite lherzolite. The deep SCLM (>160 km) comprises high Cr2O3 lherzolite with elevated TiO2 and FeO. We interpret the litho‐chemical stratification of the SCLM to reflect a multi‐stage top‐down growth. The shallow SCLM reflects an amalgamation of Precambrian cratonic nuclei characterized by heterogeneity in geochemical enrichment and depletion. Interaction of the shallow SCLM with mantle plumes accreted melts along the paleo‐lithosphere‐asthenosphere boundary, which now occurs as a MLD. The deep SCLM represents depleted mantle residue formed during mantle plume impingement and thickened during orogenesis. This domain has been metasomatized and refertilized by high‐T melts from the asthenosphere.

This study investigates the age and composition of a suite of mafic dykes in the southeastern Gawler Craton. Mafic dykes intrude the gneissic fabric of the ca 1850 Ma Donington Suite and were previously interpreted to have been emplaced at ca 1845 Ma. However, sensitive high-resolution ion microprobe U–Pb dating of zircon within one of these mafic dykes shows it was emplaced at 1564 ± 4 Ma. The sampled dyke also contains a population of inherited zircon cores with an age of 1770 ± 6 Ma, and one grain with an age of ca 1860 Ma, likely derived from country rock. Whole-rock geochemistry from this dyke and nearby dykes with similar structural and mineralogical features show that there is a suite of dykes in the region with gabbroic, low SiO2 and TiO2 contents and tholeiitic characteristics. The dykes are enriched in Ba, K and Rb, with low to moderate MgO, Ni and Cr contents, and moderate light rare earth element enrichment. Negative Nb and Ta anomalies with subtle negative Ti anomalies suggest some interaction with continental crust. Sm–Nd isotopic data have εNd(1560 Ma) between −6.8 and −2.9, and depleted mantle model ages >2.5 Ga. Th/Nb ratios are 0.21–0.73 consistent with a metasomatised, subduction modified lithospheric mantle source. The relatively primitive nature of the tholeiites suggests the crustal-like signatures are inherited from the source region, which likely represents an enriched continental lithospheric mantle in the eastern Gawler Craton. This ca 1564 Ma mafic magmatism is newly named the Daly Head Metadolerite. In addition, narrow high-strain zones overprint the dated mafic dyke and locally the Donington Suite wall rocks. A syn-kinematic granitic dyke intrusion within one high-strain zone has been dated via laser ablation-inductively coupled plasma mass spectrometry U–Pb zircon methods and was emplaced at ca 1555 Ma. This localised ca 1555 Ma deformation is a previously unrecognised tectonic event in the southern Gawler Craton. This study adds to the growing database showing magmatism and deformation in the Gawler Craton continued after the voluminous Gawler Range Volcanics and Hiltaba Suite magmatism (ca 1596–1575 Ma). These younger tectono-magmatic events typically occur around the margins of the Gawler Craton, suggesting the internal 'core' of the craton may have been substantially less fertile for melting during these younger thermal/structural events, likely because of the high-temperature nature of the early Mesoproterozoic Gawler Range Volcanics and Hiltaba Suite magmatism. Geochronology shows mafic dykes in southeastern Gawler Craton emplaced at 1564 ± 4 Ma. Mafic dykes are tholeiitic, derived from a metasomatised, subduction modified lithospheric mantle source. Narrow high-strain zones overprint the dated mafic dyke and contain syn-kinematic granitic dyke dated at ca 1555 Ma. Localisation of post-ca 1575 Ma tectono-magmatic events occur around margins of the craton, reflecting reduced melt fertility in the centre owing to previous high-temperature events. [ABSTRACT FROM AUTHOR]

The application of finite element analysis is used to simulate the relative distribution and magnitude of stress–strain conditions during a geologically brief, NNW-SSE-oriented, extensional event (1595 Ma to 1590 Ma), co-incident with IOCG-hydrothermal fluid flow and mineralisation across the Mt Woods Inlier, Gawler Craton, South Australia. Differential stress and shear strain maps across the modelled terrane highlight regions that were predisposed to strain localization, extensional failure and fluid throughput during the simulated mineralisation event. These maps are integrated with other datasets and interpretation layers, one of which is a proposed structural–geometrical relationship apparent in many world-class IOCG deposits, including Prominent Hill, Olympic Dam, Sossego, Salobo, Cristalino and Candelaria. These deposits occur at steeply plunging, pipe-like intersections of conjugate extensional systems of faults, shears and/or contacts, wherein the obtuse angle may have been bisected by the maximum principal extensional axis (viz., σ3) during mineralisation. Several other layers are also used for the generation of targets, such as distance from major shear zones, favourable host lithologies, and proximity to tectonostratigraphic contacts of markedly contrasting competency. The result is an integrated target index or heat map for IOCG prospectively across the Mt. Woods Inlier. [ABSTRACT FROM AUTHOR]

Ancient metamorphic processes are recorded by the formation of metallic-Pb nanospheres in zircon, a product of internal Pb mobilisation and thermally driven concentration. Here, metallic-Pb nanospheres formed within an ore deposit are characterised for the first time using high-angle annular dark field scanning transmission electron microscopy and energy-dispersive X-ray spectroscopy element-distribution mapping. Exceptional examples from the migmatite-hosted Archean–Paleoproterozoic Challenger Au deposit (Central Gawler Craton, South Australia) support widespread metallic-Pb nanosphere formation in zircon from rocks experiencing granulite-facies metamorphism. We also report new trace-element associations found with metallic-Pb nanospheres and a new mode of occurrence, in which Sc 'haloes' form adjacent to metallic-Pb nanospheres within the crystalline zircon lattice. This differs to previously characterised examples of metallic-Pb nanospheres associated with amorphous Si-rich glasses and unidentified Al–Ti, or Fe-bearing phases. Multiple modes of metallic-Pb nanosphere occurrences and trace-element associations suggests multiple modes of formation, probably dependant on zircon composition and metamorphic conditions. Identification of metallic-Pb nanospheres in a growing range of geological settings further highlights the mobility of Pb in zircon and the importance of detailed, nanoscale mineral characterisation, in order to constrain accurate geochronological histories for rocks within high-temperature geological environments. [ABSTRACT FROM AUTHOR]

In situ Pb-isotope ratios of alkali feldspars from laser ablation ICP-MS (LA-ICP-MS) were used to constrain melt-sources of the ca 1690–1670 Ma Tunkillia Suite, an important suite of intrusive rocks located in the Archean–Mesoproterozoic Gawler Craton, South Australia. Tunkillia Suite magmatism has been variously attributed to either a supra-subduction or post-collisional setting. A robust interpretation of the Tunkillia Suite's tectonic setting is important for models of the Proterozoic evolution of the Gawler Craton and Australian continent. The Pb-isotopic results indicate a regional variation involving at least two crustal Pb components corresponding to an ancient, U-depleted reservoir in the western Tunkillia Suite and another that reflects mantle–crustal hybridisation. Inheritance of unradiogenic Pb-isotope ratios seen in the western Tunkillia Suite (206Pb/204Pb = 15.060–15.785, 207Pb/204Pb = 15.154–15.426, 208Pb/204Pb = 34.963–35.766) are a globally rare phenomenon that are linked to inheritance from U/Pb-depleted granulites. Pb-isotopic reservoirs containing unradiogenic Pb are among the least melt-fertile sources and are inconsistent with granites generated during continent–continent collision. In contrast, the eastern Tunkillia Suite displays Pb-isotope ratios indicative of crust–mantle mixing, with a volumetrically dominant mantle component (206Pb/204Pb = 15.945–16.143, 207Pb/204Pb = 15.325–15.414, 208Pb/204Pb = 35.330–35.757). These values are consistent with published εNd(1680 Ma) (+2.6 to −2.1) and εHf(1680 Ma) (+5.9 to +0.7) signatures that confirm the role of mantle-melts in the petrogenesis of the Tunkillia Suite. The radiogenic isotopic signatures of the Tunkillia Suite contrast with the syn-collisional granitoids generated from crustal anatexis during the 1730–1700 Ma Kimban Orogeny (εNd(t) −11.7 to −0.7) and are consistent with the arc-related ca 1630 Ma St Peters Suite granitoids (εNd(t) +2.31 to −3.46). In addition, isotopic arrays for the Tunkillia Suite demonstrate a similar mixing phenomenon involved in continental arc magmatism of the Andean Cordillera. We contend that the Tunkillia Suite magmatic event is characterised by widespread crustal–mantle hybridisation, favouring a continental arc-like setting. Pb- and Nd-isotopic similarities of Tunkillia Suite to modern continental arc magmas. The Tunkillia Suite has geochemical similarities to modern continental arc magmas. Inheritance of unradiogenic Pb-isotopic signatures in the Tunkillia Suite require mafic melt hybridisation. The Tunkillia Suite should be reconsidered to reflect the onset of late Paleoproterozoic subduction-related tectonism in the Gawler Craton. [ABSTRACT FROM AUTHOR]

[Display omitted] • Strain distribution across the Eyre Peninsula is heterogeneous. • Dextral transpression occurs in multiple shear zones including Kalinjala. • Granulite metamorphic conditions control the nature of deformation. • Metasediments were pinched-in between basement shear zones. • Post-Kimban brittle structures are related to Gondwana breakup. • Enhances structural correlations with Terre Adélie Land, Antarctica. The southern edge of the Eyre Peninsula, experienced a separation from proto-Antarctica in the Cretaceous and has been projected to extend into Terre Adélie Craton, Antarctica. The Archaean and Palaeoproterozoic rocks of the southern Eyre Peninsula, have been modified by the Kimban Orogeny (~1730 – 1690 Ma) with the development of the regionally extensive Kalinjala Shear Zone, which has been correlated with the Mertz Shear Zone in Antarctica. In this contribution, new structural observations associated with the granulite facies Kalinjala Shear Zone, together with other shear zones, all showing similar kinematics of dextral top-to-the-north transport will be described. The Kimban Orogeny overprints and reworks a major lithospheric boundary between the Gawler Craton and a sequence of preceding events related to the ~ 1850 Ma Cornian Orogeny. Shear zones were initiated during the early stage of the Kimban Orogeny (KD 1) in a dextral simple-shear regime, transitioning into a pure-shear (KD 2) dominated regime. With shortenings of > 90% in the Kalinjala Shear Zone localized into regions containing pre-existing Tourneford Metdolerite Dykes emplaced at ~ 1810 Ma into the granites of the Donington Suite (1850–1843 Ma) and a basement of 2000–1859 Ma paragneisses. Geometrical relationships reveal the operation of oblique extrusion during the Kimban Orogeny, where a coaxial component acted sub-horizontal and orthogonal to the trend of the Kalinjala Shear Zone. Regions of low-strain and a 'pinched-in' and inverted sequence of Mesoproterozoic metasedimentary cover, the Hutchison Supergroup, are bounded by major km-scale shear zones with steep west-dipping tectonic contacts. Post-Kimban subvertical east–west-trending joints and faults record a rifting event which can be related to a Gondwana breakup. With post-rift Neogene fault activity recording additional tectonic episodes where pre-existing basement structures exert significant control on their orientation and distribution. Palaeogeographical reconstructions between the Eyre Peninsula and the Terre Adélie Craton, based on matching basement geology and structural style, are compared and reconciled with this new information. [ABSTRACT FROM AUTHOR]

[Display omitted] • The host granite belongs to the ca. 1860 Ma Donington Suite. • The host granite experienced a thermal event (>350 °C) at ca. 1770 Ma. • Porphyritic volcanic units and polylithic breccias formed at ca. 1590 Ma. • Iron Oxide Copper-Gold mineralisation formed at ca. 1585 Ma. • Uranium mineralisation, post-ore veining and late alteration formed at ca. 600–500 Ma. The Carrapateena Iron Oxide Copper-Gold (IOCG) deposit is located on the eastern margin of the Gawler Craton, approximately ∼475 km NE of Adelaide, South Australia. The deposit is hosted within a granite belonging to the Donington Suite and contains various polylithic breccias and intrusive volcanic units. Multiple stages of alteration/mineralisation are present throughout the deposit, which includes: (1) pre-mineralisation alteration; (2) hematite I; (3) Cu-Au mineralisation; (4) hematite II & REE mineralisation; (5) uranium mineralisation; (6) post-mineralisation alteration/veining. In order to establish a temporal framework, multi-mineral U–Pb geochronology was conducted on a variety of lithologies throughout the deposit and across multiple stages of alteration/mineralisation. Zircons from the host granite are predominantly discordant, with two concordant analyses from two samples producing 207Pb/206Pb ages of ca. 1880–1861 Ma, consistent with the emplacement of the Donington Suite (1860–1850 Ma). Apatite U–Pb geochronology performed on the granite-bearing samples produced ages of ca. 1775–1767 Ma, indicating the presence of a moderate temperature (≥350 °C) thermal event approximately 100 Ma after the crystallisation of the host rock. Zircon U–Pb geochronology conducted on a porphyritic volcanic unit and two polylithic breccia samples produce bi-modal age populations at ca. 1880–1860 Ma & ca. 1590 Ma. The ca. 1880–1860 Ma age reflects zircons inherited from the host granite, while the younger ca. 1590 Ma population represents the crystallisation age of the porphyritic volcanic unit and the maximum formation age of the polylithic breccias. U–Pb geochronology conducted on apatite, hematite and xenotime associated with various stages of mineralisation produce ages of ca. 1585 Ma, consistent with a major Fe-Cu-Au metallogenic event throughout the Gawler Craton. U–Pb geochronology performed on uraninite, apatite located within a late vein, and "vuggy" hematite records a second hydrothermal event from ca. 600–500 Ma, reflecting a period of minor deformation and deposit-wide fluid circulation. [ABSTRACT FROM AUTHOR]

Zircon from spatially and temporally distinct igneous rock units across the Gawler Craton, Australia, show subtle differences in trace and rare earth element ratios. These igneous suites range in composition from granite, rhyolite to gabbro and originate from the ca 2450 Ma Sleaford Complex, the ca 1850 Ma Donington Suite, the ca 1633–1608 Ma St Peter Suite, the ca 1595–1587 Ma Gawler Range Volcanics and the ca 1595–1575 Ma Hiltaba Suite granites. The geochemical characterisation of zircon is carried out on relatively unaltered samples in order to establish primary signatures and to understand the processes controlling the geochemical signatures of the igneous suites. A range of zircon morphologies and internal textures that are preserved in these igneous suites infer the geological history of the host rock, including metamorphism and multiple episodes of zircon saturation suggesting a complex magma evolution. Despite differences in whole-rock geochemistry between igneous suites, zircon largely overlaps geochemically. However, subtle differences in Th/U, U/Hf and (Nb + Ta)/P ratios are evident between the Donington Suite, Gawler Range Volcanics and Hiltaba Suite. This is likely due to the tectonic setting, composition of the crystallising magma and timing of zircon crystallisation in the magma evolution. The subtle geochemical differences in zircon show the potential of using these ratios to aid in provenance studies with large populations of zircon that are of similar age. However, as the dataset is limited and focused only on unaltered samples, further work needs to be undertaken to look at the altered counterparts of these igneous suites. Zircon recovered from unaltered samples of spatially and temporally distinct igneous suites in the Gawler Craton is used here. Th/U, U/Hf and (Nb + Ta)/P ratios of zircon can discriminate the Donington Suite, Gawler Range Volcanics and Hiltaba Suite. Zircon morphologies, internal textures and geochemical characteristics are a value aid to provenance studies. [ABSTRACT FROM AUTHOR]

Abstract The role of lithospheric architecture and the mantle in the genesis of iron oxide copper‐gold (IOCG) deposits is controversial. Using the example of the Precambrian Gawler Craton (South Australia), which hosts the giant Olympic Dam IOCG deposit, we integrate geophysical data (seismic tomography and magnetotellurics) with geological and geochemical data to develop a new interpretation of the lithospheric setting of these deposits. Spatially, IOCG deposits are located above the margin of a mantle lithospheric zone with anomalously high electrical conductivities (resistivity 1.80). The high conductivity cannot be explained by water‐bearing olivine‐rich rock alone. Relatively fertile and metasomatized peridotitic mantle with additional high‐Vp/Vs phases, for example, clinohumite, hydrous garnet, and/or phlogopite, could explain the anomalous velocity and conductivity. The top of this high‐Vp/Vsh zone marks a midlithospheric discontinuity at ~100–130 km depth that is interpreted to reflect locally orthopyroxene‐rich mantle. A sub‐Moho zone with high Vp/Vsh at ~40–80 km depth correlates spatially with primitive Nd isotope signatures and arc‐related ~1,620–1,610 Ma magmatism and is interpreted as the eclogitic root of a magmatic arc. Mafic volcanics contemporaneous with ~1,590 Ma IOCG mineralization have geochemistry suggesting derivation from subduction‐modified lithospheric mantle. We suggest that Olympic Dam formed inboard of a continental margin in a postsubduction setting, related to foundering of previously refertilized and metasomatized lithospheric mantle. Deposits formed during the switch from compression to extension, following delamination‐related uplift and exhumation.

The Mount Woods Domain in the Gawler Craton, South Australia records a complex tectonic evolution spanning the Palaeoproterozoic and Mesoproterozoic. The regional structural architecture is interpreted to represent a partially preserved metamorphic core complex that developed during the ~1600–1580 Ma Hiltaba Event, making this one of the oldest known core complexes on Earth. The lower plate is preserved in the central Mount Woods Domain, which comprises the Mount Woods Metamorphics. These rocks yield a detrital zircon maximum depositional age of ~1860 Ma and were polydeformed and metamorphosed to upper amphibolite to granulite facies during the ~1740–1690 Ma Kimban Orogeny. The upper plate comprises a younger succession (the Skylark Metasediments) deposited at ~1750 Ma. Within the upper plate, sedimentary and volcanic successions of the Gawler Range Volcanics were deposited into half graben that evolved during brittle normal faulting. The Skylark Shear Zone represents the basal detachment fault separating the upper and lower plate of the core complex. The geometry of normal faults in the upper plate is consistent with NE-SW extension. Both the upper and lower plates are intruded by ~1795–1575 Ma Hiltaba Suite granitic and mafic plutons. The core complex was extensively modified during the ~1570–1540 Ma Kararan Orogeny. Exhumation of the western and eastern Mount Woods Domain is indicated by new 40Ar/39Ar biotite cooling ages that show that rock packages in the central Mount Woods Domain cooled past ~300 °C ± 50 °C at ~1560 Ma, which was ~20 million years before equivalent cooling in the western and eastern Mount Woods Domain. Exhumation was associated with activity along major syn-Kararan Orogeny faults. Unlabelled Image • Proterozoic metamorphic core complex has been resolved in a multidisciplinary study. • One of a limited number of Proterozoic core complexes recognised globally. • The core complex is in a poorly exposed, complexly deformed, mineralised terrane. • Will inform IOCG ore genesis models for the Gawler Craton, South Australia. [ABSTRACT FROM AUTHOR]

The Australian continent, being void of active plate boundaries, is often perceived as seismically quiescent. However, earthquakes of moderate magnitude (M6+) occur on the continent around once per decade. Such intra-plate activity can pose a significant risk as these earthquakes can occur along fault lines that are either unknown or considered inactive, are often non-periodic, and poorly understood. Within Australia, the spatial distribution of intra-plate seismicity is non-uniform, instead tending to concentrate along certain weak zones of increased activity. One such region is the eastern margin of the Gawler Craton in South Australia, one of the oldest building blocks of the continent. Recently, several new temporary seismic arrays have been deployed in the region, transforming data coverage across southern Australia. In total, 139 new local earthquakes have been recorded, most of which went undetected by the national seismic network. Following relocation, the pattern of earthquakes becomes more localised and appears to coincide with the edge of the Gawler Craton. Further, a spatial association was found between earthquakes and mound springs, which act as the discharge point for groundwater migrating from the Great Artesian Basin. Enhanced fluid pressures (mantle-degassing) within permeable crustal scale fault systems, responding to a regional contractional strain field, appear to be a key driver of seismicity in the area. [Display omitted] • New earthquake catalog for the Lake Eyre Region is presented. • Seismicity associated with the NE edge of the Gawler Craton. • Left-lateral movement on crustal scale faults due to E-W compression. • Earthquakes associated with springs and discharge of groundwater from the Great Artesian Basin. • Changes in permeability of faults may lead to hydrofracturing. [ABSTRACT FROM AUTHOR]

Combined in situ monazite dating, mineral equilibria modelling and zircon U–Pb detrital zircon analysis provide insight into the pressure–temperature–time (P–T–t) evolution of the western Gawler Craton. In the Nawa Domain, pelitic and quartzo-feldspathic gneisses were deposited after ca 1760 Ma and record high-grade metamorphic conditions of ∼7.5 kbar and 850 °C at ca 1730 Ma. Post-peak microstructures, including partial plagioclase coronae and late biotite around garnet, and subtle retrograde garnet compositional zoning, suggest that these rocks cooled along a shallow down-pressure trajectory across an elevated dry solidus. In the northwest Fowler Domain (Colona Block), monazite grains from pelitic gneisses record two stages of growth/recrystallisation interpreted to represent discrete parts of the P–T path: (1) ca 1710 Ma monazite growth during prograde to peak conditions, and (2) ca 1690 Ma Y-enriched monazite growth/recrystallisation during partial garnet breakdown and cooling towards the solidus. Relict prograde growth zoning in garnet suggests rocks underwent a steep up-P path to peak conditions of ∼8 kbar at 800 °C. The new P–T–t results suggest basement rocks of the southwestern Nawa and northwestern Fowler were buried to depths of 20–25 km during the Kimban Orogeny, ca 10 Myrs after the sedimentary precursors were deposited. The P–T path for the Kimban Orogeny is broadly anti-clockwise, suggesting that at least the early phase of this event was associated with extension. Exhumation of rocks from both the southwestern Nawa and northwestern Fowler domains may have occurred during the waning stages of the Kimban Orogeny (

Abstract The approximate position of a terrane boundary between the Archean–Mesoproterozoic Gawler Craton and the Meso–Neoproterozoic Musgrave Province, central Australia, is currently inferred from magnetic and gravity anomalies. However, its precise location, structural architecture and tectonic attributes are poorly understood. Thick overlying sediments of the Neoproterozoic Officer Basin restrict outcropping basement, and the number of basement-intersecting drill holes across the proposed boundary is limited. The Gawler Craton–Musgrave Province interface is critical to interpreting the tectonic relationship between these adjacent terranes, providing insights into the mechanism of Australian Proterozoic assembly. To assist its geophysical identification, we present 14 new heat flow estimates from the Nawa and Mount Woods Domains of the Gawler Craton, along with the first heat flow value calculated from the eastern Musgrave Province. These estimates are integrated with a magnetotelluric (MT) profile that transects the study area. The new datasets show that a transition exists from heat flow values of 68–89 mW m−2 in the eastern Musgrave Province and northern Nawa Domain, through to higher heat flow values of 93–112 mW m−2 in the southern Nawa and Mount Woods Domains. This transition corresponds to a highly resistive region located between two subvertical conductive bodies observed in the MT data; seismic interpretations from the Gawler Craton–Officer Basin–Musgrave Province–Amadeus Basin (GOMA) profile indicate that it corresponds to a region located between the Sarda Bluff Fault and Karari Shear Zone within the Nawa Domain. We therefore argue that the transition from Musgrave Province to Gawler Craton lithosphere can be mapped on the basis of higher heat flow and electrical conductivity, providing sufficient contrast to constrain this interface more accurately than previous geophysical models based on magnetic and gravity data alone. Highlights • 14 heat flow estimates determined for the northern Gawler Craton. • First heat flow estimate obtained from the eastern Musgrave Province. • New heat flow data integrated with a magnetotelluric profile. • Three zones of distinctive heat flow and electrical resistivity identified. • Transition from Gawler Craton to Musgrave Province lithosphere mapped. [ABSTRACT FROM AUTHOR]

Graphical abstract Highlights • We use isotopic and geophysical data to map the location of a lithospheric boundary. • The boundary separates a Mesoarchaean and a Neoarchaean-Palaeoproterozoic terrane. • The boundary coincides with a low resistivity zone in mid-crust to upper mantle. • The position of the boundary is not reflected by potential field data. • Sub-vertical low resistivity and TMi lineaments reflect Proterozoic deformation. Abstract Major lithospheric boundaries play a fundamental role in localizing crustal deformation and metal enrichment in the crust. Their identification in poorly exposed terranes remains challenging and typically relies on a combination of sparse outcrop and drill hole data extrapolated using regional gravity and magnetic datasets. The high complexity in potential field data as well as the limited depth sensitivity to mostly upper to mid-crustal levels increases the ambiguity in identifying coherent lithospheric domains as well as the trans-lithospheric boundaries that cross into the subcontinental lithospheric mantle. Here we present a different approach using a combination of deep-probing magnetotelluric and seismic reflection methods, integrated with Nd isotope and inherited zircon ages of crustally-derived felsic igneous rocks, to locate and characterize a concealed Archean-Proterozoic lithospheric boundary within the Gawler Craton, South Australia. The boundary extends for approximately ∼600 km in the eastern part of the craton, from the supergiant iron oxide-copper-gold-uranium (IOCG-U) Olympic Dam deposit in the north to outcrops of the Kalinjala Shear Zone on southern Eyre Peninsula in the south. Using our approach we show a significant reduction in the uncertainty of the location of this boundary between these two end-points. While a range of locations are permissible based on potential field data across northern Eyre Peninsula, our integrated approach points towards a precise location east of previous interpretations, beneath the upper crustal Roopena Fault. [ABSTRACT FROM AUTHOR]

Abstract U–Pb monazite and zircon geochronology and calculated metamorphic phase diagrams from drill holes in the northern Gawler Craton, southern Australia, reveal the presence of ca. 1.45 Ga magmatism and metamorphism. Magmatism and granulite facies metamorphism of this age has not previously been recognised in the Gawler Craton. The magmatic rocks have steep LREE-enriched patterns and high Ga/Al values, suggesting they are A-type granites. Calculated metamorphic forward models suggest that this event was associated with high apparent thermal gradients and reached pressures of 3.2–5.4 kbar and temperatures of 775–815 °C. The high apparent thermal gradients may reflect pluton-enhanced metamorphism, consistent with the presence of A-type granites. The recognition of ca. 1.45 Ga tectonism in the northern Gawler Craton is added to a compilation of ca. 1.50–1.40 Ga magmatism, shear zone reactivation, rift basin development and isotope resetting throughout the South and North Australian Cratons that shows that this event was widespread in eastern Proterozoic Australia. This event is stylistically similar to ca. 1.45 Ga A-type magmatism and high thermal gradient metamorphism in Laurentia in this interval and provides further support for a connection between Australia and Laurentia during the Mesoproterozoic. The tectonic setting of the 1.50–1.40 Ga event is unclear but may record rifting within the Nuna (or Columbia) supercontinent, or a period of intracontinental extension within a long-lived convergent setting. Graphical abstract Image 1 Highlights • Drill holes in unexposed northern Gawler Craton reveal ca. 1.45 Ga A-type magmatism and metamorphism. • P–T conditions were 3.2–5.4 kbar and 775–815 °C. • 1.45 Ga tectonism is widespread throughout eastern Proterozoic Australia and southern Laurentia • 1.45 Ga event may reflect rifting within Nuna (Columbia) or a period of intracratonic extension. [ABSTRACT FROM AUTHOR]

[Display omitted] • Novel machine learning-based framework for exploring critical mineral deposits. • Improved generative adversarial network for data augmentation. • Prospectivity maps show a strong correlation with known mineral occurrences. • Models outperform standard random forest classifier. • Geophysical features crucial in mapping prospective critical mineral regions. The demand for critical minerals is rapidly increasing worldwide, yet future global supply remains uncertain due to the difficulty in discovering new deposits using traditional methods. To increase the success rate of exploration projects for these vital resources, the use of artificial intelligence is continuously increasing for big and complex data analysis. This study proposes a new machine learning-based framework that tackles common problems associated with exploring critical mineral deposits, such as the shortage of known mineral occurrences, challenges in selecting negative samples in barren regions, and unbalanced training data. Our framework combines an improved generative adversarial network with positive and unlabelled learning to enhance efficiency. To test the performance of the framework, we create prospectivity maps of mafic–ultramafic intrusion-hosted mineralisation for cobalt, chromium, and nickel in the Gawler Craton, South Australia. The models are trained on a carefully selected set of independent features based on a conceptual model derived from open-access exploration data, resulting in high and stable performance. The prospectivity maps show a strong spatial correlation between high probabilities and known mineral occurrences and predict potential greenfield regions for future exploration. Our models demonstrate a significantly higher accuracy compared to a conventional approach using a standard random forest classifier and reveal that geophysical features play a crucial role in mapping prospective regions of critical minerals. Overall, our framework has the potential to significantly enhance critical mineral exploration by providing a more accurate and efficient approach to identifying prospective regions for future mining operations. [ABSTRACT FROM AUTHOR]

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 40 Ar/ 39 Ar 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. [ABSTRACT FROM AUTHOR]

Three new U Pb ID-TIMS isotopic ages confirm previous evidence for two geochemically distinct, early Mesoproterozoic pulses of mafic magmatism along the western margin of Laurentia. The first is a U Pb baddeleyite age of 1590 ± 5 Ma from a dyke swarm in the Tobacco Root Mountains of western Laurentia. It is the first evidence for magmatism of this age in west-central Laurentia. The second is a U Pb baddeleyite age of 1592.4 ± 2.5 from the Western Channel Diabase, 2000 km to the north in NW Laurentia, which supports two previous U Pb baddeleyite ages of ca. 1590 Ma for these intrusions. The third is a U Pb baddeleyite age of 1551 ± 5 Ma, also from the Tobacco Root Mountains, and provides evidence for a distinct younger pulse of mafic magmatism. We propose that the ca. 1590 Ma mafic intrusions in northwestern and west-central Laurentia represent components of a large igneous province (LIP), which we name the “ca. 1590 Ma Mammoth-Western Channel LIP.” This 1590 Ma LIP is geochemically similar to the contemporaneous volcanic rocks in the Gawler Craton and Curnamona Province of Australia. Furthermore, the 1599 Ma Wernecke Breccias near the Western Channel Diabase are geologically similar to the 1590 Ma Olympic Dam Breccias on the South Australian craton. We propose that a mantle plume at ca. 1590 Ma centered between the Laurentian and Southern Australian cratons, located by converging dyke swarms, fed the intrusions on Laurentia plus the Gawler Range Volcanics, the Hiltaba Suite granites and the Ninnerie Supersuite on the South Australian craton. Additionally, magmatic underplating from the plume set up the hydrothermal system responsible for the formation of the Wernecke and Olympic Dam Breccias. The younger 1551 Ma magmatism in the Tobacco Root Mountains, which shows less contamination of a metasomatized subcontinental lithospheric mantle than the older 1590 Ma pulse, may represent an early stage of rifting that pre-dates the ca. 1470 Ma Belt-Purcell Basin extension of western Laurentia. Felsic magmatism, hypothesized to have accompanied the 1590–1550 Ma LIP magmatism, could be a potential source for detrital zircon, thereby reducing the requirement for a non-Laurentian source for detrital zircon ages within the 1610–1490 Ma “North American Magmatic Gap.” Additionally, the 1590 Ma and 1550 Ma ages on western Laurentia dykes provide tighter constraints for previous paleomagnetic studies. [ABSTRACT FROM AUTHOR]

Abstract: The role of lithospheric architecture and the mantle in the genesis of iron oxide copper‐gold (IOCG) deposits is controversial. Using the example of the Precambrian Gawler Craton (South Australia), which hosts the giant Olympic Dam IOCG deposit, we integrate geophysical data (seismic tomography and magnetotellurics) with geological and geochemical data to develop a new interpretation of the lithospheric setting of these deposits. Spatially, IOCG deposits are located above the margin of a mantle lithospheric zone with anomalously high electrical conductivities (resistivity <10 ohm.m, top at ~100–150 km depth), low seismic shear‐wave velocities (horizontal component, Vsh < 4.6 km/s), and unusually high ratios of compressional‐ to shear‐wave velocities (Vp/Vsh > 1.80). The high conductivity cannot be explained by water‐bearing olivine‐rich rock alone. Relatively fertile and metasomatized peridotitic mantle with additional high‐Vp/Vs phases, for example, clinohumite, hydrous garnet, and/or phlogopite, could explain the anomalous velocity and conductivity. The top of this high‐Vp/Vsh zone marks a midlithospheric discontinuity at ~100–130 km depth that is interpreted to reflect locally orthopyroxene‐rich mantle. A sub‐Moho zone with high Vp/Vsh at ~40–80 km depth correlates spatially with primitive Nd isotope signatures and arc‐related ~1,620–1,610 Ma magmatism and is interpreted as the eclogitic root of a magmatic arc. Mafic volcanics contemporaneous with ~1,590 Ma IOCG mineralization have geochemistry suggesting derivation from subduction‐modified lithospheric mantle. We suggest that Olympic Dam formed inboard of a continental margin in a postsubduction setting, related to foundering of previously refertilized and metasomatized lithospheric mantle. Deposits formed during the switch from compression to extension, following delamination‐related uplift and exhumation. [ABSTRACT FROM AUTHOR]

The ca 1600-1580 Ma time interval is recognised as a significant period of magmatism, deformation and mineralisation throughout eastern Proterozoic Australia. Within the northern Yorke Peninsula in South Australia, this period was associated with the emplacement of multiple phases of the Tickera Granite, an intensely foliated quartz alkali-feldspar syenite, a leucotonalite and an alkali-feldspar granite. These granites belong to the broader Hiltaba Suite that was emplaced at shallow crustal levels throughout the Gawler Craton. Geochemical and isotopic analysis suggests these granite phases were derived from a heterogeneous source region. The syenite and alkali-feldspar granite were derived from similar source regions, likely the underlying ca 1850 Ma Donington Suite and/or the ca 1750 Ma Wallaroo Group metasediments with some contamination from an Archean basement. The leucotonalite is sourced from a similar but more mafic/lower crustal source. Phases of the Tickera Granite were emplaced synchronously with deformation that resulted in development of a prominent northeast-trending structural grain throughout the Yorke Peninsula region. This fabric is associated with composite events resulting from folding, shearing and faulting within the region. The intense deformation and intrusion of granites within this period resulted in mineralisation throughout the region, as seen in Wheal Hughes and Poona mines. The Yorke Peninsula shares a common geological history with the Curnamona Province, which was deformed during the ca 1600-1585 Ma Olarian Orogeny, and resulted in development of early isoclinal and recumbent folds overprinted by an upright fold generation, a dominant northeast-trending structural grain, mineralisation, and spatially and temporally related intrusions. This suggests correlation of parts of the Gawler Craton with the Curnamona Province, and that the Olarian Orogeny also affected the southeastern Gawler Craton. [ABSTRACT FROM AUTHOR]

The Olympic iron oxide-copper-gold province in South Australia contains numerous deposits and prospects, including the Olympic Dam Cu-U-Au-Ag deposit and the Acropolis prospect. The Acropolis prospect comprises massive, coarse-grained magnetite-apatite veins partly replaced by a hematite-stable assemblage. The apatite grains in the veins contain zones with abundant inclusions of other minerals (including monazite and xenotime) and low trace-element concentrations relative to the inclusion-free zones. The inclusion-rich apatite zones are interpreted to be formed from the recrystallisation of the inclusion-free apatite and remobilisation of U, Th and rare earth element (REE) from apatite into monazite and xenotime. Apatite, monazite and xenotime are all established U-Th-Pb geochronometers and offer the potential to constrain the alteration history of the Acropolis prospect. The LA-ICPMS U-Pb age of inclusion-free apatite is within error of the age of the host volcanic units (ca 1.59 Ga). Inclusion-rich apatite yields both near-concordant analyses that are within error of the inclusion-free apatite as well as highly disturbed (discordant) analyses. The most concordant analyses of monazite (Th-Pb) inclusions and xenotime (U-Pb) inclusions and rim grains indicate an alteration event occurred at ca 1.37 Ga and possibly also at ca 500 Ma. The disparity in age of the inclusion-rich apatite and the REE-phosphate inclusions (and rim grains) is suggested to be owing to the apatite being initially recrystallised at ca 1.59 Ga and modified again by a later event that also formed (or coarsened) most of the inclusions. Partial resetting of the majority of the monazite inclusions as well as the presence of significant amounts of common Pb has complicated the interpretation of the monazite results. In contrast, xenotime is a more robust geochronometer in this setting. The ages of the two post-1.59 Ga events that appear to have affected the Acropolis prospect do not correspond to any events known to have occurred in the Gawler Craton. The earlier (ca 1.37 Ga) age instead corresponds best with metamorphic-magmatic-hydrothermal activity in Laurentia, consistent with the proximity of Laurentia and the Gawler Craton inferred from palaeogeographic reconstructions. The later (ca 500 Ma) event corresponds to the Delamerian Orogeny and has been shown by prior studies to have also affected the Olympic Dam deposit. [ABSTRACT FROM AUTHOR]

The Mesoproterozoic Gawler Silicic Large Igneous Province (SLIP) in the Gawler Craton and Curnamona Province, southern Australia, comprises extensive felsic and lesser mafic volcanic sequences, with only limited sedimentary successions. The Roopena Basin is a rare example of a synvolcanic sedimentary basin that formed within the Gawler SLIP in the eastern Gawler Craton. It is a north-south-trending basin with a preserved area of 75 km2, bound by the Roopena and Wizzo Well faults, and contains three units of the lower Gawler Range Volcanics; the Angle Dam Dacite, Fresh Well Formation and Roopena Basalt. The Angle Dam Dacite is a porphyritic lava and the oldest part of the volcanic succession, directly overlying basement. The Fresh Well Formation overlies the Angle Dam Dacite or basement, comprises three coarsening-upwards volcaniclastic packages of claystone, siltstone, fine-grained to coarse-grained lithic sandstone and conglomerate deposited in a fluvio-lacustrine setting, and contains three tuff members. The Roopena Basalt is interlayered with the Fresh Well Formation, and comprises auto-brecciated lavas that exhibit only local interaction with water or wet sediment. Sharp basal contacts of the prograding packages within the Fresh Well Formation provide evidence of rapid flooding events within the basin. New detrital zircon geochronology of a sandstone within the Fresh Well Formation yielded a maximum depositional age of ca 1580 Ma, with provenance dominated by felsic volcanic units of the 1635-1605 Ma St Peter Suite. Sedimentation in the Gawler SLIP appears to have occurred in isolated basins with limited areal extent. It was largely restricted to the eastern Gawler Craton, and as well as the Roopena Basin, and includes similar basins at the Olympic Dam and Prominent Hill iron oxide-copper-gold ± uranium (IOCG ± U) deposits. The coincidence of sedimentation and mafic volcanism in the eastern Gawler Craton suggests that this region underwent extension at this time, although high-temperature metamorphism and compressional deformation occurred in some parts of the Gawler Craton and Curnamona Province synchronous with the Gawler SLIP. The Roopena Basin sedimentary rocks and underlying basement contain hematite-chlorite-sericite-white mica assemblages, permissive of hematite-style IOCG mineral deposits; however, no significant ore deposit has yet been discovered in the Roopena Basin. [ABSTRACT FROM AUTHOR]

Multi-method thermochronology applied to the northern Olympic Domain of South Australia reveals a complex thermal evolution with multiple thermal events. Apatite U/Pb (closure temperature ~550–350 °C) and muscovite 40 Ar/ 39 Ar ages (~400–350 °C) record post magmatic cooling from 1850 to 750 Ma for the ~1850 Ma Donington Suite, and from ~1560–1500 Ma for the ~1590 Ma Hiltaba Suite and the Gawler Range Volcanics. Potassium feldspar 40 Ar/ 39 Ar ages (~350–150 °C) record disturbed spectra that are likely related to hydrothermal alteration at ~1000–650 Ma in the Neoproterozoic Adelaide Rift Complex. Apatite fission track (~60–120 °C), zircon (U-Th-Sm)/He (~180–200 °C), and apatite (U-Th-Sm)/He (~45–75 °C) ages reveal regional low temperature thermal events at ~1000 Ma, ~430–400 Ma, 350–330 Ma, and ~200 Ma, in addition to localised thermal events during the Cretaceous. The ~1000 Ma apatite fission track ages are amongst the oldest recorded for South Australia and are only preserved near the margins of the Olympic Domain. The ~430–400 Ma and ~350–330 Ma cooling events are interpreted to be driven by the Alice Springs Orogeny. The Mesozoic thermochronometric ages are interpreted to record localised thermal perturbations, possibly related with hydrothermal activity within the northern Olympic Domain. The presence of abundant IOCG deposits near these young thermal anomalies may indicate that these zones record more favourable thermal conditions and/or exposure levels for IOCG discoveries in the study area. [ABSTRACT FROM AUTHOR]

• We investigate Moho of eastern margin of Gawler Craton using new passive seismic data. • We test the efficacy of a resonance filter for sediment-impacted receiver functions. • Moho topography is relatively flat and ∼ 46 km deep beneath the Gawler Craton. • Deeper Moho is found for Lake Eyre region (∼ 40 km) reducing contrast with Gawler Craton. • The obtained Moho depths suggest a Proterozoic provenance of Lake Eyre region. In this study, using two recent passive seismic deployments across the Gawler Craton and Lake Eyre Basin, South Australia, we aim to examine the nature and extent of a perceived Moho offset (∼ 15 km) between the two regions using receiver functions. Together the two arrays straddle the edge of the Gawler Craton and present a unique opportunity to understand the crustal thickness variations in a hitherto under-explored region. The task is complicated however by many stations situated atop low-velocity sedimentary rocks, inducing high-amplitude low-frequency reverberations in the receiver function signal, and masking the signal from crust to mantle conversions. We, therefore, employed a resonance removal filter to dampen the sediment reverberation effect which aided the detection of the P-to-S conversion from the Moho. The obtained Moho depths dramatically increased the coverage in observations, particularly in areas inundated by Phanerozoic sediments. We detect the presence of thicker crust beneath the Lake Eyre region than previously imaged (∼ 40 km), that hints towards a shared Proterozoic provenance with building blocks of the South Australian Craton, such as the Curnamona Province. The Moho phase is consistent (∼ 46 km) and clear beneath the Gawler Craton, indicating a contrast with stations in the Lake Eyre region, although the difference with respect to previously reported crustal thickness is now substantially reduced. Our results thus illuminate the crustal structure of an important junction within continental Australia and provide valuable constraints for models of the tectonic evolution of eastern Gondwana and the assembly of Proterozoic Australia. [ABSTRACT FROM AUTHOR]

[Display omitted] • Alteration links the Peake and Denison Domain to the Mount Isa Province at 1500 Ma. • The Peake and Denison Domain is prospective for Isan-style IOCG mineralisation. • Controls on IOCG systems in Mount Isa can aid exploration in Peake and Denison. • Tectonic reconstructions valuable for determining prospectivity near plate margins. Tectonic reconstructions of Proterozoic Australia commonly place the Peake and Denison Domain of the northeastern Gawler Craton at the interface between the North and South Australian cratons prior to the reconfiguration of Australia's main tectonic components in the Mesoproterozoic. However, this reconstruction is largely based on palaeomagnetic data as the geological correlations between these regions are currently limited, particularly during the Mesoproterozoic. The early Mesoproterozoic period is significant as it corresponds to major IOCG mineralization in the eastern Gawler Craton between 1600 Ma and 1575 Ma, and IOCG mineralization in the Mount Isa Province largely between 1550 Ma and 1490 Ma. Therefore, determining the relationship of the Peake and Denison Domain to the Gawler Craton and Mount Isa Province during this period is essential to evaluating mineral prospectivity in the northeastern Gawler Craton. New U–Pb LA-ICP-MS geochronology on zircon and titanite improves our understanding of the tectonothermal and hydrothermal history the Peake and Denison Domain during the late-Palaeoproterozoic, early-Mesoproterozoic and the Cambrian–Ordovician periods. Titanite formed within largely calc-silicate alteration assemblages indicates the Peake and Denison Domain has a protracted history of hydrothermal activity, recording events at c. 1565 Ma, 1530–1515 Ma, c. 1500 Ma, c. 1465 Ma and c. 490 Ma. The highly calcic nature of the c. 1565–1500 Ma alteration in the Peake and Denison Domain shares strong similarities in age and character to the regional calcic-sodic alteration recorded in the Mount Isa Province. We suggest the two regions were influenced by similar hydrothermal systems during the early Mesoproterozoic, supporting reconstruction models that place the Peake and Denison Domain near the Mount Isa Province during the early-Mesoproterozoic. This highlights the prospectivity of the Peake and Denison Domain for Isan-style IOCG mineralization, but requires consideration of the post-1500 Ma rotation of prospective structures. [ABSTRACT FROM AUTHOR]

The far northeastern Gawler Craton, South Australia, lies at the northern margin of one of the major building blocks of the Australian continent and is a region that is important in models for the Proterozoic tectonic evolution of Australia. However, this region is overlain by Phanerozoic sedimentary cover and consequently has had no previous geological study. We report the lithotypes, geochronology, geochemistry and isotopic composition of rocks recovered in a mineral exploration drill hole in the far northeastern Gawler Craton, the sole drill hole to sample crystalline basement in this region. Lithologies within the drill hole are garnet- and pyrite-bearing metasedimentary gneiss, pyroxenite and gabbroic intrusions, along with granitic bodies. Metasedimentary gneiss has a maximum depositional age of 1841 ± 4 Ma and a provenance pattern more similar to rocks of the Aileron Province of the Arunta Region, central Australia, in particular the Lander Rock Formation, than to other metasedimentary rocks of the Gawler Craton. Amphibolite facies metamorphism occurred at c. 1780 Ma and was synchronous with emplacement of high Mg, crustally contaminated mafic rocks, along with several types of felsic intrusion. This metamorphic event is very similar in age and style to the Yambah Event of the Aileron Province, and has not been documented previously in the Gawler Craton. The overall geological features of this portion of the northern Gawler Craton support models that link it with the Aileron Province of the Arunta Region. The rocks of drill hole TB02 underwent thermal resetting recorded by a biotite 40 Ar/ 39 Ar age of c. 480 Ma, likely as a result of the Cambro-Ordovician Delamerian Orogeny along the eastern margin of Gondwana. [ABSTRACT FROM AUTHOR]

New in situ zircon Lu–Hf isotopic data are presented from magmatic rocks distributed across the Gawler Craton, Australia. These rocks range in composition from granite to gabbro, with the majority being granite or granodiorite and moderately peraluminous in composition. The new Lu–Hf isotopic data, together with previously published data, provide insight into the magmatic evolution of the craton and crust and mantle interaction through time. Increased juvenile content of magmatic rocks correlate with periods of extensional tectonism, in particular basin formation and associated magmatism during the Neoarchean to earliest Paleoproterozoic (c. 2555–2480 Ma), Middle Paleoproterozoic (c. 2020–1710 Ma) and Late Paleoproterozoic (c. 1630–160 Ma). In contrast, magmatic rocks associated with periods of orogenic activity show greater proportions of crustal derivation, particularly the magmatic rocks generated during the c. 1730–1690 Ma Kimban Orogeny. The final two major magmatic events of the Gawler Craton at c. 1630–1604 Ma and c. 1595–1575 Ma both represent periods of juvenile input into the Gawler Craton, with ε Hf (t) values extending to as positive as + 8. However, widespread crustal melting at this time is also indicated by the presence of more evolved ε Hf (t) values to − 6.5. The mixing between crust and mantle sources during these two youngest magmatic events is also indicated by the range in two stage depleted mantle model ages (T DM c) between 1.76 Ga and 2.51 Ga. Significant mantle input into the crust, particularly during formation of the c. 1595–1575 Ma Hiltaba Suite and Gawler Range Volcanics, likely facilitated the widespread crustal magmatism of this time period. Viewed spatially, average ε Hf (t) and T DM c values highlight three of the major shear zones within the Gawler Craton as potentially being isotopic as well as structural boundaries. Differences in isotopic composition across the Coorabbie Shear Zone in the western Gawler Craton, the Middle Bore Fault in the northern Gawler Craton and, to a lesser extent, the Kalinjala Shear Zone in the southern Gawler Craton, broadly correspond to crustal and even lithospheric-scale discontinuities evident in geophysical studies. Therefore, these shear zones may approximate some of the first order crustal domains within the Gawler Craton. [ABSTRACT FROM AUTHOR]

The Prominent Hill deposit is a world-class iron oxide copper–gold (IOCG) deposit in South Australia, characterized by a high Cu/S ratio of the dominant Cu-(Fe) sulfides hosted by hematite breccias. It contains a total resource of 278 Mt of ore at 0.98% Cu and 0.75 g/t Au. Prominent Hill is one of several IOCG deposits and numerous prospects in the Olympic IOCG province that are temporally associated with the 1603–1575 Ma Gawler Range Volcanics, a large igneous province including co-magmatic granitoid intrusions of the Hiltaba Suite. Globally, IOCG deposits share many similar features in terms of their geological environment and mineral association. However, it is not yet clear whether sulfur and copper originate from the same source rocks and which hydrothermal redox processes created the characteristic iron oxide enrichment. Highly variable sulfur isotope compositions of sulfides and sulfates in IOCG deposits have previously been interpreted in terms of diverse sulfur sources that may include contributions from magmatic, sedimentary, seawater or evaporitic sulfur. In order to test these alternatives, we performed a detailed sulfur isotope study of Cu-(Fe) sulfides from Prominent Hill and IOCG prospects nearby. The Prominent Hill deposit shows a wide range in δ 34 S V-CDT between − 33.5‰ and 29.9‰ for Cu-(Fe) sulfides, and a narrower range of 4.3‰ to 15.8‰ for barite. Iron sulfides (pyrite, pyrrhotite) show a narrow range in sulfur isotope composition, whereas Cu-bearing sulfides show a much wider range, and more negative δ 34 S V-CDT values on average. We propose a two-stage sulfide mineralization model for the IOCG system in the Prominent Hill area, in which all hydrothermal sulfur is ultimately derived from a magmatic source that had a composition of 4.4 ± 2‰. The diversity in sulfur isotope composition can be produced by different fluid evolution pathways along reducing or oxidizing trajectories. A reduced sulfur evolution pathway is responsible for stage I mineralization, when intrusion-derived magmatic-hydrothermal fluids produced early pyrite and minor chalcopyrite at Prominent Hill, and iron ± copper sulfides in regional magnetite skarns and in some pervasively altered volcanic rocks of the Gawler Range Volcanics. Shallow-venting magmatic-hydrothermal fluids and subaerial volcanic gases that became completely oxidized by reaction with atmospheric oxygen produced sulfate and sulfuric acid with a sulfur isotope composition equal to their magmatic source. This highly oxidized ore fluid probably consisted dominantly of water from the hydrosphere, but contained magmatic solute components, notably sulfate, acidity and Cu. Sulfate reduction produced hydrothermal Cu sulfides with a wide range in sulfur isotope compositions from very negative to moderately positive values. Partial reaction of the Cu-rich stage II fluid with earlier stage I sulfides resulted in mixing of sulfur derived from sulfate reduction and from sulfides deposited during stage I. Modeling of the sulfur isotope fractionation processes in response to reducing and oxidizing pathways demonstrates that the entire spectrum of sulfur isotope data from stage I and stage II mineralization can be explained with a single, ultimately magmatic sulfur source. Such a magmatic sulfur source is also adequate to explain the complete spectrum of sulfur isotope data of other IOCG prospects and deposits in the Olympic province, including Olympic Dam. The results of our study challenge the conventional model that suggests the requirement of multiple and compositionally diverse sulfur sources in hematite-breccia hosted IOCG style mineralization. [ABSTRACT FROM AUTHOR]

The Mesoproterozoic Prominent Hill iron-oxide copper-gold deposit lies on the fault-bound southern edge of the Mt Woods Domain, Gawler Craton, South Australia. Chalcocite-bornite-chalcopyrite ores occur in a hematitic breccia complex that has similarities to the Olympic Dam deposit, but were emplaced in a shallow water clastic-carbonate package overlying a thick andesite-dacite pile. The sequence has been overturned against the major, steep, east-west, Hangingwall Fault, beyond which lies the clastic to potentially evaporitic Blue Duck Metasediments. Immediately north of the deposit, these metasediments have been intruded by dacite porphyry and granitoid and metasomatised to form magnetite-calc-silicate skarn ± pyrite-chalcopyrite. The hematitic breccia complex is strongly sericitised and silicified, has a large sericite ± chlorite halo, and was intruded by dykes during and after sericitisation. This paper evaluates the age of sericite formation in the mineralised breccias and provides constraints on the timing of granitoid intrusion and skarn formation in the terrain adjoining the mineralisation. The breccia complex contains fragments of granitoid and porphyry that are found here to be part of the Gawler Range Volcanics/Hiltaba Suite magmatic event at 1600-1570 Ma. This indicates that some breccia formation post-dated granitoid intrusion. Monazite and apatite in Fe-P-REE-albite metasomatised granitoid, paragenetically linked with magnetite skarn formation north of the Hangingwall Fault, grew soon after granitoid intrusion, although the apatite experienced U-Pb-LREE loss during later fluid-mineral interaction; this accounts for its calculated age of 1544 ± 39 Ma. To the south of the fault, within the breccia, Ar-Ar ages yield a minimum age of sericitisation (+Cu+Fe+REE) of dykes and volcanics of ∼1575 Ma, firmly placing Prominent Hill ore formation as part of the Gawler Range Volcanics/Hiltaba Suite magmatic event within the Olympic Cu-Au province of the Gawler Craton. [ABSTRACT FROM AUTHOR]

This study utilises U-Pb geochronology, Lu-Hf, Sm-Nd isotopes and geochemistry to constrain the timing of deposition, metamorphism and provenance characteristics of buried Palaeoproterozoic meta-sedimentary and meta-igneous rocks in the northern Gawler Craton, Australia. The data suggest that sedimentary sequences were deposited between ca. 1780 and 1740 Ma across a wide region accompanied by syn -depositional magmatism. Restricted zircon age spectra, relatively radiogenic whole-rock Hf-Nd and in-situ zircon Hf isotopic compositions and enriched REE signatures support the notion of a connected series of basins or a single large basin, which developed on a common Neoarchaean substrate across the northern Gawler Craton during the Late Palaeoproterozoic. Temporal and isotopic correlation of these indurated rocks with Palaeoproterozoic basins throughout the North Australian Craton suggests they may form part of an extensive basin system that developed across the Australian continent during the Late Palaeoproterozoic. The meta-sedimentary and meta-igneous rocks of the northern Gawler Craton record high-grade crustal anatexis during the ca. 1730–1690 Ma Kimban Orogeny and subsequent Early Mesoproterozoic re-working. [ABSTRACT FROM AUTHOR]

The Olympic Cu–Au Province, Gawler Craton, is host to the Olympic Dam and Prominent Hill iron oxide–copper–gold (IOCG) deposits. Both of these deposits and the region between the two are covered by Neoproterozoic to Cenozoic sediment, making inferences about prospectivity in this portion of the Olympic Domain reliant on geophysical interpretation and sparse drill hole information. We present new U–Pb zircon sensitive high resolution ion microprobe (SHRIMP) dates from two basement intersecting drill holes in the region between Olympic Dam and Prominent Hill that show bimodal volcanism occurred at 2555 ± 5 Ma, and was followed by intrusion of tonalite at 2529 ± 6 Ma. Laser40Ar/39Ar dating of biotite and muscovite from the tonalite yields ages aroundca2000 Ma, consistent with slow cooling trends observed in Archean rocks elsewhere in the northern Gawler Craton. Step heating experiments on K-feldspar from the same tonalite yields an age spectrum with older ages around 1740 Ma from the highest temperature steps becoming progressively younger to a minimum of 1565 Ma in the lowest temperature heating steps; this is consistent with either Paleoproterozic cooling to final closure of K-feldspar by 1565 Ma or a reheating event atca1565 Ma, with the latter more likely, given the evidence for sub-solidus alteration of the K-feldspar. Sericite within hematite–sericite–chlorite altered portions of the tonalite yield a poorly defined age ofca1.6 Ga. Taken together the40Ar/39Ar data providing evidence for a fluid event affecting this region between Olympic Dam and Prominent Hill during the early Mesoproterozoic. Low temperature quartz–carbonate–adularia veins occur in <10 cm wide fractures within basalt in one drill hole in this region. Adularia from these veins yields40Ar/39Ar ages that span fromca1.3–1.1 Ga. This age range is interpreted to approximate either the timing of adularia formation during a hydrothermal event or the timing of resetting of the40Ar/39Ar systematics within the adularia as a result of fluid flow in this sample. This is evidence for a mid-Mesoproterozoic fluid event in the Gawler Craton and necessitates a reconsideration of the long-term stability of the craton, as it appears to have been affected, at least locally, by fluid flow related to a much larger event within the Australian continent, the Musgrave Orogeny. [ABSTRACT FROM AUTHOR]

Neoarchean–earliest Paleoproterozoic rocks of the Gawler Craton preserved within the Mulgathing Complex, South Australia, record metamorphism and deformation during an earliest Paleoproterozoic tectonothermal event known as the Sleafordian Orogeny. We present metamorphic data from pelitic gneisses of the Mulgathing Complex from three locations (Challenger, Mt Christie and Blackfellow Hill) in order to constrain the pressure–temperature–time ( P – T – t ) evolution of this orogeny. In situ U-Pb dating via laser ablation-inductively coupled plasma mass spectrometry, shows that monazites within garnet porphyroblasts have ages ca. 2470 Ma, providing an estimate of the timing peak P – T conditions. Monazite crystallisation from melt occurred at ca. 2460 Ma in the presence of peritectic garnet either late on the prograde path during biotite-dehydration melting, or immediately following peak- T . Lobate and patchy rims in leucosome-hosted monazite suggest a dissolution-reprecipitation process occurred during cooling across the elevated dry solidus at ca. 2440 Ma. Monazite younger than ca. 2430–2420 Ma that is located at grain boundaries between matrix minerals likely reflects monazite crystallisation during cooling across the dry solidus and/or subsolidus mineral breakdown during the waning stages of the thermal event. Phase diagram modelling of pelitic gneisses suggests peak metamorphic conditions at the three localities overlap at ∼7 kbar and 850 °C with apparent thermal gradients in the order of 125–135 °C/kbar (∼35–45 °C/km). Metamorphism involved a tight anticlockwise P – T – t path based on mineral assemblage paragenesis and indicates a slow, shallow decompressive-cooling path, sub-parallel to the apparent thermal gradient, in the order of few degrees per Myr. A protracted magmatic history involving bimodal magmatism associated with a thinned and underplated extensional basin in the Mulgathing Complex was likely a thermal precursor to the high thermal gradient metamorphism and convergent (transpressive) deformation. A significant period of post 2.4 Ga quiescence in the Gawler Craton subsequent to basin inversion suggests that this orogenesis may have occurred interior to a plate margin. The similarity in timing and style between the Sleafordian Orogeny in the Gawler Craton and the 2.5–2.28 Ga Arrowsmith Orogeny of the Rae Craton supports the notion that these terranes, together with the broader Gawler-Adélie Craton of the Mawson Continent, the North Australia Craton, elements of the North China, Sino-Korean and Dharwar cratons formed part of a family of Neoarchean terranes, described as the Rae family of cratons, with a distinctive tectono-metamorphic record as compared with other Archean cratons. We suggest the Mawson Continent is the southern member of this family, dominated as it is by terranes now present in the northern hemisphere. [ABSTRACT FROM AUTHOR]

An apatite fission track (AFT) study of crystalline basement in the central Gawler Craton reveals apparent ages in the range ofca430–58 Ma. The majority of samples underwent protracted monotonic cooling related to regional Paleozoic exhumation, consistent with long-term crustal stability as expected for cratonic interiors. However, multiple samples show evidence of Late Cretaceous–early Paleogene reheating, indicating a more dynamic low-temperature history. Inverse time–temperature modelling of AFT data indicates varying degrees of thermal overprinting between ∼60 and 110°C, with substantially overprinted and negligibly overprinted samples in close proximity (<1 km). Time–temperature histories for samples that experienced thermal overprinting reveal localised Late Cretaceous–early Paleogene (ca100–50 Ma) heating that is significantly younger than the Paleozoic–early Mesozoic exhumation recorded regionally. The highly localised nature and non-systematic patterns of overprinting combined with the lack of major Mesozoic or Cenozoic fault structures are not consistent with a regional thermal event associated with substantial reburial and later exhumation. Rather, localised reheating was most likely caused by heated groundwater from the once-overlying Mesozoic Eromanga Basin aquifer system, whose modern discharge margin (∼400 km north of the study area) is marked by thermal mound springs that produce fluids with temperatures up to 100°C. Only basement rocks in close proximity to fluid pathways in the overlying aquifer would have recorded reheating, resulting in the observed sporadic distribution of partially overprinted samples. Thermal history modelling indicates rejuvenated apatite grains cooled to near-surface temperatures in the latest Cretaceous–Paleogene. This was likely in response to local removal of the overlying Eromanga Basin aquifer unit due to a relatively minor degree of exhumation (≤1 km) recorded regionally, which consequently disrupted the anomalous heating mechanism. These results show that the flow of heated groundwater is a feasible reheating mechanism for low-temperature thermochronometers, resulting in cooling patterns that may become decoupled from exhumation in cratonic interiors. [ABSTRACT FROM AUTHOR]