Karin M. Barovich

Evidence for Early Mesoproterozoic Arc Magmatism in the Musgrave Block, Central Australia: Implications for Proterozoic Crustal Growth and Tectonic Reconstructions of Australia

The Musgrave Block in central southern Australia separates the dominantly Paleoproterozoic North Australian Craton from the Late Archean to early Mesoproterozoic Gawler Craton in southern Australia. Geochemical and Nd isotopic data from ∼1.59–1.55‐Ga felsic rocks in the Mann Ranges suggest that the early history of the Musgrave Block was linked to the development of subduction along the northern margin of the Gawler Craton. Characteristic geochemical patterns of these felsic rocks include negative anomalies in Nb, Ti, and Y and are accompanied by steep light rare earth element patterns and comparatively juvenile Nd isotopic compositions (ϵNd(1550) values from −1.2 to 0.9). The geochemical and isotopic signatures of these early Mesoproterozoic felsic rocks have similarities with island arc systems involving residual Ti‐bearing minerals and garnet. We propose that the 1.59–1.55‐Ga arclike rocks in the Musgrave Block indicate the presence of an active margin between the North Australian Craton and the South Australian Craton, with subsequent suturing of the Australian continent during the early Mesoproterozoic. The existence of arclike magmatism in the Musgrave Block during the early Mesoproterozoic suggests a period of major crustal growth in the Australian Proterozoic that has important implications for current Proterozoic reconstructions of Australia and Australias fit within the supercontinent Rodinia.

Correlations and reconstruction models for the 2500-1500 Ma evolution of the Mawson Continent

Abstract Continental lithosphere formed and reworked during the Palaeoproterozoic era is a major component of pre-1070 Ma Australia and the East Antarctic Shield. Within this lithosphere, the Mawson Continent encompasses the Gawler–Adélie Craton in southern Australia and Antarctica, and crust of the Miller Range, Transantarctic Mountains, which are interpreted to have assembled during c. 1730–1690 Ma tectonism of the Kimban–Nimrod–Strangways orogenies. Recent geochronology has strengthened correlations between the Mawson Continent and Shackleton Range (Antarctica), but the potential for Meso- to Neoproterozoic rifting and/or accretion events prevent any confident extension of the Mawson Continent to include the Shackleton Range. Proposed later addition (c. 1600–1550 Ma) of the Coompana Block and its Antarctic extension provides the final component of the Mawson Continent. A new model proposed for the late Archaean to early Mesoproterozoic evolution of the Mawson Continent highlights important timelines in the tectonic evolution of the Australian lithosphere. The Gawler–Adélie Craton and adjacent Curnamona Province are interpreted to share correlatable timelines with the North Australian Craton at c. 2500–2430 Ma, c. 2000 Ma, 1865–1850 Ma, 1730–1690 Ma and 1600–1550 Ma. These common timelines are used to suggest the Gawler–Adélie Craton and North Australian Craton formed a contiguous continental terrain during the entirety of the Palaeoproterozoic. Revised palaeomagnetic constraints for global correlation of proto-Australia highlight an apparently static relationship with northwestern Laurentia during the c. 1730–1590 Ma time period. These data have important implications for many previously proposed reconstruction models and are used as a primary constraint in the configuration of the reconstruction model proposed herein. This palaeomagnetic link strengthens previous correlations between the Wernecke region of northwestern Laurentia and terrains in the eastern margin of proto-Australia.

Temporal constraints on the timing of high-grade metamorphism in the northern Gawler Craton: implications for assembly of the Australian Proterozoic

LA-ICPMS U–Pb data from metamorphic monazite in upper amphibolite and granulite-grade metasedimentary rocks indicate that the Nawa Domain of the northern Gawler Craton in southern Australia underwent multiple high-grade metamorphic events in the Late Paleoproterozoic and Early Mesoproterozoic. Five of the six samples investigated here record metamorphic monazite growth during the period 1730–1690 Ma, coincident with the Kimban Orogeny, which shaped the crustal architecture of the southeastern Gawler Craton. Combined with existing detrital zircon U–Pb data, the metamorphic monazite ages constrain deposition of the northern Gawler metasedimentary protoliths to the interval ca 1750–1720 Ma. The new age data highlight the craton-wide nature of the 1730–1690 Ma Kimban Orogeny in the Gawler Craton. In the Mabel Creek Ridge region of the Nawa Domain, rocks metamorphosed during the Kimban Orogeny were reworked during the Kararan Orogeny (1570–1555 Ma). The obtained Kararan Orogeny monazite ages are within uncertainty of ca 1590–1575 Ma zircon U–Pb metamorphic ages from the Mt Woods Domain in the central-eastern Gawler Craton, which indicate that high-grade metamorphism and associated deformation were coeval with the craton-scale Hiltaba magmatic event. The timing of this deformation, and the implied compressional vector, is similar to the latter stages of the Olarian Orogeny in the adjacent Curnamona Province and appears to be part of a westward migration in the timing of deformation and metamorphism in the southern Australian Proterozoic over the interval 1600–1545 Ma. This pattern of westward-shifting tectonism is defined by the Olarian Orogeny (1600–1585 Ma, Curnamona Province), Mt Woods deformation (1590–1575 Ma), Mabel Creek Ridge deformation (1570–1555 Ma, Kararan Orogeny) and Fowler Domain deformation (1555–1545 Ma, Kararan Orogeny). This westward migration of deformation suggests the existence of a large evolving tectonic system that encompassed the emplacement of the voluminous Hiltaba Suite and associated volcanic and mineral systems.

A Neoproterozoic flood basalt province in southern-central Australia: geochemical and Nd isotope evidence from basin fill

Abstract Geochemical and Nd isotope studies of Neoproterozoic sedimentary successions from central and southern Australia are used to argue for the existence of a widespread flood basalt province emplaced in the Neoproterozoic, related in time to Rodinian supercontinent breakup. While major and minor element geochemistry supports a small and variable degree of input from a mafic source for at least some of the sedimentary rocks, Sm/Nd ratios and Nd isotope constraints do not allow simple physical mixing of end-member basalt and upper crustal basement terranes to achieve the relatively radiogenic eNd compositions of the rocks. Instead, preferential chemical mixing of the Nd composition of the end-member source regions is documented through chemical separation and analysis of different Nd reservoirs of the sedimentary material. Leaching tests undertaken to separate soluble/exchangeable Nd from that fixed in crystallographic sites of detrital phases indicate that the leachable portions of the higher initial eNd sedimentary samples were in isotopic equilibrium around the time of deposition in a relatively radiogenic environment, such as that which would be produced by widespread chemical erosion of a heavily glacially scoured flood basalt province. This indication of a high 143Nd/144Nd diagenetic fluid or authigenic phase is in contrast to the isotopic results from separable portions of samples with an Nd isotope composition reflective of proximal basement that indicate equilibration between the two portions, detrital and diagenetic, at around the time of deposition of the sediments. Thus, although the near-shore shallow water sediments deposited in the Neoproterozoic did not, for the most part, record a physical detrital input of the flood basalt source (which, owing to its postulated weathered fine-grained nature, is seen only in the most fine-grained and slowly accumulated sedimentary units in such an environment), they do record the input of a more radiogenic component taken up by REE adsorption and/or sediment settling of REE-rich colloidal riverine material, derived from the easily chemically weathered basalt terrane.

Sr-isotopic evidence for Late Neoproterozoic rifting in the Adelaide Geosyncline at 586 Ma: implications for a Cu ore forming fluid flux

Abstract Analyses of shales and basalts from all stratigraphic levels below the Wonoka formation in the Neoproterozoic Adelaide Geosyncline combine to define a 586±30 Ma Rb–Sr isochron with an initial 87Sr/86Sr value of 0.7180. The Sr-isotopic composition of most carbonate units deposited in this basin before this time are also altered and have Sr-isotopic compositions that fall between their primary contemporary seawater values and those of the clastic basin fill. By contrast the Neoproterozoic carbonates from strata including and younger than the late Vendian Wonoka formation conform to internationally correlated chemostratigraphic variations for both 87Sr/86Sr and δ13C. These data, together with S- and Sr-isotopic evidence from barite veins which cut late Marinoan shales, are interpreted to indicate that the Adelaidean succession experienced a phase of intrabasinal fluid flow; the fluid had an 87Sr/86Sr value of 0.7180 when convective circulation was terminated at ∼586 Ma. This timing is synchronous with down-cutting of basin fill to form canyons beneath the Wonoka formation and also coincides with the production of rift-affiliated alkaline lavas to the east of the Curnamona craton in western NSW. The interpreted changed fluid flux regime, together with the other geological features listed, may indicate the onset of a new phase of extension and rifting of East Gondwanas eastern margin at 586±30 Ma, contributing to a growing body of evidence that suggests that the main phase of proto-Pacific opening may have been Vendian rather than Sturtian in age. The proposed basinal fluid flow event is of economic importance as it mobilised Cu and other base metals, and may have carried them to depositional sites in the thin platformal western marginal succession of the basin on the Stuart shelf.

Nd isotopic and geochemical constraints on provenance of sedimentary rocks in the eastern Officer Basin, Australia: implications for the duration of the intracratonic Petermann Orogeny

Sm–Nd isotopic and geochemical data from Neoproterozoic to Cambrian sedimentary rocks in the intracratonic eastern Officer Basin in central Australia highlight the evolving provenance roles of the basement complexes that underlie and bound the basin. Initial εNd values of around −12 for the basal units indicate that both were largely derived from the late Archaean to Mesoproterozoic Gawler Craton, which bounds the basin to the south. At c. 720 Ma an influx of juvenile, glacially derived sediment indicates partial uplift of the Mesoproterozoic Musgrave Block along the basins northern margin, in a regime interpreted to be broadly extensional. At around 600 Ma, synchronous with the development of a foreland architecture, there was a large influx of Musgrave Block-derived sediments. This is interpreted to mark the onset of the intracratonic Petermann Orogeny, which was a long-lived event or series of events, spanning more than 70 Ma. Subsequent to c. 600 Ma, the Nd isotopic composition of sequences within the Officer Basin indicates an increasing contribution from the Gawler Craton despite up to 45 km of denudation of part of the Musgrave Block. This suggests that the majority of sediment derived from the Petermann Orogen bypassed the eastern Officer Basin for much of the history of the Petermann Orogeny.

Timing of Proterozoic metamorphism in the southern Curnamona Province: implications for tectonic models and continental reconstructions ∗

Chemical U – Th – Pb monazite ages from metasedimentary and meta-igneous units of the Willyama Supergroup have confirmed initial SHRIMP U – Pb metamorphic zircon ages constraining the onset of the earliest tectonometamorphic event (the Olarian Orogeny) at ca 1610 Ma in the southern Curnamona Province. An additional episode of high-grade metamorphism and heterogeneously distributed retrograde metamorphism and monazite recrystallisation occurred between ca 1570 and 1550 Ma. On the basis of monazite chemical U – Th – Pb ages from across the southern Curnamona Province, tectonometamorphic models based on ca 1690 Ma low-P, high-T metamorphism in the southern Curnamona Province are not supported. Furthermore, tectonic reconstructions that rely on the correlation of ca 1690 Ma deformation and metamorphism in the Broken Hill region with a similar aged event in the Mojave tarrane of southwestern Laurentia (AUSWUS) are not supported.

Continental ca 1.7 – 1.69 Ga Fe-rich metatholeiites in the Curnamona Province, Australia: a record of melting of a heterogeneous, subduction-modified lithospheric mantle

Mg-rich and Fe-rich metatholeiites intruded the Willyama Supergroup of the southern Australian Curnamona Province in the Late Palaeoproterozoic at ca 1700 Ma and 1685 Ma, respectively. Intrusion of the Fe-rich metatholeiites occurred during a period of punctuated extension in the Willyama basin. Major-element concentrations are variable (SiO2 45.4 – 56.5 wt%; Fe2O3* 8.5 – 20.7; TiO2 0.46 – 2.52 wt%; Mg# 70.5 – 29.1) and, in conjunction with trace-element data, support near-closed-system fractionation of a mantle-derived melt with little or no replenishment. Fractionation produced progressively Fe-rich derivative melts. Crystallising phases were dominated by clinopyroxene and olivine, whereas Fe – (Ti) oxide crystallisation was hindered. Primitive mantle-normalised immobile trace elements are characterised by variable Th, Nb, Sr, P and Ti anomalies. Chondrite-normalised rare-earth element patterns for the most primitive, Mg-rich samples from the western Broken Hill Domain have LaN/SmN < 1, whereas the most evolved Fe-rich samples from the Olary Domain have ratios of LaN/SmN > 1. Initial ϵNd values range between – 2.2 and + 2.7 for the majority of the samples, with the isotopic compositions showing no correlation with differentiation or assimilation. The combined geochemical and isotopic data suggest that the southern Curnamona Province metatholeiites were extracted from a depleted mantle in the western Broken Hill Domain, and a variably enriched, heterogeneous subcontinental lithospheric mantle in the Olary Domain. Magmatism most likely occurred in a backarc basin or intracontinental setting. It is speculated that the geochemically enriched mantle component was derived from subduction-related processes, probably related to pre-Willyama basin accretionary processes along the southern and eastern margins of the North Australian Craton.

U–Pb zircon, zircon Hf and whole-rock Sm–Nd isotopic constraints on the evolution of Paleoproterozoic rocks in the northern Gawler Craton

U–Pb zircon analyses from a series of orthogneisses sampled in drill core in the northern Gawler Craton provide crystallisation ages at ca 1775–1750 Ma, which is an uncommon age in the Gawler Craton. Metamorphic zircon and monazite give ages of ca 1730–1710 Ma indicating that the igneous protoliths underwent metamorphism during the craton-wide Kimban Orogeny. Isotopic Hf zircon data show that 1780–1750 Ma zircons are somewhat evolved with initial εHf values –4 to +0.9, and model ages of ca 2.3 to 2.2 Ga. Isotopic whole rock Sm–Nd values from most samples have relatively evolved initial εNd values of –3.7 to –1.4. In contrast, a mafic unit from drill hole Middle Bore 1 has a juvenile isotopic signature with initial εHf zircon values of ca +5.2 to +8.2, and initial εNd values of ∼+3.5 to +3.8. The presence of 1775–1750 Ma zircon forming magmatic rocks in the northern Gawler Craton provides a possible source for similarly aged detrital zircons in Paleoproterozoic basin systems of the Gawler Craton and adjacent Curnamona Province. Previous provenance studies on these Paleoproterozoic basins have appealed to the Arunta Region of the North Australian Craton to provide 1780–1750 Ma detrital zircons, and isotopically and geochemically similar basin fill. The orthogneisses in the northern Gawler Craton also match the source criteria and display geochemical similarities between coeval magmatism in the Arunta Region of the North Australian Craton, providing further support for paleogeographic reconstructions that link the Gawler Craton and North Australian Craton during the Paleoproterozoic.

Provenance of late Paleoproterozoic cover sequences in the central Gawler Craton : exploring stratigraphic correlations in eastern Proterozoic Australia using detrital zircon ages, Hf and Nd isotopic data

Provenance data from Paleoproterozoic and possible Archean sedimentary units in the central eastern Gawler Craton in southern Australia form part of a growing dataset suggesting that the Gawler Craton shares important basin formation and tectonic time lines with the adjacent Curnamona Province and the Isan Inlier in northern Australia. U–Pb dating of detrital zircons from the Eba Formation, previously mapped as the Paleoproterozoic Tarcoola Formation, yields exclusively Archean ages (ca 3300–2530 Ma), which are consistent with evolved whole-rock Nd and zircon Hf isotopic data. The absence of Paleoproterozoic detrital grains in a number of sequences (including the Eba Formation), despite the proximity of voluminous Paleoproterozoic rock units, suggests that the Eba Formation may be part of a Neoarchean or early Paleoproterozoic cover sequence derived from erosion of a multi-aged Archean source region. The ca 1715 Ma Labyrinth Formation, unconformably overlying the Eba Formation, shares similar depositional timing with other basin systems in the Gawler Craton and the adjacent Curnamona Province. Detrital zircon ages in the Labyrinth Formation range from Neoarchean to Paleoproterozoic, and are consistent with derivation from >1715 Ma components of the Gawler Craton. Zircon Hf and whole-rock Nd isotopic data also suggest a source region with a mixed crustal evolution (εNd –6 to –4.5), consistent with what is known about the Gawler Craton. Compared with the lower Willyama Supergroup in the adjacent Curnamona Province, the Labyrinth Formation has a source more obviously reconcilable with the Gawler Craton. Stratigraphically overlying the Eba and Labyrinth Formations is the 1656 Ma Tarcoola Formation. Zircon Hf and whole-rock Nd isotopic data indicate that the Tarcoola Formation was sourced from comparatively juvenile rocks (εNd –4.1 to + 0.5). The timing of Tarcoola Formation deposition is similar to the juvenile upper Willyama Supergroup, further strengthening the stratigraphic links between the Gawler and Curnamona domains. Additionally, the Tarcoola Formation is similar in age to extensive units in the Mt Isa and Georgetown regions in northern Australia, also shown to be isotopically juvenile. These juvenile sedimentary rocks contrast with the evolved underlying sequences and hint at the existence of a large-scale ca 1650 Ma juvenile basin system in eastern Proterozoic Australia.