Barramundi Orogeny Research Articles

The configuration of Greater Gondwana—Evidence from LA ICPMS, U–Pb geochronology of detrital zircons from the Palaeozoic and Mesozoic of Southeast Asia and China

Detrital zircons from samples of Palaeozoic to Mesozoic sedimentary rocks have been collected in Malaysia, Thailand, Laos, Vietnam, Cambodia and China, dated by the LA ICPMS, U–Pb technique and assigned to tectonic terranes or regions within terranes. The combined results from each region or terrane are compared with published detrital zircon age data from Australia, Asia and elsewhere using Kolmogorov–Smirnov (K–S) statistics.Generally low P-values (probability values) are found when comparing terranes, possibly because each large terrane sourced zircons from different areas. However, very high P-values obtained in this study suggest that the Indochina terranes (Truong Son, Loei and Central Vietnam), southern China terranes (Ailaoshan, NE Vietnam, Yangtze) and the Tethyan Himalayas may have been close to similar source areas. This supports models that place South China and the Indochina terranes close to the western Himalayas. The Early Palaeozoic palaeobiogeographic data and single sample K–S comparisons from the Himalayas and from Australia suggest that North China was close to Gondwana, but our K–S inter-terrane comparisons do not support this hypothesis.High Kolmogorov–Smirnov P-values of 0.895 are found between the Late Cambrian–Early Ordovician Tarutao Formation of Sibumasu and the Ordovician Tumblagooda Sandstone Fm of Western Australia. High P values of 0.925 and 0.958 are also found between the Tethyan Himalaya and the Tarutao Formation. Visual comparisons of probability plots of zircons from quartzite clasts from the Tarutao Formation and from quartzite and granite clasts in Permian glacimarine mudstones (Kaeng Krachan Group, Sibumasu) have age spectra in common with terranes of western and northern Australia particularly the Meso-Neoproterozoic-age Pinjarra–East Antarctic–Eastern Ghats Orogen and the northern Australian area affected by the c.1850Ma Barramundi Orogeny. A characteristic widespread assemblage of zircons previously recognized along the length of the Himalayas by Myrow et al. (2010) with a dominant peak at 950Ma and other peaks at 600Ma (Pan African Orogeny), at 1200–1000Ma (Grenvillian Orogeny) and at 2500Ma are also found in the peri-Gondwana Terranes of Truong Son, South China, Qiangtang, Lhasa and Sibumasu and suggest a common distal source region in the Pinjarra–East Antarctic–Eastern Ghats Orogen.The formations of the Triassic Lampang and Song Groups of northern Thailand are dated using zircons and their detrital zircons suggest probable sources from the Indochina terranes for basins of the Sukhothai Terrane.

Pre-1.8 Ga tectono-magmatic evolution of the Kalkadoon–Leichhardt Belt: implications for the crustal architecture and metallogeny of the Mount Isa Inlier, northwest Queensland, Australia

New geochemical, U–Pb zircon and Nd–Hf isotope data for felsic and mafic components of the Kalkadoon–Leichardt Belt (KLB) in the Mount Isa Inlier of northwest Queensland confirm that the evolution and tectonic make-up of this belt prior to 1.8 Ga was closely aligned with that of the Western Fold Belt. Like pre-1.8 Ga magmatic rocks of the Western Fold Belt, those in the KLB are characterised by late Archean to Paleoproterozoic crustal residence ages (TDM ca 2.6–2.3 Ga) but the geochemical data suggest stronger within-plate affinities, implying that the KLB intrusions underwent a greater degree of crustal assimilation and/or were emplaced further inboard of the active subduction margin. A new SHRIMP U–Pb zircon age of ca 1.86 Ga from a felsic intrusion in the northern KLB confirms earlier age constraints for the main phase of the Kalkadoon Granite. Nd isotope patterns for intrusions in the Western Fold Belt and the KLB are distinct from those of ca 1.7–1.5 Ga intrusions in the Eastern Fold Belt. This isotopic discrepancy suggests the Eastern Fold Belt underwent a separate evolutionary history and was accreted to the WFB/KLB at some stage prior to, or during, the ca 1.86 Ga Barramundi Orogeny. The occurrence of widespread, isotopically homogeneous ca 1.72 Ga magmatism (Argylla Event) across the entire Mount Isa Inlier implies that amalgamation of the allochthonous Eastern Fold Belt with the North Australian Craton was completed by that time. The significantly elevated metallogenic potential of the Eastern Fold Belt for ca 1540–1500 Ma Fe-oxide–copper–gold, relatively low endowment of the Kalkadoon–Leichhardt Belt, and predominance of ca 1650–1550 Ma base metal occurrences in the Western Fold Belt, are all consequences of the tectonic interplay and lithospheric processes that controlled the evolution of the Mt Isa Inlier prior to ca 1.8 Ga.

High-K granites of the Rum Jungle Complex, N-Australia: Insights into the Late Archean crustal evolution of the North Australian Craton

The Late Archean (c. 2.54–2.52 Ga) high-K granitoids of the Rum Jungle Complex, Northern Australia, display the igneous mineral assemblage of K-feldspar, quartz, plagioclase, biotite, and magnetite, and accessories such as zircon, monazite, titanite, allanite, apatite, and ilmenite. The granites underwent a variably severe greenschist facies alteration and associated deformation during the Barramundi Orogeny (1.88–1.85 Ga). The K-rich granitoids have variable compositions, mainly comprising syenogranite and quartz-monzonite. They can be subdivided into two major groups, (1) felsic granites and (2) intermediate to felsic granites, quartz-monzonites, and diorite. The felsic group (69–76 wt.% SiO 2) shares many features with typical Late Archean potassic granites. They are K- and LILE-rich and show marked depletion in Sr and Eu and the high field strength elements (HFSE), particularly Nb and Ti, relative to LILE and LREE. Compared to the average upper crust they have anomalously high Th (up to 123 ppm) and U (up to 40 ppm). The intermediate to felsic group (56–69 wt.% SiO 2) differs from the felsic group in having weakly lower Th and U but higher Mg#, Ti, Ba, Sr, Ni, Cr and REE, with a less pronounced negative Eu anomaly. This group displays well-defined trends in Harker diagrams, involving a negative correlation of Si with Sr, Ca, Na, and P whereas K, Rb, and Ba increase in the same direction, suggesting fractional crystallization of feldspar was more prominent than in the felsic suite. The mineralogical and geochemical characteristics of the felsic group are consistent with granite formation by intracrustal melting of plagioclase-rich igneous protoliths, probably of tonaltic to granodioritic composition, at moderate crustal levels. The intermediate to felsic granites, on the other hand, appear to be the products of mantle–crust interaction, possibly by melting of or mixing with more mafic igneous rocks. As evidenced by the presence of older inherited zircons crustal recycling of a pre-greenstone crust of the North Australian Craton of > 3.5 Ga played an important role in the formation of the Late Archean granites of the Rum Jungle Complex.

The age and significance of the Ngadarunga Granite in Proterozoic central Australia

The emplacement of the Ngadarunga Granite in the Arunta Region of central Australia directly constrains the timing of the first high-grade metamorphic, tectonic and magmatic event in the Arunta Region, and the timing of the geographically extensive unconformity that separates the earliest regional basin phase from younger, overlying sedimentary successions. Previous dating had correlated this event with the 1880–1840 Ma Barramundi Orogeny interpreted in far north Australia, linking the Arunta Region to the ‘Barramundi’ model of widespread synchronous cratonisation in the period 1880–1840 Ma. New data revise this granite emplacement to 1803 ± 6 Ma, placing it in the younger 1810–1800 Ma Stafford Event of the Arunta Region. The provenance of detrital zircons in early Arunta Region sedimentary rocks was dominated by crystalline rocks formed in the period 1840–1880 Ma. Thus, the earliest rocks in the Arunta Region were deposited after ca. 1840 Ma in a basin marginal to 1880–1840 Ma continental crust, and their subsequent tectonism began with the Stafford Event.

Evolution of Pre-1.8 Ga basement rocks in the western Mt Isa Inlier, northeastern Australia—Insights from SHRIMP U–Pb dating and in-situ Lu–Hf analysis of zircons

We present new SHRIMP zircon U–Pb data from pre 1.8 Ga basement rocks (Yaringa Metamorphics, Kurbayia Migmatite) on both sides of the Mt Isa Fault in the western Mt Isa Inlier. These data confirm that felsic intrusions were emplaced into the western Kalkadoon-Leichhardt Belt at 1849 ± 4 Ma (2 σ), and constrain the Barramundi Orogeny in the western Fold Belt to ca. 1.87 Ga, at the bottom part of the previously reported range of ca . 1.90–1.87 Ga. Integration of in situ Hf isotope analysis and SHRIMP zircon age data support the notion that there is no lithospheric break across the Mount Isa Fault. Furthermore, the 176Hf/ 177Hf isotope data confirm that Archaean–Palaeoproterozoic magmatic zircons on both sides of the Mount Isa Fault were sourced from the same parental lithospheric reservoir which evolved over time from more primitive mantle to supracrustal compositions, without significant contributions from juvenile sources in the Palaeoproterozoic. The oldest inherited zircons in samples from the Yaringa Metamorphics reflect the participation of Archaean (ca . 3300–3600 Ma) crustal components in the western Mt Isa Inlier. These zircons, together with isotopic data from other studies, may allow for a tectonic reconstruction involving Archaean crust underlying much of the Proterozoic succession at least in the western Mt Isa Inlier. Alternatively, the Archaean zircons could represent detrital components incorporated from Palaeoproterozoic metasedimentary rocks. As detrital zircons can be transported laterally for hundreds of kilometres, these grains cannot be diagnostic of the nature and age of the basement beneath the western Mt Isa Inlier. Consequently, neither model can be conclusively excluded given the current data set.

New SHRIMP U-Pb zircon geochronology for the central Pine Creek Orogen, Northern Territory: implications for Top End orogenesis

The Palaeoproterozoic Pine Creek Orogen, northern Australia, forms part of the North Australia Craton, and is a highly prospective terrain, with abundant mineral occurrences including gold and uranium. Geologically, it comprises sedimentary sequences deposited on rifted Archaean basement that were deformed, metamorphosed, and intruded by granitoids and mafic bodies during the ca. 1880-1850 Ma Nimbuwah Event, one of the constituent events of the Barramundi Orogeny. The stratigraphy of the central Pine Creek Orogen is well-characterised due to its extensive exposure, preservation, and low grade greenschist facies metamorphism. It contains units suitable for isotopic dating, permitting determination of absolute ages within a well-controlled stratigraphic framework. We present new zircon U-Pb SHRIMP results for volcanics and volcanogenic strata from various intervals within the pre-orogenic stratigraphy. These data: (a) indicate the presence of volcanic activity in the Pine Creek Orogen at ca. 2025 Ma; (b) provide revised constraints on the tectono-thermal evolution of the Pine Creek Orogen, specifically a revision of the Nimbuwah Event by some 20 Ma; (c) suggest that volcanism was widespread across the Pine Creek Orogen at ca. 1860 Ma; and (d) permit assessment of relative deposition rates of and time intervals between deposition of the Palaeoproterozoic stratigraphic sequences.

Synthesis of the proterozoic evolution of the Mt Isa Inlier

By virtue of its large area of exposure of different crustal levels, and preservation of a protracted (∼400 million years) Palaeoproterozoic to Mesoproterozoic tectonic evolution, the Mt Isa Inlier is an excellent natural laboratory to study Proterozoic tectonic processes. The inlier preserves evidence of intracontinental basin development, plutonism, low-pressure metamorphism, orogenesis at different crustal levels, and crustal-scale metasomatism. In addition, the Mt Isa Inlier is endowed with a variety of ore deposits, including the Mt Isa Pb – Zn – Ag and Cu deposits, Century Zn – Pb – Ag deposit, Cannington Ag – Pb – Zn deposit, and the Osborne and Ernest Henry iron oxide Cu – Au deposits. Basement rocks were deformed and metamorphosed during the ca 1900 – 1870 Ma Barramundi Orogeny and intruded by the granitic rocks of the ca 1850 Ma Kalkadoon and Ewen Batholiths and their coeval Leichhardt Volcanics. Three stacked and superimposed superbasins evolved between ca 1800 and ca 1595 Ma. These basins evolved in an environment characterised by elevated heat flow and transient episodes of magmatism and basin inversion in an inferred continental backarc setting. The ca 1600 – 1500 Ma Isan Orogeny probably records two phases of orogenesis. The first phase (ca 1600 – 1570 Ma) involved approximately north – south to northwest – southeast shortening in which a northwest-vergent fold-thrust belt evolved in the Eastern Fold Belt and localised basin inversion occurred in the Western Fold Belt. The second phase (ca 1550 – 1500) involved thick-skinned deformation in the Eastern and Western Fold Belts, characterised by upright folding, reverse faulting, and dextral wrenching. Voluminous granites were emplaced throughout the Eastern Fold Belt between ca 1550 and 1500 Ma. Exhumation and cooling of the crustal pile following the Isan Orogeny were related to crustal extension and widespread erosion in eastern and southern Australia. Subtle reactivation of faults within the inlier following the Isan Orogeny records the distal effects of Mesoproterozoic to Neoproterozoic breakup events and orogenesis in central Australia.

The Proterozoic Mount Isa Fault Zone, northeastern Australia: is it really a ca. 1.9 Ga terrane-bounding suture?

In marked contrast to Palaeoproterozoic Laurentia, the location of sutures and boundaries of discrete crustal fragments amalgamated during Palaeoproterozoic formation of the North Australian Craton remain highly speculative. Interpretations of suture locations have relied heavily on the analysis of regional geophysical datasets because of sparse exposure of rocks of the appropriate age. The Mount Isa Fault Zone has been interpreted as one such Palaeoproterozoic terrane-bounding suture. Furthermore, the coincidence of this fault zone with major shale-hosted massive sulphide Pb–Zn–Ag orebodies has led to speculations that trans-lithospheric faults may be an important ingredient for the development of this deposit type. This study has integrated geophysical and geochemical data to test the statute of the Mount Isa Fault as a terrane-bounding suture. Forward modelling of gravity data shows that basement rocks on either side of the Mount Isa Fault have similar densities. These interpretations are consistent with geochemical observations and Sm–Nd data that suggest that basement lithologies on either side of the Mount Isa Fault are geochemically and isotopically indistinguishable from each other, and that the Mount Isa Fault is unlikely to represent a suture zone that separates different Palaeoproterozoic terranes. Our data indicate that the crustal blocks on both sides of the Mount Isa Fault Zone must have been in within close proximity of each other since the Palaeoproterozoic, and that the Western Fold Belt was part of the (ancestral) North Australian Craton well before the ∼1.89–1.87 Ga Barramundi Orogeny. It appears that deep crustal variations in density may be related to the boundary between a shallowly west-dipping high-density mafic to ultramafic plate and low-density basement rocks. This interpretation in turn impacts on crustal-scale models for the development of shale-hosted massive sulphide Pb–Zn mineralisation, which do not require trans-lithospheric faults to tap deep-seated metal reservoirs and/or mantle plumbing systems. The approach applied herein demonstrates the value of multi-disciplinary investigations to the critical assessment of long-lived Proterozoic fault systems which, in the absence of methodical analysis, are commonly assumed to represent terrane-bounding sutures.

Polymetallic Mineralization at the Browns Deposit, Rum Jungle Mineral Field, Northern Territory, Australia

The Rum Jungle mineral field, Northern Territory, Australia, forms part of the Paleoproterozoic Pine Creek orogen. The geology of the area comprises two Archean granitic basement domes, overlain by a Paleoproterozoic sequence of metasedimentary and subordinate metavolcanic rocks. The rocks have been deformed and metamorphosed to greenschist facies during the 1880 Ma Barramundi orogeny, but the original stratigraphic succession has been preserved. The Browns deposit (Browns and its extension Browns East), hosted within black carbonaceous pelites of the Paleoproterozoic Whites Formation, is the largest base metal deposit found to date in the Pine Creek orogen. Present resource estimates are 39 million metric tons (Mt) at 0.44 percent Cu, 3.61 percent Pb, 0.11 percent Co, and 0.09 percent Ni (Browns), and 31 Mt at 1.29 percent Cu, 1.28 percent Pb, 0.13 percent Co, and 0.13 percent Ni (Browns East). Major sulfide minerals in the ore zone are galena, sphalerite, chalcopyrite, pyrite, and the main carrier of Ni and Co, siegenite (Ni,Co) 3 S 4 . Digenite group minerals and bornite, Ca-bearing plumbogummite (PbAl 3 (PO 4 ) 2 (OH) 5 .H 2 O), arsenopyrite, and gersdorffite are present in minor quantities. Ore minerals occur as fine-grained wisps parallel to the main bedding-parallel foliation and as coarse-grained mono- and polyminerallic aggregates that crosscut the foliation. Total noncarbonate carbon contents of unaltered rocks range from 1.07 to 7.51 wt percent. Total sulfur contents range from 2.13 to 6.14 wt percent. Petrographic studies and Raman spectroscopy identify three varieties of carbonaceous matter: primary syngenetic; premetamorphic, epigenetic grain coating; and postmetamorphic, epigenetic, uraniferous migrated. Altered rocks are rarely encountered. Values of δ 34 S for sulfides range from –5 to +15 per mil and are interpreted to reflect a combination of inorganic thermochemical reduction of seawater and bacterial activity. No specific sulfur isotope patterns for individual minerals can be established indicating nonequilibrium conditions. Homogeneous lead isotope signatures of galena ( 206 Pb/ 204 Pb = 16.20–16.22, 207 Pb/ 206 Pb = 15.48–15.51, 208 Pb/ 207 Pb = 35.86–35.92) suggest that all Pb was derived from a single crustal source, and paragenetically late crosscutting galena appears to have been remobilized from bedding-parallel galena. Despite the occurrence of uranium in similar rocks nearby, uranium is quantitatively insignificant in the Browns deposit and is not genetically related to base metal mineralization. Instead, it is linked to brittle deformation in the waning stages of orogenesis. The Browns deposit differs from other well-known sediment-hosted stratiform ore deposits. Both the Zambian Copperbelt and the Polish Kupferschiefer deposits are copper dominant and hosted in sedimentary sequences with significant psammitic components. The Pb-Zn-Ag deposits of the Proterozoic Australian zinc province also have significant carbonate in their host rocks (e.g., carbonaceous dolomitic and siltstone at McArthur River) and lack economically interesting Cu, Co, and Ni. The nearby Woodcutters Pb-Zn-Ag deposit, in rocks of similar age, also differs in structural setting (veins), dominant metals, and Pb isotopes from the Browns deposit.

Reduced and Oxidized Au-Cu-Bi Iron Oxide Deposits of the Tennant Creek Inlier, Australia: An Integrated Geologic and Chemical Model

Iron oxide-associated Au-Cu-Bi deposits of the Tennant Creek gold field range from magnetite-pyrrhotite-pyrite (reduced) Cu-rich deposits, through sulfide-poor, magnetite-rich high-grade Au-Bi (intermediate- f O2) deposits, to hematite-rich high-grade Au (oxidized) deposits. Discordant magnetite-hematite-chlorite-quartz ironstone bodies that host the ore formed hydrothermally during the ~1840 to 1860 Ma Barramundi orogeny at temperatures up to ~350° to 400°C and ~2.5 to 5(?) kbars. Deposition of ironstone minerals was localized by dilatency that was generated during D1 reverse shearing and folding. A separate Au-Cu-Bi hydrothermal stage overprinted selected ironstones during D2 at or before ~1825 to 1830 Ma, where favorable D1 structures and fluid pathways were reactivated. The extremes of the reduced- to oxidized-deposit spectrum represent divergent chemical conditions that cannot be reconciled by the action of a single fluid. We have identified both reducing and oxidizing fluids that helped to form the Au-Cu-Bi deposits. At the West Peko deposit, which represents the reduced end-member subtype, constraints from oxide-silicate-sulfide mineral stabilities, fluid inclusions, and chlorite thermochemistry indicate that Au-Cu-Bi ore was introduced into ironstone at 300° to 340°C by a reducing (pyrrhotite-stable), weakly acidic, sulfur-rich and N2-CH4–rich aqueous fluid containing 3 to 10 wt percent NaCl equiv. An ore fluid source outside the relatively oxidized metasedimentary host sequence (Warramunga Formation) is implied. We suggest similar ore fluids for other reduced Cu- and sulfide-rich deposits in the district. Chemical mass transfer modeling of reactions between reducing fluid and ironstone, incorporating estimated thermodynamic properties for aqueous bismuth complexes, indicates that highly efficient gold and native Bi deposition was predominantly in response to desulfidation and oxidation of the fluid. Chalcopyrite precipitated mainly in response to increased pH. Gold-bismuth ore in the Eldorado deposit, an oxidized and hematitic end member, is interpreted to have involved mixing of an oxidizing (hematite-stable) Ca-Na-Cl brine with an intermediate- f O2, low- to moderate-salinity ore fluid, as well as reaction of both fluids with ironstone. Furthermore, the mass transfer modeling suggests that mixing of reducing and oxidizing fluids in the absence of ironstones could have resulted in high-grade Au deposits lacking Fe oxides, a subtype that has received comparatively little exploration attention in the Tennant Creek district.

Review of the application of isotopic studies to the genesis of Cu‐Au mineralisation at Olympic Dam and Au mineralisation at Porgera, the Tennant Creek district and Yilgarn Craton

This paper reviews the application of radiogenic isotopes to the study of four Cu‐U and Au deposits or deposit types in the Australasian region: Olympic Dam, Porgera, the Proterozoic Au deposits of the Tennant Creek district and the Archaean gold deposits of the Yilgarn Craton. In each case it has been possible to date the mineralisation and to correlate ore formation with a specific igneous event or stage in crustal evolution. In three cases it was also possible to use radiogenic isotopes to trace the source of the metal(s) or to constrain the fluid pathway. The results illustrate the power of radiogenic isotopes in ore‐genesis studies. At the Porgera gold deposit in Papua New Guinea K‐Ar and 39Ar/40Ar dating has shown that both the mineralisation, and the spatially associated Porgera Igneous Complex, have an age of ca 6 Ma. Sr and Pb isotopic tracing of the ore fluids indicate that these elements were derived from a mixed sedimentary‐igneous source, as might be expected for a large hydrothermal system developing around a hypabyssal igneous complex. SHRIMP U‐Pb dating of zircons from the Olympic Dam Cu‐U‐Au deposit in South Australia has constrained the age of mineralisation to be ca 1590 Ma, the same as the age of the Gawler Range thermal event in South Australia. Nd isotopic tracing of the ore fluid has shown that it contains a significant mantle component. The most likely source of mantle Nd is a suite of hydrothermally altered alkali ultramafic dykes that cut, but are coeval with, the Olympic Dam breccias. A possible common link between Porgera and Olympic Dam is that both were derived from oxidised alkali mafic/ultramafic bodies. It is suggested that these magmas had unusually high fo2 so that Cu and Au concentrated in these magmas as they fractionated to produce the Au‐ or Cu‐Au‐rich magmatic‐hydrothermal fluids that gave rise to the mineralisation. SHRIMP U‐Pb dating of zircons from felsic intrusives that cut, or are cut by, Au mineralisation constrain the age of most of the gold mineralisation in the Yilgarn Craton to lie between 2660 and 2630 Ma. Direct 39Ar/40Ar dating of hydrothermal minerals associated with the mineralisation gave ages of 2627 for Victory (Kambalda), 2629 for the Golden Mile (Kalgoorlie) and 2623 for Matilda M1 (Wiluna) that are consistent with the above constraint. An age of ca 2630 Ma correlates with late felsic magma‐tism in the Yilgarn Craton and with metamorphism in the lower crust. Mt Charlotte (Kalgoorlie), Wiluna East Lode and Lady Bountiful give younger ages of 2602, 2565 and 2590 respectively. The young age at Mt Charlotte is consistent with the field relationships and is believed to be the age of mineralisation but the Wiluna and Lady Bountiful dates may have been reset by later thermal events. Isotopic tracing at Mt Charlotte, using Nd in scheelites, showed that most of that element came from a komatiitic source. 39Ar/40Ar dating of the gold mineralisation in the Tennant Creek Block place the age of this event at 1825 Ma, towards the end of the felsic volcanism of the Barramundi Orogeny. Therefore the gold mineralisation in both the Yilgarn Craton and Tennant Creek Block can be related to the waning stages of a major period of felsic magmatism. This can be interpreted to mean that gold originated from late felsic magmas or that it was derived from the supracrustal rocks, buried deep in the crust, during the peak metamorphism in the lower crust.

Geodynamic evolution of the Proterozoic Mount Isa terrain

Abstract The Proterozoic Mount Isa terrain records the effects of four periods of intraplate tectonism. The c . 1870 Ma Barramundi Orogeny was characterized by a massive felsic magmatic event, and global correlations suggest a physical link between Australia and Laurentia at this time. Thereafter, the terrain underwent an extensional history spanning 200 Ma involving repeated episodes of rifting, post-rift subsidence and associated depositional and magmatic phases. This protracted rifting history resulted in a cumulative stratigraphic thickness of up to 25 km above attenuated continental crust. Rifting was interrupted prior to the formation of ocean crust by the compressional Isan Orogeny (1590–1500 Ma). The Isan Orogeny was synchronous with low-pressure high-temperature metamorphism and widespread metasomatism. In the waning stages of shortening, the Mount Isa terrain evolved into a wrench system characterized by an extensive network of strike-slip faults. The current level of exposure in this terrain provides spectacular examples of superimposed rifts, basin inversion, and wrench geometries developed at middle to upper crustal levels.

Time constraints on the evolution of the Tennant Creek Block, northern Australia

Recent ion-microprobe UPb zircon age determinations on crustal components of the Palaeoproterozoic Tennant Creek Inlier have identified a relatively short (∼ 30 m.y.) history for the major magmatic events in the area, including those related to the Barramundi Orogeny. This work independently confirms the revisions of the Tennant Creek stratigraphy proposed by Donnellan et al. (1991). The oldest known rocks from the area are the volcaniclastic turbidites of the Warramunga Formation, which were deposited in a rapidly subsiding basin at 1862 ± 9 to 1859 ± 13 Ma. Subordinate zircon populations in the greywackes indicate earlier magmatic activity at 1930 ± 12 and 1908 ± 15 Ma. The regional shortening (D1) and contemporaneous intrusion of voluminous and chemically homogeneous granites (and associated felsic porphyry dykes), known across northern Australia as the Barramundi Orogeny, occurred here between 1858 ± 12 and 1845 ± 4 Ma. Following uplift, the felsic volcanics and volcaniclastics of the Flynn Subgroup were extruded between 1845 ± 4 and 1827 ± 9 Ma. During this interval, felsic porphyry dykes and minor granite bodies probably related to the Flynn Subgroup volcanism intruded the Warramunga Formation sediments. Magma source regions contain components as old as 3.0 Ga, as revealed by zircon inheritance in most of the analysed rocks. The youngest recognised igneous activity in the area are the intrusion of the “Warrego granite” at 1700-1650 Ma and the Gosse River East granite at 1712 ± 5 Ma. The chronostratigraphy presented here is remarkably similar to that of parts of the well-exposed Palaeoproterozoic Trans-Hudson and Wopmay orogens of northern America.

UPb zircon dating of tectonomagmatic events in the northern Arunta Inlier, central Australia

The Mount Doreen area of the northern Arunta Inlier has a Proterozoic magmatic and tectonic history that extends over 300 Ma. The oldest unit, the turbiditic Lander Rock beds (LRB), was folded and metamorphosed from greenschist to granulite grade during the Yuendumu Tectonic Event. A UPb zircon age of 1880±5 Ma for the late-tectonic Ngadarunga Granite provides a minimum age for this event and supports its correlation with the widespread Barramundi Orogeny of northern Australia. Two subsequent major deformations, the Hardy and the Wabudali Tectonic Phases, considered to represent discrete phases of the Strangways Orogeny, are tentatively placed at around 1770 Ma. The Hardy Tectonic Phase locally retrogressed the LRB and produced strong foliations in some granites, including one of the Carrington Suite dated at 1779±6 Ma. The Wabudali Tectonic Phase formed high-strain zones, in places more than 2 km wide, within which the sedimentary Reynolds Range Group was tightly folded and the LRB were refolded and retrogressed. Felsic volcanics and arenites of the fault-bound Nicker beds and Patmungala beds, dated at 1772±5 Ma and 1799±10 Ma, respectively, were also tightly folded during the Strangways Orogeny. Juxtaposition of low-grade and high-grade LRB took place during faulting that occurred after the 1770 Ma tectonism, but prior to post-tectonic granites which may be indirectly related to the ∼ 1600 Ma Chewings Orogeny of the southern Arunta Inlier. One post-tectonic granite (1635±9 Ma) is associated with a mafic to intermediate intrusive complex and another (1567±11 Ma) is part of an extensive megacrystic suite that intrudes folded Reynolds Range Group. Zircon inheritance was found in five of the six analysed samples, with ages ranging from 1.85 to 3.45 Ga.

Geochronology of early to middle Proterozoic fold belts in northern Australia: a review

This geochronological review integrates geologically relevant isotopic data from the several early to middle Proterozoic fold belts of northern Australia. A number of firm chronological benchmarks, largely established by means of U-Pb zircon studies, now provide a time framework within which to better quantify the tectonostratigraphic history of many of these terranes. The apparent, worldwide dearth of crustal events in the earliest Proterozoic, between 2500 and 2000 Ma, was broken in northern Australia with the advent of a major crust-forming episode between 1880 and 1850 Ma ago. These rocks may have evolved from an initial mantle or lower crustal melting and fractionation process about 400–300 Ma earlier, that is evidenced from Sm-Nd model ages. The extent, involvement, and/or degree of assimilation of any pre-existing Archaean crust is small, but whether or not it is negligible or zero is not satisfactorily known. The 1880–1850 Ma event, the Barramundi Orogeny, is well represented in northern Australia, both lithologically and analytically, and the rocks that pre- and post-date it have a similar tectonic setting over very wide areas of the continent. Two consistent and widespread elements of this tectonism are regional metamorphism and deformation of the first cycle of supracrustals (Barramundi Orogeny), and crystallization of I-type, K-rich felsic magmas closely following and, in some cases, overlapping with deformational processes. In the Halls Creek Inlier, the ages of this rapid deep crustal to supracrustal tectonic transition cannot be distinguished within the range 1860-1850 Ma. This major yet short-lived tectonism is mirrored in other fold belts such as Pine Creek, Tennant Creek, and Mount Isa, in which U-Pb zircon ages give slightly older constraints of 1885–1870 Ma, 1920-1870 Ma and 188510 Ma, respectively. The ensuing felsic magmatism in these latter terranes continued for a few tens of millions of years, with the crystallization and emplacement of comagmatic volcanic/plutonic pairs throughout, in the interval 1870-1860 Ma. In the Georgetown and Arunta Inliers, direct evidence of this otherwise ubiquitous event, if present, is masked by younger high-grade metamorphism. In the latter, however, metamorphic crustal components having approximate protolith ages of this order can be inferred from their evolved isotopic signatures. The geochronological and geochemical coherency of the extensive early Proterozoic, ∼1870 Ma magmatism contrasts with that of post-1800 Ma magmatism, which is less extensive, generally anorogenic, commonly bimodal in character, and varies in age from one terrane to another. Several major sedimentary basins were being filled at this time. Major igneous events at 1790-1740 Ma, 1670 Ma and ∼1500 Ma are recognized. Elongate, sublinear volcanic and plutonic belts, 1790-1740 Ma old, are present at Mount Isa. In high-grade granitic gneisses of the Arunta Inlier, a few U-Pb zircon ages and extrapolated Rb-Sr protolith ages are coincident at about 1760-1750 Ma, indicating that this event may be important in the development of the ‘Division 2’ sequences of that fold belt. The platformal Hart Dolerite and Oenpelli Dolerite, two of the largest mafic intrusions in the world, were emplaced at 1762 ± 25 Ma and 1688 ± 13 Ma. Younger felsic plutonism and volcanism gave rise to rapakivi-type granites in the Mount Isa, Tennant Creek and The Granites-Tanami Inliers at ∼ 1670 Ma, a time close to that of the Aileron deformational/metamorphic event in central Australia. Further, at ∼ 1650 Ma, there is growing evidence of an unexpectedly coherent hydrothermal episode that reset or disturbed many Rb-Sr ages, gave rise to pegmatites, and was possibly associated with mineralization in the Davenport and eastern Arunta Inliers. Discrete middle Proterozoic deformational events, between 1610 and 1470 Ma, punctuate the tectonostratigraphic history in the Arunta, Mount Isa and Georgetown fold belts where they are best documented.

The Proterozoic Davenport province, central Australia: regional geology and geochronology

The Davenport province forms the southern part of the Tennant Creek Inlier and lies to the north of the Arunta Inlier. The oldest rocks exposed are turbidites and minor 1880-1870 Ma old felsic volcanics of the Warramunga Group. These were folded, probably during the Barramundi Orogeny, and intruded by granite before being overlain by the Hatches Creek Group, a sequence up to 10 000 m or more thick of fluvial to shallow marine sedimentary and bimodal volcanic rocks. A rift-sag model of basin development involving crustal extension in an intracratonic setting is suggested for this group. Interpretation of U-Pb zircon data for felsic volcanics in the lower part of the Hatches Creek Group is hampered by problems of ancient Pb inheritance, but a preferred crystallization age of 1820-1810 Ma is indicated. Two episodes of upright concentric folding, about NW-SE- and NE-SW-trending axes, preceded emplacement of granite at ∼ 1660 Ma or earlier. Rb-Sr whole-rock data for felsic volcanics from the Hatches Creek Group are tentatively interpreted to indicate a region-wide hydrothermal alteration event at 1645 ± 44 Ma; this alteration may have been associated locally with W, Cu, Bi and Mo mineralization.

Age of the barramundi orogeny in northern Australia by means of ion microprobe and conventional U-Pb zircon studies

U-Pb zircon geochronological studies are used to quantify the tectonostratigraphic history of a major crust-forming event in early Proterozoic terranes of northern Australia. Magmatism and tectonic processes associated with this event, the Barramundi Orogeny, appear similar over very wide areas, about one third of the Australian continent. The Barramundi event marks the deformation, metamorphism and cratonization of the earliest Proterozoic ∼2.0−1.9 Ga basinal successions, and it was followed by and closely linked to extensive orogenic felsic magmatism. The Yaringa Metamorphics are an inlier of paragneiss and schist that pre-dates 1865 ± 3 Ma Leichhardt felsic magmatism and younger basin formation in the Mount Isa Inlier. From an ion microprobe U-Pb zircon study of massive and migmatitic gneiss, the time of Yaringa metamorphism is established at 1890±8 Ma. Recognized younger Proterozoic deformations in the interval 1610−1550 Ma are generally not evident in zircon U-Pb systems, but have totally reset local Rb-Sr whole-rock values. Conventional U-Pb work on multi-grain zircon samples of Yaringa gneiss gives a geologically meaningless age (2090±40 Ma) that is an artifact of complex zircon growth, part of which was initially inherited from a 2.55 to 2.2 Ga provenance, and the other major part of which was formed in situ during the 1890 Ma high-grade metamorphism. Predictably, for simple zircon systems in low-grade metavolcanic térranes, conventional and ion microprobe zircon ages are in close agreement. Dating of volcaniclastic sequences above and below the Barramundi tectonic break in the Pine Creek Inlier brackets the orogeny in this terrane to a similar time frame, 1885–1870 Ma. Some zircons which crystallized at this time form selvedges around older cores whose age of 2100-2000 Ma may be relics of an earlier deep crustal underplating. The uniform chemistry of post-Barramundi felsic magmatism, and the similar tectonic setting of the areally extensive Barramundi event, are mirrored by their temporal coherency. Cycles of geosynclinal deposition, burial, metamorphism and uplift took place during intervals of several million years or less, implying comparable rates for early Proterozoic orogenesis to those established for Tertiary and Quaternary settings.

Geochronology of a rapid 1.85–1.86 Ga tectonic transition: Halls Creek orogen, northern Australia

Early Proterozoic orogenic rocks of the Halls Creek orogen are characterized by widespread, ensialic orogeny and magmatism, and linear, post-tectonic igneous complexes several hundred kilometres long. Conventional UPb zircon techniques are applied to erect a precise chronological framework quantifying the tectonic evolution of this fold belt. Volcanism associated with early rifting (Ding Dong Downs Volcanics, lowermost Halls Creek Group) whose age has not yet been determined, is followed by a quartz-rich, arenaceous formation, and in turn by fine-grained, variably volcanogenic, phyllitic deposits with abundant carbonates. Stratabound, high-level ‘rhyolitic’ sills are emplaced into younger parts of this Biscay Formation (∼ middle Halls Creek Group). These have distinct incompatible trace element compositions, with large enrichments in Zr, Nb and Y, and are regarded as second stage A-type melts derived from a Rb-depleted granulite source. They are possibly coeval with tuffs in the same unit and, if so, the sill's UPb zircon age of 1856 ± 5 Ma closely dates this sequence, specifically the onset of turbidite deposition and commencement of orogenic activity in inferred provenance zones to the immediate west. However, confirmation of such an age interpretation depends on substantiation of this inferred coeval link between the dated sill and the Biscay Formation tuffs, and until such the 1856 ± 5 Ma result remains a minimum for the age of the Halls Creek Group. Subsequent compressional orogeny of the basinal trough sediments was accompanied by deformation, high-temperature polymetamorphism, and syn-tectonic plutonism. Anatectic pegmatite, believed to have formed as a melt product of granulite-facies metamorphism, has a UPb zircon age of 1854 ± 6 Ma. This age for high-grade metamorphism is in agreement with reassessed RbSr whole-rock ages measured previously. It closely controls the timing of the Barramundi orogeny as being somewhat younger in this subprovince than elsewhere in northern Australia, and may imply a relatively short interval, of a few to 13 million years, between supracrustal deposition and deep crustal orogenesis. A better constrained and even more rapid tectonic transition is evident from the Whitewater Volcanics, late tectonic, felsic volcanism dated at 1850 ± 5 Ma. The onset of this unconformably younger volcanism is marked by a concomitant change in tectonic style. This changeover from a pre-cratonic to cratonic setting took place in a few million years or less.