Tectonic models for the latest Paleoproterozoic to earliest Mesoproterozoic evolution of eastern Australia (circa 1620–1500 Ma) are diverse and either emphasize plume or plate margin activity, neither of which satisfactorily explains all geological observations. The dichotomy is largely attributed to geochemical, spatial and temporal data that suggest voluminous A‐type felsic magmas are plume related, whereas distribution of arc‐related magmas and intense orogenic overprint suggest plate margin activity. The salient geological events include arc‐related magmatism at circa 1620–1610 Ma followed by a magmatic hiatus coincident with north‐south crustal shortening (1610–1590 Ma) and a magmatic flare‐up of A‐type felsic magmas throughout the Gawler Craton (circa 1595–1575 Ma). These magmas form the oldest component of a northward younging hot spot track that extends to the Mount Isa Inlier. At circa 1590–1550 Ma, arc magmatism resumed along the northern margin of the Gawler Craton and the rest of eastern Australia records a 90° shift in the regional shortening direction related to activity along the eastern margin of the Australian continent. A plume‐modified orogenic setting satisfies all of the spatial and temporal relationships between magma generation and orogenic activity. In this model, the Gawler Craton and the adjacent subduction zone migrated over a mantle plume (circa 1620–1610 Ma). Resultant flat subduction caused transient orogenesis (1610–1595 Ma) in the overriding plate. Slab delamination and thermal assimilation of the plume and the subducting slab caused a switch to crustal extension in the overriding plate, resulting in extensive mantle‐derived and crustal melting in the Gawler Craton (1595–1575 Ma).

Granitic melt migration and pluton emplacement are commonly closely associated with transcurrent shear zones. The processes that link granites to shear zones are not yet fully understood. The dextral-transpressive Karakoram shear zone in Ladakh, NW India, exposes anatectic rocks where synkinematic melt migration and ponding at kilometer scale were controlled by competency contrasts. Metasedimentary rocks and a dominantly granodioritic calc-alkaline intrusion underwent fluid-present partial melting at upper-amphibolite facies to produce leucogranite sheets and irregular intrusive masses dated at 21-14 Ma. Leucogranitic magmas ponded in the low-pressure strain shadow of the competent granodioritic talc-alkaline pluton, giving rise to (a) migmatitic rocks that are pervaded by irregular leucogranite intrusions at a scale of meters or tens of meters, and (b) the growth of the Tangtse pluton, a kilometer-scale sheeted complex. Thus, magmas accumulated during shearing and anatexis in a low-pressure strain shadow within the Karakoram shear zone. This magma provided a readily available magma source that could have been tapped to feed larger plutons at shallower levels by modifications in the pressure distribution accompanying changes in shear zone geometry and kinematics. We conclude that shear zones tapping anatectic regions act as magma pumps, creating and destroying magma traps at depth as they evolve, and leading to incremental magma addition to upper-crustal plutons.

Efficient extraction of granitic magma from crustal sources requires the development of an extensive permeable network of melt-bearing channels during deformation. We investigate rocks that have undergone deformation and melting within the Karakoram Shear Zone of Ladakh, NW India, in which leucosome distribution is inferred to record the permeable network for magma extraction. Delicate structures preserved in these rocks record the development of this permeable magma network and its subsequent destruction to form a mobile mass of melt and solids, resulting from the interplay between folding and magma migration. During folding, magma migrated from rock pores into layer-parallel and axial-planar sheets, forming a stromatic migmatite or metatexite with two communicating sets of sheets, intersecting parallel to the fold axis. Once the network was developed, folding and stretching was eased by magma migration and slip along axial planar magma sheets. Folding and magma migration led to layer disaggregation, transposition, and the formation of a diatexite where rock coherency and banding were destroyed. A number of structures developed during this process such as cuspate fold hinges, disharmonic folds, truncated layering, shear along axial planar leucosomes, and flow drag and disruption of melanosomes. In this system, magma migration was an integral part of deformation and assisted the folding and stretching of metatexites, while folding gave rise to a magma sheet network, now preserved as leucosomes, as well as the pressure gradients that drove magma migration and the breakup of the metatexite. Thus, metatexite folding increased melt interconnectivity, while magma mobility increased strain rate and released differential stresses.

Protracted metal and sulfur contributions to the Eastern Succession iron-oxide–Cu–Au (IOCG) province of the Proterozoic Mount Isa Block occurred primarily as a consequence of long-lived fluid fluxes, stimulated by repeated emplacement of voluminous magmas during rifting and thin-skinned convergence cycles. Although there is a direct role for felsic intrusions of the ca. 1530 Ma Williams–Naraku Batholith in hydrothermal ore genesis, these intrusions came at the culmination of protracted metal reorganization in the crust, not as the sole cause, as indicated by geochronology, mineral paragenesis, and the shapes of some orebodies relative to pre-1530 Ma structures. Spatial and geochemical data on mafic rocks suggests that the concentration of copper and gold into some of the mineral deposits involved a significant component of m- to 1000 m-scale remobilization and reworking of early enrichments, formed during basin evolution and initial inversion, by later regional metamorphic and magmatic–hydrothermal fluids. Osborne (eastern domain) and Eloise-type ores (or ore precursors) initially formed during or before the 1600 Ma regional metamorphic peak, by interaction of basinal or early metamorphic fluids with mafic rocks and ironstones, whereas younger oxidised brines released by the Williams/Naraku intrusions at ∼1530 Ma overprinted magnetite ± sulfides at Osborne (western domain) and Starra to produce the presently mined hematite–chalcopyrite ores. CO2 with mantle-like stable isotope character is abundant at all stages of the hydrothermal evolution and is present in high concentrations even in felsic magmas. We thus infer that CO2 was released directly from enriched mantle, or indirectly from mafic magmas, contaminating the process of volatile release from the top of felsic magma chambers and contributing to production of carbonate gangue in orebodies. Ernest Henry, the largest IOCG deposit in the district, remains the best candidate for a true syn-granite magmatic–hydrothermal orebody. We infer that ore deposition occurred when mantle- or mafic-derived H–C–O–S fluid mixed with saline, oxidised brine derived from the Williams/Naraku Batholith, stripping some ore components (Fe, Sr, Cu) from the local wallrocks, in particular mafic rocks. The protracted hydrothermal evolution is reminiscent of modern back-arcs but the position of the arc during the post-1800 Ma history was hundreds of kilometres east. We propose that mantle enrichment in volatiles occurred around a pre-1840 Ma plate boundary leaving the Kalkadoon–Leichhardt belt as a magmatic arc remnant. This metasomatised mantle was subsequently re-tapped during prolonged distal back-arc spreading and periodic shortening accompanying ongoing magmatism.

We present new SHRIMP zircon U–Pb data from pre 1.8Ga 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±4Ma (2σ), and constrain the Barramundi Orogeny in the western Fold Belt to ca. 1.87Ga, at the bottom part of the previously reported range of ca. 1.90–1.87Ga. 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. 3300–3600Ma) 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.

Proterozoic rocks of the Cloncurry district in NW Queensland, Australia, are host to giant (tens to hundreds of square kilometers) hydrothermal systems that include (1) barren regional sodic–calcic alteration, (2) granite-hosted hydrothermal complexes with magmatic–hydrothermal transition features, and (3) iron oxide–copper–gold (IOCG) deposits. Fluid inclusion microthermometry and proton-induced X-ray emission (PIXE) show that IOCG deposits and the granite-hosted hydrothermal complexes contain abundant high temperature, ultrasaline, complex multisolid (type 1) inclusions that are less common in the regional sodic–calcic alteration. The latter is characterized by lower salinity three-phase halite-bearing (type 2) and two-phase (type 3) aqueous inclusions. Copper contents of the type 1 inclusions (>300 ppm) is higher than in type 2 and 3 inclusions (<300 ppm), and the highest copper concentrations (>1,000 ppm) are found both in the granite-hosted systems and in inclusions with Br/Cl ratios that are consistent with a magmatic source. The Br/Cl ratios of the inclusions with lower Cu contents are consistent with an evaporite-related origin. Wide ranges in salinity and homogenization temperatures for fluid inclusions in IOCG deposits and evidence for multiple fluid sources, as suggested by halogen ratios, indicate fluid mixing as an important process in IOCG genesis. The data support both leaching of Cu by voluminous nonmagmatic fluids from crustal rocks, as well as the direct exsolution of Cu-rich fluids from magmas. However, larger IOCG deposits may form from magmatic-derived fluids based on their higher Cu content.

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The three-dimensional crustal architecture of the eastern part of the Mount Isa Inlier is investigated from serial cross-sections constructed using geological map data, revised chronostratigraphy, gravity, magnetics, worms (multiscale wavelet edges of potential field data) and seismic data. The top part of the crust consists of rift and platform type metasediments that were deposited in three cover sequences from 1850 to 1610 Ma. These rocks constitute the Mount Isa Eastern Succession, and they were intruded by mafic–felsic plutons, dykes and sills of various ages before and during the Isan Orogeny (ca. 1.6–1.5 Ga). The Eastern Succession overlies a felsic metamorphic basement, which in turn sits on a tonalitic–gabbroic lower crust. The depositional basin architecture for the Eastern Succession was controlled by major N–S trending structures that penetrated the lower crust, and accommodated E–W extension. These structures also underlie major upper crustal structures such as the Mitakoodi Culmination and Snake Creek Anticline that were formed by contraction in the Isan Orogeny. Positive inversion may therefore have been a key process in the evolution of the eastern part of the inlier, and governs its architecture at the crustal scale. Inversion involved reactivation of basement-penetrating structures, which localised contractional structures in the cover sequences above, as well as influencing pluton emplacement. The felsic metamorphic basement may have been penetratively deformed during inversion. The spatial association between the basin-controlling and contractional structures suggests that either early extensional displacements were completely reversed by later contraction, or that much of the Eastern Succession has remained essentially parauthochthonous relative to the basement.

[Extract] Geochemical zonation in the breccia-hosted Ernest Henry iron-oxide-Cu-Au deposit of the Proterozoic Mt Isa Block occurs in an oscillatory fashion at micro-scales and irregular to broadly concentric fashions at broader scales.

Mesoproterozoic A-type magmatic rocks in the Gawler Craton, Curnamona Province and eastern Mount Isa Inlier, form a palaeo-curvilinear belt for reconstructed plate orientations. The oldest igneous rocks in the Gawler Craton are the Hiltaba Granite Suite: c. 1600-1575 Ma. The youngest in the Mount Isa Inlier are the Williams-Naraku Batholiths: c. 1545-1500 Ma. The belt is interpreted as a segment of a hotspot track that evolved between c. 1600 and 1500 Ma. This hotspot track may define a quasilinear part of Australia's motion between 1636 and 1500 Ma, and suggests that Australia drifted to high latitudes. An implication of this interpretation is that Australia and Laurentia may not have been fellow travellers leading to the formation of Rodinia. A hotspot model for A-type magmatism in Australia differs from geodynamic models for this style of magmatism on other continents. This suggests that multiple geologic processes may be responsible for the genesis of Proterozoic A-type magmas.

Fluid inclusions in six quartz veins associated with Cu-Au mineralisation at the giant Ernest Henry iron oxide-copper-gold deposit (167 Mt 1.1% Cu, 0.54 ppm Au) in northwest Queensland, have been analysed for naturally occurring and neutron produced noble gas isotopes of Ar, Kr and Xe.A combination of thermal and mechanical decrepitation methods enables distinction between four types of fluid inclusion. Ultra-high-salinity (similar to 30 to 70 wt. % NaCl eq.) fluid inclusions have compositions that define two end-members that are variably mixed in different samples. The first end-member has a Ar-40/Ar-36 value of similar to 29,000, a Ar-40(E)/Cl value of similar to 3 x 10(-3) and mantle-like Br/Cl and I/Cl values of 1-2 x 10(-3) and similar to 11 x 10(-6), respectively. The second end-member has a much lower Ar-40/Ar-36 value of less than 2500, a Ar-40(E)/Cl value of similar to 10(-6), low Br/Cl values of similar to 0.4 x 10(-3) and I/Cl values of 1-2 x 10(-6) (all ratios are molar). Carbon dioxide and later, lower salinity liquid-vapour fluid inclusions have similar Ar-40/Ar-36 values of less than similar to 2500 in all samples.These data are compatible with genetic models in which Cu-Au mineralisation formed at a depth of 6-10 km, from circulation of magmatic fluids derived from regionally abundant 'A-type' granites and a high salinity halite dissolution brine generated from sedimentary formation waters in the upper crust. The largest source of CO2 was probably carbonate-rich lithologies in the mid-crust. Later, lower salinity fluids with a surficial origin diluted the mineralising brines and are preserved in the latest, secondary fluid inclusions.These data provide insight on the composition of crustal fluids during the Proterozoic. Furthermore, the magmatic fluid end-member, derived from melts generated by re-melting lower-crustal Paleoproterozoic igneous rocks with a mantle source, preserves mantle-like Br/Cl and I/Cl. These geochemical characteristics are interpreted to provide insight on I-recycling at subduction zones and the composition of seawater in the Paleoproterozoic. (C) 2007 Elsevier B.V. All rights reserved.

The Eastern Fold Belt of the Proterozoic Mt Isa Inlier of NE Australia is widely affected by Na-Ca metasomatism (albitisation) and hosts several economically important Fe-oxide-Cu-Au (IOCG) deposits that formed at mid-crustal levels of 6-10km. The intense albitisation and mineralization are usually related to aqueous and carbonic fluids preserved as fluid inclusions in coeval quartz veins. Similar fluid inclusions are seen in other IOCG provinces including prospects from the Wernecke Mountains, Canada. In most cases, the fluid inclusions are dominated by fluids that are geochemically similar to typical sedimentary formation waters with (40)Ar/(36)Ar of similar to 300-2,500, favouring an upper-crustal origin. Furthermore, Br/Cl values as low as 0.3x10(-3) and maximum salinities of similar to 30-70 wt % NaCl eq. favour the widespread dissolution of halite. However, some samples from both the Isan and Wernecke IOCG provinces contain fluid inclusions with maximum (40)Ar/(36)Ar values of greater than similar to 25,000 that are most likely to represent deeply-derived magmatic fluids. Magmatic fluids may have been sourced from regionally extensive A-type granites in the Mt Isa Inlier but have an uncertain source in the Wernecke mountains. Liquid CO(2) fluid inclusions have variable (40)Ar/(36)Ar values, but are dominated by (20)Ne/(22)Ne values of <9.8 indicating a dominantly crustal, metamorphic-origin. However, the highest value of similar to 10, accompanied by a (40)Ar/(36)Ar value of similar to 14,000 is arguably compatible with a minor magmatic component derived from a juvenile source. Finally, the Br/Cl and I/Cl values of these samples, and those from elsewhere in the Proterozoic Mt Isa Inlier, encompass a similar range as Phanerozoic fluid inclusions, suggesting similar processes have controlled halogen geochemistry since at least similar to 1.5 Ga.

Noble gas isotopes of He, Ar, Kr and Xe and the halogens Cl, Br, I present within fluid inclusions of hydrothermal quartz or sulphide, provide new insights on the origin of mineralising fluids. He and Ar isotopie ratios enable contributions of meteoric, crustal or mantle volatiles to be quantified. Together with Kr and Xe they can also provide evidence for phase separation or the presence of modern air. The halogens Cl, Br and I provide otherwise unavailable information on the acquisition of salinity. Contrasting styles of Cu-rich ore deposit in the Mt Isa terrane have been selected for study. The noble gas and halogen data indicate the composition of Proterozoic crustal fluids of diverse origin and from a deeper level of the crust than has hitherto been sampled. Magmatic and metamorphic fluid end-members provide insights into the composition of the Proterozoic mantle and deep crustal devolatilisation processes. Mineralisation resulted from mixing of surface- derived crustal fluids and deeply derived magmatic fluids in the east, and metamorphic devolatilisation fluids in the west.

The Proterozoic rocks of the Cloncurry district preserve the effects of some of the world's largest hydrothermal systems associated with extensive albitisation, brecciation and No-Ca alteration. These hydrothermal systems are broadly coeval with magmatism, and also host numerous structurally controlled Fe oxide and Cu-Au deposits (ca 1.60 Ga, 1.55-1.50 Ga). Fluid-inclusion, stable-isotope, and geochemical data from Cu-Au deposits indicate that the ore-forming fluids were high-T (>300-500 degrees C), highly saline (>26-70 wt% NaClequiv), typically CO2-bearing, and are mainly considered to be sourced by crystallising intrusions with contributions from other fluid sources and/or host rocks. Fe oxide and Cu-Au mineralisation in the district exhibit a range of interrelationships based upon the metal endowment, relative timing of Fe oxides and sulfides, and Cu:Au ratio. These interrelationships may be divided into four categories: (i) barren magnetite and/or hematite ironstones; (ii) Fe oxide-hosted Cu-Au mineralisation, where relatively Au-rich ore associated with pyrite and hematite overprints older magnetite-rich rocks: (iii) Fe oxide Cu-Au mineralisation, where both Fe oxides and Cu-Au mineralisation are cogenetically deposited; and (iv) Fe oxide-poor Cu-Au mineralisation, where relative Cu-rich mineralisation is associated with pyrrhotite and rare magnetite, and is hosted in relatively reduced rocks such as carbonaceous metasedimentory rocks. These categories reflect variations in fluid redox, fS, aFe, and temperature, as well as host-rock composition. The spectrum from Cu-rich to Au-rich mineralisation is a common phenomenon in Fe oxide-Cu-Au districts and predominantly reflects an increase in the redox of the ore-forming system. The apparent relationship between pH and metal solubility at different redox conditions suggests that Cu-Au mineralisation occurred as a result of decreasing fluid acidity by wall-rock reaction at the site of ore deposition, or potentially by mixing of fluids of different acidity. Fluid mixing provides an effective means to produce high-grade ore deposits via changing pH, cooling, and dilution in hydrothermal systems involving little wall-rock interaction.