The Whundo Group, in the Pilbara Craton of northwestern Australia, is exceptional amongst Mesoarchaean, or older, volcanic sequences in that it preserves geochemical characteristics that are extremely difficult to interpret in any way other than reflecting modern-style subduction processes, most likely at an intra-oceanic arc. The group includes boninites, interlayered tholeiitic and calc-alkaline volcanics, Nb-enriched basalts, adakites, and shows evidence for flux melting of a mantle wedge. The geochemical data are also consistent with geological relationships that infer an exotic terrane with no felsic basement. These data provide clear evidence for modern-style subduction processes at 3.12 Ga.

Describes a suite of LREE-enriched basaltic to felsic magmas from the Maillina Basin, Pilbara Craton. Uses geochemistry and Sm-Nd isotopic data to argue for the operation of subduction (of oceanic crust) processes at c. 3.0 Ga.

This education resource comprises; - 10 page booklet with background information and descriptions of each image - includes world plate boundaries and earthquake distribution, distribution of earthquakes in Australia and examples of earthquake events, Australia's Seismological Network managed by Geoscience Australia, how earthquakes are measured, a case study of Tennant Creek and a map depicting Australia's earthquake hazard. - 15 slides Suitable for primary level Years 5-6 and secondary level Years 7-12.

This slide set on Australian volcanoes comprises - 12 page booklet with background information and descriptions of each image - 15 slides - student question/s for each slide Learn the history of Australia's hot spot volcanoes over 60 million years. Compare and contrast recent Australian volcanoes with those elsewhere and examine 9 Australian volcanoes in detail. Suitable for primary levels Years 5-6 and secondary levels Years 7-10

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The timing and mechanisms of crustal growth, the role (if any) of modern-style plate tectonics and potential secular changes, during the Archaean are poorly understood. To provide constraints on these questions, we present isotopic and geochemical data for the well exposed, classic, Paleoarchean to Mesoarchean Pilbara Craton (>3.5 to <2.8 Ga), and the large, but poorly outcropping, largely Neoarchean Yilgarn Craton (>3.0 to 2.6 Ga), both in Western Australia. Both are dominated by typical Archaean granite-greenstone geology. Regional Sm-Nd data from felsic magmatism indicates both cratons are comprised of large proto-cratonic cores with relatively uniform Nd TDM model ages - c. 3.5-3.6 Ga for the eastern Pilbara, c. 3.1-3.3 Ga for the western Yilgarn. Distinct isotopic breaks separate these proto cratons from marginal terranes with both significantly younger, but also more domainally-variable, TDM model ages. The cratonic nucleii are characterised by episodic felsic magmatism spanning 650 Ma (from >3.47 Ga to 2.85 Ga) for the Pilbara Craton and 350 Ma years (3.0 Ga to 2.63 Ga) for the Yilgarn Craton. In both, this magmatism was dominated by transitional TTG-type compositions, and shows secular variations to more potassic, siliceous compositions, consistent with an increasing component of crustal reworking. Definitive arc-related magmatism, e.g., boninites, calc-alkaline andesites, sanukitoids, are largely absent. The surrounding marginal terranes are characterised by isotopically younger domains that broadly correspond to geological domains. Importantly, these domains are either characterised by primitive isotopic signatures (i.e., Nd TDM ages close to crystallisation ages), and/or contain evidence for arc-related magmatism, i.e., boninites, sanukitoids (Pilbara), calc-alkaline andesites (Yilgarn). The Pilbara cratonic nucleus is best interpreted to have formed as a result of vertical crustal growth in an episodic plume-environment. The Yilgarn cratonic nucleii possibly formed in a similar manner, though the evidence is not as clear. Subsequent marginal arc-related magmatism affected both cratons and the marginal terranes in both are best interpreted as representing lateral crustal growth and terrane accretion, not dissimilar to modern day plate tectonics. Best indications are that such accretion commenced at least by 3.2 Ga.

Felsic units of the Hiltaba Association Granites and the comagmatic Gawler Range Volcanics (together the GRHVP) can be divided into four supersuites: the I-type Malbooma and Jenners Supersuites; and the A-type Roxby and Venus Supersuites. All units are aged between ~1595 - 1575 Ma. Major and trace element modelling of granites of both the strongly fractionated and evolved Malbooma and moderately fractionated and evolved Jenners Supersuites suggests derivation by crystal fractionation from granodiorite compositions. Neodymium isotopes of the granites and volcanics indicate a more primitive Nd input than available from the known Archaean and Palaeoproterozoic crust alone. However, these felsic rocks are thought to be derived by partial melting of granodiorite compositions, rather than being the result of extensive fractionation from basalts. Mafic rocks of the GRHVP have variable isotopic and chemical signatures. The Lady Jane Diorite at Tarcoola has Nd ~0.2, and a composition incompatible with OIB derivation, but compatible with partial melting of a crustally-contaminated MORB. Some of the alkaline mafic/ultramafic rocks have Nd values as high as +4 [1]. Maximum zircon saturation temperatures of ~800C and ~900C for the I- and A-type supersuites respectively, are significantly lower than those of ~1000C measured by other geothermometers [2] for the Yardea Dacite (Roxby Supersuite), but show that the A-type supersuites were higher temperature than the I-type supersuites. The distribution of high temperature A-type granites shows some correlation with areas of coeval iron oxide copper-gold mineralisation. The coincidence of very high temperature granites with crustal Nd signatures, and mafic rocks with primitive to weakly evolved signatures indicates an extensional environment with very elevated geotherm and mantle upwelling. However, the felsic rocks are dissimilar to those associated with mantle plumes, and therefore a back arc distal to a continental-oceanic subduction zone setting is suggested, perhaps analagous to the present Altiplano Puna region of the Central Andes.

Presented at the Evolution and metallogenesis of the North Australian Craton Conference, 20-22 June 2006, Alice Springs. The North Australian Craton, which stretches from the Kimberley Craton, in the west, to the Mt Isa Inlier, in the east, and from the Pine Creek Orogen, in the north, to the Warumpi Province in the south, began in the late Archaean and continued through much of the Palaeoproterozoic, terminating at about 1635 Ma with accretion of the Warumpi Province during the Leibig Orogeny (Close et al., 2006). The growth of this craton was accompanied by mineral systems that produced world class lode gold (Callie), Zn-Pb-Ag (Mt Isa-type-MIT: Mt Isa, Hilton, HYC and Century; and Broken Hill-type-BHT: Cannington), unconformity U (Jabiluka), and iron oxide-copper-gold (IOCG: Ernest Henry) as well as smaller, but still economic, magmatic-related W-Mo and Sn-Ta deposits, and uneconomic volcanic-hosted massive sulphides (VHMS) and layered mafic intrusion-related Ni-Cu-PGE deposits. Over the past fifteen years workers at Geoscience Australia, the Northern Territory Geological Survey, and the Geological Survey of Western Australia have established temporally constrained geological and tectonic frameworks for the constituent parts of the North Australia Craton, into which, mineral systems can be placed. Although some of the frameworks presented here are well established, others are speculative and are presented to assess potential implications to the evolution of the North Australian Craton. <p>Related product:<a href="https://www.ga.gov.au/products/servlet/controller?event=GEOCAT_DETAILS&amp;catno=64764">Evolution and metallogenesis of the North Australian Craton Conference Abstracts</p>

Well-preserved volcanic sequences span the Paleoarchean to Neoarchean evolution of the Pilbara Craton, in northwestern Australia. This region provides the best physical evidence bearing on the stage of Earth's history when modern-style tectonic processes began. Paleoarchean assemblages in the eastern nucleus of the craton (the 3.51-3.24 Ga Pilbara Supergroup) show few features that can reasonably be interpreted as evidence for modern-style subduction processes. Incompatible trace element-enriched felsic volcanic horizons show geochemical evidence for the interaction between mafic magmas and crust, but this evidence, on its own, can equally well be interpreted in terms of either a subduction-enriched mantle source or local and limited assimilation of felsic crust into the voluminous tholeiitic magmas that dominate the Pilbara Supergroup. Viewed in context within the thick autochthonous and consistently upward-younging Pilbara Supergroup, these felsic units are most likely related to the same plume-dominated processes that formed the basalts that dominate the supergroup. It is very unlikely that modern-style plate tectonic processes played any role in the Paleoarchean evolution of the Pilbara Craton, although some form of nonuniformitarian (e.g. flat) subduction process may have operated. In stark contrast, the Mesoarchean units of the West Pilbara Terrane and the late-tectonic basins that cover that boundary between the West and East Pilbara Terranes, show clear evidence for modern-style convergent margin processes. Igneous rocks in this belt, which flanks the old eastern cratonic nuclei, have enriched geochemical signatures that cannot be accounted for by crustal contamination. This region is also characterised by a linear magmatic and structural fabric, by the presence of lithologically and geochronologically exotic belts, and by the presence of a broad belt of isotopically more juvenile crust. The collective strength of these arguments provides compelling evidence that a modern-style oceanic arc fringed the East Pilbara Terrane at 3.12 Ga and accreted to that terrane by 2.97 Ga. These assemblages mark the minimum age for the birth of modern-style plate subduction process.

Archaean TTGs, as originally defined comprise intermediate to felsic rocks characterised by high Na2O/K2O, low to moderate LILE contents and no potassium-enrichment with increasing differentiation. The majority of such rocks also carry a high-pressure signature, identified by elevated Sr (i.e., are Sr-undepleted) and Eu, fractionated REEs, with low HREE (Y- and HREE-depleted), and high Sr/Y. These latter characteristics are also often used to define TTGs and are commonly thought to reflect an origin via slab melting (with or without mantle-wedge interaction), largely as a necessary corollary of a warmer Archaean mantle. Our work, however, shows that within many Archaean terranes there exists a subclass of granites (which we call transitional TTGs), that when compared to `true? TTGs have higher LILE contents, show strong enrichment in LILEs (e.g., K2O) with increasing differentiation, and tend towards more siliceous compositions (68-77% SiO2), but still possess a similar high-pressure signature. Such transitional TTGs are contemporaneous with, or postdate true TTGs but where present also grade to more mafic compositions that overlap with true TTGs. These Transitional TTGs dominate some cratons, the best example being the Yilgarn Craton where true TTGs form only a small percentage of total granites. Sm-Nd isotopic and inherited zircon data indicate that the petrogenesis of most transitional TTGs requires the involvement of pre-existing crust. What is not clear, given the difficulty in reconstructing tectonic environments in the Archaean, is whether this crustal component represents input via the subduction process (e.g., subducted sediments), represents a response to thicker pre-existing crust (AFC processes), or whether these rocks form from pure crustal melts in thickened Archaean crust. Comparison of both TTG-types with ?apparent? modern-day TTG analogues ? adakites ? shows somewhat similar groupings. The major adakite group (group 1, mostly 58-68% SiO2), is characterised by a narrow range in La/Sm (5.5-3.0), and Sm/Yb (1.5-3.5), moderate Sr (400-700 ppm) and low to moderate LILE. This group overlaps significantly with true TTGs although the latter tend to have higher La/Sm (up to 9) and Sm/Yb (up to 10+). The second adakite group has higher Sm/Yb (6-10), La/Sm (6-9) and Sr (<500 to 1500 ppm), and typically higher LILE contents, and appears to be confined to continental arc regimes and is most similar to transitional TTGs. Notably both TTG-types extend to significantly more silica and LILE-rich compositions than seen in the majority of adakites. A distinctive, significantly more mafic (50-60+% SiO2) adakite group with high to very high Sr (up to 1500-2500 ppm), and high Sm/Yb (to 10-12), appears distinct from all Archaean TTGs. Group 1 adakites are most consistent with melting of a MORB source leaving an amphibole-bearing (i.e., non-eclogitic) residue, while group 2 adakites are interpreted to represent either melting at higher pressure or greater degrees of slab melting (leaving an eclogitic residue), with their higher LILE contents reflecting either subducted sediment input or processes related to the presence of continental crust (e.g., AFC). In contrast, the range in La/Sm and Sm/Yb in true TTGs suggests greater involvement of garnet during melting in Archaean times (garnet amphibolite to eclogite residue) relative to modern day (group 1) adakites, perhaps reflecting a greater depth of generation or drier melting. Importantly, although pure crustal melting can not be ruled out, analogies with group 2 adakites shows that transitional TTGs can be produced as slab melts particularly in continental arc environments ? both models maybe applicable and may have varied in relative importance through time. Further, the presence of transitional TTGs in Archaean cratons can be used to infer significant pre-existing continental crust. (THIS ABSTRACT MODIFIED FROM ORIGINAL).