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Curtis, Michael S., Simon P. Holford, Mark A. Bunch, and Nick J. Schofield. "Seismic, petrophysical and petrological constraints on the alteration of igneous rocks in the Northern Carnarvon Basin, Western Australia: implications for petroleum exploration and drilling operations." APPEA Journal 62, no. 1 (May 13, 2022): 196–222. http://dx.doi.org/10.1071/aj21172.
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The Northern Carnarvon Basin (NCB) hosts an extensive record of Jurassic–Cretaceous rift-related igneous activity, manifested by a >45 000 km2 intrusive complex and series of volcanic centres constrained by seismic mapping. However, there are relatively few well penetrations of these igneous rocks (<1% of ~1500 exploration wells) in comparison to other basins that witness extensive magmatism, and thus, their lithological and petrophysical characteristics are poorly understood. Here, we describe the properties of igneous rocks encountered in nine petroleum exploration wells and scientific boreholes in the NCB and evaluate their impacts on exploration and development issues. Igneous rocks in the NCB are characterised by pervasive alteration, with ramifications for seismic imaging and drilling. For example, low acoustic velocities in mafic lavas altered to clays in Toro-1 were mistaken for overpressure, whilst intrusive rocks in Palta-1 were initially unrecorded and only recognised due to subsequent post-drilling thermal history analysis. The alteration of mafic igneous rocks to clays reduces acoustic impedance contrasts relative to sedimentary host rocks, making their identification prior to drilling more challenging. Whilst the preferential emplacement of intrusive rocks in Triassic strata deeper than reservoir targets is primarily responsible for the paucity of well penetrations, our findings of extensive alteration of igneous rocks in the NCB suggests that additional wells may intersect as yet unrecognised intrusive or extrusive sequences.
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Rickard, David. "Michael John O'Hara. 22 February 1933 — 24 November 2014." Biographical Memoirs of Fellows of the Royal Society 61 (January 2015): 305–30. http://dx.doi.org/10.1098/rsbm.2015.0019.
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Michael John (Mike) O'Hara was born in Sydney, Australia, but came to the UK when he was one year old. He received his BSc and PhD degrees from Cambridge University. He was appointed assistant lecturer at the Grant Institute of Geology at Edinburgh University in 1958, where he rose to a personal chair in 1970. He moved to the University College of Wales Aberystwyth in 1978 as Head of Department and was appointed Distinguished Research Professor at Cardiff University in 1993. Mike O'Hara was one of the leading igneous petrologists of his generation, a pioneering mountaineer and eminent science administrator. He made fundamental contributions to a wide range of topics in igneous petrology, including identifying rocks from the Earth's deep mantle, experimental petrology, the primary magma problem and mathematical modelling of igneous rock formation. Mike O'Hara's name is legendary in climbing circles because he made the first ascents of 39 of the finest rock climbs in the UK. As a national science administrator he was mainly responsible for the present profile of Earth science teaching and research in UK universities.
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Elliot, David H., James D. L. White, and Thomas H. Fleming. "Chapter 2.1a Ferrar Large Igneous Province: volcanology." Geological Society, London, Memoirs 55, no. 1 (2021): 75–91. http://dx.doi.org/10.1144/m55-2018-44.
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AbstractPreserved rocks in the Jurassic Ferrar Large Igneous Province consist mainly of intrusions, and extrusive rocks, the topic of this chapter, comprise the remaining small component. They crop out in a limited number of areas in the Transantarctic Mountains and southeastern Australia. They consist of thick sequences of lavas and sporadic occurrences of volcaniclastic rocks. The latter occur mainly beneath the lavas and represent the initial eruptive activity, but also are present within the lava sequence. The majority are basaltic phreatomagmatic deposits and in at least two locations form immense phreatocauldrons filled with structureless tuff breccias and lapilli tuffs with thicknesses of as much as 400 m. Stratified sequences of tuff breccias, lapilli tuffs and tuffs are up to 200 m thick. Thin tuff beds are sparsely distributed in the lava sequences. Lava successions are mainly 400–500 m thick, and comprise individual lavas ranging from 1 to 230 m thick, although most are in the range of 10–100 m. Well-defined colonnade and entablature are seldom displayed. Lava sequences were confined topographically and locally ponded. Water played a prominent role in eruptive activity, as exhibited by phreatomagmatism, hyaloclastites, pillow lava and quenching of lavas. Vents for lavas have yet to be identified.
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Horbe, Adriana Maria Coimbra, and R. R. Anand. "Bauxite on igneous rocks from Amazonia and Southwestern of Australia: Implication for weathering process." Journal of Geochemical Exploration 111, no. 1-2 (October 2011): 1–12. http://dx.doi.org/10.1016/j.gexplo.2011.06.003.
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Black, Lance P., John W. Sheraton, Robert J. Tingey, and Malcolm T. Mcculloch. "New U-Pb zircon ages from the Denman Glacier area, East Antarctica, and their significance for Gondwana reconstruction." Antarctic Science 4, no. 4 (December 1992): 447–60. http://dx.doi.org/10.1017/s095410209200066x.
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Two new U-Pb zircon ages from the area immediately west of Denman Glacier in Antarctica show that its geological history differs from that of the Obruchev Hills and Bunger Hills, to the east of the glacier. A crystallization age of 516.0 ± 1.5 Ma for syenite is by far the youngest primary age reported for this region, whereas tonalitic orthogneiss from Cape Charcot, the oldest known local rock, was derived by the high-grade metamorphism and deformation at 2889 ± 9 Ma of a 3003 ± 8 Ma igneous precursor. Both major populations of zircon in this rock lost Pb at 500–600 Ma. Although the Sm-Nd characteristics of the entire region resemble those of the Albany Mobile Belt of Western Australia, the Sm-Nd systematics of the felsic gneisses and plutonics are too old to allow direct correlation with the rocks of the Naturaliste Block (Western Australia), a potential key element for Gondwana reconstruction. However, the possibility exists that there is an indirect relationship between the Naturaliste Block and the region immediately west of Denman Glacier.
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Adams, C. J., J. D. Bradshaw, and T. R. Ireland. "Provenance connections between late Neoproterozoic and early Palaeozoic sedimentary basins of the Ross Sea region, Antarctica, south-east Australia and southern Zealandia." Antarctic Science 26, no. 2 (July 18, 2013): 173–82. http://dx.doi.org/10.1017/s0954102013000461.
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AbstractThick successions of turbidites are widespread in the Ross–Delamerian and Lachlan orogens and are now dispersed through Australia, Antarctica and New Zealand. U-Pb detrital zircon age patterns for latest Precambrian, Cambrian and Ordovician metagreywackes show a closely related provenance. The latest Neoproterozoic–early Palaeozoic sedimentary rocks have major components, at c. 525, 550, and 595 Ma, i.e. about 40–80 million years older than deposition. Zircons in these components increase from the Neoproterozoic to Ordovician. Late Mesoproterozoic age components, 1030 and 1070 Ma, probably originate from igneous/metamorphic rocks in the Gondwanaland hinterland whose exact locations are unknown. Although small, the youngest zircon age components are coincident with estimated depositional ages suggesting that they reflect contemporaneous and minor, volcanic sources. Overall, the detrital zircon provenance patterns reflect the development of plutonic/metamorphic complexes of the Ross–Delamerian Orogen in the Transantarctic Mountains and southern Australia that, upon exhumation, supplied sediment to regional scale basin(s) at the Gondwana margin. Tasmanian detrital zircon age patterns differ from those seen in intra-Ross Orogen sandstones of northern Victoria Land and from the oldest metasediments in the Transantarctic Mountains. A comparison with rocks from the latter supports an allochthonous western Tasmania model and amalgamation with Australia in late Cambrian time.
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de Caritat, Patrice, Anthony Dosseto, and Florian Dux. "A strontium isoscape of inland southeastern Australia." Earth System Science Data 14, no. 9 (September 22, 2022): 4271–86. http://dx.doi.org/10.5194/essd-14-4271-2022.
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Abstract. The values and distribution patterns of the strontium (Sr) isotope ratio 87Sr/86Sr in Earth surface materials are of use in the geological, environmental, and social sciences. Ultimately, the 87Sr/86Sr ratios of soils and everything that lives in and on them are inherited from the rocks that are the parent materials of the soil's components. In Australia, there are few large-scale surveys of 87Sr/86Sr available, and here we report on a new, low-density dataset using 112 catchment outlet (floodplain) sediment samples covering 529 000 km2 of inland southeastern Australia (South Australia, New South Wales, Victoria). The coarse (<2 mm) fraction of bottom sediment samples (depth ∼ 0.6–0.8 m) from the National Geochemical Survey of Australia were milled and fully digested before Sr separation by chromatography and 87Sr/86Sr determination by multicollector-inductively coupled plasma mass spectrometry. The results show a wide range of 87Sr/86Sr values from a minimum of 0.7089 to a maximum of 0.7511 (range 0.0422). The median 87Sr/86Sr (± median absolute deviation) is 0.7199 (± 0.0071), and the mean (± standard deviation) is 0.7220 (± 0.0106). The spatial patterns of the Sr isoscape observed are described and attributed to various geological sources and processes. Of note are the elevated (radiogenic) values (≥∼ 0.7270; top quartile) contributed by (1) the Palaeozoic sedimentary country rock and (mostly felsic) igneous intrusions of the Lachlan geological region to the east of the study area; (2) the Palaeoproterozoic metamorphic rocks of the central Broken Hill region; both these sources contribute radiogenic material mainly by fluvial processes; and (3) the Proterozoic to Palaeozoic rocks of the Kanmantoo, Adelaide, Gawler, and Painter geological regions to the west of the area; these sources contribute radiogenic material mainly by aeolian processes. Regions of low 87Sr/86Sr (≤∼ 0.7130; bottom quartile) belong mainly to (1) a few central Murray Basin catchments; (2) some Darling Basin catchments in the northeast; and (3) a few Eromanga geological region-influenced catchments in the northwest of the study area; these sources contribute unradiogenic material mainly by fluvial processes. The new spatial Sr isotope dataset for the DCD (Darling–Curnamona–Delamerian) region is publicly available (de Caritat et al., 2022; https://dx.doi.org/10.26186/146397).
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Kent, Ray W., Simon P. Kelley, and Malcolm S. Pringle. "Mineralogy and 40Ar/39Ar geochronology of orangeites (Group II kimberlites) from the Damodar Valley, eastern India." Mineralogical Magazine 62, no. 3 (June 1998): 313–23. http://dx.doi.org/10.1180/002646198547701.
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AbstractA suite of ultramafic-mafic alkaline igneous rocks in the Damodar Valley, eastern India, contains carbonate, phosphate and titanate minerals that are not characteristic or common in minettes or lamproites, but are typical of orangeites (Group II kimberlite) from southern Africa. Phlogopite grains from the Damodar alkaline rocks yield mean 40Ar/39Ar ages of 116.6±0.8 Ma, 113.5±0.5 Ma and 109.1±0.7 Ma (1σ errors) using laser dating techniques. These ages are similar to the Rb-Sr ages of African orangeites, which lie mostly in the range 121 to 114 Ma. Prior to this study, only one possible occurrence of orangeite (the ∼820 m.y.-old Aries pipe, Western Australia) was known outside the Kaapvaal craton and its environs. If the Damodar alkaline rocks are bona fide orangeites, it is likely that they were generated at depths of >150 km, within the stability field of diamond.
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Wang, Da Yong, Yong Chen Song, Yu Liu, Yi Zhang, Tian Qi, Ming Long Zhao, and Wei Haur Lam. "Influence of Decrease in Water Saturation of Host Rocks with Dehydration Reactions on the Reconstruction of the Thermal Evolution of Igneous-Intrusion-Bearing Basins." Advanced Materials Research 383-390 (November 2011): 3739–43. http://dx.doi.org/10.4028/www.scientific.net/amr.383-390.3739.
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This study presents a numerical investigation of the effect of decrease in water saturation of host rocks with dehydration reactions on the reconstruction of the thermal evolution of igneous-intrusions-bearing basins based on complex heat conduction models. The Bena 3 dike of Gippsland Basin (Australia) is selected as an example in this study. Results indicate: (1) the consideration of decrease in water saturation of host rocks (sandstone) with dehydration reactions in the models can obviously increase the predicted peak temperature Tpeak of host rocks. The corresponding maximum deviation of Tpeak occurs at the contact and reaches ~270 °C; (2) if water saturation of host rocks vary with dehydration reactions, the Tpeak can also be influenced by the quartz content of host rocks. The predicted Tpeak is higher for the host rocks with low quartz content. The maximum deviation of Tpeak caused by the quartz content can attain 115 °C. However, the deviation of Tpeak above 20 °C only occurs in a narrow region which is near the intrusion. Out of this region, the quartz content of sandstone has only a slight effect on Tpeak.
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MA, XIAO, KUNGUANG YANG, and ALI POLAT. "U–Pb ages and Hf isotopes of detrital zircons from pre-Devonian sequences along the southeast Yangtze: a link to the final assembly of East Gondwana." Geological Magazine 156, no. 06 (August 22, 2018): 950–68. http://dx.doi.org/10.1017/s0016756818000511.
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AbstractThe Early Palaeozoic geology of the South China Craton (SCC) is characterized by an Early Palaeozoic intracontinental orogen with folded pre-Devonian strata and migmatites, MP/MT metamorphic rocks and Silurian post-orogenic peraluminous magmatic rocks in both the Yangtze and the Cathaysia blocks. In this contribution, we present new zircon U–Pb ages and Hf isotope data for detrital zircons from the Neoproterozoic to Silurian sedimentary sequences in the southeastern Yangtze Block. Samples from Neoproterozoic rocks generally display a major peak at 900–560 Ma, whereas samples from Lower Palaeozoic rocks are characterized by several broader peaks within the age ranges 600–410 Ma, 1100–780 Ma, 1.6–1.2 Ga and 2.8–2.5 Ga. Provenance analysis indicates that the 900–630 Ma detritus in Cryogenian to Ediacaran samples was derived from the Late Neoproterozoic igneous rocks in South China that acted as an internal source. The occurrence of 620–560 Ma detritus indicates the SE Yangtze was associated with Late Neoproterozoic arc volcanism along the north margin of East Gondwana. The change of provenance resulted in the deposition of 550–520 Ma and 1.1–0.9 Ga detrital zircons in the Cambrian–Ordovician sedimentary rocks. The εHf(t) values of these detrital zircons are similar to those of zircons from NW Australia–Antarctica and South India. This change of provenance in the Cambrian can be attributed to the intracontinental subduction between South China and South Qiangtang, and the convergence of India and Australia when East Gondwana finally amalgamated.
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Percival, John A. "Orthopyroxene–poikilitic tonalites of the Desliens igneous suite, Ashuanipi granulite complex, Labrador–Quebec, Canada." Canadian Journal of Earth Sciences 28, no. 5 (May 1, 1991): 743–53. http://dx.doi.org/10.1139/e91-064.
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The Ashuanipi complex of the Archean Superior Province consists of an older sequence of sedimentary rocks cut by sills and goblet-shaped intrusions of the Desliens igneous suite (DIS). The complex was regionally metamorphosed to granulite facies and subsequently intruded by peraluminous granodiorite batholiths. Tonalites of the DIS contain characteristic < 2 cm inclusion-filled orthopyroxene crystals of probable igneous origin, variably recrystallized and overgrown by garnet, biotite and blocky orthopyroxene that suggest metamorphic P–T conditions of 0.5–0.62 GPa and 750–850 °C. Andesine in tonalite contains abundant drop-like quartz inclusions. Inclusion-filled pyroxene and plagioclase are both inferred to have nucleated on partly resorbed quartz and plagioclase grains within a melt. Similar poikilitic textures characterize subordinate leucotonalite, diorite, gabbro, and pyroxenite, which together with tonalite make up the DIS. Some of the petrological characteristics of the suite are unusual, but known from other regions: (i) some felsic magmatic rocks in the southern Sierra Nevada and Barrington Tops (Australia) batholiths contain primary orthopyroxene; (ii) goblet-shaped plutons are common in orogenic belts, and tonalites with this geometry occur within a sedimentary succession in the Trinity Alps of California; (iii) orthopyroxene oikocrysts characterize parts of the Bjerkreim–Sokndal lopolith of southwestern Norway.
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Gatehouse, Robyn D., I. S. Williams, and B. J. Pillans. "Fingerprinting windblown dust in south-eastern Australian soils by uranium-lead dating of detrital zircon." Soil Research 39, no. 1 (2001): 7. http://dx.doi.org/10.1071/sr99078.
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The U-Pb ages of fine-grained zircon separated from 2 dust-dominated soils in the eastern highlands of south-eastern Australia and measured by ion microprobe (SHRIMP) revealed a characteristic age ‘fingerprint’ from which the source of the dust has been determined and by which it will be possible to assess the contribution of dust to other soil profiles. The 2 soils are dominated by zircon 400–600 and 1000–1200 Ma old, derived from Palaeozoic granites and sediments of the Lachlan Fold Belt, but also contain significant components 100–300 Ma old, characteristic of igneous rocks in the New England Fold Belt in northern New South Wales and Queensland. This pattern closely matches that of sediments of the Murray-Darling Basin, especially the Mallee dunefield, suggesting that weathering of rocks in the eastern highlands has contributed large quantities of sediment to the arid and semi-arid inland basins via internally draining rivers of the present and past Murray–Darling River systems, where it has formed a major source of dust subsequently blown eastwards and deposited in the highland soils of eastern Australia.
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Holford, Simon, Nick Schofield, Mark Bunch, Alan Bischoff, and Ernest Swierczek. "Storing CO2 in buried volcanoes." APPEA Journal 61, no. 2 (2021): 626. http://dx.doi.org/10.1071/aj20056.
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Australia contains rich natural gas resources, but many of Australia’s currently producing and undeveloped gas fields contain relatively high CO2 contents; if not captured and stored, the venting of co-produced CO2 could hinder efforts to meet Australia’s emission reduction targets. The most mature technology for isolating produced CO2 from the atmosphere is by containing it in deep sedimentary formations (e.g. saline aquifers or depleted oil and gas reservoirs). The effectiveness of this approach is dependent on factors such as reservoir capacity, the presence of low-permeability seals that physically impede vertical migration of injected CO2, the chemical reactivity of both reservoir and seal minerals, the risk for leakage, and a gas-entrapping structure. An alternative and attractive mechanism for permanent storage of CO2 is geochemical or mineral trapping, which involves long-term reactions of CO2 with host rocks and the formation of stable carbonate minerals that fill the porosity of the host rock reservoir. Natural mineral carbonation is most efficient in mafic and ultramafic igneous rocks, due to their high reactivity with CO2. Here we review the outcomes from a series of recent pilot projects in Iceland and the United States that have demonstrated high potential for rapid, permanent storage of CO2 in basalt reservoirs, and explore the practicalities of geochemical trapping of CO2 in deeply buried basaltic volcanoes and lava fields, which are found in many basins along the southern (e.g. Gippsland Basin) and northwestern (e.g. Browse Basin) Australian margins, often in close proximity to natural gas fields with high CO2 content.
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Alavi, Norman, Leon Bagas, Peter Purcell, Irena Kivior, and John Brett. "Lower Paleozoic stratigraphy and petroleum potential of the Wallal Rift System, southwest Canning Basin, Western Australia." APPEA Journal 54, no. 2 (2014): 521. http://dx.doi.org/10.1071/aj13094.
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The Wallal Rift System (new name) extends north-northwest for more than 300 km along the southwestern margin of the Canning Basin. The rift contains the Wallal and the Waukarlycarly embayments and the Samphire Graben. The rift segments vary in depth to 4.5 km and are all under-explored. Seismic coverage is better in the north than in the south. Six shallow wildcat and stratigraphic wells in the north provide some control on the age of the pre-Permian section. Another well on the northeastern flank of the Samphire Graben terminated in Neoproterozoic granitic rocks beneath the Lower Ordovician Nambeet Formation. The well is tied to a seismic line that indicates a synrift Ordovician section in the graben. An equivalent section is inferred in the Wallal and the Waukarlycarly embayments, and Permian syn-rift sediments are recognised in all rifts. Transtension along a regional geosuture—the Camel-Tabletop Fault Zone—may have caused initial rifting during the waning of the Paterson Orogeny (c. 550 Ma), co-incident with extrusion in the Kalkarindji Large Igneous Province. Thus, Cambrian volcano-clastics deposits may be present at the base of the (2–3 km thick) pre-Permian section, which is considered to be primarily Early Paleozoic sediments and expected to contain potential source rocks. A relatively hot Proterozoic crust and eruption of continental flood basalts during the Cambrian may have facilitated source rock maturation. Reservoirs may be more common along rift-margins and intra-rift ridges, where fault-controlled traps are also present.
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Dickins, C. A., K. F. Cassidy, and M. E. Barley. "Evolution of Late Archean HFSE-enriched igneous rocks of the Gindalbie Domain, Eastern Yilgarn Craton, Western Australia." Geochimica et Cosmochimica Acta 70, no. 18 (August 2006): A140. http://dx.doi.org/10.1016/j.gca.2006.06.297.
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Borissova, Irina, Chris Southby, George Bernardel, Jennifer Totterdell, Robbie Morris, and Ryan Owens. "Northern Houtman Sub-basin prospectivity—preliminary results." APPEA Journal 56, no. 2 (2016): 577. http://dx.doi.org/10.1071/aj15083.
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In 2014–15 Geoscience Australia acquired 3,300 km of deep 2D seismic data over the northern part of the Houtman Sub-basin (Perth Basin). Prior to this survey, this area had a very sparse coverage of 2D seismic data with 50–70 km line spacing in the north and an industry grid with 20 km line spacing in the south. Initial interpretation of the available data has shown that the structural style, major sequences, and potential source rocks in this area are similar to those in the southern Houtman and Abrolhos sub-basins. The major difference between these depocentres, however, is in the volume and distribution of volcanic and intrusive igneous rocks. The northern part of the Houtman Sub-basin is adjacent to the Wallaby Plateau Large Igneous Province (LIP). The Wallaby Plateau and the Wallaby Saddle, which borders the western flank of the Houtman Sub-basin, had active volcanism from the Valanginian to at least the end of the Barremian. Volcanic successions significantly reduce the quality of seismic imaging at depth, making it difficult to ascertain the underlying thickness, geometry and structure of the sedimentary basin. The new 2D seismic dataset across the northern Houtman Sub-basin provides an opportunity for improved mapping of the structure and stratigraphy of the pre-breakup succession, assessment of petroleum prospectivity, and examination of the role of volcanism in the thermal history of this frontier basin.
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Griffin, T. J., R. W. Page, S. Sheppard, and I. M. Tyler. "Tectonic implications of Palaeoproterozoic post-collisional, high-K felsic igneous rocks from the Kimberley region of northwestern Australia." Precambrian Research 101, no. 1 (May 2000): 1–23. http://dx.doi.org/10.1016/s0301-9268(99)00084-4.
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Wang, Wei, Peter A. Cawood, Christopher J. Spencer, Manoj K. Pandit, Jun-Hong Zhao, Xiao-Ping Xia, Jian-Ping Zheng, and Gui-Mei Lu. "Global-scale emergence of continental crust during the Mesoarchean–early Neoarchean." Geology 50, no. 2 (November 9, 2021): 184–88. http://dx.doi.org/10.1130/g49418.1.
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Abstract The timing of the emergence of subaerial landmasses is equivocally constrained as post-Archean and continues to be a much-debated issue. In this study, we document exceptionally 18O-depleted (δ18O < 4.7‰) Mesoarchean to early Neoarchean magmatism in India that shows a similarity with the coeval low-δ18O magmas reported from Australia, South America, and northern China. Such global-scale low-δ18O magmatism would require high-temperature meteoric water–rock interaction in the uppermost crust synchronous with magma generation, necessitating the emergence of a substantial volume of the continental crust. The timing of this low-δ18O magmatism coincides with the development of extensive, subaerial large igneous provinces, a downward shift in δ18O and Δ17O values in pelitic rocks, the rise of normalized 87Sr/86Sr in seawater, and an intermittent upsurge in the proportion of atmospheric oxygen. We propose that the emergence of substantial volumes of continental crust initiated at ca. 3.2 Ga and peaked at 2.8–2.6 Ga, facilitating the generation of globally distributed low-δ18O magmas, and this event can be linked to the first appearance of atmospheric oxygen.
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Smith, I. E. M., A. J. R. White, B. W. Chappell, and R. A. Eggleton. "Fractionation in a zoned monzonite pluton: Mount Dromedary, southeastern Australia." Geological Magazine 125, no. 3 (May 1988): 273–84. http://dx.doi.org/10.1017/s0016756800010219.
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AbstractMount Dromedary pluton is one of several predominantly monzonite plutons and smaller intrusive bodies which constitute the Dromedary igneous complex in southeastern New South Wales. The pluton exhibits a striking arrangement of petrographically, but not always chemically, distinct zones ranging from mafic monzonite at the outside to quartz monzonite in the centre. The rocks display a mineralogical and geochemical integrity which indicates a consanguineous relationship. Minor compositional discontinuities between zones, together with observed and inferred minor intrusive zone boundaries, suggest that each zone has to some extent evolved independently. Negative Eu anomalies in REE abundance patterns show that some of the zones have been affected by fractionation of feldspar, but complementary accumulates are not found at the present levels of exposure. The pattern of zoning can be explained by a process of shallow fractional crystallization in which variations within zones are the result of lateral accretion of alkali feldspar as well as settling and/or lateral accretion of mafic phases at lower levels in the intrusion and upward displacement of fractionated magma. The parental magma of the pluton probaby originated by partial melting of an alkali basalt composition with an amphibolite mineralogy at the base of the crust.
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Carpenter, Chris. "Reservoir Characterization, Scenario-Based Models Optimize Development Planning." Journal of Petroleum Technology 73, no. 07 (July 1, 2021): 48–49. http://dx.doi.org/10.2118/0721-0048-jpt.
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This article, written by JPT Technology Editor Chris Carpenter, contains highlights of paper SPE 202273, “Reservoir Characterization and Scenario-Based Modeling To Optimize Development Planning of the Jurassic Plover Formation in the Ichthys Field, North West Shelf of Australia,” by Kazuyuki Yamamoto, SPE, Shuji Yamamoto, and Toby Jones, INPEX, et al., prepared for the 2020 SPE Asia Pacific Oil and Gas Conference and Exhibition, originally scheduled to be held in Perth, Australia, 20–22 October. The paper has not been peer reviewed. The Plover Formation is one of two reservoirs in the Ichthys field of the Australian North West Shelf. The objective of this study is to build multiple scenario-based models to optimize development planning in preparation for the upcoming production phase. The authors have integrated data and interpretations of thin sections, cores, well logs, and seismic data to create multiple geological concepts for the field and to identify key geological uncertainties. Introduction The Ichthys liquefied natural gas project is one of the world’s largest and involves the development of a gas-condensate field in the Browse Basin. The field is approximately 220 km offshore Western Australia and covers an area of approximately 800 km2 with an average water depth of approximately 250 m. The field is currently under preparation for the development of the Plover Formation. The authors conducted an integrated subsurface evaluation and built reservoir models with newly reprocessed 3D seismic data to optimize Plover development planning. Considering the geological uncertainty given the limited production data gathered before the production phase, the multiple deterministic approach was selected as the best option to optimize development planning. In this approach, it is important to capture all geological scenarios that may occur in the field and to build reservoir models in which the scenario concepts are explicitly integrated. A multidisciplinary team was organized to conduct this study. Geology of the Plover Formation The Plover Formation consists of sandstones, shales, igneous rocks, and a minor amount of coal. The depositional environment is fluvial to shallow marine. The average thickness of the formation is approximately 360 m. Based on the stratigraphic correlation anchored by mainly palynological biostratigraphic data, the formation has been subdivided into five stratigraphic members. The formation is overlain by the Ichthys Formation, which is composed mainly of argillaceous sandstone and shale deposited in a tidally influenced, lower-delta-to-shelf environment. Although the nine existing exploration wells broadly cover the entire field, the spacing between the wells is still large (8–10 km). Further-more, core coverage is low, especially in the reservoir sandstone intervals. Igneous rock, predominantly basaltic in composition and likely extrusive in origin, occurs more in the eastern part of the field. Igneous activity has complicated the distribution and connectivity of the reservoir sandstones in the Ichthys field. Key Geological Uncertainties Rock Type (RT). The results of petrographic analysis of rock samples from the Ichthys field and other surrounding fields indicate that the sandstones of the Plover Formation can be separated into multiple RTs: RT1 and RT2, with RT1 subdivided into RT1a and RT1b. Very little data exist from RT2 in the fluvial/distributary channel sandstones in the Ichthys field in comparison with other fields; this is considered to be the result of limited core. The assumption that RT2 exists in the field is critical to prepare for the possibility that a future well may be drilled that might have some nontrivial quantity of RT2.
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Sheraton, John W., Robert J. Tingey, Lance P. Black, and Robin L. Oliver. "Geology of the Bunger Hills area, Antarctica: implications for Gondwana correlations." Antarctic Science 5, no. 1 (March 1993): 85–102. http://dx.doi.org/10.1017/s0954102093000112.
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The Bunger Hills area of the East Antarctic Shield consists of granulite-facies felsic orthogneiss, with subordinate paragneiss and mafic granulite. The igneous precursors of granodioritic orthogneiss were emplaced 1500-1700 Ma ago, and late Archaean (2640 Ma) tonalitic orthogneiss occurs in the nearby Obruchev Hills. Peak metamorphism (M1) (at about 750-800°C and 5-6kb) occurred 1190 ±15 Ma ago (U-Pb zircon age), and was accompanied by the first of three ductile deformations (D1). Emplacement of voluminous, mainly mantle-derived plutonic rocks, ranging from gabbro, through quartz monzogabbro and quartz monzodiorite, to granite, followed between 1170 (during D3) and 1150 Ma. Intrusion of abundant dolerite dykes of four chemically distinct suites at about 1140 Ma was associated with shear zone formation, indicating at least limited uplift; all subsequent deformation was of brittle-ductile type. Alkaline mafic dykes were emplaced 500 Ma ago. Marked geochronological similarities with the Albany Mobile Belt of Western Australia suggest that high-grade metamorphism occurred during collision between the Archaean Yilgarn Craton of Australia and the East Antarctic Shield about 1200 Ma ago.
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Creaser, Robert A., and Chris M. Gray. "Preserved initial in apatite from altered felsic igneous rocks: A case study from the Middle Proterozoic of South Australia." Geochimica et Cosmochimica Acta 56, no. 7 (July 1992): 2789–95. http://dx.doi.org/10.1016/0016-7037(92)90359-q.
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Cuney, Michel. "Felsic magmatism and uranium deposits." Bulletin de la Société Géologique de France 185, no. 2 (February 1, 2014): 75–92. http://dx.doi.org/10.2113/gssgfbull.185.2.75.
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Abstract The strongly incompatible behaviour of uranium in silicate magmas results in its concentration in the most felsic melts and a prevalence of granites and rhyolites as primary U sources for the formation of U deposits. Despite its incompatible behavior, U deposits resulting directly from magmatic processes are quite rare. In most deposits, U is mobilized by hydrothermal fluids or ground water well after the emplacement of the igneous rocks. Of the broad range of granite types, only a few have U contents and physico-chemical properties that permit the crystallization of accessory minerals from which uranium can be leached for the formation of U deposits. The first granites on Earth, which crystallized uraninite, dated at 3.1 Ga, are the potassic granites from the Kaapval craton (South Africa) which were also the source of the detrital uraninite for the Dominion Reef and Witwatersrand quartz pebble conglomerate deposits. Four types of granites or rhyolites can be sufficiently enriched in U to represent a significant source for the genesis of U deposits: peralkaline, high-K metaluminous calc-alkaline, L-type peraluminous and anatectic pegmatoids. L-type peraluminous plutonic rocks in which U is dominantly hosted in uraninite or in the glass of their volcanic equivalents represent the best U source. Peralkaline granites or syenites are associated with the only magmatic U-deposits formed by extreme fractional crystallization. The refractory character of the U-bearing minerals does not permit their extraction under the present economic conditions and make them unfavorable U sources for other deposit types. By contrast, felsic peralkaline volcanic rocks, in which U is dominantly hosted in the glassy matrix, represent an excellent source for many deposit types. High-K calc-alkaline plutonic rocks only represent a significant U source when the U-bearing accessory minerals (U-thorite, allanite, Nb oxides) become metamict. The volcanic rocks of the same geochemistry may be also a favorable uranium source if a large part of the U is hosted in the glassy matrix. The largest U deposit in the world, Olympic Dam in South Australia is hosted by highly fractionated high-K plutonic and volcanic rocks, but the origin of the U mineralization is still unclear. Anatectic pegmatoids containing disseminated uraninite which results from the partial melting of uranium-rich metasediments and/or metavolcanic felsic rocks, host large low grade U deposits such as the Rössing and Husab deposits in Namibia. The evaluation of the potentiality for igneous rocks to represent an efficient U source represents a critical step to consider during the early stages of exploration for most U deposit types. In particular a wider use of the magmatic inclusions to determine the parent magma chemistry and its U content is of utmost interest to evaluate the U source potential of sedimentary basins that contain felsic volcanic acidic tuffs.
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Wade, C. E., J. L. Payne, K. Barovich, S. Gilbert, B. P. Wade, J. L. Crowley, A. Reid, and E. A. Jagodzinski. "ZIRCON TRACE ELEMENT GEOCHEMISTRY AS AN INDICATOR OF MAGMA FERTILITY IN IRON OXIDE COPPER-GOLD PROVINCES." Economic Geology 117, no. 3 (May 1, 2022): 703–18. http://dx.doi.org/10.5382/econgeo.4886.
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Abstract Extrusive and intrusive felsic magmas occur throughout the evolution of silicic-dominated large igneous province magmatism that is temporally related to numerous economically significant iron oxide copper-gold (IOCG) deposits in southern Australia. We investigate zircon trace element signatures of the felsic magmas to assess whether zircon composition can be related to fertility of the volcanic and intrusive suites within IOCG-hosted mineral provinces. Consistent with zircon forming in oxidizing magmatic conditions, the rare earth element (REE) patterns of zircon sourced from both extrusive and intrusive magmatic rocks are characterized by light REE depletions and a range of positive Ce and negative Eu anomalies. The timing of the major phase of IOCG mineralization overlaps with the early part of the first phase of Lower Gawler Range Volcanics magmatism (1593.6–1590.4 Ma) and older intrusive magmatism of the Hiltaba Suite (1593.06–1590.50 Ma). Zircon in these mineralization-related intrusives and extrusives is distinguished from zircon in younger, mineralization-absent rocks by higher Eu/Eu*, Ce/Ce*, and Ti values and separate magma evolution paths with respect to Hf. These zircon characteristics correspond to lower degrees of fractionation and/or crustal assimilation, more oxidizing magmatic conditions, and higher magmatic temperatures, respectively, in magmas coeval with mineralization. In this respect, we consider higher oxidation state, lower degrees of fractionation, and higher magmatic temperatures to be features of fertile magmas in southern Australian IOCG terrains. Similar zircon REE characteristics are shared between magmas associated with southern Australian IOCG and iron oxide-apatite (IOA) rhyolites from the St. Francois Mountains, Missouri, namely high Ce/Ce* and high Dy/Yb, indicative of oxidized and dry magmas, respectively. The dry and more fractionated nature of the IOCG- and IOA-associated magmas contrasts with the hydrous and unfractionated nature of fertile porphyry Cu deposit magmas. As indicated by high Ce/Ce* ratios, the oxidized nature is considered a key element in magma fertility in IOCG-IOA terrains. In both IOCG and IOA terrains, the trace element compositions of zircon are able to broadly differentiate fertile from nonfertile magmatic rocks.
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Watson, Douglas, Simon Holford, Nick Schofield, and Niall Mark. "Failure to predict igneous rocks encountered during exploration of sedimentary basins: A case study of the Bass Basin, Southeastern Australia." Marine and Petroleum Geology 99 (January 2019): 526–47. http://dx.doi.org/10.1016/j.marpetgeo.2018.10.034.
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SMITHIES, R. H., and D. C. CHAMPION. "Late Archaean felsic alkaline igneous rocks in the Eastern Goldfields, Yilgarn Craton, Western Australia: a result of lower crustal delamination?" Journal of the Geological Society 156, no. 3 (May 1999): 561–76. http://dx.doi.org/10.1144/gsjgs.156.3.0561.
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Tusch, Jonas, Carsten Münker, Eric Hasenstab, Mike Jansen, Chris S. Marien, Florian Kurzweil, Martin J. Van Kranendonk, Hugh Smithies, Wolfgang Maier, and Dieter Garbe-Schönberg. "Convective isolation of Hadean mantle reservoirs through Archean time." Proceedings of the National Academy of Sciences 118, no. 2 (December 21, 2020): e2012626118. http://dx.doi.org/10.1073/pnas.2012626118.
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Although Earth has a convecting mantle, ancient mantle reservoirs that formed within the first 100 Ma of Earth’s history (Hadean Eon) appear to have been preserved through geologic time. Evidence for this is based on small anomalies of isotopes such as182W,142Nd, and129Xe that are decay products of short-lived nuclide systems. Studies of such short-lived isotopes have typically focused on geological units with a limited age range and therefore only provide snapshots of regional mantle heterogeneities. Here we present a dataset for short-lived182Hf−182W (half-life 9 Ma) in a comprehensive rock suite from the Pilbara Craton, Western Australia. The samples analyzed preserve a unique geological archive covering 800 Ma of Archean history. Pristine182W signatures that directly reflect the W isotopic composition of parental sources are only preserved in unaltered mafic samples with near canonical W/Th (0.07 to 0.26). Early Paleoarchean, mafic igneous rocks from the East Pilbara Terrane display a uniform pristine µ182W excess of 12.6 ± 1.4 ppm. Fromca. 3.3Ga onward, the pristine182W signatures progressively vanish and are only preserved in younger rocks of the craton that tap stabilized ancient lithosphere. Given that the anomalous182W signature must have formed byca. 4.5 Ga, the mantle domain that was tapped by magmatism in the Pilbara Craton must have been convectively isolated for nearly 1.2 Ga. This finding puts lower bounds on timescale estimates for localized convective homogenization in early Earth’s interior and on the widespread emergence of plate tectonics that are both important input parameters in many physical models.
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Boreham, C. J., J. E. Blevin, A. P. Radlinski, and K. R. Trigg. "COAL AS A SOURCE OF OIL AND GAS: A CASE STUDY FROM THE BASS BASIN, AUSTRALIA." APPEA Journal 43, no. 1 (2003): 117. http://dx.doi.org/10.1071/aj02006.
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Only a few published geochemical studies have demonstrated that coals have sourced significant volumes of oil, while none have clearly implicated coals in the Australian context. As part of a broader collaborative project with Mineral Resources Tasmania on the petroleum prospectivity of the Bass Basin, this geochemical study has yielded strong evidence that Paleocene–Eocene coals have sourced the oil and gas in the Yolla, Pelican and Cormorant accumulations in the Bass Basin.Potential oil-prone source rocks in the Bass Basin have Hydrogen Indices (HIs) greater than 300 mg HC/g TOC. The coals within the Early–Middle Eocene succession commonly have HIs up to 500 mg HC/g TOC, and are associated with disseminated organic matter in claystones that are more gas-prone with HIs generally less than 300 mg HC/g TOC. Maturity of the coals is sufficient for oil and gas generation, with vitrinite reflectance (VR) up to 1.8 % at the base of Pelican–5. Igneous intrusions, mainly within Paleocene, Oligocene and Miocene sediments, produced locally elevated maturity levels with VR up to 5%.The key events in the process of petroleum generation and migration from the effective coaly source rocks in the Bass Basin are:the onset of oil generation at a VR of 0.65% (e.g. 2,450 m in Pelican–5);the onset of oil expulsion (primary migration) at a VR of 0.75% (e.g. 2,700–3,200 m in the Bass Basin; 2,850 m in Pelican–5);the main oil window between VR of 0.75 and 0.95% (e.g. 2,850–3,300 m in Pelican–5); and;the main gas window at VR >1.2% (e.g. >3,650 m in Pelican–5).Oils in the Bass Basin form a single oil population, although biodegradation of the Cormorant oil has resulted in its statistical placement in a separate oil family from that of the Pelican and Yolla crudes. Oil-to-source correlations show that the Paleocene–Early Eocene coals are effective source rocks in the Bass Basin, in contrast to previous work, which favoured disseminated organic matter in claystone as the sole potential source kerogen. This result represents the first demonstrated case of significant oil from coal in the Australian context. Natural gases at White Ibis–1 and Yolla–2 are associated with the liquid hydrocarbons in their respective fields, although the former gas is generated from a more mature source rock.The application of the methodologies used in this study to other Australian sedimentary basins where commercial oil is thought to be sourced from coaly kerogens (e.g. Bowen, Cooper and Gippsland basins) may further implicate coal as an effective source rock for oil.
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Southgate, Peter, Keith Sircombe, and Christopher Lewis. "New insights into reservoir sand provenance in the Exmouth Plateau and Browse Basin." APPEA Journal 51, no. 2 (2011): 715. http://dx.doi.org/10.1071/aj10095.
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A pilot study to determine if zircons present in reservoir facies of the North West Shelf can be used to identify provenance and sediment transport pathways has analysed samples from three wells: Guardian–1 and Hijinx–1 (Carnarvon Basin), and Burnside–1 (Browse Basin). Operating companies Chevron, Santos and Hess collected 3–5 kg of cuttings from sandstone bodies intersected in the three wells. Samples were sent to Geoscience Australia for zircon separation and analysis at the Geochronology Laboratory on a sensitive high-resolution ion microprobe (SHRIMP). To provide a statistically meaningful representation of ages in each sample, 70–80 grains were randomly selected for analysis. During the past 20 years, Geoscience Australia and the state geological surveys of WA, NT, Queensland and SA, together with the ANU, UWA and Curtin University, have analysed zircons found in igneous and sedimentary rocks that outcrop in WA and central Australia. This analysis has been done to determine the ages of emplacement, extrusion or maximum depositional ages. This dataset permits the ages of potential onshore provenance areas to be differentiated; hence, correlations can be made between zircons contained within the transported sands and their potential source regions from onshore Australia. In this extended abstract, the spectrum of ages in each sample will be shown, and potential provenance and sediment transport pathways will be discussed. The abstract concludes with the outline of a 2–3 year project to obtain a dataset that will provide a regional stratigraphic and spatial coverage of the North West Shelf for provenance studies.
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Randive, Kirtikumar, and Tushar Meshram. "An Overview of the Carbonatites from the Indian Subcontinent." Open Geosciences 12, no. 1 (March 26, 2020): 85–116. http://dx.doi.org/10.1515/geo-2020-0007.
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AbstractCarbonatites are carbonate-rich rocks of igneous origin. They form the magmas of their own that are generated in the deep mantle by low degrees of partial melting of carbonated peridotite or eclogite source rocks. They are known to occur since the Archaean times till recent, the activity showing gradual increase from older to younger times. They are commonly associated with alkaline rocks and be genetically related with them. They often induce metasomatic alteration in the country rocks forming an aureole of fenitization around them. They are host for economically important mineral deposits including rare metals and REE. They are commonly associated with the continental rifts, but are also common in the orogenic belts; but not known to occur in the intra-plate regions. The carbonatites are known to occur all over the globe, majority of the occurrences located in Africa, Fenno-Scandinavia, Karelian-Kola, Mongolia, China, Australia, South America and India. In the Indian Subcontinent carbonatites occur in India, Pakistan, Afghanistan and Sri Lanka; but so far not known to occur in Nepal, Bhutan, Bangladesh and Myanmar. This paper takes an overview of the carbonatite occurrences in the Indian Subcontinent in the light of recent data. The localities being discussed in detail cover a considerable time range (>2400 Ma to <0.6 Ma) from India (Hogenakal, Newania, Sevathur, Sung Valley, Sarnu-Dandali and Mundwara, and Amba Dongar), Pakistan (Permian Koga and Tertiary Pehsawar Plain Alkaline Complex which includes Loe Shilman, Sillai Patti, Jambil and Jawar), Afghanistan (Khanneshin) and Sri Lanka (Eppawala). This review provide the comprehensive information about geochemical characteristics and evolution of carbonatites in Indian Subcontinent with respect to space and time.
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Ewers, G. R., D. E. Mackenzie, D. Wyborn, B. S. Oversby, J. McPhie, and A. S. Andrew. "Regional 18 O depletions in igneous rocks from the northern Drummond Basin, Queensland, Australia, and their implications for epithermal gold mineralization." Economic Geology 89, no. 3 (May 1, 1994): 662–73. http://dx.doi.org/10.2113/gsecongeo.89.3.662.
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Schmidt, P. W., and B. J. J. Embleton. "Prefolding and overprint magnetic signatures in Precambrian (∼2.9–2.7 Ga) Igneous rocks from the Pilbara Craton and Hamersley Basin, NW Australia." Journal of Geophysical Research 90, B4 (1985): 2967. http://dx.doi.org/10.1029/jb090ib04p02967.
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Semeniuk, V., and M. Brocx. "The Archaean to Proterozoic igneous rocks of the Pilbara region, Western Australia –internationally significant geology of a globally unique potential geopark." International Journal of Geoheritage and Parks 7, no. 2 (June 2019): 56–71. http://dx.doi.org/10.1016/j.ijgeop.2019.06.001.
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Petersson, Andreas, Anthony I. S. Kemp, Chris M. Gray, and Martin J. Whitehouse. "Formation of early Archean Granite-Greenstone Terranes from a globally chondritic mantle: Insights from igneous rocks of the Pilbara Craton, Western Australia." Chemical Geology 551 (September 2020): 119757. http://dx.doi.org/10.1016/j.chemgeo.2020.119757.
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Kislov, Evgeniy V., Anna V. Aseeva, Vladislav V. Vanteev, Anton Yurievich Sinyov, and Olga A. Eliseeva. "Naryn-Gol Creek Sapphire Placer Deposit, Buryatia, Russia." Minerals 12, no. 5 (April 20, 2022): 509. http://dx.doi.org/10.3390/min12050509.
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A new gem corundum occurrence has been discovered in the Naryn-Gol Creek placer of the Dzhida volcanic field (Russia). In this placer deposit, sapphire associates with large crystals of garnet, spinel, augite, olivine, enstatite, ilmenite, Ti-magnetite, and alkali feldspar. Such a combination of minerals is typical for the placer deposits associated with alkali basalts widely distributed in Southeastern Asia and Australia. We have also found sapphire crystals in phonotephrites of the nearby Cenozoic alkali-basalt paleovolcano Barun Khobol Pravyi, and in basalt sample and trachybasalt from the valley flood basalts. The chemical composition of sapphire is generally typical for ‘basalt’ corundum: it is rich in Fe, and depleted in Ti and Cr. The δ18O SMOW values of corundum and related megacrysts range from 4.6 to 6.8 ‰, thus corresponding to the isotopic signature of igneous rocks. Etched and corroded surfaces of sapphire and other megacrysts indicate that they are in non-equilibrium with their host alkali basalts. Volatile components, CO2 in particular, played a significant role during sapphire formation as gas inclusions reveal.
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Smith, P. M., and M. Whitehead. "Seismic, gravity and magnetics, a complementary geophysical study of the Paqualin Structure, Timor Sea, Australia." Exploration Geophysics 20, no. 2 (1989): 25. http://dx.doi.org/10.1071/eg989025.
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The presence of a large anomalous structure in the northern part of Permit AC/P2 in the Timor Sea has been recognised ever since seismic data were first acquired in the area. Historically, however, sparse seismic coverage has always prevented a detailed and unambiguous interpretation of the complicated structure. In order to overcome this problem, some 2000 km of 3D seismic data were acquired over the feature. In conjunction with this seismic survey, detailed gravity and magnetic data sets were also recorded over the structure.Interpretation of the new seismic data indicated the presence of a piercement structure which is associated with a small negative Bouguer gravity anomaly and a magnetic intensity anomaly resulting from a positive susceptibility contrast. Modelling of the magnetic data indicated that an acidic or intermediate intrusive body was the most likely cause of the piercement structure. The presence of an acidic intrusive body was consistent with the gravity data which indicated that no large density contrast existed between the material of the piercement structure and the surrounding sediments.The combined interpretation of these three data sets was tested by a well, Paqualin-1, drilled on the flank of the piercement structure. The well encountered a thick evaporite sequence with associated thin bands of magnetitie and intermediate igneous rocks. It was logged with a three component downhole magnetic probe and forward magentic modelling work incorporating the results of the magnetic log gave good agreement with the observed aeromagnetic profiles.
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Turner, Simon P., and Kurt Stüwe. "Low-pressure corona textures between olivine and plagioclase in unmetamorphosed gabbros from Black Hill, South Australia." Mineralogical Magazine 56, no. 385 (December 1992): 503–9. http://dx.doi.org/10.1180/minmag.1992.056.385.06.
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AbstractOlivine-plagioclase corona textures occur in ophitic to sub-ophitic olivine gabbros at Black Hill, South Australia. Contrasting with many corona and symplectite textures previously described, these do not involve spinel or garnet as reaction products and did not form under high-pressure conditions. Rather, the coronas formed at no more than 1 kbar pressure and are composed of a shell of orthopyroxene around the olivine often succeeded by a shell of amphibole or occasionally biotite. Beyond this, a vermicular symplectite of anorthite containing orthopyroxene and rarer amphibole vermicules extends out to host plagioclase of labradorite composition. Textural relations are used to infer a subsolidus igneous origin for all but the orthopyroxene shell which may have formed in the presence of some magma. Compositional zonation is absent from all the constituent phases except the amphibole shell which is strongly zoned in Mg# and may have a late origin. An average maximum corona width of 150- 200 μm indicates a limiting distance for subsolidus chemical diffusion. The corona products involve the reactants olivine and plagioclase in the proportions 1:3 and symplectite formation may have been promoted by a Na potential gradient. The system must also have been open to minor components including H2O and TiO2, with H2O possibly being derived from a hydrothermal system. Such systems may have been set up in the country rocks on intrusion of the magma and subsequently collapsed inwards into the pluton during sub-solidus cooling.
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Abraham, Andrew P. G., and Edward T. C. Spooner. "Late Archean regional deformation and structural controls on gold-quartz vein mineralization in the northwestern Slave Province, N.W.T., Canada." Canadian Journal of Earth Sciences 32, no. 8 (August 1, 1995): 1132–54. http://dx.doi.org/10.1139/e95-094.
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Late Archean crustal accretion in the northwestern Slave Province is suggested to have involved approximately west-northwest–east-southeast directed horizontal compression that produced three episodes of deformation recognizable in the northwestern Anialik River igneous complex (ARIC) and Anialik River greenstone belt (ARGB). Observations show that the ARIC was probably emplaced as a series of synvolcanic sills prior to the earliest deformational event. Regional shortening produced a pervasive foliation, downdip lineations and folding in the ARGB, and an early, subsequently folded, foliation in the northwestern ARIC. Postfold ductile and brittle–ductile deformation produced regional- and outcrop-scale shear zones including the Sheeted Zone, which defines the ARIC–ARGB contact. Younger rocks of the northwestern ARGB appear to have been tectonically juxtaposed along the Sheeted Zone against the older rocks of the northwestern ARIC. Greater brittle response, enhanced permeability, and cyclical increases in fluid pressure led to the development and concentration of an anastamosing network of gold-quartz vein bearing shear zones in the ARIC. Steep to subvertical shear-related linear fabrics show that regional-scale and mineralized shear zones have a large component of vertical shear with predominantly east-side-up movement. The age relationships, proximity, and similarity of deformational structures in the Kangguyak gneiss belt, containing a craton-scale ductile deformation zone, and shear zones within the Arcadia Bay area, suggest contemporaneous development and regional late Archean structural relationships similar to those of shear zone hosted gold-quartz vein mineralization seen in the Abitibi Subprovince (Canada) and Yilgarn Craton (Australia).
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Kemp, A. I. S. "Petrology of high-Mg, low-Ti igneous rocks of the Glenelg River Complex (SE Australia) and the nature of their interaction with crustal melts☆." Lithos 78, no. 1-2 (October 2004): 119–56. http://dx.doi.org/10.1016/j.lithos.2004.04.044.
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Kanowski, John, M. S. Hopkins, Helene Marsh, and J. W. Winter. "Ecological correlates of folivore abundance in north Queensland rainforests." Wildlife Research 28, no. 1 (2001): 1. http://dx.doi.org/10.1071/wr99098.
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The ecological factors controlling the distribution and abundance of the folivorous marsupials endemic to the rainforests of northern Australia are not understood. In this study, we surveyed folivore abundance at 40 sites stratified by altitude and geology in rainforests of the Atherton Tableland, north Queensland. All five species of folivore that inhabit the study area were more abundant in highland (800–1200 m) than in upland (400–800 m) forests. Allowing for the effects of altitude, four species of folivore were more abundant in forests on nutrient-rich basalts than in forests on nutrient-poor acid igneous or metamorphic rocks. The abundance of two folivore species also varied inversely with rainfall. Altitudinal variation in folivore abundance in the study area has been attributed to habitat destruction, Aboriginal hunting, the distribution of host plants and climate; however, none of these hypotheses has been tested. Variation in folivore abundance with geology is plausibly explained as a response to the nutritional quality of foliage. Foliage quality may also explain the inverse relationship between two of the folivores and rainfall. The results of this study show that only a relatively small proportion of north Queensland rainforests support abundant populations of the endemic folivorous marsupials.
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Ashley, P. M., N. D. J. Cook, and C. M. Fanning. "Geochemistry and age of metamorphosed felsic igneous rocks with A-type affinities in the Willyama Supergroup, Olary Block, South Australia, and implications for mineral exploration." Lithos 38, no. 3-4 (September 1996): 167–84. http://dx.doi.org/10.1016/0024-4937(96)00011-4.
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McPhie, J. "Evolution of a non-resurgent cauldron: the Late Permian Coombadjha Volcanic Complex, northeastern New South Wales, Australia." Geological Magazine 123, no. 3 (May 1986): 257–77. http://dx.doi.org/10.1017/s0016756800034749.
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AbstractThe Coombadjha Volcanic Complex is the remnant of a Late Permian cauldron. It is part of an extensive sequence of silicic calc-alkaline volcanics that covers the southeastern portion of the New England Orogen in NSW. The Complex is elliptical, measuring 15 × 24 km, and is outlined by a ring pluton and an arcuate fault. Bedding in the volcanic units of the Complex defines a structural basin, with steep inward dips at the monoclinal rim and gentle to horizontal orientations near the centre. An older group of outflow ignimbrites, lavas, breccias and volcaniclastic rocks at least 1500 m thick, is conformably overlain by more than 500 m of texturally homogeneous, crystal-rich, dacitic ignimbrite. Ignimbrites of the older group are the products of several discrete eruptions from separate vents, all of which were situated outside the Coombadjha area. Silicic lava domes with volcaniclastic aprons, and a tuff ring, mark the positions of local vents active on a small scale during intervals between the emplacement of the outflow ignimbrites. No significant subsidence occurred, nor did a caldera exist at this stage. Cauldron subsidence occurred in response to the large magnitude eruption that produced the crystal-rich ignimbrite. The central cauldron block was lowered at least 2000 m by downwarping and fault displacement, and remained largely intact. There is no evidence for resurgent doming of the cauldron after subsidence, although igneous activity continued with intrusion of an adamellite ring pluton along much of the cauldron margin. The crystal-rich ignimbrite and the ring pluton are similar in composition and may have been successive products of a common magma source that sustained this simple, single cauldron cycle.
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Chappell, B. W., and W. E. Stephens. "Origin of infracrustal (I-type) granite magmas." Earth and Environmental Science Transactions of the Royal Society of Edinburgh 79, no. 2-3 (1988): 71–86. http://dx.doi.org/10.1017/s0263593300014139.
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ABSTRACTI-type granites are produced by partial melting of older igneous rocks that are metaluminous and hence have not undergone any significant amount of chemical weathering. In the Lachlan Fold Belt of southeastern Australia and the Caledonian Fold Belt of Britain and Ireland there was a major magmatic event close to 400 Ma ago involving a massive introduction of heat into the crust. In both areas, that Caledonian-age event produced large volumes of I-type granite and related volcanic rocks. Granites of these two areas are not identical in character but they do show many similarities and are markedly different from many of the granites found in Mesozoic and younger fold belts. These younger, dominantly tonalitic, granites have compositions similar to those of the more felsic volcanic rocks forming at the present time above subduction zones. The Palaeozoic granites show little evidence of such a direct relationship to subduction. Within both the Caledonian and Lachlan belts there are some granites with a composition close to the younger tonalites. A particularly interesting case is that of the Tuross Head Tonalite of the Lachlan Fold Belt, which can be shown to have formed from slightly older source rocks by a process that we refer to as remagmatisation which has caused no significant change in composition. Since remagmatisation has reproduced the former source composition in the younger rocks, the wrong inference would result from the use of that composition to deduce the tectonic conditions at the time of formation of the tonalite. Granites, particularly the more mafic ones, will generally have compositions reflecting the compositions of their source rocks, and attempts to use granite compositions to reconstruct the tectonic environment at the time of formation of the granite may be looking instead at an older event. This is probably also the case for some andesites formed at continental margins.Several arguments can be presented in favour of a general model for the production of I-type granite sources by underplating the crust, so that the source rocks are infracrustal. Such sources may contain a component of subducted sediments with the consequence that some of the compositional characteristics of sedimentary rocks may be present in I-type source rocks and in the granites derived from them. The small bodies of mafic granite and gabbro associated with island arc volcanism have an origin that can be related to the partial melting of subducted oceanic crust or of mantle material overlying such slabs and can be referred to as M-type. These rocks have compositions indistinguishable from those of the related volcanic rocks, except for a small component of cumulative material. The tonalitic I-type granites characteristic of the Cordillera are probably derived from such M-type rocks of basaltic to andesitic composition, which had been underplated beneath the crust. Some of the more mafic tonalites of the Caledonian-age fold belts may also have had a similar origin. More commonly, however, the plutonic rocks of the older belts are granodioritic and these probably represent the products of partial melting of older tonalitic I-type source rocks in the deep crust, these having compositions and origins analogous to the tonalites of the Cordillera. In this way, multiple episodes of partial melting, accompanied by fractionation of the magmas, can produce quite felsic rocks from original source rocks in the mantle or mantle wedge. These are essential processes in the evolution of the crust, since the first stages in this process produce new crust and the later magmatic events redistribute this material vertically without the addition of significant amounts of new crust.
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Wade, B. P., M. Hand, D. W. Maidment, D. F. Close, and I. R. Scrimgeour. "Origin of metasedimentary and igneous rocks from the Entia Dome, eastern Arunta region, central Australia: a U – Pb LA-ICPMS, SHRIMP and Sm – Nd isotope study." Australian Journal of Earth Sciences 55, no. 5 (July 2008): 703–19. http://dx.doi.org/10.1080/08120090801982868.
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Moreno, Teresa, Fulvio Amato, Xavier Querol, Andrés Alastuey, and Wes Gibbons. "Trace element fractionation processes in resuspended mineral aerosols extracted from Australian continental surface materials." Soil Research 46, no. 2 (2008): 128. http://dx.doi.org/10.1071/sr07121.
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Unconsolidated surface soil and dust samples of varying trace element (TE) content were collected from remote locations in central and south-eastern Australia. The finer grained fraction of the samples (<10 µm, PM10) was separated and geochemically compared to the parent particulate matter (PMPAR). TE are mostly hosted in phosphates and oxides/hydroxides or adsorbed to clay minerals, and are normally fractionated into the PM10, producing PM10/PMPAR ratios >1, especially in siliceous, TE-depleted dusts. In contrast, samples TE-enriched by primary silicate minerals eroded from igneous and metamorphic rocks can produce PM10/PMPAR <1 for more mobile elements such as K, Na, Ba, Rb, and Sr. K/Rb is normally lower in PM10 (unless the PMPAR is muscovite-rich) as is the light/heavy rare earth elements (LREE/HREE) ratio because both Rb and HREE are preferentially adsorbed by fine clay particles. Zr and Hf are mostly hosted by zircon crystals initially >10 µm but these diminish in size with time and sedimentological transport so that PM10 aerosol concentrations of these elements are typically telescoped into a narrower range than the PMPAR. Nb is strongly fractionated into PM10, with Nb/TiO2 ratios characteristic of the durable host mineral rutile in all but the most TE-enriched PM. TE content of PM10 in continental dusts is controlled by both physical and chemical processes. Fresh primary silicates suppress PM10/PMPAR ratios of TE with low ionic potential, whereas the opposite effect is induced by hydraulic sorting and/or physical attrition during surface transport, as well as clay absorbtion and fixation of TE in small, resistant accessory minerals.
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Turner, Simon, Janne Blichert-Toft, Bruce Schaefer, Francis Albarède, and John Foden. "A reappraisal of the evolution of the palaeo-Pacific margin of Gondwana from the Pb and Os isotope systematics of igneous rocks from the southern Adelaide fold belt, South Australia." Gondwana Research 45 (May 2017): 152–62. http://dx.doi.org/10.1016/j.gr.2017.01.006.
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Franz, Gerhard, Oleksii Vyshnevskyi, Michail Taran, Vladimir Khomenko, Michael Wiedenbeck, Ferry Schiperski, and Jörg Nissen. "A new emerald occurrence from Kruta Balka, Western Peri-Azovian region, Ukraine: Implications for understanding the crystal chemistry of emerald." American Mineralogist 105, no. 2 (February 1, 2020): 162–81. http://dx.doi.org/10.2138/am-2020-7010.
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Abstract We investigated emerald, the bright-green gem variety of beryl, from a new locality at Kruta Balka, Ukraine, and compare its chemical characteristics with those of emeralds from selected occurrences worldwide (Austria, Australia, Colombia, South Africa, Russia) to clarify the types and amounts of substitutions as well as the factors controlling such substitutions. For selected crystals, Be and Li were determined by secondary ion mass spectrometry, which showed that the generally assumed value of 3 Be atoms per formula unit (apfu) is valid; only some samples such as the emerald from Kruta Balka deviate from this value (2.944 Be apfu). An important substitution in emerald (expressed as an exchange vector with the additive component Al2Be3Si6O18) is (Mg,Fe2+)NaAl–1☐–1, leading to a hypothetical end-member NaAl(Mg,Fe2+)[Be3Si6O18] called femag-beryl with Na occupying a vacancy position (☐) in the structural channels of beryl. Based on both our results and data from the literature, emeralds worldwide can be characterized based on the amount of femag-substitution. Other minor substitutions in Li-bearing emerald include the exchange vectors LiNa2Al–1☐–2 and LiNaBe–1☐–1, where the former is unique to the Kruta Balka emeralds. Rarely, some Li can also be situated at a channel site, based on stoichiometric considerations. Both Cr- and V-distribution can be very heterogeneous in individual crystals, as shown in the samples from Kruta Balka, Madagascar, and Zimbabwe. Nevertheless, taking average values available for emerald occurrences, the Cr/(Cr+V) ratio (Cr#) in combination with the Mg/(Mg+Fe) ratio (Mg#) and the amount of femag-substitution allows emerald occurrences to be characterized. The “ultramafic” schist-type emeralds with high Cr# and Mg# come from occur-rences where the Fe-Mg-Cr-V component is controlled by the presence of ultramafic meta-igneous rocks. Emeralds with highly variable Mg# come from “sedimentary” localities, where the Fe-Mg-Cr-V component is controlled by metamorphosed sediments such as black shales and carbonates. A “transitional” group has both metasediments and ultramafic rocks as country rocks. Most “ultramafic” schist type occurrences are characterized by a high amount of femag-component, whereas those from the “sedimentary” and “transitional” groups have low femag contents. Growth conditions derived from the zoning pattern—combined replacement, sector, and oscillatory zoning—in the Kruta Balka emeralds indicate disequilibrium growth from a fluid along with late-stage Na-infiltration. Inclusions in Kruta Balka emeralds (zircon with up to 11 wt% Hf, tourmaline, albite, Sc-bearing apatite) point to a pegmatitic origin.
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Duvert, C., M. K. Stewart, D. I. Cendón, and M. Raiber. "Time-series of tritium, stable isotopes and chloride reveal short-term variations in groundwater contribution to a stream." Hydrology and Earth System Sciences Discussions 12, no. 8 (August 18, 2015): 8035–89. http://dx.doi.org/10.5194/hessd-12-8035-2015.
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Abstract. A major limitation to the accurate assessment of streamwater transit time (TT) stems from the use of stable isotopes or chloride as hydrological tracers, because these tracers are blind to older contributions. Also, while catchment processes are highly non-stationary, the importance of temporal dynamics in older water TT has often been overlooked. In this study we used lumped convolution models to examine time-series of tritium, stable isotopes and chloride in rainfall, streamwater and groundwater of a catchment located in subtropical Australia. Our objectives were to assess the different contributions to streamflow and their variations over time, and to understand the relationships between streamwater TT and groundwater residence time. Stable isotopes and chloride provided consistent estimates of TT in the upstream part of the catchment. A young component to streamflow was identified that was partitioned into quickflow (mean TT ≈ 2 weeks) and discharge from the fractured igneous rocks forming the headwaters (mean TT ≈ 0.3 years). The use of tritium was beneficial for determining an older contribution to streamflow in the downstream area. The best fits were obtained for a mean TT of 16–25 years for this older groundwater component. This was significantly lower than the residence time calculated for the alluvial aquifer feeding the stream downstream (≈ 76–102 years), outlining the fact that water exiting the catchment and water stored in it had distinctive age distributions. When simulations were run separately on each tritium streamwater sample, the TT of old water fraction varied substantially over time, with values averaging 17 ± 6 years at low flow and 38 ± 15 years after major recharge events. This was interpreted as the flushing out of deeper, older waters shortly after recharge by the resulting pressure wave propagation. Overall, this study shows the usefulness of collecting tritium data in streamwater to document short-term variations in the older component of the TT distribution. Our results also shed light on the complex relationships between stored water and water in transit, which are highly nonlinear and remain poorly understood.
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Wyborn, L. A. I., R. W. Page, and A. J. Parker. "Geochemical and Geochronological Signatures in Australian Proterozoic Igneous Rocks." Geological Society, London, Special Publications 33, no. 1 (1987): 377–94. http://dx.doi.org/10.1144/gsl.sp.1987.033.01.26.
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Duvert, C., M. K. Stewart, D. I. Cendón, and M. Raiber. "Time series of tritium, stable isotopes and chloride reveal short-term variations in groundwater contribution to a stream." Hydrology and Earth System Sciences 20, no. 1 (January 18, 2016): 257–77. http://dx.doi.org/10.5194/hess-20-257-2016.
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Abstract. A major limitation to the assessment of catchment transit time (TT) stems from the use of stable isotopes or chloride as hydrological tracers, because these tracers are blind to older contributions. Yet, accurately capturing the TT of the old water fraction is essential, as is the assessment of its temporal variations under non-stationary catchment dynamics. In this study we used lumped convolution models to examine time series of tritium, stable isotopes and chloride in rainfall, streamwater and groundwater of a catchment located in subtropical Australia. Our objectives were to determine the different contributions to streamflow and their variations over time, and to understand the relationship between catchment TT and groundwater residence time. Stable isotopes and chloride provided consistent estimates of TT in the upstream part of the catchment. A young component to streamflow was identified that was partitioned into quickflow (mean TT ≈ 2 weeks) and discharge from the fractured igneous rocks forming the headwaters (mean TT ≈ 0.3 years). The use of tritium was beneficial for determining an older contribution to streamflow in the downstream area. The best fits between measured and modelled tritium activities were obtained for a mean TT of 16–25 years for this older groundwater component. This was significantly lower than the residence time calculated for groundwater in the alluvial aquifer feeding the stream downstream ( ≈ 76–102 years), emphasising the fact that water exiting the catchment and water stored in it had distinctive age distributions. When simulations were run separately on each tritium streamwater sample, the TT of old water fraction varied substantially over time, with values averaging 17 ± 6 years at low flow and 38 ± 15 years after major recharge events. This counterintuitive result was interpreted as the flushing out of deeper, older waters shortly after recharge by the resulting pressure wave propagation. Overall, this study shows the usefulness of collecting tritium data in streamwater to document short-term variations in the older component of the TT distribution. Our results also shed light on the complex relationships between stored water and water in transit, which are highly non-linear and remain poorly understood.