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Pasbakhsh P.,Sunway University | Churchman G.J.,University of Adelaide | Keeling J.L.,Geological Survey of Western Australia
Applied Clay Science | Year: 2013

There is increasing research interest on new industrial applications for the clay mineral halloysite where greater use is made of its natural tubular morphology, nano-scale diameter and contrasting chemistry on external and internal surfaces. Halloysite nanotubes, commonly referred to as HNTs, have potential applications as microfibre fillers, carriers for the supply and controlled or sustained release of active agents for drug delivery and anticorrosion coatings, in nanoreactors or nanotemplates, and for the uptake of contaminants or pollutants. In this study, various properties were measured on 6 halloysites from different geographical and geological environments from Australia, New Zealand and the USA. From the results, inferences were drawn on their comparative suitability for new uses. The characterisation included identification of impurities by X-ray diffraction (XRD), morphology, surface area and pore volume by electron microscopy and nitrogen absorption, the determination of exchangeable cations, and measurement of zeta potential over a wide range of pH. Halloysite content in individual samples ranged from 84 to 98%. Impurities included minor quartz, cristobalite, kaolinite, gibbsite, alunite, iron oxides and anatase. Variation in halloysite morphology and the levels of impurities had the most effect on surface area and internal pore volume. Samples with low levels of impurities and regular, thin-walled tubes reported the highest pore volumes associated with the cylindrical cavity or lumen in halloysite tubes. Surface areas varied from 22 to 81m2.g-1 and the proportion of pore space associated with the HNT lumen ranged from 11 to 39%. When the properties of the 6 different halloysites were assessed relative to the requirements for halloysite as nanotubes for either additives or carriers, one showed exceptional characteristics for both types of application but it occurs only rarely. Another halloysite that is moderately suitable for use as an additive but not a carrier occurs in a large deposit. The other samples each showed some limitations of suitability for use as an additive and/or as a carrier. © 2012 Elsevier B.V.

News Article | February 27, 2017
Site: www.eurekalert.org

Today's Earth is a dynamic planet with an outer layer composed of giant plates that grind together, sliding past or dipping beneath one another, giving rise to earthquakes and volcanoes. Others separate at undersea mountain ridges, where molten rock spreads out from the centers of major ocean basins. But new research suggests that this was not always the case. Instead, shortly after Earth formed and began to cool, the planet's first outer layer was a single, solid but deformable shell. Later, this shell began to fold and crack more widely, giving rise to modern plate tectonics. The research, described in a paper published February 27, 2017 in the journal Nature, is the latest salvo in a long-standing debate in the geological research community: did plate tectonics start right away--a theory known as uniformitarianism--or did Earth first go through a long phase with a solid shell covering the entire planet? The new results suggest the solid shell model is closest to what really happened. "Models for how the first continental crust formed generally fall into two groups: those that invoke modern-style plate tectonics and those that do not," said Michael Brown, a professor of geology at the University of Maryland and a co-author of the study. "Our research supports the latter--a 'stagnant lid' forming the planet's outer shell early in Earth's history." To reach these conclusions, Brown and his colleagues from Curtin University and the Geological Survey of Western Australia studied rocks collected from the East Pilbara Terrane, a large area of ancient granitic crust located in the state of Western Australia. Rocks here are among the oldest known, ranging from 3.5 to about 2.5 billion years of age. (Earth is roughly 4.5 billion years old.) The researchers specifically selected granites with a chemical composition usually associated with volcanic arcs--a telltale sign of plate tectonic activity. Brown and his colleagues also looked at basalt rocks from the associated Coucal formation. Basalt is the rock produced when volcanoes erupt, but it also forms the ocean floor, as molten basalt erupts at spreading ridges in the center of ocean basins. In modern-day plate tectonics, when ocean floor basalt reaches the continents, it dips--or subducts--beneath the Earth's surface, where it generates fluids that allow the overlying mantle to melt and eventually create large masses of granite beneath the surface. Previous research suggested that the Coucal basalts could be the source rocks for the granites in the Pilbara Terrane, because of the similarities in their chemical composition. Brown and his collaborators set out to verify this, but also to test another long-held assumption: could the Coucal basalts have melted to form granite in some way other than subduction of the basalt beneath Earth's surface? If so, perhaps plate tectonics was not yet happening when the Pilbara granites formed. To address this question, the researchers performed thermodynamic calculations to determine the phase equilibria of average Coucal basalt. Phase equilibria are precise descriptions of how a substance behaves under various temperature and pressure conditions, including the temperature at which melting begins, the amount of melt produced and its chemical composition. For example, one of the simplest phase equilibria diagrams describes the behavior of water: at low temperatures and/or high pressures, water forms solid ice, while at high temperatures and/or low pressures, water forms gaseous steam. Phase equilibria gets a bit more involved with rocks, which have complex chemical compositions that can take on very different mineral combinations and physical characteristics based on temperature and pressure. "If you take a rock off the shelf and melt it, you can get a phase diagram. But you're stuck with a fixed chemical composition," Brown said. "With thermodynamic modeling, you can change the composition, pressure and temperature independently. It's much more flexible and helps us to answer some questions we can't address with experiments on rocks." Using the Coucal basalts and Pilbara granites as a starting point, Brown and his colleagues constructed a series of modeling experiments to reflect what might have transpired in an ancient Earth without plate tectonics. Their results suggest that, indeed, the Pilbara granites could have formed from the Coucal basalts. More to the point, this transformation could have occurred in a pressure and temperature scenario consistent with a "stagnant lid," or a single shell covering the entire planet. Plate tectonics substantially affects the temperature and pressure of rocks within Earth's interior. When a slab of rock subducts under the Earth's surface, the rock starts off relatively cool and takes time to gain heat. By the time it reaches a higher temperature, the rock has also reached a significant depth, which corresponds to high pressure--in the same way a diver experiences higher pressure at greater water depth. In contrast, a "stagnant lid" regime would be very hot at relatively shallow depths and low pressures. Geologists refer to this as a "high thermal gradient." "Our results suggest the Pilbara granites were produced by melting of the Coucal basalts or similar materials in a high thermal gradient environment," Brown said. "Additionally, the composition of the Coucal basalts indicates that they, too, came from an earlier generation of source rocks. We conclude that a multi-stage process produced Earth's first continents in a 'stagnant lid' scenario before plate tectonics began." The research paper, "Earth's first stable continents did not form by subduction," Tim Johnson, Michael Brown, Nicholas Gardiner, Christopher Kirkland and Hugh Smithies, was published February 27, 2017 in the journal Nature. This work was supported by The Institute of Geoscience Research at Curtin University, Perth, Australia. The content of this article does not necessarily reflect the views of this organization. University of Maryland College of Computer, Mathematical, and Natural Sciences 2300 Symons Hall College Park, MD 20742 http://www. @UMDscience The College of Computer, Mathematical, and Natural Sciences at the University of Maryland educates more than 7,000 future scientific leaders in its undergraduate and graduate programs each year. The college's 10 departments and more than a dozen interdisciplinary research centers foster scientific discovery with annual sponsored research funding exceeding $150 million.

Zhou C.H.,Zhejiang University of Technology | Keeling J.,Geological Survey of Western Australia
Applied Clay Science | Year: 2013

This brief overview comments on recent trends in scientific research and development of clay minerals and was stimulated by the compilation of papers for this special issue to pay tribute to the 34th International Geological Congress held in 2012. The essentially geological context of the conference was a reminder that increased understanding of the genesis and evolution of clays and clay minerals provides insights that have applications in mining, environmental management, paleoclimate, Earth and extraterrestrial sciences. The requirement for multidisciplinary knowledge, including geology, mineralogy, chemistry and materials science, and modern instrumentation and analysis of clay minerals, is essential to a full understanding of the genesis, role and potential new uses for these fine-grained industrial minerals. Latest studies are typically focused on processing and modifying of clay minerals as adsorbents, catalysts, and biomaterials. The emphasis for future work is on advanced clay-based nanomaterials for use in new approaches to sustainable energy, green environment, and human health. © 2013 Elsevier B.V.

Morris P.A.,Geological Survey of Western Australia | Kirkland C.L.,Geological Survey of Western Australia
Lithos | Year: 2014

Subduction processes on early earth are controversial, with some suggestions that tectonics did not operate until the earth cooled to a sufficient point around the Archean-Proterozoic boundary. One way of addressing this issue is to examine well-preserved successions of Archean supracrustal rocks. Here we discuss petrography, whole-rock chemical and isotopic data combined with zircon Hf isotopes from andesites, high-magnesium andesites (HMA), dacites, high-magnesium dacites (HMD), rhyolites and coeval felsic intrusive rocks of the c. 2730Ma Marda Volcanic Complex (MVC) in the central Yilgarn Craton of Western Australia. We demonstrate that these rocks result from melting of a metasomatized mantle source, followed by fractional crystallization in a crustal magma chamber. Contamination of komatiite by Archean crust, to produce the Marda Volcanic Complex andesites, is not feasible, as most of these crustal sources are too radiogenic to act as viable contaminants. The εNd(2730) of MVC andesites can be produced by mixing 10% Narryer semi-pelite with komatiite, consistent with modelling using Hf isotopes, but to achieve the required trace element concentrations, the mixture needs to be melted by about 25%. The most likely scenario is the modification of a mantle wedge above a subducting plate, coeval with partial melting, producing volcanic rocks with subduction signatures and variable Mg, Cr and Ni contents. Subsequent fractionation of cognate phases can account for the chemistry of dacites and rhyolites. © 2013.

Morris P.A.,Geological Survey of Western Australia
Geochemistry: Exploration, Environment, Analysis | Year: 2013

The fine fraction (<50 μm; 'silt - clay') of regolith from an area dominated by thick (up to 120 m) transported regolith is shown to be a viable sampling medium for detecting bedrock and bedrock-hosted mineralization. A partial digest of the fine fraction of regolith reveals that elements which have migrated vertically from bedrock have become sequestered at a shallow depth in regolith. Nickel, Cr, Li, Mn, V, Co and Rb are useful in tracing the extent of different bedrock types, with Ni, Cr, V and Co particularly useful for identifying more mafic bedrock. Higher concentrations of Au (maximum 29 ppb; median 2 ppb; n = 835) are spatially related to either Archean greenstones or unconformity-related uranium - base metal - gold mineralization. Although some samples with anomalous Au concentrations are carbonaterich, there is no consistent relationship between elevated Au concentrations and the carbonate content of regolith. Deionized water digestion of the <50-μm fraction of 50 samples correlates with aqua regia data for several elements (particularly Au, Ni), suggesting that some mineralization- or bedrock-related elements in the fine fraction of regolith are either labile or microparticulate. © 2013 AAG/Geological Society of London.

Pirajno F.,Geological Survey of Western Australia | Pirajno F.,University of Western Australia
Journal of Geodynamics | Year: 2010

In the orogenic belts of the Central Asian Orogenic Belt (CAOB), many mafic and felsic plutons are temporally and spatially associated with orogen-scale strike-slip faults. The CAOB is a huge and complex orogenic collage of accreted terranes that was formed in the Early to Mid-Palaeozoic. In the CAOB, orogen-scale strike-slip faults extend for 100-1000. s of kilometres marking the boundaries of tectonic units and terranes. I use examples from southern Siberia and NW China to illustrate the important role that strike-slip faults have in localising intraplate magmatism and associated metallogeny. Cases from the Altay-Sayan in southern Siberia, the Altay and Tianshan orogens in NW China, are compelling for providing good evidence of the control that strike-slip structures exert for the emplacement of magmas and related mineral systems. These strike-slip faults controlled the emplacement of mafic-ultramafic intrusions, alkaline mafic and felsic magmatism in the period 280-240. Ma, which coincides with mantle plume(s) activity that led to the emplacement of the Tarim and Siberian large igneous provinces (LIPs). Mineral systems that are associated with these LIPs include magmatic Ni-Cu in sill-like intrusions, concentrically zoned mafic-ultramafic intrusions (e.g. Kalatongke, the second largest Ni-Cu sulphide deposit in China, after Jinchuan), epithermal systems, breccia pipes, polymetallic hydrothermal veins, granitoid-related greisen and rare earth pegmatites, as well as kimberlite fields. In the Altay-Sayan and NW China regions, orogen-scale translithospheric strike-slip faults provided the channels for the emplacement of magmas, resulting from lateral flow of mantle melts along the base of the lithosphere. This lateral flow is interpreted to have resulted from the impingement of mantle plumes to the base of the lithosphere of what was, to all intents and purposes, a stationary plate. Lateral flow from mantle plumes head was sustained or facilitated, during stages of extension and movements along orogen-scale strike-slip faults. In the Altay-Sayan and NW China, decompression melting of the mantle material produced mafic-ultramafic magmas that were emplaced along the comparatively narrow conduits of the strike-slip zones, forming concentrically zoned complexes that locally, where favourable conditions allowed it (e.g. crustal contamination), host magmatic Ni-Cu sulphides. Flow of mantle melts into translithospheric strike-slip structures also caused partial melting of a thinned and metasomatised lithosphere, resulting in alkaline magmatic products and a wide range of related mineral systems, from polymetallic veins to greisens. Partial melting of the lower crust also produced A-type granitic magmas that locally vented to the surface, forming calderas hosting epithermal and porphyry systems, as observed in NW China. © 2010 Elsevier Ltd.

Van Kranendonk M.J.,Geological Survey of Western Australia
Journal of African Earth Sciences | Year: 2011

A thick, upward-younging stratigraphy and presence of crustal contamination in even the oldest rocks of the Barberton greenstone belt precludes crust formation through tectonic stacking of oceanic lithosphere above a subduction zone. Rather, structural and geochronological evidence for simultaneous formation of dome-and-keel structure in the footwall of the belt, greenstone-down extensional shearing and radially inward-plunging lobe-cusp folds around the belt margins, and recumbent folds and thrusts in the core of the belt is uniquely explained by sinking of thick, dense greenstones into partially molten granitic middle crust during partial convective overturn at 3.26-3.22. Ga. High-pressure (P), moderate-temperature (T) metamorphism in vertically-lineated greenstone septae around granite domes contrasts with moderate P-T assemblages in the cores of the same domes in the footwall, reflecting initial sinking of cool greenstone drips from the base of the belt. These data suggest crust formation as a long-lived volcanic plateau affected by intracrustal modification. © 2011.

The oldest part of the Pilbara Craton is 3.80-3.55Ga crust. Between 3.53 and 3.22Ga, mantle plume activity resulted in eight successive volcanic cycles forming the Pilbara Supergroup. Large volumes of granitic magma were intruded during the same period. By 3.22Ga, a thick continental crust, the East Pilbara Terrane, had been established. Between 3.22 and 3.16Ga, rifting of the East Pilbara Terrane separated off two additional terranes (Karratha and Kurrana), with intervening basins of oceanic crust. After 3.16Ga, the three terranes began to converge, resulting in both obduction of oceanic crust (Regal Terrane) and, in another area, subduction to form a 3.13Ga island arc (Sholl Terrane). At 3.07Ga, the Karratha, Regal, and Sholl Terranes collided to form the West Pilbara Superterrane, and this collided with the East Pilbara Terrane. The 3.05-2.93Ga De Grey Superbasin was deposited as a succession of basins: Gorge Creek, Whim Creek, Mallina, and Mosquito Creek. Eventual closure of the basins, between 2.94 and 2.93Ga, formed two separate orogenic belts on either side of the East Pilbara Terrane. Post-orogenic granites were intruded between 2.89 and 2.83Ga. The 2.78-2.63Ga Fortescue Basin developed in four stages: (i) rifting of the Pilbara Craton; (ii) folding and erosion; (iii) large igneous province (LIP) volcanism; and (iv) marine sedimentation on a passive margin. A review of all known evidence for early life in the Pilbara Craton is provided. In hydrothermal settings, most of the evidence occurs as filamentous and spheroidal microfossils, organic carbon, microbial mats, and rare stromatolites. By contrast, shallow-water marine sedimentary rocks contain a diverse range of stromatolites, and microbial mats. Lacustrine and shallow-water marine carbonate rocks in the Fortescue Basin contain abundant and morphologically diverse stromatolites, widespread microbial mats, and organic carbon. © 2012 Blackwell Publishing Asia Pty Ltd.

McLoughlin S.,Swedish Museum of Natural History | Martin S.K.,Geological Survey of Western Australia | Beattie R.,119a Merrigang St
Gondwana Research | Year: 2015

A survey of Australian Jurassic plant fossil assemblages reveals examples of foliar and wood damage generated by terrestrial arthropods attributed to leaf-margin feeding, surface feeding, lamina hole feeding, galling, piercing-and-sucking, leaf-mining, boring and oviposition. These types of damage are spread across a wide range of fern and gymnosperm taxa, but are particularly well represented on derived gymnosperm clades, such as Pentoxylales and Bennettitales. Several Australian Jurassic plants show morphological adaptations in the form of minute marginal and apical spines on leaves and bracts, and scales on rachises that likely represent physical defences against arthropod herbivory. Only two entomofaunal assemblages are presently known from the Australian Jurassic but these reveal a moderate range of taxa, particularly among the Orthoptera, Coleoptera, Hemiptera and Odonata, all of which are candidates for the dominant feeding traits evidenced by the fossil leaf and axis damage. The survey reveals that plant-arthropod interactions in the Jurassic at middle to high southern latitudes of southeastern Gondwana incorporated a similar diversity of feeding strategies to those represented in coeval communities from other provinces. Further, the range of arthropod damage types is similar between Late Triassic and Jurassic assemblages from Gondwana despite substantial differences in the major plant taxa, implying that terrestrial invertebrate herbivores were able to successfully transfer to alternative plant hosts during the floristic turnovers at the Triassic-Jurassic transition. © 2013 International Association for Gondwana Research.

News Article | May 18, 2016
Site: www.techtimes.com

Australian researchers have stumbled on proof of a massive asteroid colliding with Earth during our planet's early life. The impact – deemed bigger than anything experienced by humans – produced tiny glass beads known as spherules, which formed from vaporized matter. These beads were recently discovered in northwestern Australia. “The impact would have triggered earthquakes orders of magnitude greater than terrestrial earthquakes, it would have caused huge tsunamis and would have made cliffs crumble,” said study author and Australian National University professor Andrew Glikson, adding that asteroid impact material also would have spread around the world. The spherules were detected in seafloor sediments dating back 3.46 billion years. Glikson and Arthur Hickman from the Geological Survey of Western Australia found them in a Marble Bar drill core, in some of Earth’s oldest known sediments. Highly precise dating was made possible by two volcanic layers sandwiching the sediment layer, originally situated on the ocean floor. Additional testing saw that the elements in the samples – including nickel, platinum and chromium – matched those found in asteroids. The involved asteroid, apart from being the second oldest known, is among the largest to hit the planet, at an estimated 20 to 30 kilometers (12 to 19 miles) across and likely creating a crater spanning hundreds of kilometers wide. About 3.9 billion years earlier, before the collision of the said asteroid, the moon was already hit by numerous ones that produced craters dubbed as mare. These are still seen from Earth today. According to Glikson, it remains unknown specifically where the asteroid hit the planet. Craters from that time on the planetary surface have since been wiped out by volcanic motion and tectonic movements. He added, however, that this is only “the tip of the iceberg,” as there could be hundreds more while scientists have only found proof of 17 impacts older than 2.5 billion years. Asteroid impacts of this magnitude are believed to lead to significant tectonic shifts as well as massive magma flows, and probably had a substantial effect on Earth’s evolution. The findings were discussed in the Precambrian Research journal. Researchers from Dublin in Ireland also recently tested the alternative asteroid crater theory by analyzing a relatively younger asteroid crater: the Sudbury impact crater located in Ontario, Canada. They proposed that contrary to previously thought, zircon crystals – the oldest rock pieces on the planet – may have been formed in the impact craters left by ancient asteroids. © 2017 Tech Times, All rights reserved. Do not reproduce without permission.

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