Ray Cas
Monash University, School of Earth, Atmosphere and Environment, Faculty Member
Understanding the dynamics of pyroclastic flows is an important step in developing better models for the internal physical processes within these flows and in providing better hazard assessment to local populations. Fluidization and... more
Understanding the dynamics of pyroclastic flows is an important step in developing better models for the internal physical processes within these flows and in providing better hazard assessment to local populations. Fluidization and related reduced internal friction is a key contributor to this for fines-rich flows, with particle settling and exsolution of gas from juvenile tephra being the primary contributors. Scaled analogue experiments have been conducted in order to investigate the degree to which high pore pressure controls the mechanism of flows generated from sustained supply of material at source. Sub-80 micron diameter silica beads are released into a flume capable of providing a pre-determined basal gas flux along the length of the channel. The gas flux can be set from zero through to the minimum fluidization velocity of the particles at which the material is fully supported by internal pore pressure. Vertical release from a large hopper provides a relatively sustained se...
Research Interests:
Research Interests:
We report sensitive high mass resolution ion microprobe, stable isotopes (SHRIMP SI) multiple sulfur isotope analyses (32S, 33S, 34S) to constrain the sources of sulfur in three Archean VMS deposits—Teutonic Bore, Bentley, and Jaguar—from... more
We report sensitive high mass resolution ion microprobe, stable isotopes (SHRIMP SI) multiple sulfur isotope analyses (32S, 33S, 34S) to constrain the sources of sulfur in three Archean VMS deposits—Teutonic Bore, Bentley, and Jaguar—from the Teutonic Bore volcanic complex of the Yilgarn Craton, Western Australia, together with sedimentary pyrites from associated black shales and interpillow pyrites. The pyrites from VMS mineralization are dominated by mantle sulfur but include a small amount of slightly negative mass-independent fractionation (MIF) anomalies, whereas sulfur from the pyrites in the sedimentary rocks has pronounced positive MIF, with ∆33S values that lie between 0.19 and 6.20‰ (with one outlier at −1.62‰). The wall rocks to the mineralization include sedimentary rocks that have contributed no detectable positive MIF sulfur to the VMS deposits, which is difficult to reconcile with the leaching model for the formation of these deposits. The sulfur isotope data are best explained by mixing between sulfur derived from a magmatic-hydrothermal fluid and seawater sulfur as represented by the interpillow pyrites. The massive sulfide lens pyrites have a weighted mean ∆33S value of −0.27 ± 0.05‰ (MSWD = 1.6) nearly identical with −0.31 ± 0.08‰ (MSWD = 2.4) for pyrites from the stringer zone, which requires mixing to have occurred below the sea floor. We employed a two-component mixing model to estimate the contribution of seawater sulfur to the total sulfur budget of the two Teutonic Bore volcanic complex VMS deposits. The results are 15 to 18% for both Teutonic Bore and Bentley, much higher than the 3% obtained by Jamieson et al. (2013) for the giant Kidd Creek deposit. Similar calculations, carried out for other Neoarchean VMS deposits give value between 2% and 30%, which are similar to modern hydrothermal VMS deposits. We suggest that multiple sulfur isotope analyses may be used to predict the size of Archean VMS deposits and to provide a vector to ore deposit but further studies are needed to test these suggestions.
Research Interests:
A detailed magnetotelluric survey of Mount St. Helens shows that a conduit like zone of high electrical conductivity beneath the volcano is connected to a larger zone of high conductivity at 15 km depth that extends eastward to Mount... more
A detailed magnetotelluric survey of Mount St. Helens shows that a conduit like zone of high electrical conductivity beneath the volcano is connected to a larger zone of high conductivity at 15 km depth that extends eastward to Mount Adams. We interpret this zone to be a region of connected melt that acts as the reservoir for the silicic magma
Research Interests:
Research Interests:
... Fig. 1. Location map of Muskox kimberlite (star) in Slave craton (grey region). Inset, map of Canada. View Within Article. The Muskox pipe is situated on the east side of a ~ 400 m diameter lake, with most of the kimberlite buried ...
Research Interests:
Exceptional exposure through a Permian intra-caldera ignimbrite fill within the 42 × 40 km Ora caldera (>1,290 km3 erupted volume) provides an opportunity to study welding textures in a thick intra-caldera ignimbrite succession. The... more
Exceptional exposure through a Permian intra-caldera ignimbrite fill within the 42 × 40 km Ora caldera (>1,290 km3 erupted volume) provides an opportunity to study welding textures in a thick intra-caldera ignimbrite succession. The ignimbrite succession records primary dense welding, a simple cooling unit structure, common crystallisation zones, and remarkably preserves fresh to slightly hydrated glass in local vitrophyre zones. Evidence for primary syn- and post-emplacement welding consists of (a) viscously deformed and sintered juvenile glass and relict shard textures; (b) complete deposit welding; (c) subtle internal welding intensity variations; (d) vitrophyre preserved locally at the base of the ignimbrite succession; (e) persistent fiamme juvenile clast shapes throughout the succession at the macroscopic and microscopic scales, defining a moderate to well-developed eutaxitic texture; (f) common undulating juvenile clast (pumice) margins and feathery terminations; (g) a general loss of deposit porosity; and (h) perlitic fracturing. A low collapsing or fountaining explosive eruption column model is proposed to have facilitated the ubiquitous welding of the deposit, which in turn helped preserve original textures. The ignimbrite succession preserves no evidence of a time break through the sequence and columnar joints cross-gradational ignimbrite lithofacies boundaries, so the ignimbrite is interpreted to represent a simple cooling unit. Aspect ratio and anisotropy of magnetic susceptibility (AMS) analyses through stratigraphic sections within the thick intra-caldera succession and at the caldera margin reveal variable welding compaction and strain profiles. Significantly, these data show that welding degree/intensity may vary in an apparently simple cooling unit because of variations in eruption process recorded in differing lithofacies. These data imply complex eruption, emplacement, and cooling processes. Three main crystallisation textural zones are identified in the ignimbrite succession: localised vitrophyre zones, widespread microcrystalline to sparsely spherulitic pseudomorphed vitriclastic textural zones, and thick granophyric zones. These zones record a typical spectrum from rapid to prolonged cooling. The non-uniform crystallisation patterns reflect variations in deposit thickness, the relative position of deposits within the larger ignimbrite succession, the type of substrate material, and the degree of confinement in the intra-caldera setting. We support previous work suggesting that traditional welding classifications (e.g. Smith, US Geological Survey Professional Paper 354-F 1960b) are most appropriate for use within altered and/or ancient ignimbrite successions.
Research Interests:
... Ray AF Cas & Heather MN Wright & Christopher B. Folkes & Chiara Lesti & Massimiliano Porreca... more
... Ray AF Cas & Heather MN Wright & Christopher B. Folkes & Chiara Lesti & Massimiliano Porreca & Guido Giordano & Jose G. Viramonte ... 1 Diamante, 2 Aguas Calientes, 3 Tacuil, 4 Hualfin, 5 Laguna Media, 6 El Toro, 7 Antofagasta de al Sierra, 8 Northwest of Antofagasta, 9 ...
Research Interests:
Anisotropy of magnetic susceptibility (AMS) data reveal heterogeneous pyroclastic flow processes and variable flow directions within the intra-caldera setting of the Permian rhyolitic welded Ora ignimbrite. Magnetic fabric is primary,... more
Anisotropy of magnetic susceptibility (AMS) data reveal heterogeneous pyroclastic flow processes and variable flow directions within the intra-caldera setting of the Permian rhyolitic welded Ora ignimbrite. Magnetic fabric is primary, orientated during the pyroclastic flow emplacement, and is controlled by paramagnetic and ferromagnetic mineral phases. The ignimbrite has typically weak mean magnetic susceptibilities (1.32–21.8×10−4 SI) but with a large spread and low anisotropy degrees (1.003–1.023), which vary in different parts of the caldera. The intra-caldera magnetic fabric provides significant information on the dynamics of the intra-caldera setting, relating to changing vertical and lateral flow emplacement processes. AMS shape ellipsoids range from oblate to prolate; these are interpreted to reflect the heterogeneous nature of the flow resulting from the influence of underlying topography, constraints of the caldera walls, primary welding and post-emplacement mineral growth....
Research Interests:
The Newer Volcanics Province of SE Australia is a very large continental basaltic province, with an area of >23 000 km2, a dense rock equivalent volume of <900 km3 and >400 monogenetic volcanoes; it has been active since c. 8 Ma.... more
The Newer Volcanics Province of SE Australia is a very large continental basaltic province, with an area of >23 000 km2, a dense rock equivalent volume of <900 km3 and >400 monogenetic volcanoes; it has been active since c. 8 Ma. Lava fields, shields, scoria cones are common, and there are >40 maars and volcanic complexes. Maars occur dominantly in the south where magmas erupted through Tertiary sedimentary aquifers, whereas in the north, over Palaeozoic crust, there are few. Complex interactions of the magma volatile content, magma ascent rates, conduit characteristics and the availability and depth of aquifers caused diverse eruption styles. Volcanoes commonly occur close to major crustal faults, which acted as magma conduits. There is no simple age pattern of volcanism across the province. Volcanism was probably triggered by transtensional decompression in the crust where fault sets intersect, affecting hot, hydrated mantle that had welled up through edge-driven conve...
Research Interests:
Quench fragmentation is a non-explosive process that occurs when molten magma is super-cooled to glass upon contact with ambient water. This occurs when coherent lavas are erupted subaqueously, when they flow into water, when magma... more
Quench fragmentation is a non-explosive process that occurs when molten magma is super-cooled to glass upon contact with ambient water. This occurs when coherent lavas are erupted subaqueously, when they flow into water, when magma intrudes into water-saturated sediments, and when magma and water interact explosively during phreatomagmatism. Quench fragmentation also occurs alongside explosive phreatomagmatic activity. Although products of quench fragmentation (hyaloclastite sensu stricto) have been discussed qualitatively in the volcanological literature, compared to explosive fragmentation processes very little is known about the exact dynamics of quench fragmentation of magma and how this relates to the rheology and physical properties of volcanic glass. Based on literature from materials engineering, we present a detailed review of the processes by which glass forms, the properties of glass, and the fracture mechanics that cause it to fragment non-explosively. We also consider how this can be applied to understanding the dynamics behind the volcanological processes of in-situ glass fragmentation during quenching in wet environments and phreatomagmatism. Important parameters for the occurrence of quench fragmentation are the temperature difference between the magma and the ambient water and how much the ambient water is superheated above its Leidenfrost temperature. The geometry of the lava or magma intrusion, the thermal conductivity and the thermal expansion are also of great importance. The resistance of the magma against fragmentation can be increased with the presence of crystals provided the thermal expansion of the crystals does not greatly exceed that of the glass; vesicles have the opposite effect, unless the magma is highly vesicular. This overview then provides a solid basis for further quantitative study of quench fragmentation and hyaloclastite formation.
Research Interests:
ABSTRACT The Crusader Complex, part of the Agnew gold camp of the Lawlers Anticline of the Yilgarn Craton, Western Australia, is located close to or along the contact between the Lawlers Basalt and Agnew Ultramafics units. Au... more
ABSTRACT The Crusader Complex, part of the Agnew gold camp of the Lawlers Anticline of the Yilgarn Craton, Western Australia, is located close to or along the contact between the Lawlers Basalt and Agnew Ultramafics units. Au mineralization within the four orebodies that form the Crusader Complex is dominated by very pure Au, containing less than 1 wt.% Ag, with Au variably associated with scheelite, Bi-tellurides and minor chalcopyrite within a magnetite and titanite gangue assemblage. Hydrothermal alteration associated with this style of mineralization is characterized by increasing concentrations of Mo, Be, Li, Sn and Fe and depletions in Na, Cu, Ba, Pb, Mn, Zn, Si, and K relative to protolith concentrations; these enrichments are more typical in orebodies associated with felsic intrusive-related mineralizing systems rather than the more well-known orogenic Au deposits found elsewhere within the Lawlers Anticline (e.g. at Waroonga) and within the greater Yilgarn Craton. We propose that flexures of the contact between the Lawlers Basalt and Agnew Ultramafic units acted as conduits for Au-bearing felsic intrusive-derived fluids and generated structural traps that enhanced fluid flow. The mineralizing fluids that formed the Crusader deposits were derived from the Lawlers granitoid pluton that intruded into the study area. Enhanced fluid flow promoted interaction between hydrothermal fluids and the reactive mafic–ultramafic rock sequence, augmenting the amount of Au that was precipitated during formation of the orebodies at Crusader. The magnetite-dominated quartz- and sulfide-poor intrusion-related mineralization at Crusader contrasts sharply with other late Archean intrusion-related deposits of the Yilgarn Craton that are usually sulfide- and/or quartz-rich. This may in turn suggest that the Crusader deposit represents a new class of under-explored intrusion-derived deposits, possibly opening new mineral exploration opportunities for the Agnew region, and potentially the wider Eastern Goldfields Superterrane. Enrichments in Mo and Sn and significant depletions in Cu suggest that other parts of the Lawlers batholith may also be prospective for base metal mineralization. Integration of stratigraphic interpretation with the identification of key structural fluid pathways and the presence of felsic intrusive bodies, as presented in this study, enables the delineation of the key elements that underlie mineralization at the Crusader Complex. We propose that these key elements provide vital information for future gold exploration models that can be used within other Archean terranes and within the Eastern Yilgarn Craton in particular.
Research Interests:
Research Interests:
Research Interests:
Research Interests:
Research Interests:
ABSTRACT The ∼5 ka Mt. Gambier Volcanic Complex in the Newer Volcanics Province, Australia is an extremely complex monogenetic, volcanic system that preserves at least 14 eruption points aligned along a fissure system. The complex... more
ABSTRACT The ∼5 ka Mt. Gambier Volcanic Complex in the Newer Volcanics Province, Australia is an extremely complex monogenetic, volcanic system that preserves at least 14 eruption points aligned along a fissure system. The complex stratigraphy can be subdivided into six main facies that record alternations between magmatic and phreatomagmatic eruption styles in a random manner. The facies are (1) coherent to vesicular fragmental alkali basalt (effusive/Hawaiian spatter and lava flows); (2) massive scoriaceous fine lapilli with coarse ash (Strombolian fallout); (3) bedded scoriaceous fine lapilli tuff (violent Strombolian fallout); (4) thin–medium bedded, undulating very fine lapilli in coarse ash (dry phreatomagmatic surge-modified fallout); (5) palagonite-altered, cross-bedded, medium lapilli to fine ash (wet phreatomagmatic base surges); and (6) massive, palagonite-altered, very poorly sorted tuff breccia and lapilli tuff (phreato-Vulcanian pyroclastic flows). Since most deposits are lithified, to quantify the grain size distributions (GSDs), image analysis was performed. The facies are distinct based on their GSDs and the fine ash to coarse+fine ash ratios. These provide insights into the fragmentation intensities and water–magma interaction efficiencies for each facies. The eruption chronology indicates a random spatial and temporal sequence of occurrence of eruption styles, except for a “magmatic horizon” of effusive activity occurring at both ends of the volcanic complex simultaneously. The eruption foci are located along NW–SE trending lineaments, indicating that the complex was fed by multiple dykes following the subsurface structures related to the Tartwaup Fault System. Possible factors causing vent migration along these dykes and changes in eruption styles include differences in magma ascent rates, viscosity, crystallinity, degassing and magma discharge rate, as well as hydrological parameters.
Research Interests:
Research Interests:
The Koala kimberlite, Northwest Territories, Canada, is a small pipe-like body that was emplaced into the Archean Koala granodiorite batholith and the overlying Cretaceous to Tertiary sediments at ~53 Ma. Koala is predominantly in-filled... more
The Koala kimberlite, Northwest Territories, Canada, is a small pipe-like body that was emplaced into the Archean Koala granodiorite batholith and the overlying Cretaceous to Tertiary sediments at ~53 Ma. Koala is predominantly in-filled by a series of six distinct clastic deposits, the lowermost of which has been intruded by a late stage coherent kimberlite body. The clastic facies are easily distinguished from each other by variations in texture, and in the abundance and distribution of the dominant components. From facies analysis, we infer that the pipe was initially partially filled by a massive, poorly sorted, matrix-supported, olivine-rich lapilli tuff formed from a collapsing eruption column during the waning stage of the pipe-forming eruption. This unit is overlain by a granodiorite cobble-boulder breccia and a massive, poorly sorted, mud-rich pebbly-sandstone. These deposits represent post-eruptive gravitational collapse of the unstable pipe walls and mass wasting of tephra forming the crater rim. The crater then filled with water within which ~20 m of non-kimberlitic, wood-rich, silty sand accumulated, representing up to 47,000 years of quiescence. The upper two units in the Koala pipe are both olivine rich and show distinct grain-size grading. These units are interpreted to have been deposited sub-aqueously, from pyroclastic flows sourced from one or more other kimberlite volcanoes. The uppermost units in the Koala pipe highlight the likelihood that some kimberlite pipes may be only partially filled by their own eruptive products at the cessation of volcanic activity, enabling them to act as depocentres for pyroclastic and sedimentary deposits from the surrounding volcanic landscape. Recognition of these exotic kimberlite deposits has implications for kimberlite eruption and emplacement processes.
Research Interests:
... Acknowledgements This study is part of the PhD of Adrian Pittari, supported by an Australian Postgraduate Award Scholarship, Monash University ... Elsevier, Amsterdam Baer EM, Fisher RV, Fuller M, Valentine G (1997) Turbulent... more
... Acknowledgements This study is part of the PhD of Adrian Pittari, supported by an Australian Postgraduate Award Scholarship, Monash University ... Elsevier, Amsterdam Baer EM, Fisher RV, Fuller M, Valentine G (1997) Turbulent transport and deposition of the Ito pyroclastic flow ...
Research Interests:
... Ray AF Cas . Joe J. Monaghan . Joan Martí ... 1994; Ablay and Kearey 2000). Since ~2 Ma multiple cycles of phonolitic explosive volcanism, each culminating in a climactic caldera-forming event, have dominated the Las Cañadas edifice... more
... Ray AF Cas . Joe J. Monaghan . Joan Martí ... 1994; Ablay and Kearey 2000). Since ~2 Ma multiple cycles of phonolitic explosive volcanism, each culminating in a climactic caldera-forming event, have dominated the Las Cañadas edifice and its summit caldera (Fig. 1; Martí et al. ...
Research Interests:
ABSTRACT Understanding explosive volcanic eruptions, especially phreatomagmatic eruptions, their intensities and energy budgets is of major importance when it comes to risk and hazard studies. With only a few historic occurrences of... more
ABSTRACT Understanding explosive volcanic eruptions, especially phreatomagmatic eruptions, their intensities and energy budgets is of major importance when it comes to risk and hazard studies. With only a few historic occurrences of phreatomagmatic activity, a large amount of our understanding comes from the study of pre-historic volcanic centres, which causes issues when it comes to preservation and vegetation. In this research, we show that using 3D geometrical modelling it is possible to obtain volume estimates for different deposits of a pre-historic, complex, monogenetic centre, the Mt. Gambier Volcanic Complex, south-eastern Australia. Using these volumes, we further explore the energy budgets and the magnitude of this eruption (VEI 4), including dispersal patterns (eruption columns varying between 5 and 10 km, dispersed towards north-east to south), to further our understanding of intraplate, monogenetic eruptions involving phreatomagmatic activity. We also compare which thermodynamic model fits best in the creation of the maar crater of Mt. Gambier: the major-explosion-dominated model or the incremental growth model. In this case, the formation of most of the craters can best be explained by the latter model.
Research Interests:
The dominant type of pyroclasts found in kimberlite deposits are crystals of rounded to subrounded olivine that have no apparent quenched melt or magma attached. We refer to these as free-olivine pyroclasts. Rounded to sub-rounded... more
The dominant type of pyroclasts found in kimberlite deposits are crystals of rounded to subrounded olivine that have no apparent quenched melt or magma attached. We refer to these as free-olivine pyroclasts. Rounded to sub-rounded juvenile lapilli comprising olivine grains mantled by a thin rim of (micro) crystalline coherent kimberlite are also common but they are generally subordinate to free olivine grains. Within the juvenile lapilli vesicles are rare to absent, and the rims of quenched kimberlite can show alignment of microlites. The rounded nature of these juvenile pyroclasts is generally considered to be a manifestation of surface tension processes operating on a very low viscosity melt (i.e. kimberlite melt) although there are no direct measurements of physical properties for kimberlite melt. We suggest that the properties of kimberlite pyroclasts can be used to constrain the physical properties of kimberlite magmas and the styles of volcanic eruption. Specifically, we consider the implications that the morphology and internal structure of these pyroclasts has for the melt properties of kimberlite magmas. We also explore how pyroclast shape and size distributions can be used to constrain eruption dynamics and depositional processes. Lastly, we assess the significance of the highly abundant free olivine crystals in terms of the transport and eruption processes assumed to be responsible for liberating these crystals from their host melt.
Research Interests:
Page 1. RESEARCH ARTICLE Columnar jointing in vapor-phase-altered, non-welded Cerro Galán Ignimbrite, Paycuqui, Argentina Heather MN Wright &amp;amp;amp;amp;amp;amp;amp;amp; Chiara Lesti &amp;amp;amp;amp;amp;amp;amp;amp; Raymond... more
Page 1. RESEARCH ARTICLE Columnar jointing in vapor-phase-altered, non-welded Cerro Galán Ignimbrite, Paycuqui, Argentina Heather MN Wright &amp;amp;amp;amp;amp;amp;amp;amp; Chiara Lesti &amp;amp;amp;amp;amp;amp;amp;amp; Raymond AF Cas &amp;amp;amp;amp;amp;amp;amp;amp; Massimiliano Porreca &amp;amp;amp;amp;amp;amp;amp;amp; José G. Viramonte &amp;amp;amp;amp;amp;amp;amp;amp; Chris B. Folkes &amp;amp;amp;amp;amp;amp;amp;amp; Guido Giordano ...
Research Interests:
Research Interests: Geology()
()
Vickers-Rich, P., Soleimani, S., Farjandi, F., Zand, M., Linnemann, U., Hofmann, M., Wilson, S.A., Cas, R. & Rich, T.H. November, 2017. A preliminary report on new Ediacaran fossils from Iran. Alcheringa 42, 231–244. ISSN 0311-5518.... more
Vickers-Rich, P., Soleimani, S., Farjandi, F., Zand, M., Linnemann, U., Hofmann, M., Wilson, S.A., Cas, R. & Rich, T.H. November, 2017. A preliminary report on new Ediacaran fossils from Iran. Alcheringa 42, 231–244. ISSN 0311-5518. Recent exploratory field mapping of marine sedimentary sequences in the Koushk Mine locality of the Bafq region in Central Iran, and on the northern slopes of the Elborz Mountains south of the Caspian Sea, has yielded large complex body and trace fossils of Neoproterozoic–early Cambrian age. The recovered specimens resemble the previously documented Precambrian discoidal form Persimedusites, and a the tubular morphotype Corumbella, which is a novel occurrence for Iran and otherwise only recorded before from Brazil and the western USA. Additional enigmatic traces can not yet be interpreted unequivocally, but suggest that future work may uncover more unusual Ediacaran fossils from various localities in Central Iran. Patricia Vickers-Rich* [prich@swin.edu.au, pat.rich@monash.edu], Faculty of Science, Swinburne University of Technology, Melbourne (Hawthorn), Victoria 3122, Australia; Sara Soleimani [sara_soleimani@yahoo.com], Palaeontology Department, Geological Survey of Iran, Tehran, Iran; Farnoosh Farjandi [farnooshfarjandi@gmail.com], Department of Geochemical Exploration, Geological Survey of Iran, Tehran, Iran; Mehdi Zand [zand.mehdi.geo@gmail.com], Geology Department, Bafq Mining Company, Koushk Mine, Yazd, Iran. Ulf Linnemann [ulf.linnemann@senckenberg.de], and Mandy Hofmann [mandy.hofmann@senckenberg.de], Senckenberg Naturhistorische Sammlungen, Dresden, Museum für Mineralogie und Geologie, Sektion Geochronologie, Koenigsbruecker Landstrasse 159, D-01109, Dresden, Germany; Siobhan A. Wilson [sasha.wilson@monash.edu], School of Earth, Atmosphere and Environment, Monash University, Melbourne (Clayton), Victoria 3800, Australia; Raymond Cas [ray.cas@monash.edu], School of Earth, Atmosphere and Environment, Monash University, Melbourne (Clayton), Victoria 3800, Australia; Thomas H. Rich† [trich@museum.vic.gov.au], Museum Victoria, Exhibition Gardens, PO Box 666, Melbourne, Victoria, 3001 Australia. *Also affiliated with: School of Earth, Atmosphere and Environment, Monash University, Melbourne (Clayton), Victoria 3800, Australia; School of Environmental Sciences, Deakin University, Melbourne (Burwood), Victoria, Australia 3125; Palaeontology Department, Museum Victoria, Carlton Gardens, PO Box 666, Melbourne, Victoria 3001, Australia. †Also affiliated with: School of Earth, Atmosphere and Environment, Monash University, Melbourne (Clayton), Victoria 3800, Australia; Faculty of Science, Swinburne University of Science and Technology, Melbourne (Hawthorn), Victoria 3122, Australia.
Research Interests:
Research Interests: Geology()
()
The Archean Hollandaire volcanogenic massive sulfide deposit is a felsic–siliciclastic VMS deposit located in the Murchison Domain of the Youanmi Terrane, Yilgarn Craton, Western Australia. It is hosted in a succession of turbidites,... more
The Archean Hollandaire volcanogenic massive sulfide deposit is a felsic–siliciclastic VMS deposit located in the Murchison Domain of the Youanmi Terrane, Yilgarn Craton, Western Australia. It is hosted in a succession of turbidites, mudstones and coherent rhyodacite sills, has been metamorphosed to upper greenschist/lower amphibolite facies and includes a pervasive S1 deformational fabric. The coherent rhyodacitic sills are interpreted as syndepositional based on geochemical similarities with well-known VMS-associated felsic rocks and similar foliations to the metasediments. We offer several explanations for the absence of textural evidence (e.g. breccias) for syn-depositional origins: (1) the subaqueous sediments were dehydrated by long-lived magmatism such that no pore-water remained to drive quench fragmentation, (2) pore-space occlusion by burial, and/or (3) alteration overprinting and obscuring of primary breccias at contact margins. Mineralisation occurs by sub-seafloor replacement of original host rocks in two ore bodies, Hollandaire Main (∼125 × >500 m and ∼8 m thick) and Hollandaire West (∼100 × 470 m and ∼5 m thick), and occurs in three main textural styles, massive sulfides, which are exclusively hosted in turbidites and mudstones, and stringer and disseminated sulfides, which are also hosted in coherent rhyodacite. Most sulfides have textures consistent with remobilisation and recrystallisation. Hydrothermal metamorphism has altered the hangingwall and footwall to similar degrees, with significant gains in Mg, Mn and K and losses in Na, Ca and Sr. Garnet and staurolite porphyryoblasts also exhibit a footprint around mineralisation, extending up to 30 m both above and below the ore zone. High precision thermal ionisation mass spectrometry of zircons extracted from the coherent rhyodacite yield an age of 2759.5 ± 0.9 Ma, which along with geochemical comparisons, places the succession within the 2760–2735 Ma Greensleeves Formation of the Polelle Group of the Murchison Supergroup. Geochemical and geochronological evidence link the coherent rhyodacite sills to the Peter Well Granodiorite pluton ∼2 km to the W, which acted as the heat engine driving hydrothermal circulation during VMS mineralisation. This study highlights the importance of both: detailed physical volcanological studies from which an accurate assessment of timing relationships, particularly the possibility of intrusions dismembering ore horizons, can be made; and identifying synvolcanic plutons and other similar suites, for VMS exploration targets in the Youanmi Terrane and worldwide.
Research Interests:
The occurrence of pyroclastic flow deposits is not restricted to polygenetic and/or felsic volcanic systems, but can also occur at mafic monogenetic volcanic centres. At the c. 5 ka Mt Gambier Volcanic Complex, Australia, two small-volume... more
The occurrence of pyroclastic flow deposits is not restricted to polygenetic and/or felsic volcanic systems, but can also occur at mafic monogenetic volcanic centres. At the c. 5 ka Mt Gambier Volcanic Complex, Australia, two small-volume pyroclastic flow deposits resulted from phreatomagmatic eruptive phases of the Blue Lake East and the Valley Lake maar craters. The facies descriptions of the two massive, poorly sorted lapilli tuff and tuff breccia deposits are given. Low-grade carbonized wood fragments in the deposits mark low emplacement temperatures (180–270°C) for these deposits with only c. 12–23% of the total thermal energy of the original magma preserved at the time of deposition. The Blue Lake East vent erupted by forming a short-lived vertical eruption column, which could not be sustained and collapsed. The Valley Lake pyroclastic flow deposit has a highly asymmetric dispersal to the west, indicating that this deposit was formed during an eruptive phase with a large westward-directed lateral component. Such massive, poorly sorted deposits outside the maar crater indicate that some similar deposits in diatremes may have originated from surface eruptions and not just from subsurface debris jets.
Research Interests:
Quench fragmentation is a non-explosive process that occurs when molten magma is super-cooled to glass upon contact with ambient water. This occurs when coherent lavas are erupted subaqueously, when they flow into water, when magma... more
Quench fragmentation is a non-explosive process that occurs when molten magma is super-cooled to glass upon contact with ambient water. This occurs when coherent lavas are erupted subaqueously, when they flow into water, when magma intrudes into water-saturated sediments, and when magma and water interact explosively during phreatomagmatism. Quench fragmentation also occurs alongside explosive phreatomagmatic activity. Although products of quench fragmentation (hyaloclastite sensu stricto) have been discussed qualitatively in the volcanological literature, compared to explosive fragmentation processes very little is known about the exact dynamics of quench fragmentation of magma and how this relates to the rheology and physical properties of volcanic glass. Based on literature from materials engineering, we present a detailed review of the processes by which glass forms, the properties of glass, and the fracture mechanics that cause it to fragment non-explosively. We also consider h...
Research Interests:
Lithic-rich pyroclastic units and facies are often associated with caldera-forming eruptions. Petrographic and quantitative studies on the variety of lithic types, and the spatial and vertical variations in their proportions, provide a... more
Lithic-rich pyroclastic units and facies are often associated with caldera-forming eruptions. Petrographic and quantitative studies on the variety of lithic types, and the spatial and vertical variations in their proportions, provide a powerful tool for understanding (a) the subsurface and pre-caldera geology, and (b) conduit-vent processes during caldera eruptions. In particular, lithic assemblages may include unique samples of deep plutonic-basement
Research Interests:
We review the main characteristics of volcanic successions that commonly host important resources of gold, silver, nickel, copper, lead, zinc, and diamonds, and outline the connections between volcanic and ore-forming processes.... more
We review the main characteristics of volcanic successions that commonly host important resources of gold, silver, nickel, copper, lead, zinc, and diamonds, and outline the connections between volcanic and ore-forming processes. Volcanic-hosted massive sulfide deposits form in submarine volcanic successions. They form at the same time as the volcanic facies accumulate, at or below the seafloor, and are by-products of the concentration of magmatic heat in areas of active submarine volcanism. Nickel sulfide deposits in komatiite successions comprise nickel sulfide minerals that precipitate directly from komatiite lava or intrusions. The sulfur is derived from an external source, such as assimilated sulfur-bearing sediment. Whether or not komatiite lavas or intrusions are mineralized, depends on their physical properties, especially the high temperature, high density, and low viscosity, all of which favor assimilation. Epithermal gold–silver deposits are formed by hydrothermal fluid circulation driven by heat from cooling intrusions and/or heat tapped by deeply penetrating faults. Because the fundamental mechanism for ore deposition is boiling of the hydrothermal fluid, these systems typically operate in subaerial settings. However, the mineralizing events can be significantly younger than the host rocks. Silicic calderas, silicic domes, andesitic cone volcanoes, and rhyolite maar volcanoes are all known to host epithermal deposits. Kimberlite pipes are the main source of diamonds worldwide. The diamonds in kimberlite magmas are xenocrysts and the magma simply serves to transport diamonds from their deep mantle source. Pipes are mainly filled by volcaniclastic facies generated by explosive fragmentation of kimberlite magma and wall rock. Kimberlite pipes probably connected to small pyroclastic cones at the surface but these landforms are rarely preserved.
Research Interests:
Research Interests:
Monogenetic volcanism can produce eruptive suites showing considerable complexity in compositional features and pre-eruptive magma evolution. The ~5 ka Mount Gambier Volcanic Complex (MGVC), a monogenetic volcanic centre in SE Australia’s... more
Monogenetic volcanism can produce eruptive suites showing considerable complexity in compositional features and pre-eruptive magma evolution. The ~5 ka Mount Gambier Volcanic Complex (MGVC), a monogenetic volcanic centre in SE Australia’s Newer Volcanics Province (NVP), is a good example. It displays a complex stratigraphy of interbedded deposits related to different eruption styles from a multi-vent system. Formation of the MGVC proceeded through simultaneous eruption of two alkali basaltic magma batches: a more alkaline and light rare earth element enriched basanite batch (Mg# 58-62) in the west and a trachybasalt batch (Mg# 58-64) enriched in SiO2 and CaO in the east.Trace element modelling suggests an origin of both magma batches from a single parental melt formed by 4-5% partial melting of a metasomatized lherzolite source in the asthenospheric mantle (2·2GPa; ~80 km). At the base of the lithosphere, part of this parental melt interacted with a deep-seated pyroxenite contaminan...
Research Interests:
A pattern of shifting current direction is revealed by the anisotropy of magnetic susceptibility (AMS) in the quartz latite ignimbrite associated with the Pleistocene Cimini dome complex in central Italy. High-field AMS documents that... more
A pattern of shifting current direction is revealed by the anisotropy of magnetic susceptibility (AMS) in the quartz latite ignimbrite associated with the Pleistocene Cimini dome complex in central Italy. High-field AMS documents that both paramagnetic and ferrimagnetic minerals contribute to the magnetic fabric of the ignimbrite. The results of low field AMS studies suggest that the pyroclastic density current
Research Interests:
Research Interests:
Research Interests:
... bomb” shaped, or highly vesicular in nature like pumice or scoria, or spherical pelletal lapilli. Accretionary lapilli are distinctive spherical aggregates of fine ash that commonly indicate the influence of ... to imply a size... more
... bomb” shaped, or highly vesicular in nature like pumice or scoria, or spherical pelletal lapilli. Accretionary lapilli are distinctive spherical aggregates of fine ash that commonly indicate the influence of ... to imply a size affinity without necessarily implying a specific genetic origin (Fig ...
Research Interests:
Research Interests:
Research Interests:
Research Interests:
Research Interests:
Research Interests:
... (e) Pelletal lapilli (right) showing ... Note also microlites cross-cutting olivine grain boundaries (far right and top), which clearly indicate a post-depositional replacement origin. View Within Article. (b), Serpentine in... more
... (e) Pelletal lapilli (right) showing ... Note also microlites cross-cutting olivine grain boundaries (far right and top), which clearly indicate a post-depositional replacement origin. View Within Article. (b), Serpentine in phenocryts, crystal fragments, xenoliths, matrix and groundmass. ...