Wed 29th May @ noon, Rm 312.222

Abstract:

Fluid inclusion gas analysis by mass spectrometry is a rare yet valuable geochemical tool used to tease out additional information from geothermal and hydrothermal systems but also from other geologic materials.  This talk is subdivided into two sections, the first dealing with the methodology and gas interpretation.  The second is a series of case histories that range from ore deposits to space exploration to ancient oxygen, and more.

Fluid inclusion gas interpretation can: discriminate fluid sources, identify processes, constrain redox, apply gas geothermometry, correct isochores, and provide key data for calculating metal solubility of hydrothermal fluids.  Some recent key findings include measuring Neoproterozoic oxygen levels at 10-12% pO2 from halite.  Also, methane was the killer cause of the end-Permian mass extinction.  At the Hishikari gold deposit in Japan, the best grades correlate with condensation rather than boiling.  For Mississippi-Valley type Pb-Zn mineralisation, two mechanisms and potentially three fluid sources are evident.  Methane was found in Martian meteorites, providing a potential food source for life on Mars, if it once existed.

The Browne Formation in Australia has been the focus of interest owing to its state of preservation and recently for the measurements of atmospheric oxygen from halite inclusions. Primary halite inclusions were analysed and the atmospheric oxygen found to be 10-12% pO2, suggesting that abundant oxygen was present to allow for the evolution of animal life prior to the Cambrian explosion.

 

Short bio:

Nigel is an Assistant Professor at the Department of Earth Sciences at Western University. Nigel is a geochemist who specializes in fluid inclusion and geochemical applications to geothermal systems, hydrothermal ore deposits, and petroleum basins.

Wed 1st May @ noon, Rm 312.222

Abstract:

We have compiled ample evidence showing that Lesser Antilles magmas are very wet (≥ 4.5 wt% of initial H₂O). Elevated H₂O content of Lesser Antilles magmas and its variation from island to island is reflected in crustal structure of the arc. We used an inversion approach combining constraints from petrology of magmatic crustal xenoliths and seismic receiver functions with additional information from experimental petrology, chemistry of lavas and melt inclusions to reconstruct crustal structure of the Lesser Antilles island arc. Lesser Antilles xenoliths show considerable island-to-island variation in xenolith petrology from plagioclase-free ultramafic lithologies to gabbros and gabbronorites with variable proportions of amphibole, indicative of changing magma differentiation depths. Xenoliths represent predominantly cumulate compositions with equilibration depths in the range 5 to 40 km. We use xenolith mineral modes and compositions to calculate seismic velocities (v_P, v_S) and density at the estimated equilibration depths. We create a five-layer model of crustal structure for testing against receiver functions (RF) from island seismic stations along the arc. Lowermost layer (5) comprises peridotite with physical characteristics of mantle xenoliths from Grenada. Uppermost layer (1) consists of 5 km of volcaniclastics and sediments, whose physical properties are determined via a grid inversion routine. The three middle layers (2) to (4) comprise igneous arc crust with compositions corresponding to the xenoliths sampled at each island. By inversion we obtain a petrological best-fit for the RF on each island to establish the nature and thicknesses of layers (2) to (4).

Along the arc we see variations in the depth and strength of both Moho and mid-crustal discontinuity (MCD) on length-scales of tens of km. Moho depths vary from 25 to 37 km; MCD from 11 and 25 km. Both discontinuities are located at greater depths in the northern arc. The Moho is the dominant discontinuity beneath some islands (St. Kitts, Guadeloupe, Martinique, Grenada), whereas the MCD dominates beneath others (Saba, St. Eustatius). Along-arc variability in MCD depth and strength is consistent with variation in the inferred magmatic H₂O contents and differentiations depths that, in turn, influence xenolith lithologies. A striking feature is steep, along-arc gradients in v_P similar to those observed at other oceanic arcs. These gradients are reflected in abrupt changes in rates and processes of magma generation in the underlying crust and mantle. We find no evidence for large, interconnected bodies of partial melt beneath the Lesser Antilles. Instead, the crustal velocity structure is consistent with magma differentiation in vertically-extensive, crystal mush-dominated reservoirs. Along-arc variation in crustal structure may reflect heterogeneous upwelling within the mantle wedge, itself driven by variation in slab-derived H₂O fluxes.

 

Short bio:

 Elena (Lena) Melekhova is experimental petrologist, with interest in evolution of magmas, specifically: the chemistry of melts, minerals and fluids; role of water in subduction zone environment; and formation of new continental crust. Lena’s main tool is high-pressure, high-temperature experiments, which she combines with field observations and microanalyses of natural rocks and experimental run products. She obtained her undergraduate and M.Sc degree in Geology from Irkustk State University, Russia, and her PhD in experimental petrology from ETH-Zurich, Switzerland. She is has been based at University of Bristol, UK,  since 2007. For the past 12 years Lena’s main focus was the Lesser Antilles volcanic arc and its magmatic evolution. She has also been involved in projects on primitive magmatism in Kamchatka and Vanuatu volcanic arcs, and recently in a project looking at heterogeneity of mantle wedge under Colima volcano Mexico. Currently she is part of a large, strategic, collaborative research project FAMOS (From Arc Magmas to Ore Systems).

Wed 3rd April @ noon, Rm 312.222

Abstract:

Borosilicate glass is an important material used in various industries due to its chemical durability, such as for the immobilization of high-level nuclear waste. However, it is susceptible to aqueous corrosion, recognizable by the formation of surface alteration layers (SALs). In the talk, I will present results of novel in situ fluid-cell Raman spectroscopic experiments providing unprecedented real-time insights into reaction and transport processes during the aqueous corrosion of a borosilicate glass. The formation of a several micrometre-thick water-rich zone between the SAL and the glass, interpreted as an interface solution, is detected, as well as pH gradients at the glass surface and within the SAL. By replacing the solution with a deuterated solution, it is observed that water transport through the SAL is not rate-limiting. The data supports an interface-coupled dissolution-reprecipitation process for SAL formation. Fluid-cell Raman spectroscopic experiments open up new avenues for studying solid-water reactions, with the ability to in situ trace specific sub-processes in real time by using stable isotopes.

 

Short bio:

Thorsten Geisler-Wierwille studied Mineralogy at the University of Hamburg (Germany), where he also received his doctoral degree. After various postdoc periods in Hamburg, Cambridge (UK), Münster (Germany), and Perth (Australia) he became a professor at the University of Bonn (Germany). His main interest is to understand the mechanisms and kinetics of solid-fluid interactions and the application of Raman spectroscopy to various problems in Materials Research and Geosciences.

 

Wed 27th March@ noon, Rm 312.222

Abstract:

Modern views of igneous systems are moving increasingly away from the long-standing large magma chamber paradigm towards a more nuanced concept of transcrustal magmatic mushes, wherein the dominant mechanism of igneous differentiation is percolative reactive flow, rather than traditional crystal settling. The melts that populate these mushy systems have significantly higher dissolved volatile (H2O, CO2) contents than previously assumed, with important consequences for their transport properties and chemical evolution. In this talk I will review the evidence for mushy magmatic systems and outline recent numerical and petrological models of dynamic transcrustal magma systems. I will discuss the implications for volcanism, magma chemistry and hydrothermal ore formation with reference to a number of studies of active volcanic systems in the Altiplano (Bolivia), Cascades (USA) and Lesser Antilles.

 

Short bio:

Jon Blundy is an igneous petrologist, with interest in all things magmatic, from magma generation in the crust and mantle to trace element geochemistry, active volcanism and hydrothermal mineralisation. He approaches these topics through a combination of field observations, thermodynamics, microbeam analysis, and high pressure-temperature experiments. He is based at the University of Bristol (UK), where he has been since 1989. He has held visiting positions at the universities of Oregon and Nagoya (Japan), California Institute of Technology and, currently, UWA. He has received a number of awards for his research, including the Ted Ringwood Medal of the European Association of Geochemistry (2016), and the Bigsby (2005) and Murchison (2016) Medals of the Geological Society. He was elected Fellow of the Royal Society in 2008.

Wed 20th March @ noon, Rm 312.222

Abstract:

At the present day, different tectonic settings exhibit variations in heat flow that are registered as contrasting metamorphic facies series in distinct terranes; how far back in time these relationships are reliable is unclear. Here I use a dataset of temperature (T), pressure (P) and thermobaric ratio (T/P at the metamorphic ‘peak’), and age of metamorphism (timing of the metamorphic ‘peak’) for 564 localities from the Cenozoic to the Eoarchean to interrogate the crustal record of metamorphism in relation to secular change and geodynamics. Based on T/P, metamorphic rocks are classified into three natural groups: high T/P type (>775 °C/GPa, arithmetic mean ~1105 °C/GPa), including common and UHT granulites, intermediate T/P type (775–375 °C/GPa, arithmetic mean ~575 °C/GPa), including HP granulites and HT/MT eclogites, and low T/P type (<375 °C/GPa, arithmetic mean ~255 °C/GPa), including blueschists, LT eclogites and UHP rocks. Plots of T, P and T/P for high or intermediate T/P metamorphism, and the PDF of age for all localities show that since c. 3.0 Ga cyclic variations in the heat budget of the crust have been superimposed on secular cooling. The cyclicity is similar to that for global glaciations, but slightly younger in timing. Stable subduction and the emergence of a sustainable network of plate boundaries became possible after the balance between heat production and heat loss changed in favor of secular cooling, possibly as early as c. 3.0 Ga in some areas, which enabled the rise of protocontinents and the accumulation of sediments at continental edges to lubricate subduction. The Proterozoic was characterized by stability from the formation of Columbia to the breakup of Rodinia, generating higher than average T and T/P of high T/P metamorphism, a lower volume of continental crust and the occurrence of massif-type anorthosites, particularly in the Mesoproterozoic. Notwithstanding several low T/P localities, collision was generally warm rather than cold due to shallow slab breakoff. Deeper slab breakoff and cold collision, to generate and preserve the widespread record low T/P metamorphism that is a characteristic of orogenesis in the modern tectonic regime, occurred once the ΔT_P of ambient mantle had decreased to <100 °C after c. 1.0 Ga, possibly related to the after effects of the ‘snowball’ earth.

 

Short bio:

Michael Brown obtained his BA and PhD degrees from the University of Keele in the UK. He held academic appointments at the rank of Lecturer to Professor in the UK between 1972 and 1990, including eight years as a Head of Department. In 1990, he moved to the USA as Professor of Geology and Chair of Department at the University of Maryland. He was reappointed Chair four times, finishing in 2011, and in 1998–2000 was concurrently the Interim Director of the Earth System Science Interdisciplinary Center. Brown has held visiting appointments at Kingston University, Kyoto University, the Universidade do Estado do Rio de Janeiro, the Johannes Gutenberg-Universität Mainz, Curtin University (twice) and ETH Zurich.

Brown’s research has contributed to understanding the petrogenesis of migmatites and associated granites, high/ultrahigh temperature and high/ultrahigh pressure metamorphism, the tectonics of metamorphic belts and secular change in metamorphism. This work has furthered our knowledge of processes associated with reworking and differentiation of the continental crust, particularly how heat and mass are transferred, the role of crustal melting in the development of orogens, and the secular evolution of geodynamic regimes on Earth. Over the past 48 years, Brown’s research has been made available through several books, >160 peer-reviewed chapters and articles in books and journals, >70 other articles, conference proceedings, editorials, reviews and field excursion guides, and by >440 presentations at scientific meetings. He founded the Journal of Metamorphic Geology in 1982 and has contributed extensive service to several major scientific societies, most recently as President of the Mineralogical Society of America. In recognition of his accomplishments, he received the Collins Medal from The Mineralogical Society of Great Britain and Ireland for 2014 and the Major John Sacheverell A’Deane Coke Medal from The Geological Society for 2005.

Wed 20th February @ noon, Rm 312.222

Abstract:

Deep learning methods have achieved great success in various areas including computer vision, speech recognition, natural language processing, robotics, bioinformatics, chemistry, finance, and many others. Contrary to classical machine learning approaches, methods based on deep learning and big data achieve high efficiency and superhuman performance in many complex tasks. When applied to geophysical data, these technologies have the potential to completely transform various problems in simulations, data processing, imaging, and interpretation. In this talk, I will present several applications of deep learning in geophysical exploration and production. One of them is deep learning inversion that can provide reliable estimates of the subsurface properties orders of magnitude faster than conventional techniques. In relatively simple settings, deep neural networks trained even on relatively small datasets can reliably estimate the unknown parameter distribution with high precision. In complex geological settings, the networks can provide instantaneous estimates of the initial distribution of formation parameters to assist in fast decision-making or be used as a starting model for inversion. For some forward modelling applications, deep neural networks can approximate physical simulations with a high degree of accuracy and in orders of magnitude less time. In particular, a combination of spatial and sequence neural networks can be highly efficient in forecasting various dynamic processes. The above-mentioned problems are only a tiny fraction of the full spectrum of problems in geophysics and geology where artificial intelligence can potentially make a significant contribution. In the last part of the talk, I will discuss the recent progress in deep learning for cutting-edge areas such as robotics and video games.

Short bio:

Vladimir Puzyrev is a Senior Research Fellow at the Curtin University Oil and Gas Innovation Centre and the School of Earth and Planetary Sciences. He joined Curtin University in 2016 as a Research Fellow. Prior to taking this position, Vladimir worked at Barcelona Supercomputing Center on the development of a high-performance framework for inversion of large-scale geophysical data. His current research focuses on applications of artificial intelligence and deep learning in geosciences. His research interests also include numerical methods for PDEs, computational electromagnetics and high-performance computing.

Wed 13th February @ noon, Rm 312.222

Abstract:

The reaction calcite + quartz => wollastonite + CO₂ is the archetypal model for metamorphic decarbonation. Silicate-carbonate reactions of this type operate in a wide range of rock types, are ubiquitous during metamorphism in subduction zones and orogenic belts, and have operated for most of geologic time. Metamorphic decarbonation releases CO₂ to the mantle wedge and arc magmas in subduction zones. This flux is augmented by stoichiometric dissolution of carbonate minerals where fluid fluxes are high. In collisional mountain belts, CO₂ is released by a host of metamorphic processes, particularly orogenic thickening and associated self heating. Our recent estimate of the areal orogenic flux (~10¹² mol CO₂ km^-2 Myr^-1; Stewart and Ague, 2018, EPSL) is comparable to that for volcanic arcs and mid-ocean ridges. Progressive CO₂ release during the Devonian Acadian orogeny coincides with warming and sea level rise, and may have helped drive the Taghanic biocrisis. Given the role that CO₂ has played in the development of Earth as a habitable planet, it is unlikely that life as we know it would have evolved without metamorphic decarbonation.

 

Short bio:

Jay Ague is the Henry Barnard Davis Memorial Professor of Geology and Geophysics and Curator-in-Charge of Mineralogy and Meteoritics at the Yale Peabody Museum of Natural History. He grew up in the Detroit, Michigan, area and earned his B.S. and M.S. degrees from Wayne State University before moving out to California for his Ph.D. work at UC Berkeley. He joined Yale as an Assistant Professor in 1988. He studies the metamorphic and igneous rocks that comprise the deep roots of mountain belts, with a focus on heat and fluid transport through rocks and implications for earthquake hazards, volcanism, economic mineral deposits, and the roles of mountain building and subduction in global carbon and climate cycles. He has led or participated in geological research expeditions to numerous places around the globe including British Columbia, California, Greece, New England, New Zealand, Papua New Guinea, Scotland, Spitzbergen, and Washington State. He was the Chair of the Department of Geology and Geophysics from 2012 to 2018, and the Acting Director of the Peabody Museum in 2008. He has served as a mentor for more than 35 students and postdoctoral associates. He is heavily involved in public outreach through his work at the Yale Peabody Museum of Natural History.

Wed 23rd January @ noon, Rm 312.222

Abstract:

The Moon was once though to be a cold undifferentiated body that never could have been capable of generating an internal Earth-like magnetic  field. It thus came as a surprise to find that many of the lunar rocks collected during the Apollo missions were magnetized, and that orbital magnetic field data showed portions of the crust to be associated with large magnetic anomalies. The evidence that the Moon had a long lived magnetic field generated by a core dyanmo will be summarized in this talk, and the various models that have been proposed to power the dyanmo will described. The strongest magnetic anomalies appear to be correlate with the largest impact basin on the Moon, and it will be  argued that the materials responsible for these anomalies are derived from remnants of the iron-rich projectiles that formed these basins.

 

Short bio:

Mark Wieczorek’s research focuses on using geophysical data (topography, gravity, and magnetic fields) and remotely sensed geochemical data to decipher the interior structure and geologic evolution of the terrestrial planets and moons. He was a co-investigator of the orbiting SMART-1 and Chandrayaan-1 X-ray fluorescence spectrometers, and NASA’s lunar gravity mapping mission GRAIL. In addition to his work with the Moon, he is a co-investigator associated with NASA’s geophysical mission to Mars, Insight, NASA’s mission to Psyche, and the laser altimeters on ESA’s BepiColombo mission to Mercury and JUICE mission to Ganymede. He was the leader of the Planetary and Space Sciences group at the Institut de Physique du Globe de Paris from 2012 to 2016, and he was the editor-in-chief of the Journal of Geophysical Research Planets from 2011 to 2015. He is currently a director of research (CNRS) at the Observatoire de la Côte d’Azur, Laboratoire Lagrange.

Wed 4th December @ noon, Rm 312.222

Abstract:

Mountain belts have always intrigued human beings and were first looked with defiance as the home of the gods. They appeared as gigantic and resisting the assaults of the natural elements even though it was already understood in Ancient Greece that erosion could potentially play a major role in their destruction. More recently, it was realized that mountain belts are not so resistant and that they instead hide a hot and tender heart at the source of their decline. Indeed, the exhumed roots of orogenic belts is made of migmatites and granites, former partially molten rocks and magmas, respectively, that display a geological record attesting for an intimate link between partial melting, orogenic evolution and crustal differentiation from the rise of mountain belts to their collapse.

This lecture, will present the evolution of ideas regarding the orogenic cycle and discuss the significance of examples taken through the Alpine belt s.l. from the Western Alps to the Aegean domain, through the Tibetan plateau. It will also propose some perspectives for future research on the deep roots of mountain belts.

 

Short bio:

Olivier VANDERHAEGHE is a field geologist with additional expertise in structural geology, petrology, geochemistry, geochronology, tectonics, and geodynamics. He is currently Professor at the Université Paul Sabatier, Toulouse 3 and Adjunct Director of the Géosciences Environnement Toulouse (GET) laboratory. He obtained his Master Degree in 1991 at the Université de Montpellier and completed his PhD at the University of Minnesota in 1997. Olivier VANDERHAEGHE has also spent 2 years (1991-1993) in French Guiana as a geologist of the French Survey (BRGM) trying to decrypt the geology of the basement beneath the luxurious rain forest and 2 years (1997-1999) in Halifax as a postdoctoral fellow in the Geodynamics group at Dalhousie University trying to bridge geology and geodynamics. He was then appointed on an Associate Professor position at the Université de Lorraine in 1999 before moving to Toulouse. His research started with the structural analysis of migmatites, which opened new avenues to the understanding, first of the tectonic evolution of orogenic belts, and then on the mechanisms of crustal growth and differentiation with applications to mineral systems.