Wed 7th October @ 12 pm, Rm 312.222

Abstract

When John Woodward died in 1728, in his sixtieth year, he left a will that for geology was to resonate to the present day. Not only did he leave £150 for the establishment of a professorship, still in existence today, but he also willed the University of Cambridge his precious geological collection. Although Professor of Physick at Gresham College, geology became Woodward’s passion. His collection of rocks, minerals and fossils lead him to write his ‘Natural History of the Earth’ in 1695, a work notable as much for, to us, its bizarre explanation for the formation of rocks, as for its basis in observation and experimentation.

Woodward was the first true geologist, inventing a classification of rocks, minerals and fossils that was used through much of the 18th century, and laying the foundation for geology as a modern science. Unfortunately, because of his acerbic nature, he was much maligned by his contemporaries – an ‘egregious coxcomb’, one called him. To Richard Mead, whom he fought in a duel over a disagreement on how to treat smallpox, he was ‘a man equally ill-bred, vain and ill-natured’. Despite such sword fights, being pilloried in satirical plays and pamphlets, and being accused of plagiarism, Woodward emerges as a man of vision and responsible for dragging geology out of the Dark Ages and into the Age of Enlightenment.

Wed 16th September @ 12 pm, Rm 312.222

Abstract

One enduring early Earth enigma is the absence of evidence in the terrestrial record for meteorite impacts during the Hadean. Given the low likelihood of discovering an intact Hadean impact crater, the sedimentary record of detrital shocked minerals created by the erosion of such craters may offer the best opportunity to discover direct evidence of early terrestrial impacts. Zircon is an excellent recorder of shock deformation and is a ubiquitous mineral in siliciclastic sediments of any age, as evidenced by the preservation of detrital zircons up to 4.4 Ga. No shocked Hadean zircons have been identified thus far, but the recent discovery of shocked zircons in Paleozoic and Precambrian sedimentary rocks demonstrates their preservation potential over deep time. However, to construct an impact chronology from ex situ shocked zircons requires demonstrating that crystal domains analyzed for U-Pb age either formed or were age-reset during impact. Characterization of diagnostic shock microstructures is thus crucial for interpretation of geochronological data. In this talk I will first discuss different zircon morphotypes found in impact environments and how they have been applied to dating terrestrial impact structures. I will then show examples of detrital shocked zircons from impacts of known age that highlight the strengths and limitations of conventional in situ geochronology. The two main conclusions are: (1) Dating impacts with zircons that have been separated from their host rocks is challenging, and requires a marriage of geochronology and microstructural analysis at the micro- to nano-scale, and (2) Detrital shocked zircons provide excellent analogs for developing new analytical strategies to overcome challenges for extracting impact ages from ex situ shocked zircons from any environment, including lunar impact breccias, detrital populations, and other planetary materials.

Wed 2nd September @ 12 pm, Rm 312.222

Wed 19th August @ 12 pm in  Rm 312.22

Abstract

The strong resilience of the mineral zircon and its ability to host a wealth of isotopic information make it the best deep-time archive of Earth’s continental crust. Zircon is found in most felsic igneous rocks, can be precisely dated and can fingerprint magmatic sources; thus, it has been widely used to document the formation and evolution of continental crust, from pluton- to global-scale. Here, we present a review of major contributions that zircon studies have made in terms of understanding key questions involving the formation of the continents. These include the conditions of continent formation on early Earth, the onset of plate tectonics and subduction, the rate of crustal growth through time and the governing balance of continental addition v. continental loss, and the role of preservation bias in the zircon record.

Wed 5th August @ 12 pm, Rm 312.222

Wed 3rd June, 12 – 1 pm, Rm 312.222

Abstract

Much of our knowledge about the driving forces of plate tectonics is derived from analyzing present-day Earth. However, reconstructing the motions of the Earth’s tectonic plates over geological timescales provides fundamental insights into the nature of geodynamic processes plate-driving forces. Plate motions during Pangea breakup are well constrained by the record of seafloor spreading. This presentation will illustrate how quantitative analysis of these reconstructions helps us to understand the history of relative and absolute plate motions, and plate boundary processes, at a global scale.

Bio:

Simon Williams joined the School of Geosciences at the University of Sydney in January 2010. He obtained a PhD in geophysics from the University of Leeds, having completed a degree in geology at Liverpool University. From 2004 to 2009 he worked as a geophysicist at GETECH in the UK, a potential-field geophysics consultancy. Since arriving in Sydney, his research has encompassed various aspects of plate tectonic reconstructions, geodynamics, and machine learning. He was also chief scientist aboard a 2011 voyage of the CSIRO research vessel Southern Surveyor, which collected new magnetic profiles, swath bathymetry data and dredge samples in the Perth Abyssal Plain, eastern Indian Ocean.

Wed 27th May, 12 – 1 pm, Rm 312.222

Wed 6th May, 12 – 1 pm, Rm 312.222

Abstract

The ~66 Ma Cretaceous–Paleogene (KPg) boundary marks one of the most significant biological turnovers in Earth history, leaving an evolutionary imprint still visible in the modern biota. Two major geologic events, the Chicxulub bolide impact and the eruptions of the Deccan Traps continental flood basalts that cover a surface area of ≈500 000 km2 in western India, occurred near the KPg boundary, and both have been identified as possible triggers for the extinction. Establishing causal relationships remains difficult, however, as recent high-precision geochronology demonstrates that the main phase of the Deccan eruptions began ≈250 000 years prior to the KPg boundary and the associated impact, and ended ≈750 000 years later. In order to address this issue, we measured sulfur abundance and isotope composition at two exceptionally well-preserved terrestrial KPg boundary sections in Alberta, Canada in order to trace atmospheric sulfur injections from these two events. Our results suggest that, in the immediate vicinity of the KPg boundary, the onset of a Deccan volcanic episode coincided with the impact. This episode lasted for ~5 times longer than any direct geochemical evidence for the impact and was followed by a second distinct volcanic episode, thousands of years later. This chronology of events may help explain the delayed recovery of terrestrial and marine ecosystems into the brave new Paleocene world.

Biography

Boz Wing is an Associate Professor and Dawson Chair in Geology in the Department of Earth and Planetary Sciences at McGill University. He is currently seated at UWA in the Centre for Exploration Targeting where he holds a Geldden Fellowship to work with Marco Fiorentini. He received his PhD in Metamorphic Geology from Johns Hopkins University, where he worked on monazite petrology and inverse theory for crustal fluid flow with John Ferry.  He moved to the University of Maryland for a post-doc, building a stable isotope laboratory and thinking about Precambrian atmospheric chemistry with James Farquhar. Almost a decade ago he moved to McGill where he oversees the Stable Isotope Laboratory with his colleague Galen Halverson, and tries to keep up with the awesome students and post-docs who actually run the lab.  His research program is roughly split between projects that focus on the peculiar mineralizing environments of the Precambrian, and those that try to maximize the gain on geochemical signals of early biological evolution, neither of which he will talk about in his presentation.

Wed 29th April, 12 – 1 pm, Rm 312.222

Abstract

The youngest (ultra-) high pressure ((U)HP) eclogites on Earth are exposed in the gneiss domes of the D’Entrecasteaux Islands of Papua New Guinea. This area is unique in that it remains in the Neogene geodynamic setting – the active Woodlark Rift – that was responsible for rapid exhumation of rocks from mantle depths, and consequent lack of overprinting by unrelated metamorphic events.  Eclogites from this region thus provide a rare opportunity to examine the changing conditions, and our ability to assess changing metamorphic conditions, in subduction-exhumation settings.

The growth of a distinct new mineral assemblage involving coarse rutile, zircon, apatite and quartz in a sample of mafic eclogite from the core zone of the Mailolo Dome, Fergusson Island, provides our starting point.  From there, I will use textures, mineral compositional zoning, and results of Zr-in-rutile geothermometry and garnet-clinopyroxene geothermobarometry to explore some complexities that may arise in interpreting the rapidly-evolving metamorphic P-T conditions in eclogite terranes. 

Wed 22nd April, 12 – 1 pm, Rm 312.222

Abstract

A flurry of new radiometric ages confirms the synchronicity in the onset and demise of two global glaciations in the Neoproterozoic Era (1000–541 million years ago). These data strengthen support for the snowball Earth hypothesis, which posits that the entire Earth froze over for millions of years at a time, only to thaw abruptly in cataclysmic but transient super greenhouse events. These new geochronological data highlight how extraordinary the climatic perturbation must have been to trigger the ice albedo runaway that ushered in snowball glaciation. A combination of Nd isotopes on mudstones and Sr isotopes on marine carbonates through the Neoproterozoic imply that the weathering of extensive continental flood basalts, which covered large parts of Rodinia, was responsible for the initiation of snowball Earth through a enhanced silicate weathering and primary production in the oceans. By the same reasoning, weathering of continental flood basalts likely played a direct role in driving the high marine carbon isotope ratios that characterize much of the Neoproterozoic and regulating oxygenation of the surface environment.

Biography

Galen Halverson is the T.H. Chair in sedimentary geology and petroleum geology at McGill University in Montreal, Canada. Galen is a sedimentary geologist and geochemist whose interests lie in reconstructing and deciphering the stratigraphic record. His research involves a combination of fieldwork, basin analysis, and analytical geochemistry. The ultimate aim of this research is to document, calibrate, and interpret Earth system evolution spanning the great transition from a world that supported only relatively simple, mostly unicellular life to a habitable world that fostered the origin and rapid diversification of animal life. Galen began to study geology as an undergraduate student at the University of Montana and subsequently honed his passion for Proterozoic geology as a PhD student with Paul Hoffman at Harvard University, where he was involved in the early articulation of the snowball Earth hypothesis. He later lived and worked in Namibia, France, and Australia prior to relocating to Montreal in 2010. He is currently a Gledden Fellow at the University of Western Australia working to date mafic igneous events in North America and Australia related to the break-up of the supercontinent Rodinia.