Wed 27th April @ 12 pm, Rm 312.222

Thermal waters at Yellowstone National Park contain high concentrations of arsenic (up to 15 mg/L), lithium (up to 8 mg/L), boron (up to 28 mg/L), fluoride(up to 48 mg/L), and silica (up to 800 mg/L). Their geochemical source, redox transformations, and transport have been challenging to decipher. Arsenic speciation requires knowledge of thioarsenites and thioarsenates. We have measured the mass flux of these elements into 2 major rivers and found that there is little to no attenuation for 20‐30 miles downstream. These results have implications for arsenic poisoning in other countries.

A short bio.:

Currently a senior scientist of 40 years experience with the U.S. Geological Survey, Dr. D. Kirk Nordstrom is recognized internationally for his research on acid mine drainage, radioactive waste disposal, thermodynamic data evaluation, geothermal chemistry, arsenic geochemistry, and geochemical modeling. He has more than 250 publications in hydrogeochemistry that include analytical chemistry, field studies on surface and ground water, experimental geochemistry, geomicrobiology, thermodynamics, and the development and evaluation of speciation models. He is particularly known for his research on the measurement of negative pH in mine waters, his evaluation and compilation of thermodynamic properties for aqueous speciation calculations, and evaluating natural background concentrations at mine sites.

Wed 23rd March @ 12 pm, Rm 312.222

Wed 16th March @ 12 pm, Rm 312.222

Wed 2nd March @ 12 pm, Rm 312.222

Abstract

There is probably no such thing as a “typical” passive margin, although the southern margin of Australia comes close.  On this margin an Upper Jurassic rift propagated through an ancient cratonic block, deep within a continent, culminating in the generation of oceanic crust and the eventual separation of Australia from Antarctica – albeit with a significant delay between early slow spreading and later rapid spreading.

 By contrast the western margin of Australia contains suture zones across which the final stages of continental accretion occurred relatively shortly before the onset of sedimentary basin formation, while the north west margin of Australia appears to have been located close to a continental margin throughout much of its history.  Rift basins have developed intermittently over a period of about 300 Ma on the western margin, culminating in the separation of Grater India from Australia in the Early Cretaceous, while a series of continental ribbons appear to have detached from the north west margin of Australia over a shorter time period.  The tectonic setting in which ribbons can separate from a continental margin remains enigmatic.

 The Carboniferous and Permian was probably the time at which the fundamental architecture of the rift system was established, but understanding the tectonics of this period is made difficult by poor imaging of these sections on seismic data – a result at of the depth at which they occur.  However, integrating observations from onshore basins and the margins of offshore basins is beginning to shed light on events in this period and may help to explain the origin of the large depocentre on the Exmouth Plateau in which significant thicknesses of Triassic sediment accumulated.

 Lower to Middle Jurassic rifting is clearly (and beautifully) imaged on several seismic data sets.  Although generally associated with the separation of Argoland, and formation of the Argo Abyssal Plain, it is much less uniform both in timing and location than is often assumed.  The orientation of extension across the margin is also variable, hinting at a much greater influence of the early stages of India-Australia rifting at this time.

 Upper Jurassic and Lower Cretaceous deformation is widely attributed to India-Australia separation, although deformation appears to be confined to two widely separated areas of the NW Shelf – the Exmouth sub-basin (close to the site of separation) and the Vulcan sub-basin (far removed from it).  Deformation in the Exmouth sub-basin is unusually short lived, associated with uplift and erosion, and extensive igneous activity.  Uplift and erosion is also marked on the western Australian margin, although extensional faulting is probably more pronounced.  A recently proposed mantle plume may explain a number of these observations, and has implications for heat flow and maturity of petroleum source rocks.

 The final enigma is the presence of a number of inversion structures of Pliocene to Recent age, mainly confined to the western margin, which suggests that it is not such a passive margin after all.

 Wed 18th November @ 12 pm, Rm 312.222

Eclogitic xenoliths from kimberlite are occasionally diamond-bearing, and are often interpreted as having an origin as subducted oceanic crust [1]. The existence of diamonds in these rocks constrains equilibrium temperatures and pressures of some eclogites to the upper mantle. However the additional critical parameter controlling the stability of diamonds, oxygen fugacity (ƒO2), is unknown in eclogitic assemblages.

A series of piston-cylinder experiments were conducted using model carbonate and kyanite bearing eclogite assemblages to determine the ƒO2 of the limiting reaction for graphite vs. diamond:

CaMg(CO3)2 + 2SiO2 = CaMgSi2O6 + 2C + 2O2  [2]

as a function of pressure (P=3.5-6 GPa) and temperature (T=900-1300oC).

The oxygen fugacity in the experiments was determined using Fe-Ir alloy fO2 sensors [3] and a newly developed Fe-Pd-based redox sensor [4]. The experimental data allowed calibration of two redox reactions (involving garnet-clinopyroxene [5] and garnet-kyanite as oxybarometers to determine ƒO2 of eclogitic rocks. Both reactions can be used to evaluate the ƒO2 of UHP metamorphic eclogites and eclogite xenoliths from kimberlite. The accuracy of the ƒO2 thus calculated is highly dependent on precision of the garnet Fe3+/ΣFe measurements, which were obtained using the flank method [6] and the synchrotron based Fe K-edge XANES method [7]. Both reactions were calibrated and used to estimate ƒO2 of diamond, kyanite and coesite bearing eclogite xenoliths from Udachnaya kimberlite pipe, Yakutia, Russia. The relatively high ƒO2 of diamond stability in eclogite relative to peridotite at the upper mantle PT conditions may explain the higher abundance of diamonds in eclogite xenoliths [8] and constrains the mechanism of transport of carbon to the deep mantle.

 [1] Jacob (2004) Lithos 77, 295-316 [2] Luth (1993) Science 261, 66-68 [3] Woodland & O’Neill (1997) GCA, 61(20), 4359-4366 [4] Vasilyev et al. (2014) IMA 2014 abstracts, 40 [5] Stagno et al. (2015) CMP 169, 16. [6] Höfer, Brey (2007) Am.Min. 92, 873-885 [7] Berry et al. (2010) Chem.Geol. 278, 31-37 [8] Cartigny (2005) Elements 1, 79-84

Thurs 5th November @ 12 pm, Rm 302.001 (please note the venue)

New mapping techniques allow us to define with unpreceded detail seafloor morphology; scientific literature is flooded with a growing number of researches based on high-resolution bathymetry and/or morphometry depicting new geological features and processes. Such techniques however will give an important, up to essential, contribute to the management of the marine areas by national agencies and local authorities; EU is heading in this direction with recent regulations and laws.

In order to have a functional base for the management, a solid procedure for data acquisition, processing and interpretation is needed, providing homogeneous cartography in all the region. Moreover, the retrieving of all the collected data (mainly from scientific institutes) and their integration with new acquisition is also advisable.

This is exactly the story of the Italian MAGIC (MArine  Geohazard along the Italian Coast) project, a just-finished 5 years initiative, funded with 5.25 M€ by the National Civil Defense Department. The project involved the whole Italian marine geology scientific community (3 CNR institutes, 7 universities, OGS-Trieste) and provided 73 sheets of the “Map of Geohazard Features of the Italian  Seas” plus a web-GIS database (Infor.Mare) to retrieve in real time all the maps present in scientific literature dealing with the marine geology of the Italian Seas.

Some 39.000 nautical miles of multibeam data have been acquired and integrated with 10.000 from previous surveys. Almost 2/3 of the Italian coasts have been covered by the project as we excluded shallow epicontinental seas (e.g. Northern-central Adriatic, northern Tyrrhenian, Sicily Channel) as in general they host few geohazard features. The depth range we investigated is 50-1000m w.d. even if we reached shallower water at canyon head or everywhere needed and we stop deeper (80-90m) where wide shelves were present.

The setting-up of common procedures for data acquisition, processing, interpretation and cartographic representation has been complex and reiterative due to the need of having a standard methods suitable for the different realms (shelf to slope, volcanic/rocky to sedimentary-covered seafloor, erosion dominated to deposition dominated environments, …) and trying to differentiate between morphological (objective) and genetic (interpretative) representation of the depicted features.

The target has been achieved by the establishment of a complex and comprehensive nomenclature and legend, a four level of interpretation and cartographic representation, ranging in scale from 1:250.000 to 50.000 (mainly) and up to more detailed scales for specific point of interest.

The Magic project has been very successful and the results exceeded the expectation. In fact we were able to: (1) furnish the country of a opertaive tool to identify geohazards and to manage emergencies; (2) highlight the extent (and the speed) of morphogenetic processes in geological active areas such the Italian Seas; (3) create a new generation of marine scientists and a very large database that will boost marine sciences researches for the decades to come.

Wed 4th November @ 12 pm, Rm 312.222

 Wed 28th October @ 12 pm, Rm 312.222

Abstract

The geotectonic history of the interior of East Antarctica is poorly known due to limited bedrock exposure and patchy geophysical imaging. Outcrop of the Nimrod Group in the adjacent central Transantarctic Mountains reveals a crustal history beginning by 3.1 Ga, with significant additions at ~2.5 and ~1.7 Ga, followed by pervasive thermomechanical overprinting within the active-margin Ross Orogen at ~500 Ma. Because of the limited outcrop, valuable new evidence is provided by indirect ‘sampling’ of the ice-covered basement with airborne potential-field geophysics, detrital zircon geochronology, sampling of basement clasts from glacial moraines, and geochemical exchange between Ross-age granitoids and older basement. In particular, sampling of glacial moraine clasts at the edges of large catchments eroding the interior, and isotopic signatures from late orogenic granitoids can provide useful constraints on the otherwise covered subglacial geology. Together, these approaches provide evidence for a rich, previously unknown Archean and Proterozoic crustal history of the East Antarctic shield that has close ties to both Australia and Laurentia.

Wed 21st October @ 12 pm, Rm 312.222

The treatment of metamorphism as a sequence of near-equilibrium reactions responding to progressive changes in temperature and pressure (T,P) forms the basis of our understanding of crustal evolution. In fluid-producing reactions during progressive burial of a sediment, there may be an argument to support this, since mineral reactions in the presence if fluid are fast compared to expected rates of T,P increase.

However, much of the Earth’s lower and middle crust and a significant fraction of the upper mantle do not contain free fluids. These parts of the lithosphere exist in a metastable state, both in terms of the temperature as well as the state of stress, and are mechanically strong. When subjected to changing temperature and pressure conditions at plate boundaries or elsewhere, these rocks do not react until exposed to externally derived fluids. Metamorphism of such rocks may consume  fluids through hydration reactions as well as causing recrystallization and deformation, and takes place far from equilibrium through a complex coupling between fluid infiltration, chemical reactions, deformation and mass transfer. Disequilibrium metamorphism is characterized by fast reaction rates, dissipation of large amounts of energy as heat and work, generation of a range of dissipative structures which often controls transport properties and thus further reaction progress, and a strong coupling to far-field tectonic stress. Fluid consuming metamorphism almost invariably leads to mechanical weakening, and strain localization in the lower crust is mainly controlled by the availability of fluids.

A critical issue is the (age-old) question of whether rock volume is preserved during hydration reactions. Hydration reactions that involve an increase in molar volume (e.g. serpentinization) may lead to rock fracture, but I will present a (compelling) example where the stress produced by hydration is coupled to mass transfer in an open system with no deformation involved. The implications are as profound as they are disturbing and suggest much higher fluid fluxes than are generally currently accepted.  You are invited to pick holes in the argument.

Wed 23rd September @ 12 pm, Rm 312.222

Abstract

Pb isotope system is a powerful tool that played a significant role in emergence of current understanding of differentiation and evolution of the Earth. Since initial recognition that variability of Pb isotope compositions in many rocks can be linked to the existence of several planetary scale reservoirs, Pb data have been used in combination with other isotope systems to develop modern field of mantle geodynamics that links major chemical features of the Earth in the frame work of plate tectonics model. One significant question that remains mostly unresolved is timing and mechanism of initial differentiation that formed existing global reservoirs on the planet.

In contrast to the terrestrial Pb evolution models, development of similar constraints for Mars was stalled by an extended argument about Pb-Pb ages of Martian meteorites, while on the Moon they have been hindered by very radiogenic Pb composition of lunar materials and persisting laboratory contamination.

Our recent SIMS work on some Martian meteorites and lunar basalts indicates a possibility to overcome some of these problems. Several distinct reservoirs on Mars and Moon can be characterized with respect to their Pb isotope variations and some initial conclusions about the timing of their formation can be made based on the small initially collected data set. Some of this data also allow reevaluation of current ideas about initial stages of differentiation that formed diversity of major terrestrial reservoirs.