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Department of Earth and Planetary Sciences - USRG

U-Series Research Group

Projects



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Time scales of magma differentiation: moderately large systems


    Kamchatka. Magma differentiation and degassing time scales at Klyuchevskoy and Bezymyanni volcanoes, Kamchatka. A 238U-230Th-226Ra-210Pb study of lavas erupted over the last 100 years being undertaken in collaboration with Drs Ken Sims (WHOI) and Mark Reagan (IOWA).
    Katmai. The largest eruption of the 20th century is the focus of an ongoing stratigraphically controlled Uranium series investigation into the time scales of differentiation in large, chemically-zoned magma bodies. This work is in collaboration with Mark Reagan, Wes Hildreth, Mike Sandiford and Chris Hawkesworth.
    Mount St. Helens. The recent (1980-1986) and current eruption of Mount St Helens providea good opportunity to study short-lived members of the U-series decay chain. Of particular interest is the disequilibria between 226Ra and 210Pb which gives information regarding magma degassing on timescales of weeks to decades prior to the eruption. This work is the basis of Kim Berlo's PhD thesis at the University of Bristol.
Rhyolites at Mt. Katmai

Rhyolites and Mt. Katmai

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Time scales of magma differentiation: smaller systems

    Ruapehu, positioned at the southern end of the Taupo volcanic zone is an exceptionally well-studied, yet complex stratovolcano. How multidynamic, open-system processes responsible for creating small, geochemically variable magma batches are manifested in terms of U-Th-Ra isotope fractionation is a major goal of this work, being undertaken with Richard Price, John Gamble and Craig Cook.
    White Island volcano, positioned at the northern most extreme of the Taupo volcanic zone, is also the focus of a parallel Uranium-series study by Monash University Honours student Zara Heyworth.
    Rabaul volcano, New Britain arc. The time scales of magma differentiation, storage and shallow-level degassing at this persistently active volcano will be examined as part of Heather Cunningham's PhD thesis. She is also collaborating with Jim Gill and Simon Day.
    Tofua volcano, Tonga arc. A stratigraphically-controlled and detailed U-series study of this volcano's highly depleted lavas will reveal rates and changes over time of several volcanic processes.
Rabaul volcano

Rabaul volcano from http://vulcan.wr.usgs.gov/Vdap/Responses/Rabaul94/photos_vdap.html

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Landscape evolution, timescale of weathering and sediment transport

  • What is the time required to produce soils?
  • How fast are sediments transported through a river basin?
  • How does erosion respond to external forcings such as climate variability or human perturbation?


    • Dr Anthony Dosseto uses the uranium-series isotopic composition of soils, river sediments and waters to address these questions. Tony has shown that, surprisingly, the timescale for sediment production and transport in the Murray-Darling basin (dry to temperate climate, tectonically stable; SE Australia) is similar to what has been inferred for the Amazon River and its tributaries draining the Andes (Dosseto et al., 2006): a few thousands of years. This has been related to recent climate variations and interpreted as the strong control of climate variability on how sediments are mobilized and transported through a river basin (Dosseto et al., in press). This work has been undertaken in collaboration with Dr Grant Dougals, CSIRO Land and Water, WA.

    Other projects include:
  • small river catchments in Puerto Rico to focus on the dynamics of soil erosion and sediment transport in tropical climate (in collaboration with Dr Joe Troester, USGS)
  • soil profiles in temperate SE Australia to infer rates of soil formation (in collaboration with Liz Green, UC Berkeley)

Rio Beni in Bolivia, roaming the floodplain at the base of the Andes.

Rio Beni in Bolivia, roaming the floodplain at the base of the Andes. .

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Melting dynamics in Ocean Island Basalts

Mantle plumes and associated ocean island basalts (OIB) provide insights into the composition of the Earth's mantle and processes of magma generation and evolution. The U-series systematics in oceanic basalts can be used to constrain many processes in mantle plume settings that are still poorly understood, such as their upwelling velocities and the porosity of the melt region. Compared to other oceanic tracers (e.g. the incompatible elements) the initial mantle source compositions of the U-series (e.g. 230Th/238U) are well known and their decay products (e.g. 226Ra, 222Rn, 210Pb) start in secular equilibrium, irrespective of the bulk composition. The extent of this disequilibrium signature depends on dynamic parameters such as residual porosity, degree of partial melting, mantle upwelling rate, and partition coefficients. The latter have been experimentally and/or theoretically determined and, if combined with mathematical models, allow the investigation and modelling of the dynamic parameters by measured U-decay series isotopes. This study aims to:

  • investigate radiogenic isotopes, volatiles (i.e. CO2, H2O) from several plume locations
  • to compare their upwelling veolcities and thermal structures
  • covering a wide range of buoyancy fluxes and chemical compositions
Pico island in the Azores archipelago

Pico island in the Azores archipelago.



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U-series disequilibria in Mid-Ocean Ridge Basalts

Lavas erupted along Mid-Ocean Ridges provide important information on melt formation and movement beneath the oceanic lithosphere. Despite the fact that the majority of lavas are erupted along the spreading axis itself, it has been proposed that a small quantity of lavas are erupted off-axis at distances >5 km. The East Pacific Rise has a fast (5.5 cm/yr) half spreading rate and so the age of lavas sampled off-axis are well constrained assuming an on-axis origin. in cooperation with Dr. Yaoling Niu from Durham University, UK, we analyse U-Th-Ra disequilibria in lavas 10-30 distant from the ridge axis. We aim to answer the following questions:

  • Is there any evidence for either 230Th or 238U excess off-axis?
  • If so, are these signatures due to melting on- or off-axis?

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Characterisation of actinide particles in the environment for Nuclear Safeguards using Mass Spectrometric Techniques

Nuclear Safeguards has been moving from surveillance and accountancy control methods to monitoring by environmental sampling (air filters, surface swipes collected during inspections) and the use of high sensitivity analytical techniques. There still exists several areas however where available analytical techniques aren't able to provide answers required by the nuclear regulators. Two such analyses are in identification of provenance and composition of individual particles collected from environmental samples and age dating of nuclear particles. It is possible to provide such information through the application of mass spectrometric analyses however several technical challenges need to be overcome in order to apply these techniques to this application.

There are several mass spectrometry techniques that are potentially useful to Nuclear Safeguards. It is our goal to determine which of these represent current state of the art capability for detection of nuclear material in environmental samples, and also in the forensic style analysis of particles of nuclear origin. Such analyses include elemental and isotopic fingerprinting, determination of irradiation history, determination of fuel processing history by fuel particle dating and analysis of particle breakdown and environmental migration.

Enhancements to the actinides analysis capability on the ANTARES Accelerator Mass Spectrometry (AMS) facility at ANSTO will be applied and evaluated. This technique currently provides the potential to provide state of the art sensitivity for the chosen investigations. 		ANTARES Accelerator Mass Spectrometry Beam Hall

ANTARES Accelerator Mass Spectrometry Beam Hall.


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The effect of recycled components to melting

Over the last decades it has become increasingly clear that the Earth's upper mantle is compositionally heterogeneous. It is widely believed that one of the sources of these heterogeneities is recycling of near-surface materials, such as oceanic crust or sediments, back into the mantle at subduction zones.It is expected that that recycled components may affect melting processes or may even controll them. Short-lived, U-series isotopes provide a unique opportunity to constrain melting rates because uncertainties in source composition are circumvented. Therefore, we tackle this outstanding issue by

  • establishing local U-series disequilibria for melting processes in NMORB from the Manus back-arc basin
  • assessing the ffects of recycled sediment and volatile contribution from the nearby New Britain arc
  • combining the geochemical findings with geophysical constraints and numerical models to develop a better physical model for mantle flow, melt generation and extraction


    • This project is done in close cooperation with Prof. Wolfgang Bach from the University of Bremen, Germany.

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Structural controls on lava geochemistry

At caldera complexes, post-caldera volcanic activity commonly occurs around the rim of the caldera on ring fractures. This shows that weaknesses in the crust can facilitate the movement of magma beneath volcanoes. Spatial variations in post-caldera lava geochemistry (caldera rim vs. intra-caldera lavas) at Ijen Volcanic Complex in East Java provide a great opportunity to investigate whether sub-volcanic structure exerts control on the geochemistry of erupted rocks. We propose that magmatic storage at shallower depths is prevented beneath volcanoes located on the caldera rim (cf. intra-caldera magmas) at Ijen due to the presence of ring fractures, which focus and facilitate migration of magma towards the surface and inhibit the formation of shallow level storage chambers. As a result, caldera-rim magmas do not undergo substantial shallow level degassing or extensive plagioclase fractionation, compared to intra-caldera magmas (Handley et al., 2007). Therefore, volcanic structure exerts some control on the depths at which the melts can pond.
Sketch map of Ijen Volcanic Complex.

Sketch map of Ijen Volcanic Complex and associated post-caldera volcanoes, East Java, Indonesia.

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