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 provide a 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 CunninghamÕs 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.
Küstenaufschluß mit Laven und Dykes am Ponta da Ferraria, São Miguel.

Küstenaufschluß mit Laven und Fördergängen am Ponta da Ferraria, São Miguel.





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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

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    		 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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    		 Pico island in the Azores archipelago

    Pico island in the Azores archipelago.


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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 generaation and extraction
    • This project is don in close cooperation with Prof. Wolfgang Bach from the University of Bremen, Germany.
      
      
    		 Pico island in the Azores archipelago

    Pico island in the Azores archipelago.