U-Series Research Group
Main Research Themes
Uranium-series isotopes provide chronological information in the range 500 kyr down to seconds that is not accessible through other radiogenic or paleontological methods. As these time scales are similar to those on which many Earth processes occur they can provide unique information on the mechanisms involved. The U-series Research Group in the Department of Earth and Planetary Sciences at Macquarie University has two main research themes that drive a significant number of PhD and post-doctoral projects. However, the group as a whole work in a multi-disciplinary manner.
For about a decade we have used U-series isotopes to investigate the time scales of magmatic processes and to use these to constrain physical mechanisms. Beginning with understanding the nature of the on-set of melting we are particularly interested in the transition from porous flow to channelled flow at very low melt fractions in the mantle in a variety of tectonic settings. We hope to combine the U-series constraints with experimental observations using the D-DIA at the Australian Synchrotron. Subsequent to segregation, melts ascend and differentiate. We have an ongoing series of projects that are using U-series isotopes to determine the time scales of differentiation (including processes of assimilation and mixing). These provide new insights into the thermal conditions and rapidity of evolution of magmatic systems (e.g. depth, volume) that can, for example, be used to inform models for volcanic hazards. In relation to the latter, we also have a series of projects investigating the time scales of magmatic degassing.
Weathering and erosion processes
Landscape evolution is central to studies of climate change, soil sustainability and neotectonics. In order to understand landscape evolution it is important to know how rapidly soils are produced and transported through the system. We have been strongly involved in efforts to use U-series isotopes, often in conjunction with cosmogenic isotopes, to delineate these time scales. There are a number of different approaches currently employed and on-going research is aimed at appraising their relative merits. By comparing results from both temperate and arid environments we hope to assess the consequences of climate change in ways that can be built into models for future climate change.
Prof. Simon P. Turner
Phone: +612 9850 8363
Prof. Simon P. Turner
Building E5B, Room 215
Phone: +612 9850 8363
A/Prof. Heather Handley
Phone: +612 9850 4403
Dr. Chris Firth
Phone: +612 9850 4405
Dr Lucy McGee
Phone: +612 9850 4405
Dr Michael Turner
Phone: +612 9850 4405
Currently at GEOMAR, Germany until July 2018
Phone: +612 9850 4406
Projects: Current & Past
Elucidating drivers of high and low magnitude eruptions at an arc volcano: Yasur, Vanuatu
Activity at Yasur volcano, in the Vanuatu Arc, currently manifests itself through persistent Strombolian eruptions, which have continued throughout the historical record. Such activity is juxtaposed by the presence of a voluminous ignimbrite and associated caldera, which represent an earlier phase of activity from the same volcanic system. By combining physical volcanology, petrology and geochemistry we hope to clarify the record of activity in the Yasur volcanic system and unravel the magmatic processes that led to these two vastly different eruption regimes. Of particular interest is variation in the rates of magma replenishment between these regimes, which can be elucidated through numerical modelling of U-series isotopes. This project was the basis of Chris Firth's PhD project, supervised by Prof. Simon Turner, A/Prof. Heather Handley and Prof. Shane Cronin.
Yasur Volcano, Tanna, Vanuatu
Montserrat - timescales of gas transfer during magma recharge
It is commonly thought that the heat and gas transfer associated with mafic magma recharge is responsible for triggering volcanic eruptions. We propose to undertake measurements of 210Pb disequilibria in mafic enclaves and host andesites from the on-going eruption on Montserrat in order to assess the timing and amounts of gas transfer from recharge magma. This project will be carried out by Dr Lucy McGee, A/Prof Heather Handley, Prof. Simon Turner and Dr Michael Turner in conjunction with Dr Mark Reagan (Iowa), Dr Jenni Barclay (East Anglia) and Prof. Steve Sparks (Bristol).
Soufrière Hills volcano, Montserrat
Magmatic evolution in the Tonga-Kermadec arc
A currently popular paradigm holds that the evolution of silicic arc magmas takes place in deep crustal hot zones. Experimental phase equilibria are being determined for andesite and dacite from Late and Fonualei volcanoes in the Tonga arc to appraise this model. The data will be combined with U-series disequilibria to assess the timescales of magma evolution. This is an ongoing project with A/Prof. Tracy Rushmer, Dr John Adam and Prof. Simon Turner.
Constraints on weathering and erosion using suspended and overbank river sediments from recent floodwaters in Australia
Suspended sediments carried by high magnitude floodwaters within major river catchments provide a representative sample of the lithological and chemical variety of the Earth’s surface and permit estimation of the average geochemical and isotopic composition of the Earth’s upper crust. Uranium-series disequilibria in suspended sediments and their deposits can also be used to constrain the timescales of sediment residence within major catchments. This project will determine new trace element, Sr-Nd radiogenic isotope and Uranium-series isotope data for suspended particulate river sediments and overbank sediment deposits collected from the Cooper Creek and Darling River during the 2009 and 2010 widespread flooding events in Australia. The Uranium series data will be modelled to constrain the residence time of sediment (i.e. timescale for erosion) within the respective catchments. This information is invaluable to further our knowledge and understanding of the rates of landscape evolution. This project is being undertaken by Dr Heather Handley, Dr Michael Turner, Prof Simon Turner and A/Prof Bruce Schaefer.
Cooper Creek in flood, 2009
U-series disequilibria in bedrock: when does the clock start?
Estimation of sediment U-series comminution ages and hence, residence times, requires knowledge of the initial (234U/238U) activity ratio of the sediment source, i.e. bedrock. However, few published studies to date have provided direct measurements of the U-series activity ratios of the source material. Most comminution studies have assumed that prior to physical weathering, fractionation of 234U–238U is negligible and therefore, the (234U/238U) ratio of the source will be in secular equilibrium (equal to 1). This project will determine uranium-series isotope ratios for >1 Ma bedrock samples of variable sedimentary lithology from the Flinders Ranges in South Australia and the Murrumbidgee River catchment to investigate isotopic disequilibrium and determine the timescales of any leaching events. This project is being conducted by Dr Michael Turner, A/Prof Heather Handley and Prof Simon Turner.
Flinders Ranges, South Australia
The impact of dust on sediment U-series comminution ages
The impact of dust on calculated U-series isotope residence timescales of soil and fluvial sediment has received little attention in previous studies, despite the fact that the typical grain size of aeolian material overlaps with that of interest in the comminution approach (<50 μm) and dust deposits were prevelant throughout the Quaternary in SE Australia. The potential of aeolian material to modify bulk soil or fluvial U-series signatures will depend on its (234U/238U) ratio and its volume percentage contribution to the deposit. The geochemistry and U-series isotope ratios of aeolian material from the 2009 Sydney dust storm and sand dune deposits in New South Wales, Queensland and South Australia are being undertaken to investigate the impact of dust upon estimated comminution ages. This project is being carried out by A/Prof Heather Handley, Dr Michael Turner and Prof Simon Turner in collaboration with Dr. Paul Hesse (Dept. of Environment, Macquarie University).
Sydney dust storm, 2009 (photo: Miro Bzduch)
The mantle water cycle - determination of water in clinopyroxene
With advances in analytical techniques there has been much recent interest in the mantles water cycle. We are using the SHRIMP-SI at ANU to measure the water contents of clinopyroxenes in plume-related basalts to assess the water content of the mantle over time. These are being compared with both experimental and sub-arc mantle xenolith data to constrain the major inputs and outputs of water from the mantle. This project is being conducted by Dr Michael Turner and Prof. Simon Turner in collaboration with Prof. Hugh O’Neill and Prof. Trevor Ireland (ANU).
Timescales and mechanisms of mantle metasomatism
Surprisingly little is known about the onset of melt movement and mantle metasomatism. Measurements of U-series disequilibria in basalts and metasomatised mantle xenoliths are being used to place constraints on the timescales and melt fractions involved beneath arcs and continents. This project is being conducted by Prof. Simon Turner in conjunction with Michael Turner and Bernard Bourdon (Lyon).
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.
Timescales of alteration on CM chondrites
It is also well documented that carbonaceous chondrites, particularly the CI, CM and CR subtypes, are aqueously altered and this must have occurred on the parent body. However, for some CI’s, CM’s and CR’s, it has never been shown that aqueous alteration really ever ceased and so U-series isotopes will be used to test this hypothesis. This project is being conducted by Prof. Simon Turner and Dr Lucy McGee in conjunction with Prof. Munir Humayun (Florida).
Pb and Os constraints on the nature of the mantle beneath the Delamerian fold belt
Data from late Delamerian intrusive rocks have been used to infer that this magmatism was triggered by convective removal of the lower lithospheric mantle. Pb and Os isotope data from these rocks will be compared with data from mantle xenoliths in order to appraise this connection. This project is being conducted by Prof. Simon Turner in collaboration with A/Prof Bruce Schaefer and Prof. Janne Blichert-Toft (Lyon).
Quary into the Delamerian, Black Hill gabbros
U-series isotopes and magma chamber processes beneath mid-ocean ridges
Although U-series disequilibria in mid-ocean ridge basalts are typically used to constrain melting processes, the effect (if any) of magma chamber processes has received less attention. A suite of rocks spanning from basalt to rhyolite in composition have been dredged from a single ridge segment in the eastern Manus Basin. U-series data from these will be used to assess magma chamber processes including recent models proposing that suggest that recharge-tapping-fractionation cycles control MORB composition. This project is being conducted by Prof. Simon Turner in collaboration with Dr Christoph Beier (Erlangen).
Mid Ocean Ridge Basalt
U-series clean lab facilities
Nu Plasma MC-ICP-MS
Finnigan Triton TIMS
Analytical issues and challenges
Decay chains of the U-series isotopes (activity = λN). Click to enlarge
U isotope analysis by MC-ICP-MS
234U/238U standard measurements of TML. True value= 1. Click to enlarge.
Th isotope analysis by MC-ICP-MS
TML-230Th/232Th bracketed with Th'U'. True value= 5.80x10-6. Click to enlarge.
TML-230Th/238U bracketed with Th'U'. True value= 1. Click to enlarge
Ra isotope analysis by TIMS
TML standard measurements for 226Ra/230Th. True value= 1. Click to enlarge.
210Pb isotope analysis by α-counting
Ortec Octete Plus α-counter.