U-Series Research Group

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.

Igneous processes

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.

Contact: 

Prof. Simon P. Turner

Phone: +612 9850 8363

Email: simon.turner@mq.edu.au

Our People

S T 

Prof. Simon P. Turner

Email: simon.turner@mq.edu.au

Building E5B, Room 215

Phone: +612 9850 8363

  • the processes of partial melting and magma formation beneath ocean island basalts and island arcs
  • the application of short-lived, U-series isotopes to constraining the time scales of magma formation, transport and differentiation
  • post-orogenic granite petrogenesis
  • continental flood basalts
  • potassic lavas associated with high plateau formation
  • sediment provenance and crustal growth

H H 

A/Prof. Heather Handley

Email:  heather.handley@mq.edu.au
Building E5B, Room 203

Phone: +612 9850 4403

Web: www.heatherhandley.com

  • Petrogenesis of volcanic rocks in subduction zone settings: using geochemical, isotopic and petrological tools to place constraints on magmatic source components and differentiation processes operating at volcanoes
  • U-Th-Ra constraints on timescales of magma formation, transport and storage at island arc and intra-plate volcanoes
  • 210Pb-226Ra disequilibria in volcanic rocks
  • Hf and O isotope ratios of volcanic rocks
  • The geodynamic evolution of arc systems and geochemical constraints on sub-volcanic structure
  • Sediment residence time and landscape evolution in semi-arid Australia
  • Improving our understanding of the use of U-series isotopes in landscape evolution studies: new analytical methods

C F 

Dr. Chris Firth 

Email: christopher.firth@mq.edu.au
Building: Building E5B, Room 214

Phone: +612 9850 4405

  • Understanding the petrogenesis of island arc volcanoes, including source components and differentiation processes, through geochemical means including major and trace elements and Sr, Nd and U-series isotopes.
  • Investigating the timescales of magmatic processes, including magma formation and  magma chamber residence times, using U-Th-Ra isotopes.
  • Resolving the eruptive history of active volcanoes in the south-west Pacific, through examination of their geological record.
  • Integrating geochemistry and volcanology to understand the influence of magmatic processes on eruptive behaviour. 

Dr Lucy McGee

Email: lucy.mcgee@mq.edu.au
Building: Building E5B, Room 216

Phone: +612 9850 4405

  • Currently working on deducing timescales of degassing at Soufriere Hills volcano, Montserrat using 210Pb isotopes, utilising this short-lived isotope to constrain dynamic and time-related details of the magmatic system of this highly active volcano. 
  • Past and ongoing work in collaboration with the University of Chile involved trialling U-Th dating on geothermal carbonates. This work continues at Macquarie in the U-series area, which is providing important information on competing magmatic and source component-related signatures. 
  • Previous work focussed on the melting processes which have given rise to a city of miniature, Quaternary-age volcanoes: the Auckland Volcanic Field. This was achieved using radiogenic and U-series isotopes and major and trace element modelling.

Dr Michael Turner 

Email: micheal.turner@mq.edu.au
Adjunct Researcher / Affiliated Researcher

Phone: +612 9850 4405 

  • Using U-series isotopes to look at volatile movement within the magma system (i.e., 210Pb).
  • Using techniques such as SHRIMP SI and FTIR to determine the water content of pyroxenes from mantle and volcanic rocks. This data is used to estimate the volatile budget of the mantle through determining volatile inputs at subduction zones through to volatile loss by volcanism.
  • Constraining factors that fractionate U-series isotopes within the erosional environment of the Earth’s crust.


Rachel Bezard

Currently at GEOMAR, Germany until July 2018
  • Subduction zone processes
  • Magma genesis and evolution
  • Origin and signification of ophiolites

Louise Goode
Supervisors: Heather Handley, Shane Cronin and Simon Turner

Email: louise-rebecca.goode@students.mq.edu.au
Building: Building E7A, Room 414

Phone: +612 9850 4406

  • Volcanology and Pre-eruptive magma storage conditions of East Javanese volcanoes.
  • Elucidating the driving forces of effusive and explosive activity at Kelud Volcano using a combination of field studies combined with geochemical and petrological techniques, with the aim of investigating changing magma storage, ascent and eruption conditions associated with the two eruptions.

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.

Tonga

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).


The water cycle

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).

 

Mantle Xenolith

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.

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

Analytical Facilities

Laboratories

  • Newly constructed clean lab facilities with four self-contained laboratories, including two dedicated solely for U-series work. 
    The clean lab area includes 7 laminar flow workstations and two separate balance rooms
Laboratories

U-series clean lab facilities

  • Nu Plasma high resolution multi-collector ICPMS, equipped with an RPQ filter (Installed Nov. 2003)
  • Sample in solution of 2% HNO3, sprayed into the plasma using a DSN 100
Nu Plasma MC-ICP-MS

Nu Plasma MC-ICP-MS

  • Finnigan Triton TIMS (Installed March 2005) Equipped with RPQ filter, SEM and oil-free scroll pump.
  • Ra samples loaded onto outgassed, zone-refined Re filamentsusing a Ta-HF-H3PO4activator solution
Triton

Finnigan Triton TIMS

Analytical issues and challenges

  • traditional α-counting yields a precision of ∼4-10%
  • Th and Pa have thermal ionisation efficiency <0.01% (PIMS)
  • Th and Pa are highly insoluble
  • Ra has a thermal ionisation efficiency ∼5-14% (TIMS)
  • Ra and Pa only present at fg/g levels
  • 234U/238U ratios ∼10-5230Th/232Th ratios ∼10-6
  • 238U and 232Th "tail" onto 234U and 230Th, respectively

Spikes

  • Mixed 236U-229Th spike for U-Th analysis (Oak Ridge)
  • 228Ra spike milked from equilibrium 232Th solution (NIST3159)
  • 233Pa spike milked from 237Np or derived by irradiation of 232Th
  • 209Po spike available from NIST
  • Calibration against SRM solution standards
  • Cross-check with analysis of secular equilibrium material (TML)
  • Th and Pa spikes need ∼0.01M HF to keep in solution

Decay chains of the U-series isotopes.

Decay chains of the U-series isotopes (activity = λN). Click to enlarge

U isotope analysis by MC-ICP-MS

  • U analysis using CRM145 or CRM960 standard
  • Comparison of measured 238U/235U ratio to the true ratio (137.88) yields mass bias fractionation.
  • Comparison of mass fractionation-corrected 234U/238U to the true ratio (5.286x10-5) yields ion counter gain
  • Intersperse samples with CRM145 analyses
  • 234U on Ion Counter 0 (IC0)
  • 235U on Faraday cup L2
  • 238U on Faraday cup H1
  • 236U on IC0
  • 238U on Faraday cup L1

Standard measurements of TML

234U/238U standard measurements of TML. True value= 1. Click to enlarge.

Th isotope analysis by MC-ICP-MS

  • A solution of 20ppb Th yields a beam of and ∼1V of 232Th, 100s of cps of 230Th
  • 230Th is collected on an ion counter preceded by a RPQ deceleration lens. Typical abundance sensitivity is ∼450ppb at 1 a.m.u. for a transmission of 95-98% (190ppb at 2 a.m.u. but transmission not determined)
  • Th analysis using CRM145 or CRM960 and Th 'U' standards
  • Comparison of measured 238U/235U ratio to the true ratio (137.88) yields mass bias fractionation.
  • Comparison of mass fractionation-corrected 234U/238U to the true ratio (5.286x10-5) yields ion counter gain
  • Intersperse samples with Th 'U' analyses to get βTh

Standard measurements of TML

TML-230Th/232Th bracketed with Th'U'. True value= 5.80x10-6. Click to enlarge.

  • 230Th on IC0
  • 232Th on Faraday cup L1
  • 229Th on IC0
  • 232Th on axial Faraday cup (Ax)
Standard measurements of TML

TML-230Th/238U bracketed with Th'U'. True value= 1. Click to enlarge

Ra isotope analysis by TIMS

  • Slow heating to 1200°C then use 138Ba to focus
  • Scan masses 224-230 to check for Ra and hydrocarbons
  • Build Ra beam (100-1000 cps @ 1250-1350°C)
  • Dynamic collection on SEM ∼80 ratios with 8 second integration times (precision <0.5%)

TML for<sup> 226</sup>Ra/<sup>230</sup>Th

TML standard measurements for 226Ra/230Th. True value= 1. Click to enlarge.

210Pb isotope analysis by α-counting

  • 210Pb concentrations are determined from 210Po on separate 1-2 g sample dissolutions which are spiked with a 209Po tracer calibrated against a value of 7.95 dpm/g for TML
  • Samples are loaded onto a 1 ml anionic column in 1N HCl containing H3BO3where most major and trace elements were washed off in 1N and 0.5N HCl after which Po is eluted in warm 7.5N HNO3
  • Po is autoplated onto a Ag disc above a magnetic stirrer for 6-8 hours in 150 ml of warm 0.5N HCl which contained ascorbic acid. 210Po and 209Po were counted for ∼1 week to achieve a precision of <4%
α-counter

Ortec Octete Plus α-counter.

Back to the top of this page