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Western Australian Argon Isotope Facility
40Ar/39Ar geochronology
40Ar/39Ar geochronology
The 40Ar/39Ar dating method is used to measure the age and timing of a large variety of geological processes, from meteorite samples as old as the Earth (4.5 billion years) to the age of historical events such as the Vesivius eruption (79 AD). The Ar technique can be applied to any rocks and minerals that contain K (e.g. hornblende, sanidine, plagioclase and basalts). 40Ar/39Ar method is also used to date a myriad of other geological events such as volcanism, tectonic plate movements, mountain building rates, sediment formation, weathering and erosion, hydrothermal fluid movements, and alteration and diagenesis of minerals.
Principle
40Ar/39Ar dating utilises the natural decay of radioactive 40K to 40Ar. Typically, we need to irradiates the sample along with known age standards with fast neutrons in the core of a nuclear reactor. This process converts another isotope of potassium (39K) to gaseous 39Ar.
This allows the simultaneous isotopic noble gas measurement of both the parent (39ArK) and daughter (40Ar) isotopes in the same aliquot. The main advantage of Ar-Ar dating is that it allows much smaller samples to be dated, and more age and composition (e.g. Ca/K) information can be obtained from each sample.
The Western Australian Argon Isotope Facility
The WAAIF has access to a range of sample preparation tool as as Selfrag (a machine which uses high voltage pulses to break rock along mineral boundaries), Frantz magnetic separator, and high resolution binocular picking microscope and cameras.
The WAAIF is equipped with an ARGUS VI (Thermofisher), a new generation low volume Multiple Collector Noble Gas Mass Spectrometers (MC-NG-MS) equipped with 5 faraday cups and one CDD multiplier that has recently become commercially available, offering three advantages. our ARGUS VI is equipped with 10^12 (on mass 40, 38 and 37) and 10^13 (on mass 39) -ohm resistor faraday collectors and a ultra-low background CDD (ion counter) multiplier on mass 36. The ARGUS VI mass spectrometer is connected to a dedicated ultra-low volume custom noble gas extraction line equipped with a PhotonMachine CO2 laser capable of delivering a homogeneous laser beam of up to 6mm wide. The line volume can be adjusted using pneumatic valves and is equipped with 2 AP10 and 1 GP50 SAES getters and a electric cryocooler to be able to purify a range of gas loads (from single grain extraterrestrial sample to hundreds of mg of thousand years old samples). The facility is automated and can be controlled remotely via VNC iphone technology. Our set up offer a range of advantages:
1 - A better sensitivity allows the measurement of a larger dynamic range of Ar ion beam signal on much smaller (and thus likely purer) and younger sample aliquots and provides analytical precision between 4 and 10 times better than with previous generation instruments.
2 - Analyzing phases that are poor to ultra poor in K (e.g. pyroxene, chondrules) due to the 10^13 ohm resistor equipped on the faraday associated with mass 39.
3 - Much faster sample analysis (i.e., 30-35 analyses/day compared to the current 10-12 analyses/day for single collector instruments.
NEW!!!! The WAAIF has received a LIEF Grant which will enable the purchase and installation of a second machine, an ARGUS VI++ with important retrofitable technological improvements compared to the original ARGUS VI. installation expected during Q4 of 2021.
List of mineral analyzable by 40Ar/39Ar at the WAAIF
Micas – muscovite, biotite, phengite
Feldspars – K-feldspar and plagioclase.
Amphiboles. – hornblende, glaucophane
Whole rocks – volcanic groundmass, slates, phyllites.
Pyroxenes – augite, orthopyroxene, clinopyroxene
Feldspathoids – leucite, nepheline.
Clays – celadonite (hard aggregates).
Sulphates – alunite (hard aggregates), jarosite.
Evaporites – polyhalite, langbeinite.
Glass – obsidian, tektites, pseudotachylite, chondrule.
Manganese oxides – cryptomelane, hollandite.
Tourmaline - Shorl, Dravite, Elbaite
Application of 40Ar/39Ar dating technique
Timing of volcanic eruptions and magmatic episodes.
Determining thermal histories of metamorphic rocks.
Dating igneous rock crystallization ages and thermal histories.
Dating paleaomagnetic sequences.
Determining ages of terrestrial impact craters.
Dating meteorite and lunar samples.
Dating of deformation events.
Dating of hydrothermal and alteration events.
Dating of sediments. Sedimentary provenance studies.
Dating of authigenic growth events.
Dating hominid evolution.
Determining ages and thermal events of sandstone feldspar cements.
Main projects developed at the WAAIF
(1) 40Ar/39Ar dating and isotopic geochemistry of large igneous provinces (CAMP, Karoo, Umkondo, Kalkarindji, Madagascar, Ethiopia) and relation with mass extinctions and continental breakup
(2) 40Ar/39Ar dating and thermochronology of meteorites (impact, volcanism)
(3) 40Ar/39Ar dating of impact craters and relation between impact and mass extinction
(4) 40Ar/39Ar methodological development (standard calibrations, 39Ar and 39Ar recoil, inherited and excess 40Ar*, 40K decay constant and alteration effect)
(5) 40Ar/39Ar geochronology of volcanoes and small volcanic provinces (Hawaii, Tore Madeira rise, Heard Island)
(6) 40Ar/39Ar geochronology and thermochronology of Shear zones (Argentina, Thailand, Spain, Australia)
(7) Thermochronology of metamorphic phases (mountain building processes)
(8) Potentially anything that involves Ar isotopes…. bring it on!
40Ar/39Ar laboratory rates.
Categories – conventional step-heating analysis Per sample (10-15 steps) exclusive of GST (+10% for Australian institutions)
Consortium (Curtin University/UWA - LIEF partners) AU$ 695*
Collaborative Research AU$ 1050* ($A 1010 for batch of +10 plus processing)
Commercial (step-heating analysis + sample prep.) AU$ 3995
* These reduce rates are for collaborative research only; i.e. resulting in co-authored publication.
Sample preparation and processing
Samples preparation: from AU$ 200 up to AU$ 690 each* depending on the time required.
Quotes / Estimations supplied via Email - Please apply to Lab Manager: celia.mayers@curtin.edu.au
Processing Cost Examples:
Processing/picking typical plagioclase from basalt rock A$690.00 max
Processing/picking typical ground mass from basalt rock A$460.00 max
*Note that processing costs can be significantly reduced if crushed rock is supplied to the laboratory, and supplying a concentrate of the target mineral will particularly reduce the cost of processing.
Contacts
Director
Prof. Fred Jourdan
Professor & 40Ar/39Ar laboratory director Western Australian Argon Isotope Facility School of Earth and Planetary Sciences
John de Laeter Centre / Space Science and Technology Centre / TIGeR. Curtin university. GPO Box U1987, Perth, WA 6845
Office: +61 (0)8 9266 2412 / Ar lab: +61 (0)8 9266 4731 / Cell phone: +61 (0)4 2417 4984
Email: f.jourdan@curtin.edu.au
Technical Officers
Mrs Celia Mayers (Lab manager)
Western Australian Argon isotope facility, JdL Centre. Curtin university, GPO Box U1987, Perth, WA 6845
Ar lab: +61 (0)8 9266 4731 / Cell phone: +61 (0)4 0920 2764
Mr Adam Frew (Lab engineer)
Western Australian Argon isotope facility, Department of Applied Geology and JdL Centre. Curtin University, GPO Box U1987, Perth, WA 6845.
Ar lab: +61 (0)8 9266 4731 / Cell phone: +61 (0)4 0203 6860
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