Skip to content

Ar-Ar Geochronology Laboratory

The Ar-Ar geochronology laboratory is housed in the the IGG Pisa headquarters.

The Laboratory

Time is a fundamental parameter in Earth sciences, knowing which is essential for estimating the duration and rate of geological processes. The 40Ar-39Ar method, a variant of the K-Ar dating technique, is based on the natural decay of 40K (half-life 1.25 Ga) into 40Ar.

The 40Ar-39Ar technique , applied to K-containing systems (minerals or glasses), represents one of the most powerful geochronological investigation methods available today in Earth sciences, applicable to multiple geological problems and to rocks ranging in age from a few thousand years to rocks as old as the solar system.

The development of the laser extraction technique has expanded the fields of application of the method, which today include among others:

  • study of the relationships between microstructural data and isotopic records in minerals;
  • dating of pseudotachylytes of endogenous (coseismic faults) or exogenous origin (connected with the impact of comets or asteroids;
  • deformation dating;
  • provenance studies of detrital phases in clastic sediments;
  • dating of the most recent geological past (from Pleistocene to Holocene systems), through the analysis of potassium-rich phases of volcanic origin;
  • dating of phyllosilicates in shallow faults;
  • direct measurement of the diffusion of Ar isotopes in minerals and of the partition coefficients between minerals and silicate melts.

In recent years, the emergence of a new generation of multicollector mass spectrometers, combined with the development of new detectors, has generated renewed interest in the 40Ar-39Ar method. Recent instrumental advances allow geochronological analyses on increasingly smaller sample quantities, with improved analytical precision of up to approximately one order of magnitude.
A new-generation noble gas mass spectrometer was recently installed and is operational at the 40Ar-39Ar Gechronology Laboratory of the Institute of Geosciences and Earth Resources.

The 40Ar–39Ar laboratory at IGG–CNR after the recent renovation (2019)
Eocene-age (>50 Ma) coseismic fault geometrically reactivating an Ordovician (460–440 Ma) mylonite (near Black Ridge, northern Victoria Land, Antarctica)
Melting a sanidine crystal using a CO2 laser
In situ dating of a biotite plate using pulsed UV laser

Instruments

Mass Spectrometer and Laser Probes

The analytical system consists of:

  • ARGUS VI multicollector noble gas mass spectrometer (Thermo Fisher Scientific) and associated high vacuum, low volume extraction line;
  • Mass Analyser Products Ltd. MAP 215-50 single collector mass spectrometer and associated high vacuum, low volume extraction line;
  • laser extraction system equipped with three different laser probes.

The laser probes include a pulsed ultraviolet flashlamp laser, whose fundamental radiation is quadrupled and Q-switched (266 nm), a fiber laser (RedEnergy G4 50W EP-Z, SPI Lasers) and a continuous emission CO2 laser (MIR10-30 system, New Wave Research).
RGUS VI mass spectrometer represents the state of the art in noble gas mass spectrometry applied to 40Ar-39Ar geochronology. Equipped with 6 collectors and an electrostatic deflector system, it allows the simultaneous acquisition of the 5 isotopes of interest (40Ar, 39Ar, 38Ar, 37Ar, 36Ar).
The ARGUS VI mass spectrometer installed at IGG-CNR is currently equipped with a Faraday cup with a 1012 Ω resistor (cup H2), 4 Faraday cups with a 1013 Ω resistor (cup H1-Ax-L1-L2), and a low-noise multiplier (CuBe Compact Discrete Dynode) that allows the measurement of 36Ar with high precision.

ARGUS VI Multicollector Mass Spectrometer (Thermo Fisher Scientific)
MAP 215-50 Single Collector Mass Spectrometer (Mass Analyzer Products)
The UV (Nd:YAG) and IR (Fiber laser) laser probe, optics and the microscope used to view the sample
The extraction system equipped with CO2 laser (MIR10-30)

Staff and Contacts

The laboratory staff is composed of:

  • Dr. Gianfranco di Vincenzo (Laboratory Manager)

Contacts:

Phones

  • +39 050 6212281 (Dr. Gianfranco di Vincenzo)
  • +39 050 6212269 (Laboratory)

email:

  • gianfranco.divincenzo@igg.cnr.it
  • ararlab@igg.cnr.it

Methods and Applications

Laser extraction techniques

The main advantage of the laser extraction technique over the conventional method (induction or radiofrequency furnace) lies in the fact that the use of the laser allows the analysis of very small samples (up to a few micrograms or even smaller quantities, under favorable conditions).

The ability to analyze such small quantities of material leads to high analytical versatility.

This makes it possible to tackle a geological problem with the aid of different extraction techniques, sometimes complementary and not necessarily alternative, but a single tool:

  • in situ dating of rock portions, a technique that allows the preservation of microstructural information;
  • step-heating analysis, to date an entire population of crystals or to analyze significant quantities of sample (up to several tens of milligrams), a useful technique for analyzing young (<<1 Ma) and/or K-poor geological systems;
  • total melting of single crystals, a technique that allows the resolution of mixed populations of grains (e.g., potassium detrital phases of a clastic sediment).

Recent instrumental developments, with the new generation of multicollector mass spectrometers, together with recent efforts to improve their accuracy through the calibration of the most popular standards by astronomical tuning, have brought the 40Ar-39Ar method closer to the temporal resolution of the CA-ID-TIMS (chemical abrasion-isotope dilution-thermal ionization mass spectrometry) U–Pb dating method applied to zircon.

Applications


The method can be applied to a variety of potassium-containing systems, the most commonly dated phases include: feldspars, micas, silicate glasses, and groundmass of volcanic rocks.

Age maps within a low-grade metamorphic rock from the Northern Apennines. Ages are relative to white mica. Data obtained using the ARGUS VI multicollector mass spectrometer. Ages are reported in Ma (±2σ, analytical uncertainty).
SEM-BSE image of phlogopite VUT191_11 (Mt. Vulture, Southern Italy) after removal of the Pt coating used for ion probe analysis. SIMS craters are indicated by arrows. The contrast due to chemical inhomogeneity is clearly visible (Scordari et al., 2010). This investigation is part of the study of the crystal chemistry of volcanic micas and benefited from in-situ SIMS measurement of Li and volatiles (H, F) on single crystals.
Age maps within a fault psudotachylite and probability age plot (Alps, Italy). Data obtained using a MAP215-50 single-collector mass spectrometer. Ages (Ma) and K/Ca ratios are reported for each analysis, along with analytical uncertainties (±2σ).
Reflected-light optical micrographs of opx in BM90-6 (Balmuccia, Western Alps, Italy), showing SIMS spots and corresponding Cl contents (ppm). Orthopyroxene reacted in the presence of a metasomatic agent with Cl incorporation that appears to follow a diffusive law. Cl enrichment is highest along the crystal edge—with contents up to 108 ppm Cl—and indicates that the metasomatic agent diffused along the grain boundaries, represented by white spots in the micrograph (Ottolini & Le Fevre, 2008).
Ages of individual detrital micas obtained by total melting (Wm(d)) separated from a low-grade metapelite (turbidites of the Roberton Bay Terrane, northern Victoria Land, Antarctica)
New 40Ar-39Ar data obtained using a multi-collector mass spectrometer (ARGUS VI) on the San Vincenzo rhyolites. The results highlighted the presence of excess Ar in the biotite, which was not present in the sanidine. The performance of the new instrumentation allowed us to determine a placement age with a relative uncertainty of 0.1% (±2σ).

Scientific Projects and Interests

Project:

  • Over the past 10 years, the laboratory has been actively involved in numerous projects related to the PNRA programming (PNRA18_00037, PNRA16_00072, PNRA16_00040, PdR_2013/AZ2.08, PdR_2013/B2.07, PdR_2013/AZ2.07, PdR_2010A2.02, PdR_2010/A2.12).
    Main research interests include the geodynamic evolution of the Antarctic continent in the Proterozoic and Paleozoic, the geodynamics of the Ross Sea during the Cenozoic, and the evolution of the climate-cryosphere system in the Neogene and Quaternary.
  • Biandera RITMARE project funded by MIUR [SP4 (Deep Sea)-WP1].
  • DESCRAMBLE, drilling in supercritical geothermal conditions (EU Horizon 2020).
  • PRIN_2017 20177BX42Z, Intraplate deformation, magmatism and topographic evolution of a diffuse collisional belt: Insights into the geodynamics of the Arabia-Eurasia collisional zones.

Scientific Interests:

Geochronology of ductile (mylonites) and brittle (pseudotachylytes) faults; fault and shear zone reactivation processes; provenance studies of siliciclastic sediments; high-precision dating of Quaternary impact glasses and volcanics; chronology of Italian Pliocene-Pleistocene magmatism; chronostratographic applications; study of the relationships between tectono-metamorphic evolution and the isotopic record in metamorphic minerals; planetary geology.

Priestley Glacier, Northern Victoria Land (Antarctica)
Moldavite, a tektite generated by the impact that produced the Ries crater (diameter ~24 km) in Germany ~15 million years ago
Mount Melbourne, a Quaternary stratovolcano (2732 m) in northern Victoria Land
Electron microscopy (EMS) image of the microstructures of a fault pseudotachylite that resemble those of volcanic rocks.
Mylonite developed in a ductile shear zone, Mount Emison (Northern Victoria Land, Antarctica)

Publications

  • Di Vincenzo G. (2022). High precision multi-collector 40Ar/39Ar dating of moldavites (Central European tektites) reconciles geochrological and paleomagnetic data. Chemical Geology, 608, 121026. https://doi.org/10.1016/j.chemgeo.2022.121026.
  • Del Carlo P., Di Roberto A., Di Vincenzo G., Re G., Albert P.G., Nazzari M., Smith V.C, Cannata A. (2022). Tephrostratigraphy of proximal pyroclastic sequences at Mount Melbourne (northern Victoria Land, Antarctica): insights into the volcanic activity since the last glacial period. Journal of Volcanology and Geothermal Research, 107457. https://doi.org/10.1016/j.jvolgeores.2021.107457.
  • Di Vincenzo G., Vezzoni S., Dini A., Sergio Rocchi S. (2022). Timescale of a magmatic‐hydrothermal system revealed by 40Ar–39Ar geochronology: the Mio‐Pliocene Campiglia Marittima system (Tuscany, Italy). Scientific Reports, 12:7128, https://doi.org/10.1038/s41598-022-10867-9.
  • Di Vincenzo G., Godard G., Molli G. (2022). Dating low-grade deformation: role of lithology and strain partitioning on Ar isotope records in the Alpi Apuane of northern Apennines (Italy). Tectonics, https://doi.org/10.1029/2022TC007248.
  • Nania L., Montomoli C., Iaccarino S., Di Vincenzo G., Carosi R. (2022). A thermal event in the Dolpo region (Nepal): a consequence of the shift from orogen perpendicular to orogen parallel extension in central Himalaya? Journal of the Geological Society of London, 179, jgs2020-261. https://doi.org/10.1144/jgs2020-261.
  • Di Giuseppe P., Agostini S., Di Vincenzo G., Manetti P., Savaşçın M.Y., Conticelli S. (2021). From subduction to strike slip‐related volcanism: insights from Sr, Nd, and Pb isotopes and geochronology of lavas from Sivas–Malatya region, Central Eastern Anatolia. International Journal of Earth Sciences. https://doi.org/10.1007/s00531-021-01995-0.
  • Di Roberto A., Scateni B., Di Vincenzo G., Petrelli M., Fisauli G., Barker S.J., Del Carlo P., Colleoni F., Kulhanek D.K., McKay R., De Santis L. (2021). Tephrochronology and provenance of an early Pleistocene (Calabrian) tephra from IODP Expedition 374 Site U1524, Ross Sea (Antarctica). Geochemistry, Geocphysics, Geosystems, 22, e2021GC009739. https://doi.org/10.1029/2021GC009739.
  • Di Vincenzo G., Folco L., Suttle M.D., Brase L., Harvey R.P. (2021). Multi-collector 40Ar/39Ar dating of microtektites from Transantarctic Mountains (Antarctica): A definitive link with the Australasian tektite/microtektite strewn field. Geochimica et Cosmochimica Acta, 298, 112–130. https://doi.org/10.1016/j.gca.2021.01.046.
  • Conte A.M., Perinelli C., Bosman A., Castorina F., Conti A., Cuffaro M., Di Vincenzo G., Martorelli E., Bigi S. (2020). Tectonics, dynamics and Plio-Pleistocene magmatism in the central Tyrrhenian Sea: insights from the submarine transitional basalts of the Ventotene volcanic Ridge (Pontine Islands, Italy). Geochemistry Geophysics Geosystem, 21, e2020GC009346, https://doi.org/10.1029/2020GC009346.
  • Di Roberto A., Albert P.G, Colizza E., Del Carlo P., Di Vincenzo G., Gallerani A., Giglio F., Kuhn G., Macrì P., Manning C.J., Melis R., Miserocchi S., Scateni B., Smith V.C., Torricella F., Winkler A. (2020). Evidence for a large-magnitude Holocene eruption of Mount Rittmann (Antarctica): A volcanological reconstruction using the marine tephra record. Quaternary Science Reviews, 250, 106629. https://doi.org/10.1016/j.quascirev.2020.106629.
  • Di Vincenzo G., Pennacchioni G., Bestmann M. (2019). Exploring the Ar isotope record of an early Miocene pseudotachylyte in an early Oligocene intrusion (Rieserferner pluton, eastern Alps). Lithos, 338–339, 1–17. https://doi.org/10.1016/j.lithos.2019.04.009.
  • Cardello G.L., Di Vincenzo G., Giorgetti G., Zwingmann H., Mancktelow N. (2019). Initiation and development of the Pennine Basal Thrust (Swiss Alps): a structural and geochronological study of an exhumed megathrust. Journal of Structural Geology, 126, 338–356. https://doi.org/10.1016/j.jsg.2019.06.014.
  • Moratti G., Benvenuti M., Santo A.P., Laurenzi M.A., Braschi E., Tommasini S. (2018). New 40Ar-39Ar dating of Lower Cretaceous basalts at the southern front of the Central High Atlas, Morocco: insights on Upper Mesozoic tectonics, sedimentation and magmatism. International Journal of Earth Sciences, 107(7), 2491-2515. doi: 10.1007/s00531-018-1609-7.
  • Njonfang E., Laurenzi M.A., Wonkwenmendam NGuet P., Cozzupoli D. (2018). 40Ar-39Ar ages from the Sabongari and Nana complexes, Cameroon Line magmatism (central Africa). Journal of African Earth Sciences, 147, 20-27. doi: 10.1016/j.jafrearsci.2018.06.006.
  • Di Vincenzo G., Grande A., Prosser G., Cavazza W., DeCelles P.G. (2016). 40Ar–39Ar laser dating of ductile shear zones from central Corsica (France): Evidence of Alpine (middle to late Eocene) syn-burial shearing in Variscan granitoids. Lithos, 262, 369–383, http://dx.doi.org/10.1016/j.lithos.2016.07.022.
  • Martin S., Godard G., Laurenzi M.A., Viganò A. (2016). Pseudotachylytes of the Tonale nappe (Italian Alps): Petrogenesis, 40Ar-39Ar geochronology and tectonic implications. Italian Journal of Geosciences135(2), 217-235. doi: 10.3301/IJG.2015.09.
  • Laurenzi M. A., Braschi E., Casalini M., Conticelli S. (2015). New 40Ar–39Ar dating and revision of the geochronology of the Monte Amiata volcano, central Italy. Italian Journal of Geosciences, 134 (2), 255-265, doi:10.3301/IJG.2015.11.
  • Di Vincenzo G., Grande A., Rossetti F. (2014). Paleozoic siliciclastic rocks from northern Victoria Land (Antarctica): provenance, timing of deformation and implications for the Antarctica/Australia connection. Geological Society of America Bulletin, 126, 1416–1438, https://doi.org/10.1130/B31034.1.
  • Abbate E., Bruni P., Ferretti M.P., Delmer C., Laurenzi M.A., Hagos M., Bedri O., Roo L., Sagri M., Libsekal Y. (2014). The Oligocene intertrappean beds: regional distribution, depositional environments and Afro/Arabian mammal dispersal corridors. Journal of African Earth Sciences, 99, 463-489. doi: 10.1016/j.jafrearsci.2013.11.001.
  • Di Vincenzo G., Rossetti F., Viti C., Balsamo F. (2013). Constraining the timing of fault reactivation: Eocene coseismic slip along a Late Ordovician ductile shear zone (northern Victoria Land, Antarctica). Geological Society of America Bulletin, 125, 609–624, https://doi.org/10.1130/B30670.1.