Ar-Ar Geochronology Laboratory
Time is a fundamental parameter in the Earth Sciences whose knowledge is essential for estimating the length and rate of geological processes. The 40Ar-39Ar method, variant of the K-Ar method, is based on the radioactive decay of the naturally occurring parent 40K (half-life 1.25 Ga) to the daughter 40Ar over geological time.
The 40Ar-39Ar method, applied to K-bearing systems (minerals or glass), represents one of the most powerful geochronological tools currently available to constrain the timing of geological processes. It can be applied to a wide range of geological problems and to rocks ranging in age from a few thousand years to the oldest rocks available.
The development of the laser extraction technique has expanded fields of application, including among others:
- the study of the relationship between mineral-textural information and Ar isotope records in minerals;
- dating fault-generated and impact-related pseudotachylytes;
- dating deformation;
- the study of the provenance of detrital phases in clastic sediments;
- dating the recent past (as young as Pleistocene to Holocene) by analyzing high-potassium volcanogenic minerals;
- dating clay minerals from sediments and shallow faults;
- direct measurements of argon diffusion in minerals and of argon partition coefficients between minerals and silicate melts.
Mass spectrometer and laser probes
The analytical system consists of:
- a Mass Analyser Products Ltd. MAP 215-50 noble gas mass spectrometer (MS);
- a low volume UHV gas inlet system;
- a laser extraction system consisting of three different laser probes.
The laserprobe system includes two Nd:YAG lasers (a CW diode-pumped Nd-YAG infrared laser with ~20W maximum power and a pulsed flashlamp Nd-YAG ultraviolet laser, frequency quadrupled and Q-switched) and a MIR10-30 (New Wave Research) CW CO2 laser system.
Gianfranco di Vincenzo Ph.D. (CNR Researcher - Head Laboratory)
Dr. Marinella Ada Laurenzi (CNR Researcher)
Antonietta Grande Ph.D.
+39 050 6212269 (Laboratory)
+39 050 6212270 (Gianfranco di Vincenzo office)
+39 050 6212272 (Marinella Ada Laurenzi office)
METHODS AND APPLICATIONS
Laser extraction techniques
The greatest advantage of the laser extraction method over the conventional furnace extraction is that it permits analysis of very small samples (down to a few micrograms or even less in same cases). The ability to analyze very small samples allows a great analytical versatility. A geological problem maybe in principle approached using different extraction methods and just one instrument, including:
- in-situ dating of rock chips, which allows to preserve textural information;
- step-heating analysis of bulk samples, to date a whole population or analyze large samples, useful when dealing with young (<<1 Ma) and/or low-K systems;
- total-fusion analysis of single grains, which enables to solve mixed populations of grains (e.g., detrital potassic minerals in clastic sediments).
The method can be applied to a variety of K-bearing systems, including among others: feldspars, amphiboles, micas, silicate glasses, and volcanic groundmasses.
The 40Ar–39Ar facility at IGG was funded by the Programma Nazionale di Ricerche in Antartide (PNRA) and it is part of the intalian network of antarctic laboratories (SIA).
During the past ten years the IGG 40Ar-39Ar geochronology laboratory was actively involved in several scientific projects funded by the: PNRA (PdR_2013/AZ2.08, PdR_2013/B2.07, PdR_2013/AZ2.07, PdR_2010A2.02, PdR_2010/A2.12, PdR_2009/A2.16, PdR2009/A2.19, PdR_2004/4.01, PdR_2004/4.06, PdR_2004/5.04, PdR_2002/4.1, PdR_2002/4.6, PdR_2002/5.4). Within the 2005-2010 period the laboratory was involved in the international ANDRILL-SMS project to constrain the age model of the AND-2A core. Researches span from the geodynamic evolution of Antarctica during the Proterozoic-Paleozoic, geodynamics of the Ross Sea region during the Cenozoic, to evolution of the climate-cryosphere system during the Neogene-Quaternary.
Other recent significant Projects
- RITMARE FLAGSHIP (funded by MIUR) Project [SP4 (Deep Sea)-WP1].
- DESCRAMBLE, Drilling in supercritical geothermal conditions (EU Horizon 2020).
Geochronology of ductile (mylonites) and brittle (pseudotachylytes) faults; reactivation of faults and shear zones; provenance studies of siliciclastic sediments; high-precision dating of impact glasses (tektites) and Quaternary volcanic rocks; chronological reconstruction of Italian Plio-Pleistocenic magmatism; chronostratigraphic applications; relationship between tectono-metamorphic evolution and isotope records in metamorphic minerals.
- 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
- Martin S., Godard G., Laurenzi M.A., Viganò A. (2015). Pseudotachylytes of the Tonale nappe (Italian Alps): Petrogenesis, 40Ar-39Ar geochronology and tectonic implications. Italian Journal of Geosciences, in stampa, doi:10.3301/IJG.2015.09
- 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, doi:10.1130/B31034.1
- 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. Doi:10.1130/B30670.1
- Di Vincenzo G., Bracciali L., Del Carlo P., Panter K., Rocchi S. (2010). 40Ar–39Ar dating of volcanogenic products from the AND-2A core (ANDRILL Southern McMurdo Sound Project, Antarctica): correlations with the Erebus Volcanic Province and implications for the age model of the core. Bulletin of Volcanology, 72, 487–505. doi: 10.1007/s00445-009-0337-z
- Conticelli S., Laurenzi M.A., Giordano G., Mattei M., Avanzinelli R., Melluso L., Tommasini S., Boari E., Cifelli F., Perini G. (2010). Leucite-bearing (kamafugitic/leucititic) and –free (lamproitic) ultrapotassic volcanic rocks and associated shoshonites in the Italian Peninsula: the role of sedimentary recycling in their genesis and evolution in a post-collisional geodynamic setting. Journal of the Virtual Explorer, 36, paper 20, doi:10.3809/jvirtex. 2010.00251
- D’Oriano F., Angeletti L., Capotondi L., Laurenzi M.A., López Correa M., Taviani M., Torelli L., Trua T., Vigliotti L., Zitellini N. (2010). Coral Patch and Ormonde seamounts as a product of the Madeira hot spot, Eastern Atlantic Ocean. Terra Nova, 22, 494-500, doi: 10.1111/j.1365-3121.2010.00973.x
- Boari E., Tommasini S., Laurenzi M.A., Conticelli S. (2009). Transition from ultrapotassic kamafugitic to sub-alkaline magmas: Sr, Nd, and Pb isotope, trace element and 40Ar–39Ar age data from the Middle Latin Valley volcanic field, Roman Magmatic Province, Central Italy. Journal of Petrology, 50, 1327-1357, doi:10.1093/petrology/egp003
- Di Vincenzo G., Skála R. (2009) 40Ar–39Ar laser dating of tektites from the Cheb Basin (Czech Republic): evidence for coevality with moldavites and influence of the dating standard on the age of the Ries impact. Geochimica et Cosmochimica Acta, 73, 493–513, doi:10.1016/j.gca.2008.10.002
- Bigazzi G., Laurenzi M.A., Soligo M., Tuccimei P. (2008). Multi-method approach to dating glass: the case of Basiluzzo Islet (Aeolian archipelago, Italy). Journal of Volcanology and Geothermal Research, 177, 244-250, doi: 10.1016/j.jvolgeores.2007.10.005
- Curzio P., Folco L., Laurenzi M.A., Mellini M., Zeoli A. (2008). A tephra chronostratigraphic framework for the Frontier Mountain blue ice field (northern Victoria Land, Antarctica). Quaternary Science Review, 27, 602-620, doi: 10.1016/j.quascirev.2007.11.017
- Folco L., Rochette P., Perchiazzi N., D’Orazio M., Laurenzi M.A., Tiepolo M. (2008). Microtektites from Victoria Land Transantarctic Mountains. Geology, 36(4), 291-294, doi: 10.1130/G24528A.1
- Di Vincenzo G., F. Talarico F., Kleinschmidt G. (2007). An 40Ar–39Ar investigation of the Mertz Glacier area (George V Land, Antarctica): implications for the Ross Orogen – East Antarctic Craton relationship and Gondwana reconstructions. Precambrian Research, 152, 93–118, doi: 10.1016/j.precamres.2006.10.002
- Laurenzi M.A., Balestrieri M.L., Bigazzi G., Hadler Neto J.C., Iunes P.J., Norelli P., Oddone M., Osorio Araya A.M., Viramonte J.G (2007). New constraints on ages of glasses proposed as reference materials for Fission-Track dating. Geostandards and Geoanalytical Research, 31, 105-124, doi: 10.1111/j.1751-908X.2007.00844.x
- Di Vincenzo G., Tonarini S., Lombardo B., Castelli D., Ottolini L. (2006). Comparison of 40Ar-39Ar and Rb-Sr data on phengites from the UHP Brossasco-Isasca Unit (Dora Maira Massif, Italy): implications for dating white mica. Journal of Petrology, 47, 1439–1465, doi: 10.1093/petrology/egl018
- Di Vincenzo G., Carosi R., Palmeri R. (2004). The relationship between tectono–metamorphic evolution and argon isotope records in white mica: constraints from in situ 40Ar-39Ar laser analysis of the Variscan basement of Sardinia (Italy). Journal of Petrology, 45, 1013–1043, doi: 10.1093/petrology/egh002
- Di Vincenzo G., Rocchi S., Rossetti F., Storti F. (2004). 40Ar-39Ardating of pseudotachylytes: the effect of clast-hosted extraneous argon in Cenozoic fault-generated friction melts from the West Antarctic Rift System. Earth and Planetary Science Letters, 223, 349–364, doi: 10.1016/j.epsl.2004.04.042
- Di Vincenzo G., Viti C., Rocchi R. (2003). The effect of chlorite interlayering on 40Ar-39Ar biotite dating: an 40Ar-39Ar laserprobe and TEM investigation of variably chloritised biotites. Contributions to Mineralogy and Petrology, 145, 643–658, doi: 10.1007/s00410-003-0472-z
- Laurenzi M.A., Bigazzi G., Balestrieri M.L., Bouska V. (2003). 40Ar-39Ar laser probe dating of the Central European tektite-producing impact event. Meteoritics and Planetary Science, 38, 887-894.
- Di Vincenzo G., Ghiribelli B., Giorgetti G., Palmeri R. (2001) Evidence of a close link between petrology and isotope records: constraints from SEM, EMP, TEM and in situ 40Ar–39Ar laser analyses on multiple generations of white micas (Lanterman Range, Antarctica). Earth and Planetary Science Letters, 192, 389–405, doi: 10.1016/S0012-821X(01)00454-X