40Ar/39Ar dating

As pointed out by Swisher and Prothero (1990) relatively recent advances (1989-1990) in mass spectrometric techniques and the development of laser-fusion 40Ar/39Ar dating techniques have resulted in the ability to date individual volcanic crystals, Multiple analysis and the ability to date single crystals allow the identification of multiplc-agc components due to detrital contamination, and thus permit improved precision and accuracy. To date, studies have been directed to North American chronology, notably minerals (biotite, anor, plag) found in Nebraska and Wyoming. 

Swisher, C.C., III, and D.R. Prothero "Single-Crystal 40Ar/39Ar Dating of the Eocene-Oligocene Transition in North America/ Science, 760 (August, 17, (1990)). 

This volcano consists of three main centres (San Venanzo, Pian di Celle and Celli) whose explosive and effusive products cover an area of about 0.15 km2 (Stoppa 1996). Lava flows and dykes occur at Pian di Celle. These are olivine melilitites that are known locally as venanzite. The juvenile pyroclastic material has an apparently less mafic composition than the lavas (Stoppa 1996). 40Ar/39Ar dating on minerals separated from Pian di Celle volcanics yields an age of 265 ka (Laurenzi et al. 1994). 

D Orazio M, Laurenzi MA, Villa IM (1991) 40Ar/39Ar dating of a shoshonitic lava flow of the Radicofani volcanic center (Southern Tuscany). Acta Vulcanol, 1,... 

Reichow M. K., Saunders A. D., White R. S., Pringle M. S., Al Mukhamedov A. I., Medvedev A. 1., and Kirda N. P. (2002) 40Ar/39Ar dates from the West Siberian Basin Siberian flood basalt province doubled. Science 296, 1846-1849. 

Henocque, O., Ruffet, G., Colin, F Feraud, G. (1998) 40Ar/39Ar dating of West African lateritic cryptomelanes. Geochimica et Cosmochimica Acta 62, 2739-2756. 

A lava flow from the core of Mt. Early yielded a K-Ar date of 15.86 0.30 Ma (Stump et al. (1980, 1990a) which is middle Miocene. K-Ar dates of three lava flows at Sheridan Bluff reported by Stump et al. (1980, 1990b) have a mean of 18.32 0.35 Ma. The 40Ar/39Ar dates of two lava flows on Sheridan Bluff (19.43 0.65 and 19.75 1.57 Ma) are concordant. 

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