The 39Ar-40Ar technique is often used to date the metamorphic evolution of basement rocks. The present review article examines systematic aspects of the K-Ar decay system in different mineral chronometers frequently found in mono- and polymetamorphic basements (amphibole, biotite, muscovite/phengite, K-feldspar). A key observation is that the measured dissolution rate of silicates in aqueous fluids is many orders of magnitude faster, and has a much lower activation energy, than the rate of Fickian diffusion of Ar. The effects of this inequality are patchy age zonations, very much like those observed in many U-Pb chronometers, unaccompanied by intra-crystalline bell- shaped Ar loss profiles. Recognizing the importance of the respective rates in field situations leads to re-evaluating the ages and the interpretive paradigms in classic examples such as the Central Alpine "Lepontine" amphibolite facies event and the Western Alpine eclogitic event.

Villa, I. (2015). 39Ar-40Ar geochronology of mono- and polymetamorphic basement rocks. PERIODICO DI MINERALOGIA, 84(3B), 615-632 [10.2451/2015PM0454].

39Ar-40Ar geochronology of mono- and polymetamorphic basement rocks

Villa, IM
2015

Abstract

The 39Ar-40Ar technique is often used to date the metamorphic evolution of basement rocks. The present review article examines systematic aspects of the K-Ar decay system in different mineral chronometers frequently found in mono- and polymetamorphic basements (amphibole, biotite, muscovite/phengite, K-feldspar). A key observation is that the measured dissolution rate of silicates in aqueous fluids is many orders of magnitude faster, and has a much lower activation energy, than the rate of Fickian diffusion of Ar. The effects of this inequality are patchy age zonations, very much like those observed in many U-Pb chronometers, unaccompanied by intra-crystalline bell- shaped Ar loss profiles. Recognizing the importance of the respective rates in field situations leads to re-evaluating the ages and the interpretive paradigms in classic examples such as the Central Alpine "Lepontine" amphibolite facies event and the Western Alpine eclogitic event.
Articolo in rivista - Articolo scientifico
39; Ar-; 40; Ar dating; Diffusion; Eclogite dating; Geochronology; Lepontine event;
9Ar-40Ar dating; diffusion; geochronology; eclogite dating; Lepontine event
English
615
632
18
Villa, I. (2015). 39Ar-40Ar geochronology of mono- and polymetamorphic basement rocks. PERIODICO DI MINERALOGIA, 84(3B), 615-632 [10.2451/2015PM0454].
Villa, I
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Utilizza questo identificativo per citare o creare un link a questo documento: https://hdl.handle.net/10281/100008
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