Geochronology of metasomatic events

Villa, Igor Maria; Williams, Michael L (2013). Geochronology of metasomatic events. In: Harlov, Daniel E.; Austrheim, Hakon (eds.) Metasomatism and the Chemical Transformation of Rock. Lecture Notes in Earth System Sciences (pp. 171-202). Heidelberg: Springer 10.1007/978-3-642-28394-9_6

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In order to date any geological event, suitable mineral geochronometers that record that and only that event must be identified and analyzed. In the case of metasomatism, recrystallisation is a key process that controls both the petrology and the isotopic record of minerals. It can occur both in the form of complete neocrystallisation (e.g. in a vein) and in the form of pseudomorphism, whereby dissolution/reprecipitation at the submicroscopic scale plays a central role. Recrystallisation may be complete or not, raising the possibility that relicts of a pre-metasomatic assemblage may be preserved. Because recrystallisation is energetically less costly at almost any temperature than diffusion, and because radiogenic isotopes (except 4He) never diffuse faster than major elements forming the mineral structure, there is a strong causal link between petrographic relicts and isotopic inheritance (as demonstrated for zircon, monazite, titanite, amphibole, K-feldspar, biotite, and muscovite). Metasomatic assemblages commonly contain such mixtures between relicts and newly formed phases, whose geochronology is slightly more complex than that of simple, ideal systems, but can be managed by techniques that have become routine in the last decade and which are described in this chapter. Because of its crucial role in controlling the isotope systematics, the petrogenesis of a mineral needs to be understood in extreme detail, especially using microchemical analyses and micro-imaging techniques, before mineral ages can be correctly interpreted. As the occurrence of recrystallization is limited by the availability of water, minerals act as “geohygrometers” that allow constraints to be placed on the nature and age of fluid circulation episodes, especially metasomatic events.

Item Type:	Book Section (Book Chapter)
Division/Institute:	08 Faculty of Science > Institute of Geological Sciences
UniBE Contributor:	Villa, Igor Maria
Subjects:	500 Science > 550 Earth sciences & geology
ISSN:	2193-858X
ISBN:	978-3-642-28393-2
Series:	Lecture Notes in Earth System Sciences
Publisher:	Springer
Language:	English
Submitter:	Igor Maria Villa-Toscani
Date Deposited:	14 Aug 2014 10:29
Last Modified:	05 Dec 2022 14:31
Publisher DOI:	10.1007/978-3-642-28394-9_6
URI:	https://boris.unibe.ch/id/eprint/46895