K-feldspar hygrochronology


Autoria(s): Villa, Igor Maria; Hanchar, John M.
Data(s)

01/01/2013

Resumo

The significance of the multi-isotopic record preserved in K-feldspars is assessed on samples from the Aar metagranite, Central Alps, Switzerland having very tight independent geological constraints. Stepwise leaching reveals that two diachronically grown K-feldspar generations coexist: Kfs-1 (≥ 35 Ma old, Ca-poor, Rb-Cl-rich, with low 87Sr/86Sr and high 206Pb/204Pb) and Kfs-2 (≤ 10 Ma old, antithetic isotopic signatures deriving from external fluids). Microtextures imaged by cathodoluminescence, backscattered electrons, and electron probe microanalysis are patchy and chemically heterogeneous, with pronounced enrichments in Ba in the retrogressed regions. This confirms the simultaneous presence of fluid-dominated retrogression and recrystallization and isotopic inheritance. The staircase-shaped 40Ar/39Ar age spectrum correlates with the Ca/K and Cl/K signatures. This reflects a mixture of heterochemical K-feldspar generations, and not an intracrystalline Ar gradient caused by diffusion. The shape of the age spectrum and the in vacuo release kinetics proceed from entirely different physical and geological phenomena. What K-feldspars can be effectively used for is to constrain the timing of the fluids that interacted with them by multi-isotopic analyses, rather than to model a “cooling history” from 39Ar release alone. The identification of multiple mineral generations by imaging combined with multi-isotopic analysis enables the accurate dating of the events of a multistage evolution after the initial crystallization of the rock in which the minerals occur.

Formato

application/pdf

Identificador

http://boris.unibe.ch/47059/1/Villa_Hanchar.pdf

Villa, Igor Maria; Hanchar, John M. (2013). K-feldspar hygrochronology. Geochimica et cosmochimica acta, 101, pp. 24-33. Elsevier Science 10.1016/j.gca.2012.09.047 <http://dx.doi.org/10.1016/j.gca.2012.09.047>

doi:10.7892/boris.47059

info:doi:10.1016/j.gca.2012.09.047

urn:issn:0016-7037

Idioma(s)

eng

Publicador

Elsevier Science

Relação

http://boris.unibe.ch/47059/

Direitos

info:eu-repo/semantics/restrictedAccess

Fonte

Villa, Igor Maria; Hanchar, John M. (2013). K-feldspar hygrochronology. Geochimica et cosmochimica acta, 101, pp. 24-33. Elsevier Science 10.1016/j.gca.2012.09.047 <http://dx.doi.org/10.1016/j.gca.2012.09.047>

Palavras-Chave #550 Earth sciences & geology
Tipo

info:eu-repo/semantics/article

info:eu-repo/semantics/publishedVersion

PeerReviewed