We present Ar-39-Ar-40 dating of phengite, muscovite and paragonite from a set of mafic and metasedimentary rocks sampled from the high-pressure (HP) metaophiolites of the Voltri Group (Western Alps) and from clasts in the basal layer conglomerates from the Tertiary molasse which overlie the high-pressure basement. The white mica-bearing rocks display peak eclogitic and blueschist-facies parageneses, locally showing complex greenschist-facies replacement textures. The internal discordance of age spectra is proportional to the chemical complexity of the micas. High-Si phengites from eclogite clasts record a Ar-39-Ar-40 age of ca. 49 Ma for the eclogite stage and ca. 43 Ma for the blueschist retrogression; phengites from a blueschist basement sample yield an age of ca. 40 Ma; low-Si muscovite from a metasediment dates the formation of the greenschist paragenesis at ca. 33 Ma. Our data indicate that the analyzed samples reached high-pressure conditions at different times over a time-span of c.a. 10 Ma. Subduction was continuing during exhumation and blueschist retrograde re-equilibration of higher-pressure, eclogite-facies rocks. This process kept the isotherms depressed, allowing the older HP-rocks to escape thermal re-equilibration. Our results, added to literature data, fit a tectonic model of a subduction-exhumation cycle, with different tectonic slices subducted at different times from Early Eocene until the Eocene-Oligocene boundary. (C) 2005 Elsevier B.V. All rights reserved.

Federico, L., Capponi, G., Crispini, L., Scambelluri, M., Villa, I. (2005). 39Ar/40Ar dating of high-pressure rocks from the Ligurian Alps: Evidence for a continuous subduction-exhumation cycle. EARTH AND PLANETARY SCIENCE LETTERS, 240(3-4), 668-680 [10.1016/j.epsl.2005.09.062].

39Ar/40Ar dating of high-pressure rocks from the Ligurian Alps: Evidence for a continuous subduction-exhumation cycle

VILLA, IGOR MARIA
2005

Abstract

We present Ar-39-Ar-40 dating of phengite, muscovite and paragonite from a set of mafic and metasedimentary rocks sampled from the high-pressure (HP) metaophiolites of the Voltri Group (Western Alps) and from clasts in the basal layer conglomerates from the Tertiary molasse which overlie the high-pressure basement. The white mica-bearing rocks display peak eclogitic and blueschist-facies parageneses, locally showing complex greenschist-facies replacement textures. The internal discordance of age spectra is proportional to the chemical complexity of the micas. High-Si phengites from eclogite clasts record a Ar-39-Ar-40 age of ca. 49 Ma for the eclogite stage and ca. 43 Ma for the blueschist retrogression; phengites from a blueschist basement sample yield an age of ca. 40 Ma; low-Si muscovite from a metasediment dates the formation of the greenschist paragenesis at ca. 33 Ma. Our data indicate that the analyzed samples reached high-pressure conditions at different times over a time-span of c.a. 10 Ma. Subduction was continuing during exhumation and blueschist retrograde re-equilibration of higher-pressure, eclogite-facies rocks. This process kept the isotherms depressed, allowing the older HP-rocks to escape thermal re-equilibration. Our results, added to literature data, fit a tectonic model of a subduction-exhumation cycle, with different tectonic slices subducted at different times from Early Eocene until the Eocene-Oligocene boundary. (C) 2005 Elsevier B.V. All rights reserved.
Articolo in rivista - Articolo scientifico
Ligurian Alps; eclogite; Ar-39-Ar-40 phengite dating; subduction; exhumation
English
15-dic-2005
240
3-4
668
680
none
Federico, L., Capponi, G., Crispini, L., Scambelluri, M., Villa, I. (2005). 39Ar/40Ar dating of high-pressure rocks from the Ligurian Alps: Evidence for a continuous subduction-exhumation cycle. EARTH AND PLANETARY SCIENCE LETTERS, 240(3-4), 668-680 [10.1016/j.epsl.2005.09.062].
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Utilizza questo identificativo per citare o creare un link a questo documento: https://hdl.handle.net/10281/2400
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