Radiometric age constraints on mineral growth, metamorphism, and tectonism of the Gummfluh klippe, Brianconnais domain of the Prealpes, Switzerland

Détails

ID Serval
serval:BIB_BFF0D5D85884
Type
Article: article d'un périodique ou d'un magazine.
Collection
Publications
Institution
Titre
Radiometric age constraints on mineral growth, metamorphism, and tectonism of the Gummfluh klippe, Brianconnais domain of the Prealpes, Switzerland
Périodique
Contributions to Mineralogy and Petrology
Auteur(s)
Cosca M.A., Hunziker J.C., Huon S., Masson H.
ISSN-L
0010-7999
Statut éditorial
Publié
Date de publication
1992
Peer-reviewed
Oui
Volume
112
Pages
439-449
Langue
anglais
Notes
ISI:A1992KA98700001
Résumé
A combined Ar-40/Ar-39, K/Ar, Rb/Sr and stable isotope study has been
made of white micas from the Gummfluh klippe (Brianconnais domain of the
Prealpes), Switzerland. The klippe consists mainly of Mesozoic to early
Tertiary carbonate rocks metamorphosed from anchizonal to epizonal
conditions. At the base of the klippe is a 10-50 m thick, ductilely
deformed marble mylonite containing deformed authigenic quartz
segregations. Stable isotope measurements of the coexisting calcite
(deltaO-18SMOW=24.5) and quartz (deltaO-18SMOW=28.4) from the mylonite
indicate relatively low temperatures (< 300-degreesC) during
mylonitization. Analyses of white mica separates of varying size
fractions from the mylonitic rocks by K/Ar and Rb/Sr techniques yield
ages between 57 and 103 Ma. This variation is correlated with two
parameters, the size of the mineral fraction, and the proportion of 2M1
(more phengitic) to 1M (more muscovitic) polytype in the sample. The
K/Ar and Rb/Sr ages are generally younger in the smaller size fractions,
which also containless 2M1 phengite. High precision Ar-40/Ar-39 age
spectra from different size fractions of these micas record three
distinct components, a small Hercynian component (ca. 200-300 Ma), a
significant Eoalpine component (64-80 Ma) forming Ar-40/Ar-39 age
plateaus, and a very minor Tertiary component (ca. 20-40 Ma).
Characterization of the samples by SEM indicates the presence of two
white mica populations, a coarser grained, deformed, detrital mica that
probably corresponds to the 2M1 phengite and a finer grained neoformed
1M mica. Collectively these observations suggest that the Gummfluh
samples contain a mixture of detrital phengites of Hercynian age
together with neocrystallized muscovites grown during the late Eoalpine
metamorphic event followed by minor argon loss during the Tertiary. The
main geologic episode recorded in the Ar-40/Ar-39 age spectra of white
micas in the mylonite is of Late Cretaceous/Early Tertiary age (64-80
Ma), representing the first reliable Eoalpine ages ever to be reported
from the Prealpes. Contrary to tectonic models, the marble mylonite at
the base of the Gummfluh klippe appears to be a Cretaceous thrust plane
and not the thrust surface formed during transport of the klippe into
its present position from the Penninic Alps during the Tertiary. The
late Cretaceous thrust developed during marine sedimentation at a depth
of 800 m below the seafloor at temperatures of approximately
280-degrees-C, facilitated by warm fluids along the tectonic
discontinuity.
Création de la notice
05/12/2012 21:20
Dernière modification de la notice
20/08/2019 16:34
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