Cadomian and Variscan metamorphic events in the Léon Domain (Armorican Massif) resolved by trace element analysis in monazite and garnet
Schulz, Bernhard
Krenn, Erwin
Finger, Fritz
Brätz, Helene
Klemd, Reiner
Universitätsverlag Göttingen
Article in Anthology
Verlagsversion
Deutsch
Schulz, Bernhard; Krenn, Erwin; Finger, Fritz; Brätz, Helene; Klemd, Reiner, 2006-03: Cadomian and Variscan metamorphic events in the Léon Domain (Armorican Massif) resolved by trace element analysis in monazite and garnet. In: Philipp, S.; Leiss, B; Vollbrecht, A.; Tanner, D.; Gudmundsson, A. (eds.): 11. Symposium "Tektonik, Struktur- und Kristallingeologie"; 2006, Univ.-Verl. Göttingen, p. 203 - 205., DOI https://doi.org/10.23689/fidgeo-1896.
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The question, whether crustal domains
are allochthonous terranes or not is
crucial for plate tectonic models of
the Ibero-Armorican segment of the
Variscan belt. The Léon Domain in
the Armorican Massif appears as a displaced
crustal block as it bears a resemblance
to the South Armorican Domain
of the internal Variscan belt (Le Corre
et al. 1989). In the central part of the
Léon, the amphibolite-facies Conquet-
Penze Micaschist Unit (CPMU) overlies
the high-grade Lesneven Gneiss Unit
(LGU). At the base of the LGU, a
high-pressure stage at 700°C/>13 kbar,
recorded by garnet-clinopyroxene assemblages
in eclogites was followed by a
high-temperature event at 800°C/8 kbar
with garnet and cordierite in aluminous
paragneisses. Maximal temperatures in
the upper parts of the LGU were
630°C/6 kbar. In the micaschists of
the Conquet-Penze Unit, microstructures
indicate a crystallization of garnet
and then staurolite during the development
of S1 and S2 foliations. Zoned
garnet in assemblages with staurolite
recorded prograde P–T paths from 490–
610°C at 5–8 kbar in the upper and at 6–
9 kbar in the lower parts of the CPMU. The foliation S2 was overprinted by shear bands with a top-to-
SW directed normal sense of shear, corresponding
to a dextral strike-slip movement
(Balé & Brun 1986).
A younger population of monazite with
variable Y contents displays Variscan
Th-U-Pb ages (EMP dating method)
between 340 and 300Ma. In
contrast, an older population of Cadomian
monazite at 552–517Ma is uniformly
rich in Y and was observed in
samples with only few or even no garnet.
As the 330–340Ma Saint Renan-
Kersaint granite postdates the foliations
S1 and S2 with peak metamorphic
assemblages one can conclude that
340–300Ma Variscan monazites should
postdate garnet crystallization.
Statistik:
View StatisticsSubjects:
Armorikanisches GebirgeVariskische Gebirgsbildung
Assyntische Faltungsphase
Metamorphose <Geologie>
Monazit
Geochronologie
Amorikanisches Massiv und Randzonen {Geologie}
Metamorphe Komplexe, übriges Europa {Petrologie}
Schwerminerale
Geochronologie einzelner Regionen im allgemeinen
Lanthanoiden Lanthaniden, Seltene Erden {Geochemie}
Analysedaten von Mineralen und Mineralparagenesen