Electron probe petrochronology of monazite- and garnet-bearing metamorphic rocks in the Saxothuringian allochthonous domains (Erzgebirge, Granulite and Münchberg massifs)

In the Saxothuringian Zone, a unique assemblage of high- to ultra-high-pressure and ultra-high-temperature
metamorphic units is associated with medium- to low-pressure and temperature rocks. The units were
studied in a campaign with garnet and monazite petrochronology of gneisses, micaschists and phyllites, and
monazite dating in granites. P–T path segments of garnet crystallization were reconstructed by geothermobarometry
and interpreted in terms of the monazite stability field, EPMA Th–U–Pb monazite ages and garnet Y +
HREE zonations. One can recognize (1) Cambrian plutonism (512–503 Ma) with contact metamorphism in the
Münchberg Massif. Subordinate monazite populations may indicate a (2) widespread but weak Silurian (444–
418 Ma) thermal event. A (3) Devonian (389–360 Ma) high-pressure metamorphism prevails in the Münchberg
and Frankenberg massifs. In the ultra-high-pressure and high-pressure units of the Erzgebirge the predominant
(4) Carboniferous (336–327 Ma) monazites crystallized at the decompression paths. In the Saxonian Granulite
Massif, prograde–retrograde P–T paths of cordierite-garnet gneisses can be related to monazite ages from 339 to
317 Ma. A (5) local hydrothermal overprint at 313–302 Ma coincides partly with post-tectonic (345–307 Ma)
granite intrusions. Such diverse monazite age pattern and P–T time paths characterize the tectono-metamorphic
evolution of each crustal segment involved in the Variscan Orogeny.