Publisher © Czech Geological Survey, ISSN: 2336-5757 (online), 0514-8057 (print)
Isotopic geochemistry and geochronology of the skarn from Slatina, Moldanubian zone of the Bohemian Massif
Abstract
Nd isotopic dating of garnet-pyroxene skarn from Slatina (20 km N of Znojmo, Gföhl nappe of the Moldanubian unit) indicates a major metamorphic event at 415 ˝ 24 Ma (2ň; WR-grt-cpx isochron with MSWD = 0.07). This is, within an error, identical with an age calculated on the basis of the grt-WR pair only (420 ˝ 42 Ma) and resemles Sm-Nd metamorphic ages of eclogite and granulite from Winklarn, Bavaria (von QUADT - GEBAUER 1993). As the closure temperature of the Nd diffusion in garnet is high (MEZGER 1990, HENSEN - ZHOU 1995), the obtained ages are interpreted as being close to the garnet growth during the high-grade metamorphism. Significantly lower e415Nd for zircon (-8.4) compared to WR, cpx and grt (-7.3) probably indicates presence of older, inherited cores, which are indeed observable in the BSE. High Sr initial ratio (87Sr/86SR415 ~ 0.713), and, above all, the low ţ415Nd (-7.3) and high two-stage Nd model age (T DMNd = 1.7 Ga; LIEW - HOFMANN 1988) support a long crustal residence of the protolith and rule out its direct derivation from depleted or CHUR-like mantle in Silurian-early Devonian times.
