THE INTRUSION OF THE MEISSEN PLUTON (ELBE VALLEY-ZONE) - EVIDENCE FROM GEOCHEMICAL AND ISOTOPIC DATA

Geochemical and mineralogical investigations of plutonic rocks from th e Meissen massif indicate different magmatic evolution trends of the F reital sequence as well as for the central part of the complex [10]. C onstant epsilon-Nd(T-345) Values of -1.5 of the Freital sequence and m ajor/trace element data point to a fractional crystallization process. Based on epsilon-Nd values, Sm-147/Nd-144 ratios as well as on geoche mical data affinities to alkali basalts cannot be excluded. Analogous conclusions have been drawn regarding mineral chemical data [101 and c athodoluminescence spectra of apatite [13]. Assimilation of old contin ental crust, reflected by relics of apatite and zircon, may be the rea son that the epsilon-Nd values plot at the lower end of the ''mantle a rray''. The pyroxene-monzodiorite from Groba belongs to the same sourc e environment as the Freital sequence (Nd-characteristics). The geolog ical evolution of the central part of the studied plutonic complex is completely different to the Freital sequence: most of the intrusions s how signatures of open system fractionation processes. The epsilon-Nd( T-345) value of -1.46 of the Leuben monzonite indicates a narrow relat ion to the Freital sequence, whereas the epsilon-Nd(T-345) value of +2 .27 of the Spitzgrund monzonite either reflects the derivation of anot her basic material then the Freital-type or the participation of other mixing component(s) from geologically young crust. Fabric and mineral chemical investigations of the porphyry-like granite GPI point to a m ixing process of basic xenocrysts, resembling the corresponding minera ls of the Freital sequence, and granite melts [10]. Large amounts of o ld zircon cores [11] indicate the inheritance of continental crust com ponents by the Hauptgranit. Isotopic investigations on various graniti c samples (GPI, Hauptgranit and Riesensteingranit) reflect an increasi ng trend towards the crustal source(s) of their parental melts. The ep silon-Nd(T-345) values are -3.75, -4.16 and -6.13, respectively. Chemi cal parameters and the epsilon-Nd(T) value of the Riesensteingranit ag ree with data of granites from the Saxonian Granulite Massif (see e.g. Wand et al. [8]; von Quadt, 1992). Thus, it may be possible that both granite types derived from similar sources.