SAME SAME BUT DIFFERENT – ZIRCONS FROM GRANITOIDS OF THE SAXONIAN GRANULITE MASSIF

Within the Saxonian Granulite Massif (SGM) four main types of granites can be distinguished according to their degree of deformation: i) Mittweida granite body, ii) Berbersdorf granite body, iii) granite gneisses (“Lagergranite”), and iv) smaller granitic dykes. Whereas the Mittweida granite is not deformed, the Berbersdorf granite is strongly to moderately and the granite gneisses are very strongly deformed. The smaller granitic dykes show every degree of deformation (Gottesmann 1987).

In this case study we compare zircons from i) the large granitic intrusion of Mittweida, from ii) a small dyke from Penig, and from iii) a granite gneiss from a sill collected near Hermsdorf. The whole amount of investigated zircon grains is about 400. They were separated by standard methods. Following analyses included CL- and BSE-imaging, the latter one to realize morphological studies after Pupin (1980). Finally, measurements of U-Th-Pb isotope ratios on zircons were performed by LA-SF-ICP-MS (Laser Ablation-Sector Field-Inductively Coupled Plasma-Mass Spectrometry).

First results show differences in morphology and ages of zircon populations from the different types of granite. The new data help to precise timing of exhumation and deformation processes within the SGM. In addition, they allow a better understanding of the final consolidation of the granulitic body.

Pupin, J.-P. (1980): Zircon and Granite Petrology. – Contributions to Mineralogy and Petrology, 73: 207-220, Berlin, Heidelberg.

Gottesmann, B. (1987): Petrographic studies of granite gneisses and granites from the Sächsisches Granulitgebirge. – In: H. Gerstenberger (Editor), Contributions to the Geology of the Saxonian Granulite Massif (Sächsisches Granulitgebirge). ZfI-Mitt., 133: 309-337, Leipzig.