K-rich plutonic rocks and lamprophyres from the Meissen Massif (northern Bohemian Massif): Geochemical evidence for variably enriched lithospheric mantle sources
Wenzel, Thomas; Oberhänsli, Roland; Mezger, Klaus
published: Sep 1, 2000
ArtNo. ESP154017503002, Price: 29.00 €
K-rich plutonic rocks and lamprophyres from the Meissen Massif (northern Bohemian Massif) intruded at about 330 Ma in the Elbe Zone. The plutonic complex consists of about 50 % gabbroic to mainly monzonitic rocks and of about 50 % granites. The gabbroic to monzonitic rocks are characteristic of the shoshonitic suite in their strong enrichment in LILE and LREE and a relative depletion of HFSE. The slightly silica-undersaturated gabbroic rocks (SiO2 53 wt. %) crystallized mainly from a more differentiated, more enriched magma pulse. Additionally, the monzonites are affected by crustal contamination including mechanical entrainment of zircon and apatite. Similar ƐNd(330 Ma)-values of the majority of the gabbroic to monzonitic rocks and a kersantite demonstrate that these rock types can be derived from similar sources probably enriched by subduction of oceanic crust. In contrast, associated minette dikes originated from CLM sources with evolved 87Sr/86Sr (330 Ma) ratios of 0.70686 to 0.70738 and ƐNd(330 Ma) of -4.1 to -4.3. The most primitive minette sample with the lowest Nb content is most enriched in Th (91 ppm) and U (23 ppm) which is typical for K-rich rocks from CLM modified by subduction of upper continental crust. Upper Devonian/Lower Carboniferous subduction and collision processes are thought to be responsible for the formation of variably enriched CLM domains from which the several K-rich Meissen magmatic rocks were extracted about 20 Ma later. Melt formation and intrusion are directly related to strike-slip along the Elbe Zone.