International Geologiical Congress - Oslo 2008

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MPN-01 General contributions to metamorphic petrology

 

Geochemistry and provenance of metasedimentary rocks of the radlovac metamorphic complex, Papuk, Croatia

 

Vanja Bisevac, University of Zagreb, Faculty of Science (Croatia)
Drazen Balen, University of Zagreb, Faculty of Science (Croatia)
Friedrich Finger, University of Salzburg (Austria)
Darko Tibljas, University of Zagreb, Faculty of Science (Croatia)
 

 

Radlovac low grade metamorphic complex, situated on Mt. Papuk 200 kilometers east from Zagreb, comprise typical low-grade metamorphic rocks (slates, phyllites, metasandstones and metaconglomerates) intruded by sills of metabasic igneous rocks. Biostratigraphy determined by Brkic et al. (1974) indicate Carboniferous age.
Whole rock chemical analyses of metasedimentary rocks of Radlovac metamorphic complex provide insight into their provenance and depositional history. Two sample groups (metapelites and metapsammites) were distinguished by their texture and geochemical data. Major elements data clearly differentiate metapsammites from metapelites by their higher silica and lower Al2O3, Fe2O3, MgO and TiO2 contents. The content of Na2O and K2O show similarity between two groups, but tend to be higher in metapelites. Overall these results reflect the greater content of clay minerals (illite and chlorite) and advanced albitization of detrital plagioclase in metapelites. Based on the mostly K2O-rich modal composition of the metasediments and their uniformly low contents of Cr, V and Ni, we interpret that the source area(s) were dominated by felsic igneous or metaigneous rocks (or metasediments derived from such rocks). Systematically high Th/Sc in metapelites (0,8-1,5) and even higher in metapsammites (1,1-6,0), together with Y/Ni-Cr/V and Ni-TiO2 relationships indicate that mafic or ultramafic rocks were absent or, at most, volumetrically very minor in the source(s). Slight positive Cr, V and Ni anomalies on upper continental crust normalized element distribution diagram indicate minor contribution of the mafic rocks as source material for the metapelites (2-3% according to Y/Ni-Cr/V relationship). An attempt was made to evaluate the paleotectonic settings of the Radlovac metasediments using discrimination diagrams based on relatively immobile trace elements (Bathia and Crook, 1986). In the ternary La-Th-Sc and Zr/10-Th-Sc discrimination diagrams samples plot preferentially in the continental arc (metapelites) and the passive margin field (metapsammites).
The geochemical data together with age dating of detrital monazite from metapsammite (Carboniferous age) are consistent with a model according to which the metasediments of the Radlovac metamorphic complex represent the detritus of the surrounding granites, migmatites and metamorphic rocks of the local Variscan crust.

References:

Bathia, M.R. & Crook, K.A.W. (1986): Trace elements characteristics of graywackes and tectonic setting discriminations of sedimentary basins. Contrib. to Mineral. Petrol., 92, 181-193.
Brkic, M., Jamicic, D. & Pantic, N. (1974): Carboniferous deposits on Papuk (northeast Croatia). Geol. vjesn., 27, 53-58, Zagreb (in croatian).

 

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