engleski

K-Ar dating of Cretaceous metamorphism recorded in the eastern part of Mt. Papuk, Slavonia, Croatia

The Papuk is a mountain in Slavonia, the northeastern region of Croatia, situated 200 km east from Zagreb located on the very edge of Požega Valley. Three metamorphic complexes, characterized with several phases of deformation and metamorphism, can be distinguished in the Slavonia region: Psunj (Kutjevo), Papuk (Jankovac) and Radlovac (JAMIČIĆ, 1983). The research is based on studies concerning the Radlovac metamorphic complex and the Kutjevo transect (including sedimentary rocks and Psunj metamorphic complex). Analyzed samples comprise different varieties of rocks of the different petrological characteristics and age (Table 1) which range from the Late Precambrian to the Early Triassic (JAMIČIĆ & BRKIĆ, 1987 ; JAMIČIĆ et al., 1987). K– Ar dating was performed on whole rocks and fraction <2 μ m. Concentration of potassium was determined by flamephotometryandtheamountofradiogenic40Ar was measured by isotope dilution. All samples were also studied with X-ray powder diffraction method (XRPD) to determine the mineral composition. The whole rock XRPD analysis on samples from the Radlovac metamorphic complex (R) and Kutjevo transect (K) yields quartz, illite– muscovite and chlorite in all samples, with K-feldspar in all “ K” samples and plagioclase in all “ R” samples. Hematite was found in sample K8, chloritoid in samples K4 and K7 and pyrophyllite in sample K4. According to the measured K– Ar data (Table 1), Cretaceous metamorphic (thermal) event(s) around 85 Ma (Figure 1), can be established. This metamorphism was recorded within the fraction <2 μ m i.e. “ illite fraction” , so these ages represent the time of dehydration of smectite and fixation of K+ cation in the crystal lattice of illite. The older whole rock ages can be explained by the well known fact that parametamorphic rock types frequently contain older, detrital components. References JAMIČIĆ, D. (1983): Structural fabric of the metamorphosed rocks on Mt. Krndija and the eastern part of Mt. Papuk (in Croatian).– Geol. vjesnik, 36, 51– 72. JAMIČIĆ, D & BRKIĆ, M. (1987): Basic Geological Map of Yugoslavia in scale 1:100000, sheet Orahovica.– Sav. geol. zavod Beograd. JAMIČIĆ, D., BRKIĆ, M., CRNKO, J. & VRAGOVIĆ, M. (1987): Basic Geological Map of Yugoslavia– Explanatory notes for sheet Orahovica (in Croatian).– Geol. zavod Zagreb (1986), Sav. geol. zavod Beograd, 72 p.

K-Ar ; age dating ; Cretaceous ; illite crystallinity ; very low grade metamorphism ; Papuk

nije evidentirano