engleski

Revealing hidden ages: The Cretaceous very low- to low-grade metamorphism recorded on illite fraction (Mt. Papuk)

The Slavonian Mountains, including Mt. Papuk, are located along the southern edge of the Pannonian Basin in the northeastern Croatia and are considered as one of the best exposures of the crystalline basement of the Tisia Unit which is locally covered by Permian-Mesozoic sediments. Jamičić (1983) distinguished three tectono-metamorphic units: (1) the Psunj (Kutjevo) medium-grade metamorphic complex ; (2) the Papuk (Jankovac) medium-grade metamorphic complex, and (3) the Radlovac very low-grade metamorphic complex. This research is based on Radlovac metamorphic complex and Kutjevo transect samples (including sedimentary rocks and Psunj (Kutjevo) metamorphic complex). Analyzed samples comprise different varieties of rocks with different petrological characteristics and age which, according to Jamičić & Brkić (1987), range from Late Precambrian to Early Triassic (Fig. 1). K-Ar dating was performed on whole rock, <6μ m and <2μ m fractions of nine samples for which Kübler index values indicate thermal alterations of approx. 300°C. Cretaceous ages, not registered so far, show systematic difference between whole rock ages and ages obtained on separated finer fractions. This difference is expected due to increasing modal proportion and prolonged formation of the clay minerals. The prolonged clay mineral formation took place below the closure temperatures of most mineral constituents of the rock. This suggests that the oldest K-Ar ages constrain the lowest age for the metamorphic event which have reset all mineral ages in the dated rock. The youngest ages (measured on <2μ m fractions) set the oldest limit for the termination of illite formation.

K-Ar ages ; Cretaceous ; metamorphism ; illite ; Papuk

nije evidentirano