engleski

Petrology and geochemistry of Paleogene tonalites from the easternmost parts of the Periadriatic Zone

The Pohorje Mts. and Karavanke plutons found in the easternmost parts of the Periadriatic Zone are composed largely of tonalites with subordinate granodiorites and rare diorites with prominant cumulate structure grading into gabbros. The analyzed rocks display largely medium-K calc-alkaline affinity, but the most basic rock is an olivine tholeiite. Major and trace element data indicate that gabbrodiorites originated by fractional crystallization of a primary mafic magma, but some trace element data of tonalites indicate a significant contribution of continental crust. REE are characterized by enriched suggesting fractional crystallization of primary mafic magma during which separation of amphibole of edenite-pargasite composition was favoured over that of clinopyroxene. The mesured 87Sr/86Sr ratio and ?18O vary from 0.7067-0.7076 vs. 6.7-7� for gabbrodiorites, 0.7071-0.7070 vs. 7.7-7.9� for granodiorites and 0.7079-0.7081 vs. 8.1-8.3� for tonalites, indicating that only on the basis of Sr isotopic composition no real upper mantle melt can be recognized. The 87Sr/86Sr vs. ?18O diagram demonstrates that all analyzed rocks plot in the middle parts of the Adamello field. All analytical data obtained indicate that primary mafic magma was of olivine tholeiite affinity. Based on element modelling data it is reasonable to assume that metasomatized pargasiteągarnet lherzolite was the source rock which was subjected to partial melting. The governing AFC processes produced crustal isotopic signatures due to crustal assimilation and melting which produced the most acid members of the tonalite suite.

Periadriatic Line; Oligocene; gabbro-diorite; tonalite; granodiorite; major-trace elements

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