Mineralogy and Petrology (2000) 70: 121±141 Petrology and geochemistry of Paleogene tonalites from the easternmost parts of the Periadriatic Zone J. Pamic  1 and L. Palinkas Ï 2 1 Croatian Academy of Sciences, Zagreb, Croatia 2 Department of Mineralogy, Petrology and Geochemistry, University of Zagreb, Croatia With 10 Figures Received July 7, 1999; revised version accepted November 26, 1999 Summary The Pohorje Mts. and Karavanke plutons occur in the easternmost parts of the Periadriatic Zone separating the Eastern Alps from the Southern Alps and the northwesternmost Dinarides, respectively. The plutons, which are composed largely of tonalites with subordinate granodiorites and rare diorites mainly of medium-K calc- alkaline af®nity, are part of a series of mid-Tertiary intrusives emplaced over 700 km E-W along the Periadriatic Zone. Major and trace element data indicate that gabbrodiorites originated by fractional crystallization of a primary ma®c magma, but with a signi®cant contribution of continental crust. REE patterns are steep and characterized by LREE enrichment, and a weak Eu anomaly, suggesting fractional crystallization of primary ma®c magma. 87 Sr/ 86 Sr ratios indicate that on the basis of Sr isotopic composition an upper mantle melt contribution cannot be recognized. The 87 Sr/ 86 Sr vs.  18 O diagram demonstrates that all analyzed rocks plot near the centre of the Adamello pluton ®eld. Tonalite plutonism was genetically controlled by previously subducted Mesozoic oceanic crust, metasomatized upper mantle wedge, and overlying continental crust. All analytical data obtained indicate that primary ma®c magma was of olivine tholeiite af®nity. Based on element modelling data it is reasonable to assume that a garnet peridotite, probably slightly metasomatized, was the source rock which was subjected to partial melting. The governing AFC processes resulted in crustal isotopic signatures due to crustal assimilation and melting which produced the most acid members of the tonalite suite.