Izvorni znanstveni članak

https://doi.org/10.4154/GC.2015.03

Petrology, geochemistry and tectono-magmatic affinity of gabbroic olistoliths from the ophiolite mélange in the NW Dinaric-Vardar ophiolite zone (Mts. Kalnik and Ivanščica, North Croatia)

†Boško Lugović
Damir Slovenec ; Hrvatski geološki institut
Ralf Schuster ; Austrian Geological Survey
Winfried H. Schwarz ; University of Heidelberg
Marija Horvat ; Croatian Geological Survey

Sažetak

Mafic intrusive rocks are subordinately represented fragments of the oceanic crust in the ophiolite mélange exposedat Mts. Kalnik and Ivanščica located in the NW Dinaric-Vardar ophiolite zone. This ophiolite mélange occurs in thenorthern area of the Kalnik Unit and represents the SW surface boundary of the Zagorje-Mid-Transdanubian ShearZone. The mélange, except for mafic intrusive rocks, consists of a chaotic mixture of various extrusive rocks formedin different tectonic settings of the Repno Oceanic Domain (ROD). The ROD was the segment of Neo-Tethys thatconnects the Meliata-Maliak and Dinaric-Vardar oceanic systems. Previous study of mafic extrusive sequences suggestedan 80 Ma period of tectono-magmatic evolution of the ROD from intra-continental rifting during the Anisian,to the formation of proto-arc crust during the Callovian-Oxfordian. The domain exposes ophiolitic rocks in four mélangeareas. Isotropic gabbroic rocks that are abundant in two northern areas (Mts. Kalnik and Ivanščica), can be discriminatedinto three distinct geochemical groups: (A) N-MORB-type gabbro [(Th/Nb)n = 0.99–1.10; (Nb/La)n =0.95–0.99], (B) IAT-type amphibole gabbro with clear supra-subduction characteristics [(Th/Nb)n = 6.04–8.16; (Nb/La)n = 0.32–0.42] and (C) BABB-type amphibole-bearing gabbro [(Th/Nb)n = 2.88–4.02; (Nb/La)n = 0.58–0.69].Representative gabbro samples of each geochemical group were dated by the Ar-Ar and/or the K-Ar dating method.The Early Jurassic N-MORB-type gabbros (geochemical group A), ~185 Ma old, signifies a peculiar stage of Palaeo-Tethyan slab break-off. The Late Jurassic IAT-type gabbros (geochemical group B), ~147 Ma old, is the vestige of anascent intra-oceanic arc, whilst the Early Cretaceous BABB-type gabbros (geochemical group C), ~100 Ma old,provides evidence of magmatism in the back-arc marginal basin. The analyzed gabbroic rocks enable refinement andcompletion of the geodynamic evolution of the ROD, from the opening of an ensialic back-arc basin during the Ladinianand a continuous spreading event until the Bajocian. Intra-oceanic convergence was initiated in the Bathonian,with the formation of a nascent island-arc during the Tithonian, leading to formation of a Cretaceous ensimatic backarcmarginal basin. There are many lines of evidence that correlate the geodynamic evolution of the ROD with theAlbanide-Hellenide Neo-Tethyan oceanic segment.

Ključne riječi

petrology and geochemistry; N-MORB; IAT; BABB; gabbro; ophiolite mélange; Dinaric-Vardar ophiolite zone; Mts. Kalnik and Ivanščica; Croatia

Hrčak ID:

141051

URI

https://hrcak.srce.hr/141051

Datum izdavanja:

27.2.2015.

Posjeta: 1.582 *