Triassic Magmatism in the Area of the Central Dinarides (Bosnia and Herzegovina): Geochemical Resolving of Tectonic Setting

Triassic magmatic rocks in the Central Dinarides in Bosnia and Herzegovina are known from two separate geotectonic units: (1) the Adriatic Carbonate Platform (Outer Dinarides) and (2) the Palaeozoic–Triassic allochthonous complex. They are assigned to the same regional, genetic and geochemical unit. Their emplacement age is inferred from contacts with the surrounding marble and sedimentary rocks (post-Anisian for intrusives and Ladinian for effusives). The magmatic rocks display different levels of emplacement and crystallization (intrusive, effusive and dyke rocks). They represent different stages of magmatic differentiation, from gabbro/basalt via diorite/andesite to granodiorite/dacite and granites. The most frequent dyke rock is diabase. Pillow basalts indicate eruption under subaquatic conditions. Pyroclastic rocks within the volcano–sedimentary unit point to the temporary explosive character of orogenic magmatic activity. Most rocks are affected and modified by post-magmatic alteration and hydrothermal fluids. This led to the formation of spilite, keratophyre, quartz keratophyre and rarely K spilite. New geochemical data support the opinion that subduction was the main process which triggered the Triassic magmatic activity in the Central Dinarides. Although some of the investigated rocks reveal MORB characteristics (in the selected geochemical discriminations), most samples are enriched in all elements which are reported as characteristic for arc magmatism at convergent margins including incorporation of sediments

Origin of the Jurassic Tethyan Ophiolites in Bosnia: A Geochemical Approach to Tectonic Setting

The ophiolites from Bosnia are products of the Jurassic spreading of the Neo-Tethys, and are fragments of a long chain of ophiolites of the same origin. Their geological characteristics are the absence of a sheeted dyke complex and the tectonic disruption of the cumulate sequence. Upper crust volcanics as well as lower crust cumulates show low metamorphic changes of the prehnite/laumontite type, except for some marginal localities of large ophiolite massifs (Visegrad, Konjuh, Krivaja, Ozren) in which the metamorphic grade reaches the amphibolite facies. The characteristic features of these ophiolites are as follows: The mantle rocks are lherzolites and harzburgites, both characterized by a negative Eu-anomaly and a few of them have a negative Ce anomaly, which is explained as alteration due to contact with sea water. The cumulate rocks are gabbroic to ultramafic. Numerous amphibolites reveal a chemical character of cumulus rocks. Early crystallization of plagioclase in the magma chamber caused positive Eu anomalies in these rocks. The upper crust rocks are basalts, diabases and gabbros. Most of them reveal REE patterns which are typical for basalts from constructive plate margins. A few of them which have a slight enrichment of LREE are explained as the partial melt products of a mantle less depleted than the one which produced the majority of basalts. Chemical discrimination diagrams show that the magmatic rocks are of the mid-oceanic ridge type, i.e. that they formed at the spreading of oceanic plates without any influence from a subducted slab. A comparison with recent spreading zones shows that ophiolites of the described type (absence of a sheeted dyke complex, areas of tectonic disruption in the upper and lower crust, local amphibolitisation and eruptions of “enriched” MORB) probably have formed in areas of the intersection of spreading and a transform fault. In most of their characteristics the ophiolites from Bosnia show a close similarity to the Ligurian ophiolites which obducted in about the same period of time and which are also products of the spreading of Neo-Tethys