Evolution of the arc-derived orthogneiss recorded in exotic xenoliths of the K?r?s Complex (Tisza Megaunit, SE Hungary)

摘要

The pre-Neogene basement of the Pannonian Basin consists of different terranes, which became juxtaposed during subsequent tectonic events from the Palaeozoic up to the Miocene. One of the largest terranes is the Tisza?Megaunit, an assemblage of metamorphic blocks of different lithology and P-T-t-d evolution. In the present study, petrological data?from orthogneiss bodies representing numerous neighbouring crystalline highs hidden beneath sediments of the Pannonian Basin are presented. Characteristic textures and mineral assemblages of the orthogneisses are identical in the whole studied area. Based on geochemical data, the orthogneiss precursor was quartz monzodiorite to granodiorite. The metamorphic conditions were estimated at around 580-600 °C based on two-feldspar thermometry, co-existing amphibole-plagioclase equilibria, and Theriak/Domino modelling. The most conspicuous petrographic feature of the orthogneiss is the presence of various types of xenoliths and xenocrysts. Most xenoliths are mafic and represent eclogite and diverse amphibolite varieties, but ultramafic, carbonate, and felsic granulite also occur. All record LP-HT (low pressure, high temperature) overprint under the same conditions at which the orthogneiss formed. Evolution of the orthogneiss body can be understood in the frame of the subduction-accretionary model. Xenoliths of various origins could represent an accretionary prism material that was picked up by the ascending granitoid melt that was subsequently solidified and metamorphosed to an?orthogneiss.