Eclogitic garnet amphibolite samples from the Southern Steep Belt of the Central Alps show evidence of several stages of metamorphic evolution and exhumation. A method for unravelling this evolution is presented and applied to these samples. It involves a combination of detailed petrographic analysis and microchemical characterization with quantitative models of the thermodynamically stable phase relations for speci®c compositional domains of each sample. Preserved mineral relics and textural evidence are compared to model predictions to identify the important irreversible reactions. The interpretation of the exhumation history is thus based on the consistency of a wide spectrum of observations with predicted phase diagrams, leading to robust reconstruction of a pressure±temperature (P±T) path even where the mineralogical relics in samples are insuf-®cient, due to retrogression, to warrant application of multi-equilibrium thermobarometric techniques.The formation of compositionally different domains in the metabasalt samples studied is attributed to prograde growth of porphyroblasts (e.g. garnet, plagioclase, zoisite) in the matrix, implying substantial metamorphic differentiation at the scale of a few millimetres. Chemical interaction among different domains during the subsequent P±T evolution is shown to have been very limited. This led to different reaction sequences during exhumation, in which relics preserved in different domains re¯ect a range of continually changing P±T conditions. For samples from a single outcrop, we deduce a Barrovian prograde path to eclogite facies (23 AE 3 kbar, 750 AE 50 C), followed by (rapid) decompression to 8 AE 1 kbar and 675 AE 25 C, and a ®nal heating phase at similar pressures reaching 750 AE 40 C. This evolution is attributed to the Alpine cycle involving subduction3collision and slab breakoff3extrusion of tectonic fragments that make up the Southern Steep Belt of the Central Alps. Figure 1. (a) Tectonic overview of the Southern Steep Belt (SSB) and adjacent crystalline nappes of the Central Alps near Bellinzona. Ma®c lenses in the SSB and Cima Lunga unit commonly preserve eclogite-facies relics. Samples analysed in this study are from one such location, immediately north of the village of Gorduno. (b) Eclogitic amphibolite lens (grey) enclosed in migmatitic biotite gneiss of the Zone of Mergoscia-Arbedo in the SSB.Outcrops near the road from Gorduno to Alpe Arami show a weak foliation de®ned by the highpressure assemblage inside the lens. The strong foliation of enveloping gneisses is virtually perpendicular and lies in the regional E±W strike of the SSB. 164t. m to  th, v. grandjean and m. engi

The Pannonian Basin consists of several deep sub-basins separated by uplifted basement highs. One of the largest and deepest sub-basins is the Be Âke Âs Basin in SE Hungary which is surrounded to the north by several crystalline domes. Of these, the Szeghalom Dome is the best known petrologically, and has been used for studying the Neogene exhumation history of the area.On the basis of metabasite bulk chemistry, the Szeghalom Dome can be subdivided into four distinct zones, the borders of which correspond closely to geophysical anomalies. The four zones exhibit different pre-Variscan and Variscan pressure±temperature± time (P±T±t) histories. In zone I, high-pressure relics (600 C, >12 kbar) occur. Peak-metamorphic conditions of the main Barrovian overprint were c. 700 C and 6 kbar, and amphibole K/Ar ages scatter around 260 Ma. Zone II shows similar characteristics, with the formation of anatectic granite at peak conditions. K/Ar ages are as low as 220 Ma. Zones III and IV show similar evolution to each other with high-grade Barrovian relics (700 C), peak metamorphism at 570 C and amphibole ages of 300 Ma.Throughout the dome, ®ngerprints of a three-fold Neogene tectonic evolution can be observed. An early detachment fault formed quartz±feldspar±mylonite in zone IV, while chloritic breccia developed at the border of zones II and III. Following the thermal subsidence phase of the basin evolution, the area was dominated geodynamically by the reactivation of older strike-slip fault systems. These movements were responsible for the horizontal transport of the crystalline blocks at both the southern and northern¯anks of the dome.