High-Mg chloritoid (X_Mg = 0·40–0·47) and relatively high-Mg staurolite (X_Mg = 0·25–0·28) coexisting with kyanite and garnet were identified in a mica–garnet-rich rock associated with very high-pressure eclogites in the Bughea Complex of the Leaota Massif (South Carpathians). Major and trace element geochemical data for both fresh eclogites and associated rocks which represent a metasomatic or retrograde alteration rind of the eclogites, indicate a pelitic precursor. Magnesian chloritoid was found as inclusions in garnet as part of a chloritoid–kyanite–garnet assemblage which is indicative of high-pressure conditions. The host garnet shows a typically prograde chemical zoning pattern. The chloritoid-bearing assemblage is confined to the inner part of the garnet porphyroblasts, whereas the matrix assemblage in equilibrium with Mg-rich garnet rims has exceeded the thermal stability limit of chloritoid. Pressure–temperature pseudosections for simplified compositions approaching the rock bulk-chemistry show a high-pressure field for the identified chloritoid-bearing assemblage in good agreement with pressure–temperature estimates in the CFMASH and KCFMASH chemical subsystems using analysed mineral compositions. The derived pressure–temperature path is clockwise, indicating overprinting during exhumation from 1·8 GPa and 580°C to 1·15 GPa and 620°C, at a water activity approaching a_H2O = 1. These conditions were attained in a subduction mélange indicating transient thermal perturbations of a subduction channel.

The Tisza and Dacia mega-units constitute a central part of the Alps-Carpathians-Dinarides orogenic system. Polyphase medium-grade metamorphism observed in mineral assemblages from the crystalline basement is often correlated with Variscan and pre-Variscan events. However, a mid-Cretaceous Sm–Nd garnet age (103.6 ± 1.8 Ma) from the Apuseni Mountains is at odds with this interpretation. Electron-microprobe U-Th–Pb dating of monazite in samples from the Apuseni Mountains, the Rodna Mountains, as well as the Şimleu Silvaniei, Ticău and Preluca inselbergs revealed a complex pattern of Alpine and pre-Alpine age clusters. Pre-Variscan and Variscan ages were obtained from the core of zoned monazite grains and from samples that apparently escaped Alpine overprinting. Relic monazite in the latter is often replaced by rhabdophane and/or surrounded by allanite coronas. Permian to Early Triassic monazite ages correlate with the intrusion of granitic melts and pegmatites. Early Cretaceous ages from rims of chemically zoned grains and from monazite inclusions in garnet, biotite and staurolite represent newly formed metamorphic grains that crystallized on the prograde path during Alpine metamorphism. Petrographic observations of prograde allanite breakdown reactions, Sm–Nd garnet analyses and thermobaric estimates (500–550 °C/5–8 kbar) from parts of the Tisza and Dacia mega-units constrain medium-grade conditions during Early Cretaceous times. Exclusively mid-Cretaceous monazite ages from the inselbergs and the Rebra-Unit of the Rodna Mountains, allow extending the Alpine prograde overprint across the Transylvanian basin. Together with other studies from the basement of the Pannonian basin, this implies that the Dacia Mega-Unit and parts of the Tisza Mega-Unit experienced a medium-grade metamorphic overprint and synkinematic garnet-growth during late Early Cretaceous times. The Alpine prograde medium-grade overprint is pronounced in the contact zone between the Tisza and Dacia mega-units and forms a continuous belt with the Cretaceous metamorphic imprint in the Eastern Alps, when back-rotated to its original position during the Cretaceous.

A retrogressed eclogite from the Lotru Metamorphic Suite in the South Carpathians containing peraluminous sapphirine in the fine-grained breakdown assemblage replacing kyanite was subjected to detailed petrographic and analytical studies. Textural analysis reveals that sapphirine is not directly related to decomposing kyanite; instead it grew by digestion of former spinel-bearing symplectites, which, together with corundum + plagioclase intergrowths, replaced kyanite as a first step. Initial kyanite breakdown to plagioclase, spinel, and corundum occurred through metasomatic addition of Ca, Na, Mg, and Fe, while Al and Si behaved as immobile components at the scale of the aggregate. The mechanism responsible for the breakdown was fluid-mediated intergranular diffusion of the mobile elements. All kyanite pseudomorphs exhibit a domain structure containing the alternative corundum + plagioclase or spinel + plagioclase two-phase assemblages, bounded by monomineralic plagioclase seams, across which short-scale ...