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Granulite massifs and high-grade gneisses, exposed on the surface in the Moldanubian and Saxothuringian zones (Bohemian Massif), usually contain lenses of eclogites and garnet peridotites. The peridotites have affinity to lithospheric mantle rocks and their textural relations show pressure increase from spinel to garnet facies, reaching UHP conditions. Beside eclogites associating with mantle peridotites, some eclogites have composition of subalkaline basalt and contain prograde zoning garnet with kyanite.
They indicate pressures similar to that in garnet peridotites (up to 3.5 GP/850 oC). With exception of UHP conditions, based on the coesite- and diamond-bearing gneisses from the Saxothuringain zone, thermobarometric calculations give maximum 2-2.3 GPa pressures for the rest gneisses and granulites. Their HP mineral assemblages with ternary feldspars, quartz, garnet, kyanite and rutile are mostly reequilibrated during high-temperature/medium- to low- pressure granulite and amphibolite facies overprint.
It is not always clear, if the surrounding felsic granulite experienced medium-temperature eclogite facies metamorphism or they have lower crust origin. The studied granulites are characterized by the presence of leucocratic stripes and discrete veins sub-parallel to the foliation, which similar to the host felsic granulite contain garnet and kyanite. In addition to inclusions of Ti-rich muscovite, some garnet encloses pseudomorphs after muscovite and amphibole (?). They are represented by K-feldspar + Al-rich phase or by plagioclase + Fe phase, respectively. Garnet composition depends on bulk rock compositions and on the degree of partial melting of granulites. The host granulite contains Ca-rich garnet (Grs43) and garnet of similar composition occurs in the core of low-Ca and high-Mg garnet in the leucocratic stripes.
The mantle garnet has diffusion rim, formed during cooling, but shows high compositional gradient to the garnet core. The felsic granulites usually have layers and lenses of mafic granulites which contain diopsidic clinopyroxene and/or orthopyroxene. As omphacite was found as inclusions in garnet, the presence of diopside and orthoyroxene is evidence for decompression to medium/lower pressure conditions in most mafic granulites. In addition to eclogite with prograde zoning garnet, some Ca-rich garnet from felsic granulite also shows a slight zoning profile with rimward increase of Mn that is typical for a prograde zoning garnet. Such zoning together with high compositional gradient between the core and rim of garnet in the leucocratic stripes suggest for prograde metamorphism of crustal rocks in subduction zone with relatively short-time granulite facies metamorphic overprint.
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