The juxtaposition of eclogite and mid-crustal rocks in the Orlica-Snieznik Dome, Bohemian Massif

Eclogite, felsic orthogneiss and garnetstaurolite metapelite occur in a 5 km long profile in the area of Miedzygorze in the OrlicaSnieznik dome (Bohemian Massif). Petrographic observations and mineral equilibria modelling, in the context of detailed structural work, are used to document the close juxtaposition of high-pressure and medium-pressure rocks. The structural succession in all lithologies shows an early shallow-dipping fabric, S1, that is folded by upright folds and overprinted by a heterogeneously developed subvertical foliation, S2. Late recumbent folds associated with a weak shallow-dipping axial-plane cleavage, S3, occur locally. The S1 fabric in the eclogite is defined by alternation of garnet-rich (grs = 2229 mol.%) and omphacite-rich (jd = 3336 mol.%) layers with oriented muscovite (Si = 3.263.31 p.f.u.) and accessory kyanite, zoisite, rutile and quartz, indicating conditions of similar to 1922 kbar and similar to 700-750 degrees C. The assemblage in the retrograde S2 fabric is formed by amphibole, plagioclase, biotite and relict rutile surrounded by ilmenite and sphene that is compatible with decompression and cooling from similar to 9 kbar and similar to 730 degrees C to 56 kbar and 600-650 degrees C. The S3 fabric contains in addition domains with albite, chlorite, K-feldspar and magnetite indicating cooling to greenschist facies conditions. The metapelites are composed of garnet, staurolite, muscovite, biotite, quartz, ilmenite and chlorite. Chemical zoning of garnet cores that contain straight ilmenite and staurolite inclusion trails oriented perpendicular to the external S2 fabric indicates prograde growth, from similar to 5 kbar and similar to 520 degrees C to similar to 7 kbar and similar to 610 degrees C, during the formation of the S1 fabric. Inclusion trails parallel with the S2 fabric at garnet and staurolite rims are interpreted to be a continuation of the prograde path to similar to 7.5 and similar to 630 degrees C in the S2 fabric. Matrix chlorite parallel to the S2 foliation indicates that the subvertical fabric was still active below 550 degrees C. The axial planar S2 fabrics developed during upright folding are associated with retrogression of the eclogite under amphibolite facies conditions, and with prograde evolution in the metapelites, associated with their juxtaposition. The shared part of the eclogite and metapelite PT paths during the development of the subvertical fabric reflects their exhumation together.