Tracing the cryptic Sardic (Ordovician) metamorphism across Alpine Europe: the Krndija region in the Slavonian Mountains, Croatia

Results of a combined petrological, geochemical and geochronological study suggest that metasedimentary rock units in the Krndija region of the Slavonian Mountains, Croatia, were affected by at least three major tectonometamorphic imprints: during the Middle Ordovician (Sardic event), the early Carb...

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Published in:	International journal of earth sciences : Geologische Rundschau 2023-04, Vol.112 (3), p.829-853
Main Authors:	Mayer, B. Starijaš, Zeh, A., Krenn, E., Gerdes, A., Finger, F.
Format:	Article
Language:	eng
Subjects:	Alpine regions Andalusite Arc deposition Cambrian Carboniferous Cretaceous Earth and Environmental Science Earth Sciences Electron microprobe Electron probes Exposure Garnet Garnets Geochemistry Geochronology Geology Geophysics/Geodesy Gondwana Ilmenite Isotopes Lithology Magma Metamorphism Metamorphism (geology) Mineral Resources Monazite Mountains Ordovician Original Paper Orogeny Radiometric dating Rock Rocks Rutile Sedimentology Segments Structural Geology Subduction
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Summary:	Results of a combined petrological, geochemical and geochronological study suggest that metasedimentary rock units in the Krndija region of the Slavonian Mountains, Croatia, were affected by at least three major tectonometamorphic imprints: during the Middle Ordovician (Sardic event), the early Carboniferous (Variscan event), and the Cretaceous (Alpine event). All three metamorphic phases are established by electron microprobe-based in-situ U–Th–Pb dating of monazite grains. The Sardic metamorphic event is additionally confirmed by a precise Lu–Hf garnet-whole-rock isochron age of 466.0 ± 2.3 Ma. Taken together, the data unveil a relatively large and well-preserved piece of the cryptic Sardic orogen in central Krndija, that we name the Kutjevo Zone. A Sardic subduction-related metamorphic event (ca. 540-580 ℃, 8–11 kbar) at ca. 466 Ma is manifested in the mineral paragenesis Ca-rich garnet plus rutile. A low degree of retrograde reequilibration suggests a subsequent fast exhumation. Low-Ca cores in some garnets and staurolite relics record a pre-HP metamorphic event that involves isobaric heating from 570 to 610 ℃ at ~ 7 kbar. We attribute this (so far undated) event to mid-crustal contact metamorphism caused by early Sardic magmatism. Southern parts of Krndija (the Gradište Zone) experienced an (additional?) clockwise PT evolution in Variscan times at ca. 350 Ma. Garnet formed with ilmenite during a PT increase from 580 ℃/5 kbar to 600 ℃/6 kbar and underwent later strong retrograde resorption. Slow Variscan exhumation resulted in andalusite formation at
ISSN:	1437-3254 1437-3262