Zircon ages of high-grade gneisses in the Eastern Erzgebirge (Central European Variscides)—constraints on origin of the rocks and Precambrian to Ordovician magmatic events in the Variscan foldbelt

摘要: This study is an attempt to unravel the tectono-metamorphic history of high-grade metamorphic rocks in Eastern Erzgebirge region. Metamorphism has strongly disturbed primary petrological genetic characteristics rocks. We compare geological, geochemical, and data, zircon populations as well isotope geochronological data for major gneiss units Erzgebirge; (1) coarse- medium-grained “Inner Grey Gneiss”, (2) fine-grained “Outer (3) “Red Gneiss”. The Inner Outer Gneiss (MP–MT overprinted) have very similar geochemical mineralogical compositions, but they contain different populations. found be igneous origin documented by presence long-prismatic, oscillatory zoned zircons (540 Ma) relics granitic textures. Geochemical classify precursor a S-type granite. In contrast, samples are free long-prismatic with signs mechanical rounding through sedimentary transport. indicate greywackes main previous precursor. most euhedral document Neoproterozoic (ca. 575 source eroded form these greywackes. U–Pb-SHRIMP measurements revealed three further ancient sources, which survived both Gneiss: (600–700 Ma), Paleoproterozoic (2100–2200 Archaean (2700–2800 Ma). These results point absence Grenvillian type sources derivation crust from West African Craton. granite magma was probably derived situ melting protolith indicated geological relationships, composition, Nd model ages, inherited ages. Red occurs separate bodies within fine- grey gneisses gneiss–eclogite zone (HP–HT overprinted). comparison Gneisses, clearly differs composition lower contents refractory elements. Rocks (480–500 zonation indicating protoliths. display obvious granites partial deeper crustal obtained time marks magmatic activity Ma, ca. 540 500–480 compared adjacent Saxothuringian zone. all units, pattern prove evolution during Neoproterozoic–Ordovician time.