Age and geochemical constraints for partial melting of granulites in Estonia

Trans-Baltic Palaeoproterozoic correlations towards the reconstruction of supercontinent Columbia/Nuna

“…Chemically, some charnockites can be attributed to a calc-alkaline I-type series, likely generated due to the melting of lower crust under granulite facies conditions along with the emplacement of mafic dykes at ca. 1.77 Ga (Soesoo et al, 2006). This is somewhat younger than the 1.81 Ga age of granulite facies metamorphism in northern Latvia (Mansfeld, 2001), into which the SEG domain continues.…”

“…In the present study, the ages of the granulite-facies metamorphism in the West Estonian metasedimentary rocks (sample Valgu 99) and the granulites of the South Estonian domain (sample Kõnnu 300) were of particular interest because of the previously reported 1.78-1.75 Ga ages of their metamorphism Soesoo et al, 2006), which are much younger than anything known from comparable Svecofennian parts of the Baltic/Fennoscandian Shield. Summing up the new and previous datings of the granulites in Estonia, we conclude that they were formed by several events, comprising:…”

“…1), the Tallinn (TN), Tapa (T) and Alutaguse (Al) differ markedly from the other Estonian tectonic units by their dominantly amphibolite facies of metamorphism that passes gradually into the granulite facies at ca. 3-5 kbar (Puura et al, 1983;Soesoo et al, 2006). They are made up of metasedimentary and metavolcanic rocks ca.…”

“…(a) high-temperature melting of the crust and crystallization of Stype garnet-orthopyroxene granodiorites (sample Kõnnu 300) in the lower-middle crust at 1891 ± 3 Ma followed by slow cooling and retrogression in the granulite to high amphibolite facies along with deformation at 1858 ± 4 Ma; (b) burial and lower granulite-facies metamorphism of the West Estonian sedimentary rocks (sample Valgu 99) in the middle crust at 1842 ± 1 Ma followed by slow uplift and retrogression along a near-isobaric evolution path similar to the path of the Kõnnu 300 granulite ; (c) shearing of the crust on both sides of the Middle Estonian fault zone at 1798 ± 2 Ma (sample Valgu 99), semi-simultaneously with mafic dyking at 1774 ± 20 Ma (Soesoo et al, 2006). The final uplift of the Estonian granulites into the upper crust occurred at 1728 ± 24 Ga (garnet Sm-Nd age, Puura et al, 2004).…”

“…2a), which have been intruded by 1.77 Ga metagabbro-norites (Soesoo et al, 2006). The dated granulite, sampled from a core depth of 515 m, has been derived from a coarse-grained S-type granodiorite, formed by the high-T melting of mixed sources, probably comprising rocks of various compositions, like greywacke, semipelites, and even mafic rocks.…”