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The origin conditions of primary and detrital scheelite related to the Variscan granites in the Central Sudetes (SW Poland)
Published in Adam Piestrzyński, Mineral Deposits at the Beginning of the 21st Century, 2001
The studied area (Fig. 1) is situated in Central Sudetes within the northern margin of the Bohemian Massif. Sudetes, an exposed Variscan orogen, is the easternmost part of the European Hercynian Belt. In this area Late Hercynian igneous rocks formed plutons different in shape, size and mineral composition and were emplaced in the continent-continent collision zones and the active margins of the continental plates above subduction zones. In Central Sudetes the Variscan granites are represented by the late-tectonic Kłodzko–Złoty Stok pluton built of I-type granites and the vein-type body of the syntectonic Jawornik granite. The magmatic rocks, derived from pre-collisional magmas and mantle fractionates (Lorenc 1994), comprise metaluminous calc-alkaline igneous rocks of cafemic association rich in biotite and hornblende. Late magmatic and post-magmatic activity formed dykes of spessartites, vogesites, pegmatites and quartz veins. This intrusion is interpreted as an Andean-type pluton within the European Hercynides (Lorenc 1994). The Kłodzko–Złoty Stok intrusion was formed during the Asturian phase of the Hercynian orogeny (K-Ar dating - 298 Ma; Depciuch 1972) and is about 35 Ma younger than the Jawornik granite. The roof part of the intrusion contains irregularly distributed relics of the Late Proterozoic to Early Paleozoic volcanic and sedimentary rocks comparable to the members of the Orlica-Śniežnik metamorphic complex adjacent to the intrusion in the east. The metamorphic complex is composed of Lower Paleozoic metasedimentary rocks intercalated with mafic and felsic metaintrusives and metavolcanics of the amphibolite facies.
Compositional characteristics of mineralised and unmineralised gneisses and schist around the Abansuoso area, southwestern Ghana
Published in Applied Earth Science, 2023
Raymond Webrah Kazapoe, Olugbenga Okunlola, Emmanuel Arhin, Olusegun Olisa, Daniel Kwayisi, Elikplim Abla Dzikunoo, Ebenezer Ebo Yahans Amuah
The gneisses of the study area have dominantly metaluminous to weakly peraluminous characteristics, contain moderate to high total alkalis (Na O2 + K2O = 2.71–8.38 wt-%), which are features usually associated with I-type granitoids, and the chemical composition suggests that they are products by partial melting of a mafic mantle-derived igneous source material (probably of a sub-crustal underplate, but subducted-slab crust or older high-level pluton sources cannot be excluded) (Barbarin 1990; 1999). The occurrence of biotite-hornblende and biotite-bearing gneiss rocks within the study area, and the absence of two-mica granitoids also rules out sediment contribution in the Abansuoso area (Grenholm 2011). The gneisses on the multi-element diagrams normalised to UCC show high HREE fractionation (Figure 8(c,d)). According to Grenholm (2011), the high degree of HREE-fractionation observed in some granitoids in the Birimian terrain of the WAC can be linked to the stability of garnet in the residue hence implying deeper crustal levels even though fractionation of HREEs may also be the result of residual accessory phases such as zircon. The trace element characteristics of the gneisses are akin to I-type rocks, and thus can be interpreted as derivatives from mafic igneous precursor (thickened mafic lower crust), generated in convergent margins (Liu et al. 2019; Sakyi et al. 2020).
Cleaning up the record – revised U-Pb zircon ages and new Hf isotope data from southern Sweden
Published in GFF, 2021
In spite of being relatively rich in mafic minerals, the sample has a granitic composition both in the TAS and P-Q diagrams, with 72.3 wt% SiO2 (Fig. 3). Like sample 84093, it plots just inside the field of metaluminous granitoids (A/CNK = 0.98) and is alkali-calcic, but it is ferroan rather than magnesian. Unlike all the other Eastern Segment gneiss samples, it falls on the boundary to A-type granites in Figure 3D, and inside the within-plate granite field in Figure 3E. Like the red gneiss sample 85015, sample 85018 has strong negative Ba, Nb, P and Ti anomalies, as well as a strongly negative Eu anomaly of 0.29, as it is similarly poor in plagioclase (Fig. 4).
Character and tectonic setting of plutonic rocks in the Gällivare area, northern Norrbotten, Sweden
Published in GFF, 2019
Zmar Sarlus, Olof Martinsson, Tobias E. Bauer, Christina Wanhainen, Joel B. H. Andersson, Roger Nordin
Granite and syenite in general have metaluminous characters, with two samples (nos. 4 and 20 in Fig. 1) showing weak peraluminous character (Fig. 8A). A dominantly metaluminous character, relative high sodium content and normative corundum less than 1 weight-% were attributed to I-type granites by Chappell & White (2001).