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Early Proterozoic Magmatism and Geodynamics — Evidence of a Fundamental Change in the Earth’s Evolution
Published in O.A. Bogatikov, R.F. Fursenko, G.V. Lazareva, E.A. Miloradovskaya, A. Ya, R.E. Sorkina, Magmatism and Geodynamics Terrestrial Magmatism Throughout the Earth’s History, 2020
This has been described by Bogatikov and Birkis (Bogatikov, 1979), and is located in western Latvia. The pluton, which is completely overlain by a platform cover, 900–1,800 m thick, has been recognized from drilling records. The pluton is irregular-oval in shape. Its northern part is formed of rapakivi granite. In addition to rapakivi, drilling logs indicate the presence of granosyenite, quartz-syenite, quartz-monzonite and monzonite to the south. Abundant basic rocks (predominantly anorthosite and norite–anorthosite, in places supplemented with norite and gabbronorite containing thin layers of troctolite and plagioclase olivinite), appear in the southern part of the pluton. As in the Korosten pluton, the rocks form separate sublatitunidal bodies (blocks). The bodies are 100–200 km2 in size, with the largest of them (Priekule) reaching 1,000 km2 in area.
Recognising the different types of building stone
Published in John A. Hudson†, John W. Cosgrove, Understanding Building Stones and Stone Buildings, 2019
John A. Hudson†, John W. Cosgrove
The Bodmin granite shown in Figure 3.6 is dominated by plagioclase, i.e., white feldspars. The tabular shape of these crystals is apparent and, as noted above, reflects the fact that these were the first minerals to crystallise from the magma. When conspicuous crystals are larger than the grains of the rock groundmass, they are termed phenocrysts. Minerals such as quartz that crystallise out later, have to crystallise in the gaps within the crystal mix of feldspars and, as a result, the quartz crystals are smaller and less well formed. The Kemnay granite shown in Figure 3.6 is also dominated by plagioclase feldspars. It is finer grained than the Bodmin Moor granite, indicating that it cooled more rapidly. The Rapakivi granite which is also shown in Figure 3.6 has an easily recognisable texture: the feldspars form large, ovoid phenocrysts 10 to 50 mm in diameter set in a finer groundmass. The feldspars are composite, i.e., made up of two types: the centres are pink or brown orthoclase which is entirely mantled by grey plagioclase. The word ‘Rapakivi’ in Finnish means ‘weathered rock’.
Textural and mineral chemical evidence of an Upper Carboniferous rapakivi granite in the Erzgebirge/Krušné Hory
Published in Adam Piestrzyński, Mineral Deposits at the Beginning of the 21st Century, 2001
According to the definition of rapakivi granites after Haapala and Rämö (1992) as “A-type granites characterized by the presence, at least in larger batholiths, of granite varieties showing the rapakivi texture”, the porphyritic microgranite of Altenberg-Frauenstein may be considered as rapakivi granite in the broader sense and with limitations. High tFe/(tFe+Mg) in the mafic silicates, high K-feldspar content, plagioclase composition of andesine and oligoclase, occurrence of an older quartz generation, and albite crystallisation in the late magmatic stage found in the microgranites are characteristics of common rapakivi granites (Rämö & Haapala, 1995). The porphyritic microgranites show field, textural and geochemical evidence suggesting that they have formed as a result of the interaction between felsic and mafic magmas. This bimodal silicic-mafic interaction is a feature of rapakivi granites on a global scale. The microgranite may referred to I-type granites (“Gebirgsgranite”) with some A-type tendency (Seltmann et al., 2001). Caused by the Carboniferous age and the only known occurrence of a granite with rapakivi texture in the German part of the Variscan belt, the microgranite of Altenberg-Frauenstein holds an exceptional position.
Late Paleoproterozoic deposition and Mesoproterozoic metamorphism of detrital material in the southernmost Baltic Sea region (Gdańsk IG1 borehole): monazite versus zircon and chemical versus isotopic age record
Published in GFF, 2023
Dominik Gurba, Anna Grabarczyk-Gurba, Ewa Krzemińska
The youngest few grains suggest detrital material has to be derived from a source as young as 1643–1661 Ma (Fig. 10A; Table 2). This may reflect the erosion of the Wiborg batholith (SE Finland), formed at 1646–1627 Ga (Rämö et al. 2014), or Ahvenisto massif (satellite of Wiborg batholith), which yields ages of ca. 1640 Ma (Heinonen et al. 2010b). Similar ages of 1640–1645 Ma were obtained for Obbnäs and Bodom rapakivi-granite massifs in S Finland (Heinonen et al. 2010b). An alternative area remains the westernmost margin of TIB-2. A similar U–Pb zircon ages of 1661 ± 27 and 1674 ± 7 Ma, interpreted as tectonically reworked TIB-2 rocks, have been recognized within the Eastern Segment north of the Vänern lake (Söderlund et al. 1999). A concise compilation of all possible source areas is listed in Table 2.
Geochemical systematics and U–Pb zircon age of the Vulvara anorthosite massif, Lapland granulite belt, Baltic shield: magmatic sources and metamorphic alteration of the rocks
Published in Applied Earth Science, 2021
Lyudmila I. Nerovich, Tatiana V. Kaulina, Evgeniy L. Kunakkuzin, Maria A. Gannibal
Zircon-1 is considered to be magmatic zircon with the age equal or similar to the age of magmatic paragenesis formation. Morphological populations corresponding to zircon-2 and zircon-3 were encountered not only in all studied anorthosite massifs of LGB (Mitrofanov and Nerovich 2003) and all LGB granulites (Bibikova et al. 1993) but also in all granulite complexes of the world (Krasnobaev 1986; Bibikova 1989; Kaulina 2010). Zircon-2 is a typical granulite zircon, and zircon-3 corresponds to the stage of postgranulite retrograde transformations. Zircon-4 and zircon-5 formation is presumably associated with crystallization from a high-temperature pneumatolytic-hydrothermal fluid accompanying the intrusion of pegmatite and quartz monzonite veins into anorthosite bodies. The formation of zircons due to ‘the input of components, at the stage when the rock-forming minerals are still unaltered’ is described, in particular, by Bibikova (1989). Morphology of acicular and spear-shaped zircon varieties indirectly favours the connection between their formation and the intrusion of plagiopegmatites and quartz monzonites. Morphologically identical varieties were described in the anorthosite-rapakivi-granite complexes of the Ukrainian Shield as zircon of the pegmatite and pneumatolytic stages (Nosyrev et al. 1989).
Origin of the Baltic Sea basin by Pleistocene glacial erosion
Published in GFF, 2020
Adrian Hall, Mikis van Boeckel
The outline of the northern part of the present BSB corresponds roughly with that of three intra-cratonic sedimentary basins that today hold the Bothnian Bay, the Bothnian Sea and the Baltic Sea proper (Fig. 1). Crustal thinning and aborted rifting during the Mesoproterozoic was accompanied by rapakivi granite intrusion and the deposition of Jotnian arkosic sandstones of km thickness (Buntin et al. 2019). Only the southern Baltic basin was affected subsequently by Caledonian orogenesis and Mesozoic rifting (Van Balen & Heeremans 1998). Today, the Precambrian crystalline basement plunges to depths of >3 km below the southern shore of the present Baltic Sea (Šliaupa & Hoth 2011), whilst the sub-Cambrian basement unconformity remains close to present sea level further north (Fig. 1).