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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.
Origin of the apatite-ilmenite deposit of Sept-Îles, Québec, Canada
Published in Adam Piestrzyński, Mineral Deposits at the Beginning of the 21st Century, 2001
The silicate rocks range from troctolite, gabbro-nelsonite to olivine gabbro. These assemblages were injected by the massive, fine to medium grained sterile olivine-microgabbro that represents 40% of the total volume of the Critical Zone. The silicate rocks of the Critical Zone are composed largely of olivine, plagioclase and clinopyroxene. Lath-shaped crystals of plagioclase exhibit a distinct preferred orientation with their long axes aligned subparallel to the lithological layering. Analyses of olivine and plagioclase crystals from both silicate and oxide-rich rocks present respectively a systematic change from Fo67 and An55 at the base to Fo36 and An40 at the top of the Critical Zone. These variations can be explained in terms of fractional crystallization processes.
Lexicon of lithostratigraphic units for the Sudan
Published in J.R. Vail, Lexicon of Geological Terms for the Sudan, 2022
The complex is said to consist of a series of ring-dykes and stocks of granitic and gabbroic rock. The central units are troctolite and olivine gabbro followed by hornblende-biotite granite and biotite granite. The complex is emplaced in greenschists and gneisses, and late dykes cut across all earlier rock types.
Seasonal assessment of heavy metal contamination of groundwater in two major dumpsites in Sierra Leone
Published in Cogent Engineering, 2023
Abdul Aziz Sankoh, Joseph Amara, Tamba Komba, Cynthia Laar, Alusine Sesay, Nana Sarfo Derkyi, Ronnie Frazer-williams
The environments under study are characterized by a large extension of Mesozoic fractured ultrabasic igneous rocks. The igneous rocks belong to various formations and consist of fractured gabbros (secondary porosity) and are referred to as the Freetown Layered Complex and other intrusive. Figure 2 shows the hydrogeological map of the study areas. The exposed part of the Freetown layered intrusion is crescent-shaped and consists of a 6 km thick, westward dipping sequence of gabbroic rock (Bowles et al., 2000; Chalokwu, 2001). The layering is curved and the dips increase from around 20° in the east to 40° to 50° in the west. Geophysical evidence indicates that the intrusion extends farther to the west under the Atlantic Ocean and that it is approximately circular. Five zones (zones 1–4 and an unexposed lower zone) have been identified; each showing an upward progression from troctolite through olivine, gabbro and leucogabbro to anorthosite (Bowles et al., 2000; Chalokwu, 2001). The Freetown layered complex comprises plagioclase , magnetite , Imenite ((, and olivine (mixed crystals of and ) rocks (Umeji, 1983).
Petrogenesis of the Kalka, Ewarara and Gosse Pile layered intrusions, Musgrave Province, South Australia, and implications for magmatic sulfide prospectivity
Published in Australian Journal of Earth Sciences, 2023
W. D. Maier, B. Wade, Sarah-Jane Barnes, R. Dutch
The Anorthosite Zone (AZ) forms the uppermost portion of the Kalka intrusion. It is up to 800 m thick and consists of locally well-layered anorthositic, leucogabbroic and leucotroctolitic rocks that commonly contain up to ∼5–10 vol% magnetite and ilmenite. The base of the zone is defined by the lenticular, 0.5–3 m Olivine-Magnetite Member containing ∼40 vol% interstitial magnetite, olivine (Fo63), ilmenite and green spinel. Additional thin magnetite/ilmenite-rich layers may occur throughout the zone. A characteristic feature of the zone is the irregular lenses and schlieren of heteradcumulate troctolite within adcumulate anorthosite termed mottled or clump texture by Goode (1977c). In addition, Goode (1970) described sedimentary-like structures including channel-like truncations resembling Bushveld potholes, cross-bedding, load casts, and graded layering (both normal and reversed). Interstitial phases such as Fe-oxides, biotite, hornblende and sulfides (mainly pyrrhotite and chalcopyrite) as well as transgressive mafic pegmatites are more common in this zone than in the underlying zones, albeit still occurring in accessory to minor amounts. In the uppermost portion, rare apatite occurs.
The early–middle Silurian Delite monzogranite and quartz syenite, East Kunlun Orogenic Belt, NW China: petrogenesis and implications for tectonic evolution of the Proto‑Tethys
Published in Australian Journal of Earth Sciences, 2023
F. C. Wang, J. Y. Li, Y. J. Shen, T. Tian, Y. Qian, F. Y. Sun, H. X. Wang
Recently, abundant A-type granites were identified in the EKOB, including the Wulonggou A2-type granites (426–424 Ma) (Xin et al.,2018), the 419 Ma Houtougou A-type granites (Yan et al.,2016), 422 Ma Baiganhu A-type granites (Chen et al.,2012), 392 Ma Dagangou A-type granites (Tian et al.,2016), 396 Ma Lalingzaohuo A-type granites (Chen, Xie, Li, et al.,2013) and 389 Ma Wulanwuzhuer A-type granites (Guo et al.,2011). Rocks proposed to have formed in a post-collision setting include the 427 Ma metamorphic amphibolite in the high-angle thrust zone of the Middle Kunlun Fault (Chen et al.,2002), the ca 425 Ma Delite quartz syenite (this study), the 391 Ma Xiarihamu granites (Wang et al.,2013), the 380 Ma pyroxene troctolite (Wang, 2017) and the 380 Ma Kayakedengtage granodiorite (Hao et al.,2015). Therefore, the EKOB was in a post-collision extension setting since the middle Silurian (ca 427 Ma) (Figure 10).