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Underground Geologic Repositories
Published in Stephen M. Testa, Geological Aspects of Hazardous Waste Management, 2020
Basalts are the most abundant of rock types, comprising the deep ocean floor in addition to widespread occurrences on the continents, notably as flood basalts. Extensive flood basalt provinces include the Karroo in southern Africa, the Parana in South America, the Deccan basalts in India, and the Columbia River basalts in the northwestern U.S. The most impressive aspect of flood basalts are their overall dimensions. Single lava flows may exceed 500 km3 in volume with an areal extent of 40,000 km2 or more. Entire lava fields may have volumes on the order of 100,000 to 1 million km3. Basalts also comprise dikes and sills which can also be extensive. The feeder dike swarms of the Grande Ronde dike swarm of Oregon, Washington, and Idaho extend for some 200 km and have a width of about 50 km. The location of the Columbia River basalt group is shown in Figure 12-6.
Terrestrial and Lunar Magmatism: An Evolutionary Overview
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
E.V. Sharkov, O.A. Bogatikov, V.I. Kovalenko
According to current views (Ringwood, 1979; Bogatikov and Frikh-Har, 1984; Taylor and McLennan, 1985; etc.) the main structural features of the lunar surface are the ancient continents and mares, composed by different types of rocks. The continents are formed by earliest anorthositie crust and more younger magnesian-suite magmatic rocks from the highlands of the Moon, represented by high-Al basalts and intrusive rocks of anorthosite-norite-troctolite series (ANT) which intruded the primary anorthositic crust (Snyder et al., 1996). Significantly younger (approximately 0.3–0.4 Ga younger) roughly circular mare composed of basalts with elevated Ti content. The average thickness of the latter is relatively low, and their total volume does not exceed 1% of the lunar crust. In their geology, these basalts are reminiscent of flood basalts (trap formations) on the Earth.
Volcanic activity
Published in F.G. Bell, Geological Hazards, 1999
The term ‘flood basalt’ was introduced by Tyrrell (1937) to describe large areas, usually at least 130 000 km , that are covered by basaltic lava flows (Figure 2.4). These vast outpourings have tended to build up plateaux; for instance, the Deccan plateau extends over 640 000 km2 and at Bombay reaches a thickness of approximately 3000 m. The individual lava flows that comprise these plateau basalt areas are relatively thin, varying between 5 and 13 m in thickness. In fact, some are less than 1 m thick. They form the vast majority of the sequence, pyroclastic material being of very minor importance. That the lavas were erupted intermittently is shown by their upper parts, which are stained red by weathering. Where weathering has proceeded further, red earth or bole has been developed. It is likely that flood basalts were erupted by both fissures and central-vent volcanoes. For instance, Anderson and Dunham (1966) wrote that the distribution of lava types on Skye suggests that they were extruded by several fissures, which were related to a central volcano. The several groups into which the lavas of Skye have been divided all thin away from centres, which have been regarded as the sites of their feeders. Consequently, the flood basalts are believed to have been built up by flows from several fissures operating at different times and in different areas, the lavas from which met and overlapped to form a succession that does not exceed 1200 m. The most notable flood basalt eruption that occurred in historic times took place at Laki in Iceland in 1783 (Thorarinsson, 1970). Torrents of lava were emitted from a fissure approximately 32 km long and overwhelmed 560 km2. As the volcanic energy declined the fissure was choked, but eventually pent-up gases broke through to the surface at innumerable points and small cones, ranging up to 30 m or so high, were constructed.
Stratigraphy of the Agnew-Wiluna Greenstone Belt: review, synopsis and implications for the late Mesoarchean to Neoarchean geological evolution of the Yilgarn Craton
Published in Australian Journal of Earth Sciences, 2022
Q. Masurel, N. Thébaud, J. Sapkota, M. C. De Paoli, M. Drummond, R. H. Smithies
In light of the current debate, the key to proposing a coherent model for the ca 2820–2690 Ma geological evolution of the Yilgarn Craton may lie in deciphering the geodynamic trigger for the ca 2730 Ma regional stratigraphic unconformity (Figure 14). In theory, a mantle plume impacting the base of the crust can lead to crustal uplift of up to 1 km in amplitude with a radius of about 400 km prior to flood basalt volcanism (Griffiths & Campbell, 1991; Saunders et al., 2007). Such a model may elegantly reconcile the occurrence of a ca 2730 Ma regional stratigraphic unconformity followed by the major thermal event associated with eruption of the ca 2720–2690 Ma Kalgoorlie Large Igneous Province. Yet, in the absence of systematic metamorphic studies across the craton, it remains very difficult to test whether or not rapid uplift and the ca 2730 Ma regional unconformity resulted from: (1) intraplate tectonic forces (i.e. failed subduction zone and docking of the Narryer Terrane against the Youanmi Terrane at ca 2740 Ma); (2) deformation induced by mantle flow (i.e.ca 2730 Ma mantle upwelling zone and Kalgoorlie Large Igneous Province); or (3) both (Figure 15). Of critical importance beyond such geodynamic speculations is that we demonstrate for the first time in the Yilgarn Craton the existence of a magmatic continuum (i.e. no significant magmatic hiatus) between ca 2820 and 2690 Ma, providing the missing link between the geological record of the Youanmi Terrane and that of the Eastern Goldfields Superterrane.
The Lord Howe Volcanic Complex, Australia: its geochemistry and origins
Published in New Zealand Journal of Geology and Geophysics, 2022
Megan L. Williams, Brian G. Jones
The greatest difference is shown by Middleton Reef, whose primitive mantle-normalised pattern resembles lithospherically-contaminated continental flood basalt (Xia & Li 2019) but with much larger P and Ti anomalies. It has, however, Nb/La > 1, no negative Nb anomaly, and P2O5/TiO2 consistent with the LHVC. Given that these members of the chain appear to have a plume origin a possible explanation is that its source was affected by carbonatitic metasomatism with apatite and Ti-bearing minerals remaining in the source at low degrees of partial melting. Along-chain variations in source behaviour are also apparent in Figure 7, particularly for the Chesterfield Plateau and Middleton Reef, where the former exhibits greater influence of residual garnet in the source and the latter shows greater influences from LREE enrichment.
Seve terranes of the Kebnekaise Mts., Swedish Caledonides, and their amalgamation, accretion and affinity
Published in GFF, 2018
Per-Gunnar Andréasson, Ann Allen, Oskar Aurell, Daniel Boman, Jonas Ekestubbe, Ute Goerke, Anders Lundgren, Patrik Nilsson, Stefan Sandelin
Host rocks of the VIC demonstrate that the complex was emplaced into continental sedimentary rocks, and at shallow (andalusite stability) crustal levels. The weakly alkaline character of the dolerites, their higher K contents as compared to MORB and their REE enrichment suggest a continental rift setting. The high HREE contents of both dolerite and granite suggest generation above the garnet–spinel transition in a thinning continental lithosphere (e.g., Ellam 1992). In discrimination diagrams based on LREE versus Nb enrichment (Fig. 16B), their compositions approach the fields of flood basalt reference compositions. Heat from the intrusions melted the upper crust and the Vistas Granite and hybridic varieties were formed.