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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.
Plutonic Rocks
Published in Dexter Perkins, Kevin R. Henke, Adam C. Simon, Lance D. Yarbrough, Earth Materials, 2019
Dexter Perkins, Kevin R. Henke, Adam C. Simon, Lance D. Yarbrough
The Mackenzie Dike Swarm, shown in Figure 6.37, is one of several dozen dike swarms in the Canadian Shield. It is the largest dike swarm in the world and covers a huge area of the shield—more than 500 kilometers (310 miles) wide and 3000 kilometers (1900 miles) long—from near the Great Lakes to the Arctic. The dikes are in a fan-like pattern and all seem to radiate from a point on southern Victoria Island in the Arctic. Most petrologists believe that a large mantle plume carried heat and magma up in that region. The rising plume caused the crust to fracture, providing conduits for dike formation. The Muskox layered mafic intrusion, the Coppermine River and Ekalulia flood basalts (also shown in Fig. 6.37), and several major plutonic complexes were all emplaced in the region at the same time—additional evidence for an active mantle plume that provide magma for both plutonic and volcanic rocks.
Tertiary precious-metal deposition in time and space in the Great Basin, USA
Published in Adam Piestrzyński, Mineral Deposits at the Beginning of the 21st Century, 2001
S. Ludington, D. John, J. Rytuba
The deposits in the BM assemblage are not part of this pattern, but are instead scattered throughout a NS elongate, 1000 x 300 km belt that is crudely symmetric about the northern Nevada rift dike swarm, the most prominent manifestation of the initiation of the Yellowstone hot spot in the Great Basin (Fig. 1).
An updated catalogue of New Zealand’s mantle peridotite and serpentinite
Published in New Zealand Journal of Geology and Geophysics, 2020
Most of the Westland Dike Swarm peridotites examined are harzburgite (Figure 2). The bulk rock Al2O3 < 0.33 wt%, olivine Mg# extending to 92.3 and spinel Cr# of up to 73 show that the sampled lithospheric mantle extends to extremely depleted compositions (Tulloch and Nathan 1990; McCoy-West et al. 2013; Scott et al. 2016b, 2019a). Although similar depleted compositions are often attributed to Archean cratonic environments, Os isotope data yield Proterozoic to Cambrian model ages (1.76-0.52 Ga) and the olivine-spinel compositions tend to plot off the Archean trend (Scott et al. 2019a). Two samples from which clinopyroxene has been extracted yield variable initial 87Sr/86Sri (0.70282 and 0.70878) but the same radiogenic 143Nd/144Ndi (0.51282) (McCoy-West et al. 2016). The 206Pb/204Pbi (19.0-19.6), 207Pb/204Pbi (15.4-15.6) and 208Pb/204Pbi (38.3-31.9) are also radiogenic (McCoy-West et al. 2016). Since the clinopyroxene (McCoy-West et al. 2015) and orthopyroxene (Scott et al. 2016b) trace elements in these depleted rocks also display evidence for light rare Earth element (LREE)-enrichment, the lithospheric mantle has been metasomatised and the isotopic compositions (perhaps excluding the anomalously radiogenic Sr analysis) likely represent the composition of the metasomatising agent.
Volcanoes of Zealandia and the Southwest Pacific
Published in New Zealand Journal of Geology and Geophysics, 2020
The volcanoes and volcanic centres shown in Figure 1 are symbolised according to the age and interpreted regional tectonic setting of each magmatic system. The scale of compilation, however, has demanded much merging and simplification of mapped volcanic rocks, especially on land. For example, some South Island Cenozoic volcanic fields comprise dozens of dikes and outliers that outcrop across many tens of kilometres (Coombs et al. 2008, fig. 2), and the Auckland Volcanic Field comprises > 50 separate small volcanoes (Lindsay et al. 2011). For the purposes of this continental-scale compilation, each point symbol on Figure 1 represents: (1) an individual seamount, guyot, stratovolcano or caldera (eg Mt Ruapehu); (2) a single volcanic field comprising a number of monogenetic cones or mapped formations (eg Auckland Volcanic Field, Mount Somers Volcanics Group); or (3) more rarely, a dike swarm (eg Alpine Dike Swarm).
The Ross–Delamerian Orogen in the southwest Pacific and Antarctica: an active plate boundary for Gondwana in the late Neoproterozoic and Cambrian
Published in New Zealand Journal of Geology and Geophysics, 2023
DV2 rocks comprise a number of plutons of mainly undeformed granite and quartz monzonite that are usually discordant. The extensive Vanda Dike swarm appears to be chemically related although some dikes cut DV2 plutons. The dikes range widely in composition and form scattered sheets to intensive dike swarms that, in places, make up more than 50% of the rock volume (Cox et al. 2012 and references therein). DV2 pluton geochronology typically ranges from 498 to 490 Ma and the Vanda Dike swarm from 495–491 Ma (summarised in Cox et al. 2012), and together date a period of significant extension.