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Igneous Petrology and the Nature of Magmas
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
Ultramafic magmas, which must originate in the mantle, do not reach the surface to produce ultramafic volcanic rocks today. However, they made it to the surface when the mantle melted, in part or completely, during Earth’s early history. Thus, we find rare komatiites (volcanic rocks having ultramafic compositions) scattered around Earth in very old (Archean) terranes, and only very rarely in younger terranes. Figure 5.46 shows approximately 2.7 billion year old komatiites exposed at Pyke Hill, in western Ontario. The lack of young ultramafic volcanic rocks is probably due to the cooling of our planet. The young Earth was much hotter than today’s Earth, because of heat produced by radioactive decay and more residual heat left over from the original accretion. Because ultramafic magmas crystallize at high temperatures, a cooler Earth means that they are less likely to make it to the surface today, compared with Earth’s early days. However, within Earth, where temperatures are still high, ultramafic plutonic rocks are common. They comprise most of the mantle but only reach the surface as tectonic fragments caught up in mountain building or as much smaller xenoliths carried up by magmas.
Metalliferous deposits: Tectogenesis and mineralisation controls
Published in Adam Piestrzyński, Mineral Deposits at the Beginning of the 21st Century, 2001
The origin of this orebody is widely interpreted to have developed during volcanic eruption and emplacement of komatiite lava. Lava flow within a NNE - SSW oriented thermo-mechanical erosion channel(s) is interpreted as facilitating the genesis and distribution of disseminated low grade Ni ore (Hill, Barnes & Perring 1996, Hopf & Head, 1998). Hence, it is considered to be lithologically controlled with no tectonic deformation contribution.
Lithium in pegmatites of the Fennoscandian Shield and operation prospects for the Kolmozero deposit on the Kola Peninsula (Russia)
Published in Applied Earth Science, 2022
P. V. Pripachkin, N. M. Kudryashov, T. V. Rundkvist, L. N. Morozova
The Kolmozero-Voronya greenstone belt is made up of 2.9–2.8 Ga volcano-sedimentary sequence consisting of aluminous gneisses, garnet–biotite and biotite schists, amphibolites, metamorphosed tholeiitic basalts intercalated with komatiite and the intermediate and felsic metavolcanic rocks (Belolipetskii et al. 1980; Vrevsky 1989; Glebovitskii 2005). The belt occupies the contact zone of the Murmansk and Kola blocks, where most of the pegmatites are concentrated forming the pegmatite fields or clusters, including the Porosozero, Soldat-Mylk, Polmos-Tundra (Polmostundrovskoye), Oleny ridge, Okhmylk and Vasin-Mylk. The Kolmozero-Voronya greenstone belt also hosts gold and Cu, Mo-porphyry deposits and occurrences (Kalinin and Kudryashov 2021).