China
Africa
Explore chapters and articles related to this topic
Phanerozoic Androgenic Magmatism
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
The deep-seated xenoliths from the kimberlites, which represent primarily fragments of ancient continental lithosphere, have highly variable compositions. Together with lower-crastal formations, represented mainly by garnet granulites and eclogites, there are various mantle rocks, originating from a depth of 260 km and more. The xenoliths include all possible peridotites and pyroxenites (containing both garnet and spinel and transitional spinel-garnet), chrominum-bearing dunites and olivinites, all types of eclogites (both bimineralic type and those containing corundum, kyanite, coesite and sanidine as essential rock-forming minerals), specific high-Ti ultramafic rocks with ilmenite, phlogopite, amphibole, and glimmerite, as well as marides (phlogopite–garnet–pyroxene rocks), alkremites and eutectoid (graphic) ilmenite-pyroxene rocks (Sobolev, 1974; Laz’ko, 1988; etc.).
Volcanoes and Their Products
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
Magmas are composed of molten or semi-molten rock, sometimes xenoliths, and usually small amounts of volatiles (gases). Xenoliths and volcanic gases give us samples and valuable chemical data about regions deep within Earth—information that we cannot obtain in any other way. Xenoliths in magmas include individual crystals and rock fragments that are products of partial magma crystallization, or that were scavenged from surrounding solid rock that a magma passed through on its way to the surface. The general term xenolith describes all such inclusions, and the term xenocryst is used if an inclusion comprises a single mineral crystal. True xenoliths, sometimes called exotic xenoliths, have a distinctly different origin than the magma that incorporates them. Other xenoliths, which may be genetically related to the magma, are sometimes called autoliths or cognate xenoliths/xenocrysts. The amounts and natures of xenoliths vary greatly for different magmas and eruptions.
Two types of the diamondiferous kimberlites from the Arkhangelsk province, Russia
Published in Adam Piestrzyński, Mineral Deposits at the Beginning of the 21st Century, 2001
V.K. Garanin, G.P. Kudryavtseva, T.V. Possoukhova, M. Tikhova, E.M. Verichev
Mineralogy of the M.V. Lomonosov deposit was discussed in detail in our book (Bogatikov et al. 1999) and here we summarized main peculiarities only. First of all, the kimberlites of the M.V. Lomonosov deposit are characterized by low content of heavy fraction (1.3-1.8 kg/t). Chromite prevails (24-58 g/t) and contents of garnet (4-7 g/t) and clinopyroxene (6-15 g/t) are low. Ilmenite is absent. Megacrysts (discrete nodules) of picroilmenite, low chromium clinopyroxene, low chromium Ti-pyrope were not established. Ti-chromite prevails in the kimberlite groundmass and contents of Cr-ulvospinel (<20%) and sphene (<10%) are low. Picroilmenite, rutile and Mgulvospinel are not found in the groundmass. Xenoliths of spinel and pyrope peridotites (lherzolites, harzburgites and dunites) and eclogites prevail. All mantle xenoliths have intensive alteration peculiarities but ilmenite-bearing rocks and sheared lherzolites are absent.
Composition and Miocene deformation of the lithospheric mantle adjacent to the Marlborough Fault System in North Canterbury
Published in New Zealand Journal of Geology and Geophysics, 2023
Sophie J. Bonnington, James M. Scott, Marshall C. Palmer, Nadine P. Cooper, Malcolm R. Reid, Claudine H. Stirling
Peridotite and pyroxenite are coarse-grained ultramafic rocks that dominate Earth’s upper mantle. Since mantle xenoliths lock in the mantle composition at the time of their entrainment, their investigation can provide direct insight into mineralogy, temperature, buoyancy, deformation and age of the middle to lower lithosphere (e.g. Griffin et al. 1988; Carlson et al. 2005; Pearson et al. 2014, 2021). New Zealand has over 70 known mantle xenolith locations (Scott (2020) and references therein) and these give a snapshot of the composition of the lithospheric mantle underpinning the continental crust portion of Zealandia. However, the Canterbury region is relatively unstudied, with the only known mantle xenolith locations being the little-studied Le Bons Bay basanite plug in Akaroa and in the Little Lottery Intrusives in NW Canterbury (Figure 1) (Coote 1987; Sewell et al. 1993; McCoy-West et al. 2013, 2015, 2016).
Intraplate volcanism on the Zealandia Eocene-Early Oligocene continental shelf: the Waiareka-Deborah Volcanic Field, North Otago
Published in New Zealand Journal of Geology and Geophysics, 2020
James M. Scott, James D. L. White, Petrus J. le Roux
In contrast to the aforementioned xenolith occurrences, the intra-vent lapilli tuff breccia enclosed within bedded surtseyan lapilli tuff on a marine platform at Kakanui (Figure 5A) contains a spectacular array of xenocrystic and xenolithic material set in a calcite and zeolite-cemented primary volcaniclastic matrix (Figure 5B) (Mantell 1850; Dickey 1968a, Dickey 1968b; Reay and Sipiera 1987; White and Houghton, 2006). The most xenolith-rich location, South Head, is the centre of a single surtseyan volcano (Corcoran and Moore 2008). Here, the Kakanui Mineral Breccia contains spinel lherzolite and harzburgite, cut in places by amphibole-phlogopite-bearing veins, as xenoliths up to about 20 cm in diameter (but commonly much smaller and usually heavily replaced by carbonate) within thin-rinded bombs of melanephelinite (Figure 5C, D) (Dickey 1968a; Reay and Sipiera 1987; Klemme 2004; McCoy-West et al. 2013; Scott et al. 2014b). These xenoliths are fragments of the mantle lithosphere from under the volcanic field. Olivine (Mg# = 100*Mg/(Mg + Fe) = 89.3–91.0) and spinel (Cr# = 100*Cr/(Cr + Al) = 8.8–44.4) compositions from lherzolites and harzburgites indicate that this mantle is fairly to moderately fertile (Reay and Sipiera 1987; McCoy-West et al. 2013; Scott et al. 2014b; Moorhouse 2015). A single whole rock Os analysis (187Os/188Os = 0.11953; McCoy-West et al. 2013) and three clinopyroxene Hf analyses (εHf = +100 to +14; Scott et al. 2014b) indicate depletion ages that range back to Proterozoic time; the geological significance of the old ages remains debated, with suggestions that the underlying mantle is either a vast block of ancient lithosphere (McCoy-West et al. 2013) or that it is young lithosphere with embedded ancient fragments (Liu et al. 2015; Scott et al. 2019). Enriched clinopyroxene trace element data show that the underlying mantle was metasomatized after depletion (Scott et al. 2014b; McCoy-West et al. 2015), and this is supported by the occurrence of apatite crystals and crystallised fluoride melt in one xenolith (Klemme 2004) and the amphibole-phlogopite-bearing veins (Figure 5D).