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The Sources and Origin of Magmas
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
The basis of another concept is the generally accepted theory that the mantle is the source region for various types of magma. Therefore, deep magmas may serve as an important source of information about the composition of parental melts. The intensive, detailed study of the geochemistry and isotopic composition of volcanics that are presumed to have a subcrustai origin, as carried out over the past few years, has led to the idea of several different mantle sources for the magmas. This new evidence has allowed us to postulate an undifferentiated “primitive” mantle and its derivatives — magma sources geochemically and isotopically depleted or enriched as compared with primary mantle. These magma sources are the mantle reservoirs, i.e. deep-seated zones with corresponding isotope-geochemical composition are implied (Balashov, 1985; Hart, 1988; Allegre, 1987; etc.).
Nuclear and Hydro Power
Published in Anco S. Blazev, Energy Security for The 21st Century, 2021
The average abundance of uranium in meteorites is about 0.008 parts per million (ppm, or gram/ton), while the abundance of uranium in the Earth’s “primitive mantle” (prior to the extraction of the continental crust) was 0.021 ppm. Allowing for the extraction of a core-forming iron-nickel alloy with no uranium (because of the characteristic of uranium which makes it combine more readily with minerals in crustal rocks rather than iron-rich ones), this still represents a roughly two-fold enrichment in the materials forming the pro-to-Earth compared with average meteoritic materials.
The Other Energy Markets
Published in Anco S. Blazev, Global Energy Market Trends, 2021
The average abundance of uranium in meteorites is about 0.008 parts per million (ppm, or gram/ton), while the abundance of uranium in the Earth’s “primitive mantle” (prior to the extraction of the continental crust) was 0.021 ppm. Allowing for the extraction of a core-forming iron-nickel alloy with no uranium (because of the characteristic of uranium which makes it combine more readily with minerals in crustal rocks rather than iron-rich ones), this still represents a roughly two-fold enrichment in the materials forming the proto-Earth compared with average meteoritic materials.
The isotope geochemistry of host rocks of the late Archean Guandi and Banshigou banded iron formations, southern Jilin Province: temporal and tectonic significance
Published in Australian Journal of Earth Sciences, 2023
The primitive-mantle-normalised incompatible element patterns of the PHG–BSG and PA–GD samples are characterised by Nb, Ta, and Ti troughs (Figure 14). These features can be explained by either of the following two petrogenetic models: (1) the samples are from mantle-derived magmas that were contaminated by crustal material (Puchtel et al., 1998); or (2) the samples were formed by the partial melting of a mantle source that was metasomatised by slab-derived fluid or melt (McKenzie, 1989). As stated above, samples PA–GD and PA–BSG are contaminated by crustal material, but we cannot dismiss the possibility of input from slab-derived fluids or metasomatising melts. PA–GD has εHf(t) values of −1.3 to +2.8, and PHG–BSG has εHf(t) values of −1.5 to +2.7 (Figure 17). While there is a relatively wide range of εHf(t) values across the CHUR line, most are relatively close to the depleted mantle array. Generally, for mantle-sourced basaltic rocks, Hf model age that approaches the magmatic crystallisation age indicates a depleted mantle source. An Hf model age greater than the magmatic crystallisation age indicates that the source was either contaminated by crustal materials or derived from an enriched mantle (Wu et al., 2007). PA–GD has TDM(Hf) values of 2903 to 2750 Ma, and PHG–BSG yields TDM(Hf) values of 2914 to 2751 Ma. These values indicate that the protoliths were contaminated, which is consistent with the observed enrichment in LREE.
Isotopic investigations of the Nova-Bollinger Ni–Cu–Co deposit in the Fraser Zone, Albany-Fraser Orogen, Western Australia
Published in Australian Journal of Earth Sciences, 2022
V. Taranovic, Stephen J. Barnes, K. Baublys, K. Bathgate, M. L. Fiorentini
Figure 9 shows some theoretical isotopic mixing models for Nd and Sr in an attempt to identify potential contaminants in the immediate country rocks. Mixing lines are shown for hypothetical Nova parent magmas, having 100ppm Sr and 10ppm Nd, with the two analysed Snowys Dam samples, the Marble Gneiss and the Garnet Gneiss (Figure 9a) and for a hypothetical lower crust contaminant (Figure 9b). In the absence of a reliable estimate for the parent Nova magma, we took two hypothetical isotopic starting compositions, one corresponding to a ‘MORB’ depleted mantle (DM), and one based on a chondritic primitive mantle (PM), both at 1300 Ma (see Table 2 for assumptions). Given the large uncertainties in the assumptions, the Bollinger globular ores are consistent with contamination of a DM-like parent magma with around 20% Marble Gneiss contaminant, or a PM-like parent with a component of both Marble Gneiss and Garnet Gneiss. This is consistent with the presence of unusually calcic assemblages including primary magmatic carbonate associated with the sulfides in these rocks, and the proximity of these globular ores to the Marble Gneiss unit. This interpretation contrasts with that of Blanks et al. (2020) for a number of alkalic systems, where the evidence suggests that a CO2-rich volatile phase associated with magmatic sulfides was mantle-derived.
Petrogenesis and tectonic setting of granitic plutons in the Guaizihu region, North Alxa Block, China: constraints from whole-rock geochemistry, zircon U–Pb ages and Hf isotope compositions
Published in Australian Journal of Earth Sciences, 2021
F. Q. Xie, Y. H. Sun, L. D. Wang, J. Y. Cao, W. Z. Xiao, J. H. Wu
The Rb/Sr and differentiation index (DI) values are important indicators for determining fractional crystallisation (Sami et al.,2020). Samples from the granites in the Guaizihu region have high Rb/Sr (0.07–5.60; mean = 1.54) and DI (70–94; mean = 84.76) values (Table S2), which implies a moderate fractional crystallisation. Negative correlations of SiO2 with Al2O3, CaO, TiO2, K2O, P2O5, Na2O, MgO, and Fe2O3T (Figure 4) may also result from the fractional crystallisation. The granites also show a positive correlation of Rb with Ba (Figure 8a) and a negative correlation of Rb with Sr (Figure 8b), indicating fractional crystallisation of plagioclase. Chondrite-normalised REE plots show right-decreasing oblique trends and slightly depleted Eu, despite differences in element contents. Weak negative Eu anomalies indicate that fractional crystallisation of plagioclase during magma evolution (Figure 6a). Depletions in Ti, Sr, Ba and Nb in the primitive mantle-normalised trace-element patterns (Figure 6b) indicate the fractional crystallisation of Ti-rich minerals (ilmenite, titanite) and Sr-rich and Ba-rich minerals (feldspar) during the evolution of the magma.