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Incompatible element
About: Incompatible element is a research topic. Over the lifetime, 2420 publications have been published within this topic receiving 154052 citations.
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TL;DR: In this paper, the Zerenda series metamorphic rocks from the Kokchetav massif are reported and the results show that these rocks exhibit distinctive geochemical characteristics compared to typical crustal rocks, including microdiamond inclusions in garnets and other indicators of ultrahigh pressure metamorphism.
Abstract: Isotopic and geochemical data of the Zerenda series metamorphic rocks from the Kokchetav massif are reported. Some of these rocks contain microdiamond inclusions in garnets and other indicators of ultrahigh pressure metamorphism (P > 40 kbar, T = 900–1000 °C). The diamond-bearing rocks exhibit distinctive geochemical characteristics compared to typical crustal rocks. The REE patterns range from LREE depleted to slightly LREE enriched [chondrite normalized (La/Yb)N– 0.1–5.4] with a negative Eu anomaly. They are depleted in incompatible elements (e.g. Sr, Ba, U, Th) with respect to the upper crust. In contrast non-diamondiferous rocks of the Zerenda series exhibit normal crustal geochemistry. All rocks of the Zerenda series have very radiogenic lead isotopes. The measured μ values (238U/204Pb) compared with those calculated for the interval between crust formation and ultrahigh pressure (UHP) metamorphism suggest a decrease by factors of up to 200 during the UHP metamorphism. The Sm-Nd mineral isochrons from the diamond-bearing rocks and other rock types of the Zerenda series give a Middle Cambrian (524–535 Ma) age of metamorphism. The Nd model ages show that crust formation occurred about 2.3 Ga ago. Significant fractionation of Sm and Nd and loss of incompatible elements may be due to partial melting of the protoliths. The Ar-Ar age determinations of secondary biotite and muscovite from the diamond-bearing rocks yield an age of 517 ± 5 Ma. This cooling age requires a short time interval between UHP metamorphism and uplift to a crustal level. Ultrahigh pressure metamorphism might be a significant source of Pb for the mantle. We propose that the radiogenic Pb of the oceanic array is the contamination traces of numerous UHP events. Beside the geological aspect we demonstrate a method of dating a high grade metamorphic terrain using Nd isotopes. We compare whole rock isochrons and mineral isochrons and in this way get some insight into the behaviour of the Sm-Nd system during very high grade metamorphic events.
140 citations
TL;DR: In this paper, it was suggested that these differences are not a result of simple partial melting, fractional crystallization, zone refining, residual minerals or isotopic disequilibrium between minerals and melt during melting, but have existed for some 1500 Ma or more.
Abstract: The suboceanic mantle has on the basis of incompatible element and isotope ratios two chemically distinct units; the mantle source for ocean island basalts and the mantle source for ocean ridge basalts. Ocean island alkali basalts have an enriched light rare earth element (REE) source with K/Rb = 400, K/Ba = 28, Zr/Nb = 6.6. Ocean ridge tholeiites have a depleted light REE source, with K/Rb = 1060, K/Ba = no, and Zr/Nb = 37. 87 Sr/ 86 Sr and 206 Pb/ 204 Pb ratios are generally lower in the ocean ridge basalts than in the basalts from ocean islands. It is suggested that these differences are not a result of simple partial melting, fractional crystallization, zone refining, residual minerals or isotopic disequilibrium between minerals and melt during melting. Instead, the differences between the sources are real, and have existed for some 1500 Ma or more. Nephelinite, alkali basalt, and tholeiites from ocean islands have similar isotopic and incompatible element ratios. The nephelinites and alkali basalts are, however, progressively much more enriched in the light REE than are the tholeiites, yet the light REE in nephelinites and alkali basalts appear to be incompatible. This may be explained by the occurrence of small (average 4 cm thick), closely spaced pyroxenite veins (within tens of cm) in the mantle source for ocean island basalts. The occurrence of a network of veins which melt preferentially may lead to melts which have apparent sources with a much greater enrichment in incompatible elements than the total mantle source and may also give the appearance of a source whose ratio for slightly compatible elements changes as a function of extent of melting.
140 citations
TL;DR: In this paper, the authors used acteristics to infer the temporal evolution of the mantle lithosphere and the processes involved in Pb/Pb 40·28-41·5.
Abstract: Lavas from the eastern Virunga province, Rwanda, are dominated to lie within the continental mantle lithosphere (e.g. Fraser et al., 1986; Nelson et al., 1986; Dudas, 1991; by K-hawaiites, K-basanites and latites. All lavas are shoshonitic with 1 < K2O/Na2O < 2 and strongly enriched in incompatible Rogers et al., 1992; Gibson et al., 1995) of which they are a complementary sample to that provided by peridotite elements. Sr/Sr varies from 0·70586 in the K-basanites to 0·70990 in the latites, Nd/Nd from 0·51254 to 0·51206, xenoliths (e.g. Menzies et al., 1987; Jochum et al., 1989). In addition, their trace element and isotopic charand Pb isotopes define sub-vertical trends on isotope diagrams ( Pb/Pb 19·30–19·51, Pb/Pb 15·69–15·93 and acteristics can be used to infer the temporal evolution of the mantle lithosphere and the processes involved in Pb/Pb 40·28–41·5). Ar/Ar ages of leucite and phlogopite separates suggest that the latites are between 100 and 200 ka and lithosphere stabilization. Potassic magmas are also among the most compositionally extreme products of processes the K-basanites <100 ka. The latites are hybrid magmas produced by mixing between a K-basanite melt with a silicic melt from the that scavenge and fractionate incompatible elements in the upper mantle. Hence their geochemical variations deep crust. The low-silica K-basanites reflect interaction between a mafic K-basanitic melt with Nd/Nd ~0·51204, Sr/Sr can also be used to investigate the time-integrated effects of these processes on the radiogenic isotope evolution of ~0·707, and a nephelinite with Nd/Nd ~0·51267 and Sr/Sr ~0·7045. Both are derived from the mantle lithosphere the mantle lithosphere and to explore links between their lithospheric source regions and those of ocean-island with source ages of 1 Ga and 0·5 Ga, respectively, and the youngest ages correspond to the deepest magma sources. The magma production basalt (OIB) (McKenzie & O’Nions, 1983, 1995; Turner et al., 1996). rate in the Virunga is low (~0·04 km/yr), and reflects prolonged (10–15 My) heating of the lithosphere by the East African mantle The Virunga province of the western branch of the African Rift is a classic example of intra-plate potassic plume. magmatism, and the Ugandan part of the province was first described in remarkable detail by Holmes & Harwood (1937). They presented both excellent field and petrographic descriptions of mineralogically and
139 citations
TL;DR: In this article, the first radiometric age data and a comprehensive geochemical data set (including major and trace element and Sr-Nd-Pb-Hf isotope ratios) for samples from the Hikurangi Plateau basement and seamounts on and adjacent to the plateau obtained during the R/V Sonne 168 cruise, in addition to age and geochem data from DSDP Site 317 on the Manihiki Plateau.
139 citations
TL;DR: In this paper, an analysis of water in MORB glasses has been performed using mass spectrometry techniques on speciments selected from worldwide localities (Mid Atlantic Ridge, East Pacific Rise, Red Sea, Lau Basin). Specimens belong to both normal and enriched types.
139 citations