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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 authors examined the interplay of crustal thickness and magmatic differentiation using a global geochemical dataset compiled from active volcanic arcs and elevation as a proxy for thickness.

137 citations

Journal ArticleDOI
TL;DR: In this article, the authors investigated the role of the crustal contribution in the formation of the Poladpur Formation and the Mahabaleshwar Formation and concluded that the latter is derived from a mantle source with a history of slight trace-element enrichment relative to the Ambenali source.
Abstract: three formations on the basis of the trace elements Sr, Ba, Rb, Zr and Nb. The lowermost unit, the Poladpur Formation, is characterized by high Ba, Rb, and Zr/Nb, and low Sr. These features are accompanied by high K and Si, high and variable 87Sr/86Sr initial ratios (0.7043-0.7196), and low and variable eNd values (+2.6 to - 17.4). The formation is interpreted as having developed by contamination of the overlying Ambenali magma-type with ancient granitic crust, with simultaneous fractionation of a gabbroic mineral assemblage. The more basic members of the formation are found towards the base of the succession and are more contaminated than the upper flows. The succeeding Ambenali Formation, characterized by the Ambenali magma type, has low Ba, Rb, Sr and Zr/Nb, and low and rather uniform 87Sr/86Sr initial ratios (0.7038-0.7043) coupled with high and relatively uniform eNd (+4.7 to +6.4). It is interpreted as being essentially uncontaminated and derived from a mantle source with a history of slight trace-element enrichment relative to m.o.r.b.-source. The uppermost group of flows, the Mahabaleshwar Formation, is, like the Poladpur, enriched in Ba, Rb, K and Si relative to the Ambenali, but has lower Zr/Nb and higher Sr. 87Sr/86Sr initial ratios (0.7040-0.7056) are slightly higher than in the Ambenali, and eNd lies in the range + 7.1 to -3.0. In this formation Sr correlates positively with the other incompatible elements and with 87Sr/86Sr initial ratios. This is in strong contrast to the relations observed in the Poladpur, and we believe that the behaviour of Sr may be a simple pointer to the distinction between mantle and crustal contributions. Assuming that late-stage crystal fractionation processes can be allowed for, if Sr correlates positively with elements such as K, Rb and Ba then mantle enrichment processes are clearly implied. Conversely, as for example in the Poladpur, if the correlation is negative, crustal contamination is suspected because Sr is unlikely to behave as an incompatible element in most crustal derived melts or fluids because of buffering by residual plagioclase. Furthermore, the relative uniformity of the Mahabaleshwar Formation, the position on the Sr and Nd isotope diagram close to the 'mantle array', the fact that in terms of both incompatible element concentrations and isotopes the rocks are similar to tholeiites from oceanic islands such as Hawaii and Kerguelen, are all factors that reinforce the conclusion that these are mantle derived magmas which have suffered insignificant crustal contamination. They are, however, derived from a mantle which is trace-element enriched relative to the Ambenali source. Thus in the succession as a whole the crustal contribution appears to be small. Maximum amounts of contamination in the Poladpur Formation are difficult to determine but the average amount is probably in the region of 6-12 percentage mass. The whole sequence therefore contains a crustal contribution of about 2-3 %.

137 citations

Journal ArticleDOI
17 May 2007-Nature
TL;DR: It is shown that the fluxes of rare-earth elements through olivine and chromite by lattice diffusion are sufficiently rapid at magmatic temperatures to re-equilibrate completely the rare- earth-element patterns of trapped melt inclusions in times that are short compared to those estimated for the production and ascent of mantle-derived magma or for magma residence in the crust.
Abstract: Tiny droplets of melt that are trapped in minerals crystallizing at high temperature have been hailed as preserving the initial melts produced in the Earth's upper mantle. This view rests on the assumption that such melt inclusions remain chemically isolated by their host crystals from chemical re-equilibration with the magma that transports them to the Earth's surface, but a lab study of basalts dredged from the southern Mid-Atlantic Ridge suggests that this assumption is unfounded. Chemical diffusion and partitioning data reveal rates of chemical diffusion between crystals and magma at high temperature that are so fast that any anomalous chemical signature of deep mantle melting preserved in the crystals will be eliminated before the magma reaches the surface. Instead, it's possible that these anomalous chemical signatures originated by assimilation of crustal rocks in shallow magma chambers. Inclusions from melt trapped in early crystallizing phenocrysts can be used to infer the composition of partial melts at depth, and it has been assumed that incompatible elements in olivine- and chromite-hosted melt inclusions are chemically isolated. Spandler and co-authors now show that this is not so: the fluxes of rare-earth elements through olivine and chromite are sufficiently rapid at magmatic temperatures to re-equilibrate completely over time periods that are short compared to those estimated for the production and ascent of mantle-derived magma. The chemical composition of basaltic magma erupted at the Earth’s surface is the end product of a complex series of processes, beginning with partial melting and melt extraction from a mantle source and ending with fractional crystallization and crustal assimilation at lower pressures. It has been proposed that studying inclusions of melt trapped in early crystallizing phenocrysts such as Mg-rich olivine and chromite may help petrologists to see beyond the later-stage processes and back to the origin of the partial melts in the mantle1,2. Melt inclusion suites often span a much greater compositional range than associated erupted lavas, and a significant minority of inclusions carry distinct compositions that have been claimed to sample melts from earlier stages of melt production, preserving separate contributions from mantle heterogeneities1,2,3,4. This hypothesis is underpinned by the assumption that melt inclusions, once trapped, remain chemically isolated from the external magma for all elements except those that are compatible in the host minerals1,2. Here we show that the fluxes of rare-earth elements through olivine and chromite by lattice diffusion are sufficiently rapid at magmatic temperatures to re-equilibrate completely the rare-earth-element patterns of trapped melt inclusions in times that are short compared to those estimated for the production and ascent of mantle-derived magma5,6 or for magma residence in the crust7. Phenocryst-hosted melt inclusions with anomalous trace-element signatures must therefore form shortly before magma eruption and cooling. We conclude that the assumption of chemical isolation of incompatible elements in olivine- and chromite-hosted melt inclusions1,2 is not valid, and we call for re-evaluation of the popular interpretation that anomalous melt inclusions represent preserved samples of unmodified mantle melts.

137 citations

Journal ArticleDOI
TL;DR: The trace element characteristics of the experimentally rehomogenised inclusions include high LREE contents, a pronounced enrichment in LILE, with spikes of Cs, Ba, Pb and high U/Th.

136 citations

Journal ArticleDOI
TL;DR: In this paper, an extensive suite of modern basalts was analyzed for trace element chemistry via laser ablation ICP-MS, with barium (Ba), thorium (Th), uranium (U), and tungsten (W) concentrations typically determined to ≤ 5% (2σ) uncertainty.

136 citations


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Performance
Metrics
No. of papers in the topic in previous years
YearPapers
20237
202216
202157
202056
201960
201851