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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: This paper used a two-component local equilibrium model to assess the effects of interaction between slab-derived aqueous fluids and wedge lherzolite on the trace element and isotopic composition of island arc basalts.
Abstract: Recently measured partition coefficients for Rb, Th, U, Nb, La (Ce), Pb, Sr, Sm, Zr, and Y between lherzolite assemblage minerals and H2O-rich fluid (Ayers et al 1997; Brenan et al 1995a,b) are used in a two-component local equilibrium model to assess the effects of interaction between slab-derived aqueous fluids and wedge lherzolite on the trace element and isotopic composition of island arc basalts (IAB) The model includes four steps representing chemical processes, with each process represented by one equation with one adjustable parameter, in which aqueous fluid: (1) separates from eclogite in the subducted slab (Rayleigh distillation, mass fraction of fluid released F fluid); (2) ascends through the mantle wedge in isolated packets, exchanging elements and isotopes with depleted lherzolite (zone refining, the rock/fluid mass ratio n); (3) mixes with depleted lherzolite (physical mixing, the mass fraction of fluid in the mixture X fluid); (4) induces melting to form primitive IAB (batch melting, mass fraction of melt F melt) The amount of mantle lherzolite processed by the fluid in step (2) determines its isotopic and trace element signature and the relative contributions of slab and wedge to primitive IAB Assuming an average depleted lherzolite composition and mineralogy (70% olivine, 26% orthopyroxene, 3% clinopyroxene and 1% ilmenite) and using nonlinear regression to adjust parameter values to obtain an optimal fit to the average composition of IAB (McCulloch and Gamble 1991) yields values of F fluid= 020, n= 26, X fluid= 017, and F melt= 015, with r 2= 0995 and the average relative error in trace element concentration = 6% The average composition of IAB can also effectively be modeled with no contribution from the slab other than H2O (ie, skip model step 1): n= 27, X fluid= 021, F melt= 017, with r 2= 0992 By the time the fluid reaches the IAB source, exchange with depleted wedge lherzolite reduces the 87Sr/86Sr ratio isotopic composition to near-mantle values and the slab contribution to <50% for all but the most incompatible elements (eg, Pb) The IAB may retain the slab signature for elements such as B and Be that are highly incompatible and that have very low concentrations in the depleted mantle wedge The relatively high equilibrium D mineral / fluid values measured by Ayers et al (1997), Brenan et al (1995a) and Stalder et al (1998) suggest that large amounts of fluid (>5 wt%) must be added to lherzolite in the IAB source Decreasing X fluid below 005 causes model results to have unacceptably high levels of error and petrologically unreasonable values of F melt That H2O contents of IAB are generally <6 wt% suggests that not all of the H2O that metasomatizes the IAB source remains in the source to dissolve in the subsequently formed melt Modeling of the compositions of specific primitive IAB from oceanic settings with low sediment input and depleted mantle wedges (Tonga, Marianas) shows a generally lower level of fluid-wedge interaction (low n), and therefore a larger slab component in primitive IAB

267 citations

Journal ArticleDOI
TL;DR: In this article, isotope dilution data of the shergottite meteorite QUE 94201 has been used to identify a leachable crustal component in the meteorite, which can affect the isochrons by selectively altering the isotopic systematics of the leachates and some of the mineral fractions.

265 citations

Journal ArticleDOI
01 Mar 2003
TL;DR: In this paper, the authors examine the case presented by Hanan et al. [2000] and conclude that their arguments are flawed and show that the data plot in their NMORB field on an eHf versus eNd diagram.
Abstract: [1] Icelandic basalt ranges in composition from voluminous tholeiite, erupted in the rift zones, to small-volume, mildly alkaline basalt erupted off-axis. In addition, small-volume flows of primitive basalt, highly depleted in incompatible elements, are sometimes found in the actively spreading rift axes. Relative incompatible-element depletion or enrichment in Icelandic basalt is correlated with variation in radiogenic isotope ratios, implying that the mantle beneath Iceland is heterogeneous and that the relative contribution of the various mantle components relates to eruption environment (on- or off-axis) and hence to degree of melting. Thus small-degree off-axis melting preferentially samples an enriched and more fusible mantle component, whereas more extensive melting beneath the rift axes produces magma that more closely represents the bulk Iceland plume mantle composition. The small-volume flows of depleted basalt represent melts that have preferentially sampled a depleted and more refractory mantle component. A debate has arisen over the nature of the depleted component in the Iceland plume. Some authors [e.g., Hanan and Schilling, 1997] argue that the depleted component is ambient upper mantle, the source of normal mid-ocean ridge basalt (NMORB) in this region. Others [e.g., Thirlwall, 1995; Kerr et al., 1995; Fitton et al., 1997], however, have used various lines of evidence to suggest that the plume contains an intrinsic depleted component that is distinct from the NMORB source. Hanan et al. [2000] attempt to refute the existence of a depleted Iceland plume (DIP) component through a critical evaluation of the Nb-Zr-Y arguments advanced by Fitton et al. [1997] and the Hf-Nd-isotopic evidence presented by Kempton et al. [1998]. In this paper we examine the case presented by Hanan et al. [2000] and conclude that their arguments are flawed. Firstly, their trace-element data set excludes data from depleted Icelandic basalt samples and so it is not surprising that they find no evidence for a DIP component. Secondly, they present two new Hf-isotope analyses of a single depleted Icelandic basalt sample and show that the data plot in their NMORB field on an eHf versus eNd diagram. However, new data allow the resolution of distinct NMORB and depleted Icelandic basalt fields on this diagram. We conclude that trace-element and radiogenic isotope data from Iceland require the existence of a DIP component.

264 citations

Journal ArticleDOI
TL;DR: In this paper, the authors proposed that across-arc differences in the geochemistry of Izu-Bonin arc magmas are controlled by the addition of fertile-slab fluids to depleted mantle at the volcanic front without slab melting or contemporaneous back arc spreading.
Abstract: [1] We propose that across-arc differences in the geochemistry of Izu-Bonin arc magmas are controlled by the addition of fertile-slab fluids to depleted mantle at the volcanic front, and residual-slab fluids to fertile mantle in the back arc without slab melting or contemporaneous back arc spreading. The arc consists of a volcanic front, an extensional zone, and seamount chains (the Western Seamounts) that trend into the Shikoku Basin. Each province produces a distinct suite of arc-like volcanic rocks that have relative Nb depletions and high ratios of fluid-mobile elements to high field strength elements. The volcanic front has the lowest concentrations of incompatible elements and the strongest relative enrichments of fluid-mobile elements (high U/Nb, Ba/Nb, Pb/Zr, Th/Nb, 206Pb/204Pb, ɛNd, and 87Sr/86Sr). A fluid derived from both sediment and altered oceanic crust explains most of the slab-related characteristics of the volcanic front. The Western Seamounts and some of the extensional zone rocks have lower ɛNd, 87Sr/86Sr, 206Pb/204Pb, Ba/Th, and U/Th; moderate Ba/Nb and U/Nb; and similar or higher Th/Nb and Th/Nd. Although the lower ɛNd and higher Th/Nd tempt a sediment melt explanation, a lack of correlation between the strongest sediment proxies, such as ɛNd, Th/Nb, and Ce/Ce*, precludes sediment melts. The subduction component for the Western Seamounts is probably a fluid dehydrated from a residual slab that was depleted in fluid-mobile elements beneath (as well as trenchward of) the volcanic front. This depleted fluid is added to elementally and isotopically more enriched mantle beneath the Western Seamounts.

263 citations

Journal ArticleDOI
TL;DR: In this article, it was shown that the lower komatiite was contaminated during eruption by thermal erosion and assimilation of a mixture of sediment and tholeiite; and the compositions of the Kambalda high-Mg basalts result from up to 25% contamination of komatisite, at depth, by material with the composition of modern upper continental crust.

262 citations


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