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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, major and trace element and Sr-Nd isotope compositions were determined for Quaternary volcanic rocks from NE Sulawesi (the Sangihe are), Indonesia, in order to examine the origin of across-arc variation in lava and magma source chemistry.
Abstract: Major and trace element, and Sr-Nd isotope compositions were determined for Quaternary volcanic rocks from NE Sulawesi (the Sangihe are), Indonesia, in order to examine the origin of across-arc variation in lava and magma source chemistry. The arc is formed in an intraoceanic tectonic setting and is not associated with a backarc basin, thereby minimizing possible contributions from non-arc geochemical reservoirs. The geochemistry of these arc lavas is likely to provide essential information about the chemical characteristics of subduction components. All incompatible elements, except Pb, increase away from the volcancic front. Major element data for Mg-rich lavas together with available experimental data, suggest that primary magmas are produced at higher pressured by smaller degrees of partial melting beneath the backarc-side volcanoes. Rb/K and Ba/Pb are higher, and 87Sr/86Sr and 143Nd/144Nd are lower in backarc-side lavas. These variations may be attributed to generation of hydrous fluids in the downdragged hydrous peridotite layer at the base of the mantle wedge through the following reactions: decompositions of pargasitic amphibole to form phlogopite and breakdown of phlogopite to crystallize K-richterite, beneath the volcanic front and the backarc-side volcanoes, respectively.

73 citations

Journal ArticleDOI
TL;DR: In this paper, the authors compared the chemical compositions of basaltic lavas to the models of ridge segmentation, mantle flow and melt focusing, and found that the results of these models are not consistent with active upwelling to explain crustal thickness variations along nontransform offset bounded segments.
Abstract: Models of ridge segmentation, mantle flow and melt focusing predict how the chemical compositions of mantle melts should vary along a mid-ocean ridge axis. The compositions of basaltic lavas can be compared to these predictions to test the models. Such tests have been carried out using basalts from the neovolcanic zone south of the Kane fracture zone (the MARK area), where there are both a large transform and nontransform offsets. Before evaluating mantle models, the effects of differentiation must be accounted for. Fractional crystallization at low pressures (constrained by new melting experiments on these samples) does not account for the data. High pressure or in situ crystallization better account for the differentiation trends; however, these two processes imply different relationships between magmatic differentiation and position within a segment. Irrespective of the differentiation model, significant differences exist among parental magmas. Magmas near the transform have much lower levels of highly incompatible trace elements but higher levels of moderately incompatible trace elements, suggesting both lower extents of melting and a more depleted source. These two characteristics may be natural consequences of the truncation of a melting regime by a large-offset transform: depleted mantle from across the transform may contribute to the melting regime, while the cooler thermal environment produces less melt. Quantitative modeling of these geochemical characteristics produces thin crust near the transform, consistent with seismic and gravity studies. In contrast, thin crust adjacent to nontransform offsets is associated with no reduction in extent of mantle melting. These results, along with data from other regions, suggest that nontransform offsets overlie a continuous melting regime, and melt focusing creates the variations in crustal thickness. Focused flow may also lead to incompatible element enrichment at segment centers, and relative depletion at segment margins. Only offsets that truncate the melting regime, such as large transforms, are associated with diminished extents of melting within the mantle. Petrological evidence obtained thus far is not consistent with active upwelling to explain crustal thickness variations along nontransform offset bounded segments.

73 citations

Journal ArticleDOI
TL;DR: In this article, the authors used a progressive leaching procedure on magnetic separates and whole rock fractions to obtain Rb-Sr and Sm-Nd ages of the Moon's Northwest Africa (NWA) basalt.

73 citations

Journal ArticleDOI
TL;DR: In this article, the Li and Mg isotope ratios of a suite of samples from the Horoman peridotite massif were analyzed and it was shown that most Li and all mg isotopic compositions are constant over 100 metres of continuous outcrop, yielding values for pristine mantle of δ7Li = 3.8 ± 1.4 ‰ (2SD, n = 9), δ25Mg = -0.12 ± 0.02 ‰ and δ26Mg= -0 0.23 ± 0.04 ‰

72 citations

Journal ArticleDOI
TL;DR: In this article, a case study of the Whistle mine embayment is presented, where the olivine-textured sublayer matrix is geochemically unlike the main mass norites, quartz gabbros, and granophyres.
Abstract: More than half of the giant Ni-Cu-platinum-group element (PGE) sulfide ores of the Sudbury Igneous Complex are associated with a discontinuous unit at the base of the main mass known as the "sublayer." The sublayer is comprised of two fragment-rich members: (1) a metamorphic-textured footwall breccia, and (2) an igneous-textured contact sublayer. The contact sublayer occurs as a thick unit in depressions at the base of the Sudbury Igneous Complex termed "embayments"; it is associated with disseminated to massive sulfides and contains a range of inclusion types such as diabase, melanorite, olivine melanorite, metamorphosed melanorite, wehrlite, and dunite. We present data for a case study of the Whistle mine embayment and show that the igneous-textured sublayer matrix is geochemically unlike the main mass norites, quartz gabbros, and granophyres. For example, the igneous-textured sublayer matrix in the Whistle mine has La/Sm = 4.0, La/ Nb = 5.1, and Th/Zr = 0.02, and the main mass norites, quartz gabbros, and granophyres have ratios of 5.5 to 7, 2.8 to 4.2, and 0.04 to 0.05, respectively. This matrix contains partially digested hornfels diabase fragments and ghost textures of magnetite remaining from the melting of diabase. The igneous-textured sublayer matrix at the Whistle mine can be modeled with small amounts of assimilation of local country-rock granitoids ( approximately 10%), large degrees of assimilation of diabase that are not derived from the immediate country rocks ( approximately 70%), and small contributions from the main mass magma type ( approximately 20% mafic norite). The amount of diabase assimilation would be too large for traditional assimilation models controlled by the available heat of the mafic magma; even with a superheated magma, 70 percent assimilation is too large. A model is proposed where the melting of the target rocks initially produces a felsic melt sheet which is laden with mafic fragments. These fragments sink to the base of the melt sheet in the crater and are concentrated and further melted to produce the mafic sublayer. There are significant differences in the composition of the igneous-textured sublayer matrix between different embayments which may reflect differing degrees of digestion of compositionally different protolith fragments. The melanorite inclusions in the sublayer at the Whistle mine have ratios of the incompatible trace elements essentially similar to those of the inclusions in the igneous-textured sublayer matrix, but they have similar high incompatible element concentrations (e.g., olivine melanorites have 20-65 ppm Ce in rocks with 15-21 wt % MgO), 1 to 10 percent interstitial sulfide, up to 0.5 percent apatite, 1 to 15 percent biotite, and 1.85 Ga age zircon and baddeleyite. The mafic-ultramafic inclusions are interpreted to be the broken-up remnants of an earlier cumulate formed at depth from a main mass magma; this parental magma has compositional traits which suggest that crystal accumulation took place from a magma which contains a large contribution from the diabase. Olivine compositional data for the mafic inclusions (Fo (sub 71-79) ; 500-3,800 ppm Ni), in the absence of reequilibration, indicate that olivine crystallization both predated and postdated sulfur saturation of the magma. Cr-rich spinels from these rocks confirm that the parental magma was especially Cr rich, and based on the olivine compositional data, had a tholeiitic Mg/Fe ratio.

72 citations


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