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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 trace element contents of Proterozoic Nain Plutonic Suite (NPS) mafic and anorthositic cumulates, and from plagioclase and orthopyroxene megacrysts were calculated.
Abstract: Equilibrium melt trace element contents are calculated from Proterozoic Nain Plutonic Suite (NPS) mafic and anorthositic cumulates, and from plagioclase and orthopyroxene megacrysts. Assumed trapped melt fractions (TMF) <20% generally eliminate all minor phases in most mafic cumulate rocks, reducing them to mixtures of feldspar, pyroxene and olivine, which would represent the high-temperature cumulus assemblage. In anorthosites, TMF <15% generally reduce the mode to a feldspar-only assemblage. All model melts have trace element profiles enriched in highly incompatible elements relative to normal mid-ocean ridge basalt (NMORB); commonly with negative Nb and Th anomalies. Most mafic cumulates yield similar profiles with constant incompatible element ratios, and can be linked through fractional crystallization. High K–La subtypes probably represent crust-contaminated facies. Mafic cumulates are inferred to belong to a tholeiitic differentiation series, variably contaminated by upper and lower crustal components, and probably related to coeval tholeiitic basaltic dyke swarms and lavas in Labrador. Model melts from anorthosites and megacrysts have normalized trace element profiles with steeper slopes than those calculated from mafic cumulates, indicating that mafic cumulates and anorthosites did not crystallize from the same melts. Orthopyroxene megacrysts yield model melts that are more enriched than typical anorthositic model melts, precluding an origin from parental melts. Jotunites have lower K–Rb–Ba–Y–Yb and higher La–Ce than model residues from fractionation of anorthositic model melts, suggesting they are not cosanguineous with them, but provide reasonable fits to evolved mafic cumulate model melts. Incompatible element profiles of anorthositic model melts closely resemble those of crustal melts such as tonalites, with steep Y–Yb–Lu segments that suggest residual garnet in the source. Inversion models yield protoliths similar to depleted lower crustal granulite xenoliths with aluminous compositions, suggesting that the incompatible trace element budget of the anorthosites are derived from remobilization of the lower crust. The similarity of the highly incompatible trace elements and LILE between anorthositic and mafic cumulate model melts suggests that the basalts parental to the mafic cumulates locally assimilated considerable quantities of the same crust that yielded the anorthosites. The reaction between underplating basalt and aluminous lower crust would have forced crystallization of abundant plagioclase, and remobilization of these hybrid plagioclase-rich mushes then produced the anorthosite massifs.

133 citations

Journal ArticleDOI
TL;DR: This article showed that the chemistry of lavas is a direct consequence of the presence of the cold, thick lithospheric edge of Nazca plate exposed at the intersection with the Inca transform, which has resulted in excess magmatism and the eruption of only FeTi basalts.
Abstract: Glassy to sparsely phyric submarine lavas were recovered from nine Alvin dive sites located along the eastern Galapagos rift and at the intersection with the Inca transform. Samples include quartz-normative tholeiitic basalts (MORB), numerous Fe- and Ti-enriched basalts (FeTi basalts) and a smaller number of oceanic andesites (55.9–64.3 wt % SiO2). MORB have light rare earth element (REE) and large ion lithophile (LIL) element depletions but exhibit slight REE fractionation (CeN/YbN 0.6–1.0) and increasing negative Europium anomalies (0.96–0.66) with progressive differentiation. Andesites have sixfold to tenfold enrichments of incompatible elements and volatiles compared to the least fractionated (Mg number < 60) basalt recovered. REE and LIL enrichments in the FeTi basalts and andesites are up to 70% greater than those predicted from closed-system fractional crystallization models computed using major and trace element data. Trace element data indicate that extreme fractional crystallization of MORB liquids (40–65%) has occurred in order for the most evolved FeTi basalt to be generated and further crystallization (40–50%) of FeTi basalt residual liquid is required to produce andesites. Magma mixing has occurred on a small scale in the evolved liquids and can partially explain the chemical characteristics of basaltic andesites. All data point to extensive amounts of fractional crystallization during the evolution of these lavas; however, mantle heterogeneity and other processes such as partial melting, open-system fractional crystallization, and convection-driven thermogravitational diffusion may also play minor roles in influencing magmatic evolution. The principal tectonic controls which influence magmatic evolution along this accretionary boundary are (1) the presence of the cold, thick lithospheric edge of Nazca plate exposed at the intersection with the Inca transform, and (2) attempted rift propagation across the Inca transform intersection, which has resulted in excess magmatism and the eruption of only FeTi basalts. Three subrift, accretionary magmatic domains result from the interplay of transform effects and attempted propagation. The chemistry of lavas is a direct consequence of the magmatic domain that prevails along an accretionary boundary.

133 citations

Journal ArticleDOI
TL;DR: In this article, major and trace elements have been analyzed from alkaline basalts from southwestern Japan, Korea, and northeastern China, and it was shown that the upper mantle beneath southwestern Japan has been weakly affected by metasomatism caused by dehydration and/or partial melting of subducted Pacific plate.
Abstract: Major and trace element have been analyzed from alkaline basalts from southwestern Japan, Korea, and northeastern China. No significant differences were found in the immobile incompatible element ratios, such as Zr, Y, Hf, Th, and Ti. These ratios, as well as normalized incompatible element patterns, resemble those of continental and oceanic island alkaline basalts. However, southwestern Japanese alkaline basalts show evidence of K, Ba, and Rb enrichment and a slight depletion in Ta relative to La, implying a weak island arc signature. Korean and Chinese alkaline basalts do not have such a signature. Rare earth elements (REE) show near-constant La/Sm ratios and a crossover at the high REE end of patterns for each areas studied. The parallelism in light REE can be derived if the magmas are mixtures formed by (1) relatively large degrees of partial melting of an enriched mantle plume from deeper in the mantle and (2) a small degree of partial melting of a depleted mid-ocean ridge basalt (MORB)-type source. These observations when combined with seismic results suggest that the upper mantle beneath southwestern Japan has been weakly affected by metasomatism caused by dehydration and/or partial melting of subducted Pacific plate (not Philippine Sea plate). The mantle plume may have reacted with weakly metasomatized MORB-type depleted mantle to produce alkaline basalt magmas retaining mild island arc characteristics in southwestern Japan. However, the metasomatism by the subduction of the Pacific plate has not affected the mantle beneath Korea and northeastern China. Here the interaction between plume and MORB-type mantle produced alkaline basalt magma similar to normal continental and oceanic alkaline basalts.

133 citations

Journal ArticleDOI
TL;DR: In this paper, the authors suggest that the source for the alkali basaltic end-member was a garnet-bearing amphibole peridotite that had experienced partial dehydration.
Abstract: Plio-Pleistocene volcanism in the Golan and Galilee (northeastern Israel) shows systematic variability with time and location: alkali basalts were erupted in the south during the Early Pliocene, whereas enriched basanitic lavas erupted in the north during the Late Pliocene (Galilee) and Pleistocene (Golan). The basalts show positive correlations in plots of ratios of highly to moderately incompatible elements versus the concentration of the highly incompatible element (e.g. Nb/Zr vs Nb, La/Sm vs La) and in diagrams of REE/HFSE (rare earth elements/high field strength elements) vs REE concentration (e.g. La/Nb vs La). Some of these correlations are not linear but upward convex. 87 Sr/ 86 Sr ratios vary between 0� 7031 and 0� 7034 and correlate negatively with incompatible element concentrations and positively with Rb/Sr ratios. We interpret these observations as an indication that the main control on magma composition is binary mixing of melts derived from two end-member mantle source components. Based on the high Sr/Ba ratios and negative Rb anomalies in primitive mantle normalized trace element diagrams and the moderate slopes of MREE–HREE (middle REE–heavy REE) in chondrite-normalized diagrams, we suggest that the source for the alkali basaltic end-member was a garnet-bearing amphibole peridotite that had experienced partial dehydration. The very high incompatible element concentrations, low K content, very low Rb contents and steep MREE–HREE patterns in the basanites are attributed to derivation from amphibole- and garnet-bearing pyroxenite veins. It is suggested that the veins were produced via partial melting of amphibole peridotites, followed by complete solidification and dehydration that effectively removed Rb and K. The requirement for the presence of amphibole limits both sources to lithospheric depths. The spatial geochemical variability of the basalts indicates that the lithosphere beneath the region is heterogeneous, composed of vein-rich and vein-poor domains. The relatively uniform 143 Nd/ 144 Nd («Nd ¼ 4� 0–5� 2) suggests that the two mantle sources were formed by dehydration and partial melting of an originally isotopically uniform reservoir, probably as a result of a Paleozoic thermal event.

132 citations

Journal ArticleDOI
TL;DR: A suite of metasomatised xenoliths from the Letlhakane kimberlite (Botswana) formed a metasomatic sequence from garnet peridotite to garnet phlogopite peridotsite to phlogophore peridotesite, and the pseudomorphs were used to measure the flux of trace elements through detailed modal analysis as mentioned in this paper.
Abstract: A suite of metasomatised xenoliths from the Letlhakane kimberlite (Botswana) forms a metasomatic sequence from garnet peridotite to garnet phlogopite peridotite to phlogopite peridotite. Before the modal metasomatism, most of the Letlhakane xenoliths were depleted harzburgites that had been subjected to an earlier cryptic metasomatic event. Modal phlogopite and clinopyroxene ± Cr-spinel increase at the expense of garnet and orthopyroxene with increasing degrees of metasomatism. The most metasomatised xenolith is a wehrlite. With progressive modal metasomatism, the clinopyroxene becomes enriched in Sr, Sc and the LREE, orthopyroxene becomes depleted in Ca and Ni, but enriched in Al and Mn, and olivine becomes depleted in Al and V. Garnet chemical composition largely remains unchanged. The garnet replacement reaction seen in most xenoliths allows the measurement of the flux of trace elements through detailed modal analysis of the pseudomorphs. Mass balance calculations show that the modally metasomatised rocks became enriched in incompatible elements such as Sr, Na, K, the LREE and the HFSE (Ti, Zr and Nb). Major elements (Al, Cr and Fe) and garnet-compatible trace elements (V, Y, Sc, and the HREE) were removed during this metasomatic process. The modal metasomatism caused a strong depletion in Al, and the results challenge previous suggestions that this metasomatic process merely occurred within an Al-poor environment. The data suggest that the xenoliths represent the mantle wallrock adjacent to a major conduit for an alkaline basic silicate melt (with high contents of volatile and incompatible elements). The volatile and incompatible element-enriched component of this melt percolated into the wallrock along a strong temperature gradient and caused the observed range of metasomatism.

132 citations


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