Incompatible element

About: Incompatible element is a research topic. Over the lifetime, 2420 publications have been published within this topic receiving 154052 citations.

Relationships between Basic and Silicic Magmatism in Continental Rift Settings: A Petrogeochemical Study of Carboniferous Post-collisional Rift Silicic Volcanics in Tianshan, NW China

Abstract: Petrogeochemical data are reported for silicic volcanic rocks from the Tianshan Carboniferous rift, with the aim of discussing the petrogenesis of silicic magmas. Incompatible element vs. incompatible element diagrams display smooth positive trends for the Tianshan Carboniferous rift-related volcanic rocks; the isotope ratios of the silicic lavas [87Sr/86Sr(t)=0.69988–0.70532; eNd(t)=4.76–8.00; 206Pb/204Pb(t)=17.435–18.017; 207Pb/204Pb(t)=15.438–15.509; 208Pb/204Pb(t) = 37.075–37.723] encompass those of the basic lavas. These data suggest a genetic link between rhyolites and basalts, but are not definitive in establishing whether silicic rocks are related to basalts through fractional crystallization or partial melting. Geochemical modeling of incompatible vs. compatible elements excludes the possibility that silicic melts are generated by the melting of basaltic rocks, and indicates a derivation by fractional crystallization plus moderate assimilation of wall rocks (AFC) starting from intermediate rocks to silicic rocks. Continuous AFC from basalt to rhyolite, with small rates of crustal assimilation, best explains the geochemical data. The presence or absence of bimodal volcanism (the “Daly Gap”) might be related to cooling rates of magma chambers. In central and eastern Tianshan, the crust was thinner and the cooling rates of the magma chamber within the crust were greater. These conditions resulted in a rapid fall in temperature within the magma reservoir and caused a narrow temperature interval over which intermediate melts formed, effectively reducing the volume of the intermediate melts.

Early Cretaceous Granitic and Monzonitic Rocks of the Southern Part of the Zhuravlevka Terrane (Sikhote-Alin): Geochemical Composition and Melt Sources

Abstract: The article presents new geological, geochronological, mineralogical, geochemical, and isotopic data on the Early Cretaceous granitic rocks of the southern part of the Zhuravlevka Terrane (Sikhote-Alin). It is shown that four intrusive complexes containing significant amounts of granitic rocks were formed almost simultaneously in this area in the Early Cretaceous (about 100 Ma). These magmatic associations differ in rock set, their mineralogical characteristics, and chemical composition, varying from medium-potassium tonalites and granodiorites depleted in incompatible elements to shoshonitic monzonitic rocks enriched in HFSE and REE. The geochemical and isotopic characteristics of the granitic rocks indicate that the source of their melts was dominated by essentially juvenile metabasite crust with a limited contribution of the upper-crustal metasedimentary rocks. The diversity of geochemical types of the granitic rocks is explained by variable metabasite and metapelite contributions to their source, upper crustal contamination during magma ascent, as well as the variable contribution of the mantle source and different mechanisms of mantle–crust interaction.

Mafic whole-rock geochemistry and neodymium isotopes, Green Mountain and Rowe/Prospect Rock slices, Vermont Appalachians

Abstract: Mafic rocks containing sodic-calcic amphibole in the Green Mountain slice (GMS) and Rowe/Prospect Rock slice (R/PRS), Vermont Appalachians were originally subalkaline basalts emplaced as melts during Neoproterozoic rifting of Rodinia that led to the formation of the Iapetus Ocean basin. Relatively high degrees of partial melting of asthenosphere that was highly depleted in incompatible elements produced R/PRS magma(s), which may have been contaminated locally by continental crust and/or fluids. Trace element chemistry suggests that mafic bodies from different locations in the R/PRS may be fractionated magmatic equivalents. Mafic rocks in the GMS formed from magmas produced by relatively low degrees of partial melting of mantle that was relatively enriched in incompatible elements compared to depleted mantle. These enriched melts may have been derived from a plume and/or enriched lithospheric components, potentially continental crust, embedded in depleted upper mantle. A depleted mantle signature preserved locally in the GMS probably reflects increasing asthenospheric input during crustal thinning, opposed to crustal or fluid contamination. Whole-rock minor and trace element data from the GMS and R/PRS are distinct from analyses of glaucophane schist from the Tillotson Peak Complex in northern Vermont, which may be exhumed Iapetan ocean floor. Exhumed mafic rocks in the GMS and R/PRS were formed as lower plate melts prior to relatively high pressure subduction zone metamorphism, providing evidence for subduction of the Laurentian margin, not subduction erosion. Low pressure greenschist facies mafic rocks that occur structurally between the GMS and R/PRS were sourced from depleted or highly depleted mantle in a supra-subduction zone environment, potentially a forearc or backarc basin; an ophiolitic origin is equivocal. Geochemical and isotopic data and interpretations are compatible with rift-related tectonomagmatic models for the peri-Laurentian realm of the northern Appalachians.

The Distribution of Rare Metals in the LCT Pegmatites from the Giraúl Field, Angola

Abstract: The Giraul granitic pegmatite field in Angola is composed of five pegmatite types, the most evolved belong to the beryl-columbite, beryl-columbite-phosphate and spodumene types. Pegmatites are concentrically zoned with increased grain size toward a quartz core; the most evolved pegmatites have well-developed replacement units. These pegmatites are rich in Nb-Ta oxide minerals and the field has a moderate interest for critical elements such as Ta and Hf. Tourmaline, garnet and micas occur as accessory minerals. The abundance of Zr and Nb-Ta minerals increases with the evolution of the pegmatites, as well as the proportions of beryl and Li-rich minerals. The Ta/(Ta + Nb) ratio in Nb-Ta oxide minerals and the Hf/(Hf + Zr) ratio in zircon also increase with the evolution of the pegmatites and within each pegmatite body from border to inner zones, and especially in the late veins and subsolidus replacements. Textural patterns and occurrence of late veins with Ta-rich minerals suggest that Nb and especially Ta can be enriched in late hydrothermal fluids exsolved from the magma, along with Hf and other incompatible elements as Sn, U, Pb, Sb and Bi.