Incompatible element

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

Complications to Carbonate Melt Mobility due to the Presence of an Immiscible Silicate Melt

Abstract: The relative interfacial energies of immiscible carbonate and silicate number of incompatible elements, and can be very mobile. Their mobility is a result of their low viscosities melts were investigated in olivine and clinopyroxene matrices. Carbonate melt has a higher melt–solid interfacial energy than does the [0·01–0·1 Pa s at temperatures >500°C, for a range of compositions (Dawson et al., 1990; Wolff, 1994; Dobson coexisting silicate melt. The silicate melt therefore selectively wets the grain-edge channels between solid phases, excluding the carbonate et al., 1996)] and their ability to form an interconnected grain-edge melt at low melt fractions. Dunitic assemblages melt to the center of melt pockets, away from grain edges. This prevents the carbonate melt from migrating independently of the (and probably other mineralogies) with an interconnected carbonate melt should have a high permeability to flow. silicate melt and the carbonate melt is unable to separate from the silicate melt in a solid-dominated assemblage. The carbonate melt These melts may transport a variety of trace elements and can infiltrate long distances into the country rock will migrate effectively only after the silicate melt has solidified, or by separating from the silicate melt within liquid-dominated reservoirs surrounding melt channels, altering the chemistry and isotopic systems of the host rock. Diffusion is fast within (sills, dikes, or chambers), unrestricted by solid interfaces. This relative wetting behavior may help explain the close association of these melts, so even a stagnant interconnected melt can greatly enhance the transport of trace and major elements carbonate and silicate magmas in alkali complexes, and their relative timing of emplacement. These results also place constraints on the (Watson, 1991). generation and separation of derivative melts in carbonated silicate The relative interfacial energy between grain–grain melt systems and on the style and timing of alkali wall-rock contacts and grain–fluid contacts can be parameterized metasomatism. by the dihedral angle, the angle subtended at a fluid– grain–grain junction. Dihedral angles >60° indicate that system interfacial energy is minimized by reducing the contact of the fluid with the solid, whereas systems with dihedral angles <60° minimize interfacial energy by

Uranium, rare metals, and granulite-facies metamorphism

Abstract: During granulite-facies metamorphism of metasedimentary rocks by the infiltration of carbonic fluids, the disappearance of hydrated minerals leads to the liberation of aqueous fluids. These fluids are strongly enriched in F and Cl, and a series of Large-Ion-Lithophile (LIL) elements and rare metals, resulting in their depletion in granulites. To sum up the fate of these elements, we focus on three domains representing different crustal levels and showing distinct behaviours with respect to these elements. The Lapland metasedimentary granulites illustrate the behaviour of the LILE and rare metals during lower crustal metamorphism. There is no change in Ba, moderate loss in Rb, and extreme depletion in Cs, Li, and Sn. F and Cl contents are also very low compared to the protoliths or average upper continental crust. Biotite and amphibole breakdown leads to the incorporation of their partitioning into a fluid or a melt. The Tranomaro metasomatized marbles recrystallizing under granulite-facies conditions represent a demonstrative example of fluid transfer from granulite-facies supracrustals to traps represented by regional scale skarns. Such fluids may be at the origin of the incompatible element enrichment detected in leucosomes of migmatites from St Malo in Brittany (France) and Black Hills in South Dakota. The northern French Massif Central provides us with an example of a potential association between incompatible element enrichment of granitic melts and granulite-facies metamorphism. U- and F-enriched fine-grained granites are emplaced along a crustal scale shear zone active during the emplacement within the St Sylvestre peraluminous leucogranitic complex. We propose that during granulite-facies metamorphism dominated by carbonic waves in a deep segment of the continental crust, these shear zones control: (i) the percolation of F-, LILE-, rare metal-rich fluids liberated primarily by the breakdown of biotite; (ii) the enhancement of partial melting by F-rich fluids at intermediate crustal levels with the generation of F-, LILE-, rare metal-rich granitic melts; (iii) their transfer through the crust with protracted fractionation facilitated by their low viscosity due to high F-Li contents; and finally (iv) their emplacement as rare metal intrusions at shallow crust levels.

Lateral chemical heterogeneity in the Palaeocene upper mantle beneath the Scottish Hebrides

Abstract: The early major products of Tertiary volcanicity in both Skye and Mull are transitional basic lavas, similar in their major-element chemistry to world-wide alkali basalt series. In contrast, their contents of incompatible trace elements bear more resemblance to those of olivine tholeiites. The Mull basalts have similar ranges of silica saturation, Mg/(Mg+Fe), Y and Yb, but lower overall abundance ranges of strongly incompatible elements than the Skye basalts. The variation of incompatible elements in the Mull and Skye lavas is consistent with a model of a mantle source from which a small amount of melt (no more than 1 % ?) had been extracted, with the pre-Tertiary upper-mantle fusion beneath Mull slightly greater than beneath Skye. Chemical and tectonic considerations suggest that this mantle was neither residual from the formation of the Archaean Lewisian complex, nor emplaced as a result of tension associated with the Gainozoic rifting of the North Atlantic. Data on major and trace elements for a mafic alkalic dyke of the Permian swarms that pass through western Scotland show that these have the requisite geochemical characteristics to have caused this depletion. Such dykes are more abundant in the region of Mull than Skye.