Incompatible element

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

Petrogenesis of High-MgO Lavas of the Lower Mull Plateau Group, Scotland: Insights from Melt Inclusions

Abstract: Published data on Palaeogene flood basalts of the lower Mull Plateau Group (Scotland) show that the most primitive lavas (MgO > 8 wt %) have the greatest extent of crustal assimilation, inconsistent with a simple coupled assimilation–fractional crystallization (AFC) model. We present elemental data on rehomogenized olivine-hosted melt inclusions from four high-MgO flows to investigate the nature of crustal assimilation and melt aggregation processes during the initial stages of flood basalt magmatism on Mull. Whole-rock compositions have been variably modified by hydrothermal alteration associated with the nearby Central Complexes. Nd isotope compositions, which should be insensitive to this alteration, are lower than typical mantle values (eNd + 2·4 to −5·7), indicating variable modification by crustal assimilation in all four samples. Melt inclusions are protected against alteration effects within their host olivine crystals, and provide more robust estimates of magmatic liquid compositions than whole-rocks, particularly for the alkali elements Na, K and Ba. The whole-rock samples show limited variations in Na2O (2·4–2·8 wt %) and K2O (0·23–0·29 wt %), despite a wide range in immobile elements (e.g. Zr 62–126 ppm). In contrast, the melt inclusions show far greater variability in Na2O (1·8–4·0 wt %) and K2O (0·02–0·35 wt %) and positive correlations between K and Na. Melt inclusions from different samples show systematic correlations between alkalis (K + Na) and incompatible element ratios (e.g. Zr/Y), indicating that the inclusions record magmatic values for the fluid-mobile elements. For the two most incompatible-element-enriched samples, the whole-rock analyses are similar to the melt inclusions except for lower Na and higher Ba that are related to alteration. Therefore, the crustal assimilation in these magmas must have taken place prior to growth of the olivines. For the two more depleted samples, the inclusions have less contaminated compositions than the whole-rocks, and show broad trends of increasing K/Ti with decreasing Fo% of the host olivine. For these samples, crustal assimilation must have taken place both during and after growth of the olivines and in an AFC style in which assimilation is linked to magmatic differentiation. Melt inclusions from single samples show limited variability in Zr/Y compared with K/Ti, indicating that aggregation of melts from different parts of the melt column must have occurred at deeper levels prior to growth of the olivines in the samples. Although the whole-rock compositional variations capture the broad details of crustal assimilation and melting histories for the Mull lavas despite the variable effects of hydrothermal alteration, the melt inclusion data more clearly resolve significant details of these magmatic processes. The extent of assimilation and differentiation is linked to the depth of magma stalling: primitive, contaminated magmas in the lower crust vs. evolved, uncontaminated magmas at sub-Moho depths.

Geochemical Characteristics of the Granites of Bundelkhand Massif, Central India

Abstract: The Bundelkhand massif comprises various types of granites. On the basis of field relations, three compositionally distinct granitic phases have been delineated. These are hornblende granite, biotite granite and leuco granite in stratigraphic sequence. The major elements variations against SiO 2 , display smooth trends which should be expected for a composite massif evolved by fractionai crystallization. The variations of incompatible elements compared to the compatible elements suggest a partial melting process for the evolution of the massif.

Minettes from Schirmacher Oasis, East Antarctica — indicators of an enriched mantle source

Abstract: Minette dykes intersect the Precambrian crystalline basement of Schirmacher Oasis, East Antarctica. The rocks have intermediate to basic compositions, showing shoshonitic to ultrapotassic character. The samples show enhanced concentrations of compatible elements and high mg# combined with extreme enrichments in LILE (especially Ba) and LREE. Mantle-normalized trace element patterns are characterized by coupled relative depletions of Nb and Ti and strong fractionations between LILE and HFSE. The minettes display fractionated chondrite-normalized REE patterns with high and varying LREE concentrations in contrast to relative low and nearly constant HREE contents. High magma-ascent and cooling rates of lamprophyric magmas argue against a fundamental change of the primary geochemical signatures in minette magmas by interactions with the continental crust during ascent. The major and trace element abundances of the studied minettes point to varying degrees of partial melting of a mantle source, which was enriched in LILE and LREE during or before the melting event. Incompatible element signatures argue for the involvement of subducted pelagic sediments.

Petrogenesis of Songshugou dunite body in the Qinling orogenic belt, Central China: Constraints from geochemistry and melt inclusions

Abstract: The Songshugou dunite body, which occupies an area of about 20 km 2 , is the largest ultramafic massif in the eastern Qinling orogenic belt, Central China. The major component of this body is dunitic rocks including mylonitic dunite and coarse-grained dunite; they occupy about 95 vol% of the total body. Petrography, mineral composition, major and trace elements and primitive melt inclusions have been investigated in this paper; all revealed that this dunite body is the product of melt-rock interaction by porous percolation flow. In comparison with dunite sills or veins in harzburgite from the basal part of Oman ophiolite, this dunite body is characterized by lower contents of Al 2 O 3 , CaO and HREE but higher content of highly incompatible elements and Zr and Hf. The LREE enriched patterns and primitive mantle normalized spidergrams of trace elements are also different from the Oman dunite. Combining with melt inclusions observed in olivines, we conclude that this dunite body is the product of large- scale porous percolation flow of high-MgO melts within depleted mantle peridotites. The high-MgO magma, in essence, was most probably produced at the hot head of an upwelling mantle plume. The occurrence of the Songshugou dunite body is closely associated with the activity of mantle super-plume in Neo-Proterozoic era in the Yangtze Craton.