Metasomatism-controlled hydrogen distribution in the Spitsbergen upper mantle

Abstract Hydrogen concentrations in minerals of peridotite xenoliths in alkali basaltic rocks from Quaternary volcanoes in northwest Spitsbergen were measured using polarized Fourier transform infrared spectroscopy (FTIR) to trace the effects of geologic processes on hydrogen distribution in the continental lithospheric mantle. The mineral grains show hydrogen profiles with lower concentrations at rims suggesting diffusive hydrogen loss during the entrapment and transport of the xenoliths in magma. However, hydrogen concentrations in the centers of the grains are uniform and appear to represent hydrogen abundances in the Spitsbergen upper mantle. The olivine, orthopyroxene, and clinopyroxene contain 1–10, 130–290, and 350–560 ppm H2O, respectively. Hydrogen abundances away from metasomatic melt conduits recorded by Type 1 xenoliths are correlated with the concentrations of incompatible trace elements, indicating that hydrogen distribution is related to mantle metasomatism. By contrast, hydrogen near the melt conduits, recorded by Type 2 xenoliths, shows no regular correlations with incompatible trace elements (except Nb in clinopyroxene) and may be affected by fractional crystallization of amphibole in the conduits. Hydrogen contents decrease away from the melt conduits and are controlled by the interaction between the depleted host mantle and percolating metasomatic melts. Therefore, the metasomatic melt could have variably hydrated the Spitsbergen upper mantle via different processes. The H2O/Ce ratios of the melt in equilibrium with clinopyroxene near the metasomatic melt conduits range from 93 to 218, i.e., within the oceanic island basalt (OIB) range. This is consistent with that the metasomatic melt could have been derived from OIB-type sources evidenced by the Sr-Nd isotope compositions of the xenoliths.

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Isotopic analyses of clinopyroxene in mantle xenoliths demonstrate the effects of kimberlite melt metasomatism upon the lithospheric mantle

10.5194/egusphere-egu2020-5331 ◽

2020 ◽

Author(s):

Angus Fitzpayne ◽

Andrea Giuliani ◽

Janet Hergt ◽

Jon Woodhead ◽

Roland Maas

Keyword(s):

Trace Element ◽

Lithospheric Mantle ◽

Mantle Metasomatism ◽

Mantle Xenoliths ◽

Isotopic Compositions ◽

Isotopic Analyses ◽

Cretaceous Magmatism

As clinopyroxene is the main host of most lithophile elements in the lithospheric mantle, the trace element and radiogenic isotope systematics of this mineral have frequently been used to characterise mantle metasomatic processes. To further our understanding of mantle metasomatism, both solution-mode Sr-Nd-Hf-Pb and in situ trace element and Sr isotopic data have been acquired for clinopyroxene grains from a suite of peridotite (lherzolites and wehrlites), MARID (Mica-Amphibole-Rutile-Ilmenite-Diopside), and PIC (Phlogopite-Ilmenite-Clinopyroxene) rocks from the Kimberley kimberlites (South Africa). The studied mantle samples can be divided into two groups on the basis of their clinopyroxene trace element compositions, and this subdivision is reinforced by their isotopic ratios. Type 1 clinopyroxene, which comprises PIC, wehrlite, and some sheared lherzolite samples, is characterised by low Sr (~100&#8211;200 ppm) and LREE concentrations, moderate HFSE contents (e.g., ~40&#8211;75 ppm Zr; La/Zr < 0.04), and restricted isotopic compositions (e.g., 87Sr/86Sri = 0.70369&#8211;0.70383; &#949;Ndi = +3.1 to +3.6) resembling those of their host kimberlite magmas. Available trace element partition coefficients can be used to show that Type 1 clinopyroxenes are close to equilibrium with kimberlite melt compositions, supporting a genetic link between kimberlites and these metasomatised lithologies. Thermobarometric estimates for Type 1 samples indicate equilibration depths of 135&#8211;155 km within the lithosphere, thus showing that kimberlite melt metasomatism is prevalent in the deeper part of the lithosphere beneath Kimberley. In contrast, Type 2 clinopyroxenes occur in MARID rocks and coarse granular lherzolites, which derive from shallower depths (<130 km), and have higher Sr (~350&#8211;1000 ppm) and LREE contents, corresponding to higher La/Zr of >~0.05. The isotopic compositions of Type 2 clinopyroxenes are more variable and extend from compositions resembling the &#8220;enriched mantle&#8221; towards those of Type 1 rocks (e.g., &#949;Ndi = -12.7 to -4.4). To constrain the source of these variations, in situ Sr isotope analyses of clinopyroxene were undertaken, including zoned grains in Type 2 samples. MARID and lherzolite clinopyroxene cores display generally radiogenic but variable 87Sr/86Sri values (0.70526&#8211;0.71177), which might be explained by the interaction between peridotite and melts from different enriched sources with the lithospheric mantle. In contrast, the rims of these Type 2 clinopyroxenes trend towards compositions similar to those of the host kimberlite and Type 1 clinopyroxene from PIC and wehrlites. These results are interpreted to represent clinopyroxene overgrowth during late-stage (shortly before/during entrainment) metasomatism by kimberlite magmas. Our study shows that an early, pervasive, alkaline metasomatic event caused MARID and lherzolite genesis in the lithospheric mantle beneath the Kimberley area, which was followed by kimberlite metasomatism during Cretaceous magmatism. This latter event is the time at which discrete PIC, wehrlite, and sheared lherzolite lithologies were formed, and MARID and granular lherzolites were partly modified.

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

Philosophical Transactions of the Royal Society of London. Series A, Mathematical and Physical Sciences ◽

10.1098/rsta.1980.0212 ◽

1980 ◽

Vol 297 (1431) ◽

pp. 229-244 ◽

Cited By ~ 35

Keyword(s):

Trace Elements ◽

North Atlantic ◽

Upper Mantle ◽

Major Element ◽

Major And Trace Elements ◽

The North ◽

Incompatible Elements ◽

Major Element Chemistry ◽

Pass Through ◽

Incompatible Trace Elements

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.

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Phytochemical and Micromorphological Traits of Geranium dalmaticum and G. macrorrhizum (Geraniaceae)

Natural Product Communications ◽

10.1177/1934578x1300800526 ◽

2013 ◽

Vol 8 (5) ◽

pp. 1934578X1300800 ◽

Cited By ~ 5

Author(s):

Dario Kremer ◽

Dubravka Vitali Čepo ◽

Valerija Dunkić ◽

Ivna Dragojević Müller ◽

Ivan Kosalec ◽

...

Keyword(s):

Trace Elements ◽

Essential Oil ◽

Epidermal Cell ◽

Pollen Morphology ◽

Glandular Trichomes ◽

High Concentration ◽

Subcuticular Space ◽

Type 3

A study of types and distribution of trichomes, pollen morphology, chemical composition of essential oil, and the content of macroelements and trace elements was conducted on endemic and previously uninvestigated Geranium dalmaticum (Beck) Rech. f. and widely distributed G. macrorrhizum L. growing in Croatia. The essential oil of G. dalmaticum was characterized by a high concentration of monoterpenes (82.2%) and the oil of G. macrorrhizum by mainly sesquiterpenes (76.7%). Among the investigated macroelements, the content of Ca was the highest (19,125.6 mg/kg and 22,439.6 mg/kg in G. dalmaticum and G. macrorrhizum, respectively). The content of trace elements ranged from 0.16 (Cr) to 110.01 mg/kg (Al) in G. dalmaticum, and from 0.01 (Cd) to 101.8 mg/kg (Al) in G. macrorrhizum. Non-glandular trichomes and two (in G. dalmaticum three) types of capitate glandular trichomes (type 1 composed of one basal epidermal cell, and one head cell with subcuticular space; type 2 composed of one basal epidermal cell, one or two stalk cells, and one head cell with subcuticular space; type 3 composed of one basal epidermal cell, 2–6 stalk cells, and one head cell with subcuticular space) were observed on leaves, stems and calyxes.

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An evaluation of major element heterogeneity in the mantle sources of basalts

Philosophical Transactions of the Royal Society of London. Series A, Mathematical and Physical Sciences ◽

10.1098/rsta.1980.0223 ◽

1980 ◽

Vol 297 (1431) ◽

pp. 383-407 ◽

Cited By ~ 134

Keyword(s):

Trace Elements ◽

Trace Element ◽

Major Element ◽

Major Elements ◽

Element Abundances ◽

Ocean Island ◽

Basaltic Rocks ◽

The North ◽

Mantle Sources ◽

Incompatible Trace Elements

Understanding the evolution of the mantle requires a knowledge of the relative variations of the major elements, trace elements and isotopes in the mantle. Most of the evidence for mantle heterogeneity is based on variations in the trace element and isotopic ratios of basaltic rocks. These ratios are presumed to reflect variations in the mantle sources. To compare major element heterogeneities with trace element and isotopic heterogeneities, it is necessary that the major element abundances in basalts also reflect variations in the mantle sources. Probably the only major element for which this is so is iron. If a basalt has only undergone fractional crystallization of olivine, then the abundance of FeO in the basalt reflects the FeO/MgO ratio of the mantle source, the degree of melting, and the pressure at which melting occurs. Relative pressures and degrees of melting can often be constrained, so that variations in the abundances of FeO can be used to obtain information about variations in the FeO/MgO ratio of the mantle sources of basalts. Comparison of FeO contents with trace element and isotopic contents of basalts shows some striking correlations and leads to the following conclusions. 1. Parental magmas for Kilauean basalts from Hawaii may be related by different degrees of melting of a homogeneous, garnet-bearing source. 2. Mid-ocean ridge basalts from the North Atlantic show a negative correlation of La/Sm with FeO, suggesting that the sources that are most enriched in incompatible trace elements are most depleted in FeO relative to MgO, and are probably also depleted in the other components of basalt. This correlation does not apply to the entire suboceanic mantle. 3. A comparison of tholeiites from near the Azores and from Hawaii shows that sources with similar Nd and Sr isotope ratios may have undergone distinctly different histories in the development of their major and trace element abundances. 4. Ocean island tholeiites tend to be more enriched in FeO than ocean floor tholeiites. Either the ocean island sources have greater FeO/MgO ratios, or melting begins at significantly greater pressures beneath ocean islands than beneath ocean ridges. 5. Major element variations in the mantle are controlled mainly by tectonics and the addition or removal of silicate melts. Trace element variations, however, may be controlled by the addition or removal of fluids as well. Thus major elements, trace elements and isotopes may each give a different perspective important to the understanding of the evolution of the mantle.

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Modelling clinopyroxene/melt partition coefficients for higher upper mantle pressures

10.5194/egusphere-egu21-12478 ◽

2021 ◽

Author(s):

Julia Marleen Schmidt ◽

Lena Noack

Keyword(s):

Trace Elements ◽

Trace Element ◽

Thermodynamic Model ◽

Upper Mantle ◽

Partition Coefficients ◽

Trace Element Partitioning ◽

Partial Melt ◽

Element Partitioning ◽

Incompatible Trace Elements ◽

Free Element

When partial melt occurs in the mantle, redistribution of trace elements between the solid mantle material and partial melt takes place. Partition coefficients play an important role when determining the amount of trace elements that get redistributed into the melt. Due to a lower density compared to surrounding solid rock, partial melt that was generated in the upper mantle will rise towards the surface, leaving the upper mantle depleted in incompatible trace elements and an enriched crust. Studies investigating trace element partitioning in the mantle typically rely on constant partition coefficients throughout the mantle, even though it is known that partition coefficients depend on pressure, temperature, and composition. Between the pressures of 0-15 GPa, partition coefficients vary by two orders of magnitude along both, solidus and liquidus. Since partition coefficients exhibit a parabolic relationship in an Onuma diagram, a similar variation is expected for all trace element partition coefficients that can be derived from the sodium partition coefficients.In this study, we developed a thermodynamic model for sodium in clinopyroxene after Blundy et al. (1995). With the thermodynamic model results, we were able to deduce a P-T dependent equation for sodium partitioning that is applicable up to 12 GPa between the peridotite solidus and liquidus. Because sodium is an almost strain-free element in jadeite, it can be used as a reference to model partition coefficients for other elements, including heat producing elements like K, Th, and U. This gives us the opportunity to insert P-T dependent partition coefficient calculations of any trace element into mantle melting models, which will have a big impact on the accuracy of elemental redistribution calculations and therefore, if the partitioning of the heat producing elements is taken into account, also the evolution of the mantle and crust.Blundy, J. et al. (1995): Sodium partitioning between clinopyroxene and silicate melts, J. Geophys. Res., 100, 15501-15515.Schmidt, J.M. and Noack, L. (2021): Parameterizing a model of clinopyroxene/melt partition coefficients for sodium to higher upper mantle pressures (to be submitted)

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