Isotopic and trace element evidence from lavas, bearing on mantle heterogeneity beneath Kenya

Nd, Sr and Pb isotope data, together with new major and trace element data are presented for lavas from northern Kenya. A general trend towards silica saturation and decreasing incompatible element contents is observed from the Miocene to the present day. Significantly, the abundances of different incompatible elements decrease The Nd, Sr and Pb isotope compositions of the basic lavas are similar to those observed on the Atlantic ocean islands. Comparison of the Sm/Nd ratios required to produce the Nd isotope ratios with those observed in the rocks indicates that light rare earth elements (r.e.e.) have probably been added to the source region of the lavas comparatively recently. A model involving recent metasomatism of the subcontinental mantle beneath Kenya, which could account for the correlated silica undersaturation and incompatible element content of the lavas, is proposed.

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Trace element evidence for mantle heterogeneity beneath the Scottish Midland Valley in the Carboniferous and Permian

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

10.1098/rsta.1980.0213 ◽

1980 ◽

Vol 297 (1431) ◽

pp. 245-257 ◽

Cited By ~ 16

Keyword(s):

Trace Elements ◽

Trace Element ◽

Partial Melting ◽

Mantle Source ◽

Incompatible Element ◽

Mantle Heterogeneity ◽

Alkaline Rocks ◽

Elemental Abundances ◽

Peridotite Mantle ◽

Incompatible Trace Elements

The alkaline rocks of Carboniferous to Permian age in the Midland Valley province range in composition from hypersthene-normative, transitional basalts to strongly undersaturated basanitic and nephelinitic varieties. They were formed by varying degrees of equilibrium partial melting of a phlogopite peridotite mantle. Ba, Ce, Nb, P, Sr and Zr were strongly partitioned into the liquid during melting; K and Rb were retained by residual phlogopite for small degrees of melting only. The composition of the mantle source is inferred to have been broadly similar to that from which oceanic alkaline basalts are currently being generated. It was, however, heterogeneous as regards distribution of the incompatible trace elements, with up to fourfold variations in elemental abundances and ratios. The mantle beneath the province may be divisible into several areas, of some hundreds of square kilometres each, which retained a characteristic incompatible element chemistry for up to 50 Ma and which imparted a distinctive chemistry to all the basic magmas generated within them.

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Assimilation and crystallization in basic magma chambers: trace-element and Nd-isotopic variations in the Kerns sill, Nipissing diabase province, Ontario

Canadian Journal of Earth Sciences ◽

10.1139/e89-061 ◽

1989 ◽

Vol 26 (4) ◽

pp. 737-754 ◽

Cited By ~ 15

Author(s):

Peter C. Lightfoot ◽

Anthony J. Naldrett

Keyword(s):

Trace Element ◽

Incompatible Element ◽

Basaltic Magma ◽

Basic Magma ◽

Magma Chambers ◽

Degree Of Contamination ◽

Incompatible Elements ◽

Laboratory Investigations ◽

Isotopic Variations ◽

Isotopic Effects

An investigation has been made of the trace-element and Nd-isotopic effects of assimilation at the roof of the Proterozoic Kerns sill in the 2.2 Ga Nipissing diabase province in Ontario. The ratios Th/Zr, La/Zr, and U/Zr and the concentrations of incompatible elements all tend to increase with decreasing Mg#, Ni, and Cr. These variations have been simulated by computer models in which assimilation and fractionation are coupled (AFC) and the most fractionated magmas (identified by low Mg#, Ni, and Cr and by high incompatible-element concentrations) are also the most contaminated (indicated by higher Th/Zr, La/Zr, and U/Zr and lower 143Nd/144Ndo). The results suggest that the ratio (r) of the change of magma mass due to assimilation relative to the change due to fractionation gradually increased. The latent heat of crystallization may have contributed sufficient heat to melt the roof of the intrusion where ponded crustal melts were separated from the underlying basic magma by a double-diffusive interface. Field relations suggest that this interface was progressively destroyed by convective erosion; thus the degree of contamination increased as the magma became more fractionated. These results are consistent with laboratory investigations designed to simulate assimilation at the roof of basaltic magma chambers.

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Meso-Neoproterozoic Mafic Sills along the South-Eastern Margin of the Siberian Craton, SE Yakutia: Petrogenesis, Tectonic and Geochemical Features

Minerals ◽

10.3390/min10090805 ◽

2020 ◽

Vol 10 (9) ◽

pp. 805 ◽

Cited By ~ 1

Author(s):

Aleksandr D. Savelev ◽

Sergey V. Malyshev ◽

Valery M. Savatenkov ◽

Daniil D. Ignatov ◽

Anastasia D. Kuzkina

Keyword(s):

Trace Element ◽

Lithospheric Mantle ◽

Aqueous Fluid ◽

Major Element Composition ◽

Nd Isotope ◽

Depleted Mantle ◽

Mid Ocean Ridge ◽

Ocean Ridge ◽

Light Rare Earth Elements ◽

Early Neoproterozoic

We report major and trace element concentrations, along with Nd isotope compositions, for Late Mesoproterozoic to Early Neoproterozoic dolerite sills from the Sette-Daban ridge (southern Verkhoyansk, south-east Siberia). Based on their major element composition, all rocks correspond to low-Ti (<3 wt% TiO2) moderately alkaline basalts. The intrusions can be subdivided into two groups based on their trace element compositions. One group includes sills mainly distributed in the southern part of the study area (Yudoma group), with mid-ocean ridge basalt (MORB) trace element patterns enriched in aqueous fluid mobile incompatible (FMI) elements (Sr, Pb, Ba, U). The second group includes sills mostly distributed in the northern part of the study area, enriched in immobile incompatible (II) elements (Th, Nb, light rare earth elements (LREE)) and to a lesser extent, in aqueous fluid mobile elements. The Nd isotope signatures of the dolerites characterize a depleted mantle source, with a small enrichment from recycled continental crust. The geochemical characteristics of these igneous rocks are analogous to low-Ti basalts of large intraplate provinces (e.g., the Karoo and Siberian Traps). We propose that they formed by rifting-induced melting of the heterogeneous metasomatized shallow spinel-bearing mantle zone. We suggest that two different melting sources were involved in the generation of the two geochemically distinct sill groups, including the addition of two different subduction components. The southern sills were formed by melting of depleted lithospheric mantle enriched with FMI elements, corresponding to subduction-induced metasomatic alteration by fluids at shallow depths. The northern dolerites were formed by melting of depleted lithospheric mantle enriched with II elements, associated with the melting of subducted sediments at deeper depths.

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Major-trace element and Sr-Nd isotope compositions of mafic dykes of the Singhbhum Craton: Insights into evolution of the lithospheric mantle

Lithos ◽

10.1016/j.lithos.2020.105959 ◽

2021 ◽

Vol 382-383 ◽

pp. 105959

Author(s):

Om Prakash Pandey ◽

Klaus Mezger ◽

Dewashish Upadhyay ◽

Debajyoti Paul ◽

Ajay Kumar Singh ◽

...

Keyword(s):

Trace Element ◽

Lithospheric Mantle ◽

Nd Isotope ◽

Mafic Dykes ◽

Singhbhum Craton

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Geochemistry of Ferrar Dolerite sills and dykes at Terra Cotta Mountain, south Victoria Land, Antarctica

Antarctic Science ◽

10.1017/s0954102095000113 ◽

1995 ◽

Vol 7 (1) ◽

pp. 73-85 ◽

Cited By ~ 11

Author(s):

A.D. Morrison ◽

A. Reay

Keyword(s):

Trace Element ◽

Mantle Source ◽

Source Region ◽

Crustal Component ◽

Enriched Mantle ◽

Victoria Land ◽

Trace Element Signature ◽

Geochemical Variation ◽

Element Enrichment ◽

Taylor Glacier

At Terra Cotta Mountain, in the Taylor Glacier region of south Victoria Land, a 237 m thick Ferrar Dolerite sill is intruded along the unconformity between basement granitoids and overlying Beacon Supergroup sedimentary rocks. Numerous Ferrar Dolerite dykes intrude the Beacon Supergroup and represent later phases of intrusion. Major and trace element data indicate variation both within and between the separate intrusions. Crystal fractionation accounts for much of the geochemical variation between the intrusive events. However, poor correlations between many trace elements require the additional involvement of open system processes. Chromium is decoupled from highly incompatible elements consistent with behaviour predicted for a periodically replenished, tapped and fractionating magma chamber. Large ion lithophile element-enrichment and depletion in Nb, Sr, P and Ti suggests the addition of a crustal component or an enriched mantle source. The trace element characteristics of the Dolerites from Terra Cotta Mountain are similar to those of other Ferrar Group rocks from the central Transantarctic Mountains and north Victoria Land, as well as with the Tasmanian Dolerites. This supports current ideas that the trace element signature of the Ferrar Group is inherited from a uniformly enriched mantle source region.

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Ore and Geochemical Specialization and Substance Sources of the Ural and Timan Carbonatite Complexes (Russia): Insights from Trace Element, Rb–Sr, and Sm–Nd Isotope Data

Minerals ◽

10.3390/min11070711 ◽

2021 ◽

Vol 11 (7) ◽

pp. 711

Author(s):

Irina Nedosekova ◽

Nikolay Vladykin ◽

Oksana Udoratina ◽

Boris Belyatsky

Keyword(s):

Trace Element ◽

Mantle Source ◽

Crustal Evolution ◽

Trace Element Data ◽

The Urals ◽

Nd Isotope ◽

Enriched Mantle ◽

Depleted Mantle ◽

Mantle Sources ◽

Geochemical Specialization

The Ilmeno–Vishnevogorsk (IVC), Buldym, and Chetlassky carbonatite complexes are localized in the folded regions of the Urals and Timan. These complexes differ in geochemical signatures and ore specialization: Nb-deposits of pyrochlore carbonatites are associated with the IVC, while Nb–REE-deposits with the Buldym complex and REE-deposits of bastnäsite carbonatites with the Chetlassky complex. A comparative study of these carbonatite complexes has been conducted in order to establish the reasons for their ore specialization and their sources. The IVC is characterized by low 87Sr/86Sri (0.70336–0.70399) and εNd (+2 to +6), suggesting a single moderately depleted mantle source for rocks and pyrochlore mineralization. The Buldym complex has a higher 87Sr/86Sri (0.70440–0.70513) with negative εNd (−0.2 to −3), which corresponds to enriched mantle source EMI-type. The REE carbonatites of the Chetlassky сomplex show low 87Sr/86Sri (0.70336–0.70369) and a high εNd (+5–+6), which is close to the DM mantle source with ~5% marine sedimentary component. Based on Sr–Nd isotope signatures, major, and trace element data, we assume that the different ore specialization of Urals and Timan carbonatites may be caused not only by crustal evolution of alkaline-carbonatite magmas, but also by the heterogeneity of their mantle sources associated with different degrees of enrichment in recycled components.

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