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Evidence from mantle xenoliths for an enriched lithospheric keel under the Outer Hebrides (1987)

Menzies, Martin A. ; Halliday, Alexander N. ; Palacz, Zenon ; [et al.]

[s.l.] : Nature Publishing Group

Nature 325 (1987), S. 44-47

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ISSN: 1476-4687

Source: Nature Archives 1869 - 2009

Topics: Biology , Chemistry and Pharmacology , Medicine , Natural Sciences in General , Physics

Notes: [Auszug] The report7 of diverse suites of mafic and ultramafic xenoliths, the best evidence for heterogeneity in the Scottish mantle,.prompted investigation of the chemical constitution., of the mantle below the Lewisiah crust. We now report'results for the Loch Roag monchiquite dyke, oi" Tertiary age (M. ...

Type of Medium: Electronic Resource

URL: http://dx.doi.org/10.1038/325044a0

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Petrogenesis of late stage magmatism at Hold with Hope, East Greenland (1998)

Ellam, Rob M. ; Upton, Brian G. J. ; Fitton, J. Godfrey

Springer

Contributions to mineralogy and petrology 133 (1998), S. 51-59

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ISSN: 1432-0967

Source: Springer Online Journal Archives 1860-2000

Topics: Geosciences

Notes: Abstract The Myggbukta caldera complex and a swarm of basic dykes constitute the latest Tertiary magmatism in the Hold with Hope region, East Greenland. The Sr and Nd isotope ratios of these rocks show coherent variations which extend to high 87Sr/86Sr and low 143Nd/144Nd values and require a contribution from continental lithosphere. Broad correlations with major element differentiation indices suggest that the continental component was incorporated during magmatic differentiation thereby favouring a crustal contamination process. Trace element concentrations are strongly correlated with isotopic compositions but display ranges for many incompatible elements which extend beyond likely crustal contaminant compositions. This is readily modelled by AFC processes in which the dominant cause of trace element enrichment is the concentration effect of fractional crystallisation rather than the composition of the contaminant. The simplest such models still require unrealistically high degrees of fractional crystallisation to explain the ten-fold enrichment of some trace elements. This can be overcome if the primary magmas entering the crust already had highly variable trace element compositions. Such variability is readily achieved if melts from different parts of the melting column escape without thorough homogenization. An AFC model which incorporates variability in parental magma composition is then able to simulate the range of compositions observed at Hold with Hope. This carries the implication that the variations observed are more readily attributed to changes in uncontaminated parental magma than to variations in the composition or amount of contaminant.