Hostname: page-component-78c5997874-ndw9j Total loading time: 0 Render date: 2024-11-20T00:14:04.971Z Has data issue: false hasContentIssue false
  • English
  • Français

The paragenesis of upper-mantle xenoliths from the Quaternary volcanics south-east of Gees, West Eifel, Germany

Published online by Cambridge University Press:  05 July 2018

F. E. Lloyd ,
A. D. Edgar ,
D. M. Forsyth  and
R. L. Barnett
F. E. Lloyd
Affiliation:
Department of Geoscience, University of Reading, Reading, England RG6 2AB
A. D. Edgar
Affiliation:
Department of Geology, University of Western Ontario, London, Ontario, Canada N6A 5B7
D. M. Forsyth
Affiliation:
Department of Geology, University of Western Ontario, London, Ontario, Canada N6A 5B7
R. L. Barnett
Affiliation:
Department of Geology, University of Western Ontario, London, Ontario, Canada N6A 5B7
Get access Rights & Permissions [Opens in a new window]

Abstract

Group I xenoliths, orthopyroxene-rich and orthopyroxene-free, contain Cr-spinel and clinopyroxene ± phlogopite, and occur together with Group II clinopyroxenites ± Ti-spinel ± phlogopite in K-mafic pyroclastics southeast of Gees. The petrography and clinopyroxene chemistry of orthopyroxene-rich (opx-rich sub-group) Group I xenoliths is consistent with an ‘original’ harzburgitic mantle that has been transformed to lherzolite by the addition of endiopside. In harzburgites, orthopyroxenes are reacting to diopside + olivine + alkali-silicate melt, and, by inference, the orthopyroxene-free (opx-free subgroup) Group I, dunite-wehrlite series can be linked to the opx-rich sub-group via this reaction. Progressive enrichment of dunitic material in endiopside-diopside has resulted in the formation of wehrlite. Phlogopite is titaniferous and occurs as a trace mineral in opx-rich, Group I xenoliths, whereas substantial phlogopite vein-networks are confined to the opx-free sub-group (dunite-wehrlite series). Interstitial, alkali-felsic glass occurs are veins within, and as extensions of, the phlogopite networks. Clinopyroxenes in phlogopite-veined xenoliths are decreased in Mg/(Mg + FeTotal) (mg) and Cr and increased in Ti, Al and Ca, compared with clinopyroxenes in xenoliths which have trace phlogopite. It is proposed that harzburgitic and dunitic mantle has been infiltrated by a Ca- and alkalirich, hydrous silicate melt rather than an ephemeral carbonatite melt. Dunite has been transformed to phlogopite wehrlite by the invasion of a Ca-, Al-, Ti- and K-rich, hydrous silicate melt. Ca-activity was high initially in the melt and was reduced by clinopyroxene precipitation. This resulted in enhanced K-activity which led to phlogopite veining of clinopyroxene-rich mantle. Group II phlogopite clinopyroxenites contain Ti-spinel and salites that are distinct in their Ti, Al and Cr contents from endiopsides and diopsides in Group I xenoliths. It is unlikely that these Group II xenoliths represent the culmination of the infiltration processes that have transformed dunite to wehrlite, nor can they be related to the host melt. These xenoliths may have crystallised from Ca- and K-bearing, hydrous silicate melts in mantle channelways buffered by previously precipitated clinopyroxene and phlogopite. Gees lherzolites contain pyroxenes and spinel with distinctly lower Al contents than these same minerals in lherzolites described previously from other West Eifel localities, which may reflect a distinctive lithology and/or processes of modification for the Gees mantle.

Keywords

xenolithsolivinepyroxeneupper mantleGeesWest Eifel, Germany
Type
Research Article
Information
Mineralogical Magazine , Volume 55 , Issue 378 , March 1991 , pp. 95 - 112
Copyright
Copyright © The Mineralogical Society of Great Britain and Ireland 1991

Access options

Get access to the full version of this content by using one of the access options below. (Log in options will check for institutional or personal access. Content may require purchase if you do not have access.)

References

Aoki, K. and Kushiro, I. (1968) Clinopyroxenes from ultramafic inclusions in Dreiser Weiher, Eifel. Contrib. Mineral. Petrol., 18, 324–37.CrossRefGoogle Scholar
Becker, H. J. (1977) Pyroxenites and horblendites from the maar-type volcanoes of the Westeifel, Federal Republic of Germany. Ibid. 65, 45–52.Google Scholar
Brown, G. M., Pinsent, R. H., and Coisy, P. (1980) The petrology of spinel-peridotite xenoliths from the Massif Central, France. Am. J. Sci., 280A, 471–98.Google Scholar
Collre, A. L. G. (1963) A fabric study of lherzolites with special reference to ultrabasic nodular inclusions in the lavas of Auvergne (France). Leidse. Geol. Med., 28, 1–102.Google Scholar
Conrad, W. K. and Kay, R. W. (1984) Ultramafic and mafic inclusions from Adak Island: crystallisation history and implications for the nature of primary magmas and crutal evolution in the Aleutian arc. J. PetroL, 24, 88–125.CrossRefGoogle Scholar
Edgar, A. D., Green, D. H., and Hibberson, W. O. (1976) Experimental petrology of a highly potassic magma. Ibid. 17, 335–56.Google Scholar
Edgar, A. D., Lloyd, F. E., Forsyth, D. M., and Barnett, R. L. (1989) Origin of glass in upper mantle xenoliths from the Quaternary volcanics SE of Gees, West Eifel, Germany. Contrib. Mineral. Petrol., 103, 277–86.CrossRefGoogle Scholar
Embey-Isztin, A., Scharbert, H. G., Dietrich, H., and Poultidis, H. (1989) Petrology and geochemistry of peridotite xenoliths in alkali basalts from the Transdanubian Volcanic Region, West Hungary. J. Petrol., 30, 79–105.CrossRefGoogle Scholar
Frechen, J. (1959) In Die Vulcanische Eifel (Frechen, J., Hopman, M., and Knetsch, G., eds.). Wilhelm Stollfuss, Verlag, Bonn.Google Scholar
Frechen, J. (1962) Fuhrer zu vulkanologischepetrographischen Exkursionen im Siebengebirge am Rhein, Laacher Vulkangebeit und Maargebiet der Westeifel. Stuttgart.Google Scholar
Frechen, J. (1963) Kristatlisation, Mineralbestand, Mineralchemismus und Forderfolger in der Mafitite vom Dreiser Weiher in der Eifel. Neues Jahrb. Mineral. Mh., 205.Google Scholar
Frey, F. A. and Prinz, M. (1978) Ultramafic inclusions from San Carlos, Arizona: petrologic and geochemical data bearing on their petrogenesis. Earth Planet. Sci. Lett., 38, 129–76.CrossRefGoogle Scholar
Green, D. H. and Wallace, M. E. (1988) Mantle metasomatism by ephemeral carbonatite melts. Nature, 336, 459–62.CrossRefGoogle Scholar
Irvine, T. N. (1967) Chromian spinel as a petrogenetic indicator, Part 2, Petrologic applications. Can. J. Earth. Sci., 4, 71–103.CrossRefGoogle Scholar
Irving, A. (1980) Petrology and geochemistry of composite ultramafic xenoliths in alkalic basalts and implications for magmatic processes within the mantle. Am. J. Sci., 280A, 389–426.Google Scholar
Jakěs, P. and Vokurka, K. (1987) Central Europe. In Mantle Xenoliths (Nixon, P. H., ed.). Wiley, London, 125–34.Google Scholar
Kempton, P. D., Harmon, R. S., Stosch, H.-G., Hoefs, J., and Hawkesworth, C. J. (1988) Open-system O-isotope behaviour and trace element enrichment in the sub-Eifel mantle. Earth. Planet. Sci. Lett., 89, 273–87.CrossRefGoogle Scholar
Lloyd, F. E. (1972) The petrogenesis of strongly alkaline mafic lavas and associated nodule suites from the West Eifel and southwest Uganda. Ph.D. Thesis, Univ. Reading.Google Scholar
Lloyd, F. E. (1987) Mantle metasomatic fluids in spinel lherzolites and alkali clinopyroxenites from the West Eifel and South West Uganda. In Mantle Metasomatism (Menzies, M. and Hawkesworth, C. J., eds.). Academic Press, 91–123.Google Scholar
Lloyd, F. E. and Bailey, D. K. (1969) Carbonatites in the tufts of the West Eifel, Germany. Contrib. Mineral. PetroL, 23, 136–9.CrossRefGoogle Scholar
Lloyd, F. E. and Bailey, D. K. (1975) Light element metasomatism of the continental mantle: the evidence and the consequences. Phys. Chem. Earth, 9, 389–416.CrossRefGoogle Scholar
Lloyd, F. E., Huntingdon, A. T., Davies, G. R., and Nixon, P. H. (1990) Phanerozoic volcanism of south west Uganda: a case for regional K and LILE enrichment of the lithosphere beneath a domed and rifted continental plate. In Phanerozoic Magmatism and Structural Evolution of the African Plate (Kumpunza, A. B. and Lubala, R. T., eds.). Springer Veralg, Bonn, in press.Google Scholar
Mercier, J. C. and Nicholas, A. (1975) Textures and fabrics of upper mantle peridotites as illustrated by xenoliths from basalts. J. Petrol., 16, 454–87.CrossRefGoogle Scholar
Mertes, H. and Schmincke, H-U. (1985) Mafic potassic lavas of the Quaternary West Eifel volcanic field. Major and trace elements. Contrib. Mineral. Petrol., 89, 130–45.CrossRefGoogle Scholar
Nixon, P. H. (1987) Mantle Xenoliths. Wiley and Sons, Chichester. 844 pp.Google Scholar
Paul, D. K. (1971) Strontium isotope studies on ultramafic inclusions from Dreiser Weiher, EifeI, Germany. Contrib. Mineral Petrol., 34, 22–8.CrossRefGoogle Scholar
Poldvervaart, A. and Hess, H. H. (1951) Clinopyroxenes in the crystallisation of basaltic magmas. J. Geol., 59, 472–89.CrossRefGoogle Scholar
Seck, H. A. and Reese, D. (1979) Enstehung und Zusamensetzung von Glasern in Peridotiten der Westeifel. Fortschr. Mineral., 57, Bh. 224–5.Google Scholar
Stosch, H. G. and Seck, H. A. (1980) Geochemistry and mineralogy of two spinel peridotite suites from Dreiser Weiher W. Germany. Geochim. Cosmochim. Acta, 44, 457–70.CrossRefGoogle Scholar
Stosch, H. G. and Lugmair, G. W. (1986) Trace element and Sr and Nd isotope geochemistry of peridotite xenoliths from the Eifel (West Germany) and their bearing on the evolution of the subcontinental lithosphere. Earth. Planet. Sci. Lett., 80, 281–98.CrossRefGoogle Scholar
Wass, S. Y. (1979) Multiple origins of clinopyroxenes in alkali basaltic rocks. Lithos, 12, 115–32.CrossRefGoogle Scholar