Olivine clinopyroxenite xenoliths in the Oslo Rift, SE Norway

E. R. Neumann*, T. Andersen, E. W. Mearns

*Corresponding author for this work

Research output: Contribution to journalArticle

17 Citations (Scopus)

Abstract

Olivine clinopyroxenite xenoliths in a basalt flow at Krokskogen in the Oslo rift consist mainly of Al-Ti-rich clinopyroxene and alteration products after olivine (possibly also orthopyroxene). The clinopyroxene contains primary inclusions of Cr-Al-bearing titanomagnetite, pyrite and devitrified glass, and secondary fluid inclusions rich in CO2. On the basis of petrography, mineral compositions and bulk major and trace element chemistry, it is concluded that the xenoliths represent cumulates with about 5% trapped liquid, formed from a mildly alkaline basaltic magma. Microthermometrical analysis of secondary or pseudosecondary fluid inclusions give a minimum pressure of formation of 5.5 to 6 kbars, that is a depth greater than 16-17 km. The host lava has initial e{open}Nd=+4.16±0.17 and e{open}Sr=-5.50±0.26, which is believed to reflect the isotopic composition of the lithospheric mantle source region under south Norway in early Permian time. The isotopic character of the magma which gave rise to the xenoliths is preserved in clinopyroxenes which have e{open}Nd t=+1.9 to +2.6 and e{open}Sr t= -1.1 to -1.8. The isotopic differences between the host magma and the xenoliths reflect some degree of crustal contamination of the xenolith's parent magma. The xenoliths of this study represent an important source of information about the large masses of dense cumulates found at depth in the crust under the Oslo rift.

Original languageEnglish
Pages (from-to)184-193
Number of pages10
JournalContributions to Mineralogy and Petrology
Volume98
Issue number2
DOIs
Publication statusPublished - Feb 1988

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