Computer Science
Scientific paper
Mar 1987
adsabs.harvard.edu/cgi-bin/nph-data_query?bibcode=1987e%26psl..82..121d&link_type=abstract
Earth and Planetary Science Letters, Volume 82, Issue 1-2, p. 121-135.
Computer Science
42
Scientific paper
Sr and Nd isotope analyses and REE patterns are presented for a suite of well-documented mantle-derived xenoliths from the French Massif Central. The xenoliths include spinel harzburgites, spinel lherzolites and some pyroxenites. They show a wide range of textures from undeformed protogranular material through porphyroclastic to equigranular and recrystallised secondary types. Textural differences are strongly linked to trace element geochemistry and variations in radiogenic isotope ratios. Many undeformed protogranular xenoliths are Type IA LREE-depleted with MORB-type ɛSr values between - 30.7 and - 23.6, and ɛNd values + 13.9 to + 9.4. A second group of undeformed xenoliths are Type IB LREE-enriched with higher ɛSr values (- 22.7 to - 10.6) and lower ɛNd values (+ 11.9 to + 5.6). Deformed xenoliths with porphyroclastic, equigranular and secondary recrystallised textures are all Type IB (LREE-enriched, ɛNd < 6.4, ɛSr > 11.8). It is proposed that two separate events have given rise to the observed mixing arrays: (1) MORB-source depleted mantle was enriched by a component derived from an enriched mantle. Deformation and recrystallisation accompanied this event. (2) Subsequently, unenriched MORB-source mantle interacted with magmas chemically akin to the host basalts, and enrichment occurred with little deformation. Hypotheses of Tertiary mantle diapirism resulting in isochemical deformation and refinement of protogranular mantle to equigranular mantle are untenable because of differences in REE patterns and isotopic ratios between different textural groups.
Downes Hilary
Dupuy Claude
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