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Five Quaternary interglacial periods are represented in core 57-7 from the Iceland Sea. Analysis of coccolith and planktonic foraminiferal assemblages from the interglacial periods (Oxygen Isotope Stages 1, 5, 7, 9 and 11) shows both similarities and differences in the assemblages. The differences indicate that the palaeoenvironment was not identical in the five interglacial periods. Oxygen Isotope Substage 5e reflects the warmest period, with the greatest inflow of warm Atlantic water. During this interval the Arctic Front apparently had a more westerly position than it has today. Substages 5a and 5c were periods when Arctic water masses dominated, as at the present day. In Oxygen Isotope Stages 7 and 9 inflow of Atlantic water was limited. Oxygen Isotope Stage 11 reflects a period of great productivity, but the region was still dominated by Arctic water masses. The position of the Arctic Front was possibly close to that of today, but not at the extreme western position it had in Oxygen Isotope Substage 5e. 相似文献
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Orogenic peridotites occur enclosed in Proterozoic gneissesat several localities in the Western Gneiss Region (WGR) ofwestern Norway; garnet peridotites typically occur as discretezones within larger bodies of garnet-free, chromite-bearingdunite and are commonly closely associated with pyroxenitesand eclogites. The dunites of the large Almklovdalen peridotitebody have extremely depleted compositions (Mg-number 92–93·6);the garnet peridotites have lower Mg-number (90·6–91·7)and higher whole-rock Ca and Al contents. Post-depletion metasomatismof both rock types is indicated by variable enrichment in thelight rare earth elements, Th, Ba and Sr. The dunites can bemodelled as residues after very high degrees (>60%) of meltextraction at high pressure (5–7 GPa), inconsistent withthe preservation of lower degrees of melting in the garnet peridotites.The garnet peridotites are, therefore, interpreted as zonesof melt percolation, which resulted in refertilization of thedunites by a silicate melt rich in Fe, Ca, Al and Na, but notTi. Previous Re–Os dating gives Archaean model ages forthe dunites, but mixed Archaean and Proterozoic ages for thegarnet peridotites, suggesting that refertilization occurredin Proterozoic time. At least some Proterozoic lithosphere mayrepresent reworked and transformed Archaean lithospheric mantle. KEY WORDS: Archaean mantle; Proterozoic mantle; Western Gneiss Region, Norway; mantle metasomatism; garnet peridotite 相似文献
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