New data from the Holsteinian interglacial site Öje, central Sweden     

KARIN GARCIA AMBROSIANI  ANN-MARIE ROBERTSON 《Boreas: An International Journal of Quaternary Research》1998,27(4):289-295

The stratigraphy at Öje, central Sweden, has been reinvestigated. Till-covered organic sediments were encountered in two out of three excavations, while in one excavation only till occurred. One sediment succession was analysed for pollen and macrofossils. The vegetation represented by both pollen and macrofossil flora indicates a correlation with (the latter) part of the Holsteinian Interglacial, also in accordance with the predominantly acidophilous diatom flora.  相似文献   

Geochemical and Isotopic Evolution of Loihi Volcano, Hawaii   总被引：2，自引：6，他引：2  

GARCIA  MICHAEL O.; FOSS  DAVID J. P.; WEST  H. B.; MAHONEY  JOHN J. 《Journal of Petrology》1995,36(6):1647-1674

A 680m thick section from the deeply dissected east flank ofLoihi Volcano was sampled using the Pisces V submersible toevaluate the volcano's geochemical evolution. Three types oflavas were recovered: tholeiitic, weakly alkalic and stronglyalkalic. The ratio of alkalic to tholeiitic lavas varies systematicallywith depth, from predominantly alkalic at the base of the sectionto tholeiitic at the top. Glasses from these rocks have similarratios of highly incompatible elements and Pb, Sr and Nd isotopes,but distinct ratios of highly to moderately incompatible elements.Partial melting modeling indicates that these tholeiitic andalkalic lavas could be derived by variable degrees of partialmelting of a slightly heterogeneous source. Many distinct parentalmagmas were generated for each rock type during the 100–150k.y. that the east flank section was formed. Crystal fractionationand olivine accumulation were the dominant processes controllingcompositional variation among lavas of the same rock type. Magmamixing features were observed in only a few of the lavas collected. Loihi typifies the preshield stage of Hawaiian volcanism whenthe volcano drifts closer to the focus of the hotspot. The compositionalvariation in Loihi's east flank section, which may represent40% of the volcano's extrusive history, is consistent with thepredicted increase in partial melting during this drift. Thetransition from dominantly alkalic to tholeiitic volcanism onLoihi was fitful but relatively rapid and is now nearly complete.This transition is the opposite of that which occurs duringthe post-shield stage of Hawaiian volcanism as the volcano migratesaway from the hotspot focus. Loihi's tholeiitic lavas overlap in ratios of incompatible traceelements and Pb, Sr and Nd isotopes with lavas from its moreactive neighbor, Kilauea. The small differences in major elementcontents between lavas from these adjacent volcanoes can beexplained by high-pressure orthopyroxene fractionation of Loihimagmas, which may be a consequence of a low magma-supply rate,or by slightly shallower depths of melt segregation for Kilaueamagmas. KEY WORDS: Loihi volcano; Hawaii; geochemistry; Sr-Nd-Pb isotopes  相似文献