Origin of Paleoproterozoic Komatiites at Jeesiorova, Kittila Greenstone Complex, Finnish Lapland |
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Authors: | GANGOPADHYAY AMITAVA; WALKER RICHARD J; HANSKI EERO; SOLHEID PETER A |
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Institution: | 1 ISOTOPE GEOCHEMISTRY LABORATORY, DEPARTMENT OF GEOLOGY, UNIVERSITY OF MARYLAND, COLLEGE PARK, MD 20742, USA
2 DEPARTMENT OF GEOSCIENCES, UNIVERSITY OF OULU, P.O. BOX 3000, FIN-90014 UNIVERSITY OF OULU, FINLAND
3 INSTITUTE FOR ROCK MAGNETISM, 291 SHEPHERD LABS, 100 UNION STREET S.E., MINNEAPOLIS, MN 55455-0128, USA |
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Abstract: | Komatiites from the 2 Ga Jeesiörova area in Finnish Laplandhave subchondritic Al2O3/TiO2 ratios like those in Al-depletedkomatiites from Barberton, South Africa. They are distinct inthat their Al abundances are higher than those of the Al-depletedrocks and similar to levels in Al-undepleted komatiites. Moderatelyincompatible elements such as Ti, Zr, Eu, and Gd are enriched.Neither majorite fractionation nor hydrous melting in a supra-subductionzone setting could have produced these komatiites. Their highconcentrations of moderately incompatible elements may haveresulted from contamination of their parental melt through interactionwith metasomatic assemblages in the lithospheric mantle or enrichmentof their mantle source in basaltic melt components. ReOsisotope data for chromite from the Jeesiörova rocks yieldan average initial 187Os/188Os of 0·1131 ± 0·0006(2), Os(I) = 0·1 ± 0·5. These data, coupledwith an initial Nd of +4, indicate that melt parental to thekomatiites interacted minimally with ancient lithospheric mantle.If their mantle source was enriched in a basaltic component,the combined OsNd isotopic data limit the enrichmentprocess to within 200 Myr prior to the formation of the komatiites.Their OsNd isotopic composition is consistent with derivationfrom the contemporaneous convecting upper mantle. KEY WORDS: Finnish Lapland; Jeesiörova; komatiites; mantle geochemistry; petrogenesis; redox state; Re/Os isotopes; Ti enrichment |
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Keywords: | : Finnish Lapland Jeesiö rova komatiites mantle geochemistry petrogenesis redox state Re/Os isotopes Ti enrichment |
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