Nd-Sr-Os SYSTEMS OF ECLOGITES IN THE LITHOSPHERIC MANTLE OF THE KASAI CRATON (Angola)
L.P. Nikitina1,2, E.S. Bogomolov1,3,4, R.Sh. Krymsky5, B.V. Belyatsky5, N.M. Korolev1, V.N. Zinchenko6
1Institute of Precambrian Geology and Geochronology, nab. Makarova 2, St. Petersburg, 199034, Russia
2St. Petersburg State University, Institute of Earth Sciences, Universitetskaya nab. 7/9, St. Petersburg, 199034, Russia
3A.P. Karpinsky Russian Geological Research Institute
4Srednii prosp. 74, St. Petersburg, 199106, Russia
5A.P. Karpinsky Russian Geological Research Institute, Srednii prosp. 74, St. Petersburg, 199106, Russia
6Department of Geology, Catoca Geological-Mining Community, Luanda, Republic of Angola
Keywords: Upper mantle, eclogites, Nd-Sr-Os systems, model isotopic age, genesis
Abstract
We studied the Sm-Nd, Rb-Sr, and Re-Os isotope compositions of mantle xenoliths (eclogites and peridotites) from diamondiferous kimberlites of the Catoca cluster of the Kasai Craton. In the eclogites, the primary strontium isotope composition 87Sr/86Sr varies from 0.7056 to 0.7071, and the neodymium isotope composition εNd, from 1.8 to 2.6. The 187Re/188Os and 187Os/188Os ratios range from 135 to 80 and from 1.3110 to 1.9709, respectively, which indicates a significant portion of radiogenic 187Os: γOs = 129-147. These isotope values exceed the values assumed for model reservoirs (primitive upper mantle (PUM) and bulk silicate Earth (BSE)) and those of chondrites. The isotope composition of the studied systems indicates the formation of eclogites from a rhenium-enriched source, namely, the subducted oceanic crust transformed as a result of metasomatism and/or melting under upper-mantle conditions.
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