Abstract
This article reports new geochemical, Sr-Nd-Hf-Pb and Re-Os data on the rocks of the Middle Paleoproterozoic (1.99 Ga) Tiksheozero ultramafic-alkaline-carbonatite complex confined to the northeastern margin of the Karelian Craton. We focus on the poorly studied silicate rocks. Based on petrographic and geochemical research, the silicate rocks are subdivided into two groups: an ultramafic-mafic series depleted in REE, and other incompatible elements and an alkaline series enriched in these elements. Isotope studies showed that all rocks have juvenile isotope signatures and were likely derived from a primitive OIB-type mantle source with possible contributions of the subcontinental lithospheric mantle (SCLM). Insignificant crustal contamination is recorded by Pb and Os isotopic compositions. The incompatible element enrichment in the alkaline rocks and depletion in ultramafic-mafic rocks of the mildly alkaline series with allowance for insignificant crustal contamination confirm their derivation from different primary melts. However, a narrow range of Sr, Nd, Hf, and Pb isotope compositions and compact clusters in 207Pb/204Pb-206Pb/204Pb, Nd-87Sr/86Sr and Hf-Nd isotope diagrams indicate their origination from a common mantle source. A model of subsequent two-stage melting is being most consistent with the geochemical data for this complex.
Highlights
Alkaline-ultramafic carbonatite massifs are made up of a compositionally contrasting series: ultramafic, alkaline series, and carbonatites
Silicate rocks were sampled from three blocks of the Tiksheozero
The addition of small amounts of average continental crust (
Summary
Alkaline-ultramafic carbonatite massifs are made up of a compositionally contrasting series: ultramafic (dunite, peridotite, wehrlite, pyroxenite, and others), alkaline (foidolites, alkaline gabbro, nepheline syenite) series, and carbonatites. It is generally accepted that the formation of these massifs is related to the mantle plume activity and usually occurs in an intracontinental rift setting [1,2], being a part of large igneous provinces. Details of their genesis, parental magmas, and mutual relationships remain a hotly debatable problem [3,4,5,6]. Silicate rocks received either little attention, or have even remained beyond the scope of the studies, which made it impossible to solve the above-mentioned genetic problems
Sign-in/Register to view highlights & summary Sign-in/Register to access full text options 
Free) 
Talk to us
Join us for a 30 min session where you can share your feedback and ask us any queries you have
Schedule a call
