Recent Data on the Isotope–Geochemical Composition of Kimberlites in the TSNIGRI-Arkhangelskaya Pipe, Arkhangelsk Diamondiferous Province (Northern East European Platform)

Abstract

Recent data on the bulk and isotopic (Sr, Nd) composition of kimberlites from the low-diamondiferous TsNIGRI–Arkhangelskaya pipe, located in the Kepino field of the Arkhangelsk diamondiferous province, are presented. It is shown that the kimberlites belong to the moderate titanium type of kimberlites of the province and differ significantly from the previously studied kimberlites of the Kepino field in the lower concentrations of TiO₂, Ba, high field strength, and light rare earth elements. Among all the kimberlites of the province, the kimberlites from the TsNIGRI–Arkhangelskaya pipe have the most radiogenic Sr composition (⁸⁷Sr/⁸⁶Sr t from 0.7068 to 0.7089), which may be related to a combination of several factors. It has been established that the kimberlites from the pipe are represented by two varieties, having differences both in the concentrations of major and trace elements and in the Sr and Nd isotopic composition. The Nd isotopic composition (ε_Nd from 0 to –0.6) for type-I kimberlites indicates their enriched source in the lithospheric mantle. The type-II kimberlites have a less radiogenic Nd composition (ε_Nd from –3.5 to –4.9), which is interpreted ambiguously: their formation from an even more ancient enriched source inside the lithospheric mantle compared to type-I kimberlites cannot be excluded.