Mineralogical and geochemical features and the formation mechanism of
the picritic gabbro-dolerite horizon of the north-eastern branch of the Talnakh
intrusion (Norilsk region)
Kuzmin I.A, Tolstykh N.D.
Sobolev Institute of Geology and Mineralogy of the Siberian Branch of the RAS, Novosibirsk, Russia;
Keywords: Talnakh intrusion, main layered series, picritic gabbro-dolerites, inverse zoning, hybrid magma.
Abstract
Norilsk-type intrusions are characterized by unique reserves, disseminated copper-nickel mineralization, which is localized in picrite and taxitic gabbro-dolerites. At the same time, if picrite and taxitic gabbro-dolerites are usually genetically separated from each other, then the mechanism of formation of picrite gabbro-dolerites themselves is still under discussion. Most often, they are considered as a cumulative part of a layered series. The work shows a sharp geochemical contact between the layered series and picrite gabbro-dolerites, in the section of which, in turn, we have identified an inverse geochemical zoning, expressed in the patterns of accumulation of petrogenic elements that do not fit into a single trend of crystallization differentiation with the rocks of the main layered series. The discreteness of rocks within the horizon of picritic gabbro-dolerites is demonstrated - two intervals are distinguished: the lower one with low chromium concentrations, with stable europium and strontium anomalies, and the upper one, which is characterized by abnormally elevated Cr2O3 contents, reduced LILE concentrations and the absence of a pronounced europium maximum, typical of the lower part of picritic gabbro-dolerites. Based on the known models of formation of inverse zonality of marginal zones of layered massifs, the article presents a new genetic scheme for the formation of picritic gabbro-dolerites as products of pulsation intrusion, which suggests that the lower part of picritic gabbro-dolerites was formed from hybrid magma, and the upper one - from primitive magma, due to pulsation filling of the formation chamber, which, in our opinion, is associated with inverse zonality and accumulation of chromium in the upper part of picritic gabbro-dolerites.
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