Chemical zonation in serpentinized dunites of Guli massif, Polar Siberia.

Zaitsev V.A.

 GEOKHI RAS

 

The Guli Alkaline-Ultramafic Complex, located on the north eastern rim of the Siberian Craton, represents the world’s largest complex of that type. The predominant part of the massif is ultramafic  complex.  Ultramafic complex of Guli massif are composed of dunite with occasional highly disseminated to schlieren-type chromitite occurrences, subordinate wehrlite and clinopyroxenites.

We have studied  drill core G13 (660m long) from the periphery of ultramafic  complex, rather close to the alkaline suite.

The dunites of core G13 is strongly serpentinised (i.e. up to 80%). Accessory minerals comprise of Fe-Cr spinels, Ti-magnetite (with lamels of ilmenite), clinopyroxene and very rare sulphides, dissiminated in mass of serprntine.

Chemical compositon of dunites was studied by XRF analys. Fig. 1 show that majority of dunite have very slight chemical variation except of Cr2O3 concentration, which reflect variations of chromite proportions.  Two levels: 129 m and -119 m show significant enrichment in Ca, Fe and Ti and low concentrations of  MgO and NiO.

Rocks on this levels have mineralogical features: they contain clinopyroxene cryctalls and titanomagnetite with exsolution lamellae of ilmenite.

 

Fig. 1 Composition variation of dunites in G-13 core.

 

The correlation diagrams like NiO-MgO, NiO-TiO2, NiO-MnO et al. show, that mineralogical and geochemical feature of this rocks may reflect the metosomatic influence of Ti-rich melt, similar with porphyritic peridotite.