The first petrological data about Kontay differentiated sub-alkaline intrusion, Polar Siberia, Russia.

Zaitsev V.A.

Vernadsky institute for geochemistry and analytical chemistry, RAS

 

Kontay intrusion located 40 km SW from Guli massif (Maimecha-Kotui province, Polar Siberia, Russia). Samples from drill hole up to 1231 m were studied. Intrusion is build up of layered sequence strongly differentiated from subalkaline gabbro in the lower part to the monzonites and granosyenites in the upper part.

Rock-forming minerals are clinopyroxen (ortopyroxen was found in one sample), phlogopite-annite, containing 2-5% TiO2, magnesiohorblendite (Na_0.3K_0.1-0.2)(Ca_1.6-1.8Na_0.2-0.4)(Mg_2.1-2.2Fe²⁺_1.9-2.1Fe³⁺_0.6-0.8Ti_0.1Mn_0.1)[Si₇Al_0.7-0.9Fe³⁺_0.1-0.3…., plagioclase An₅₇-An₂₆, anorthoclase and quartz. Accessory minerals are apatite, titanite, ilmenite and titanomagnetite and sulphides.

There are two group of clinopyroxen compositions, both are diopside-hedenbergite. The high-titanium pyroxene (1-1.2% TiO₂ 2-2.5% Al₂O₃ 0.2-0.3 % MnO, 0,3-0,35% Na₂O) present only in the lower part of intrusion. Low-titanium pyroxene present overall, Mg# decrease from 0.7 to 0.63, concentration of Al₂O₃ increase from 0.7 to 1.3, TiO₂ increase from 0.4 to 0.6, MnO from 0.4 to 0.7 and Na₂O decreace from 0.32 to 0.28 wt%.

Secondary minerals are chlorite, albite, prenite, and fluor and alumina rich titanite. The alteration temperature was estimated as 200-400°C. 

These observations seem to indicate that Kontay intrusion is notably different from the alkaline-ultramafic intrusions of Maimecha-Kotui province and, probably, belong to gabbro-syenite formation. This may question as is Kontay intrusion result of the same plume manifestation as alkaline-ultamafic intrusions of Maimecha-Kotui province and Siberian traps?