| Kontay intrusion is located in the north-west part of Maimecha-Kotuy province, (part of
Siberian Large Igneous Province) in the northern part of the Siberian Platform. Intrusion is
fully overlaid and practically not studied before. Geophysical data evident that intrusion has
form of laccolite with diameter ∼7.5 km and thickness ∼ 2.5 km [1]. Initially lower part of
intrusion was described as “gabbro-anortozite and anortositic gabbro” and higher part – as
“leucocratic granophyric anortosites” [2].
Complex mineralo-petrological-geochemical study allow to divide intrusion section
on three zones: Lower zone (below 1100 m) - layered sequence of leucocratic
and melanocratic of biotite- and ortopyroxene-bearing gabbro, with minor alkaline
feldspar, Middle zone (1100-700m) - biotite- and K-feldspar bearing gabbro and
monzonotes, interstitial space often contain micrographical structures. Biotite corroded
clinopyroxene and form interstitial crystals and Upper zone (700-214 m) - petrographically
monotone porthyric quartz-monzonites and granosyenites with rare phenocrysts of
plagioclase, magnetite, clinopyroxene and biotite. The main secondary minerals are
albite, amphibole (edenite-feroedenite), secondary biotite, chlorite, and F,Al-bearing
titanite.
Rocks of the all parts fall in the same trends on the binary petrochemical diagrams, they
belong to the High-K calc-alkaline seria. They are clearly more alkaline then intrusions of
Norilsk district and less alkaline then alkaline-ultramafic intrusions of Maymecha-Kotuy
province.
Volcanic rocks of Norilsk and Maymecha-Kotuy area was subdivided for four
geochemical types, mainly by the Ti-content, Th/U, Gd/Yb and Sm/Yb ratio: Low-Ti-1
(predominated), Low-Ti-2 (well –developed in Norilsk region), Moderate-Ti (developed only
in the lower part of volcanic formation in Norilsk region), High-Ti (rare in Norilsk region, but
widely spread in Mailecha-Kotuy area) [3]. Kontay intrusion rocks belong to Moderate-Ti
group. The closest analog is Ivakinsky-1 subsute.
Cumulus minerals composition changed systematically upward.
Two populations of clinopyroxene occur, both are diopside-hedenbergite. The pyroxenes
of first population contain 1-1.2% TiO22-2.5% Al2O3 0.2-0.3 % MnO, 0.3-0.35% Na2O,
Mg/(Mg+Fe)=0.44-0.50 present only in the lower part of intrusion. These pyroxenes was
formed from the melt of High-Ti geochemical type; the second population of pyroxene
present overall, Mg/(Mg+Fe) 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 decrease from
0.32 to 0.28 wt%.
Biotite Mg/(Mg+Fe) increase from 0.60-0.62 up to 0.76-0.78, TiO2 content decrease from
5 -6.2% to 1.9-2.4%, and MnO content increase from 0.1 to 0.3-0.4%.
Plagioclase in the lowest part of intrusion contains An60-An45 cores and An32-An26rims,
but in the middle and upper zone plagioclase composition of plagioclase changed
systematically with an increase in Ca.
Based on the petrochemical and mineralogical data, Kontay intrusion is an example of
strongly in-situ differentiated layered intrusion, formed in subvolcanic conditions form the
subalkaline moderate-Ti melt with admixture of crystals, genetically linked with high-Ti
melts.
This study was financially supported by the Russian Science Foundation (grant
115-17-30019)
[1] Kushnir (2005) Ph.d. thesises, 25.00.10 Ekatirenburg, 154.
[2] Lopatin and Kalashnik (2004) Mineral resourses and perspectives of Taimyr district.
154-156
[3] Fedorenko et al. (2000) International Geology Review. 42. 769-804. |