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THE
MATTER COMPOSITIONS AND ISOTOPE AGES OF UPPER PALEOZOIC GRANITOIDS
OF THE DZHIDA PALEOZOID ZONE (ON EXAMPLE OF SHABARTAI MASSIF)
Khromova E.A.
Geological
Institute SB RAS, Ulan-Ude,
Russia, elenachrom@mail.ru
The
Dzhida zone is situated in north-eastern part of the Central Asian
Fold Belt. Its area comprises the basins of the big rivers Dzhida
(south-west Transbaikalia), Uri-Gol and Egijn-Gol (North Mongolia).
It
is by far a complicated problem to trace back the formation of the
Dzhida paleozoid zone main stages, because of lacking the reliable
data on time of structural and matter complex formation,
particularly in final stage (Gordienko et al. 207). Granitoids of
various genetic types and formational belonging that are widely
spread there play a significant role in this respect.
One
of the very interesting objects (its study can effect a solution of
the problem) is the Shabartai granitoid massif as well as the
analogous Daban, Ulegchinskiy, Sangino-Mylinskiy plutons in the
Dzhida river basin, and Erdenibulganskiy, Bayan,
Boril'zhugijngolskiy and other massives of the Egijn-Gol river basin
of North Mongolia. All of them were included in “the single
Dzhida intrusion” (Naleotov et al. 1941). Papers of different
authors (Distanova 1975, Gordienko 1987) are devoted to the problem
of its separation into various complexes and their belonging to
definite geodynamic settings. A.N.Distanova (1975) distinguished the
gabbro-norite, tonalite-diorite complexes that have island arc
nature and also tonalite-plagiogranite complex that formed in the
collisional stage of regional development. In addition, she
distinguished the Daban complex of Middle Paleozoic, where a number
of massives with granite-granosyenite composition (Daban, Inkurskiy,
Zimkinskiy, including Shabartai) was referred to. Later, a group of
the higher alkalinity postcollisional intrusions (Utukhtuiskiy
complex) was determined. I.V.Gordienko (1987) combined all those
granitoids into the syenite-granosyenite-granite formation of the
Middle-Upper Paleozoic.
The
Shabartai granitoid massif lies in the Shabartai river basin (right
tributary of the Dzhida river). Its area is near 200 km2.
An oval form of the pluton does not agree to direction of main fold
structures in the region. The flyschoidal carbonate-terrigene
deposits cut the massif in the east and volcanogenic-sedimentary and
magmatic formations of the Dzhida guyot – in the west. The
massif is composed by rocks of two phases, i.e. the first phase of
the massif is represented by leucocratic irregular-grained
granosyenites and porphyry-like syenites. The second phase was
formed by brick-red leucogranites. The content of
microcline-perthite varies from 60 % in granites to 80-90% in
syenites. The contents of dark colour minerals (biotite and
hornfels) do not exceed 10%. Alkaline amphiboles (riebeckite) occur
in some varieties of rocks, such as syenites and quartz syenites.
Among rock varieties, granosyenites prevail being ubiquitously cut
by bodies of aplite-like granites. Contacts with host rocks are
intrusive. Hornfels and scarns form here in dependence on
composition of host rocks.
The
granitoids that compose the Shabartai massif belong to rocks of
subalkaline series. SiO content reaches 72 % in some varieties.
The
total alkalinity of rocks ranges from 6 to 12 % with dominant
content of K2O.
All rocks have higher concentrations of zirconium. Distribution of
REE is characterized by clearly observed Eu anomaly and predominance
of light elements over heavy ones.
The
settings of intercontinental riftogenesis dominated in the area of
the Dzhida zone in the Late Carboniferous – Early Permian. The
figurative points of the Shabartai intrusion rocks fall into the
fields of interpolate granitoids in the discriminational diagrams of
J.Pirs. Biotite was extracted from the selected granite sample of
the Shabartai massif, and the dating 289± 2.5 Ma was obtained
on biotite by 39Ar-40Ar
technique (A.V.Travin, IGM of SB RAS). The more exact data 298±
1 Ma ware obtained for syenite of the Shabartai massif by U-Pb
method on zircon (Reznitsky et al. 2006). The obtained data testify
to the Late Carboniferous – Early Permian period of the
Shabartai massif formation in final stage of the Dzhida paleozoid
zone development.
References
Distanova A.N. (1975)
The Early Paleozoic granitoid complex of the Dzhida region
(South-West Transbaikalia) // Early Paleozoic granitoid formations
of West Trabnsbaikalia
and Kuznetskiy Alatau: Novosibirsk, Nauka,
P.49-123.
Gordienko I.V. (1987) Paleozoic magmatism and
geodynamics of Central Asian Fold Belt. M., Nauka, 238p.
Gordienko I.V.,
Filimonov A.V., Minina O.R., Gornova M.A., Medvedev A.Ya., Klimuk
V.S., Elbaev A.L., Tomurtogoo O. (2007). The Dzhida island arc
system of Paleo-Asian Ocean: structure and main stages of geodynamic
evolution in the Vend-Paleozoic // Geology and Geophysics. V.48, N1,
P.120-140.
Khromova E.A., Elbaev A.L. (2004) The island-arc and collisional granitoids of the Dzhida
zone caledonides (South-West Transbaikalia) // Abstracts of reports
at the 2nd
International Siberian Conference of young researchers on Earth
sciences. Novosibirsk, Novosibirsk state university, P.190-192.
Naleotov P.I., Shalaev K.A., Deulya T.T. (1941) Geology
of Dzhida ore district. Irkutsk, Irkutsk regional publ. house, 282p.
Reznitsky L.Z., Barash I.G., Kovach V.P., Belichenko V.G., Sal'nikova E.B., Kotov A.B.
(2005) Paleozoic intrusive magmatism of the Dzhida terrane –
new geochronological and Nd isotope data // Lithospheric geodynamic
evolution of Central Asian mobile belt (from ocean to continent).
Irkutsk, IZK
SB
RAS,
v.2,
P.77-80.
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