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GRANITE MAGMATISM OF THE
LATE-DEVONIAN-EARLY-COAL STAGE AND
METALLOGENY WITHIN KOBDINIAN
TERRANE OF THE WESTERN MONGOLIA
ON EXAMPLE
OF LEUCOGRANITS
OF THE KHARHIRINIAN COMPLEX
Konovalenko S.I., Buharova O.V.
Tomsk State University,
Tomsk, Russia, getina@ggf.tsu.ru
Leucogranites
and alaskits of the Kharhirinian complex are part of a homodromous
row of rocs of the granite – alkali granite formation appeared
in the northern part of Kobdinian terrain during it joining to the
early Caledonian Central - Asian continent. Hybridized acid rocks of
the Turgenulian complex 413 - 373 million
years on a K-Ar method were the earliest in this row. Then
leucogranit massifs of the Kharhirinian complex 360±10 million
years an U - Pb method were formed and the row was completed with
alkaline alaskits of the Elynian complex 330±10 million years
the U - Pb method (Fomenko, 1999). Batholitic intrusions in the
middle of the row were sharply dominating over volume of rocks. Two
of them being a subject of consideration, practically entirely form
the vast Kharhirinian upland region. It is the homonymous
Kharhirinian massif with the area of 3700 km2
and located CZ Achitnurian with the area about 1600 km2.
Both were formed in two phases, first of which is presented with
pinky -grey coarse-grained porphyry two-feldspar granites turning
into leucogranites of the variable granularity. The second one
consists of uniformly grainy pinkyî-grey leucocratic granites of the
medium and fine granularity. The additional dyke phase is presented
with fine-medium-grained aplite leucocratic granites and more rarely
with pegmatites.
An identical
petrographic set of rocks in a structure of Achitnurian and
Kharhirinian plutons, similar petrochemistry
just as spatial closeness of massifs allowed considering them as an
uniform very large pluton presented on the modern erosive cut with
two separated outcrops (Fomenko, 1999). However, to some extent
heterogeneity of mineralization revealed during geological work,
connected with that and another massifs contradicted this
considiration. In the Achitnurian one the nonindustrial field of
intragranite crystals pegmatites and appearance of Sn-W greisens and
in the Kharhirinian one - hydrothermal Sn-sulphidic appearance and
skarn mineralization Cu and Ag were revealed.
The
generalization and the analysis of original geochemical data allow
revealing geochemical features of massifs. Elements –
impurities being part of investigated granits can be subdivided into
three groups: scarce, clàrê
and overclark. The first one is Mn, Ti, Ba, Zr, V and Bå. Clark
elements are - Sr, Ga, Ge, Nb, Y. In overclark ones Cu, Bi, Pb, Ni,
Cr, Co, Sn, Yb, Rb, Li are found out. The further geochemical
analysis allowed revealing indicator elements carrying typomorphic
load in the rocks of massif complexes. Cu are such elements for
Achitnurian massif and Sn, Li, Yb, Rb for Kharhirinian one.
Calculations
of differentiation coefficients of massif rocks have shown that
granitoids of the I phase of Kharhirinian complex of Achitnurian
massif are conditionally differentiated (Kd=0,9)
that is in fact fixed by the presence of facial varieties of granits
within a phase. Other granitoids differ in weak differentiation
(Kd<<1).
Granitoids of the massifs under consideration corresponding to the
basic phases of complexes on its petro -and geochemical
characteristics get in the group of industrially ore-bearing solids
except for the II phase of Kharhirinian complex of Achitnurian massif
determined as limited ore-bearing one. Granitoids of massifs, judging
by their geochemistry are specialized on Sn, Rb, Li at the same time
leading position occupies the Kharhirinian one.
Using results
of typomorphic features of biotite (Buharova, 2007), the data on
physical and chemical conditions of granitoid formation have been
received. Thus the granitoids of Kharhirinian complex differ in high
activity of oxygen among mineral formation. The Achitnurian massif
was crystallized on depth of formation under hypabyssal conditions
and the Kharhirinian massif both under meso-and under hypabyssal
conditions. The temperature of crystallization of Kharhirinian
complex within the Achitnurian pluton was about 850 – 700Ñ
with the insignificant tendency of decrease of the temperature
gradient from the first phase to additional one. Within Kharhirinian
plution the crystallization of granitoids of the I phases began with
700Ñ
and could drop up to 550Ñ
at crystallization of the vein additional phase, the initial
temperature of crystallization of II phase - 850 – 700Ñ.
Evolution of formation of the Kharhirinian complex within Achitnurian
massif were going on a background of alkalinity decrease of a granite
melt in contrast to similar rocs of the Kharhirinian complex of the
similar massif.
Consideration
of geochemical features of leucogranite mineralization of two massifs
on a level of rocs and on a level of typechemism of the minerals
forming them, especially micas, has shown that the established
distinctions
are objective and it in its turn forces to assume the presence of two
separated magmatic centers at formation of massifs. Influence of
distinctions in chemism of a remelted substratum is less obvious.
Influence of a mobile zone on metallogenetic load of massifs is not
excluded as postmagmatic mineralization is frequently dated for
exocontacts of massifs.
References
Buharova O.V., Konovalenko S.I.
Geochemical features of granitoids of the Kharhirinian and
Achitnurian massifs of the Kharhirinian complex of the Western
Mongolia / Petrology of magmatic and metamorphic complexes. Iss.6.
Materials of the
All-Russia petrographic conference. Tomsk: SNTI, 2007. P.26 - 31.
Gavrilova S.P. Granitoid formations of the Western
Mongolia // Granitoid and alkaline formations in structures of the
Western and Northern Mongolia. M.: Nauka, 1975. P.50-164.
Interpretation of geochemical data.
M.:Interlit. Engineering, 2001.
288p.
Fomenko A.E. Evolution of granitoid
magmatism of the Kharhirinian upland region in the Western Mongolia.
Article I. The
homodromous row of granite – alkali granite formation // Press
of institute of higher education. Geology and investigation. ¹4,
1999. P.80-90.
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