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Alkaline
magmatism of the Ukrainian shield in connection by zones of tectonic-
magmatic activation.
Galeckiy
L.S.*, Komskiy N.M.**, Remezova E.A.*
*-Institute
of Geological Sciences of NAS
of Ukraine, Kiev, Ukraine; *- State Geological Appraisal of Projects and
Estimates of Ukraine
*geos@geolog.kiev.ua;
remezova-e@mail.ru; ** nkom@I.ua
The averaged
соntent
of petrogenetic and large number of small chemical elements on the row
of acid and alkaline magmatic formations of the north-western, central
and Azov parts of the Ukrainian shield, and also south of Byelorussia,
and also on some ore formations, related to these structures are
presented.
For comparison, the same information over is given on the granitic
complexes of the Mongol-Okhotsk plicate belt of Asia.
Granitoids of the early and late stages of plicate–metamorphic areas
forming, on territory of these two largest areas of their distribution,
is characterized by considerable geochemical difference. Complexes,
related to the stages of activation of the before formed plicate areas,
differ usually by the clearly marked rare-metal specialization. For
synplicate granites is not characteristic such specialization.
Within the limits of the Ukrainian shield and south of Byelorussia there
are magmatic complexes of acid row - the stages of activation, also
appeared different for geochemistry and on age formings. On the content
levels of rare metals and chalcophilic associations, and also, with
involvement of geochronological information, two groups of granitoid
complexes, respective two age-dependent intervals are selected.
More early complexes can be united within the framework «korosten’
epoch»: granitoids of Korosten’ and Korsun'-Novomirgorod plutons,
massifs of syenites and granosyenites of South-Kal'chik complex. The
most active phase of this epoch falls on a period of 1700-1800 million
years.
To the same epoch the October massif of nephelite syenites is attributed
in Azov region. With nepheline syenites and related to them
metasomatites associates Ta-Nb-Zr mineralization, and with non-nepheline
syenites - rare-earth-zirconium mineralization.
Particular interest is presented by the group of more young complexes,
younger than 1450 million years, including acid and alkaline volcanites
of Zbran'ky suite - Ovruch graben, hypabyssal granite
porphyry (and diabases) within the limits of north-west of the Ukrainian
shield, industrially important rare-metal Perha and Zhitkovichy
complexes. On territory of central part of the Ukrainian shield in this
age-dependent group, possibly, Russkopolyana will appear rare-metal
granites, and on territory of Azov region – Azov syenitic stock, bearing
rich zirconium -
rare-earth ores, and also, that not eliminated, small massifs of
rare-metal granites of Kamennomogil'sky type. These formations can be
incorporated within the framework of «ovruch epoch».
Magmatizm of this late stage of activation, as far as it is possible to
judge on its representatives exposed by erosion to the real moment , and
also – within the framework of the done suppositions, had two main
tendencies of evolution:
·
the first tendency developed in direction from the rare-metal granites
of normal alkalinity, to the subalkaline differences, with ore
mineralization, at times in industrially meaningful scales - beryllium,
tantalum and with the large group of concomitant: with tin, tungsten,
thorium, often with chalcophilic elements: zinc, lead, silver,
molybdenum, cadmium, including their rare representatives. This last
circumstance is the closest association of rare metals with a
chalcophilic group, are alike characteristic feature of rare
metalgranites of late Proterozoic epoch of activation.
·
The second tendency showed up in direction of granitoids of enhanceable
alkalinity, to syenites and melanocratic syenites. This branch is
presented by rare metal alkaline rocks of Zhitkovichy horst on the south
of Byelorussia, Yastrebets massif within the limits of Suschany-Perha
zone, alkaline-basaltic volcanites of upper-zbran’ky suite, and also
and syenites of the Azov deposit. The eventual members of this alkaline
row are characterized by a zirconium - rare-earth association, in
north-western part of Ukrainian shield and in Byelorussia – with a
beryllium.
Thus, it is offered the opinion of two epoches of tectonic- magmatic
activation, divided by the «period of calmness» duration of which
was no less than 250-300 million years. Such presentations, if they
reliably will be confirmed, must will be bring in certain changes in
understanding of metallogeny of territory, and also in general strategy
of metallogenic researches and searching works. |