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CLASSIFICATION AND
GEODYNAMIC ENVIRONMENTS OF PALEOZOIC GRANITOIDS FROM MONGOLIA
Demberel O.,
Ganbat E.
Institute
of Geology and Mineral Resources, Mongolian Academy of Sciences,
Ulaanbaatar, Mongolia Igmr_mn@yahoo.com
Novadays, the
concept of plate tectonic is being widely used in geological science
and the
majority
of granitoid classifications methods that were proposed in recent
years refer in the origin to the geodynamic environments.
The Variety
of formulated methods is geochemical
methods and
based
on major and trace petrogenic elements in rock composition, purposed
to define their origin of geodynamic environments and regimes of
concrete granitoid bodies.
These methods are not so
suitable for classification of granitoids distributed on wide
territories (Barbarin, 1999). Our investigation on territory of
Mongolia, where Paleozoic granitoids widely distributed, shows that
the method of classification based on the peculiarities of
mineralogical and petrographical composition of granitoids is useful.
According to
this method the granitoids classified into rich in Al crust
originated, toleiitic and alkaline of mantle origin, calc-alkaline of
mixed origin which are divided into six types: muscovite bearing Al,
cordierite-bearing Al, amphibole bearing calc-alkaline, potassium
bearing calc-alkaline, riftogenic toleiitic, and alkaline,
peralkaline and the geodynamic environments according to the plate
tectonic theory could be interpreted
as Wilson cycle of granitoid origin.
More than 30
different in ages and
types igneous
rocks from Proterozoic to beginning of Cretaceous are distinguished
on the geological map of Mongolia at scale 1:1000000 (1999), and
among them Paleozoic granitoids related to geological
and
tectonical
evolution
of the Central Asian Orogenic Belt have big significance.
Though those
granitoids geochemically
investigated
poorly and at
different level their
mineralogical and petrographycal characteristics are determined on
the various stage of geological work. All
Paleozoic granitoids were classified by mentioned above methods and
their geodynamic environments were suggested and preliminary results
of study are shown on the map at scale 1:2500000.
The map shows
that the amphibole bearing calc-alkaline
and the potassium calc-alkaline types of subduction,
active
continental margin
and intracontinental
collisional granitoids
are widely distributed and arc tholeiitic and rift alkaline,
peralkaline types of granitoids have subordinated distributions.
In
this way all Proterozoic and Mesozoic granitoids can be classified.
References
Barbarin B. A
review of the relationships between granitoid types, their origins
and their geodynamic environments // Lithos 46., 1999.
P.605-626.
Geological map of Mongolia. 1999.
Scale 1:1 000 000.
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