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GRANITOID MAGMATISM IN
TURBIDITE PALEOBASINS:
COMPOSITION, SOURCES AND
FORMING MECHANISMS
Kruk N.N., Khromykh S.V.,
Kuibida M.L.
Institute of Geology and
Mineralogy SB RAS, Novosibirsk, Russia, kruk@sbras.nsc.ru
One
of the character of Central Asia Folded Belt is wide spreading of
turbidite paleobasins fragments in its structures. That basins were
accreted to continental block’s margins as a result of
accretionaly-collisional processes. Abundance of weakly
metamorphized consequently water saturated and easily melted
sedimentary thicknesses in such paleobasins cause the wide spreading
of different age and different geodynamic and geochemical
type of granitoids. Author’s performed geologic-petrologic and
isotopic-geochemical investigations show that composition and
evolution of granitiod magmatism in the paleobasins are appreciably
differ from ones in both an ancient-crust continental blocks and
typical accretion-island arc blocks.
Study
of turbidite paleobasins in Gorny Altai and Eastern Kazakhstan show
that granitoid magmatism in geodynamic environments of continental
margin and collision presented by wide number of petrogeochemical
associations: tonalite-trondhjemite-granodiorite (M-type),
diorite-tonalite-granodiorite-granite (I-type),
granodiorite-granite-leucogranite (S-type after (Chappel, White,
1974; Whalen et al., 1987). Petrologic researches (Titov at. al.,
1997; 2001; Kuibida et. al., 2004; 2008; Kruk et. al., 2007)
demonstrate that magmatism evolution from M-granites through
I-granites to S-granites in a number of cases reflect the uplift of
magma-generative front and the decrement of initial granite magmas
forming depth. Petrogeochemical researches show that changes of
granite formation conditions and changes of their substratum
compositions happened synchronously.
Tonalite-trondhjemite-granodiorite (M-type) associations are the
result of melting of metabasic oceanic basements in turbidite
paleobasins; diorite-tonalite-granodiorite-granite (I-type)
associations have mixed source (oceanic basement metabasites +
turbidites); and S-granites usually composing the main volume of
granitoid batholiths indicate involving a weakly metomorphized
sedimentary rocks in the granite formation processes.
Isotopic-geochemical composition of granitoids in described
consecution also changes from typical for oceanic basalts to
identical with sedimentary rocks in turbidite sections.
Described
magmatic evolution essentially differ from one observing in
geoblocks with ancient continental crust and accretion-island arcs
typical blocks (e.g. island arcs with oceanic basement) where
development of magmatic column involve in granite formation younger
and more unripe substratums. The analysis of the principles of
granitoid magmatism evolutions allows diagnosing fragments of
turbidite basins enclosed in heterogeneous accretion-collision
terrain collages independently of tectonic transformation and rock’s
metamorphism grade. Application of this method allows in particular
prove that Olkhon terrain interpreted some researchers as block with
ancient continental crust (Rosen, Fedorovsky, 2001) is in fact a
fragment of back-arc basin (Vladimirov et. al., 2008)
Investigations was carried out
with Financial Support of Presidium SB RAS (Integration project No
7.10.2) and Russian Fund of Basic Researches (projects 07-05-00853,
07-05-00980).
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