|
Alkaline
gabbro and gabbro-syenite-alkaline granite series in Eastern Kazakhstan
as indicators of mantle plume activity
Khromykh S.V.*,**,
Kotler P.D.*
*
Novosibirsk
state
university,
Novosibirsk,
Russia
**
V.S.
Sobolev Institute of geology and mineralogy SB RAS, Novosibirsk, Russia
serkhrom@mail.ru
Eastern Kazakhstan area is the part of Altay collision system formed in
Late Paleozoic during collision of Siberian and Kazakhstan continents [Vladimirov
et. al., 2003]. Evolution of the structure started from closing of Ob-Zaisan
paleo-oceanic basin at the end of Early Carboniferous and accompanied
with subduction of oceanic lithosphere under margins of Siberian and
Kazakhstan continents. Forming of collision orogen started in Middle
Carboniferous (320 – 300 Ma) and accompanied with occuring of
plagiogranite-granite complexes in Rudny Altay, Central and Eastern
Kazakhstan areas (Zharma-Saur zone). Further magmatism in Eastern
Kazakhstan (at 300-275 Ma) occurred in intraplate environment and the
boom of igneous activity occurred at that time – varios magmatic
complexes there were formed: sub-alkaline and alkaline picritoids and
gabbro, alkaline gabbro-syenite-granite series, high-alumina
plagiogranites and sub-alkaline granodiorite-granite-leucogranite (dacite-rhyodacite-rhyolite)
series. This variety of magmatic complexes including contrast basic-granitoid
series evidence for active mantle role and considerable mantle-crust
interaction. Massifs of alkaline gabbro and picrites are indicators of
mantle activity and gabbro-syenite-alkaline granite series are
indicators of mantle-crust interaction.
Alkaline mafic magmatism presents of two complexes – Argimbay
plagiosyenite-gabbro and Maksut picrites. There are about 50 massifs.
The alkaline gabbro earlier than sub-alkaline picrites and intruded by
them. Rocks of Argimbay complex are fine- and medium-grained gabbro and
rocks of Maksut complex present of two main types – Ol dolerites and
picrites. Gabbroids of Argimbai complex as with picritoids of Maksut
complex possess enhanced alkalinity (Na2O+K2O from
5.2 to 7.8 wt % in gabbroids and from 2 to 5 wt % in picritoids),
enhanced content of potassium (K2O to 2.8 wt. % in gabbroids
and to 1.3 wt % in picritoids) and phosphorus (P2O5
to 0.8 wt. % in gabbroids and to 0.3 wt % in picritoids). The enhanced
contents of light rare-earth elements, Ba (up to 1000 ppm), Sr (up to
980 ppm), Zr (up to 350 ppm), Rb (up to 25 ppm) are typical for gabbro
of Argimbai complex. Concentrations of rare and rare-earth elements in
picrodolerites and picrites of Maksut complex are decreased in
comparison with gabbro of Argimbai complex but they are higher than the
same in ultrabasic rocks (Ba up to 280 ppm, Sr up to 830 ppm, Zr up to
110 ppm, Rb up to 8 ppm). We have fulfilled the geochonological study
for gabbro of Argimbai complex by U-Pb isotopic method and for
picrodolerites and picrites of Maksut complex by 40Ar/39Ar
method. For U-Pb isotopic method age determination has carried out on
individual zircon grains using ion microprobe
SHRIMP-II in A.P.
Karpinsky Russian Geological Research Institute, St. Petersburg.
40Ar/39Ar geochronological study for
picrodolerites and picrites of Maksut complex has carried by step
heating in IGM SB RAS, Novosibirsk.
For alkaline gabbro of
Argimbay complex concordant age was determined in 293 ± 2 Ma. For
sub-alkaline picrites from 3 massifs was determined in 280 ± 2 Ma for
biotites and 278 ± 3 for hornblende. Geochronological data allows
determining two stages of mantle magmatism manifestations within Eastern
Kazakhstan: about 293 Ma – subalkaline gabbro of Argimbai complex and
about 280 Ma – picrodolerites and picrites of Maksut complex.
Gabbro-syenite-alkaline granite series in Eastern Kazakhstan present of
Tastau, Preobrazhensky and Delbegeteisky complexes [Ermolov et. al.,
1983] that compose few massifs. Tastau massif has annular structure and
consist of mainly alkaline and subalkaline granites and also syenites
and subalkaline Ol dolerites. Age of subalkaline Ol dolerites was
determined by
40Ar/39Ar
method and make up 280±2 Ma [Khromykh et. al., 2011]. The rocks of
Tastau massif have subalkalie composition and correspond to high-K
igneous rocks series. Geochemical data confirm about two magma sources –
mafic and felsic. Gabbroids and granitoids have unrelated trends in MgO,
Al2O3, K2O, P2O5
behaviour. Preobrazhensky massif has square about 100 km2,
and consist of mainly monzonites, syenites, granosyenites, granites and
leucogranites. The mafic rock presented by Ol dolerites are in ancillary
abundance. The rocks of Preobrazhensky massif have subalkalie
composition and characterized by heightened alkalinity, and in P2O5,
TiO2, FeO concentrations. Geochemical data confirm about two
magma sources – gabbro-monzonite-syenite group and ganosyenite-granite
group with unrelated trends in MgO, Al2O3, K2O,
P2O5 behaviour. Age of Preobrazhensky massif
forming was determined by U-Pb dating (Shrimp-II) on zircones from
syenites and make up 284±5 Ma.
For all gabbro-syenite-alkaline granite massifs the common patterns are
determined. There are three or more intrusive phases, homodromous
sequence of intrusion, high-alkalinity (and high-K) composition and its
bimodal distribution with different gabbro-monzonite-syenite and
granosyenite-granite rock groups. Also often the last intrusive phases
of these intrusions are dolerites with similar composition to earlier Ol
dolerites that prove sub-synchronous forming of all rocks from the same
magma pocket. So the evolution of gabbro-syenite-alkaline granite
intrusions reflect the process of differentiation of mantle magmas and
its interaction with crust rocks accompanied with anatexis and forming
of hybrid melts.
Age of alkaline gabbro-picrite complexes and gabbro-syenite-alkaline
granite complexes from geochronological studies was determined at
interval 290-280 Ma.
These data are similar
to ages of Late Carboniferous – Early Permian trap formations in Tarim
plate and Junggar unit and to ages of magmatic complexes
in Northwestern China, Tien Shan and Western Mongolia [review in Qin et.
al., 2011 and others]. These complexes are bimodal basalt-comendite
associations (305–285 Ma), monzodiorite-granosyenite-granite complexes
(300–270 Ma), picrite massifs with Cu-Ni-PGE mineralization (285–280
Ma). The formation of these complexes presumed as a result of Tarim
mantle plume activity.
Composition of alkaline gabbro and picrites and gabbro-syenite-alkaline
granite series in Eastern Kazakhstan also prove that these complexes
formed from enriched mantle source and occurred as a result of Tarim
mantle plume activity. The analysis of geological and geochemical data
shows the antidromic consecution of earlier mantle magmatism (Argimbay
and Maksut complexes) and homodromic consecution of later mantle-crust
magmatism (gabbro-syenite-alkaline-granite complexes). This consecution
may be explained using model of interaction between thermochemical plume
and lithosphere [Dobretsov, 2008]. Under the model there are early and
late stages of “plume – lithospehere” interaction with a 10-15 Ma apart.
This interval stipulated by hard lithosphere response time. For the
case of Tarim plume we suggest the early stage of plume activity
occurred in ~290 Ma when “plume – lithosphere” interaction accompanied
by low degree of melting of lithospheric upper mantle sources that
reduced to appearance in Eastern Kazakhstan Argimbai gabbro enriched of
incompatible elements. The late stage of “plume – lithosphere”
interaction occurred at 285-280 Ma when “plume – lithosphere”
interaction accompanied by higher degree of melting of lithospheric
upper mantle sources as a result of prolonged warming-up of lithospheric
base. These events reduced to appearance picrodolerite and picrite
intrusions and then their interaction with crust reduced to appearance
contrast gabbro-syenite-alkaline granite series.
This work was supported by grant MK-1753.2012.5 from the Grant Council
of President of Russian Federation and joint project 17 from Presidium
SB RAS (state reg. No
01201253409)
.
Vladimirov A.G., Kruk N.N., Rudnev S.N., Khromykh S.V. Geodynamics and
granitoid magmatism of collision orogens // Geologiya I Geofizika. v.
44. Iss. 12. p. 1321-1338
Dobretsov N.L. 2008. Geological implications of the thermochemical plume
model // Russian Geology and Geophysics. V. 49 (7), 441-454.
Ermolov P.V., Vladimirov A.G., Izokh A.E., Polyanskii N.V., Kuzebnyi V.S.,
Revyakin P.S., Bortsov V.D. 1983. Orogenic magmatism of ophiolitic belts
(on example of Eastern Kazakhstan) [in Russian]. Nauka.
Novosibirsk.
Khromykh S.V., Vladimirov A.G., Travin A.V., Lobanov S.S. Gabbro-picrite
massifs in the folded system of the eastern Kazakhstan Hercynides: An
indicator of plume-collisional lithosphere interaction // Doklady Earth
Sciences. V. 441. Iss. 2. P. 1624-1628
Qin K-z., Su B-x., Sakyi P.A., Tang D-m., Li X-h., Sun H., Xiao Q-h.,
Liu P-p. Sims zircon U-Pb geochronology and Sr-Nd isotopes of
Ni-Cu-bearing mafic-ultramafic intrusions in Eastern Tianshan and
Beishan in correlation with flood basalts in Tarim basin (NW China):
constraints on a ca. 280 Ma mantle plume // American Journal of Science.
2011. v. 311. Iss. 3. p. 237-260. |