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Abstracts of International conference

Ore potential of alkaline, kimberlite

and carbonatite magmatism

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 2802 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 2845 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 (305285 Ma), monzodiorite-granosyenite-granite complexes (300270 Ma), picrite massifs with Cu-Ni-PGE mineralization (285280 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.