New data about age of granitoids of Kalba-Narym polychronal batholith

Kotler P.D.

V.S. Sobolev Institute of Geology and Mineralogy SB RAS, Novosibirsk, Russia

Novosibirsk state university, Novosibirsk, Russia

[e-mail]

Kalba-Narym granitoid batholith, located in EastKazakhstan, is one of the largest intrusions in the CIS. Batholith has polychronal structure and consists of rocks of several intrusive complexes, which differ in composition and formation time. This area is one of the oldest mining region of Kazakhstan therefore extent of its examination is very high. The first geological data of the Kalba-Narym batholith were obtained at the end of the XIX century. Up until the 80s of XX century this area became the subject of detailed geological and petrological studies.

During these works it was determined that a variety of granitoid magmatism brings difficulties in the dismemberment of rocks on the complexes and to determine volumes of complexes. By the end of the XX century it was make four correlation schemes of Kalbinsky polychronous batholith magmatism [1, 2, 3]. They are based on many years of geological, petrological and petrographic studies carried out by several teams of specialists. The sequence of formation and age of magmatic complexes was determined by direct geological observations, or data based on the correlation of mineralogical and petrochemical composition. As a result of the formation of the Kalbinsky batholith was estimated in the range of about 100 million years - from the Early Carboniferous (kushbarlyksky and babylonian complexes C₁ [1, 2]) to the Triassic (mirolyubovsky complex T₁ [1, 2, 3]). First determinations of absolute age 6y U-Pb dating were characterized by low accuracy and are not allowed to make significant refinements to the accepted scheme [4].

In recent years 24 Ar-Ar and 3 U-Pb isotopic datings received, that allow to make some additions to the understanding of granitoid magmatism in Kalba-Narym region. This paper presents results of isotopic dating in the central part of the Kalb-Narym batholith and ita generalization. The studies included data of 19 granitoid massifs. The studied rocks compose the 5 complexes, that common in this territory.

Kunushsky complex. We studied the rocks that form Tochkinsko-Medvedkinsky and Karagoin-Saryozeksky intrusive belt, rocks of Besterek massif, and dikes in the edging of Zhilandinsky massif. In Tochkinsko-Medvedkinsky intrusive belt rocks of the complex represented by leucocratic plagiogranite-porphyres consisted of zoned plagioclase phenocrysts (25-30%) andesine composition (An_35-40) and the holocrystalline matrix consisting of the second generation small plagioclase (20-25%) oligoclase composition (An_25-30), and quartz (30%), feldspar (1%), scaled biotite (~ 15%) and green amphibole (3%). In Zhilandinsky massif biotite plagiogranites have uniform granular granite structure and are composed of quartz (40%), shortprizmatic plagioclase (45%) and scaly biotite (15%). Age of plagiogranites was obtained using ion mass spectrometer SHRIMP-II (VSEGEI, St. Petersburg). Obtained data evidence of a close age of magmatic zircons from plagiogranites Zhilandinsky massif (306,7 ± 8,7 Ma) with 10 experimental points and the Tochka (299 ± 2,3 Ma) and 7 experimental points [5].

Kaltuginsky complex. As part of kaltuginsky granite-granodiorite complex were taken rocks of Irtysh and Chernovinsky massif edges and dike belt in the central part of the region. The structure of the complex is three phases: granodiorites, granites and dykes of granodiorite, granite-porphyries and aplites. Isotope dating was obtained using Ar-Ar method on the rocks of each phase. The first phase - a fine-grained granodiorite from the southern border of the Irtysh massif, the second phase - the granite from the southwest border Chernovinsky massif, and the third phase - the granite-porphyry dike near the Shuruq village, that break depositionof burobaysky formation. Ages obtained for each phase were 286 ± 1,278 ± 2,272 ± 1 Ma, respectively.

Kalbinsky complex. Granitoids of Kalbinsky complex are the most common in the Kalba-Narym batholith. The volume of rocks and number of phases for this complex is still a debatable problem. As objects for the Ar-Ar isotopic dating were selected Belogorskiy, Narymsky, Priirtyshstky, Peschansky, Podgornensky, Chernovinsky arrays and mica of spodumene pegmatites and greisen associated with deposits of rare metal deposit Asubulak (13 dating in all). 8 out of 13 the results indicate Early Permian age of the granitoids, the remaining three have a younger age, until the early Triassic. Age obtained for Belogorsky and Podgornensky massifs (257 ± 2 and 248 ± 3 Ma, respectively) is conditionally accepted as unreliable due to the large difference between the main group of results. A possible reason for this rejuvenation of ages was defective sampling or error at the stage of the isotope-geochronological analysis.

The main part of dating (10 pieces) of kalbinsky complex rocks may be divided into two: young, with an average age of 277 ± 4 Ma and older, with age, around 290 ± 3 Ma. The first group includes: biotite porphyritic granite Peschansky array (275 ± 3, 280 ± 3 Ma), Chernovinsky array (277 ± 1 Ma) and Narymsky array (275 ± 3 Ma). The second: biotite porphyritic granite Irtysh massif (fine-grained - 287 ± 1 million years old, medium - 287 ± 1 Ma), and micas from greisen - 294 ± 4, 292 ± 4 Ma and from spodumene pegmatite - 292 ± 4, 295 ± 4Ma of rare metal deposit Asubulak [6].

Monastyrsky complex. In the selected area to the monastyrsky complex presented by Monastyrsky and Sibinsky leucogranite arrays, Voylochevsky massif and small tabular bodies into endocontacts of Mirolyubovsky and Kaindinsky arrays [3]. On the rocks of this complex were obtained 4 dating by Ar-Ar method and one dating by U-Pb isotopic method. The oldest ages obtained by U-Pb method for the leucogranites Sibinsky array - 284 ± 4 Ma. For Voylochevsky array obtained two Ar-Ar dating - 272 ± 1 Ma (coarse-grained biotite leucogranites) and 277 ± 1 Ma (leucocratic granite). Age obtained for the tabular arrays in a frame of Mirolyubovsky and Kaindinsky array - 269 ± 3 and 272 ± 3 Ma, respectively. Data on the age of the Monastyrsky complex arrays are similar to data on age Kalbinsky complex.

Kaindinsky complex. This complex was first selected by V.S. Shulygin and O.V. Navozov [3], and included Kaindinsky, Mirolyubovsky, Chernovinsky arrays, the eastern part of Kurchumsky and northern part of Voylochevsky

Fig. The definitions of absolute age of rocks from central part of Kalba-Narym batholith. Gray background color shows previously accepted intervals of magmatic complexes forming. The inset shows the time intervals of the formation of intrusive complexes according to the obtained dating.

massifs. The complex is selected on the basis of cutting the aplite dikes of the Monastyrsky complex younger coarse-grained porphyritic granites. According to other authors, these geological observations were not confirmed and rock of these massifs assigned to Kalbinsky complex [2]. Thus, the selection of this complex is still controversial and requires additional investigation. By samples assigned to Kaindinsky complex was carried out four Ar-Ar age determination for Mirolyubovsky, Chernovinsky and Voylochevsky massifs. The oldest age obtained on biotite porphyritic granites Chernovinsky array - 285 ± 1 Ma. The dating of rocks Mirolyubovsky array shows the age of - 277 ± 3 Ma. For rocks of Voylochevsky array has two results of isotopic-geochronological dating of 277 ± 1 and 270 ± 1 Ma.

A generalization of the results of isotope-geochronological dating is shown in Fig. Analysis of data shows that the vast part of granitoids, forming Kalba-Narym polychronal batholith generated in a relatively narrow time period of about 25 million years (295-270 Ma).

The forming of plagiogranitoids of Kunushsky complex occurred separately in time with respect to the main part of the granites in the range from 315 to 300 million years.

The results of dating obtained for the of Kaindinsky complex rocks questioned the feasibility of separation of the complex. The data of age can be attributed to Kalbinsky (286-275 Ma) and Monastyrsky (271-269 Ma) complexes.

The obtained results show about the development of magmatic activity within the Kalba-Narym area from the Late Carboniferous to Early Permian, and cause the need for additional review and revise existing schemes of the correlation of magmatic complexes in the region.

The author thanks Vladimirov A.G., Navozov O.V., Travin A.V., Khromykh S.V., Kuibida M.L. for providing a database of isotopic dating of Kalba-Narym batholith.

This work was supported by the project of partnership investigations from SB RAS № 10.3.

References:

1. Lopatnikov V.V. et al. Magmatism and ore content of Kalba-Narym area of East Kazakhstan // M.: Nauka. 1982. 248p.

2. Dyachkov B.A. et al. Granitoid and ore formation of Kalba-Narym belt // Almaty: Gylym, 1994. – 208p.

3. Shulygin V.S., Navozov O.V. Magmatic complexes of Kalba-Narym zone // Proceedings. AS KazSSR. Geological series. 1986. №5. P. 36-45.

4. Vladimirov A.G. et al. The main historic boundaries of intrusive magmatism of Kuznetsky Alatau, Altai, and Kalba (according to U-Pb isotope dating) // Geology and Geophysics, 2001, v. 42, № 8, P. 1157-1178

5. Kuibida M.L. et al. U-Pb-isotopic age, composition and sources of Kalbinsky Ridge plagiogranites (Eastern Kazakhstan) // Reports of the Academy of Sciences, 2009, v. 424, №1, P. 84-88

6. Kruk N.N. et al. Age, composition, and Sm-Nd isotope systematics of Kalba-Narym zone granitoids (Eastern Kazakhstan)// Geodynamic evolution of lithosphere Central-Asian mobile belt (from ocean to continent): Proceedings of the conference. Edition. 5. - 2007. – V.1. – p. 123-125.

Material composition of the Late Permian granite-rhyolitic formation of islands of Peter the Great bay (Sea of Japan)

Kramchanin K.Y., Anokhin V.V., Ogorodny A.A.

V.I. Il’ichev Pacific Oceanological Institute FEB RAN, Vladivostok, Russia

[e-mail]

The considered territory is located in a southwest part of Primorski Krai in which limits following large tectonic constructions: I. Laoelin-Grodekovsky terribly-folding system with the West seaside zone II. Activated southern suburb of preriphean of the Hankajsky massive with zones Barabashsko-Muravevskaya and Dunajsko-Anuchinskaya, III. Sihote-Alinskaja terribly-folding system. In water area of Peter the Great bay there is a set of islands the majority from which is concentrated in a strip traced in a southwest direction from peninsula Muravyova-Amurskogo on the distance about 60 km. Largest of them are islands Russian, Popova, Rejneke, Rikorda and the Big Pelis, concerning the Barabashsko-Muravevsky tectonic zone. Two large islands – Askold and Putjatin – are located to the south peninsula Danube (the Dunajsko-Anuchinsky tectonic zone).

Late Permian granite-rhyolitic formation of islands of Peter the Great bay (Sea of Japan). As a result of formation analysis of the late Permian magmatic formations of islands of Peter the Great bay among them allocate following vulkano-plutonic associations

A. Gabbro-basaltic: 1) cover facies: barabashskaja suite; 2) subvolcanic and intrusive facies: muravevsky complex.

B. granite-rhyolitic (sedankinsky a complex): 1) subvolcanic and extrusive facies: rhyolites; 2) subvolcanic facies of granites.

Sedankinsky complex. Massives of the sedankinsky complex were generated as a result of three intrusive phases accompanied dikes and lodes bodies. The first phase is presented hornblendic and biotite-hornblendic quartz diorites, the second – hornblende-biotitic granodiorites, often passing in biotitic granites, the third – granite-porphyries. Mutual relations between these phases are most accessible to supervision and are in details studied in the massifs bared on islands Russian, Popova, Moiseyev and others. For the first time they have been established in a massive located in pool of the river Pioneer (Sedanka) on peninsula Muraveva-Amurskogo, whence the complex has received the name. Granodiorites and leucocratic granites of the second and third phases are connected among themselves, along with phase mutual relations as well facial transitions, and with quartz diorites of the first phase have only active contacts. Leucocratic granites quite often border the central parts of the massifs combined by granitoids of the second phase, and represent, in this case formations of the regional facies. The petrotypes of a sedankinsky complex is considered a massive of an island Russian where formations of granitoids of all three intrusive phases are most full presented. It is necessary to notice also that granodiorites and granites of a considered massive quite often contain xenoliths in various degree granitized and hornfelsed rocks of a gabbro-diabase of a complex.

Subvolcanic and extrusive facies. Rhyolites, felsorhyolites white, violet, pink, glassy, it is frequent fluidal, albitized, chloritized and sericitized. They are combined stock bodies and dykes; the central parts powerful dykes by granite-porphyries. Porphyritic allocation (0–10%) in rhyolites are presented albite-oligoclase (№ 10–25), is more rare andesine and quartz. A great bulk – quartz-feldspathic, vitrophyric. Rhyolites find out all scale of transitions with granite-porphyries which form the whole group of small rods. These are pink porphyritic shape of rock to which phenocrist are presented by albite and, less often, quartz – in the form of roundish grains in the size to 2-3 mm against aplitic or granophyric basic mass. With rhyolites spatially also are genetically closely connected rhyodacite – gray and light gray aphyric glassy rocks which differ from rhyolites presence nodules of amphibole (1–3%).

Facies of subvolcanic granites. Biotitic granites pink, red, medium-grained, porphyric, consist of a microwedge (35–40 %), a plagioclase, albite and oligoclase (20–24 %), quartz (30–38 %) and a biotite (2–5 %). Biotitic granites are connected by gradual transitions (through granite-porphyries) with rhyolites: such mutual relations can be observed at the western coast of passage of Stark. Granosienites red, medium-grained, are combined by potassium feldspar (to 60 %), quartz (10–15 %), a plagioclase (5–10%), a horn blende (8–15 %) and a biotite (1–3 %).

Late Cambrian granite-rhyolitic formation of Primorski Krai. Late Cambrian granite-rhyolitic formation represents the vulkano-plutonic community which all members are connected by gradual transitions. It consists of: 1) suputinskaja stratum of rhyolites and them tuff, lying down with angular disagreement on bottom Cambrian and with stratigraphic disagreement blocked Devonian flora-bearing volcanites (cover facies); 2) extrusives of rhyolites (funnel facies) and 3) massifs of subvolcanic type of voznesenskie granites.

Suputinskaja stratum (cover facies). Tuffolava of felsorhyolites, felsorhyolites – pink, green, violet, white, spherolitic, fluidal and massive rocks. They consist of spherolites (10–30 %) the size 0,5–1,0 sm combined by felsite, and fluidal quartz-feldspathic groundmass felsitic structure. Felsorhyolites sometimes contain rare nodules of potassium feldspar and a plagioclase. Potassium field spars pertitized, forms prismatic crystals with the melted off edges, chloritized and sericitized. Plagioclases are marked also in the form of prismatic crystals; sometimes on them develop grains of leucocsenized sphen. The groundmass of rocks possesses micropoikilitic, spherolitic, occasionally micropegmatitic structure; sometimes quartz forms worm-shaped enclosures in potassium feldspar. Fluidal differences of felsorhyolites, having glassy and microfelsitic structure, consist of cryptocrystallic not individualized substance, in which there are non-uniformly distributed grains of quartz or streaks of secondary quartz.

Crystalolithovitroclastic tuffs consist of fragments (0,3–0,4 mm) of felsorhyolites (5–10 %), splinters of crystals potassium feldspar, quartz, plagioclase (in the sum – about 20 %), volcanic glass (65–70 %). Lithovitrocrystaloclastic tuffs on 75–80 % consist of large (from 0,1 mm to 2–5 mm) splinters of crystals potassium feldspar, quartz, plagioclase and rare fragments of glassy rhyolites. The cementing weight of tuffs is combined by acute-angled fragments of volcanic glass. Lithocrystalovitroclastic psammitic tuffs consist of fragments (40 %) of volcanic glass (80 %), felsorhyolites (10 %), potassium feldspars (5 %), quartz (5 %) and individual grains of a plagioclase and andesites. Lithocrystaloclastic tuffs psefo-psammitic are formed by fragments (60 %) of quartz (55 %), felsorhyolites (43 %) and potassium feldspar (2 %). The groundmass of rocks – similar to a felsite, sometimes crystallized epidotized. Crystalolithoclastic tuffs psefo-psammitic (gravelic) consists of splinters (50 %) of quartz (50 %), potassium feldspar (40 %), felsorhyolites (10 %) and individual fragments of granites. The groundmass of tuffs similar to a felsite, sericitized. Crystaloclastic tuffs psammitic are combined by splinters (35–40 %) of potassium feldspar (50 %), quartz (30 %) and a sour plagioclase (20 %). The groundmass at them ashes, similar to a felsite, sericitized and chloritized.

Extrusives of rhyolites (funnel facies). Extrusive massifs are combined by fluidal rhyolites, felsorhyolites and massive orthophyres which are usually developed among integumentary volcanites. When volcanites bodies break through low Cambrian adjournment, we, possibly, deal with roots of extrusive or with subvolcanoes when the magmatic center didn't incorporate to a surface. However, to distinguish facial an accessory of the given formations it is not obviously possible.

One of large (3×5 km) extrusive massifs ellipsoidal forms with fault restrictions acts in vicinities with village Ljalichi where forms Alunitovaja hill. It is remarkable that it has the root zone opened with erosion presented by the Chapaevsky massif of voznesensky granites which is located on its northwest continuation and is tracked in a river valley Oozy by boreholes. In a development area extrusive rhyolites with abruptly put fluidal fields are observed secondary quartzites, pyrophyllites, dyckites, alunites and sericitized rocks. Most intensively changed volcanites are dated for the central part of a file, and its regional zones are combined by gray and dark-violet rhyolites to which phenocrysts (30–40 %) are presented by quartz, an orthoclase and a biotite, and the groundmass has microfelsitic and spherolitic structure.

Massifs of the voznesensky granites subvolcanic type. Biotitic granites – gray, pink-gray, medium-grained, it is frequent porphyric, hypidiomorphic-granular. They consist of potassium feldspar – a microwedge (30–55 % – 46–50 %), quartz (25–40 % – 32–35 %), a sour plagioclase (11–18 % – 15–30 %) – oligoclase №17–20, more rare №11–13, № 25–27 and albite №5–8, biotite (1-20 %), tourmaline (to 4 %), muscovite (0,8 %), horn blende (0,5 %), ore minerals (0,2-0,7 %) and zircon (0,3–0,4 %). Alaskitic porphyric granites differ from them presence of rather insignificant quantity of a biotite, more sour composition of plagioclases (albite-oligoclase) and the big maintenance potassium field spars – a microwedge (36–60 %). Often meeting granites containing tourmaline hypidiomorphic-granular or micropegmatitic structures are combined by potassium feldspar – a microwedge (33–54 %), quartz (25–30 %), plagioclase (9–22 %) – oligoclase №17–20, №11–13, tourmaline (to 4–7 %; Sometimes to 15 %), a biotite (0,3–2 %), muscovite (0,6 %), ore mineral (0,3 %), zircon (0,2 %) and fluorite (0,7 %). In porphyric granites and granite-porphyries nodules belong to a microwedge (to 7 %), to quartz (5–10 %) and a plagioclase (1–5 %); the basic hypidiomorphic-granular weight the microwedge (44–56 %), a plagioclase (7–15 %) – oligoclase №11–13 form, a biotite (1–2 %).

Besides, on contacts of voznesensky granites with low Cambrian limestones meet trondemites, close to those of Southern Norway, Mountain and Ore Altai. They have hypidiomorphic-granular structure and are combined by oligoclase №18–25 (50–60 %), quartz (15–32 %) and a microwedge (4–13 %). And on contacts of granites with low Cambrian clay slates are established quartz sienites hypidiomorphic-granular structures consisting of a microwedge (40–65 %), oligoclase №25–27 (30–55 %) and quartz (5–10 %).

Above have been considered two similar on composition, but uneven-age vulkano-plutonic associations, first of which contains the sulphidic mineralization which is not representing interest in the industrial purposes, and the second containing industrial mineralization. In formation voznesensky biotitic and Li-F granites and connected with them deposits (fluorite, tantalum, tin, beryl etc.) fluorine played large role. In gaseous-liquid inclusions concentration of fluorine are met to 0.6m. Richest with fluorine voznesensky Li-F granites, containing Ta-Nb mineralization and deposits and in which exocontact blue cap carbonate rocks are transformed to fluorite deposits (Voznesensky, Boundary, etc.). Lower maintenance of fluorine is characteristic for biotitic granites of voznesensky complex and other granitoids.

References:

1. L. A. Izosov, V. T Sedin, T. A. Emeljanova, etc. (2008) The new data on magmatic complexes of island Popova and some problems of geology of Peter the Great bay: the Current state and tendencies of change of environment of Peter the Great bay of sea of Japan. M: GEOS. 355–378.

2. A.M. Aksjuk, A. A. Konyshev, L. A. Izosov. (2010) Experimental researches of fusion of granites and physical and chemical conditions of formation of deposits of Voznesensky ore knot, Primorski Krai: Theses of reports of XVI Russian meeting for experimental mineralogy. On September, 21-23st, 2010 IEM the Russian Academy of Sciences (Chernogolovka). 35–36.

2. L. A. Izosov, S. N. Kononets, M. G. Valitov. (2008) Voznesenskaya granite-rhyolitic formation of Primorski Krai: problems of geology and metallogeny: Regional problems №10. 55–63.

Petrogenesis of island-arc volcanic rocks from the Char suture-shear zone (East Kazakhstan)

Kurganskaya E.V., Safonova I.Y., Simonov V.A.

V.S. Sobolev Institute of Geology and Mineralogy SB RAS, Novosibirsk, Russia

[e-mail]

The Char suture-shear zone (SSZ) of East Kazakhstan is an important segment of the Central Asian Orogenic Belt. It is special for an extremely complicated tectonic structure and co-occurrence of ultramafic-mafic ophiolitic units, various volcano-sedimentary sequences, and Paleozoic basaltic lavas [2,3]. Its study is important for reconstructing the geodynamic history of the western parts of the CAOB including vast folded areas in East Kazakhstan, SW Siberia, NE China and western Mongolia. The main feature of the Char SSZ is the Char opiholitic belt hosting Late Devonian-Early Carboniferous oceanic basalts [6] and located in its central axial part. Previously, Belyaev [2] mentioned andesitic to dacitic volcanic rocks east of the Char suture. During the 2008-2009 field works we found volcanic and subvolcanic rocks of possibly suprasubduction origin west of the Char suture. In this paper, we present first geochemical data on these volcanics.

The rocks under study are tholeiitic to calc-alkaline basalts, andesibasalts and andesites. The proportions of FeO, MgO and TiO₂ suggest two magma series: higher-Fe tholeiitic (SiO₂ = 52.3; TiO₂ = 0.58; #Mg = 38; CaO/Al₂O₃=0.5) and lower-Fe calc-alkaline SiO₂ = 54.5; TiO₂ = 1.1; #Mg = 51; CaO/Al₂O₃=0.3). The tholeiitic varieties are less enriched in the LREE, then the calc-alkaline ones and have lower Nb and Th (La/Yb_N = 1.1 and 3.0; Nb = 0.65 and 3.93; Th = 0.54 and 1.86, respectively). One sample (Ch-59-08) is a high-Mg and low-Ti andesibasalt, which is characterized by higher Ni, Cr, Zn, Al₂O₃, lower LREE, Sr, P, Y, Nb, and Th compared to the tholeiites and calc-alkaline varieties. Preliminary, we regard it boninite. Compositionally, for both major and trace elements, the bulk calc-alkaline and tholeiitic rocks are similar to the melt inclusions from their hosted clinopyroxenes. Simonov et al. [7] showed that the composition of melt inclusions suggests that magmatism evolved from primitive island arc with boninites to mature island arc with calc-alkaline melts. Their trace element composition is also close to island-arc tholeiitic and calc-alkaline series. The parental melts crystallized at 1150–1190°C. Numerical simulation and in-situ ion-microprobe analysis indicate that the melts contained up to 1 and 0.84 wt % water, respectively. The calculated liquidus temperatures are consistent with the temperatures of homogenization of melt inclusions. The calculations based on melt inclusion composition showed that the primary melts of the Char island-arc basalts were produced at 1350–1530°C temperatures and 50–95 km depths, i.e. close to the parameters of melting of typical Pacific tholeiitic and boninitic island-arc magmas. Thus, the compositions of whole-rock samples and melt inclusions in clinopyroxene suggest their formation in an active continental margin setting, including tholeiitic and calc-alkaline island-arc systems [7].

In the binary diagrams MgO is positively correlated with FeO and CaO and negatively with SiO₂, Al₂O₃ and TiO₂ suggesting fractionation of plagioclase and clinopyroxene and, to a lesser degree, titanomagnetite. For petrogenetic implications we performed modeling of clinopyroxene fractional crystallization and melting based on the mantle source parameters and approaches discussed in Pfander et al. [5]. For clinopyroxene fractionation modeling in the Nb versus Zr system we chose two samples, basalt (C-21b-08) and andesibasalt (Ch-59-08), which are characterized by lowest contents of Nb and highest MgO. Our results showed that in most of the samples clinopyroxene fractionation did not notably affect the relationships in the Nb versus Zr/Nb system. Two samples, Ch-69-08 and Сh-44-09, could be derived from the melt, which produced high-Mg basalt C-21b-08, due to clinopyroxene fractionation.

Fig. Main geochemical features of Char volcanic rocks. A – Al₂O₃-FeO*+TiO₂-MgO classification diagram [4]; tholeiitic series: TA – andesite, TD –dacite, TR – rhyolite; calc-alkaline series: CB – basalt, CA – andesite, CD – dacite, CR– rhyolite; kom – komatiite. B - primitive mantle-normalized multi-component trace element patterns; the normalization values are from Sun and McDonough [8].

In addition, we checked the fractionation of pyroxene as a probable factor controlling the content of Ti (Ti versus Nb system) and found that the observed variations of Ti concentrations in several samples can be achieved by fractionation of 10 to 30% of pyroxene. For the calculations we used a Nb-depleted MORB-type melt and a hypothetical melt compositionally similar to the most Ti-Nb-depleted sample Ch-09-08. Such fractionation could be possible in a shallower magma chamber.

For melting modeling we used the Nb–Yb systematics to calculate the composition of melts produced by different degrees of melting and variable source compositions, applying the equation for nonmodal batch melting [1]. We tested the melting of primitive (garnet peridotite, spinel lherzolite) and moderately and high-Nb-depleted mantle sources (depleted harzburgites), which could probably produce the basaltic melts ([6] and references therein). The modeling suggests that most Char volcanics formed from the melts derived from depleted harzburgite.

Thus, for the first time we identified volcanic rocks with suprasubduction chemical characteristics which occur as tectonic sheets in the western part of the Char ophiolite belt. The volcanic rocks are tholeiitic and calc-alkaline basalts to andesites. They are characterized by nearly flat REE patterns and Nb negative peaks in the multi-element diagrams. According to petrological data and geochemical modeling the melts, which produced the Char volcanic rocks, were derived from a strongly depleted mantle source (sub-arc harzbirgite), experienced fractionation of clinopyroxene and crystallized at relatively high temperatures.

References:

1. Albarède, F. (1995) Introduction to geochemical modeling. Cambridge University Press, Cambridge.

2. Belyaev, S.Yu. (1985) Tectonics of the Chara zone (East Kazakhstan) (in Russian), IGiG SO AN SSSR, Novosibirsk.

3. Buslov, M.M., Watanabe, T., Fujiwara, Y., Iwata, K., Smirnova, L.V., Safonova, I.Yu., Semakov, N.N., Kiryanova, A.P. (2004) Late Paleozoic faults of the Altai region, Central Asia: tectonic pattern and model of formation. Journal of Asian Earth Sciences 23, 655-671.

4. Jensen, L.S. (1976) A new cation plot for classifying subalkalic volcanic rocks – Ontario Division Mines Misc., 66.

5. Pfandler, J.A., Jochum, K.P., Kozakov, I., Kroner, A., Todt, W. (2002) Coupled evolution of back-arc and island arc-like mafic crust in the late-Neoproterozoic Agardagh Tes-Chem ophiolite, Central Asia: evidence from trace element and Sr-Nd-Pb isotope data. Contribution to Mineralogy and Petrology 143, 154-174.

6. Safonova, I., Simonov, V.A., Obut, O.T., Kurganskaya, E.V., Romer, R., Seltmann, R. (2012) Late Paleozoic oceanic basalts hosted by the Char suture-shear zone, East Kazakhstan: geological position, geochemistry, petrogenesis and tectonic setting. Journal of Asian Earth Sciences. doi: 0.1016/j.jseaes.2011.11.015.

7. Simonov V.A., Safonova I.Yu., Kovyazin S.V. (2010) Petrogenesis of island-arc complexes of the Char zone, East Kazakhstan. Petrology 18, 59-72.

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