Early Devonian volcanics of southeastern Gorny Altai: Geochemistry, isotope (Sr, Nd, and O) composition, and petrogenesis (Aksai complex)

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ScienceDirect Russian Geology and Geophysics 59 (2018) 905–924 www.elsevier.com/locate/rgg

Early Devonian volcanics of southeastern Gorny Altai: geochemistry, isotope (Sr, Nd, and O) composition, and petrogenesis (Aksai complex) V.I. Krupchatnikov a,*, V.V. Vrublevskii b, N.N. Kruk c,d a

Gorno-Altaiskaya Ekspeditsiya, ul. Sovetskaya 15, Maloeniseiskoe 659370, Altai Territory, Russia b National Research Tomsk State University, pr. Lenina 36, Tomsk, 634050, Russia c V.S. Sobolev Institute of Geology and Mineralogy, Siberian Branch of the Russian Academy of Sciences, pr. Akademika Koptyuga 3, Novosibirsk, 630090, Russia d Novosibirsk State University, ul. Pirogova 2, Novosibirsk, 630090, Russia Received 15 February 2017; received in revised form 8 November 2017; accepted 18 December 2017

Abstract Geological, geochemical, and isotope (Sr, Nd, and O) parameters of Early Devonian (405 Ma) volcanics of southeastern Gorny Altai (Aksai and Kalguty volcanotectonic structures) are discussed. The studied igneous rock association comprises magnesian andesitoids, Nb-enriched andesite basalts, and A-type peraluminous silicic rocks (dacites, rhyolites, granites, and leucogranites). Magnesian andesitoids (mg# > 50) are characterized by a predominance of Na among alkalies (K2O/Na2O ≈ 0.1–0.7), medium contents of TiO2 (~0.8–1.3 wt.%) and Al2O3 (~12–15 wt.%), enrichment in Cr (up to 216 ppm), and low Sr/Y ratios (4–15). The Nb-enriched (Nb = 10–17 ppm) andesite basalts have high contents of TiO2 (1.7–2.7 wt.%) and P2O5 (0.4–1.4 wt.%). The A-type granitoids are characterized by high contents of K(K2O/Na2O ≤ 60) and alumina (ASI ≤ 2.9) and depletion in Ba, Sr, P, and Ti. The magnesian andesitoids and Nb-enriched andesite basalts are products of melts generated in the metasomatized lithospheric mantle; silicic magmas were formed through the melting of Cambrian–Ordovician metaturbidites of the Gorny Altai Group and, partly, Early–Middle Cambrian island-arc metabasites. The above rock association might have resulted from a plume impact on the lithospheric substrates of the continental paleomargin during the evolution of the Altai–Sayan rift system. © 2018, V.S. Sobolev IGM, Siberian Branch of the RAS. Published by Elsevier B.V. All rights reserved. Keywords: Early Devonian magmatism; magnesian andesitoids; Nb-enriched andesite basalts; A-type granitoids; geochemistry; Gorny Altai; Central Asian Orogenic Belt

Introduction The Devonian Stage of the geological history of the Altai–Sayan Folded Area (ASFA) was characterized by the presence of two contrasting geodynamic regimes: a rifting regime, caused by the activity of a mantle plume, and a continental-margin regime, caused by the subduction of the oceanic lithosphere of the Ob’–Zaisan basin under the edge of the Siberian continent (Berzin and Kungurtsev, 1996; Berzin et al., 1994; Shokal’skii et al., 2000; Vorontsov et al., 2010; Yarmolyuk and Kovalenko, 2003). Rifting processes led to the formation of large superimposed troughs (Minusinsk, Agulsk, Tuva, Rybinsk, etc.) filled with bimodal volcanic series of predominantly increased sodium alkalinity

* Corresponding author. E-mail address: [email protected] (V.I. Krupchatnikov)

(Babin et al., 2004; Vorontsov et al., 2013), as well as to the development of intrusive alkali basic magmatism (Vrublevskii et al., 2014, 2016). Considering the large size of the magmatic area, its cross-cutting position relative to earlier geological structures, and the significant volumes and specific composition of volcanics, Yarmolyuk and Kuzmin raised the issue of identifying the Altai–Sayan rift area, similar to large igneous provinces of plume origin (Kuzmin et al., 2010; Yarmolyuk and Kovalenko, 2003; Yarmolyuk et al., 2000). Continental-margin volcanic formations form a system of linear belts along the boundary of the Siberian paleocontinent (Rotarash et al., 1982; Berzin and Kungurtsev, 1996; Shokal’skii et al., 2000). Syntectonic sedimentary terrigenousvolcanic-carbonate sequences simular in structure to accretion wedged are known in the northern (Orlov Formation) and southern (Kystav-Kurchum Formation) parts of the Kalba–

1068-7971/$ - see front matter D 201 8, V.S. So bolev IGM, Siberian Branch of the RAS. Published by Elsevier B.V. All rights reserved. http://dx.doi.org/10.1016/j.rgg.201 + 8.07.012

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Fig. 1. Diagram of the geological structure of the Aksai volcanic complex according to (Krupchatnikov et al., 2015; Ponomarev et al., 2010; Shokal’skii et al., 2000) with changes. 1, Cenozoic loose sediments; 2, Triassic–Jurassic granitoids; 3, Early Middle Triassic: monzonitoids (a), lamprophyre and lamproite dikes (b); 4–7, carbonate and terrigenous deposits: 4, Middle–Late Devonian, 5, Early Devonian, 6, Silurian–Early Devonian, 7, Middle Cambrian–Early Ordovician (Gorny Altai Group); 8, metamorphic formations; 9–14, Early Devonian Aksai volcanic complex: 9, basaltic andesites, 10, 11, effusive (10) and subvolcanic (11) dacites and rhyolites, 12, granodiorites, 13, leucogranites, 14, basalts and andesites of the Oyum paleovolcano; 15, faults; 16, contours of volcanotectonic structures: 1, Aksai, 2, Kalguty. Intrusive massifs in the Aksai VTS: A, Aksai, U, Ulandryk, O, Oyum. The inset shows the location of the Middle–Late Paleozoic volcanoplutonic belts in the western part of the Altai–Sayan folded area: 1, Cenozoic deposits of the Biya–Katun’ depression; 2, Aksai volcanic complex.

Narym zone of East Kazakhstan (D’yachkov et al., 1994; Fedak et al., 2012; Navozov et al., 2010). The issue of the scale of volcanism caused by plume- and plate-tectonic events, the relationship between their melt sources, as well as the assignment of individual manifestations of endogenous activity to a particular regime has been the subject of a long-standing discussion. This problem is especially acute for the Gorny Altai region, which is in the zone of influence of both the Altai–Sayan rift system and the Altai continental margin. According to the results of geological survey, the Middle Paleozoic magmatic formations of the region are divided into two volcanoplutonic belts: Altai– Minusa (D1–2) and Salair–Altai (D–C1) (Shokal’skii et al., 2000) (Fig. 1, inset). The formation of the second belt is undoubtedly associated with the development of the active continental margin, whereas the position of the first belt is still unclear. According to previous studies (Kruk, 2015; Rudnev et al., 2001), the formation of this belt marked the transformation of the Altai margin of the Asian continent from a passive into an active margin under the action of an intraplate source; i.e., it preceded the beginning of subduction. The alternative point of view expressed by Vorontsov et al. (2010, 2013) relates the formation of this belt to the interference of plate- and plume-tectonic processes (the impact of a

mantle plume on the already existing active continental margin). In connection with this problem, we have undertaken a geological and geochemical study of volcanic rocks of the Aksai andesite–dacite–rhyolite complex in southeastern Gorny Altai. Derivatives of this complex fill the spatially close Aksai and Kalguty volcanotectonic structures (VTSs) and a number of small graben-like structures between them and in their surroundings (Fig. 1). A distinctive feature of the complex is the increased potassium content in most of its constituent rocks (Amshinskii, 1973; Fromberg, 1993; Gusev et al., 2008; Mariich, 1975; Rodygin, 1959, 1960). The results of U–Pb isotopic dating of zircons from subvolcanic rhyolites (Kalguty VTS) and leucogranites of the Aksai, Ulandryk, and Oyum blocks (Aksai VTS) indicate an Early Devonian age of 402–405 Ma for the Aksai complex, which corresponds to the Early Emsian (Gusev et al., 2008; Ponomarev et al., 2010). New geochemical and isotopic (Sr–Nd–O) data along with features of the geological position provide an understanding of the petrogenetic features of volcanic rocks of the Aksai complex, the sources of their melts, and the possible setting of their formation in the Altai–Minusa belt.

V.I. Krupchatnikov et al. / Russian Geology and Geophysics 59 (2018) 905–924

Geological-petrographic characteristics of the Aksai complex The Aksai and Kalguty VTSs are located in southeastern Gorny Altai, in the basins of the Ulandryk, Aksai, Chagan– Burgazy, Kalguty, and Zhumaly Rivers and partly extend into Mongolia (Fig. 1). Both structures are confined to the southeastern periphery of the Kholzun–Chuya anticlinorium and are imposed on tectonized metaturbidite rocks of the Cambrian–Ordovician Gorny Altai Group. Both VTSs are composed, in addition to volcanics, of fragments of terrigenous-carbonate deposits of different ages (from the Early Silurian to the Early Devonian) and later (from the Middle Devonian to the Early Jurassic) intrusive formations. The Aksai and Kalguty VTSs differ significantly from each other in internal structure, which, apparently, reflects different erosion levels. In the Aksai VTS, the complex comprises mainly sheet facies, among which lava facies dominate over pyroclastic ones and subvolcanic formations are poorly represented. The high-potassium series includes an early dacite association and a late rhyolitoid association in a volume ratio of 1:5. The dacites are characterized by massive fine-porphyritic (plagioclase, rarely opacitized mafic mineral) structure with amygdaloidal and fluidal textures and hyalopilitic or felsic bulk compositions. The rhyolitoid association is composed of rhyolites and comagmatic subvolcanic leucogranite and microgranite porphyries, usually highly alkali. The rhyolites are fine-porphyritic and massive or more rarely fluidal, mottled or spherulitic; phenocrysts are represented by quartz, K-feldspar, and plagioclase in different proportions. In subvolcanic rhyolite and microgranite porphyries, the phenocryst composition is similar, with rare occurrences of muscovite and biotite in the matrix. The largest subvolcanic bodies (Aksai, Ulandryk, Oyum, Buraty, Sogonolu, and Chagan–Burgazy blocks), composed of leucogranites of different alkalinity (low to moderately alkali), are located in the central-axial and peripheral parts of the VTS and presumably mark the location of eruptive centers. The rocks are composed of quartz, K-feldspar, and acid plagioclase. Rare small segregations of biotite and muscovite, in aggregate, do not exceed 3–4%. In the Kalguty VTS, effusive rocks are not common and are homodromously developed (early basaltic andesites, late rhyodacites, and rhyolites) with a great predominance of silicic derivatives. All varieties are porphyritic, and the proportion of phenocrysts is usually not more than 4–5% in basaltic andesites (plagioclase, pseudomorphs of mafic minerals) and 15% in dacites, rhyodacites, and rhyolites (quartz, plagioclase, K-feldspar, biotite). Subvolcanic formations form a single unit which almost completely determines the VTS contour and are composed of several intrusion phases in the following sequence: (1) rhyolites and rhyodacites; (2) dacites; (3) granodiorites and granites; (4) leucogranites. The rocks of the first three phases are characterized by an abundance of porphyry inclusions (30–60, sometimes up to 70% of the rock volume), represented by various combinations of quartz, plagioclase, K-feldspar, biotite, and occasionally hypersthene (in dacites).

907

Leucogranites, as a rule, are aplite-like or micropegmatitic. Occasionally large microperthite phenocrysts are found. The rocks are 90–95% composed of quartz and K-feldspar, are practically devoid of mafic minerals, and contain small amounts of acid plagioclase. The Oyum paleovolcano appears as two disjointed fragments in the northwestern frame of the Aksai VTS. The larger eastern fragment has a thick (more than 600 m) section composed of a poorly differentiated effusive series, dominated by andesites interbedded with strongly subordinate basalts and dacites. Volcanic rocks of similar composition in the western fragment fill a small graben on the left bank of the Sebystei River (southwestern margin of the Chuya basin). The close spatial association implies that the volcanics of the Oyum paleovolcano and the Aksai VTS formed at relatively the same time. Unlike the Aksai complex rocks with potassium derivatives, the rocks of the Oyum paleovolcano are characterized by sodium specificity and significant development of magnesian varieties. The rocks have fine-porphyritic microlithic structures and coarse-fluidal massive or amygdaloidal textures. The phenocrysts of deanorthized plagioclase and chlorite pseudomorphs of pyroxene (?) amount to 25% of the rock volume. Dacites contain small amounts of quartz phenocrysts.

Analytical methods The contents of petrogenic and rare-earth elements in rocks were measured by X-ray fluorescent analysis (XRF, ARL9900XL ThermoScientific and AxiosAdvanced spectrometers) and inductively coupled plasma mass spectrometry (ICP-MS, Elan-DRC-6100 and Finnigan MAT high-resolution spectrometers) at the Collective-Use Center of Multielement and Isotope Analysis of SB RAS (Novosibirsk) and the analytical centers of the Institute of Mineralogy, Geology, and Crystal Chemistry of Rare Elements (IMGRE, Moscow) and the Russian Geological Research Institute (VSEGEI, St. Petersburg). The Sm–Nd and Rb–Sr isotopic composition was studied by a standard procedure using Finnigan MAT-262 and Triton mass spectrometers at the Institute of Precambrian Geology and Geochronology (IPGG) of RAS and VSEGEI (St. Petersburg). Element concentrations were determined with an error not more than ±1 rel.%. The error 2σ did not exceed 0.5 rel.% for 147Sm/144 Nd, 1.0 rel.% for 87Rb/86Sr, 0.005 rel.% for 143 Nd/144Nd, and 0.1 rel.% for 87Sr/86Sr. The isotope ratios were normalized according to the NBS SRM-987 (87Sr/86Sr = 0.710235) and LaJolla (143Nd/144Nd = 0.511860) standards. The epsilon error and the primary Nd and Sr isotope ratios were calculated for an U–Pb age of 405 Ma of accessory zircon in granitoids of the Aksai complex (modern CHUR 143 Nd/144Nd = 0.512638 and 147Sm/144Nd = 0.1967 and UR 87 86 Sr/ Sr = 0.7045 and 87Rb/86Sr = 0.0827) (Faure, 1989). The ratio δ18O (± 0.2‰, SMOW) in bulk rock samples was determined on a MI-1201V mass spectrometer at the Geological Institute of RAS, Moscow.

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Chemical composition and isotopic characteristics of rocks of the Aksai complex Representative chemical compositions of rocks of the complex are given in Table 1, and their silica distribution in both VTSs and in the Oyum paleovolcano is illustrated by histograms (Fig. 2). Petrogeochemical typification Basaltic andesites of the Kalguty VTS. In the TAS diagram, the compositions of basaltic andesites, with a silica content of 52.9–55.4 wt.%, tend to the line of separation of the fields of normally and moderately alkali varieties, and in the SiO2–K2O coordinates, they correspond to high-potassium derivatives (Fig. 3a, b). Andesibasalts are low-magnesian (mg# = 12–26, MgO = 1.17–1.92 wt.%) (Fig. 4) and depleted in Cr (7–30 ppm) and Ni (9–44 ppm), indicating that the rocks might have formed from a differentiated melt. In addition, they have low alumina contents (Al2O3 = 12.7–13.8 wt.%, CaO/Al2O3 = 0.33–0.42) but increased total and potassium alkalinity (Na2O + K2O = 4.3–6.2, K2O = 2.2–3.2 wt.%) at high concentrations of titanium (TiO2 = 1.7–2.7 wt.%) and

Fig. 2. Histograms of silica distribution of Aksai complex rocks. The number of samples is given in parentheses. In addition to tabular data (Table 1), analysis of GSR-50 materials were used.

phosphorus (P2O5 = 0.4–1.4 wt.%), which makes the studied rocks similar to rift-related volcanics, in particular, the basic rocks of the Ethiopian rift (K2O = 0.6–1.3 wt.%, TiO2 = 1.4–2.6 wt.%, P2O5 = 0.3–0.7 wt.% (Kurkura et al., 2009)). Among other features are the anomalous enrichment in Cs (8–24 ppm), distinct Ba and Sr minima in the rare-earth element spectrum (Fig. 5a), and a poorly differentiated rare-earth spectrum (La/Yb)N ≈ 3–4) with an insignificant negative Eu anomaly (Eu/Eu* = 0.77–0.94). Despite the pronounced Ta–Nb minimum, basaltic andesites are enriched in Nb (10–17 ppm), unlike typical island-arc basites (less than 10 ppm (Kelemen et al., 2003; Kovalenko et al., 2010)). This, along with other indicators (Th = 7.8–9.9 ppm, Zr/Hf = 30–41, (Gd/Yb)N = 1.5–1.9, Ta = 0.96–1.1 ppm, Nb/Ta ≈ 9–16, and [(Ta/Th)+ (Ta/La)]PM ≈ 0.8–0.9), suggests, according to (Polat and Kerrich, 2001; Ujike and Goodwin, 2003) that they belong to the group of Nb-enriched basalts and andesites (NEBA). Silicic rocks of the Aksai and Kalguty VTSs. The chemical composition of silicic derivatives is characterized by wide variations in silica content (SiO2 ≈ 62–79 wt.%) and total alkalinity (Na2O + K2O ≈ 3–10 wt.%), with most varieties having normal and increased alkalinity (Fig. 3a). In the Aksai VTS, the compositions show clear bimodality in the absence of rhyodacites. In the SiO2–K2O diagram, most volcanics belong to the ultrapotassium (shoshonite) series. The K2O/Na2O ratio is almost always higher than 1 (in dacites, sometimes <1) and reaches limiting values (up to 60) in low-alkali rhyolites and leucogranites. A characteristic feature of the entire rock series is a high alumina content: the ASI value is predominantly 1.0–1.5 and reaches 2.9 in rhyolites; in the A/NK–A/CNK diagram, almost all compositions are located in the field of peraluminous granitoids (Fig. 3c). Most varieties are characterized by increased iron content (Fig. 3d) and low phosphorous content (in rhyodacites, rhyolites, granites, and leucogranites, the P2O5 content is usually less than 0.1 wt.%). A distinctive geochemical feature of silicic rocks is their rare-earth element spectra with deep negative anomalies of Ba, Sr, P, and Ti contents (Fig. 5c, e). The Ta–Nb trough and the Pb maximum are less pronounced. The distribution of rare-earth elements is characterized by their increased contents (in dacites and granodiorites, ΣREE is 96–343 ppm, and in rhyolites and leucogranites, it is 103– 350 ppm), moderate fractionation ((La/Yb)N ≈ 1–9, (La/Gd)N ≈ 2–5), and a negative Eu anomaly (Eu/Eu* = 0.1–0.9). Based on a number of features, such as an increased iron content, the total enrichment in HFS elements (the sum of Nb + Zr + Ce + Y is usually greater than 350 ppm), and increased Ga concentrations (the 10,000Ga/Al ratio is often more than 2.6), the silicic derivatives of the Aksai complex are comparable to A-type granitoids and correspond to the A2 subtype, and in the Rb–(Y + Nb) diagram, most of the compositions are shifted to the region of intraplate granitoids (Fig. 6b–d). The rock series of the Oyum paleovolcano is characterized by a moderate differentiation and a unimodal silica distribution of compositions with a total maximum in the interval of andesitoids (SiO2 = 54–64 wt.%) (Figs. 2 and 3).

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V.I. Krupchatnikov et al. / Russian Geology and Geophysics 59 (2018) 905–924 Table 1. Representative chemical compositions of rocks of the Aksai complex Component

1

2

3

4

5

6

7

8

9

10

11

12

13

30002

30061

Ul-1

Ul-7

1073-1

5187

5188

1075-1

1074

302

BSh-3

Ul-4

Ul-5

SiO2

64.3

62.3

63.4

62.6

62.2

66.3

65.2

64.8

64.8

71.3

74.5

74.9

74.5

TiO2

1.07

1.76

1.04

0.96

1.19

0.88

1.14

1.10

1.09

0.81

0.19

0.16

0.18

Al2O3

13.4

14.9

13.8

14.3

13.9

14.0

13.1

14.5

14.0

15.8

13.6

12.8

12.9

FeO*

6.51

2.98

7.41

9.83

7.98

7.70

9.03

7.56

6.95

1.40

1.22

2.06

2.06

MnO

0.14

0.08

0.06

0.12

0.09

0.03

0.09

0.04

0.05

0.03

0.03

0.03

0.03

MgO

0.26

2.90

1.12

1.77

1.86

1.5

2.04

1.45

1.59

0.49

0.32

0.33

0.05

CaO

4.35

3.91

1.38

0.91

2.58

0.49

1.09

0.66

1.77

1.09

0.08

0.17

0.17

Na2O

0.97

3.23

4.53

1.11

2.2

2.23

4.26

3.11

3.69

2.06

0.60

2.97

2.35

K2O

2.33

2.10

4.14

2.91

3.62

4.01

1.70

4.43

2.62

4.62

7.56

5.31

6.83

P2O5

0.21

0.09

0.34

0.291

0.34

0.26

0.38

0.35

0.36

0.27

0.02

0.02

0.03

LOI

5.65

4.86

1.91

3.92

3.08

2.48

1.99

1.90

2.34

2.24

1.77

0.90

0.68

Total

99.16

99.10

99.09

98.74

99.09

99.87

100.02

99.94

99.34

100.05

99.89

99.63

99.83

Ba

470

99

676

446

558

342

343

649

278

931

629

869

283

Sr

65

84

69

37

89

49

93

63

50

29

21

56

38

Rb

106

104

113

146

187

235

66

161

114

184

253

206

216

Cs

13.7

9.1

1.7

5.0

9.2

8.4

1.2

5.8

3.7

2.6

4.5

7.4

5.4

Sc

11.5

26

38.8

43.5

17.7

17.7

25

14.3

15.4

34

1.6

23.9

22.5

Th

12.8

8

13.5

16.9

10

14.5

12.8

12.5

9.8

16.7

18.2

20.4

23.8

U

4.2

2.7

3.4

3.9

3.4

4

3.7

3.9

3.1

2.3

5.7

4.5

5

Zr

161

225

370

304

344

376

380

363

365

401

235

222

256

Hf

5.8

5.6

10.4

9.8

9.7

10

8.8

10.4

8.9

10

7.5

8.1

9.9

Nb

21

15.6

18.2

14.7

18.1

18

15.6

18.8

19.6

14.2

21.3

21

27.5

Ta

2.6

0.9

1.7

1.8

1.35

1.34

1.22

1.13

1.4

1.1

2.1

2.2

2.9

Y

59

54

57.1

55.7

67

59

48

68

65

46.4

78.5

75

80.9

La

11.9

25

26.9

39.5

47

70

36

70

12.6

50.1

32.5

59.5

58.2

Ce

27

56

60.7

89.7

98

135

74

141

27

107.3

71.1

127.7

141.3

Pr

3.9

7.7

7.8

11.1

13.5

18.4

10.6

18.9

3.8

11.7

8.5

15.9

16.3

Nd

17

33

32.7

44.4

54

68

41

76

16.7

44.6

33.2

62

64

Sm

5.3

7.8

7.6

10.0

11.6

12.4

8.5

16.3

4.8

8.9

8

13.8

14.8

Eu

1.1

1.8

1.8

2.2

3

2

1.7

3.5

1

1.6

1.1

1.9

0.6

Gd

7.1

8

8.1

9.7

11.3

10.1

8.3

14.1

7.1

9

9.8

13.3

13.8

Tb

1.4

1.4

1.4

1.6

1.83

1.54

1.28

2

1.4

1.4

1.8

2.1

2.4

Dy

9.1

8.2

9.5

10.1

10.9

9.7

7.9

11.2

8.7

8.5

12.3

13

15.5

Ho

1.9

1.6

2.1

2.2

2.1

1.98

1.67

2.3

1.9

1.8

2.6

2.7

3.2

Er

5.8

4.6

6.2

6.4

6.2

6.3

5.1

6.7

5.3

4.9

7.2

7.8

9.3

Tm

0.91

0.7

0.89

0.94

0.96

1.01

0.84

1.03

0.77

0.7

1.06

1.17

1.36

Yb

5.8

4.3

5.76

5.98

5.7

6.3

5.3

6.1

4.9

4.1

6.57

7.41

8.7

Lu

0.81

0.57

0.91

0.92

0.8

0.94

0.81

0.87

0.71

0.6

0.97

1.13

1.34

V

109

203

57

43

80

62

66

60

48

38

8

8

7

Cr

11

12

67

6

32.00

6

5.5

9.10

10

40

6

10

10

Co

12

24

10

11

10.20

8.6

11.7

7.40

8

2

2

2

2

Ni

30

<5

45

20

25

13

<5

8.1

9

6

28

21

12

Pb

14.1

5.1

–

–

8.3

22

6.9

10.3

5.9

–

–

–

–

Ga

–

–

21.9

24.7

–

–

–

–

–

16

21.4

22.2

25.4

(continued on next page)

910

V.I. Krupchatnikov et al. / Russian Geology and Geophysics 59 (2018) 905–924

Table 1 (continued) Component

14

15

16

17

18

19

20

21

22

23

24

25

26

5141

5176

5177

5178-1

5186

30058-1

30062

1091-1

BSh-7

5119-1

OYu-3

503

501

SiO2

74.5

76.6

75.9

78.4

77.0

78.2

74.4

72.6

74.8

75.7

74.2

53.8

55.4

TiO2

0.16

0.15

0.21

0.21

0.16

0.07

0.09

0.26

0.15

0.18

0.34

2.69

2.35

Al2O3

12.6

11.6

12.1

12.1

12.1

11.5

11.1

11.0

11.9

12.4

13.0

13.5

12.7

FeO*

3.64

3.22

3.64

1.17

1.83

1.42

2.17

5.49

1.96

2.50

2.26

13.95

14.85

MnO

0.03

0.03

0.03

0.03

0.04

0.02

0.07

0.05

0.03

0.04

0.03

0.28

0.19

MgO

0.64

0.32

0.27

0.13

0.13

0.39

0.4

0.96

0.05

0.17

0.05

1.92

1.17

CaO

0.23

0.26

0.13

0.15

0.15

0.12

2.14

2.46

0.09

0.15

0.25

4.97

4.14

Na2O

2.85

0.66

1.20

0.28

0.30

1.07

1.02

0.58

2.95

2.51

2.74

3.45

2.56

K2O

3.92

6.18

5.52

6.01

6.79

4.65

5.9

2.88

6.47

4.88

5.60

2.44

2.17

P2O5

0.03

0.03

0.03

0.01

0.03

0.03

0.03

0.11

0.02

0.04

0.08

1.39

1.28

LOI

1.51

1.14

1.11

1.32

1.49

2.32

3.5

3.22

1.46

1.09

1.15

1.02

0.60

Total

100.10

100.13

100.13

99.76

100.04

99.82

100.79

99.58

99.87

99.73

99.65

99.34

97.41

Ba

522

787

629

636

439

164

245

580

363

378

609

328

303

Sr

31

47

29

27

23

16

27

170

30

27

52

209

179

Rb

139

222

214

235

224

140

143

109

215

159

161

177

150

Cs

2.5

10

4

4.8

1.67

4.1

2.8

10.9

1.8

4.9

2.5

24.1

12.9

Sc

5

5.9

3

6.1

5.1

2.3

3.5

6.2

9.5

1.64

20

38.3

48.1

Th

15.1

15.4

17.7

17.5

15.5

22

15.8

15.2

21

12.8

23.7

7.8

8.8

U

5

5.4

3.9

4

3.2

5.6

2.3

3.5

4.6

3.5

5.3

2.1

2.8

Zr

199

241

379

398

236

93

125

228

281

199

241

259

218

Hf

6

6.6

10.5

10.2

9

4.5

5.3

8.8

10.3

6.5

9

6.3

7.3

Nb

23

19.7

17.9

17.7

29

24

29

24

28.3

29

12.6

13.1

10.1

Ta

1.95

1.53

1.54

1.3

2.2

2.5

2.2

1.97

2.5

1.95

1.8

1

1.1

Y

40

48

62

65

89

90

32

30

81.5

74

47.8

64.6

67.1

La

68

31

54

59

35

20

13.5

34

50.6

21

23.8

34.2

29.5

Ce

139

66

110

117

157

46

30

60

130.7

52

52.7

83

71.7

Pr

18

6.3

16.2

16.8

11.5

6.7

4.3

7.1

14.9

6.3

6

11.5

9.9

Nd

65

31

62

62

44

28

16.4

24

57.3

25

22.3

51.9

44.7

Sm

11.5

6.2

13

12.9

9.3

7.9

4

4.2

13.5

6

5.1

12.8

11.4

Eu

1.48

0.99

2.2

2.3

1.15

0.6

0.25

0.77

1.2

0.84

0.9

4.1

3.5

Gd

9.4

6.1

13.7

13.5

10

9.2

4.1

3.8

12.7

7.7

5.8

14

13

Tb

1.19

1.07

2.1

2.1

2.2

1.8

0.69

0.64

2.2

1.7

1.2

2.1

2.1

Dy

6.5

7.2

12

11.8

16

12

4.8

4.4

14.2

11.8

8.2

13.2

13

Ho

1.4

1.65

2.4

2.3

3.4

2.5

1.02

0.95

3

2.5

1.9

2.7

2.8

Er

4.2

5.1

6.9

6.6

9.8

7.8

3.4

3.4

8.8

7.2

5.7

7.2

7.9

Tm

0.71

0.84

1.07

1.03

1.54

1.28

0.63

0.58

1.33

1.09

0.88

1.01

1.13

Yb

4.7

5.2

6.7

6.5

9.6

8.2

4.7

4.1

8.54

6.5

5.8

6.18

7.05

Lu

0.68

0.68

0.99

0.96

1.34

1.16

0.64

0.62

1.31

0.87

0.9

0.9

1.03

V

4.8

5.4

2.5

1.83

3.5

4

7.4

43

6

7.1

19

195

173

Cr

8.8

11.6

8.9

11.7

13.4

8

15.7

16.30

1

10

3

13

7

Co

1.9

2.2

1.44

1.67

1.74

1

2.1

4.30

2

1.77

4

22

31

Ni

5

5

5

14

6.3

9

<5

22

6

<5

2

44

18

Pb

12.2

12

22

17.3

8.2

6.2

11.2

6.8

–

15.6

–

–

–

Ga

–

–

–

–

–

–

–

–

22.9

–

19.6

–

–

(continued on next page)

911

V.I. Krupchatnikov et al. / Russian Geology and Geophysics 59 (2018) 905–924 Table 1 (continued) Component

27

28

29

30

31

32

33

34

35

36

37

38

ZhU-1

170

5252

ZhU-4

ZhU-11

30068

ZhU-6

ZhU-12

ZhU-2

ZhU-3

8035

30052

SiO2

64.6

70.5

71.3

74.5

75.5

67.4

69.7

70.4

69.2

73.1

52.9

54.9

TiO2

1.01

0.45

0.45

0.31

0.24

0.56

0.65

0.56

0.49

0.07

2.39

1.67

Al2O3

14.8

14.6

14.8

12.5

12.9

13.4

15.0

14.2

14.9

12.7

13.3

13.8

FeO*

6.40

1.79

2.97

2.26

1.56

2.86

4.09

4.37

2.84

0.60

11.68

7.48

MnO

0.11

0.04

0.03

0.03

0.03

0.03

0.03

0.08

0.03

0.03

0.15

0.19

MgO

1.85

0.82

0.58

0.42

0.82

1.24

0.50

0.13

0.80

0.39

1.43

1.47

CaO

2.67

2.54

0.21

0.58

0.19

1.47

0.34

0.25

1.20

1.15

4.80

5.74

Na2O

2.30

1.42

0.78

3.12

0.81

5.47

2.62

2.91

3.32

1.50

1.77

3.00

K2O

3.25

3.13

7.00

4.47

6.30

4.73

4.94

4.36

5.06

8.04

2.56

3.22

P2O5

0.265

0.13

0.11

0.08

0.09

0.20

0.18

0.17

0.15

0.06

1.14

0.42

LOI

1.26

3.84

1.48

1.50

1.32

2.22

1.57

1.58

1.55

2.33

6.61

6.89

Total

6.40

99.28

99.73

99.72

99.76

99.60

99.58

98.98

99.56

99.98

97.73

98.80

Ba

650

222

716

527

588

576

515

558

1040

481

180

134

Sr

186

42

23

89

28

63

43

27

137

43

63

60

Rb

114

190

212

167

216

156

165

209

161

201

137

115

Cs

7.3

4.3

4.5

2.9

5

10.2

3.3

5.2

3.6

2.8

7.9

15.9

Sc

8.6

27

7.3

1

1

13.7

4.3

1.0

1.5

1.8

38

23

Th

17.8

15.7

17.7

11.5

14

13.2

15.7

12.7

15

8.5

8

9.9

U

3.7

3.2

3.3

2.4

2.9

2.3

3.4

2.8

2

3.9

3

3.4

Zr

491

251

262

169

180

288

304

164

274

64

307

229

Hf

12.1

6.4

7.3

4.7

5.2

7.6

7.8

4.8

7.3

2.7

8

6.3

Nb

17

10.3

13.2

9.5

10.6

15.5

12.2

10.8

11.8

11.2

17.2

13.4

Ta

1.2

0.9

1.2

1

1.1

0.97

1

1.2

1.1

1.6

1.1

0.96

Y

63.2

41.7

43

32.7

62

60

48.6

58.1

51.4

15.3

80

49

La

53.4

39.8

39

25.1

14.1

61

40.5

12.7

39.6

1.4

36

24

Ce

118.4

86.6

80

57.6

33

132

90.2

29.9

83.4

3.9

83

54

Pr

14.5

10.2

10.8

6.6

4

17.5

10.7

3.7

9.9

0.6

12.2

7.8

Nd

58.1

38.2

45

24.8

16.3

67

41.7

15.1

38.5

2.7

55

34

Sm

12.4

8

9

5.5

4.5

12.3

9.1

4.3

8.6

1.1

13.3

8.3

Eu

2.4

1.6

1.3

0.9

0.7

2

1.6

0.6

1.9

0.3

3.6

2.2

Gd

11.6

8

8.6

4.8

5.8

10.5

8.7

5.3

8.2

1.5

13.5

9.1

Tb

1.8

1.3

1.2

0.8

1.2

1.57

1.3

1.1

1.4

0.3

2.1

1.5

Dy

10.7

7.8

7.4

5.4

8.5

9.6

8.1

8.1

8.4

2.4

13.3

9

Ho

2.2

1.6

1.4

1.1

1.9

1.78

1.7

1.8

1.7

0.5

2.7

1.77

Er

6

4.5

4.1

3.2

5.8

5.2

4.6

5.5

4.8

1.6

7.5

5

Tm

0.85

0.7

0.62

0.49

0.92

0.75

0.64

0.9

0.7

0.28

1.15

0.72

Yb

5.25

3.9

3.8

3.26

5.65

4.7

3.97

5.3

4.33

2.11

6.9

4.3

Lu

0.81

0.6

0.57

0.49

0.83

0.64

0.59

0.8

0.64

0.34

0.98

0.61

V

88

36

25

20

14

43

57

12.7

32

7

168

182

Cr

17

48

23

5

20

30

10

2.2

1

2

13

30

Co

14

25

2

3

2

5

2

2.2

5

1

14

24

Ni

41

1

11

6

17

3

5

8.0

1

3

9

30

Pb

–

–

11.3

–

–

7.9

–

–

–

–

10.2

10.7

Ga

19.7

–

–

14.4

13.5

–

19.8

13.6

17.5

12.4

–

–

(continued on next page)

912

V.I. Krupchatnikov et al. / Russian Geology and Geophysics 59 (2018) 905–924

Table 1 (continued) Component

39

40

41

42

43

44

45

46

47

48

49

50

51

10176-2

30053

8040

R-1/13

8053

30008-1

OYu-5

R-5/6

IR-182

R-1/10

R-1/15

30009

R-5/7

SiO2

77.5

74.5

76.4

71.7

75.6

56.8

55.1

58.3

55.8

58.3

56.3

61.9

56.1

TiO2

0.17

0.32

0.2

0.15

0.23

0.98

0.99

0.88

1.07

0.78

1.02

0.83

1.05

Al2O3

11.0

13.4

12.8

17.0

12.7

18.9

15.6

16.3

15.5

15.2

17.9

16.3

18.7

FeO*

2.51

3.33

2.68

1.89

2.72

7.06

9.05

7.87

10.39

7.03

7.92

5.29

9.20

MnO

0.04

0.05

0.03

0.02

0.04

0.08

0.04

0.19

0.15

0.09

0.05

0.09

0.13

MgO

0.32

0.3

0.29

0.66

0.21

4.20

5.16

5.30

6.55

6.55

4.82

2.45

3.29

CaO

1.06

0.11

0.58

0.26

0.22

0.70

1.17

2.15

0.88

1.16

0.69

2.15

1.22

Na2O

1.45

1.12

2.05

2.95

2.17

4.94

6.65

4.31

3.68

5.59

6.95

3.92

3.63

K2O

2.83

4.01

2.96

3.63

5.02

2.26

1.07

0.69

0.57

0.83

1.04

2.63

1.88

P2O5

0.04

0.07

0.05

0.08

0.12

0.21

0.40

0.19

0.34

0.19

0.23

0.23

0.27

LOI

2.68

2.41

1.84

1.55

0.72

3.04

4.20

3.42

4.14

3.97

3.22

3.41

3.32

Total

99.62

99.58

99.82

99.86

99.72

99.21

99.33

99.55

99.10

99.67

100.16

99.18

98.78

Ba

162

142

78

294

688

682

265

652

108

256

214

386

612

Sr

37

78

32

74

77

233

72

231

82

122

127

183

107

Rb

93

137

124

130

163

71

17

21

27

30

42

106

128

Cs

4.5

7.6

10.9

2.8

3.1

3.6

0.5

0.8

3.4

5.1

2.7

5.9

4.1

Sc

3.8

6.6

4.4

4.7

4.6

11.2

28

30

36

16.4

15.7

12.8

28.0

Th

17

14

21

8.9

11.4

11.3

10.8

5.9

9

8

8.1

9.6

12.3

U

3.8

2.9

3.6

1.2

2.4

3.0

1.8

1.3

2.1

1.6

1.6

2.7

5.3

Zr

152

502

225

96

143

191

142

116

158

178

185

195

226

Hf

4.9

12.3

6.7

3

4.3

5.7

4.7

3

3.8

4.6

4.9

5.6

5.5

Nb

13.1

29

14.1

12.4

12.1

16.1

10.8

5.9

9.5

9.1

11.0

10.5

12.1

Ta

1.2

1.8

1.2

1.2

1.04

1.1

0.8

0.4

0.6

0.6

0.8

0.9

1.1

Y

36

50

58

15.4

53

17.6

18.4

15.8

17.8

25

21.0

31.0

23.9

La

37

45

49

11.4

16.7

16

44.8

17.1

29.8

24

12.4

28.0

42.8

Ce

71

99

102

21

35

33

93.2

37.5

64.3

51

26.0

58.0

90.3

Pr

9.5

13.4

13.2

2.6

5

4.3

11.3

4.4

7.5

6.6

3.7

7.6

10.3 37.7

Nd

38

53

54

9.7

21

17

42.6

17.3

29.5

28

16.4

29.0

Sm

8.9

11.1

10.6

1.9

5.4

3.2

7.8

3.6

5.4

5.7

3.7

5.6

6.8

Eu

1.2

2.1

1.07

0.5

0.82

0.7

1.8

1

1.2

1.4

1.0

1.2

1.6

Gd

6.4

9.2

9.3

1.9

5.6

3.1

5.4

3.3

4.4

4.9

3.2

5.4

5.4

Tb

1

1.4

1.45

0.3

1.14

0.4

0.7

0.5

0.6

0.7

0.5

0.8

0.8

Dy

6.1

8

8.7

2.2

7.8

2.9

3.9

3

3.5

4.2

3.1

5.0

4.6

Ho

1.2

1.6

1.82

0.5

1.71

0.6

0.8

0.6

0.7

0.8

0.7

1.0

0.9

Er

3.6

4.9

4.9

1.3

5.1

2

2.2

1.8

1.9

2.3

2.0

2.9

2.6

Tm

0.56

0.83

0.76

0.22

0.83

0.34

0.35

0.3

0.3

0.37

0.34

0.45

0.40

Yb

3.6

5.3

4.5

1.58

5.2

2.2

2.23

1.7

1.8

2.3

2.30

2.70

2.40

Lu

0.56

0.81

0.61

0.23

0.74

0.34

0.35

0.3

0.3

0.31

0.32

0.38

0.40

V

8

2

7.3

26

14.7

127

165

71

183

131

117

92

258

Cr

9

7

7.2

13

17.2

102

56

185

146

216

52

39

87

Co

5

5

5.2

5

4.3

20

26

32

45

32

34

16

32

Ni

8

10

3.5

16

3.6

58

50

128

91

75

40

24

58

Pb

14.4

19

4.1

2.7

4

25

–

9.3

9.1

3.9

2.3

6.9

–

Ga

–

–

–

–

–

–

–

–

–

–

–

–

–

Note. Oxides in wt.%, and rare elements in ppm. FeO*, total iron calculated as FeO. Dash, not detected. 1–24, Aksai VTS: 1–9, dacites, 10–21, rhyodacites and rhyolites, 22–24, leucogranites of the Aksai (22), Ulandryk (23), and Oyum (24) massifs; 25–36, Kalguty VTS: 25–26, Nb-enriched basaltic andesites, 27, dacite, 28, 29, rhyodacites, 30, 31, rhyolites, 32, granodiorite, 33–35, granites, 36, leucogranite; 37–43, grabens between the Aksai and Kalguty VTSs: 37, 38, Nb-enriched andesibasalt, 39–43, rhyodacites and rhyolites; 44–51, Oyum paleovolcano: 44–50, magnesian andesites and basaltic andesites, 51, basaltic andesite.

V.I. Krupchatnikov et al. / Russian Geology and Geophysics 59 (2018) 905–924

913

Fig. 3. Petrochemical diagrams for Aksai complex rocks. Rock composition: 1, Aksai VTS; 2, Kalguty VTS; 3, Oyum paleovolcano. Silicic derivatives (SiO2 > 60 wt.%) are given in diagrams (c) and (d). a, According to (Petrographic Code, 2009); b, according to (Rickwood, 1989); (c), according to (Maniar and Piccoli, 1989), (d), according to (Frost et al., 2001). Mol. A/NK, Al2O3/(Na2O+ K2O); mol. A/CNK, Al2O3/(CaO+ Na2O+ K2O). Fe-index = FeOtot/(FeOtot + MgO), wt.%.

Most samples show a predominance of sodium in the alkali balance (K2O/Na2O ≈ 0.1–0.7) and an increased magnesium content, which allows the rocks to be classified as magnesian andesites (MA) (Fig. 4). The rock association is characterized by moderate contents of titanium (TiO2 ≈ 0.8–1.3 wt.%), alumina (Al2O3 ≈ 12–15 wt.%), and phosphorus (P2O5 is mainly 0.2–0.4 wt.%). In the classification diagrams, the compositions of the paleovolcano volcanics are confined to the fields of moderately alkali varieties of predominantly lowand medium-potassium series (Fig. 3). The rare-earth element composition is characterized by high Cr concentrations (39– 216 ppm), depletion in Sr (72–233 ppm), low Sr/Y ratios (4–15), and distinct Ta–Nb, Ti, and Sr minima in the spider diagram (Fig. 5). Rare-earth element spectra are characterized by a low to moderate degree of fractionation ((La/Yb)N ≈ 4–15), an indistinct negative Eu anomaly (Eu/Eu* = 0.6–0.9), and low total concentrations of REEs (76–217 ppm). Generally, the products of the Oyum paleovolcano are comparable in petrogeochemical parameters to suprasubduction magma-

Fig. 4. Ratio of silica and magnesium contents in Aksai complex rocks. 1, Oyum paleovolcano rocks; 2, Nb-enriched basaltic andesites. Line separating the fields of normal and magnesian andesites according to (McCarron and Smellie, 1998). mg# = 100Mg/(Mg + Fetot), atomic ratio.

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V.I. Krupchatnikov et al. / Russian Geology and Geophysics 59 (2018) 905–924

Fig. 5. Distribution of rare elements in Aksai complex rocks. Compositions of primitive mantle, chondrite, and oceanic island basalts (OIB) according to (Sun and McDonough, 1989), basalts of island arcs and active continental margins (IAB), according to (Kovalenko et al., 2010). a, b, 1, Nb-enriched basaltic andesites, 2, magnesian basaltic andesites and andesites of Oyum paleovolcano; c–f, 1, Aksai VTS, 2, Kalguty VTS; c, d, dacites and granodiorites, d, e, rhyodacites, rhyolites, granites, and leucogranites.

tites, which, in particular, is seen in the Th–Hf/3–Ta discrimination diagram (Fig. 6a). Nd–Sr–O isotopic systematics The isotopic compositions of rocks of the complex were determined from 11 samples (Table 2). The primary ratios of

87

Sr/86Sr (405) and 143Nd/144Nd (405) vary in the ranges 0.7035–0.7096 and 0.512063–0.512220, respectively. In the Sr–Nd isotopic coordinates, two disparate subparallel trends are directed from the mantle sequence to the region of the EM2 reservoir, with the isotopic composition of the Oyum paleovolcano rocks characterized by more radiogenic neodymium (εNd(T) = 1.46–2.02) compared with the silicic association

V.I. Krupchatnikov et al. / Russian Geology and Geophysics 59 (2018) 905–924

915

Fig. 6. Discrimination diagrams for Aksai complex rocks. a: 1, magnesian andesites and basaltic andesites of the Oyum paleovolcano; 2, Nb-enriched basaltic andesites; b–d, compositions of silicic (SiO2 > 60 wt.%) derivatives: a, (Wood, 1980); b, (Whalen et al., 1987); c, (Eby, 1992); d, (Pearce et al., 1984).

of the Kalguty and Aksai VTSs (εNd(T) = +0.67...–1.03) (Fig. 7). The observed isotopic ratios indicate the possible mixing of the material and the participation of both rock series of radiostrontium-depleted and -enriched material in melts. The presence of radiostrontium is confirmed by features of the oxygen isotope composition of the rocks studied (Vrublevskii et al., 2007): the δ18OSMOW value varies within 9.3–12.8‰, which implies the interaction of magma with terrigenous sediments (10–15‰ (Pokrovskii, 2000)). Discussion of the results Magmas sources and petrogenesis conditions of volcanic rocks of the Aksai complex Magnesian andesites and Nb-enriched basaltic andesites. In contemporary geodynamic settings, magnesian

andesites (MA) occur mostly in suprasubduction zones (the Kuriles, Kamchatka, the Japanese islands, the Andes, California), and sometimes in collision belts (Tibet). Often, they are genetically related to adakites and have mutual compositional transitions with them (Castillo, 2006). Three models are used to interpret the origin of MAs: (1) the crystallization differentiation of primary igneous melts formed upon melting of the depleted upper mantle; (2) the melting of lower-crust metabasite blocks partially submerged in the mantle and the interaction of the melt with mantle peridotites (based on the example of the Tibet collision belts); (3) subduction model: interaction of fluids and melts separated from the slab with peridotites of the mantle wedge under the assumption that MAs can be generated in two ways: by assimilation of the mantle material by silicic melts or by partial melting of the metasomatized mantle. For the studied magnesian andesites, the first model can be excluded since they do not have a high content of radiogenic neodymium (εNd > +7) and contain no

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V.I. Krupchatnikov et al. / Russian Geology and Geophysics 59 (2018) 905–924

Table 2. Isotope composition of rocks of the Aksai complex Sample No.

Rock

Sm, ppm

Nd, ppm

(147Sm/144Nd)meas

(143Nd/144Nd)meas

(143Nd/144Nd)T

εNd(T)

Ul-1

D

6.9

30.3

0.1382

0.512517 ± 5

0.51215

0.67

30002

D

4.6

14.6

0.1887

0.512641 ± 2

0.512141

0.47

30061

D

7.1

29.4

0.147

0.512480 ± 6

0.51209

–0.51

Zhu-1

D

11.5

53.7

0.1295

0.512445 ± 6

0.512102

–0.29

R-1/13

R

3.5

13

0.1628

0.512495 ± 3

0.512063

–1.03

Zhu-4

LG

5.2

24.4

0.13

0.512453 ± 4

0.512108

–0.16

503

AB(Nb)

10.9

44.2

0.1498

0.512523 ± 6

0.512126

0.18

30052

AB(Nb)

7.4

30.2

0.1484

0.512514 ± 8

0.51212

0.08

30008-1

MAB

3

14.7

0.1221

0.512515 ± 2

0.512191

1.46

Oyu-5

MAB

6.8

37.7

0.1094

0.512510 ± 7

0.51222

2.02

R-1/10

MA

3.5

16.3

0.1311

0.512550 ± 3

0.512202

1.68

87

86

87

86

( Sr/ Sr)T

εSr(T)

δ18OSMOW, ‰

0.732341 ± 5

0.704772

10.63

11.8

0.730760 ± 54

0.703509

–7.31

–

Sample No.

Rock

Rb, ppm

Sr, ppm

( Rb/ Sr)meas

( Sr/ Sr)meas

Ul-1

D

110

66.7

4.78

30002

D

99.8

61.2

4.725

87

86

30061

D

93.2

77.3

3.489

0.726274 ± 13

0.706154

30.27

–

Zhu-1

D

109.6

180.1

1.762

0.717314 ± 5

0.707152

44.44

12.1

R-1/13

R

107

61.4

5.053

0.737938 ± 65

0.708794

67.77

–

Zhu-4

LG

162.8

86.1

5.48

0.736170 ± 3

0.704564

7.68

12.8

503

AB(Nb)

247

293

2.443

0.721663 ± 7

0.707573

50.42

9.3

30052

AB(Nb)

112.6

61.8

5.279

0.734398 ± 24

0.703964

–0.84

–

30008-1

MAB

32.6

236.9

0.397

0.711937 ± 10

0.709645

79.86

–

Oyu-5

MAB

17.5

75.9

0.667

0.709990 ± 10

0.706143

30.11

11.1

R-1/10

MA

23.9

123.3

0.561

0.710870 ± 17

0.707633

51.28

–

Note. Samples: UL-1, 30002, and 30061 from the Aksai VTS; 503, Zhu-1, and Zhu-4 from the Kalguty VTS; 30008-1, R-1/10, and Oyu-5 from the Oyum paleovolcano; 30052 and R-1/13 are graben and dike. D, dacite, R, rhyolite, LG, leucogranite, AB(Nb), Nb-enriched andesibasalt, MAB, magnesian andesibasalt, and MA, magnesian andesite.

olivine phenocrysts, as required by the theoretical and experimental prerequisites (Hirose, 1997; Yogodzinski et al., 1995). According to numerous studies, there are no significant material differences between collisional and subduction MAs. Apparently, so far the only criterion is the isotopic composition of Nd, which in collisional MAs is usually characterized by εNd < 0. This suggests that the source of MAs of the Aksai complex (εNd ≈ 1.5–2) was of subduction origin. This is indirectly confirmed by the ratio of Sr and O isotopes in the rocks (Fig. 7), indicating the absence of a noticeable amount of material of the ancient (lower) crust in the source. Available data lead to the conclusion that the source of melts of the studied magnesian andesitoids was heterogeneous and included depleted mantle material and crustal material. Their interaction is manifested in the form of increased magnesian rocks, their enrichment in Cr, Ni, and V, and positive εNd values, which contrast with the Sr and O isotope compositions of volcanics, indicating possible contamination with pelagic sediments or Phanerozoic terrigenous deposits, e.g., flyschoids of the Gorny Altai Group. In the SiO2–mg# diagram (Fig. 4), the MA compositions form a broad cluster, generally corresponding to the trend of negative correlation between the silica and magnesium concentrations. This may indicate that the geochemical diversity of volcanics is mainly

due to variations in the degree of melting of the metasomatized mantle, as evidenced by the practically identical level of enrichment in radiogenic Nd and the pattern of change in the La/Yb ratio in rocks (Fig. 8). Furthermore, the comparatively low Yb contents (1.7–2.7 ppm) and the differentiated rareearth spectrum of some samples (La/Yb)N up to 12–15) probably reflect the presence of a small amount of garnet in the source. The origin of Nb-enriched basalts and andesites (NEBAs) does not have an unambiguous genetic interpretation. The frequent occurrence of these basic rocks in subduction zones with adakite-MA associations is regarded by many investigators as evidence of the genetic commonality of this triad,and the formation of NEBAs is associated with the melting of the lithospheric mantle previously metasomatized and enriched in niobium due to the involvement of melts, in particular, adakite ones, separated from the slab (Martin et al., 2005; Polat and Kerrich, 2001; Wang et al., 2007; and the references in these papers). At the same time, the increased contents of highly charged elements (Nb, Ta, Zr, Ti, P) in the rocks have led to the alternative hypothesis that Nb-enriched basalts and andesites are produced from an OIB type source (Castillo, 2008). A compromise point of view based on the results of study of NEBAs of Kamchatka was expressed by Perepelov (2014).

V.I. Krupchatnikov et al. / Russian Geology and Geophysics 59 (2018) 905–924

917

Fig. 7. Isotopic composition of neodymium, strontium, and oxygen in Aksai complex rocks. 1, Nb-enriched basaltic andesites; 2, dacites, 3, rhyolite; 4, leucogranite; 5, magnesian andesites and basaltic andesites. a, the Mantle array region and the locations of the PREMA, EM1, and EM2 reservoirs in accordance with their modern isotopic parameters according to (Zindler and Hart, 1986); the location of the DMM reservoir according to (Workman and Hart, 2005). MT is the overall composition of Cambrian–Ordovician metaturbidites ((Gorny Altai Group of the Kholzun–Chuya anticlinorium (Kruk, 2015) and the Habahe association similar of the Chinese Altai (Chen and Jahn, 2002; Long et al., 2010)). b, primitive mantle (M), island-arc mantle (AM), and mixing trends I–III (dotted line) according to (Davidson et al., 2005): I, basalt + juvenile crust and pelagic sediments, II, basalt + ancient crust, III, mantle + ancient subduction sediments (source contamination).

Taking into account, on the one hand, that the magnesian andesites + NEBAs + adakites associations are confined to local structures in extended active margins, and, on the other hand, that they formed in synchronism with typical island-arc series, he concluded that the formation of highly niobium basalts and andesites occurs in areas of slab discontinuity (the so-called slab portals) and is associated with the effect of an enriched asthenospheric source on the eclogitized slab and the lithospheric mantle transformed by subduction processes. Here it should be noted the NEBAs of Kamchatka are similar to rocks of the Aksai complex in rare-earth element characteristics and geochemical indicator ratios: despite the generally increased concentrations of highly charged elements, they exhibit selective depletion in Nb, Ta, and Ti (and enrichment in Pb) typical of suprasubduction magmas in multielement diagrams (Perepelov, 2014). The geological position, the association with MAs, and the elemental composition of Nb-enriched basaltic andesites of the Aksai complex are quite consistent with the subduction model of its origin. In contrast to OIB derivatives, the rocks have low indicator ratios of the HFS elements (Nb/U = 3–6, Ce/Pb = 5–8, La/Yb = 4–6), are characterized by distinct Ta–Nb–Ti minima, and are markedly enriched in radiostrontium (εSr ≈ 50). In the Th–Hf/3–Ta diagram (Fig. 6a), the rock compositions fall in the field of suprasubduction varieties and hence can be classified as melting products of the lithospheric mantle transformed by subduction processes. The increased concentrations of Rb, Cs, K, and P may indicate the participation of phlogopite and apatite in the melting process. On the other hand, the observed balance of these elements might have been affected by crustal contamination. Analysis of the Sr–O isotopic data suggests that the contaminant of Nb-enriched basaltic andesites, as in the case of magnesian andesites, is of

heterogeneous origin (Fig. 7b): along with pelagic sediments and juvenile crustal material, ancient crustal material was involved in the contamination process. The effect of the participation of crustal material is also reflected in the Sr–Nd isotopic system—the composition of Nb-enriched andesibasalt is shifted to the region characteristic of rocks of the upper continental crust (Fig. 7a). Thus, the isotopic and geochemical parameters of the magnesian andesites and Nb-enriched basaltic andesites of the Aksai complex do not exhibit significant deviations from those of subduction formations and can be considered as the products of differentiation of the parent magmas generated in the metasomatized lithospheric mantle.

Fig. 8. Variation of the La/Yb ratio in Aksai complex rocks. 1, magnesian andesites and basaltic andesites of the Oyum paleovolcano, 2, Nb-enriched basaltic andesites.

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V.I. Krupchatnikov et al. / Russian Geology and Geophysics 59 (2018) 905–924

Fig. 9. Harker diagrams for Aksai complex rocks. 1, Nb-enriched basaltic andesites, 2, 3, silicic rocks of the Aksai (2) and Kalguty (3) VTSs.

Rocks of silicic series (A-type granites). Numerous studies (Bonin, 2007; Creaser et al., 1991; Frost and Frost, 2011; King et al., 1997; Whalen et al., 1987; and others) have found that A-type granitoids are genetically diverse and can be produced by various processes: (1) differentiation of basic mantle magmas; (2) melting of crustal substrates; (3) a combination of the first two mechanisms, including contamination and mixing of magmas. The origin of silicic (SiO2 > 60 wt.%) rocks of the Aksai and Kalguty VTSs (hereinafter referred to as granitoids) by sequential fractionation of basic melts seems unlikely. The thick section of the Oyum paleovolcano rocks, differentiated from basalt to dacite, regardless of silica content, shows a high sodium concentration and no tendency toward the formation of high-potassium derivatives. In addition, compared to granitoids, MAs have a more radiogenic Nd isotopic composition and a similar Sr composition. The Sr–Nd isotopic parameters of Nb-enriched basaltic andesites are similar to those of

granitoids, but the behavior of petrogenic and rare-earth elements (Fig. 9) does not suggest a relationship between these rock associations as products of fractionation of a single melt: the distribution of silicic rocks is more random and does not fit into a distinct differentiated series. Furthermore, the silica gap—the Daly Gap—with a slight distribution of Nb-enriched basaltic andesites (less than 1% of the total area of granitoids) rather indicates the genetic isolation between basites and silicic rocks. A number of material features of the Aksai complex granitoids indicate the dominating role of crustal material. These, in particular, are the low calcium content, the high alumina content (the A/CNK ratio is generally more than 1.1), increased concentrations of K and Rb, and enrichment in a heavy oxygen isotope (δ18O = 11.8–12.8‰). According to experimental studies (Patino Douce, 1999), similar peraluminous A-granitoids can be formed by melting of metasedimentary protoliths. In the region of the Aksai complex, the

919

V.I. Krupchatnikov et al. / Russian Geology and Geophysics 59 (2018) 905–924 Table 3. Distribution coefficients of rare elements between minerals and melt for granitoids Element

Qz

Pl

Bt

Hyp

Ilm

Ap

Cs

0.29

0.105

3

–

–

–

Rb

0.041

0.048

3.2

0.014

–

–

Ba

0.022

0.36

9.7

0.044

–

–

Th

0.009

0.048

0.997

0.13

0.463

41

U

0.025

0.093

0.773

0.21

0.517

43.7

K

0.013

0.263

1.01

0.081

–

–

3.167

Ta

0.008

0.035

1.567

0.43

Nb

–

0.025

6.367

0.8

142

La

0.015

0.38

5.713

0.1

1.223

Ce

0.014

0.267

4.357

0.15

1.64

569

Pb

–

0.972

0.767

0.37

0.8

0.03

Sr

–

15.633

0.447

0.022

–

–

Nd

0.016

0.203

2.56

1.24

2.267

855

P

–

–

–

–

–

10000

Hf

0.03

0.148

0.703

0.52

1.883

0.73

Zr

–

0.135

1.197

4

–

0.9

Sm

0.014

0.165

2.117

0.27

2.833

1105

Ti

0.038

0.05

–

7

190

0.1

Y

–

0.1

1.233

2.46

0.31

162

Yb

0.017

0.077

1.473

0.86

0.077

2216

0.1 456

Note. The coefficients are given according to (GERM...; Sklyarov et al., 2001). Qz, quartz; Pl, plagioclase; Bt, biotite; Hyp, hypersthene; Ilm, ilmenite; Ap, apatite.

stratigraphic sequence is composed of a thick (at least 10 km, according to (Ponomarev et al., 2010)) layer of metaturbidites of the Cambrian–Ordovician Gorny Altai Group, small tectonized fragments of presumably Early–Middle Cambrian OIB oceanic basalts (Krupchatnikov et al., 2011) and thin layers of Silurian terrigenous-carbonate deposits. Assessment of these stratigraphic units as substrates for the production of Aksai granitoids shows that the most probable protolith is

Cambrian–Ordovician metaturbidites. Based on calculations of model melts (Tables 3 and 4, Fig. 10), rhyodacites, rhyolites, granites, and leucogranites of the Aksai and Kalguty VTSs could have been produced by melting of metapelites and/or metagraywacke of the Gorny Altai Group under conditions similar to the conditions of experimental dehydration melting of chemically similar natural samples (Koester et al., 2002): a pressure of 5 kbar, temperatures of 800–900 °C, and degrees

Fig. 10. Comparison of compositions of high-silica rocks of the Aksai complex and model melts from metaturbidites of the Gorny Altai Group.

Fig. 11. Zircon saturation temperatures in Aksai complex rocks. The temperatures were calculated by the formula (according to (Miller et al., 2003; Watson and Harrison, 1983)): T (°C) = 12900/[3.8 + 0.85(M – 1) + lnDzr] – 272. M = (Na + K + 2Ca)/(Al + Si) cation ratio. Dzr = 496000/Zrmelt. 1, Aksai VTS; 2, Kalguty VTS and grabens.

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V.I. Krupchatnikov et al. / Russian Geology and Geophysics 59 (2018) 905–924

Table 4. Composition of model melts from metaturbidites of the Gorny Altai Group Parameter

Melting conditions

P, kbar

5

5

T, C

800

900

F, %

32

57

Mineral

Mineral composition of restite paragenesis, %

Quartz

44

58

Plagioclase

34

26

Biotite

17

–

Hypersthene

4

14

Ilmenite

0.98

1.98

Apatite

0.02

0.02

Component

D

C0

CL

CL/PM

D

C0

Cs

0.673

4.7

6.04

188.8

0.706

4.7

5.38

168.2

Rb

0.579

81

113.5

178.7

0.582

81

98.74

155.5

Ba

1.783

397

259.08

37.1

1.762

397

299.07

42.8

Th

0.208

8.5

18.43

216.8

0.223

8.5

12.77

150.2

U

0.196

2.4

5.29

252

0.219

2.4

3.61

172.1

K

0.27

15,771.9

31,314.93

125.3

0.259

15,771.9

23,147.9

92.6

Ta

0.358

0.8

1.42

34.6

0.432

0.8

1.06

25.8

Nb

1.123

9.1

8.4

11.8

1.201

9.1

8.38

11.7

La

1.214

23.8

20.77

30.2

1.208

23.8

21.84

31.8

Ce

0.974

49

49.9

28.1

0.986

49

49.3

27.8

Pb

0.484

11.6

17.88

96.6

0.451

11.6

15.19

82.1 3.1

CL

CL/PM

Sr

5.392

154

38.63

1.8

4.144

154

65.48

Nd

0.754

25.3

30.38

22.4

0.887

25.3

26.59

19.6

P

2

437.0

260.12

2.7

2

437.0

305.6

3.2

Hf

0.222

4.1

8.7

28.2

0.286

4.1

5.92

19.1

Zr

0.41

150

250.62

22.4

0.799

150

164.2

14.7

Sm

0.682

5

6.38

14.4

0.726

5

5.67

12.8 1.2

Ti

2.176

4200.0

2333.98

1.8

4.815

4200.0

1590.6

Y

0.377

24.7

42.83

9.4

0.619

24.7

29.55

6.5

Yb

0.762

2.7

3.22

6.5

0.832

2.7

2.91

5.9

Note. Melting conditions and mineral composition of restite paragenesis according to (Koester et al., 2002). Model melt compositions (CL) were calculated by the formula CL = C0(1/(D + F(1 – D))), where C0 is the average composition of metaturbidites of the Gorny Altai Group, D is the total distribution coefficient, and F is the degree of melting (in fractions of unity). PM is the primitive mantle composition according to (Sun and McDonough, 1989).

of melting of 32–57%. The relatively high temperatures of the experiment are comparable to the zircon saturation temperatures for the Aksai complex rocks, 710–970 °C (average of 853 °C) (Fig 11). In the diagrams (Fig. 12), the compositions of the most silicic derivatives of the complex (rhyolites and leucogranites) are concentrated mainly in the fields of experimental melts of mafic (biotite) metapelites and metagraywacke, which agrees with the calculated melting temperatures higher than those for felsic (muscovite) metapelites (less than 800 °C (Patino Douce and Harris, 1998)). The compositions of dacites and granodiorites are interpreted differently. According to the results of the experiments, a similar silica content (less than 68–70 wt.% SiO2) in the melts cannot be provided by melting of only metasedimentary substrates and

most likely indicates the participation of a mafic component in the source or parent magmas (Patino Douce, 1999). The contribution of this component to the generation of granitoids of the Aksai complex is recorded in petrochemical diagrams, in which the compositions of dacites, granodiorites, and, partly, rhyodacites and granites are arranged along the mixing trends of metasedimentary and metabasite protoliths (Fig. 12a) or mafic and silicic melts (Fig. 12b). The origin of the mafic component is not uniquely determined. Potentially, it could be supplied by melts of Nb-enriched basites (magma mixing); however, the absence of petrographic evidence for hybridism, in particular, mafic inclusions in granitoids, does not provide grounds for assuming this mechanism. It is more likely that the melting involved a metabasite (amphibolite) protolith with

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Fig. 12. Position of the compositions of Aksai complex rocks in experimental melt diagrams. Aksai complex: 1, dacites and granodiorites, 2, rhyodacites, rhyolites, granites, and leucogranites. a, according to (Gerdes et al., 2002); b, according to (Patino Douce, 1999): LP and HP are the mixing lines of melts of tholeiitic basalts and metapelites, respectively, at a low (5 kbar or less) and high (12–15 kbar) pressure.

a short period of conservation in the crust; this can explain the atypical combination of the mantle-crustal Sr–Nd and crustal O isotopic parameters of dacites and granodiorites. This conclusion is indirectly supported by the distribution of lowto medium-potassium (K2O/Na2O = 0.4–1.0) metaperaluminous dacite varieties similar in composition to experimental amphibolite melts (Beard and Lofgren, 1991; Rapp and Watson, 1995). However, there is no plausible explanation for the deviation of the Sr–Nd isotopic parameters of rhyolites and leucogranites from the isotopic characteristics of the probable protolith (metaturbidites of the Gorny Altai Group) toward the mantle values (Fig. 7a). This may be due to the melting of horizons of a metaterrigenous substrate enriched in juvenile basic material. The latter could have been supplied by the Early–Middle Cambrian island-arc volcanics of the Sugash Complex occurring slightly west of the Kalguty VTS. The slightly differentiated rare-earth profile of granitoids (the (La/Yb)N ratio is mainly 3–8) and the relatively high content of heavy rare-earth elements (Yb is predominantly 3–7 ppm) suggests that the melts were generated above the zone of garnet stability in the middle or upper crust. A geochemical feature of the Aksai complex granitoids is the distinctly positive correlation between the Th/La and Sm/La ratios, which is rarely observed in igneous rocks (Fig. 13). In previous studies of the high-potassium magmatism of the Alpine–Himalayan belt (Tommasini et al., 2011; Wang et al., 2017), this correlation was associated with the melting of the hypothetical SALATHO reservoir, which has a specific epidote–lawsonite (or lawsonite) composition and formed as a result of the high-pressure metamorphism of the crustal substrate. In the case of silicic rocks of the Aksai complex, this behavior of Th and REE has a different explanation; in particular, it reflects variations in melting parameters. Thus, analysis of the compositions of model melts

from metaturbidites of the Gorny Altai Group (Kruk, 2015) shows that the Th/La and Sm/La ratios increase synchronously as the temperature and the degree of melting decrease. Geodynamic regime of formation of the Aksai complex The geodynamic interpretation of Early Devonian magmatism in Gorny Altai is debatable. According to the traditional point of view, the pre-Devonian stage (Ordovician–Silurian) of the development of the region was amagmatic and corresponded to a passive continental margin setting, and the intense magmatic activity, which began in the early Devonian (the Emsian), is associated with the development of an active continental margin of the Andian type as a result of subduction of the Ob’–Zaisan oceanic plate under the Siberian paleocontinent (Berzin et al., 1994; Buslov et al., 2013; Shokal’skii et al., 2000). In this regard, it is assumed that the formation of the Aksai complex occurred in the axial zone of the suprasubduction system (Fedak et al., 2011; Turkin and Fedak, 2008). It should be noted that in the area of Rudny Altai, which is the frontal zone of the Altai active paleomargin, adjacent to Gorny Altai, the earliest manifestations of Devonian magmatism are dated as Late Emsian (Gusev et al., 2015). This suggests that in the preceding period (Lochkovian–Early Emsian), magmatic activity in Gorny Altai was due to other factors. It is more probable that Early Devonian (pre-Late Emsian) magmatism in Gorny Altai is a consequence of the development of the Altai–Sayan rift system formed on the active margin of the Siberian paleocontinent under the impact of a mantle plume (Kruk, 2015; Vorontsov et al., 2010, 2013; Yarmolyuk and Kovalenko, 2003). This hypothesis is consistent with the views on the development of Early Devonian magmatism in the adjacent Chinese Altai region of similar geological structure. In this fragment of the continental

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Fig. 13. Positive correlation of the Th/La and Sm/La ratios in silicic rocks of the Aksai complex. 1, 2, Aksai complex: 1, dacites and granodiorites, 2, rhyodacites, rhyolites, granites, and leucogranites; 3, compositions of model melts (Kruk, 2015) at pressures of 5 kbar (a) and 10 kbar (b); the numbers at figurative points are temperatures (°C). The arrow shows the direction of temperature increase (T) and the degree of melting (F). SALATHO reservoir according to (Tommasini et al., 2011), N-MORB according to (Sun and McDonough, 1989). The island-arc basites are volcanic rocks of the Early–Middle Cambrian Sugash complex in the Kholzun–Chuya anticlinorium.

paleomargin, maximum magmatic activity is assumed to occur about 400 Ma and is associated with a high geothermal gradient and with asthenospheric diapirism (Cai et al., 2011). An indirect limitation for the plume hypothesis is that alkali derivatives and OIB basalts characteristic of plume magmatism are absent from the Early Devonian magmatic associations in southeastern Gorny Altai. This may be due to the fact that the center of the plume of the system is located to the east of the region in question (presumably, in the region of Tuva and Western Mongolia). In this case, the plume activity manifested itself almost exclusively in the thermal effect on the Altai segment of the lithosphere, resulting in melting of the mantle (volcanics of the Oyum paleovolcano and Nb-enriched basites) and crustal (silicic derivatives of the Aksai complex) substrates modified by Early Paleozoic subduction processes.

tized fragments of the lithospheric mantle. Silicic magmas were formed by melting of Cambrian–Ordovician metaturbidites of the Gorny Altai Group and, partly, Early Cambrian island-arc metabasites. 3. Taking into account the geological structure and development of Gorny Altai in general and its southeastern fragment, in particular, it is assumed that the complex developed under the impact of a thermal plume on the lithospheric substrates of the continental margin. We are grateful to the staff of the Collective-Use Center of Multielement and Isotope Analysis of SB RAS (Novosibirsk), the Analytical Center of the IMGRE, the Laboratory of Isotope Geochemistry and Geochronology of GIN RAS (Moscow), IPPG RAS, and the Central Laboratory and the Center of Isotope Research of VSEGEI (St. Petersburg) for participating in the research. The work was supported by the Ministry of Education and Science of the Russian Federation.

Conclusions The geological and geochemical studies of Early Devonian volcanics in southeastern Gorny Altai lead to the following conclusions. 1. The Aksai volcanic complex is a series of rocks of three petrogeochemical types: (1) magnesian andesitoids (Oyum paleovolcano); (2) Nb-enriched basaltic andesites; (3) peraluminous A-type granitoids (dacite–rhyolite–granite–leucogranite association) (Aksai and Kalguty VTSs). 2. The rocks of the Oyum paleovolcano and Nb-enriched basaltic andesites are derivative melts generated in metasoma-

References Amshinskii, N.N., 1973. Vertical Petrogeochemical Zonation of Granitoid Plutons (on the Example of Altai) [in Russian]. Zap.-Sib. Kn. Izd., Novosibirsk. Babin, G.A., Vladimirov, A.G., Kruk, N.N., Sergeev, S.A., Sennikov, N.V., Gibsher, A.S., Sovetov, Yu.K., 2004. Age of the initiation of the Minusa basins (Southern Siberia). Dokl. Earth Sci. 395 (3), 307–310. Beard, J.S., Lofgren, G.E., 1991. Dehydration melting and water-saturated melting of basaltic and andesitic greenstones and amphibolites at 1, 3, and 69 kbar. J. Petrol. 32, 365–401.

V.I. Krupchatnikov et al. / Russian Geology and Geophysics 59 (2018) 905–924 Berzin, N.A., Kungurtsev, L.V., 1996. Geodynamic interpretation of Altai– Sayan geological complexes. Geologiya i Geofizika (Russian Geology and Geophysics) 37 (1), 63–81 (56–74). Berzin, N.A., Coleman, R.G., Dobretsov, N.L., Zonenshain, L.P., Xia Xuchang, Chang, E.Z., 1994. Geodynamic map of the western part of the Paleoasian Ocean. Geologiya i Geofizika (Russian Geology and Geophysics) 35 (7–8), 8–28 (5–22). Buslov, M.M., Geng, H., Travin, A.V., Otgonbaatar, D., Kulikova, A.V., Chen Ming, Stijn, G., Semakov, N.N., Rubanova, E.S., Abildaeva, M.A., Voiteshek, E.E., Trofimova, D.A., 2013. Tectonics and geodynamics of Gorny Altai and adjacent structures of the Altai–Sayan folded area. Russian Geology and Geophysics (Geologiya i Geofizika) 54 (10), 1250–1271 (1600–1627). Bonin, B., 2007. A-type granites and related rocks; evolution of a concept, problems and prospects. Lithos 97, 1–29. Cai, K., Sun, M., Yuan, C., Long, X., Hiao W., 2011. Geological framework and Paleozoic tectonic history of the Chinese Altai, NW China: a review. Russian Geology and Geophysics (Geologiya i Geofizika) 52 (12), 1619–1633 (2056–2074). Castillo, P.R., 2006. An overview of adakite petrogenesis. Chinese Sci. Bull. 51, 257–268. Castillo, P.R., 2008. Origin of the adakite–high-Nb basalt association and its implications for postsubduction magmatism in Baja California, Mexico. Geol. Soc. Am. 120 (3–4), 451–462. Chen, B., Jahn, B.M., 2002. Geochemical and isotopic studies of the sedimentary and granitic rocks of the Altai orogen of northwest China and their tectonic implications. Geol. Mag. 139, 1–13. Creaser, R.A., Price, R.C., Wormald, R.J., 1991. A-type granites revisited: assessment of a residual-source model. Geology 19, 163–166. D’yachkov, B.A., Maiorova, N.P., Shcherba, G.N., Abdrakhmanov, K.A., 1994. Granitoid and Ore Formations of the Kalba–Narym Belt [in Russian]. Gylym, Almaty. Davidson, J.P., Hora, J.M., Garrison, J.M., Dungan, M.A., 2005. Crustal forensics in arc magmas. J. Volcanol. Geotherm. Res. 140, 157–170. Eby, G.N., 1992. Chemical subdivision of the A-type granitoids: petrogenetic and tectonic implications. Geology 20, 641–644. Faure, G., 1989. Principles of Isotope Geology [Russian translation]. Mir, Moscow; Wiley, New York, 1986. Fedak, S.I., Turkin, Yu.A., Gusev, A.I., Shokal’skii, S.P., Rusanov, G.G., Borisov, B.A., Belyaev, G.M., Leont’eva, E.M., 2011. State Geological Map of the Russian Federation, Scale 1:1,000,000 (third generation). Altai–Sayan series. Sheet M-45—Gorno-Altaisk. Explanatory Note [in Russian]. VSEGEI, St. Petersburg. Fedak, S.I., Turkin, Yu.A., Selin, P.F., Rusanov, G.G., Povazhuk, G.A., 2012. State Geological Map of the Russian Federation, Scale 1:200,000 (second generation). Altai Group. Sheet M-44-III (Novoegor’evskoe). Explanatory Note [in Russian]. VSEGEI, St. Petersburg. Fromberg, E.D., 1993. Ultrapotassium Rhyolites: Geology, Geochemistry, and Petrology: Extended Abstract of Doctoral (Geol.-Mineral.) Dissertation. Moscow State University, Moscow. Frost, B.R., Barnes, C.G., Collins, W.J., Arculus, R.J., Ellis, D.J., Frost, C.D., 2001. A geochemical classification for granitic rocks. J. Petrol. 42 (11), 2033–2048. Frost, C.D., Frost, B.R., 2011. On Ferroan (A-type) Granitoids: their compositional variability and modes of origin. J. Petrol. 52 (1), 39–53. Gerdes, A., Montero, P., Bea, F., Fershater, G., Borodina, N., Osipova, T., Shardakova, G., 2002. Peraluminous granites frequently with mantle-like isotopic compositions: the continental-type Murzinka and Dzhabyk batholiths of the eastern Urals. Int. J. Earth Sci. (Geol Rundsch) 91, 3–19. GERM Partition coefficient database. https://EarthRef.org. Gusev, N.I., Shokal’skii, S.P., Saltykova, T.E., Gusev, A.I., Ponomarev A.L., 2008. Composition, age and metallogeny of the Aksai volcanic complex (Gorny Altai). Regional’naya Geologiya i Metallogeniya, No. 35, 34–47. Gusev, N.I., Vovshin, Yu.E., Kruglova, A.A., Pushkin, M.G., Nikolaeva, L.S., Rusanov, G.G., Plekhanov, O.A., Bogomolov, V.P., Stroev, T.S., Moreva, N.V., Sergeeva, L.Yu., 2015. State Geological Map of the Russian Federation, Scale 1:1,000,000 (third generation). Altai–Sayan Series. Sheet M-44—Rubtsovsk. Explanatory Note [in Russian]. VSEGEI, St. Petersburg.

923

Hirose, K., 1997. Melting experiments on Iherzolite KLB-1 under hydous conditions and generation of high-magnesian andesitic melts. Geology 25, 42–44. Kelemen, P.B., Hanghoj, K., Greene, A.R., 2003. One View of the Geochemistry of Subduction-related Magmatic Arcs, with an Emphasis on Primitive Andesite and Lower Crust: Treatise on Geochemistry. Elsevier Ltd. 3, 593–659. King, P.L., Whit, A.J.R., Chappell, B.W., Allen, C.M., 1997. Characterization and origin of aluminous A-type granites from the Lachlan Fold Belt, southeastern Australia. J. Petrol. 38, 371–391. Koester, E., Pawley, A.R., Fernandes, L.A.D., Porcher, C.C., Soliani, E., 2002. Experimental melting of cordierite gneiss and the petrogenesis of syntranscurrent perfluminous granites in Southern Brasil. J. Petrol. 43 (8), 1595–1616. Kovalenko, V.I., Naumov, V.B., Girnis, A.V., Dorofeeva, V.A., Yarmolyuk, V.V., 2010. Average compositions of igneous melts from main geodynamic settings according to the investigation of melt inclusions in minerals and quenched glasses of rocks. Petrology 18 (1), 3–28. Kruk, N.N., 2015. Evolution of the Continental Crust and Granitoid Magmatism of Gorny Altai: Extended Abstract of Doctoral (Geol.-Mineral.) Dissertation. Institute of Geology and Mineralogy, SB RAS, Novosibirsk. Krupchatnikov, V.I., Vrublevskii, V.V., Gertner, I.F., Krivchikov, V.A., 2011. OIB-type basalts of the Irbistu River basin (Southeast Mountain Altai): Evidence for the HIMU component in the magmatic source. Dokl. Earth Sci. 439 (2), 1127–1130. Krupchatnikov, V.I., Vrublevskii, V.V., Kruk, N.N., 2015. Early Mesozoic lamproites and monzonitoids of southeastern Gorny Altai: geochemistry, Sr–Nd isotopic composition, and sources of melts. Russian Geology and Geophysics (Geologiya i Geofizika) 56 (6), 825–843 (1057–1079). Kurkura, K., Sawnda, Y., Roser, B., 2009. Compositional differences between felsic volcanic rocks from the margin and center of the northern Main Ethiopian Rift. Middle East Journal of Science (MEJS) 1 (1), 4–35. Kuzmin, M.I., Yarmolyuk, V.V., Kravchinsky, V.A., 2010. Phanerozoic hot spot traces and paleogeographic reconstructions of the Siberian continent based on interaction with the African large low shear velocity province. Earth Sci. Rev. 102, 29–59. Long, X.P., Yuan, C., Sun, M., Xiao, W.J., Zhao, G.C., Wan, Y.J., Cai, K.D., 2010. Detrital zircon ages and Hf isotopes of the early Paleozoic Flysch sequence in the Chinese Altai, NW China: new constraints on depositional age, provenance and tectonic evolution. Tectonophysics 480, 213–231. Maniar, P.D., Piccoli, P.M., 1989. Tectonic discrimination of granitoids. Geol. Soc. Am. Bull. 101, 635–643. Mariich, I.V., 1975. Apo-Effusive Micro-Pegmatite Granites of Gorny Altai [in Russian]. Zap.-Sib. Knizhn. Izd., Novosibirsk. Martin, H., Smithies, R.H., Rapp, R., Moyen, J.-F., Champion, D., 2005. An overview of adakite, tonalite–trondhjemite–granodiorite (TTG), and sanukitoid: relationships and some implications for crustal evolution. Lithos 79, 1–24. McCarron, J.J., Smellie, J.L., 1998. Tectonic implications of fore-arc magmatism and generation of high-magnesian andesites: Alexander Island, Antarctica. J. Geol. Soc. 155 (2), 269–280. Miller, C.F., McDowell, S.M., Mapes, R.W., 2003. Hot and cold granites? Implications of zircon saturation temperatures and preservation of inheritance. Geology 31 (6), 529–532. Navozov, O.V., Klepikov, N.A., Lakomova, A.V., Zhdanova, L.Ya., 2010. Problems of stratigraphy of ore-bearing Carboniferous strata in southwestern Great Altai, in: Great Altai—a Unique Rare-Metal–Gold–Polymetallic Province of the Central Asia. Proc. Int. Conf. East Kazakhstan State Tech. Univ., Oskemen, pp. 30–31. Patino Douce, A.E., 1999. What do experiments tell us about the relative contributions of crust and mantle to the origin of granitic magmas? Geol. Soc. London Spec. Publ. 168, 55–75. Patino Douce, A.E., Harris, N,. 1998. Experimental constraints on Himalayan anatexis. J. Petrol. 39, 689–710. Pearce, J.A., Harris, N.B.W., Tindle, A.G., 1984. Trace element discrimination diagrams for the tectonic interpretation of granitic rocks. J. Petrol. 25, 956–983.

924

V.I. Krupchatnikov et al. / Russian Geology and Geophysics 59 (2018) 905–924

Perepelov, A.B., 2014. Cenozoic Magmatism of Kamchatka during Changes of Geodynamic Settings: Extended Abstract of Doctoral (Geol.-Mineral.) Dissertation. Institute of Geography SB RAS, Irkutsk. Petrographic Code of Russia: Magmatic, Metamorphic, Metasomatic, and Impact Formations, third ed. [in Russian], 2009. VSEGEI, St. Petersburg. Pokrovskii, B.G., 2000. Crustal Contamination of Mantle Magmas from Data of Isotope Geochemistry (Trans. GIN RAN, Issue 535) [in Russian]. Nauka, Moscow. Polat, A., Kerrich, R., 2001. Magnesian andesites, Nb-enriched basalt-andesites, and adakites from late-Archean 2.7 Ga Wawa greenstone belts, Superior Province, Canada: implications for late Archean subduction zone petrogenetic processes. Contrib. Mineral. Petrol. 141 (1), 36–52. Ponomarev, A.L., Krupchatnikov, V.I., Krivchikov, V.A., Popova, O.M. (Eds.), 2010. State Geological Map of the Russian Federation, Scale 1:200,000 (second edition). The Altai Group. Sheet M-45-XXIII, XXIX (Kosh-Agach). Explanatory Note [in Russian]. VSEGEI, St. Petersburg. Rapp, R.P., Watson, E.B., 1995. Dehydration melting of metabasalt at 8–32 kbar: implications for continental growth and crust-mantle recycling. J. Petrol. 36 (4), 891–931. Rickwood, P.C., 1989. Boundary lines within petrologic diagrams which use oxides of major and minor elements. Lithos, 22, 247–263. Rodygin, A.I., 1959. On the age of the effusive-sedimentary Aksai Formation of the Sailyugem Ridge. Nauchnye Doklady Vysshei Shkoly. GeologoGeograficheskie Nauki, No. 2, 101–104. Rodygin, A.I., 1960. On the petrography and age of the Aksai granite intrusion in southeastern Gorny Altai. Trudy Tomsk Univ. 146, 160–169. Rotarash, I.L., Samygin, S.G., Gredyushko, E.A., 1982. Devonian active continental margin in southwestern Altai, Geotektonika, No. 1, 44–59. Rudnev, S.N., Kruk, N.N., Gusev, A.I., Shokal’skii, S.P., Kotov, A.B., Sal’nikova, E.B., Levchenkov, O.A., 2001. Origin of the Altai–Minusa volcanoplutonic belt (according to geochemical and U–Pb geochronological studies), in: Topical Issues of Geology and Mineralogy in Southern Siberia. Proc. Sci.-Pract. Conf. [in Russian]. Izd. IGiL SO RAN, Novosibirsk, pp. 231–242. Shokal’skii, S.P., Babin, G.A., Vladimirov, A.G., Borisov, S.M. Gusev, N.I., Tokarev, V.N., Zybin, V.A., Dubskii, V.S., Murzin, O.V., Krivchikov, V.A., Kruk, N.N., Rudnev, S.N., Fedoseev, G.S., Titov, A.V., Sergeev, V.P., Likhachev, N.N., Mamlin, A.N., Kotelnikov, E.I., Kuznetsov, S.A., Seifert, L.L., Yashin, V.D., Noskov, Yu.S., Uvarov, A.N., Fedak, S.I., Gusev, A.I., Vustavnoi S.A., 2000. Correlation of Magmatic and Metamorphic Complexes of the Western Part of the Altai–Sayan Folded Area [in Russian]. Izd. SO RAN, Filial Geo, Novosibirsk. Sklyarov, E.V., Gladkochub, D.P., Donskaya, T.V., Ivanov, A.V., Letnikova, E.F., Mironov, A.G., Barash, I.G., Bulanov, V.A., Sizykh, A.I., 2001. Interpretation of Geochemical Data [in Russian]. Intermet Inzhiniring, Moscow. Sun, S., McDonough, W.F., 1989. Chemical and isotopic systematics of oceanic basalts: implications for mantle composition and processes, in: Saunders, A.D., Norry, M.J. (Eds.), Magmatism in the Ocean Basins. Geol. Soc. Spec. Publ. 42, 313–345. Tommasini, S., Conticelli, S., Avanzinelli, R., 2011. The Th/La and Sm/La conundrum of the Tethyan realm lamproites. Earth Planet. Sci. Lett. 301, 469–478. Turkin, Yu.A., Fedak, S.I., 2008. Geology and Structural-Material Complexes of Gorny Altai [in Russian]. Izd. STT, Tomsk. Ujike, O., Goodwin, A.M., 2003. Origin of Archean adakites and NEBA from the Upper Keewatin assemblage, the Lake of the Woods greenstone belt,

Western Wabigoon Subprovince, Superior Province. Goldschmidt Conference Abstracts. Vorontsov, A.A., Yarmolyuk, V.V., Fedoseev, G.S., Nikiforov, A.V., Sandimirova, G.P., 2010. Isotopic and geochemical zoning of Devonian magmatism in the Altai–Sayan rift system: Composition and geodynamic nature of mantle sources. Petrology 18 (6), 596–609. Vorontsov, A.A., Fedoseev, G.S., Andryushchenko, S.V., 2013. Devonian volcanism in the Minusa basin in the Altai–Sayan area: geological, geochemical, and Sr–Nd isotopic characteristics of rocks. Russian Geology and Geophysics (Geologiya i Geofizika) 54 (9), 1001–1025 (1283–1313). Vrublevskii, V.V., Gertner, I.F., Gutierrez-Alonso, G., Hofmann, M., Grinev, O.M., Tishin, P.A., 2014. Isotope (U–Pb, Sm–Nd, Rb–Sr) geochronology of alkaline basic plutons of the Kuznetsk Alatau. Russian Geology and Geophysics (Geologiya i Geofizika) 55 (11), 1264–1277 (1598–1614). Vrublevskii, V.V., Grinev, O.M., Izokh, A.E., Travin, A.V., 2016. Geochemistry, isotope triad (Nd–Sr–O) and 40Ar–39Ar age of Paleozoic alkali mafic intrusions of the Kuznetsk Alatau (by the example of the Belaya Gora pluton). Russian Geology and Geophysics (Geologiya i Geofizika) 57 (3), 464–472 (592–602). Vrublevsky, V.V., Krupchatnikov, V.I., Gertner, I.F., 2007. Composition and isotopic evolution of potassic volcanic rocks from the southeastern Gorny Altai. Dokl. Earth Sci. 416, 1090–1095. Wang, Q., Wyman, D.A., Zhao, Z.-H., Xu, J.-F., Hua Bai, Z.-H., Xiong, X.-L., Dai, T.-M., Li, Ch.-F., Chu, Z.-Y., 2007. Petrogenesis of carboniferous adakites and Nb-enriched arc basalts in the Alataw area, northern Tianshan Range (Western China): Implications for Phanerozoic crustal growth in the Central Asia orogenic belt. Chem. Geol. 236, 42–64. Wang, Y., Preleviæ, D., Buhre, S., Foley, S.F., 2017. Constraints on the sources of post-collisional K-rich magmatism: the roles of continental clastic sediments and terrigenous blueschists. Chem. Geol. 455, 192–207. Watson, E.B., Harrison, T.Ì., 1983. Zircon saturation revisited: temperature and composition effects in a variety of crustal magma types. Earth Planet. Sci. Lett. 64, 295–304. Whalen, J.B., Currie, K.L., Chappell, B.W., 1987. A-type granites: geochemical characteristics, discrimination and petrogenesis. Contrib. Mineral. Petrol. 95, 407–419. Wood, D.A., 1980. The application of a Th–Hf–Ta diagram to problems of tectonomagmatic classification and to establishing the nature of crustal contamination of basaltic lavas of the British Tertiary volcanic province. Earth Planet. Sci. Lett. 50, 11–30. Workman, R.K., Hart, S.R., 2005. Major and trace element composition of the depleted MORB mantle (DMM). Earth Planet. Sci. Lett. 231 (1–2), 53–72. Yogodzinski, G.M., Kay, R.W., Volynets, O.N., Koloskov, A.V., Kay, S.M., 1995. Magnesian andesite in the western Aleutian Komandorsky region: implication for slab melting and processes in the mantle wedge. Geol. Soc. Am. Bull. 107, 505–519. Yarmolyuk, V.V., Kovalenko, V.I., 2003. Deep geodynamics, mantle plumes: Implications for the origin role of the Central Asian fold belt. Petrologiya 11 (6), 556–586. Yarmolyuk, V.V., Kovalenko, V.I., Kuz’min, M.I., 2000. North-Asian superplume in the Phanerozoic: magmatism and deep geodynamics. Geotektonika, No. 5, 3–29. Zindler, A., Hart, S.R., 1986. Chemical geodynamics. Ann. Rev. Earth Planet. Sci. 14, 493–571.

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