Neoproterozoic alkaline magmatism and associated igneous rocks in the western framing of the Siberian craton: petrography, geochemistry, and geochronology

Available online at www.sciencedirect.com

Russian Geology and Geophysics 53 (2012) 1176–1196 www.elsevier.com/locate/rgg

Neoproterozoic alkaline magmatism and associated igneous rocks in the western framing of the Siberian craton: petrography, geochemistry, and geochronology I.V. Romanova a, A.E. Vernikovskaya a,*, V.A. Vernikovsky a,b, N.Yu. Matushkin a,b, A.N. Larionov c a

A.A. Trofimuk Institute of Petroleum Geology and Geophysics, Siberian Branch of the Russian Academy of Sciences, pr. Akademika Koptyuga 3, Novosibirsk, 630090, Russia b Novosibirsk State University, ul. Pirogova 2, Novosibirsk, 630090, Russia c A.P. Karpinsky Russian Geological Research Institute, Srednii pr. 74, St. Petersburg, 199106, Russia Received 22 March 2012; accepted 21 June 2012

Abstract The formation and evolution conditions for alkaline magmatism and associated igneous rocks in the western framing of the Siberian craton are shown by the example of alkaline and subalkaline intrusive bodies of the Yenisei Ridge. Here we present petrographic, mineralogical, geochemical, and geochronological data for the rocks of the Srednetatarka and Yagodka plutons located within the Tatarka–Ishimba suture zone. Ferroan and metaluminous varieties enriched with rare elements (Nb, Ta, Zr, Hf, and REE) are making up most of the studied rocks. They formed at the stages of fractional crystallization of alkaline magma in a setting of active continental margin in the west of the Siberian craton in the Late Neoproterozoic (710–690 Ma). As differentiates of mantle magmas, these rocks associate with Nb-enriched rocks—A-type leucogranites and carbonatites. Sm/Nd and Rb/Sr isotopic data imply a predominance of the mantle component in the magmatic sources of the mafic and intermediate rocks as well as contamination processes of various volumes of continental crustal material by this magma. © 2012, V.S. Sobolev IGM, Siberian Branch of the RAS. Published by Elsevier B.V. All rights reserved. Keywords: alkaline magmatism; mineralogy; petrography; geochemistry; geochronology; Neoproterozoic; active continental margin; southwestern framing of the Siberian craton

Introduction Alkaline igneous rocks in the Neoproterozoic accretionarycollisional structure of the Yenisei Ridge (southwestern framing of the Siberian craton) form small plutons, located in the Tatarka–Ishimba N–NW trending suture zone, which demarks the accreted terranes from the passive continental margin (Vernikovsky et al., 2003, 2007) (Fig. 1). This suture zone is one of the major and long-lived structural elements of the region (Vernikovsky et al., 2011). It hosts collisional granites with U/Pb ages 760–750 Ma (Vernikovskaya et al., 2002; Vernikovsky et al., 2003) and younger Late Neoproterozoic alkaline rocks, which are the subject of our study. The Late Neoproterozoic complex of alkaline and associating rocks marks the end of the Precambrian magmatic evolution in the

* Corresponding author. E-mail address: [email protected] (A.E. Vernikovskaya)

region. It formed synchronously and in a subparallel line with island arc igneous rocks of the Yenisei ophiolites and island arcs belt, which accreted to the Siberian margin 700–630 Ma (Vernikovsky et al., 1999, 2001, 2008). The island arc formations and ophiolites in the west of the orogen mark the Yenisei suture zone that also is host to the latest subalkaline and alkaline anorogenic igneous formations—Devonian A-type granitoids as well as Triassic alkaline syenites, nepheline syenites and associating carbonatites (Vernikovskaya et al., 2010). The northern part of the Tatarka–Ishimba suture zone contains subalkaline and alkaline volcanic and subvolcanic rocks of the Zakhrebetnyi complex, forming the structure of the Verkhnevorogovka graben-syncline. They are represented by subalkaline basalts, trachyandesibasalts, trachyandesites, trachydolerites, teschenites, alkaline trachytes, alkaline syenites, nepheline syenites and other rocks (Diner, 2000). The 40 Ar/39Ar age of biotite from a trachydolerite of this complex is 696 Ma (Postnikov et al., 2005). This tectonothermal event

1068-7971/$ - see front matter D 201 2, V . S. S o bolev IGM, Siberian Branch of the RAS. Published by Elsevier B.V. All rights reserved. http://dx.doi.org/10.1016/j.rgg.2012.09.005 +

I.V. Romanova et al. / Russian Geology and Geophysics 53 (2012) 1176–1196

Fig. 1. Tectonic scheme of the Yenisei Ridge and the geological position of the Tatarka complex plutons, from (Vernikovsky et al., 2008) with additions. 1, Tatarka active continental margin complex (alkaline nepheline and quartz syenites, ijolites, trachybasalts, trachyandesibasalts, trachyandesites, trachydolerites, teschenites, alkaline trachytes, carbonatites, A-type granites), 711–630 Ma; 2, post-collisional Glushikha leucogranitic complex, 750–720 Ma; 3, syncollisional Ayakhta granitoid complex, 760–750 Ma; 4, terrane boundaries; 5, faults (a), thrusts (b); 6, Tatarka–Ishimba suture zone. Roman numerals in circles are terranes: I, Isakovka, ophiolite and island arc complex with plagiogranites (697 Ma); II, Central Angara, flyshoid and carbonate deposits, metamorphosed in greenschist-amphibolite facies conditions (MP–NP), Rybnaya–Panimba ophiolite belt (MP), Teya collisional granitoids (880–865 Ma); III, East Angara, terrigenous-carbonate deposits of the Siberian craton passive continental margin (MP-NP); IV, Predivinsk, ophiolite and island arc complexes with plagiogranites (628 Ma) and rhyolites (637 Ma); V, Angara–Kan, mostly granuliteamphibolite complexes (PP3). Numbers in rectangles are plutons: 1, Zakhrebetnyi; 2, Tatarka; 3, Srednetatarka; 4, Yagodka; 5, Chistopol’e. Letters in rectangles are faults: A, Angara; An, Ankinov, I, Ishimba; T, Tatarka; Y, Yenisei.

took place at the same time as the formation of the Kutukass complex A-type leucogranites in the marginal part of the Verkhnevorogovka graben-syncline, considering their zircon U/Pb age 690 Ma (Nozhkin et al., 2008). In the central part of the Tatarka–Ishimba suture zone the Tatarka syenites, granites, and A-type leucogranites with zircon age 629 Ma (Vernikovsky and Vernikovskaya, 2006) have been established, as well as intruding steeply dipping carbonatite bodies of the Penchenga complex (Zabrodin and Malyshev, 1975). The latter associate with Nb-enriched fenites. 40Ar/39Ar age

1177

estimates for the carbonatites have a wide range (Vrublevskii et al., 2011): 725 Ma for magnesioarfvedsonite and 637 Ma for phlogopite. In the same part of the tectonic zone the Srednetatarka nepheline syenites are located. K/Ar, Rb/Sr and Sm/Nd age estimates for various minerals (nepheline, lepidomelane, albite, aegirine, fluorite, biotite and muscovite) and whole rock samples from the alkaline rocks of this pluton are also not decisive and fall into a wide time range from 675 to 610 Ma (Sazonov et al., 2007; Sveshnikova et al., 1976). In the southern part of the Tatarka–Ishimba suture zone the Yagodka pluton alkaline syenites associating with granites (Krendelev, 1971; Kuznetsov, 1941, 1988) and Chistopol’e A-type leucogranites with U/Pb zircon age 683 Ma (Vernikovskaya et al., 2007) have been identified. Similar plutons have been described in suture zones of the southern framing of the Siberian craton at the margins of large orogenic belts—East Sayan, Cis-Baikal, Transbaikalian (Yarmolyuk and Kovalenko, 1991; Yarmolyuk et al., 2006). In this paper we show the conditions of formation and evolution of the alkaline and associating magmatism in the western framing of the Siberian craton on the example of alkaline and subalkaline intrusions of the Transangarian and South-Yenisei fragments of the Yenisei Ridge. Petrographic, mineralogical, geochemical and geochronological data are presented for the rocks of the Srednetatarka and Yagodka plutons, located in the Tatarka–Ishimba suture zone. These investigations are based on the study of a samples collection we accumulated in field trips from 2005 to 2008. The results we obtained are important in understanding the nature and age of alkaline rocks and magmatic bodies associating with them, as well as their place and role in the formation of active continental margin orogens.

Analytic methods The determinations of major elements contents in the rocks were done by X-ray fluorescence method with a 1–5% error in Vinogradov Institute of Geochemistry SB RAS (Irkutsk). Rare-earth and other trace elements determinations were obtained by ICP-MS with a 5–10% error. For the Yagodka pluton this was done using a quadrupole Agilent7500ce mass spectrometer and with a high resolution magnetic sector ELEMENT2 mass spectrometer in IG SB RAS (Irkutsk) by the procedure given in (Smirnova et al., 2010). For the Srednetatarka pluton element concentrations were determined applying an ELEMENT mass spectrometer in IGM SB RAS (Novosibirsk) by the procedure published in (Nikolaeva et al., 2008). Minerals analyses were performed on a Comebax-Micro X-ray microanalyzer in IGM SB RAS (Novosibirsk). Isotopic U–Pb analyses of sphene from the Srednetatarka foyaite (sample 05-01-9-6) were performed using a multicollector Finnigan MAT-261 mass spectrometer in IPGG RAS (St. Petersburg). The zircons dissolution and U and Pb extraction were performed by a modified procedure of Krogh (1973). The accuracy of U/Pb ratio determinations is 0.5%. The blank was below 0.1 ng for Pb and 0.005 ng for U. The

1178

I.V. Romanova et al. / Russian Geology and Geophysics 53 (2012) 1176–1196

aeroabrasion of zircons was done after Krogh (1982). The preliminary (HF + HNO3) acid etching of zircons was performed with varying exposition at 220 °C (Mattinson, 1994). The experimental data were processed with the PbDAT and ISOPLOT programs (Ludwig, 1991a,b; 1999). The decay constants of uranium of Steiger and Jäger (1976) were used in age calculations. Corrections for common lead were introduced according to model values (Stacey and Kramers, 1975). Additionally, U, Th and Pb isotope analyses of zircons from the same Srednetatarka foyaite sample 05-01-9-6, as well as the Yagodka quartz syenite sample V-07-6 and granite sample V-07-5-2 were performed using the SIMS SHRIMP-II at CIR VSEGEI (St. Petersburg) according to standard procedure (Larionov et al., 2004; Williams, 1998) using a secondary electron multiplier in peak-jumping mode through mass range from 196(Zr2O) to 254(UO) (4 mass specra). The primary O−2 ion current for the elliptic analytical point of ~25 × 20 µm was –4.0 / –5.0 nA. The mass resolution M/∆M ≥ 4300 (at 254 amu) excludes isobaric overlapping in the analyzed mass range. Only areas without visible fractures and inclusions in euhedral grains were selected for analysis. The zircons were cast in an epoxy matrix along with standard 91500 (Wiedenbeck, 1995) and Temora (Black et al., 2003) zircons, polished approximately to half thickness and vacuum-coated with a ~100 Å layer of 99.999% gold. The zircons internal structure was studied using optical microscope imaging and cathodoluminescence (CL). The analytical results were processed with the SQUID v1.12 and ISOPLOT/Ex. 3.22 programs (Ludwig, 2005a,b) using the decay constants recommended by Steiger and Jäger (1976). Corrections for common lead were made according to the Stacey and Kramers (1975) model using measured 204Pb/206Pb ratio. The isotopic Sm, Nd, Rb, and Sr analysis was performed using a 7-collector Triton T1 mass spectrometer in VSEGEI (St. Petersburg) according to techniques described in (Pervov et al., 2005; Skublov et al., 2010).

ing to geophysical data they are marked by a single gravitational anomaly elongated towards the northwest. These intrusions were emplaced in Neoproterozoic weakly metamorphosed deposits, folded in a N–S trending brachysynclinal structure and consisting mostly of limestones with interbeds of quartz–chlorite–sericite, sometimes carbon-bearing schists, and argillaceous schists northeasterly of the pluton. The foyaite contact zones have a steep dip (65°–90°) and are complicated by multiple offshoots (apophyses) 2–50 m thick and up to 100 m long that are confined to jointing areas. In these contact zone areas as well as in the more elongated ENE and WNW trending fracturing zones within the pluton multiple foyaite–pegmatite dikes and veins with rare element mineralization are located. Contact metamorphic formations (the aureole’s width is up to 200–500 m) are represented by marbleized limestones and closer to the contact also include argillaceous schists: quartz– mica, andalusite and pyroxene hornfels with rutile, tourmaline and garnet. In the ijolites, which form a NW trending elongated body in the apical part of the pluton, at the contact with foyaites multiple limestone and schists xenoliths have been identified reaching hundreds of meters in size. Xenolith schists retain schistosity elements, whose orientation corresponds to the bedding of host rocks. The ijolites close to the contacts and in jointing zones are intensively microclinised and albitized and at times display a taxitic structure, while the foyaites are enriched by mafic minerals. The presence of ijolite xenoliths in foyaites and, on the other hand, the presence of injections of the foyaites in ijolites shows that ijolites crystallized somewhat earlier than foyaites. The geologic position of the Srednetatarka pluton and its satellite as well as that of the Penchenga carbonatites (Zabrodin and Malyshev, 1975) located in the same tectonic zone 80 km to the northeast, clearly demonstrates that their emplacement took place after the accretion of terranes and establishment of the Tatarka–Ishimba suture zone. The orientation of structural elements and of the igneous bodies themselves shows their genetic connection with tectonic processes within this zone.

Geologic setting Srednetatarka pluton Geologists have studied the Srednetatarka nepheline syenite pluton (previously named the Transangarian pluton) since the 50s of the previous century, and its detailed geological study in the 1960–1970s was motivated by particular interest in the discovered rare element mineralization of alkaline rocks (Savanovich and Sergeeva, 1970; Sveshnikova, 1965; Sveshnikova et al., 1976; etc.). The Srednetatarka alkaline pluton (Fig. 2, a) located in the middle reach of Tatarka River is a small stock (the outcropping area is ~15 km2) of heterogeneous composition—its central part is composed of feldspar ijolites with tributary urtites, while the marginal zone consists of alkaline syenites and dominating nepheline syenites (foyaites). A similar but smaller satellite-stock has been identified to the southeast of the pluton. Both stocks are located in an intercrossing zone between sublatitudinal and northwest trending faults. Accord-

Yagodka pluton The geologic description of the Yagodka pluton alkaline rocks is based on the works of Yu.A. Kuznetsov (1941) and F.P. Krendelev (1971), and also on materials of various geological maps (Glazyrin and Vrublevich, 1967; Kachevsky et al., 1998; Savanovich and Sergeeva, 1970). The Yagodka pluton, located in the Yagodkina and Malaya Yagodkina river basin, consists of a group of elongated syenite stocks, including alkaline variations, intruding biotite and biotite– muscovite, often gneissic granites and leucogranites (Fig. 2, b). Yu.A. Kuznetsov (1941) who was the first to study the alkaline syenites of this pluton noted that these rocks are distinguished by exceptional freshness and lack of cataclasis. The alkaline rock intrusions have a sublongitudinal strike and are oval in shape (length 1–2.5 km, width ~0.5 km). In association with the syenites small trachybasalt occurrences in the form of rope lava flows have been identified. The granites

Fig. 2. Geological schemes of the Srednetatarka (a) and Yagodka (b) alkaline plutons, after (Glazyrin and Vrublevich, 1967; Kachevsky et al., 1998; Savanovich and Sergeeva, 1970; Sveshnikova et al., 1976). 1, sedimentary cover: clays, sands, sand loams, gravels (Pg3–N1); 2, Shirokinsk series, Sukhokhrebtinsk (Kirgiteisk) Formation: argillaceous schists, metasandstones, trachybasalts (NP1–2); 3–5, Tokminsk (Gorevka) Formation limestones (NP): 3, Lower Subformation, 4, Middle Subformation, 5, Upper Subformation; 6, Kuzeevsky complex of the Angara–Kan terrane: plagiogneisses, gneisses (PP3); 7–10, Tatarka magmatic complex: 7, granites, gneiss-granites, A-type leucogranites, 711–683 Ma; 8–9, Srednetatarka pluton alkaline and nepheline syenites (8) and ijolites (9), 711 Ma; 10, Yagodka pluton alkali feldspar syenites, alkaline quartz syenites, trachybasalts, 691 Ma; 11, contact metamorphism aureoles; 12, carbonate xenoliths (a) and terrigeneous-carbonate metaschists and limestones xenoliths (b); 13, unconformable boundaries; 14, verified fault (a), inferred fault (b), upthrow (c); 15, bedding; 16, sampling sites for U/Pb geochronological studies.

I.V. Romanova et al. / Russian Geology and Geophysics 53 (2012) 1176–1196 1179

1180

I.V. Romanova et al. / Russian Geology and Geophysics 53 (2012) 1176–1196

and syenites are located in a mostly metapelite—metasandstones formation, with the level of metamorphic alteration corresponding to the greenschist facies of regional metamorphism. The acid intrusive rocks belong to the calc-alkaline and alkali-calcic magmatic series. Among them are also slightly peraluminous, iron-enriched rocks, belonging to A-type leucogranites. Southwesterly of these magmatic bodies the Late Neoproterozoic Chistopol’e pluton is located. It is composed of A-type leucogranites and its host rocks are Paleoproterozoic gneisses and plagiogneisses of the Kuzeevsky complex. The granitoids form a wide contact aureole of hornfelsed rocks. The igneous bodies of the Yagodka and Chistopol’e plutons associate with large NNW striking faults, which are part of the southern fragment of the Tatarka–Ishimba tectonic zone, located in the NNW part of the South-Yenisei Ridge (Kachevsky et al., 1998, and other geological mapping data). The proximity, orientation of the acid intrusions and their association with the same structures suggest their close emplacement ages. Petrography and mineralogy Srednetatarka pluton Most of the studied alkaline rocks samples were taken from outcrops on the left bank of Tatarka River (right tributary of

Angara River) and eluvial blocks on the north and northwestern rims of the Srednetatarka pluton. Among them are nepheline syenites (foyaites), alkaline syenites, and feldspar ijolites. Chemical compositions of the minerals in the studied igneous rocks are given in Tables 1–4. Foyaites are represented by medium- and coarse-grained as well as pegmatoid rocks with poikilitic structure, consisting mostly of potassic feldspar (microcline) (40–65 vol.%), nepheline (30–40 vol.%) and aegirine (5–15 vol.%). These rocks also contain sphene, fluorite, individual grains of arfvedsonite, biotite, astrophyllite, as well as eudialite, pyrochlore, and analcime mostly occurring in pegmatites. Potassic feldspar and nepheline grains length varies from 0.5–2 to 15 cm in pegmatites and aegirine grains reach 0.1–0.3 to 8 cm in pegmatites, taking into account data from E.V. Sveshnikova et al. (1976). Arfvedsonite grains length varies from 0.1–4 to 2 cm in pegmatites, whereas for biotite it does not exceed first millimeters. Astrophyllite forms individual blades <0.5 mm long as well as stellate aggregates up to 3–10 cm in pegmatites. Fluorite, sphene and apatite grains are comparable in sizes, which reach deciles of mm, less often—first mm. Alkaline syenites are leucocratic medium-grained rocks, consisting of potassic feldspar (~70 vol.%), albite (~15 vol.%), and aegirine (up to 15 vol.%). Biotite, fluorite, and zircon occur in small amounts. Potassic feldspar-perthite forms

Table 1. Microprobe analyses for representative grains of the main aluminosilicate minerals from alkaline and subalkaline rocks of the Srednetatarka and Yagodka plutons Component

FI

FP

AS

AFS

QS2

TB

TB

TB

FI

F

FP

AS

AFS

QS1

FI

F

FP

Kfs

Kfs

Kfs

Kfs

Kfs

Pl

Pl

Pl

Ab

Ab

Ab

Ab

Ab

Ab

Nph

Nph

Nph

SiO2, wt.%

65.0

65.3

65.2

64.7

64.9

56.6

51.0

53.3

67.9

69.6

69.7

69.5

69.3

68.9

43.6

43.2

42.3

TiO2

0.10

0.13

0.00

0.00

0.01

0.04

0.02

0.03

0.00

0.07

0.10

0.02

0.00

0.00

0.00

0.07

0.28

Al2O3

18.1

18.3

17.4

18.3

18.4

27.8

30.7

29.1

19.2

19.1

19.0

18.4

19.6

19.4

34.4

33.7

34.5

Fe2O3

0.02

0.19

0.11

0.00

0.07

0.10

0.03

0.24

0.03

0.11

0.17

0.61

0.00

0.00

0.51

0.27

0.32

MnO

0.00

0.06

0.01

0.00

0.00

0.00

0.00

0.01

0.34

0.01

0.04

0.00

0.00

0.20

0.01

0.00

0.01

MgO

0.01

0.04

0.01

0.04

0.01

0.02

0.02

0.06

0.00

0.01

0.03

0.01

0.00

0.05

0.01

0.01

0.01

CaO

0.03

0.04

0.00

0.02

0.00

10.7

14.0

11.8

0.03

0.00

0.04

0.02

0.03

0.26

0.05

0.00

0.12

Na2O

0.29

0.56

1.08

0.46

1.00

5.30

3.28

4.40

11.9

11.9

10.7

11.6

11.8

11.7

16.0

16.5

16.3

K2O

16.0

14.2

15.6

16.2

15.4

0.07

0.04

0.14

0.09

0.02

0.09

0.15

0.13

0.06

5.98

6.15

6.65

Total

99.56

98.81

99.42

99.78

99.88

100.55 99.08

99.04

99.54

100.85 99.87

100.22 100.78 100.60 100.46 99.86

Si, f.u.

3.01

3.02

3.03

3.00

3.00

2.53

2.34

2.43

2.99

3.01

3.03

3.03

3.00

2.99

8.30

8.31

8.13

Ti

0.00

0.00

0.00

0.00

0.00

0.00

0.00

0.00

0.00

0.00

0.00

0.00

0.00

0.00

0.00

0.01

0.04

0.99

1.00

0.95

1.00

1.00

1.46

1.66

1.57

1.00

0.98

0.97

0.94

1.00

1.00

7.73

7.64

7.81

Al Fe

3+

100.40

0.00

0.01

0.00

0.00

0.00

0.00

0.00

0.01

0.00

0.00

0.01

0.02

0.00

0.00

0.07

0.04

0.05

Mn

0.00

0.00

0.00

0.00

0.00

0.00

0.00

0.00

0.01

0.00

0.00

0.00

0.00

0.01

0.00

0.00

0.00

Mg

0.00

0.00

0.00

0.00

0.00

0.00

0.00

0.00

0.00

0.00

0.00

0.00

0.00

0.00

0.00

0.00

0.00

Ca

0.00

0.00

0.00

0.00

0.00

0.51

0.68

0.58

0.00

0.00

0.00

0.00

0.00

0.01

0.01

0.00

0.02

Na

0.03

0.05

0.10

0.04

0.09

0.46

0.29

0.39

1.02

1.00

0.90

0.98

0.99

0.99

5.90

6.16

6.07

K

0.95

0.84

0.93

0.96

0.91

0.00

0.00

0.01

0.01

0.00

0.01

0.01

0.01

0.00

1.45

1.51

1.63

Total

4.98

4.92

5.01

5.00

5.00

4.97

4.98

4.98

5.02

4.99

4.92

4.98

5.00

5.00

23.48

23.68

23.75

Note. Srednetatarka pluton: FI, feldspar ijolite, 05-01-9-12; F, foyaite, 05-01-9-10; FP, foyaite-pegmatite, 05-01-9-16; AS, alkaline syenite, 05-01-9. Yagodka pluton: TB, trachybasalt, V-07-6-3; AFS, alkaline feldspar syenite, V-07-7-1; QS1 and QS2, quartz syenites, V-07-6-4 and V-07-6, respectively. Oxides are given in wt.%. Nephelines crystal-chemical formulas are calculated for 32 oxygen atoms, others—for 8 oxygen atoms. Tables 1–4 use mineral names abbreviations from (Whitney and Evans, 2010).

1181

I.V. Romanova et al. / Russian Geology and Geophysics 53 (2012) 1176–1196 Table 2. Microprobe analyses for representative clinopyroxene grains from alkaline and subalkaline rocks of the Srednetatarka and Yagodka plutons Com- FI ponent 1

F 2

3

FP

AS

TB

QS1

QS2

4 (r*) 4 (c) 5 (r) 5 (c) 6 (r) 6 (c) 7 (r) 7 (c) 8 (r) 9 (r) 9 (c) 9 (c) 10 (r) 10 (c) 11 (rl) 12 (r) 12 (c) 13 (r) 13 (c)

Aeg- Aeg- Aeg- Aeg Aug Aug Aug

Aeg Aeg Aeg Aeg Aeg- Aeg- Aeg- Aug Aug Di Aug Aug Aug

Di

Hed

Hed

Aug

Hed

Aug

Aug

Aug

SiO2, wt.%

50.6 51.3 50.8 52.2

52.0 51.7 52.1 52.3 52.0 51.3 51.4 51.0 50.6 51.1 51.8 49.3

49.1

48.3

48.1

48.7

48.0

47.7

TiO2

0.75 0.32 0.25 0.75

2.67 1.92 2.37 0.35 0.22 0.17 0.32 1.26 1.06 0.94 0.90 0.27

0.24

0.25

0.07

0.22

0.25

0.17

Al2O3 1.32 1.42 1.20 1.61

1.91 1.61 1.75 0.13 0.14 0.15 0.24 3.10 4.57 3.98 2.06 0.37

0.33

0.31

0.23

0.34

0.43

0.32

Fe2O3 8.63 8.24 9.19 30.0

24.6 25.9 24.1 28.7 23.2 19.7 15.7 0.86 1.88 0.65 1.62 0.09

1.12

0.39

1.83

1.30

3.24

0.76

FeO

12.5 11.8 12.8 0.41

3.32 2.13 3.50 2.56 6.64 7.88 11.3 6.98 4.36 5.53 4.28 27.0

25.3

26.8

25.6

27.9

26.2

33.4

MnO

1.12 1.05 1.21 0.49

0.57 0.83 0.85 0.53 0.79 1.45 1.36 0.24 0.16 0.15 0.17 1.08

1.32

1.08

1.14

0.91

0.99

1.33

MgO

4.08 5.04 3.34 0.16

0.04 0.17 0.17 0.58 0.99 1.60 1.69 14.1 14.7 15.1 15.3 1.26

1.30

1.95

1.49

1.75

1.88

1.65

CaO

15.5 16.6 14.9 0.63

1.07 1.84 1.72 2.15 4.43 8.21 9.95 21.1 20.5 21.3 22.5 20.4

20.8

19.2

20.2

18.8

19.5

14.1

Na2O 4.38 3.96 4.69 13.2

12.8 12.5 12.4 12.0 10.2 8.36 7.16 0.58 0.97 0.47 0.46 0.59

0.71

0.43

0.50

0.52

0.43

0.32

K2O

0.05 0.03 0.03 0.00

0.00 0.03 0.03 0.04 0.02 0.02 0.02 0.01 0.00 0.01 0.01 0.00

0.00

0.00

0.00

0.01

0.00

0.00

Total

98.83 99.69 98.39 99.39 98.93 98.66 99.00 99.36 98.65 98.86 99.09 99.15 98.86 99.14 99.12 100.34 100.21 98.68 99.13 100.32 100.91 99.71

Si, f.u. 1.99 1.99 2.01 2.00

2.00 2.00 2.01 2.02 2.04 2.02 2.03 1.91 1.88 1.89 1.92 2.00

1.99

1.99

1.98

1.99

1.95

1.99

AlIV

0.00 0.00 0.00 0.00 0.00 0.00 0.00 0.09 0.12 0.11 0.08 0.00

0.01

0.01

0.01

0.01

0.02

0.01

0.01 0.01 0.00 0.00

AlVI

0.05 0.05 0.06 0.07

0.09 0.07 0.08 0.01 0.01 0.01 0.01 0.04 0.08 0.07 0.01 0.02

0.01

0.01

0.00

0.00

0.00

0.00

Ti

0.02 0.01 0.01 0.02

0.08 0.06 0.07 0.01 0.01 0.01 0.01 0.04 0.03 0.03 0.03 0.01

0.01

0.01

0.00

0.01

0.01

0.01

3+

0.26 0.24 0.27 0.87

0.71 0.75 0.70 0.83 0.68 0.58 0.46 0.02 0.05 0.02 0.05 0.00

0.03

0.00

0.06

0.04

0.10

0.01

Fe2+

0.41 0.38 0.42 0.01

0.11 0.07 0.11 0.08 0.22 0.26 0.37 0.22 0.14 0.17 0.13 0.92

0.87

0.94

0.88

0.95

0.89

1.17

Mn

0.04 0.03 0.04 0.02

0.02 0.03 0.03 0.02 0.03 0.05 0.05 0.01 0.01 0.00 0.01 0.04

0.05

0.04

0.04

0.03

0.03

0.05

Mg

0.24 0.29 0.20 0.01

0.00 0.01 0.01 0.03 0.06 0.09 0.10 0.79 0.81 0.83 0.85 0.08

0.08

0.12

0.09

0.11

0.11

0.10

Fe

Ca

0.65 0.69 0.63 0.03

0.04 0.08 0.07 0.09 0.19 0.35 0.42 0.84 0.82 0.84 0.90 0.89

0.90

0.85

0.89

0.82

0.85

0.63

Na

0.33 0.30 0.36 0.98

0.95 0.93 0.93 0.90 0.78 0.64 0.55 0.04 0.07 0.03 0.03 0.05

0.06

0.03

0.04

0.04

0.03

0.03

K

0.00 0.00 0.00 0.00

0.00 0.00 0.00 0.00 0.00 0.00 0.00 0.00 0.00 0.00 0.00 0.00

0.00

0.00

0.00

0.00

0.00

0.00

Total

4.00 4.00 4.00 4.00

4.00 4.00 4.00 4.00 4.00 4.00 4.00 4.00 4.00 4.00 4.00 4.00

4.00

4.00

4.00

4.00

4.00

4.00

Di

23.43 28.99 19.31 0.88

0.23 0.94 0.88 3.21 5.34 9.03 9.32 74.59 79.46 79.89 83.17 7.07

7.50

10.62 8.68

9.42

10.58 7.60

Hed

43.84 41.37 45.41 2.85

11.62 9.23 13.05 9.68 22.57 29.59 39.29 21.43 13.74 16.88 13.58 88.65 87.13 86.36 87.52 86.92 86.30 90.48

Aeg

32.72 29.63 35.28 96.28 88.15 89.83 86.07 87.10 72.09 61.38 51.38 3.97 6.81 3.23 3.25 4.28

5.36

3.01

3.80

3.66

3.12

1.92

Note. Crystal-chemical clinopyroxenes formulas are calculated for 4 cation atoms and 6 oxygen atoms. Total measured Fe content in clinopyroxenes was recalculated for FeO and Fe2O3 based on stoichiometry. Clinopyroxenes end-members calculation: Di = Mg, Hed = Fe2+ + Mn, Aeg = Na. * r, Rim; c, center; rl, relict. For other notes, see Table 1.

porphyritic crystals ~5 mm long. Mafic minerals represented by aegirine and biotite (0.3–0.5 mm, less often up to 2 mm long) are common in interstitions between potassic feldspar and albite grains. Feldspar ijolites are dark gray medium/coarse-grained rocks with taxitic structure. Nepheline (45–50 vol.%), potassic feldspar (20–25 vol.%), aegirine-augite (25–30 vol.%) are dominant, accessory minerals include sphene, apatite, and fluorite. Potassic feldspar forms xenomorphic or subhedral (hypidiomorphic) elongated grains, in foyaites and ijolites this mineral diplays tartan twinning. Potassic feldspar often includes poikilitic inclusions of most magmatic minerals (Fig. 3, a, b). Albitization and pelitization are common secondary alterations of this mineral. Feldspars are close to pure

minerals. Both potassic feldspar and albite contain small amounts of Na and Fe (ref. Table 1). From foyaites to foyaite-pegmatite Na content decreases in albite while Fe content increases. Nepheline forms subhedral grains with fragments of hexand quadrangular sections. This mineral is replaced by liebnerite, in some cases by cancrinite. Nephelines display elevated SiO2 contents and low K2O contents (ref. Table 1). In crystal-chemical formulas of these minerals the potassium content is in the lowest limit, being <1 f.u. In foyaites and their pegmatites the increase of SiO2 and Al2O3 in nephelines is accompanied by a decrease of the Na2O + K2O sum (22.65–20.53 wt.%) and Na2O/K2O values (2.68–3.25). The small amount of Fe3+ and Mg impurities in nephelines increases in the latest igneous rocks—the foyaite-pegmatites.

1182

I.V. Romanova et al. / Russian Geology and Geophysics 53 (2012) 1176–1196

Table 3. Microprobe analyses for representative amphibole, biotite, ilmenite and hematite grains from alkaline and subalkaline rocks of the Srednetatarka and Yagodka plutons Com- TB ponent Mhb

QS1 Prg

Fprg Ed

1 (c*) 1 (r) 2

3

QS2

Act

Fed

Hst

Hst

4

5 (r) 5 (r) 6

FP

TB

AFS QS1 QS2 TB

QS1 QS2

Fed

Fed

Hst

Gru

Gru

Bt

Bt

Bt

Bt

Bt

Bt

Ilm

Ilm

Ilm

Hem

7

8

9

10

11

12

13

13

14

15

16

17

18

19

20

SiO2, wt.%

46.5

42.2 42.8 44.9 52.2 40.0 38.8 37.8 40.7 40.4 37.5 46.7 47.3 33.7 38.2 37.4 34.5 33.5 33.1 0.03 0.02 0.05 0.14

TiO2

0.83

0.91 0.61 0.44 0.14 0.53 0.12 0.33 1.00 0.79 0.04 0.04 0.10 2.36 1.19 0.92 3.01 2.88 2.71 52.5 49.8 48.1 0.40

Al2O3 7.95

12.8 13.3 11.2 3.64 7.45 9.35 9.91 6.97 6.32 9.32 0.23 0.31 14.3 14.4 14.5 11.1 11.9 11.1 0.00 0.00 0.00 0.00

Fe2O3 1.31

1.16 0.29 1.45 1.05 3.93 4.33 4.53 2.01 1.68 5.85

FeO

14.5

15.9 16.7 14.9 12.0 27.9 27.5 28.0 30.2 31.7 28.0 44.0 43.7 32.9 16.9 17.6 36.0 36.6 37.3 42.6 39.1 43.2 1.17

MnO

0.26

0.26 0.23 0.24 0.24 2.01 1.75 0.73 0.84 1.00 0.83 3.05 2.93 2.47 0.15 0.18 0.00 0.48 0.60 2.91 6.99 3.59 0.08

MgO

11.7

9.34 8.60 10.8 15.1 1.29 1.03 0.98 1.51 0.67 0.56 0.85 0.88 1.12 14.4 14.0 1.18 0.17 0.86 0.14 0.01 0.04 0.01

CaO

11.7

11.6 11.6 11.7 12.2 9.71 10.1 10.7 10.5 9.39 9.95 0.71 0.76 0.43 0.05 0.04 0.01 0.23 0.14 0.47 0.19 0.02 0.20

Na2O 1.48

1.96 1.97 1.82 0.77 1.65 1.53 1.13 1.77 1.87 1.77 0.21 0.29 0.22 0.11 0.11 0.05 0.40 0.07 0.17 0.04 0.03 0.07

K2O

1.05 0.98 0.89 0.32 1.62 2.25 2.68 1.43 1.57 2.35 0.01 0.05 7.50 9.58 9.59 8.78 9.08 8.23 0.01 0.00 0.00 0.02

0.56

1.05 0.09 0.42 97.4

SrO

0.00 0.00 0.00 0.00 0.00 0.00 0.00 0.00

0.00 0.00 0.00

0.03 0.06 0.05

ZrO2

0.05 0.05 0.06 0.08 0.00 0.00 0.00 0.00 0.01

0.02 0.01 0.00

0.06 0.03 0.00

Nb2O5

0.39 0.32 0.32 0.23 0.51 0.36 0.33 0.50 0.27

0.08 0.19 0.42

1.71 3.47 1.31

Ce2O3

0.01 0.01 0.00 0.00 0.00 0.00 0.00 0.00 0.01

0.00 0.07 0.00

0.03 0.04 0.00

Cl

0.15

0.28 0.41 0.24 0.06 0.46 0.64 1.53 0.65 0.46 0.38 0.03 0.01

0.22 0.24 1.40 1.36 0.20

O=Cl

0.03

0.05 0.08 0.04 0.01 0.08 0.12 0.28 0.12 0.08 0.07 0.00 0.00

0.04 0.04 0.26 0.25 0.04

Total

96.93 97.36 97.33 98.50 97.68 96.88 97.61 98.42 97.73 96.24 96.86 96.14 96.85 95.24 95.19 94.51 95.88 96.61 94.74 99.87 98.05 99.07 100.90

Si, f.u. 6.95

6.38 6.46 6.65 7.55 6.63 6.40 6.26 6.69 6.78 6.28 7.90 7.92 5.55 5.76 5.72 5.80 5.66 5.65 0.00 0.00 0.00 0.00

IV

1.05

1.62 1.54 1.35 0.45 1.37 1.60 1.74 1.31 1.22 1.72 0.05 0.06 2.45 2.24 2.28 2.20 2.34 2.23 0.00 0.00 0.00 0.00

VI

Al

0.35

0.66 0.83 0.59 0.18 0.08 0.22 0.19 0.04 0.04 0.12 0.00 0.00 0.33 0.33 0.33 0.01 0.02 0.00

Ti

0.09

0.10 0.07 0.05 0.02 0.07 0.01 0.04 0.12 0.10 0.01 0.01 0.01 0.29 0.14 0.11 0.38 0.37 0.35 0.99 0.97 0.93 0.01

3+

0.15

0.13 0.03 0.16 0.11 0.49 0.54 0.56 0.25 0.21 0.74

2+

Fe

1.81

2.01 2.11 1.84 1.45 3.86 3.80 3.88 4.16 4.46 3.92 6.24 6.12 4.53 2.14 2.25 5.06 5.17 5.33 0.90 0.85 0.93 0.03

Mn

0.03

0.03 0.03 0.03 0.03 0.28 0.24 0.10 0.12 0.14 0.12 0.44 0.42 0.34 0.02 0.02 0.00 0.07 0.09 0.06 0.15 0.08 0.00

Mg

2.61

2.11 1.94 2.37 3.25 0.32 0.25 0.24 0.37 0.17 0.14 0.22 0.22 0.28 3.25 3.19 0.30 0.04 0.22 0.01 0.00 0.00 0.00

Ca

1.88

1.88 1.88 1.86 1.89 1.72 1.78 1.90 1.84 1.69 1.78 0.13 0.14 0.08 0.01 0.01 0.00 0.04 0.03 0.01 0.01 0.00 0.01

Na

0.43

0.57 0.58 0.52 0.22 0.53 0.49 0.36 0.56 0.61 0.57 0.07 0.09 0.07 0.03 0.03 0.02 0.13 0.02 0.01 0.00 0.00 0.00

K

0.11

0.20 0.19 0.17 0.06 0.34 0.47 0.57 0.30 0.34 0.50 0.00 0.01 1.58 1.85 1.87 1.88 1.96 1.79 0.00 0.00 0.00 0.00

Al

Fe

0.02 0.00 0.01 1.93

Sr

0.00 0.00 0.00 0.00 0.00 0.00 0.00 0.00 0.00 0.00 0.00 0.00 0.00 0.00

0.00 0.00 0.00

Zr

0.00 0.00 0.01 0.01 0.00 0.00 0.00 0.00 0.00

0.00 0.00 0.00

0.00 0.00 0.00

Nb

0.03 0.02 0.02 0.02 0.04 0.03 0.03 0.04 0.02

0.01 0.01 0.03

0.02 0.04 0.02

0.00 0.00 0.00 0.00 0.00 0.00 0.00 0.00 0.00 0.00 0.00 0.00 0.00 0.00

0.00 0.00 0.00

Ce Total

15.45 15.70 15.65 15.60 15.20 15.73 15.85 15.88 15.79 15.80 15.92 15.07 15.03 15.52 15.76 15.82 15.65 15.81 15.74 2.00 2.00 2.00 2.00

Cl

0.04

mg** 0.59

0.07 0.10 0.06 0.01 0.10 0.15 0.35 0.15 0.11 0.09 0.01 0.00

0.05 0.05 0.33 0.32 0.05

0.51 0.48 0.56 0.69 0.08 0.06 0.06 0.08 0.04 0.03 0.03 0.03 0.06 0.60 0.59 0.06 0.01 0.04

Note. Crystal-chemical formulas of amphiboles (1–11) are calculated for 23 oxygen atoms, of biotites (12–16)—for 22 oxygen atoms, of ilmenites (17–19) and hematites (20)—for 2 cation atoms and 3 oxygen atoms. Hornblende (1–9) compositions are recalculated into formulas after the J.C. Schumacher method (Leake et al., 1997) where Fe3+ is considered the average between maximum and minimum acceptable values. For grunerites (10–11) the Fe3+ content is 0. Total measured Fe content in ilmenites and hematites was recalculated for FeO and Fe2O3 based on stoichiometry. * r, Rim; c, center. ** mg = Mg/(Mg + Fe2+). For other notes, see Table 1.

1183

I.V. Romanova et al. / Russian Geology and Geophysics 53 (2012) 1176–1196

Table 4. Microprobe analyses for representative astrophyllite and sphene grains from alkaline and subalkaline rocks of the Srednetatarka and Yagodka plutons Component

FP Ast

FI Ast

Ast

Spn

TB Spn

Spn

QS1 Spn

Spn

Spn

Spn

SiO2, wt.%

33.8

34.4

33.9

29.1

29.7

30.0

30.8

29.7

29.2

29.9

TiO2

11.0

10.5

10.5

32.6

33.7

35.6

36.3

33.7

28.6

31.9

Al2O3

1.43

1.83

1.38

Fe2O3

2.08

1.70

2.96

2.48

2.80

3.85

2.87

2.71

2.46

0.92

0.62

2.03

2.50

2.01

FeO

26.9

26.2

25.2

MnO

10.5

9.89

10.8

0.02

0.02

0.05

0.03

0.20

0.15

0.13

MgO

0.33

0.27

0.38

0.04

0.06

0.10

0.06

0.02

0.01

0.04

CaO

1.88

1.75

1.80

26.4

26.7

27.4

26.9

27.5

26.9

27.2

Na2O

1.93

1.91

2.01

0.12

0.13

0.05

0.03

0.07

0.06

0.08

K2O

6.03

6.03

5.64

0.06

0.05

0.20

0.00

0.02

0.00

0.01

SrO

0.11

0.01

0.00

0.00

ZrO2

0.78

1.23

0.06

0.04

0.06

Nb2O5

0.45

1.09

0.96

4.01

1.98

Ce2O3

0.40

0.00

0.05

0.00

97.02

95.33

96.11

F

2.06

1.21

0.94

1.28

0.72

O=F

0.61

0.36

0.28

0.38

0.21

92.99

93.88

95.17

98.28

97.71

Total

95.52

95.19

Note Ast, Astrophyllite. For other notes, see Table 1.

Alkaline pyroxene in foyaites and alkaline syenites forms subhedral elongated grains, in foyaite-pegmatites it is often in stellate aggregates, while in feldspar ijolites small poikilitic inclusions of this mineral occur in nepheline and potassic feldspar. Pyroxenes from foyaites correspond to aegirine in composition, those from feldspar ijolites correspond to aegirine-augite, and those from alkaline syenites—to both mineral variations (Fig. 4, a). On the Di–Hed–Aeg diagram (Fig. 4, b) one can clearly observe a Ca–Na pyroxene evolution trend line towards the increase of the aegirine component from feldspar ijolites and alkaline syenites to foyaites. In pyroxenes within zones of more elevated Ti contents lower Fe concentrations have been detected (ref. Table 2). For example, the zoning of aegirine crystals can be observed in grains with “hourglass” structure, where it is revealed as elevations of Ti content in the growth sectors of the pyroxene rhomboid prism planes as compared to pinacoid {100} growth sectors (ref. Fig. 3, b). Alkaline amphibole occurs in foyaites and foyaite-pegmatites as single tabular and xenomorphic grains as well as their aggregates in pegmatitic veins. This mineral occurs in metasomatitic albite–arfvedsonite formations after nepheline syenites, forming fine-grained aggregates and thin rims, replacing aegirine. E.V. Sveshnikova et al. (1966) classified it as a fluorine-containing magnesian variation, containing F, Mn, Li, Ti, Zn, Rb, Cs, and Zr impurities. An amphibole close in composition—fluormagnesioarfvedsonite has been identified in various areas of the Vishnevye Mountains alkaline massif in the Southern Urals in phlogopite-amphibole rocks (fenites) associating with carbonatites in the Vishnevye Moun-

tains as well as in metaultrabasite rocks of the Il’meny mountains miaskite massif (Bazhenov et al., 2000). Biotite of dark brown colour occurs in foyaites and their pegmatites. In foyaite-pegmatites this mineral has high Fe2+ contents, lower Al and low Mg contents, which is typical for biotites from nepheline syenites (Deer et al., 1966). Among impurities it has Ti, Mn, Na, Ca, and Nb (ref. Table 3). Biotite from foyaites is classified as a ferrous variation with 65–70% of the annite, 25–30% of the siderophyllite and ~5% of the phlogopite minals according to (Bailey, 1984; Rieder, 1998) (Fig. 5). The Srednetatarka pluton micas also contain Rb, Cs, and Li (Sveshnikova et al., 1976). Astrophyllite occurs in small quantities in foyaites and foyaite-pegmatites. Its crystallization time is close to that of aegirine and biotite (ref. Fig. 3, a, c). In astrophyllite from foyaite-pegmatite low Ti concentrations have been detected, as well as Mn, Mg, Ca, and Al impurities, and in smaller amounts—Ce, Sr, Zr, and Nb (ref. Table 3). Sphene is widespread in feldspar ijolites as well as in foyaites. It forms individual grains with a wedge shaped cross section, in some cases aggregates of those (ref. Fig. 3, d). This mineral often occurs as poikilitic inclusions in nepheline, potassic feldspar, aegirine (ref. Fig. 3, a, b). In feldspar ijolites a Fe3+ and Al3+ variation of this mineral has been identified (ref. Table 4). It contains small amounts of F, Mg, Mn, Na, and K. In sphene from foyaites we found areas with reduced Si and Ti concentrations, which correlate with elevated Ca, Nb and Zr contents (ref. Fig. 3, d). The latest, Ce, La and F enriched phase that replaces sphene is probably fluocerite (ref. Fig. 3, e).

1184

I.V. Romanova et al. / Russian Geology and Geophysics 53 (2012) 1176–1196

Fig. 3. Relationships between minerals in foyaite-pegmatites, sample 05-01-9-16 (a–c) and sample 05-01-9-10 (e, f) and in the foyaite, sample 05-01-9-14 (d); Srednetatarka pluton, backscattered electron photomicrographs. a, Microcline crystallization began after the formation of sphene, aegirine and astrophyllite, the crystallization time of the last two minerals was partly coeval; albite replaces microcline; b, sphene is the earliest mineral, enclosed in aegirine grains; c, an epitaxic intergrowth of biotite with astrophyllite, the biotite pinacoid plane {001} grows over the astrophyllite pinacoid plane {100}; the crytallization time of astrophyllite and aegirine was partly coeval; d, a sphene grains aggregate; the largest sphene grain includes bright white subparallel elongated intergrowths of the mineral phase with elevated Ca, Nb, Zr contents and depleted Si and Ti contents comparatively to those of sphene; e, sphene grain in analcime; the latest white mineral phase (fl) (fluocerite? (Ce,La)F3) partially replaces and forms a rim around sphene; f, eudialite contains several zones with a considerably lower light REE content and elevated Zr content, which are close in composition to parakeldyshite (Na2ZrSi2O7). On the photo these zones are darker than eudialite, similarly to the zone with the black circle. The eudialite grain also contains several inclusions of aegirine and mineral phases with elevated Nb (Nb2O5 up to 60%) and U content (light gray zones on the photomicrograph), as well as REE fluoride phases (fluocerite?), these are the bright white zones. 1, microcline; 2, nepheline; 3, aegirine; 4, albite; 5, sphene; 6, astrophyllite; 7, biotite; 8, analcime; 9, eudialite.

I.V. Romanova et al. / Russian Geology and Geophysics 53 (2012) 1176–1196

1185

Fig. 4. Coposition of pyroxenes from the Srednetatarka (1–4) and Yagodka (5–7) rocks after the classification by (Morimoto, 1988) on Q–J diagrams (a), compared with pyroxene compositional trends for alkaline rocks of other complexes (A–J) (b) and for Ca–Mg–Fe-pyroxenes (c). Panel (a) shows the division of pyroxenes into chemical groups: Q = Ca + Mg + Fe2+, J = 2Na. Di, diopside; Aeg, aegirine; Hed, hedenbergite; En, enstatite; Wo, wollastonite; Fs, ferrosilite. 1, feldspar ijolite, sample 05-01-9-12; 2, nepheline syenite-pegmatite, sample 05-01-9-16; 3, nepheline syenite, sample 05-01-9-10; 4, alkaline syenite, sample 05-01-9; 5, trachybasalt, sample V-07-6-3; 6, quartz syenite, sample V-07-6; 7, quartz syenite, V-07-6-4. Alkaline plutons and complexes: A, Ilimaussaq, South Greenland (Larsen, 1976); B, Föhn, Norway (Mitchell, 1980); C, South Qôroq, South Greenland (Stephenson, 1972); D, Coldwell, Canada (Mitchell and Platt, 1983); E, Alnö, Sweden (Hode Vuorinen et al., 2005); F, Grønnedal-Ika, South Greenland (Halama et al., 2005); G, Morotu, Sakhalin (Yagi, 1953); H, Eastern Uganda (Tyler and King, 1967); I, Iron Hill, Colorado (Nash, 1972); J, Nandewar, Australia (Abbott, 1969).

Eudialite occurs in foyaite-pegmatites; its grains are pink or pink-brown in colour, often isometric, up to 1 × 1 cm in size. It forms aggregates with aegirine and analcime, and also contains inclusions of idiomorphic pyroxene grains. Eudialite includes Zr, Nb, REE, Ce, and U-enriched mineral phases (ref. Fig. 3, f). Analcime occurs in foyaite-pegmatite as individual 5 mm long grains and as filling of fractures in eudialite, sometimes in aegirine, associating with Nb-, REE-, and F-containing

minerals—pyrochlore, fersmite, fluocerite, and sphene (ref. Fig. 3, e). Fluorite is a widespread accessory mineral in the rocks of the Srednetatarka pluton. Most often it has pink-magenta or purple colour. It forms individual euhedral grains of square cross section up to several mm across and their aggregates. Fluorite is located in interstices between other mineral grains, in some cases associating with aegirine and sphene, as well as in the form of poikilitic inclusions in aegirine. Impurities

1186

I.V. Romanova et al. / Russian Geology and Geophysics 53 (2012) 1176–1196

Fig. 5. Composition of biotites from the Srednetatarka and Yagodka plutons on a AlIV vs. Fe/(Fe + Mg) diagram after (Bailey, 1984). Filled blue circle, alkali feldspar syenite, sample V-07-7-1. Other symbols are the same as in Fig. 4. Iron is calculated from FeOtot.

of Sr, Ce, and REE were found in this mineral (Sveshnikova et al., 1976). Alkaline rocks of the Srednetatarka pluton also include lavenite, euxenite, monazite, ramsayite, ilmenite and other REE-enriched minerals according to E.V. Sveshnikova et al., (1976). Yagodka pluton According to (Krendelev, 1971; Kuznetsov, 1988) the alkaline rocks of the Yagodka pluton are coarse-grained alkaline syenites with taxitic structure. They are mostly composed of alkali feldspar (90–95%) and small amounts of aegirine-augite, hornblende, riebeckite, biotite, sphene, zircon, and ilmenite. Yu.A. Kuznetsov (1988) noted that in these rocks potassic feldspar has an antiperthitic structure, develops a tartan twin pattern, and often forms Carlsbad twins, whereas aegirine-augite is overgrown by riebeckite. These alkaline syenites are intruded by veins of lamprophyres and syeniteaplites. In this work we studied subalkaline rocks of the intrusivevolcanic association of the Yagodka pluton that we sampled in the bed and on the banks of the middle reach of Yagodkina River (right tributary of Yenisei River), among which we identified quartz and alkali feldspar syenites and trachybasalts. We were unable to determine any interactions with alkaline rocks in field trip conditions, which evidently requires additional mapping of this geologic feature. Alkali feldspar syenites and quartz syenites are gray, medium- and coarse-grained rocks with taxitic structure. The taxitic aggregates, among large alkali feldspar grains (up to 2 × 3.5 mm) contain aggregates of mafic minerals, associating with accessory and ore minerals. In alkali feldspar syenites the potassic feldspar content is ~85 vol.%, biotite content is ~10 vol.%, quartz, apatite, zircon, and ore minerals occur in small amounts. Potassic feldspar in places displays a thin tartan twin pattern, forms Carlsbad twins, shows an antiperthitic and perthitic structure, and acquires an albite rim. In quartz syenites the potassic feldspar contents are reduced to 55–70 vol.%, quartz—5–15 vol.% and acid plagioclase (al-

bite-oligoclase) occurs (10–15 vol.%). Subordinate minerals include mafic minerals, such as augite, hornblende, grunerite, biotite (together up to 10 vol.%), accessory minerals—zircon, sphene, apatite, fluorite, and ore minerals—ilmenite, hematite. Secondary alterations include carbonatization. Trachybasalts are black coloured rocks with porphyritic texture. Phenocrysts are represented by plagioclase (labradorite) grains (4–5 mm) and augite grains (1 mm), occupying 40–60 vol.% and <10 vol.%, respectively. The ground mass occupies 40–60 vol.% of the rock and consists of plagioclase, hornblende, biotite, sphene, zircon, also ore minerals, including ilmenite. Plagioclase has undergone saussuritization. Alkali feldspars and acid plagioclases in alkali feldspar and quartz syenites contain Fe3+, Ca, Mg, and Mn impurities. The former also contain Na, and the latter—K (ref. Table 1). The plagioclases from trachybasalts show zoning, and their compositions correspond to labradorite with Ca content varying from 0.51 to 0.68 f.u. and Al from 1.46 to 1.66 f.u. Pyroxenes in quartz syenites and trachybasalts form subhedral grains up to 1 mm long, often with only relict minerals preserved. They are replaced by amphibole as well as chlorite and iron hydroxides. In quartz syenites the pyroxenes correspond by composition to augite and hedenbergite, those in trachybasalts—to augite and diopside, according to the classification in (Morimoto et al., 1988) (ref. Table 2, Fig. 4, a). In pyroxenes from quartz syenites the hedenbergite minal content is 83–90%, that of the diopside minal—7–13% and that of the aegirine minal—2– 8%. At the same time in trachybasalts the diopside component is dominant, its content increases to 71–83% (ref. Table 2, Fig. 4, c), while the aegirine component has the same content. In pyroxenes from quartz syenites and trachybasalts the Na concentrations are lower and Ca concentrations are higher in comparison to pyroxenes from the Srednetatarka alkaline rocks. Maximum Al concentrations have been determined in these minerals from trachybasalts, maximum Ti concentrations—from foyaites. The diagram on Fig. 4, b shows a composition trend line for Yagodka pluton pyroxenes from magnesian variations in trachybasalts enriched with the diopside component to ferrous variations in quartz syenites enriched with the hedenbergite component. Hornblende is widespread as a primary magmatic mineral in the form of individual (up to several mm long) subhedral grains and multiple poikilitic inclusions (up to 0.1 mm long) in potassic feldspar. It is also a secondary mineral. In hornblende the Ca content reaches 1.66–1.91 f.u. and Ti content does not exceed 0.20 f.u. According to the 1997 nomenclature (Leake et al., 1997) the following calcic amphiboles have been identified in the Yagodka pluton rocks: hastingsite and ferro-edenite in quartz syenites; magnesiohornblende and edenite, rarely pargasite, ferropargasite and actinolite in trachybasalts. Hastingsite is replaced by biotite with excess of quartz. According to the 2004 nomenclature (Leake et al., 2004) in some Yagodka pluton quartz syenites there is some monoclinal Mg–Fe–Mn amphibole—grunerite (Fig. 6, a, b). Therefore quartz syenites

I.V. Romanova et al. / Russian Geology and Geophysics 53 (2012) 1176–1196

1187

Fig. 6. Compositions of amphiboles from the Yagodka subalkaline rocks on classification diagrams for Ca-amphiboles (a) and Mg-Fe-Mn-Li-amphiboles (b) after (Leake et al., 1997, 2004). Symbols are the same as in Fig. 4.

contain highly ferrous amphibole variations (mg < 0.09), commonly enriched in Mn, Na, and Cl. Trachybasalts are characterizd by magnesian amphiboles (mg up to 0.7) (ref. Table 3). In amphiboles from quartz syenites Nb and Zr impurities have been determined. Biotite forms aggregates, located in interstices between grains. It replaces hornblende or forms aggregates with amphibole, ilmenite and sphene. Compared to the micas from Srednetatarka foyaite-pegmatites the biotites from Yagodka alkali feldspar and quartz syenites have higher K, Fe2+ and Ti contents and lower Al, Mg, Mn, and Ca contents (ref. Table 3). In alkali feldspar and quartz syenites the biotites contain 70–85% of the annite, 15–25% of the siderophyllite and ~5% of the phlogopite minals according to (Bailey, 1984; Rieder, 1998) (Fig. 5). Biotites from trachybasalts, as opposed to those from syenites, have elevated Mg and Al concentrations, reduced Fe2+, Ti, Cl, and Mn concentrations and contain F (up to 0.68 f.u.). Annite, siderophyllite, and phlogopite minals contents equal to 40–50%, 15–30%, and 30–35% respectively. Impurities in biotites of the studied plutons include Na and Nb. Sphene forms rims around ilmenite grains located in aggregates and inclusions in amphibole and biotite from quartz syenites and trachybasalts. It also displays reduced Ti content as compared to stoichiometry (ref. Table 4), which is explained by the replacement of Ti by Nb, Al, Fe, Zr, and Ce. Apatite forms small grains 1.5 µm in size with rectangular or hexagonal cross sections. It is often found in inclusions in

biotite or hornblende. It is characterized by pleochroic haloes, indicating the presence of radioactive elements in this mineral. Fluorite forms isometric or irregular lilac coloured grains. It has been identified in inclusions in hornblende as well as in the form of aggregates (up to several mm in diameter), along with quartz in potassic feldspar. Ilmenite from quartz syenites contains Nb, Ce, Zr, and Sr impurities. Niobium has been also identified in hematite in these Yagodka pluton rocks (ref. Table 4).

Major and trace elements The chemical compositions of the basic and intermediate rocks of the Srednetatarka and Yagodka plutons are given in Tables 5 and 6 respectively. Their alkali-enriched trend is indicated by their location in the alkali magmatic series field on the Na2O + K2O – CaO (MALI) vs. SiO2 diagram after (Frost and Frost, 2008) (Fig. 7, a). The maximum alkali content (K2O + Na2O = 12.37–14.03 wt.%) has been determined in the Srednetatarka rocks, with variations in SiO2 contents from 51.21 to 64.53 wt.% and the dominance of Na2O over K2O (Na2O/K2O = 1.2–2.4), as opposed by the more SiO2-enriched (61.85–66.82 wt.%) Yagodka rocks (K2O + Na2O = 11.27–12.02 wt.%) with a wide scatter of Na2O/K2O ratio values (0.7–2.3). For the Yagodka pluton rocks higher K2O and Fe2O3 contents are typical, which is comparable, respectively, to alkaline syenites and feldspar ijolites of the

1188

I.V. Romanova et al. / Russian Geology and Geophysics 53 (2012) 1176–1196

Table 5. Chemical composition of the Srednetatarka pluton alkaline rocks Component

Feldspar ijolite

Foyaite

Alkaline syenite

Component

05-01-9-12 05-01-9-14 05-01-9-13 05-01-9-6 05-01-9-7 05-01-9 SiO2, wt.% 51.21

Feldspar ijolite

Foyaite

Alkaline syenite

05-01-9-12 05-01-9-14 05-01-9-13 05-01-9-6 05-01-9-7 05-01-9

56.28

57.27

57.87

59.35

64.53

Nb

210

150

100

70

140

70

TiO2

0.94

0.29

0.08

0.03

0.05

0.23

Cs

3.4

3.1

2.8

2.9

2.3

1.43

Al2O3

21.63

22.71

23.14

23.72

22.17

17.84

Ba

700

850

30

15

9

170

Fe2O3 tot.

5.85

3.57

2.7

2.17

2.86

3.59

La

64

67

106

53

81

38

MnO

0.19

0.17

0.16

0.15

0.16

0.15

Ce

93

102

165

81

126

31

MgO

0.4

< 0.05

< 0.05

< 0.05

< 0.05

< 0.05

Pr

9.4

9.3

15.7

7.5

12.2

7.6

CaO

4.74

1.81

1.21

0.78

0.74

0.31

Nd

29

27

45

22

35

25

Na2O

9.12

8.36

8.68

9.87

9.29

6.65

Sm

4.7

3.5

6.1

3.3

5.4

4.9

K2O

4.46

5.54

5.13

4.16

4.43

5.72

Eu

1.22

0.67

1.00

0.33

0.49

0.94

P2O5

0.22

0.08

0.07

0.07

0.05

0.08

Gd

4.7

2.9

5.4

2.9

4.8

3.8

LOI

1.28

1.18

1.61

1.24

0.95

0.92

Tb

0.84

0.46

0.90

0.49

0.84

0.64

Total

100.04

100.02

100.05

100.06

100.05

100.02

Dy

5.6

3.1

5.9

3.1

5.6

3.9

Be, ppm

8.0

6.0

4.8

4.0

4.0

9.0

Ho

1.3

0.66

1.3

0.69

1.3

0.78

Sc

2.0

0.94

0.92

0.85

0.95

2.49

Er

4.4

2.2

4.1

2.4

4.0

2.4

Ti

5 100

1 650

460

148

260

1 225

Tm

0.84

0.40

0.69

0.47

0.68

0.47

V

100

7.50

2.00

1.4

0.65

9.0

Yb

5.4

2.9

4.3

3.5

4.7

3.4

Cr

7.5

10

5.0

8.0

9.0

13

Lu

0.76

0.48

0.63

0.60

0.71

0.54

Co

4

1

<1

<1

<1

5

Hf

21

13

12

11

19

11

Ni

<0.05

<0.05

<0.05

<0.05

<0.05

<0.05

Ta

5.9

5.5

3.4

4.8

10

5.1

Cu

8

8

5

6

4

5

Pb

13

15

8

5

16

11

Zn

160

110

100

50

70

60

Th

31

25

28

14

23

21

Ga

39

28

34

31

32

28

U

8.0

4.7

7.1

2.6

7.5

7.1

Rb

200

230

250

250

280

310

(La/Yb)CN 8.1

15.5

16.6

10.5

11.9

7.8

Sr

1100

730

70

30

13

50

Eu/Eu*

0.64

0.53

0.33

0.30

0.67

Y

45

22

42

22

38

24

(La/Sm)CN 8.50

11.95

10.85

10.03

9.37

4.84

Zr

1000

620

590

470

790

430

(Gd/Yb)CN 0.70

0.81

1.02

0.67

0.83

0.90

0.79

Note. Element content ratios are normalized for chondrite (McDonough and Sun, 1995): (La/Yb)CN, (La/Sm)CN, (Gd/Yb)CN and Eu/Eu* = EuCN/[GdCN × SmCN]0.5.

Srednetatarka pluton. Besides Na2O the Srednetatarka rocks have the highest Al2O3 and P2O5 contents. Nepheline-containing rocks form an increasing trend of the MALI index with the increase of rocks acidity, which is typical for igneous rocks formed as a result of fractional crystallization. The rather steep angle of the trend indicates low Si activity (i.e., SiO2-undersaturation of the rocks whose norm contains nepheline and olivine). Alkaline syenites as well as alkali feldspar and quartz syenites of the Yagodka pluton are SiO2-enriched rocks, their norm contains quartz. Most of the studied rocks are ferroan (except magnesian trachybasalts), metaluminous, in rare cases they are borderline peraluminous (Fig. 7, b, c) according to (Frost and Frost, 2008). In nepheline-containing rocks the agpaitic index (Ka = (Na2O + K2O)/Al2O3, mol.qu.) varies from 0.86 to 0.96, which corresponds to the miaskite trend. Unlike other studied rocks the trachybasalts have the lowest SiO2 (46.28–48.10 wt.%) and alkali (Na2O + K2O ≤ 4.38 wt.%) concentrations, with Na2O prevailing over K2O

(Na2O/K2O = 1.8–2.3), and the highest—CaO (11–12 wt.%) and MgO (5.23–8.27 wt.%) concentrations. For all Yagodka (except trachybasalts) and Srednetatarka rocks a high ΣREE is typical, varying respectively in intervals 155–587 and 123–362 ppm. Their maximum values have been established in alkaline quartz syenites, in which also deep negative Eu anomalies (Eu/Eu* = 0.22–0.43) have been found, which are close to the most differentiated foyaite variations with (Eu/Eu* = 0.30–0.64) (ref. Table 5, 6, Fig. 8, a, c). The rocks are enriched in light REE, with the steeper distribution spectra being those of the Srednetatarka rocks ((La/Sm)CN = 4.8–12), and the more smooth—in the intermediate Yagodka rocks ((La/Sm)CN= 3.3–6.9). All rocks have flat heavy REE distributions ((Gd/Yb)CN = 0.7–1.3) (Fig. 8, a, c). Spider diagrams show that the studied rocks are characterized by depletion of Ba, Sr, P, and Ti and are enriched in Rb, Th, U, Nb, Ta, Hf, Zr, Tb, and Y (Fig. 8, b, d). The less fractionated specters, determined for basic rocks—feldspar ijolites and trachybasalts, are possibly a reflection of the early differen-

1189

I.V. Romanova et al. / Russian Geology and Geophysics 53 (2012) 1176–1196 Table 6. Chemical composition of the Yagodka pluton subalkaline rocks Component

Trachybasalt V-07-6-1

V-07-6-3

Alkali feldspar syenite

Alkaline quartz syenites

V-07-7-1

V-07-6-2

V-07-7-2

V-07-6-4

V-07-6 66.82

SiO2, wt.%

46.28

48.10

61.85

63.60

64.09

66.42

TiO2

1.86

1.69

0.38

0.45

0.44

0.16

0.42

Al2O3

19.70

14.12

17.28

17.35

16.11

17.25

14.72

Fe2O3 total

9.75

11.45

5.27

4.30

6.29

3.84

5.47

MnO

0.15

0.23

0.12

0.10

0.18

0.11

0.15

MgO

5.23

8.27

0.16

0.36

0.15

<0.05

0.22

CaO

12.02

10.97

1.42

1.92

1.94

1.18

1.74

Na2O

2.94

2.80

4.88

6.09

5.23

5.62

4.75

K2O

1.26

1.58

7.14

5.18

5.43

5.42

5.48

P2O5

0.39

0.33

0.05

0.05

0.06

0.03

0.07

LOI

0.49

0.53

1.47

0.51

0.16

0.00

0.28

Total

100.08

100.06

100.00

99.91

100.08

100.02

100.12

Be, ppm

1.2

4.0

8.7

6.5

7.1

9.3

6.3

Co

36.8

46.2

1.8

3.5

2.9

4.6

2.0

Cu

45

38

<5

46

<5

<5

7

Zn

130

180

90

80

110

90

80

Ga

17.7

17.0

26.2

29.9

25.1

27.9

23.5

Ge

1.1

1.6

1.9

1.7

1.7

1.7

1.4

Rb

90

210

320

180

220

240

250

Sr

630

424

44

136

42

40

34

Y

22.1

32.8

31.0

82.4

50.0

31.5

56.8

Zr

165

213

189

1392

295

216

144

Nb

48.4

44.3

124.5

218.8

182.1

118.2

155.6

Sn

6

11

10

9

4

9

5

Ba

444

343

122

389

96

122

145

La

38.7

40.0

57.8

137.2

68.0

28.7

81.0

Ce

73.5

74.0

99.5

258.1

119.5

64.9

143.6

Pr

7.78

8.02

9.27

26.13

13.07

6.95

14.28 47.4

Nd

28.3

27.9

29.2

86.5

42.6

24.4

Sm

5.52

6.24

5.27

16.21

8.97

5.43

9.12

Eu

1.90

1.92

0.73

1.13

1.00

0.72

1.24

Gd

5.17

6.02

5.17

15.57

8.40

4.78

9.17

Tb

0.83

1.05

0.89

2.57

1.58

1.09

1.50

Dy

4.21

6.28

5.49

16.85

10.45

6.76

9.13

Ho

0.96

1.29

1.12

3.67

2.16

1.41

2.12

Er

2.78

3.55

3.48

9.99

6.39

4.19

6.08 0.99

Tm

0.35

0.50

0.56

1.55

0.99

0.70

Yb

1.87

2.98

3.72

9.76

6.08

4.31

6.16

Lu

0.32

0.45

0.64

1.44

1.11

0.79

0.95

Hf

4.3

6.0

5.5

34.4

9.1

8.1

5.5

Ta

3.1

3.8

13.5

12.0

12.3

11.2

12.1

W

<2

4

3

6

16

36

2

Pb

<3

13

11

11

11

10

10

Th

4.0

7.7

16.4

33.2

29.0

30.9

36.2

U

1.1

1.7

1.5

7.2

4.7

3.0

6.7

(La/Yb)CN

14.0

9.0

10.5

9.5

7.5

4.5

8.9

Eu/Eu*

1.09

0.96

0.43

0.22

0.35

0.43

0.41

(La/Sm)CN

4.38

4.00

6.85

5.29

4.73

3.30

5.55

(Gd/Yb)CN

2.24

1.63

1.12

1.29

1.12

0.90

1.20

For note, see Table 5.

1190

I.V. Romanova et al. / Russian Geology and Geophysics 53 (2012) 1176–1196

Fig. 7. Na2O + K2O – CaO (MALI alkaline-calcic index) vs. SiO2 (a), Fe* vs. SiO2 (b), Al vs. Fe* (c) diagrams after (Frost and Frost, 2008) for the alkaline and subalkaline rocks of the Srednetatarka and Yagodka plutons, respectively. (a) shows fields for the calcic, calc-alkaline, alkaline-calcic and alkaline magmatic series; (b), above the Fe*-line is the field of ferroan rocks, below it—the field of mangesian rocks; Fe* = FeO + 0.9Fe2O3/(FeO + 0.9Fe2O3 + MgO). Oxides contents are taken from Tables 5 and 6. Symbols are the same as in Fig. 4.

tiation stages. This is also indicated by the presence of a positive Sr anomaly in feldspar ijolites. For example, such distributions have been determined for Paleogenic aegirinecontaining nepheline syenites of the Yongsheng pluton, located in the northeastern framing of the North-China craton (Fuyuan et al., 2001). The authors consider the lithospheric mantle as a source for these rocks.

Isotope geochemistry and geochronology Sphene from the Srednetatarka foyaite (sample 05-01-9-6) is represented by homogeneous honey yellow fragments larger than 200 µm in size and characterized by insignificant inverse discordance. The average 206Pb/238U age obtained for three sphene fractions (Table 7), including the residue after aeroabrasion treatment, is 700 ± 2 Ma; MSWD = 0.45 (Fig. 9, a). The zircons from the Srednetatarka foyaite are pink-brown translucent and turbid euhedral crystals of hyacinth (dipyramidalprismatic) habit with elongation ranging from 1.8 to 3.0. The size of zircon crystals varies from 80 to 300 µm. Most crystals are zoned in transmitted light, whereas the growth zoning is vague in cathodoluminescence (CL) images

(Fig. 9, b). In the CL light, zircons are dark and homogeneous in cores and finely zoned at the rims. Zircons are characterized by a low intensity of cathodoluminescence owing to the elevated U and Th contents (Fig. 9, b; Table 8), Th/U = 0.11–1.05. The morphology of zircons indicates their magmatic origin. We performed 12 U/Pb local (SIMS) measurements in 10 zircon grains of the foyaite sample 05-01-9-6. The discordia for 10 points has intercepts at 705 ± 18 and 254 ± 210 Ma (MSWD = 1.09). The concordant age of 711 ± 3 Ma (MSWD = 0.66, probability 0.42) calculated for 6 points is the most accurate estimation of the zircon age. The older 207 Pb/206Pb age of 1221–1281 Ma was obtained for subhedral rounded zircon grain No. 1 (Fig. 9, b, Table 8), which most likely is a xenocryst. The zircons from the Yagodka quartz syenite (sample V-07-6) are mostly euhedral, of zircon habit, translucent, moderately elongated (elongation ranges from 1 to 3, Fig. 9, c). Their simple concentrical growth zoning is sometimes complicated by structurally unconformable domains with curvilinear outline and low cathodoluminescence. Isotopic analysis (4.1 and 4.2, Table 8) demonstrated that these domains are not inherited cores, but rather a product of the

I.V. Romanova et al. / Russian Geology and Geophysics 53 (2012) 1176–1196

1191

Fig. 8. REE distributions and spider diagrams for the alkaline and subalkaline rocks of the Srednetatarka (a, b) and Yagodka (c, d) plutons. Element contents are normalized for chondrite and primitive mantle after (McDonough and Sun, 1995). Symbols are the same as in Fig. 4.

initial zircons crystallization, subjected to partial reabsorption (judging by the curvilinear outline). Results of SIMS analyses (Table 8, Fig. 9, c) form a cluster on the concordia diagram, in which 2 subgroups can be determined. The concordant age for all 11 results equals 681 ± 7 Ma (MSWD = 0.006). However, considering the elevated U and Th concentrations, and therefore the high probability of radiogenic lead losses, we consider the concordant age for the five most “ancient” results (691 ± 10 Ma, MSWD = 0.0007) as the most authentic. Zircons in the Yagodka granite (sample V-07-5-2) are mostly translucent, euhedral, of hyacinth habit, with elongation varying from 2 to 5. Their internal structure is characterized by simple concentric growth zoning. In some zircons there are structurally unconformable domains in the central areas, which could be inherited cores. This is confirmed by the presence of xenomorphic (rounded) grains, indicating a xenogenic (inherited) component. For U/Pb analysis we selected areas free of probable cores. The analysis results indicate somewhat more elevated Th/U ratios in the central parts (for example 8.1 and 9.1 in Table 8) as compared to the periphery (6.1 in Table 8). Analysis results for 10 zircons (Table 8, Fig. 9, d) form a concordant cluster on the graph. Excluding one slightly too young result and the three most ancient results, the age from 6 analysis equals 711 ± 10 Ma (MSWD = 0.33). The performed Sm, Nd, Rb and Sr isotopic analysis showed that the alkaline and subalkaline Srednetatarka and Yagodka

rocks formed mostly from a mantle source (Tables 9, 10). For the rocks of these plutons εNd(T) values vary in the interval 0.7–6.4, while the initial 87Sr/86Sr ratio does not exceed 0.70330. The obtained Meso-Neoproterozoic estimates of the Sm/Nd model age (TNd(DM) = 1499–856 Ma) probably indicate a different input from the ancient continental crustal material in the magmatic source of the studied rocks.

Discussion and conclusions Our study, based on a combination of detailed petrographic, mineralogical, geochemical and geochronological investigations of the alkaline and subalkaline mostly intrusive rocks of the Srednetatarka and Yagodka plutons, located in the Tatarka–Ishimba suture zone of the Yenisei Ridge, allowed us to determine their age, magmatic sources and geodynamic conditions of their formation. In the Srednetatarka pluton nepheline-containing alkaline rocks are dominant (foyaites, feldspar ijolites). They contain Na, Fe, and Mg-enriched alkaline mafic minerals—aegirine, aegirine-augite and F-enriched magnesioarfvedsonite. They are classified as SiO2-undersaturated miaskitic rocks. At the same time, in the pegmatitic variations of foyaites our studies showed that the products of the more geochemically evolved magma contain minerals typical for agpaitic rocks (Igneous

1192

I.V. Romanova et al. / Russian Geology and Geophysics 53 (2012) 1176–1196

Table 7. U/Pb isotopic results for sphene from the Srednetatarka nepheline syenite (sample 05-01-9-6) No.

Charge, Content, ppm mg Pb U

Isotope ratios 206

204

Pb/

Rho

Pb

207

Pb/

206

a

208

Pb

206

Pb/

a

Pb

207

235

Pb/

U

206

238

Pb/

Age, Ma Pb/235U

U

207

206

Pb/238U

207

Pb/206Pb

1

6.28

7.34

44.5

139

0.0625 ± 1

0.0356 ± 1

0.9902 ± 20

0.1149 ± 2

0.62

699 ± 2

701 ± 1

691 ± 4

2

1.75

28.7

171

133

0.0625 ± 1

0.0330 ± 1

0.9864 ± 21

0.1145 ± 2

0.65

697 ± 2

699 ± 1

690 ± 4

3*

0.65

19.7

123

148

0.0623 ± 1

0.0336 ± 1

0.9860 ± 23

0.1147 ± 2

0.59

697 ± 2

700 ± 1

686 ± 4

Note. a Isotope ratios corrected for procedure blank and common lead. * Sphene subjected to aeroabrasion treatment (Krogh, 1982). Uncertainty values correspond to the last significant digit. Rho, correlation factor of U/Pb ratios. Uncertainties are given at the 2σ level.

Table 8. U/Th/Pb isotopic investigations results for zircons from the Srednetatarka nepheline syenite (sample 05-01-9-6), Yagodka quartz syenite (sample V-07-6) and granite (sample V-07-5-2) Analytical Content, ppm point No. U Th

Isotope ratios 206

Pb*

232

Th/

238

U

Rho % 206

Pbc

(1) 207 Pb*/235U (± %)

(1) 206 Pb*/238U (± %)

Age, Ma

D, %

206

(1) Pb/238U

207

(1) Pb/206Pb

Sample 05-01-9-6 1.1 1.2 2.1 2.2 3.1 4.1 5.1 6.1 7.1 8.1 9.1 10.1

1285 1338 3394 9900 815 4978 5078 5478 484 933 911 5935

494 405 2200 1038 251 897 2698 1243 490 230 497 3858

255.5 241.7 355.7 918.7 85.7 441.9 508.7 505.8 48.5 95.7 90.8 594.6

0.40 0.31 0.67 0.11 0.32 0.19 0.55 0.23 1.05 0.26 0.56 0.67

5.01 0.88 4.03 0.09 4.41 0.06 0.00 0.18 0.31 3.03 0.02 0.16

2.6621 ± 3.0 2.5992 ± 1.0 1.0428 ± 2.0 0.9271 ± 1.0 1.0489 ± 4.1 0.8818 ± 0.7 1.0080 ± 0.6 0.9307 ± 0.7 1.0033 ± 2.2 1.0100 ± 3.8 1.0181 ± 0.9 1.0054 ± 0.7

0.2198 ± 0.5 0.2085 ± 0.5 0.1171 ± 0.5 0.1079 ± 0.4 0.1170 ± 0.6 0.1033 ± 0.4 0.1166 ± 0.4 0.1073 ± 0.4 0.1164 ± 0.7 0.1158 ± 0.6 0.1160 ± 0.6 0.1164 ± 0.4

0.18 0.44 0.23 0.40 0.15 0.62 0.62 0.53 0.31 0.15 0.62 0.55

1281 ± 6 1221 ± 5 714 ± 3 661 ± 3 714 ± 4 634 ± 3 711 ± 2 657 ± 2 710 ± 5 706 ± 4 707 ± 4 710 ± 3

1379 ± 57 1434 ± 18 761 ± 42 685 ± 20 774 ± 86 671 ± 12 698 ± 10 705 ± 13 691 ± 44 717 ± 80 730 ± 15 696 ± 12

8 17 7 4 8 6 –2 7 –3 2 3 –2

466 282 638 764 3837 511 678 370 829 1010 410

111.0 67.6 165.0 210.0 379.0 119.0 140.0 92.6 134.0 64.4 119.0

0.43 0.41 0.38 0.36 1.04 0.42 0.47 0.39 0.60 1.51 0.35

0.01 0.10 0.03 0.02 0.05 0.25 0.13 0.23 0.09 0.10 0.67

1.01 ± 3.6 0.956 ± 3 0.938 ± 2.2 0.97 ± 2.2 0.99 ± 2.1 0.943 ± 3 0.934 ± 2.7 0.952 ± 4 0.943 ± 2.5 0.912 ± 3 1.004 ± 4.7

0û.1149 ± 2 0.1111 ± 1.9 0.1102 ± 1.9 0.1119 ± 1.9 0.1155 ± 1.8 0.1106 ± 1.9 0.1089 ± 1.9 0.111 ± 1.9 0.1096 ± 1.9 0.108 ± 1.9 0.1149 ± 1.9

0.56 0.64 0.83 0.86 0.89 0.63 0.70 0.47 0.73 0.64 0.40

701 ± 13 679 ± 12 674 ± 12 684 ± 12 704 ± 12 676 ± 12 666 ± 12 679 ± 12 670 ± 12 661 ± 12 701 ± 13

732 ± 21 688 ± 16 663 ± 8 705 ± 8 680 ± 6 667 ± 15 684 ± 13 681 ± 25 688 ± 12 646 ± 15 722 ± 31

4 1 –2 3 –3 –1 3 0 3 –2 3

85 235 149 460 126 180 274 87 498 125

45.8 78.8 75.3 52.3 55.6 117 47.6 11.1 54.8 61.5

0.20 0.31 0.20 0.92 0.24 0.16 0.62 0.77 1.01 0.21

0.02 0.02 0.58 0.24 1.79 0.12 2.74 1.23 8.11 0.46

1.072 ± 2.6 1.026 ± 2.2 1.047 ± 6 1.033 ± 4 1.009 ± 6.8 1.045 ± 2.6 1.085 ± 8.4 0.93 ± 17 0.87 ± 25 0.983 ± 6.4

0.1221 ± 1.9 0.1172 ± 1.9 0.1153 ± 1.9 0.1174 ± 1.9 0.1166 ± 2.0 0.119 ± 1.9 0.1186 ± 2.0 0.1098 ± 2.5 0.1147 ± 2.1 0.1175 ± 1.9

0.74 0.83 0.32 0.48 0.29 0.71 0.24 0.15 0.08 0.30

743 ± 13 715 ± 13 703 ± 13 716 ± 13 711 ± 13 725 ± 13 723 ± 14 672 ± 16 700 ± 14 716 ± 13

732 ± 12 725 ± 9 803 ± 46 735 ± 26 698 ± 45 732 ± 13 816 ± 66 674 ± 115 412 ± 99 629 ± 38

–2 1 14 3 –2 1 13 0 –41 –12

Sample V-07-6 1.1 2.1 3.1 4.1 4.2 5.1 6.1 7.1 8.1 9.1 10.1

1131 707 1742 2190 3818 1253 1494 968 1425 693 1200

Sample V-07-5-2 1.1 2.1 3.1 4.1 5.1 6.1 7.1 8.1 9.1 10.1

436 782 756 517 545 1139 454 117 511 606

Note. Uncertainties are given at the 1σ level; for sample 05-01-9-6 the 91500 standard 1σ calibration error is 0.35%; for samples V-07-6 and V-07-5-2 the TEMORA1 standard 1σ calibration error is 0.79%; 206Pbc and 206Pb* are common and radiogenic lead, respectively; (1), common lead corrected from measured 204Pb; Rho, correlation factor of U/Pb ratios; D, %, discordance.

I.V. Romanova et al. / Russian Geology and Geophysics 53 (2012) 1176–1196

1193

Fig. 9. Concordia diagrams for sphene from the Srednetatarka nepheline syenite (a) (sample 05-01-9-6) and for zircons (b) from the same sample, from the Yagodka quartz syenite (c) (sample V-07-6) and granite (d) (sample V-07-5-2). Fig. 9, b shows photomicrographs of typical zircon crystals from sample 05-01-9-6: (A) optical microscope image, (B) cathodoluminescence image. Fig. 9, c, d show cathodoluminescence zircons photomicrographs from samples V-07-6 and V-07-5-2. Ellipses are uncertainties (2σ) of SHRIMP-II analytical results at particular points (Table 4). Dashed ellipses represent unused analyses.

Rocks, 1997). The presence of nonaluminous silicates such as eudialite, cancrinite, Ti–Zr–Nd-disilicates in pegmatoid foyaites indicates that the agpaitic “barrier” has been overcome. Nb, REE, F-containing minerals—pyrochlore, fersmite, and fluocerite, as well as sphene are widespread accessory and late igneous minerals in Srednetatarka foyaite-pegmatites. The enrichment of nepheline syenites in these elements is related to processes of volatile components separation and crystallization differentiation at the stages of agpaitic magma formation (Kogarko, 1990). The analysis of the pyroxenes composition from these rocks demonstrated their closeness to pyroxenes from alkaline rocks of silicate-carbonatite complexes (Hode Vuorinen and Skelton, 2004; Hode Vuorinen et al., 2005; Nash, 1972). For example, genetic interactions of the Late Neoproterozoic Alnö complex in Central Sweden (~590 Ma), in which Ca-carbonatites occur in association with nepheline syenites, ijolites and pyroxenites, is explained by the authors through the incompatibility of silicate-carbonate mantle magmas (Hode Vuorinen and Skelton, 2004; Hode

Vuorinen et al., 2005). Silicate rocks of this complex are regarded as products of the olivine-melilitic magma, which was a derivative of a mantle source depleted in large-ion lithophyle elements, and whose further evolution took place through the enrichment in volatile components and rare elements during partial melting processes. Our results do not exclude the possibility that the studied alkaline rocks of the Srednetatarka pluton are part of such a silicate-carbonatite magmatic complex. The geologic data for the carbonatites of the so-called Penchenga complex of the Transangarian (Zabrodin and Malyshev, 1975), which are located in the same tectonic zone, does not contradict this possibility. In the Yagodka pluton the subalkaline intermediate intrusive rocks and associating volcanics have been studied for the first time. Alkali feldspar and quartz syenites of this pluton are SiO2 enriched rocks that do not contain alkaline mafic minerals. Their mineral composition includes pyroxenes (augite and hedenbergite) and Ca-amphiboles (ferrous in

1194

I.V. Romanova et al. / Russian Geology and Geophysics 53 (2012) 1176–1196

Table 9. Sm-Nd isotopic data for whole rock samples of the Srednetatarka (foyaite, sample 05-01-9-14, foyaite-pegmatite, sample 05-01-9-6, alkaline syenite, sample 05-01-9) and Yagodka (alkali feldspar syenite, sample V-07-7-1, trachybasalt, sample V-07-6-1) plutons Sample

U-Pb age, Ma

Sm, ppm

147

Sm/144Nd

Nd, ppm

143

Nd/144Nd*

εNd(0)

εNd(T)

TNd(DM), Ma

05-01-9-14

711

9.995

44.16

0.13684

0.512395 ± 4

–4.7

0.7

1499

05-01-9-6

711

3.02

19.05

0.0958

0.512401 ± 2

–4.6

4.6

970

05-01-9

711

3.846

18.94

0.12274

0.512332 ± 8

–6.0

0.8

1372

V-07-7-1

691

4.824

26.16

0.11151

0.512578 ± 6

–1.2

6.4

856

V-07-6-1

691

6.163

25.19

0.14794

0.512712 ± 3

1.4

5.8

1019

Note.

143Nd/144Nd*,

uncertainty values (2σ) correspond to the last significant digit.

Table 10. Rb/Sr isotopic data for whole rock samples of the Srednetatarka (foyaite, sample 05-01-9-14, feldspar ijolite, sample 05-01-9-12) and Yagodka (quartz syenite, sample V-07-6, trachybasalt, sample V-07-6-1) plutons Sample

U-Pb age, Ma

Rb, ppm

Sr, ppm

87

Rb/86Sr

87

Sr/86Sr

(87Sr/86Sr)0

05-01-9-14

711

268.2

813.0

0.95361

0.711926 ± 8

0.70225

05-01-9-12

711

225.5

1404

0.46403

0.707197 ± 9

0.70249

V-07-6-1

691

82.57

621.8

0.38375

0.707082 ± 8

0.70330

Note.

87Sr/86Sr,

uncertainty values (2σ) correspond to the last significant digit.

intermediate rocks—hastingsite and ferro-edenite, and magnesian in mafic volcanics—magnesiohornblende and edenite, in fewer cases—actinolite, pargasite, and ferropargasite). The presence of hastingsite (which is often seen in alkaline, SiO2-undersaturated rocks) in quartz syenites forming rims around pyroxenes is a mineralogical particularity of these rocks. Uncommon in quartz syenites a highly ferrous amphibole—grunerites was found. It replaces ferrous hornblende together with chlorite, showing that metamorphic processes already took place. Mafic and ore minerals from Yagodka rocks display impurities of Nb, Zr, and REE: hornblende (Nb, Zr), grunerite (Nb), biotite (Nb, Zr, REE), sphene (Nb, Zr, REE), ilmenite (Nb, Zr, REE), hematite (Nb). Comparison in compositions of mafic minerals from Yagodka pluton rocks, considering the data of Yu.A. Kuznetsov (1941) on the presence of alkaline silicates, showed their similarity to the compositions of minerals from a laminated pluton in Southern Greenland (Ilimaussaq intrusion). The Ilimaussaq rocks formed in a continental rift setting ~1160 Ma and contain pyroxenes ranging from augite-hedenbergite to aegirine, and amphiboles ranging from hastingsite to arfvedsonite (Larsen, 1976; and others). The formation of this intrusion is connected with three pulses of more and more differentiated magmas up to agpaitic peralkaline in composition (in small amounts), for which the parent magma is considered to be close in composition to augite syenite. Close pyroxenes compositions are also observed in the Lovozero massif of laminated peralkaline intrusions (Kogarko et al., 2006). The presence of negative Ba, Sr, Eu, P, and Ti anomalies in the spectra of the studied Srednetatarka and Yagodka rocks indicates an evolved fractional crystallization process on the development stages of the alkaline magma. It is linked mostly to the fractionation of potassic feldspar (Ba), plagioclase (Sr, Eu), apatite (P), sphene or ilmenite (Ti). The less fractionated

spectra, the presence of a Sr positive anomaly, identified for feldspar ijolites and trachybasalts, probably are a reflection of early magma differentiation stages and of faster rise of the magma (in the case of volcanic rocks). Ferroan, metaluminous variations that constitute most of the studied rocks (except the trachybasalts, which are magnesian), are formed by differentiation or partial melting of basic magmas in intraplate settings, most of them on continents, possibly in ocean marginal settings, as well as from evolved magmas of oceanic islands. We believe that the formation of the studied alkaline and rare elements enriched (first of all Nb as well as Ta, Zr, Hf, REE) igneous rocks of the Tatarka– Ishimba tectonic zone took place in an active continental margin setting in the west of the Siberian craton. According to our U/Pb dating of zircons and sphene on the early stages of this event the alkaline and subalkaline igneous rocks of the Srednetatarka and Yagodka plutons were formed ~711 and ~691 Ma, respectively, which is close to the emplacement age of the subalkaline and alkaline rocks of the Zakhrebetnyi complex. These basic and intermediate intrusive and volcanic rocks that we combine into the Tatarka magmatic complex formed synchronously with Nb-enriched rocks—granitoids, including A-type leucogranites, and carbonatites. According to U/Pb data for zircons the age estimates for granites and leucogranites of the Yagodka and Chistopol’e plutons fall into a close interval—711–683 Ma. The latest magmatic formations of the Tatarka complex are the granites and A-type leucogranites of the Tatarka pluton, formed 630 Ma (Vernikovskaya et al., 2005; Vernikovsky et al., 2003). Our Sm/Nd and Rb/Sr isotopic data, probably indicate the prevailing of the mantle component in magmatic sources for the basic and intermediate rocks, and also justifies the variously manifested contamination processes of different volumes of continental crustal material by this magma. The data also agrees with earlier studies (Vernikovskaya et al.,

I.V. Romanova et al. / Russian Geology and Geophysics 53 (2012) 1176–1196

2007) suggesting that the associating acid bodies are mostly continental crustal in nature. Based on our data we have established that the alkaline enriched rocks of the Tatarka– Ishimba suture zone formed at the same time as the island arc complex rocks and their accretion to the margin of Siberia 700–630 Ma. We can assume that their formation was due to the subduction of the oceanic plate under the continent from the side of the western margin of the Siberian craton. The alkaline enriched rocks were emplaced in the inner, suprasubductional zone as the subducting plate reached the asthenospheric layer. The study was financially assisted by the Russian foundation for basic research (project No. 11-05-00131-a) and by the Earth Sciences Division of the RAS (project ONZ 9.1).

References Abbott, M.J., 1969. Petrology of the Nandewar volcano, N.S.W., Australia. Contrib. Mineral. Petrol. 20, 115–134. Bailey, S.W. (Ed.), 1984. Micas: Reviews in Mineralogy, Vol. 13. Mineralogical Society of America, BookCrafters Inc., Chelsea. Bazhenov, A.G., Nedosekova I.L., Krinova T.V., Mironov A.B., Khvorov P.V., 2000. Fluormagnesioarfvedsonite NaNa2(Mg,Fe2+)4Fe3+[Si8O22] (F,OH)2—a new mineral species in the amphibole group (Il’meny–Vishnevye mountains alkaline massif, the South Urals). Zap. RMO (Proc. Rus. Mineral. Soc.) 129 (6), 28–31. Black, L.P., Kamo, S.L., Allen, C.M., Aleinikoff, J.N., Davis, D.W., Korsch, R.J., Foudoulis, C., 2003. Temora 1: a new zircon standard for Phanerozoic U/Pb geochronology. Chem. Geol. 200, 155–170. Diner, A.E., 2000. The reference for the Zakhrebetnyi trachybasalt–alkaline trachyte complex (Yenisei Ridge) [in Russian]. Krasnoyarskgeols”emka, Krasnoyarsk. Deer, W.A., Howie, R.A., Zussman, J., 1966. Rock Forming Minerals, Vol. 3: Layered Silicates [in Russian]. Mir, Moscow. Frost, B.R., Frost, C.D., 2008. A geochemical classification for feldspathic igneous rocks. J. Petrol. 49 (11), 1955–1969. Fuyuan, W.U., Wilde, S.A., Deyou, S., 2001. SHRIMP U/Pb zircon age of the youngest exposed pluton in eastern China. Chin. Sci. Bull. 46 (20), 1727–1731. Glazyrin, Yu.N., Vrublevich, E.I., 1967. Geological Map of the USSR, Scale 1 : 200,000. Yenisei Series. Sheet O-46-XXII. Explanatory Note [in Russian]. Nedra, Moscow. Halama, R., Vennemann, T., Siebel, W., Markl, G., 2005. The Grønnedal-Ika Carbonatite-Syenite Complex, South Greenland: Carbonatite Formation by Liquid Immiscibility. J. Petrol. 46 (1), 191–217. Hode Vuorinen, J.H., Skelton, A.D.L., 2004. Origin of silicate minerals in carbonatites from Alnö Island, Sweden—Magmatic crystallisation or wall rock assimilation? Terra Nova 16, 210–215. Hode Vuorinen, J., Halenius, U., Whitehouse, M.J., Mansfeld, J., Skelton, A.D.L., 2005. Compositional variations (major and trace elements) of clinopyroxene and Ti-andradite from pyroxenite, ijolite and nepheline syenite, Alnö Island, Sweden. Lithos 81, 55–77. Igneous Rocks: A Classification and Glossary of Terms: Recommendations of the International Union of Geological Sciences Subcommission on the Systematics of Igneous Rocks, 1997 [in Russian]. Nedra, Moscow. Kachevsky, L.K., Kachevskaya, G.I., Grabovskaya, Zh.M., 1998. Geological Map of the Yenisei Ridge. Scale 1:500,000 [in Russian]. Krasnoyarskgeols”emka, Krasnoyarsk. Kogarko, L.N., 1990. Ore-forming potential of alkaline magmas. Lithos 26, 167–175. Kogarko, L.N., Williams, C.T., Woolley, A.R., 2006. Compositional evolution and cryptic variation in pyroxenes of the peralkaline Lovozero intrusion, Kola Peninsula, Russia. Mineral. Mag. 70 (4), 347–359.

1195

Krendelev, F.P., 1971. Clarkes of Radioactive Elements in Precambrian Rocks of the Yenisei Ridge [in Russian]. Nauka, Moscow. Krogh, T.E., 1973. A low-contamination method for hydrothermal decomposition of zircon and extraction of U and Pb for isotopic age determination. Geochim. Cosmochim. Acta 37, 485–494. Krogh, T.E., 1982. Improved accuracy of U-Pb zircon by the creation of more concordant systems using an air abrasion technique. Geochim. Cosmochim. Acta 46, 637–649. Kuznetsov, Yu.A., 1941. Petrology of the Precambrian of the South Yenisei Ridge, in: Materials on the Geology of Western Siberia [in Russian]. Izd. ZSGU, Tomsk, Issue 15 (57). Kuznetsov, Yu.A., 1988. Petrology of the Precambrian of the South Yenisei Ridge. Selected Works. Book 1 [in Russian]. Nauka, Novosibirsk. Larionov, A.N., Andreichev, V.A., Gee, D.G., 2004. The Vendian alkaline igneous suite of northern Timan: ion microprobe U/Pb zircon ages of gabbros and syenite, in: Gee, D.G., Pease, V.L. (Eds.), The Neoproterozoic Timanide Orogen of Eastern Baltica. Geological Society, London, Memoirs 30, pp. 69–74. Larsen, L.M., 1976. Clinopyroxenes and coexisting mafic minerals from the alkaline Ilimaussaq intrusion. J. Petrol. 17, 258–290. Leake, B.E., Woolley, A.R., Arps, C.E.S., Birch, W.D., Gilbert, M.C., Grice, J.D., Hawthorne, C., Kato, A., Kisch, H.J., Krivovichev, V.G., Linthout, K., Laird, J., Mandarino, J.A., Maresch, W.V., Nickel, E.H., Rock, N.M.S., Schumacher, J.C., Smith, D.C., Stephenson, C.N., Ungaretti, L., Whittaker, E.J.W., Youzhi, G., 1997. Nomenclature of amphiboles: report of the subcommittee on amphiboles of the International Mineralogical Association, commission on new minerals and mineral names. Can. Mineral. 35, 219–246. Leake, B.E., Woolley, A.R., Birch, W.D., Burke, E.A.J., Ferraris, G., Grice, J.D., Hawthorne, F.C., Kisch, H.J., Krivovichev, V.G., Schumacher, J.C., Stephenson, N.C.N., Whittaker, E.J.W., 2004. Nomenclature of amphiboles: additions and revisions to the International Mineralogical Association’s amphibole nomenclature. Am. Mineral. 89, 883–887. Ludwig, K.R., 1991a. PbDAT for MS-DOS, Version 1.21. U.S. Geol. Survey Open-File Rept., 1 88–542. Ludwig, K.R., 1991b. ISOPLOT for MS-DOS, Version 2.5. U.S. Geol. Survey Open-File Rept., 1 88–557. Ludwig, K.R., 1999. ISOPLOT/Ex.Version 2.06. A Geochronological Toolkit for Microsoft Excel. Berkley Geochronology Center Spec. Publ. 1a. Ludwig, K.R., 2005a. SQUID 1.12 A User’s Manual. A Geochronological Toolkit for Microsoft Excel. Berkeley Geochronology Center Sp. Publ. Ludwig, K.R., 2005b. User’s Manual for ISOPLOT/Ex 3.22. A Geochronological Toolkit for Microsoft Excel. Berkeley Geochronology Center Spec. Publ. Mattinson, J.M., 1994. A study of complex discordance in zircons using step-wise dissolution techniques. Contrib. Mineral. Petrol 116, 117–129. McDonough, W.F., Sun, S.-S., 1995. The composition of the Earth. Chem. Geol. 120, 223–254. Mitchell, R.H., 1980. Pyroxenes of the Fen alkaline complex, Norway. Am. Mineral. 65, 45–54. Mitchell, R.H., Platt, R.G., 1983. Primitive nephelinitic volcanism associated with rifting and uplift in the Canadian Arctic. Nature 303, 609–612. Morimoto, N., Fabries, J., Ferguson, A.K., Ginzburg, I.V., Ross, M., Seifert, F.A., Zussman, J., Aoki, K., Gottardi, G., 1988. Nomenclature of pyroxenes. Am. Mineral. 73, 1123–1133. Nash, W.P., 1972. Mineralogy and petrology of the Iron Hill carbonatite complex, Colorado. Geol. Soc. Am. Bull. 83, 1361–1382. Nikolaeva, I.V., Palesskii, S.V., Koz’menko, O.A., Anoshin, G.N., 2008. Analysis of geologic reference materials for REE and HFSE by inductively coupled plasma–mass spectrometry (ICP-MS). Geochem. Int. 46 (10), 1016–1022. Nozhkin, A.D., Turkina, O.M., Bayanova, T.B., Berezhnaya, N.G., Larionov, A.N., Postnikov, A.A., Travin, A.V., Ernst, R.E., 2008. Neoproterozoic rift and within-plate magmatism in the Yenisei Ridge: implications for the breakup of Rodinia. Russian Geology and Geophysics (Geologiya i Geofizika) 49 (7), 503–519 (666–688). Pervov, V.A., Bogomolov, E.S., Levskii, L.K., Sergeev, S.A., Larchenko, V.A., Minchenko, G.V., Stepanov, V.P., Sablukov, S.M., 2005. Rb-Sr

1196

I.V. Romanova et al. / Russian Geology and Geophysics 53 (2012) 1176–1196

age of kimberlites of the Pionerskaya pipe, Arkhangelsk diamondiferous province. Dokl. Earth Sci. 400 (1), 67–71. Postnikov, A.A., Nozhkin, A.D., Nagovitsyn, K.E., Travin, A.V., Stanevich, A.M., Kornilova, T.A., Yudin, D.S., Yakshin, M.S., Kochnev, B.B., 2005. New data on age of Neoproterozoic deposits of Chingasan and Vorogovo series of Yenisei Ridge, in: Geodynamic Evolution of Lithosphere of Central-Asian Mobile Belt (from Ocean to Continent): Abstracts of Conference [in Russian]. Irkutsk, pp. 71–74. Rieder, M., Cavazzini, G., D’yakonov, Y.S., Frank-Kamenetskii, V.A., Gottardi, G., Guggenheim, S., Koval’, P.V., Muller, G., Neiva, A.M.R., Radoslovich, E.W., Robert, J.L., Sassi, F.P., Takeda, H., Weiss, Z., Wones, D.R., 1998. Nomenclature of the micas. Can. Mineral. 36, 905–912. Savanovich, L.G., Sergeeva, Zh.I., 1970. Geological Map of the USSR, Scale 1 : 200,000. Yenisei Series. Sheet O-46-XVI. Explanatory Note [in Russian]. Nedra, Moscow. Sazonov, A.M., Fedorova, A.V., Zvyagina, E.A., Leont’ev, S.I., Vrublevsky, V.V., Gertner, I.F., Gavrilenko, V.V., 2007. The Transangara alkaline pluton, Yenisei Range: Rb-Sr and Sm-Nd isotope ages and sources of feldspathoid magmas in Late Precambrian. Dokl. Earth Sci. 413 (3), 469–473. Skublov, S.G., Berezin, A.V., Rizvanova, N.G., Bogomolov, E.S., Sergeeva, N.A., Vasil’eva, I.M., Guseva, V.F., Marin, Y.B., 2010. Complex isotopic-geochemical (Sm-Nd, U-Pb) study of Salma eclogites. Dokl. Earth Sci. 434 (2), 1396–1400. Smirnova, E.V., Flem, B., Anchutina, E.A., Mysovskaya, I.N., Lozhkin, V.I., Petrov, L.L., 2010. Determination of REE, Y, Nb, Zr, Hf, Ta, Th and U in LSHC-1 and Amf-1 Geological RMs by Solution and Laser Ablation ICP-MS. Geostand. Geoanal. Res. 34 (1), 49–65. Stacey, J.S., Kramers, I.D., 1975. Approximation of terrestrial lead isotope evolution by a two-stage model. Earth Planet. Sci. Lett. 26 (2), 207–221. Steiger, R.H., Jäger, E., 1976. Subcomission of Geochronology: convension of the use of decay constants in geo- and cosmochronology. Earth Planet. Sci. Lett. 36 (2), 359–362. Stephenson, D., 1972. Alkali clinopyroxenes from the nepheline syenites of the South Qôroq centre, south Greenland. Lithos 5, 187–201. Sveshnikova, E.V., 1965. The Transangarian nepheline-syenite complex (Yenisei Ridge), in: Alkaline Magmatism of the Folded Framing in the South of the Siberian Platform [in Russian]. Nauka, Moscow, pp. 5–98. Sveshnikova, E.V., Lomeiko, E.I., Yershova, Z.P., Usenko, A.M., 1966. Fluorine enriched magnesian arfvedsonites from alkaline rocks of the Yenisei Ridge, in: New Data on Minerals of the USSR [in Russian]. Proc. Mineral. Museum, Moscow 17, pp. 224–228. Sveshnikova, E.V., Semenov, E.I., Khomyakov, A.P., 1976. Trans-Angara alkali massif, its rocks and minerals [in Russian]. Nauka, Moscow. Tyler, R.C., King, B.C., 1967. The pyroxenes of the alkaline igneous complexes of eastern Uganda. Mineral. Mag. 36, 5–22. Vernikovskaya, A.E., Vernikovsky, V.A., Sal’nikova, E.B., Datsenko, V.M., Kotov, A.B., Kovach, V.P., Travin, A.V., Yakovleva, S.Z., 2002. Yeruda and Chirimba granitoids (Yenisei Ridge) as indicators of Neoproterozoic collisions. Geologiya i Geofizika (Russian Geology and Geophysics) 43 (3), 259–272 (245–259). Vernikovskaya, A.E., Vernikovsky, V.A., Sal’nikova, E.B., Kotov, A.B., Kovach, V.P., Datsenko, V.M., 2005. A Neoproterozoic anorogenic event in the Yenisei Ridge: new geochemical and isotopic-geochronological data. Dokl. Earth Sci. 403 (6), 833–837. Vernikovskaya, A.E., Vernikovsky, V.A., Sal’nikova, E.B., Kotov, A.B., Kovach, V.P., Travin, A.V., Wingate, M.T.D., 2007. A-type leucogranite magmatism in the evolution of continental crust on the western margin of the Siberian craton. Russian Geology and Geophysics (Geologiya i Geofizika) 48 (1), 3–16 (5–21). Vernikovskaya, A.E., Vernikovsky, V.A., Matushkin, N.Yu., Romanova, I.V., Berejnaya, N.G., Larionov, A.N., Travin, A.V., 2010. Middle Paleozoic

and Early Mesozoic anorogenic magmatism of the South Yenisei Ridge: first geochemical and geochronological data. Russian Geology and Geophysics (Geologiya i Geofizika) 51 (5), 548–562 (701–716). Vernikovsky, V.A., Vernikovskaya, A.E., 2006. Tectonics and evolution of granitoid magmatism in the Yenisei Ridge. Russian Geology and Geophysics (Geologiya i Geofizika) 47 (1), 32–50 (35–52). Vernikovsky, V.A., Vernikovskaya, A.E., Sal’nikova, E.B., Kotov, A.B., Chernykh, A.I., Kovach, V.P., Berezhnaya, N.G., Yakovleva, S.Z., 1999. New U-Pb data on the formation of the Predivinsk paleoisland-arc complex (Yenisei Range). Geologiya i Geofizika (Russian Geology and Geophysics) 40 (2), 255–259 (256–261). Vernikovsky, V.A., Vernikovskaya, A.E., Chernykh, A.I., Sal’nikova, E.B., Kotov, A.B., Kovach, V.P., Yakovleva, S.Z., Fedoseenko, A.M., 2001. Porozhnaya granitoids of the Enisei ophiolite belt: Indicators of Neoproterozoic events on the Enisei Ridge. Dokl. Earth Sci. 381A (9), 1043–1046. Vernikovsky, V.A., Vernikovskaya, A.E., Kotov, A.B., Sal’nikova, E.B., Kovach, V.P., 2003. Neoproterozoic accretionary and collisional events on the western margin of the Siberian Craton: new geological and geochronological evidence from the Yenisey Ridge. Tectonophysics 375, 147–168. Vernikovsky, V.A., Vernikovskaya, A.E., Wingate, M.T.D., Popov, N.V., Kovach, V.P., 2007. The 880–864 Ma granites of the Yenisey Ridge, western Siberian margin: geochemistry, SHRIMP geochronology, and tectonic implications. Precambrian Res. 154, 175–191. Vernikovsky, V.A., Vernikovskaya, A.E., Sal’nikova, E.B., Berezhnaya, N.G., Larionov, A.N., Kotov, A.B., Kovach, V.P., Vernikovskaya, I.V., Matushkin, N.Yu., Yasenev, A.M., 2008. Late Riphean alkaline magmatism in the western framework of the Siberian craton: a result of continental rifting or accretionary events? Dokl. Earth Sci. 419 (2), 226–230. Vernikovsky, V.A., Vernikovskaya, A.E., Polyansky, O.P., Laevsky, Yu.M., Matushkin, N.Yu., Voronin, K.V., 2011. A tectonothermal model for the formation of an orogeny at the post-collisional stage (by the example of the Yenisei Ridge, Eastern Siberia). Russian Geology and Geophysics (Geologiya i Geofizika) 52 (1), 24–39 (32–50). Vrublevskii, V.V., Reverdatto, V.V., Izokh, A.E., Gertner, I.F., Yudin, D.S., Tishin, P.A., 2011. Neoproterozoic carbonatite magmatism of the Yenisei Ridge, Central Siberia: 40Ar/39Ar geochronology of the Penchenga rock complex. Dokl Earth Sci. 437 (2), 443–448. Whitney, D.L., Evans, B.W., 2010. Abbreviations for names of rock-forming minerals. Am. Mineral. 95, 185–187. Wiedenbeck, M., Alle, P., Corfu, F., Griffin, W.L., Meier, M., Oberli, F., von Quadt, A., Roddick, J.C., Spiegel, W., 1995. Three natural zircon standards for U/Th/Pb, Lu/Hf, trace element and REE analyses. Geostandards Newsletters 19, 1–23. Williams, I.S., 1998. U/Th/Pb Geochronology by ion microprobe. In: Applications in microanalytical techniques to understanding mineralizing processes. Rev. Econ. Geol. 7, 1–35. Yagi, K., 1953. Petrochemical studies of the alkali rocks of the Morotu district, Sakhalin. Geol. Soc. Am. Bull. 64, 769–810. Yarmolyuk, V.V., Kovalenko, V.I., 1991. Riftogenic Magmatism of Active Continental Margins and Its Mineralization [in Russian], Bogatikov, O.A. (Ed.). Nauka, Moscow. Yarmolyuk, V.V., Kovalenko, V.I., Kovach, V.P., Rytsk, E.Yu., Kozakov, I.K., Kotov, A.B., Sal’nikova, E.B., 2006. Early stages of the Paleoasian ocean formation: results of geochronological, isotopic and geochemical investigations of Late Riphean and Vendian–Cambrian complexes of the Central Asian foldbelt. Dokl. Earth Sci. 411 (8), 1184–1190. Zabrodin, V.Yu., Malyshev, A.A., 1975. New complex of alkali-mafic rocks and carbonatites in Yenisei Ridge. Dokl. Akad. Nauk SSSR 223, 1223–1226.

Editorial responsibility: V.S. Shatsky