This article appeared in a journal published by Elsevier. The attachedcopy is furnished to the author for internal non-commercial researchand education use, including for instruction at the authors institution

and sharing with colleagues.

Other uses, including reproduction and distribution, or selling orlicensing copies, or posting to personal, institutional or third party

websites are prohibited.

In most cases authors are permitted to post their version of thearticle (e.g. in Word or Tex form) to their personal website orinstitutional repository. Authors requiring further information

regarding Elsevier’s archiving and manuscript policies areencouraged to visit:

http://www.elsevier.com/copyright

Author's personal copy

Deciphering Caledonian events: Timing and geochemistryof the Caledonian magmatic arc in the Kyrgyz Tien Shan

Dmitry Konopelko a,*, Georgy Biske a, Reimar Seltmann b, Maria Kiseleva a,Dmitry Matukov c, Sergey Sergeev c

a Geological Faculty, St. Petersburg State University, 7/9 University Embankment, St. Petersburg 199034, Russiab Centre for Russian and Central EurAsian Mineral Studies, Department of Mineralogy, Natural History Museum, Cromwell Road, London SW7 5BD, UK

c Center of Isotopic Research, A.P. Karpinsky All Russia Geological Research Institute (VSEGEI), 74 Sredny Pr., St. Petersburg 199106, Russia

Abstract

In the Kyrgyz Tien Shan (also known as Tian Shan in literature) the Caledonian (Cambro-Silurian) intrusions comprise an extensivemagmatic arc stretching from east to west for more than 1000 km. The characteristic feature of the arc is its relatively homogeneouscomposition of rock types over the whole structure. The Kichy-Naryn and Djetim intrusions presented in this study are slightly elongatedin an east–west direction and occupy an area of ca. 100 km2. The main rock types are diorite, granodiorite and granite. Geological andgeochemical features of the Kichy-Naryn and Djetim intrusions demonstrate characteristics of I-type granite series. Rocks of the twointrusions define a continuous high-K calc-alkaline series. Diorite and granite of the Kichy-Naryn intrusion yielded early Silurian crys-tallisation ages of 436 ± 2 Ma (U–Pb, zircon). Diorite from pebbles in the conglomerate sampled close to the contact of the Kichy-Narynintrusion yielded a significantly older early Ordovician crystallisation age of 466 ± 10 Ma. The obtained ages of 466 and 436 Ma matchages of two major regional magmatic pulses at ca. 435–440 and 460–470 Ma which took place during continuous subduction from theCambrian to the Silurian. The amount of granites in the Northern Tien Shan, their prolonged history of formation and pronouncedI-type geochemical characteristics suggest their formation in an Andean-type active margin environment.� 2007 Elsevier Ltd. All rights reserved.

Keywords: Tien Shan; U–Pb geochronology; I-type granite; Active margin

1. Introduction

The giant Altaids orogenic collage, occupying a signifi-cant part of Central Asia (Fig. 1), formed as a result of con-tinuous accretion of terranes from Riphean to Permian.During Paleozoic there were two major phases of accretionknown as the Caledonian (Cambro-Silurian with culmina-tion in Late Ordovician–Early Silurian) and Hercynian(Late Devonian–Early Permian with culmination in LateCarboniferous–Early Permian) orogenic events. WhileHercynian structures are relatively well preserved, the Cal-edonian structures are less well understood due to a muchlower degree of preservation. The major and best preserved

Caledonian units are regionally developed magmatic arcs.Understanding of the geodynamic settings in which thearcs have been formed and timing of events in the arcsare major tools in the reconstruction of the Lower Paleo-zoic history of the Altaids.

In the Kyrgyz Tien Shan the Caledonian intrusionscomprise an extensive magmatic arc extending from eastto west for more than 1000 km (Fig. 2). The characteristicfeature of the arc is its relatively homogeneous compositionof rock types. While the ages of a few intrusions are wellconstrained by the overlying sediments the majority of Cal-edonian magmatic rocks have not been studied utilizingmodern geochronological methods and their positionswithin the arc are poorly understood. As a result, on exist-ing maps, the Caledonian intrusions are often shown ascomposite bodies with ages varying from the Cambrianto the Silurian within a single pluton.

1367-9120/$ - see front matter � 2007 Elsevier Ltd. All rights reserved.

doi:10.1016/j.jseaes.2007.10.017

* Corresponding author.E-mail address: konopelko@inbox.ru (D. Konopelko).

www.elsevier.com/locate/jaes

Available online at www.sciencedirect.com

Journal of Asian Earth Sciences 32 (2008) 131–141

Author's personal copy

In this paper we present new data for two intrusions in aca. 100 km long and 50 km wide region in the Kyrgyz TienShan south of Lake Issyk-Kul (Fig. 2). The data presentedinclude U–Pb zircon SHRIMP (Sensitive High-ResolutionIon Microprobe) ages and geochemistry. The conclusionsderived for the region under study are then extrapolatedinto the whole magmatic arc and more broad regional geo-dynamic and metallogenic implications are discussed.

2. Geological setting

There are two major approaches to reconstruct the geo-logical history of the eastern Altaids. According to theideas of Sengor et al. (1993) and Sengor and Natal’in(1996), modified by Yakubchuk (2004), the Paleozoic his-tory of the Altaids is characterised by the development ofone or more major arcs with continental basements sepa-rated in the Late Precambrian from Baltica and Siberia.The arcs underwent oroclinal bending due to the relativerotation of Baltica and Siberia and subsequent collisionwith the Tarim and Karakum continents which in thePaleozoic occurred in two major stages known in theregion as Caledonian and Hercynian orogenic cycles. Otherauthors (e.g. Lomize et al., 1997; Biske, 2001) consider thebasements of Kazakhstan and the Tien Shan, as well asTarim and Karakum, as fragments rifted off easternGondwana which drifted north (in present day coordi-

nates) and were accreted in the course of Caledonian andHercynian orogenic events. Both groups of authors how-ever agree that by the end of the Ordovician the Paleo-Kazakhstan continent was formed by accretion of severalterranes including the Northern Tien Shan. In the courseof this process two major Cambro-Ordovician magmaticarcs situated in the Northern Tien Shan and NorthernKazakhstan were formed. These Caledonian magmatic arcsare shown in Fig. 1. The focus of this paper is the NorthernTien Shan terrane comprising an extensive magmatic arc(Fig. 2). The Kyrgyz Tien Shan is usually divided into threeterranes: the Northern, the Middle and the Southern TienShan (Fig. 2). The Southern Tien Shan is a fold and thrustbelt formed during Hercynian collision between the Tarimand Paleo-Kazakhstan (e.g. Biske, 2001) and is not consid-ered in this paper. A short overview of the geological his-tory of the Northern and Middle Tien Shan is given below.

It is usually accepted that the opening of an ocean sep-arating the Middle and the Northern Tien Shan terranesoccurred in the Late Precambrian. The Kyrgyz-Terskeibasin, separating the Middle and the Northern Tien Shanterranes, represented a part of a larger Paleo-Asian ocean(Lomize et al., 1997). Whether the Northern Tien Shanwas at that time a part of the Paleo-Kazakhstan plate orwas separated from it by another ocean or a back-arc basinis not clear (Lomize et al., 1997). The opening of the oceancontinued until the Late Cambrian–Early Ordovician when

Fig. 1. Geotectonic map of Asia (from Yakubchuk et al., 2003, modified by the authors). Thick white dashed lines show Caledonian magmatic arcs inKazakhstan and Tien Shan. The rectangle represents the area shown in Fig. 2.

132 D. Konopelko et al. / Journal of Asian Earth Sciences 32 (2008) 131–141

Author's personal copy

a subduction zone formed at its northern margin (presentday coordinates). Subduction under the Northern TienShan turned it into an active Andean-type margin withabundant I-type magmatism (Fig. 2). This magmatism cul-minated in the Early Ordovician when, as was suggested byGhes (1999, 2006), a mature arc was accreted to the North-ern Tien Shan. The Middle Tien Shan terrane during thewhole history of the ocean closure represented a passivemargin and was accreted to the Northern Tien Shan inthe Late Ordovician as a result of ongoing subduction tothe north. This Late Ordovician collision was accompaniedby the main magmatic pulse comprising huge volumes ofLate Ordovician–Early Silurian granites (Fig. 2). Howeverthis magmatic pulse was not accompanied by significantregional metamorphism and did not affect the Middle TienShan terrane which by the Early Silurian was alreadyaccreted to the Northern Tien Shan and Paleo-Kazakhstan(Ghes, 1999, 2006). The crust of the newly formed Paleo-Kazakhstan continent underwent further growth in thecourse of Silurian accretion in the south-east and north-west and as a result of Devonian active margin-type mag-matism. In the Late Devonian–Lower CarboniferousPaleo-Kazakhstan was covered by continental and shelfsediments and later affected by the Late Carboniferous–Permian deformations and magmatism related to Hercy-nian collision with Tarim. Post-Silurian rocks which hidethe Caledonian basement, are not shown in Fig. 2.

3. The intrusions

The area under study (Fig. 3) is situated south of LakeIssyk-Kul and along the valleys of the Kichy-Naryn andArchaly rivers. Within the area two intrusions of granitoidrocks, the Kichy-Naryn and Djetim, were studied in detail.The intrusions are slightly elongated in an east–west direc-tion and occupy an area of ca. 100 km2. The intrusionscrosscut volcanic and sedimentary suites varying in agefrom Riphean to Cambrian (Osmonbetov et al., 1982);the contacts, where preserved, are baked with 100–150 mthick zones of hornfels. The southern contact of the Djetimintrusion is tectonic and is cut by the Nikolaev line, a majorCaledonian lineament separating the Northern and MiddleTien Shan, or by its closest offset (Fig. 3). The rock typesdescribed in all intrusions are rather similar. The mainphase is represented by the coarse grained slightly porphy-ritic or even grained amphibole–biotite granodiorite. Atypical feature of the main phase granodiorite is a locallydeveloped porphyritic texture characterised by abundantK-feldspar megacrysts situated in a greenish matrix. Thisvariety, shown in Fig. 4, is mined for dimension stone inthe Kashkasu intrusion situated ca. 70 km to the east. Thisvariety forms irregular areas within even grained or slightlyporphyritic granodiorite and the character of the K-feld-spar megacrysts gives the impression of a metasomaticsolid state overgrowth origin. The main phase granodiorite

Fig. 2. Terranes of Tien Shan and distribution of Caledonian granites in the Northern Tien Shan. After Ghes (2006), modified by the authors.

D. Konopelko et al. / Journal of Asian Earth Sciences 32 (2008) 131–141 133

Author's personal copy

is shown on regional maps as Middle–Upper Ordovician(Zhukov, 1961).

The second important rock type is represented by bio-tite–amphibole diorite–granodiorite, which is a coarsegrained greyish rock with euhedral amphibole crystals.The diorite usually occupies marginal parts of the intru-sions, and its contacts with the main phase granodiorite

are transitional. The diorite is shown on regional maps asCambrian in age.

The latest major intrusive phase is represented by redcoarse grained slightly porphyritic granite and leucogranitethat usually crosscut the granodiorite. This rock is shownon maps as Silurian. Mineral compositions of the threemajor rock types are given in Table 1.

The rocks are generally undeformed. The fabric in thediorite is late and related to movements along the Nikolaevline shear zone. However, almost all rock types are affectedby alteration expressed by replacement of mafic silicates bychlorite minerals.

All the major rock types of the intrusions are crosscut bydikes and small bodies of gabbroic composition. The dikesare composed of fine grained gabbroic or dioritic rock andhave chilled margins. Locally the dikes provided enoughheat for extensive melting of the country diorite or

Fig. 4. Granodiorite: polished surface. Scale 1:1.

Table 1Mineral composition of the rocks of Kichy-Naryn and Djetim intrusions(vol. %)

Diorite Granodiorite Granite

Plagioclase 50–70 42–60 40–60K-feldspar 0–13 10–20 15–30Quartz 0–10 20–30 25–32Biotite 10–20 3–5 1–4Amphibole 10–25 8–12 0–2

Fig. 3. Schematic geological map of study area.

134 D. Konopelko et al. / Journal of Asian Earth Sciences 32 (2008) 131–141

Author's personal copy

granodiorite which resulted in formation of aplitic graniteforming net- and back-veining structures. Larger bodiesof aplitic granite not associated with gabbroic rocks mayrepresent products of such melting at depth. Our prelimin-ary data show that aplitic granites are extremely rich in Ferelative to Mg and may represent a formation of A-typemelt in situ. This, however, will be the subject of a separatestudy.

The Caledonian rock assemblage was eroded andunconformably overlain by the Lower Carboniferous con-glomerates and limestones which lie almost undeformed ona well preserved post-Silurian erosion surface (Fig. 3).

4. Geochemistry

Chemical analyses of the rocks of Kichy-Naryn andDjetim intrusions are presented in Table 2. Although a lim-ited dataset, the nine samples represent all major rock types

of the intrusions. Major and trace elements were analysedin VSEGEI, St. Petersburg by XRF and ICP-MS methods,respectively. The rocks of the main intrusive phases, ana-lysed in this study, form a series with SiO2 range from 60to 72 wt%. They are characterised by relatively low FeO/MgO and moderate K2O/Na2O ratios. The rocks are rela-tively depleted in LIL and HFS elements and enriched inP2O5, Ba and Sr. On a TAS classification diagram (Middle-most, 1994) the rocks, with one exception, plot in the fieldsof diorite, granodiorite and granite and form a trend char-acteristic for high-potassium calc-alkaline series (Fig. 5a).The rocks are meta-aluminous or slightly peraluminous(Zen, 1986) in composition (Fig. 5b). They plot in the fieldof calc-alkaline rocks on the TAS diagram (Fig. 5a). Ondiscrimination diagrams of Pearce et al. (1984) they plotin the field of volcanic arc granites (Fig. 5c and d). Therocks have moderately fractionated REE patterns withoutEu anomalies and are slightly enriched in LREE (Fig. 6).

Table 2Chemical composition of the rocks from Kichy-Naryn and Djetim intrusions

Rock-type Diorite Granodiorite Granite

SiO2 60.30 61.70 64.10 66.10 68.00 68.60 69.90 72.10 72.20TiO2 1.00 0.67 0.90 0.66 0.64 0.62 0.48 0.40 0.37Al2O3 16.80 15.40 14.70 15.70 15.00 14.70 14.90 15.00 14.40FeOtot 5.27 5.22 4.76 3.71 3.23 3.28 2.18 1.73 1.98MnO 0.10 0.13 0.88 0.11 0.07 0.08 0.07 0.04 0.04MgO 2.34 3.87 2.51 1.55 1.40 1.22 0.87 0.57 0.73CaO 3.84 4.86 3.67 2.81 3.03 3.00 2.09 1.75 1.19Na2O 3.40 4.15 2.73 3.88 3.57 3.57 3.94 3.63 3.96K2O 4.65 1.61 3.96 3.19 3.39 3.40 3.99 3.80 3.85P205 0.28 0.17 0.33 0.21 0.18 0.18 0.13 0.10 0.11LOI 1.32 1.52 1.39 1.60 0.98 0.87 1.22 0.70 0.85Cr 88.0 156.0 # 12.7 7.6 # # 53.2 78.6Ni 9.5 23.4 # 8.6 6.6 # # 1.7 1.5V 86 119 # 59 54 # # 19 19Rb 135 66 # 131 135 # # 87 108Ba 1080 468 # 981 776 # # 864 923Sr 593 489 # 465 392 # # 328 258Ga 18.3 17.2 # 17.1 15.0 # # 15.3 15.4Zr 268 84 # 158 136 # # 77 84Hf 6.31 2.00 # 3.68 3.67 # # 2.08 2.42Y 20.2 9.7 # 14.6 12.5 # # 4.8 5.8Nb 18.1 3.5 # 17.0 14.4 # # 11.4 9.8Ta 1.20 0.19 # 1.47 1.28 # # 0.99 0.79U 4.15 0.35 # 3.10 3.35 # # 1.51 2.63Th 18.4 0.9 # 16.5 12.4 # # 6.6 9.2La 39.5 7.8 # 45.2 31.3 # # 15.3 26.6Ce 77.9 17.1 # 79.6 56.4 # # 31.6 47.8Pr 8.8 2.2 # 8.1 6.0 # # 3.4 5.2Nd 30.1 9.2 # 26.3 20.7 # # 11.2 16.6Sm 5.6 2.2 # 5.1 4.2 # # 2.6 2.7Eu 1.59 0.79 # 1.11 1.04 # # 0.59 0.68Gd 4.96 2.27 # 3.91 3.46 # # 1.71 2.19Tb 0.74 0.34 # 0.58 0.47 # # 0.22 0.29Dy 3.85 1.86 # 2.97 2.39 # # 1.24 1.42Ho 0.72 0.38 # 0.61 0.47 # # 0.23 0.28Er 2.00 1.09 # 1.61 1.37 # # 0.64 0.68Tm 0.35 0.19 # 0.22 0.24 # # 0.09 0.09Yb 2.00 0.98 # 1.51 1.22 # # 0.57 0.49Lu 0.28 0.18 # 0.26 0.21 # # 0.10 0.10

SiO2–LOI (wt%); Cr–Lu (ppm); #, element not determined.FeOtot, total Fe as FeO.

D. Konopelko et al. / Journal of Asian Earth Sciences 32 (2008) 131–141 135

Author's personal copy

Thus, the main rock-types of the Kichy-Naryn and Djetimintrusions are geochemically similar and form a continuouscalc-alkaline trend.

5. Geochronology

5.1. Sample description

Four samples were chosen for U–Pb zircon SHRIMP-IIchronology. Two samples represent the rocks of the Kichy-Naryn intrusion: sample 412200 (N 41� 42.047, E 76�43.092) represents marginal amphibole rich greyish grano-diorite shown on a map as Cambrian (Zhukov, 1961). Sam-ple 412600 (N 41� 42.910, E 76� 40.431) represents a redgranodiorite in the central part of the intrusion shown ona map as Silurian and crosscutting the main granite bodyshown as Ordovician. These two varieties are similar tothose described in the Djetim intrusion where they are alsoshown on a map as Cambrian and Ordovician in age. The

0.5 1.0 1. 5 2.0

0.6

1.0

1.4

1.8

2.2

2.6

3.0

Peralkaline

Metaluminous Peraluminous

A/CNK

AN

K

1 10 100 10001

10

dioritegranodioritegranite

100

1000

VAG+Syn-COLG

WPG

ORG

Y

Nb

1 10 100 10001

10

100

1000

2000

Syn-COLG WPG

ORGVAG

Y+Nb

Rb

SiO2

35 40 45 50 55 60 65 70 75

15

10

5

0

Na 2

O+K

2O

1

2

3

6

5

9 11

8

4

10

7

12

1315

14

Fig. 5. Analyses of the rocks of the Kichy-Naryn and Djetim intrusions plotted on (a) total alkali vs silica (TAS) diagram. Fields after Middlemost (1994):(1) foidolite, (2) foid gabbro, (3) peridotitic gabbro, (4) foid monzodiorite, (5) monzogabbro, (6) gabbro, (7) foid monzosyenite, (8) monzodiorite, (9)gabbroic diorite, (10) monzonite, (11) diorite, (12) foid syenite, (13) syenite and quartz monzonite, (14) granodiorite, (15) granite. Dashed line separatesfields of alkaline and calc-alkaline rocks (Irvine and Baragar, 1971). (b) ANK vs ACNK diagram, ANK = Al2O3/(Na2O + K2O) mol, ACNK = Al2O3/(Na2O + K2O + CaO) mol. (c) Nb vs Y diagram and (d) Rb vs Y + Nb diagram; (c) and (d) after Pearce et al. (1984).

1

10

100

200

LaCe

PrNd

PmSm

EuGd

TbDy

HoEr

TmYb

Lu

Sam

ple/

Cho

ndrit

e

diorite

granodiorite

granite

Fig. 6. Chondrite-normalized (Sun and McDonough, 1989) REE patternsfor the rocks of Kichy-Natyn and Djetim intrusions.

136 D. Konopelko et al. / Journal of Asian Earth Sciences 32 (2008) 131–141

Author's personal copy

other two samples 413100 and 413101 (N 41� 40.948, E 76�37.692) represent two separate elongate diorite pebbles thatwere collected approximately 1 km south of the Kichy-Naryn intrusion from a conglomerate layer in the Djetim-tau volcanic suite consisting of tuffs and tuffo-conglomer-ates basic to intermediate in composition (Zhukov, 1961).The Djetimtau suite was considered as Upper Riphean(Osmonbetov et al., 1982) or Lower–Middle Cambrian(Zhukov, 1961) in age. The conglomerate layer is the onlyone that exhibits abundant diorite pebbles in tuffaceousmatrix. The thickness of this conglomerate layer is about10 m, the amount of diorite pebbles approximately 10%and their sizes vary from 10 to 40 cm (Fig. 7). The dioritein the pebbles is deformed and probably represents theearly episode of I-type magmatism related to collision ofthe mature arc with the Northern Tien Shan (Fig. 2). Thewhole volcanic unit is crosscut by the Kichy-Naryn intru-sion with baked contact.

5.2. Analytical procedure

Selected zircon grains were hand picked up andmounted in epoxy resin together with chips of theTEMORA standard zircons with an accepted age of416.75 Ma (Black and Kamo, 2003). The grains were sec-

tioned approximately in half and polished. Prior to analy-sis, the zircons were investigated in transmitted andreflected light and under a scanning electron microscopeequipped with cathodoluminescence (CL) and back-scat-tered electron units. The U–Th–Pb isotope analyses weremade using the SHRIMP-II ion-microprobe in the Centerof Isotopic Research, VSEGEI, St. Petersburg, Russia.Each analysis consisted of four scans through the massrange. The diameter of spot was about 20 lm, and primarybeam intensity was about 4 nA. The data have beenreduced in a manner similar to that described by (Williams,1998 and references therein), using the SQUID ExcelMacro of Ludwig (2000). The Pb/U ratios were normalizedrelative to a value of 0.0668 for the 206Pb/238U ratio of theTEMORA reference zircons (Black and Kamo, 2003). Cor-rections for common Pb were made using 204Pb isotope(f206%, where f206 denotes common 206Pb/total measured206Pb). The present day terrestrial average Pb-isotopiccomposition (Stacey and Kramers, 1975) was used for cor-rections for common Pb. Uncertainties given for individualanalyses in Table 3 (ratios and ages) are at the one r levelhowever the uncertainties in calculated concordia ages(Fig. 8a–c) are reported at two r level. The concordia plots(Tera and Wasserburg, 1974) have been constructed usingISOPLOT/EX macro (Ludwig, 1999).

5.3. Results

Zircon grains recovered from sample 412200 representprismatic, slightly elongate grains with distinct facets. Theyvary in size from 100 to 250 lm with length/width ratiosfrom 2 to 5. The zircons are transparent or yellowish intransmitted light without inherited cores. On BSE andCL images the zircon grains are homogeneous with intenseoscillatory magmatic zoning more characteristic for outerparts of the grains. Five spots were analysed in five grainscovering both outer and inner parts of the grains. All dataplot on concordia (Fig. 8a). If one outlying analysis withyounger age of 416 Ma is excluded from calculation, theremaining four analyses yield a 206Pb/238U concordia ageof 435 ± 3 Ma (MSWD 0.046).

Zircon grains recovered from sample 412600 are similarto those described in sample 412200. However they are moreintensely elongated with length/width ratios up to 8–10 andshow more pronounced oscillatory zoning. Nine spots wereanalysed in six grains covering both outer and inner partsof the grains. All data plot on concordia (Fig. 8b) and yielda 206Pb/238U concordia age of 437 ± 3 Ma (MSWD 0.077)which within error limits corresponds to the age obtainedfor sample 412200. If data from samples 412600 and412200 are calculated together they yield a 206Pb/238U con-cordia age of 436 ± 2 Ma (MSWD 0.13) which is consideredas the preferred crystallisation age of the Kichy-Narynintrusion.

Zircon grains recovered from pebble samples 413100and 413101 are similar and comprise large (200–500 lm)stubby grains almost without elongation with poorly devel-

Fig. 7. Volcanic rocks in the contact zone of the Kichy-Naryn intrusion:(a) tuffo-conglomerate and (b) conglomerate layer with dioritic pebbles intuffaceous matrix.

D. Konopelko et al. / Journal of Asian Earth Sciences 32 (2008) 131–141 137

Author's personal copy

oped prismatic facets. However well pronounced oscilla-tory and sector zoning indicates their magmatic origin.Because rocks of two pebbles and zircon grains recoveredfrom them are similar, they were considered as one sample.In particular two spots were analysed in two grains fromsample 413100 and three spots in three grains in sample413101. All five analyses plot on concordia (Fig. 8c) as atight cluster and yield a 206Pb/238U concordia age of466 ± 10 Ma.

Thus two compositional varieties of the Kichy-Narynintrusion yielded early Silurian crystallisation ages of436 Ma. Diorite from pebbles in the conglomerate sampledclose to the contact of the intrusion yielded a significantlyolder early Ordovician crystallisation age of 466 Ma.

6. Discussion

6.1. Geodynamic implications

The rocks of the two intrusions analysed in this studyform calc-alkaline series (Fig. 5a). The rocks evolve frommeta-aluminous to peraluminous (Fig. 5b). Most sampleshave A/CNK values below 1.1 and plot in the field of I-type granites (Chappell and White, 1974). The two mostevolved granites plot marginally above A/CNK 1.1 line

in the field of S-type granites (Fig. 5b). However, Chappellet al. (1998) emphasized that fractionated I-type granitesmay be slightly peraluminous. All major rock types are rep-resented by amphibole-bearing varieties and both intru-sions contain dioritic and gabbroic rocks. Thus,geological and geochemical features of the rock assemblageunder study well match the characteristics of I-type graniteseries (Chappell and White, 1974; Chappell et al., 1998;Pearce, 1996). Rocks of the two intrusions are similarand form a continuous geochemical trend indicating an ori-gin from a similar source and by similar differentiation pro-cess. These conclusions may be extrapolated for the wholemagmatic arc where similarity of the rock types over largeareas was emphasised by several authors who distinguisheda number of regionally developed granite complexes(Osmonbetov et al., 1982; Ghes, 2006).

The obtained ages of 466 and 435 Ma of the two mag-matic pulses in the Northern Tien Shan well match thepublished data. Mikolaichuk et al. (1997) reported U–Pbzircon ages of the Northern Tien Shan granites obtainedby conventional method in previous decades. The histo-gram in Fig. 9, where the data from present study and datafor Devonian intrusions from Konopelko et al. (2006) arealso included, shows the distribution of ages with twomajor peaks at ca. 435–440 and 460–470 Ma. It also shows

Table 3U–Pb analytical data and calculated ages

Samplespot #a

Concentrations Isotope ratiosc Age (Ma)

U(ppm)

Th(ppm)

Th/U

206Pbf(ppm) f206b

(%)

207Pb/206Pbf ±1r(%)

207Pb/235Uf ±1r(%)

206Pb/238Uf ±1r(%)

Err.corr.d

206Pb/238Uf ±1r(%)

Disc.e %

Sample 412200 diorite

412200.1.1 1041 905 0.90 62.8 0.54 0.0553 3.3 0.532 3.4 0.0698 0.8 0.22 435.1 3.2 �3412200.2.1 488 278 0.59 28.7 0.36 0.0557 4.3 0.524 5.4 0.0682 3.3 0.61 425.0 13 4412200.3.1 1158 635 0.57 69.3 0.26 0.0567 2.8 0.543 2.9 0.0694 0.7 0.23 432.6 2.7 11412200.4.1 1223 820 0.69 71.1 1.44 0.0563 5.8 0.518 5.9 0.0667 0.8 0.14 416.0 3.3 12412200.5.1 1309 787 0.62 79.1 0.15 0.0554 2.1 0.536 2.2 0.0703 0.7 0.31 437.8 2.9 �3

Sample 412600 granite

412600.1.1 1171 726 0.64 70.0 0.16 0.0558 2.7 0.535 2.8 0.0694 0.7 0.27 432.7 3.1 3412600.1.2 1096 605 0.57 65.1 0.25 0.055 2.6 0.523 3.4 0.069 2.1 0.63 430.0 8.8 �4412600.2.1 884 398 0.47 54.5 0.54 0.0562 4.5 0.552 4.6 0.0713 0.8 0.18 444.1 3.6 3412600.2.2 1056 461 0.45 63.8 0.53 0.0574 3.6 0.554 4.2 0.0699 2.1 0.51 435.8 9.0 16412600.3.1 638 361 0.58 39.5 2.58 0.0577 11 0.559 11 0.0702 1.2 0.11 437.5 5.0 19412600.3.2 1106 595 0.56 65.4 0.87 0.0594 4.6 0.559 5.0 0.0682 2.2 0.43 425.4 9.0 37412600.4.1 100 40 0.42 5.9 2.36 0.0510 23 0.480 24 0.0676 2.6 0.11 422.0 10 �38412600.5.1 841 357 0.44 51.6 0.72 0.0544 4.4 0.532 4.4 0.0709 0.8 0.17 441.5 3.2 �12412600.6.1 362 266 0.76 21.5 0.48 0.0538 5.2 0.511 5.4 0.0688 1.3 0.23 429.1 5.2 �15

Samples 413100 and 413101 diorite pebbles

413100.1.1 103 53 0.53 6.41 0.17 0.0607 5.3 0.607 6.0 0.0725 2.7 0.46 451.0 12 39413100.3.1 194 67 0.36 12.6 1.20 0.053 10 0.548 10 0.075 2.5 0.24 466.0 11 �30413101.2.1 226 85 0.39 14.4 0.47 0.0586 5.0 0.594 5.6 0.0735 2.5 0.44 457.0 11 20413101.3.1 200 98 0.51 13.3 0.73 0.0509 7.9 0.539 8.3 0.0768 2.5 0.30 477.0 11 �51413101.4.1 155 79 0.53 10.3 0.55 0.0537 6.4 0.568 6.8 0.0767 2.5 0.37 477.0 12 �25

a The last two digits denote number of grain and number of analytical spot within the grain.b f206 denotes 100 * (common 206Pb)/(total measured 206Pb).c Corrected for 204Pb.d Error correlation 207Pb/235U � 206Pb/238U.e Disc. % denotes 100 * ((1 � (age 206Pb/238U)/(age 207Pb/206Pb)).f Radiogenic Pb.

138 D. Konopelko et al. / Journal of Asian Earth Sciences 32 (2008) 131–141

Author's personal copy

that production of granites was not discrete and continuedfrom the Cambrian to the Silurian. The Early Devonianepisode however is discrete and probably corresponds toa different geodynamic environment (Konopelko et al.,2006). The age of 466 Ma obtained for pebbles from a con-

glomerate layer shows that the early magmatic pulse wasfollowed by a rapid uplift and erosion of granites. It alsoshows that a number of undivided volcanic units shownon maps as Riphean or Cambrian may be of Early Ordovi-cian–Early Silurian age.

The amount of granites in the Northern Tien Shan,shown in Fig. 2, their prolonged history of formationand pronounced I-type geochemical characteristics are evi-dence in favour of their formation in an Andino-type activemargin environment.

The geodynamic reconstruction of Caledonian historyof the Northern Tien Shan presented by Mikolaichuk

Samples 413101 & 413100diorite pebbles

Sample 412200 - diorite

Sample 412600 - granite

500 480480 460 440 420

470 450 430 410

0.01

0.03

0.05

0.07

0.09

13.0 13.4 13.8 14.2 14.6 15.0 15.4 15.8238U/ 206Pb

207 Pb206 Pb

Concordia Age = 435.0 ±3.4 Ma(2σ, decay-const. errs included)

MSWD (of concordance)=0.046,Probability (of concordance)=0.83

238

238

U/

U/

206

206

Pb

Pb

207Pb206 Pb

0.03

0.05

0.07

0.09

0.01

0.03

0.05

0.07

0.09

0.03

0.05

0.07

0.09

13.0

13.012.0 14.0 15.0

13.4 13.8 14.2 14.6 15.0 15.4 15.8

470 450 430 410

Concordia Age = 437.0 ±3.2 Ma(2σ , decay-const. errs included)

MSWD (ofc oncordance)= 0.077,Probability( of concordance) =0.78

Concordia Age = 466 ±10 Ma(2σ, decay-const. errs included)

MSWD (of concordance) = 0.000,Probability (of concordance) = 0.999

207Pb206Pb

0.01

0.03

0.05

0.07

0.09

Fig. 8. Concordia diagrams for zircon U–Pb SHRIMP data of the Kichy-Naryn intrusion.

Age, Ma

N=56

Num

ber o

f sam

ples

0

2

4

6

8

10

12

14

360 400 440 480 520 560

Fig. 9. Histogram showing distribution of ages of Caledonian granites inthe Northern Tien Shan. Data from Mikolaichuk et al. (1997) and Kiselev(1999). Data from this study and an early Devonian age from Konopelkoet al. (2006) are included.

Riphean - Cambrian: opening of the ocean

Since Cambrian: subduction to the north

Early Silurian: cessation of subduction and docking of Middle Tien Shan,second granitoid pulse

S N

Early-Middle Ordovician: first granitoid pulse

Fig. 10. A model for Cambro-Silurian geodynamic evolution of theNorthern and Middle Tien Shan terranes.

D. Konopelko et al. / Journal of Asian Earth Sciences 32 (2008) 131–141 139

Author's personal copy

et al. (1997) and shown in Fig. 10 can now be discussed tak-ing into consideration new geochronological and geochem-ical data. In general, production of I-type granites fromCambrian to Early Silurian indicates continuous subduc-tion to the north (present day coordinates) under an activemargin with Precambrian basement. The geodynamic causeof the early 470 Ma magmatic pulse is not clear. FollowingGhes (2006) it is tentatively considered as a result of colli-sion with a mature island arc. However due to low degreeof preservation of Caledonian formations such an arc maybe hardly recognized in the field and on regional maps.Subduction of a spreading centre or another geodynamicmechanism may as well apply for the origin of the earlymagmatic episode at 470 Ma.

The latest magmatic episode dated at 435 Ma is believedto be a result of the closure of the Paleo-Asian ocean andfinal collision of the Middle and Northern Tien Shan terr-anes (Ghes, 1999, 2006). However geological and geochem-ical data do not fully comply with the post-collisionalorigin of the Early Silurian granites. First, the Early Silu-rian magmatism is restricted to the Northern Tien Shanterrane and it did not affect the Middle Tien Shan as mightbe expected for post-collisional granites and as is character-istic for Hercynian post-collisional magmatic complexes inthe same region (Konopelko et al., 2006). Secondly, thegeochemical characteristics of the Early Silurian granitesstill point to a subduction-related origin (Fig. 5c and d)and no typical collision-related S-granites or other post-collisional rock types (e.g. shoshonitic rocks) are knownin the region. Third, the sedimentary records of the Middleand Northern Tien Shan terranes still differ up to the LatePaleozoic time (Lomize et al., 1997; Biske, 2001). A possi-ble scenario explaining all these features involves cessationof subduction without major frontal collision and gentledocking of the Middle Tien Shan passive margin to thepresent day north with subsequent position of the MiddleTien Shan as a depressed shelf of the Paleo-Kazakhstanwhich explains the difference in Lower Carboniferous sed-iments: marine in the Middle and terrestrial in the North-ern Tien Shan (Biske, 2001). An example of such scenariowas reported for the Paleoproterozoic Ketilidian orogenin Greenland where cessation of subduction was proposedto explain its geodynamic evolution (Garde et al., 2002).

6.2. Metallogenic aspect

The Caledonian magmatic arc of Kazakhstan hosts anumber of volcanogenic massive sulfide, porphyry andgranitoid-related Cu, Au, Cu–Au and Cu–Au–Zn deposits(Yakubchuk et al., 2005) while, in contrast, in Kyrgyzstanthere are only very few known ore deposits of Early Paleo-zoic age. Among those are the Taldybulak–Andash groupof copper–gold porphyry deposits hosted by Ordoviciangranites and the Jerooy orogenic gold deposit emplacedin Ordovician granitoid rocks (Seltmann and Porter, 2005).

That the Kyrgyz magmatic arc is less mineralized thanits extension into Kazakhstan has pendants in other large

and generally barren Andean-type magmatic arcs. Anexample of such mostly ‘‘barren’’ arc is represented bythe Transscandinavian Igneous Belt or TIB (Hogdahlet al., 2004 and references therein). The other example isthe Ketilidian orogen in Greenland (Garde et al., 2002).It is suggested that the mineral potential of a terrane is con-trolled, among other factors, by the degree of preservationof ore deposits (e.g. Groves et al., 2005). We here followthis opinion and suggest that the Caledonian arc inKyrgyzstan was eroded deeper than that in northernKazakhstan. As the known deposits are situated exclu-sively in the westernmost part of the Kyrgyz magmaticarc, we conclude that the eastern part of the arc was erodeddeeper. The eroded deposits might have been recycled andlater contributed to extensive Hercynian mineralizationemplaced in the same area in two pulses: early Devonianand early Permian.

7. Conclusions

Geological and geochemical features of the Kichy-Naryn and Djetim intrusions demonstrate characteristicsof I-type granite series. Rocks of the two intrusions aresimilar and form a continuous high-K calc-alkaline series.

Thus two compositional varieties of the Kichy-Narynintrusion yielded early Silurian crystallisation ages of436 Ma. Diorite from pebbles in the conglomerate sampledclose to the contact of the Kichy-Naryn intrusion yielded asignificantly older early Ordovician crystallisation age of466 Ma.

The ages of various rock types within a single intrusioncoincide within error limits and the regional maps, whichoften show variations of ages within the same intrusionfrom Cambrian to Silurian, should be corrected.

The obtained ages of 466 and 436 Ma well match ages oftwo major regional magmatic pulses at ca. 435–440 and460–470 Ma which took place during continuous produc-tion of granites from Cambrian to Silurian.

The amount of granites in the Northern Tien Shan, theirprolonged history of formation and pronounced I-typegeochemical characteristics are evidence in favour of theirformation in an Andean-type active margin environment.

Acknowledgements

We are greatly indebted to Alexander Neyevin and histeam for their generous support in the field in remotemountain areas. Cooperation and discussions with MikhailGhes significantly improved our understanding of the Cal-edonian history of Tien Shan. We are grateful to SergeyPetrov for assistance in zircon separation. We appreciateinspiring discussions with Krister Sundblad and AdamGarde. Chris Halls and Chris J. Stanley reviewed and com-mented an early draft of the manuscript. David Hustonand Franco Pirajno are thanked for their reviews and help-ful comments which greatly improved the paper. D.K.appreciates the support through the Natural History Mu-

140 D. Konopelko et al. / Journal of Asian Earth Sciences 32 (2008) 131–141

Author's personal copy

seum, London where part of the study was carried out inthe frame of Research Fellowships at the Centre for Rus-sian and Central EurAsian Mineral Studies (CERCAMS).This is a contribution to the project IGCP-473 ‘‘GIS Met-allogeny of Central Asia’’.

References

Biske, Yu.S., 2001. Paleogeodynamics of the Turkestan ocean. II.Reconstruction of the Late Paleozoic. Vestnik Sankt PeterburgskogoUniversiteta 7 (2), 3–16 (in Russian).

Black, L.P., Kamo, S.L., 2003. TEMORA 1: a new zircon standard for U–Pb geochronology. Chemical Geology 200, 155–170.

Chappell, B.J., White, A.J.R., 1974. Two contrasting granite types. PacificGeology 8, 173–174.

Chappell, B.J., Bryant, C.J., Wyborn, D., White, A.J.R., Williams, I.S.,1998. Resource Geology 46 (4), 225–235.

Garde, A.A., Hamilton, M.A., Chadwick, B., Grocott, J., McCaffrey,K.J.W., 2002. The Ketilidian orogen of South Greenland: geochro-nology, tectonics, magmatism, and fore-arc accretion during Palaeo-proterozoic oblique convergence. Canadian Journal of Earth Sciences157, 765–793.

Ghes, M.D., 1999. Magmatism and geodynamic evolution of theCaledonian orogen of Tien Shan. IzvestiaNAN Kyrgyskoy Respubliki,Bishkek, Ilim, pp. 33–42 (in Russian).

Ghes, M.D., 2006. Terrane structure and geodynamic evolution of theTien Shan Caledonides. Extended abstract of doctoral dissertation,Bishkek, 48 pp (in Russian, unpublished).

Groves, D.I., Condie, K.C., Goldfarb, R.J., Hronsky, J.M.A., Vielreicher,R.M., 2005. Secular changes in Global Tectonic Processes and TheirInfluence on the Temporal Distribution of Gold-Bearing MineralDeposits. 100th Anniversary Volume of Economic Geology, pp. 1035–1068.

Hogdahl, K., Andersson, U., B., Eklund, O. (Eds.), 2004. The Transscan-dinavian Igneous Belt (TIB) in Sweden: a review of its character andevolution. Geological Survey of Finland, Special Paper 37, 123 pp.

Irvine, T.N., Baragar, W.R.A., 1971. A guide to chemical classification ofthe common volcanic rocks. Canadian Journal of Earth Sciences 8,523–548.

Kiselev, V.V. 1999. Uranium-lead (zircon) geochronology of magmaticformations of the Northern Tien Shan. Izvestia NAN KyrgyskoyRespubliki, Bishkek, Ilim, pp. 21–33 (in Russian).

Konopelko, D., Seltmann, R., Biske, G., Matukov, D., Sergeev, S., 2006.Hercynian magmatism in the Tien Shan: new SHRIMP ages andmetallogenic implications. In: Proceedings of the IGCP-486 andIGCP-473 Joint Workshop on Porphyry and Epithermal Deposits ofthe Chatkal-Kurama Region, 22–30 April 2006, Tashkent, pp. 29–35.

Lomize, M.G., Demina, L.I., Zarshchikov, A.A., 1997. The Kyrgyz-Terskei Paleoceanic Basin, Tien Shan. Geodynamics 6, 35–55, Englishtransl. by MAIK Nauka/Interperiodica. N.

Ludwig, K.R., 1999. User’s manual for Isoplot/Ex, Version 2.10, Ageochronological toolkit for Microsoft Excel. Berkeley GeochronologyCenter Special Publication No. 1a, 2455 Ridge Road, Berkeley CA94709, USA.

Ludwig, K.R., 2000. SQUID 1.00, A User’s Manual; Berkeley Geochro-nology Center Special Publication. No.2, 2455 Ridge Road, Berkeley,CA 94709, USA.

Middlemost, E.A.K., 1994. Naming materials in the magma/igneous rocksystem. Earth-Science Reviews 37, 215–224.

Mikolaichuk, A.V., Kurenkov, S.A., Degtyarev, K.E., Rubtsov, V.I.,1997. Northern Tien Shan main stages of geodynamic evolution in theLate Precambrian–Early Paleozoic. Geodynamics 6, 16–34, Englishtransl. by MAIK ‘‘Nauka/Interperiodica. N..

Osmonbetov, K.O., Knauf, V.I., et al. (Eds.), 1982. Stratified and intrusiveformations of Kyrgyzia, vols. 1 and 2, Ilim Publishing House, Frunze,Kyrgyz SSR.

Pearce, J., 1996. Sources and settings of granitic rocks. Episodes 19 (4),120–125.

Pearce, J.A., Harris, N.B.W., Tindle, A.G., 1984. Trace element discrim-ination diagrams for the tectonic interpretation of the granitic rocks.Journal of Petrology 25, 956–983.

Seltmann, R., Porter, M., 2005. The porphyry Cu–Au/Mo deposits ofcentral Eurasia: 1. Tectonic, geologic & metallogenic setting andsignificant deposits. In: Porter, T.M. (Ed.), Super Porphyry Copper &Gold Deposits: A Global Perspective, vol. 2. PGC Publishing,Adelaide, pp. 467–512.

Sengor, A.M.C., Natal’in, B.A., 1996. Turkic-type orogeny and its role inthe making of the continental crust. Annual Reviews of Earth andPlanetary Sciences 24, 263–337.

Sengor, A.M.C., Natal’in, B.A., Burtman, V.S., 1993. Evolution of theAltaid tectonic collage and Palaeozoic crustal growth in Eurasia.Nature 364, 299–307.

Stacey, J.S., Kramers, J.D., 1975. Approximation of terrestrial leadisotopic evolution by two-stage model. Earth and Planetary ScienceLetters 26, 207–221.

Sun, S.S., McDonough, W.F., 1989. Chemical and isotopic systematics ofoceanic basalts: implications for mantle composition and processes. In:Saunders, A.D., Norry, M.J. (Eds.), Magmatism in the Ocean Basins,vol. 42. Geological Society, Special Publications, London, pp. 313–345.

Tera, F., Wasserburg, G., 1974. U–Th–Pb systematics on lunar rocks andinferences about lunar evolution and age of the Moon. In: Proceedingsof the Fifth Lunar Scientific Conference. Geochimica et CosmochimicaActa Supplement 5 (2), 1571–1599.

Williams, I.S., 1998. U–Th–Pb geochronology by ion microprobe. In:McKibben, M.A., Shanks, W.C. III, Ridley, W.I. (Eds.), Applicationsof Microanalytical Techniques to Understanding Mineralizing Pro-cesses. Reviews in Economic Geology 7, 1–35.

Yakubchuk, A., 2004. Architecture and mineral deposit settings of theAltaid orogenic collage: a revised model. Journal of Asian EarthSciences 23, 761–779.

Yakubchuk, A., Seltmann, R., Shatov, V., 2003. Tectonics and metallog-eny of the western part of the Altaid orogenic collage. In: Mao, J.,Goldfarb, R., Seltmann, R., Wang, D., Xiao, W., Hart, C. (Eds.),Tectonic Evolution and Metallogeny of the Chinese Altay andTianshan. International Association on the Genesis of Ore Deposits(IAGOD), London, Guidebook Series 10, 7–16.

Yakubchuk, A.S., Shatov, V.V., Kirwin, D., Edwards, A., Tomurtogoo,O., Badarch, G. Buryak, V.A., 2005, Gold and Base Metal Metallog-eny of the Central Asian Orogenic Supercollage, 100th AnniversaryVolume of Economic Geology, pp. 1035–1068.

Zen, Tan, 1986. Aluminium enrichment in silicate melts by fractionalcrystallisation: some mineralogic and petrographic constraints. Jour-nal of Petrology 27, 1095–1117.

Zhukov, Yu V., 1961. Geologicheskaya karta SSSR, 1:200 000. SeriyaSevero-Tianshanskaya, List K-43-XXIII. Leningrad, VSEGEI.

D. Konopelko et al. / Journal of Asian Earth Sciences 32 (2008) 131–141 141