Hercynian post-collisional magmatism in the context of Paleozoic magmatic evolution of the Tien Shan...

Journal of Asian Earth Sciences 42 (2011) 821–838

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Journal of Asian Earth Sciences

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Hercynian post-collisional magmatism in the context of Paleozoic magmaticevolution of the Tien Shan orogenic belt

Reimar Seltmann a,⇑, Dmitry Konopelko b, Georgy Biske b, Farid Divaev c, Sergei Sergeev d

a Center for Russian and Central EurAsian Mineral Studies, Department of Mineralogy, Natural History Museum, Cromwell Road, London SW7 5BD, UKb Geological Faculty, St. Petersburg State University, 7/9 University Embankment, St. Petersburg 199034, Russiac Department of Regional Geology and Metallogeny, Institute of Mineral Resources, 11a Shevchenko Street, Tashkent, Uzbekistand Center of Isotopic Research, Russian Geological Research Institute (VSEGEI), 74 Sredny Pr., St. Petersburg 199106, Russia

a r t i c l e i n f o

Article history:Available online 19 September 2010

Keywords:Tien ShanLate PaleozoicPost-collisional magmatismGranitoidsShrimp geochronologyGeodynamic evolution

1367-9120/$ - see front matter Crown Copyright � 2doi:10.1016/j.jseaes.2010.08.016

⇑ Corresponding author. Tel.: +44 207942 5042; faxE-mail address: [email protected] (R. Seltma

a b s t r a c t

The Hercynian Tien Shan (Tianshan) orogen formed during Late Palaeozoic collision between theKarakum–Tarim and the Kazakhstan paleo-continents. In order to constrain timing of Hercynian post-collisional magmatism, 27 intrusions were sampled for U–Pb zircon dating along a ca. 2000 km – longprofile in Uzbekistan and Kyrgyzstan. The samples were dated utilizing sensitive high resolution ionmicroprobe (SHRIMP-II). The obtained ages, together with previously published age data, allowed thetiming of Hercynian post-collisional magmatism to be constrained and interpreted in the context ofthe Paleozoic magmatic evolution of the region. Apart from Hercynian post-collisional magmatism,two older magmatic episodes have been recognized, and the following sequence of events has beenestablished: (1) approximately 10 Ma after cessation of continuous Caledonian magmatism a numberof Late Silurian–Early Devonian intrusions were emplaced in the Middle and Northern Tien Shan terranesbetween 420 and 390 Ma. The intrusions probably formed in an extensional back arc setting during coe-val subduction under the margins of Caledonian Paleo-Kazakhstan continent; (2) the next relatively shortLate Carboniferous episode of subduction under Paleo-Kazakhstan was registered in the Kurama range ofthe Middle Tien Shan. Calc-alkaline volcanics and granitoids with ages 315–300 Ma have distinct metall-ogenic affinities typical for subduction-related rocks and are not found anywhere outside the Middle TienShan terrane west of the Talas–Farghona fault; (3) the Early Permian Hercynian post-collisional magma-tism culminated after the closure of the Paleo-Turkestan ocean and affected the whole region acrossterrane boundaries. The post-collisional intrusions formed within a relatively short time span between295 and 280 Ma. The model for Hercynian post-collisional evolution suggests that after collision the TienShan was affected by trans-crustal strike-slip motions which provided suitable conduits for ascendingasthenospheric material and heat influx in the crust. This produced both granitoid magmas and hydro-thermal fluid flow. As a result post-collisional intrusions and orogenic Au deposits, known in the region,formed coevally and were tectonically controlled; (4) between 240 and 220 Ma a Triassic thermal eventaffected the region resulting in resetting and growth of new zircon grains which is detected on a regionalscale. Probably the influx of heat into the crust during the Triassic was tectonically focused and variedsignificantly in different terranes. In the region under investigation the Triassic thermal event was notaccompanied by any significant magmatic activity. Thus, after cessation of Hercynian post-collisionalmagmatism ca. 280 Ma ago there was a long magmatically quiet period in the Tien Shan.

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1. Introduction

A post-collisional geodynamic setting represents a particularstage of the global tectonic cycle, characterized by large scale hori-zontal movements of terranes and by voluminous, mainly potassicmagmatism (e.g. Liégeois et al., 1998 and references therein). TheHercynian Tien Shan accretionary orogen in Central Asia presents

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an example where post-collisional tectonics and magmatism areclosely associated with large orogenic Au deposits making thisregion the richest gold province of Eurasia (Yakubchuk et al.,2002). The timing of the strike-slip motions and Au mineralizationin the Tien Shan was recently defined in a series of publications(Laurent-Charvet et al., 2003; Mao et al., 2004; Morelli et al.,2007). However, the timing of post-collisional magmatism, andspacial and temporal relationships between subduction-relatedand post-collisional magmatism and between post-collisionalmagmatism and Au mineralization in the Hercynian Tien Shan are

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822 R. Seltmann et al. / Journal of Asian Earth Sciences 42 (2011) 821–838

still poorly understood. Here we present sensitive high resolutionion microprobe (SHRIMP) U–Pb zircon ages for 27 granitoid andalkaline intrusions sampled along a ca. 2000 km – long profile fromAral Sea in Uzbekistan to Han-Tengry – Pobeda Peak in Kyrgyzstan(Fig. 1). Most sampled intrusions represent important tectonic indi-cators and/or are associated with major ore deposits. Recently pub-lished ion-probe U–Pb zircon ages for another 15 intrusions fromthe area are added to the dataset. The data obtained provide agesfor several important mineralized systems, development of regio-nal shear zones and extensional regimes, and allow us to constraintiming of the post-collisional magmatism and to propose a tectonicmodel for the post-collisional stage. Finally, using a broader datasetfor Paleozoic intrusions we compare Hercynian and Caledonianmagmatism, and discuss other magmatic episodes and the generaltectonic evolution of the Tien Shan belt in former USSR. Voluminousage data for magmatic rocks in the Chinese Tien Shan are out of thescope of this paper. A synthesis involving the data for the ChineseTien Shan and comparison of various tectonic subdivisions foundin the literature will be a focus of a separate future work.

2. Geology of the Tien Shan orogenic belt

The Hercynian Tien Shan orogen formed during Late Palaeozoiccollision between the Karakum–Tarim continent and the Paleo-Kazakhstan continent, a Caledonian component of the Altaid Col-lage (Zonenshain et al., 1990; S�engör et al., 1993). The western partof the Tien Shan in Kazakhstan, Kyrgyzstan, Tajikistan and Uzbeki-stan is composed of three major structural units or terranes(Fig. 1): (1) the Northern Tien Shan, the deformed margin of thePaleo-Kazakhstan continent; (2) the Middle Tien Shan, a LatePaleozoic volcano-plutonic arc; and (3) the Southern Tien Shan,an intensely deformed fold and thrust belt formed during the finalclosure of the Paleo-Turkestan ocean (Zonenshain et al., 1990). InChinese territory, the Borohoro arc and Paleo-Kazakhstan terranesbordering the Northern Tien Shan, are also considered as parts ofthe Tien Shan orogen (e.g. Chen et al., 1999; Zhou et al., 2001).These terranes are shown in Fig. 1 as the North-East Tien Shan.

The Northern Tien Shan in Kyrgyzstan is represented by theEarly Palaeozoic continental arc and its Precambrian basementformed as a result of progressive subduction to the north (present

Fig. 1. Principal terranes and tectonic lineaments of the Tien Shan, and distribution of Hintrusions (1–42) correspond to running numbers in Table 1. Muruntau dike, Nr. 7, has a T– North-Eastern Tien Shan, MTS – Middle Tien Shan, STS – Southern Tien Shan, NL – Nik

day coordinates) and subsequent closure of the Terskey ocean inthe Late Ordovician and accretion of the Middle Tien Shan tothe Northern Tien Shan (Lomize et al., 1997; Ghes, 2008). InKyrgyzstan, the Northern and Middle Tien Shan are separated bythe Nikolaev Line, a Hercynian strike-slip fault generally following aCaledonian suture. The oldest ophiolites in the Northern Tien Shanhave Cambrian ages (Lomize et al., 1997; Mikolaichuk et al., 1997)and are coeval with primitive sodic tonalites. Further developmentof the Northern Tien Shan arc is documented by continuousAndean type magmatism which created voluminous subduction-related Ordovician and post-collisional Early Silurian granitoids(Konopelko et al., 2008 and references therein). The main compo-nent of the Middle Tien Shan is the Beltau-Kurama volcano-plutonic belt developed west of the Talas–Farghona fault. This beltis a complex structure consisting of Late Carboniferous volcano-plutonic arc rocks which unconformably overlay and crosscut sim-ilar arc-related Silurian–Early Devonian arc series. All these rockswere probably formed on a Caledonian and/or Precambrian base-ment as a result of northward subduction during the evolutionand closure of the Paleo-Turkestan ocean to the south (presentday coordinates). The subduction-related series in the Kuramaand Chatkal ranges west of the Talas–Farghona fault form two dis-crete short lived associations of Silurian–Early Devonian and LateCarboniferous ages. East of the Talas–Farghona fault the subduc-tion was amagmatic or its evidence was eroded or hidden underthe cover of younger rocks (Alekseev et al., 2009). The Beltau-Kurama belt is usually considered as a southern active continentalmargin of the Palaeo-Kazakhstan (e.g. Shayakubov and Dalimov,1998). The Southern Tien Shan includes intensely deformed fore-arc accretionary complexes together with passive margin sedi-ments of the Karakum–Tarim continent. The Middle and SouthernTien Shan terranes are separated by the Southern Tien Shan Suturedefined by ophiolites with ages ranging from the Early Ordovicianto Early Carboniferous (Kurenkov and Aristov, 1995; Gao et al.,1998; Chen et al., 1999). In Uzbekistan and Kyrgyzstan the South-ern Tien Shan is traditionally divided into three segments fromwest to east: the Kyzylkum segment, the Alay segment and theKokshaal segment (Fig. 1). Despite the similarities, the threesegments have rather different geological structures (Biske andSeltmann, 2010 and references there in). The Kyzylkum segmentis built up on a Neoproterozoic–Caledonian basement with no or

ercynian granites. Intrusions dated by ion-probe are shown out of scale. Numbers ofriassic age not shown in the legend. Abbreviations: NTS – Northern Tien Shan, NETSolaev Line, STSS – Southern Tien Shan Suture, TF – Talas–Farghona strike-slip fault.

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few Early Precambrian slices. The Alay segment probably has a Pre-cambrian continent in its basement. The Kokshaal segment is builtup on Tarim passive margin and its Precambrian basement under-thrust to the north. The sedimentary units include Silurian to Mid-dle Carboniferous pelagic, mainly deep sea sediments andintraplate volcanics of oceanic rise or passive margin type, andthick carbonate platforms, formation of which culminated in theLate Devonian–Early Carboniferous. The carbonate platforms areespecially widespread in the Alay and Kokshaal segments. Aunique feature of the Kokshaal segment is the thick pile of clasticsediments of the Tarim continental slope varying in age fromMiddle Devonian to Middle Carboniferous (Biske and Seltmann,2010). Thick Late Carboniferous–Early Permian fordeep turbiditesand molasses indicate the final closure of the Paleo-Turkestanocean and uplift. Estimations of the age of Tarim–Paleo-Kazakh-stan collision vary from Carboniferous to Early Permian, howeverin the Chinese part there are indications of a Devonian collisionalevent (cf. Windley et al., 1990; Allen et al. 1992; Chen et al.,1999; Carroll et al., 2001; Zhou et al., 2001; Gao et al., 2009; Biskeand Seltmann, 2010). The Talas–Farghona dextral strike-slip faultseparates the western terranes of the Tien Shan, the Kyzylkumand Alay segments of the Southern Tien Shan and Chatkal–Kuramaranges of the Middle Tien Shan, from the eastern terranes (Fig. 1).An eye-catching feature of the present day Tien Shan geology is anumber of major east–west striking trans-crustal strike-slip faultsdividing the Tien Shan into a series of tectonic blocks. At least someof these faults formed in the Early Permian (Laurent-Charvet et al.,2003) and controlled post-collisional magmatism and importantmineralization (e.g., Mao et al., 2004; Seltmann and Porter, 2005).

3. Outline of the Late Paleozoic magmatism

Regional distribution of the 320–270 Ma granitoid intrusions inthe Tien Shan is shown in Fig. 1. The published ages of magmaticrocks are mostly based on K–Ar and Rb–Sr isotopic systems thatare sensitive to post-magmatic processes. However, two magmaticpulses are clearly distinguished in the literature (Jenchuraeva,1997). The Middle Tien Shan west of the Talas–Farghona faultcomprises calc-alkaline intrusions and thick volcanic units of theBeltau-Kurama arc shown on the regional geological maps asMiddle-Late Carboniferous (Zhukov et al., 1965; Shayakubov,1998; Seltmann et al., 2005; Zhukov et al., 2008). This calc-alkalinemagmatism presumably indicates active subduction and predatesthe closure of the Paleo-Turkestan ocean. The metallogeny of theMiddle Tien Shan is characterized by the presence of porphyryCu–Au–Mo deposits and epithermal Au deposits typical for arc-related magmatism (Jenchuraeva, 1997; Seltmann et al., 2005).

In contrast to subduction-related calc-alkaline magmatism, spa-tially associated with the Middle Tien Shan, post-collisional mag-matism affected the whole region across terrane boundaries(Konopelko et al., 2007; De Boorder et al., 2010). On the regionalmaps the post-collisional intrusions are usually shown as LateCarboniferous–Early Permian. In the Kyzylkum and Alay segmentsthe post-collisional magmatism is voluminous and diverse incomposition while in the Kokshaal segment the post-collisionalintrusions are smaller in size and represented mostly by A-typegranites (Nenakhov et al., 1992; Ahmedov, 2000; Konopelkoet al., 2007). Outside the Southern Tien Shan the post-collisionalmagmatism comprises batholiths and thick volcanic units of theKaramazar complex in the Middle Tien Shan and small to mediumsize intrusions situated far north in the Northern Tien Shan and farsouth in the Tarim paleo-continent (Osmonbetov and Knauf, 1982;Ahmedov, 2000; Jenchuraeva, 2001). Compositionally, mostpost-collisional rocks are potassium alkali-calcic granites. How-ever, several calc-alkaline (high-potassium I-type) complexes are

known within the Southern Tien Shan or immediately north of it(Nenakhov et al., 1992; Ahmedov, 2000; Konopelko et al., 2007;Konopelko et al., 2009). Peraluminous S-type granites are rareand are known only in the Alay and Kyzykum segments of theSouthern Tien Shan (Nenakhov et al., 1992; Ahmedov, 2000). In afew cases post-collisional granitoids are associated with maficand/or silica undersaturated alkaline rocks (Ahmedov, 2000;Konopelko et al., 2007). Metallogeny of the post-collisional intru-sions is characterized by the presence of intrusion-related Audeposits, Au skarns, orogenic Au deposits and greisen-type Sn–Wdeposits (Jenchuraeva, 2001; Seltmann et al., 2005; Seltmannet al., 2010). Intrusions and pipes of silica undersaturated alkalinerocks and carbonatites are characteristic for all the three segmentsof the Southern Tien Shan and for the terranes outside theSouthern Tien Shan. On regional maps they are shown as UpperPermian or Triassic. Despite the diverse character, most of thepost-collisional intrusions are tectonically controlled and associ-ated with major tectonic lineaments.

The Devonian magmatic pulse was originally out of the scope ofthis paper. However, because of the new discoveries of Devonianintrusions and growing evidence for the regional character of thismagmatism, it is also included in the discussion. Thick EarlyDevonian volcanics form a large belt on the eastern margin ofthe Paleo-Kazakhstan orocline (Filippova et al., 2001). A part of thisbelt may be seen in the Kyrgyz range in the Kyrgyz Northern TienShan. Formation of this volcanic belt is explained by subduction tothe south (present day coordinates) under Paleo-Kazakhstan(Jenchuraeva, 2001). On the other hand, Early Devonian volcanicsof the Kurama range in the Middle Tien Shan may be a result ofcoeval northward subduction under the southern margin of thePaleo-Kazakhstan (Shayakubov and Dalimov, 1998; Filippovaet al., 2001). The data presented in this study show that a numberof granitoid intrusions inside Paleo-Kazakhstan and in the North-ern Tien Shan, in particular, were formed coevally with the twovolcanic belts described above. The intrusions host REE, base metaland other deposits, and the whole Early Devonian magmatic pulsemay have significant metallogenic importance. The Early Devonianintrusions are not shown on the regional geological maps. The sig-nificance and nature of this magmatism is discussed below.

4. Aim of the study, description of intrusions and samplingstrategy

This study was focused on Hercynian post-collisional intrusionsin the Tien Shan orogenic belt. The aim of the study was to deter-mine the timing and the distribution of post-collisional magma-tism, and to improve the understanding of the regionalgeodynamic evolution and metallogenic potential. Subduction-related intrusions were sampled for comparison. Descriptions ofintrusions and sample details are given in Table 1. Regional distri-bution of sampled intrusions is shown in Fig. 1. Post-collisionalintrusions chosen for dating were those in the Southern Tien Shanand situated as far north as possible in the Middle and NorthernTien Shan terranes. For navigation we used regional geologicalmaps (Zhukov et al., 1965; Shayakubov, 1998; Seltmann et al.,2005; Zhukov et al., 2008). The intrusions chosen for dating in-cluded important tectonic indicators and intrusions associatedwith major ore deposits. The most tectonically important intru-sions are represented by the Gatcha-Temirkobuk and Chattik com-plexes. The Gatcha S-type granite and Temirkobuk I-type complexwere emplaced in a large North Nurata range extensional structuredeveloped along the Southern Tien Shan Suture. Both complexesform a single elongate batholith and probably originate from melt-ing of different protoliths along a trans-crustal shear zone. TheChattik intrusion is a fracture filling body in which orientation of

Table 1Description of intrusions, sample details, and obtained ages.

Nr. Sample nr. Intrusion Description and significance for dating Age, Ma Comments ReferenceCoordinatesWGS-84

Rock-type Type of age,MSWD

Southern Tien Shan, Kyzylkum and Northern Nurata range, Uzbekistan1 400900 Altyntau One of the granite intrusions in the north Kyzylkum area

(Ahmedov, 2000)281 ± 2 This study

E 63.6989,N 42.1836

Granite Concordia ageMSWD = 0.34

2 406601k Karashoho pipe One of mafic alkaline pipes in Kyzylkum – indicators ofextensional regime (Golovko and Kaminsky, 2008)

No meaningful ageobtained

Xenocrysts 443 ± 2,861 ± 6 Ma

This studyE 63.5967,N 42.4281

Lamproite

3 3 Granite dyke crosscutting Karashoho lamproite pipe Puts minimum age on Karashoho pipe in Kyzylkum(Golovko and Kaminsky, 2008)

276 ± 4 Xenocrysts 314 ± 6, 512 ± 9,761 ± 14 Ma

This studyE 64.5348,N 42.4675

Concordia ageMSWD = 0.17

4 401201 Saritau Small granite intrusion hosting Mo skarn deposit(Ahmedov, 2000)


Xenocryst 436 ± 4 Ma This studyE 64.1961,N 42.1967

Leucogranite

5 MT 45 North Tamdinsky Granite intrusion in the area of Muruntau Au deposit(Ahmedov, 2000)

287.5 ± 1.4 Minimum age Kempe et al.(2004)E 64.2794,

N 41.6720Amphibole-bearing granite

6 MT 44 North Tamdinsky See previous sample 293.3 ± 2.1 Minimum age Kempe et al.(2004)E 64.2826,

N 41.6741Leucocratic granite

7 SG-10 Post-ore porphyry dyke in Muruntau open pit The only Triassic rock dated so far by U–Pb zirconmethod

236 ± 2 Hall (2007)E 64.5758,N 41.5142

Concordia age

8 400800 Dzhizlan-Chattik Fracture filling intrusion in which orientation ofmagmatic gneissosity indicates emplacement in anactive regional shear zone (Ahmedov, 2000)

293 ± 5 This studyConcordia ageMSWD = 0.5

E 65.2761,N 40.4042

Granite

9 400300 Temirkobuk Gatcha S-type granite and Temirkobuk I-type complexemplaced in a large North Nurata range extensionalstructure developed along the Southern Tien ShanSuture (Ahmedov, 2000)

287 ± 2 Inherited core 691 ± 7 MaReset grains 219 ± 2 Ma237 ± 2 Ma

This studyE 66.5369,N 40.5597

Granodiorite Concordia ageMSWD = 0.0019

10 400500 Gatcha See previous sample. Both complexes form a singleelongate batholith and probably originate from meltingof different protoliths along a trans-crustal shear zone

281 ± 1 Minimum age, inheritedcore 734 ± 5 Ma

This studyE 66.2869,N 40.6942

Two-mica S-type granite Concordia ageMSWD = 0.44

11 Ch1 Chagatai Carbonatite pipe in Kyzylkum – indicator of extensionalregime (Djuraev and Divaev, 1999)


Xenocrysts 291 ± 4, 328 ± 5,427 ± 10, 577 ± 7, 599 ± 15,681 ± 10, 827 ± 11,843 ± 9 Ma

This studyE 66.5703,N 40.2211

Carbonatite pipe

12 401700 Koshrabad Composite pluton. Main phase – rapakivi-like granite.Hosts two large intrusion-related Au deposits:Charmitan and Guzhumsay (Abzalov, 2007)

286 ± 2 This studyE 66.7728,N 40.3597


13 414600 Aktau One of the granite intrusions in south Kyzylkum area(Ahmedov, 2000)

276 ± 9 This studyE 66.4725,N 40.2828


Middle Tien Shan, Kurama range, west of Talas–Farghona fault, Uzbekistan14 406701 Kyzata Devonian monzonite (Shayakubov, 1998; Ahmedov,

2000)416 ± 9 This study

E 69.5928,N 40.7972

Monzonite Concordia ageMSWD = 0.44

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15 406501 Almalyk Multi-phase intrusion hosting Kalmakyr porphyry Cu–Mo–Au deposit (Golovanov et al., 2005; Ahmedov, 2000)

308 ± 1 This studyE 69.6902,N 40.7990

Larger monzonite body outside open pit Concordia ageMSWD = 0.043

16 414700 Almalyk See previous sample 308 ± 4 Xenocryst 402 ± 11 Ma This studyE 69.6446,N 40.8141

Altered monzonite in open pit close to porphyrystock


17 406403 Almalyk See previous sample 315 ± 1 This studyE 69.6446,N 40.8141

Granite porphyry stock in open pit Concordia ageMSWD = 0.03

18 406801 Kara-Kiya Deformed granite in Almalyk ore district, Silurian on amap (Shayakubov, 1998; Ahmedov, 2000)

317 ± 8 This studyE 69.6069,N 40.7105

Deformed granite Concordia ageMSWD = 1.03

19 406301 Akcha suite at Tangeldy sai Late Carboniferous Akcha volcanic suite hostingepithermal Au mineralization (Ahmedov, 2000)

305 ± 3 Minimum age This studyE 69.6869,N 40.6724

Acid volcanic Concordia ageMSWD = 0.0042

20 414802 Kochbulak Au deposit, open pit extrusive andesite ofNadak suite

Late Carboniferous Nadak volcanic suite hostingepithermal Au mineralization (Ahmedov, 2000)

301 ± 4 This studyE 70.1373,N 40.9426


21 415001 Sary-Cheku open pit Multi-phase intrusion hosting Sary-Cheku porphyry Cu–Mo–Au deposit (Golovanov et al., 2005; Ahmedov, 2000)


E 69.8100,N 40.7723

Ore-bearing granodiorite-porphyry

22 415000 Sary-Cheku open pit See previous sample 297 ± 3 This studyE 69.8100,N 40.7723

Post-ore granite in the upper part of the pit Concordia ageMSWD = 0.14

Middle Tien Shan, east of Talas–Farghona fault, Kyrgyzstan23 26 Small body of Kyrgysh complex, Karasu river Foliated granite body in the Talas–Farghona fault zone

(Osmonbetov and Knauf, 1982)279 ± 5 This studyConcordia ageMSWD = 0.75

E 73.1406,N 41.6214

Foliated pegmatoidal granite

24 27 Small body of Kyrgysh complex, Karasu river See previous sample 279 ± 5 This studyE 73.1355,N 41.6193

Foliated pegmatoidal granite Concordia ageMSWD = 0.47

25 320100 Makmal Granite intrusion hosting Makmal skarn-type Au deposit(Osmonbetov and Knauf, 1982)

286 ± 5 This studyE 73.9992,N 41.2000


26 NT-8 Song-Kul Large undeformed intrusion of mafic rocks and granite(Osmonbetov and Knauf, 1982).

293 ± 1 Alekseev et al.(2009)Concordia age

MSWD = 0.22E 75.4165,N 41.7384

Granite

27 416000 Terektinsky Ca. 100 km long deformed granite body north ofSouthern Tien Shan Suture (Osmonbetov and Knauf,1982)

291 ± 5 Konopelko et al.(2009)E 79.0860,

N 42.0600Deformed granite Concordia age

MSWD = 0.094

28 416705 Terektinsky See previous sample 294 ± 5 Konopelko et al.(2009)E 79.0983,

N 42.0443Diorite from mafic enclave Concordia age

MSWD = 0.63

Northern Tien Shan, Kyrgyzstan29 IK-02 Kiukmoinokski intrusion of Akkulen complex Small granite body crosscutting deformed granites of

Caledonian basement (Osmonbetov and Knauf, 1982;Glorie et al., 2010)

292 ± 5 Glorie et al. (2010)E 75.8769,N 42.3097

Granodiorite Concordia ageMSWD = 3.0

30 320000 Aktyuz Undeformed granite hosting Aktyuz REE deposit, EarlyPermian on a map (Osmonbetov and Knauf, 1982)


E 76.9347,N 42.8597

Granite

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Table 1 (continued)

Nr. Sample nr. Intrusion Description and significance for dating Age, Ma Comments ReferenceCoordinatesWGS-84

Rock-type Type of age,MSWD

31 340002 Akkulen Large composite syenite intrusion hosting U deposits(Osmonbetov and Knauf, 1982)

292 ± 1 This studyE 76.1461,N 42.2972

Megacrystic alkaline syenite Concordia ageMSWD = 0.15

Southern Tien Shan, Kokshaal range, Kyrgyzstan, China32 012-2 Surteke Composite alkaline semi-ring intrusion (Osmonbetov

and Knauf, 1982)284 ± 1 Minimum age This study

E 76.0669,N 40.9967

Alkaline gabbro Concordia ageMSWD = 0.0002

33 280701 Kok-Kiya A-type granite intrusion (Osmonbetov and Knauf, 1982) 280 ± 3 Konopelko et al.(2007)E 76.5458,

N 40.8911Granite Concordia age

MSWD = 0.084

34 280001 Mudryum A-type granite intrusion (Osmonbetov and Knauf, 1982) 281 ± 2 Konopelko et al.(2007)E 76.6042,


MSWD = 8.7

35 217001 Ulan Deformed calc-alkaline intrusion of mafic rocks andgranite (Osmonbetov and Knauf, 1982)

303 ± 3 Inherited core 9998 ± 8 Ma This studyE 77.4411,N 41.4647


36 206801 Uch-Koshkon A-type granite intrusion hosting greisen-type Sn deposit(Osmonbetov and Knauf, 1982)

279 ± 8 Konopelko et al.(2007)Concordia age

MSWD = 4.9E 78.6772,N 41.7756

Leucogranite

37 209202 Djangart A-type granite intrusion hosting Au mineralization(Osmonbetov and Knauf, 1982)

297 ± 4 Konopelko et al.(2007)E 78.7958,

N 41.6614Rapakivi granite Concordia age

MSWD = 0.69

38 215701 Ak-Shiyrak A-type granite intrusion (Osmonbetov and Knauf, 1982) 292 ± 3 This studyE 78.9297,N 41.7756

Rapakivi granite Concordia ageMSWD = 0.00027

39 416506 Tashkoro Sn-bearing evolved A-type granite intrusion(Osmonbetov and Knauf, 1982)

299 ± 4 Konopelko et al.(2009)E 79.1244,


MSWD = 0.068

40 416801 Inylchek (Lesisty) See previous sample 295 ± 4 Konopelko et al.(2009)Concordia age

MSWD = 1.05E 79.1333,N 42.0333

Granite

41 416803 Maida’adir See previous sample 289 ± 6 Konopelko et al.(2009)E 79.2802,

N 42.0985Leucogranite Concordia age

MSWD = 1.00

42 HYS73 Chinese Southern Tien Shan Post-collisional granite in Chinese Southern Tien Shan(Long et al., 2008)

285 ± 4 Long et al. (2008)Coordinates notavailable

Granite Mean age MSWD = 1.2

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magmatic gneissosity indicates emplacement in an active regionalshear zone. The intrusions associated with major ore deposits in-clude the Koshrabad and Makmal granitoid plutons (Table 1). Alka-line complexes and pipes were of particular interest beingindicators of an extensional regime. We sampled the mafic alkalineKarashoho pipe and carbonatite Chagatai pipe in the Kyzylkumsegment of the Southern Tien Shan, and Surteke and Akkulen alka-line intrusions situated in the Kokshaal segment of the SouthernTien Shan and in the Northern Tien Shan, respectively. In the Kara-shoho pipe a granite vein crosscutting the pipe rocks was also sam-pled. Subduction-related magmatic rocks were sampled forcomparison in the Kurama range of the Middle Tien Shan. In partic-ular, they included intrusions hosting major porphyry type Cu–Mo–Au deposits (Almalyk, Sary-Cheku) and regionally developedvolcanic suites hosting epithermal Au mineralization (Akcha, Na-dak). The sampling was focused on the even grained rocks of themain intrusive facies, however porphyritic rocks in the mineralizedporphyry systems were also sampled. Petrography and geochemis-try of the intrusions under study will be published separately andis not discussed in this paper.

5. Analytical procedure

Selected zircon grains were hand picked and mounted in epoxyresin together with chips of the standard zircon grains. The grainswere sectioned approximately in half and polished. Prior to analy-sis, the zircon grains were investigated in transmitted and reflectedlight and under a scanning electron microscope equipped withcathodoluminescence (CL) and back-scattered electron (BSE)detectors. The U–Th–Pb isotope analyses were made using theSHRIMP-II ion microprobe in the Center of Isotopic Research, VSE-GEI, Saint Petersburg, Russia. Each analysis consisted of four scansthrough the mass range. The diameter of spot was about 30 lm,and primary beam intensity was about 4 nA. Each fourth measure-ment was carried out on the grain of zircon standard TEMORA 1,with an accepted 206Pb/238U age of 416.75 ± 0.24 Ma (Black andKamo, 2003). The Pb/U ratios have been normalized relative to avalue of 0.0668 for the 206Pb/238U ratio of the TEMORA 1. The zir-con standard 91500, with U concentration of 81.2 ppm and an ac-cepted 206Pb/238U age of 1065 Ma (Wiedenbeck et al., 1995) wasapplied as the ‘‘U-concentration” standard. Grains of the zirconstandard 91500 measured within the same session yielded a con-cordant age of 1068 ± 7 Ma (n = 6). The data were reduced in amanner similar to that described by Williams (1998) and refer-ences therein, using the SQUID Excel Macro of Ludwig (2000). Cor-rections for common Pb were made using 204Pb isotope (measured204Pb/206Pb) and the present day terrestrial average Pb-isotopiccomposition (Stacey and Kramers, 1975). Uncertainties given forindividual analyses in Table 2 (ratios and ages) are at the 1r level,however the uncertainties in calculated concordia ages (Table 1,Figs. 2–5) are reported at 2r level. The concordia plots were con-structed using ISOPLOT/EX macro (Ludwig, 1999).

6. Geological interpretation of SHRIMP data

Precision of the ion-probe U–Pb analysis is significantly lowerthan the precision of the TIMS method. In order to estimate thereliability of our SHRIMP data we undertook several proceduresincluding external control of SHRIMP results by LA-ICP-MS andTIMS methods, blind dating of duplicate samples and of the samerock types from individual intrusions, and double dating of criticalsamples in various analytical sessions. These procedures showedexcellent reproducibility of SHRIMP-II facility in CIR VSEGEI, anda good match of SHRIMP, LA-ICP-MS and TIMS ages. However cer-tain limitations of the SHRIMP method have been revealed. In par-

ticular, magmatic episodes which are closely associated in time areoften documented in the zoned magmatic zircon grains, where thedifference in ages between rims and cores of the grains may varyfrom 10 to 15 Ma. This difference in ages can be distinguished bythe LA-ICP-MS method, but cannot be statistically proved bySHRIMP analysis. Such a prolonged magmatic history of zircongrains, as well as Pb loss and/or U enrichment of zircon in thecourse of partial thermal resetting, recrystallization and alterationoften results in a wide cluster of analyses spread along concordiafor 20–30 Ma, and in the presence of older and younger outliers.The common practice in such cases is to exclude the outliers fromcalculations and to use a tight cluster of the oldest data for which a‘‘concordia” age can be calculated. For such cases a notion of ‘‘min-imum” age is usually applied with the understanding that the realage may be somewhat older. In contrast, when a homogeneouspopulation of magmatic zircon grains is analyzed, and a tight clus-ter of concordant data is obtained, the calculated concordia age isusually referred to as a ‘‘crystallization” age. We understand thatsome of the calculated ‘‘concordia” ages presented in Table 1may be, in fact, ‘‘minimum” ages, and that ‘‘crystallization” agesof the corresponding samples may be slightly older. We also admitthat errors of the calculated SHRIMP ages may be underestimated.This makes it difficult to distinguish between magmatic eventsthat are closely associated in time; and the difference betweentwo similar ages (even when outside 2r error limits) may haveno geological significance. Another important instrumental limita-tion of the SHRIMP dating is analysis of high uranium zircon grainswhich may cause instrumental problems. Finally the interpretationof highly discordant and reverse discordant analyses is an addi-tional problem. However, because highly discordant data are notincluded in the dataset presented here, it is not discussed in thispaper. Despite the limitations discussed above, we believe thatthe data presented in this work provide reliable geochronologicalconstraints and allow effectively to distinguish between differentmagmatic episodes, especially on a regional scale. This is supportedby the fact that similar ages were obtained for individual intrusionsof each magmatic pulse indicating that the data are internally con-sistent (given that our sampling was not biased and the resultswere not predetermined).

An important application of in situ analysis is to distinguish be-tween growth zones with different ages in the same crystal, andthe study of inherited cores and zircon xenocrysts was given a spe-cial emphasis in this paper. The inherited cores and xenocrysts car-ry information about the rocks at depth which is important for theSouthern Tien Shan where basement outcrops are scarce or absent.CL images of an inherited core in a zircon grain and of a typical zir-con xenocryst are shown in Fig. 6a and b. Finally, thermal resetting,recrystallization and growth of new zircon may also registerimportant tectonic and metamorphic events. In this study a regio-nal Triassic thermal event, that caused resetting and growth of newzircon detectable on a regional scale, was established. A CL imageof a zircon grain with a Triassic age is shown in Fig. 6c.

7. Results and discussion

7.1. New facts about Hercynian post-collisional magmatism:geodynamic and metallogenic implications

As seen from Table 1 and in Figs. 7–9, Hercynian post-collisionalintrusions in and outside the Southern Tien Shan terrane were em-placed within a relatively narrow time span between 295 and280 Ma. Ages of syn-tectonically emplaced intrusions (this study,Konopelko et al., 2009) and direct dating (Laurent-Charvet et al.,2003) showed that regional strike-slip faults or trans-crustal shearzones already formed and were active from 295 to 290 Ma. Major

Table 2U–Pb analytical data and calculated ages.

Sample-spot #a Concentrations Isotope ratiosc Age (Ma)

U Th Th/U 206PbA f206b 207PbA ±1r 207PbA ±1r 206PbA ±1r Err.d 206PbA ±1rppm ppm ppm % 206PbA % 235U % 238U % Corr. 238U

Sample 400900, Altyntau granite400900.1.1 764 58 0.08 29.6 0.08 0.0521 1.3 0.324 1.5 0.0450 0.86 0.560 284.0 2.4400900.2.1 386 52 0.14 14.8 0.35 0.0512 2.8 0.315 2.9 0.0446 0.94 0.321 281.3 2.6400900.3.1 532 79 0.15 20.7 0.10 0.0516 1.8 0.322 2.0 0.0453 0.89 0.444 285.6 2.5400900.4.1 562 98 0.18 21.6 0.15 0.0517 2.2 0.318 2.4 0.0445 0.91 0.380 280.9 2.5400900.5.1 1001 181 0.19 37.6 0.19 0.0512 1.6 0.308 1.9 0.0436 0.85 0.461 275.1 2.3

Sample 406601 k, Karashoho lamproite pipe406601.1.1 291 194 0.69 17.8 0.05 0.0539 1.7 0.528 1.8 0.0712 0.6 0.316 443.2 2.4406601.2.1 119 109 0.95 14.6 0.32 0.0659 2.3 1.299 2.5 0.1429 0.7 0.304 861.0 6.0

Sample 3, Granite croscutting Karashoho lamproite pipe3.2.1 323 137 0.44 11.8 0.46 0.0531 4.3 0.310 4.8 0.0422 2.0 0.410 266.7 5.03.5.1 326 345 1.09 11.9 0.30 0.0524 3.5 0.307 4.0 0.0425 1.9 0.479 268.1 5.03.1.1 446 253 0.59 16.4 0.27 0.0503 3.3 0.296 3.8 0.0426 1.9 0.492 269.1 5.03.9.1 1037 719 0.72 38.8 0.21 0.0517 1.8 0.310 2.6 0.0434 1.8 0.706 274.1 5.03.8.1 842 491 0.60 32.0 0.28 0.0517 2.1 0.314 2.8 0.0441 1.8 0.657 277.9 5.03.7.1 717 512 0.74 27.9 0.20 0.0528 2.0 0.330 2.7 0.0453 1.8 0.687 285.5 5.03.3.1 510 321 0.65 19.9 0.32 0.0521 2.8 0.326 3.4 0.0453 1.9 0.568 285.6 5.03.4.1 196 147 0.77 8.4 0.54 0.0512 5.3 0.353 5.7 0.0499 2.0 0.358 313.9 6.03.6.1 697 300 0.44 49.9 0.87 0.0596 2.6 0.679 3.2 0.0826 1.8 0.571 511.8 9.03.10.1 166 147 0.92 17.8 0.05 0.0645 1.9 1.115 2.7 0.1254 2.0 0.713 761.0 14.0

Sample 401201, Saritau leucogranite401201.1.1 317 124 0.41 19 0.00 0.0549 1.5 0.530 1.7 0.0700 0.91 0.522 436.1 3.8

Sample 400800, Dzhizlan-Chattik granite400800.1.1 4502 523 0.12 185 1.38 0.0524 1.9 0.341 2.4 0.0472 1.4 0.583 297.6 4.0400800.2.1 1799 147 0.08 75.7 13.64 0.0561 15.0 0.327 15.0 0.0423 1.7 0.108 267.2 4.4400800.3.1 1215 227 0.19 47.7 0.39 0.0516 2.1 0.324 2.5 0.0455 1.4 0.553 286.9 3.9400800.4.1 954 159 0.17 38.6 0.67 0.0506 2.7 0.326 3.0 0.0467 1.4 0.470 294.4 0.1

Sample 400300, Temirkobuk granodiorite400300.1.1 938 269 0.30 28.4 2.20 0.0521 3.7 0.248 3.8 0.0345 0.9 0.236 218.8 1.9400300.2.1 1724 332 0.20 67.2 0.14 0.0520 1.0 0.324 1.3 0.0453 0.81 0.647 285.4 2.3400300.3.1 371 106 0.30 14.4 0.27 0.0521 2.9 0.324 3.0 0.0451 0.95 0.314 284.2 2.6400300.4.1 505 114 0.23 20.2 0.27 0.0524 2.1 0.335 2.3 0.0464 0.94 0.415 292.5 2.7400300.5.1 697 161 0.24 27.5 0.50 0.0520 2.0 0.327 2.2 0.0457 0.89 0.411 287.9 2.5400300.6.1 116 64 0.57 11.5 2.13 0.0628 4.7 0.979 4.8 0.1132 1.1 0.236 691.1 7.4400300.7.1 2170 359 0.17 69.8 0.07 0.0510 0.9 0.263 1.3 0.0374 0.98 0.733 236.8 2.3

Sample 400500, Gatcha granite400500.8.1 1044 263 0.26 36.7 0.18 0.0525 1.5 0.296 1.6 0.0409 0.4 0.266 258.3 1.1400500.5.1 679 205 0.31 24.7 0.07 0.0507 2.0 0.296 2.1 0.0423 0.4 0.212 267.4 1.2400500.1.1 1081 60 0.06 39.4 0.28 0.0501 1.7 0.293 1.8 0.0424 0.4 0.205 267.5 0.9400500.6.1 433 184 0.44 16.1 0.04 0.0521 2.0 0.311 2.1 0.0433 0.5 0.255 273.3 1.4400500.2.1 1719 211 0.13 65.6 0.03 0.0519 1.0 0.318 1.1 0.0444 0.3 0.304 280.3 0.9400500.7.1 328 155 0.49 12.6 0.17 0.0513 2.7 0.315 2.8 0.0445 0.6 0.216 280.7 1.7400500.4.1 1526 31 0.02 58.6 0.12 0.0513 1.2 0.316 1.2 0.0446 0.3 0.274 281.4 0.9400500.3.1 164 284 1.79 17.0 0.16 0.0630 2.0 1.046 2.2 0.1205 0.7 0.313 733.7 4.7

Sample Ch1, Chagatai carbonatite pipeCH1.4.1 340 146 0.44 13.7 1.11 0.0570 11.0 0.363 11.0 0.0462 1.5 0.135 291.2 4.4CH1.3.1 150 108 0.74 6.6 4.67 0.0550 31.0 0.370 31.0 0.0487 2.4 0.078 306.5 7.2CH1.6.1 690 587 0.88 30.9 0.40 0.0524 4.7 0.375 4.9 0.0520 1.2 0.250 326.7 3.9CH1.8.1 547 616 1.16 25.2 0.85 0.0545 8.3 0.399 8.4 0.0531 1.3 0.153 333.5 4.2CH1.3.2 137 54 0.40 6.7 5.14 0.0660 25.0 0.490 25.0 0.0541 2.9 0.113 339.4 9.5CH1.1.1 384 221 0.59 23.5 3.68 0.0576 14 0.544 14.0 0.0685 2.4 0.168 427.1 9.7CH1.10.1 284 224 0.81 22.9 0.00 0.0601 2.2 0.777 2.5 0.0937 1.3 0.530 577.2 7.4CH1.7.1 69 79 1.19 5.9 2.24 0.0520 22.0 0.700 22.0 0.0974 2.7 0.123 599.0 15.0CH1.9.1 173 112 0.67 16.6 0.31 0.0622 5.6 0.956 5.8 0.1115 1.6 0.271 681.0 10.0CH1.5.1 243 163 0.69 28.8 0.73 0.0658 4.9 1.242 5.1 0.1368 1.4 0.267 827.0 11.0CH1.2.1 509 281 0.57 61.8 1.02 0.0665 4.2 1.279 4.4 0.1396 1.2 0.266 842.5 9.3

Sample 401700, Koshrabad granite401700.1.1 546 116 0.22 21.5 0.13 0.0521 2.8 0.3286 2.9 0.0457 0.61 0.212 288.2 1.7401700.2.1 812 183 0.23 31.7 0.15 0.0518 2.1 0.3235 2.2 0.0453 0.59 0.270 285.8 1.7401700.3.1 553 112 0.21 21.6 0.23 0.0519 3.7 0.325 3.7 0.0454 0.64 0.170 286.2 1.8401700.4.1 891 190 0.22 34.4 0.13 0.0517 2.2 0.3198 2.3 0.0448 0.58 0.257 282.8 1.6

Sample 404600, Aktau granite414600_1.1 387 329 0.88 14.5 0.19 0.0486 3.2 0.291 4.8 0.0435 3.5 0.739 274.3 9.5414600_2.1 235 67 0.29 8.9 0.20 0.0560 4.4 0.340 5.7 0.0440 3.6 0.639 277.3 9.8414600_3.1 421 203 0.50 15.9 0.44 0.0505 4.8 0.305 6.0 0.0439 3.5 0.591 276.7 9.6414600_4.1 424 168 0.41 15.7 0.23 0.0506 3.3 0.301 4.8 0.0431 3.5 0.732 272.1 9.4414600_5.1 281 137 0.50 10.9 0.44 0.0492 7.3 0.304 8.1 0.0448 3.6 0.447 283.0 10.0


Table 2 (continued)



Sample 406701, Kyzata monzonite406701.1.1 276 121 0.45 16.3 3.06 0.0576 12 0.528 12 0.0665 1.8 0.151 414.9 7.1406701.2.1 66 36 0.56 3.8 1.80 0.0570 19 0.519 19 0.0655 2.6 0.133 409 10.0406701.3.1 233 75 0.33 13.5 0.62 0.0569 6.0 0.527 6.2 0.0672 1.7 0.271 419.0 6.8

Sample 406501, Almalyk monzonite406501.1.1 2005 1692 0.87 85.0 0.20 0.0527 1.3 0.358 1.4 0.0492 0.34 0.241 309.7 1.0406501.2.1 1090 649 0.62 46.3 0.25 0.0526 2.0 0.357 2.0 0.0493 0.44 0.216 310.0 1.3406501.3.1 2049 1132 0.57 85.7 0.18 0.0526 1.2 0.352 1.2 0.0486 0.31 0.260 305.75 0.9406501.4.1 2594 2328 0.93 110.0 0.58 0.0525 1.5 0.355 1.5 0.0490 0.3 0.193 308.65 0.9

Sample 414700, Almalyk altered monzonite414700.9.1 585 440 0.78 24.0 0.13 0.0539 2.3 0.354 2.8 0.0476 1.7 0.593 299.7 4.9414700.6.1 666 559 0.87 27.6 0.07 0.0520 2.1 0.345 2.7 0.0481 1.7 0.615 302.9 4.9414700.5.1 487 224 0.47 20.2 0.06 0.0518 2.3 0.344 2.9 0.0482 1.8 0.609 303.5 5.2414700.2.1 954 723 0.78 40.0 0.13 0.0517 2.3 0.348 2.9 0.0487 1.7 0.577 306.8 5.0414700.3.1 590 275 0.48 24.9 0.22 0.0531 2.7 0.359 3.2 0.0490 1.7 0.524 308.4 5.0414700.8.1 527 322 0.63 22.3 0.10 0.0518 2.2 0.351 2.8 0.0491 1.7 0.601 309.0 5.1414700.1.1 493 343 0.72 21.4 0.19 0.0526 2.9 0.365 3.4 0.0503 1.7 0.503 316.5 5.2414700.4.1 336 188 0.58 15.7 6.65 0.0530 20.0 0.373 20.0 0.0507 2.1 0.104 319.1 6.6414700.7.2 148 77 0.54 8.1 0.38 0.0570 4.3 0.498 4.8 0.0634 1.9 0.407 396.4 7.5414700.7.1 90 63 0.72 5.1 0.62 0.0535 7.4 0.484 7.7 0.0656 2.2 0.283 409.4 8.7

Sample 406403, Almalyk porphyry406403.4.1 581 153 0.27 24.8 0.02 0.0531 1.4 0.364 1.6 0.0497 0.8 0.519 312.8 2.5406403.3.1 755 208 0.28 32.4 0.02 0.0518 1.2 0.357 1.2 0.0499 0.4 0.324 314.1 1.2406403.2.1 845 249 0.30 36.5 0.07 0.0533 1.5 0.369 1.5 0.0503 0.4 0.252 316.2 1.2406403.1.1 852 268 0.32 36.9 0.10 0.0528 1.6 0.367 1.6 0.0503 0.4 0.240 316.6 1.2

Sample 406801, Kara-Kiya granite406801.1.1 800 442 0.57 35.8 0.47 0.0516 3.4 0.370 3.7 0.0519 1.5 0.394 326.3 4.7406801.2.1 770 341 0.46 34.9 0.18 0.0526 2.5 0.381 2.9 0.0526 1.5 0.512 330.4 4.7406801.3.1 1033 362 0.36 43.6 0.16 0.0518 2.0 0.350 2.6 0.0490 1.7 0.663 308.4 5.3406801.4.1 596 253 0.44 24.9 0.37 0.0513 2.9 0.342 3.3 0.0484 1.5 0.469 304.7 4.6406801.5.1 606 211 0.36 25.9 0.28 0.0533 2.8 0.365 3.2 0.0497 1.5 0.463 312.4 4.5

Sample 406301, Akcha suite, acid volcanic406301.3.1 1245 238 0.20 51.2 — 0.0526 1.1 0.347 1.2 0.0479 0.4 0.307 301.5 1.1406301.2.1 944 174 0.19 39.3 0.06 0.0524 2.3 0.350 2.4 0.0484 0.4 0.180 305.0 1.3406301.1.1 1538 321 0.22 64.7 0.12 0.0523 1.0 0.353 1.1 0.0489 0.3 0.314 307.9 1.0

Sample 414802, Nadak suite andesite414802.1.1 549 275 0.52 23.2 0.00 0.0521 2.4 0.354 2.9 0.0493 1.7 0.571 310.2 5.1414802.2.1 458 259 0.58 18.1 0.00 0.0527 2.2 0.335 2.9 0.0461 1.8 0.619 290.4 5.0414802.3.1 415 215 0.54 17.0 0.06 0.0511 2.5 0.336 3.0 0.0477 1.7 0.566 300.6 5.0414802.4.1 662 419 0.65 28.1 0.31 0.0504 3.6 0.342 4.0 0.0493 1.7 0.417 310.4 5.0414802.5.1 469 226 0.50 19.3 0.27 0.0518 3.5 0.341 3.9 0.0477 1.7 0.435 300.4 5.0414802.6.1 958 720 0.78 39.1 0.00 0.0532 1.5 0.349 2.2 0.0476 1.6 0.726 299.7 4.8414802.7.1 507 220 0.45 20.7 0.21 0.0515 2.8 0.336 3.3 0.0474 1.7 0.514 298.2 4.9414802.8.1 466 223 0.49 18.8 0.26 0.0521 3.2 0.336 3.6 0.0468 1.7 0.473 294.8 4.9

Sample 415001, Sary-Cheku porphyry415001.1.1 649 264 0.42 28.0 0.00 0.0518 1.9 0.359 2.5 0.0503 1.7 0.653 316.2 5.1415001.2.1 797 427 0.55 33.3 0.49 0.0511 3.2 0.341 3.6 0.0484 1.6 0.454 304.9 4.9415001.3.1 766 315 0.43 32.4 0.29 0.0518 2.7 0.351 3.1 0.0491 1.6 0.526 309.0 5.0415001.4.1 1126 492 0.45 46.1 0.43 0.0510 3.1 0.334 3.5 0.0475 1.6 0.465 298.9 4.7415001.5.1 1451 730 0.52 60.5 0.22 0.0520 2.0 0.347 2.6 0.0484 1.6 0.625 304.8 4.8415001.6.1 772 340 0.45 32.3 0.12 0.0535 1.9 0.359 2.5 0.0486 1.6 0.656 305.9 4.9415001.7.1 652 280 0.44 27.4 0.25 0.0531 2.5 0.358 3.1 0.0488 1.9 0.594 307.3 5.6415001.8.1 1334 649 0.50 56.8 0.17 0.0531 2.0 0.362 2.6 0.0495 1.6 0.621 311.1 4.9415001.9.1 1103 533 0.50 44.2 0.13 0.0527 1.7 0.339 2.4 0.0466 1.6 0.681 293.6 4.6

Sample 415000, Sary-Cheku post-ore granite415000.1.1 723 305 0.44 29.2 0.15 0.0519 2.2 0.335 2.7 0.0469 1.7 0.602 295.1 4.8415000.2.1 767 301 0.41 32.2 0.10 0.0516 2.0 0.347 2.6 0.0488 1.6 0.644 307.1 4.9415000.3.1 681 272 0.41 27.9 0.13 0.0513 2.2 0.336 2.8 0.0475 1.7 0.602 299.4 4.9415000.4.1 725 328 0.47 29.3 0.04 0.0532 1.8 0.345 2.5 0.0470 1.6 0.670 296.0 4.8415000.5.1 745 344 0.48 29.7 0.16 0.0520 2.1 0.332 2.7 0.0463 1.7 0.613 291.7 4.7415000.6.1 707 222 0.32 28.8 0.37 0.0520 3.1 0.338 3.6 0.0472 1.7 0.467 297.0 4.8415000.7.1 860 393 0.47 34.7 0.12 0.0523 1.9 0.338 2.5 0.0469 1.6 0.652 295.2 4.7415000.8.1 781 391 0.52 31.5 0.23 0.0522 2.7 0.337 3.2 0.0468 1.6 0.522 294.6 4.7

Sample 26, Karasu pegmatoidal granite26.1.1 8151 185 0.02 305 0.06 0.0516 0.6 0.309 2.5 0.0435 2.5 0.974 274.2 6.626.2.1 3793 76 0.02 148 2.50 0.0526 2.6 0.321 3.6 0.0443 2.5 0.689 279.4 6.826.3.1 4737 371 0.08 206 7.78 0.0515 7.4 0.332 8 0.0467 3.1 0.386 294.4 8.926.4.1 5812 154 0.03 220 0.48 0.0529 1.1 0.320 2.7 0.0439 2.5 0.912 277.1 6.726.5.1 5530 277 0.05 222 1.71 0.0517 2.7 0.326 3.6 0.0458 2.5 0.683 289.0 7.0

(continued on next page)


Table 2 (continued)



26.6.1 6698 450 0.07 250 3.31 0.0524 6.2 0.303 6.7 0.0420 2.6 0.391 265.4 6.926.7.1 4280 282 0.07 194 4.10 0.0545 5.8 0.381 6.4 0.0507 2.7 0.420 318.5 8.426.8.1 3316 47 0.01 125 0.11 0.0503 1.3 0.304 2.8 0.0439 2.5 0.891 277.1 6.8

Sample 27, Karasu pegmatoidal granite27.1.1 5776 58 0.01 214 — 0.0515 0.6 0.306 2.6 0.0431 2.6 0.973 272.1 6.827.2.1 6348 57 0.01 238 0.05 0.0518 0.6 0.312 2.5 0.0437 2.5 0.972 275.5 6.727.3.1 5477 62 0.01 215 0.01 0.0519 0.6 0.327 2.5 0.0457 2.5 0.972 288.1 7.027.4.1 6588 54 0.01 256 0.03 0.0519 0.6 0.324 2.5 0.0452 2.5 0.976 285.0 6.927.5.1 5108 47 0.01 194 0.02 0.0517 0.6 0.314 2.6 0.0441 2.5 0.969 278.3 6.827.6.1 7944 82 0.01 307 — 0.0516 0.5 0.320 2.5 0.0450 2.5 0.981 283.6 6.927.7.1 13139 195 0.02 560 0.02 0.0519 0.5 0.355 2.5 0.0496 2.5 0.982 311.8 7.627.8.1 4936 51 0.01 183 0.09 0.0521 0.8 0.310 2.6 0.0432 2.5 0.951 272.7 6.6

Sample 320100, Makmal granite320100.1.1 597 275 0.48 23.2 0.22 0.0516 2.6 0.322 3.0 0.0452 1.5 0.495 285.2 4.1320100.2.1 2757 1308 0.49 105.0 0.86 0.0519 1.9 0.315 2.3 0.0440 1.4 0.598 277.7 3.8320100.3.1 3235 1053 0.34 128.0 0.17 0.0525 1.1 0.333 1.8 0.0460 1.4 0.785 289.9 3.9320100.4.1 6543 1426 0.23 269.0 0.03 0.0518 0.6 0.341 1.5 0.0478 1.4 0.925 300.9 4.0320100.5.1 564 309 0.57 21.7 0.20 0.0510 4.0 0.314 4.3 0.0447 1.5 0.354 281.8 4.2320100.6.1 3625 730 0.21 139.0 0.10 0.0514 1.0 0.316 1.7 0.0447 1.4 0.817 281.7 3.8

Sample 320000, Aktyuz granite320000.1.1 323 92 0.29 18.6 0.29 0.0548 3.9 0.504 4.2 0.0667 1.5 0.365 416.5 6.2320000.2.1 776 279 0.37 43.3 0.25 0.0553 1.8 0.494 2.3 0.0648 1.4 0.616 404.6 5.7320000.3.1 822 401 0.50 47.9 0.12 0.0543 1.9 0.507 2.3 0.0677 1.4 0.607 422.4 5.8

Sample 340002, Akkulen alkaline syenite340002.1.1 2309 1828 0.82 95.6 8.94 0.0481 12.0 0.291 12.1 0.0439 0.7 0.058 276.9 1.9340002.4.1 1350 623 0.48 53.5 0.22 0.0522 1.3 0.331 1.3 0.0460 0.3 0.241 290.1 0.9340002.3.1 1599 765 0.49 63.8 0.07 0.0517 1.1 0.331 1.1 0.0464 0.3 0.261 292.5 0.8340002.2.1 706 228 0.33 28.4 0.06 0.0523 1.3 0.337 1.4 0.0467 0.5 0.339 294.4 1.4

Sample 012-2, Surteke alkaline gabbro012-2.3.1 3659 737 0.21 137.6 0.11 0.0515 0.7 0.310 0.8 0.0437 0.3 0.323 275.8 0.7012-2.2.1 2997 25 0.01 115.4 — 0.0519 0.9 0.321 0.9 0.0448 0.3 0.301 282.7 0.7012-2.1.1 3582 708 0.20 139.0 0.22 0.0521 0.8 0.324 0.9 0.0451 0.2 0.291 284.2 0.7012-2.5.1 2771 55 0.02 108.2 0.50 0.0519 1.1 0.324 1.1 0.0452 0.2 0.204 285.2 0.601-2.4.1 1289 588 0.47 51.1 0.10 0.0514 1.1 0.327 1.1 0.0461 0.3 0.289 290.8 0.9

Sample 217001, Ulan granite217001.1.1 302 205 0.70 12.5 0.41 0.0522 3.9 0.345 4.0 0.0479 0.8 0.192 301.6 2.3217001.2.1 166 72 0.45 6.9 0.61 0.0519 5.7 0.342 5.8 0.0477 1.1 0.184 300.6 3.1217001.3.1 274 155 0.58 10.6 0.38 0.0518 4.7 0.321 4.8 0.0450 0.9 0.183 283.6 2.4217001.4.1 122 71 0.60 5.2 0.68 0.0513 6.1 0.347 6.2 0.0491 1.2 0.200 308.7 3.7217001.5.1 124 51 0.42 17.9 0.40 0.0720 2.7 1.663 2.9 0.1676 0.9 0.314 998.7 8.4217001.6.1 149 100 0.69 6.3 0.75 0.0510 7.2 0.344 7.3 0.0489 1.3 0.180 307.7 4.0217001.7.1 203 104 0.53 8.3 0.44 0.0512 6.9 0.333 7.0 0.0472 1.0 0.148 297.4 3.0217001.8.1 238 100 0.43 10.0 0.57 0.0513 5.5 0.342 5.5 0.0484 0.9 0.162 304.7 2.7

Sample 215701, Ak-Shiyrak granite215701.1.1 340 101 0.31 13.9 0.36 0.0510 7.7 0.334 7.8 0.0475 0.97 0.125 299.3 2.8215701.2.1 440 144 0.34 17.4 0.23 0.0521 5.5 0.33 5.5 0.0459 0.81 0.147 289.6 2.3215701.3.1 148 61 0.42 6.02 0.34 0.0511 6.2 0.333 6.3 0.0473 1.1 0.176 297.7 3.2215701.4.1 283 90 0.33 11 0.61 0.0513 6.3 0.319 6.3 0.0451 0.97 0.153 284.4 2.7215701.4.2 403 111 0.28 16.2 0.10 0.0525 3.3 0.338 3.4 0.0467 0.68 0.204 294.1 2.0215701.5.1 485 161 0.34 19.2 0.25 0.0525 2.8 0.332 2.8 0.0459 0.61 0.215 289.1 1.7

A Radiogenic Pb.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.


orogenic gold deposits were also emplaced within this narrow timespan (Fig. 7): an age of 287.5 ± 1.7 Ma was obtained for the mainstage gold mineralization at the Muruntau deposit (Morelli et al.,2007), and an age of 288–284 Ma was reported for the KumtorAu deposit (Mao et al., 2004). The metallogenic potential of thepost-collisional magmatism was also established in the course ofthis study by dating the Koshrabad pluton hosting two large intru-sion-related Au deposits Guzhumsay and Charmitan (Abzalov,2007), and the Makmal pluton associated with a skarn-type Au de-posit (Osmonbetov et al., 1982). Both plutons were dated in thisstudy at ca. 286 Ma. Finally, ages obtained for alkaline complexes

(Surteke – 284 Ma, Akkulen – 292 Ma, and a minimum age of theKarashoho pipe – 276 Ma) indicate a regional extension character-istic for the 295–280 Ma time interval. It should be noted that out-side the Middle Tien Shan, the post-collisional magmatic pulse waspreceded and followed by 40–50 Ma long periods lacking anyintrusive magmatism (Fig. 9). To explain the geodynamic environ-ment in which Hercynian post-collisional intrusions were formed,Konopelko et al. (2007) suggested a model of post-collisional plate-scale displacements based on the model for the San Andreas fault(Teyssier and Tikoff, 1998). In this model the transfer of displace-ment from the mantle to the upper crust is accommodated in the

290 280 270

0.046

0.048

0.050

0.052

0.054

21.2 21.6 22.0 22.4 22.8 23.2 23.6238U/ 206Pb

N=5, Concordia Age = 281 ±2 Ma(2 , decay-const. errs included)MSWD (of concordance) = 0.34,

Probability (of concordance) = 0.56

400900(1)

290 270250

0.044

0.048

0.052

0.056

0.060

20.5 21.5 22.5 23.5 24.5 25.5238U/ 206Pb

22

22

00

00

77

77

PP

PP

bb

bb

//

//

22

22

00

00

66

66

PP

PP

bb

bb

N=7, Concordia Age = 276 ± 4 Ma(2 , decay-const. errs included)MSWD (of concordance) = 0.17,


3(3)

280290300310

0.045

0.047

0.049

0.051

0.053

0.055

20.0 20.4 20.8 21.2 21.6 22.0 22.4 22.8238U/ 206Pb

N=3, Concordia Age = 293 ±5 Ma(2 , decay-const. errs included)MSWD (of concordance) = 0.50,Probability (of concordance) = 0.48

400800(8)

300 290 280

0.047

0.049

0.051

0.053

0.055

20.8 21.2 21.6 22.0 22.4 22.8238U/ 206Pb

N=4, Concordia Age = 287 ± 2 Ma(2 , decay-const. errs included)MSWD (of concordance) = 0.0019,

400300(9)


290 280270 260 250

0.046

0.048

0.050

0.052

0.054

21.5 22.5 23.5 24.5 25.5

238U/ 206Pb

207 Pb

/206 Pb

N=3, Concordia Age = 281 ±1Ma(2 , decay-const. errs included)MSWD (of concordance) = 0.44,

400500(10)


292 284

0.045

0.047

0.049

0.051

0.053

0.055

0.057

21.4 21.6 21.8 22.0 22.2 22.4 22.6 22.8

238U/ 206Pb

207 Pb

/206 Pb

N=4, Concordia Age = 286 ±2 Ma(2 , decay-const. errs included)

MSWD (of concordance) = 0.066,Probability (of concordance) = 0.80

401700(12)

Fig. 2. Concordia diagrams for zircon U–Pb SHRIMP data of the Southern Tien Shan intrusions. Dashed ellipses show data not included in age calculations. N is number ofanalyses for which a concordia age was calculated. Sample numbers as in Tables 1 and 2. Numbers in brackets are running numbers of intrusions from Table 1: 1 – Altyntau, 3– granite dike from Karashoho pipe, 8 – Dzhizlan-Chattik, 9 – Temirkobuk, 10 – Gatcha, 12 – Koshrabad.


lower-middle crust by flat-lying detachment zones. This transpres-sional system provides suitable conduits for ascending astheno-

spheric material and influx of heat into the crust. Mantle-derivedmelts probably triggered melting of the basements of accreted

22

22

00

00

77

77

PP

PP

bb

bb

//

//

22

22

00

00

66

66

PP

PP

bb

bb

260280300320

0.036

0.040

0.044

0.048

0.052

0.056

0.060

0.064

19.5 20.5 21.5 22.5 23.5 24.5 25.5238U/ 206Pb



414600(13)

430 410 390

0.02

0.03

0.04

0.05

0.06

0.07

0.08

0.09

14.0 14.4 14.8 15.2 15.6 16.0 16.4238U/ 206Pb



406701(14)

316 312 308 304

0.0495

0.0505

0.0515

0.0525

0.0535

0.0545

0.0555

19.9 20.1 20.3 20.5 20.7 20.9238U/ 206Pb



406501(15)

340 320 300

0.03

0.04

0.05

0.06

0.07

0.08

18 19 20 21 22238U/ 206Pb


Probability (of concordance) =0.70

414700(16)

312320

0.0492

0.0502

0.0512

0.0522

0.0532

0.0542

0.0552

19.5 19.7 19.9 20.1 20.3 20.5238U/ 206Pb

2

20

07

7P Pb b/ /2

20

06

6P Pb b



406403(17)

340320 300

0.044

0.046

0.048

0.050

0.052

0.054

0.056

0.058

17.5 18.5 19.5 20.5 21.5238U/ 206Pb

N=5, Concordia Age = 317 ±8 Ma(95% confidence, decay-const. errs included)


406801(18)

Fig. 3. Concordia diagrams for zircon U–Pb SHRIMP data of the Southern and Middle Tien Shan intrusions. N is number of analyses for which a concordia age was calculated.Sample numbers as in Tables 1 and 2. Numbers in brackets are running numbers of intrusions from Table 1: 13 – Aktau, 14 – Kyzata, 15–17 – Almalyk, 18 – Kara-Kiya.


terranes and emplacement of post-collisional granites. Coeval alka-line magmas originated from the lithospheric keels of accretedcontinental blocks. These post-collisional processes probably af-

fected large volumes of the crust and produced both considerableamounts of granitic rocks and hydrothermal fluid flow. Theregional fluid flow and emplacement of gold deposits, as well as

312 308 304 300

0.047

0.049

0.051

0.053

0.055

20.1 20.3 20.5 20.7 20.9 21.1238U/ 206Pb

22

22

00

00

77

77

PP

PP

bb

bb

//

//

22

22

00

00

66

66

PP

PP

bb

bb



406301(19)

320300

280

0.044

0.046

0.048

0.050

0.052

0.054

0.056

19 20 21 22 23238

238

U/

U/

206

206

Pb

Pb



414802(20)

330310

290

0.044

0.046

0.048

0.050

0.052

0.054

0.056

18.5 19.5 20.5 21.5 22.5238U/ 206Pb

N=9, Concordia Age = 306 ± 3 Ma(2 , decay-const. errs included)


415001(21)

290310330

0.045

0.047

0.049

0.051

0.053

0.055

0.057

19 20 21 22 23



415000(22)

270310

0.039

0.043

0.047

0.051

0.055

0.059

19 21 23 25 27238U/ 206Pb

207 Pb

/206 Pb



26(23)

300

280

260

0.0503

0.0507

0.0511

0.0515

0.0519

0.0523

0.0527

0.0531

20 21 22 23 24 25238U/ 206Pb

207 Pb

/206 P b



27(24)

Fig. 4. Concordia diagrams for zircon U–Pb SHRIMP data of the Middle Tien Shan intrusions. N is number of analyses for which a concordia age was calculated. Samplenumbers as in Tables 1 and 2. Numbers in brackets are running numbers of intrusions from Table 1: 19 – Akcha volcanics, 20 – Nadak volcanics, 21 and 22 – Sary-Cheku, 23and 24 – Kyrgysh.


post-collisional granitoid magmatism were focused and controlledby the regional trans-crustal shear zones. It seems that this modelmay be suitable for Hercynian post-collisional magmatism in the

whole Tien Shan, including the Chinese Tien Shan, and may be sug-gested for intrusions related to a Late Carboniferous–Early Permianrifting and wrenching stage in Europe (e.g. Timmerman et al.,

2 20 07 7P Pb b/ /2 20 06 6P Pb b320300

280

0.045

0.047

0.049

0.051

0.053

0.055

0.057

19.5 20.5 21.5 22.5 23.5238U/ 206Pb



320100(25)

430410

390

0.047

0.049

0.051

0.053

0.055

0.057

0.059

0.061

14.0 14.4 14.8 15.2 15.6 16.0238U/ 206Pb

N=3, Concordia Age = 414 ±7 Ma(2 , decay-const. errs included)MSWD (of concordance) = 0.12,Probability (of concordance) =0.73

320000(30)

302 298 294 290 286 282 278 274 270

0.033

0.037

0.041

0.045

0.049

0.053

0.057

0.061

0.065

20.8 21.2 21.6 22.0 22.4 22.8 23.2 23.6238U/ 206Pb

2 20 07 7P Pb b/ /2 20 06 6P Pb b



340002(31)

294 290 286 282 278 274 270

0 .0495

0 .0505

0 .0515

0 .0525

0 .0535

21.2 21.6 22.0 22.4 22.8 23.2238U/ 206Pb

N=3, Concordia Age = 284 ±1 Ma(2 decay-const. errs included)


012-2(32)

320 310 300 290

0.037

0.041

0.045

0.049

0.053

0.057

0.061

19.4 19.8 20.2 20.6 21.0 21.4 21.8238U/ 206Pb

207 Pb

/206 P b



217001(35)

310 300 290 280

0.038

0.042

0.046

0.050

0.054

0.058

0.062

20.2 20.6 21.0 21.4 21.8 22.2 22.6 23.0238U/ 206Pb

207 Pb

/206 Pb



215701(38)

Fig. 5. Concordia diagrams for zircon U–Pb SHRIMP data of the Southern, Middle, and Northern Tien Shan intrusions east of Talas–Farghona fault. Dashed ellipses show datanot included in age calculations. N is number of analyses for which a concordia age was calculated. Sample numbers as in Tables 1 and 2. Numbers in brackets are runningnumbers of intrusions from Table 1: 25 – Makmal, 30 – Aktyuz, 31 – Akkulen, 32 – Surteke, 35 – Ulan, 38 – Ak-Shiyrak.


2009). However, it should be admitted that such a post-collisionalenvironment is rather unique. As seen in Fig. 9, the Caledonian

magmatic evolution of the Tien Shan differs markedly from theHercynian. In particular, post-collisional granites are not found

a

b

c

Fig. 6. CL images of analyzed zircon grains: a – inherited core in zircon grain fromTemirkobuk intrusion, b – zircon xenocrysts from Chagatai carbonatite pipe, noterounded shape of zircon xenocryst indicating metasedimentary origin, c –overgrown or reset zircon grain from Temirkobuk intrusion illustrating the resultof Triassic thermal event. Spot numbers are as in Table 2.

250

260

280

300

320

270

290

310

330Age, Ma

Kyzylkum SegmentSouthern Tien Shan

Tien Shan terraneseast of Talas-Farghona fault

Subduction-related intrusionsMiddle Tien Shan

Post-collisionalintrusions MURUNTAU Au KUMTOR Au

Fig. 7. Evolution of Hercynian magmatism in the Tien Shan. Ages of intrusions areshown as 2r error bars. Grey rectangles show ages (within 2r error limits) of thetwo major Au deposits: Muruntau in the Kyzylkum segment (Morelli et al., 2007)and Kumtor east of the Talas–Farghona strike-slip fault (Mao et al., 2004). Data fromTable 1.

0

1

2

3

4

5

0

1

2

3

4

5

6

260

260

270

270

280

280

290

290

300

300

310

310

320

320

330

330

a

b

Age, Ma

N=8

N=28Nm

bam

eu

erof

spl

s

Fig. 8. Histogram showing distribution of ages of Hercynian subduction-relatedintrusions in the Kurama range, Middle Tien Shan west of the Talas–Farghona fault(a) and post-collisional Hercynian intrusions outside Kurama range (b). Data fromTable 1.

0

2

4

6

8

10

12

14

16

150 200 250 300 350 400 450 500 550 600Age, Ma

N=106 CaledonianPost-

collisional?Post-collisional

Subduction-related?Subduction-

related

Hercynian LateSilurian-

EarlyDevonian

Back arcextension

underestimatedin thisstudy

Triassicthermalevent

underestimatedin thisstudy

Num

ber o

f sam

ples

Fig. 9. Histogram showing distribution of ages of Paleozoic granitoid intrusions inthe Tien Shan. Data for Hercynian intrusions from Table 1. Other data fromMikolaichuk et al. (1997), Kiselev (1999), Zhang et al. (2007), Konopelko et al.(2008), Apayarov (2010), and Glorie et al. (2010).


(or are not preserved) outside the Northern Tien Shan magmaticarc. As a result, post-collisional Caledonian granites, tentativelyshown in Fig. 9, are, in fact, barely distinguished from continuoussubduction-related magmatism.

7.1.1. Nature of the Kyzylkum basementA set of large orogenic Au deposits, including the super-large

Muruntau deposit, is situated in the Kyzylkum segment of theSouthern Tien Shan (Yakubchuk et al., 2002; De Boorder et al.,2010). Consequently, the Kyzylkum basement is important forunderstanding the source of the gold in the Muruntau and otherdeposits. The oldest regionally metamorphosed rocks exposed in


the Kyzylkum segment are thick Neoproterozoic–Early Paleozoicturbidites. One exception is a gneiss from the Djungartau suitewith an age of 1750 Ma (Shayakubov and Dalimov, 1998). Thus,the two options for the source of gold include derivation from Neo-proterozoic–Early Paleozoic turbidites and direct derivation fromasthenospheric or lithospheric mantle. Based on the lead isotopedata on magmatic and metasedimentary rocks as well as oredeposits, Chiaradia et al. (2006) concluded that in the Kyzylkumsegment there is no evidence for a high-grade Paleo-Proterozoicand Archaean basement, and that the basement in this region ismainly composed of low-grade metamorphosed Neoproterozoicand Early Paleozoic rocks. According to Chiaradia et al. (2006)the only exception is represented by the cluster of orogenic Audeposits of Muruntau, Amantaitau, and Daugyztau whose thoro-genic Pb component suggests leaching of old metamorphic rocks,perhaps representing a hidden Precambrian basement sliver. Inthis study we present age data for 13 zircon xenocrysts and inher-ited cores in zircon grains from six intrusions situated north of theMuruntau deposit and in the southern Kyzylkum area in the NorthNurata range (Fig. 1). The obtained ages, presented in Fig. 10, showthat ages older than 1 Ga were not registered in the analyzed sam-ples. It gives further evidence for the Neoproterozoic–Early Paleo-zoic age of the Kyzylkum basement. However, due to the relativelyscarce data available for the vast Kyzylkum region the existence ofPrecambrian slivers, especially in Muruntau area, cannot be ruledout with certainty.

7.2. Subduction-related magmatism in the Middle Tien Shan west ofthe Talas–Farghona fault

The ages of subduction-related magmatic rocks, sampled in theKurama range of the Middle Tien Shan vary from 316 to 300 Ma,and practically do not overlap with the ages of post-collisionalintrusions (295–280 Ma) (Figs. 7–9). It should be noted that post-collisional intrusions are also common in the Middle Tien Shan(Shayakubov and Dalimov, 1998). West of the Talas–Farghona faultthey include granite plutons of the Karamazar complex and thickEarly Permian volcanics situated in Tajikistan. In this study post-collisional intrusions of the Kurama range are represented by thepost-ore granite from the Sary-Cheku deposit with an age of297 Ma. This voluminous post-collisional magmatism in the MiddleTien Shan west of the Talas–Farghona fault followed Hercynian col-lision and probably was a result of so-called ‘‘subduction memory”.However, as is shown in this study, the intrusions with ages 303–320 Ma were not registered anywhere outside the Middle Tien Shanwest of the Talas–Farghona fault. Thus, in the Kurama range in theMiddle Tien Shan there is the only known so far fragment of theLate Carboniferous mature volcanic arc or active continental mar-gin well constrained in terms of age (this study), geochemistry(Seliverstov and Ghes, 2001; Ghes, 2008), and metallogenic features(Shayakubov and Dalimov, 1998; Golovanov et al., 2005). The latterare typical for a subduction environment and include major Cu–

400

600

800

1000

1200

Ae,

Ma

g

Fig. 10. Ages of inherited cores and zircon xenocrysts found in the intrusions ofKyzylkum segment of Southern Tien Shan. Ages are shown as 2r error bars. Datafrom Table 1.

Mo–Au porphyry type deposits (the Kalmakyr deposit hosted bythe Almalyk intrusion) (Golovanov et al., 2005; Seltman and Porter,2005), and volcanic-hosted epithermal Au deposits (the Kochbulakdeposit hosted by acid volcanics of the Nadak suite and others)(Shayakubov and Dalimov, 1998). To constrain the ages of mag-matic rocks hosting important mineralization we sampled porphy-ritic and coarse grained monzonites of the Almalyk intrusion andacid volcanics of the regionally developed Akcha and Nadak suites.The volcanics of the Akcha and Nadak suites yielded consistent agesof ca. 305 and 301 Ma, respectively, while the highly U-rich zirconsfrom the Almalyk intrusion yielded two age clusters of 315 and308 Ma. We applied a statistical approach and calculated aweighted average mean age of 314 Ma for the whole Almalyk rockassemblage. This age of 314 Ma is considered as a preliminary esti-mate for the age of the Almalyk porphyry system hosting the super-large Cu–Mo–Au Kalmakyr deposit.

7.3. Late Silurian–Early Devonian intrusions

Two Late Silurian–Early Devonian intrusions, previously unrec-ognized on regional maps, have been identified in the course of thisstudy. The Kyzata monzonite body with an age of 416 Ma is situ-ated in the Kurama range of the Middle Tien Shan. The Aktyuzintrusion with an age of 414 Ma was emplaced in the NorthernTien Shan terrane. The obtained ages, together with previouslypublished (Kiselev, 1999; Apayarov, 2010) and unpublished datashow that a number of intrusions in the Northern and Middle TienShan terranes have ages between 420 and 400 Ma. This Late Silu-rian–Early Devonian magmatic pulse, shown in Fig. 9, occurredca. 10 Ma after the termination of Early Silurian post-collisionalmagmatism at the end of the Caledonian orogeny. However,composition, spatial distribution, metallogenic potential, andgeodynamic setting of Devonian intrusions differs from those ofthe Caledonian plutons. The Devonian intrusions comprise unde-formed alkali-calcic granites and leucogranites different fromdeformed calc-alkaline I-type granitoids of the Caledonian stage.They are similar in the field to the Early Permian post-collisionalgranites, and many of them have been mapped as Permian. Inthe eastern part of the Kyrgyz Northern Tien Shan the ore depositsof Caledonian age are not preserved due to the deep erosion levelof the Caledonian paleo-terrane (Konopelko et al., 2008). All theore deposits in this region were previously considered as relatedto the Early Permian post-collisional intrusions emplaced at muchhigher crustal levels compared with the surrounding Caledoniangranites. However after recognition of the Devonian age of theAktyuz intrusion hosting a large REE deposit, it became clear thatother intrusions and related ore deposits in this area (e.g. the Boor-du and Mironovskoe deposits) may also be of Early Devonian age.The geodynamic setting of the Late Silurian–Early Devonian intru-sions is still unresolved. However, it is noticeable that they formedwithin a narrow time span coevally with the subduction-relatedmagmatic series of the Kurama range in the Middle Tien Shanand of Central Kazakhstan. Relative to the southern and northernactive margins of the Paleo-Kazakhstan (present day coordinates)the Late Silurian–Early Devonian intrusions occupy an intraplateposition. Because their ages match the relatively short and distinctperiod of the Late Silurian–Early Devonian subduction under Paleo-Kazakhstan we suggest that the Late Silurian–Early Devonianintrusions formed in a back arc extensional setting.

7.4. Triassic thermal event

Newly grown rims and recrystallized parts of zircon crystalsusually yield ages corresponding to the major crust-formingevents. For example, in Tien Shan rims of Caledonian (Ordovician)age are found in Precambrian zircon grains from mafic rocks which


are crosscut and surrounded by the Caledonian granites. Similarly,Early Devonian rims were found in older zircon grains from theCaledonian basement in the eastern part of the Northern Tien Shan(Konopelko, unpublished data). Both episodes of growth of newzircon correspond to regional magmatic pulses and may be ex-plained by the influx of heat into the crust. However, there isincreasing evidence for a younger Triassic thermal event in theTien Shan which was not accompanied by magmatic activity.K–Ar and Ar–Ar Triassic ages of 240–220 Ma have been repeatedlyreported for micas and K-feldspars from intrusive rocks and oredeposits all over the Tien Shan (e.g. Osmonbetov and Knauf,1982; Ahmedov, 2000; Wilde et al., 2001). It is not the purposeof this paper to collect and analyze all the published K–Ar andAr–Ar Triassic ages. We would like to emphasize that temperaturesduring the Triassic thermal event were high enough to initiateresetting and growth of new zircon grains which can be detectedon a regional scale. This is illustrated in Fig. 9. The nature of the Tri-assic thermal event is not clear. Because Triassic K–Ar and Ar–Arages of micas are often reported from the regional shear zones(e.g. Shayakubov and Dalimov, 1998), the influx of heat was prob-ably tectonically focused and varied significantly in various terr-anes. In this study the Triassic thermal event was registered inthe Kyzylkum segment of the Southern Tien Shan but was notfound in the other terranes. Interestingly, the Triassic event wasnot accompanied by significant magmatic activity. However, atleast one porphyry dyke with an age of 236 Ma has been foundin the Muruntau open pit in the Kyzylkum segment (Hall, 2007).On the other hand, al least two alkaline intrusions, previouslyshown on the maps as Triassic, yielded Early Permian U–Pb zirconSHRIMP ages (Table 1). Probably more work has to be done in thefuture to the numerous alkaline and carbonatite pipes in the TienShan to distinguish between Hercynian and younger intrusions.

8. Conclusions

Using U–Pb zircon SHRIMP ages of 27 Late Paleozoic intrusionssampled along a 2000 km – long profile in Kyrgyzstan and Uzbeki-stan, and previously published ion-probe and TIMS ages, we wereable to reconstruct the Paleozoic magmatic evolution of the TienShan orogen and to define the timing and spatial distribution ofHercynian post-collisional intrusions, and their relationships withother episodes of magmatic activity in the region.

It was shown that termination of continuous Andean-type Cal-edonian magmatism in the Northern and Middle Tien Shan terr-anes occurred ca. 430 Ma ago. Approximately 10 Ma later in theLate Silurian–Early Devonian (420–390 Ma) a number of graniteintrusions was emplaced in these terranes. The intrusions are coe-val with a distinct period of subduction under Paleo-Kazakhstan,and probably formed in an extensional back arc setting. The intru-sions were emplaced at much higher crustal levels compared to thesurrounding granites of the eroded Caledonian basement and mayhave a significant metallogenic potential.

The Late Carboniferous episode of subduction under Paleo-Kazakhstan was registered in the Kurama range of the Middle TienShan. Calc-alkaline volcanics and granitoids with ages 315–300 Mahave distinct metallogenic affinities typical for subduction-relatedrocks and are not found anywhere outside the Middle Tien Shanterrane west of the Talas–Farghona fault. An age of 314 Ma, ob-tained for the rocks of the Almalyk intrusion, is considered as apreliminary estimate for the age of the Almalyk porphyry systemhosting super-large Cu–Mo–Au Kalmakyr deposit. Acid volcanicsof the Nadak suite hosting the epithermal Kochbulak Au deposityielded an age of 301 Ma.

Early Permian Hercynian post-collisional magmatism culmi-nated after the closure of the Paleo-Turkestan ocean and affected

the whole region across terrane boundaries. The majority of post-collisional intrusions were emplaced within a relatively short timespan between 295 and 280 Ma. It was shown that the ages of intru-sions emplaced syn-kinematically into the regional shear zones,and ages of alkaline intrusions and pipes indicating regional exten-sion also match the 295–280 time span. Identical ages of 286 Mawere obtained for the Koshrabad and the Makmal intrusions host-ing large Au deposits. Similar ages were reported for the major oro-genic Kumtor and Muruntau Au deposits (Mao et al., 2004; Morelliet al., 2007). According to the proposed model, subsequent toHercynian collision the Tien Shan was affected by strike-slip mo-tions resulting in the formation of plate-scale shear zones. Theseshear zones provided suitable conduits for ascending astheno-spheric material and heat influx in the crust. These processes prob-ably affected large volumes of the crust and produced bothgranitoid magmas and hydrothermal fluid flow. The emplacementof post-collisional intrusions, as well as regional fluid flow andemplacement of orogenic gold deposits were focused and con-trolled by the regional shear zones.

Between 240 and 220 Ma the Triassic thermal event affected theregion resulting in resetting and growth of new zircon grainswhich is detected on a regional scale. The nature of the Triassicevent is not clear. Probably the influx of heat into the crust was tec-tonically focused and varied significantly in different terranes. TheTriassic thermal event was not accompanied by any significantmagmatic activity. Thus, after cessation of Hercynian post-colli-sional magmatism ca. 280 Ma ago there was a long magmaticallyquite period in the Tien Shan.

These conclusions fit for the Uzbek and Kyrgyz Tien Shan, andshould be applied with caution to the easternmost Tien Shan terr-anes in China.

Acknowledgements

We are indebted to Alexander Pyatkov, Alexandra Golovko andmany other colleagues who helped to organize field work inremote areas. We are grateful to Sergey Petrov for assistance inzircon separation. The staff of the Center of Isotopic Research(CIR VSEGEI St. Petersburg) are acknowledged for their generoussupport and assistance. D. K. appreciates the support through theNatural History Museum, London where part of the study wascarried out in the frame of a research fellowship at NHM’s Centerfor Russian and Central EurAsian Mineral Studies (CERCAMS). R.S. appreciates the financial contribution from AngloGold AshantiLimited for the geochronological study of auriferous intrusions inthe Tienshan that was pivotal for this research. Comments of twoanonymous reviewers greatly improved the manuscript. This is acontribution to the Project IGCP-510 ‘‘A-type Granites and RelatedRocks through Time” and to INTAS Nr 05-1000008-7938,‘‘Diamond and graphite in carbonate magmas”.

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