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Precambrian Research 235 (2013) 163– 189

Contents lists available at SciVerse ScienceDirect

Precambrian Research

jou rn al h om epa ge: www.elsev ier .com/ locate /precamres

he Neoproterozoic granitoids from the Qilian block, NW China:vidence for a link between the Qilian and South China blocks

uo-an Tunga,∗, Houng-yi Yangb, Dun-yi Liuc, Jian-xin Zhangd, Huai-jen Yangb,en-hong Shaue, Chien-yuan Tsengb

National Museum of Natural Sciences, Taichung 40453, TaiwanDepartment of Earth Sciences, National Cheng Kung University, Tainan 70101, TaiwanBeijing SHRIMP Centre, Institute of Geology, Chinese Academy of Geological Sciences, Beijing 100037, ChinaInstitute of Geology, Chinese Academy of Geological Sciences, Beijing 100037, ChinaDepartment of Marine Biotechnology and Resources, National Sun Yat-sen University, Kaohsiung 80424, Taiwan

r t i c l e i n f o

rticle history:eceived 29 January 2013eceived in revised form 28 June 2013ccepted 29 June 2013vailable online xxx

eywords:ranitoidseoproterozoicilian blockouth China blockectonomagmatic environment

a b s t r a c t

The field occurrence, petrography, geochemistry, Sm–Nd isotopes, and geochronology of the Neopro-terozoic granitoids exposed at Tuole, Huangyuan, Gahai, Haiyan, Riyueshan, Baokuhe, and Maxianshanin the Qilian block were studied. The Neoproterozoic granitoids in the Qilian block form two age groups:ca. 800 Ma and ca. 900 Ma. The ca. 800 Ma group granitoids consist of granodiorite and granite, whereasthe ca. 900 Ma group granitoids quartz diorite, granodiorite, and potassic granite. They have intrudedthe Huangyuan Group in the basement sequence of the Qilian block. The foliations are moderately towell-developed and are concordant with those of the country rocks. The granitoids of both age groups allshow enrichment in LREEs, but this enrichment is more pronounced in the ca. 800 Ma group than in theca. 900 Ma group. All granitoids show negative europium anomalies, but the ca. 800 Ma group granitoidsare more varied in Eu/Eu* values (0.23–0.83) than most of the ca. 900 Ma group granitoids (0.54–0.98).Spider diagrams of both groups also exhibit enrichment in large ion lithophile elements, i.e., Rb, Th, U,and K, and negative anomalies in Nb–Ta, Sr, P, Ti, and, with exception of the Maxianshan quartz diorite,Ba. The εNd(1 Ga) and TDM are −6.7 to −12.7 and 2.2–3.0 Ga for the ca. 800 Ma granitoids and are −4.3 to−5.2 and 2.0–2.3 Ga for the ca. 900 Ma granitoids. The granitoids of the ca. 900 Ma group are interpretedto have formed in an arc tectonomagmatic environment on an active continental margin, whereas thoseof the ca. 800 Ma group are thought to form in a continental rift environment. The ca. 900 Ma granitoidsare I-type and could be formed from partial melting of K-rich metabasalt or eclogite with significantamount of mantle components at a pressure of 1–4 GPa in the lower crust. The strongly peraluminous orperaluminous Gahai granites and Haiyan granodiorite are S-type and could be derived from melting of

clay-poor, mature psammitic sources.

Similarities in age and tectonic environment of magma genesis suggest a correlation of Neoproterozoicgranitoid magmatism between the Qilian and South China block. This correlation gives a strong supportto the consideration that the two blocks might be unified in the Neoproterozoic. In other words, the Qilianblock might be a part of the South China block or, more precisely, the Sibao orogen, in the Neoproterozoictime.

© 2013 Elsevier B.V. All rights reserved.

. Introduction

The tectonic framework of China consists of three major Precam-rian blocks (North China, South China, and Tarim) amalgamatedlong the Phanerozoic orogenic belts during different periods as

∗ Corresponding author. Tel.: +886 4 23226940x630; fax: +886 4 23231730.E-mail addresses: kat@mail.nmns.edu.tw, kuoannkimo@yahoo.com.tw

K.-a. Tung).

301-9268/$ – see front matter © 2013 Elsevier B.V. All rights reserved.ttp://dx.doi.org/10.1016/j.precamres.2013.06.016

well as numerous small Precambrian microcontinents (Zhao andCawood, 2012; Zheng et al., 2013). The Qilian block, with an areaof approximately 200,000 km2 and located in NW China, is one ofthese microcontinents. The Qilian block and the neighboring micro-continents are either in direct fault contact with or sutured by thelower Paleozoic orogenic belts (Fig. 1).

In the Qilian block, lower Paleozoic granitoids are widespreadand very voluminous, whereas Neoproterozoic granitoids are muchless abundant. Only approximately twenty small stocks of Neopro-terozoic granitoids have been mapped on a 1/1,000,000 geological

164 K.-a. Tung et al. / Precambrian Research 235 (2013) 163– 189

Fig. 1. Simplified geological map of the Qilian block. The Tuole pasture, Huangyuan, and Maxianshan areas are enlarged in a, b, and c, respectively. The sample localities areindicated with circled Arabic numbers. The age data of the granitoids are indicated for the Qilian block and the neighboring areas. The sources of the age data are given inTable 1. The Arabic numbers in brackets affixed to each age datum refer to the locality numbers in Table 1.

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ap of Qinghai and Gansu Provinces in China (BGMRGP, 1989;GMRQP, 1991). They are mostly distributed in the Huangyuan,uole, and Maxianshan areas (Fig. 1).

For the Qilian block, recent studies focused on tectonic settingsnd affinity toward the South China block. Guo et al. (1999a) andan et al. (2000) studied sedimentology and geochemistry of the

asement metasedimentary rocks and suggested an active conti-ental margin for the Qilian block during the Neoproterozoic time.an et al. (2000) further added that the interbedded metabasaltic

ocks in the middle part of the basement rock sequence showedeochemical characteristics of a within-plate environment. Tungt al. (2012) studied the amphibolite-facies metamorphosed maficocks from Maxianshan and also suggested an arc environment forhe Qilian block during early Neoproterozoic.

Regarding the tectonic setting of the Qilian block in the loweraleozoic, the extensive occurrence of arc granitoids (e.g., Gehrelst al., 2003; Wen, 1996; Chen et al., 2008; Liu et al., 2006) andrc mafic-ultramafic rocks (Zhang et al., 1997; Liu et al., 2005;seng et al., 2009) suggest an active continental margin. Ther39–Ar40 dating of metamorphic biotites separated from the base-ent paragneisses indicates the occurrence of an extensive lower

aleozoic regional metamorphism up to the amphibolite-facies inhe Qilian block (Lin, 2003a,b; Chang, 2004), also suggesting anctive continental margin tectonic environment for the Qilian blockn the lower Paleozoic time.

Zhang et al. (2006c) and Wan et al. (2003) studied the TDM ages ofhe basement rocks of the Qilian block and suggested that the Qilianlock is more affinitive to the South China block than to the Northhina block. Similarly, Zhang et al. (2006c)found that the basementocks and granitoids of the Qilian block are highly radiogenic in Pbsotopic composition and also suggested a strong affinity betweenhe Qilian and South China blocks.

Reports on the Neoproterozoic granitoids are limited. Guo et al.1999b) and Wan et al. (2000, 2003) described the Neoproterozoicranitoids from the Huangyuan and Maxianshan areas respectivelynd categorized them as arc- or collision-type based on their geo-hemical characteristics. High-quality age data, as shown in Fig. 1nd listed in Table 1, indicate that the ages of the Neoproterozoicranitoids in the Qilian block range from 751 Ma to 943 Ma. Thisge distribution is strikingly similar to that of the Jinningian grani-oids in the South China block (e.g., Bai et al., 1996; Li et al., 2003a,c,008b; Ye et al., 2007). This similarity between the Qilian and Southhina blocks suggests that the granitoid magmatism between thewo blocks may be correlatable; hence, the two blocks could beectonically affinitive with each other and even unified in the Neo-roterozoic. This possibility is particularly profound geologically as

t is a key to understanding the early geological history of the Qilianlock.

In the present work, the authors pursue this geologicallymportant possibility by studying the petrological characteristics,eochemical features, isotopic compositions, and ages of the Neo-roterozoic granitoids from the Qilian block in an attempt toeconstruct a Neoproterozoic geological history for the Qilian block.

. Tectonic position and general geology of the Qilian block

The Qilian block is roughly lensoidal with its long axis orientedWW-SEE. To the north, it is sutured with the Alaxa block by the

ower Paleozoic North Qilian orogenic belt (Song et al., 2013). It isruncated by a sinistral strike-slip Altyn-Tagh fault and in directontact with the Tarim block in the northwest. In the southeast, it

s also in fault contact with the Ordos basin and Qinling orogenicelt. The North Qaidam ultrahigh-pressure metamorphic (UHPM)elt is the southwestern boundary between the Qilian and Qaidamlocks. Song et al. (2006) considered the Qilian and Qaidam blocks

earch 235 (2013) 163– 189 165

to be a unified continent and the North Qaidam UHPM belt to be aresult of continental subduction/exhumation in the lower Paleozoictime. Most recently, Song et al. (2013) proposed a South-West ChinaUnited Continent of which the Qaidam-Qilian block links the Tarimand South China blocks.

Lithologically, the Qilian block consists of a bulky Precambrianbasement rock sequence, a thin layer of supracrustal Phanerozoiccover strata, and voluminous lower Paleozoic granitoids.

The lower part of the Precambrian basement rock sequence,named the Yemananshan Group in the west, Huangyuan Groupin the middle, and Maxianshan Group in the east, consists ofstrongly deformed orthogneisses, paragneisses, migmatites, schists(most commonly mica quartz schists, amphibole schists, and gar-net quartz schists), marbles, quartzites, and amphibolites of highgreenschist- to amphibolite-facies and was intruded by a smallamount of Proterozoic granitoids. The middle part, locally knownas the Danghe Group in the west, Huangzhong Group in themiddle, and Xinglongshan Group in the east, consists of slates,phyllites, marbles, quartzites, low-grade schists (most commonlychlorite schists, mica schists, and quartz schists), and metavolcanicrocks with well-preserved original sedimentary structures and dis-conformably overlies the lower part of the sequence. The upperpart, locally referred to as the Tuolainanshan Group in the west,Huashihshan Group in the middle, and Gaojiawan Group in theeast, consists of an essentially unmetamorphosed, very extensivelayer of carbonate rocks and small amount of Fe–Mn deposits andunconformably overlies the middle part of the sequence.

The cover strata unconformably overlying the basement rocksequence can be divided into three unconformably related series.The lower series consists of lower Paleozoic moderately to stronglydeformed arc and backarc volcano-sedimentary rock associations.The middle series consists of upper Paleozoic to Triassic moderatelydeformed continental to shallow marine sedimentary formations.The upper series is composed of extensive gently folded to hori-zontal Cenozoic deposits.

In the Qilian block, the granitoids are mostly lower Paleozoic.They have intruded the lower Paleozoic series of cover strata aswell as the basement rock sequence and commonly occur as hugebatholiths, particularly in the western half of the Qilian block. TheNeoproterozoic granitoids which are studied in the present workare relatively uncommon and only occur as small stocks in thelower part of the basement rock sequence. They have intruded theHuangyuan Group and often injected along bedding planes, frac-ture surfaces, fissures, or schistosities into country rocks to formmigmatites. A Proterozoic granitoid stock intruding the HuangyuanGroup near Huangyuan county was dated 2469 Ma and was oncethought to be Paleoproterozoic (BGMRQP, 1991). However, this agehas recently been repeatedly discredited by many SHRIMP and LAICP-MS age data (Table 1) showing that this Proterozoic granitoidis actually Neoproterozoic.

Mesozoic granitoids are rare and only present in the southeast-ernmost part of the block.

3. Description of the Neoproterozoic Granitoids

The Neoproterozoic granitoid samples were collected from thestocks in the Tuole, Huangyuan, and Maxianshan areas for thepresent study (Fig. 1). In the field, the granitoid stocks can beobserved to intrude the Huangyuan Group rock formations, andcontact zones up to a few meters wide have usually developed. Inthe contact zones, the granitoid veins or tongues can be seen to pen-

etrate the country rocks along the foliations, joints, fractures, andbedding planes. Fragments or blocks of the country rocks up to afew meters across can be found in the granitoids close to the contactsurfaces (Fig. 2a). Contact metamorphic aureoles up to a few tens

166 K.-a. Tung et al. / Precambrian Research 235 (2013) 163– 189

Table 1U–Pb ages of the zircons of the Neoproterozoic granitoids from the Qilian block and neighboring North Qilian Orogenic belt and North Qaidam Ultrahigh-Pressure Metamorphicbelt.

Locality no. Latitude longitude Rock type Age (Ma) Method Tectonic environment Reference

1 38◦48.69′N 97◦56.56′E Granitic plutonic rock 922 ± 5 ID-TIMS Arc Gehrels et al. (2003)2 37◦56.15′N 94◦58.75′E Granite 928 ± 10 ID-TIMS Arc Gehrels et al. (2003)3 37◦23.93′N 95◦30.77′E Gneissic granite 891 ± 31 SHRIMP Not reported Zhang et al. (2008)4 38◦08.90′N 99◦58.20′E Gneissic granite 776 ± 10 SHRIMP Not reported Tseng et al. (2006)5 37◦16.10′N102◦47.30′E Gneissic granite 774 ± 23 SHRIMP Not reported Tseng et al. (2006)6 37◦05.65′N100◦37.33′E Mylonitic granite 790 ± 12 SHRIMP Not reported Tung et al. (2007)7 36◦40.20′N101◦19.70′E Gneissic granite 930 ± 8 SHRIMP Not reported Tung et al. (2007)8 35◦43.80′N104◦01.40′E Diorite 918 ± 14 SHRIMP Not reported Tung et al. (2007)9 36◦04.99′N102◦13.98′E Weakly foliated granite 875 ± 8 LA-ICPMS Not reported Xu et al. (2007)

10 35◦43.80′N104◦01.40′E Granitoid rocks 943 ± 28 ID-TIMS Continent–continent collision Wan et al. (2000)11 35◦46.50′N103◦57.80′E Biotite leptite 930 ± 70 ID-TIMS Continent–continent collision Wan et al. (2003)12 36◦03.13′N102◦16.79′E Gneissic potassic granite 750 ± 30 ID-TIMS Continent–continent collision Wan et al. (2003)13 39◦34.80′N 97◦17.30′E Calc-alkaline quartz-diorite 751 ± 14 ID-TIMS Arc Su et al. (2004)14 36◦40.50′N101◦22.20′E Gneissic granodiorite 917 ± 12 ID-TIMS Syn-collision Guo et al. (2000)15 37◦09.10′N101◦32.50′E Gneissic biotite granite 858 ± 2 LA-ICPMS Not reported Yong et al. (2008)

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f centimeters wide developed along the contact surfaces are occa-ionally conspicuous. Besides, mylonites also occur locally alonghe contact surfaces. Foliations are in general better developed inhe margin of a granitoid body than in the interior and are con-ordant with those in the surrounding rocks. The stock rock typesnclude quartz diorite, granodiorite, potassic granite, and granite.

.1. Tuole granitoid (89-2101A, 38◦45.38′N, 98◦27.74′E)

A group of four Neoproterozoic granitoid stocks, each with anxposed area of less than 30 km2, crop out in the Tuole area (Fig. 1).he rock for the present study was sampled from one of thesetocks, approximately 8 km south of Tuole Pasture, Qilian CountyFig. 1a, 1 ). Macroscopically the rock is light-colored and coarse-rained potassic granite. The layering is not conspicuous due tocarcity of dark minerals. It is allotriomorphic-hypidiomorphic andranular, and consists predominantly of quartz, potash feldspar,lagioclase, and a small amount of biotite. The weakly stretcheduartz grains and flaky micaceous minerals form weak lineationsnd foliations. The potash feldspar has been slightly sericitized ands mostly perthite. Microcline, orthoclase, and micrographic inter-rowth of quartz and orthoclase are also present in small amounts.he plagioclase is dusty, altered albite-oligoclase. Myrmekitic inter-rowth of oligoclase and wormy quartz is common. The dark,rownish biotite flakes intergrown with fine to coarse lamellae ofe-rich chlorite parallel to their basal cleavages are disseminated,ut are oriented in a parallel fashion. Trace fluorite fills the inter-tices.

.2. Haiyan granitoids (88-0301C, 36◦52.48′N, 100◦55.58′E)88-0302A, 36◦50.86′N, 100◦56.91′E)

A group of three Neoproterozoic granitoid stocks, each withn exposed area of approximately 20 km2, occur around Haiyanounty in the Huangyuan area (Fig. 1b, 9 and 10

). The handpecimens of the Neoproterozoic granitoids, more specifically gra-odiorite, are whitish gray, equigranular, fine- to medium-grainednd allotriomorphic-hypidiomorphic. No layering is observedn the rock samples, but alternating, S-shaped micaceous anduartzofeldspathic bands can be recognized with petrographicicroscopy. The micaceous bands consist of aligned biotite

nd muscovite flakes, and plagioclase (Fig. 2b), whereas theuartzofeldspathic bands consist of quartz, potash feldspar, andlagioclase. The quartz grains are strongly stretched and sutured,ith undulose extinction. The plagioclase is commonly twinned

3 LA-ICPMS Not reported Yong et al. (2008)2 LA-ICPMS Not reported Yong et al. (2008)2 LA-ICPMS Not reported Yong et al. (2008)

oligoclase or myrmekite and has been slightly saussuritized. Thewhitish potash feldspar containing up to 5.39% BaO is mostly ortho-clase and is interstitial. Minute thin platy ilmenite is also present,but very rare.

3.3. Gahai granitoids (87-1404A, 87-1404E, 87-1404G,37◦5.65′N, 100◦37.33′E)

The Gahai Neoproterozoic granitoid samples were collectedfrom a small stock with only 25 km2 of exposed area approxi-mately 6 km north of Gahai Lake in the Huangyuan area (Fig. 1b,6 , 7 , and 8 ). The rocks are granites and are whitish gray,

fine- to medium-grained, and allotriomorphic to hypidiomorphic.Locally, as is most conspicuous in sample 87-1404G, the gran-ites show sheared and granulated textures, and the constituentquartz grains are strongly stretched to form monomineralic rib-bons and show undulose extinction. Faint layerings are observedin sample 87-1404A, which shows alternating thin layers oftwo contrasting mineral assemblages: quartz-potash feldspar andbiotite-muscovite-chlorite-plagioclase. Potash feldspar is whitishand mostly orthoclase. Biotite, muscovite, and chlorite are con-centrated in thin layers and are well-aligned. The plagioclase istwinned, compositionally oligoclase (samples 87-1404E and G) oralbite-oligoclase (samples 87-1404A), and very dusty due to saus-suritization. Rutile is elongated and is sandwiched between chloritesheets replacing biotite. Chlorite occurs as discrete flakes or inter-grown lamellae in biotite flakes. It is noteworthy that considerableamounts of monazite and xenoclasts of almandine garnet (Alm70–74Prp10–14 Grs2–4 Sps10–16) (Fig. 2c) are present in samples 87-1404Gand 87-1404E, respectively.

3.4. Huangyuan granitoids (90-0501A, 36◦36.90′N, 101◦21.93′E)(90-0502A, 36◦40.20′N, 101◦19.70′E)

The Huangyuan samples were collected from a Neoprotero-zoic stock approximately 10 km southeast of Huangyuan County(Fig. 1b, 2 and 3 ). They are granodiorite. The rocks are grayish,medium- to coarse-grained and allotriomorphic-hypidiomorphic.Layerings are indistinct on the rock samples, but quartz streaks areobvious. Sample 90-0502A was apparently sheared and granulateddue to cataclastic deformation and thus contains abundant coarse-

grained clasts of feldspars. The rocks consist chiefly of biotite,plagioclase, potash feldspar, and quartz. The biotite and minor mus-covite flakes are aligned and, together with quartz streaks, definethe lineation and foliation for the rocks. The plagioclase, commonly

K.-a. Tung et al. / Precambrian Research 235 (2013) 163– 189 167

Fig. 2. (a) Intruding granitoid (G) captured a piece of biotite gneiss fragment (S) from the country rock. Photomicrographs (b) and (e) were taken with cross-polarizedlight, and (c), (d), and (f) with plane-polarized light. Al: metamict allanite, Bt: biotite, Ep: epidote, Fac: ferroactinolite, Grt: garnet, Hbl: hornblende, Mus: muscovite, Pl:p n the

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lagioclase, Qtz: quartz. (b) Haiyan granodiorite (88-0301C). (c) Xenoclastic garnet if ferroactinolite and quartz (87-1701C). (e) A euhedral grain of epidote enclosing maokuhe granodiorite (98-0704A).

winned and zoned, is compositionally oligoclase-andesine and haseen partly altered to clinozoisite. The potash feldspar is mostlyrthoclase and microcline commonly containing abundant sericitend minute muscovite flakes. The quartz grains are elongated andhow undulose extinction. The titanite occurs as inclusions in theiotite. A few euhedral grains of almandine garnet (Alm45–53 Prp1–2rs35–43 Sps6–11) are present.

.5. Riyueshan granitoids (87-1701A, 87-1701C, 36◦32.03′N,01◦7.94′E)

The Riyueshan samples were collected from a Neoproterozoicranitoid stock having an exposed area of approximately 200 km2,ocated approximately 20 km southwest of Huangyuan County in

Gahai granite (87-1404E). (d) A hornblende core consisting of intimate intergrowthict allanite in the Maxianshan quartz diorite (86-1619). (f) A euhedral garnet in the

the Huangyuan area (Fig. 1b, 4 and 5 ). The constituent granitoidrocks are granodiorite and are grayish and medium-grained andhypidiomorphic to allotriomorphic. The major constituent miner-als are biotite, hornblende, plagioclase, potash feldspar, and quartz.Biotite sheets, prismatic hornblende, and weakly undulose quartzgrains form the weak lineations and foliations for the rocks. Biotitehas been topotaxially replaced by chlorite. When biotite is partlyaltered to chlorite, they are interdigited and share basal cleavageto form a single biotite-chlorite composite grain. Abundant minutegrains of titanite form stringers skirting biotite or occur as inclu-

sions along cleavage planes in biotite. Prismatic hornblende hasbeen partly altered to actinolite or completely replaced by actinoliteand titanite. It occasionally contains a core consisting of labradoriteand intimate intergrowth of ferroactinolite and quartz (Fig. 2d).

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ath-shaped plagioclase, usually twinned and saussuritized, isompositionally andesine. Occasionally, oligoclase intergrows withormy quartz to form myrmekite. Titanite substitutes for ilmenite,

ften leaving behind a small residual ilmenite grain as core. Potasheldspar is mainly pinkish orthoclase and is interstitial.

.6. Maxianshan granitoids (86-1619, 35◦43.80′N, 104◦1.50′E)86-1605, 35◦43.70′N, 104◦0.94′E) (98-0501A, 35◦46.70′N,03◦52.20′E)

Three Maxianshan granitoid samples were collected from threeiscrete stocks in the Maxianshan area approximately 30 km southf Lanzhou City (Fig. 1c, 12

, 13 , and 14

). Sample 86-1619 is aray, medium-grained, and allotriomorphic-granular quartz dior-te. The layerings are indistinct and the major constituent mineralsre plagioclase, hornblende, biotite, and quartz. Plagioclase is ande-ine, twinned, and strongly saussuritized. The biotite grains areark brown and commonly show submicroscopic interstratifica-ions of biotite and chlorite sheets. Hornblende is compositionallyastingsite-tschermakite. Flaky biotite and prismatic hornblendere randomly oriented. Quartz grains show undulose extinction andolycrystalline and are slightly stretched to form weak lineations.otash feldspar is minor and is orthoclase containing up to 4.78%aO. Epidote is euhedral and commonly encloses metamict allaniteFig. 2e), and is considered primary. Ilmenite and titanomagnetitere usually replaced and, thus surrounded, by titanite.

Sample 86-1605 is a whitish, medium-grained and hypidiomor-hic to allotriomorphic potassic granite with indistinct layeringsnd consists chiefly of biotite, muscovite, plagioclase, K-feldspar,nd quartz. Biotite, muscovite, and elongated quartz grains definehe lineations and foliations for the rock. Biotite is partly altered toe-rich chlorite. K-feldspar is whitish and is orthoclase, microcline,r microperthite. Plagioclase is untwinned, slightly saussurizedligoclase-albite and occasionally intergrown with quartz to formyrmekites. The quartz grains are stretched and polycrystalline,

nd show weak undulose extinction.Sample 98-0501A is also potassic granite. It is grayish-

inkish, massive, and porphyritic. The very coarse-grained pinkish-feldspar phenocrysts are set in a medium-grained K-feldspar-lagioclase-biotite-muscovite-quartz groundmass. The layeringsre indistinct. K-feldspar is orthoclase containing up to 1.15% BaO.lagioclase is untwinned oligoclase and has been partly saussuri-ized. Biotite is flaky and iron-rich, but is only weakly oriented.pidote is euhedral and contains up to approximately fourteenxide percents of rare earth elements. Other accessory mineralsnclude zircon, apatite, goethite, thorite, and REE minerals.

.7. Baokuhe granitoid (98-0704A, 37◦9.10′N, 101◦33.63′E)

This granitoid sample was collected from a lenticular stockhich has an exposed area of approximately 20 km2 and is located

pproximately 30 km north of Tatung County in the Huangyuanrea (Fig. 1b, 11

). The granitoid intruded schists of the Huangyuanroup with well-developed foliations concordant with schistos-

ty of the country rocks. This grayish sample is granodiorite,nd shows porphyric texture with very coarse-grained K-feldsparnd plagioclase phenocrysts and medium- to coarse-grainediotite-muscovite-feldspar-quartz groundmass. The plagioclase,ompositionally oligoclase-andesine, is twinned and has beenartly altered to zoisite-epidote, prehnite, and sericite. The K-eldspar is orthoclase but occasionally has small albite inclusions.

laky Fe-rich biotite grains are well-oriented and define folia-ions for the rock. Titanite occurs as discrete euhedral grains or asmall inclusions in biotite. Quartz grains are slightly stretched andhow weak undulose extinction. Other accessory minerals include

earch 235 (2013) 163– 189

euhedral garnet (Alm46–50 Prp39–43 Grs2–3 Sps8–10) (Fig. 2f), zircon,and apatite.

4. SHRIMP zircon U–Pb geochronology

Eight samples of the Neoproterozoic granitoids described in theprevious section were selected for geochronological study withSHRIMP in the present work. Cathodoluminescent images weretaken before the zircon grains were analyzed for U-Th-Pb abun-dances and isotopic ratios using SHRIMP II at the Beijing SHRIMPCenter of the Chinese Academy of Geological Science. The pro-cedures suggested by Compston et al. (1984) were followed. Thecommon Pb was calibrated with the measured 204Pb. Zircon stan-dard SL13 (572 Ma, 238 ppm U) was used to calibrate U, Th, andPb concentrations of the samples and standard. The TEMORA stan-dard (417 Ma) was used to calibrate the Pb/U and UO/L values (Blacket al., 2003). The ages of the analyzed zircons were calculated usingthe ISOPLOT program (Ludwig, 2003). The analysis results are givenin Table 3 and are described individually for each of the eight sam-ples below.

4.1. Tuole sample (89-2101A)

The zircon grains are short prismatic and euhedral with well-developed crystal faces and edges. The longer axes are measuredapproximately 200–300 �m with aspect ratios of approximately2:1. Cathodoluminescent images (Fig. 3a) show that the zircongrains display oscillatory zonings parallel to the crystal faces.Twenty-four spot measurements were made on twenty-one zircongrains. All spots define a discordia array with an upper interceptat 896 ± 15 Ma and lower intercept at 213 ± 27 Ma (Table 3 andFig. 3b).

4.2. Haiyan sample (88-0301C)

The zircon grains show sector or oscillatory zonings internallyand narrow bright margins in cathodoluminescent images (Fig. 3c).The zircon crystals are stout prismatic and their longer axes aremeasured 80–150 �m with aspect ratios approximately 2:1 to 1:1.Twenty-two age measurements were performed on twenty zircongrains (Table 3 and Fig. 3d). An age of 795 ± 7 Ma is obtained for thisgranitoid stock from a cluster of 13 concordant analyses. Moreover,clusters of five and two concordant analyses yield 1825 ± 14 Ma and1683 ± 22 Ma respectively for two groups of presumably inheritedzircons (Table 3 and Fig. 3d).

4.3. Gahai samples (87-1404E and 87-1404G)

The zircon grains from the sample 87-1404E are stout prismaticeuhedral crystals. Their longer axes are measured approximately100–200 �m with aspect ratios of approximately 2:1. The grainsshow oscillatory zonings parallel to the crystal faces in the cathodo-luminescent images (Fig. 3e). Age measurements were performedon seventeen spots on seventeen zircon grains (Table 3 and Fig. 3f).Fourteen concordia analyses yield a weighted average age of816 ± 5 Ma. In three other concordia analyses, two clusters wereapproximately 2541 ± 26 Ma and one was 1739 ± 15 Ma respec-tively (Table 3 and Fig. 3f). These values are presumably the ages ofinherited zircons.

The zircon grains from the sample 87-1404G are stout prismaticcrystals. The longer axes are approximately 80–100 �m with aspect

ratios of approximately 2:1 to 1:1. These grains exhibit sector andoscillatory zonings and some are mantled by a narrow dark marginin cathodoluminescent images (Fig. 4a). Sixteen age measurements,obtained from sixteen zircon grains, are all concordant analyses

K.-a. Tung et al. / Precambrian Research 235 (2013) 163– 189 169

F iagramG circle

(mta

4

das(m

ig. 3. Cathodoluminescent images of zircon grains and SHRIMP U–Pb concordia dahai granite (87-1404E). The analytical spots on the zircon grains are indicated by

Table 3 and Fig. 4b). The ages of thirteen spots cluster at approxi-ately 800 Ma and yield a weighted average age of 788 ± 6 Ma. The

hree other concordia analyses at 2679 Ma, 1813 Ma, and 1750 Mare presumably the ages of inherited zircons (Table 3 and Fig. 4b).

.4. Baokuhe sample (98-0704A)

The zircon grains separated from sample 98-0704A are euhe-ral and long prismatic crystals with long axes of 300–400 �m and

spect ratios of 2:1 to 4:1 (Fig. 4c). The cathodoluminescent imageshow clear oscillatory zonings parallel to the crystal edges and facesFig. 4c). All fifteen analyses, obtained from fifteen spot measure-

ents on fifteen zircon grains, are concordant and give an average

s for the Tuole potassic granite (89-2101A), Haiyan granodiorite (88-0301C), ands.

weighted 206Pb/238U age of 920 ± 4 Ma (Table 3 and Fig. 4d) for thisgranitoid.

4.5. Maxianshan sample (98-0501A)

Most of the zircon grains separated from sample 98-0501Aare euhedral and short prismatic crystals with long axes of100–200 �m and aspect ratios of approximately 2:1 (Fig. 4e). A fewgrains are long prismatic crystals with long axes of approximately300 �m and 3:1 aspect ratios (Fig. 4e). Their Th/U ratios range from

0.21 to 0.48 (Table 3). Fifteen spot measurements were made onfifteen zircon grains (Fig. 4e). Fourteen analyses fall on the concor-dant line, and thirteen give an average weighted 206Pb/238U age of932 ± 4 Ma (Table 3 and Fig. 4f) for this granitoid.

170 K.-a. Tung et al. / Precambrian Research 235 (2013) 163– 189

F agramp by cir

4

mwemmtcacac

ig. 4. Cathodoluminescent images of zircon grains and SHRIMP U–Pb concordia diotassic granite (98-0501A). The analytical spots on the zircon grains are indicated

.6. Riyueshan samples (87-1701C, 87-1701A)

The zircon grains from sample 87-1701C are euhedral pris-atic crystals having longer axes of approximately 100–200 �mith aspect ratios of approximately 4:1 to 2:1. The zircon grains

xhibit delicate oscillatory zonings internally and occasional brightargins in the cathodoluminescent images (Fig. 5a). Nineteen ageeasurements were made on eighteen grains (Table 3). Eigh-

een of the analyses are concordant. Fifteen of these analysesluster at approximately 800 Ma and yield a weighted aver-

ge age of 809 ± 5 Ma (Table 3 and Fig. 5b). The two otheroncordant analyses at 1480 ± 24 Ma and 2537 ± 10 Ma (Table 3nd Fig. 5b) are presumably the ages of two inherited zir-ons.

s for Gahai granite (87-1404G), Baokuhe granodiorite (98-0704A) and Maxianshancles.

The euhedral zircon grains separated from sample 87-1701Aexhibit well-formed prisms and pyramids. Their longer axesare approximately 100–150 �m with aspect ratios of approxi-mately 2:1 to 3:1. The oscillatory zonings are well-developed(Fig. 5c). Twenty analyses were made on twenty zircon grains(Table 3). An average weighted 206Pb/238U age of 826 ± 7 Mawas obtained for the zircon from nineteen concordia analyses(Fig. 5d).

In summary, the zircon ages of the Neoproterozoic granitoidsfrom the Qilian block form two groups: ca. 800 Ma (826 Ma, 809 Ma,

788 Ma, 816 Ma, and 795 Ma) and ca. 900 Ma (896 Ma, 920 Ma, and932 Ma).

Interesting features emerge in Fig. 6, in which the ages areplotted against (Th/U) ratios for the zircon grains analyzed in the

K.-a. Tung et al. / Precambrian Research 235 (2013) 163– 189 171

F agramz

pogwa8a

ig. 5. Cathodoluminescent images of zircon grains and SHRIMP U–Pb concordia diircon grains are indicated by circles.

resent study and published in the literature for the granitoidsf ca. 800 Ma and ca. 900 Ma groups. The (Th/U) ratios of zirconrains from the granitoids of the ca. 800 Ma group vary widely,hereas those from the granitoids of the ca. 900 Ma group have

relatively limited distribution. Moreover, the granitoids of the ca.

00 Ma group have many presumed inherited zircon grains of olderges, whereas those of the ca. 900 Ma group have only a few.

Fig. 6. Ages plotted against (Th/U) ratio of the zircons for t

s for Riyueshan granodiorite (87-1701C and 87-1701A). The analytical spots on the

5. Whole-rock geochemistry

Fourteen samples of the Neoproterozoic granitoids describedin the earlier section were analyzed at the Geoanalytical Labora-tory, Washington State University, USA, for their major and trace

elements with XRF and ICP-MS. The analytical results are given inTables 4 and 5 and are described below.

he Neoproterozoic granitoids from the Qilian blocks.

172 K.-a. Tung et al. / Precambrian Research 235 (2013) 163– 189

Fig. 7. (a) (K2O + Na2O) vs. SiO2 for the Neoproterozoic granitoids from the Qilian block. The alkalic–subalkalic boundary of Miyashiro (1978) is shown. The classificationa positN terozg

5

sBogtgsc(fiomMSg

nd nomenclature of rocks by Middlemost (1994) are adopted. (b) Normative comeoproterozoic granitoids from the Qilian block. (c) K2O vs. SiO2 plots for the Neoproranitoids from the Qilian block.

.1. Major elements

Total alkalis are plotted against silica for fourteen granitoidamples in Fig. 7a. The granitoids from the Haiyan, Huangyuan,aokuhe, and Riyueshan stocks are plotted in the field of granodi-rite, whereas those from Gahai and Tuole stocks in the field ofranite. For the Maxianshan stocks, the granitoid (86-1619) is plot-ed in the field of granodiorite but very close to diorite, whereasranitoids 86-1605 and 98-0501A in the field of granite. To clas-ify these granitoids based on feldspar minerals, their normativeompositions are plotted in an An-Ab-Or diagram by O’Connor1965) (Fig. 7b). The results show that they are distributed in theelds of tonalite (Maxianshan, 86-1619, and Riyueshan), granodi-rite (Huangyuan and Baokuhe), trondhjemite (Haiyan), quartz

onzonite (Maxianshan, 86-1605), and granite (Gahai, Tuole, andaxianshan, 98-0704A). The compositional plots in the K2O vs.

iO2 diagram (Fig. 7c) show that the Gahai granite, Tuole potassicranite, Maxianshan potassic granites, and one of the Huangyuan

ions of feldspars are plotted in the An-Ab-Or diagram of O’Connor (1965) for theoic granitoids from the Qilian block. (d) A/NK vs. A/CNK plots for the Neoproterozoic

granodiorites (90-0501A) are high-K calc-alkaline, whereasthe Maxianshan quartz diorite, Riyueshan granodiorite, Haiyangranodiorite, Baokuhe granodiorite, and another Huangyuan gra-nodiorite (90-0502A) are medium-K calc-alkaline.

As shown in the A/NK vs. A/CNK diagram (Fig. 7d), twoRiyueshan granodiorites are metaluminous and all others are per-aluminous or strongly peraluminous.

5.2. Trace elements

The distribution patterns of rare-earth elements for the ca.800 Ma group and ca. 900 Ma group granitoids are plotted sepa-rately in Fig. 8. The most striking feature is that the Gahai granite(87-1404G) which contains considerable amounts of monazite and

apatite is extraordinarily high in total REE abundance (578.6 ppm)and, especially, in total LREE abundance (509.8 ppm) (Table 5 andFig. 8d). The enrichment of lighter LREEs is more pronounced in theca. 800 Ma group granitoids than in the ca. 900 Ma group, resulting

K.-a. Tung et al. / Precambrian Research 235 (2013) 163– 189 173

zoic gr

i(gHa(

c0

Fig. 8. REE distribution patterns for the Neoprotero

n steeper LREE patterns (Fig. 8). This feature is also shown by theirLa/Gd)N values (Table 5), which are higher for the ca. 800 Ma groupranitoids (10.90–14.35) than the ca. 900 Ma group (7.66–11.18).owever, the HREE distribution patterns of both groups are rel-tively flat, as is apparent from Fig. 8 and their (Gd/Yb)N values

mostly 1.32–2.14, except sample 87-1404G) in Table 5.

All granitoids show negative europium anomalies (Table 5). Thea. 900 Ma group granitoids have Eu/Eu* values mostly between.54 and 0.98, except the Tuole sample (89-2101A) which have a

anitoids from the Qilian block. Symbols as in Fig. 7.

Eu/Eu* value of 0.25. In contrast, the ca. 800 Ma group granitoids aremore varied in Eu/Eu* values ranging from 0.23 to 0.83 (Table 5).

The primitive mantle-normalized multi-element plots for theca. 800 Ma group and ca. 900 Ma group granitoids are also shownseparately in Fig. 9. All patterns have clear Ti, P, and Nb–Ta neg-

ative anomalies. Ba negative anomaly is also apparent for allsamples except the Maxianshan quartz diorite (86-1619) in whichpotash feldspars contain substantial amounts of BaO, as veri-fied by EDS analysis. The Nb/Ta ratios of these Neoproterozoic

174 K.-a. Tung et al. / Precambrian Research 235 (2013) 163– 189

c gran

gd(T9rre(t

Fig. 9. Multi-element plots for the Neoproterozoi

ranitoids (4.7–16.2, Table 5) are all lower than that of C1 chon-rite (17.3–17.6, Sun and McDonough, 1989) or primitive mantle17.5, McDonough and Sun, 1995). Among these analyses, theuole, Huangyuan, Riyueshan, and Gahai granitoids (89-2101A,0-0502A, 87-1701C, and 87-1404A) have particularly low Nb/Taatios (8.07, 8.77, 4.68, and 5.34, respectively, Table 5). Low Nb/Taatios are characteristics of highly fractionated granitoids (Zhao

t al., 2008). Moreover, it is noteworthy that the Gahai granite87-1404G), which has a considerable amount of monazite, is par-icularly enriched in Th.

itoids from the Qilian block. Symbols as in Fig. 7.

6. Sm–Nd isotopic composition

The analytical data in Table 6 show that the granitoids of thetwo groups have distinct Nd isotopic compositions. The mea-sured 143Nd/144Nd ratios of the ca. 800 Ma group granitoids varyfrom 0.511566 to 0.511766, whereas those of the ca. 900 Magroup granitoids vary from 0.511826 to 0.512003. The initial

143Nd/144Nd values, calculated from the measured 143Nd/144Ndand 147Sm/144Nd values and the SHRIMP zircon ages, are nearlyequal (0.511154–0.511208) for the ca. 900 Ma group granitoids, but

n Research 235 (2013) 163– 189 175

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K.-a. Tung et al. / Precambria

ary largely (0.510873–0.511158) for the ca. 800 Ma group grani-oids (Table 6).

The Sm–Nd isotopic compositions of the granitoids, obtained inhe present study and published in the literature, are plotted in the47Sm/144Nd vs. 143Nd/144Nd diagram (Fig. 10a) which shows thathe compositional points of the ca. 900 Ma group granitoids formn isochron, whereas those of the ca. 800 Ma group granitoids arecattered. The εNd(1 Ga) values and TDM values for the ca. 800 Maroup granitoids range from −6.7 to −12.7 and 2.2 Ga to 3.0 Ga,hereas those for the ca. 900 Ma group granitoids from −4.3 to5.2 and 2.0 Ga to 2.3 Ga, respectively (Table 6). As shown in thed isotopic evolutionary plot (Fig. 10b), the Nd evolutionary plots of

he granitoids of the two groups of granitoids are clearly separated.

. Discussion

.1. Ages of the zircons and Neoproterozoic granitoid magmatismn the Qilian block

The zircon grains used in SHRIMP age determination all showell-developed crystal forms and oscillatory zonings (Figs. 3–5).

heir (Th/U) ratios are generally high (Table 3). All these character-stics suggest that these zircon grains are of magmatic origin; thus,heir ages can be considered as the crystallization ages for the gran-toids or granitoid magmatism for the Qilian block. These age data,ombined with the high-quality age data reported in the literaturefter 2000 (Table 1), are used to construct an age spectrum for theilian block in Fig. 11a.

The age data of the present study alone show two distinct ageroups: ca. 800 Ma (826 Ma, 809 Ma, 788 Ma, 816 Ma, and 795 Ma)nd ca. 900 Ma (896 Ma, 920 Ma, and 932 Ma). When the publishedge data are included, the two age groups remain still distinct and ahird group emerges at ca. 850 Ma (Fig. 11a and Table 1). Thus, thege spectrum of granitoid magmatism in the Qilian block appar-ntly consists of two major groups at ca. 800 Ma and ca. 900 Mand one minor group at ca. 850 Ma. The previous age data of theranitoids in the Qilian block reported by Wang and Chen (1987)nd BGMRQP (1991) range widely from 874 Ma to 2469 Ma. How-ver, the detailed analytical procedures and data are not given forhese age measurements, preventing a meaningful interpretation ofranitoid magmatism for the Qilian block. Therefore, based only onhe zircon age groups obtained in the present study and publishedn recent literature (Table 1 and Fig. 11a), the granitoid magmatismn the Qilian block consists of two major phases at ca. 800 Ma and ca.00 Ma, corresponding to the late and early Jinningian magmatismf Bai et al. (1996), and a minor phase at ca. 850 Ma.

.2. Granitoid types and petrogenesis

The Riyueshan granodiorites (87-1701A and 87-1701C) withSI of 0.97 and 0.77 are metaluminous (Table 4 and Fig. 7d) andonsidered I-type. This classification is supported by the follow-ng mineralogical and geochemical features: pinkish K-feldspar,ommon occurrence of biotite and hornblende, euhedral epidote,patite inclusions in biotite, relatively low FeO in the biotite compo-ition (mostly less than 19% in 87-1701C and 20.10% in 87-1701A),elatively high CaO (4.08 and 5.63%), K2O/Na2O ratios of 0.56 and.78, and normative diopside (Tables 2 and 4).

The fact that the ca. 900 Ma granitoids studied herein asell as those reported in the literature form an isochron in the

47Sm/144Nd vs. 143Nd/144Nd plot (Fig. 10a) and have nearly equal

nitial 143Nd/144Nd values suggests that the ca. 900 Ma granitoidsn the Qilian block are not only coeval but also co-genetic. In other

ords, they belong to a single igneous rock series produced in aingle granitoid magmatic event. Li et al. (2007a) noted that the Ta

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.-a. Tung

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esearch 235 (2013) 163– 189

Table 3SHRIMP zircon U–Pb data of the Neoproterozoic granitoids from the Qilian block.

Spot number f206 (%) U (ppm) Th (ppm) Th/U 206Pb/238UAge (Ma)

207Pb/206PbAge (Ma)

208Pb/232ThAge (Ma)

Discordant % 207Pb/206Pb ±1� (%) 207Pb/235U ±1� (%) 206Pb/238U ±1� (%) Err. corr.

89-2101A Tuole sample1.1 0.40 659 311 0.47 879 ± 5 916 ± 27 901 ± 14 4.0 0.0696 1.32 1.4021 1.44 0.1462 0.56 0.392.1 0.11 447 196 0.45 877 ± 19 891 ± 22 913 ± 24 2.0 0.0687 1.04 1.3806 2.56 0.1457 2.34 0.912.2 0.28 638 172 0.28 641 ± 4 849 ± 28 754 ± 16 33.0 0.0674 1.34 0.9708 1.47 0.1045 0.60 0.413.1 0.38 834 323 0.40 873 ± 8 926 ± 25 908 ± 16 6.0 0.0699 1.20 1.3984 1.53 0.1451 0.95 0.624.1 0.57 5627 3185 0.58 291 ± 1 501 ± 33 259 ± 3 72.0 0.0572 1.48 0.3646 1.52 0.0462 0.38 0.255.1 0.50 531 229 0.45 830 ± 4 903 ± 37 863 ± 24 9.0 0.0691 1.78 1.3095 1.87 0.1374 0.56 0.306.1 0.71 854 394 0.48 909 ± 4 906 ± 36 966 ± 18 0.0 0.0692 1.75 1.4461 1.82 0.1515 0.51 0.287.1 0.64 2926 889 0.31 747 ± 13 844 ± 27 793 ± 20 13.0 0.0672 1.29 1.1374 2.26 0.1228 1.86 0.828.1 0.57 10,494 4035 0.40 624 ± 2 777 ± 23 645 ± 7 25.0 0.0651 1.08 0.9113 1.13 0.1016 0.33 0.299.1 0.35 449 215 0.49 914 ± 17 862 ± 35 890 ± 24 −6.0 0.0678 1.69 1.4236 2.59 0.1523 1.97 0.76

10.1 0.32 612 207 0.35 870 ± 10 918 ± 27 919 ± 20 6.0 0.0697 1.30 1.3869 1.77 0.1444 1.20 0.6811.1 0.27 363 168 0.48 916 ± 17 933 ± 36 885 ± 25 2.0 0.0702 1.74 1.4776 2.64 0.1527 1.99 0.7512.1 0.22 828 277 0.35 852 ± 4 879 ± 22 886 ± 14 3.0 0.0683 1.09 1.3320 1.18 0.1414 0.47 0.4012.2 3.61 4823 959 0.21 327 ± 2 647 ± 176 438 ± 42 98.0 0.0612 8.17 0.4387 8.20 0.052 0.68 0.0814.1 0.32 543 353 0.67 918 ± 17 894 ± 28 915 ± 21 −3.0 0.0688 1.34 1.4530 2.37 0.1531 1.95 0.8215.1 0.21 537 204 0.39 894 ± 5 883 ± 24 906 ± 15 −1.0 0.0685 1.18 1.4043 1.30 0.1487 0.55 0.4216.1 0.08 376 160 0.44 903 ± 6 887 ± 23 910 ± 14 −2.0 0.0686 1.11 1.4217 1.32 0.1503 0.71 0.5413.1 0.26 1630 480 0.30 745 ± 10 847 ± 21 774 ± 19 14.0 0.0673 1.02 1.1370 1.80 0.1225 1.48 0.8217.1 0.74 1875 611 0.34 755 ± 8 876 ± 33 813 ± 20 16.0 0.0683 1.61 1.1694 1.99 0.1243 1.17 0.5918.1 0.25 773 353 0.47 916 ± 16 916 ± 24 900 ± 21 0.0 0.0696 1.16 1.4645 2.25 0.1527 1.93 0.8619.1 1.50 4243 1400 0.34 602 ± 2 795 ± 58 607 ± 20 32.0 0.0656 2.75 0.8856 2.78 0.0979 0.43 0.1620.1 0.43 414 150 0.37 878 ± 18 881 ± 36 880 ± 28 0.0 0.0684 1.76 1.3766 2.82 0.1460 2.21 0.7820.2 0.19 665 511 0.79 882 ± 16 898 ± 32 850 ± 19 2.0 0.0690 1.56 1.3940 2.49 0.1466 1.94 0.7821.1 3.70 2544 537 0.22 663 ± 8 738 ± 175 781 ± 110 11.0 0.0639 8.29 0.9549 8.39 0.1084 1.32 0.1698-0501A Maxianshan sample

1.1 0.40 430 92 0.21 920 ± 4 896 ± 35 819 ± 35 −2.6 0.0719 1.10 1.5270 1.20 0.1539 0.50 0.432.1 0.45 327 72 0.22 945 ± 5 905 ± 44 886 ± 46 −4.4 0.0711 1.30 1.5510 1.40 0.1583 0.52 0.383.1 0.60 38 146 0.39 931 ± 4 888 ± 29 874 ± 19 −4.9 0.0719 0.80 1.5460 0.96 0.1560 0.49 0.514.1 0.56 358 144 0.40 930 ± 5 906 ± 48 879 ± 38 −2.6 0.0722 0.90 1.5500 1.00 0.1557 0.52 0.515.1 0.25 603 132 0.22 936 ± 4 894 ± 21 858 ± 22 −4.7 0.0712 0.70 1.5370 0.81 0.1567 0.46 0.576.1 0.31 393 137 0.35 926 ± 5 885 ± 27 832 ± 18 −4.6 0.0730 0.80 1.5640 0.97 0.1553 0.54 0.567.1 0.37 226 62 0.28 941 ± 10 921 ± 43 953 ± 44 −2.2 0.0695 1.20 1.5050 1.70 0.1571 1.20 0.698.1 0.31 295 112 0.38 940 ± 5 949 ± 31 924 ± 18 1.0 0.0716 1.30 1.5510 1.40 0.1571 0.54 0.399.1 0.18 698 234 0.34 940 ± 4 916 ± 21 912 ± 10 −2.6 0.0709 0.90 1.5370 0.98 0.1572 0.41 0.42

10.1 0.45 301 143 0.48 932 ± 5 917 ± 32 901 ± 21 −1.7 0.0718 0.90 1.5450 1.10 0.1560 0.55 0.5111.1 0.88 487 83 0.17 930 ± 4 901 ± 58 600 ± 88 −3.2 0.0767 0.70 1.6550 0.83 0.1566 0.44 0.5312.1 0.57 225 96 0.43 920 ± 6 869 ± 39 871 ± 27 −5.8 0.0711 1.20 1.5100 1.40 0.1540 0.63 0.4513.1 0.41 349 119 0.34 928 ± 6 909 ± 61 911 ± 46 −2.1 0.0703 0.90 1.5010 1.10 0.1550 0.59 0.5514.1 0.48 237 71 0.30 931 ± 6 922 ± 42 915 ± 39 −1.0 0.0706 1.80 1.5150 1.90 0.1556 0.63 0.3415.1 0.74 201 64 0.32 925 ± 6 908 ± 79 868 ± 63 −1.9 0.0721 1.20 1.5380 1.30 0.1548 0.68 0.5087-1404E Gahai sample

1.1 1.49 83 84 1.04 821 ± 12 800 ± 180 819 ± 41 −2.5 0.0658 8.80 1.2300 8.90 0.1358 1.60 0.182.1 1.51 100 93 0.96 820 ± 10 789 ± 150 840 ± 32 −3.7 0.0655 7.00 1.2230 7.20 0.1356 1.30 0.183.1 0.93 107 144 1.40 827 ± 10 963 ± 74 899 ± 33 16.5 0.0712 3.60 1.3440 3.90 0.1369 1.30 0.334.1 0.85 118 111 0.98 807 ± 9 849 ± 100 840 ± 27 5.2 0.0674 4.80 1.2390 4.90 0.1334 1.10 0.235.1 1.10 179 196 1.13 828 ± 8 862 ± 110 857 ± 24 4.1 0.0678 5.10 1.2820 5.20 0.1371 10.0 0.196.1 0.25 49 36 0.76 2572 ± 31 2540 ± 20 2687 ± 66 −1.3 0.1682 1.20 11.3700 1.90 0.4903 1.50 0.787.1 0.44 89 48 0.56 2634 ± 24 2542 ± 18 2614 ± 67 −3.5 0.1685 1.10 11.7200 1.50 0.5047 1.10 0.738.1 0.27 125 75 0.62 1739 ± 15 1731 ± 25 1768 ± 36 −0.5 0.1059 1.40 4.5210 1.70 0.3096 0.99 0.599.1 0.90 133 223 1.73 810 ± 8 769 ± 93 815 ± 16 −5.1 0.0648 4.40 1.1970 4.50 0.1339 1.10 0.23

10.1 1.21 141 176 1.29 806 ± 8 737 ± 130 812 ± 23 −8.5 0.0639 6.10 1.1720 6.20 0.1331 1.10 0.18

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235 (2013) 163– 189177

Table 3 (Continued)

Spot number f206 (%) U (ppm) Th (ppm) Th/U 206Pb/238UAge (Ma)

207Pb/206PbAge (Ma)

208Pb/232ThAge (Ma)

Discordant % 207Pb/206Pb ±1� (%) 207Pb/235U ±1� (%) 206Pb/238U ±1� (%) Err. corr.

11.1 0.95 120 97 0.83 813 ± 9 826 ± 92 866 ± 27 1.6 0.0666 4.40 1.2340 4.60 0.1343 1.10 0.2412.1 0.61 216 178 0.85 821 ± 10 765 ± 84 812 ± 25 −6.8 0.0647 4.00 1.2120 4.20 0.1358 1.30 0.3213.1 0.81 190 216 1.18 808 ± 7 752 ± 85 830 ± 18 −6.9 0.0643 4.00 1.1840 4.10 0.1335 0.92 0.2214.1 0.47 126 88 0.72 813 ± 8 812 ± 58 835 ± 21 −0.1 0.0662 2.80 1.2260 3.00 0.1344 1.00 0.3515.1 0.99 142 179 1.30 825 ± 9 706 ± 140 824 ± 25 −14.5 0.0629 6.60 1.1850 6.70 0.1366 1.10 0.1616.1 3.58 51 88 1.78 808 ± 17 763 ± 360 802 ± 45 −5.6 0.0650 17.0 1.1900 17.0 0.1335 2.20 0.1317.1 1.24 112 152 1.41 815 ± 9 846 ± 120 846 ± 22 3.8 0.0673 5.60 1.2500 5.70 0.1348 1.20 0.2187-1701C Riyueshan sample

1.1 0.06 911 237 0.27 807 ± 4 831 ± 15 833 ± 10 3.1 0.0668 0.71 1.2275 0.88 0.1333 0.51 0.592.1 0.22 689 274 0.41 804 ± 6 808 ± 27 814 ± 13 0.6 0.0661 1.30 1.2098 1.53 0.1328 0.81 0.533.1 0.70 207 98 0.49 825 ± 7 814 ± 77 852 ± 37 −1.3 0.0662 3.70 1.2474 3.80 0.1366 0.85 0.224.1 0.08 763 144 0.2 2056 ± 14 2356 ± 6 2150 ± 46 14.6 0.1509 0.37 7.8118 0.87 0.3756 0.79 0.915.1 0.44 187 105 0.58 820 ± 7 889 ± 61 859 ± 26 8.4 0.0687 3.00 1.2850 3.10 0.1357 0.95 0.316.1 0.68 245 100 0.42 822 ± 7 813 ± 58 874 ± 29 −1.1 0.0662 2.76 1.2417 2.89 0.1360 0.86 0.307.1 0.41 285 146 0.53 819 ± 5 852 ± 35 881 ± 16 4.1 0.0675 1.68 1.2597 1.82 0.1354 0.70 0.398.1 0.92 159 70 0.45 816 ± 7 795 ± 81 829 ± 37 −2.6 0.0656 3.87 1.2217 3.98 0.1350 0.94 0.249.1 0.21 648 188 0.3 800 ± 4 818 ± 28 837 ± 18 2.2 0.0664 1.35 1.2092 1.44 0.1322 0.51 0.36

10.1 0.20 235 111 0.49 819 ± 6 790 ± 32 853 ± 15 −3.9 0.0655 1.52 1.2268 1.69 0.1359 0.74 0.4411.1 0.14 535 556 1.07 800 ± 4 808 ± 23 808 ± 8 1.4 0.0661 1.10 1.1980 1.20 0.1316 0.55 0.4412.1 0.00 406 212 0.54 822 ± 6 830 ± 23 866 ± 12 0.8 0.0668 1.10 1.2550 1.30 0.1363 0.72 0.5413.1 0.39 222 139 0.65 1489 ± 10 1480 ± 24 1538 ± 26 −0.6 0.0926 1.28 3.3198 1.48 0.2599 0.74 0.5014.1 0.15 828 313 0.39 799 ± 6 842 ± 18 824 ± 11 5.8 0.0671 0.85 1.2166 1.21 0.1314 0.86 0.7115.1 0.68 211 126 0.62 806 ± 6 830 ± 99 850 ± 20 3.0 0.0668 4.75 1.2255 4.82 0.1331 0.81 0.1716.1 0.56 260 179 0.71 810 ± 10 824 ± 59 840 ± 21 1.7 0.0665 2.81 1.2279 3.08 0.1338 1.28 0.4117.1 0.15 206 74 0.37 2512 ± 15 2537 ± 10 2620 ± 42 1.0 0.1679 0.58 11.036 0.94 0.4766 0.74 0.7818.1 0.24 306 369 1.25 810 ± 5 797 ± 54 844 ± 11 −1.6 0.0657 2.60 1.2130 2.70 0.1339 0.69 0.2618.2 1.26 100 69 0.72 820 ± 9 685 ± 126 850 ± 36 −16.6 0.0623 5.88 1.1674 6.00 0.1359 1.18 0.2087-1701A Riyueshan sample

1.1 0.94 229 128 0.58 813 ± 17 808 ± 77 785 ± 34 −0.6 0.0660 3.67 1.2232 4.28 0.1343 2.20 0.512.1 0.20 577 120 0.22 808 ± 14 770 ± 31 766 ± 27 −4.8 0.0649 1.48 1.1938 2.40 0.1335 1.89 0.793.1 0.83 184 93 0.52 828 ± 20 956 ± 81 826 ± 41 13.4 0.0709 3.94 1.3396 4.70 0.1370 2.57 0.554.1 1.05 218 107 0.51 827 ± 16 750 ± 85 810 ± 39 −10.3 0.0642 4.01 1.2129 4.52 0.1369 2.09 0.465.1 1.74 100 100 1.03 837 ± 18 757 ± 159 837 ± 40 −10.6 0.0645 7.55 1.2315 7.89 0.1386 2.30 0.296.1 0.72 184 108 0.61 815 ± 16 751 ± 76 758 ± 30 −8.5 0.0643 3.59 1.1942 4.14 0.1347 2.06 0.507.1 0.74 206 163 0.82 836 ± 16 777 ± 52 802 ± 22 −7.7 0.0651 2.45 1.2432 3.19 0.1386 2.04 0.648.1 0.92 211 56 0.27 820 ± 16 878 ± 91 893 ± 66 6.6 0.0683 4.38 1.2784 4.83 0.1357 2.04 0.429.1 0.95 236 163 0.72 830 ± 16 844 ± 77 809 ± 30 1.7 0.0672 3.71 1.2742 4.22 0.1375 2.02 0.48

10.1 1.10 150 87 0.60 832 ± 17 783 ± 88 795 ± 36 −6.3 0.0653 4.21 1.2399 4.71 0.1378 2.12 0.4511.1 1.14 200 106 0.55 837 ± 16 685 ± 98 811 ± 44 −22.2 0.0623 4.61 1.1909 5.04 0.1386 2.04 0.4112.1 0.65 165 106 0.66 797 ± 16 799 ± 79 780 ± 30 0.2 0.0658 3.75 1.1939 4.29 0.1317 2.09 0.4913.1 0.50 219 127 0.60 818 ± 15 878 ± 43 848 ± 23 6.8 0.0683 2.06 1.2739 2.87 0.1353 2.01 0.7014.1 0.63 181 124 0.70 844 ± 16 824 ± 73 834 ± 29 −2.3 0.0666 3.48 1.2832 4.04 0.1398 2.05 0.5115.1 0.98 100 66 0.68 822 ± 17 766 ± 83 796 ± 31 −7.3 0.0647 3.95 1.2138 4.53 0.1360 2.21 0.4916.1 0.37 302 133 0.46 841 ± 15 813 ± 39 818 ± 26 −3.5 0.0662 1.85 1.2725 2.69 0.1394 1.95 0.7317.1 0.26 336 239 0.74 836 ± 15 831 ± 39 843 ± 20 −0.7 0.0668 1.87 1.2756 2.69 0.1386 1.94 0.7218.1 0.21 103 27 0.27 1934 ± 35 2353 ± 22 2246 ± 81 17.8 0.1506 1.30 7.2650 2.48 0.3499 2.11 0.8519.1 0.80 128 99 0.80 840 ± 17 768 ± 97 828 ± 32 −9.5 0.0648 4.62 1.2440 5.08 0.1393 2.12 0.4220.1 0.55 218 124 0.59 824 ± 15 822 ± 64 795 ± 29 −0.2 0.0665 3.07 1.2497 3.66 0.1363 2.00 0.5587-1404G Gahai sample

1.1 0.4 135 138 1.05 790 ± 15 814 ± 43 794 ± 20 3.0 0.0662 2.05 1.1904 2.89 0.1303 2.04 0.712.1 0.13 361 522 1.49 783 ± 14 775 ± 29 1074 ± 22 −1.0 0.0650 1.36 1.1581 2.34 0.1292 1.91 0.823.1 0.11 150 136 0.94 2735 ± 31 2679 ± 10 2769 ± 45 −2.0 0.1829 0.62 13.329 1.51 0.5285 1.38 0.914.1 0.37 57 94 1.69 805 ± 18 801 ± 70 816 ± 24 −0.6 0.0658 3.33 1.2077 4.06 0.1331 2.31 0.57

178K

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esearch 235 (2013) 163– 189

Table 3 (Continued)

Spot number f206 (%) U (ppm) Th (ppm) Th/U 206Pb/238UAge (Ma)

207Pb/206PbAge (Ma)

208Pb/232ThAge (Ma)

Discordant % 207Pb/206Pb ±1� (%) 207Pb/235U ±1� (%) 206Pb/238U ±1� (%) Err. corr.

5.1 0.75 148 65 0.45 815 ± 14 841 ± 100 809 ± 51 3.1 0.0671 4.81 1.2473 5.14 0.1348 1.80 0.356.1 0.10 285 142 0.51 785 ± 15 754 ± 32 794 ± 19 −4.1 0.0644 1.53 1.1494 2.49 0.1295 1.96 0.797.1 0.57 148 106 0.74 775 ± 7 906 ± 70 745 ± 22 17.0 0.0692 3.41 1.2189 3.56 0.1277 1.03 0.298.1 0.31 316 76 0.25 1617 ± 11 1750 ± 17 1509 ± 46 8.2 0.1070 0.95 4.2068 1.21 0.2851 0.75 0.629.1 0.56 95 42 0.46 1767 ± 28 1813 ± 38 1818 ± 83 2.7 0.1109 2.12 4.8186 2.81 0.3153 1.84 0.66

10.1 5.30 27 19 0.72 790 ± 21 809 ± 502 863 ± 142 2.5 0.0661 24.0 1.1872 24.1 0.1303 2.80 0.1211.1 0.08 372 206 0.57 799 ± 15 735 ± 27 794 ± 18 −8.8 0.0638 1.29 1.1605 2.38 0.1319 2.00 0.8412.1 0.36 227 169 0.77 791 ± 7 819 ± 43 813 ± 15 3.4 0.0664 2.05 1.1956 2.24 0.1306 0.88 0.4013.1 0.33 358 216 0.62 782 ± 6 814 ± 37 809 ± 14 4.1 0.0662 1.79 1.1781 1.94 0.1290 0.75 0.3914.1 0.17 232 140 0.62 799 ± 15 764 ± 32 777 ± 18 −4.5 0.0647 1.50 1.1769 2.46 0.1319 1.96 0.7915.1 0.17 175 133 0.79 797 ± 15 773 ± 42 786 ± 20 −3.1 0.0650 2.00 1.1784 2.85 0.1316 2.03 0.7116.1 0.37 57 94 1.69 805 ± 18 801 ± 70 816 ± 24 −0.6 0.0658 3.33 1.2077 4.06 0.1331 2.31 0.5788-0301C Haiyan sample

1.1 0.22 483 353 0.75 2305 ± 12 2600 ± 7 2702 ± 24 12.8 0.1743 0.43 10.3310 0.75 0.4298 0.62 0.822.1 1.08 86 49 0.59 801 ± 18 885 ± 110 811 ± 45 9.5 0.0685 5.40 1.2490 5.90 0.1322 2.30 0.393.1 2.08 36 28 0.80 1667 ± 27 1750 ± 93 1601 ± 97 5.0 0.1071 5.10 4.3572 5.43 0.2951 1.85 0.344.1 0.58 275 373 1.40 809 ± 15 827 ± 63 806 ± 20 2.1 0.0667 3.00 1.2290 3.60 0.1337 2.00 0.555.1 0.86 294 253 0.89 805 ± 15 689 ± 72 792 ± 23 −16.8 0.0624 3.40 1.1450 3.90 0.1330 2.00 0.506.1 1.49 132 182 1.42 796 ± 8 700 ± 136 794 ± 21 −12.1 0.0628 6.37 1.1378 6.47 0.1315 1.13 0.177.1 0.70 257 294 1.18 793 ± 7 780 ± 73 796 ± 15 −1.7 0.0652 3.48 1.1757 3.60 0.1309 0.90 0.258.1 0.57 344 202 0.61 787 ± 15 873 ± 65 773 ± 26 9.8 0.0681 3.20 1.2200 3.70 0.1299 2.00 0.539.1 0.59 213 250 1.21 800 ± 16 845 ± 77 807 ± 23 5.3 0.0672 3.70 1.2250 4.20 0.1321 2.10 0.49

10.1 0.33 175 55 0.32 2344 ± 19 2588 ± 13 2353 ± 63 10.4 0.1731 0.75 10.4660 1.21 0.4386 0.95 0.7811.1 0.54 237 127 0.55 785 ± 6 786 ± 79 816 ± 23 0.1 0.0654 3.74 1.1667 3.84 0.1295 0.85 0.2212.1 0.67 152 104 0.71 1813 ± 15 1834 ± 29 1821 ± 41 1.1 0.1121 1.61 5.0208 1.86 0.3248 0.95 0.5113.1 0.86 116 28 0.25 1823 ± 17 1810 ± 38 1773 ± 124 −0.7 0.1107 2.08 4.9867 2.34 0.3268 1.06 0.4613.2 0.61 104 123 1.23 1834 ± 21 1784 ± 47 1887 ± 40 −2.7 0.1091 2.57 4.9479 2.89 0.3291 1.31 0.4514.1 0.57 276 125 0.47 816 ± 7 818 ± 73 826 ± 36 0.2 0.0664 3.50 1.2349 3.62 0.1350 0.89 0.2515.1 0.43 168 137 0.84 789 ± 16 855 ± 49 740 ± 21 7.7 0.0676 2.40 1.2130 3.20 0.1303 2.10 0.6716.1 0.31 161 100 0.64 1828 ± 14 1826 ± 22 1887 ± 35 −0.1 0.1116 1.19 5.0436 1.49 0.3278 0.91 0.6117.1 0.73 118 64 0.56 1833 ± 17 1789 ± 37 1789 ± 61 −2.4 0.1094 2.05 4.9611 2.33 0.3289 1.09 0.4718.1 0.20 366 327 0.92 1686 ± 12 1680 ± 14 1656 ± 19 −0.4 0.1031 0.76 4.2472 1.13 0.2989 0.84 0.7419.1 0.96 191 219 1.18 781 ± 7 769 ± 91 784 ± 18 −1.5 0.0648 4.31 1.1519 4.42 0.1288 0.97 0.2220.1 1.08 158 149 0.98 800 ± 17 768 ± 100 755 ± 28 −4.1 0.0648 4.90 1.1800 5.40 0.1321 2.20 0.4120.2 1.08 438 275 0.65 803 ± 15 802 ± 62 773 ± 25 −0.1 0.0659 2.90 1.2040 3.50 0.1326 1.90 0.5598-0704A Baokuhe sample

1.1 0.19 588 134 0.24 926 ± 4 933 ± 21 901 ± 19 0.7 0.0702 1.03 1.4950 1.14 0.1546 0.49 0.432.1 0.30 522 110 0.22 929 ± 5 934 ± 26 869 ± 27 0.5 0.0702 1.28 1.4995 1.40 0.1550 0.57 0.413.1 1.94 116 35 0.31 916 ± 9 974 ± 103 922 ± 94 5.9 0.0716 5.04 1.5081 5.16 0.1528 1.10 0.214.1 0.10 1048 211 0.21 916 ± 3 935 ± 15 928 ± 13 2.1 0.0702 0.75 1.4780 0.85 0.1526 0.41 0.485.1 0.24 241 65 0.28 911 ± 6 953 ± 46 956 ± 25 4.4 0.0708 2.24 1.4817 2.36 0.1517 0.75 0.326.1 0.09 1049 358 0.35 912 ± 7 916 ± 14 901 ± 11 0.5 0.0696 0.70 1.4577 1.07 0.1519 0.81 0.757.1 0.03 1027 177 0.18 925 ± 4 920 ± 14 967 ± 11 −0.5 0.0697 0.70 1.4828 0.85 0.1542 0.48 0.578.1 0.64 174 74 0.44 911 ± 10 908 ± 75 967 ± 39 −0.4 0.0693 3.63 1.4504 3.80 0.1518 1.13 0.309.1 0.11 1374 166 0.12 919 ± 7 966 ± 20 1036 ± 19 4.9 0.0713 0.97 1.5068 1.30 0.1533 0.87 0.67

10.1 0.04 1333 209 0.16 921 ± 4 900 ± 13 925 ± 11 −2.4 0.0690 0.63 1.4617 0.82 0.1536 0.52 0.6311.1 0.06 879 141 0.17 924 ± 4 973 ± 25 1071 ± 23 5.0 0.0715 1.23 1.5209 1.32 0.1542 0.49 0.3712.1 0.04 831 115 0.14 927 ± 5 894 ± 16 968 ± 14 −3.7 0.0688 0.77 1.4682 0.94 0.1547 0.53 0.5613.1 0.08 447 66 0.15 915 ± 6 1011 ± 25 976 ± 35 9.5 0.0729 1.22 1.5334 1.40 0.1525 0.68 0.4914.1 0.01 802 291 0.37 914 ± 4 905 ± 16 901 ± 12 −1.0 0.0692 0.77 1.4531 0.91 0.1523 0.49 0.5315.1 0.01 1179 157 0.14 917 ± 4 925 ± 13 988 ± 19 0.9 0.0699 0.61 1.4724 0.76 0.1528 0.45 0.59

Errors are 1-sigma; f206 (%) indicates the percentage of the common 206Pb in total 206Pb.Common Pb is corrected using measured 204Pb.

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235 (2013) 163– 189179

Table 4Whole-rock major element compositions and CIPW norms of the Neoproterozoic granitoids from the Qilian block.

Sample number 89-2101A 90-0501A 90-0502A 87-1701A 87-1701C 87-1404A 87-1404E 87-1404G 88-0301C 88-0302A 98-0704A 98-0501A 86-1605 86-1619Locality Tuole Huangyuan Riyueshan Gahai Haiyan Baokuhe Maxianshan

Rock type Potassic granite Granodiorite Granodiorite Granite Granodiorite Granodiorite Potassic granite Quartz Diorite

Age (Ma) 896 ± 15 n.d. 930 ± 8b 826 ± 7 809 ± 5 790 ± 12b 816 ± 5 788 ± 6 795 ± 7 n.d. 920 ± 4 932 ± 4 n.d. 918 ± 14b

(wt%)SiO2 76.80 68.22 68.91 67.99 69.92 71.69 71.42 73.09 67.14 68.26 68.96 71.51 70.56 62.38TiO2 0.15 0.47 0.48 0.87 0.64 0.28 0.44 0.49 0.70 0.64 0.45 0.45 0.36 0.92Al2O3 12.21 15.73 16.02 12.35 11.05 14.17 14.20 13.24 15.12 14.40 15.96 13.48 14.88 17.73FeOa 1.28 4.02 3.75 5.23 4.49 2.69 3.36 3.31 5.36 5.82 3.06 2.59 2.47 5.51MnO 0.02 0.06 0.06 0.09 0.10 0.06 0.10 0.05 0.12 0.11 0.06 0.03 0.05 0.09MgO 0.15 0.88 0.98 3.95 2.99 0.97 1.41 1.35 1.97 2.06 0.93 0.70 0.55 1.67CaO 1.11 3.08 3.15 4.08 5.63 1.12 1.36 1.23 1.64 1.15 3.27 1.46 1.89 5.25Na2O 2.63 3.29 4.00 2.34 1.66 4.33 3.35 2.45 4.01 4.27 3.48 2.50 3.12 3.43K2O 4.75 3.54 2.10 1.32 1.29 3.53 3.41 3.77 2.62 2.38 2.72 4.56 4.99 1.82P2O5 0.028 0.140 0.119 0.150 0.126 0.055 0.067 0.067 0.117 0.115 0.120 0.080 0.143 0.203L.O.I. 0.61 0.62 0.66 2.10 2.38 1.02 0.70 0.79 0.81 0.83 0.89 1.31 0.98 1.03Total 99.73 100.05 100.22 100.47 100.28 99.92 99.81 99.83 99.61 100.04 99.90 98.67 99.99 100.03Mg# 17.28 28.06 31.77 57.37 54.27 39.12 42.79 42.09 39.58 38.68 35.13 32.51 28.41 35.07Na2O/K2O 0.55 0.93 1.90 1.77 1.29 1.23 0.98 0.65 1.53 1.79 1.28 0.55 0.63 1.88A/CNK 1.06 1.06 1.10 0.97 0.77 1.09 1.22 1.28 1.22 1.23 1.09 1.15 1.07 1.03A/NK 1.29 1.70 1.81 2.34 2.68 1.29 1.54 1.63 1.60 1.50 1.84 1.49 1.41 2.33NormQ 40.18 25.09 27.02 31.82 38.37 27.54 31.78 37.86 23.89 24.82 27.98 34.44 27.26 18.48Or 28.34 21.06 12.48 7.94 7.79 21.11 20.35 22.51 15.69 14.19 16.27 27.73 29.81 10.88Ab 22.42 27.97 33.95 20.10 14.33 37.00 28.57 20.91 34.30 36.38 29.74 21.72 26.62 29.24An 5.39 14.55 15.00 19.58 19.26 5.30 6.41 5.77 7.55 5.07 16.42 7.45 8.64 25.11C 0.77 1.17 1.69 0.00 0.00 1.31 2.68 3.05 2.98 2.97 1.33 1.81 1.21 1.01Di wo 0.00 0.00 0.00 0.05 3.56 0.00 0.00 0.00 0.00 0.00 0.00 0.00 0.00 0.00Di en 0.00 0.00 0.00 0.02 1.76 0.00 0.00 0.00 0.00 0.00 0.00 0.00 0.00 0.00Di fs 0.00 0.00 0.00 0.02 1.73 0.00 0.00 0.00 0.00 0.00 0.00 0.00 0.00 0.00Hy en 0.38 2.21 2.46 10.01 5.88 2.45 3.56 3.41 4.98 5.19 2.35 1.80 1.40 4.22Hy fs 2.16 6.74 6.22 8.44 5.79 4.63 5.67 5.40 9.00 9.90 5.04 4.18 4.06 8.84Il 0.29 0.90 0.92 1.68 1.24 0.54 0.84 0.94 1.35 1.23 0.86 0.88 0.68 1.77ap 0.06 0.31 0.26 0.33 0.28 0.12 0.15 0.15 0.26 0.25 0.01 0.00 0.31 0.45Totals 100 100 100 100 100 100 100 100 100 100 100 100 100 100

a Total Fe as FeO, Mg#: molar 100*MgO/(MgO + FeO), A/CNK: molar Al2O3/(CaO + Na2O + K2O), n.d.: not determind.b Age data (Tung et al., 2007).

180 K.-a. Tung et al. / Precambrian Research 235 (2013) 163– 189

F 7Sm/1

e

Pt9t(TitHTgceliTahBCstI

opiTK(bng

FL(

ig. 10. (a) Nd and Sm isotopic compositions are plotted in the 143Nd/144Nd vs. 14

volutionary plots for the Neoproterozoic granitoids from the Qilian block.

2O5 content of granitoids is a useful criterion for distinguishing I-ype from S-type granitoids. Plots of the compositions of the ca.00 Ma granitoids in the P2O5 vs. SiO2 diagram (Fig. 12a) showhat P2O5 content decreases with increasing SiO2 from 0.203% P2O5the Maxianshan quartz diorite, SiO2 = 62.38%) to 0.028% P2O5 (theuole potassic granite, SiO2 = 76.80%), characteristics of I-type gran-toids (Chappell, 1999; Broska et al., 2004; Li et al., 2007a). Thus,he granitoids of the ca. 900 Ma group (the Maxianshan, Baokuhe,uangyuan, and Tuole granitoids) are classified as I-type granitoids.his classification is supported by the following mineralogical andeochemical features. The Maxianshan quartz diorite (86-1619) isharacterized by a frequent occurrence of biotite and hornblende,uhedral primary epidote and magnetite, high CaO (5.25%), and aow K2O/Na2O ratio (0.53) (Tables 2 and 4). All of these character-stics suggest I-type granitoid for the Maxianshan quartz diorite.he presence of pinkish K-feldspar and euhedral primary epidote,patite and titanite inclusions in biotite, high CaO (3.08–3.27%), andigh Na2O/K2O ratios (0.93–1.90) suggest that the Huangyuan andaokuhe granodiorites are also of I-type granitoids. High K2O, lowaO and MgO, very low Nb/Ta, and a substantial amount of inter-titial fluorite of late differentiate (Tables 2 and 4) suggest thathe Maxianshan and Tuole potassic granites are highly fractionated-type granitoids.

The Haiyan granodiorites (88-0301C and 88-0302A) and twof the Gahai granites (87-1404E and 87-1404G) are stronglyeraluminous with ASI 1.22–1.28 (Table 4). The third Gahai gran-

te (87-1404A) is peraluminous with an ASI of 1.09 (Table 4).hese samples are characterized by the presence of whitish-feldspar, muscovite, intergranular apatite, almandine garnet

Alm70–74 Prp10–14 Grs2–4 Sps10–16), euhedral ilmenite, and Fe-rich

iotite (19.11–25.88% FeO) and by low CaO (1.12–1.64%) and highormative corundum (1.31–3.05) (Tables 2 and 4). These petro-raphic and geochemical characteristics suggest that these samples

ig. 11. Age spectrum of the Neoproterozoic granitoids for the Qilian (a) and the South Ci et al. (2002b, 2003c), Wang et al. (2004, 2006a,b), Li (1999), Li et al. (2003a, 2006, 20082002), Wu et al. (2005a,b, 2006), Ma et al. (2002), Liu et al. (2009), Shen et al. (2000), Lin

44Nd diagram for the Neoproterozoic granitoids from the Qilian blocks. (b) εNd(T)

are all S-type granitoids. In addition to these characteristic petro-graphic and geochemical features for S-type granitoids, two Gahaigranite (87-1404E and 87-1404G) have high K2O/Na2O ratios (1.02and 1.54) (Table 4).

Being I-type granitoids, the ca. 900 Ma group granitoids weremost likely derived from the partial melting of igneous rock sources.Compositional plots in the MgO vs. SiO2 diagram of Wang et al.(2006a,b) (Fig. 12b) indicate that melts from metabasalt and eclog-ite at 1–4 GPa could produce the ca. 900 Ma group granitoids.However, Roberts and Clemens (1993) pointed out that high-K,I-type granitoids magmas could be derived only from the par-tial melting of hydrous, transitional to high-K, calc-alkaline, maficto intermediate metamorphic rocks in the crust. Accordingly, theauthors consider that the igneous source rocks for the ca. 900 Magroup granitoids were K-rich metabasalt or eclogite to account forthe medium to high-K nature of the ca. 900 Ma group granitoids(Table 4 and Fig. 7c). Roberts and Clemens (1993) further pointedout that these K-rich protoliths were derived from the enrichedsubcontinental lithospheric mantle and so that the protoliths andtheir partial melts have a more or less direct mantle connection inits isotopic signature. In accordance with this argument, the pres-ence of the substantial amount of mantle component in the ca.900 Ma granitoids could be explained as a direct consequence ofthe partial fusion of a K-rich metabasaltic protolith which in turnwas derived from enriched mantle and carried sufficient amountof mantle material. Plots in the MgO vs. SiO2 diagram (Fig. 12b)also show that the partial melts from metabasalt or eclogite at1–4 GPa required to assimilate mafic crustal rocks during the ascen-sion to produce the I-type Riyueshan granitoids. This assimilationof mafic crustal rocks by the Riyueshan granodiorite magma is indi-

cated by the existence of mafic restite as cores in the hornblende(Fig. 2d). The mafic restite originally consisting of calcic plagioclaseand clinopyroxenes has been altered to labradorite and intimate

hina block (b). References for constructing the age spectrum in (b): Ye et al. (2007),b, 2009, 2010), Ling et al. (2003, 2006), Chen et al. (2009), Cheng (1993), Zhou et al.g et al. (2001), Guo et al. (1998) and Zeng et al. (2005).

K.-a.

Tung et

al. /

Precambrian

Research

235 (2013) 163– 189181

Table 5Whole-rock trace element compositions of the Neoproterozoic granitoids from the Qilian block.

Sample number 89-2101A 90-0501A 90-0502A 87-1701A 87-1701C 87-1404A 87-1404E 87-1404G 88-0301C 88-0302A 98-0704A 98-0501A 86-1605 86-1619Locality Tuole Huangyuan Riyueshan Gahai Haiyan Baokuhe Maxianshan

Rock type Potassic granite Granodiorite Granodiorite Granite Granodiorite Granodiorite Potassic granite Quartz Diorite

Age (Ma) 896 ± 15 n.d. 930 ± 8a 826 ± 7 809 ± 5 790 ± 12a 816 ± 5 788 ± 6 795 ± 7 n.d. 920 ± 4 932 ± 4 n.d. 918 ± 14a

(ppm)Sc 3.0 12.2 12.4 12.2 11.1 7.6 9.3 9.7 13.1 11.8 10.4 10.4 4.5 8.7V 10.0 13.0 45.0 93.0 72.0 13.0 32.0 31.0 81.0 81.0 45.5 32.0 13.0 72.0Cr 0.4 9.0 13.0 115.0 84.0 9.0 32.0 30.0 65.0 62.0 15.2 14.0 2.0 25.0Ni 6.0 2.0 6.0 56.0 40.0 11.0 15.0 8.0 19.0 23.0 5.8 1.0 6.0 12.0Cu 0.0 6.0 10.0 13.0 6.0 3.0 6.0 9.0 19.0 25.0 8.9 15.0 1.0 6.0Zn 24.0 85.0 73.0 64.0 57.0 64.0 79.0 93.0 82.0 89.0 58.7 31.0 40.0 76.0Ga 18.0 19.0 23.0 17.0 14.0 20.0 20.0 19.0 20.0 18.0 15.0 17.0 17.0 25.0Rb 213.0 132.0 152.0 59.0 62.0 142.0 126.0 137.0 255.0 94.0 120.0 123.0 214.0 73.0Sr 49.0 165.0 139.3 266.7 346.1 219.5 233.7 168.3 307.6 253.1 170.0 187.0 150.8 210.6Y 39.06 28.87 22.58 29.74 25.66 35.97 34.42 36.89 23.01 20.64 23.30 26.83 33.03 25.48Zr 114.0 188.3 209.2 236.0 161.4 233.0 243.7 280.0 204.0 187.9 123.0 184.0 165.3 429.1Nb 6.62 11.51 16.04 14.25 10.90 17.47 16.61 20.59 12.98 11.85 11.30 9.93 10.30 17.30Cs 5.68 6.12 7.46 2.53 3.74 4.65 4.42 4.29 234.09 24.30 7.28 5.74 7.73 3.04Ba 307.0 694.3 282.3 327.8 296.5 778.2 749.8 672.2 796.9 486.9 732.0 1016.0 672.0 952.0La 41.63 32.17 36.85 48.29 36.22 57.73 52.22 130.20 47.61 40.48 30.10 46.27 31.89 30.08Ce 77.61 60.89 68.46 97.29 67.01 102.87 92.63 241.27 81.92 69.72 56.50 93.03 65.88 66.03Pr 8.06 6.93 7.43 10.51 7.31 10.55 9.67 25.62 8.76 7.57 6.68 10.60 7.97 7.92Nd 29.08 27.13 27.65 37.86 28.04 39.16 35.18 93.62 32.47 27.92 24.20 38.47 29.89 32.24Sm 6.34 6.13 5.66 7.56 5.92 8.69 7.17 17.95 6.36 5.60 5.08 7.49 6.57 6.07Eu 0.50 1.31 1.02 1.57 1.31 1.07 1.13 1.17 1.53 1.36 1.33 1.31 1.12 1.86Gd 5.83 5.49 4.97 5.56 4.89 7.24 6.06 13.35 5.16 4.52 4.65 6.09 6.13 5.57Tb 1.03 0.86 0.77 0.95 0.78 1.17 0.98 1.77 0.76 0.68 0.70 0.92 1.07 0.88Dy 6.42 5.13 4.45 5.17 4.64 7.13 6.14 8.83 4.46 3.93 4.09 5.27 6.14 4.92Ho 1.37 1.03 0.87 1.09 0.93 1.41 1.29 1.47 0.86 0.77 0.83 1.03 1.25 1.02Er 3.79 2.82 2.32 3.06 2.54 3.82 3.64 3.26 2.31 2.06 2.34 2.77 3.41 2.88Tm 0.58 0.43 0.32 0.42 0.38 0.60 0.55 0.41 0.34 0.30 0.35 0.41 0.5 0.44Yb 3.67 2.74 1.93 2.84 2.34 3.86 3.53 2.43 2.08 1.87 2.36 2.67 3.01 2.9Lu 0.59 0.45 0.32 0.43 0.35 0.61 0.55 0.38 0.33 0.29 0.35 0.41 0.43 0.46Hf 4.04 5.58 5.93 5.89 4.46 7.36 7.00 8.28 5.63 5.16 3.26 5.11 4.9 9.57Ta 0.82 0.96 1.83 1.17 2.33 3.27 1.11 1.27 0.94 0.86 1.04 0.82 0.73 1.19Pb 30.39 30.80 19.25 11.32 9.31 27.64 26.35 28.77 18.17 20.29 22.10 27.22 26.79 12.91Th 25.23 10.74 13.57 15.68 11.24 17.17 16.05 36.82 12.52 11.31 12.80 23.16 21.28 11.01U 2.20 2.63 2.78 1.93 1.38 2.26 2.27 3.11 2.40 1.68 1.74 1.24 1.75 1.27�REE 225.6 182.4 185.6 252.3 188.3 281.9 255.1 578.6 217.9 187.7 162.9 243.6 198.3 188.8�LREE 163.2 134.6 147.1 203.1 145.8 220.1 198.0 509.8 178.6 152.7 123.9 197.2 143.3 144.2Eu/Eu* 0.25 0.69 0.59 0.74 0.74 0.41 0.52 0.23 0.81 0.83 0.83 0.59 0.54 0.98(La/Gd)N 10.51 8.63 10.91 12.77 10.90 11.74 12.69 14.35 13.57 13.20 9.53 11.18 7.66 7.95(Gd/Yb)N 1.32 1.66 2.14 1.63 1.73 1.55 1.42 4.56 2.05 2.00 1.63 1.89 1.69 1.59Nb/Ta 8.07 11.99 8.77 12.18 4.68 5.34 14.97 16.21 13.81 13.78 10.86 12.11 14.11 14.54

Eu/Eu* = EuN/((SmN)(GdN))1/2, (La/Gd)N, (Gd/Yb)N = all normalized by N-type MORB (Sun and McDonough (1989)). n.d.: not determined.a Age data (Tung et al., 2007).

182 K.-a. Tung et al. / Precambrian Research 235 (2013) 163– 189

Fig. 12. (a) SiO2–P2O5 correlation diagrams for the ca. 900 Ma granitoids from the Qilian block. Shadowed and solid line-enclosed areas are the Early Paleozoic I-type granitoidsof the Lachlan Fold Belt, Australia (Chappell, 1999) and the Hercynian I-type granitoids of western Carpathian Mountain, Europe (Broska et al., 2004), respectively. (b) MgOv eld ofb ter (1R s from

iohRtrCoaB

gs1isaDoodoampdSo

s. SiO2 plots for the I-type Neoproterozoic granitoids from the Qilian block. The fiy Wang et al. (2006a,b). (c) Plots in the CaO/Na2O vs. Al2O3/TiO2 diagram of Sylvesb/Ba vs. Rb/Sr diagram of Sylvester (1998) for the S-type Neoproterozoic granitoid

ntergrowth of ferroactinolite and quartz as described in a previ-us section. Note that the Riyueshan granodiorites are unusuallyigh in Ni (56 and 40 ppm) and Cr (115 and 84 ppm) and low inb/Sr (0.22 and 0.18) (Table 5). This finding could be attributed tohe resorption of clinopyroxenes in the assimilated mafic crustalocks, which could accommodate considerable amount of Ni andr and are low in Rb/Sr ratios. Furthermore, the residual phasesf the partial melting were most likely dominated by plagioclase,s these granitoids show low Sr concentrations (Patino Douce andeard, 1995).

Relatively high CaO/Na2O ratios (0.26–0.50, Table 4) sug-est plagioclase-rich, clay-poor psammitic rock sources for thetrongly peraluminous Haiyan and Gahai granitoids (Sylvester,998). Occurrence of almandine garnet restites in the Gahai gran-

toid further suggests that partial melting of the psammitic rockources likely occurred at pressures above 10 kbar and temper-tures below 1000 ◦C to produce these S-type granitoids (Patinoouce and Beard, 1995). Moreover, as Al2O3/TiO2 ratio is a measuref temperature and thus degree of partial melting, the compositionsf the S-type granitoids are plotted in a CaO/Na2O vs. Al2O3/TiO2iagram (Fig. 12c) showing the vapor-absent melting experimentsf synthetic biotite paragneiss by Patino Douce and Beard (1995)nd Sylvester (1998). The results show that the partial meltingostly occur 900–975 ◦C in temperature and 20–50% in degree of

artial melting. Likewise, compositional plots in the Rb/Ba vs. Rb/Sr

iagram (Fig. 12d) also indicate that the source rocks for these-type granitoids were clay-poor. As barium is mostly adsorbedn surface of, or occurs as exchanged cations in, clay minerals in

metabasaltic and eclogite experimental melts (1–4.0 GPa) is after the compilation998) for the S-type Neoproterozoic granitoids from the Qilian block. (d) Plots in the

the Qilian block. Symbols as in Fig. 7.

sedimentary rocks (e.g., Nesbitt et al., 1980), these S-type grani-toids, being derived from the partial melting of clay-poor sources,are expectedly characterized by barium negative anomalies (Fig. 9dand f). For comparison, the source rocks of the corresponding ca.800 Ma S-type granitoids from the southern margin of the Yangtzeblock are noted below. Just like the ca. 800 Ma S-type granitoidsfrom the Qilian block, the ca. 800 Ma S-type granitoids from north-ern Guangxi, southern Anhui, and northern Jiangxi along southernmargin of the Yangtze block are characterized by higher CaO/Na2O(>0.3), lower Rb/Sr (0.48–2.7), lower Rb/Ba (0.1–0.7) and nega-tive barium anomalies, also suggesting clay-poor psammitic sourcerocks for these granitoids (Li et al., 2003a; Ge et al., 2001; Wu et al.,2005a,b; Qiu et al., 2002). However, the sources for the ca. 800 MaS-type leucogranites with lower CaO/Na2O (<0.3), higher Rb/Sr(3.4–330), higher Rb/Ba (1.1–170) and negative barium anomaliesfrom northern Guangxi were clay-rich pelitic rocks (Li et al., 2003a;Ge et al., 2001).

The ca. 800 Ma group granitoids for the Qilian block arecharacterized by varied initial 143Nd/144Nd values and scatteredcompositional points in the 147Sm/144Nd vs. 143Nd/144Nd plot(Fig. 10a), suggesting unrelated source rocks for each of the ca.800 Ma group granitoids. Apparently, each had its own source withan initial 143Nd/144Nd value and other geochemical characteristicsdifferent from others. Note that the ca. 800 Ma S-type granitoidsfrom the southern margin of the Yangtze block are similarly charac-

terized (e.g. Li et al., 2003a), also suggesting that the source rocks forindividual granitoids were unrelated and had different geochemicalcharacteristics.

n Research 235 (2013) 163– 189 183

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For the Qilian block, the lower εNd(1 Ga) values (−6.7 to −12.7)nd the older TDM ages (2.2–3.0 Ga) of the ca. 800 Ma group grani-oids than those (−4.3 to −5.2, 2.0–2.3 Ga) of the ca. 900 Ma groupranitoids imply more input of mantle material during magmaeneration for the ca. 900 Ma group granitoids than that for thea. 800 Ma group granitoids. Similarly, for the Yangtze block, thea. 800 Ma granitoids also have lower εNd(T) values (−9.03 to4.54) and older TDM ages (1.50–2.22 Ga) than the ca. 900 Maranitoids and the equivalent intermediate felsic volcanic rocksεNd(T) = −1.74 to +8.8, TDM = 0.9–1.72 Ga) (Li et al., 2003a, 2009;

ang et al., 2004; Chen et al., 2009; Ling et al., 2001, 2003).

.3. Tectonomagmatic environment

Compositional plots of the ca. 900 Ma granitoids from theresent study in the Sr/Y vs. Y diagram (Fig. 13a) of Drummond andefant (1990) and the Rb vs. (Nb + Y) diagrams (Fig. 13b) of Pearcet al. (1984) suggest an arc environment for the magma genesisn the Qilian block in the early Neoproterozoic era. The associated

axianshan mafic-ultramafic rocks with an age of ca. 910 Ma werelso shown to have formed in an arc environment by Tung et al.2012). Gehrels et al. (2003) studied the ∼920–930 Ma granitoidsrom the Qilian terrane and also suggested an early Neoproterozoicrc environment, albeit with less certainty. The Sm–Nd isotopicompositions suggest coeval and co-genesis for the ca. 900 Ma gran-toids (Fig. 10a). The εNd(900 Ma) values suggest considerable inputf mantle material for the ca. 900 Ma granitoids (Table 6). Thesenterpretations of the Sm–Nd isotopic compositions are consistent

ith magma generation in an arc environment for the ca. 900 Maranitoids. However, based on a plot of major element composi-ions in the R1–R2 discriminating diagram of Batchelor and Bowden1985), Guo et al. (1999b) suggested that the 917 Ma granitoid fromhe Huangyuan area was syn-collisional granite. The 930 Ma and40 Ma granitoids from Maxianshan were interpreted by Wan et al.2000, 2003) as products of continent-continent collision, althoughhey are plotted in the field of arc rocks in Sr/Y vs. Y and Rb vs.Nb + Y) diagrams (Fig. 13a and b). In short, the present and previoustudies all suggest an active continental margin in a compressivenvironment during the late Mesoproterozoic-early Neoprotero-oic and the existence of a geologically yet identified orogeny inhat time period for the Qilian block.

For granitoids originated by anatexis, their geochemical char-cteristics often reflect a tectonomagmatic environment for theirource rocks, but not for the granitoids themselves (Arculus, 1987;wist and Harmer, 1987; Roberts and Clemens, 1993). Conse-uently, the assessment of the tectonomagmatic environment forranitoids relies heavily on the associated mafic rocks. While theresent study offers no direct evidence to discriminate tectono-agmatic environment for the granitoid genesis in the Qilian block

n the mid-Neoproterozoic time, following three previous studiesn mafic rocks have suggested a continental rift environment. First,ong et al. (2010) considered that the 850 Ma continental floodasalts from a piece of subducted continental crust in the Northaidam UHPM belt, NW China, were derived in a continental set-

ing and were, perhaps, genetically associated with a mantle plumen a continental rift stage. This consideration implies that the Qil-an block was in a continental rift tectonomagmatic environmentn the mid-Neoproterozoic time. Second, the metavolcanic rocksnterbedded with pelitic and psammitic schists or gneisses in thepper part of the Huangyuan Group, most likely later than 850 Ma,ere shown by Bai et al. (1998) to have originated in a continental

ift environment. Thirdly, the metabasaltic lava flows and tuffs from

he Xinglongshan Group, equivalent to the Huangzhong Groupnd younger than the Huangyuan Group, was interpreted to be ofontinental origin and to have formed in an extensional environ-ent (Wan et al., 2000). Before any evidence is presented to prove Ta

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184 K.-a. Tung et al. / Precambrian Research 235 (2013) 163– 189

F t (19( toids f

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ig. 13. (a) Plots in the Sr/Y vs. Y discriminating diagram of Drummond and DefanNb + Y) discriminating diagram of Pearce et al. (1984) for the Neoproterozoic grani

therwise, the present study suggests a continental rift environ-ent for the Qilian block during the middle to late Neoproterozoic

eriod of time.As mentioned earlier for the Qilian block, the ca. 800 Ma group

ranitoids are characterized by the highly scattered composi-ional points in the 147Sm/144Nd vs. 143Nd/144Nd plot, varied initial43Nd/144Nd values, lower εNd(1 Ga), and older TDM ages, whenompared with the arc-type ca. 900 Ma group granitoids. It is inter-sting to note that, for the Yangtze block, the well-documentedift-type ca. 800 Ma granitoids also have the same isotopic charac-eristics when compared with the arc-type ca. 900 Ma granitoidsLi et al., 2002a, 2003a; Ye et al., 2007). Perhaps, these similaritiesn Sm–Nd isotopic characteristics between two ca. 800 Ma grani-oids from the Qilian and Yangtze blocks respectively could lendupport to the consideration that the ca. 800 Ma granitoids are alsoift-type and formed in a continental rift environment. It is thoughthat the upwelling of a mantle plume, like the one proposed by Lit al. (1999, 2003c), Li et al. (2003a), and Wang et al. (2009) for theouth China block, caused the rifting and provided necessary heato melt the crustal rocks to produce the ca. 800 Ma granitoids forhe Qilian block.

The results of this and previous studies presented aboveuggest a convergent plate tectonic environment in the lateesoproterozoic-early Neoproterozoic and a continental divergent

late tectonic environment in the middle to late Neoproterozoic forhe Qilian block.

.4. Correlations of Neoproterozoic granitoid magmatism andlate tectonic environment between the Qilian and South Chinalocks

The preceding discussion on ages and tectonomagmatic envi-onments indicates that the granitoid magmatism in the Qilianlock appears to consist of a major phase of arc magmatism at ca.00 Ma (875–943 Ma), a minor phase of rift magmatism in its earlytage at ca. 850 Ma, and another major phase of syn-rift magma-ism at ca. 800 Ma (751–815 Ma) (Fig. 11a). Apparently, the Qilianlock experienced arc tectonism on an active continental margin

n a compressional environment followed by rift tectonism in anxtensional environment from the early Neoproterozoic throughhe late middle Neoproterozoic.

Abundant age data are also available for constructing an age

pectrum of granitoid magmatism for the South China blockFig. 11b). This age spectrum shows that Neoproterozoic granitoid

agmatism in the South China block also consists of two majorhases and one minor phase. The earlier major phase of granitoid

90) for the Neoproterozoic granitoids from the Qilian block. (b) Plots in the Rb vs.rom the Qilian block. Symbols as in Fig. 7.

magmatism occurred at ca. 900 Ma (905–1007 Ma) correspondingto the early Jinningian magmatism of Bai et al. (1996) and is shownto be arc-type magmatism related to the assembly of the Yangtzeand Cathaysia blocks to form the South China block (e.g., Li et al.,2002b; Wang et al., 2004; Ye et al., 2007). The minor phase ofgranitoid magmatism occurred at ca. 850 Ma (848–864 Ma) and isinterpreted to be intra-plate magmatism marking the onset of therifting of the Rodinia supercontinent (e.g., Zhou et al., 2002; Li et al.,2003b, 2006, 2010). The later major phase of granitoid magmatismoccurred at ca. 800 Ma (744–829 Ma) and is suggested to be syn-rift magmatism related to the major episode of the rifting of theRodinia supercontinent (e.g., Li et al., 2003a,c, 2008b).

The arc-type granitoids at Xiqiu and Tahong (905 Ma and913 Ma) (Ye et al., 2007), Changsanbei (926 Ma) (Wang et al., 2004),and Huiqingou (1007 Ma) (Li et al., 2002b) and arc-type volcanicrocks at Beiwu (926 Ma) and Zhangcun (875 Ma, 891 Ma, 904 Ma)(Cheng, 1993), Xixiang (895 Ma, 950 Ma) (Ling et al., 2003) andPingshui (904 Ma, 906 Ma) (Chen et al., 2009; Li et al., 2009) alsosuggest an active continental margin in a compressional tectonicenvironment in the early Neoproterozoic. Furthermore, rifting oran extensional tectonic environment in the mid-Neoproterozoichas been thoroughly documented (e.g., Wang, 2000; Wang and Li,2003; Li et al., 2003c, 2008a) for the South China block.

In summary, the South China block experienced a similar evo-lutionary history to the Qilian block, from arc tectonism to rifttectonism in the Neoproterozoic era. Remarkable similarities inages and tectonomagmatic environment suggest that the grani-toid magmatism and plate tectonic environment of the Qilian blockcould be broadly correlated with those of the South China block.

7.5. Geological implication

The correlation of the early to middle Neoproterozoic granitoidmagmatism and plate tectonic environment between the Qilianand South China blocks, as established in the preceding subsection,implies a strong affinity between the two blocks. Worthy of noteis the ages of the inherited zircons, which consist of three groups:ca. 1.4 Ga, 1.7–1.8 Ga, and 2.5–2.7 Ga (Table 3). Interestingly, thesethree age groups of the Qilian block can be broadly correlated withthose of three major stages of tectonothermal events or crustalgrowth in the Yangtz block at 1.2–1.4 Ga, 1.8–2.0 Ga and 2.4–2.9 Ga

(Li et al., 1991; Gan et al., 1996; Wang et al., 2007; Zhang et al.,2006a,b), also suggesting a strong affinity between the two blocks.Previous studies on TDM ages (Wan et al., 2003; Zhang et al., 2006c),Pb isotopic compositions (Zhang et al., 2006c), and mafic-ultramafic

K.-a. Tung et al. / Precambrian Research 235 (2013) 163– 189 185

Table 7Summary of the similarities/differences in geological features between the Qilian and South China blocks during the late Mesoproterozoic-early Paleozoic. For details andreferences, see text.

Qilian block South China block

SimilaritiesHighly radiogenic Pb isotopic composition in basement

rocks and granitoids.Highly radiogenic Pb isotopic composition in granitoids.

ca. 910 Ma arc-type mafic–ultramafic rocks. 895–970 Ma arc type mafic rocks.875–891 Ma oceanic island basalt. ca. 970 Ma oceanic rocks (ophiolite suites).896–930 Ma arc-type granitoids. 905–1000 Ma arc-type granitoids.917 Ma and 943 Ma collision-type granitoids.888 Ma and 891 Ma granitoids.915 Ma arc-type (?) metabasalt. ca. 875–950 Ma arc-type volcanic rocks.850 Ma intra-plate continental flood basalt. 849 Ma continental rift-type dolerite. 850 Ma and 857 Ma anorogenic granitoids.858 Ma and 846 Ma granitoids 863 Ma and 864 Ma granitoidsRift-type basaltic rocks in the Huangyuan group. 827–760 Ma rift-type volcanic rocks.751–826 Ma granitoids 744–829 Ma granitoidsTDM ages of basement rocks from 0.75 Ga to 2.5 Ga: crustal

growth in Proterozoic.TDM ages of Phanerozoic igneous rocks from 0.5 Ga to 2.3 Ga. TDM ages ofsedimentary and metamorphic rocks from 1.1 Ga to 3.3 Ga: crustal growth inProterozoic.

Ages of the inherited zircons: ca. 1.4 Ga, 1.7–1.8 Ga, and2.5–2.7 Ga.

Ages of the tectonothermal events or the major stages of crustal growth;1.2–1.4 Ga, 1.8–2.0 Ga and 2.4–2.9 Ga.

Rapid uplift-erosion of juvenile crust and sedimentaccumulation in early Neoproterozoic.

Short-term recycling of juvenile crust in early Proterozoic.

Extensive carbonate layers in the late Sinian. Extensive carbonate layers in the late Sinian.DifferencesDepositional hiatus in early-middle Cambrian. Continuous deposition from Sinian through early Paleozoic.Regionaly metamorphosed (up to amphibolite-facies) Weakly metamorphosed (up to greenschist-facies) Neoproterozoic formations.

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Neoproterozoic formations accompanied by extensiveearly Paleozoic arc granitoids and mafic-ultramafic rocksand strongly deformed sedimentary formations.

ocks (Gao et al., 2010; Tung et al., 2012) have also led to the sameonclusion, as summarized below.

Wan et al. (2003) and Zhang et al. (2006c) reported that the TDMges of the basement rocks range from 0.73 to 2.26 Ga with a peakt ∼2.1 Ga for the Qilian block and that the crustal growth of the Qil-an block mainly occurred in the Neoproterozoic era. Likewise, theDM ages of the Neoproterozoic formations, Danzhou, Shangxi, andanxi groups, range from 1.54 to 2.14 Ga for the South China block,

mplying a major period of crustal growth in the Neoproterozoicra as well (Chen and Jahn, 1998; Li and McCulloch, 1996; Li et al.,991; Zhu, 1994; Zhang et al., 2002). Zhang et al. (2006c) reportedhat the Pb isotopic composition of the basement rocks and grani-oids in the Qilian block is highly radiogenic with 206Pb/204Pb > 18.0,07Pb/204Pb > 15.5, and 208Pb/204Pb > 38.0. The Pb isotopic composi-ion of the granitoids in the South China block is also characterizedy high radiogenic composition (Zhang et al., 2006c). For example,he 207Pb/204Pb of the Mesozoic granitoids from the South Chinalock is higher than 15.5 (Zhang, 1995), comparable to that of theranitoids of the Qilian block.

Most recently, Tung et al. (2012) reported the occurrence ofhe mafic-ultramafic rocks of arc-type from the Maxianshan, Qilianlock, which could be correlated with the mafic-ultramafic rocks,lso of arc-type, at Pingshui, NW Zhejiang (Cheng, 1993; Li et al.,009), Yanbian, S. Sichuan (Li et al., 2006, 2007b), and Xixiang, S.hangxi (Ling et al., 2003) in the southern and northwestern mar-in around the Yangtze block and thus suggested a strong affinityetween the two blocks.

Other geological features of the Qilian and South China blocksavoring a strong affinity between the Qilian and South China blocksre presented below.

The protolith of the plagioclase amphibolite in the Hualonroup, Qilian block, has a geochemical signature of OIB (Gao et al.,010). Although it was interpreted as a continental basalt (Gaot al., 2010), it is also possible that it is an oceanic island basalt

rom a ca. 900 Ma oceanic crust and could be correlated with theeoproterozoic ophiolitic suites in the South China block.

Xu et al. (2007) obtained an age of 891 Ma for the detrital zirconsn the paragneiss of the Hualong Group in the Qilian block and an

age of 875 Ma for the primary zircons in the intruding granite inthe same paragneiss. Based on these age data, the formation timewas constrained to only 16 million years for the Hualong Groupand a process of rapid crustal uplift-erosion of juvenile crust andsediment accumulation for the Qilian block was suggested for thattime period. Similarly, the results of a combined geochronologicaland geochemical study by Wu et al. (2006) also suggest a short-term recycling of juvenile crust for the southeastern margin of theYangtze block in the early Neoproterozoic.

For the sake of clarity and convenience, the similarities anddifferences in the geochemical characteristics, geological ages ofgranitoids, tectonomagmatic environment, and geotectonic eventsbetween the Qilian and South China blocks or, more exactly, theSibao orogen are summarized in Table 7. These similarities betweenthe two blocks are correlatable and thus could be used to supportthe idea that they were affinitive to each other and could even beunified in the Proterozoic. More specifically, the Qilian block couldbe part of the Sibao orogen in that period of time.

This unification of the two blocks seems to have lasted throughthe Proterozoic, because near the end of the Proterozoic (Deny-ing stage in the late Sinian) both the Qilian and South Chinablocks still had thick, continuous, extensive layers of carbonaterocks in common (e.g., BGMRQP, 1991; Zhang and Lao, 1991; Baiet al., 1996). The separation of the Qilian block from the SouthChina block most likely occurred shortly after the Denying stagein the late Sinian or the beginning of the early Cambrian becausethe geological histories of the two blocks were completely dif-ferent from each other after the Denying stage. In the Yangtzeblock, the state of a passive continental margin and depositionof extensive layers of carbonate rocks had continued from theSinian through at least the Ordovician (e.g., Yang et al., 1986; Ma,1992; Bai et al., 1996). In contrast, in the Qilian block, there wasa depositional hiatus during the period from the lower to middleCambrian and a state of active continental margin, as manifested

by strongly deformed sedimentary-volcanic associations, intensegranitoid magmatism, and extensive regional metamorphism, hadprevailed through at least the lower Paleozoic (BGMRGP, 1989;BGMRQP, 1991).

186 K.-a. Tung et al. / Precambrian Research 235 (2013) 163– 189

Fig. 14. Three one-dimensional schematic geological sections along A-B-C, shown in the index map, across the South China block, illustrating the origin, migration, andcollision with the Alaxa block. Index map is adopted from Li et al. (2002b) and Ye et al. (2007). (a) The South China block, presumably a part of the supercontinent Rodinia,consists of the Yangtze block, Cathaysia block, and the suturing Sibao orogen. The Sibao orogen consists of deformed pre-rift volcanic-sedimentary association and granitoids,syn-rift volcanic-sedimentary associations, and post-rift nearly horizontal glacial, argillo-arenaceous, and carbonate cover layers. (b) The breakup of the supercontinentR a. TheC o formb bonat

nToabtbak

8

1

2

odinia fragmented the South China block and thus opened the Paleo-Tethysian Sehina block and migrated away. (c) The Qilian block collided with the Alaxa block tlock remained stable in a passive continental setting and the deposition of the car

In summary, the Qilian and Yangtze blocks, as a unified conti-ent, had had similar evolutionary histories in the Neoproterozoic.he Qilian block, being a piece of fragment of the South China blockr, more specifically, the Sibao orogen, had had its own evolution-ry history independent of, and vastly different from, the Yangtzelock after the Proterozoic, when it rifted off the Yangtze block afterhe Proterozoic, migrated away, and finally collided with the Alaxalock in the Ordovician period to form the North Qilian orogen. Thebove evolutionary histories of the Qilian block, deduced from thenown geological features, are depicted in Fig. 14.

. Conclusions

. The Neoproterozoic granitoids in the Qilian block form two agegroups, ca. 900 Ma and ca. 800 Ma.

. The ca. 800 Ma group granitoids at Haiyan and Gahai are S-typeand could be formed by the solidification of a partial melt of

Qilian block was a piece of a fragment of the Sibao orogen that rifted off the South the North Qilian orogen and thus closed the Proto-Tethysian Sea. The South China

e layer continued through the lower Paleozoic.

clay-poor, mature psammitic rocks at pressure above 10 kbarand temperatures between 900 ◦C and 975 ◦C.

3. The ca. 900 Ma group granitoids are I-type and could be producedfrom partial melts of K-rich metabasaltic or eclogitic protolithswith significant amount of mantle components in the lowercrust. To produce I-type Riyueshan granodiorite (809 Ma and826 Ma), the partial melts from metabasaltic or eclogitic pro-toliths in the lower crust had assimilated mafic crustal rocksduring ascension.

4. The ca. 900 Ma group granitoids formed in an arc envi-ronment on an active continental margin, whereas the ca.800 Ma group granitoids originated in a continental riftenvironment.

5. The granitoid magmatism in the Qilian and South China blocks

could be correlated. This correlation together with other geo-logical, geochemical, and tectonic features further suggests thatthese two blocks could be unified in the Neoproterozoic. In other

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words, the Qilian block might be part of the South China blockor, more exactly, the Sibao orogen, during that time period.

cknowledgements

The authors would like to express their sincere gratitude to theditor Guochun Zhao and three reviewers who have enthusiasti-ally offered constructive comments and suggestions for improvinghe manuscript. This study was supported financially by researchrants (NSC 97-2116-M-178-001-MY2 and 98-2116-M-178-001)rom the National Science Council, ROC.

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