Contrasting deep crustal compositions between the Altai and East Junggar orogens, SW Central Asian Orogenic Belt: Evidence from zircon Hf isotopic mapping

Accepted Manuscript Contrasting deep crustal compositions between the Altai and East Junggar orogens, SW Central Asian Orogenic Belt: Evidence from zircon Hf isotopic mapping

Peng Song, Tao Wang, Ying Tong, Jianjun Zhang, He Huang, Qie Qin PII: DOI: Reference:

S0024-4937(19)30007-6 https://doi.org/10.1016/j.lithos.2018.12.039 LITHOS 4931

To appear in:

LITHOS

Received date: Accepted date:

5 September 2018 30 December 2018

Please cite this article as: Peng Song, Tao Wang, Ying Tong, Jianjun Zhang, He Huang, Qie Qin , Contrasting deep crustal compositions between the Altai and East Junggar orogens, SW Central Asian Orogenic Belt: Evidence from zircon Hf isotopic mapping. Lithos (2019), https://doi.org/10.1016/j.lithos.2018.12.039

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ACCEPTED MANUSCRIPT Contrasting deep crustal compositions between the Altai and East Junggar orogens, SW Central Asian Orogenic Belt: Evidence from zircon Hf isotopic mapping

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, Ying Tong a, Jianjun Zhang a, He Huang a, Qie Qin a

Key Laboratory of Deep–Earth Dynamics of Ministry of Natural Resources, Institute of Geology,

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a

a, b *

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Peng Song a, Tao Wang

Beijing SHRIMP Center, Beijing 100037, China

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b

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Chinese Academy of Geological Sciences, Beijing 100037, China

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* Corresponding author at: Institute of Geology, Chinese Academy of Geological Sciences. Baiwanzhuang Road 26, Beijing 100037, P. R. China. Tel: +86 10 68999672; Fax: +86 10 68997803;

Abstract

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E–mail addresses: [email protected] (P. Song); [email protected] (T. Wang)

There are long–standing uncertainties over the deep crustal composition and basement nature of the Chinese Altai and Junggar orogens of the southwestern Central Asian Orogenic Belt (CAOB). Zircon Lu–Hf isotopic tracer techniques applied to granitoids are helpful in distinguishing old from young deep crustal compositions. This study aims to characterize the basement nature (ancient & 1

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juvenile) of the Chinese Altai and East Junggar orogens using Hf isotopic mapping of granitoids (510–200 Ma). Zircon Hf isotopic data (18 new and 98 published samples) indicate that the study area can be divided into six Hf isotopic provinces on the basis of TDMC ages: Province I, >1.4 Ga; II, 1.4–1.2 Ga; III, 1.2–1.0 Ga; IV, 1.0–0.8 Ga; V, 0.8–0.6 Ga; and VI, 0.6–0.4 Ga. Provinces I, II, and

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III occur mainly in the central (units 2 and 3) and southern (unit 4) Altai orogen, and have slightly

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positive zircon ε Hf(t) values of +0.5 to +9.1 with slightly old TDMC ages of 1.53–0.81 Ga. Provinces

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IV and V are mainly distributed in the northern (unit 1) and southernmost (unit 5) Altai orogen, with

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zircon εHf(t) values of +7.5 to +11.1 and young TDMC ages of 0.84–0.60 Ga. In contrast, Province VI (East Junggar orogen) has zircon εHf(t) values of +11.6 to +14.9, with much younger TDMC ages of

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0.59–0.35 Ga, except for the small Taheir area with a negative εHf(t) value of –2.5 and an older TDMC age of 2.5 Ga. There is a sharp contrast between the deep crustal compositions of the Altai and

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Junggar orogens, which are ancient in central Altai and relatively juvenile in East Junggar. This

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confirms that significant Neoproterozoic–Phanerozoic continental crustal growth occurred in the southern Altai and Junggar orogens, with juvenile crust occupying ~78% of the study area, and that

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the CAOB is a site of significant Phanerozoic continental growth. The distribution of juvenile and ancient crust in the Altai and East Junggar orogens provides new evidence for the tectonic division of the two orogens by the Erqis fault zone, and explains the heterogeneity of crustal growth in the southwestern CAOB. Keywords : Granitoids; Hf isotopic mapping; Deep crustal compositions; Continental growth; Central Asian Orogenic Belt

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ACCEPTED MANUSCRIPT 1. Introduction The Central Asian Orogenic Belt (CAOB, Jahn, 2004; Windley et al., 2007; also known as the Altaid tectonic collage, Sengör et al., 1993) is considered the largest Phanerozoic accretionary orogenic belt (Sengör et al., 1993; Wickham et al., 1996; Jahn et al., 2000a, 2000b, 2004; Kovalenko

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et al., 2004; Wilhem et al., 2012; Xiao et al., 2015). It contains numerous tectonic units including

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subduction accretionary complexes, magmatic arcs, microcontinents, oceanic plateaus and islands

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(Şengör et al., 1993; Windley et al., 2007; Xiao et al., 2015). The CAOB is also considered the most

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significant site of Phanerozoic continental growth (e.g., Jahn et al., 2004; Windley et al., 2007; Wilhem et al., 2012; Xiao et al., 2015). However, there is debate on these topics. Şengör et al. (1993)

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proposed that almost half of the CAOB is juvenile crust, with Nd isotopic studies of massive granitoids in the CAOB confirming significant crustal growth (e.g., Jahn et al., 2000a, 2000b;

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Kovalenko et al., 2004; Wang et al., 2009). However, Kröner et al. (2014, 2017) suggested that

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previous studies might have overestimated Phanerozoic crustal growth because the involvement of recycled old crustal materials was ignored. Further research is therefore required to determine

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whether and where such large–scale crustal growth occurred. The identification of ancient and juvenile terranes and the division of tectonic units, also require deep crustal evidence. The Altai and East Junggar orogens, in southwestern CAOB, represent two typical CAOB areas but the nature of their basements has long been controversial. Regional geological (e.g., high–grade metamorphic rocks) and Nd isotopic studies (e.g., Sengör et al., 1993; Windley et al., 2007; Hu et al., 2000; Wang et al., 2009) imply that the Altai orogen has a Precambrian basement. However, zircon Hf isotopic studies (e.g., Sun et al., 2008; Cai et al., 2011) indicate that no Precambrian basement 3

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exists in this region. It is also disputed whether Precambrian basement exists in the East Junggar orogen (Carroll et al., 1990; Chen et al., 2004; Charvet et al., 2007; Bazhenov et al., 2012; Xiao et al., 2013; Zhang et al., 2013; Xu et al., 2015). Some studies have indicated juvenile compositions and young nature for the basement (e.g., Han et al., 1997, 1999; Chen et al., 2004), while others have

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found older basement compositions in the Junggar region (e.g., Xu et al., 2015). Spatio–temporal

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variations in data from all these studies should be comprehensively evaluated on the basis of regional

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mapping.

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Voluminous granitoids occur in the Altai and East Junggar orogens. Granitic rocks are primarily derived from partial melting of middle to lower crust, with compositions being controlled by crusta l

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sources (e.g., Johannes and Holtz, 1996; Tamic et al., 2011). Zircon is a common accessory mineral in granitoid rocks, and its Lu–Hf isotopic composition is a powerful tool in tracing the nature of

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basement rocks and determining the age of continental crust (Griffin et al., 2000, 2004; Kemp et al.,

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2006). Hf isotopic mapping is an effective method for identifying processes of magma generation, and the stability of zircon Hf isotopic composition provides an important advantage over whole–rock

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Nd isotopic technique (Kinny et al., 2003). In this study, we conducted zircon Hf isotopic mapping of granitoids in the Altai–East Junggar orogens, with the aims of tracing spatio–temporal variations in their sources, describing distributions and relative proportions of juvenile and ancient crustal areas, and evaluating the amount of Phanerozoic crustal growth. This study confirms that the East Junggar orogen is dominated by juvenile basement, except for a small area with an ancient composition. The Altai orogen has a relatively ancient crustal composition in its central part. Our results offer new insights into the deep crustal composition, continental crustal growth and tectonic division in the 4

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CAOB, and confirm that the Junggar orogen is one of the most significant sites of Phanerozoic continental growth in the CAOB.

2. Geological setting

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The Chinese Altai and East Junggar orogens are situated between the Sayan Mountains of

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southern Siberia to the north and the Tianshan–Beishan Mountains to the south. They are important

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tectonic units of the southwestern CAOB, and are separated by the Erqis fault zone. This zone is one

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of the largest strike–slip faults in Asia and an important structural element in the tectonic framework of the CAOB. This zone extends, with a width of up to 50 km and NW–trending, for more than 1000

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km into Mongolia to the southeast and Kazakhstan to the northwest. The zone experienced dextral movement during Late Carboniferous–Permian.

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The Chinese Altai orogen, lying to the north of the Erqis fault zone, can be divided into northern,

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central and southern parts, consisting of the following five units (units 1 to 5) from north to south according to Windley et al. (2002) (Fig. 1). The northern Altai, mainly composed of unit 1, consists

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predominantly of Middle–Upper Devonian andesites, dacites and Upper Devonian to Lower Carboniferous meta–sediments (shale, siltstone, greywacke, sandstone, and limestone). The Devonian volcanic rocks formed in an island arc setting (Xiao et al., 2004), and the sediments were deposited conformably on the island arc in forearc basins. The central Altai mainly consists of units 2 and 3 and is separated by Kangbutiebao–kuerte fault to the northern Altai. Unit 2 consists of Neoproterozoic (Sinian) to Middle Ordovician low–grade metamorphic volcano–sedimentary rocks (the Habahe Group), with minor Lower Devonian volcano–sedimentary rocks. Unit 3 contains 5

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amphibolite– and greenschist–facies metasediments and metavolcanics. According to some researchers, units 2 and 3 may belong to a single tectonic unit, they were considered as an important part of the Altai microcontinent or Precambrian basement (e.g., Windley et al., 2002; Xiao et al., 2004; Wang et al., 2009). The southern Altai are complex and is composed of units 4 and 5. Unit 4

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consists predominately of Silurian to Devonian low–grade metamorphic volcanic rocks. It was a

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continental arc accreted to/collided into unit 3 in the Devonian. Nonetheless, there exists old

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continental fragment that probably derive from the central Altai (Wang et al., 2006, 2009). Unit 5 is

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mainly composed of Devonian fossiliferous successions that are overlain by Upper Carboniferous formations. It contains Proterozoic gneisses imbricated with Ordovician–Silurian island arcs

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(Windley et al., 2002; Xiao et al., 2004). These schist and gneiss are also interpreted as Precambrian basement (Qu and Chong, 1991).

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The East Junggar orogen is located to the south of the Erqis fault zone and separated from the

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Tianshan orogenic belt by the Kelameili ophiolite zone to the south. The East Junggar orogen can be divided into two units (units 6 and 7) by the Armantai zone (or fault) (Fig. 1). Unit 6 is composed

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almost of Devonian island arc rocks, with a small amount of Ordovician limestone and some Carboniferous island arc volcanics (Xiao et al., 2004). Unit 7 is mainly composed of Devonian volcano–sedimentary rocks, with some Ordovician–Carboniferous rocks. In contrast to the Altai orogenic belt in China, the rocks in East Junggar orogen record only low–grade metamorphism and contain fewer sedimentary rocks (Wan et al., 2011).

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ACCEPTED MANUSCRIPT 3. Spatio–temporal distribution and genetic types of Phanerozoic granitoids 3.1 Granitoids in the Altai Granitoids are widely exposed in the Chinese Altai and have been intensely studied (e.g., Wang et al., 2006; Yuan et al., 2007; Sun et al., 2008, 2009; Cai et al., 2011; Liu et al., 2012). These

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granitoids can be divided into early to middle Palaeozoic (480–360 Ma), late Palaeozoic (290–270

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Ma), and Mesozoic (220–150 Ma) groups (e.g., Wang et al., 2006). In addition, the magmatic activity

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peaked at ~400 Ma (Fig. 2; Wang et al., 2006; Yuan et al., 2007; Tang et al., 2017).

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The early to middle Palaeozoic granitoids mainly occur in the central Altai (units 2, 3 and 4). These granitoids can be divided into two subgroups, i.e., 480–390 Ma and 390–360 Ma; the former is

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characterized by calc–alkaline series, and the latter by high–K calc–alkaline series (Song et al., 2017). Both subgroups comprise mainly I–type granitoids, with minor S–type granitoids (Wang et al., 2006;

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Cai et al., 2011; Zhang et al., 2016). Most of these plutons are deformed and are foliated parallel to

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the regional structural trend (Wang et al., 2006; Yuan et al., 2007). These early–middle Palaeozoic granitoids formed in a continental arc setting (e.g., Wang, et al., 2006; Sun et al., 2008).

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The late Palaeozoic (290–270 Ma) granitoids occur predominately in the southern Altai (units 4 and 5) and are of bimodal magmatic rocks (felsic and mafic). The felsic rocks comprise A–type alkaline granites and highly differentiated I–type granites (Wang et al., 2005; Tong et al., 2006), and the mafic intrusions are mainly gabbro (Zhang et al., 2010, 2014). They formed in a post–collisional environment (e.g., Wang et al., 2010; Tong et al., 2014). Small volumes of Mesozoic non–orogenic granitoids and numerous pegmatite dykes occur in units 3 and 4 (e.g., Wang et al., 2007). Most of these intrusions are A–type alkaline granites or highly 7

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differentiated calc–alkaline granites (Wang et al., 2014), extending southeastwards to Beishan area (Li et al., 2013a).

3.2 Granitoids in East Junggar

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Granitoids in East Junggar were mostly emplaced in late Palaeozoic, and mainly have zircon

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ages of 330–265 Ma, peaked at ca. 300 Ma (Fig. 2. e.g., Han et al., 2006; Liu et al., 2013). They were

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distributed cross important geological boundaries (such as an ophiolite zone, Han et al., 2006). The

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rock types are predominantly granodiorite, monzogranite, K–feldspar granite and alkaline granite, with A–type and I–type features (e.g. Liu et al., 2013). These granitoids formed in a post–collisional

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setting (e.g., Chen et al., 2004; Han et al., 2010; Yang et al., 2011). In addition, minor middle Palaeozoic granitoids also occur in East Junggar and are regarded to

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be emplaced in an island arc environment (e.g., Zhang et al., 2006, Li et al., 2012).

4. Dataset for Hf isotopic mapping

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The granitoids mentioned above are suitable for isotopic mapping because (a) they are widespread in the Altai and East Junggar orogens and most have been dated by the U–Pb zircon method; (b) numerous isotopic data have been obtained from them; and (c) they can serve as a “probe” into the lower part of the continental crust.

4.1 Hf isotope data from literature The data come from 66 Phanerozoic (mainly 510–200 Ma) granitoid plutons (Appendix 1). In 8

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this study, we mainly chose granitoids for the Hf isotopic study to investigate their sources and assess the composition of the continental crust at depth. In total, 79 samples with 1500 sets of Lu–Hf data (69 for Palaeozoic and 10 for Mesozoic samples) in the study region were collected from the literature (publications from 2008 to 2017). Regionally, the 79 samples for the gr anitoid plutons are

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distributed in two orogens: 49 from the Altai orogen (4 from unit 2, 28 from unit 3, 14 from unit 4

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and 3 from unit 5) and 30 from the East Junggar orogen (3 from unit 6 and 27 from unit 7). In

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addition, Early–middle Palaeozoic (507–360Ma) plutons for these samples mainly occurred in the

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Altai and are characterized by I–type granites. Late Palaeozoic (354–268Ma) granitoids mainly occurred in East Junggar orogen and are of A–type and I–type granitoids. Mesozoic (238–151Ma)

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granitoid samples from the Altai are characterized by A–type and highly fractionated I–type. To verify the reliability of the data, we recalculated the parameters of all samples (see Appendix

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3 and formulas therein), which indicates that most of the data are of high quality except for a small

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number with insufficient precision (Data evaluation and selection are described in Chapter 5.1).

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4.2 New Lu–Hf isotope data

4.2.1 Granitoid intrusions and samples description In this study, our new sampling and research mainly focused on some important areas which are key to study the Altai and Junggar orogens and lack of Hf data. Fourteen samples from the Chinese Altai (mainly in the eastern part) and three samples from East Junggar (Fig. 1).

4.2.1.1 Samples in the Chinese Altai 9

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Ten samples were collected from the central Altai (units 2 and 3). Sample 4123, located in unit 2, is gneissic biotite monzogranite from the Kanas pluton. This sample consists of medium–grained plagioclase (20–25%), K–feldspar (30–35%), quartz (30–35%) and biotite (10–15%). Accessory minerals include magnetite, zircon and others. Other nine samples were collected from eight

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granitoid plutons in unit 3. Sample A14829–1 is medium– to fine–grained granodiorite and sample

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A15706–5 is fine–grained granodiorite. They were collected from different locations of the

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Kungeyite pluton and both consist of plagioclase (55–65%), K–feldspar (10–20%), quartz (20–25%),

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biotite (2–5%) and muscovite (1–2%). The accessory minerals are magnetite, zircon and apatite (Fig. 3a). Sample A14830–2 is medium– to fine–grained granodiorite collected from the Songkeke pluton,

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consisting of plagioclase (50–55%), K–feldspar (10–15%), quartz (20–25%), hornblende (3–5%) and biotite (10%). The accessory minerals include zircon, apatite, titanite and allanite (Fig. 3b). Sample

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3002 is quartz diorite, collected from the Zhusiling pluton, consists of plagioclase (80–85%), quartz

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(5–10%), and biotite (10%), and the accessory minerals are magnetite, titanite and allanite. Sample A15706–1 is fine–grained quartz diorite from the Lekete pluton and contains plagioclase (75–80%),

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quartz (5–10%), hornblende (10%) and biotite (5–10%). The accessory minerals are zircon, apatite and magnetite (Fig. 3c). Sample A15707–1 is medium– to fine–grained granodiorite from the Halaayila pluton and consists of plagioclase (60–65%), K–feldspar (10%), quartz (20–25%) and biotite (3–5%). The accessory minerals include zircon, apatite, titanite and others. Sample A15707–2 is porphyritic tonalite collected from the Halaqiaola pluton. The phenocrysts are composed mainly of plagioclase (5–10%), and the groundmass is composed of plagioclase (60–65%), quartz (20–25%) and biotite (10%). The accessory minerals are zircon, apatite, titanite and magnetite (Fig. 3d). 10

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Sample 120/3 is of coarse– to medium–grained granodiorite from the Keketuohai pluton. This sample is composed of plagioclase, alkali feldspar, quartz, and biotite. (Wang et al., 2006). Sample 3045 is biotite granodiorite from the Kuerti pluton. The minerals comprise plagioclase, alkali feldspar, quartz, biotite and muscovite (＜3%) (Wang et al., 2006).

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Four samples were collected from the southern Altai (units 4 and 5). Sample A15704–3,

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collected from the Chagan–East pluton in unit 4, is medium– to fine–grained quartz diorite and

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consisits mainly of plagioclase (75–80%), quartz (5–10%), biotite (10–15%) and hornblende (5–

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10%). The accessory minerals are zircon, apatite, titanite and magnetite (Fig. 3e). Sample A15704–4 is porphyritic granodiorite from the Chagan pluton in unit 4. The phenocrysts are composed mainly

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of plagioclase (15–20%), and the groundmass is composed of plagioclase (40–45%), K–feldspar (10%), quartz (20–25%) and biotite (10%). The accessory minerals are zircon, apatite and magnetite.

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Sample A15707–4 is medium– to fine–grained tonalite from the Qiaergou–South pluton in unit 4. It

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consists of plagioclase (65–70%), quartz (20–25%), biotite (10–15%) and K–feldspar (2–3%). The accessory minerals are zircon, apatite, allanite and magnetite. Sample A15703–4 is medium– to fine–

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grained granite obtained from the Areletuobie pluton in unit 5, consisting of plagioclase (25–30%), K–feldspar (45–50%), quartz (25–30%) and biotite (1–2%). The accessory minerals are zircon, apatite and magnetite (Fig. 3f).

4.2.1.2 Samples in East Junggar Four samples were collected from East Junggar (units 6 and 7). Sample A15703–1, collected from the Guersi pluton in unit 6, is medium– to fine–grained quartz diorite and composed of 11

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plagioclase (70–75%), K–feldspar (10–15%), quartz (5–10%), biotite (5%) and hornblende (3–5%). Accessory minerals, including zircon, apatite, titanite and magnetite, are common. Sample A15703–2 is coarse– to medium–grained monzonite obtained from the Hadanxun pluton in unit 6. This sample contains plagioclase (45–50%), K–feldspar (40–45%), biotite (5%) and clinopyroxene (3–5%), with

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accessory minerals such as zircon, apatite and magnetite (Fig. 3g). Sample A15703–3 is porphyritic

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monzogranite with a typical porphyritic texture collected from the Wutubulake pluton in unit 6. The

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phenocrysts are composed of plagioclase (20–25%), K–feldspar (10–15%), quartz (5–10%) and

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biotite (5%), and the groundmass is composed of plagioclase (15–20%), K–feldspar (15–20%) and quartz (10–15%). The accessory minerals are zircon, apatite and magnetite (Fig. 3h). Sample

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T15709–2 is fine–grained diorite collected from the Wuzunbulake pluton in unit 7 and consists of plagioclase (70–75%), quartz (2–3%), biotite (3–5%) and hornblende (20–25%). The accessory

4.2.2 Analytical methods

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minerals are zircon, apatite and magnetite (Fig. 3i).

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Zircon U–Pb isotopic analyses were performed using a Thermo Finnigan Agilent 7700x coupled to a Geolas Pro laser–ablation system, with a beam size of 32 μm and a laser pulse frequency of 9 Hz, at the Center of Experimental Tests, Xi’an Center of Geological Survey. The standards NIST SRM 610 glass and 91500 zircon were used as external standards. Isotope ratios and elemental concentrations were calculated and plotted using the software program GLITTER 4.0 (Macquarie University). Age calculations and plotting of concordia diagrams were performed using Isoplot/Ex 3.71 (Ludwig, 2003). 12

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In situ zircon Hf isotopic analyses were conducted using a Neptune Plus multi–collector ICP– MS coupled to a COMPex Pro 193 laser ablation microprobe at the Institute of Geology, Chinese Academy of Geological Sciences, Beijing, China. Instrumental conditions and data acquisition methods are described in detail by Hou et al. (2007) and Wu et al. (2006). A stationary spot was used

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for the analyses, with a beam diameter of 44 μm. Helium was used as a carrier gas to transport the

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ablated sample from the laser ablation cell to the ICP–MS torch via a mixing chamber, where the

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Lu/175 Lu=0.02658 and

ratios were normalized to a 179

Yb/173 Yb=0.796218 were used (Chu et al., 2002). The Yb isotope

Yb/173 Yb ratio of 1.35274 (Chu et al., 2002), and the Hf isotope ratios

Hf/177 Hf ratio of 0.7325 assuming that the exponential mass bias behaviour

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were normalized to a

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Yb on 176 Hf, the

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ratios

176

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helium was mixed with argon. To correct for isobaric interferences of 176 Lu and

of Lu followed that of Yb. The mass bias correction process is described in detail by Wu et al. (2006)

Hf/177 Hf ratio of 0.282015±8 (2σ; n=10) during the course of the analyses.

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4.2.3 Analytical results

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and Hou et al. (2007). Zircon GJ1 was used as the reference standard and yielded a weighted mean

In this paper, we newly obtained 15 zircon U–Pb ages and Hf isotopic data from 18 granitoid samples. Zircon CL images see Appendix 4 and LA–ICP–MS zircon U–Pb age dating results see Appendix 2. The zircon U–Pb concordia diagrams are shown in Fig. 4, and the results are shown in Table 1.

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ACCEPTED MANUSCRIPT 5. Hf isotopic mapping and provinces 5.1 Characteristics of Hf isotopic data Zircon Hf isotopic data for 97 samples from Phanerozoic granitoids (mainly 510–200 Ma) in the Chinese Altai and East Junggar (79 from the literature and 18 obtained in this study) were used to 176

Yb/177 Hf,

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Lu/177 Hf and

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Hf/177 Hf), the values of

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map. Based on four data categories (Age,

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εHf(0), εHf(t), fLu/Hf, TDM1 and TDMC are recalculated, using the parameters and formulas presented in

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Appendix 3, in order to eliminate any inconsistencies in the calculation of different parameters and

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Yb/177 Hf＞0.25 were also discarded because of Griffin et al. (2000) proposed

accurate results up to

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Yb/177 Hf ≈ 0.20.

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some data with

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formulas. First, the data for the large error of 176 Hf/177 Hf with 2σ＞0.00005 were excluded. Second,

The εHf(t) values range from –22.2 to +18.6 with TDMC from 3873 to 146 Ma (Figs. 6 and 7).

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Almost all of the TDMC and εHf(t) values exhibit a good linear correlation (Fig. 5), which constitutes a

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convincing statistical relationship. For the Hf isotopic mapping, average value of zircon εHf(t) and

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TDMC for each sample was used in this study.

5.2 Hf isotopic mapping

Isotopic mapping is effective in elucidating relationships between geochemistry and evolution of tectonic terranes. Isotopic maps based on εHf(t) values and TDMC ages (listed in Appendix 3) are presented in Figs 8–11. 5.2.1 Spatio–temporal variations in Altai Hf isotopic compositions Early–middle Palaeozoic granitoid plutons are widespread in the Altai orogen, with zircon εHf(t) values of +0.5 to +9.1 and TDMC ages of 1.53–0.83 Ga. Late Palaeozoic granitoid plutons, which 14

ACCEPTED MANUSCRIPT occur mainly in southern Altai, with a few in central Altai, have zircon εHf(t) values of +3.5 to +11.1 and TDMC ages of 1.08–0.60 Ga. Mesozoic granitoid plutons have zircon εHf(t) values of +0.5 to +5.5 and TDMC ages of 1.20–0.90 Ga. The εHf(t) values generally increase with age initially, then decrease (Fig. 7). Such isotopic evolution trends may provide important information on compositional

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changes in the granitoids and/or the process of crustal growth. These Hf isotopic compositions

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exhibit strong spatial variations, with zircon εHf(t) values of granitoid intrusions increasing from

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central to southern Altai (units 2, 3, and 4, to 5; Fig. 8) with a corresponding decrease in model ages

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(Fig. 9). In central Altai (units 2 and 3), ε Hf(t) values range from +0.5 and +8.6 with TDMC ages of 1.46–0.83 Ga. In southern Altai (unit 4), granitoid zircon εHf(t) values range from +0.5 to +9.9 with

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TDMC ages of 1.53–0.81 Ga. In southernmost Altai (unit 5), granitoid zircons have εHf(t) values of +7.5 to +11.1, with younger TDMC ages of 0.83–0.60 Ga.

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5.2.2 Spatio–temporal variations in East Junggar Hf isotopic compositions

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Hf isotopic compositions are similar throughout East Junggar (Figs 10, 11). Early–middle Palaeozoic granitoids there have highly positive zircon εHf(t) values of +9.7 to +13.6 and TDMC ages

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of 0.81–0.51 Ga. Late Palaeozoic granitoids have similar εHf(t) values (+7.9 to +14.9) and TDMC ages (0.81–0.38 Ga). In northern (unit 6) and southern (unit 7) Junggar, granitoid zircon εHf(t) values range from +7.9 to +13.6 and +9.7 to +14.9, with TDMC ages of 0.80–0.49 and 0.81–0.38 Ga, respectively (although one has an εHf(t) value of –2.5 and a TDMC age of 2.48 Ga). From the Chinese Altai to East Junggar, zircon εHf(t) values of granitoid plutons increase southwestward, from units 2 and 3, through units 4 and 5, to units 6 and 7, with a corresponding decrease in model ages (Figs 10, 11). 15

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5.3 Hf isotopic provinces The Altai and East Junggar study region can be divided into six Hf isotopic provinces on the basis of zircon U–Pb ages and spatio–temporal variations in zircon Hf isotopic compositions (Fig. 11), as follows.

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5.3.1 Province I (TDMC = 2.5–1.4 Ga)

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Province I is characterized by old TDMC ages of 2.5–1.4 Ga and low εHf(t) values of –2.5 to +2.2.

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It can be subdivided into two small parts: Province I–a in eastern Altai (units 3 and 4), characterized by TDMC ages of 1.6–1.4 Ga and slightly positive ε Hf(t) values of +0.5 to +2.2, with granitoids (507–

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441 Ma) being mainly S–type; and Province I–b in East Junggar (unit 7), with the lowest εHf(t) value

5.3.2 Province II (TDMC = 1.4–1.2 Ga)

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(–2.5) and oldest TDMC age (2.5 Ga).

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Province II is distributed in central Altai (units 2 and 3), with zircon εHf(t) values of +0.7 to +4.3 and old TDMC ages of 1.4–1.2 Ga. The granitoids (456–216 Ma) are mainly I– and S–type.

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5.3.3 Province III (TDMC =1.2–1.0 Ga)

Province III occupies most of units 2–4 in the Altai orogen, with zircon εHf(t) values of +0.5 to

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+6.9, and slightly old TDMC ages of 1.2–1.0 Ga. The granitoids (453–188 Ma) are mainly I–type. 5.3.4 Province IV (TDMC = 1.0–0.8 Ga) Province IV exhibits younger TDMC ages (1.0–0.8 Ga) with εHf(t) values of +4.6 to +9.7. It occurs as several small independent areas in the Chinese Altai, with only one sample in unit 7 of East Junggar. These granitoids were emplaced at 421–151 Ma. 5.3.5 Province V (TDMC = 0.8–0.6 Ga) Province V exhibits much younger TDMC ages (0.8–0.6 Ga) with highly positive zircon εHf(t)

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values of +7.9 to +11.8. It is located mainly in the Erqis zone (unit 5) of the Chinese Altai. The granitoids (313–267 Ma) are mostly highly fractionated I–type granitoids. One sample (413 Ma) is from the south of unit 7. 5.3.6 Province VI (TDMC = 0.6–0.4 Ga)

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Province VI is characterized by the youngest TDMC age (0.6–0.3 Ga) with the highest positive

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zircon εHf(t) values of +11.6 to +14.9. It is the largest province and occurs in most areas of the East

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Junggar orogen (unit 7 and eastern unit 6). The granitoids were emplaced at 425–290 Ma, and most

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are late Palaeozoic I– and A–type, with a few early–middle Palaeozoic I–type granitoids.

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6. Discussion

6.1 Different sources of Chinese Altai and East Junggar granitoids

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Petrography and mineral assemblages indicate that the early–middle Palaeozoic granitoids in the

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Altai orogen are of I–type granites. Granitoids of the central Altai (Provinces I, II, III, and IV) have zircon εHf(t) values of +0.5 to +8.6 and TDMC ages of 1.46–0.83 Ga, indicating they are derived from

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heterogeneous crust of mixed ancient and juvenile sources. Lots of old continental zircons and some mafic microgranular enclaves are found in several of the plutons, suggesting the granitoid source had a mainly Precambrian continental composition, with a small amount of mantle–derived juvenile (Palaeozoic) material (e.g., arcs, ophiolites, accretionary complexes, and mafic intrusions, Chen et al., 2002). In contrast, granitoids of the southern Altai (Provinces III, IV, and V) have higher zircon εHf(t) values (+2.8 to +12.9) and younger model ages (1.13–0.60 Ga), indicating a more juvenile source. Most late Palaeozoic granitoids (310–270 Ma) in East Junggar (Province VI) have very highly

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al., 2010). Most late Palaeozoic granitoids are highly fractionated I– and A–type granites, likely

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produced by crustal contamination during fractional crystallization (e.g., Han et al., 1999; Tong et al.,

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2014). Granitoids with a negative zircon εHf(t) value of –2.5, an old TDMC age of 2.5 Ga, and very old

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inherited zircons (e.g., 3.3 Ga) have been found locally in East Junggar (Xu et al., 2015), suggesting that some ancient materials might exist in the deep crust of the East Junggar orogen (Province I–b).

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In summary, granitoids of central Altai (units 2 and 3), southern Altai (units 4 and 5), and East Junggar (units 6 and 7) have distinct sources: mixed old sources (I–type granites, with small

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quantities of S– and A–type granites) in central Altai; and juvenile mantle–derived sources in

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southernmost Altai and East Junggar. The sources become younger from central Altai, to southern Altai to East Junggar, consistent with results of Nd isotopic mapping (Wang et al., 2009) and zircon

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xenocryst mapping (Zhang et al., 2017).

6.2 Contrasting basement between the Altai and East Junggar orogens The CAOB comprises many juvenile accretionary terranes and ancient blocks (microcontinents) (e.g., Windley et al., 2007, Zhou et al., 2017), with recent studies indicating that reworking of ancient blocks and materials played an important role in its development (e.g., Kröner et al., 2014, 2017). Accurate identification of these ancient blocks and young terranes is key to the understanding of 18

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crustal architecture and continental growth of the belt. The composition and architecture of the Altai and East Junggar sections of the CAOB effectively reflect characteristics of ancient (Proterozoic) blocks trapped in this relatively young orogenic belt. 6.2.1 Ancient Altai basement

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Units 2 and 3 of the Chinese Altai may be the same unit (Windley et al., 2002), but there is little

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evidence for this. Whole–rock Nd isotopic mapping indicates that granitoids in these units have very

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similar εNd(t) values (–4 to +2) and Nd model ages (1.6–1.1 Ga), implying they are of the same

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tectonic unit (Wang et al., 2009). Furthermore, Nd isotopic mapping indicates that old crustal compositions are widely distributed in the basement of units 2 and 3 in the Altai orogen (Wang et al.,

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2009). Zircon Hf isotopic mapping here also indicates that the granitoids have relatively old crustal compositions compared with surrounding areas such as East Junggar. Our Hf isotopic mapping, Nd

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isotopic mapping of Wang et al. (2009), and zircon xenocryst mapping of Zhang et al. (2017)

components.

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consistently indicate that central Chinese Altai contains old (pre–Neoproterozoic) crustal

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Hf isotopic mapping also identifies the slightly old Province III in most of unit 4, suggesting that ancient crust occurs in this unit, especially the oldest Province I in eastern unit 4. This is supported by our discovery of 1.8 Ga zircon with negative εHf(t) value and Palaeoarchaean model age in the Kalateyubie pluton in unit 4. This provides strong evidence for the existence of ancient materials or old continental fragments in this region (Wang et al., 2009). We therefore conclude that ancient crustal compositions are widely distributed in units 2, 3, and eastern unit 4 and that they may be the same unit. Unit 5, the part of Erqis fault or tectonic zone, has a complex geological structure 19

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with young compositions in Provinces IV and V. Zircon Hf isotopic values are much more radiogenic than whole–rock Nd isotopic signatures, indicating decoupling of Nd and Hf. This discrepancy may result from disequilibrium melting processes, inheritance from magma sources (e.g., Cai et al., 2011b; Long et al., 2012), or

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contamination by subducted pelagic sediments (e.g., Chauvel et al., 2014). In the study area, we

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consider that negligence and loss of information recorded by xenocrystic zircons in felsic igneous

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rocks could be the major reason for such discrepancy. Because zircon Hf isotopic compositions are

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generally obtained and reported from crystallized zircons, or crystallized domains of zircon, rather than pre–magmatic zircon cores. The omission of old Hf isotopic compositions of xenocrystic

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zircons or pre–magmatic zircon cores may thus result in significantly higher ε Hf(t) values than εNd(t) values, as shown by zircon xenocryst mapping (Zhang et al., 2017).

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Previously studies suggested that the Altai orogen has a Precambrian basement, with its

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composition including gneisses (Qu and Chong, 1991) and Nd isotopic data for granitoids (e.g., Hu et al., 2000; Chen and Jahn, 2002; Wang et al., 2009). However, the juvenile signature of zircon Hf

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isotopic compositions (e.g., Sun et al., 2008; Cai et al., 2011a, 2011b, 2012; Zhang et al., 2016) indicates that there is no Precambrian basement in the Altai orogen. We suggest there are at least two reasons for such contradictory interpretations. (1) Zircon Hf isotopic mapping indicates that ambiguities arise through differences in their study areas. Most previous zircon Hf isotopic studies focused on granitoids of southern Altai (such as the Habahe, Chonghuer, and Tarlang plutons), which have positive εHf(t) values and display juvenile characteristics, suggesting no Precambrian basement (e.g., Sun et al., 2008; Cai et al., 2011). However, isotopic provinces and source regions differ 20

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between central and southern Altai, with the former being relatively ancient and the latter is young (Figs 8, 9). Very old compositions are increasingly recognized in most areas of central Altai, especially in the eastern area (e.g., Lv et al., 2012; Zhang et al., 2016; Song et al., 2017), confirming the existence of ancient crustal compositions there. (2) Negligence of many old xenocrystic/inherited

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zircons in previous studies resulted in such discrepancy. Numerous old xenocrystic/inherited zircons

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exhibit much lower negative εHf(t) values and older model ages, indicating that central Altai contains

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abundant old continental crustal components. Thus, lost information from these zircons must have

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resulted in more juvenile signatures. Mapping of these xenocrystic/inherited zircons in the Altai and Junggar orogens indicates that central Altai contains many older xenocrystic/inherited zircons than

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the Junggar region, with the former having a more ancient composition at depth than the latter (Zhang et al., 2017).

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There are several interpretations for origin and meaning of the deep crustal ancient

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compositions of central Altai: (1) The old compositions may be derived from a reworked or an unexposed residual Precambrian basement; (2) They may reflect old sources of Palaeozoic

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sedimentary rocks, which could have come from the Tuva–Mongolian microcontinent in southern Siberia (Sun et al., 2008; Jiang et al., 2011; Liu et al., 2012); (3) Residual crystals during the melting of oceanic sediments (e.g., Zhang et al., 2016). We consider the first interpretation more likely because isotopic mapping indicates that old Provinces I–III are widespread in the lower crust of central Altai (units 2 and 3), with large areas of homogeneous old compositions best being explained as buried large–area old compositions i.e. reworked Precambrian basement. The central Altai was surrounded by juvenile crust including the lake zone to the north, distant from the Tuva–Mongolian 21

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microcontinent (e.g., Kröner et al., 2014; Zhang et al., 2017). Residual crystals from oceanic sediment melting are precluded by old continental zircons in the central and southern (unit 4) Altai being mostly characterized by euhedral morphology with no evidence of long–distance transportation, suggesting old continental crust substrate in the deep crust. And although most εHf(t) values are

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positive, Provinces I and II in central Altai are much older than Provinces V and VI. Dong et al.

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(2016) reported the oldest age of felsic rocks (~2.6 Ga quartzite) from the Supute Group in the

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Qinghe area of Chinese Altai, proving the existence of Precambrian basement.

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In summary, we suggest that a reworked, unexposed Precambrian (perhaps Proterozoic) basement exists in the deep crust, as identified by old zircons and Hf isotopic compositions, and is

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interpreted as reworked old continental block/microcontinent. Many microcontinental blocks identified by zircon U–Pb ages and Hf isotopic data are widely d istributed in eastern, western, and

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central segments of the CAOB (e.g., Kroner et al., 2013; Zhou et al., 2017). Central Altai could thus

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be a reworked Precambrian microcontinent or old continental fragment. 6.2.2 Juvenile East Junggar basement

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The East Junggar basement has been considered as juvenile (e.g., Han et al., 1997; Chen et al., 2004). Recently, old sources for granitoids and their gneiss enclaves indicate an ancient basement (e.g., Xu et al., 2013, 2015). Our Hf isotopic mapping indicates that both juvenile and ancient basement exist in East Junggar, and it is important to determine their distributions. Zircon εHf(t) values of granitoids in the East Junggar orogen (Province VI) are highly positive with the youngest model ages indicating a high proportion of young material. Granitoids in units 6 and 7 of the East Junggar orogen have similar zircon εHf(t) values (+7.7 to +14.9) and TDMC(Hf) ages 22

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(0.81–0.35 Ga), indicating relatively young crustal compositions. Their similar rock types and isotopic characteristics indicate that units 6 and 7 may constitute a single unit. The youngest Province VI thus indicates that most areas of East Junggar are juvenile rather than ancient, consistent with Nd isotopic studies (e.g., Zheng et al., 2007; Wang et al., 2009; Liang et al., 2016; Zhang et al.,

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2017).

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Regarding the distribution of old (Palaeoproterozoic–Archaean) rocks, our zircon Hf isotopic

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mapping indicates that only one dioritic sample occurs locally in the Taheir area, suggesting old

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Province I–b is local and very small in extent. The existence and extent of ancient Precambrian components in East Junggar thus remains open to question. Even if the Junggar Basin contains

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ancient continental basement, it may be small in extent and probably intensely modified by underplating of mantle–derived magma (e.g., Han et al., 1999). We conclude that East Junggar is

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dominated by juvenile basement (no large Precambrian basement), a typical accretionary belt of the

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CAOB.

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6.3 Implications for tectonic divisions The newly defined zircon Hf isotopic Provinces I–VI (Fig. 11) indicate boundaries of tectonic units. The isotopic section from northwest Altai to southeast East Junggar (Fig. 12) indicates distinctive Hf isotopic compositions and contrasting basement between the Altai and East Junggar orogens. The boundary between Provinces I–V and VI is consistent with the Erqis fault zone and displays distinctive deep compositions on both sides of the fault (Fig. 11), indicating that the fault zone is a boundary between the two contrasting basements. Our zircon Hf isotopic mapping thus 23

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provides deep crustal compositional evidence for the existence and extension of the Erqis fault zone, an important tectonic boundary in the CAOB.

6.4 Crustal growth in the Altai and East Junggar orogens

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Previous studies have emphasized voluminous crustal growth, and considered the CAOB to be

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the most significant site for Phanerozoic continental growth (e.g., Jahn et al., 2000a, b, 2004), with

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whole–rock Nd isotopic mapping being used to evaluate such growth. Kovalenko et al. (2004)

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estimated continental growth in Mongolia (central CAOB) by mapping Nd isotopic provinces, and concluded that important crust–forming events took place during the Phanerozoic, at a minimum rate

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less than the average for Earth’s continent formation. Wang et al. (2009) estimated significant continental growth (25%–36%) in the Chinese Altai orogen, also by detailed Nd isotopic mapping.

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Yang et al. (2017) conducted similar studies in the Great Xin’an Range and found that the ratio of

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continental growth reaches to 64% from the Neoproterozoic to the Mesozoic in southeastern CAOB, with this high ratio being typical for this part of the CAOB. However, recent studies have indicated

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that the amount of continental growth is similar to that in other accretionary orogens throughout Earth’s history (Kröner et al., 2014, 2017), with the addition of juvenile crust during the Palaeozoic being restricted to relatively short time periods, and magma generation rates being similar to those along modern subduction zones (e.g., Tang et al., 2017). Therefore, they argued that there was no excessive continental growth in the CAOB, and the volume of truly juvenile crustal material there is ~20% of the total crust. Our Hf isotopic mapping (TDMC ages) re–evaluates continental growth in the southwestern 24

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CAOB. Provinces I, II, and III (>1.0 Ga) are distributed mainly in the Altai orogen, with old to slightly old crustal regions. Province I (>1.4 Ga), the oldest crustal region, occurs in eastern Altai. Province II (1.4–1.2 Ga) is an old crustal region distributed mainly in central Altai (units 2 and 3). Province III (1.2–1.0 Ga) is the slightly old crustal region, distributed over the central and southern

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Altai (units 2–4). Young crust (1.0–0.6 Ga) is distributed mainly in northern and southmost Altai,

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with Province IV (1.0–0.8 Ga) being scattered over the whole Altai orogen. Unit 5 is dominated by

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juvenile crust (Province V, 0.8–0.6 Ga). Measured by distribution area, the growth of continental

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crust in Altai is substantially less than that estimated by Sengör et al. (1993), but there is no doubt that there was significant addition of juvenile continental crust during the Phanerozoic.

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Zircon Hf isotopic mapping (Figs 10, 11) indicates that East Junggar generally has the young TDMC ages (Provinces V and VI, 0.81–0.38 Ga), and is the youngest crustal region in the CAOB. Our

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data indicate significant late Palaeozoic vertical growth in units 6 and 7 in East Junggar. Juvenile

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material in post–collisional granitoids there may be derived from underplating of newly formed mantle–derived magmas. The formation of large quantities of mafic rocks during this period suggests

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that abundant mantle–derived material was added to the crust, causing vertical growth ( Jahn, 2004; Li et al., 2013a, b; Song et al., 2018). Therefore, compared to Altai, the East Junggar orogen includes significant juvenile crust, representing major crustal growth. Provinces I, II, III, IV, V, and VI are estimated to cover areas of 2,250 km2 , 8,830 km2 , 68,450 km2 , 94,800 km2 , 38,540 km2 , and 143,880 km2 , accounting for 0.6%, 2.5%, 19.2%, 26.6%, 10.8%, and 40.3% of the study area, respectively. Therefore, if Provinces IV, V, and VI are considered to represent juvenile crust, as defined by Nd isotopic mapping (e.g., Wang et al., 2009), the total 25

ACCEPTED MANUSCRIPT juvenile crust area would be 277,220 km2 , contributing ~78% of the study area. This is remarkably higher than in most other orogens worldwide. It is clear that the estimation of the amount of continental growth depends on the constrained or chosen regions of large orogenic systems such as the CAOB. More large areas or even the whole CAOB should therefore be studied using the same

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methods. Moreover, juvenile materials identified from massive early–middle Palaeozoic granitic

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rocks represent synorogenic horizontal crustal growth, with the synorogenic area comprising ~27%

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of the total. In East Junggar, late Palaeozoic post–orogenic granitoids are voluminous, and the

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proportion of vertical crustal growth is ~51%. Our results thus confirm that crustal growth was heterogeneous in the Altai and East Junggar orogens during the Phanerozoic, and that significant

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continental crust growth occurred mainly in East Junggar.

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7. Conclusions

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1. Six Hf isotopic provinces were identified by zircon Hf isotopic mapping of granitoids in the Chinese Altai and East Junggar orogens. These provinces confirm that central Altai was dominated

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by mixed or reworked slightly old crust (Provinces I, II, and III, with TDMC = 1.46–1.0 Ga and εHf(t) values of +0.5 to +6.9), whereas southern Altai was mainly juvenile crust (Provinces III, IV, and V, with TDMC = 1.1–0.6 Ga and εHf(t) values of +2.8 to +12.9). 2. Granitoids in East Junggar are predominantly characterized by highly positive zircon ε Hf(t) values of +7.9 to +14.9, and young TDMC ages of 0.81–0.38 Ga, confirming that the East Junggar orogen is characterized by the youngest crust (Province VI). Ancient materials occur only locally in the small Taheir area, and are characterized by zircon εHf(t) value of –2.5 and old TDMC age of 2.5 Ga. 26

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3. The sharp contrast of Hf isotopic characteristics of granitoids between the Altai and East Junggar orogens indicates different deep compositions or basements: the slightly ancient in central Altai and juvenile in the Junggar orogen. This provides new evidence for the division of the Altai and Junggar orogens by the Erqis fault zone.

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4. Crustal growth was heterogeneous in the Chinese Altai and East Junggar orogens during the

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Phanerozoic. Significant continental crust growth occurred mainly in southern Altai and East Junggar,

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occupying ~78% of the study area.

Acknowledgements

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We are very grateful to Xiaoxia Wang, Shan Li, Lei Zhang and Alfred Kröner for their constructive comments. We thank the editors and two anonymous referees for their helpful comments.

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This research was supported financially by the NSFC projects (U1403291, 41830216, and 41802074)

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and projects of the China Geological Survey (Nos. DD20160024, DD20160123, and DD20160345).

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understanding the Devonian Tectonics of the Northwest China Altai orogen. International Geology Review 58(5), 540–555. Zhou, J.B., Wilde, S.A., Zhao, G.C., Han, J., 2017. Nature and assembly of microcontinental blocks within the

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Captions to figures and tables

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Fig. 1 Geological sketch map of the Altai and East Junggar regions and granitoids distribution (modified from

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Windley et al., 2002 and Wang et al., 2009). Main tectonic subdivisions are modified from Xiao et al.,

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2014.

Fig. 2 Histograms of zircon U–Pb ages for granitoids in the Chinese Altai (a) and East Junggar (b) orogens

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(Data resources are listed in Appendix 1).

Fig. 3 Photomicrographs of granitoids from the Altai and East Junggar orogens.

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Altai:(a) Granitic texture of granodiorite from the Kungeyite pluton; (b) Granitic texture of granodiorite from the Songkeke pluton; (c) Hornblende of quartz diorite from the Lekete pluton; (d) Porphyritic texture of tonalite from the Halaqiaola pluton; (e) Hornblende of quartz diorite from the Chagan–East pluton; (f) Granitic texture of granite from the Areletuobie pluton. East Junggar: (g) Clinopyroxene of monzonite from the Hadanxun pluton; (h) Porphyritic texture of monzogranite from the Wutubulake pluton; (i) Hornblende of diorite from the Wuzunbulake pluton. Qz—quartz; Pl—plagioclase; Kf—K– feldspar; Bt—biotite; Ms—muscovite; Hb—hornblende; Cpx—clinopyroxene 38

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Fig. 4 LA–ICP–MS zircon U–Pb concordia diagrams of granitoids in the southeastern Chinese Altai and East Junggar regions from 15 samples for 14 plutons (Altai: a–k; East Junggar: l–o).

Hf/177Hfi are between 0.2826 and 0.2830, including young compositions (Province VI) of 0.2828–

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176

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Fig. 5 176 Yb/177Hf vs. 176 Hf/177 Hfi diagram shows all most points of 176 Yb/177Hf are between 0 and 0.20 and of

176

Yb/177Hf＞0.25 were discarded.

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0.2830 and old composition of 0.2826–0.2828. Grey points with

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(Zircon Hf isotope are from Sun et al., 2008, 2009; Gan et al., 2010; Zhang et al., 2010; Cai et al., 2011a, 2011b, 2012; Shen et al., 2011; Xiao et al., 2011; Li et al., 2012; Liu et al., 2012, 2013; Lv et al., 2012;

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Tong et al., 2014; Wang et al., 2014; Zhao et al., 2014; Ye et al., 2015; Zhang et al., 2016; Zheng et al.,

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2016; Song et al., 2017 and this study. Data are listed in Appendix 3).

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Fig. 6 εHf(t) vs. TDMC diagram for Phanerozoic granitoids in the Chinese Altai and East Junggar

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(Data are listed in Appendix 3).

Fig. 7 εHf(t) value versus 206Pb/238U age diagram for the granitoid intrusions in different terranes of the Chinese Altai and East Junggar regions (Data are listed in Appendix 3).

Fig. 8 Isotope map (εH f(t) values and model ages) for granitoids in the Chinese Altai (Data are shown in Appendix 3).

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Fig. 9 Map of Hf model ages for granitoids in six units of the Chinese Altai (Data are shown in Appendix 3).

Fig. 10 εHf(t) values for the granitoids in the Altai and East Junggar regions (Data are shown in Appendix 3).

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Fig. 11 Hf model ages for the granitoids in the Altai and East Junggar regions (Data resources are shown in

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Appendix 3, data from Mongolia see Cai et al., 2015 and Russia see Cai et al., 2014).

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Fig. 12 Cross section of Hf isotopic data (εHf(t) value and TDMC) across the Altai–East Junggar orogens

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(position ABC see Figs. 10 and 11).

Table 1 Results from zircon U–Pb ages and Hf isotopes Sample

Rock

Pluton

1

4123

biotite monzogranite

2

A14829-1

granodiorite

3

3002

quartz diorite

4

A15706-1

quartz diorite

5

A15706-5

granodiorite

6

A15707-1

granodiorite

7

A15707-2

8

Unit

Age(Ma)

Age range(Ma)

Zircon ε Hf(t)

T DMC (Ga)

+5.2 to +13.5

1.08 to 0.53

Xenocryst(Ma)

2

398*

Kungeyite

3

260

252 to 274

-14.1 to +13.4

2.17 to 0.44

363～1286

Zhusiling

3

403

388 to 411

-8.1 to +8.3

1.91 to 0.87

499 to 1159

Lekete

3

403

389 to 420

+4.6 to +9.0

1.10 to 0.83

Kungeyite

3

404

404

+6.2 to +8.2

1.00 to 0.88

Halaayila

3

400

387 to 422

+2.7 to +7.4

1.23 to 0.93

porphyritic tonalite

Halaqiaola

3

397

382 to 406

-3.6 to +6.9

1.63 to 0.96

A14830-2

granodiorite

Songkeke

3

283

269 to 294

+11.7 to +12.8

0.56 to 0.50

9

3045

granodiorite

Kuerti

3

416**

-0.7 to +12.4

1.46 to 0.61

10

120-3

granodiorite

Keketuohai

3

409**

+0.9 to +10.7

1.35 to 0.72

11

A15704-3

quartz diorite

Chagan-East

4

402

388 to 409

+3.3 to +7.7

1.19 to 0.91

12

A15704-4

porphyritic granodiorite

Chagan

4

275

265 to 280

+5.4 to +10.1

0.95 to 0.65

13

A15707-4

tonalite

Qiaergou-South

4

393

372 to 404

+2.5 to +5.7

1.24 to 1.03

14

A15703-4

granite

Areletuobie

5

278

264 to 288

+5.8 to +11.8

1.07 to 0.55

294 to 396

East

Junggar

15

A15703-1

tonalite

Guersi

6

303

296 to 307

+11.7 to +14.8

0.57 to 0.38

331

16

A15703-2

monzonite

Hadanxun

6

290

282 to 297

+12.2 to +14.6

0.54 to 0.38

17

A15703-3

porphyritic monzogranite

Wutubulake

6

378

372 to 385

+12.0 to +16.3

0.61 to 0.34

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Kanas

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Altai

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No.

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457 to 1517

358 to 407

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T 15709-2

diorite

Wuzunbulake

7

301

287 to 312

+10.2 to +15.7

*Age of 4123 from Tong et al., 2007; **Age of 3045 and 120 -3 from Wang et al., 2006.

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Appendix 1 Data for zircon U–Pb ages

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Appendix 2 U–Pb age dating results

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Appendix 3 Hf isotope data

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Appendix 4 zircon CL images

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0.66 to 0.32

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Hf isotopic mapping determines six provinces in the Altai and East Junggar orogens. These provinces indicate a sharp contrast basement between the two orogens.

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Crustal growth is heterogeneous and its proportion reaches to ~78% in the study area.

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Figure 1

Figure 2

Figure 3

Figure 4

Figure 5

Figure 6

Figure 7

Figure 8

Figure 9

Figure 10

Figure 11

Figure 12