Tectonic evolution of the East Junggar terrane: Evidence from the Taheir tectonic
window, Xinjiang, China
Xing-Wang Xu a,b,⁎, Neng Jiang a, Xian-Hua Li a, Xun Qu c, Yue-Heng Yang a, Qian Mao a, Qi Wu a,
Yong Zhang d, Lian-Hui Dong c
a
Key Laboratory of Mineral Resources, Institute of Geology and Geophysics, Chinese Academy of Sciences, Beijing 100029, China
b
Xinjiang Research Center for Mineral Resources, Chinese Academy of Sciences, Urumqi 830011, China
c
Xinjiang Bureau of Geology and Mineral Resources, Xinjiang, Urumqi 830000, China
d
Tianjin Institute of Geology and Mineral Resources, China Geological Survey, Tianjin 300170, China
a b s t r a c t
a r t i c l e i n f o
Article history:
Received 5 April 2012
Received in revised form 26 October 2012
Accepted 3 November 2012
Available online xxxx
Handling Editor: Z. Zhang
Keywords:
Tectonic evolution
East Junggar
Taheir tectonic window
Yemaquan arc
The Taheir tectonic window is located at the southern part of the Yemaquan magmatic arc in East Junggar.
This paper reports detailed petrology, mineral chemistry, whole rock and Sr–Nd isotope geochemistry, horn-
blende 40Ar/39Ar dating, in-situ zircon U–Pb dating and Hf isotope analyses from igneous and meta-igneous
rocks from this region. Our new results show that the Taheir tectonic window consists of metamorphic and
deformed Ordovician volcanic rocks and granitic porphyries, Ordovician–Silurian granites and undeformed
Silurian–Devonian granitic diorite, diorites and rhyolitic porphyries. The Ordovician volcanic rocks and gra-
nitic porphyries and Ordovician–Silurian granites in the Taheir tectonic window exhibit distinct features of
Andean-type continental arc, such as enrichment in Pb, K and U, depletion in Nb, P and Ti, negative Eu anom-
alies, high La/Yb, Th/Yb and Ta/Yb values, a high proportion of dacite, rhyolite and andesite of the
calc-alkaline series, massive contemporary granitic intrusions, mixtures of the juvenile material and
>2.5 Ga crust, and extensive crystallization differentiation. These Ordovician volcanic rocks witnessed a se-
ries of tectonic events, including burial associated with the intrusion of 454–449 Ma granitic porphyries, un-
derthrusting and subsidence to a depth in the middle crust associated with the intrusion of 443–432 Ma
granites. The formation of albite–hornblende schists, hornblende–albite–quartz leptynites and amphibolites,
the transformation from continental to continental island arc at approximately 432 Ma, the exhumation as-
sociated with the intrusion of 416–406 Ma diorites with geochemical signatures of continental island arc, and
exhumation and erosion between 398 Ma and 390 Ma are also identified. The arc types that are associated
with the Taheir tectonic window and its host, the Yemaquan magmatic arc, changed from Andean-type con-
tinental arc to continental island arc after the intra-arc rifting that began at 432 Ma. On the basis of the new
evidence, the tectonic regime of the East Junggar terrane is redefined and a new model is proposed. It is
suggested that the East Junggar terrane is related to the southward subduction of the Paleo-Asian ocean
plate beneath the Junggar continent in the early Paleozoic and later shift to intra-oceanic subduction.
© 2012 International Association for Gondwana Research. Published by Elsevier B.V. All rights reserved.
1. Introduction
The East Junggar terrane is one of the important tectonic units of the
Central Asian Orogenic Belt (CAOB; Zonenshain et al., 1990). Debate
surrounds the tectonics of the East Junggar area, including tectonic set-
ting, age, basement nature and subduction polarity (e.g., Xiao et al.,
2011; Long et al., 2012). Among the two popular models, one suggests
that the Junggar is a continental block (e.g. Zhang et al., 1984, 1993;
Watson et al., 1987; Xiao et al., 1992; He et al., 1994; Li et al., 2000;
Charvet et al., 2001, 2007; Xu et al., 2003; Zhao et al., 2003; Buslov et
al., 2004; Xu and Ma, 2004; Dong et al., 2009; Bazhenov et al., 2012;
Choulet et al., 2012; Zhang et al., 2012). The other model proposes
that the Junggar has a basement of Paleozoic oceanic crust
(e.g., Carroll et al., 1990; Zheng et al., 2007) or oceanic island
arc complexes (e.g., Coleman, 1989; Chen and Jahn, 2004;
Windley et al., 2007) of the Altaid Paleozoic rocks (e.g., Sengör
et al., 1993; Sengör and Natal'in, 1996; Allen and Vincent, 1997;
Filippova et al., 2001; Xiao et al., 2004a, 2004b, 2008, 2009, 2010a,
2010b, 2012). The tectonics in the Eastern Junggar area are
interpreted to be related to late Paleozoic intra-oceanic accretion in-
duced by northward subduction of the Junggar oceanic lithosphere
(e.g. Xiao et al., 2008, 2009; Biske and Seltmann, 2010; Wan et al.,
2011; Yang et al., 2011) or by the southward subduction of the
Paleo-Asian oceanic lithosphere (Zhang et al., 2004; Wong et al.,
2010; Su et al., 2012).
Gondwana Research xxx (2012) xxx–xxx
⁎ Corresponding author at: Key Laboratory of Mineral Resources, Institute of Geology
and Geophysics, Chinese Academy of Sciences, Beijing 100029, China. Tel.: +86 10
82998198; fax: +86 10 62010846.
E-mail address: xuxw@mail.iggcas.ac.cn (X.-W. Xu).
GR-00950; No of Pages 23
1342-937X/$ – see front matter © 2012 International Association for Gondwana Research. Published by Elsevier B.V. All rights reserved.
http://dx.doi.org/10.1016/j.gr.2012.11.007
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Please cite this article as: Xu, X.-W., et al., Tectonic evolution of the East Junggar terrane: Evidence from the Taheir tectonic window, Xinjiang,
China, Gondwana Research (2012), http://dx.doi.org/10.1016/j.gr.2012.11.007
In this contribution, we report new data from the metamorphosed
volcanic rocks and magmatic rocks from the Taheir tectonic window
in the East Junggar region which is situated between the Zaisan–
Erqis–the Main Mongolian Lineament-suture and the Kelameili suture
and occupies the central area of the CAOB. The new results help to con-
strain the tectonic evolution of the Yemaquan arc and the basement and
to address the evolution of East Junggar.
2. Regional tectonic setting
The Junggar terrane consists of the East and West Junggar terranes
and the Junggar block and is bound by the Zaisan–Erqis—Main Mongolian
Lineament/suture in the north (e.g., Chen and Jahn, 2004; Xiao et al.,
2008). The Zaisan–Erqis–Main Mongolian Lineament-suture, represent-
ed by a Devonian–Carboniferous ophiolite belt (e.g., Zhang et al., 2003;
Wu et al., 2006a; Kröner et al., 2007), possibly marks the final line of clo-
sure of the Paleoasian ocean between the Altaids and the Junggar terrane
(Fig. 1a). The successive northward subduction of the Paleoasian
ocean produced Altaids, separated by sequential ophiolites with
ages of 1020 to 325 Ma, from the present margin of the Siberian cra-
ton to southern Siberia and northern Mongolia as well as to the main
Mongolian Lineament in the Carboniferous (Windley et al., 2002;
Kröner et al., 2007).
The East Junggar terrane to the east of the Junggar basin consists of
the NW-trending Sawuer Devonian–Carboniferous oceanic island arc,
the Armantai Cambrian–Ordovician ophiolite belt, the Yemaquan
Paleozoic volcanic arc and the Kelameili Devonian–Carboniferous
ophiolite belt from north to south (Xiao et al., 2006) (Fig. 1b).
The Sawuer oceanic island arc to the south of the Zaisan–Erqis–
the Main Mongolian Lineament suture is characterized by the oc-
currence of Devonian adakites, porphyry Cu–Au deposits and
Nb-enriched basalts (Zhang et al., 2004, 2006, 2009; Dong et al.,
2009). The Armantai ophiolite belt has an age of 503–481 Ma (Jian
et al., 2003; Xiao et al., 2006). The Yemaquan magmatic arc is charac-
terized by the occurrence of the Silurian–Devonian intermediate-
acid stocks and copper-bearing porphyries in the Qiongheba area
(Dong et al., 2009; Qu et al., 2009; Du et al., 2010) and abundant al-
kaline granites associated with Sn deposits in the Kelameili area
(Lin et al., 2007; Tang et al., 2007). The Kelameili ophiolites were
emplaced into the Devonian–Carboniferous volcanic-sedimentary
rocks between the East Junggar terrane and the Junggar block
(Fig. 1b; Shu and Wang, 2003; Bu et al., 2005) and have an age of
403 to 336 Ma (Ping et al., 2005; Tang et al., 2007), which is consis-
tent with the occurrence of
Tuvaella fauna in both the south and
north sides of the Kelameili ophiolite belt (Zhang et al., 1983;
Wang and Li, 1989).
Fig. 1. Location (a) and tectonic units (b) of East Junggar and geological map (c) with an enlargement (d) of the Taheir area. Panels a and b are after Sengör and Natal'in (1996), Xiao et al.
(2008, 2010) and Lehmann et al. (2010), panel c revised after RGSTXJBGMR (1978) and panel d is from the present study. JB: Junggar block, S1: Zaisan–Erqis–the Main Mongolian Lineament–
Okhotsk suture, S2: Kazakhstan–Tienshan–Solonker Suture, S3: Ural suture, S4: W. Kunlun–Altyn–Qilian–Qinling–Dabie Suture, S5: Alpine–Himalayan suture, SOIA: Sawuer oceanic island
arc, YMA: Yemaquan magmatic arc.
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Please cite this article as: Xu, X.-W., et al., Tectonic evolution of the East Junggar terrane: Evidence from the Taheir tectonic window, Xinjiang,
China, Gondwana Research (2012), http://dx.doi.org/10.1016/j.gr.2012.11.007
3. Geology of Taheir
Taheir is located at the southern part of the Yemaquan magmatic
arc which is bound by the Kelameili ophiolite belt to the south and
about 150 km northwest of the town of Barkol, Xinjiang, China
(Fig. 1b). The rocks in the Taheir area consist of a tectonic window
with some intrusive bodies, Silurian siliceous rocks, Devonian volca-
nic and sedimentary rocks, Carboniferous sedimentary rocks and
Quaternary sediments (Fig. 1c).
The exposed rocks in the Taheir tectonic window include metamor-
phosed volcanic and intrusive rocks termed as Ordovician Huangcaopo
Group based on regional stratigraphic correlation (RGSIXJBGMR, 1978;
XBGMR, 1993). On the basis of composition and the deformation and
metamorphic grade of the volcanic rocks and their associated intru-
sions, these rocks can be divided into two units by a NE-trending nor-
mal fault (F2, Fig. 1c), a lower unit at the northwest and an upper unit
in the middle and eastern part.
The volcanic rocks of the lower unit (
Oha) consist of dacite, agglom-
erate and breccia dacite, and volcanic block, breccia and tuff. The lower
unit rocks are characterized by abundant pyroclastic lava rocks
(Fig. 2a–d). Most of the block and breccia are rhyolite and dacite, with
minor andesite, trachyte and trachyandesite. Plagioclase phenocrysts
are common in these lavas, whereas glomerocrysts with accumulated
textures and granite breccia are present in some rhyolite blocks and
breccias (Fig. 2e and f). The exposed thickness of the lower unit is ap-
proximately 275 m (RGSIXJBGMR, 1978). All of these pyroclasts are in-
tensely stretched parallel to lineations in gneisses and amphibolites,
from the megascopic to the microscope scales (Fig. 2a–d), and have an
average axial ratio of 6.9:2:1, corresponding to a strain
k parameter of
2.45. These volcanic rocks experienced greenschist-facies to epidote–
amphibolite–facies metamorphism. The fine-grained amphibolites con-
sist of nearly equal amounts of hornblende and andesine with little mag-
netite and have intensive lineation that is observed by the alignment of
elongate grains of hornblende (Figs. 2d and 3a). There are some
Fig. 2. Field photographs (a, b and c), back scattered electron image (d) and polarized microscopic images (e and f) showing the composition and deformation features of meta-
morphic volcanic rocks from the Taheir tectonic window. Image d is from a thin section of sample ZF10-3-1 collected at site ZF10-3 in image c. Both the glomerocrysts of plagioclase
(GCP) with the tower-shape accumulated structure (referring after Xu et al., 2009) (image e) and granite breccia (GB) (image f) are from thin section of rhyolite block 10TH05-2 in
image a. The coin in image a is 2 cm in diameter. The marker pen in image b is 14 cm long. The star and associated label in images a and c show the location and number of the collected
samples. Ab: albite, Amp/AT: amphibolites from andesitic tuff, Bi: biotite, D: dacite, DA: dacite agglomerate, DB/PL: plagioclase leptynite metamorphosed from dacite breccia, HPB: horn-
blende porphyroblast, Olg: oligoclase, Q: quartz, RB: rhyolite block, Ttn: titanite.
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Please cite this article as: Xu, X.-W., et al., Tectonic evolution of the East Junggar terrane: Evidence from the Taheir tectonic window, Xinjiang,
China, Gondwana Research (2012), http://dx.doi.org/10.1016/j.gr.2012.11.007
hornblende porphyroblasts with intragranular andesine inclusions with
relict albite, and some albite–hornblende schist strips in these amphib-
olites (Fig. 3a and b). σ-structures are presented by hornblende
porphyroblasts associated with albite–hornblende schist tails on two
sides (Fig. 3a). Both the σ-structures and the curved lineation in the
albite–hornblende schist are bounded by straight lineations in the
host amphibolite, implying that these rocks had suffered two-stage de-
formation. The gneiss consists of oligoclase, hornblende, K-feldspar,
quartz, biotite and magnetite and has a distinctly banded structure,
such as the quartz–oligoclase layer and the hornblende–oligoclase
layer shown in Fig. 3c and the biotite–quartz–K-feldspar–oligoclase
layer shown in Fig. 3d. The leptynites consist of granular quartz and ol-
igoclase with minor biotite and magnetite (Fig. 3e). The grain sizes of
metamorphic plagioclase are typically 50–100 μm in length. Intensive
stretching lineations are NE-trending on the horizontal foliations.
In contrast, the dacite lavas and agglomerate and rhyolite blocks
and breccias are weakly metamorphosed. They are characterized by
the replacement of oligoclase by albite and the occurrence of horn-
blende, biotite, epidote, titanite and magnetite in a foliation zone.
Some rhyolite blocks have a 150–200-μm-wide magnetite–albite
shell, while some andesite breccias have a 200-μm-wide epidote
shell. Some elongated microbreccias of dacite are metamorphosed
to form andesine leptynites in amphibolites (Fig. 2d), while an
augen of hornblende–albite leptynite is observed in thin section of
an amphibolite specimen (ZF10-3-2). The oriented pyroclasts and
the metamorphic plagioclase, hornblende and biotite formed foliation
structures, which display an EW-trending gentle anticline structure
(Fig. 1c and profile A–A′).
There are many foliated granite stocks and granitic porphyry dikes
embedded in the metamorphic volcanic rocks of the lower unit
(Fig. 1d). All of the granites and granitic porphyries experienced
greenschist to epidote–amphibolite facies metamorphism and ductile
deformation with foliation parallel to the schistosity in the metamor-
phic volcanic rocks (Fig. 4a). Network-like foliation and lenticular
Fig. 3. Back scattered electron images showing amphibolites containing hornblende porphyroblasts and albite–hornblende schist (a) and an enlargement of intragranular andesine
inclusions with relict albites (b), quartz–hornblende–oligoclase gneiss (c), biotite–quartz–K-feldspar–oligoclase gneiss (d) and biotite leptynite (e) from the lower unit of the
Taheir tectonic window. Ab: albite, AHS: albite–hornblende schist, Amp: amphibolites, Bi: biotite, H: hornblende, Kf: K-feldspar, Mt: magnetite, Olg: oligoclase, Q: quartz. L1 and
L2 are lineation in albite–hornblende schist and amphibolites, respectively.
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Please cite this article as: Xu, X.-W., et al., Tectonic evolution of the East Junggar terrane: Evidence from the Taheir tectonic window, Xinjiang,
China, Gondwana Research (2012), http://dx.doi.org/10.1016/j.gr.2012.11.007
structures (Fig. 4c and d) are present in some moderately deformed
granites, whereas banding relicts and parallel foliation zones presented
by oriented biotite, chlorite, albite and quartz (Fig. 4e and f) occur in
intensively deformed granites. There are some narrow epidote–
hornblende–albite (epidote–amphibolite facies) mylonite zones in
the intensively foliated granites. The granitic porphyries are composed
of 0.5- to 3-mm-sized oligoclase, quartz and K-feldspar phenocrysts
that are set in a 100- to 200-μm-sized groundmass of quartz, oligoclase
and K-feldspar. However, oligoclase was partly or completely replaced
by albite in intensive deformation zones. The grain size of the ground-
mass was reduced to 20- to 50-μm in diameter by dynamic recrystalli-
zation to form mylonite zones (Fig. 4b). The granites consist of
oligoclase (50 vol.%, 400–600 μm in length), quartz (40 vol.%, 400–
600 μm in diameter) and K-feldspar (10 vol.%, 400–800 μm in length).
Similarly, oligoclase and K-feldspar in these foliated granites are partly
or completely replaced by albite. Recrystallized quartz (20–50 μm in di-
ameter), albite (50–100 μm in length), biotite and chlorite arrange
along mylonite zones and schistosity structures, which are parallel to
the schistosity in metamorphosed volcanic rocks. RGSIXJBGMR (2000)
suggested that the foliated granites are of Proterozoic age, based on a
207Pb/206Pb age of 933 Ma. However, the 207Pb/206Pb age of zircon is
not consistent with the 206Pb/238U and 207Pb/235Th ages of 249 Ma
and 326 Ma, respectively, and this 207Pb/206Pb age (933 Ma) is not con-
sidered to represent the formation age of the analyzed granite (Hu and
Wei, 2003).
Volcanic rocks of the upper unit (
Ohb) consist mainly of
trachyandesite, andesite, andesitic porphyry, agglomerate and breccia
trachyandesite and andesite, and volcanic breccia and tuff. Their exposed
thickness is approximately 1113 m (RGSIXJBGMR, 1978). Compared
with the volcanic rocks of the lower unit (
Oha), the metamorphism and
deformation of those in the upper unit are relatively weak and character-
ized by the occurrence of calcite–chlorite–albite schist interlayered with
some epidote–albite–hornblende schist in intensive deformation zones
adjacent to the lower unit and to fault F2. Chloritization and albitization
are present in the middle, eastern part of the Taheir tectonic window.
Moreover, there are many rhyolitic porphyry dikes embedded in the vol-
canic rocks of the upper unit (
Ohb). These rhyolitic porphyries also con-
tain glomerocrysts (GC) with accumulated textures, such as the five
oligoclase tablets that were packed in the GA1 and shown in Fig. 5a.
These rhyolitic porphyries had suffered brittle shear deformation
Fig. 4. Field photographs (left) and polarized microphotographs (right) of foliated granitic porphyry (a and b), generally (c and d) and intensively (e and f) foliated granites from
the Taheir tectonic window. Image a shows the relationship among the Ordovician volcanic rocks (OVR), granitic porphyry (GP), schistosity (S1) and diorite (a). Images b, d and e
are taken from thin sections of sample ZF10-1, TH6 and TH8, respectively. Their locations are shown by the star in image a, c and d correspondingly. The coin in image c is 2 cm in
diameter. Dashes in images show the attitude of schistosity. Ab: albite, Bi: biotite, GB: granite band, GL: granite lens, GM: groundmass, Kf: K-feldspar, MZ: mylonite zone, Mt: mag-
netite, Olg: oligoclase, PC: phenocryst, Q: quartz.
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Please cite this article as: Xu, X.-W., et al., Tectonic evolution of the East Junggar terrane: Evidence from the Taheir tectonic window, Xinjiang,
China, Gondwana Research (2012), http://dx.doi.org/10.1016/j.gr.2012.11.007
associated with carbonatization and weakly albitization, and some phe-
nocrysts were broken and dislocated (Fig. 5b).
Except for granite, granitic and rhyolitic porphyries, some diorite
dikes and a granodiorite stock intruded and cut the metamorphic vol-
canic rocks and foliated granites and granitic porphyries in the Taheir
tectonic window (Figs. 1c, d and 3a). There are some dioritic porphy-
ry inclusions in the granitic diorite stock. These granodiorite and dio-
rites show weak albitization and chloritization.
The metamorphosed volcanic rocks with deformed granitic por-
phyries and granites and undeformed granitic diorites are uncon-
formably overlain by Devonian volcanic and sedimentary rocks,
which consist of limestone containing
Thamnopora sp.,
Syringaxon
sp.,
Syringaxon cf.
bakterion and
Isorthis sp. bioclasts in the lower
part, andesite and andesitic porphyry in the middle part; and tuff in
the upper part. The Carboniferous sedimentary rocks consist of con-
glomerates and sandstones.
Most faults within and adjacent to the Taheir tectonic window,
such as F1, F2 and F3 in Fig. 1c and F5 in Fig. 1d, are detachment faults,
which caused the metamorphic and deformed volcanic rocks to be
exposed at the present surface. However, fault F4 at the southwest
side of the Taheir residential area is a west-dipping reverse fault,
which caused the Silurian siliceous rock to thrust over the Carbonifer-
ous sandstone. Some felsophyre bodies intruded along these faults,
while some felsophyre bodies embedded in Carboniferous sedimen-
tary rocks.
4. Sample selection and analytical techniques
After petrographic examination, a total of 20 representative fresh
rock samples were selected from metamorphic rocks, various lavas
and intrusive bodies. A total of 18 samples were selected for whole
rock geochemistry, 13 samples were selected for in situ zircon U–Pb
dating and Hf isotopic analysis, 11 samples were selected for electron
microprobe analysis, 14 samples were selected for Sr–Nd isotope
analysis, and 2 samples were selected for 40Ar/39Ar dating. The loca-
tion, rock type and analytical methods used for these samples are
presented in Table 1. All analyses were conducted at the Institute of
Geology and Geophysics, Chinese Academy of Sciences (IGGCAS).
For geochemical analyses, hand specimens were crushed in a
tungsten carbide swing mill, sieved, ultrasonically cleaned several
times in deionized water and then ground in an agate mortar. Rock
powders (~1.2 g) were then dissolved with Li2B4O7 (6 g) in a
TR-1000 S automatic bead fusion furnace at 1100 °C for 10 min.
Major element abundances (wt.%) were determined on whole-rock
powder pellets by X-ray fluorescence (XRF) using an XRF-1500 se-
quential spectrometer. Analytical uncertainties are 1 to 3% for major
elements. Loss on ignition was obtained by weighing after 1 h of cal-
cinations at 1100 °C. For rare earth element (REE) and trace element
analyses, rock powders (50 mg) were dissolved using a mixed acid
(HF:HClO4=3:1) in capped Savillex Teflon beakers at 120 °C for
6 days, and subsequently dried to wet salt and redissolved in 0.5 ml
HClO4. The solutions were then evaporated to wet salt at 140 °C and
redissolved in 1 ml HNO3 and 3 ml water for cr. 24 h at 120 °C. The
solutions were diluted in 2% HNO3 for analysis. REE and trace element
concentrations were determined by inductively coupled plasma mass
spectrometry (ICP-MS) using a PQ2 Turbo system. Uncertainties
based on repeated analyses of internal standards are ±5% for REE
and ±5–10% for trace elements.
Compositions of minerals from 16 thin sections from metamor-
phic and igneous rocks in the Taheir area were analyzed using a
CAMECA SX51 electron microprobe at IGGCAS. The accelerating volt-
age was 21 kV and the sample current was 10 nA. Beam diameters
ranging from 5 to 10 μm were used, depending on the contents of vol-
atile components within the mineral being analyzed. The counting
times for all elements were 10 s. Well defined natural minerals
were used as standards.
Samples for isotopic analysis were dissolved in Teflon bombs after
being spiked with 84Sr, 87Rb, 150Nd and 147Sm tracers prior to
HF+HNO3 (with a ratio of 2:1) dissolution. Rb, Sr, Sm and Nd were sep-
arated using conventional ion exchange procedures and measured
using a Finnigan MAT 262 multi-collector mass spectrometer (Yang et
al., 2004). Procedural blanks were b100 pg for Sm and Nd and
b500 pg for Rb and Sr. 143Nd/144Nd were corrected for mass fraction-
ation by normalization to 146Nd/144Nd=0.7219, and 87Sr/86Sr ratios
were normalized to 86Sr/88Sr=0.1194. Typical within-run precision
(2σ) for Sr and Nd was estimated to be ±0.000015. The measured
values for the La Jolla and BCR-1 Nd standards and the NBS-607 Sr stan-
dard were 143Nd/144Nd=0.511853±7 (2σn, n=3) and 0.512604±7
(2σn, n=3), respectively, and 87Sr/86Sr=1.20042±2 (2σn, n=12)
during the period of data acquisition (Yang et al., 2006).
Zircon grains were separated using conventional heavy fraction and
magnetic techniques. Representative zircon grains, together with zircon
standard 91500 were mounted in epoxy mounts which were then
polished to a section of the crystals in half for analysis. More than one
thousand zircon grains were separated from most samples, and about
two hundred of them were mounted in a row, excepting that less
than two hundred zircon grains were obtained from samples TH7,
TH05-1 and ZF8 and all of them were used. All mounted zircons
were documented with transmitted and reflected light micrographs
as well as cathodoluminescence (CL) images to reveal their internal
structures, and the mount was vacuum-coated with high-purity
gold prior to secondary ion mass spectrometry (SIMS) analysis.
Following the CL and other imaging, the samples were vacuum-coated
with high-purity gold.
Measurements of U, Th and Pb were conducted using the Cameca
IMS–1280 SIMS. U–Th–Pb ratios and absolute abundances were
Fig. 5. Polarized microphotographs showing glomerocrysts (GC) (a) and fracture (b) in rhyolitic porphyry from the Taheir tectonic window. The images are taken from thin section
of samples ZF8-2. PC1-5: plagioclase crystal 1–5. Calc: calcite, Pl: plagioclase, Q: quartz.
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Please cite this article as: Xu, X.-W., et al., Tectonic evolution of the East Junggar terrane: Evidence from the Taheir tectonic window, Xinjiang,
China, Gondwana Research (2012), http://dx.doi.org/10.1016/j.gr.2012.11.007
determined relative to the standard zircon 91500 (Wiedenbeck et al.,
1995), analyses of which were interspersed with those of unknown
grains, using operating and data processing procedures similar to
those described by Li et al. (2009). A long-term uncertainty of 1.5%
(1 RSD) for 206Pb/238U measurements of the standard zircons was
propagated to the unknowns (Li et al., 2010), despite that the mea-
sured 206Pb/238U error in a specific session is generally around 1%
(1 RSD) or less. Measured compositions were corrected for common
Pb using non-radiogenic 204Pb. Corrections are sufficiently small to
be insensitive to the choice of common Pb composition, and an aver-
age of present-day crustal composition (Stacey and Kramers, 1975) is
used for the common Pb assuming that the common Pb is largely sur-
face contamination introduced during sample preparation. Uncer-
tainties on individual analyses in data tables are reported at a 1 σ
level; mean ages for pooled U/Pb (and Pb/Pb) analyses are quoted
with 95% confidence interval. Data reduction was carried out using
the Isoplot/Ex v. 2.49 programs (Ludwig, 2001).
In situ zircon Lu–Hf isotopic analyses were carried out using a
Neptune MC-ICPMS with an ArF excimer laser ablation system. Hf iso-
topic analyses were obtained on the same zircon grains that were
previously analyzed for U–Pb isotopes, with ablation pits of 40 μm
in diameter, and a laser repetition rate of 10 Hz with 100 mJ was
used. Details of the technique are described by Xu et al. (2004), Wu
et al. (2006b) and Li et al. (2010). During analyses, the 176Hf/177Hf
and 176Lu/177Hf ratios of standard zircon (91500) were 0.282294±
15 (2σn, n=20) and 0.00031, similar to the commonly accepted
176Hf/177Hf ratio of 0.282284±3 (1σ) measured using the solution
method (Goolaerts et al., 2004; Woodhead et al., 2004).
Hornblende separates from samples ZF10-3 and TH05-1 for 40Ar/
39Ar analyses were obtained by crushing the sample in a tungsten car-
bide swing mill, sieving and collecting crystal bigger than 200 μm,
and hand-picking under a binocular microscope to be 99% pure. The
hornblende separates were irradiated for 37 h at the Beijing Nuclear
Research Institute Reactor. Argon extraction for incremental heating
was performed on the MIR10-50 Laser Fusing and Heating System
in the Laboratory of Isotope Geochronology. The purified gas fractions
were analyzed on a MM5400 mass spectrometer; a number of inter-
national neutron fluence monitors (standards) have been inter-
calibrated (Wang et al., 2005). The procedure used for CO2 laser
fusion on MM5400 of the IGGCAS follows Wang et al. (2006). Age cal-
culations were made using decay constants given by Steiger and Jäger
(1977) and formulas of Wang et al. (1985) and Wang (1992).
5. Analytical results
5.1. Whole rock geochemistry
Major and trace element data from the analyzed samples of the
Taheir area are summarized in Table 2. The 5 metamorphic lava samples
have a large range in major element concentrations, with SiO2 of
52.54–79.26 wt.%, Al2O3 of 11.37–15.23 wt.%, Fe2O3 of 1.21–4.6 wt.%,
FeO of 1.01–4.36 wt.%, MgO of 0.9–4.69 wt.%, CaO of 1.13–7.04 wt.%,
Na2O of 3.41–6.39 wt.%, and K2O of 0.42–3.36 wt.%. However, they
have similar trace element concentrations and ratios, with REE of
114–160 ppm, (La/Yb)N of 7.13–8.43 and Eu/Eu* of 0.74–0.87, low Rb
(5.65–26.87 ppm), Nb (3.46–5.13 ppm), Y (16.35–21.01 ppm), Ta
(0.2–0.31 ppm), Yb (1.81–2.49 ppm) and Ce/Pb (5.54–13.41), and
high Ba/Nb (29–338), La/Yb (10.58–12.51) and Th/Yb (2.73–3.68)
(Table 2). These lavas plot in the fields of rhyolite, dacite, trachyte and
trachy-andesite in a total alkali versus silica (TAS) diagram (Fig. 6a)
and are calc-alkaline (Fig. 6b). They have similar REE pattern with pro-
nounced negative Eu anomalies (Fig. 7a) and are enriched in Pb and U
and depleted in Nb, P and Ti in trace element spider diagrams
(Fig. 7b). These rocks plot in the field of volcanic arc granites (VAG) in
the Rb versus Ta+Yb diagram (Fig. 8a; Pearce et al., 1984 ), in the con-
tinental crust field in the Ce/Pb versus Ce diagram (Fig. 8b; Hofmann,
1988), in and near the field of arc volcanic rocks in the Ba/Nb versus
La/Nb diagram (Fig. 8c; Jahn et al., 1999), in the field of continental
arc in the Th/Yb versus Ta/Yb diagram (Fig. 8d; Pearce, 1983), and in in-
terspace between the field of Andean-type continental arc and that of
continental island arc in La/Yb versus Sc/Ni diagram (Fig. 8e; Bailey,
1981).
Compared with the metamorphic lava samples, the granite and gra-
nitic and rhyolitic porphyry samples have a more restricted range in
major element, with SiO2
of 70.07–76.02 wt.%, Al2O3
of 11.28–
14.06 wt.%, Fe2O3 of 0.68–2.53 wt.%, FeO of 0.29–1.29 wt.%, MgO of
0.38–2.05 wt.%, CaO of 0.85–4.21 wt.%, Na2O of 2.84–5.5 wt.%, and K2O
of 0.6–3.71 wt.%. They also have similar trace element concentrations
and ratios, with REE of 85–175 ppm, (La/Yb)N of 5.69–11.99 and Eu/Eu*
of 0.62–0.81, low Rb (6.7–48.16 ppm), Nb (3.78–5.81 ppm), Y (14.44–
25.44 ppm), Ta (0.22–0.49 ppm), Yb (1.6–2.8 ppm) and Ce/Pb (6.08–
12.28), and high Ba/Nb (26–229) and Th/Yb (2.03–5.95) (Table 2).
These rocks plot in the field of granite (rhyolite) in the TAS diagram
(Fig. 6a) and are calc-alkaline (Fig. 6b). They have similar REE and trace
element patterns (Fig. 7) and plot in the same fields in the Rb versus
Table 1
Sample location, rock type and analytical method for metamorphic and igneous rocks from the Taheir area, East Junggar.
Sample number
Location
Rock type
Analytical method
Major and rare
element
Electron
microprobe
Sr–Nd
isotope
SIMS zircon U-Pb
age dating
LA-ICPMS zircon
Hf isotope
Ar–Ar
dating
TH1
N44°36′34.6″/E91°46′28.4″
Granitic diorite
√
√
TH5
N44°36′26.4″/E91°47′25.3″
Granitic porphyry
√
√
√
√
TH6
N44°36′07.3″/E91°47′54.2″
Foliated Granite
√
√
√
√
√
TH7
N44°36′07.21″/E91°47′56.9″
Diorite
√
√
√
√
√
TH8
N44°36′05.0″/E91°48′00.2″
Foliated Granite
√
√
√
√
√
TH9
N44°35′58.3″/E91°47′40.8″
Granitic diorite
√
√
√
√
√
TH9-2
N44°35′58.3″/E91°47′40.8″
Dioritic porphyry inclusion
√
TH12
N44°35′32.9″/E91°46′57.3″
Rhyolitic porphyry
√
ZF5
N44°36′45.6″/E91°47′49.1″
Andesitic porphyry
√
√
√
√
ZF7
N44°36′06.6″/E91°48′13.2″
Rhyolitic porphyry
√
ZF8
N44°36′04.0″/E91°48′16.9″
Rhyolitic porphyry
√
√
√
√
√
ZF10-1
N44°36′07.7″/E91°47′57.6″
Granitic porphyry
√
√
√
√
√
ZF10-3
N44°36′06.2″/E91°47′57.4″
Amphibolite
√
√
ZF10-4
N44°36′07.3″/E91°47′56″
Gneiss
√
TH02-3
N44°36′07.0″/E91°47′55.5″
Trachyandesite
√
√
√
√
TH03-3
N44°36′03.8″/E91°47′48.5″
Trachyte agglomerate
√
√
√
√
√
TH03-4
N44°36′03.8″/E91°47′48.5″
Trachyandesite agglomerate
√
TH05-1
N44°36′04.5″/E91°47′46.8″
Diorite
√
√
√
√
√
√
TH05-2
N44°36′05.4″/E91°47′46.8″
Rhyolite block
√
√
√
√
TH05-3
N44°36′05.4″/E91°47′46.8″
Dacite
√
√
√
√
√
7
X.-W. Xu et al. / Gondwana Research xxx (2012) xxx–
xxx
Please cite this article as: Xu, X.-W., et al., Tectonic evolution of the East Junggar terrane: Evidence from the Taheir tectonic window, Xinjiang,
China, Gondwana Research (2012), http://dx.doi.org/10.1016/j.gr.2012.11.007
Ta+Yb diagram (Fig. 8a), Ce/Pb versus Ce diagram (Fig. 8b), Ba/Nb
versus La/Nb diagram (Fig. 8c) and Th/Yb versus Ta/Yb diagram
(Fig. 8d) as the metamorphic lavas. However, the granites and gra-
nitic porphyries have higher La/Yb (12.79–17.78) and plot in or
near the field of Andean-type continental arc, whereas the rhyolitic
porphyries plot in the field of continental island arc in the La/Yb ver-
sus Sc/Ni diagram (Fig. 8e).
The granodiorite and dioritic porphyry samples have similar major
and trace element contents, with SiO2 of 52.65–65.9 wt.%, Al2O3 of
16.31–19.04 wt.%, Fe2O3 of 1.26–4.21 wt.%, FeO of 1.37–4.39 wt.%, MgO
of 0.83–4.68 wt.% and TiO2 of 0.28–0.67 wt.%, CaO of 5.24–6.97 wt.%,
Na2O of 2.06–2.76 wt.%, K2O of 1.35–2.09 wt.%, P2O5 of 0.12–0.24 wt.%,
REE of 51–87 ppm, (La/Yb)N of 5.64–7.17 and Eu/Eu* of 0.93–1.12,
and relatively low Rb (22.93–32.31ppm), Nb (2.21–2.31 ppm),
Y (8.75–16.27 ppm), Ta (0.09–0.16 ppm), Yb (0.87–1.24 ppm) and
Ce/Pb (4.48–11.49), and high Sr (552–769 ppm), Sr/Y (47–63) and
Ba/Nb (178–335) (Table 2). These rocks are calc-alkaline (Fig. 6b) and
adakitic (Defant and Drummond, 1990), and have similar REE patterns
(Fig. 7a). Trace element spider diagrams indicate that they are enrich-
ment of Pb, U and Sr and depletion of Nb, P and Ti (Fig. 7b). They plot
Table 2
Major (wt.%) and trace element (ppm) concentrations for igneous rocks from the Taheir area, East Junggar.
Sample
TH02-3 TH03-3 TH03-4 TH05-2
TH05-3 TH5
TH6
TH8
ZF10-1 ZF7
ZF8
TH12
TH1
TH9
TH9-2
TH7
TH05-1 ZF5
SiO2
56.94
60.09
52.54
69.26
66.83
74.64
76.02
70.07
71
72.42
73.89
70.13
65.9
62.32
52.65
51.38
49.98
57.76
TiO2
0.55
0.45
0.53
0.36
0.48
0.31
0.33
0.52
0.48
0.45
0.38
0.63
0.28
0.45
0.67
1.67
1.68
1.43
Al2O3
15.08
15.23
13.18
11.37
14.3
12.82
11.91
12.28
13.91
14.06
11.28
12.19
17.21
16.31
19.04
14.94
14.98
14.86
Fe2O3
4.6
1.21
4.46
1.24
3.01
1.36
0.79
1.98
1.72
1.36
0.68
2.53
1.26
2.44
4.21
6.59
5.94
4.41
FeO
3.83
1.01
4.36
1.08
2.08
0.86
1.49
1.92
1.24
1.67
0.71
0.29
1.37
2.57
4.39
7.11
7.38
4.62
MnO
0.13
0.06
0.16
0.04
0.1
0.05
0.05
0.08
0.05
0.03
0.05
0.14
0.07
0.09
0.15
0.22
0.22
0.2
MgO
4.69
1.15
5.08
0.9
2.49
0.38
1.03
1.21
0.68
1.07
0.46
2.05
0.83
2.49
4.68
4.69
5.57
3.57
CaO
5.43
6.32
7.04
1.13
2.91
1.87
0.85
1.54
1.79
2.89
4.25
4.21
6.97
5.24
6.69
8.16
8.48
5.72
Na2O
5.5
6.39
5.71
3.41
5.95
3.55
4.51
4.92
5.5
2.84
3.09
2.97
2.19
2.76
2.06
2.59
2.82
2.27
K2O
1.2
2.75
0.42
3.36
0.62
1.92
1.68
3.71
2.41
1.63
0.6
1.95
1.8
2.09
1.35
1.1
1.21
1.33
P2O5
0.15
0.11
0.12
0.1
0.13
0.05
0.07
0.15
0.13
0.13
0.1
0.13
0.12
0.16
0.24
0.3
0.21
0.26
LOI
1.62
5.26
3.46
8.26
1.04
2.83
1.18
1.65
1.08
1.57
3.73
1.84
1.92
2.9
3.9
1.37
0.88
3.18
TOTAL
99.72
100.03
97.06
100.51
99.94
100.65
99.9
100.02
99.99 100.11 100.23 100.06
99.91
99.82 100.03 100.12
99.35
99.62
Li
9.3
5.19
8.78
6.21
7.46
1.61
1.39
7.07
3.6
2.12
2.02
7.08
1.12
16.15
30.95
9.84
10.69
22.03
Be
0.75
0.49
0.58
0.78
1.08
0.68
1.01
1.3
1.17
1.16
0.72
0.93
0.92
0.9
1.2
0.62
0.77
0.92
Sc
23.52
9.25
23.81
8.96
17.78
3.7
4.91
12.25
9.09
9.48
4.87
1.67
3.45
9.46
20.51
37.99
39.76
29.06
V
193.74
51.28
200.14
39.95 108.49
26.24
24.94
48.7
40.38
33.54
14.57
6.32
47.44
95.27 190.8
425.52 304.3
210.67
Cr
399.08
5.49
100.93
9.37
58.53
59.49 108.34
62.97
0.5
1.64
0.94
50.39
54.65
67.28
38.98
38.61
40.14
17.91
Co
23.59
5.23
27.98
6.11
15.81
2.25
3.18
4.86
3.59
2.33
1.56
0.64
3.95
11.37
21.94
31.15
40.42
17.62
Ni
61.39
4.11
61.21
3.2
15.41
8.84
2.87
21.67
20.84
2.72
1.65
1.25
1.63
7.2
15.97
16.01
23.4
8.46
Cu
21.08
31.18
53
11.64
49.76
10.24
1.3
1.2
12.93
2.12
3.99
0.82
1.78
15.99 231.06 122.95 370.2
30.98
Zn
70.78
35.12
73.6
36.88
55.79
48.35
46.06
48.28
58.37
71.56
26.07
21.35
53.54
61.49
85.59 120.28 176.5
105.4
Ga
14.86
9.57
13.97
11.44
16.29
12.68
11.8
15.67
13.79
15.5
10.27
12.63
17
16.25
23.01
17.92
20.54
18.13
Rb
20.66
26.87
5.65
27.42
7.21
17.56
20.11
48.16
17.01
18.67
6.7
24.35
27.92
32.31
22.93
18.93
19.95
19.95
Sr
548.44
143.75
279.86
245.34 312.61
78.82 210.5
444.43 144.93 122.52 109.43 107.37 551.92 689.25 768.69 528.47 628.23
486.26
Y
16.35
21.01
17.15
19.67
20.97
14.44
17.64
25.44
21.28
23.23
19.14
17.49
8.75
12.3
16.27
28.34
34.92
28.96
Zr
144.72
204.32
133.26
194.82 181.76
191.83 197.31
214.47 201.51 169.43 137.43 104.84
94.67 100.73
61.53
85.06 129.76
115.48
Nb
3.57
5.13
3.46
4.68
4.58
4.8
4.15
5.12
4.84
4.46
3.78
5.81
2.31
2.21
2.21
3.09
2.75
3.98
Cs
0.31
0.09
0.11
0.14
0.13
0.2
0.17
0.63
0.07
0.34
0.21
0.25
0.38
0.58
0.41
0.28
0.39
0.25
Ba
436.61
671.85
99.69
1580.63 138.89
243.37 407.98 1173.2
791.98 152.02 143.75 149.15 774.41 546.18 393.57 169.27 363.32
480.32
La
20.33
31.14
23.76
28.06
25.5
28.45
25.33
35.33
31.43
27.68
17.73
17.06
9.25
12.16
15.05
7.33
10.27
11.57
Ce
43.65
63.31
45.73
58.47
53.76
59.33
54.93
70.24
65.54
60.55
41.34
32.69
20.86
24.66
33.12
18.24
24.44
27.32
Pr
6.14
8.36
6.05
7.54
7.2
6.38
6.55
9.09
8.19
7.72
5.19
3.37
2.58
3
4.46
2.78
3.89
3.88
Nd
24.29
32.42
25.1
28.71
30
22.78
26.13
34.15
32.2
30.9
20.44
19.47
10.1
12.11
18.16
13.09
18.9
17.75
Sm
5.12
6.27
5
5.62
5.83
3.75
4.84
6.65
5.97
6.4
4.41
3.92
2.02
2.62
3.9
4.11
5.55
5.23
Eu
1.29
1.37
1.29
1.28
1.29
0.74
1.03
1.54
1.48
1.48
1
0.52
0.67
0.8
1.07
1.44
1.83
1.74
Gd
4.46
5.29
4.15
4.85
4.81
3.09
3.99
5.66
5.19
4.9
3.83
1.69
1.65
2.31
3.19
4.51
5.88
4.65
Tb
0.63
0.76
0.61
0.68
0.71
0.44
0.58
0.83
0.74
0.79
0.57
0.23
0.25
0.36
0.49
0.78
1.08
0.81
Dy
3.45
4.13
3.4
3.73
3.93
2.5
3.3
4.71
4.11
4.55
3.34
3.26
1.47
2.14
3.03
5.2
6.95
5.38
Ho
0.67
0.86
0.7
0.78
0.82
0.51
0.69
0.94
0.85
0.96
0.72
0.25
0.3
0.45
0.62
1.1
1.49
1.15
Er
1.89
2.39
1.91
2.24
2.3
1.5
1.94
2.6
2.37
2.72
2.04
0.72
0.85
1.27
1.79
3.07
4.22
3.25
Tm
0.28
0.37
0.29
0.36
0.36
0.23
0.3
0.4
0.35
0.41
0.31
0.11
0.13
0.19
0.28
0.46
0.61
0.49
Yb
1.81
2.49
1.95
2.37
2.41
1.6
1.98
2.62
2.27
2.8
2.1
1.7
0.87
1.24
1.8
2.93
3.86
3.16
Lu
0.3
0.39
0.31
0.39
0.39
0.29
0.32
0.4
0.36
0.43
0.32
0.31
0.14
0.2
0.28
0.44
0.6
0.47
Hf
4.24
6.04
3.94
5.68
5.29
5.78
5.88
6.46
5.91
4.89
3.88
3.2
2.69
2.9
1.94
2.57
3.9
3.15
Ta
0.22
0.31
0.2
0.28
0.27
0.31
0.24
0.31
0.27
0.27
0.22
0.49
0.16
0.13
0.09
0.2
0.19
0.25
Tl
0.09
0.13
0.05
0.13
0.06
0.1
0.09
0.17
0.08
0.08
0.06
0.12
0.1
0.13
0.1
0.09
0.09
0.09
Pb
3.25
11.42
5.41
8.97
6.03
9.76
3.97
7.49
10.34
4.93
4.98
4.93
4.65
2.64
2.88
2.15
4.51
5.4
Bi
0.05
0.05
0.04
0.05
0.12
0.24
0.03
0.1
0.08
0.08
0.05
0.06
0.02
0.02
0.1
0.02
0.3
0.06
Th
5.98
9.16
5.32
8.11
7.67
9.52
8.05
8.88
7.58
5.99
4.27
5.25
1.45
2.19
0.47
0.58
1.38
1.38
U
1.91
2.61
1.43
2.36
2.3
3.06
1.78
2.62
2.18
1.67
1.29
1.07
0.72
1.1
1.09
0.4
0.87
0.47
REE
114.31
159.55
120.25
145.08 139.31
131.59 131.91
175.16 161.05 152.29 103.34
85.3
51.14
63.51
87.24
65.48
89.57
86.85
Eu/Eu*
0.83
0.73
0.87
0.75
0.74
0.66
0.72
0.77
0.81
0.81
0.74
0.62
1.12
0.99
0.93
1.02
0.98
1.08
LaN/YbN
7.57
8.43
8.21
7.98
7.13
11.99
8.62
9.09
9.33
6.66
5.69
6.77
7.17
6.61
5.64
1.69
1.79
2.47
Ce/Pb
13.41
5.54
8.46
6.52
8.92
6.08
13.84
9.38
6.34
12.28
8.31
6.63
4.48
9.34
11.49
8.48
5.42
5.06
Ba/Nb
122
131
29
338
30
51
98
229
164
34
38
26
335
247
178
55
132
121
La/Nb
5.69
6.07
6.87
6.00
5.57
5.93
6.10
6.90
6.49
6.21
4.69
2.94
4.00
5.50
6.81
2.37
3.73
2.91
Th/Yb
3.30
3.68
2.73
3.42
3.18
5.95
4.07
3.39
3.34
2.14
2.03
3.09
1.67
1.77
0.26
0.20
0.36
0.44
Ta/Yb
0.12
0.12
0.10
0.12
0.11
0.19
0.12
0.12
0.12
0.10
0.10
0.29
0.18
0.10
0.05
0.07
0.05
0.08
Sr/Y
33.54
6.84
16.32
12.47
14.91
5.46
11.93
17.47
6.81
5.27
5.72
14.34
63.11
56.02
47.24
18.65
17.99
16.79
Sc/Ni
0.38
2.25
0.39
2.80
1.15
0.42
1.71
0.57
0.44
3.49
2.95
1.34
2.12
1.31
1.28
2.37
1.70
3.43
La/Yb
11.23
12.51
12.18
11.84
10.58
17.78
12.79
13.48
13.85
9.89
8.44
10.04
10.63
9.81
8.36
2.50
2.66
3.66
8
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in the same fields in the Rb versus Ta+Yb diagram (Fig. 8a), Ce/Pb ver-
sus Ce diagram (Fig. 8b) and Ba/Nb versus La/Nb diagram (Fig. 8c)
with metamorphic felsic lava, granites, and granitic and rhyolitic
porphyries. However, two granodiorite samples plot in the field of
continental arc, while the dioritic porphyry sample plots in inter-
space between the field of oceanic island arc (OIA) and that of within
plate basalts (WPB) in the Th/Yb versus Ta/Yb diagram (Fig. 8d).
Moreover, all the three granitic diorite and dioritic porphyry samples
plot in the field of continental island arc in the La/Yb versus Sc/Ni di-
agram (Fig. 8e).
Two diorite samples and one andesitic porphyry have similar major
and trace element contents: SiO2 (49.98–57.76 wt.%), Al2O3 (14.86–
14.98 wt.%), Fe2O3
(4.41–6.59wt.%), FeO (4.62–7.38 wt.%), MgO
(3.57–5.57 wt.%) and TiO2 (1.43–1.68 wt.%), CaO (5.72–8.48 wt.%),
Na2O (2.27–2.82 wt.%), K2O (1.1–1.33 wt.%), P2O5 (0.21–0.3 wt.%),
REE (65–90 ppm), (La/Yb)N (1.69–2.74) and Eu/Eu* (0.98–1.08), low
Rb (18.93–19.95 ppm), Nb (2.75–3.98 ppm), Y (28.34–34.42 ppm), Ta
(0.19–0.25 ppm), Yb (2.93–3.86 ppm) and Ce/Pb (5.42–8.46), and
high Sr (486–628 ppm) and Ba/Nb (55–132) (Table 2). These rocks
have similar flat REE patterns (Fig. 7a) and trace element spider
Fig. 6. TAS diagram (after Le Bas et al., 1986) (a) and AFM (after Irvine and Baragar, 1971) (b) of igneous rocks from the Taheir area. The black circles show plots of lava micro
breccias, schists, leptynites, gneisses and amphibolites, whose compositions are estimated by the mineral composition and content reported in Supplementary table 1.
Fig. 7. REE (a) and trace element (b) spider diagrams of igneous rocks from the Taheir area. The REE and primitive mantle values are after Boynton (1984) and Sun and McDonough
(1989), respectively.
9
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diagrams indicate that they are enriched with Pb and Sr and depleted of
Th, Nb, Pr and Zr (Fig. 7b). They plot in the same fields in the Rb versus
Ta+ Yb diagram (Fig. 8a), the Ce/Pb versus Ce diagram (Fig. 8b) and the
Ba/Nb versus La/Nb diagram (Fig. 8c) with metamorphic felsic lava, gra-
nitic and rhyolitic porphyries, and granitic diorite and dioritic porphyry.
However, these rocks all plot in or near the field of other oceanic arc in
the La/Yb versus Sc/Ni diagram (Fig. 8e), and in between the continental
arc (CA), oceanic island arc (OIA) and within plate basalts (WPB) fields
in the Th/Yb versus Ta/Yb diagram (Fig. 8d). The diorite samples contain
high Fe and Mg, and belong to the tholeiite series (Fig. 6b).
5.2. Mineral chemistry and protolith composition
Electron microprobe analyses were performed on hornblende,
plagioclase, K-feldspar, biotite and chlorite from 16 thin sections
from various metamorphic rocks and intrusive bodies in the Taheir
tectonic window. Mineral compositions are used to constrain the
classification of metamorphic rocks and to estimate the composition
of micro-lava breccias and the protolithic composition of some
schists, gneisses, leptynites and amphibolites.
5.2.1. Mineral chemistry
Plagioclases from granites, granitic and rhyolitic porphyries, rhyo-
lite and dacite are albite and oligoclase with anorthite content up to
18%, while andesine from diorite and granitic diorite has an anorthite
content of 30–34% (Fig. 9a). The composition of metamorphic plagio-
clase varies regularly with the grade of the metamorphic rocks. Albite
is the major feldspars in the schists, while oligoclase is dominant in
the gneisses and andesine in the amphibolites (Fig. 9a). The oligoclase
from the gneisses has an anorthite content of 10–22%, and the
Fig. 8. (a) Rb versus Ta+Yb diagram (after Pearce et al., 1984), (b) Ce/Pb versus Ce diagram (after Hofmann, 1988), (c) Ba/Nb versus La/Nb diagram (after Jahn et al., 1999), (d) Th/Yb
versus Ta/Yb diagram (after Pearce, 1983) and (e) La/Yb versus Sc/Ni diagram (Bailey, 1981) for igneous rocks from the Taheir area. AV: arc volcanics, CA: continental arc, CCA: continental
crust average, DOIB: Dupal oceanic island basalt, OIA: oceanic island arc, MORB: midocean ridge basalts, OIB: oceanic island basalt, ORG: ocean ridge granites, PM: primitive mantle,
syn-COLG: syn-collision granites, VAG: volcanic arc granites, WPB: within plate basalts, WPG: within plate granites.
10
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Please cite this article as: Xu, X.-W., et al., Tectonic evolution of the East Junggar terrane: Evidence from the Taheir tectonic window, Xinjiang,
China, Gondwana Research (2012), http://dx.doi.org/10.1016/j.gr.2012.11.007
andesine from the amphibolite has an anorthite content of 33–46%.
Most K-feldspar from the igneous rocks, gneiss and amphibolites are
sanidine and orthoclase, with an orthoclase content of >73%.
Amphiboles from metamorphic rocks, diorite and granitic diorite
are hornblendes with diagnostic parameters that include CaB =
1.73–1.94, (K+Na) A = 0.15–0.45, Mg/(Mg+Fe2+) = 0.52–0.73, and
plot in the field of tschermakite in the nomenclature diagram
shown in Fig. 9b (Leake et al., 1997). However, hornblendes from dif-
ferent metamorphic and igneous rocks have a variety of composi-
tions. For example, hornblendes from hornblende oligoclase gneiss
have high SiO2 (48.61–51.46 wt.%) and MgO (13.28–14.29 wt.%),
and low Al2O3 (3.92–5.73 wt.%) and FeO (13.14–15.22 wt.%) con-
tents, while those from an epidote–hornblende–albite–quartz schist
in foliated granite have low SiO2
(44.86–46.08 wt.%) and MgO
(10.1–10.81 wt.%) and high Al2O3 (8.14–8.81 wt.%) and FeO (18.77–
19.68 wt.%) contents (Supplementary Table 1). Hornblendes from
the amphibolites contain higher Al2O3 (5.73–9.68 wt.%) and FeO
(16.19–20.3 wt.%) and lower SiO2 (44.05–44.82 wt.%) and MgO
(9.39–12.39 wt.%) contents than those from gneiss. Hornblendes
from the diorite and granitic diorite have low Mg/(Mg+Fe2+) values
of 0.54–0.61.
5.2.2. Protolith composition
On the assumption that the compositional alterations of these
schists, leptynites, gneisses and amphibolites during metamorphism
are negligible, the protolithic composition of some representative
schists, leptynites, gneisses, amphibolites and micro breccias are estimat-
ed according to their mineral assemblages, contents and compositions.
The obtained protolithic compositions show that the amphibolites and
albite hornblende schists are metamorphosed equivalents of basaltic an-
desitic tuffs and the hornblende oligoclase gneisses were derived from
andesitic and trachytic tuffs (Supplementary Table 1, Fig. 6a). 6 of the 9
studied lava micro breccias are rhyolite, while the other two are trachyte,
and the remaining one is trachyandesite. All of these lava micro breccias,
medium grade metamorphic rocks and their protolithic tuffs are calc-
alkaline (Fig. 6b). This is consistent with the whole rock geochemistry
described above.
5.3. Sr and Nd isotope data
The Rb, Sr, Sm and Nd concentrations, 143Nd/144Nd and 87Sr/86Sr
ratios, and TDM ages for igneous rocks in Taheir area are listed in
Table 3. The initial 143Nd/144Nd and 87Sr/86Sr ratios and εNd (t) values
have been calculated at their corresponding zircon U–Pb concordia
age reported below. Depleted mantle model ages (TDM) are reported
using the model of DePaolo (1981).
The early Paleozoic igneous rocks, including metamorphic lavas, gra-
nitic porphyries, granites and granitic diorite, have low 147Sm/144Nd
values ranging from 0.1156 to 0.126725, and plot in the field of Andean
andesite in the 143Nd/144Nd versus 143Sm/144Nd plot (Fig. 10a; Goldstein
Fig. 9. Composition of feldspar plotted on the Anorthite–Albite–Orthoclase diagram (a) and hornblende plotted in the nomenclature diagram after Leake et al. (1997) (b) for meta-
morphic and igneous rocks from the Taheir tectonic window. HOG: hornblende oligoclase gneiss, HAL: hornblende albite leptynite, EHAQS: epidote–hornblende–albite–quartz
schist, EAHS: epidote–albite–hornblende schist.
Table 3
Sm-Nd-Rb-Sr isotope data for igneous rocks from the Taheir area, East Junggar.
Sample Age
(Ma)
Sm
(ppm)
Nd
(ppm)
147Sm/
144Nd
143Nd/
144Nd
(143Nd/144Nd)i (143Nd/144Nd)chur(t)
εNd(t)
TDM
(Ma)
Rb
(ppm)
Sr
(ppm)
87Rb/86Sr 87Sr/86Sr
Error
(2σ)
(87Sr/86Sr)i
TH1
432
1.949
9.826 0.119935 0.512747 0.512407
0.512081
6.36
656 27.28
583.0
0.135388 0.704997 0.000011 0.704164
TH5
446
3.118
11.16
0.143932 0.512818 0.512398
0.512063
6.53
726 25.81
118.8
0.628928 0.707298 0.000012 0.703302
TH6
443
5.330
26.17
0.115600 0.512664 0.512328
0.512067
5.10
756 19.90
232.7
0.247457 0.705937 0.000012 0.704358
TH7
406
4.025
13.27
0.183330 0.512974 0.512486
0.512115
7.25
885 15.20
532.1
0.082670 0.704858 0.000013 0.704380
TH8
432
4.96
24.22
0.1240
0.512671 0.512320
0.512081
4.66
814 20.02
554.6
0.1044
0.705305 0.000009 0.704647
TH9
432
3.210
12.57
0.126725 0.512817 0.512459
0.512081
7.37
583 33.38
778.7
0.124038 0.704957 0.000009 0.704194
ZF5
390
4.701
17.63
0.161240 0.512927 0.512515
0.512136
7.42
648 19.71
494.6
0.115345 0.706054 0.00001
0.705413
ZF8
398
7.580
31.99
0.143239 0.512682 0.512309
0.512125
3.58
1,011 18.41
121.8
0.437416 0.706862 0.00001
0.704370
ZF10-1
455
6.320
32.80
0.116483 0.512689 0.512342
0.512052
5.67
723 17.82
158.6
0.325256 0.706931 0.000011 0.704799
TH02-3 442
4.64
22.52
0.1248
0.512681 0.512319
0.512069
4.90
805
5.516 275.0
0.0580
0.704955 0.000012 0.704591
TH03-3 440
5.78
29.82
0.1172
0.512666 0.512328
0.512071
5.02
765 27.60
142.9
0.5590
0.707522 0.000013 0.704018
TH05-1 416
5.45
18.51
0.1783
0.512983 0.512509
0.512115
7.68
721 19.13
634.5
0.0873
0.704902 0.000012 0.704397
TH05-2 454
5.37
27.84
0.1167
0.512668 0.512321
0.512053
5.23
758 26.91
246.7
0.3157
0.706658 0.000011 0.704611
TH05-3 453
5.48
26.99
0.1230
0.512672 0.512307
0.512054
4.93
804
6.999 307.8
0.0658
0.705258 0.000012 0.704833
11
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et al., 1984), whereas two diorites have high 147Sm/144Nd values of
0.1783 and 0.18333.
The εNd (t) values and initial 87Sr/86Sr ratios of igneous rocks in the
Taheir area range from +3.5 to +7.68 and from 0.703302 to
0.705413, respectively. Plots of these rocks in the Nd isotope diagram
(Fig. 10b) display four points (diorite, andesitic porphyry and granitic
diorite) near the depleted mantle line proposed by Nelson and
Depaolo (1985), and the other points extend downwards. Data points
in the εNd (t) versus (87Sr/86Sr)i diagram (Fig. 10c) are located mostly
in, and a few adjacent to, the North Andean volcanic zone or the
Japanese arc fields. These igneous rocks have TDM (Nd) ages between
1011 Ma and 583 Ma, which are older than the oldest ophiolite in
East Junggar (Fig. 10d).
5.4. Zircon features, U–
Pb ages and Lu–
Hf isotopes
The CL images of representative zircons selected for U–Pb dating
and Hf analyses are shown in Fig. 11. SIMS zircon U–Th–Pb isotopic
data are presented in Supplementary Table 2 and illustrated in
Fig. 12. LA-ICPMS zircon Hf isotopic data are reported in Supplemen-
tary Table 3. The initial εHf (t) values and corresponding depleted
mantle model ages (TDM (Hf)) have been calculated at their corre-
sponding zircon 206Pb/238U age.
Three metamorphosed lavas, including the rhyolite block (TH05-2),
dacite (TH05-3) and trachyandesite (TH02-3), contain zircons that have
concentric oscillatory zoning and gray color in CL images and euhedral-
to-subhedral and equant-to-stubby forms with average elongation ra-
tios of approximately 1.5 (Figs. 11a, 12b and d). Zircons from sample
TH05-2 (rhyolite block) have 108–222 ppm U, 60–229 ppm Th and
10–23 ppm Pb with Th/U ratios in the range of 0.56–1.03, 206Pb/238U
ages ranging from 448.3±6.5 Ma to 466.6±6.8 Ma with a concordia
age of 454.4±1.7Ma (MSWD=0.13) (Supplementary Table 2,
Fig. 12a), and 176Hf/177Hf values from 0.282816 to 0.282915, εHf (t)
values from +11.3 to +14.6, and TDM2(Hf) ages from 503 Ma to
722 Ma for 14 analyzed crystals (Supplementary Table 3). Zircons
from sample TH05-3 (dacite) contain 38–126 ppm U, 19–93 ppm Th
and 3–12 ppm Pb with Th/U ratios in the range of 0.52–0.83 and have
206Pb/238U ages ranging from 441.2±6.4 Ma to 478.3±8.4 Ma with a
concordia age of 453.0±4.4Ma (MSWD=0.67) (Supplementary
Table 2, Fig. 12b), 176Hf/177Hf values from 0.28283 to 0.282894, εHf (t)
values from +2.4 to +13.9, and TDM2(Hf) ages from 545 Ma to
933 Ma (Supplementary Table 3). Zircons from sample TH02-3 have
30–218 ppm U, 19–271 ppm Th and 3–23 ppm Pb with Th/U ratios in
the range of 0.54–1.24, and 206Pb/238U ages ranging from 433.2±
6.6 Ma to 456.5±7.1 Ma with a concordia age of 442.4±1.9 Ma
(MSWD=0.21) for 12 analyzed single crystals (Supplementary Table 2,
Fig. 12c), 176Hf/177Hf values from 0.282326 to 0.282938, εHf (t) values
from −6.4 to +14.9, and TDM2(Hf) ages from 465 Ma to 1829 Ma for 20
analyses (Supplementary Table 3).
Another trachyte block (sample TH03-3) contains euhedral-
to-subhedral and stubby zircons with bright rims and gray cores
and some anhedral detrital zircons (Fig. 11c). The results of 11 analy-
ses on 11 single zircons revealed that they have U–Pb–Hf isotopic
compositions as follows: 32–190ppm U, 18–220ppm Th and
3–19 ppm Pb, Th/U ratios from 0.57 to 1.16, 206Pb/238U ages range from
429.5±6.4 Ma to 453.2±6.6 Ma with a concordia age of 441.7±2.0 Ma
Fig. 10. 143Nd/144Nd versus 143Sm/144Nd (after Goldstein et al., 1984; Nelson and Depaolo, 1985) (a), Nd isotope (b) and εNd(t) versus (87Sr/86Sr)i (after Winter, 2001) (d) plots and
spectra of the TDM (c) for igneous rocks from the Taheir area. AA: Andean andesite, CAVZ: Central Andean volcanic zone, DM: depleted mantle, DML: depleted mantle line, EPO:
early Paleozoic ophiolite in East Junggar, OIAA: oceanic island arc andesite, OIAB: oceanic island arc basalt, MORB: midocean ridge basalts, NAVC: North Andean volcanic zone,
OIB: oceanic island basalt, SAVZ: South Andean volcanic zone, WPB: within plate basalts.
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Please cite this article as: Xu, X.-W., et al., Tectonic evolution of the East Junggar terrane: Evidence from the Taheir tectonic window, Xinjiang,
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(MSWD=0.17) (Supplementary Table 2, Fig. 12d), and 176Hf/177Hf values
from 0.282698 to 0.282900, εHf (t) values from +6.3 to +13.2, and TDM2(Hf)
ages from 530 Ma to 1008 Ma (Supplementary Table 3). A detrital zircon
(S3 in Fig. 11c) contains 107 ppm U, 235 ppm Th and 26 ppm Pb
with Th/U ratios of 2.19 and has 206Pb/238U age of 837.6±12.0 Ma,
a 176Hf/177Hf value of 0.282963, and a εHf (t) value of +5.5, corresponding
to a TDM2(Hf) age of 1382 Ma.
All the weakly deformed granitic porphyries (sample ZF10-1 and
TH5) and granite (sample TH6) have zircons that are euhedral to
subhedral and equant to stubby with average elongation ratios of ap-
proximately 1.6 and concentric oscillatory zoning (Figs. 11e, 12f and g).
The 18 analyzed zircon crystals from sample ZF10-1 have gray rims
and dark cores in the CL images, and have 31–644 ppm U, 17–
1482 ppm Th and 3–84 ppm Pb, Th/U ratios from 0.56 to 2.3, 206Pb/
238U ages ranging from 444.8±7.1 Ma to 468.1±7.6 Ma with a
concordia age of 455.4±1.7Ma (MSWD=0.43) (Supplementary
Table 2, Fig. 12e), 176Hf/177Hf values from 0.282022 to 0.282920, εHf (t)
values from −16.9 to +14.9, and TDM2(Hf) ages from 495 Ma to
Fig. 11. Cathodoluminescence (CL) images of representative zircon grains selected for SIMS U–Pb dating and LA–ICPMS Hf isotope analysis from igneous rocks from the Taheir area.
The red ellipses show the location and size of laser ablating for SIMS U–Pb dating, while the blue circle for LA–ICPMS Hf isotope analysis. The spot number and 206Pb/238U age num-
ber of zircon was labeled aside the red ellipses and blue circle. Ab: albite, Ap: apatite.
13
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Please cite this article as: Xu, X.-W., et al., Tectonic evolution of the East Junggar terrane: Evidence from the Taheir tectonic window, Xinjiang,
China, Gondwana Research (2012), http://dx.doi.org/10.1016/j.gr.2012.11.007
Fig. 12. Zircon SIMS U–Pb concordia age plots of igneous rocks from the Taheir area.
14
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2503 Ma (Supplementary Table 3). Zircons from sample TH5 contain
57–268 ppm U, 28–236 ppm Th and 5–27 ppm Pb with Th/U ratios
from 0.31 to 0.88 and have 206Pb/238U ages ranging from 438.7±
6.4 Ma to 468.1±7.6 Ma with a concordia age of 448.6±1.5 Ma
(MSWD=0.006) (Supplementary Table 2, Fig. 12f), 176Hf/177Hf values
from 0.282785 to 0.282934, εHf (t) values from +9.7 to +15.0, and
TDM2(Hf) ages from 472 Ma to 811 Ma for 18 analyzed crystals (Supple-
mentary Table 3). Zircons from sample TH6 have 82–278 ppm U,
28–261 ppm Th and 7–30 ppm Pb with Th/U ratios from 0.44 to 1.33,
have 206Pb/238U ages ranging from 434±6.3 Ma to 459.5±6.7 Ma
with a concordia age of 443.2±1.7 Ma (MSWD=0.38) (Supplementa-
ry Table 2, Fig. 12f), 176Hf/177Hf values from 0.282823 to 0.282925, εHf (t)
values from +10.9 to +14.7, and TDM2(Hf) ages from 492 Ma to 726 Ma
for 15 analyzed crystals (Supplementary Table 3).
The intensely deformed granite (sample TH8) contains zircons
that are euhedral to subhedral and stubby with average elongation
ratios of approximately 1.6 and concentric oscillatory zoning with
bright-gray color in CL images (Fig. 11h). Few of them have primary
zircon cores. The results of 26 analyses on 26 single zircons revealed
that they have the following U–Pb–Hf isotopic compositions:
44–296 ppm U, 22–240 ppm Th and 4–26 ppm Pb, Th/U ratios from
0.37 to 0.96, 206Pb/238U ages ranging from 424±6.2 Ma to 457.4±
6.6Ma with a concordia age of the following 431.7±1.4Ma
(MSWD = 0.12) (Supplementary Table 2, Fig. 12h), 176Hf/177Hf values
from 0.282356 to 0.282974, εHf (t) values from −5.6 to +15, and
TDM2(Hf) ages from 455 Ma to 1786 Ma (Supplementary Table 3).
One primary zircon core (spot 5) contains 537 ppm U, 135 ppm Th
and 83 ppm Pb with Th/U ratios of approximately 0.25 and has a
206Pb/238U age of 824.8±12.1 Ma, a 176Hf/177Hf value of approxi-
mately 0.282963, and a εHf (t) value of +5.2 with a TDM2(Hf) age of
1390 Ma.
The granitic diorite (sample TH9) has relatively larger zircons that
are euhedral to subhedral and equant to stubby forms with length
ranging from 127 μm to 258 μm with elongation ratios from 1.0 to
2.2 (Fig. 11i). The 20 analyses on the 20 single zircons show that
these zircon have 21–100 ppm U, 10–33 ppm Th and 2–8 ppm Pb
with Th/U ratios from 0.3 to 0.65, 206Pb/238U ages ranging from
425.8±6.2 Ma to 436.8±6.3 Ma with a concordia age of 431.8±
1.5 Ma (MSWD=3.5) (Supplementary Table 2, Fig. 12i), 176Hf/177Hf
values from 0.282889 to 0.282943, εHf (t) values from +13.3 to
+15.2, and TDM2(Hf) ages from 448 Ma to 567 Ma (Supplementary
Table 3).
The diorites contain only few zircons. Only about 150 zircon grains
were separated from a 100 kg rock sample (sample Th7) from a dio-
rite stock; these zircons can be divided into four groups (Fig. 11j).
Group-A zircons are euhedral to subhedral, have concentric oscillato-
ry zoning and stubby forms with average elongation ratios of approx-
imately 2.0 and have 83–553 ppm U, 40–311 ppm Th and 6–46 ppm
Pb with Th/U ratios from 0.45 to 1.15, 206Pb/238U ages ranging from
393.3±5.3 Ma to 421.7±6.2 Ma with a concordia age of 405.8±
5.7 Ma (MSWD=0.7) (Supplementary Table 2, Fig. 12j), 176Hf/177Hf
values from 0.282233 to 0.282720, εHf (t) values from −11 to +6.3,
and TDM2(Hf) ages from 989 Ma to 2089 Ma for 9 analyses (Supple-
mentary Table 3). Group-B zircons are euhedral to subhedral, have
concentric oscillatory zoning and equant to stubby forms with aver-
age elongation ratios of approximately 1.5 and have 67–278 ppm U,
34–139 ppm Th and 6–23 ppm Pb with Th/U ratios from 0.38 to
0.72, 206Pb/238U ages ranging from 431.2±6.3 Ma to 465.5±7.2 Ma
with a concordia age of 446.4±5.8 Ma (MSWD=1.16) (Supplemen-
tary Table 2, Fig. 12k), 176Hf/177Hf values from 0.282669 to 0.282939,
εHf (t) values from +5.7 to +15.1, and TDM2(Hf) ages from 465 Ma to
1657 Ma for 12 analyses (Supplementary Table 3). Group-C zircons
are unitary and have a dark-gray color and concentric oscillatory
zoning in the CL images, have euhedral to subhedral and equant to
stubby forms with average elongation ratios of approximately 1.5,
and have 483–3068 ppm U, 304–1111 ppm Th and 48–272 ppm Pb
with Th/U ratios from 0.3 to 1.35, 206Pb/238U ages range from 474.5±
7.2 Ma to 488.8±7.3 Ma with a concordia age of 480.2±1.3 Ma
(MSWD=0.049) (Supplementary Table 2, Fig. 12l), 176Hf/177Hf values
from 0.282091 to 0.282219, εHf (t) values from −14.2 to −9.4, and
TDM2(Hf) ages from 2048 Ma to 2344 Ma for 12 analyses (Supplementa-
ry Table 3). Group-D zircons vary greatly and have 206Pb/238U ages
ranging from 500.3±7.4 Ma to 1922.2±25.3 Ma (Supplementary
Table 2), and 176Hf/177Hf values from 0.281405 to 0.282555 with
corresponding εHf (t) values from −22.3 to +6.7 and TDM2(Hf) ages
from 1257 Ma to 3076 Ma (Supplementary Table 3). Evidence that
the diorite stock emplaced and cut the foliated granitic porphyry
with a concordia age of 432 Ma indicates that the group-A zircons
may have crystallized from diorite and that the other three group
zircons are detrital. The group-B zircons may be from ambient rocks,
and the unitary group-C zircons may be from a deep-situated granitic
pluton.
Sample TH05-1 from a diorite dike (Fig. 1d) yielded about 30 zir-
con grains from a 5 kg rock sample, and the 12 largest of them were
analyzed. These 12 zircon grains are dark-gray, have absent of or
indiscernible zoning structures and are round to anhedral. They are
equant to stubby forms with lengths ranging from 60 μm to 85 μm
with average elongation ratios of approximately 1.5 (Fig. 11m).
They have 252–1946 ppm U, 50–384 ppm Th and 29–711 ppm Pb
with Th/U ratios from 0.03 to 0.68, 206Pb/238U ages ranging from
433.5±6.3 Ma to 2368±29.8 Ma and 206Pb/207Pb ages from
372.4±21.2 Ma to 2297.4±4.4 Ma (Supplementary Table 2), 176Hf/
177Hf values from 0.281281 to 0.282663, εHf (t) values from −7.7 to
+3.5, and TDM2 (Hf) ages from 1151 Ma to 2993 Ma for the 12 analy-
ses (Supplementary Table 3). Except for grains G11 and G12, the
other 10 zircon grains have concordant ages that plot on or close to
the crust evolution line (Fig. 12m). Moreover, error ellipse of ten
older (>1800 Ma) zircons is oriented towards the location of G6
plot located. These 12 analyzed zircons may be detrital.
The rhyolitic porphyry does not contain many zircons, and only 9
zircon grains were separated from 10 kg of rocks (sample ZF8). These
zircons are euhedral to subhedral and stubby and have bright rims
and dark-gray cores and some are anhedral, bright detrital zircons
(Fig. 11k). The results of 11 analyses on 8 zircons revealed that they
have 145–1780 ppm U, 49–1920 ppm Th and 11–160 ppm Pb with
Th/U ratios from 0.33 to 1.08, 206Pb/238U ages ranging from 385.6±
5.6 Ma to 405.8±6 Ma with a concordia age of 398.4±1.7 Ma
(MSWD = 0.24) (Supplementary Table 2, Fig. 12n), 176Hf/177Hf values
from 0.282579 to 0.282690, εHf (t) values from +1.9 to +5.0, and
TDM2(Hf) ages from 1065 Ma to 1274 Ma (Supplementary Table 3). A
detrital zircon (S3 in Fig. 11k) contains 27 ppm U, 13 ppm Th and
2 ppm Pb with Th/U ratios of 0.47 and has a 206Pb/238U age of
460.56±4.7 Ma, a 176Hf/177Hf value of about 0.282822, and a εHf (t)
value of about +11.5, corresponding to a TDM2(Hf) age of 703 Ma.
The andesitic porphyry (sample ZF5) contains dark-gray zircons
that have concentric oscillatory zoning and lengths ranging from
59 μm to 107 μm with average elongation ratios of approximately 1.5
(Fig. 11l). The results of 22 analyses on 22 single zircons showed that
they have 23–406 ppm U, 9–417 ppm Th and 2–36 ppm Pb with Th/U
ratios from 0.22 to 1.03, 206Pb/238U ages ranging from 380.2±5.6 Ma
to 403.7±5.9 Ma with a concordia age of 390.4±3.1 Ma (MSWD=
0.58) (Supplementary Table 2, Fig. 12o), 176Hf/177Hf values from
0.282623 to 0.283016, εHf (t) values from +2.7 to +15.3, and TDM2(Hf)
ages from 406 Ma to 1210 Ma (Supplementary Table 3).
5.5. Hornblende 40Ar/39Ar age
The results from argon isotope dating of hornblende crystals from
the diorite (sample TH05-1) and amphibolite (sample ZF10-3) from
the lower unit of the Taheir tectonic window are shown in Table 4
and Fig. 13.
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xxx
Please cite this article as: Xu, X.-W., et al., Tectonic evolution of the East Junggar terrane: Evidence from the Taheir tectonic window, Xinjiang,
China, Gondwana Research (2012), http://dx.doi.org/10.1016/j.gr.2012.11.007
The hornblendes from the diorite (sample TH05-1) yield a 40Ar/
39Ar plateau age of 416±6 Ma (at increments 8–13; 83.6% of 39Ar re-
leased) with a normal isochron age of 414±6 Ma (Fig. 13a and b),
and an overprinting age of 387 Ma with a 39Ar content of 3.08% at in-
crement 8. The hornblendes from amphibolite (sample ZF10-3) have
40Ar/39Ar ages from 398 to 416 Ma (increments 7–11), which yield a
Table 4
Summary of argon isotopic results of hornblende from diorite (TH05-1) and amphibolite (ZF10-3) from the Taheir tectonic window.
T(°C)
(40Ar/39Ar)m
(36Ar/39Ar)m
(37Ar/39Ar)m
40Ar%
39Ark(10−12 mol)
39Ark (%)
40Ar/39Ark
Age(Ma)
±1σ
TH05-1,diorite, W=37.3 mg, J=0.002405
750
648.78
0.293
8.107
59.8
0.12
1.08
566.2
1550.5
±85
850
460.10
0.155
8.086
63.3
0.16
1.44
417.2
1253.6
±67
930
415.45
0.128
8.148
72.2
0.28
2.53
380.3
1171.7
±44
980
396.17
0.218
9.698
66.1
0.19
1.71
334.7
1065.4
±36
1020
308.09
0.202
9.867
62.5
0.15
1.35
250.9
851.8
±30
1060
186.34
0.132
7.818
68.7
0.23
2.07
148.8
551.8
±25
1120
186.97
0.160
8.877
74.4
0.29
2.62
141.5
528.3
±20
1160
123.38
0.084
6.269
79.8
0.34
3.08
99.40
386.6
±15
1200
127.55
0.061
4.944
95.8
0.62
5.62
110.3
420.8
±10
1250
111.45
0.012
4.107
96.8
3.67
33.4
108.8
418.3
±4
1300
111.65
0.015
4.786
96.1
2.08
18.9
107.9
416.4
±6
1350
111.58
0.021
5.871
94.4
1.35
12.4
106.3
410.6
±7
1400
112.59
0.017
4.332
95.5
1.52
13.8
108.2
417.1
±8
ZF10-3,amphibolte, W=29.3 mg, J=0.002423
750
533.20
0.1333
3.773
62.8
0.21
1.27
495.5
1423.7
±94
850
415.71
0.0952
3.291
69.3
0.32
1.92
388.7
1198.0
±66
930
269.52
0.0455
3.253
75.5
0.47
2.85
283.9
945.3
±52
980
277.41
0.0759
4.307
73.4
0.42
2.52
256.1
871.6
±45
1050
202.43
0.0506
3.574
70.2
0.68
4.10
188.2
678.4
±38
1100
168.71
0.0677
3.630
74.2
0.43
2.61
149.4
557.7
±33
1140
113.82
0.0764
4.802
79.4
0.37
2.24
81.90
528.3
±26
1180
116.12
0.0551
4.012
90.8
0.71
4.30
101.9
398.2
±18
1220
110.62
0.0247
3.815
93.9
1.17
7.09
103.9
405.4
±14
1280
109.66
0.0136
3.425
98.1
3.86
23.4
106.8
415.6
±8
1350
106.69
0.0073
3.434
97.8
5.92
35.9
105.1
416.4
±6
1400
107.91
0.0149
5.195
96.5
1.94
11.8
104.3
410.6
±10
Fig. 13. 40Ar/39Ar plateau and isochron ages of hornblende from diorite (a and b) and amphibolite (c and d) from the Taheir tectonic window.
16
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Please cite this article as: Xu, X.-W., et al., Tectonic evolution of the East Junggar terrane: Evidence from the Taheir tectonic window, Xinjiang,
China, Gondwana Research (2012), http://dx.doi.org/10.1016/j.gr.2012.11.007
40Ar/39Ar plateau age of 409±6 Ma (82.5% of 39Ar released) with a
normal isochron age of 408±8 Ma (Fig. 13c and d).
6. Discussion
6.1. Age spectrum of volcanic, intrusive, metamorphic and deformation
events
Zircons from weakly metamorphosed lava and foliated granitic
porphyries and granites in the Taheir tectonic window have well de-
veloped concentric oscillatory zoning, which is typical of magmatic
zircons (Corfu et al., 2003). This indicates that the zircon U–Pb ages
reported above should represent the crystallization age of zircons
and their host igneous rocks. Lavas from the lower and upper units
have ages of 454–453 Ma and 442 Ma, respectively, granitic porphy-
ries were emplaced between 454 Ma and 449 Ma, and granites in-
truded between 443 Ma and 432 Ma. Therefore, the Taheir tectonic
window, composed of metamorphic volcanic rocks, deformed gran-
ites and granitic porphyries, and the undeformed granitic diorite, be-
longs to the early Paleozoic era.
The existence of 480 Ma granitic plutons represented by the
Group-C detrital zircons in sample TH7 from a diorite suggests that
magmatism in the Taheir area began before 480 Ma. Based on the ev-
idence that the 432 Ma granite (sample TH8) was intensely foliated
and underwent low- to medium-grade metamorphism, and the
undeformed granitic diorite was intruded into the metamorphic vol-
canic rocks at 432 Ma, it is suggested that the main deformation and
metamorphic event formed the low- to medium-grade metamorphic
rocks and granitic mylonite in the Taheir tectonic window is most
likely at 432 Ma.
The 40Ar/39Ar age of hornblendes and the U–Pb age of zircons
from diorites indicate that diorites in the Taheir tectonic window
were emplaced from 416 Ma to 406 Ma. The unconformable tectonic
event between the Taheir tectonic window and the Devonian volcanic
and sedimentary rocks took place between 398 Ma (rhyolitic porphy-
ry, sample ZF8) and 390 Ma (andesitic porphyry, sample ZF5). Volca-
nism in the Taheir area lasted until the middle Devonian epoch.
The hornblendes from the amphibolite (sample ZF10-3) have 40Ar/
39Ar ages of 398 Ma, 405 Ma, 410 Ma and 416 Ma with a 39Ar content
of approximately 4.3%, 7.09%, 11.8% and 59.1%, respectively. Three of
the four 40Ar/39Ar ages are very similar to the crystallization ages of
the rhyolitic porphyry (sample ZF8, 398 Ma) and a diorite (sample
TH7, 406 Ma) and the closure age of another diorite dike (sample
TH05-1, 416 Ma). This indicates that these hornblendes have a first clo-
sure temperature that is similar to that of the 416 Ma diorite and are
overprinted by the 406 Ma diorite and the 398 Ma rhyolitic porphyry.
Additionally, hornblendes both from the analyzed diorite (sample
TH05-1) and amphibolite (sample ZF10-3) have 40Ar/39Ar ages of
410 Ma with a 39Ar content of 12.4% and 11.8% respectively, strongly
implying a intrusive event at this time. It is suggested this intrusion
may have resulted in another diorite dike.
6.2. Arc type and evolution of the Taheir tectonic window
All analyzed igneous rocks from the Taheir area show geochemical
features of arc-type magmatism, such as low Rb, Nb, Y, Ta and Yb con-
tents, low Ce/Pb values, high K and U contents and Ba/Nb values
(Fig. 8a, b, c) (Pearce et al., 1984; Hofmann, 1988; Jahn et al., 1999),
and depletion in Nb and enrichment in Pb (Fig. 7b) (Winter, 2001).
Moreover, the early Paleozoic igneous rocks have some geochemical fea-
tures that are different from Devonian igneous rocks in the Taheir area.
6.2.1. The pre-432 Ma Taheir tectonic window arc type
The Ordovician volcanic rocks and granitic porphyries and the
Ordovician–Silurian granite show some distinct evidence of Andean-
type continental arcs such as the following: 1) geochemical signatures
including slight enrichment in LREE, negative Eu anomalies, enrichment
in Pb, K and U and depletion in Nb, P and Ti (Winter, 2001), high Th/Yb
and Ta/Yb values for a continental arc (Fig. 8d; Pearce, 1983), and high
La/Yb values for an Andean-type continental arc (Fig. 8e; Bailey, 1981);
2) calc-alkaline series with high proportions of dacite, rhyolite and an-
desite, and a large quantity of contemporary granites; and 3) similar
Sm–Nd–Rb–Sr isotopic compositions to Andean arc volcanic rocks
(Fig. 10a and c). This evidence indicates that the early Paleozoic volcanic
rocks, granitic porphyries and granites most likely formed at a continen-
tal margin setting. This conclusion is supported by the nature of the
basement and other properties of the Taheir crust.
6.2.2. The nature of Taheir crust basement
The basement nature of the Taheir crust can be evaluated from Nd
and Hf isotopic signatures. The fact that all the analyzed igneous rocks
from the Taheir area have older TDM (Nd) ages (583–1011 Ma) than
formation ages and the oldest ophiolite in East Junggar (Fig. 10d) in-
dicate that these igneous rocks are mixtures of the juvenile material
and old crust (Fig. 10b; Nelson and Depaolo, 1985) and that the
older crust is not likely the oldest oceanic crust in East Junggar. Sim-
ilarly, zircons from these igneous rocks have εHf (t) values from +15.9
to −22.3 with TDM2 (Hf) ages between 405 Ma and 3076 Ma (Supple-
mentary Table 3). It further suggests that these igneous rocks might
have been derived from distinct sources related to mixtures of the ju-
venile material and old crust (Fig. 14) and that a large quantity of old
crustal material had been incorporated into these igneous rocks. Evi-
dence from the Paleozoic magmatic zircons in the εHf (t) versus U–Pb
age diagram that are present in a rectangle that extend from the de-
pleted mantle line and downward to the 2.5 Ga crust line (Fig. 14) in-
dicate that the old crust may be >2.5 Ga.
The old crustal component of these igneous rocks in the Taheir
tectonic window may be directly derived from the old basement for-
mation or the younger sediments with old material (Davidson et al.,
2005) or indirectly imparted on the source by the simple subduction
of sediment (Tera et al., 1986; Othman et al., 1989; Plank and
Langmuir, 1993). If sediments are carried down on the subducted
plate, then there must be a similar sedimentary column within the
upper plate (Davidson et al., 2005). This means that the Taheir crust
should contain old basement formation or sediments with old mate-
rial. The occurrence of detrital old zircons with straight crystal
forms (Fig. 11j and m) indicates that these old zircons should have
not suffered long distance transportation and erosion by rive or
magma flow and may be from adjacent old formations or rock
Fig. 14. Diagram of εHf (t) versus U–Pb age for zircons from igneous rocks from the
Taheir area. Depleted mantle (DM) growth curve from Bodet and Scharer (2000).
CHUR, chondritic uniform reservoir. AP: andesitic porphyry, DZ: detrital zircon, EPO:
early Paleozoic ophiolite in East Junggar, GP: granitic porphyry, QM: quartz monzonite,
RP: rhyolitic porphyry.
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Please cite this article as: Xu, X.-W., et al., Tectonic evolution of the East Junggar terrane: Evidence from the Taheir tectonic window, Xinjiang,
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fragments. This suggests that the basement of the Taheir crust con-
tains old basement formation or sediments with old rock fragments
and that the Taheir tectonic window should be or have been the mar-
gins of an ancient continent. Additionally, the nine older (>1800 Ma)
zircons of sample TH05-1 plotting along the 3.0 Ga crustal line
(Fig. 14) show that the ancient continent may have contained
3.0 Ga crust.
6.2.3. The density of the Taheir crust
The occurrences of glomerocrysts with accumulated structures
(Figs. 2e and 5a) in rhyolite and rhyolitic porphyries in the Taheir tec-
tonic window imply that these phenocryst populations and associat-
ed granite breccia were formed in intermediate magma chambers,
and the granitic magma had undergone differentiation (Xu et al.,
2009). This suggests that the Taheir crust may have a low density
that retarded ascent and caused these granitic magmas to stagnate
and form magma chambers and granitic plutons.
6.2.4. The post-432 Ma Taheir tectonic window arc type
The Devonian diorites and andesitic porphyry have some oceanic
island arc geochemical characteristics, such as belonging to tholeiite
series (Fig. 6a), having a flat REE pattern (Fig. 7a), enrichment in Pb,
K, U and Sr and depletion in Nb, Pr and Zr (Fig. 7b; Macdonald et al.,
2000), and εHf (t) values similar to contemporary depleted mantle
(Fig. 10b; Jakeš and White, 1971; Winter, 2001). On the other hand,
these rocks have some characteristics of continental crust, such as
their TDM (Nd) and TDM2 (Hf) ages older than their formation ages.
Moreover, the 398 Ma rhyolitic porphyries have some geochemical
signatures that are similar to the pre-432 Ma igneous rocks, such as
being of the calc-alkaline series, the slight enrichment in LREE, the
negative Eu anomalies, the enrichment in Pb, K and U and the deple-
tion in Nb, P and Ti, and the high Th/Yb and Ta/Yb values, but moder-
ate La/Yb values and plotting in the field of continental island arc
(Fig. 8e). The characteristics indicate that the Taheir late Silurian–
Devonian arc may be a continental island arc (Bailey, 1981), similar
to the Japanese island arc (Taira, 2001). This is consistent with the
occurrence of continental island arc-type Silurian graywackes in
the Yemaquan area and Carboniferous sedimentary rocks in the
East Junggar Basin (Long et al., 2012; Yang et al., 2012). The
432 Ma granitic diorite and dioritic porphyry have geochemical fea-
tures that are transitional between the pre-432 Ma igneous rocks
and the Devonian diorites and andesitic porphyry, such as being
calc-alkaline, having a slight enrichment in LREE, having a slight en-
richment in Pb, K, U and Sr and depletion in Nb, Th, Pr, P and Ti, and
having εHf (t) and εNd (t) values close to the depleted mantle line.
Moreover, the 432 Ma granitic diorite and dioritic porphyry and
398 Ma rhyolitic porphyries have similar La/Yb values and plot in
the same field of continental island arc (Fig. 8e). This suggests that
the transformation from the Andean-type continental arc to conti-
nental island arc for the Taheir arc may have occurred at 432 Ma.
This transformation is possibly related to intra-arc rifting and
spreading of back arc oceanic basin (Wilson, 1966).
6.3. The tectonic evolution of the Taheir tectonic window
6.3.1. Magma intrusion and tectonic movements
Generally, granite plutons are commonly emplaced in the middle
crust at a depth 8–10 km (e.g., Sides, 1980; Guillot et al., 1995;
Jowhar, 2001; Tomiya et al., 2010) and porphyries at a depth of be-
tween 1 and 6 km, with an average depth of 1.8 km and a modal
depth of 2.8 km (Seedorff et al., 2005; Kesler and Wilkinson, 2008).
Therefore, the Ordovician volcanic rocks in the Taheir tectonic win-
dow were transferred down to the middle crust between 443 Ma
and 432 Ma, and subsequently exhumed before 390 Ma. The defor-
mation structures of these Ordovician volcanic rocks indicate that
the subsidence and first-stage shear deformation were most likely
related to underthrusting, whereas the exhumation was possibly as-
sociated with the second-stage horizontal stretching deformation in-
duced by uplifting and rifting.
6.3.2. The tectonic evolution of the Taheir tectonic window and
Yemaquan arc
In summary, the Taheir tectonic window consists of Ordovician vol-
canic rocks formed at continental margins. The lower unit underwent a
series of tectonic processes, including 1) progressive burial associated
with the intrusion of a 454–449 Ma granitic porphyries at shallow
levels; 2) underthrusting and subsidence to a depth in the middle
crust, with an intrusion of 443–432 Ma granites along the way,
resulting in metamorphism for the albite–hornblende schists and am-
phibolites; 3) departing from their continental land and formation of
continental island arc at 432 Ma; 4) uplifting and exhumation, associat-
ed with the intrusion of a 416–406 Ma diorite with geochemical signa-
tures of a continental island arc environment; 5) erosion and retrograde
metamorphism; and 6) exhumation between 398 Ma and 390 Ma.
Therefore, the Yemaquan magmatic arc, as the host of the Taheir tec-
tonic window, formed before 480 Ma and evolved from an Andean-type
continental arc to a continental island arc after intra-arc rifting at
432 Ma. Additionally, the occurrence of tin deposits in the Kelameili
area at the southern side of the Yemaquan arc further indicates that
the Yemaquan arc is most likely an Andean-type continental arc and
that the locations of these tin deposits represent a landward side and
back-arc environment (Kearey et al., 2009) because the tin deposits
are specific to Andean-type subduction and tin is absent in oceanic is-
land arcs (Kearey et al., 2009).
Most recently, Yang et al. (2011) reported geochemical data on
the Huangyangshan granitoid pluton in the Kelameili area and
suggested that these rocks were related to partial melting of an
enriched subcontinental lithospheric mantle of the Kelamaili island
arc. However, their granitoid rocks have pronounced negative Eu
anomaly, and are enrichment in Zr and depleted in Nb, Sr, P and Ti
(Table 3 and Fig. 5 of Yang et al., 2011). This is a typical signature of
continental arc rather than oceanic island arc, because igneous rocks
formed at oceanic island arc are usually enrichment in Sr, Th and P,
and depleted in Zr (Bailey, 1981; Ellam and Hawkesworth, 1988;
Winter, 2001). Occurrence of the Shareshike Tin deposit associated
with the Huangyangshan granitoid pluton indicates that the Kelamaili
island arc is not oceanic island arc (Kearey et al., 2009). Moreover,
these post-collision granitoid rocks plot in the field of continent–
continent collision both in the Nb–Y–Ce and Rb/Nb versus Y/Nb dia-
gram (Fig. 8c and d of Yang et al., 2011), implying that they were
formed at continent–continent collision setting. Therefore, evidence
from the Huangyangshan granitoid pluton in the Kelameili area also
indicates that the Yemaquan arc is a continental arc.
6.4. The tectonic evolution of East Junggar
Tectonic regime of East Junggar is redefined by the regular arrange-
ment of the Erqis Devonian–Carboniferous ophiolite belt; the Sawuer
Devonian–Carboniferous oceanic island arc; the Armantai Cambrian–
Ordovician ophiolite belt; the Yemaquan Ordovician Andean-type con-
tinental arc that became a continental island arc after the Silurian
NW-trending intra-arc rifting in the Taheir area at the southern side,
the landward side and the backarc environment; and the Kelameili
Devonian–Carboniferous ophiolite belt from north to south. According
to modern plate tectonics theory (Wilson, 1966), this regime requires
that the Junggar ocean represented by the Kelameili ophiolite belt is a
type of back-arc basin and that the Junggar block is an ancient continent
because intra-arc rifts, as a part of the rifting systems of back-arc basins,
are located adjacent to a back-arc basin (Yamaji, 1990) and both the
back-arc basin and potential continent should occur at the back side of
the continental island arc and away from oceanic crust or oceanic island
arc (Wilson, 1966). The arrangement that the Devonian–Carboniferous
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xxx
Please cite this article as: Xu, X.-W., et al., Tectonic evolution of the East Junggar terrane: Evidence from the Taheir tectonic window, Xinjiang,
China, Gondwana Research (2012), http://dx.doi.org/10.1016/j.gr.2012.11.007
Sawuer oceanic island arc occurs on the north side of the Ordovician
Yemaquan Andean-type continental arc calls for a southward subduc-
tion of the Paleo-Asian oceanic lithosphere, which was presented at
the adjacent northern West Junggar Region (Shen et al., 2012).
On the basis of the newly obtained evidence, the tectonic regimes
of East Junggar and their potential tectonic setting, we contest a tec-
tonic evolution model for East Junggar in the central part of the
Central Asian Orogenic Belt as following (Fig. 15):
1) The Yemaquan Ordovician Andean-type continental arc was
formed by the southward subduction of early Paleozoic Paleo-
Asian ocean lithosphere beneath the Junggar continent. The
Armantai Cambrian–Ordovician ophiolites are relict fragments of
the subducted oceanic crust.
2) This subduction began before 480 Ma. The lower unit of the Taheir
tectonic window experienced burial metamorphism between
454 Ma and 449 Ma and subsidence to a depth in the middle
crust during the period from 443 Ma to 432 Ma. This rapid subsi-
dence is related to regional compression and crust thrusting.
3) The period of approximately 432 Ma marks an important tectonic
shifting point. At this time, intra-arc rifts developed at the back
side as a result of mantle upwelling that may have been related
to the rollback of the subducted oceanic lithosphere, resulting in
rift tectonics associated with extension and the formation of am-
phibolites in the lower unit and rapid exhumation induced by
detachment faults in the Taheir area. Some detachment faults
cut through the lower crust and propagated into the upper mantle
lithosphere of the Junggar continent.
4) When some of these faults cut the upper mantle lithosphere of the
Junggar block, new intensive upwelling of the asthenosphere oc-
curred at the edges of these faults and propagated upwards along
these faults during the period between 432 Ma and 416 Ma, causing
massive normal faulting and rifting and back-arc basin and crustal
thinning along the line formed by the Kelameili ophiolite belt. Dur-
ing this period, the granodiorites with a geochemical signature of
continental island arcs intruded into the lower unit of the Taheir tec-
tonic window.
5) Continuous rifting caused the lithosphere to break off, resulting in
the detachment of the Yemaquan arc from the Junggar continent
and the formation of Junggar ocean. These events may have been
complete by 416 Ma. Then, the Yemaquan arc behaved as a conti-
nental island arc, and the contemporary 416–406 Ma diorites in
the Taheir tectonic window have geochemical signature of conti-
nental island arc. During this period, many intermediate-acid
stock and porphyries associated with porphyry Cu–Mo deposits
in the Qiongheba area at the eastern part of Yemaquan arc formed
(Dong et al., 2009; Qu et al., 2009; Du et al., 2010).
6) The chronology of the copper-bearing porphyries in Halasu area
(Zhang et al., 2004; Zhang et al., 2006; Xiang et al., 2009) indicate
that the intra-ocean subduction and the formation of the Sawuer
Fig. 15. Tectonic evolution model for the East Junggar. The green dot with label a, b, c, e and f shows the location of the lower unit of the Taheir tectonic window.
19
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xxx
Please cite this article as: Xu, X.-W., et al., Tectonic evolution of the East Junggar terrane: Evidence from the Taheir tectonic window, Xinjiang,
China, Gondwana Research (2012), http://dx.doi.org/10.1016/j.gr.2012.11.007
arc may have begun at approximately 400 Ma. Namely, at this
time, the subduction zone of the Paleoasian oceanic plate
retracted from the Armantai area northward to the Erqis area.
7) The fact that the Kelameili ophiolite belt is cut by the Hongliuxia
EW-trending ductile shear zone that formed at approximately
344 Ma (Wu et al., 2012) indicates that the collision between
the Junggar block, the Yemaquan arc, the Sawuer oceanic island
arc and the Altaids may have occurred during the early Carbonif-
erous period before 344 Ma. After 320 Ma, the East Junggar is
transited to be post collisional extensional setting, and some relat-
ed alkaline granites emplaced and volcanic rocks erupted (Su et
al., 2008, 2012; Gan et al., 2010; Liu et al., 2012). Then, the present
tectonic regime of East Junggar formed. The Kelameili ophiolites
are relict fragments of the Junggar back arc oceanic crusts.
This scenario is displayed in the western Pacific region during the
Cenozoic era (Taira, 2001). However, additional details of the tectonic
processes of formation of the Junggar back arc ocean and the collision
events during the early Carboniferous period remain unclear. The
Carboniferous volcanic rocks located over the Junggar block may
have been formed at the post-collision stage and be related to conti-
nental rifting tectonics (Gu et al., 2000).
6.5. Basement nature of the Junggar terrane
The occurrence of Andean-type continental arc in the Taheir area
indicates that there should have been a continent in the Junggar ter-
rane in the early Paleozoic. The suggestion that the Paleozoic igneous
rocks in the Taheir area are derived from a mixture of the juvenile
material and ≥2.5 Ga crust (Fig. 14) indicates that the Taheir tectonic
window and its host Junggar terrane have a ≥2.5 Ga basement crust.
The nine older (>1800 Ma) zircons from sample TH05-1 plotting
along the 3.0 Ga crustal line (Fig. 14) show that the Junggar continent
may have contained 3.0 Ga crust. These conclusions are consistent
with the documented geological and geophysical features of the
Junggar terrane, including (1) the wide angle seismic reflection and
magnetotelluric sounding data shows that thickness of crystalline
crust of the Junggar basin is about 43–48 km (Zhao et al., 2003),
which is greater than that of the modern oceanic crust and oceanic
island arc (Mooney et al., 1998; Dimalanta et al., 2002); and (2) the
Devonian sandstones in the northeastern Junggar block contain a
large number of Pre-Cambrian detrital zircons ranging from
550 Ma up to 3037 Ma (Lin et al., 2007), three of which (grain 9.1,
70.1 and 71.1) are metamorphic zircons with Th/U values ranging
from 0.12 to 0.27 and have an concordia age of 953±9.1 Ma
(MSWD=4.3).
Recently, Zheng et al. (2007) reported elemental and Sr–Nd–Pb
isotopic geochemistry of Late Paleozoic volcanic rocks beneath the
Junggar basin and suggested that the basaltic rocks represent trapped
late Paleozoic oceanic and the silicic rocks are products of melting of
oceanic crust. However, their data do not support their interpreta-
tions. For example, six of the seven analyzed basalts are depleted in
Nb compared to K, Rb and U, and the La/Nb values of three basalts
(sample k178, k204 and k211) are equal or greater than 1.4
(Table 2 of Zheng et al., 2007). This indicates that these basalts are
not mid-ocean ridge basalts (MORB) or ocean island basalts (OIB)
(Mahoney et al., 1993; Condie, 1999). In contrast, the Nb/U values
of the seven basalts are less than 20, showing distinct signature of
continental crust (Hofmann et al., 1986). On the other hand, these
volcanic rocks do not have geochemical features of adakitic rocks,
which are derived from partial melting of oceanic crust (Defant and
Drummond, 1990). Moreover, all the Late Paleozoic volcanic rocks plot
in the field close to the lower crust and away from MORB and OIB in
the (206Pb/204Pb)initial versus (207Pb/204Pb)initial and (208Pb/204Pb)initial
diagram (Fig. 8c and d of Zheng et al., 2007). Therefore, the Late Paleozoic
volcanic rocks beneath the Junggar basin are most likely derived from
continental crust rather than oceanic crust.
More recently, Xiao et al. (2012) reported zircon Hf isotope and
whole rock geochemistry of Late Paleozoic magmatic rocks in the
Baijiangou and Zhangpenggou area in the northeastern Junggar
block and considered the East Junggar terrane as oceanic island arc.
However, these magmatic rocks have pronounced negative Eu anom-
aly, and are enriched in Pb, Rb and U and depleted in Nb, Sr, Th and Ti
(Fig. 8 of Xiao et al., 2012), implying that they are not oceanic island
arc (Ellam and Hawkesworth, 1988). Moreover, these magmatic
rocks plot in the field of continental arc in the Th/Yb versus Nb/Yb di-
agram (Fig. 9a in the reference of Xiao et al., 2012).
In summary, the Junggar terrane contains Precambrian continent.
It is suggested that the accretionary orogeny in the Central Asian Oro-
genic Belt is more complex than in the previous models proposed by
Sengör et al. (1993) and Sengör and Natal'in (1996) and that there
may have been some ancient continental fragments, such as Junggar
block (Zhao et al., 2003; Charvet et al., 2007), Yili block (Long et al.,
2011), central Tienshan (Hu et al., 2006) and southern Kazakhstan
micro-continental fragments (Abdulin et al., 1995; Kröner et al.,
2007). These continental fragments make the history of accretionary
orogenesis more intriguing.
7. Conclusion
The Taheir tectonic window consists of metamorphosed and
deformed Ordovician volcanic rocks and granitic porphyries and
Ordovician–Silurian granites as well as undeformed Silurian– Devonian
granitic diorite, diorites and rhyolitic porphyries.
Ordovician volcanic rocks and granitic porphyries, and Ordovician–
Silurian granites in the Taheir tectonic window exhibit some distinct ev-
idence of Andean-type arc continental arcs, including low Rb, Y, Ta and
Yb content, low Ce/Pb values, high La/Yb, Ba/Nb, Th/Yb and Ta/Yb
values, enrichment in Pb, K and U and depletion in Nb, P and Ti, slight
enrichment in LREE, negative Eu anomalies, high proportions of dacite,
rhyolite and andesite of the calc-alkaline series, the presence of a large
quantity of contemporary granites, similar Sm–Nd–Rb–Sr isotopic com-
position to Andean volcanic rocks, older TDM (Nd) ages (583–1011 Ma)
than formation ages, εHf(t) values from +14.9 to −16.9 with TDM2 (Hf)
ages between 465 Ma and 2503 Ma, mixtures of the juvenile material
and ≥2.5Ga crust, intensive crystallization differentiation. These
rocks are formed at continental margins.
These Ordovician volcanic rocks underwent a series of tectonic
events, including burial metamorphism associated with the intrusion
of 454–449 Ma granitic porphyries, underthrusting and subsidence to
a depth in the middle crust associated with the intrusion of
443–432 Ma granites and the formation albite–hornblende schists,
hornblende–albite–quartz leptynites and amphibolites, departure
from continental land and formation of continental island arc around
432 Ma, the exhumation associated with the intrusion of 416–
406 Ma diorites with geochemical signatures of a continental island
arc, and the erosion and return to the surface between 398 Ma and
390 Ma.
The Taheir tectonic window arc and its host Yemaquan magmatic
arc changed from Andean-type continental arc to continental island
arc after intra-arc rifting since 432 Ma. The tectonic regime of East
Junggar and the adjacent area is redefined by the regular arrange-
ment of the Erqis Devonian–Carboniferous ophiolite belt, the Sawuer
Devonian–Carboniferous oceanic island arc, the Armantai Cambrian–
Ordovician ophiolite belt, the Yemaquan Ordovician Andean-type
continental arc that became a continental island arc after Silurian
NW-trending intra-arc rifting at the southern, landward side and in
the backarc environment, and the Kelameili Devonian–Carboniferous
ophiolite belt from north to south. This regime requires a back-arc
basin for the Junggar ocean that is represented by the Kelameili
ophiolites and an ancient continent for the Junggar block.
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Please cite this article as: Xu, X.-W., et al., Tectonic evolution of the East Junggar terrane: Evidence from the Taheir tectonic window, Xinjiang,
China, Gondwana Research (2012), http://dx.doi.org/10.1016/j.gr.2012.11.007
Acknowledgements
This research was supported by the CAS Knowledge Innovation Pro-
ject (Grant Numbers kzcx-ew-ly03 and kzcx2-yw-107), the National
Natural Science Foundation of China (Grant Number 41072060), and
the National 305 project (Grant Numbers 2011BAB06B03-3 and
2006BAB07B01-03). We are indebted to X.D. Jin for the arrangement
of the trace element analysis, Q. L. Li and Y. Liu for the help in conducting
the Cameca IMS-1280 ion microprobe, C.F. Li for the Nd isotope experi-
ment, and Y.G. Ma and X. Yan for assistance with EMP and SEM analyses.
We thank K.Z. Qin, W.J. Xiao, J.H. Guo, L.D. Ren, and G.Q. He and S. Sun
for valuable discussions. This paper was significantly improved by the
thorough and incisive review of three anonymous reviewers.
Appendix A. Supplementary data
Supplementary data to this article can be found online at http://
dx.doi.org/10.1016/j.gr.2012.11.007.
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