Granitoid evolution in the Late Archean Wutai Complex, North China Craton

Granitoid evolution in the Late Archean Wutai Complex,

North China Craton

Simon A. Wildea,*, Peter A. Cawooda, Kaiyi Wangb, Alexander A. Nemchina

aDepartment of Applied Geology, Tectonics Special Research Centre, Curtin University of Technology, Perth, WA 6845, AustraliabInstitute of Geology, Academia Sinica, Beijing 100029, China

Received 15 May 2003; revised 30 September 2003; accepted 3 November 2003

Abstract

Two temporally discrete episodes of granite magmatism have been identified in the Wutai Complex of the North China Craton, based on

SHRIMP U–Pb zircon dating of all major granitoid bodies in the area. The older period is latest Archean and ranges in age from 2560 to

2515 Ma, whereas the younger episode is Paleoproterozoic, with magmatism at 2170 and 2120 Ma. Archean magmatism can be further

separated into two pulses based on geochemistry and the association of the younger plutons with extensive coeval volcanic activity in the

Wutai Complex. The early phase of Archean activity is represented by the Lanzhishan, Ekou and portions of the Chechang-Betai granites,

with ages ranging from 2560 to 2540 Ma. The Lanzhishan Granite is the only one at Wutaishan that contains inherited zircon, with a number

of cores and individual grains giving ages in excess of 2700 Ma. These are relatively evolved granitoids, interpreted to be derived from older

basement of the Eastern Block of the North China Craton. The Shifo, Guangmingshi, the main grey phase of the Wangjiahui granite and the

major components of the Chechang-Betai granite have ages of ,2540–2515 Ma and are coeval with felsic volcanism in the Wutai Complex

which is a consequence of subduction and related arc magmatism. The Dawaliang granite and pink phase of the Wangjiahui granite are

considerably younger with Paleoproterozoic ages of ,2170 and ,2120 Ma, respectively. These are also evolved granitoids, most likely

derived by partial melting of the older basement, although we have found no evidence of inheritance. The petrogenesis of the granitoids

reflects the Precambrian amalgamation history of the North China Craton, indicating derivation along the western edge of the Eastern block

during development and amalgamation of the Wutai arc, and prior to collision with the Western block of the craton 1.8 Ga ago.

q 2004 Published by Elsevier Ltd.

Keywords: Archean magmatism; Granites; North China Craton; Wutaishan

1. Introduction

The Wutai Complex is an Archean granite-greenstone

terrain of low metamorphic grade (Bai, 1986; Wilde et al.,

1997) located within the North China Craton, approximately

200 km west–southwest of Beijing (Fig. 1). The traditional

view in China has been that the greenstones represent a

stratigraphic sequence that extends upward from lower units

of paragneiss, amphibolite, banded iron formation and

carbonate—metamorphosed to amphibolite facies—into

middle and upper sequences composed of clastic sedimen-

tary rocks and intermediate to felsic volcanic rocks—

metamorphosed to greenschist facies. However, recent work

(Cawood et al., 1998; Wang and Wilde, 2002; Wilde et al.,

2004a,b; Kroner et al., 2004) has shown that all major

components of the Wutai Complex are essentially the same

age, with previous unconformities now interpreted as

tectonic contacts. Furthermore, felsic volcanism at

Wutaishan ranges in age from 2533 ^ 8 to 2513 ^ 8 Ma,

but all samples overlap within error and yield a mean age of

2523 ^ 3 Ma; the data do not support a simple layer-cake

stratigraphic interpretation (Wilde et al., 2004a). The Wutai

Complex is in part overlain by the Hutuo Group, which is

composed of a sequence of generally low-grade metasedi-

ments with minor metavolcanics (Tian, 1991). However,

these rocks are locally tectonically interleaved with the

Wutai Complex and their classification as a ‘group’ is

similarly suspect. Rocks of the Hutuo ‘group’ should,

however, provide a minimum age for the Wutai Complex. A

conventional multigrain U–Pb zircon date from a metaba-

salt (Wu et al., 1986) gave an imprecise zircon U–Pb

multigrain age of 2350 þ 103/294 Ma. However, recent

1367-9120/$ - see front matter q 2004 Published by Elsevier Ltd.

doi:10.1016/j.jseaes.2003.11.006

Journal of Asian Earth Sciences 24 (2005) 597–613

www.elsevier.com/locate/jaes

* Corresponding author. Tel.: þ61-8-9266-3580; fax: þ61-8-9266-3153.

E-mail address: [email protected] (S.A. Wilde).

http://www.elsevier.com/locate/jseaes

SHRIMP 207Pb/206Pb zircon dates from a meta-tuff near

Taihuai (Wilde et al., 2004a,b) indicate volcanism at

2087 ^ 9 Ma, establishing both a younger age for the

Hutuo ‘group’ and that major tectonism is younger than

,2080 Ma.

A number of small to large granitic intrusions are widely

distributed throughout the Wutai Complex (Fig. 1). Field

evidence reveals a range of relationships, with many

granitoids being strongly deformed and having tectonized

contacts with the greenstone succession, so that original

contact relations are commonly obscured.

In a previous paper (Wilde et al., 1997), we presented

the SHRIMP U–Pb zircon ages of two of the granitoid

plutons associated with the Wutai Complex, namely

the Lanzhishan and Ekou granites (Fig. 1), for which

ages of ,2545 and 2555 ^ 6 Ma were determined,

respectively. These granites are older than felsic volcan-

ism within the Wutai Complex (Wilde et al., 1997,

2004a) and it is therefore important to establish the timing

of granite plutonism throughout the complex, since some

granites (e.g. the pink phase of the Wangjiahui granite)

clearly intrude the Wutai sequence.

In this paper, we complete our SHRIMP U–Pb zircon

study of major granitoid plutonism within the Wutai

Complex. The timing of emplacement for all granitoids is

related, with the aid of new geochemical data from Liu et al.

(2002), to the tectonic setting and development of the area

during the late Archean/Paleoproterozoic.

2. Previous geochronological investigations

The Lanzhishan granite (Fig. 1) has an approximate age

of ,2545 Ma, with two samples giving 207Pb/206Pb

SHRIMP zircon dates of 2553 ^ 8 and 2537 ^ 10 Ma

(Wilde et al., 1997). Granitoids within the adjacent Long-

quanguan Shear Zone of the Fuping Complex (Fig. 1) yield

similar 207Pb/206Pb ages of 2543 ^ 7, 2541 ^ 4, and

Fig. 1. Geology of the Taihangshan–Wutaishan area, showing the distribution of Precambrian granitoids and including the sample sites (modified from Wilde

et al., 2004a).

S.A. Wilde et al. / Journal of Asian Earth Sciences 24 (2005) 597–613598

2540 ^ 18 Ma (Wilde et al., 1997), indicating that the two

are closely related: both suites also contain evidence of

,2700 Ma granitoid precursors in the form of inherited

zircon whole grains and cores (Wilde et al., 1997). It is for

this reason that the conventional U–Pb multigrain zircon

age of 2560 ^ 9 Ma obtained for the Lanzhishan granite by

Liu et al. (1985) is slightly older than the SHRIMP single

zircon age and why we favor the younger age of ,2545 Ma

as being the best estimate for the time of emplacement of

this granite. The Lanzhishan granite was previously

considered to be overlain by sediments of the ‘lower’

Wutai Banyukou ‘formation’ (Tian et al., 1996). However,

the overlying metasediments cannot belong to the ‘lower’

Wutai since they contain detrital zircons as young as

2486 ^ 13 Ma (Cawood et al., 1998) and are instead

considered to belong to the younger Hutuo ‘group’. The

relation of the Lanzhishan granite to the Wutai Complex,

therefore, remains unknown.

The Ekou granite (Fig. 1) has been dated at two

localities (Wilde et al., 1997) and these give 207Pb/206Pb

SHRIMP zircon ages of 2566 ^ 13 and 2555 ^ 6 Ma.

Data for the latter are more concordant and more tightly

grouped and the age of 2555 ^ 6 Ma is considered to be

the best estimate of the emplacement age of the granite

(Wilde et al., 1997). The earlier, less precise, conventional

U–Pb zircon age for the Ekou granite of 2520 ^ 30 Ma

(Liu et al., 1985) reflects the extensive alteration of this

granitoid, including recent lead loss from zircons (Wilde

et al., 1997). The Ekou granite has previously been

considered to intrude the ‘lower’ part of the Wutai

sequence, principally the Jingangku ‘formation’ (Liu et al.,

2002). However, our recent observations of the contact at

the Ekou Iron Ore Treatment Plant suggest it is sheared.

The only published age data for the Jingangku ‘formation’

is a SHRIMP 207Pb/206Pb zircon age of 2438 ^ 6 Ma

quoted by Bai et al. (1991) from an amphibolite, which

they interpret as a metamorphic age.

The porphyritic Dawaliang granite (Fig. 1) has a207Pb/206Pb age of 2176 ^ 12 Ma (Wilde et al., 1997),

considerably younger than other plutonic and volcanic

phases at Wutaishan. It is less deformed than either the

Lanzhishan or Ekou granites, but is locally sheared along

the margins (Wang and Wilde, 2002).

Liu et al. (1985) dated the Guangmingshi granite (Fig.

1) and obtained a conventional U–Pb zircon age of

2522 ^ 17 Ma. Sun et al. (1992) obtained a Rb–Sr age of

2.3 ^ 0.5 Ga on four samples of the Chechang-Betai

granite (Fig. 1). They quoted model ages of 2.3 ^ 0.1 Ga

(Pb–Pb) and 2.46 Ga (Sm–Nd) for the same granite.

There is also a single zircon SHRIMP age of

2607 ^ 36 Ma for this pluton quoted by Bai et al.

(1991) although this is not in agreement with our new

data presented below. Finally, a single zircon U–Pb age

of 2507 ^ 17 Ma was obtained by Bai (1986) from the

Shifo granite (Fig. 1).

3. Geochronology of the granitoids

New SHRIMP U–Pb zircon ages were obtained from

five of the main granitoids in the Wutai Complex: the

Chechang-Betai, Shifo, Guangmingshi and Wangjiahui

(pink and grey phases) granites (Fig. 1). Latitudes and

longitudes quoted for all sample sites were recorded in the

field using a hand-held Garmin GPS 12 XL.

3.1. Analytical procedure

Zircon crystals were prepared for analysis using standard

rock crushing and heavy mineral separation techniques.

Individual crystals were hand picked and mounted onto

double-sided adhesive tape and then enclosed in epoxy resin

discs, along with pieces of the Curtin University Sri Lankan

gem zircon standard (CZ3)—for which a conventional U–

Pb age of 564 Ma was obtained by Pidgeon et al. (1994).

After drying, the discs were ground and polished so as to

effectively cut all zircon grains in half. Each sample was

then photographed in both transmitted and reflected light in

order to construct a map that would enable grain

identification during analysis. Cathodoluminescence (CL)

images were used to identify possible internal structural

complexities and to ensure that analytical sites did not

transgress internal boundaries.

U–Th–Pb analyses of the zircons were performed using

the SHRIMP II ion microprobe at Curtin University,

following operating techniques outlined by Nelson (1997)

and Williams (1998). An average mass resolution of 4700

was recorded during measurement of the Pb/Pb and Pb/U

isotopic ratios and Pb/U ratios were normalized to those

measured on the standard zircon (CZ3: where206Pb/238U ¼ 0.0914). The uncertainty associated with the

measurement of Pb/U isotopic ratios for the standard, at 1

standard deviation, is quoted separately for each sample as a

percentage error in the following section. The common lead

correction was modeled on the composition of Broken Hill

lead and the data were reduced using the Krill 007 program

of P.D. Kinny at Curtin University, utilizing the 204Pb

correction. The 207Pb/206Pb ages are quoted for all samples

and all stated uncertainties for weighted mean values are at

the 95% confidence level.

3.2. Chechang-Betai granite

The Chechang-Betai granite is located in the northern

part of the Wutai Complex and occupies an area of

approximately 300 km2 (Fig. 1). It is composed of several

phases and its contact relations with the Wutai sequence are

controversial. Tian et al. (1996) stated that most contacts are

faulted or sheared, whereas Li et al. (1986) considered the

Wutai rocks to unconformably overlie the granites near

Taipinggou, where three of our samples were collected (Fig.

1). Our observations at the sample sites generally support

Tian et al. (1996), with strips of granite up to 5 m wide

S.A. Wilde et al. / Journal of Asian Earth Sciences 24 (2005) 597–613 599

commonly boudinaged and lying parallel to the regional

foliation in the meta-volcanic rocks of the Wutai sequence.

These occur for up to 20 m from the main granite contact

and superficially appear like apophyses off the main pluton.

However, their sub-parallelism to the main contact, the lack

of any contact aureole associated with the main granite body

and the boudinaged nature of many of the granite strips

indicates a tectonic relationship. There is one exception to

this, with a hornblende-bearing phase (represented by

sample 95-PC-6B) being clearly intruded by the main

biotite granite phase (represented by sample WC 6).

A total of four samples have been analyzed by SHRIMP

and their locations are identified in Fig. 1.

Sample WC 5 [Lat. 3980503200; Long. 11383801400] was

collected from a blasted outcrop close to the old 51 km

marker peg along the Shahe–Taihuai road, adjacent to the

road bridge at Taipingou (Fig. 1). It is a coarse-grained

granodiorite, with a strong fabric defined by biotite, which

trends 2628/728S. The rock is composed of plagioclase,

quartz, microcline and biotite and is extensively sheared,

with deformation bands characterized by grains showing a

distinct mortar texture. Biotite has recrystallized parallel to

the regional foliation and is grouped into discrete elongate

sheaths. Quartz is also extensively recrystallized and tends

to occur in distinct clusters of sub-grains. Microcline is not

abundant and is mainly restricted to recrystallized portions

of the rock. Alteration is extensive, with strongly saussuri-

tised plagioclase, and with epidote and white mica showing

some alignment parallel to the deformation fabric. This

suggests the rock has undergone greenschist facies meta-

morphism coeval with deformation.

The zircon grains are pale lilac, well-formed, stubby to

elongate crystals with well-developed prism and pyramidal

faces and an average length to width ratio of 2.5:1. The

crystals show oscillatory zonation and contain a few rod-

like inclusions of apatite. A total of 31 analyses were made

on 26 zircon crystals selected from 2135 to þ75 mm Mag

28 fraction and were run with 11 standards that recorded an

error of 1.2% during the analytical session. Analytical sites

were located in various parts of the crystals, including up to

three sites within a single grain (Table 1), but no systematic

variation in age was detected. The sites show a range of Th/

U ratios from 0.07 to 0.68 with an average value of 0.32.

The data are slightly discordant (Table 1 and Fig. 2a), with

the total data set defining an upper intercept age of

2532 ^ 6 Ma using Isoplot (Ludwig, 2001), a lower

intercept within error of zero Ma and an MSWD of 0.40.

The 19 most concordant analyses from 16 zircon crystals

(Fig. 2a) define a weighted mean 207Pb/206Pb age of

2538 ^ 6 Ma with a chi-square value of 1.84, indicating a

component of geological scatter in the data.


collected approximately 200 m south of sample WC 5, from

a low blasted outcrop on the southern side of a tight bend in

the Shahe–Taihuai road. It is a fine-grained biotite

granodiorite with a weak deformation fabric. Large,

moderately saussuritised plagioclase grains and areas of

moderately strained quartz are set within a finer-grained,

recrystallized groundmass of plagioclase, biotite, epidote

and minor microcline which tends to wrap around the larger

grains.

The sample contains a population of mauve to pink,

stubby to weakly elongate zircon crystals with well-

developed prism and pyramidal faces and an average length

to width ratio of 2:1. The crystals show weak oscillatory

zoning, contain microfractures and commonly have numer-

ous small rod-like apatite inclusions. A total of 24 analyses

were made on 17 zircons selected from the 2135 to

þ105 mm Mag 28 fraction and these were run with eight

analyses of the standard, which recorded an error of 1.0%

during the analytical session. The analytical sites show a

range of Th/U ratios from 0.05 to 0.46, with an average

value of 0.29. The data are weakly discordant (Table 1),

with some grains slightly older or younger than the main

population (Fig. 2b), although there is no evidence of any

systematic internal age variation within the crystals. The

total data set record an Isoplot (Ludwig, 2001) age of

2546 ^ 7 Ma, with a lower intercept at 216 ^ 80 Ma and an

MSWD of 3.6. However, the main population of 13 analyses

from 11 zircons (Fig. 2b) defines a weighted mean207Pb/206Pb age of 2546 ^ 6 Ma with a chi-square value

of 1.99, indicating a component of geological scatter in the

data.


obtained from close to the northern extremity of the pluton

at the base of the western wall of a small, steep-sided valley,

approximately 11 km southeast of Shahe (Fig. 1). It is a

coarse-grained tonalite with a strong foliation and lineation

that are of variable orientation. There are some darker, fine-

grained portions and late, sub-vertical granite veins that

post-date the foliation: the sample was collected well away

from these. The rock consists of alternating quartz- and

feldspar-rich bands. The quartz is moderately to strongly

undulose with some sub-grain development. The feldspar-

rich bands are dominated by plagioclase in association with

chloritised biotite, granular epidote and weakly aligned

white mica; there is only a trace of microcline present.

These features suggest the rock has undergone greenschist

facies metamorphism at the time of deformation.

The granite contains a single population of pale pink to

mauve zircons with well-formed prism and pyramidal faces

and an average length to width ratio of 2:1. A total of 23

analyses were made on 17 zircon grains selected from the

þ135 mm NM 28 fraction and were run with 10 analyses of

the standard, which recorded an error of 1.6% during

the analytical session. All sites have low U and Th contents

and an extremely tight range of Th/U ratios from 0.31 to

0.64, with an average value of 0.45. The data form a tight

cluster of concordant points (Table 1) with 22 analyses from

17 zircons giving a weighted mean 207Pb/206Pb age of

2552 ^ 11 Ma (Fig. 2c) with a chi-square value of 2.62,

indicating a significant component of geological scatter.


Table 1

SHRIMP U–Pb–Th zircon data for Wutai Granitoid samples WC 5, WC 6, WC 7 and 95-PC-6B

Spot# U (ppm) Th (ppm) Th/U Pb (ppm) 204Pb/206Pb f 206% 207Pba/206Pba 206Pba/238U 207Pba/235U %Conc AGE 207Pba/206Pba

Sample WC5

wc5-1 46 20 0.44 27 0.00214 3.431 0.15896 ^ 435 0.4881 ^ 85 10.70 ^ 37 105 2445 ^ 46

wc5-2 58 37 0.63 33 0.00102 1.627 0.16375 ^ 313 0.4734 ^ 75 10.69 ^ 28 100 2495 ^ 32

wc5-3 93 29 0.31 49 0.00059 0.950 0.16588 ^ 183 0.4747 ^ 67 10.86 ^ 21 100 2516 ^ 19

wc5-4 149 39 0.26 77 0.00045 0.724 0.16729 ^ 134 0.4756 ^ 62 10.97 ^ 18 99 2531 ^ 13

wc5-5 245 37 0.15 128 0.00019 0.307 0.16917 ^ 85 0.4951 ^ 61 11.55 ^ 16 102 2549 ^ 8

wc5-6 203 39 0.19 104 0.00020 0.327 0.16780 ^ 97 0.4821 ^ 60 11.15 ^ 16 100 2536 ^ 10

wc5-7 114 36 0.31 60 0.00065 1.045 0.16620 ^ 163 0.4758 ^ 64 10.90 ^ 19 100 2520 ^ 16

wc5-8 443 68 0.15 150 0.00034 0.540 0.16417 ^ 85 0.3193 ^ 38 7.23 ^ 10 71 2499 ^ 9

wc5-9 340 58 0.17 151 0.00020 0.317 0.16734 ^ 81 0.4177 ^ 50 9.64 ^ 13 89 2531 ^ 8

wc5-10a 109 34 0.31 54 0.00091 1.456 0.16342 ^ 188 0.4444 ^ 60 10.01 ^ 19 95 2491 ^ 19

wc5-10b 488 100 0.20 167 0.00027 0.428 0.16624 ^ 75 0.3220 ^ 38 7.38 ^ 10 71 2520 ^ 8

wc5-12a 297 114 0.38 153 0.00016 0.253 0.17068 ^ 73 0.4639 ^ 56 10.92 ^ 14 96 2564 ^ 7

wc5-12b 240 72 0.30 109 0.00035 0.554 0.16852 ^ 97 0.4157 ^ 51 9.66 ^ 14 88 2543 ^ 10

wc5-14 42 12 0.28 24 0.00142 2.270 0.17093 ^ 360 0.4862 ^ 84 11.46 ^ 33 100 2567 ^ 35

wc5-15 39 27 0.68 23 0.00146 2.344 0.16687 ^ 386 0.4784 ^ 81 11.01 ^ 33 100 2526 ^ 39

wc5-16a 288 119 0.41 151 0.00028 0.453 0.16679 ^ 82 0.4693 ^ 56 10.79 ^ 15 98 2526 ^ 8

wc5-16b 333 64 0.19 118 0.00032 0.518 0.15955 ^ 95 0.3313 ^ 40 7.29 ^ 10 75 2451 ^ 10

wc5-16c 1099 186 0.17 143 0.00034 0.544 0.10889 ^ 75 0.1270 ^ 15 1.91 ^ 3 43 1781 ^ 13

wc5-19 305 42 0.14 141 0.00028 0.445 0.16745 ^ 82 0.4415 ^ 53 10.19 ^ 14 93 2532 ^ 8

wc5-20a 199 70 0.35 104 0.00046 0.744 0.17027 ^ 111 0.4704 ^ 58 11.04 ^ 16 97 2560 ^ 11

wc5-20b 555 366 0.66 286 0.00014 0.229 0.16819 ^ 56 0.4404 ^ 51 10.21 ^ 13 93 2540 ^ 6

wc5-22 55 28 0.51 26 0.00156 2.490 0.16449 ^ 324 0.3862 ^ 60 8.76 ^ 23 84 2502 ^ 33

wc5-23 213 117 0.55 64 0.00114 1.826 0.15920 ^ 183 0.2568 ^ 32 5.64 ^ 10 60 2447 ^ 19

wc5-24 633 163 0.26 170 0.00024 0.378 0.15715 ^ 71 0.2529 ^ 29 5.48 ^ 7 60 2425 ^ 8

wc5-25 212 38 0.18 111 0.00057 0.906 0.16788 ^ 114 0.4857 ^ 60 11.24 ^ 17 101 2537 ^ 11

wc5-26 98 36 0.37 52 0.00101 1.615 0.16525 ^ 204 0.4679 ^ 63 10.66 ^ 21 99 2510 ^ 21

wc5-27 130 34 0.26 70 0.00059 0.939 0.16825 ^ 140 0.4824 ^ 63 11.19 ^ 18 100 2540 ^ 14

wc5-28 79 37 0.47 43 0.00091 1.460 0.16669 ^ 219 0.4703 ^ 67 10.81 ^ 22 98 2525 ^ 22

wc5-29 182 56 0.31 97 0.00040 0.638 0.16635 ^ 110 0.4856 ^ 60 11.14 ^ 16 101 2521 ^ 11

wc5-30 118 34 0.29 61 0.00066 1.064 0.16756 ^ 161 0.4708 ^ 61 10.88 ^ 19 98 2533 ^ 16

wc5-31 331 24 0.07 165 0.00043 0.691 0.16655 ^ 83 0.4763 ^ 56 10.94 ^ 15 100 2523 ^ 8

Sample WC6

wc6-1a 176 41 0.23 89 0.00003 0.043 0.16862 ^ 64 0.4762 ^ 57 11.07 ^ 14 99 2544 ^ 6

wc6-1b 466 87 0.19 112 0.00007 0.108 0.16259 ^ 55 0.2292 ^ 26 5.14 ^ 6 54 2483 ^ 6

wc6-3a 245 64 0.26 79 0.00004 0.070 0.16161 ^ 64 0.2994 ^ 35 6.67 ^ 8 68 2473 ^ 7

wc6-3b 246 28 0.11 121 0.00000 0.007 0.16780 ^ 52 0.4787 ^ 56 11.08 ^ 14 99 2536 ^ 5

wc6-5a 130 51 0.39 68 0.00008 0.126 0.16866 ^ 70 0.4721 ^ 58 10.98 ^ 15 98 2544 ^ 7

wc6-5b 487 195 0.40 154 0.00007 0.110 0.16085 ^ 44 0.2890 ^ 33 6.41 ^ 8 66 2465 ^ 5

wc6-7 433 151 0.35 147 0.00011 0.175 0.16303 ^ 49 0.3118 ^ 35 7.01 ^ 8 70 2487 ^ 5

wc6-8a 98 31 0.32 48 0.00012 0.199 0.16929 ^ 94 0.4462 ^ 56 10.42 ^ 15 93 2551 ^ 9

wc6-8b 147 34 0.23 74 0.00021 0.339 0.16870 ^ 77 0.4678 ^ 56 10.88 ^ 15 97 2545 ^ 8

wc6-10a 118 34 0.29 60 0.00009 0.140 0.16752 ^ 83 0.4709 ^ 58 10.88 ^ 15 98 2533 ^ 8

wc6-10b 302 83 0.27 158 0.00003 0.045 0.16810 ^ 41 0.4876 ^ 56 11.30 ^ 14 101 2539 ^ 4

wc6-12 95 37 0.39 51 0.00007 0.120 0.16891 ^ 88 0.4903 ^ 62 11.42 ^ 16 101 2547 ^ 9

wc6-13a 38 12 0.32 19 0.00018 0.289 0.16844 ^ 171 0.4588 ^ 69 10.65 ^ 20 96 2542 ^ 17

wc6-13b 160 9 0.05 73 0.00019 0.296 0.16600 ^ 75 0.4435 ^ 53 10.15 ^ 13 94 2518 ^ 8

wc6-15a 45 10 0.22 23 0.00013 0.204 0.16890 ^ 162 0.4750 ^ 68 11.06 ^ 20 98 2547 ^ 16

wc6-15b 223 39 0.18 105 0.00009 0.144 0.16853 ^ 61 0.4489 ^ 53 10.43 ^ 13 94 2543 ^ 6

wc6-17 136 58 0.43 71 0.00004 0.057 0.16570 ^ 79 0.4749 ^ 59 10.85 ^ 15 100 2515 ^ 8

wc6-18 85 25 0.29 44 0.00003 0.046 0.17265 ^ 105 0.4805 ^ 64 11.44 ^ 17 98 2584 ^ 10

wc6-19 100 25 0.25 50 0.00002 0.039 0.16907 ^ 90 0.4707 ^ 59 10.97 ^ 16 98 2548 ^ 9

wc6-20 177 66 0.37 91 0.00004 0.064 0.17010 ^ 64 0.4680 ^ 56 10.98 ^ 14 97 2559 ^ 6

wc6-21 224 103 0.46 115 0.00005 0.088 0.16886 ^ 56 0.4594 ^ 54 10.70 ^ 14 96 2546 ^ 6

wc6-22 106 40 0.38 50 0.00001 0.017 0.16826 ^ 91 0.4368 ^ 55 10.13 ^ 14 92 2540 ^ 9

wc6-23 146 36 0.25 76 0.00001 0.022 0.16943 ^ 69 0.4912 ^ 60 11.48 ^ 15 101 2552 ^ 7

wc6-24 105 23 0.22 55 0.00001 0.021 0.16952 ^ 84 0.4919 ^ 62 11.50 ^ 16 101 2553 ^ 8

(continued on next page)


Sample 95-PC-6B [Lat. 3980403100; Long. 11383905300]

was collected at the tectonized contact of the Chechang-

Betai granite with the Wutai Complex on the apex of a tight

bend along the Shahe–Taihuai road, immediately south of

Taipinguo village (Fig. 1). It is a hornblende-rich tonalite

with amphibole defining a weak magmatic foliation. The

mineralogy consists predominantly of plagioclase and

bright green hornblende, with minor quartz and randomly

oriented orange-brown biotite. A characteristic feature is the

presence of abundant epidote crystals within most plagio-

clase laths.

The zircon crystals are clear to pale brownish-pink in

color and are euhedral with well-formed prism and

pyramidal faces and an average length to width ratio of

1.5:1. Data for 21 analyses of 18 zircon grains were obtained

from the 2105 to þ74 mm NM 28 fraction and run with

Table 1 (continued)

Spot# U (ppm) Th (ppm) Th/U Pb (ppm) 204Pb/206Pb f 206% 207Pba/206Pba 206Pba/238U 207Pba/235U %Conc AGE 207Pba/206Pba

Sample WC7

wc7-1a 36 16 0.43 19 0.00012 0.195 0.16661 ^ 200 0.4726 ^ 99 10.86 ^ 28 99 2524 ^ 20

wc7-1b 94 32 0.34 50 0.00015 0.235 0.16648 ^ 101 0.4903 ^ 95 11.26 ^ 24 102 2523 ^ 10

wc7-3 71 40 0.57 39 0.00013 0.203 0.16875 ^ 119 0.4767 ^ 94 11.09 ^ 24 99 2545 ^ 12

wc7-4 24 10 0.40 13 0.00025 0.403 0.16631 ^ 247 0.4864 ^ 108 11.15 ^ 31 101 2521 ^ 25

wc7-5a 37 18 0.47 21 0.00012 0.198 0.16759 ^ 175 0.4931 ^ 105 11.39 ^ 28 102 2534 ^ 17

wc7-5b 37 22 0.59 20 0.00017 0.271 0.16779 ^ 216 0.4674 ^ 98 10.81 ^ 28 97 2536 ^ 22

wc7-7 24 10 0.41 13 0.00023 0.367 0.16440 ^ 256 0.4906 ^ 109 11.12 ^ 32 103 2501 ^ 26

wc7-8a 36 23 0.64 20 0.00012 0.198 0.16764 ^ 192 0.4907 ^ 104 11.34 ^ 29 102 2534 ^ 19

wc7-8b 50 16 0.31 27 0.00043 0.682 0.16614 ^ 188 0.4912 ^ 100 11.25 ^ 28 102 2519 ^ 19

wc7-10 50 29 0.58 28 0.00028 0.448 0.16785 ^ 161 0.4818 ^ 98 11.15 ^ 26 100 2536 ^ 16

wc7-11a 20 10 0.49 11 0.00045 0.717 0.16462 ^ 315 0.4654 ^ 106 10.56 ^ 33 98 2504 ^ 32

wc7-11b 34 12 0.34 17 0.00004 0.072 0.17022 ^ 211 0.4514 ^ 96 10.59 ^ 27 94 2560 ^ 21

wc7-13 42 15 0.37 22 0.00011 0.182 0.16864 ^ 194 0.4790 ^ 99 11.14 ^ 28 99 2544 ^ 19

wc7-14 54 34 0.63 30 0.00005 0.082 0.17044 ^ 143 0.4816 ^ 97 11.32 ^ 26 99 2562 ^ 14

wc7-15 24 10 0.42 12 0.00017 0.278 0.16891 ^ 256 0.4734 ^ 106 11.02 ^ 31 98 2547 ^ 25

wc7-16 42 15 0.37 22 0.00002 0.027 0.16903 ^ 173 0.4764 ^ 99 11.10 ^ 27 99 2548 ^ 17

wc7-17 100 37 0.38 50 0.00012 0.184 0.16991 ^ 119 0.4599 ^ 92 10.77 ^ 24 95 2557 ^ 12

wc7-18 62 20 0.33 31 0.00022 0.348 0.16898 ^ 154 0.4566 ^ 92 10.64 ^ 24 95 2548 ^ 15

wc7-19a 38 22 0.57 21 0.00002 0.025 0.17202 ^ 178 0.4802 ^ 100 11.39 ^ 28 98 2577 ^ 17

wc7-19b 38 22 0.58 21 0.00020 0.314 0.16922 ^ 203 0.4675 ^ 98 10.91 ^ 28 97 2550 ^ 20

wc7-21 16 6 0.40 8 0.00028 0.441 0.16720 ^ 357 0.4648 ^ 109 10.72 ^ 36 97 2530 ^ 36

wc7-22a 118 39 0.33 62 0.00004 0.061 0.17375 ^ 83 0.4851 ^ 93 11.62 ^ 24 98 2594 ^ 8

wc7-22b 46 16 0.34 25 0.00009 0.144 0.16887 ^ 155 0.4930 ^ 103 11.48 ^ 27 101 2546 ^ 15

Sample 95-PC-6B

95-6b-1 499 449 0.90 237 0.00011 0.171 0.15745 ^ 54 0.3934 ^ 77 8.54 ^ 17 88 2428 ^ 6

95-6b-2 275 235 0.86 161 0.00005 0.021 0.16988 ^ 62 0.4858 ^ 95 11.38 ^ 23 100 2556 ^ 6

95-6b-3 68 42 0.63 39 0.00015 0.244 0.16589 ^ 176 0.4922 ^ 107 11.26 ^ 28 103 2517 ^ 18

95-6b-4 123 104 0.85 67 0.00010 0.159 0.16648 ^ 113 0.4466 ^ 91 10.25 ^ 23 94 2523 ^ 11

95-6b-5a 59 29 0.49 33 0.00024 0.389 0.16524 ^ 168 0.4956 ^ 107 11.29 ^ 28 103 2510 ^ 17

95-6b-5b 129 72 0.56 71 0.00011 0.170 0.16835 ^ 100 0.4809 ^ 97 11.16 ^ 24 100 2541 ^ 10

95-6b-7 60 41 0.67 34 0.00040 0.642 0.16739 ^ 174 0.4778 ^ 101 11.03 ^ 27 99 2532 ^ 17

95-6b-8 109 91 0.84 65 0.00014 0.225 0.16874 ^ 113 0.4883 ^ 99 11.36 ^ 25 101 2545 ^ 11

95-6b-9 254 146 0.57 137 0.00019 0.306 0.17025 ^ 73 0.4662 ^ 84 10.94 ^ 21 96 2560 ^ 7

95-6b-10 59 40 0.68 33 0.00013 0.204 0.16775 ^ 162 0.4729 ^ 93 10.94 ^ 25 98 2535 ^ 16

95-6b-11 220 132 0.60 122 0.00003 0.055 0.17047 ^ 72 0.4806 ^ 87 11.30 ^ 22 99 2562 ^ 7

95-6b-12 158 175 1.11 101 0.00008 0.123 0.16847 ^ 85 0.4966 ^ 91 11.53 ^ 23 102 2543 ^ 8

95-6b-13 227 29 0.13 91 0.00010 0.156 0.16684 ^ 84 0.3849 ^ 70 8.85 ^ 17 83 2526 ^ 8

95-6b-14 211 82 0.39 116 0.00003 0.054 0.17002 ^ 70 0.4987 ^ 90 11.69 ^ 22 102 2558 ^ 7

95-6b-15a 124 153 1.23 81 0.00008 0.132 0.16923 ^ 97 0.4974 ^ 92 11.61 ^ 23 102 2550 ^ 10

95-6b-15b 51 27 0.52 29 0.00017 0.272 0.16823 ^ 123 0.5034 ^ 107 11.68 ^ 28 103 2540 ^ 18

95-6b-17 165 224 1.36 108 0.00004 0.068 0.16746 ^ 82 0.4927 ^ 90 11.38 ^ 22 102 2532 ^ 8

95-6b-18 263 99 0.38 145 0.00005 0.079 0.16866 ^ 61 0.5026 ^ 90 11.69 ^ 22 103 2544 ^ 6

95-6b-19 110 109 0.99 68 0.00007 0.117 0.17030 ^ 102 0.4922 ^ 92 11.56 ^ 23 101 2561 ^ 10

95-6b-20a 71 29 0.40 39 0.00015 0.245 0.16919 ^ 140 0.4923 ^ 95 11.48 ^ 25 101 2550 ^ 14

95-6b-20b 139 64 0.46 74 0.00002 0.029 0.17057 ^ 89 0.4789 ^ 88 11.26 ^ 22 98 2563 ^ 9

a, b and c refer to multiple analyses on a single grain. f 206% is (common 206Pb/total 206Pb) £ 100. %Conc ¼ %concordance defined as [(206Pb/238U

age)/(207Pb/206Pb age)] £ 100.a Radiogenic lead 204 Pb corrected.


nine analyses of the standard, which recorded an error of

1.8% during the analytical session. The U and Th contents

mostly range from 51–275 to 27–235 ppm, respectively

(spot 95-6b-1 excluded), and the Th/U ratios for all data

points range from 0.13 to 1.36; average 0.70 (Table 1). The

results are shown on a concordia plot in Fig. 2d. The main

group of 15 analyses from 14 grains define a weighted mean207Pb/206Pb age of 2551 ^ 5 Ma with a chi-square value of

1.27, indicating a slight component of geological scatter in

the data. Four analyses, which show slight normal and

reverse discordance (Fig. 2d), define a 207Pb/206Pb age of

2522 ^ 11 Ma. This is outside of error of the main

population and may reflect disturbance coincident with the

timing of later granitoid plutonism and felsic volcanism in

the Wutai Complex (Wilde et al., 1997, 2004a.

3.3. Shifo granite

The Shifo granite is a narrow elongate pluton located

near to the eastern margin of the Wutai Complex, in close

proximity to the higher-grade Fuping Complex (Fig. 1). It

covers approximately 80 km2 in area and shows little

textural or mineralogical variation. Its contact relations with

the Wutai succession are rarely exposed. However, in

blasted outcrops along the Taihuai–Shizui road, the

contacts are everywhere sheared.

Sample 95-PC-98 [Lat. 3885503900; Long. 11383803300]

was obtained from the bank of a small stream immediately

northeast of Nanliang village, 6 km north of Jingangku. It is

a medium-grained monzogranite composed of plagioclase,

quartz, microcline and biotite, with the latter defining a

moderate to strong fabric oriented 3468/408N. In thin

section, the rock is extensively recrystallized, with quartz

and feldspars commonly reduced to aggregates of subgrains.

Within such areas, biotite laths have a random orientation;

elsewhere they tend to wrap around felsic porphyroclasts.

Quartz is extensively recrystallized and subgrains have

embayed to sutured boundaries. Microcline is generally

fresh, whereas plagioclase is extensively sericitised and also

contains irregular patches of calcite.

The rock contains a variable population of zircons that

range from colorless to pale pink, together with more

brownish crystals that appear metamict. Most grains reveal

evidence of weak to strong oscillatory zoning and some

contain single inclusions of apatite or titanite. The zircons

are mostly stubby and subhedral with an average length to

Fig. 2. Concordia diagrams of Chechang-Betai granite samples: (a) sample WC5, (b) sample WC6, (c) sample WC7, and (d) sample 95-PC-6B, each showing

weighted mean 207Pb/206Pb ages. Shaded analytical data points in (a) and (b) not included in weighted mean age calculations; shaded data points in (d) define a

slightly younger age than the main population (see discussion in text).


width ratio of 1.25:1. A total of 20 analyses of 20 zircons,

selected from the 2105 to þ74 mm NM 28 fraction were

run with six analyses of the standard, which gave an error of

2.51% during the analytical session. The spots show a range

of Th/U ratios from 0.56 to 1.14, with an average value of

0.76. The analytical data are shown in Table 2 and presented

on a concordia plot in Fig. 3a; no difference in chemistry or

age was detected between the pale pink and the brownish

zircons. The data are both normally and slightly reversely

discordant, indicating both recent lead loss and gain. The

total data set define an Isoplot (Ludwig, 2001) 207Pb/206Pb

age of 2529 ^ 6 Ma, with a lower intercept in error of zero

Ma and an MSWD of 0.84. In detail, it can be seen (Fig. 3a)

that three grains plot along a discordia line that intersects

concordia at ,2400 Ma, whereas the main population of 17

analyses from 17 separate zircon grains define a weighted

mean 207Pb/206Pb age of 2531 ^ 4 Ma (with a chi-square

value of 0.75 and MSWD of 0.80), which is taken to be the

age of crystallization of the Shifo granite.

3.4. Guangmingshi granite

The Guangmingshi granite occurs as a thin sliver

within the volcanic sequence of the Wutai Complex,

north of Taihuai (Fig. 1). It occupies an area of

approximately 16 km2 and is described as intrusive by

Tian et al. (1996), although it is strongly foliated parallel

with the host meta-volcanics. There are several other

sheet-like granitoid bodies in this area that are inter-

leaved with the Wutai succession.

Sample 95-PC-76 [Lat. 3980202600; Long. 1138370900] was

collected from along the main Shahe–Taihuai road close to

the old 39 km marker peg and opposite a small cairn. It is a

fine to medium-grained granodiorite and, although the

contact is not exposed, it appears to be tectonically

interleaved with the Wutai metamorphic rocks, since their

east–west oriented metamorphic fabrics are exactly paral-

lel. In thin section, the rock is composed predominantly of

plagioclase and quartz with minor microcline and biotite.

The overall fabric shows two domains, one dominated by

the original medium-grained quartz–feldspar igneous fabric

and another where this has recrystallized to a fine-grained

quartzo-feldspathic mosaic with discrete bands of biotite,

accompanied by epidote and local white mica. The less

deformed portions contain strongly sericitised plagioclase

with undulose quartz. The latter is locally reduced to an

aggregate of subgrains and there is a tendency for marginal

recrystallization of feldspar into a mortar texture. Biotite is

largely restricted to the recrystallized portions and defines a

braided fabric. The mineralogy of the recrystallized parts

Fig. 3. Concordia diagrams of (a) Shifo granite sample 95-PC-98, (b) Gunagmingshi granite sample 95-PC-76, (c) Wangjiahui granite (grey phase) sample 95-

PC-62 and (d) Wangjiahui granite (grey phase) sample 95-PC-63, each showing weighted mean 207Pb/206Pb ages. Shaded analytical data points not included in

weighted mean age calculation of main populations.


Table 2

SHRIMP U–Pb–Th zircon data for Wutai Granitoid samples 95-PC-98, 95-PC-76 and 95-PC-62

Spot# U (ppm) Th (ppm) Th/U Pb (ppm) 204Pb/206Pb f 206% 207Pba/206Pba 206Pba/238U 207Pba/235U %Conca AGE 207Pba/206Pb

Sample 95-PC-98

PC98-1 333 267 0.80 92 0.00021 0.335 0.16333 ^ 92 0.2338 ^ 45 5.26 ^ 11 54 2490 ^ 10

PC98-2 122 69 0.56 69 0.00010 0.163 0.16677 ^ 114 0.4970 ^ 98 11.43 ^ 25 103 2526 ^ 11

PC98-3 130 114 0.88 82 0.00011 0.173 0.16795 ^ 104 0.5127 ^ 101 11.87 ^ 25 105 2537 ^ 10

PC98-4 123 85 0.69 77 0.00003 0.042 0.16720 ^ 84 0.5317 ^ 104 12.26 ^ 25 109 2530 ^ 8

PC98-5 138 114 0.82 85 0.00000 0.000 0.16785 ^ 70 0.5096 ^ 99 11.79 ^ 24 105 2536 ^ 7

PC98-6 105 67 0.63 61 0.00004 0.066 0.16767 ^ 103 0.4991 ^ 98 11.54 ^ 25 103 2535 ^ 10

PC98-7 186 158 0.85 113 0.00008 0.121 0.16749 ^ 75 0.4990 ^ 97 11.52 ^ 23 103 2533 ^ 8

PC98-8 176 144 0.82 102 0.00010 0.154 0.16599 ^ 82 0.4790 ^ 93 10.96 ^ 23 100 2518 ^ 8

PC98-9 124 77 0.62 73 0.00005 0.083 0.16721 ^ 87 0.5106 ^ 100 11.77 ^ 25 105 2530 ^ 9

PC98-10 123 92 0.75 64 0.00031 0.493 0.15495 ^ 111 0.4396 ^ 86 9.39 ^ 20 98 2401 ^ 12

PC98-11 145 94 0.65 85 0.00002 0.032 0.16826 ^ 80 0.5056 ^ 98 11.73 ^ 24 104 2540 ^ 8

PC98-12 173 106 0.62 99 0.00002 0.035 0.16850 ^ 71 0.4993 ^ 97 11.60 ^ 24 103 2543 ^ 7

PC98-13 152 135 0.89 103 0.00004 0.070 0.16676 ^ 70 0.5598 ^ 109 12.87 ^ 26 113 2525 ^ 7

PC98-14 137 80 0.58 81 0.00001 0.015 0.16665 ^ 85 0.5181 ^ 101 11.91 ^ 25 107 2524 ^ 9

PC98-15 196 115 0.59 102 0.00006 0.099 0.16661 ^ 77 0.4487 ^ 97 10.31 ^ 21 95 2524 ^ 8

PC98-16 151 144 0.95 97 0.00001 0.014 0.16666 ^ 74 0.5199 ^ 101 11.95 ^ 24 107 2524 ^ 7

PC98-17 99 56 0.56 56 0.00002 0.035 0.16694 ^ 104 0.4957 ^ 98 11.41 ^ 24 103 2527 ^ 10

PC98-18 161 110 0.68 94 0.00005 0.087 0.16704 ^ 77 0.4988 ^ 97 11.49 ^ 24 103 2528 ^ 8

PC98-19 416 476 1.14 138 0.00029 0.464 0.15116 ^ 75 0.2598 ^ 50 5.42 ^ 11 63 2359 ^ 8

PC98-20 242 251 1.03 145 0.00001 0.021 0.16817 ^ 76 0.4765 ^ 92 11.05 ^ 22 99 2539 ^ 8

Sample 95-PC-76

pc76-1 138 124 0.90 69 0.00007 0.108 0.16835 ^ 91 0.4245 ^ 44 9.85 ^ 12 90 2541 ^ 9

pc76-2 71 35 0.49 38 0.00022 0.345 0.16609 ^ 151 0.4714 ^ 57 10.79 ^ 17 99 2519 ^ 15

pc76-3 123 94 0.77 68 0.00007 0.117 0.16692 ^ 84 0.4764 ^ 48 10.96 ^ 13 99 2527 ^ 8

pc76-4 94 47 0.49 50 0.00002 0.026 0.16778 ^ 95 0.4742 ^ 52 10.97 ^ 14 99 2536 ^ 9

pc76-5 119 79 0.66 67 0.00000 0.000 0.16829 ^ 78 0.4838 ^ 52 11.23 ^ 14 100 2541 ^ 8

pc76-6 84 47 0.56 45 0.00014 0.230 0.16495 ^ 123 0.4680 ^ 52 10.64 ^ 15 99 2507 ^ 13

pc76-7 78 42 0.55 40 0.00000 0.000 0.16692 ^ 100 0.4641 ^ 54 10.68 ^ 15 97 2527 ^ 10

pc76-8 59 29 0.50 32 0.00017 0.277 0.16734 ^ 159 0.4747 ^ 59 10.95 ^ 18 99 2531 ^ 16

pc76-9 67 36 0.54 30 0.00009 0.142 0.16822 ^ 135 0.3986 ^ 51 9.25 ^ 15 85 2540 ^ 13

pc76-10 98 60 0.61 53 0.00007 0.112 0.16760 ^ 101 0.4681 ^ 52 10.82 ^ 14 98 2534 ^ 10

pc76-11 66 33 0.50 35 0.00017 0.280 0.16634 ^ 143 0.4631 ^ 58 10.62 ^ 17 97 2521 ^ 14

pc76-12 62 31 0.50 33 0.00013 0.206 0.16845 ^ 140 0.4638 ^ 59 10.77 ^ 17 97 2542 ^ 14

pc76-13 98 47 0.47 52 0.00002 0.040 0.16843 ^ 108 0.4712 ^ 51 10.94 ^ 15 98 2542 ^ 11

pc76-14 55 33 0.61 29 0.00009 0.145 0.16658 ^ 142 0.4683 ^ 61 10.75 ^ 18 98 2524 ^ 14

pc76-15 92 61 0.66 51 0.00016 0.250 0.16553 ^ 140 0.4881 ^ 59 11.14 ^ 17 102 2513 ^ 14

pc76-16 53 34 0.65 28 0.00015 0.247 0.16603 ^ 177 0.4669 ^ 60 10.69 ^ 19 98 2518 ^ 18

pc76-17 66 44 0.67 29 0.00012 0.192 0.16678 ^ 138 0.3870 ^ 49 8.90 ^ 14 84 2526 ^ 14

pc76-18 68 36 0.52 37 0.00015 0.248 0.16762 ^ 141 0.4736 ^ 58 10.94 ^ 17 99 2534 ^ 14

pc76-19 93 47 0.51 50 0.00012 0.192 0.16693 ^ 118 0.4727 ^ 53 10.88 ^ 15 99 2527 ^ 12

pc76-20 55 28 0.50 30 0.00019 0.310 0.16794 ^ 179 0.4745 ^ 63 10.99 ^ 20 99 2537 ^ 18

Sample 95-PC-62

95-62-1 47 40 0.84 28 0.00038 0.608 0.16416 ^ 234 0.4878 ^ 167 11.04 ^ 32 102 2499 ^ 24

95-62-2 82 62 0.76 44 0.00013 0.216 0.16540 ^ 151 0.4477 ^ 103 10.21 ^ 26 95 2512 ^ 15

95-62-3 88 77 0.87 51 0.00012 0.198 0.16623 ^ 128 0.4734 ^ 107 10.85 ^ 27 99 2520 ^ 13

95-62-4 51 42 0.82 31 0.00037 0.586 0.16759 ^ 228 0.4841 ^ 115 11.19 ^ 32 100 2534 ^ 23

95-62-5 52 47 0.89 26 0.00018 0.281 0.16544 ^ 210 0.4040 ^ 95 9.22 ^ 26 87 2512 ^ 21

95-62-6 72 64 0.88 40 0.00020 0.314 0.16049 ^ 154 0.4497 ^ 103 9.95 ^ 26 97 2461 ^ 16

95-62-7 53 48 0.90 31 0.00021 0.342 0.16488 ^ 202 0.4687 ^ 111 10.65 ^ 30 99 2506 ^ 21

95-62-8 52 56 1.07 32 0.00030 0.480 0.16599 ^ 196 0.4791 ^ 113 10.96 ^ 30 100 2518 ^ 20

95-62-9 51 45 0.88 30 0.00032 0.519 0.16424 ^ 202 0.4860 ^ 116 11.00 ^ 31 102 2500 ^ 21

95-62-10 38 28 0.75 22 0.00022 0.351 0.16761 ^ 171 0.4790 ^ 119 11.07 ^ 34 100 2534 ^ 25

95-62-11 56 50 0.88 33 0.00013 0.202 0.16857 ^ 168 0.4843 ^ 113 11.26 ^ 30 100 2544 ^ 17

95-62-12 58 47 0.81 33 0.00021 0.329 0.16637 ^ 190 0.4729 ^ 111 10.85 ^ 30 99 2521 ^ 19

95-62-13 45 37 0.82 26 0.00019 0.298 0.16689 ^ 208 0.4799 ^ 115 11.04 ^ 31 100 2527 ^ 21

95-62-14 86 91 1.06 52 0.00021 0.344 0.16830 ^ 149 0.4803 ^ 109 11.14 ^ 28 100 2541 ^ 15

95-62-15 60 58 0.96 35 0.00024 0.389 0.16583 ^ 184 0.4748 ^ 113 10.86 ^ 30 100 2516 ^ 19

95-62-16 108010 5225 0.05 78642 0.00369 5.902 0.12886 ^ 813 0.5933 ^ 319 10.54 ^ 93 144 2082 ^ 111

(continued on next page)


indicates that the rock has undergone greenschist facies

metamorphism at the time of deformation.

The sample contains a single population of pale pink,

stubby zircons with good prism faces and a length to width

ratio of 1:1. A total of 20 analyses of 20 zircons from the

274 mm NM 28 fraction were analyzed along with seven


during the analytical run. The data reveal a small range in

Th/U ratios from 0.47 to 0.90, with an average value of 0.58,

and are presented in Table 2 and on a concordia plot in Fig.

3b. There is some discordancy, with the total data set

defining an upper intercept concordia age of 2530 ^ 5 Ma

using Isoplot (Ludwig, 2001), with a lower intercept within

error of zero Ma and an MSWD of 0.87. The main

population of 19 near-concordant analyses defines a

weighted mean 207Pb/206Pb age of 2531 ^ 5 Ma with a

chi-square value of 0.64. This is taken to be the crystal-

lization age of the granite.

3.5. Wangjiahui granite

The Wangjiahui granite occurs as a narrow strip close to

the western margin of the Wutai Complex (Fig. 1),

southwest of Ekou, and occupies an area of approximately

80 km2. Two phases of the Wangjiahui granite are evident

in the field; a main grey phase that locally contains abundant

country rock xenoliths and a later pink phase that is

commonly transgressive, cutting both the grey phase and the

Wutai sequence.

Grey phase. Two samples of the grey phase were

analyzed. They are mineralogically and texturally similar,

being deformed medium-grained granodiorites composed of

plagioclase quartz, microcline and biotite. There are

essentially two domains present in these rocks: the original

coarse-grained quartz-two feldspar igneous fabric and a

recrystallized fabric characterized by flakes of biotite

defining a braided foliation. Associated with the dark

brown pleochroic biotite are grains of epidote and titanite

and, in sample 95-PC-63, flakes of white mica. The felsic

minerals adjacent to the mica–epidote bands are reduced in

grain size and consist of a mosaic of quartz, plagioclase and

microcline.


was collected along a small valley approximately 450 m

east of Shi Gang village. It contains a single population of

stubby, pale brown zircons, with an average length to width

ratio of 1.5:1. A total of 20 grains from the 2135 to

þ105 mm NM 28 fraction were analyzed along with seven


during the analytical run. Spot 95-62-16 was extremely rich

in U, Th and Pb (Table 2) and is not plotted or considered in

the following calculations. The remaining population of 19

zircons shows a range of Th/U ratios of 0.75–1.13, with an

average value of 0.89. Two grains (spots 6 and 20) plot close

to 2450 Ma (Fig. 3c), whereas one spot (5) is discordant,

leaving a main concordant population of 16 analyses from

16 separate zircon crystals. The Isoplot (Ludwig, 2001)

upper intercept age of this group is 2520 ^ 9 Ma, with a

lower intercept within error of zero Ma and an MSWD of

1.60. The data define a weighted mean 207Pb/206Pb age of

2520 ^ 9 Ma (Fig. 3c) with a chi-square value of 0.59. This

is interpreted to be the age of crystallization of the granite.


was collected 200 m upstream from sample 95-PC-62 and is

of similar appearance. It contains a population of euhedral,

colorless to pale pink-brown zircons, which are stubby and

square in cross-section, with a length to width ratio of 1.5:1.

A total of 12 analyses were made on 12 separate crystals

(Table 3), selected from the þ135 mm Mag 28 fraction,

along with nine analyses of the standard that recorded an

error of 1.07% during the analytical session. With the

exception of spot 8, the Th/U ratios range from 0.74 to 1.23,

with an average value of 0.86. Spot 8 has extremely high U,

Th and Pb values giving a young 207Pb/206Pb age with very

high errors (not plotted in Fig. 3d), whereas spot 5 is

discordant with a 207Pb/206Pb age of 2443 ^ 18 Ma. Both

are omitted from the calculation and the 10 most concordant

analyses give a weighted mean 207Pb/206Pb age of

2517 ^ 12 Ma (Fig. 3d), with a chi-square value of 1.04.

This is within error of the result from sample 95-PC-62 and

is taken to be the age of igneous crystallization.

Pink phase. Three samples of the pink phase of the

Wangjiahui granite have been analyzed, including a pink

granite dyke considered to be related to the main granite

body. At several locations, especially near Chungxie

Reservoir, the pink phase is clearly intrusive into the grey

phase and both are deformed together. The pink granite

dyke, as well as apophyses from the main granite body,

extend into the adjacent supracrustal sequence and are

intensely deformed along with the layered succession.

Table 2 (continued)

Spot# U (ppm) Th (ppm) Th/U Pb (ppm) 204Pb/206Pb f 206% 207Pba/206Pba 206Pba/238U 207Pba/235U %Conca AGE 207Pba/206Pb

95-62-17 57 45 0.78 33 0.00035 0.565 0.16788 ^ 191 0.4747 ^ 112 10.99 ^ 30 99 2537 ^ 19

95-62-18 37 32 0.86 21 0.00057 0.905 0.16468 ^ 302 0.4659 ^ 118 10.58 ^ 35 98 2504 ^ 31

95-62-19 130 146 1.13 79 0.00015 0.233 0.16503 ^ 111 0.4772 ^ 107 10.86 ^ 26 100 2508 ^ 11

95-62-20 55 51 0.92 32 0.00044 0.696 0.16001 ^ 202 0.4748 ^ 112 10.48 ^ 29 102 2456 ^ 21

f 206% is (common 206Pb/total 206Pb) £ 100. %Conc ¼ %concordance defined as [(206Pb/238U age)/(207Pb/206Pb age)] £ 100.a Radiogenic lead 204 Pb corrected.


Table 3

SHRIMP U–Pb–Th zircon data for Wutai Granitoid samples 95-PC-63, 95-PC-60, 95-PC-50 and 95-PC-51

Spot# U ppm Th (ppm) Th/U Pb (ppm) 204Pb/206Pb f206% 207Pba/206Pba 206Pba/238U 207Pba/235U %Conc AGE 207Pba/206Pba

Sample 95-PC-63

95pc63-1 93 93 1.00 54 0.00008 0.120 0.16370 ^ 130 0.4597 ^ 89 10.38 ^ 23 98 2494 ^ 13

95pc63-2 65 60 0.92 37 0.00005 0.084 0.16683 ^ 163 0.4590 ^ 91 10.56 ^ 25 96 2526 ^ 16

95pc63-3 74 87 1.18 44 0.00007 0.111 0.16869 ^ 156 0.4634 ^ 92 10.78 ^ 25 96 2545 ^ 15

95pc63-4 94 115 1.23 59 0.00025 0.394 0.16704 ^ 138 0.4762 ^ 92 10.97 ^ 24 99 2528 ^ 14

95pc63-5 85 78 0.91 47 0.00042 0.667 0.15878 ^ 167 0.4425 ^ 87 9.69 ^ 23 97 2443 ^ 18

95pc63-6 98 84 0.85 56 0.00011 0.173 0.16670 ^ 120 0.4721 ^ 91 10.85 ^ 23 99 2525 ^ 12

95pc63-7 57 51 0.89 34 0.00038 0.616 0.16655 ^ 203 0.4832 ^ 98 11.10 ^ 28 101 2523 ^ 21

95pc63-8 406077 28041 0.07 801327 0.02716 43.452 0.07120 ^ 4112 0.5469 ^ 419 5.37 ^ 3.17 292 963 ^ 874

95pcv63-9 42 35 0.83 24 0.00010 0.165 0.16632 ^ 204 0.4834 ^ 102 11.08 ^ 28 101 2521 ^ 21

95pc63-10 57 50 0.88 33 0.00024 0.390 0.16417 ^ 200 0.4685 ^ 95 10.60 ^ 26 99 2499 ^ 20

95pc63-11 37 28 0.74 21 0.00084 1.346 0.16288 ^ 319 0.4641 ^ 101 10.42 ^ 32 99 2486 ^ 33

95pc63-12 63 56 0.89 36 0.00021 0.336 0.16399 ^ 182 0.4697 ^ 94 10.62 ^ 26 99 2497 ^ 19

Sample 95-PC-60

95pc60-1 107 78 0.73 38 0.00021 0.341 0.12880 ^ 153 0.2940 ^ 57 5.22 ^ 13 80 2082 ^ 21

95pc60-2 733 356 0.49 186 0.00037 0.600 0.11920 ^ 72 0.2206 ^ 40 3.63 ^ 7 66 1944 ^ 11

95pc60-3 72 96 1.33 31 0.00030 0.475 0.12943 ^ 229 0.3313 ^ 67 5.91 ^ 17 88 2090 ^ 31

95pc60-4 58 54 0.93 33 0.00011 0.178 0.16886 ^ 196 0.4624 ^ 96 10.77 ^ 27 96 2546 ^ 19

95pc60-5 148 278 1.88 76 0.00027 0.438 0.13083 ^ 112 0.3632 ^ 68 6.55 ^ 14 95 2109 ^ 15

95pc60-6 185 163 0.88 30 0.00038 0.606 0.12119 ^ 195 0.1225 ^ 23 2.05 ^ 5 38 1974 ^ 29

95pc60-7 235 486 2.07 76 0.00033 0.520 0.12568 ^ 110 0.2409 ^ 45 4.17 ^ 9 68 2038 ^ 15

95pc60-8 850 766 0.90 120 0.00058 0.934 0.10899 ^ 87 0.1150 ^ 21 1.73 ^ 4 39 1783 ^ 15

95pc60-9 1111 618 0.56 121 0.00238 3.803 0.09829 ^ 160 0.0853 ^ 15 1.16 ^ 3 33 1592 ^ 30

95pc60-10 113 68 0.61 32 0.00130 2.077 0.13027 ^ 325 0.2150 ^ 42 3.86 ^ 13 60 2102 ^ 44

95pc60-11 325 186 0.57 38 0.00033 0.534 0.12604 ^ 194 0.0943 ^ 18 1.64 ^ 4 28 2043 ^ 27

95pc60-12 194 180 0.93 65 0.00006 0.100 0.13074 ^ 98 0.2845 ^ 53 5.13 ^ 11 77 2108 ^ 13

95pc60-13 1124 624 0.56 319 0.00018 0.280 0.11180 ^ 56 0.2548 ^ 46 3.93 ^ 8 80 1829 ^ 9

95pc60-14 281 300 1.07 55 0.00056 0.889 0.12685 ^ 197 0.1507 ^ 29 2.64 ^ 7 44 2055 ^ 27

95pc60-15 93 201 2.17 28 0.00014 0.224 0.13300 ^ 204 0.2332 ^ 47 4.28 ^ 11 63 2138 ^ 27

95pc60-16 175 177 1.01 58 0.00025 0.401 0.12835 ^ 121 0.2789 ^ 52 4.94 ^ 11 76 2075 ^ 17

Sample 95-PC-50

pc50-1 36 38 1.08 18 0.00062 0.999 0.12863 ^ 331 0.4065 ^ 84 7.21 ^ 25 106 2079 ^ 45

pc50-2a 39 30 0.76 18 0.00054 0.865 0.12700 ^ 292 0.3779 ^ 78 6.62 ^ 22 100 2057 ^ 41

pc50-2b 32 27 0.86 15 0.00071 1.139 0.12691 ^ 365 0.3804 ^ 81 6.66 ^ 25 101 2056 ^ 51

pc50-4 29 32 1.11 15 0.00175 2.795 0.12988 ^ 537 0.3833 ^ 85 6.86 ^ 34 100 2096 ^ 73

pc50-5 61 54 0.89 28 0.00016 0.253 0.13316 ^ 183 0.3853 ^ 73 7.07 ^ 18 98 2140 ^ 24

pc50-6 34 36 1.05 16 0.00033 0.522 0.13174 ^ 279 0.3831 ^ 80 6.96 ^ 22 99 2121 ^ 37

pc50-7 38 40 1.03 18 0.00012 0.187 0.13498 ^ 352 0.3689 ^ 83 6.86 ^ 25 94 2164 ^ 45

pc50-8 84 108 1.28 41 0.00009 0.151 0.13034 ^ 153 0.3799 ^ 72 6.83 ^ 16 99 2102 ^ 21

pc50-9 26 26 0.99 15 0.00735 11.754 0.12485 ^ 1042 0.3343 ^ 80 5.76 ^ 52 92 2027 ^ 148

pc50-10 23 15 0.64 10 0.00063 1.004 0.12706 ^ 444 0.3626 ^ 82 6.35 ^ 28 97 2058 ^ 62

pc50-11 96 73 0.76 45 0.00019 0.306 0.13213 ^ 134 0.3962 ^ 72 7.22 ^ 16 101 2127 ^ 18

pc50-12 31 47 1.54 16 0.00033 0.529 0.13434 ^ 389 0.3714 ^ 80 6.88 ^ 26 94 2155 ^ 51

pc50-13 228 221 0.97 103 0.00297 4.757 0.13207 ^ 241 0.3183 ^ 56 5.80 ^ 16 84 2126 ^ 32

pc50-14 13 13 1.00 6 0.00077 1.227 0.12677 ^ 750 0.3855 ^ 108 6.74 ^ 46 102 2054 ^ 105

pc50-15 51 62 1.22 25 0.00019 0.302 0.13341 ^ 225 0.3760 ^ 77 6.92 ^ 19 96 2143 ^ 30

Sample 95-PC-51

pc51-1 66 64 0.96 32 0.00017 0.273 0.13115 ^ 209 0.3905 ^ 74 7.06 ^ 19 101 2113 ^ 28

pc51-2 220 174 0.79 96 0.00027 0.426 0.13239 ^ 99 0.3711 ^ 64 6.77 ^ 13 96 2130 ^ 13

pc51-3 37 24 0.65 17 0.00007 0.106 0.13470 ^ 258 0.3899 ^ 80 7.24 ^ 22 98 2160 ^ 33

pc51-4 278 206 0.74 116 0.00020 0.319 0.13029 ^ 78 0.3575 ^ 61 6.42 ^ 12 94 2102 ^ 10

pc51-5 68 37 0.55 30 0.00119 1.910 0.12751 ^ 268 0.3683 ^ 69 6.48 ^ 19 98 2064 ^ 37

pc51-6 31 27 0.88 13 0.00023 0.367 0.13369 ^ 416 0.3540 ^ 77 6.52 ^ 26 91 2147 ^ 54

pc51-8 63 55 0.87 27 0.00079 1.263 0.13173 ^ 320 0.3300 ^ 65 5.99 ^ 20 87 2121 ^ 43

pc51-9 119 42 0.35 43 0.00020 0.323 0.13210 ^ 152 0.3319 ^ 60 6.04 ^ 14 87 2126 ^ 20

pc51-10 179 150 0.84 83 0.00038 0.600 0.13560 ^ 121 0.3815 ^ 67 7.13 ^ 15 96 2172 ^ 16

pc51-11 139 92 0.66 57 0.00031 0.493 0.13193 ^ 136 0.3542 ^ 63 6.44 ^ 14 92 2124 ^ 18

pc51-12 18 20 1.10 8 0.00045 0.722 0.12351 ^ 668 0.3580 ^ 90 6.10 ^ 38 98 2008 ^ 96

a and b refer to multiple analyses on a single grain. f 206% is (common 206Pb/total 206Pb) £ 100. %Conc ¼ %concordance defined as [(206Pb/238U

age)/207Pb/206Pb age)] £ 100.a Radiogenic lead 204 Pb corrected.


The pink phase ranges from monzo- to syenogranite in

composition and is composed of quartz, plagioclase and

microcline, with minor amounts of variably chloritised

greenish biotite and muscovite. All rocks have a moderate to

strong fabric defined by the recrystallization of quartz into

long ribbons and emphasized by the recrystallization of

adjacent feldspar-rich portions to a finer grain size. The

feldspars are commonly extensively altered, with abundant

specks of hematite in the microcline. There is also some

patchy development of calcite where the feldspars have

recrystallized to smaller subgrains.


was collected from the base of a blasted outcrop along the

roadside, immediately opposite the dam wall of Chungxie

Reservoir and 2 m from the main contact of the Wangjiahui

granite with the so-called Zhuanwang ‘formation’ of the

Wutai sequence (Y.Q. Tian, pers com 1996). It is a

syenogranite with a well-defined quartz fabric, with

muscovite as the only micaceous phase. It contains a single

population of pale brownish-yellow zircon grains, com-

monly with poorly developed crystal faces and a length to

width ratio of 2:1. A total of 16 analyses were made on 16

separate zircon crystals (Table 3) from the 2135 to

þ105 mm NM 28 fraction, along with nine analyses of the

standard which recorded an error of 1.07% during

the analytical run. All analyses are discordant (Fig. 4a)

and trend to zero Ma as a result of recent Pb loss. The grains

show a range of U and Th values from 58–1124 to 54–766,

respectively. The Th/U ratios range from 0.56 to 2.17, with

an average value of 1.04, which is considerably higher than

any of the granitoids described above. The oldest and most

concordant grain (spot 4) gives an age of 2546 ^ 19 Ma,

which overlaps within error the zircon ages obtained for the

grey phase of the Wangjiahui granite, suggesting it was

inherited from that source. In an attempt to more precisely

define an age for this rock, the data were processed using

Isoplot (Ludwig, 2001). Ten of the analyses (those without

ornament in Fig. 4a) define a weighted average 207Pb/206Pb

age of 2084 ^ 20 Ma at the 95% confidence level, with an

MSWD of 1.8. This should be viewed as a minimum age for

the granite, since the total data set is highly discordant and

skewed toward younger ages along concordia (Fig. 4a).


was collected from a north-facing road cutting through an

Army Camp, 2 m west of bunker 8, and approximately 70 m

from the contact with the Jingangku ‘formation’. It is a

weakly deformed monzogranite containing both muscovite

and greenish biotite. It contains a population of pale to

darker pink zircons; the latter are metamict and were not

analyzed. The crystals show weak oscillatory zoning and

Fig. 4. Concordia diagrams of Wangjiahui Granite (pink phase) samples: (a) sample 95-PC-60, (b) sample 95-PC-50 and (c) dyke sample 95-PC-51, each

showing weighted mean 207Pb/206Pb ages. Shaded analytical data points not included in weighted mean age calculation of main populations in (a) and (c).


only rarely contain inclusions, although some show a myriad

of small cracks. The grains range in shape from stubby to

more elongate, with a range in length to width ratios of 1:1

to 3:1. A total of 15 analyses were made on 14 zircons

(Table 3) from the 2135 to þ105 mm NM 28 fraction and

were run with eight analyses of the standard that gave an

error of 1.71% over the analytical session. The zircons are

generally low in U and Th, with Th/U values quite high,

ranging from 0.64 to 1.54 with an average of 1.00. The data

are presented as a concordia plot in Fig. 4b and, although

two grains are slightly discordant (and trend to zero Ma), the

total data set has a chi-square value of 0.71 and defines a

weighted mean 207Pb/206Pb age of 2117 ^ 17 Ma, which is

interpreted as the crystallization age of the granite.

Sample 95-PC-51 [Lat. 3980103300; Long. 11380600200] is

from a dyke of pink granite intruding the Jingangku

‘formation,’ exposed in a south-facing road cutting on the

opposite side of the valley from where sample 95-PC-50

was collected, and ,50 m from the main Wangjiahui

granite contact (Fig. 1). It is a fine-grained monzogranite

with a moderately intense quartz fabric and the patchy

development of calcite. It contains pale to darker pink

zircons, with the latter distinctly metamict (these were not

analyzed). The grains are subhedral and elongate, with an

average length to width ratio of 2:1, and contain numerous

small inclusions; some grains are also cracked. A total of 12

analyses were made on 12 separate crystals selected from

the 2135 to þ105 mm NM 28 fraction and were run with

eight analyses of the standard, which recorded an error of

1.71% over the analytical period. One analysis (spot 7)

turned out not to be zircon and is omitted from Table 3. The

remaining data show a range in Th/U ratios of 0.35–1.10

with an average value of 0.76. The data are presented on a

concordia plot in Fig. 4c. With the exclusion of grain 12,

which has low U and Th and large errors, 10 of the zircons,

although variously discordant through recent Pb loss, define

a weighted mean 207Pb/206Pb age of 2124 ^ 19 Ma with a

chi-square value of 1.74 indicating a component of

geological scatter. This can be reduced by excluding the

two grains (pc-51-3 and pc51-10 in Table 3) with slightly

higher 207Pb/206Pb ages, to give a weighted mean207Pb/206Pb age of 2116 ^ 16 Ma with an MSWD of 0.90.

This is considered to be the best estimate of the age of

crystallization of the dyke, with the slightly older grains

representing xenocrysts.

3.6. Summary of results

The results presented above reveal two main groups of

ages; a relatively continuous spread from ,2552 Ma (for

two samples of Chechang-Betai granite) to ,2518 Ma (for

the youngest sample of Wangjiahui granite—grey phase)

and ages of ,2120 Ma for the pink phase of the Wangjiahui

granite. The oldest ages in the current study, obtained only

from the Chechang-Betai granite, are similar to those

recorded previously from the Lanzhishan and Ekou granites

(Wilde et al., 1997). The oldest ages of 2552 ^ 5 Ma

(95-PC-6B) and 2552 ^ 11 Ma (WC7) were obtained from

the hornblende-bearing phase of the Chechang-Betai granite

near the contact with the Wutai Complex volcanic rocks and

from the coarse-grained granite near Shahe, respectively. A

slightly younger age of 2546 ^ 3 Ma was obtained from

fine-grained granitoid sample WC6, consistent with its

cross-cutting field relations with the older sample (95-PC-

6B), although the two ages overlap within the uncertainties

of the data. The youngest age obtained from the Chechang-

Betai granite of 2538 ^ 6 Ma (WC5) is also from a coarse-

grained fraction and similarly overlaps the younger dates

within error. This date is almost identical to the

2537 ^ 10 Ma age previously recorded from a sample of

Lanzhishan granite (Wilde et al., 1997). However, it also

overlaps the oldest age of 2533 ^ 8 Ma recorded from felsic

volcanic rocks of the Wutai Complex (Wilde et al., 2004a).

The dates for the Shifo and Guangmingshi granites are

2531 ^ 4 and 2531 ^ 5 Ma, respectively. Again, these

overlap (within error) the youngest age recorded from the

Chechang-Betai granite, but are closer to the ages obtained

from felsic volcanic rocks in the Wutai Complex, which

extend from 2533 ^ 8 to 2513 ^ 8 Ma, with a mean207Pb/206Pb age of 2523 ^ 3 Ma (Wilde et al., 2004a).

Dates of 2520 ^ 9 Ma (95-PC-62) and 2518 ^ 12 Ma (95-

PC-63) from the grey phase of the Wangjiahui granite are

also essentially coeval with volcanism in the Wutai

Complex.

In marked contrast, the pink phase of the Wangjiahui

granite, with dates of ,2120 Ma, is considerably younger

than the other granite bodies investigated in this study. The

ages are close to, but younger than, the Dawaliang granite,

which has an intrusive age of 2176 ^ 12 Ma (Wilde et al.,

1997; Wang and Wilde, 2002).

Fig. 5 summarizes the geochronological results for all

Archean granitoids and felsic volcanics dated by us from

Wutaishan, including those from Wilde et al. (1997, 2004a).

This emphasizes the continuity of the ages between ,2560

and ,2515 Ma, although there is a suggestion of two sub-

groups with mean dates at approximately 2545 and

2525 Ma; this is discussed below in the light of the

geochemical and tectonic evidence.

4. Evolution of the granitoids

Sun et al. (1992) considered that all granitoids in the

Wutai Complex were I-types, with the Chechang-Betai the

only granitoid with trondhjemite–tonalite–granodiorite

(TTG) characteristics. The geochemical data of Liu et al.

(2002) has established the TTG affinity of the Chechang-

Betai granite, with one sample of Shifo granite also sharing

these characteristics. These rocks can be distinguished from

the Ekou and Lanzhishan granites (and most other Shifo

granite samples), which plot along a distinct calc-alkali

trend in the K2O–Na2O–CaO diagram (Liu et al., 2002).


However, Li et al. (1990a,b) recognized that some granites

in Wutaishan are S-types and this was supported by Wang

et al. (1992) based on limited chemical analyses revealing

high silica and alkali contents. Unfortunate, no modern data

are currently available for the younger pink phase of the

Wangjiahui granite which, from its high proportion of

quartz and alkali feldspar may also possibly be an S-type

granite, although it should be noted that no zircon

inheritance has been recorded.

Integration of granite geochronology with age data from

the Wutai Complex volcanic rocks (Wilde et al., 2004a) and

the limited geochemical data of Liu et al. (2002) suggests

that late Archean magmatism at Wutaishan between 2560

and 2515 Ma can be separated into two phases, with a

change occurring around 2540–2535 Ma ago. The older

phase is represented by the Lanzhishan, Ekou (Wilde et al.,

1997) and Chechang-Betai granites. These pre-date the

formation of the Wutai volcano-sedimentary sequence,

which developed between 2533 ^ 8 and 2513 ^ 8 Ma

(Wilde et al., 2004a) and, as such, reflect events prior to

the development of the major arc system to which the Wutai

volcanogenic rocks belong (Li and Wang, 1992; Wang et al.,

1996, 2004; Wilde et al., 2004a,b; Kroner et al., 2004).

These older granites are characterized by a TTG geochem-

ical signature (Liu et al., 2002). The second phase of

magmatic activity is represented by the Shifo, Guangming-

shi and grey phase of the Wangjiahui granite, which all have

ages between 2535 and 2515 Ma, and are coeval and

probably cogenetic with intermediate to felsic volcanism

within the Wutai Complex. Although original contact

relations between the plutonic and volcanic rocks are

generally not preserved, the granitoid bodies are spatially

associated with the Wutai volcano-sedimentary pile,

occurring as thin tectonic slices within it. Geochemical

data for most samples of the Shifo granite indicate calc-

alkaline affinities and include steep LREE patterns and lack

of negative europium anomalies, indicative of a magmatic

arc setting (Liu et al., 2002). Geochemical data for the

volcanic rocks (Wang et al., 2004) also indicate a calc-

alkaline affinity and are similarly interpreted as forming in

an arc setting (Kroner et al., 2004). No reliable geochemical

data are currently available for the Guangmingshi and

Wangjiahui granitoids.

The latest phase of granite formation occurred during the

Paleoproterozoic, with the Dawaliang (Wilde et al., 1997)

and pink phase of the Wangjiahui granite recording ages of

,2170 and ,2120 Ma, respectively. On the basis of field

relations and its virtually identical age, it is considered that

the dyke (95-PC-51), with an age of 2116 ^ 16 Ma, is indeed

an offshoot of the pink phase of the Wangjiahui granite.

Although intrusive into the Wutai Complex, the pink phase of

the Wangjiahui granite, like the Dawaliang granite (Wang

and Wilde, 2002), is also deformed, implying that it pre-dates

final deformation in the Wutai Complex (Kroner et al., 2004).

5. Conclusions and tectonic implications

Two major episodes of granitoid activity have been

identified in the Wutaishan area of the North China Craton.

Fig. 5. Summary plot of all Archean granitoid age data obtained by the authors from the Wutai Complex (including data from Wilde et al., 1997) showing error

bars. The data for samples of Wutai felsic volcanic rocks are also included for comparison (from Wilde et al., 2004a).


Using SHRIMP U–Pb zircon techniques, we have estab-

lished an early event of protracted and voluminous

magmatism close to the end of the Archean, extending

from 2560 to 2515 Ma. During the Paleoproterozoic, more

restricted magmatism has been identified, extending from

2170 to 2120 Ma. The fact that volcanogenic rocks of the

Wutai Complex are coeval with the latest phase of Archean

plutonism provides a potential time-line with which to

evaluate tectonic models of the area.

Two models have been previously proposed for the

tectonic evolution of the Wutaishan area. One favored

development of the Wutai Complex within an ensialic rift,

with the Fuping Complex to the south and the Hengshan

Complex to the north (Fig. 1) representing original

basement that rifted apart and then closed (Tian et al.,

1996). The alternative model considered the Wutai Com-

plex as an island arc that evolved between the Fuping and

Hengshan Complexes (believed to represent separate pre-

existing microcontinental nuclei) that was deformed during

their collision in the late Archean (Li et al., 1990a,b; Li and

Wang, 1992). Although recent work on the Wutai Complex

has established its arc affinity (Wang et al., 2004; Kroner

et al., 2004), comparative studies of the adjacent Fuping and

Hengshan Complexes do not support either model; instead,

they favor the view, first proposed by Sun et al. (1992), that

all three complexes represent various components of a

single complex arc system that evolved in the late Archean

(Guan et al., 2001; Zhao et al., 2002; Wilde et al., 2002,

2004a; Kroner et al., 2004). There is currently insufficient

detailed information available to more precisely determine

the nature of this arc. However, the features are not

inconsistent with the Altaid (or ‘Turkic’-type) arc model of

Sengor and Natal’in (1996a,b), especially if the younger

components in the area—the Hutuo ‘formation’, Dawaliang

granite and pink-phase of the Wanjiahui granite—are

related to the same collisional event.

In terms of the wider setting, this segment of the

North China Craton has recently been interpreted as

forming part of a major collision zone (the Trans-North

China Orogen) between two discrete continental blocks

(the Eastern and Western blocks) that came together at

,1.8 Ga (Zhao et al., 1999, 2001; Wilde et al., 2002;

Kroner et al., 2004). The U–Pb zircon data from the

Wutaishan granitoids help to place tighter constraints on

the collisional model of Zhao and co-workers. Firstly, the

older group of granitoids, with ages between 2555 and

2538 Ma, pre-date the evolution of the Wutai Complex.

We favor the view (Kroner et al., 2004) that they reflect

the onset of subduction. The evolved geochemistry of the

Ekou and Lanzhishan granites (Liu et al., 2002), with

high silica and potash contents and pronounced negative

europium anomalies (at least for the Ekou granite),

suggests an extensive crustal contribution. This is borne

out by the presence of ,2.7 Ga zircon cores and

inherited zircon grains within the Lanzhishan granite

(Wilde et al., 1997). We therefore consider that both

these granitoids evolved during initial subduction of

oceanic crust, prior to major arc development, and

involved crustal melting. The TTG rocks of the

Chechang-Betai granite extend from 2552 to 2538 Ma

and thus overlap with the ages of the Ekou and

Lanzhishan granites, and have a geochemical signature

indicative of either melting of lithospheric mantle (Wang

et al., 1996) or melting of the slab: adakites have

recently been recognized in the Wutai Complex (Wang

et al., 2004). Since the Ekou and Lanzhishan granites

require the pre-existence of continental crust and the

Chechang-Betai granite also pre-dates the time of arc

development, we consider that these granites intruded

into the Eastern block of the North China Craton, close

to its western continental margin soon after the onset of

late Archean subduction.

With the formation and subsequent development of the

Wutai arc at ,2535–2515 Ma (Kroner et al., 2004; Wilde

et al., 2004a,b), thickening of the crust led to the formation

of extensive TTG rocks in the root zones, now represented

by the granitoid gneisses in the Fuping and Hengshan

Complexes (Guan et al., 2001; Zhao et al., 2001). Ages are

coeval with the meta-volcanic rocks of the Wutai Complex

(Wilde et al., 2002; Kroner et al., 2004), which represents

the upper crustal component (Wilde et al., 2004a). At these

higher crustal levels, the Shifo, Guangmingshi and grey

phase of the Wangjiahui granite were emplaced into the

volcano-sedimentary pile, although original intrusive

relations are now largely tectonized and obscured.

Previously, there was little evidence of the nature of

geological events in the region during the earliest

Proterozoic, prior to major continental-scale collision at

,1.8 Ga (Zhao et al., 2001). However, the dating of the

Wangjiahui granite at ,2120 Ma, together with the

formation of the Dawaliang granite at ,2170 Ma (Wilde

et al., 1997; Wang and Wilde, 2002) and volcanism in the

Hutuo ‘group’ at ,2080 Ma (Wilde et al., 2004b), indicates

there was at least limited magmatic activity prior to

collision. Based on geochemical data available in the

Chinese literature, Wang et al. (1992) noted that the high

silica and alkali contents of the Dawaliang granite favored

its development in an intracontinental setting. The Hutuo

‘group’ is dominantly a clastic sedimentary sequence that is

variably deformed and metamorphosed, but which also

contains rare felsic and mafic volcanic rocks. These

volcanic rocks, the Dawaliang granite and the pink phase

of the Wangjiahui granite may therefore represent a discrete

episode of magmatism that was not directly related to

subduction. Although limited in scale, this episode may

have been widespread across the area, since meta-sediments

and meta-volcanics of the Wanzi supracrustal rocks and the

Nanying granitic gneisses in the adjacent Fuping Complex

are of similar age (Wilde et al., 2004b). There is then a gap

in our knowledge of events in the area until ,1.8 Ga, when

there was renewed subduction, resulting ultimately in a

major collisional event that brought together the Eastern and


Western blocks of the North China Craton (Zhao et al.,

2001; Kroner et al., 2004).

Acknowledgements

This work was supported by an Australian Research

Grant (A39532446) to S.A. Wilde and P.A. Cawood.

B. Cikara kindly assisted with the zircon preparation. We

thank Shuwen Liu for allowing us to view his manuscript

prior to publication and also acknowledge our many

Chinese colleagues, especially Guochun Zhao and Min

Sun, for many enlightening discussions. This is TSRC

Publication No. 227.

References

Bai, J., 1986. The Early Precambrian Geology of Wutaishan. Tianjin

Science and Technology Press, Tianjin.

Bai, J., Li, H.M., Wang, J.R., 1991. Single-grain zircon U–Pb ages of the

Wutai granite-greenstone belt and their geological implications. Journal

of Tianjin Institute of Geology and Mineral Resources 25, 1–12 (in

Chinese).

Cawood, P.A., Wilde, S.A., Wang, K.Y., Nemchin, A.A., 1998. Integrated

geochronology and field constraints on subdivision of the Precambrian

of China: data from the Wutaishan. Abstracts of ICOG-9, 1998 Beijing.

Chinese Science Bulletin 43, 17.

Guan, H., Sun, M., Wilde, S.A., Zhou, X.H., Zhai, M.G., 2001. SHRIMP

U–Pb zircon geochronology of the Fuping Complex: implications for

formation and assembly of the North China craton. Precambrian

Research 113, 1–18.

Kroner, A., Wilde, S.A., Li, J.H., Wang, K.Y., 2005. Age and evolution of a

late Archaean to early Palaeozoic upper to lower crustal section in the

Wutaishan/Hengshan terrain of northern China. Journal of Asian Earth

Sciences (this issue).

Li, J.L., Wang, K.Y., 1992. Accretion tectonics of Early Precambrian in

North China. Scientia Geologia Sinica 1, 15–29.

Li, S.X., Ji, S.K., Ma, Z.H., He, G.P., Tian, Y.Q., Yang, W.K., 1986. The

Geology of Meta-sedimentary Iron Deposits in Wutaishan Area. Jilin

Science and Technology Press, Changchun, (in Chinese with English

abstract).

Li, J.L., Wang, K.Y., Wang, Q., Liu, X., Zhao, Z., 1990a. Early Proterozoic

collision orogenic belt in Wutaishan Area, China. Scientia Geologica

Sinica 1, 1–11.

Li, S.X., Hart, S.R., Wu, T., 1990b. Rb–Sr and Sm–Nd isotopic dating of

an early Precambrian spilite–keratophyre sequence in the Wutaishan

area, North China: preliminary evidence for Nd-isotopic homogeniz-

ation in the mafic and felsic lavas during low-grade metamorphism.

Precambrian Research 47, 191–203.

Liu, D.Y., Page, R.W., Compston, W., Wu, J., 1985. U–Pb zircon

geochronology of Late Archaean metamorphic rocks in the Taihang-

shan–Wutaishan area, North China. Precambrian Research 27,

85–109.

Liu, S.W., Pan, Y.M., Zhang, J., Li, Q.G., 2002. Archean geodynamics in

the Central Zone, North China Craton: constraints from geochemistry of

two contrasting series of granitoids in the Fuping, Hengshan and

Wutaishan complexes. Precambrian Research 117, 41–56.

Ludwig, K.R., 2001. Isoplot/Ex. A geochronological toolkit for Microsoft

Excel. Version 2.49, Berkeley Geochronology Center Special Publi-

cation 1a, 58 pp.

Nelson, D.R., 1997. Compilation of SHRIMP U–Pb zircon geochronolo-

gical data, 1996, Geological Survey of Western Australia Record, 1997/

2, 189 pp.

Pidgeon, R.T., Furfaro, D., Kennedy, A.K., Nemchin, A.A., van Bronswijk,

W., Todt, W.A., 1994. Calibration of zircon standards for the Curtin

SHRIMP II. Abstracts Eighth International Conference on Geochronol-

ogy, Cosmochronology and Isotope Geology, Berkeley, 251.

Sengor, A.M.C., Natal’in, B.A., 1996a. Paleotectonics of Asia:

fragments of a synthesis. In: Yin, A., Harrison, M. (Eds.), The

Tectonic Evolution of Asia, Cambridge University Press, New York,

pp. 486–640.

Sengor, A.M.C., Natal’in, B.A., 1996b. Turkic-type orogeny and its role in

the making of continental crust. Annual Reviews of Earth and Planetary

Science 24, 263–337.

Sun, M., Armstrong, R.L., Lambert, R.St.J., 1992. Petrochemistry and Sr,

Pb, and Nd isotopic geochemistry of Early Precambrian rocks,

Wutaishan and Taihangshan areas, China. Precambrian Research 56,

1–31.

Tian, Y.Q., 1991. Geology and Gold Mineralization of Wutai–Hengshan

Greenstone Belt. Shanxi Science and Technology Press, (in Chinese

with English).

Tian, Y.Q., Ma, Z., Yu, K., Liu, Z., Peng, Q., 1996. The Early Precambrian

geology of Wutai–Hengshan Mts., Shanxi, China—T315 Field Trip

Guide, 30th International Geological Congress, Geological Publishing

House, Beijing, 54 pp.

Wang, K.Y., Wilde, S.A., 2002. Precise SHRIMP U–Pb age of the

Dawaliang granite in the Wutaishan area, Shanxi Province, North China

Craton. Acta Petrologica et Mineralogica 21, 407–420.

Wang, K.Y., Chai, Y.C., Li, J.L., 1992. On the late Archaean granitoids and

their tectonic environments of the Wutai area, Memoir of

Lithospheric Tectonic Evolution Research 1, Seismological Press,

Beijing, pp. 107–112.

Wang, K.Y., Li, J.L., Hao, J., Li, J.H., Zhou, S.P., 1996. The Wutaishan

orogenic belt within the Shanxi Province, northern China: a record

of late Archaean collision tectonics. Precambrian Research 78,

95–103.

Wang, Z.H., Wilde, S.A., Wang, K.Y., Yu, L., 2004. A MORB-arc basalt–

adakite association in the 2.5 Ga Wutai greenstone belt: late Archaean

magmatism and crustal growth in the North China Craton. Precambrian

Research 131, 323–343.

Wilde, S.A., Cawood, P.A., Wang, K.Y., 1997. The relationship and timing

of granitoid evolution with respect to felsic volcanism in the Wutai

Complex, North China Craton, Proceedings of the 30th International

Geological Congress, Beijing, vol. 17. VSP International Science

Publishers, Amsterdam, pp. 75–87.

Wilde, S.A., Zhao, G.C., Sun, M., 2002. Development of the North

China Craton during the Late Archaean and its amalgamation along

a major 1.8 Ga collision zone; including speculations on its position

within a global Paleoproterozoic Supercontinent. Gondwana


Wilde, S.A., Cawood, P.A., Wang, K.Y., Nemchin, A.A., Zhao, G.C.,

2004a. Determining Precambrian Crustal Evolution in China: a case-

study from Wutaishan, Shanxi Province, demonstrating the application

of precise SHRIMP U–Pb Geochronology. In: Malpas, J., Fletcher,

C.J.N., Ali, J.R., Aitchison, J.C. (Eds.), Aspects of the Tectonic

Evolution of China, Special Publication, 226.

Wilde, S.A., Zhao, G.C., Wang, K.Y., Sun, M., 2004b. First precise

SHRIMP U–Pb zircon ages for the Hutuo Group, Wutaishan: further

evidence for the Palaeoproterozoic amalgamation of the North China

Craton. Chinese Science Bulletin 49, 83–90.

Williams, I.S., 1998. U–Th–Pb geochronology by ion microprobe. In:

McKibben, M.A., Shanks, W.C. III, Ridley, W.I. (Eds.), Applications of

microanalytical techniques to understanding mineralizing processes,

Reviews in Economic Geology, 7., pp. 1–35.

Wu, J., Liu, D., Jin, L., 1986. The zircon U–Pb age of metabasic volcanic

lavas from the Hutuo Group in the Wutai mountain area, Shanxi

Province. Geological Reviews 32, 178–184 (in Chinese).


Zhao, G.C., Wilde, S.A., Cawood, P.A., Lu, L.Z., 1999. Thermal evolution

of two textural types of mafic granulites in the North China Craton:

evidence for both mantle plume and collisional tectonics. Geological

Magazine 136, 223–240.

Zhao, G.C., Wilde, S.A., Cawood, P.A., Sun, M., 2001. Archean blocks and

their boundaries in the North China Craton: lithological, geochemical,

structural and P–T path constraints and tectonic evolution. Precambrian


Zhao, G.C., Wilde, S.A., Cawood, P.A., Sun, M., 2002. SHRIMP U–Pb

zircon ages of the Fuping Complex: implications for Late Archean to

Paleoproterozoic accretion and assembly of the North China Craton.

American Journal of Science 302, 191–226.


Documents

Granitoid evolution in the Late Archean Wutai Complex, North China Craton