Metamorphic P–T–t paths of pelitic granulites of the Taihua metamorphic complex in the Mts. Huashan area and tectonothermal implications for the Palaeoproterozoic Trans-North China Orogen

Accepted Manuscript Metamorphic P–T–t paths of pelitic granulites of the Taihua metamorphic complex in the Mts. Huashan area and tectonothermal implications for the Palaeoproterozoic Trans-North China Orogen Guo-Dong Wang, Hao Y.C. Wang, Hong-Xu Chen, Jun-Sheng Lu, Bo Zhang, Van Tho Pham, Ji-Jun Zhang, Qing Zhang, Chun-Ming Wu PII: DOI: Reference:

S0301-9268(16)30387-4 http://dx.doi.org/10.1016/j.precamres.2016.12.008 PRECAM 4627

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Precambrian Research

Received Date: Revised Date: Accepted Date:

14 September 2016 12 December 2016 25 December 2016

Please cite this article as: G-D. Wang, H.Y.C. Wang, H-X. Chen, J-S. Lu, B. Zhang, V. Tho Pham, J-J. Zhang, Q. Zhang, C-M. Wu, Metamorphic P–T–t paths of pelitic granulites of the Taihua metamorphic complex in the Mts. Huashan area and tectonothermal implications for the Palaeoproterozoic Trans-North China Orogen, Precambrian Research (2016), doi: http://dx.doi.org/10.1016/j.precamres.2016.12.008

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A revised original research manuscript submitted to Precambrian Research

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Metamorphic P–T–t paths of pelitic granulites of the Taihua metamorphic complex in the Mts. Huashan area and tectonothermal implications for the Palaeoproterozoic Trans-North China Orogen

8 9 10

Guo-Dong Wang

a,b*

, Hao Y.C. Wang b, Hong-Xu Chen b, Jun-Sheng Lu c, Bo

Zhang d, Van Tho Pham b, Ji-Jun Zhang e, Qing Zhang f, Chun-Ming Wu b

11

a

Institute of Oceanology, Chinese Academy of Sciences, Qingdao 266071, China

12

b

College of Earth Science, University of Chinese Academy of Sciences, P.O. Box

13

4588, Beijing 100049, China

14

c

15

China

16

d

China Corporation of Coal Geology Engineering, Beijing 100040, China

17

e

Shaanxi Center of Geological Survey, Xi’an 710068, China

18

f

Institute of Geomechanics, Chinese Academy of Geological Sciences, Beijing 100081,

19

China

Institute of Geology and Geophysics, Chinese Academy of Sciences, Beijing 100029,

20

*

Corresponding author at: Institute of Oceanology, Chinese Academy of Sciences, Qingdao 266071, China. E-mail address: [email protected] (G.-D. Wang). 1

21

22

ABSTRACT

23

Metamorphic evolution and geochronology of pelitic granulites were reported

24

for the first time in the Taihua metamorphic complex, Mts. Huashan area, southern

25

segment of the Trans-North China Orogen (TNCO). Three generations of

26

metamorphic mineral assemblages are recognized: (1) the prograde metamorphic

27

mineral assemblages (M1) are represented by mineral inclusions within the garnet

28

porphyroblasts; (2) the metamorphic peak assemblage (M2) are the garnet

29

porphyroblasts and minerals in the matrix (biotite + orthopyroxene + plagioclase +

30

quartz +

31

metamorphic mineral assemblages (M3) are represented by the symplectic

32

assemblages around the garnet porphyroblasts, resulted from decomposition reactions

33

between garnet rims and neighboring minerals in the matrix. Calculated by both

34

conventional thermobarometry and pseudosection modeling in the NCKFMASHT

35

system using the Perple_X technique, the P–T conditions of these three metamorphic

36

stages are constrained to be of 4–5 kbar/520–530 °C for the M1 stage, 6.8–8.6

37

kbar/730–810 °C for the M2 stage and 4.1–6.4 kbar/570–740 °C for the M3 stage,

38

respectively. The derived clockwise P–T paths imply that the Mts. Huashan terrane

39

involved in the subduction and subsequent collision between the Eastern and Western

40

Blocks of the North China Craton (NCC) along the Palaeoproterozoic Tran-North

41

China Orogen (TNCO). High resolution SIMS U–Pb dating of metamorphic zircons

42

reveals the metamorphic ages of 1.85–1.82 Ga. Combined with geochronological data

K-feldspar + ilmenite + zircon + magnetite); and (3) the retrograde

2

43

from the literature, it is concluded that the tectonothermal evolution between the

44

Eastern and Western Blocks started as early as ~1.97 Ga and lasted as late as 1.80 Ga.

45

Furthermore, the eastern Taihua complex records older metamorphic ages and higher

46

peak metamorphic pressures than those of the western Taihua complex, possibly

47

suggesting an eastward subduction model for the TNCO.

48

Keywords: Pelitic

49

path; North China Craton.

granulites; Taihua metamorphic complex; Metamorphic P–T–t

50 51 52 53 54 55 56 57 58 59 60 61 62 63 64

3

65 66

1. Introduction

67

Extensive studies of metamorphic P–T paths on various metamorphic terranes

68

worldwide indicate that different P–T paths are generally closely related to specific

69

tectonic environments or geodynamic processes the terranes underwent (England and

70

Richardson, 1977; England and Thompson, 1984; Bohlen, 1987, 1991; Harley, 1989;

71

Lu, 1991; Spear, 1992; Brown, 1993, 2009; Zhao et al., 1998, 2000a). The

72

anticlockwise P–T paths, especially for those containing near-isobaric cooling (IBC)

73

segments, are usually suggested to be the products of magmatic intrusion and

74

underplating in the regional setting of continental magmatic arc, hot spot or

75

continental rift (Sandiford and Powell, 1986; Bohlen, 1987, 1991; Harley, 1989; Lu,

76

1991; Zhao et al., 1998, 2000a). The clockwise P–T paths, especially for those

77

containing nearly isothermal decompression (ITD) segments, are generally interpreted

78

to be the results of subduction to continental collision followed by rapid uplift or

79

exhumation (England and Thompson, 1984; Bohlen, 1991; Lu, 1991; Brown, 1993;

80

Zhao et al., 2000a). To derive metamorphic P–T conditions and metamorphic P–T

81

paths, there are two general ways, i.e., thermobarometry and thermodynamic

82

pseudosection modeling. Thermobarometry is a conventional method and is based on

83

thermodynamic equilibrium preserved in the mineral assemblages. Thermodynamic

84

pseudosection modeling (e.g., Powell and Holland, 2008) is a forward calculation

85

method in determining the mineral assemblages, mineral modes and chemical

4

86

compositions of the minerals involved at different P–T conditions, based on the

87

assumption of closed chemical system during the metamorphic process.

88

A number of investigations on the metamorphic P–T paths and geochronology

89

of the metamorphic terranes distributed within the Palaeoproterozoic Trans-North

90

China Orogen (TNCO) (Zhao et al., 1998, 2000a, 2001a, 2005, 2012) have been

91

carried out in the last two decades (e.g., Zhai et al., 1993; Mei, 1994; Liu, 1996, 1997;

92

Guo et al., 1998, 2002, 2005; Wang et al., 1991; Zhao et al., 1999, 2000b, 2001b,

93

2002, 2007, 2010b; Liu et al., 2004, 2006, 2007; Kröner et al., 2005, 2006; O’Brien et

94

al., 2005; Faure et al., 2007; Trap et al., 2007, 2008, 2009a; Xiao et al., 2011; Lu et al.,

95

2013, 2014; Qian et al., 2013, 2015, 2016; Wang et al., 2014; Chen et al., 2015). Most

96

of these metamorphic terranes recorded clockwise P–T paths involving nearly ITD

97

segments, which were generally interpreted as the results of the subduction and

98

collision between the Eastern Block and the Western Block along the N–S-striking

99

TNCO at ~1.85 Ga (Fig. 1a) (Zhao et al., 1998, 2005, 2012).

100

The Taihua metamorphic complex, exposing in the southernmost margin of the

101

TNCO, experienced high-amphibolite- to granulite-facies metamorphism (Kang et al.,

102

1988; Qi, 1991, 1992; Chen et al., 1997; Zhou et al., 1997, 1998; Wang et al., 2014)

103

and provides a perfect window to explore the tectonothermal evolution of the TNCO.

104

Researches on metamorphism were carried out on amphibolites from the Taihua

105

complex (Jiang et al., 2011; Lu et al., 2013, 2014; Wang et al., 2014; Chen et al.,

106

2015), however, no metamorphic evolution of pelitic granulite has been studied by

107

now, which restricts our whole understanding on the tectonothermal evolution of the

5

108

southern margin of the TNCO in the Paleoproterozoic. This is because pelitic graulites

109

are usually deemed as markers for recognizing Precambrian subduction/collision belts,

110

on account of that the sedimentary protoliths of pelitic granulites could only be

111

brought down to the middle/lower crustal levels and experienced granulite-facies

112

metamorphism by subduction/collison process (Zhao and Zhai, 2013). In this paper,

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we present detailed petrology, mineral chemistry and P–T conditions of

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metamorphism estimated by both conventional thermobarometry and pseudosection

115

modeling for the pelitic granulites, collected from the Taihua Group in the Mts.

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Huashan terrane, and reconstruct the P–T paths of these rocks to reveal the

117

tectonothermal history of the southernmost terminal of the TNCO in the

118

Paleoproterozoic.

119

2. Regional setting

120

The Taihua metamorphic complex, termed as the Taihua Group in the traditional

121

Chinese literature, is located in the southernmost margin of the TNCO. It is mainly

122

consisting of the Mts. Huashan terrane in the northwest, the Xiaoshan and Luoning

123

terranes in the middle and the Lushan and Wugang terranes in the southeast. In the

124

last few years, some studies were carried out on the geochronology and metamorphic

125

evolution of these terranes (e.g. Wan et al., 2006；Liu et al., 2009; Diwu et al., 2010,

126

2014; Huang et al., 2010, 2012, 2013; Lu et al., 2013, 2014; Wang et al., 2012, 2013,

127

2014; Chen et al., 2015). In the Luoning terrane, Jiang et al. (2011) and Chen et al.

128

(2015) proposed that the amphibolites, whose protolith age was 2.34–2.30 Ga,

129

recorded clockwise P–T paths containing isothermal decompression (ITD) segments,

6

130

and the metamorphism occurred during 1.97–1.94 Ga according to SIMS and

131

LA-ICP-MS U–Pb dating of metamorphic zircons. Additionally, Huang et al. (2012)

132

reported two magmatic events (2.32–2.30 Ga and 2.19–2.07 Ga) of the TTG gneisses

133

in this area. Chen et al. (2016) further found that four episodes of crustal growth and /

134

or reworking in this region have occurred at 2.85–2.72 Ga, 2.54–2.48 Ga, 2.35–2.30

135

Ga and 2.2–2.0 Ga, respectively, possibly to connect with the subduction–collision

136

between the Eastern and Western Blocks along the TNCO. In the Lushan and Wugang

137

terranes, the protolith ages of the TTG gneisses and amphibolites were recognized as

138

2.85–2.72 Ga (Liu et al., 2009; Diwu et al., 2010; Huang et al., 2010) followed by a

139

metamorphic age of 1.87–1.84 Ga (Wan et al., 2006；Yang，2008). Based on detailed

140

studies on the amphibolites from both blocks, Lu et al. (2013, 2014) proposed that

141

both of the Lushan and the Wugang terranes recorded clockwise P–T paths including

142

ITD segments and the upper amphibolite facies metamorphism occurred at ca.

143

1.95–1.86 Ga and 1.96–1.92 Ga, respectively.

144

Exposed on the northern and southern slopes of the Mts. Huashan in the

145

Shan’anxi and Henan Provinces (Fig. 1b), the Huashan metamorphic complex has

146

attracted many attentions in recent years. In summary, based on U–Pb dating of

147

zircons and

148

three obvious episodes of magmatism (~2.5 Ga, ~2.3 Ga and 1.87–1.80 Ga) and one

149

episode of metamorphism (1.80–1.96 Ga) were identified in this region (Wang et al.,

150

2012, 2013, 2014, 2016; Huang et al., 2013; Yu et al., 2013). Our previous studies on

151

petrology, mineral chemistry, geochronology and metamorphic P–T paths of the

40

Ar/39Ar dating of amphiboles from the Huashan metamorphic complex,

7

152

amphibolites from this region indicate that the Mts. Huashan metamorphic complex

153

experienced

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Paleoproterozoic. Clockwise P–T paths involving ITD segments were retrieved from

155

these amphibolites (Wang et al., 2014), which probably imply that the

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Paleoproterozoic collision occurred between the Eastern and Western Blocks of the

157

NCC along the TNCO.

high-amphibolite

to

granulite

facies

metamorphism

in

the

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The garnet-bearing pelitic granulites were not found at the outcrop but were

159

collected from the mining sites, which were confirmed to belonging to the Taihua

160

complex by field observation. Sampling locations of these samples are shown in

161

Fig.1b. Petrography and metamorphic researches were performed on three

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representative garnet-bearing pelitic granulite samples (S18, S25 and S37), and U–Pb

163

dating of metamorphic zircons were carried out on two samples (S7 and S18).

164

3. Petrography and metamorphic stages

165

Most of the pelitic granulites show retrograde “white-eye socket” texture (Fig.

166

2), which was originally named by Ma and Wang (1994) in mafic granulites to

167

explain the retrograde symplectic assemblages surrounding garnet porphyroblasts. On

168

the basis of micropetrographic observation, three stages of metamorphic mineral

169

assemblages were recognized in these granulites, designated as the prograde mineral

170

assemblages (M1), the peak mineral assemblages (M2) and the retrograde mineral

171

assemblages (M3), respectively. Detailed microstructures and reaction relationships

172

are described below. The symbols of minerals used in this study are after Whitney and

173

Evans (2010).

8

174

3.1 The prograde mineral assemblages (M1)

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The prograde metamorphic mineral assemblages (M1) are preserved as mineral

176

inclusions within the garnet porphyroblasts (Fig. 2a–d), which are mainly composed

177

of biotite (Bt1) + plagioclase (Pl1) + quartz (Qz1) ± ilmenite (Ilm1). These

178

inclusion-type minerals are distributed randomly within the garnets, representing the

179

remnants of the prograde assemblages. It is noted that some inclusion-like minerals

180

distributed along the fractures within the garnets are not actually inclusion minerals,

181

but were formed within the garnet interiors during the retrograde metamorphic stage.

182

Only the inclusion minerals not cut by late fractures within the garnets and showing

183

no Fe–Mg re-exchange features with the surrounding garnet interiors are ascribed to

184

the prograde stage.

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3.2 The metamorphic peak assemblages (M2)

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The metamorphic peak mineral assemblages (M2) are represented by the

187

coarse-grained garnet porphyroblasts (Grt2) and matrix minerals biotite (Bt2),

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orthopyroxene (Opx2), plagioclase (Pl2), quartz (Qz2), with minor K-feldspar (Kfs2),

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ilmenite (Ilm2), zircon (Zr2) and magnetite (Mag2) (Fig. 2a–d). The straight contacts

190

and nearly homogeneous chemical compositions, described below, of these minerals

191

suggest that thermodynamic equilibrium had been approached during the

192

metamorphic peak stage. It is inferred that the metamorphic peak assemblages (M2)

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were formed from the prograde assemblages (M1) possibly by the following reaction:

194 195

Bt1 + Pl1 ± Ilm1 → Grt2 +Bt2 + Opx2 + Pl2 + Kfs2 ± Mag2 ± Ilm2 (M1)

(M2) 9

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3.3 The retrograde mineral assemblages (M3)

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The retrograde metamorphic assemblages are characterized by the formation of

198

symplectic assemblages around the garnet porphyroblasts, resulted from the

199

decomposition reactions between the garnet rims and the neighboring minerals in the

200

matrix. Such kind of reaction textures, nicknamed as “white-eye socket” texture,

201

represent typical decompression and decomposition reactions in mafic granulites and

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amphibolites within the Trans-North China Orogen (e.g., Wang et al., 1991; Liu, 1996;

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Guo et al., 1998, 2002; Zhao et al., 2000b, 2001b, 2010a; O’Brien et al., 2005; Xiao et

204

al., 2011; Lu et al., 2013, 2014; Wang et al., 2014; Chen et al., 2015). The symplectic

205

mineral assemblages are mainly comprised of biotite (Bt3) + plagioclase (Pl3) + quartz

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(Qz3) ± orthopyroxene (Opx3) around the embayed garnet porphyroblasts (Fig. 2a–d),

207

suggesting the following possible reaction:

208 209 210

Grt2 (rim) + Bt2 + Pl2 → Grt3 + Bt3 + Pl3 ± Opx3 (M2)

(M3)

4. Mineral chemistry

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X-ray compositional mapping of the garnets (Fig. 3) as well as mineral chemical

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compositions of the pelitic granulite samples S18, S25 and S37 were analyzed using

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the JOEL JXA 8230 electron microprobe equipped at the School of Resources and

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Environment Engineering, Hefei University of Technology, China. The analytical

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conditions were 15 kV accelerating voltage, a beam current of 20 nA with an electron

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beam size of 5 µm and 10–20 s counting time. Natural and synthetic minerals were

217

used as standards, and the program ZAF was used for matrix correction. For each kind 10

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of mineral of any generation, at least three grains were analyzed and at least three spot

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analyses were performed for each grain. Representative mean chemical compositions

220

of the minerals are presented in Tables 1–4. The detailed compositional features of the

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minerals are described below.

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4.1. Garnet

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The bell-shaped XMn and Fe# [=Fe/(Fe+Mg)] zoning profiles of the garnet in

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metapelites were interpreted as typical prograde growth zonation of metapelitic garnet

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(Spear et al., 1990; Spear and Florence, 1992). Sometimes the bell-shaped profiles

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could hardly be preserved in high-grade metamorphic rocks, if Fe-Mg re-exchange

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occurred during slow cooling after the metamorphic peak, led to increase of Fe# value

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in the garnet rim (Spear and Florence, 1992). Simultaneous increasing of the Fe# and

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XMn values of the garnet rim suggests that the garnet rim experienced net transfer and

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Fe-Mg re-exchange reactions, lead to formation of the symplectite (Kohn and Spear,

231

2000). The X-ray mapping analyses (Fig. 3a–c) of the garnet porphyroblasts show

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homogeneous features with no or weak prograde profiles from the core to the mantle

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domains and weak Fe-Mg re-exchange in the outer rims, which suggest that

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thermodynamic equilibrium had possibly been achieved within the peak mineral

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assemblages at the metamorphic peak stage and re-equilibrium occurred during the

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retrograde stage. All the garnets are dominated by almandine (XAlm = 0.53–0.68),

237

pyrope (XPyr = 0.25–0.42) with minor grossular (XGrs = 0.01–0.11) and spessartine

238

(XSps = 0.02) components (Table 1). Consistent with the X-ray mapping analyses, the

239

rim-core-rim analytical chemical profiles of these garnets (Fig. 4a–c) also show no or

11

240

weak compositional zonation from the core to the mantle domains. Slight increases of

241

XAlm (from 0.53–0.63 to 0.60–0.68), Fe# (from 0.57–0.69 to 0.66–0.74) and a weak

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increase of XGrs (from 0.02–0.11 to 0.01–0.08) were observed towards the rims (Fig.

243

4a–c), indicating re-equilibrium occurred during the retrograde metamorphic stage.

244

No obvious increase of spessartine component corresponding to the breakdown of

245

garnet rims (Kohn and Spear, 2000) was observed, probably because of their low

246

spessartine contents (XSps = 0.02).

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4.2. Orthopyroxene

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Orthopyroxene is subhedral or anhedral, with variable grain size in the matrix

249

(Opx2) or occurs as intergrowth mineral with the matrix biotite. Symplectic

250

orthopyroxene (Opx3) is only observed in sample S25. The matrix orthopyroxene

251

(Opx2) is richer in FeO (24.47–29.20 wt%) and poorer in MgO (17.44–20.41 wt%)

252

components with XMg [=Mg/(Fe+Mg)] values varying between 0.52–0.61. The

253

symplectic orthopyroxene (Opx3) has lower FeO (23.09 wt%) and higher MgO (21.15

254

wt%) contents with XMg = 0.63 (Table 2).

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4.3. Biotite

256

Three textural types of biotite were analyzed in the pelitic granulites: the

257

inclusion-type biotite (Bt1) within the garnet porphyroblast, matrix-type biotite (Bt2)

258

intergrown with orthopyroxene in the matrix and retrograde biotite (Bt3) intergrown

259

with plagioclase and quartz in the symplectite. These three types of biotite display

260

slight differences in FeO and TiO2 components (Table 3). The Bt1 has FeO contents of

261

10.00–17.88 wt% and TiO2 contents of 2.03–4.41 wt%. In samples S18 and S37, the

12

262

Bt2 have lower FeO contents (14.46–17.39 wt%) and higher TiO2 contents (3.76–4.43

263

wt%) than those of Bt1. In sample S25, the Bt2 has higher FeO contents (13.80 wt%)

264

and lower TiO2 contents (4.09 wt%) than those of Bt1. In all these samples, the Bt3 is

265

richer in FeO (15.35–17.85 wt%) and poorer in TiO2 (3.47–4.46 wt%) contents than

266

those of the Bt2.

267

4.4. Plagioclase

268

Representative chemical compositions of three types of plagioclase are

269

summarized in Table 4: the inclusion-type plagioclase (Pl1) within the garnet

270

porphyroblast, plagioclase in the matrix (Pl2) and retrograde plagioclase (Pl3) formed

271

coeval to symplectic biotite and quartz. Most of the plagioclase grains are chemically

272

homogeneous, but chemical diversities exist for different plagioclase crystals either

273

among different samples or in the different assemblages formed at different

274

metamorphic stages within one sample.

275

In sample S18, the Pl2 and Pl3 contain similar anorthite contents (An = 29), but

276

lower than that of the Pl1 (An = 36). In sample S25, the anorthite contents in Pl1 (An =

277

16) and Pl2 (An = 16) are slightly lower than the Pl3 (An = 17). In sample S37, the

278

anorthite content increases from the Pl1 (An = 34) to the Pl2 (An = 55). The Pl3 has the

279

highest anorthite content (An = 58). The increases of anorthite contents from Pl2 to Pl3

280

in S25 and S37 suggest that the breakdown of garnet rims supplied additional CaO

281

content to the newly formed Pl3 during the retrograde stage.

282

5. Metamorphic P–T conditions

283

5.1. Geothermobarometry 13

284

Present available geothermometers and geobarometers were employed to

285

determine the P–T conditions of the Huashan pelitic granulites. However, there are no

286

suitable geobarometers for the prograde mineral assemblages (Bt1 + Pl1 + Qz1 ± Ilm1).

287

The Ti-in-biotite geothermometer for TiO2-saturated metapelites proposed by Wu and

288

Chen (2015) is appropriate with a random error of ca. ±65 °C. However, only

289

inclusion-type biotite (Bt1) in S37 contains suitable XTi (0.11), which is located in the

290

compositional limits of biotite (XTi = 0.02–0.14) for this geothemometer. A

291

temperature of 520–530 °C was determined by this geothemometer at a given pressure

292

of 4–6 kbar. The metamorphic peak and retrograde P–T conditions of these pelitic

293

granulites were determined by applying the garnet–biotite (GB) geothermometer

294

(Holdaway, 2000) combined with the garnet–biotite–plagioclase–quartz (GBPQ)

295

geobarometer (Wu et al., 2004) and the garnet–orthopyroxene–plagioclase–quartz

296

(GOPQ) geothermobarometer (Lal et al., 1993). It is noteworthy that Fe-Mg

297

re-exchanging during cooling after the metamorphic peak might occur between the

298

matrix-type ferromagnesian minerals, especially for the contacting biotite,

299

orthopyroxene and garnet. Therefore, the compositions of isolated garnet, biotite and

300

orthopyroxene were employed to calculate the peak P–T conditions. It is noted that

301

although retrograde zonings were observed on the garnet rims, thermodynamic

302

equilibrium might not have been achieved between the garnet rims and the symplectic

303

minerals (Wu et al., 2014). Therefore, accuracy of the retrograde P–T conditions

304

obtained here need to be used with caution.

305

The computed P–T conditions of the three metamorphic stages of the pelitic

14

306

granulites are listed in Table 5.

307

5.1.1 Sample S18

308

The metamorphic peak (M2) P–T conditions were estimated to be 7.2

309

kbar/730 °C by the GB geothermometer coupled with the GBPQ geobarometer.

310

Similar peak (M2) P–T conditions of 6.8 kbar/760 °C were obtained by the GOPQ

311

geothermobarometers. The retrograde assemblages (M3) recorded P–T conditions of

312

5.1 kbar/680 °C determined by GB geothermometer coupled with the GBPQ

313

geobarometer. Therefore, a clockwise P–T path was retrieved (Fig. 5a).

314

5.1.2 Sample S25

315

The M2 P–T conditions of this sample were determined to be 7.0 kbar/730 °C by

316

GB geothermometer combined with GBPQ geobarometer or 6.8 kbar/760 °C obtained

317

by the GOPQ geothermobarometers, respectively. The M3 assemblages recorded P–T

318

conditions of 4.2 kbar/680 °C determined by the GB geothermometer coupled with

319

the

320

geothermobarometers, respectively. Although the grossularite content of garnet (Xgrs

321

= 1–2%) and anorthite content of plagioclase (An = 16–17) in these two metamorphic

322

stages were lower than the recommended lower limits (Xgrs > 3%, An > 17) for the

323

GBPQ geobarometer as given in Wu et al. (2004), it still gave similar results

324

compared with the results obtained by the GOPQ geothermobarometers. Therefore, a

325

clockwise P–T path was also reconstructed (Fig. 5b).

326

5.1.3 Sample S37

327

GBPQ

geobarometer

or

4.1

kbar/570

°C

obtained

by the

GOPQ

The M2 P–T conditions were calculated as 8.6 kbar/740 °C by the GB

15

328

geothermometer coupled with the GBPQ geobarometer or 7.3 kbar/810 °C by the

329

GOPQ geothermobarometers. The M3 P–T conditions were estimated as 6.4

330

kbar/740 °C by the GB geothermometer in concert with the GBPQ geobarometer. A

331

clockwise P–T path was also reconstructed (Fig. 5c).

332

5.2. Pseudosection modeling

333

Sometimes people may make mistakes in distinguishing different mineral

334

assemblages formed at different metamorphic stages in medium to high grade

335

metamorphic rocks (e.g., Nicollet and Goncalves, 2005; Vernon et al., 2008), which

336

may result in wrong conclusions for the regional tectonic evolution. In addition,

337

thermodynamic equilibrium might not have been achieved between the garnet rims

338

and the symplectic minerals (Wu et al., 2014). To confirm the P–T conditions

339

obtained by conventional geothermobarometers, we performed a P–T pseudosection

340

on sample S18 with the Perple_X computer program (Connolly, 2005).

341

5.2.1 P–T pseudosection modeling

342

The P–T pseudosection was calculated with the Perple_X computer program

343

package (Connolly, 2005; Version of 6.68) using the internally consistent

344

thermodynamic dataset of Holland and Powell (1998, updated 2002). The bulk-rock

345

composition of the chosen sample was analyzed by X-ray fluorescence spectrometry

346

(XRF) at the Institute of Geology and Geophysics, Chinese Academy of Sciences,

347

Beijing. The above studies on petrography and mineral chemistry suggest that the

348

amounts of Mn and Fe3+ cations in the minerals are negligible; therefore the MnO and

349

Fe2O3 contents were ignored in the pseudosection calculation. On the contrary, the

16

350

noticeable Ti amount in biotite demonstrates that the TiO2 amount in bulk-rock

351

composition could affect the stable region of biotite in pseudosection constructions in

352

metapelite (Peterson et al., 1991; Dooley et al., 1996). So the P–T pseudosection was

353

calculated

354

(NCKFMASHT) system. Apatite is present in this sample, which contains most of the

355

P2O5 contents in the bulk-rock composition. So we deducted the CaO content,

356

constituent of apatite, from the bulk-rock composition according to the standard

357

molecular formula of apatite (Ca: P = 5:3, in mol). As we know, there is a great

358

variety in the FeO/Fe2O3 ratio among metapelites. Due to the high Fe3+ contents in the

359

garnet porphyroblast and the presence of magnetite in the matrix mineral assemblages,

360

83% of total Fe2O3 (Fe2O3T) is assumed to be the FeO, which means a reasonable high

361

Fe2O3 content of total Fe2O3 content of the rock. Besides, the loss on ignition (LOI)

362

was employed as the H2O content. With these reasonable assumptions, the final

363

effective bulk-rock composition of the sample (in wt%) is as follows: SiO2 = 52.64,

364

TiO2 = 0.85, Al2O3 = 17.69, FeO = 9.93, MgO = 5.87, CaO = 3.15, Na2O = 3.94, K2O

365

= 2.38 and H2O = 0.56.

in

the

Na2O–CaO–K2O–FeO–MgO–Al2O3–SiO2–H2O–TiO2

366

The minerals involved in the pseudosection construction include: garnet (Grt),

367

plagioclase (Pl), orthopyroxene (Opx), biotite (Bt), cordierite (Crd), K-feldspar (Kfs),

368

ilmenite

369

activity-composition (a-X) models used in the pseudosection calculation are those of

370

garnet (White et al., 2007), plagioclase (Newton et al., 1980), orthopyroxene (Holland

371

and Powell, 1998), biotite (Tajcmanová et al., 2009), cordierite (Holland and Powell,

(Ilm),

rutile

(Rt),

quartz

(Qz)

17

and

silicate

melt

(Liq).

The

372

1998), K-feldspar (Waldbaum and Thompson, 1968), ilmenite (White et al., 2000)

373

and melt (White et al., 2007). Rutile and quartz are essentially pure end-member

374

phases.

375

5.2.2 P–T pseudosection

376

The P–T pseudosection computed in the P–T range of 2–10 kbar/500–1000 °C in

377

the NCKFMASHT system for the pelitic granulite (S18) is shown in Fig. 6. Biotite,

378

orthopyroxene, plagioclase and K-feldspar are stable and are present in most of the

379

pseudosection regions. Garnet is a stable phase in high pressure fields with the

380

garnet-in line starting from 3 kbar/500 °C to 8.5 kbar/1000 °C. Quartz appears in most

381

fields with the quartz-out line vertically lying from 800 °C at 2 kbar to 920 °C at 10

382

kbar. Cordierite is stable only in low pressure fields (<4 kbar), and rutile is stable in

383

high pressure and low temperature fields (P>7 kbar, T<560 °C). The solidus curve

384

vertically lies from 790 °C at 2 kbar to 890 °C at 10 kbar, which is consistent with no

385

partial melting in this rock (i.e., it was a closed system).

386

It’s also difficult to estimate the prograde P–T conditions in the pseudosection

387

because no prograde chemical profiles were preserved in garnet porphyroblasts.

388

However, there must be a prograde stage for metapelite because the mud was brought

389

down to the middle/lower crustal levels and experienced granulite-facies

390

metamorphism.

391

The homogeneous chemical composition of the garnet porphyroblast from the

392

core to the mantle in sample S18, formed during the metamorphic peak stage, was

393

normalized as XAlm = 0.65, XPyr = 0.29 and Xgrs = 0.06 after removing the XSps

18

394

content. The isopleths of XAlm (ranging from 0.65 to 0.70), XPyr (ranging from 0.25 to

395

0.29) and Xgrs (ranging from 0.05 to 0.06) in garnet were shown in the P–T

396

pseudosection (Fig. 6). The P–T conditions of the metamorphic peak was constrained

397

as 7.8 kbar/810 °C by pseudosection, which is a little higher than the results of

398

6.8–7.2 kbar/730–760 °C estimated by conventional geothermobarometers. This is

399

probably due to the effect of Fe-Mg diffusion between ferromagnesian minerals after

400

the metamorphic peak stage, although the compositions of isolated garnet, biotite and

401

orthopyroxene were employed to calculate the peak P–T conditions. The

402

corresponding peak mineral assemblage is Opx + Grt + Pl + Bt + Kfs + Qz, which

403

agrees with the peak mineral assemblage we observed under microscope. Therefore, a

404

prograde reaction (dashed line in Fig. 6) from Opx + Grt + Pl + Bt + Kfs + Ilm + Qz

405

(M1) to Opx + Grt + Pl + Bt + Kfs + Qz (M2) was inferred. No Opx and Kfs were

406

observed in the inclusion-type mineral assemblages (M1, Bt + Pl + Ilm + Qz) in this

407

sample, probably suggests that no Opx and Kfs survived as inclusions in the garnet

408

during the prograde stage.

409

Analogously, composition of the garnet rim was normalized as XAlm = 0.70, XPyr

410

= 0.25 and Xgrs = 0.05 according to EPMA data. The corresponding isopleths

411

constrain the retrograde (M3) P–T conditions to be 5.0 kbar/630 °C (Fig. 6), which

412

was also similar to those (5.0 kbar/680 °C) estimated by conventional

413

geothermobarometers. So a clockwise P–T path was also obtained for the pelitic

414

granulite in the P–T pseudosection modeling.

415

5.3. Metamorphic P–T paths 19

416

The metamorphic P–T conditions of the M1, M2 and M3 assemblages were

417

estimated by both conventional geothermobarometers and P–T pseudosection

418

modeling. The prograde (M1) metamorphic P–T conditions were proposed as

419

520–530 °C/4–6 kbar (assumed). The metamorphic peak (M2) P–T conditions were

420

determined as 6.8–8.6 kbar/730–810 °C, belonging to the transition zone of high

421

amphibolite to granulite facies and intermediate P/T metamorphic facies series

422

(Miyashiro, 1961; Spear, 1993, pp. 15–22). The retrograde (M3) P–T conditions were

423

estimated as 4.1–6.4 kbar/570–740 °C. Therefore, clockwise P–T paths were

424

constructed for these pelitic granulite samples.

425

6. Geochronology

426

6.1. Analytical methods

427

Zircon grains collected from Samples S7 and S18 were mounted in epoxy

428

mounts with zircon standard Plešovice (Sláma et al., 2008) and Qinghu (Li et al.,

429

2009), which were then polished to section the crystals in half for analyses. All the

430

zircons were taken micrographs of reflected and transmitted light as well as

431

cathodoluminescence (CL) images to reveal their internal structures. The mount was

432

then vacuum-coated with high-purity gold prior to secondary ion mass spectrometry

433

(SIMS) analysis. Analyses of U, Th and Pb were performed using the Cameca

434

IMS-1280 SIMS mass spectrometer equipped at the Institute of Geology and

435

Geophysics, Chinese Academy of Sciences, Beijing. Detailed analytical procedures

436

were described by Li et al. (2009). The analytical spot was an ellipsoid with size of

437

about 30µm×20µm. Non-radiogenic 204Pb was used to correct measured compositions

20

438

for common Pb. The average of present-day crustal composition (Stacey and Kramers,

439

1975) was used for the common Pb assuming that the common Pb is largely surface

440

contamination introduced during the preparation of samples. The analytical results are

441

listed in Table 6. The uncertainties on individual analyses are reported at the 1σ level

442

and the mean ages for U/Pb (Pb/Pb) analyses are quoted with the 95% confidence

443

interval. Data reduction was carried out using the Isoplot/Ex v. 3.75 program (Ludwig,

444

2003).

445

6.2. Analytical results

446

Zircon grains from sample S7 are stubby columnar and round in shape and about

447

100–200 µm in length. Most of the zircons show homogeneous texture with low

448

luminescence in cathodoluminescence (CL) images (Fig. 7a) displaying features of

449

possible metamorphic origin. Some round grains show cores with weak magmatic

450

rhythmic textures, which are considered as detrital zircons. Twenty-eight U–Pb spot

451

analyses were obtained from 22 zircon grains. The U and Th contents and the U/Th

452

ratios of the 23 valid analytical spots performed on the metamorphic zircon grains are

453

in the range of 149–3003 ppm, 5–195 ppm and 0.02–0.1, respectively. All these

454

analytical spots are distributed on or close to the concordia and yield an upper

455

intercept age of 1824±13 Ma, which is considered as the age of metamorphism, with a

456

similar weighted mean 207Pb/206Pb age of 1846±6 Ma (Fig. 8a). The rest spot analyses

457

performed on the detrital zircons are distributed on or close to the concordia, and the

458

207

459

of the detrital zircons.

Pb/206Pb ages range from 2001 Ma to 2255 Ma, interpreted to be the formation age

21

460

In sample S18, zircon grains are also stubby columnar and round in shape and

461

about 100–200 µm in length. Some zircons show homogeneous texture with low

462

luminescence in cathodoluminescence (CL) images (Fig. 7b) implying possible origin

463

of metamorphism. Some zircons show core-rim structures in CL images (Fig. 7b). The

464

cores display oscillatory zonings, indicative of magmatic origin. Around the cores are

465

homogeneous rims with higher luminescence, indicative of possible metamorphic

466

origin. Twenty-three spot analyses were conducted on twenty zircon grains. The U,

467

Th contents and the Th/U ratios of the fourteen valid analytical spots on the zircon

468

rims or metamorphic grains are in the range of 13–124 ppm, 5–19 ppm and 0.08–0.36,

469

respectively. All of these analytical spots define a linear array on the concordia

470

diagram and yield an upper intercept age of 1818±22 Ma, possibly reflecting the age

471

of the metamorphic event, with a similar weighted mean

472

Ma (Fig. 8b). The rest eight valid spots analyzed on the magmatic cores also define a

473

linear array on the concordia diagram, yielding an upper intercept age of 2547±47 Ma,

474

possibly reflecting an age of one magmatic event; and a lower intercept age of

475

1792±310 Ma, which is close to the age of metamorphism (Fig. 8b).

476

7. Discussion

207

Pb/206Pb age of 1823±8

477

The North China Craton (NCC) is one of the oldest and largest cratons in the

478

world (as old as ~3.8 Ga; Liu et al., 1992) with widespread Archean to

479

Paleoproterozoic basement, albeit whose Precambrian crustal history is hotly debated.

480

A number of tectonic subdivision models have been proposed for the formation and

481

evolution of the basement of the NCC (eg., Wu et al., 1998; Zhao et al., 1998, 2000a,

22

482

2001a, 2005, 2012; Zhai et al., 2000, 2005, 2010; Kusky and Li, 2003; Santosh et al.,

483

2006; Faure et al., 2007; Trap et al., 2007, 2012; Zhai and Peng, 2007; Santosh, 2010;

484

Kusky, 2011; Zhai and Santosh, 2011; Peng et al., 2014). A broad consensus among

485

these diverse models is that there is a S–N-trending Paleoproterozoic tectonic belt in

486

the central part of the NCC, named either the Trans-North China Orogen (TNCO;

487

Zhao et al., 2001a, 2005), or the Central Orogenic Belt (Kusky and Li, 2003; Santosh,

488

2010; Kusky, 2011) or the Jinyu Orogenic Belt (Zhai and Peng, 2007) or the Fuping

489

Block (Faure et al., 2007; Trap et al., 2007, 2012), although there still remains

490

controversial about the boundaries of these belts. Another familiar debate focuses on

491

the formation timing of these belts, which were involved in the final amalgamation of

492

the NCC. For example, some researches believe that the final amalgamation of the

493

NCC occurred at ~1.85 Ga by continent-continent collision along the TNCO between

494

the Eastern and Western Blocks (e.g., Zhao et al., 1998, 2000a, 2012; Guo et al., 2005;

495

Kröner et al., 2005), whereas others argue that the collision between the Eastern and

496

Western Blocks occurred at ~2.5 Ga along the Central Orogenic Belt (Kusky and Li,

497

2003; Kusky, 2011). Moreover, some other different models are also presented (e.g.,

498

Faure et al., 2007; Trap et al., 2007, 2012; Zhai and Peng, 2007; Santosh, 2010; Zhai

499

et al., 2010). In the last two decades, from the north to the south, numerous

500

investigations have revealed that the metamorphic complexes in the TNCO all record

501

clockwise P–T paths with retrograde isothermal decompression (ITD) process, such as

502

the Huai’an complex (Zhai et al., 1993; Liu, 1997; Guo et al., 1998, 2002, 2005; Zhao

503

et al., 2008), the Hengshan complex (Wang et al., 1991; Guo et al., 1999; Zhao et al.,

23

504

2001b; Qian et al., 2015, 2016), the Wutai complex (Wang et al., 1996; Zhao et al.,

505

1999; Yu et al., 2001; Qian et al., 2013, 2016), the Fuping complex (Liu, 1996; Zhao

506

et al., 2000b), the Lüliang complex (Trap et al., 2009b; Zhao et al., 2010b), the

507

Zanhuang complex (Xiao et al., 2011), the Zuoquan complex (Xiao et al., 2014) and

508

the Taihua complex (Jiang et al., 2011; Lu et al., 2013, 2014; Wang et al., 2014; Chen

509

et al., 2015), which make it much more clear that the whole TNCO was involved in

510

the subduction- and collision- related processes during the amalgamation of the

511

Eastern and Western Blocks in the Paleoproterozoic, as suggested by Zhao et al.

512

(2001, 2005, 2012).

513

In this paper, it is found that the pelitic granulite from the Huashan complex

514

underwent similar tectonothermal processes. Clockwise P–T paths were reconstructed

515

for these pelitic granulite samples, also imply initial crustal thickening followed by

516

possible rapid exhumation. This is consistent with a subduction and then

517

continent-continent collision environment (England and Thompson, 1984; Bohlen,

518

1991; Lu, 1991). Fortunately, garnet-bearing amphibolites widely distribute in the

519

Taihua metamorphic complex, which record clockwise P–T paths with ITD segments,

520

indicating an initial crustal thickening followed by rapid exhumation/uplift.

521

Metamorphic evolution of the intercalated metapelitic granulites and amphibolites of

522

the Taihua complex, all suggest that the southern segment of the TNCO was also

523

involved in the amalgamation of the Eastern and Western Blocks in the

524

Paleoproterozoic.

24

525

It is widely accepted that the final amalgamation of the Eastern and Western

526

Blocks occurred at ~1.85 Ga (Zhao et al., 1998, 2000a, 2005), which was

527

demonstrated by the metamorphic ages obtained from the northern and middle

528

segments of the TNCO (e.g., Mao et al., 1999; Guo and Zhai, 2001; Zhao et al., 2002,

529

2008a,b, 2010a,b; Liu et al., 2004, 2007; Guo et al., 2005; Kröner et al., 2005, 2006;

530

Faure et al., 2007; Trap et al., 2007, 2008, 2012; Xiao et al., 2011, 2013). In recent

531

years, more and more older metamorphic ages were found from the metamorphic

532

complexes in the whole TNCO, such as 1.97–1.92 Ga from the Taihua complex (Jiang

533

et al., 2011; Wang et al., 2012, 2013, 2014; Lu et al., 2013, 2014, 2015; Diwu et al.,

534

2014; Chen et al., 2015), 1.95–1.91 Ga from the Lüliang complex (Liu et al., 2006;

535

Trap et al., 2009b), ~1.95 Ga from the Wutai complex (Qian et al., 2013), 1.96 Ga and

536

1.92 Ga from the Hengshan complex (Qian et al., 2015, 2016) and 1.95 Ga from the

537

Chengde complex (Qu et al., 2012). The widespread metamorphic ages of 1.97–1.80

538

Ga in the whole TNCO possibly indicate that the tectonothermal evolution of the

539

TNCO might be a long and complex process, which possibly started as early as ~1.97

540

Ga and lasted as late as 1.80 Ga (Chen et al., 2015).

541

Another controversy is about the polarity of the Neoarchean to Paleoproterozoic

542

subduction operated in the Tran-North China Orogen (Zhao and Zhai, 2013), mainly

543

including the eastward subduction model (Zhao et al., 2001a, 2005; Zhang et al., 2007,

544

2009, 2012) and the westward subduction model (e.g., Faure, et al., 2007; Trap et al.,

545

2007; Zhu and Zheng, 2009; Santosh, 2010; Wang et al., 2010; Kusky, 2011). The

546

metamorphic ages obtained from the Taihua complex was summarized in Table 7. We

25

547

can clearly conclude that the metamorphic ages of the Huashan complex in the west

548

(mostly≤1.90 Ga) are obviously younger than those of the Luoning, Lushan and

549

Wugang terranes in the east (mostly ≥1.90 Ga). This phenomenon possibly implies

550

that the tectonothermal event in the southern segment of the TNCO possibly started

551

from the east, and then extended to the west, which could be well explained by the

552

eastward-directed subduction model for the TNCO (Zhao et al., 2001a, 2005; Zhang

553

et al., 2007, 2009, 2012). Furthermore, the metamorphic P–T conditions of the

554

metamorphic peak show a gradually increasing trend in the pressure from the

555

Huashan terrane in the west (6.7–8.6 kbar/700–820 °C, Wang et al., 2014; this study)

556

to the Luoning, Lushan and Wugang terranes in the east (8.9–10.8 kbar/710–820 °C,

557

Lu et al., 2013, 2014; Chen et al., 2015). The existing of thermal relaxation in regions

558

where the crust is rapidly thickened (e.g., Richardson and England, 1979; England

559

and Thompson, 1984) tells us that the mineral reactions in metamorphic rocks are

560

more sensitive to the changes in pressure than in temperature. The obvious higher

561

pressure recorded in the east regions possibly implies a deeper subduction or more

562

degrees of crustal thickening occurred in the east, which also supports the

563

eastward-directed subduction model for the TNCO (Zhao et al., 2001a, 2005; Zhang

564

et al., 2007, 2009, 2012).

565

8. Conclusions

566

(1) Three generations of mineral assemblages have been identified in the pelitic

567

granulites from the Huashan terrane, Taihua metamorphic complex, southern

568

Trans-North China Orogen. Clockwise P–T paths were reconstructed by both

26

569

conventional thermobarometry and pseudosection modeling, which pass from 4–5

570

kbar/520–530 °C through 6.8–8.6 kbar/730–810 °C to 4.1–6.4 kbar/570–740 °C, and

571

suggest that the Huashan terrane was involved in the subduction/collision process

572

between the Eastern and Western Blocks along the Trans-North China Orogen.

573

(2) SIMS U–Pb dating of metamorphic zircons yielded metamorphic ages of

574

1823–1846 Ma. Combined with geochronological data from the literature, it is

575

concluded that the tectonothermal evolution of the Trans-North China Orogen could

576

be a long and complex process, which started as early as ~1.97 Ga and lasted as late

577

as 1.80 Ga.

578

(3) The older metamorphic ages and higher metamorphic peak pressures

579

preserved in the east region than those in the west of the Taihua complex suggest the

580

possible eastward-directed subduction model of the TNCO.

581 582

Acknowledgements

583

Professor Yong-Hong Shi and Miss Juan Wang are specially thanked for helping

584

the authors in electronic microprobe analyses. Xin Zhou and Xiao-Qiang Yang are

585

also thanked for their discussions and suggestions. The quality of the original

586

manuscript has been improved through reviews by two anonymous referees. This

587

work was supported by the National Natural Science Foundation of China (41225007,

588

40872125, 41130314).

589 590

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968

Precambrian Research 93, 181–199.

969

Zhao, G.C., Cawood, P.A., Wilde, S.A., Lu, L.Z., 2001b. High-pressure granulites

970

(retrograded eclogites) from the Hengshan Complex, North China Craton:

971

petrology and tectonic implications. Journal of Petrology 42, 1141–1170.

972

Zhao, G.C., Cawood, P.A., Wilde, S.A., Sun, M., Lu, L.Z., 2000a. Metamorphism of

973

basement rocks in the Central Zone of the North China Craton: implications for

974

Paleoproterozoic tectonic evolution. Precambrian Research 103, 55–88.

975

Zhao, G.C., Kröner, A., Wilde, S.A., Sun, M., Li, S.Z., Li, X.P., Zhang, J., Xia, X.P.,

976

He, Y.H., 2007. Lithotectonic elements and geological events in the

977

Hengshan–Wutai–Fuping belt: a synthesis and implications for the evolution of

978

the Trans-North China Orogen. Geological Magazine 144, 753–775.

979

Zhao, G.C., Sun, M., Wilde, S.A., Li, S.Z., 2005. Neoarchaean to Palaeoproterozoic

980

evolution of the North China Craton: Key issues revisited. Precambrian

981

Research 136, 177–202.

982

Zhao, G.C., Wilde, S.A., Cawood, P.A., Lu, L.Z., 1998. Thermal evolution of the

983

Archaean basement rocks from the eastern part of the North China Craton and

984

its bearing on tectonic setting. International Geology Review 40, 706–721.

985

Zhao, G.C., Wilde, S.A., Cawood, P.A., Lu, L.Z., 2000b. Petrology and P–T path of

986

the Fuping mafic granulites: implications for tectonic evolution of the central

45

987

zone of the North China Craton. Journal of Metamorphic Geology 18, 375–391.

988

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

989

boundaries in the North China Craton: lithological, geochemical, structural and

990

P–T path constraints and tectonic evolution. Precambrian Research 107, 45–3.

991

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

992

the Fuping Complex: Implications for Late Archean to Paleoproterozoic

993

accretion and assembly of the North China Craton. American Journal of Science

994

302, 191–226.

995

Zhao, G.C., Wilde, S.A., Sun, M., Guo, J.H., Kröner, A., Li, S.Z., Li, X.P., Wu, C.M.,

996

2008a. SHRIMP U–Pb zircon geochronology of the Huaian Complex:

997

constraints on Late Archean to Paleoproterozoic crustal accretion and collision

998

of the Trans-North China Orogen. American Journal of Science 308, 270–303.

999

Zhao, G.C., Wilde, S.A., Sun, M., Li, S.Z., Li, X.P., Zhang, J., 2008b. SHRIMP U–Pb

1000

zircon ages of granitoid rocks in the Lüliang Complex: Implications for the

1001

accretion and evolution of the Trans-North China Orogen. Precambrian

1002

Research 160, 213–226.

1003

Zhao, G.C., Li, S.Z., Zhang, J., Xia, X.P., 2010a. A comment on tectonic evolution of

1004

the Hengshan–Wutai–Fuping complexes and its implication for the Trans-North

1005

China Orogen. Precambrian Research 176, 94–98.

1006

Zhao, G.C., Yin, C.Q., Guo, J.H., Sun, M., Li, S.Z., Li, X.P., Wu, C.M., Liu, C.H.,

1007

2010b. Metamorphism of the Lüliang amphibolite: implications for the tectonic

1008

evolution of the North China Craton. American Journal of Science 310,

46

1009

1480–1502.

1010

Zhao, G.C., Zhai, M.G., 2013. Lithotectonic elements of Precambrian basement in the

1011

North China Craton: Review and tectonic implications. Gondwana Research 23,

1012

1207–1240.

1013

Zhou, H.W., Li, X.H., Zhong, Z.Q., Liu, Y., Xu, Q.D., 1997. Geochemistry of

1014

amphibolites within the Taihua complex from the Xiao Qinling area, western

1015

Henan and its tectonic implication. Geochimica 26, 87–100 (in Chinese with

1016

English abstract).

1017

Zhou, H.W., Zhong, Z.Q., Ling, W.L., Zhong, G.L., Xu, Q.D., 1998. Sm–Nd isochron

1018

for the amphibolites within Taihua complex from the Xiao Qinling area, western

1019

Henan and its geological implications. Geochimica 27, 367–372 (in Chinese

1020

with English abstract).

1021

Zhu, R.X., Zheng, T.Y., 2009. Destruction geodynamics of the North China craton

1022

and its Paleoproterozoic plate tectonics. Chinese Science Bulletin 19,

1023

3354–3366.

1024

Figure captions

1025 1026

Fig. 1. (a) Geological sketch map of the North China Craton showing the Mts.

1027

Huashan metamorphic terrane in the Trans-North China Orogen (from Zhao et al.

1028

1998, 2005) and (b) Geological sketch map of the Mts. Huashan metamorphic terrane,

1029

modified after the 1:200000 Weinan and Luonan Geological Maps. Sample locations

1030

are depicted.

47

1031

Fig. 2. Photomicropetrographs of the Mts. Huashan pelitic granulite samples (a)

1032

S18, (b–c) S25 and (d) S37, respectively. Dotted lines with arrowheads represent the

1033

EMP analytical profiles of the garnets. Mineral inclusions of Bt1 + Pl1 + Qz1 ± Ilm1

1034

within the garnet porphyroblasts comprise the prograde (M1) mineral assemblages.

1035

The metamorphic peak mineral assemblages (M2) are consisted of garnet

1036

porphyroblasts (Grt2) and matrix minerals Opx2 + Bt2+ Pl2 + Qz2 ± Ilm2 ± Mag2 ±

1037

zircon. The retrograde symplectic assemblages (M3) are consisted of Bt3 + Pl3 + Qz3 ±

1038

Opx3.

1039 1040 1041 1042

Fig. 3. X-ray compositional mapping of Fe, Mg, Ca and Mn of garnet porphyroblasts of the pelitic granulite samples (a) S18, (b) S25 and (c) S37. Fig. 4. Analytical chemical profiles of garnet porphyroblasts in the Mts. Huashan pelitic granulite samples (a) S18, (b) S25 and (c) S37.

1043

Fig. 5. Metamorphic P–T paths retrieved from the Mts. Huashan pelitic granulite

1044

samples (a) S18, (b) S25 and (c) S37. The Al2SiO5 phase transition lines are after

1045

Holdaway and Mukhopadhyay (1993), and the dashed lines are after Pattison (1992).

1046

The metamorphic facies and metamorphic facies series are from Spear (1993, p.

1047

15–22).

1048

Fig. 6. The P–T pseudosection calculated for the Huashan pelitic granulite

1049

(sample S18) in the NCKFMASHT system. The isopleths of Xgrs, XAlm and XPyr of

1050

garnet are also shown.

1051 1052

Fig. 7. The representative cathodoluminescence (CL) images of zircons separated from (a) pelitic granulite sample S7 and (b) pelitic granulite sample S18.

48

1053 1054

Fig. 8. The U–Pb concordia diagrams of analytical zircons of (a) pelitic granulite sample S7 and (b) pelitic granulite sample S18.

Table caption

1055 1056 1057

1058 1059

1060 1061

1062 1063

1064 1065

1066 1067

1068

Table 1. Representative compositions of garnet (cations are calculated based on 12 oxygens). Table 2. Representative compositions of orthopyroxene (cations are calculated based on 6 oxygens). Table 3. Representative compositions of biotite (cations are calculated based on 11 oxygens). Table 4. Representative compositions of plagioclase (cations are calculated based on 8 oxygens). Table 5. The P–T conditions of different metamorphic stages of the representative pelitic granulites of the Huashan Metamorphic Complex. Table 6. SIMS U–Pb geochronological data of zircons separated from the representative pelitic granulites of the Huashan Metamorphic Complex. Table 7. Summary of metamorphic ages for the Taihua Metamorphic Complex.

1069

49

100°

105°

110°

115°

125°

120°

130°

Abbreviations for metamorphic complexes in Fig.1(a):

Changchun

(a)

SJ

0

200 400 km

Duolun

Bayan Obo WC

GY

40° AL

Yinshan Block HL

WL JP

NH

40°

WD JN XH MY HA Khondalite Belt EH Beijing QL HS WT FP

Xi ' An

LG Pyeonrang

SL

EASTERN BLOCK

WESTERN BLOCK LL Taiyuan ZH Ordos Block 35°

NL

Gyeonggi

ES 35°

TRANS - NORTH WS CHINA OROGEN ZT DF

TH Hidden basement in the Eastern and Western Block

Xinyang Shanghai

Exposed basement in the Eastern and Western Block Hidden basement in the Paleoproterozoic orogens

30°

Exposed basement in the Khondalite Belt in the Western Block

Wuhan

Exposed basement in the Trans-North China orogen Exposed basement in the Jiao-Liao-Ji Belt in the Eastern Block Major fault

115°

110° 10´

109° 45´

125°

120°

110° 15´

110° 30´

Huayin

(b)

Huaxian

AL – Alashan; CD – Chengde; DF – Dengfeng; EH – Eastern Hebei; ES – Eastern Shandong; FP – Fuping; GY – Guyang; HA – Huai'an; HL – Helanshan; HS – Hengshan; JN – Jining; LG – Langrim; LL – Lüliang; MY– Miyun; NH – Northern Hebei; NL – Northern Liaoning; QL – Qianlishan; SJ – Southern Jilin; SL – Southern Liaoning; TH – Taihua; WD– Wulashan-Daqingshan; WL– Western Liaoning; WS – Western Shandong; WT – Wutai; XH – Xuanhua; ZH – Zanhuang; ZT – Zhongtiao.

Tongguan

N

110° 45´ 0 10000m

34° 30´

34° 30´ S37

Arth 1

S7

Arth 2

Arth 1

S18

S25

Pt 1 xl 3

34° 00´

110°30´

110°15´ Lower Taihua Group (Arth 1 )

Upper Taihua Group (Arth 2 )

Upper Xiong'er Group

Proterozoic granite

Μesozoic granite

Sample location

110°45´

34° 00´

Fig. 1

( a)

(b)

Bt 2

Opx 2

Opx 2 Opx 3 Bt 2

Bt 1 Ilm 1

Bt 2 Pl 3 +Bt 3

Grt 2

Grt 2

Qz 1

Bt 1

Bt 3 +Pl 3

Pl 1

Opx 2 Bt 2

1000µm

Opx 2

(c)

(d)

Bt 2

Opx 2

Bt 2

Opx 2

Pl 2 Pl 3 +Bt 3

Bt 2 +Opx 2 +Pl 2

Grt 2

1000µm

St 1

Qz 1 +Pl 1 +Bt 1 Opx 3 +Bt 3 +Pl 3

Grt 2 Bt 1 Pl 1 +Bt 1 +Qz 1

Ap 1

Pl 3 +Bt 3

Opx 2

2000µm

Pl 2 +Bt 2

2000µm

Fig. 2

(a) S18

Fe 500µm

Mg 500µm

Ca 500µm

Mn 500µm

Mg 500µm

Ca 500µm

Mn 500µm

Mg 1 mm

Ca 1 mm

Mn 1 mm

(b) S25

Fe 500µm

(c) S37

Fe

1 mm

Fig. 3

(a) 0.8

S18

0.6

0.4

Xalm

Xpyr

Xgros

Xsps

Fe/(Fe+Mg)

0.2

0.0 -2 0rim 246

12

222426 core2830 34 384042 46485052 rim

(b) 0.8

S25

0.6

0.4

0.2 Xalm

Xpyr

Xgros

Xsps

Fe/(Fe+Mg)

0.0 -2 0rim 2 4 6 8 101214161820222426 485052 core28303234363840424446rim

(c) S37 0.8

0.6

0.4

Xalm

Xpyr

Xgros

Xsps

Fe/(Fe+Mg)

0.2

0.0 -20 rim 2 4 6 810121416182022242628core 3032343638404244464850525456 586062 rim

Fig. 4

(a)

(b) 10

10 M2:730°C 7.2kbar (GBPQ) M2:760°C 6.8kbar (GOPQ) M3:670°C 5.0kbar (GBPQ) 8

S18 8

EA

M2:730°C 7.0kbar (GBPQ) M2:760°C 6.8kbar (GOPQ) M3:680°C 4.2kbar (GBPQ) M3:570°C 4.1kbar (GOPQ) EA M2

M2

Ky

Am

6

6

Ky

Gr

Sil

Am

M3

Gr

Sil

4

M3

4 And

And

2

2 500

600

700

800

900

500

600

700 T (°C)

T (°C) (c)

S25

800

900

(d) 10

10

S18 S25 S37

S37 M2 8

8

EA

Gr EA

6

Am

Ky

Ky

M3

M1

6 Gr

4 And

Sil

Sil

Am

M1:520~530°C (Ti in Bt) M2:740°C 8.6kbar (GBPQ) M2:810°C 7.3kbar (GOPQ) M3:740°C 6.4kbar (GBPQ)

4 And 2

2 500

600

700 T (°C)

800

900

500

600

700

800

900

T (°C)

Fig. 5

NCKFMASHT 10000

Na 2 O CaO K 2 O FeO MgO Al 2 O 3

SiO 2 H 2 O TiO 2

3.94 3.15 2.38 9.93 5.87 17.69 52.64 0.56 0.85

(wt % ) Opx Bt Pl Grt Kfs Ilm Qz Liq Opx Bt Pl Grt Kfs Ilm Liq

Opx Bt Pl Grt Kfs Qz Ru

8400

0 . 27

0 . 25 Opx Bt Pl Grt Kfs Qz

0 . 29

M2

Opx Bt Pl Grt Kfs Liq

0 . 06

0 . 05

0 . 65 Opx Bt Pl Grt Kfs Ilm Qz Ru

6800

0 . 67

Opx Bt Pl Grt Kfs Ilm Qz

0 . 69 0.70

5200

M3

Opx Bt Pl Kfs Qz Opx Bt Pl Crd Kfs Liq

3600

Opx Bt Crd Pl Grt Kfs Ilm Qz

Opx Bt Pl Crd Kfs Qz Liq Opx Bt Pl Crd Grt Kfs Qz Opx Bt Pl Crd Ilm

Opx Bt Pl Crd Kfs Qz

Opx Bt Pl Crd Kfs Qz Ilm

Opx Bt Pl Crd Kfs Ilm Qz

Opx Bt Pl Crd Kfs Ilm

2000 500

600

800

700

900

1000

T ( °C ) X Gr os = Ca/(Ca+Fe+Mg) of garnet

X Al m = F e /(Ca+Fe+Mg) of garnet

X P yr = Mg/(Ca+Fe+Mg) of garnet

Fig. 6

(a) S7 1828±6 03 04 1842±7

05 1822±9

26 1837±6

1854±3 06

17 1826±7

1832±5 07

25 1848±2

100µm

(b) S18

01 2507±9

07 1831±32

08 2572±7

2434±20 11 1868±25 12

1821±13 19 18

20 21 2402±8 1842±16

1816±18 100µm

Fig. 7

2400

0.44

(a) S7

0.40

upper intercept age： 1824±13Ma (MSWD = 0.78)

(b) S18

0.5

2600

upper intercept age： 1818±22Ma (MSWD = 0.36)

2200

2400 upper intercept age： 2547±47Ma (MSWD = 0.94)

0.4 2000

2000

0.36 207

weighted mean Pb/ Pb age： 1846±6Ma (MSWD = 8.4 , n=23) 2 07

1800

0.32

20 6

206

weighted mean Pb/ Pb age: 1823±8Ma (MSWD = 0.99 , n=14)

0.3 1600

lower intercept age: 1792±310 Ma (MSWD = 0.94)

0.2

0.28 3.5

4.5

5.5

6.5 207 Pb/ 2 3 5 U

7.5

8.5

9.5

2

4

6 207

8 Pb/ 2 3 5 U

10

12

14

Fig. 8

1070

Table 1. Representative compositions of garnets (cations are calculated based on 12 oxygens). Grt2

1071 1072 1073 1074

Grt3

Sample

S18 n=46

S25 n=34

S37 n=58

S18 n=3

SiO2

37.14

37.15

36.67 36.84

37.05 36.51

TiO2

0.02

0.02

0.04

0.04

Al2O3

21.09

21.71

21.46 20.94

21.27 21.27

FeO MnO MgO CaO

31.96 0.96 7.05 2.17

29.09 0.69 10.50 0.62

28.33 0.69 8.55 3.73

31.71 0.89 8.27 0.50

0.03 33.86 1.04 6.11 1.62

S25 n=5

S37 n=3 0.03 30.77 1.05 7.27 2.80

Na2O

0.02

0.02

0.01

0.03

0.03

0.04

K2O

0.01

0.01

0.01

0.02

0.02

0.01

Cr2O3

0.00

0.00

0.00

0.00

0.00

0.00

Total Si Ti Al

100.43 2.90 0.00 1.94

99.80 2.86 0.00 1.97

99.49 2.847 0.003 1.964

100.48 2.90 0.00 1.94

99.77 2.90 0.00 1.96

99.74 2.86 0.00 1.96

Fe2+

1.85

1.58

1.526 1.99

1.84

1.72

3+

Fe

0.26

0.32

0.340 0.26

0.25

0.32

Mn Mg Ca Na K Cr Total

0.06 0.82 0.18 0.00 0.00 0.00 8.02

0.05 1.20 0.05 0.00 0.00 0.00 8.03

0.045 0.990 0.310 0.002 0.001 0.00 8.03

0.07 0.72 0.14 0.00 0.00 0.00 8.02

0.06 0.96 0.04 0.00 0.00 0.00 8.02

0.07 0.85 0.23 0.01 0.00 0.00 8.03

XAlm

0.63

0.55

0.53

0.68

0.63

0.60

XPyr

0.28

0.42

0.34

0.25

0.33

0.30

XGros

0.06

0.02

0.11

0.05

0.01

0.08

XSps

0.02

0.02

0.02

0.02

0.02

0.02

XFe

0.69

0.57

0.61

0.74

0.66

0.67

XAlm = Fe2+/(Fe2+ + Mg + Mn + Ca); XPyr = Mg/(Fe2+ + Mg + Mn + Ca); XGros = Ca/(Fe2+ + Mg + Mn + Ca); XSps = Mn/(Fe2+ + Mg + Mn + Ca); XFe(g) = Fe2+/(Fe2+ + Mg). Ferric irons are determined according to the method of Droop (1987). Table 2. Representative compositions of orthopyroxene (cations are calculated based on 6 oxygens). Opx2 Sample

S18 n=9

Opx3 S25 n=6

S37 n=12

S25 n=3

SiO2

50.51

50.38

51.30

49.87

TiO2

0.07

0.06

0.06

0.06

Al2O3

3.23

5.08

2.32

5.00

FeO

29.20

24.47

25.91

23.09

50

MnO MgO CaO

0.16 17.44 0.11

0.13 20.41 0.01

0.16 20.14 0.17

0.09 21.15 0.01

Na2O

0.03

0.02

0.01

0.03

K2O

0.01

0.01

0.01

0.01

Cr2O3 Total Si Ti Al

0.01 100.76 1.92 0.00 0.14

0.00 100.57 1.88 0.00 0.22

0.02 100.10 1.93 0.00 0.10

0.02 99.32 1.87 0.00 0.22

Fe2+

0.92

0.74

0.79

0.68

3+

Fe

0.01

0.03

0.03

0.04

Mn Mg Ca Na K Total

0.01 0.99 0.00 0.00 0.00 4.00

0.00 1.13 0.00 0.00 0.00 4.00

0.01 1.13 0.01 0.00 0.00 4.00

0.00 1.18 0.00 0.00 0.00 4.00

0.52

0.61

0.59

0.63

XMg 1075 1076 1077 1078 1079

2+

XMg = Mg/(Mg + Fe ). Ferric irons are determined according to the method of Droop (1987).

Table 3. Representative compositions of biotite (cations are calculated based on 11 oxygens). Bt1 Sample

Bt2

S18 n=5

S25 n=3

SiO2

37.01

38.23 38.03

37.01 37.66

37.68 36.83

36.93 37.41

TiO2

3.82

4.41

4.43

3.76

3.92

Al2O3

16.12

16.07 16.31

15.92 16.06

16.15 15.82

15.77 15.78

FeO MnO MgO CaO Na2O

17.88 0.03 12.17 0.02 0.42

10.00 0.02 16.68 0.04 0.57

15.65 0.04 14.57 0.01 0.17

17.39 0.02 11.97 0.00 0.24

13.80 0.02 14.45 0.00 0.45

14.46 0.02 14.11 0.02 0.36

17.85 0.02 11.62 0.00 0.26

15.35 0.02 13.89 0.01 0.41

17.10 0.01 12.68 0.02 0.32

K2O

10.01

8.39

8.94

9.28

8.98

8.91

9.34

8.53

8.70

Cr2O3

0.01

0.05

0.03

0.02

0.02

0.03

0.03

0.05

0.04

Total Si Ti Al

97.48 2.75 0.21 1.41

94.45 2.79 0.24 1.38

95.77 2.81 0.11 1.42

96.28 2.76 0.25 1.40

95.53 2.78 0.23 1.40

95.50 2.79 0.21 1.41

96.24 2.76 0.25 1.40

94.87 2.76 0.22 1.39

95.52 2.80 0.20 1.39

Fe2+

1.11

0.61

0.97

1.09

0.85

0.89

1.12

0.96

1.07

3+

0.00

0.00

0.00

0.00

0.00

0.00

0.00

0.00

0.00

Fe

S37 n=3 2.03

S18 n=12

Bt3 S25 n=6

S37 n=11

4.09

51

S18 n=6 4.46

S25 n=6

S37 n=3 3.47

Mn Mg Ca Na K Total XFe 1080 1081 1082 1083

0.00 1.35 0.00 0.06 0.95 7.84

0.00 1.81 0.00 0.08 0.78 7.70

0.00 1.61 0.00 0.02 0.84 7.79

0.00 1.33 0.00 0.04 0.88 7.75

0.00 1.59 0.00 0.06 0.84 7.75

0.00 1.56 0.00 0.05 0.84 7.75

0.00 1.30 0.00 0.04 0.89 7.75

0.00 1.55 0.00 0.06 0.81 7.76

0.00 1.41 0.00 0.05 0.83 7.75

0.45

0.25

0.38

0.45

0.35

0.36

0.46

0.38

0.43

2+

2+

XFe = Fe /(Fe + Mg) Table 4. Representative compositions of plagioclase (cations are calculated based on 8 oxygens). Pl1

1084 1085 1086

Pl2

Sample

S18 n=3

S25 n=3

SiO2

58.41

TiO2

S37 n=3

Pl3

S18 n=18

S25 n=11

64.46 60.15

61.74

0.02

0.00

S18 n=6

S25 n=9

64.29 54.00

61.28

63.87 53.43

0.01

0.01

0.01

0.01

Al2O3

24.78

22.13 24.77

23.73

21.85 28.44

23.78

21.98 28.55

FeO MnO MgO CaO

0.53 0.02 0.00 7.75

0.13 0.00 0.01 3.43

0.32 0.00 0.00 7.28

0.07 0.01 0.01 6.17

0.05 0.00 0.00 3.33

0.12 0.01 0.01 11.87

0.15 0.01 0.00 6.24

0.23 0.01 0.00 3.52

0.13 0.00 0.01 12.61

Na2O

7.62

9.72

7.90

8.23

9.76

5.34

8.16

9.69

4.96

0.00

S37 n=9 0.01

S37 n=3 0.01

K2O

0.09

0.04

0.04

0.20

0.08

0.05

0.19

0.05

0.04

Cr2O3

0.00

0.02

0.00

0.01

0.01

0.01

0.00

0.01

0.00

Total Si Ti Al

99.23 2.64 0.00 1.32

99.94 2.84 0.00 1.15

100.44 2.68 0.00 1.30

100.17 2.74 0.00 1.24

99.39 2.85 0.00 1.14

99.87 2.45 0.00 1.52

99.81 2.73 0.00 1.25

99.37 2.84 0.00 1.15

99.75 2.43 0.00 1.53

Fe3+

0.02

0.00

0.01

0.00

0.00

0.00

0.01

0.01

0.00

Mn Mg Ca Na K Cr Total

0.00 0.00 0.38 0.67 0.01 0.00 5.03

0.00 0.00 0.16 0.83 0.00 0.00 5.00

0.00 0.00 0.35 0.68 0.00 0.00 5.02

0.00 0.00 0.29 0.71 0.01 0.00 5.00

0.00 0.00 0.16 0.84 0.00 0.00 5.00

0.00 0.00 0.58 0.47 0.00 0.00 5.03

0.00 0.00 0.30 0.71 0.01 0.00 5.00

0.00 0.00 0.17 0.83 0.00 0.00 5.00

0.00 0.00 0.61 0.44 0.00 0.00 5.02

XAn

0.36

0.16

0.34

0.29

0.16

0.55

0.29

0.17

0.58

Xab

0.64

0.83

0.66

0.70

0.84

0.45

0.70

0.83

0.41

XOr

0.00

0.00

0.00

0.01

0.00

0.00

0.01

0.00

0.00

Table 5. The P-T conditions of different metamorphic stages of the representative pelitic granulites of the Huashan Metamorphic Complex. Sample

Prograde stage (M1 ) 52

Peak stage (M2)

Retrograde stage

(M3) T (°C)

P (Kb ar)

Method

S18

S25

520– 530

S37

1087 1088 1089

4–5

Ti-in-bi otite geother momete r

T (° C)

P (Kb ar)

73 0 76 0 81 0 73 0 76 0 74 0

Meth od

8.6

GBP 68 Q 0 GOP Q 63 0 5 GBP 68 Q 0 GOP 57 Q 0 GBP 74 Q 0

7.3

GOP Q

7.2 6.8 7.8 7 6.8

81 0

T (° C)

P (Kb ar)

Metho d

5.1

GBPQ

Pseudo section 4.2

GBPQ

4.1

GOPQ

6.4

GBPQ

Table 6. SIMS U-Pb geochronological data of zircons separated from the representative pelitic granulites of the Huashan Metamorphic Complex. Spot

Content (ppm)

Th/ U

Istopic ratios 207

U

Th

Pb

S7-1

287

11

105

S7-2

1773

50

714

S7-3

337

15

124

S7-4

297

19

111

S7-5

149

21

57

S7-6

1898

45

732

S7-7

546

26

217

S7-8

291

11

108

S7-9

799

30

305

0.0 4 0.0 3 0.0 5 0.0 6 0.1 4 0.0 2 0.0 5 0.0 4 0.0 4

Pb/206 Pb

0.1113 0.1152 0.1117 0.1126 0.1114 0.1134 0.112 0.1114 0.1133

206

1σ 0.3 6 0.1 7 0.3 4 0.4 1 0.4 9 0.1 9 0.3 0.4 3 0.2 2 53

Age/(Ma)

Pb/23 U

1σ

0.3276

1.5

5.0278

0.3585

1.5

5.6959

0.327

1.5

5.0385

0.3309

1.5 3

5.1384

0.3315

1.5

5.089

0.3443

1.5

5.3812

0.353

1.5

5.4508

0.3308

1.5

5.0828

0.3391

1.5

5.2958

8

207

Pb/23 U

5

207

1σ 1.5 4 1.5 1 1.5 4 1.5 8 1.5 8 1.5 1 1.5 3 1.5 6 1.5 2

Pb/206 Pb

1 σ

1821

7

1883

3

1828

6

1842

7

1822

9

1854

3

1832

5

1823

8

1852

4

S7-1 0 S7-1 1 S7-1 2 S7-1 3 S7-1 4 S7-1 5 S7-1 6 S7-1 7 S7-1 8 S7-1 9 S7-2 0 S7-2 1 S7-2 2 S7-2 3 S7-2 4 S7-2 5 S7-2 6 S7-2 7 S7-2 8 S181 S182 S18-

157

5

58

1798

56

699

256

9

98

321

15

120

193

48

91

457

22

174

3003

195

117 4

237

10

88

144

69

77

1183

50

455

277

10

103

259

8

96

1841

97

699

264

9

99

278

11

103

2633

134

102 9

404

14

144

595

220

291

326

122

156

168

48

98

124

19

47

54

12

22

0.0 3 0.0 3 0.0 3 0.0 5 0.2 5 0.0 5 0.0 7 0.0 4 0.4 8 0.0 4 0.0 4 0.0 3 0.0 5 0.0 4 0.0 4 0.0 5 0.0 3 0.3 7 0.3 8 0.2 9 0.1 5 0.2

0.1114 0.1127 0.1121 0.111 0.123 0.1127 0.1133 0.1116 0.1422 0.1131 0.1114 0.1128 0.1139 0.111 0.1114 0.113 0.1123

0.5 1 0.1 8 0.4 1 0.4 8 0.6 9 0.4 1 0.1 6 0.3 8 0.4 8 0.2 6 0.4 9 0.3 6 0.1 3 0.3 6 0.3 7 0.1 4 0.3 6

0.3278

1.5 4

5.0327

0.3467

1.5

5.3887

0.3415

1.5 1

5.2769

0.3326

1.5

5.0922

0.3886

2.1 9

6.5924

0.3372

1.5

5.2394

0.3455

1.5

5.3985

0.331

1.5

5.0932

0.4181

1.5 1

8.2006

0.3418

1.5

5.3314

0.333

1.5

5.1126

0.3302

1.5

5.137

0.3361

1.5 4

5.2778

0.335

1.5

5.1266

0.3304

1.5

5.0734

0.3465

1.5 9

5.399

0.3188

1.5

4.9365

1.6 2 1.5 1 1.5 6 1.5 8 2.2 9 1.5 6 1.5 1 1.5 5 1.5 9 1.5 3 1.5 8 1.5 5 1.5 5 1.5 4 1.5 5 1.6 1.5 5 1.5 1 1.5 9

1822

9

1844

3

1834

7

1816

9

2001

1 2

1843

7

1853

3

1826

7

2255

8

1850

5

1822

9

1845

7

1862

2

1816

7

1822

7

1848

2

1837

6

2113

4

2102

9

9

0.1311

0.2

0.3927

1.5

7.0991

0.1303

0.5 1

0.3834

1.5 1

6.8877

0.4659

1.5

10.594 7

1.6

2507

0.3307

1.5

5.0458

1.6

1810

0.3416

1.5

5.2085

1.8

1809

0.1649 0.1107 0.1106

0.5 5 0.5 4 1.0

54

1 0 1

3 S184 S185 S186 S187 S188 S189 S1810 S1811 S1812 S1813 S1814 S1815 S1816 S1817 S1818 S1819 S1820 S1821 S1822 S1823 1090 1091 1092

25

9

10

58

13

22

85

8

32

13

5

6

218

84

142

178

71

117

99

8

38

226

73

123

28

6

10

215

82

144

48

10

19

114

44

73

251

121

172

42

10

16

74

13

29

71

14

28

627

5

321

45

8

18

81

7

31

51

9

20

3 0.3 6 0.2 2 0.1 0.3 6 0.3 8 0.4 0.0 8 0.3 2 0.2 2 0.3 8 0.2 1 0.3 8 0.4 8 0.2 5 0.1 7 0.2 0.0 1 0.1 7 0.0 9 0.1 7

0.1106 0.1109 0.1128 0.1119 0.1715 0.174 0.1114 0.1579 0.1142 0.1729 0.1107 0.1737 0.1803 0.1112 0.111 0.1113 0.155 0.1126 0.1127 0.1104

6 1.2 1 0.7 7 0.6 2 1.7 8 0.4 2 0.2 9 0.5 8 1.1 7 1.3 8 0.3 1 0.9 7 0.6 7 0.2 8 0.9 4 1.0 2 0.7 2 0.4 5 0.8 6 0.7 5 0.8 4

0.3329 0.3281 0.3308 0.3353 0.5065 0.5085 0.3387 0.4326 0.3061 0.5191 0.3379 0.4952 0.5207 0.3161 0.3333 0.3382 0.4424 0.3404 0.3326 0.3295

2 1.5 2 1.5 6 1.5 2 1.5 6 1.5 1 1.5 1.5 4 1.5 2 1.5 2 1.5 1.5 1 1.5 1 1.5 1.5 1 1.5 1 1.5 1 1.5 1.5 1 1.5 2 1.6 4

5.079 5.0182 5.1466 5.1753 11.973 3 12.199 9 5.2044 9.4193 4.8222 12.373 5.1584

1.8

11.858 1 12.941 9

1.6 5 1.5 3 1.7 8 1.8 3 1.6 7 1.5 7 1.7 4

4.8488 5.1026 5.1901 9.4533 5.2865

1810 1815 1845 1831

7

2596

5

1823 2434 1868 2586 1811 2593 2655 1820 1816 1821 2402 1842

1.7

1844

5.0137

1.8 5

1805

Table 7. Summary of metamorphic ages for the Taihua Metamorphic Complex.

9 2 2 1 4 1 1 3 2

2572

5.1707

The data with strikethrough are invalid.

55

5 1.9 4 1.7 4 1.6 4 2.3 6 1.5 7 1.5 3 1.6 4 1.9 2 2.0 5 1.5 4

1 1 2 0 2 5 5 1 8 1 1 5 1 7 1 8 1 3 8 1 6 1 4 1 5

Lushan

Wugang

Luoning

Huashan

Age (Ma)

Sample

Description

TW006/1

garnet-sillimanite gneiss

TWJ358/1

garnet gneissic granitoid

L15

amphibolite

L31

amphibolite

L40 L10 L56

amphibolite amphibolite amphibolite

L51

TTG

L54 L50

TTG gneissic granitoid

L57

amphibolite

L65

amphibolite

L66

amphibolite

HN804

amphibolite

YU19

amphibolite

YU21

amphibolite

YU23

amphibolite

04MC14

amphibolite

C21

amphibolite

C20

amphibolite

C23

metapelite

S2

amphibolite

1844 ± 66 1871 ± 14 1945 ± 25 1920 ± 12 1919 ± 8 1927 ± 7 1918 ± 5 1915 ± 14 1934 ± 7 1928 ± 5 1928 ± 6 1920 ± 17 1960 ± 26 1939 ± 19 1967 ± 32 1958 ± 32 1938 ± 9 1950 ± 20 1940 ± 10 1944 ± 5 1937 ± 11 1823 ± 4

S3

amphibolite

1890 19

S33

metapelite

1941 13

±

S51

amphibolite

1852 23

±

56

±

Method

Source

SHRIMP

Wan et al. (2006)

SHRIMP

Wan et al. (2006)

SIMS

Lu et al. (2013)

SIMS

Lu et al. (2013)

SIMS SIMS SIMS

Lu et al. (2013) Lu et al. (2015) Lu et al. (2015)

SIMS

Lu et al. (2015)

SIMS SIMS

Lu et al. (2015) Lu et al. (2015)

SIMS

Lu et al. (2014)

SIMS

Lu et al. (2014)

SIMS

Lu et al. (2014)

LA-ICP-MS

Jiang et al. (2011)

LA-ICP-MS

Jiang et al. (2011)

LA-ICP-MS

Jiang et al. (2011)

LA-ICP-MS

Jiang et al. (2011)

LA-ICP-MS

Diwu et al. (2014)

SIMS

Chen et al. (2015)

SIMS

Chen et al. (2015)

SIMS

Chen et al. (2015)

SIMS

Wang et al. (2012)

SIMS

Wang et al. (2012)

LA-ICP-MS

Wang et al. (2012)

LA-ICP-MS

Wang et al. (2012)

S24a

metapelite

1869 39

±

S25

metapelite

1848 20

±

S34

metapelite

1961 26

±

xql0912-2

gneissose pegmatitic granite

1866 19

±

xql0915-2

granitic veins

1881 24

±

THH08-62

granitic gneiss

1918 17

±

S1

amphibolite

S41

LA-ICP-MS

Wang et al. (2013)

LA-ICP-MS

Wang et al. (2013)

LA-ICP-MS

Wang et al. (2013)

LA-ICP-MS

Yu et al. (2013)

LA-ICP-MS

Yu et al. (2013)

LA-ICP-MS

Huang et al. (2013)

1846 ± 8

SIMS

Wang et al. (2014)

amphibolite

1866 17

±

SIMS

Wang et al. (2014)

08LF2

paragneiss

1928 15

±

LA-ICP-MS

Diwu et al. (2014)

S7

pelitic granite

1846 ± 6

SIMS

this study

S18

pelitic granite

1823 ± 8

SIMS

this study

1093 1094 1095

57

1096 1097

● Clockwise P–T–t paths were retrieved from the Mts. Huashan

1098

pelitic granulites.

1099

● SIMS U–Pb dating of metamorphic zircons reveal the

1100

metamorphic ages of 1.85–18.2 Ga.

1101

● The tectonothermal evolu(on of the TNCO started as early as

1102

~1.97 Ga and lasted as late as 1.80 Ga.

1103

● An eastward subduc(on model for the TNCO is suggested in

1104

this study.

1105 1106

58