Zircon U–Pb constraints on the origin of UHP meta-supracrustal rocks in the Southern Sulu orogen, eastern China

Journal of Asian Earth Sciences 42 (2011) 740–751

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Zircon U–Pb constraints on the origin of UHP meta-supracrustal rocks in the Southern Sulu orogen, eastern China Fei Yu a, Zeming Zhang b,⇑, Wei Wang a, Feng Liu a, Xin Dong b, J.G. Liou c a

Faculty of Earth Science, China University of Geosciences, Wuhan 430074, China State Key Laboratory of Continental Tectonics and Dynamics, Institute of Geology, Chinese Academy of Geological Science, No. 26 Baiwanzhaung Road, Beijing 100037, China c Department of Geological and Environmental Sciences, Stanford University, Stanford, CA 94305, USA b

a r t i c l e

i n f o

Article history: Available online 17 June 2011 Keywords: Supracrustal rock Geochronology Protolith origin UHP metamorphism Sulu orogen

a b s t r a c t Most zircons in marble and quartzite, typical meta-sedimentary rock from southern Sulu orogenic belt, have a core-rim structure, including an inherited detrital core and a metamorphic overgrowth rim. A few zircons are completely metamorphic. Most detrital cores have relatively high REE contents and Th/U ratios and yield highly variable 206Pb/238U ages ranging from 2828 to 211 Ma, with major age populations at 1800 Ma and 800 Ma for quartzites and 1300 Ma for marbles. In contrast, the metamorphic zircon rims have relatively low REE contents and low Th/U ratios, and yield consistent Triassic metamorphic ages with a weighted mean age of 231 Ma. These results indicate that the marble and quartzite, together with eclogite and orthogneiss from the southern Sulu orogenic belt, have been subjected to a coeval Triassic UHP metamorphism. The protoliths of the quartzites may have been formed in the Neoproterozoic, whereas the protoliths of the marble are probably in the Mesoproterozoic. The source regions of the UHP supracrustal rocks underwent Neoproterozoic to Paloproterozoic tectonic– thermal events, indicating that the protoliths of the Sulu UHP rocks were derived from the Yangtze craton, instead of the North China craton. Ó 2011 Elsevier Ltd. All rights reserved.

1. Introduction The Dabie-Sulu orogen was formed by collision and subduction between the Yangtze and North China cratons (e.g., Xu et al., 1992; Liou et al., 1995; Cong and Wang, 1996; You et al., 1996; Wallis et al., 1999). The present study focuses on the Donghai area in southern Sulu (Fig. 1), where a variety of ultrahigh-pressure (UHP) rocks occur (Hirajima et al., 1990; Enami et al., 1993; Zhang et al., 1994, 1995, 2000a,b, 2005a; Yang and Jahn, 2000; Hirajima and Nakamura, 2003). Their protoliths consist mainly of orthogneiss and meta-supracrustal rocks, with minor eclogite and garnet-peridotite. Numerous investigations have demonstrated that the granitic gneisses and eclogites were subjected to UHP metamorphism under the conditions of 3.0–4.5 GPa and 700–850 °C (Hirajima et al., 1990; Enami et al., 1993; Zhang et al., 1994, 1995, 2000a,b, 2005b, 2006a), with peak-UHP metamorphic ages at 240–220 Ma (Liou et al., 2009; Zhang et al., 2009a; Zheng et al., 2009; Liu and Liou, 2011 and references therein). All of their protoliths were bimodal magmatic rocks formed at 800–700 Ma (e.g., Zheng et al., 2003a, 2009; Zhang et al., 2006b, 2009a, 2011). However, the provenance, and protolith and metamorphic ages of the supracrustal rocks of the Sulu orogen are not well constrained ⇑ Corresponding author. Tel.: +86 10 68999735; fax: +86 10 68994781. E-mail address: [email protected] (Z. Zhang). 1367-9120/$ - see front matter Ó 2011 Elsevier Ltd. All rights reserved. doi:10.1016/j.jseaes.2011.05.010

(Liu et al., 2006a; Zhu et al., 2009; Liu and Liou, 2011). In this paper, we present zircon U–Pb dating results of southern Sulu marble and quartzite, typical meta-sedimentary rocks. These rocks apparently have been subjected to coeval Triassic UHP metamorphism; their protoliths were formed at Meso- to Neo-Proterozoic time, and their provenances record multi-stage tectonic–thermal events in the Neo-Achaean to Neoproterozoic, indicating a tectonic affinity with the Yangtze craton. These data provide new insights on the origin of the UHP meta-supracrustal rocks from the Sulu orogen.

2. Analytical methods Whole-rock compositions of selected quartzite samples were analyzed at the National Geological Analysis Center of China, Beijing. Oxides of major elements were determined by X-ray fluorescence (XRF) (Rigaku-3080); the analytical uncertainty is <0.5%. Zircon grains used for dating and trace element analysis were separated by crushing and sieving approximately 10–15 kg of each rock sample, followed by magnetic and heavy liquid separation. Approximately 150–200 zircon grains from each sample were mounted onto 25-mm epoxy discs and polished. Zircons were imaged by Cathodoluminescence (CL) using a JEOL JXA-8900RL electron microprobe at the Chinese Academy of Geological Sciences, Beijing.

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F. Yu et al. / Journal of Asian Earth Sciences 42 (2011) 740–751

119°00´E

Tan -L

34°50´N

Sanqingge DH08-7-2 DH09-1-1

34°50´N

10 km

Linsu

u Fa

ul t

118°40´E

Ganyu

Wuqiangshan DH09-3-1 DH09-3-3

lt

W

Q

fault

be

Tan-L u

UH

Fig.1

Qingdao

P

North China

YF

Weihai

Yellow Sea

F JX

HP

be

lt

Donghai

120km

Yangtze

34°30´N

34°30´N

Tertitary

Donghai

Cretaceous Granite Orthogneiss Meta-supracrustal rock

CCSD

Eclogite/peridotite Sampling location 118°40´E

119°00´E

Fig. 1. Geological map of the southern Sulu region, showing the sampling locations (modified after Zhang et al., 2005a). WQYF: Wulian-Qingdao-Yantai fault; JXF: JiashanXiangshui fault.

U–Pb dating and trace element analyses of zircon were conducted synchronously by LA–ICP-MS at the State Key Laboratory of Geological Processes and Mineral Resources, China University of Geosciences, Wuhan. Laser analysis of zircon grains was performed using a GeoLas 2005; an Agilent 7500a ICP-MS instrument was used to acquire ion-signal intensities. Helium was applied as a carrier gas mixing with the make-up gas of Argon added via a T-connector before entering the ICP. Nitrogen was added into the central gas flow (He+Ar) of the Ar plasma to decrease the detection limit and improve precision (Hu et al., 2008). Each analysis incorporated a background acquisition of approximately 20–30 s as a gas blank, followed by 50 s data acquisition from the sample. The laser spots are 16–32 lm in diameter. The Agilent Chemstation was utilized for the acquisition of each individual analysis. Off-line selection, integration of background analytic signals, time-drift correction and quantitative calibration for trace element analyses and U–Pb dating were performed by ICPMSDataCal (Liu et al., 2008a, 2010). Zircon 91500 was used as an external standard for

Table 1 Major element compositions of UHP supracrustal rocks from the southern Sulu orogen (in wt.%). Sample Rock

DH08-7-2 Marble

DH09-1-1 Marble

DH09-3-1 Quartzite

DH09-3-3 Quartzite

SiO2 TiO2 Al2O3 FeO Fe2O3 MnO MgO CaO Na2O K2O P2O5 H2O+ CO2

15.86 0.01 0.77 1.53 0.29 0.05 17.67 28.38 0.12 0.01 0.06 0.61 38.29

4.82 0.02 0.28 0.21 0.04 0.02 21.23 30.40 0.04 0.01 0.01 1.06 41.67

71.87 0.03 0.41 0.93 26.05 0.01 0.09 0.14 0.22 0.01 0.10 0.18 0.31

96.74 0.01 0.35 0.22 2.12 0.01 0.02 0.11 0.14 0.01 0.04 0.14 0.29

Total

99.50

99.81

100.35

100.20

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F. Yu et al. / Journal of Asian Earth Sciences 42 (2011) 740–751

Fig. 2. Cathodoluminescence (CL) images of the dated zircons, showing the analytical spot and respective U–Pb age in Ma.

Table 2 LA-ICPMS trace element analyses of zircon from the UHP supracrustal rocks (in ppm). Sample

Domain

La

Ce

Pr

Nd

Sm

Eu

Gd

Tb

Dy

Ho

Er

Tm

Yb

Lu

REE

DH08-7-2, 2 3 4 14 5 11 6 7 10

marble Metamorphic Detrital magmatic Detrital magmatic Detrital magmatic Detrital magmatic Detrital magmatic Detrital magmatic Detrital magmatic Detrital magmatic

0.061 0.024 0.17 2.50 bd 0.050 bd bd bd

2.23 7.40 9.61 54.3 2.24 2.29 4.47 3.69 2.98

0.050 0.12 0.28 2.26 bd bd 0.20 0.30 0.21

0.37 2.90 1.51 14.8 4.29 1.83 4.74 1.38 1.02

0.15 4.96 4.58 12.7 11.1 6.66 6.99 2.21 3.80

bd⁄ 0.18 0.15 2.98 0.35 0.12 0.13 0.13 0.093

1.47 27.4 29.2 25.7 20.4 16.1 11.7 8.70 5.80

0.69 7.81 8.84 8.76 3.37 3.21 1.64 1.27 1.19

7.22 91.4 114 84.8 24.2 28.8 14.4 8.84 6.06

4.13 34.8 42.2 37.3 5.27 12.2 2.57 1.82 1.08

28.4 178 222 201 19.5 71.3 8.52 6.19 3.99

7.17 32.2 39.6 39.3 3.95 16.3 1.42 0.98 0.56

71.3 312 368 349 35.2 189 8.70 10.3 3.82

17.7 55.8 67.0 62.1 6.36 35.2 1.36 1.47 0.53

141 755 907 898 136 383 66.8 47.3 31.1

DH09-1-1, 1 2 7 16 17 22 33 34 41 4 37 18 20 32 26 12 25 10 24 30 31 43 8 6 15 29 11 27 19 42 40 13 5 23 14

marble Metamorphic Metamorphic Metamorphic Metamorphic Metamorphic Metamorphic Metamorphic Metamorphic Detrital magmatic Detrital magmatic Detrital magmatic Detrital magmatic Detrital magmatic Detrital magmatic Detrital magmatic Detrital magmatic Detrital magmatic Detrital magmatic Detrital magmatic Detrital magmatic Detrital magmatic Detrital magmatic Detrital magmatic Detrital magmatic Detrital magmatic Detrital magmatic Detrital magmatic Detrital magmatic Detrital magmatic Detrital magmatic Detrital magmatic Detrital magmatic Detrital magmatic Detrital magmatic Detrital magmatic

0.37 0.27 0.016 0.013 bd 0.025 0.011 bd 0.023 0.009 0.120 0.057 0.032 0.022 0.200 0.044 0.016 0.018 0.004 0.015 0.033 0.680 0.025 0.024 bd 0.380 0.140 0.033 0.150 0.040 0.053 5.41 0.052 0.016 0.007

0.96 0.60 0.13 0.26 0.048 0.21 0.026 0.16 14.30 13.50 2.74 2.48 6.35 7.20 4.93 15.20 11.70 1.12 1.61 8.09 15.2 3.62 2.42 5.91 2.57 2.32 31.7 12.8 7.78 3.61 22.6 23.4 20.3 13.8 33.4

0.31 0.25 0.021 0.025 0.002 0.039 0.016 0.037 0.16 0.091 0.086 0.051 0.32 0.40 0.45 0.31 0.093 bd 0.062 0.089 0.29 0.36 0.09 0.27 0.059 0.170 0.095 0.21 0.16 0.041 0.50 2.15 0.15 0.090 0.082

1.59 1.23 0.10 bd bd 0.088 bd bd 3.16 1.03 1.62 0.80 4.67 6.21 1.17 5.16 2.25 0.033 0.72 1.98 5.30 2.63 1.35 4.57 1.55 1.00 0.68 3.05 1.43 0.85 7.61 13.5 3.21 2.14 1.54

0.72 0.51 bd 0.10 bd bd 0.02 bd 7.05 2.79 2.43 2.74 9.46 9.48 3.56 8.33 5.32 1.33 2.84 4.26 8.50 4.25 3.56 8.05 2.70 1.82 1.41 6.79 2.67 2.37 14.6 6.73 6.61 4.76 3.64

0.25 0.24 bd 0.027 0.038 0.030 bd 0.090 0.66 0.50 0.28 0.27 0.59 1.00 0.24 1.54 0.57 0.019 0.053 0.33 1.39 0.13 0.13 0.56 0.11 0.056 0.28 0.97 0.19 0.14 1.85 1.09 0.83 0.60 1.21

1.93 1.09 0.14 0.39 0.05 0.19 0.12 0.56 39.4 14.7 23.0 22.3 44.7 46.8 24.1 42.1 26.8 8.96 19.9 28.3 44.4 25.7 25.3 46.9 15.5 19.9 8.06 38.7 15.9 19.1 97.1 29.1 36.3 24.2 16.4

0.49 0.30 0.076 0.091 0.014 0.058 bd 0.069 14.4 5.20 9.01 10.6 13.9 14.9 9.75 14.0 9.53 4.33 9.58 9.67 14.6 9.90 9.91 14.6 5.49 10.5 3.24 13.4 5.82 6.43 30.0 8.84 12.1 9.11 4.96

5.76 2.87 1.02 1.04 0.17 0.84 0.089 1.43 185 63.4 126 159 163 178 141 181 121 69.8 147 125 186 128 134 181 73.1 175 45.3 180 85.6 69.3 347 106 143 102 58.3

1.82 0.90 0.58 0.39 0.080 0.30 0.036 0.72 70.4 25.3 51.6 65.6 58.3 63.7 55.4 65.7 43.3 29.9 62.7 46.3 70.4 50.8 52.6 64.9 26.3 75.1 19.3 68.7 34.1 21.9 118 37.6 50.3 36.0 20.1

8.44 4.32 3.42 2.40 0.32 2.00 0.13 5.35 401 130 304 361 279 328 294 325 211 169 348 233 365 293 273 306 127 416 113 350 181 100 585 170 229 164 98.6

1.66 0.94 0.84 0.73 0.065 0.38 0.080 1.14 67.4 25.9 57.0 75.7 51.0 55.8 58.3 62.6 39.2 37.2 73.5 44.6 63.9 51.9 55.4 58.3 24.4 88.2 25.9 67.8 36.5 15.5 88.2 30.9 40.6 29.0 19.4

17.0 8.91 9.50 7.64 0.94 4.46 0.66 15.2 611 252 559 748 461 494 546 575 360 370 727 421 575 485 521 506 221 858 283 636 358 125 714 263 346 249 186

3.06 1.78 2.04 1.28 0.13 0.53 0.14 2.99 118 50.2 114 146 85.9 97.0 105 111 68.4 76.8 144 80.9 117 96.4 100 96.4 44.9 166 61.6 124 71.5 22.8 127 47.9 61.8 44.2 37.1

44.4 24.2 17.9 14.4 1.9 9.2 1.3 27.7 1532 585 1251 1595 1178 1303 1244 1407 899 769 1537 1004 1467 1152 1179 1293 545 1814 594 1502 801 387 2154 746 950 679 481

0.070

17.4

0.004

0.32

1.14

0.67

5.37

1.98

26.4

11.6

66.3

15.9

174

42.9

364

DH09-3-1, quarzitte 42 Metamorphic

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F. Yu et al. / Journal of Asian Earth Sciences 42 (2011) 740–751 Table 2 (continued) Sample

Domain

La

Ce

Pr

Nd

Sm

Eu

Gd

Tb

Dy

Ho

Er

Tm

Yb

Lu

REE

51 10 54 12 1 47 41 34 56 27 16 31 40 57 30 44 48 3 2 37 50 21 18 9 39 32 22 19 28 26 38 46 55 29 23 43 17 45 13 35 49 53 24 33 25 5 36 20

Metamorphic Detrital magmatic Detrital magmatic Detrital magmatic Detrital magmatic Detrital magmatic Detrital magmatic Detrital magmatic Detrital magmatic Detrital magmatic Detrital magmatic Detrital magmatic Detrital magmatic Detrital magmatic Detrital magmatic Detrital magmatic Detrital magmatic Detrital magmatic Detrital magmatic Detrital magmatic Detrital magmatic Detrital magmatic Detrital magmatic Detrital magmatic Detrital magmatic Detrital magmatic Detrital magmatic Detrital magmatic Detrital magmatic Detrital magmatic Detrital magmatic Detrital magmatic Detrital magmatic Detrital magmatic Detrital magmatic Detrital magmatic Detrital magmatic Detrital magmatic Detrital magmatic Detrital magmatic Detrital magmatic Detrital magmatic Detrital magmatic Detrital magmatic Detrital magmatic Detrital magmatic Detrital magmatic Detrital magmatic

0.015 0.560 0.048 0.037 0.112 0.019 0.005 0.006 0.031 bd bd bd 0.031 bd 0.019 bd 0.011 0.051 0.018 0.017 0.005 bd bd 0.037 bd 0.011 0.013 0.049 0.034 0.028 0.022 0.003 bd 0.031 0.026 0.070 0.019 0.002 0.039 0.063 0.012 0.055 0.006 bd 0.018 0.042 0.033 bd

1.61 47.3 4.39 29.7 27.1 46.6 0.82 3.37 0.84 9.79 0.49 17.7 4.80 33.6 0.59 7.30 7.76 3.00 9.41 0.22 28.8 14.9 2.50 13.9 12.5 1.36 25.2 72.9 14.3 16.9 0.54 17.1 14.3 7.93 21.2 23.3 0.59 11.6 15.7 8.16 34.3 7.24 0.79 5.25 11.6 2.59 6.37 14.1

0.033 0.23 0.34 0.093 0.17 0.13 0.011 0.22 0.096 0.061 0.050 0.049 0.10 0.062 0.079 0.003 0.021 0.035 0.11 bd 0.106 0.030 0.047 0.56 0.045 0.039 0.15 0.12 0.30 0.15 0.043 0.037 0.074 0.31 0.15 0.12 0.079 0.039 0.098 0.11 0.19 0.47 0.021 0.088 0.051 0.17 0.36 0.22

0.66 1.49 5.28 1.34 1.51 2.93 0.16 2.75 2.04 1.10 0.61 1.36 1.97 0.60 0.94 0.55 0.48 0.52 2.74 1.07 2.40 0.26 0.95 7.22 1.12 0.49 1.93 2.56 3.19 2.05 0.97 1.05 1.91 4.54 2.07 2.08 0.94 0.76 1.69 1.73 3.32 6.38 bd 1.48 0.46 2.76 7.39 3.07

0.57 1.89 7.69 1.78 2.54 5.74 0.32 7.13 5.45 3.16 3.59 3.27 4.31 2.81 3.36 1.81 2.25 1.81 4.05 2.46 3.57 1.30 1.77 11.5 2.23 1.68 3.70 5.76 5.94 4.95 2.81 3.05 2.86 6.57 4.37 3.70 3.36 1.50 3.09 3.28 6.22 7.70 0.19 3.01 2.08 5.85 10.36 8.24

0.27 1.08 0.31 0.50 1.01 1.01 0.20 0.47 0.32 0.43 0.34 0.25 0.060 0.46 0.13 0.31 0.39 1.50 1.94 0.23 0.77 0.65 0.13 0.43 0.25 0.23 0.41 1.36 0.22 0.20 0.15 0.68 0.39 1.05 0.98 1.23 0.13 0.69 0.40 0.27 1.84 1.21 0.01 0.38 0.14 0.38 1.85 1.98

4.11 13.4 41.2 8.64 11.4 25.7 4.57 44.6 34.3 24.4 27.1 20.2 25.7 12.5 19.5 11.9 10.8 11.3 20.4 24.4 21.9 6.78 12.4 54.7 12.8 11.4 17.2 34.2 29.3 24.8 23.1 22.2 19.4 35.5 18.7 19.5 19.5 9.96 22.2 17.3 35.1 25.9 1.33 18.4 13.9 30.2 54.7 48.2

1.64 4.60 14.0 2.68 3.92 8.25 1.40 16.0 11.4 9.20 5.52 7.80 8.92 4.23 5.88 4.94 4.70 3.57 5.94 4.71 8.86 1.78 4.26 17.0 4.44 4.69 5.34 12.2 10.47 8.79 8.48 7.98 6.72 12.1 5.79 6.14 5.88 4.33 8.30 5.73 12.1 6.41 0.71 6.30 4.98 9.89 16.3 16.6

19.0 61.0 175 35.7 45.7 104 20.1 195 122 134 124 103 111 54.9 64.1 71.8 62.4 43.1 75.2 89.3 114 18.3 51.5 195 59.2 63.1 63.5 164 131 118 110 114 90.9 146 64.2 79.8 64.1 61.5 104 72.2 156 63.7 12.9 83.3 65.7 122 194 209

5.19 25.2 64.1 13.5 17.0 38.2 8.20 65.5 39.7 55.1 66.7 39.0 39.1 21.6 20.1 27.8 23.8 16.7 27.6 25.4 44.4 6.02 18.1 67.5 22.3 23.6 22.5 61.5 47.9 42.7 36.6 47.6 35.9 52.0 23.0 29.4 20.1 27.9 40.0 26.1 61.1 21.6 6.32 30.4 25.4 42.5 66.4 76.7

17.3 138 328 74.8 95.5 192 45.2 299 191 300 127 203 184 119 86.1 150 132 83.1 148 123 239 28.2 88.6 315 114 130 102 315 232 211 174 270 193 251 119 157 86.1 172 200 129 326 97.6 37.5 151 142 222 298 371

1.98 30.6 56.4 16.2 20.7 37.5 10.1 54.5 33.1 61.3 35.1 40.9 33.4 22.0 15.0 32.8 30.5 15.4 33.7 34.4 48.1 6.03 16.7 56.7 22.1 28.5 19.0 62.3 44.0 43.5 33.5 57.2 36.8 47.4 24.2 35.3 15.0 42.2 37.8 26.6 66.2 17.1 8.59 30.3 29.8 39.8 51.9 70.4

15.6 333 491 173 220 351 104 479 307 597 248 385 291 226 131 345 328 148 362 242 443 56 151 499 219 304 175 584 382 408 320 589 343 437 246 364 131 475 345 272 637 153 94.6 303 307 358 462 647

2.6 75.6 90.5 38.6 48.2 68.5 24.0 86.0 57.4 118 69.2 76.4 53.9 45.3 25.5 69.0 69.2 30.4 76.1 48.4 87.1 11.4 27.8 92.9 43.3 61.7 32.2 112 67.3 78.0 58.2 126 67.5 83.4 50.7 78.9 25.5 112 66.8 54.0 130 29.2 21.3 64.4 64.7 69.6 84.6 120

70.5 734 1278 396 495 881 219 1254 804 1314 708 898 759 544 372 723 672 358 767 596 1042 152 376 1331 513 631 468 1428 968 959 769 1256 813 1085 580 800 372 919 845 616 1470 437 184 697 668 906 1253 1587

DH09-3-3, 40 44 5 8 26 35 21 42 30 33 39 38 18 41 16 7 10 31 9 12 2

quartzite Metamorphic Metamorphic Detrital metamorphic Detrital metamorphic Detrital magmatic Detrital magmatic Detrital magmatic Detrital magmatic Detrital magmatic Detrital magmatic Detrital magmatic Detrital magmatic Detrital magmatic Detrital magmatic Detrital magmatic Detrital magmatic Detrital magmatic Detrital magmatic Detrital magmatic Detrital magmatic Detrital magmatic

bd 0.064 0.015 0.064 0.015 0.100 0.068 0.062 0.065 0.67 0.009 0.015 0.035 1.56 0.140 0.046 0.028 0.120 0.014 bd 0.018

0.44 1.88 3.27 10.9 5.79 18.1 21.8 7.83 16.9 29.0 22.7 12.7 12.4 24.1 20.6 3.70 13.4 49.6 33.2 7.12 9.41

0.016 0.140 0.019 0.089 0.25 0.60 0.63 0.23 0.48 1.07 0.22 0.50 0.53 0.78 0.19 0.20 0.13 1.04 0.17 0.034 0.11

0.17 1.01 0.34 0.66 3.66 11.5 10.3 4.09 7.23 9.17 4.06 6.96 7.35 4.58 2.01 3.36 1.89 15.3 2.39 0.78 2.74

0.17 0.72 0.31 0.47 4.61 15.5 13.3 5.51 11.0 11.7 6.80 10.8 11.8 6.84 3.90 4.83 4.62 19.3 3.53 1.81 4.05

0.10 0.15 0.16 0.40 0.73 0.21 0.39 0.83 1.87 1.44 0.37 2.11 0.62 0.13 0.22 3.46 0.36 7.13 0.62 0.25 1.94

0.75 1.58 1.46 2.76 18.1 56.7 52.1 29.4 61.2 58.7 39.4 63.6 47.6 33.1 21.3 21.6 19.2 64.6 8.88 12.5 20.4

0.36 0.55 0.64 1.09 5.30 17.8 15.0 9.50 20.2 17.4 13.3 21.1 13.7 11.1 6.53 6.19 6.62 15.6 1.84 4.67 5.94

7.29 8.45 8.65 16.1 60.0 205 171 112 252 208 166 248 156 134 80.5 70.3 78.2 148 15.7 62.6 75.2

3.89 3.77 4.12 6.38 19.8 67.3 54.2 35.8 87.6 71.4 58.5 88.2 50.5 44.5 28.3 20.1 26.1 44.2 4.02 24.2 27.6

26.3 22.9 25.9 40.0 96.7 277 250 161 416 291 252 385 235 198 144 89.9 124 166 16.3 126 148

7.43 6.76 6.56 8.93 16.6 52.9 43.0 31.2 72.1 53.7 47.4 73.8 39.1 35.8 25.8 14.4 21.3 31.1 2.5 23.1 33.7

81.5 84.3 75.7 103 151 450 365 269 621 455 400 628 334 296 237 123 183 270 20.0 214 362

17.5 21.1 19.9 24.7 28.6 78.9 65.3 47.7 112 79.5 65.9 111 60.8 51.4 45.8 21.0 32.8 50.5 3.51 41.4 76.1

146 153 147 216 411 1252 1062 714 1680 1288 1077 1652 969 842 616 382 512 882 113 518 767

bd⁄: Below the detection limit.

U–Pb dating and was analyzed twice every five analyses. A linear interpolation (with time) for every five analyses according to the variations of 91500 (i.e., 2 zircon 91500 + 5 samples + 2 zircon

91500) was used to correct the time-dependent drifts of U–Th– Pb isotopic ratios (Liu et al., 2010). Preferred U–Th–Pb isotopic ratios used for zircon 91500 are from Wiedenbeck et al. (1995).

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F. Yu et al. / Journal of Asian Earth Sciences 42 (2011) 740–751

10000.0

10000.0

(b) DH09-1-1, marble

1000.0

1000.0

100.0

100.0

Zircon/Chondrite

Zircon/Chondrite

(a) DH08-7-2, marble

10.0 1.0 0.1

10.0 1.0 0.1

Metamorphic zircon Magmatic zircon

0.001 0.0001

0.0001

La Ce Pr Nd Sm Eu Gd Tb Dy Ho Er Tm Yb Lu

(c) DH09-3-1, quartzite

La Ce Pr Nd Sm Eu Gd Tb Dy Ho Er Tm Yb Lu

(d) DH09-3-3, quartzite

1000.0

1000.0

100.0

100.0

Zircon/Chondrite

Zircon/Chondrite

Magmatic zircon

10000.0

10000.0

10.0 1.0 0.1 Metamorphic zircon 0.001 0.0001

Metamorphic zircon

0.001

Magmatic zircon La Ce Pr Nd Sm Eu Gd Tb Dy Ho Er Tm Yb Lu

10.0 1.0 0.1 Metamorphic zircon

0.001 0.0001

Magmatic zircon La Ce Pr Nd Sm Eu Gd Tb Dy Ho Er Tm Yb Lu

Fig. 3. Chondrite-normalized REE patterns of zircons.

Concordia diagrams and weighted mean calculations were made using Isoplot/Ex_ver3 (Ludwig, 2003). Trace element compositions of zircons were calibrated against multiple-reference materials (BCR-2G and BIR-1G) without applying internal standardization (Liu et al., 2008b). The preferred values of element concentrations for the USGS reference glasses are from the GeoReM database (http://georem.mpch-mainz.gwdg.de/). 3. Geological setting and samples The southern Sulu orogen includes two major lithotectonic units: the UHP metamorphic unit in the northern segment and the high-pressure (HP) metamorphic unit in the southern part (Fig. 1). The rocks from the UHP unit in the vicinity of Donghai consist of granitic gneiss, eclogite, peridotite and meta-supracrustal rocks. In this paper, two marbles (DH08-7-2 and DH09-1-1) and two quartzite samples (DH09-3-1 and DH09-3-3), from northeastern Donghai were selected for detailed geochronologic study (Fig. 1). The marbles occur as large blocks within the gneiss at Sanqingge, and contain centimeter – to meter-sized eclogite blocks. Primary compositional layers with distinct color bands are preserved in some thick marble layers. Impure marble layers are rich in silicate minerals whereas others contain nearly pure carbonate. Although some outcrops seem to be homogeneous, millimeterscale compositional layers can be identified on a thin-section scale. The studied marbles consist of calcite with minor diopside and tremolite (<10 vol.%). The studied quartzites form an isolated hill at Wuqiangshan, and consist chiefly of quartz, and variable amounts of phengite,

tremolite and opaque minerals. The dated sample DH09-3-1 consists of quartz (75%) and abundant magnetite (15%), whereas sample DH09-3-3 contains abundant quartz (95%) and minor magnetite (5%). Zircon occurs as a matrix mineral or as inclusion within other minerals. Raman analysis shows that the coesite and phengite, typical of UHP mineral, occur as inclusions in the rims of zircon; whereas, the low-pressure mineral inclusions of feldspar, quartz and apatite occur in the cores. The Sanqingge marbles have various CaO (28.4 and 30.4 wt.%), MgO (17. 7 and 21.2 wt.%) and SiO2 (15.9 and 4.8 wt.%) contents, with very low contents of other oxides (<2 wt.%) (Table 1). The Wuqiangshan quartzites have relatively high SiO2 (71.9 and 96.7 wt.%), various Fe2O3 (26.1 and 2.1 wt.%), and very low other oxides (<1 wt.%) contents (Table 1). The high Fe2O3 content of the quartzite sample DH09-3-1 is consistent with its abundant magnetite. 4. Zircon U–Pb dating results Zircons from marble sample DH08-7-2 are colorless and transparent, and range in grain size from 50 to 100 lm. Cathodoluminescence (CL) images reveal that the zircon grains have various internal structures. Some grains have an inner core with dark luminescence and an outer rim with bright luminescence; some grains have an inner core with weak oscillatory zoning, a mantle with dark luminescence and an outer rim with bright luminescence (Fig. 2a). Most zircons have various but relatively high Th/U ratios ranging from 0.075 to 3.111 and various REE contents (Table 2), with flat or enriched HREE patterns and negative Eu anomalies

Table 3 Zircon U-Pb data of UHP supracrustal rocks from the southern Sulu orogen. Sample

Domain

Th (ppm)

U (ppm)

Th/U

Isotopic ratios 207

Pb/206Pb

Ages(Ma) ±1r

207

Pb/235U

±1r

206

Pb/238U

±1r

207

Pb/206Pb

±1r

207

Pb/235U

±1r

206

Pb/238U

±1r

marble Metamorphic Detrital magmatic Detrital magmatic Detrital magmatic Detrital magmatic Detrital magmatic Detritalmagmatic Detrital magmatic Detrital magmatic

34.0 147.0 262.0 28.7 28.5 148.0 134.0 120.0 397.0

179.0 205.0 331.0 210.0 382.0 378.0 69.5 68.9 128.0

0.190 0.714 0.790 0.137 0.075 0.391 1.926 1.741 3.111

0.0605 0.0779 0.0658 0.1221 0.1047 0.1293 0.1107 0.1106 0.1112

0.0050 0.0080 0.0055 0.0057 0.0052 0.0055 0.0065 0.0072 0.0050

0.3389 0.4094 0.3893 4.2009 3.7000 5.5730 5.0950 5.3867 5.5062

0.0272 0.0367 0.0306 0.2182 0.1787 0.2740 0.3047 0.3557 0.2476

0.0401 0.0392 0.0435 0.2460 0.2524 0.3089 0.3291 0.3542 0.3592

0.0013 0.0011 0.0012 0.0057 0.0045 0.0069 0.0076 0.0101 0.0071

620 1146 1200 1988 1709 2089 1811 1809 1820

181 204 178 87 92 74 107 117 50

296 348 334 1674 1571 1912 1835 1883 1902

21 26 22 43 39 42 51 57 39

254 248 275 1418 1451 1735 1834 1955 1979

8 7 7 30 23 34 37 48 34

DH09-1-1, 1 2 7 16 17 22 33 34 41 4 37 18 20 32 26 12 25 10 24 30 31 43 8 6 15 29 11 27 19 42 40 13 5 23 14

marble Metamorphic Metamorphic Metamorphic Metamorphic Metamorphic Metamorphic Metamorphic Metamorphic Detrital magmatic Detrital magmatic Detrital magmatic Detrital magmatic Detrital magmatic Detrital magmatic Detrital magmatic Detrital magmatic Detrital magmatic Detrital magmatic Detrital magmatic Detrital magmatic Detrital magmatic Detrital magmatic Detrital magmatic Detrital magmatic Detrital magmatic Detrital magmatic Detrital magmatic Detrital magmatic Detrital magmatic Detrital magmatic Detrital magmatic Detrital magmatic Detrital magmatic Detrital magmatic Detrital magmatic

4.6 3.4 8.1 7.3 4.1 10.4 5.5 7.4 323.0 210.0 124.0 184.0 319.0 242.0 182.0 521.0 184.0 59.4 154.0 188.0 286.0 102.0 153.0 384.0 115.0 123.0 76.8 302.0 276.0 184.0 238.0 72.9 161.0 119.0 171.0

3980.0 3300.0 2162.0 2369.0 1971.0 2812.0 3623.0 2788.0 569.0 417.0 1235.0 1250.0 488.0 423.0 680.0 934.0 302.0 549.0 1286.0 426.0 410.0 450.0 662.0 620.0 274.0 1790.0 145.0 581.0 722.0 1039.0 320.0 129.0 217.0 185.0 253.0

0.001 0.001 0.004 0.003 0.002 0.004 0.002 0.003 0.569 0.503 0.100 0.148 0.654 0.572 0.268 0.558 0.609 0.108 0.119 0.441 0.698 0.227 0.231 0.619 0.420 0.069 0.530 0.520 0.382 0.177 0.745 0.567 0.744 0.640 0.678

0.05 0.0512 0.0511 0.0499 0.0509 0.052 0.0493 0.0484 0.0469 0.0545 0.0501 0.0573 0.0512 0.0512 0.0524 0.0503 0.0522 0.0544 0.0519 0.0563 0.0519 0.0504 0.0548 0.0539 0.051 0.0553 0.0573 0.0569 0.0588 0.0655 0.0794 0.0804 0.0845 0.0848 0.1577

0.0010 0.0011 0.0011 0.0011 0.0012 0.0010 0.0014 0.0015 0.0025 0.0021 0.0019 0.0019 0.0021 0.0029 0.0019 0.0013 0.0026 0.0022 0.0013 0.0020 0.0028 0.0026 0.0018 0.0019 0.0023 0.0013 0.0033 0.0015 0.0013 0.0018 0.0024 0.0022 0.0021 0.0022 0.0029

0.2573 0.2530 0.2595 0.2501 0.2662 0.2637 0.2534 0.2346 0.2164 0.2576 0.2400 0.2753 0.2471 0.2486 0.2573 0.2488 0.2544 0.2682 0.2605 0.2865 0.2660 0.2563 0.2809 0.2798 0.2771 0.3043 0.3270 0.5580 0.6681 0.7792 2.2271 2.4772 2.6175 2.6526 8.9299

0.0053 0.0055 0.0059 0.0058 0.0064 0.0056 0.0072 0.0073 0.0108 0.0099 0.0093 0.0101 0.0102 0.0134 0.0088 0.0065 0.0118 0.0102 0.0069 0.0098 0.0151 0.0131 0.0097 0.0095 0.0126 0.0073 0.0190 0.0154 0.0149 0.0218 0.0656 0.0707 0.0643 0.0721 0.2215

0.0372 0.0356 0.0366 0.0362 0.0378 0.0367 0.0369 0.0348 0.0333 0.0342 0.0344 0.0347 0.0352 0.0352 0.0354 0.0357 0.0358 0.0359 0.0362 0.0367 0.0368 0.0369 0.0369 0.0374 0.0395 0.0396 0.0414 0.0705 0.0825 0.0855 0.2012 0.2221 0.2240 0.2270 0.4090

0.0003 0.0003 0.0004 0.0004 0.0003 0.0003 0.0005 0.0005 0.0004 0.0004 0.0005 0.0004 0.0004 0.0005 0.0004 0.0003 0.0005 0.0005 0.0004 0.0005 0.0006 0.0006 0.0006 0.0004 0.0006 0.0003 0.0007 0.0007 0.0008 0.0012 0.0024 0.0026 0.0023 0.0024 0.0068

195 250 256 191 239 283 165 120 56 394 198 502 256 250 306 209 300 391 280 465 280 213 406 369 239 433 506 487 567 791 1181 1206 1306 1311 2431

48 44 50 19 58 46 65 68 109 85 87 72 94 125 81 94 117 93 62 76 158 122 72 84 106 54 128 59 48 62 60 55 50 51 31

233 229 234 227 240 238 229 214 199 233 218 247 224 225 232 226 230 241 235 256 240 232 251 250 248 270 287 450 520 585 1190 1265 1306 1315 2331

4 4 5 5 5 5 6 6 9 8 8 8 8 11 7 5 10 8 6 8 12 11 8 8 10 6 15 10 9 12 21 21 18 20 23

235 226 232 230 239 232 234 221 211 217 218 220 223 223 224 226 227 228 229 233 233 234 234 237 250 251 262 439 511 529 1182 1293 1303 1319 2210

2 2 2 2 2 2 3 3 3 3 3 2 3 3 2 2 3 3 2 3 4 4 4 2 3 2 5 4 5 7 13 14 12 13 31

DH09-3-1, 42 51 10 54 12

quarzitte Metamorphic Metamorphic Detrital magmatic Detrital magmatic Detrital magmatic

106.0 41.4 407.0 107.0 284.0

533.0 1049.0 752.0 241.0 557.0

0.200 0.039 0.542 0.444 0.510

0.0523 0.0494 0.0489 0.0516 0.0468

0.0030 0.0021 0.0017 0.0048 0.0018

0.2306 0.2363 0.2338 0.2453 0.2256

0.0138 0.0104 0.0079 0.0221 0.0085

0.0316 0.0342 0.0345 0.0345 0.0348

0.0006 0.0005 0.0004 0.0008 0.0004

298 169 143 333 39

136 98 86 218 89

211 215 213 223 207

11 9 7 18 7

201 217 219 219 220

4 3 3 5 3 745

(continued on next page)

F. Yu et al. / Journal of Asian Earth Sciences 42 (2011) 740–751

DH08-7-2, 2 3 4 14 5 11 6 7 10

746

Table 3 (continued) Sample

Domain

Th (ppm)

U (ppm)

Th/U

Isotopic ratios 207

DH09-3-3, 40 44 5 8 26 35 21 42 30

Detrital Detrital Detrital Detrital Detrital Detrital Detrital Detrital Detrital Detrital Detrital Detrital Detrital Detrital Detrital Detrital Detrital Detrital Detrital Detrital Detrital Detrital Detrital Detrital Detrital Detrital Detrital Detrital Detrital Detrital Detrital Detrital Detrital Detrital Detrital Detrital Detrital Detrital Detrital Detrital Detrital Detrital Detrital Detrital

magmatic magmatic magmatic magmatic magmatic magmatic magmatic magmatic magmatic magmatic magmatic magmatic magmatic magmatic magmatic magmatic magmatic magmatic magmatic magmatic magmatic magmatic magmatic magmatic magmatic magmatic magmatic magmatic magmatic magmatic magmatic magmatic magmatic magmatic magmatic magmatic magmatic magmatic magmatic magmatic magmatic magmatic magmatic magmatic

quartzite Metamorphic Metamorphic Detrital metamorphic Detrital metamorphic Detrital magmatic Detrital magmatic Detrital magmatic Detrital magmatic Detrital magmatic

Pb/

Pb

Ages(Ma) ±1r

207

235

Pb/

U

±1r

206

238

Pb/

U

±1r

207

Pb/206Pb

±1r

207

Pb/235U

±1r

206

Pb/238U

±1r

240.0 224.0 220.0 4.3 7.4 38.3 81.7 196.0 59.3 48.5 60.8 57.8 269.0 20.5 41.0 14.2 80.4 33.0 138.0 226.0 103.0 246.0 93.6 232.0 140.0 121.0 201.0 149.0 232.0 27.1 300.0 90.9 182.0 137.0 184.0 66.1 105.0 58.2 67.3 83.5 231.0 172.0 286.0 247.0

397.0 355.0 443.0 625.0 546.0 313.0 445.0 484.0 171.0 816.0 377.0 576.0 395.0 47.1 383.0 56.6 450.0 132.0 179.0 528.0 517.0 700.0 405.0 193.0 240.0 275.0 319.0 194.0 278.0 463.0 712.0 91.2 225.0 171.0 418.0 136.0 123.0 82.9 142.0 161.0 426.0 396.0 518.0 446.0

0.604 0.630 0.497 0.007 0.013 0.122 0.184 0.404 0.348 0.059 0.161 0.100 0.681 0.435 0.107 0.250 0.179 0.250 0.769 0.428 0.200 0.351 0.231 1.205 0.582 0.440 0.628 0.767 0.836 0.059 0.422 0.996 0.810 0.804 0.441 0.486 0.850 0.702 0.475 0.518 0.543 0.433 0.551 0.553

0.051 0.05 0.0516 0.0551 0.059 0.0615 0.061 0.067 0.0624 0.0659 0.0733 0.0692 0.0689 0.0688 0.0736 0.0743 0.0679 0.0712 0.0699 0.0775 0.0831 0.0839 0.0835 0.0767 0.0882 0.0833 0.0977 0.0891 0.0888 0.0927 0.0877 0.0879 0.0859 0.0913 0.0897 0.0949 0.1019 0.0911 0.105 0.0973 0.1023 0.1108 0.111 0.1653

0.0023 0.0031 0.0032 0.0016 0.0017 0.0020 0.0015 0.0018 0.0033 0.0015 0.0021 0.0033 0.0021 0.0038 0.0020 0.0038 0.0023 0.0025 0.0020 0.0016 0.0032 0.0018 0.0022 0.0022 0.0025 0.0020 0.0032 0.0033 0.0021 0.0022 0.0021 0.0055 0.0018 0.0037 0.0019 0.0023 0.0032 0.0036 0.0030 0.0024 0.0022 0.0024 0.0020 0.0030

0.2575 0.2556 0.5171 0.6080 0.7424 0.8576 0.8863 1.1283 1.0951 1.1543 1.3174 1.2695 1.2677 1.2542 1.3844 1.3894 1.4121 1.5161 1.6185 1.8807 2.0596 2.1045 2.1573 2.0039 2.5190 2.4463 2.9536 2.7398 2.8106 2.9670 2.8474 2.9025 2.8554 3.0675 3.0199 3.3964 3.7508 3.4791 4.0209 3.7852 4.0851 4.7727 4.9951 9.9361

0.0107 0.0149 0.0294 0.0186 0.0196 0.0271 0.0249 0.0328 0.0564 0.0302 0.0384 0.0555 0.0391 0.0707 0.0405 0.0645 0.0493 0.0568 0.0507 0.0474 0.0815 0.0453 0.0735 0.0566 0.0865 0.0655 0.0987 0.0941 0.0755 0.0690 0.0756 0.1703 0.0632 0.1189 0.0667 0.0849 0.1228 0.1412 0.1169 0.1006 0.0914 0.1155 0.0958 0.1922

0.0367 0.0371 0.0718 0.0798 0.0910 0.1008 0.1046 0.1213 0.1260 0.1261 0.1298 0.1311 0.1321 0.1327 0.1354 0.1385 0.1492 0.1543 0.1678 0.1745 0.1771 0.1810 0.1848 0.1894 0.2054 0.2112 0.2183 0.2210 0.2276 0.2310 0.2336 0.2361 0.2402 0.2410 0.2428 0.2589 0.2645 0.2752 0.2771 0.2809 0.2875 0.3105 0.3252 0.4339

0.0004 0.0005 0.0011 0.0012 0.0008 0.0012 0.0012 0.0013 0.0019 0.0018 0.0014 0.0016 0.0016 0.0025 0.0013 0.0027 0.0019 0.0027 0.0027 0.0026 0.0028 0.0016 0.0033 0.0023 0.0039 0.0027 0.0027 0.0029 0.0028 0.0020 0.0032 0.0041 0.0026 0.0035 0.0033 0.0034 0.0037 0.0045 0.0037 0.0037 0.0028 0.0035 0.0029 0.0048

243 195 333 417 569 657 639 839 687 806 1021 906 894 894 1031 1050 866 962 924 1144 1272 1300 1283 1122 1387 1276 1581 1406 1399 1483 1376 1380 1400 1454 1420 1528 1659 1450 1717 1573 1678 1813 1817 2511

71 138 173 67 61 70 56 53 115 42 59 103 68 115 54 104 103 73 59 42 75 41 52 57 54 46 63 38 45 44 46 120 41 78 34 46 58 77 54 48 39 41 33 31

233 231 423 482 564 629 644 767 751 779 853 832 831 825 882 884 894 937 977 1074 1135 1150 1167 1117 1278 1256 1396 1339 1358 1399 1368 1383 1370 1425 1413 1504 1582 1522 1638 1590 1651 1780 1818 2429

9 12 20 12 11 15 13 16 27 14 17 25 18 32 17 27 21 23 20 17 27 15 24 19 25 19 25 26 20 18 20 44 17 30 17 20 26 32 24 21 18 20 16 18

233 235 447 495 561 619 641 738 765 766 787 794 800 803 819 836 897 925 1000 1037 1051 1072 1093 1118 1204 1235 1273 1287 1322 1340 1353 1366 1388 1392 1401 1484 1513 1567 1577 1596 1629 1743 1815 2323

2 3 7 7 5 7 7 8 11 10 8 9 9 14 7 15 11 15 15 14 15 9 18 13 21 14 14 15 15 11 17 22 13 18 17 17 19 23 19 18 14 17 14 21

0.4 20.8 12.0 48.5 56.1 87.6 241.0 52.7 176.0

1618.0 919.0 108.0 263.0 152.0 194.0 254.0 98.9 261.0

0.0002 0.023 0.111 0.184 0.370 0.451 0.948 0.533 0.672

0.0517 0.0498 0.1218 0.1379 0.0692 0.0801 0.0772 0.0792 0.0774

0.0018 0.0021 0.0030 0.0027 0.0025 0.0032 0.0021 0.0037 0.0022

0.2393 0.2368 5.5425 6.4655 0.8997 1.5038 1.5805 1.7833 1.7582

0.0080 0.0097 0.1387 0.1264 0.0313 0.0640 0.0448 0.0837 0.0483

0.0334 0.0345 0.3286 0.3390 0.0943 0.1353 0.1476 0.1628 0.1645

0.0005 0.0006 0.0034 0.0028 0.0011 0.0022 0.0019 0.0025 0.0018

272 187 1983 2211 906 1200 1126 1177 1131

80 96 43 34 73 80 58 92 56

218 216 1907 2041 652 932 963 1039 1030

7 8 22 17 17 26 18 31 18

212 219 1832 1882 581 818 887 973 982

3 4 17 13 7 13 11 14 10

F. Yu et al. / Journal of Asian Earth Sciences 42 (2011) 740–751

1 47 41 34 56 27 16 31 40 57 30 44 48 3 2 37 50 21 18 9 39 32 22 19 28 26 38 46 55 29 23 43 17 45 13 35 49 53 24 33 25 5 36 20

206

bd⁄: Below the detection limit.

33 39 38 18 41 16 7 10 31 9 12 2

Detrital magmatic Detrital magmatic Detrita l magmatic Detrital magmatic Detrital magmatic Detrital magmatic Detrital magmatic Detrital magmatic Detrital magmatic Detrital magmatic Detrital magmatic Detrital magmatic

59.0 84.6 132.0 133.0 83.9 109.0 58.8 42.6 79.7 125.0 38.3 26.1

134.0 137.0 228.0 126.0 241.0 130.0 84.7 85.4 41.8 40.9 97.2 95.9

0.440 0.616 0.578 1.058 0.348 0.838 0.694 0.498 1.907 3.068 0.395 0.272

0.0896 0.0789 0.0784 0.0789 0.0777 0.0876 0.082 0.0853 0.1281 0.1235 0.1678 0.2123

0.0031 0.0032 0.0027 0.0021 0.0025 0.0031 0.0025 0.0025 0.0050 0.0037 0.0039 0.0041

2.1019 1.8878 1.9586 2.0450 2.0317 2.3986 2.3654 2.5900 6.1838 6.3213 10.0712 16.1221

0.0799 0.0742 0.0666 0.0525 0.0608 0.0871 0.0714 0.0746 0.2354 0.1994 0.2392 0.3066

0.1696 0.1729 0.1803 0.1871 0.1886 0.1978 0.2088 0.2202 0.3522 0.3706 0.4346 0.5507

0.0036 0.0025 0.0021 0.0019 0.0028 0.0028 0.0022 0.0024 0.0064 0.0045 0.0062 0.0043

1417 1169 1167 1170 1140 1374 1256 1324 2073 2009 2535 2923

65 80 73 58 95 67 61 62 37 54 39 31

1149 1077 1101 1131 1126 1242 1232 1298 2002 2021 2441 2884

26 26 23 18 20 26 22 21 33 28 22 18

1010 1028 1068 1106 1114 1164 1222 1283 1945 2032 2326 2828

20 14 12 11 15 15 12 13 31 21 28 18

F. Yu et al. / Journal of Asian Earth Sciences 42 (2011) 740–751

747

(Fig. 3a), suggesting a magmatic origin (Gebauer et al., 1997; Buick et al., 2006; Zhang et al., 2009b and references therein). These magmatic zircon domains yield variable 206Pb/238U ages ranging from 1979 to 248 Ma (Table 3 and Fig. 4a). In addition, one spot on the rim of a zircon has relatively low total REE (140.9 ppm) and low Th/U value (0.190) (Tables 2 and 3), suggesting a possible metamorphic origin (Williams et al., 1996; Gebauer et al., 1997; Rubatto, 2002; Buick et al., 2006), with an age of 254 Ma. Zircons from marble sample DH09-1-1 can be divided into two types. The first type is colorless, euhedral prismatic in shape, and ranges from 30 to 150 lm in size. These grains consist of an inherited detrital core with bright luminescence or weak oscillatory zoning and a thin homogeneous metamorphic rim (Fig. 2b). Most detrital cores of zircon have relatively high Th/U ratios ranging from 0.069 to 0.745 (av. 0.450), and high REE contents from 387.1 to 2153.5 ppm (av. 1112.8 ppm; Table 2), and REE patterns of HREE enrichment and distinctly negative Eu anomalies (Fig. 3b), indicating magmatic origin. These zircon cores have highly variable 206Pb/238U ages ranging from 2210 to 211 Ma (Table 3; Fig. 4b). The second type of zircon is light brown, forms short, subhedral prisms or anhedral ovals, and commonly shows very weak luminescence and weak patchy zoning (Fig. 2b). This variety has very low Th/U ratios of 0.001–0.004, and very low REE contents (av. 17.6 ppm), and shows weakly fractionated REE patterns without Eu anomalies (Fig. 3b), typical of a metamorphic origin (Williams et al., 1996; Gebauer et al., 1997; Rubatto, 2002; Buick et al., 2006). Eight spots on the second type of metamorphic zircons yielded relatively consistent 206Pb/238U ages of 239–221 Ma with a weighted mean age of 231 Ma (MSWD = 6.0) (Table 3; Fig. 4b). It is noted that the similar young ages are also obtained on the magmatic cores of some zircons (Table 3). We consider that these younger ages may represent the recrystallization of inherited magmatic zircons during the UHP metamorphism as discussed below. Zircons from the quartzite sample DH09-3-1 occur as colorless and transparent subhedral prisms, 50–150 lm long, that consist of an inherited detrital core with faint oscillatory zoning and a homogeneous metamorphic rim (Fig. 2c). The detrital cores have variable but relatively high Th/U ratios of 0.007–1.205 (av. 0.465), and high REE contents ranging from 70.5 to 1586 ppm (av. 817 ppm) (Tables 2 and 3). Their REE patterns are characterized by HREE enrichment with distinctly negative Eu anomalies (Fig. 3c), typical of magmatic zircon. These detrital zircon domains yield highly variable 206Pb/238U ages of 2323–219 Ma; most give relatively old ages of >700 Ma (Table 3 and Fig. 4c). Minor zircon grains form ovals without zoning. Two spots on these grains yielded similar 206Pb/238U ages of 201 and 217 Ma, relatively low Th/U ratios of 0.039–0.200, and low REE contents (70.5 and 364.1 ppm), typical of metamorphic origin (Tables 2 and 3). Zircons from quartzite sample DH09-3-3 are light brown and translucent, and form short prismatic or oval grains, with sizes ranging from 50 to 150 lm. CL images show that most zircons have a core-rim structure (Fig. 2d). Most cores have irregular shapes and commonly show faint oscillatory zoning. They have high Th/U ratios ranging from 0.27 to 3.07 (av. 0.89) and high REE concentrations (av. 870.0 ppm) (Tables 2 and 3). Their chondrite-normalized REE patterns are fractionated, with HREE enrichment and negative Eu anomalies (Fig. 3d), typical of a magmatic origin. These detrital cores yield relatively old and variable 206 Pb/238U ages of 2828–581 Ma. Two of the inherited cores have low Th/U ratios of 0.11 and 0.18, and low REE contents of 147.0 and 215.5 ppm, and display fractioned REE patterns without Eu anomaly (Fig. 3d), indicating a metamorphic origin. These detrital metamorphic cores yield similar 206Pb/238U ages of 1832 and

748

F. Yu et al. / Journal of Asian Earth Sciences 42 (2011) 740–751

(a) DH08-7-2, marble

0.4

2200

(b) DH09-1-1, marble

0.5

2600

2200

0.4

1800

Mean = 231±5 Ma Spots=8 MSWD = 6.0

238

Pb/

1400

0.2

206

206

Pb/

238

U

U

0.3

1000

1800 0.040

0.3 1400

0.038

0.2

230

1000

0.036 220

600

0.1

0.1 600

0.034 210 0.032 0.20

200

0.0

0

2

6

4 207

Pb/

0.0

8

0

2

4

0.22

6 207

235

Pb/

U

(c) DH09-3-1, quartzite

0.5

250 240

U

238

0.040

U

230

0.036

220 0.034 0.032

0.1 600

0.030

2200

0.4

Pb/

250 240

1400 1000

12

2600

0.038

0.2

0.30

3000

1800

206

U

206

Pb/

238

1800

0.28

10

(d) DH09-3-3, quartzite

2600

2200

0.3

0.26

235

0.6 0.4

0.24

8

210

1400

0.2 1000

200 190

180 0.028 0.18 0.20 0.22 0.24 0.26 0.28 0.30

0.0

0

2

4

6

8

10

12

0.0

0

4

207

Pb/ 235U

8

12

16

20

207

Pb/ 235U

Fig. 4. Concordia diagrams of zircon U–Pb ages.

1882 Ma (Table 3). However, two spots on the oval zircon show no zoning, have very low Th/U ratios and REE contents, typical of a metamorphic origin, and yielded 206Pb/238U ages of 212–219 Ma (Tables 2 and 3).

5. Discussion 5.1. Protolith and metamorphic ages of supracrustal rocks The available literature demonstrates that most Sulu gneisses and eclogites were subjected to Triassic HP and UHP metamorphism, and that their protoliths were formed by Neoproterozoic bimodal magmatism (e.g., Zhang et al., 2003, 2009a,b; Zheng et al., 2003a,b, 2006; Xu et al., 2006; Liu and Liou, 2011). However, the timing for the protolith age and timing of metamorphism of the supracrustal rocks from southern Sulu are only constrained by a few works (Liu et al., 2006a; Liu and Liou, 2011). The data presented above indicate that zircons from the marble and quartzite, typical of meta-supracrustal rocks, recorded Triassic metamorphism and multistage tectonic–thermal events of Neo-Archean to Neoproterozoic ages (Figs. 4 and 5a and b). The Triassic ages were mainly obtained on the metamorphic zircons without zoning, which have low Th/U ratios and low REE contents. The metamorphic zircons from marble DH09-1-1 yielded a weighted mean age of 231 Ma. Because the analyzed zircon domains contain coesite and phengite inclusions, as described above, the present study indicates that the supracrustal rocks, together with eclogites and orthogneisses from southern Sulu, were subjected to a coeval Triassic UHP metamorphism. The same UHP metamorphic age of

234 Ma has been obtained by zircon U–Pb dating for the Sanqingge marble by Liu et al. (2006a). As described above, some magmatic cores of zircon from marbles and quartzites yield Triassic ages similar to ages of the metamorphic zircons. For example, magmatic cores of detrital zircon from marble DH09-1-1 yield ages ranging from 236 to 211 Ma (Table 3); these young ages may represent recrystallization of inherited magmatic zircons during the UHP metamorphism. Although most dated magmatic cores have relatively high REE contents, and fractionated REE patterns with negative Eu anomalies, suggesting a magmatic origin, these zircon domains commonly show chaotic zoning patterns, and have variable but relatively low Th/U ratios 0.01 and 0.79 (Table 3), which have been interpreted to be characteristics of recrystallization of magmatic zircons during UHP metamorphism (Zhang et al., 2009b and references therein). Similar young ages have been obtained from many inherited magmatic zircons from the Sulu UHP eclogite and gneiss (Zhang et al., 2009a,b; Liu and Liou, 2011). Thus, zircon alteration has also been recognized in HP-UHP metamorphic rocks from other orogenic belts of the world (Gebauer et al., 1997; Rubatto and Scambelluri, 2003; Tomaschek et al., 2003; Spandler et al., 2004). In most cases, the obtained ages from these altered zircons are considered to be geologically meaningless (Zhang et al., 2009b). Most detrital zircons from the quartzites yielded highly variable ages ranging from Neo-Archean to Neoproterozoic, with an oldest age of 2828 Ma, and several age populations especially at 1830 and 800 Ma (Table 3 and Figs. 4c, d and 5a). Therefore, we speculate that the quartzite protoliths were formed in the Neoproterozoic at <800 Ma. In contrast, the detrital zircons from the marbles yield only minor Paleo- to Mesoproterozoic ages, and lack

F. Yu et al. / Journal of Asian Earth Sciences 42 (2011) 740–751

(a) Marbles from the southern Sulu

10

232 Ma

Number

Relative probability

8

6 800 Ma

4 1800 Ma

2

0 30

(b) Quartzites from the southern Sulu 220 Ma

Number

Relative probability

25 20 15 10 5

1300 Ma

749

et al., 2000, 2001, 2005; Gao et al., 2004; Zheng et al., 2004a; Wu et al., 2005; Liu et al., 2008c; Wang et al., 2010). As shown in Fig. 5c, the North China craton is dominated by rocks formed in the latest Archean at 2.5 Ga and during a Paleoproterozoic event at 1.8 Ga; whereas the Yangtze block is composed of Neoproterozoic rocks with an age peak of 820 Ma, and a minor Paleoproterozoic age peak at 1.8 Ga. The former peak was related to Neoproterozoic bimodal magmatism in the Yangtze craton associated with the breakup of the Rodinia Supercontinent (e.g., Gao et al., 1996; Li et al., 1999, 2002a, 2003a,b, 2005, 2006, 2008; Wang and Li, 2003; Zheng, 2003; Zheng et al., 2004b) or related to the active subduction followed assembly of Rodinia (Zhou et al., 2002a,b; Zhou et al., 2006). The present study indicates that the detrital zircons in the quartzites have a distinctly Neoproterozoic age population at 800 Ma (Fig. 5a), which provides strong evidence that the protoliths of some UHP meta-supracrustal rocks were derived from the Yangtze craton rather than the North China craton. In addition, two inherited cores of zircon from the quartzite yield similar metamorphic ages of 1831 and 1882 Ma (Fig. 5), which are consistent with widespread Paleoproterozoic tectonic–thermal events in the Yangtze block at 1.8 Ga (e.g., Compston et al., 1992; Maruyama et al., 1998; Bryant et al., 2004; Yang et al., 2003; Yin et al., 2003; Li et al., 2004; Liu et al., 2006b; Wu et al., 2006; Zheng et al., 2007). Therefore, we suggest that the protoliths of the UHP meta-supracrustal rocks of the Sulu orogen were derived from the Yangtze block rather than the North China craton.

0

6. Conclusions

(c) Yangtze craton North China craton 2500 Ma

Relative probability

820 Ma

1800 Ma

0

400

800

1200 1600 2000 2400 2800 3200 206

Pb/

238

U Age (Ma)

Fig. 5. Frequency diagrams of zircon U–Pb ages from the present study (a and b) and the North China and Yangtze Cratons (c) (the data are after Wu and Yu, 2000; Li et al., 2002a,b, 2003a,b; Wang et al., 2002, 2006, 2008a,b, 2010; Zhou et al., 2002a; Gao et al., 2004; Zheng et al., 2007; Xiong et al., 2009).

Neoproterozoic ages (Table 3 and Figs. 4a, b and 5b). This indicates probably that the protoliths of the marble were deposited after the Mesoproterozoic of 1200 Ma. 5.2. Provenance of the supracrustal rocks Available data demonstrate that the Sulu HP-UHP metamorphic rocks were formed during Triassic collision and subduction between the Yangtze and North China cratons. However, whether the detrital sources of their protoliths lay within the Yangtze block or North China craton remain uncertain. The meta-supracrustal rocks with the old tectonic–thermal event records of their provenance can provide important insight on the protolithic origin of UHP metamorphic rocks in the Sulu orogen. The North China craton and the Yangtze block are the two largest tectonic units in eastern China, their Precambrian evolutions have been well studied (e.g., Liu et al., 1992; Song et al., 1996; Zhao

(1) The present study indicates that the meta-supracrustal rocks, together with their associated eclogites and orthogneisses from the southern Sulu orogen belt, were subjected to coeval Triassic UHP metamorphism. They formed as a coherent tectonic slab during the continental subduction to deep mantle depths. (2) The protoliths of the UHP quartzites from southern Sulu may have been formed in the Neoproterozoic; whereas the marble protoliths were probably formed in the Mesoproterozoic. (3) The UHP metamorphosed supracrustal rocks have retained records of multistage Neoproterozoic to Paleoproterozoic tectonic–thermal events, indicating that their provenance was the Yangtze block, instead of the North China craton.

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