Geochemical and Sr–Nd isotopic characteristics of Cretaceous to Paleocene granitoids and volcanic rocks, SE Tibet: Petrogenesis and tectonic implications

Journal of Asian Earth Sciences 53 (2012) 131–150

Contents lists available at SciVerse ScienceDirect

Journal of Asian Earth Sciences journal homepage: www.elsevier.com/locate/jseaes

Geochemical and Sr–Nd isotopic characteristics of Cretaceous to Paleocene granitoids and volcanic rocks, SE Tibet: Petrogenesis and tectonic implications I-Jhen Lin a, Sun-Lin Chung a,⇑, Chiu-Hong Chu a, Hao-Yang Lee a, Sylvain Gallet a, Genyao Wu b, Jianqing Ji c, Yuquan Zhang d a

Department of Geosciences, National Taiwan University, Taipei, Taiwan Institute of Geology and Geophysics, Chinese Academy of Sciences, Beijing, China School of Earth and Space Sciences, Peking University, Beijing, China d Guangzhou Institute of Geochemistry, Chinese Academy of Sciences, Guangzhou, China b c

a r t i c l e

i n f o

Article history: Available online 4 April 2012 Keywords: Tibet Tethyan subduction Granitoids Geochemistry Sr–Nd isotopes

a b s t r a c t Northward subduction of the Neo-Tethyan oceanic lithosphere beneath South Asia gave rise to an Andean-type convergent margin with arc magmatism starting since at least the early Jurassic and lasting until the Eocene. This study reports geochemical and Sr–Nd isotope data of the early Cretaceous (133– 110 Ma) to Paleocene (60 Ma) magmatic belt that formed in the eastern Lhasa terrane, SE Tibet, including three major Transhimalayan batholiths, namely, Azhagong, Demulha, and Chayu, and an early Cretaceous volcanic succession from Ranwu area. All these rocks show relative enrichments in LILE and LREE, and depletions in HFSE, corresponding to the geochemical characteristics of arc magmas from modern subduction zones. While the Azhagong batholith consists typically of metaluminous I-type granitoids that occasionally contain mafic enclaves, highly fractionated, peraluminous S-type and A-type granites are observed from the Chayu and Demulha batholiths, respectively. These granitoids, as a whole, show heterogeneous Sr and Nd isotope ratios, with eNd(T) varying from 1.5 to 13 and ISr from 0.703 to 0.745. The Ranwu volcanic rocks, which range from basaltic to dacitic compositions, are calc-alkaline in nature. They have eNd(T) from +3 to 6 and ISr from 0.705 to 0.707, overlapping the isotopic range of the Azhagong mafic enclaves. The overall geochemical and Sr–Nd isotope data suggest three magma source components involved in the petrogenesis, which are the mantle wedge, and the lower and upper parts of the Lhasa continental crust. Accordingly, we propose a two-stage petrogenetic model involving (1) deep level differentiation of the mantle wedge-derived mafic magmas associated with assimilation by the lower continental crust of the Lhasa terrane and (2) additional differentiation and upper crustal contamination of the evolved magmas as they rise and install in shallow-level magma chambers. While the first stage can explain how the Ranwu volcanics and Azhagong enclaves formed, the second accounts for the emplacement of the Azhagong and Chayu batholiths. The shallow intrusions, moreover, may have caused low-pressure melting of existing calc-alkaline rocks of Paleoproterozoic Nd isotope model age to produce the early Cretaceous (125 Ma) A-type granites in the Demulha batholith, a specific rock type that occurs rarely in subduction zones but echoes with the notion for an extension setting in the region. This setting may have taken place after the late Jurassic-early Cretaceous continental collision between the Lhasa and Qiangtang terranes, and interacted with the back-arc evolution in the Neo-Tethyan subduction system. Ó 2012 Elsevier Ltd. All rights reserved.

1. Introduction In the Lhasa terrane of southern Tibet (Fig. 1), the east–west elongated belt of granitoids that occurs in the north of the

⇑ Corresponding author. Address: Department of Geosciences, National Taiwan University, Taipei P.O. Box 13-318, Taipei 10617, Taiwan. Tel.: +886 2 3366 2934; fax: +886 2 2363 6095. E-mail address: [email protected] (S.-L. Chung). 1367-9120/$ - see front matter Ó 2012 Elsevier Ltd. All rights reserved. http://dx.doi.org/10.1016/j.jseaes.2012.03.010

Yarlu–Tsangpo suture has been termed the ‘‘Transhimalayan batholiths’’ (Searle et al., 1987; for review and references therein) and widely regarded as a major component of the Andean-type continental margin along South Asia resulting from northward subduction of the Neo-Tethyan oceanic lithosphere before India started colliding with Asia (e.g., Allègre et al., 1984; Debon et al., 1986; Searle et al., 1987; Harris et al., 1988; TBGMR, 1993; Yin and Harrison, 2000; Chung et al., 2005; Kapp et al., 2005a; Mo et al., 2005). The Transhimalayan batholiths have been divided into two main magmatic suites, i.e., the northern plutonic belt and the

132

I-Jhen Lin et al. / Journal of Asian Earth Sciences 53 (2012) 131–150

Fig. 1. Simplified geologic map (modified from Tu et al., 1982; Pan et al., 2004) showing sample localities and outcrops of the eastern Transhimalayan batholiths, the Lhasa terrane, SE Tibet. BNS = Bangong Nujiang suture; YTS = Yarlu Tsangpo suture; STDS = South Tibet detachment system; MCT = main central thrust.

southern Gangdese Batholith (Fig. 1). Their temporal and spatial distribution, concerning how exactly the magmatic suites correlate eastward and then southeastward around the eastern Himalayan syntaxis to those in western Yunnan and Myanmar, however, remains poorly constrained. As part of a systematic investigation of the Transhimalayan magmatism (Chu et al., 2006, 2011; Lee et al., 2007, 2009; Liang et al., 2008; Wen et al., 2008a, 2008b; Chiu et al., 2009; Ji et al., 2009a, 2009b), this paper reports a geochemical analysis of the early Cretaceous to Paleocene eastern Transhimalayan batholiths, and an associated volcanic sequence, from Bomi to Chayu areas (95–97.5°E and 30–28°N) in the

easternmost part of the Lhasa terrane, SE Tibet. Our major results include (1) reporting new major/trace element and Sr–Nd isotope data, (2) identifying the coexistence of I-, S- and A-type granites in this particular part of the Neo-Tethyan subduction zone, (3) examining the petrogenesis, and (4) exploring the batholiths’ regional correlation and tectonic implication. This study helps improve our understanding of the geochemical characteristics of the eastern Transhimalayan magmatism, which, together with our comparative studies from the central part of the Lhasa terrane and Myanmar, shed new insights into the magmatic and tectonic evolution in southern Tibet before the India–Asia collision.

Fig. 2. Simplified volcanic succession and sample localities in Ranwu area, SE Tibet (modified from Wu et al., 1999).

133

I-Jhen Lin et al. / Journal of Asian Earth Sciences 53 (2012) 131–150 Table 1 Major and trace element data of the eastern Transhimalayan granitoids, SE Tibet. Sample

Azhagong batholith ET103A

ET104B

ET105A

ET105B

ET105C

ET105D

ET105E

ET105F

ET117A

ET117C

29.9542 95.3845 2636 Deformed granite 119 ± 2

29.5075 96.6044 3773 Granite 115 ± 2

29.5003 96.6066 3777 Granite

29.5003 96.6066 3777 Granite

29.5003 96.6066 3777 Granite

29.5003 96.6066 3777 Granite

29.5003 96.6066 3777 Granite

29.5003 96.6066 3777 Granite

29.3213 97.1343 3848 Granite 117 ± 2

29.3213 97.1343 3848 Granite

Major element (wt.%) SiO2 70.69 TiO2 0.28 A12O3 14.35 b Fe2O3 1.70 MnO 0.04 MgO 0.39 CaO 2.11 Na2O 2.72 K2O 4.34 P2O5 0.03 LOI 0.53 Sum 97.18

73.04 0.21 13.77 2.02 0.06 0.43 1.98 2.96 3.58 0.04 0.47 98.56

67.35 0.46 15.70 3.91 0.08 1.16 3.51 2.79 3.36 0.08 0.34 98.74

73.49 0.18 14.47 1.71 0.04 0.54 1.75 3.69 4.33 0.06 0.43 100.69

72.54 0.24 14.81 2.03 0.03 0.48 2.15 2.98 3.62 0.04 0.62 99.54

73.06 0.24 14.27 2.20 0.05 0.74 2.19 3.65 3.51 0.08 0.80 100.79

71.39 0.27 15.15 2.45 0.07 0.82 2.22 3.93 3.86 0.09 0.30 100.55

72.05 0.26 14.73 2.36 0.06 0.79 2.28 3.83 3.62 0.09 0.85 100.92

62.72 0.63 15.95 4.88 0.08 3.23 4.84 2.68 2.85 0.09 1.50 99.45

67.53 0.41 15.38 3.12 0.05 1.90 3.27 2.79 3.20 0.08 1.20 98.93

Trace element (ppm) Sc 4.11 V 14.3 Cr 7.60 Mn 284 Co 2.46 Ni 2.15 Cu – Zn 44.1 Ga 16.2 Rb 170 Sr 145 Y 14.3 Zr 127 Nb 13.1 Cs 3.08 Ba 418 La 49.8 Ce 94.1 Pr 9.69 Nd 33.4 Sm 5.54 Eu 0.87 Gd 4.51 Tb 0.61 Dy 2.88 Ho 0.55 Er 1.41 Tm 0.19 Yb 1.16 Lu 0.18 Hf 3.65 Ta 0.95 Pb 33.1 Th 20.1 U 10.7

9.82 – 1.60 517 2.66 0.83 0.97 13.6 13.7 176 105 15.4 108 8.65 6.55 183 22.1 39.8 4.01 13.9 2.53 0.50 2.36 0.38 2.15 0.46 1.38 0.22 1.58 0.26 3.08 1.07 20.9 22.2 3.65

9.96 19.1 6.90 603 6.26 1.98 1.95 32.9 15.9 161 163 19.1 153 8.85 5.68 310 22.5 41.7 4.28 15.4 2.89 0.71 2.84 0.46 2.70 0.57 1.71 0.27 1.87 0.30 3.86 0.92 19.5 21.5 2.97

6.82 14.2 3.08 361 2.56 1.01 2.00 23.7 15.7 240 94.2 26.3 71.9 10.4 4.01 283 34.5 63.3 6.34 21.9 4.41 0.58 4.11 0.69 3.91 0.81 2.43 0.39 2.67 0.42 2.86 1.65 30.5 33.2 3.80

8.35 21.4 3.09 262 3.65 1.4 7.64 21.1 16.5 242 135 19.6 62.7 10.1 3.79 379 34.6 63.5 6.17 20.4 3.59 0.69 3.31 0.48 2.64 0.55 1.62 0.26 1.78 0.28 2.02 1.65 30.5 33.2 3.80

6.99 21.9 2.97 466 3.77 1.54 1.66 33.2 15.9 219 133 17.6 57.7 8.01 4.41 339 30.1 55.4 5.31 17.9 3.32 0.72 3.04 0.47 2.63 0.54 1.60 0.25 1.76 0.27 2.08 1.11 25.1 23.5 2.87

9.03 24.4 3.43 597 4.19 1.63 4.87 47.1 17.2 253 132 21.6 66.2 10.6 6.48 296 33.9 63.5 6.09 20.8 3.91 0.74 3.67 0.58 3.31 0.68 1.99 0.32 2.18 0.33 2.35 1.36 27.4 27.1 3.03

10.6 22.7 95.2 571 4.13 2.75 4.38 37.7 16.7 248 132 20.9 60.6 9.55 9.08 344 35.2 62.6 5.96 19.9 3.67 0.74 3.43 0.55 3.14 0.65 1.91 0.30 2.07 0.32 2.14 1.22 27.5 26.5 3.08

20.9 52.6 229 608 14.6 35.1 10.1 54.1 18.7 177 229 23.9 184 11.2 11.9 314 23.6 47.5 5.39 21.2 4.20 0.84 3.95 0.64 3.56 0.71 2.01 0.30 1.89 0.28 4.58 0.92 17.4 18.9 2.19

14.1 5.06 60.9 461 8.86 24.5 6.50 16.5 17.4 186 218 14.1 114 10.2 10.7 252 28.9 51.9 5.16 17.7 3.00 0.67 2.76 0.39 2.08 0.41 1.19 0.18 1.21 0.18 3.07 1.23 22.5 27.5 3.47

Latitude (°N) Longitude (°E) Altitude (m) Rock type Agea

Sample

Azhagong batholith ET120A

ET122A

ET122B

ET122D

ET124C

ET125A

Latitude (°N) Longitude (°E) Altitude (m) Rock type

29.7417 96.0209 3021 Granite

29.7649 95.6971 3745 Gabbroic diorite

29.7649 95.6971 3745 Granite

29.7649 95.6971 3745 Granite

29.7568 95.7080 4126 Granite

Agea

109 ± l

66 ± 2

29.7565 95.7163 4072 Deformed granite 125 ± 2

69.06 0.37 15.73 2.38 0.04

70.35 0.33 15.31 1.90 0.03

71.68 0.11 15.22 0.91 0.01

68.32 0.47 15.00 2.61 0.06

Major element (wt.%) SiO2 70.43 TiO2 0.28 A12O3 15.31 Fe2O3b 2.16 MnO 0.07

54.60 1.15 17.42 7.76 0.12

73–540

73–720

73–721

73–750

Granite

Grano-diorite

Grano-diorite

Gabbro

70.44 0.26 14.54 1.58 0.03

69.86 0.41 14.51 2.83 0.04

64.09 0.70 16.13 4.66 0.09

51.24 1.24 20.76 8.89 0.17

(continued on next page)

134

I-Jhen Lin et al. / Journal of Asian Earth Sciences 53 (2012) 131–150

Table 1 (continued) Sample

Azhagong batholith ET120A

ET122A

ET122B

ET122D

ET124C

ET125A

Latitude (°N) Longitude (°E) Altitude (m) Rock type

29.7417 96.0209 3021 Granite

29.7649 95.6971 3745 Gabbroic diorite

29.7649 95.6971 3745 Granite

29.7649 95.6971 3745 Granite

29.7568 95.7080 4126 Granite

Agea

109 ± l

66 ± 2

29.7565 95.7163 4072 Deformed granite 125 ± 2

MgO CaO Na2O K2O P2O5 LOI Sum

0.68 2.47 3.27 3.76 0.05 0.32 98.80

4.78 6.74 2.67 2.48 0.28 0.67 98.67

0.83 2.47 3.09 4.40 0.09 0.50 98.96

0.53 2.04 2.74 5.11 0.07 0.42 98.83

0.19 1.45 2.25 6.31 0.01 0.40 98.54

18.7 113 46.7 915 21.6 31.7 5.77 73.1 20.2 91.7 723 27.3 178 11.5 2.05 618 24.9 57.1 7.38 31.8 6.61 1.43 5.56 0.85 4.39 0.84 2.24 0.31 1.91 0.28 3.98 0.69 10.2 6.24 0.87

16.1 – 9.55 402 4.04 4.78 3.16 21.6 18.1 179 400 16.2 194 13.1 4.06 655 40.1 72.2 7.25 25.2 3.96 0.80 3.42 0.45 2.26 0.44 1.29 0.20 1.30 0.19 4.56 1.46 25.6 36.5 3.83

18.7 – 5.87 276 2.70 2.23 2.10 8.84 17.4 167 321 8.45 208 10.6 3.11 684 43.9 79.3 7.94 27.4 3.99 0.77 3.16 0.35 1.49 0.25 0.68 0.09 0.57 0.09 4.94 0.42 30.4 45.3 4.50

5.27 13.2 2.82 141 1.26 1.08 5.09 21.1 17.5 209 501 8.62 153 5.59 5.64 1228 37.3 67.7 7.05 24.1 3.44 1.05 2.63 0.30 1.45 0.28 0.81 0.12 0.97 0.16 4.90 0.95 66.2 23.7 13.9

Trace element (ppm) Sc 6.86 V – Cr 1.81 Mn 599 Co 3.00 Ni 0.79 Cu 1.83 Zn 4.10 Ga 14.9 Rb 204 Sr 230 Y 12.3 Zr 139 Nb 7.02 Cs 5.19 Ba 353 La 31.8 Ce 54.3 Pr 5.25 Nd 17.5 Sm 2.57 Eu 0.62 Gd 2.30 Tb 0.31 Dy 1.61 Ho 0.34 Er 1.0.1 Tm 0.16 Yb 1.13 Lu 0.19 Hf 3.30 Ta 0.57 Pb 16.5 Th 16.0 U 1.84 Sample

Latitude (°N) Longitude (°E) Altitude (m) Rock type Agea

73–540

73–720

73–721

73–750

Granite

Grano-diorite

Grano-diorite

Gabbro

0.80 2.18 3.01 4.48 0.09 0.57 97.59

0.58 1.62 2.95 4.57 0.10 0.72 97.39

1.09 2.93 3.23 3.71 0.08 1.00 99.69

1.89 4.68 3.55 2.55 0.13 1.20 99.67

3.34 8.42 4.09 1.08 0.29 0.73 100.25

7.04 31.1 6.03 457 4.09 3.63 – 55.2 16.9 181 195 30.7 211 14.2 2.92 643 46.5 91.9 10.0 37.3 6.92 1.47 6.18 0.95 5.30 1.08 3.03 0.44 2.93 0.45 5.88 1.12 37.4 27.4 3.32

29.4 20.7 47.3 219 3.49 8.87 – – 22.0 360 168 15.6 123 18.2 22.6 610 30.4 62.4 7.40 25.9 5.13 0.68 4.26 0.63 3.12 0.53 1.44 0.21 1.32 0.19 4.21 1.93 64.8 24.8 6.63

36.8 49.9 44.1 334 4.84 6.06 – – 15.6 156 206 28.8 153 12.6 4.72 706 37.2 73.0 8.38 28.1 5.40 0.84 4.81 0.81 4.87 0.98 3.00 0.45 3.09 0.44 5.17 1.32 11.4 24.1 4.31

12.7 82.9 59.5 654 8.66 8.40 – – 18.3 126 288 25.2 253 11.7 5.48 636 33.7 63.7 7.41 26.3 4.92 1.05 4.62 0.73 4.36 0.90 2.63 0.42 2.64 0.43 7.59 1.07 15.2 22.5 3.69

32.8 123 52.8 1308 19.8 15.7 – – 22.5 67.3 503 27.4 167 8.99 3.29 355 15.6 36.3 4.85 19.6 4.34 1.37 4.89 0.80 4.89 1.03 2.91 0.44 2.62 0.39 4.39 0.79 7.36 2.86 1.13

Azhagong enclaves

Demulha batholith

ET105G

ET119A

ET120C

ET120D

ET120E

ET124D

ET106A2

ET219B2

ET220B

ET221B

ET222B

29.5003 96.6066 3777 Enclave

29.5074 96.7540 3836 Enclave

29.7417 96.0209 3021 Enclave

29.7417 96.0209 3021 Enclave

29.7417 96.0209 3021 Enclave

29.7568 95.7080 4126 Enclave

29.3855 96.8690 4207 Granite 123 ± 2

29.3922 96.8515 4201 Granite 125 ± 1

29.3922 96.8515 4201 Granite

29.3922 96.8515 4201 Granite

29.3922 96.8515 4201 Granite

64.14 0.47 15.43 4.05 0.07 2.17 3.24 3.25 3.31 0.11 2.80 99.04

55.23 1.09 17.93 7.91 0.13 3.33 7.00 2.80 1.78 0.24 1.30 98.74

45.03 1.87 17.99 12.78 0.19 4.91 10.76 2.53 0.86 1.03 0.57 98.52

51.13 0.98 16.59 8.94 0.19 6.94 8.79 2.42 1.12 0.16 1.10 98.36

50.23 0.89 16.29 8.50 0.23 8.13 8.75 1.78 1.99 0.17 1.60 98.56

78.30 0.07 11.66 0.78 0.02 – 0.56 2.64 4.45 – 0.81 99.29

75.61 0.08 12.39 0.72 0.02 – 0.60 2.88 4.95 – 0.73 97.98

74.17 0.08 12.89 0.78 0.02 – 0.64 2.79 5.50 – 0.70 97.57

75.27 0.08 12.32 0.79 0.02 – 0.65 2.85 4.92 – 0.80 97.70

76.14 0.08 12.25 0.77 0.02 – 0.50 2.73 5.07 – 0.58 98.14

Major element (wt.%) SiO2 52.23 TiO2 1.09 A12O3 16.27 Fe2O3b 8.85 MnO 0.15 MgO 5.58 CaO 6.92 Na2O 2.50 K2O 1.16 P2O5 0.15 LOI 5.70 Sum 100.60

135

I-Jhen Lin et al. / Journal of Asian Earth Sciences 53 (2012) 131–150 Table 1 (continued) Sample

Latitude (°N) Longitude (°E) Altitude (m) Rock type Agea

Azhagong enclaves ET119A

ET120C

ET120D

ET120E

ET124D

ET106A2

ET219B2

ET220B

ET221B

ET222B

29.5003 96.6066 3777 Enclave

29.5074 96.7540 3836 Enclave

29.7417 96.0209 3021 Enclave

29.7417 96.0209 3021 Enclave

29.7417 96.0209 3021 Enclave

29.7568 95.7080 4126 Enclave

29.3855 96.8690 4207 Granite 123 ± 2

29.3922 96.8515 4201 Granite 125 ± 1

29.3922 96.8515 4201 Granite

29.3922 96.8515 4201 Granite

29.3922 96.8515 4201 Granite

12.2 86.8 76.7 551 10.6 10.4 18.3 44.1 18.1 139 694 23.7 138 11.7 2.88 429 38.7 78.9 9.05 33.6 6.59 1.08 5.47 0.82 4.46 0.87 2.42 0.33 2.20 0.32 4.33 1.18 35.4 18.2 2.92

13.7 162 9.98 958 18.7 13.1 29.6 82.6 16.9 55.7 546 24.1 173 9.36 5.01 415 25.2 53.4 6.54 27.1 5.71 1.58 5.13 0.78 4.43 0.89 2.47 0.34 2.26 0.33 4.46 0.63 14.9 5.11 0.77

23.8 206 1.74 1416 20.6 1.68 21.4 98.3 20.6 31.1 425 39.9 62.1 8.45 1.01 103 24.6 56.2 7.49 33.8 8.27 2.19 8.05 1.32 7.63 1.53 4.10 0.54 3.36 0.46 2.12 0.61 5.96 2.78 0.56

19.5 171 208 1345 29.8 90.5 25.7 65.7 15.3 50.2 273 23.7 113 5.68 6.46 127 14.5 31.3 4.04 17.1 4.11 1.15 4.03 0.69 4.13 0.87 2.40 0.34 2.27 0.34 2.83 0.40 2.83 3.15 0.65

22.6 174 348 1796 28.3 133 6.69 100 15.9 140 264 23.7 119 5.81 12.9 118 15.5 33.9 4.33 18.3 4.31 1.16 4.18 0.69 4.21 0.85 2.39 0.33 2.23 0.33 2.94 0.40 3.07 3.48 0.63

16.3 – 3.40 178 0.29 – 16.8 – 18.7 491 6.46 115 90.8 16.2 8.99 – 20.1 49.5 6.21 25.1 8.22 0.05 9.56 2.18 14.6 3.20 9.52 1.53 9.90 1.43 4.23 2.47 30.7 48.6 13.1

4.51 1.05 1.37 200 0.55 4.21 – 23.9 20.1 644 8.91 108 105 18.4 23.9 10.7 33.7 80.1 9.62 36.6 10.6 0.11 11.1 2.42 15.6 3.38 10.0 1.57 10.3 1.48 4.73 4.02 55.2 44.4 5.71

3.82 3.75 4.72 218 0.53 0.63 – 14.7 20.7 713 11.5 135 89.1 19.1 24.3 46.2 35.2 83.5 10.1 38.9 11.8 0.15 12.8 2.84 18.7 4.01 11.8 1.86 12.1 1.74 3.92 4.11 58.5 43.7 6.84

10.7 0.71 1.18 216 0.51 0.21 – 13.9 20.5 675 9.57 135 102 19.8 26.5 14.7 36.2 86.4 10.5 40.3 12.2 0.13 13.1 2.90 19.1 4.09 12.1 1.89 12.4 1.78 4.67 4.05 51.5 47.1 8.80

6.92 – 1.82 208 0.50 0.39 – 11.1 19.7 658 9.15 130 98.1 17.6 23.3 10.2 32.4 77.4 9.43 36.8 11.3 0.11 12.2 2.69 17.6 3.78 11.2 1.77 11.6 1.67 4.58 3.88 49.5 45.5 6.31

Trace element (ppm) Sc 15.9 V 139 Cr 155 Mn 1008 Co 24.8 Ni 64.8 Cu 38.3 Zn 90.5 Ga 14.0 Rb 58.8 Sr 220 Y 24.1 Zr 103 Nb 7.19 Cs 6.79 Ba 152 La 21.1 Ce 39.8 Pr 5.11 Nd 20.9 Sm 4.83 Eu 1.29 Gd 4.64 Tb 0.77 Dy 4.61 Ho 0.94 Er 2.61 Tm 0.36 Yb 2.43 Lu 0.35 Hf 3.13 Ta 0.61 Pb 10.3 Th 6.79 U 1.23 Sample

Demulha batholith

ET105G

Chayu batholith ET107A

ET108B

ET111B

ET113A

ET115F1

ET115F2

ET116B

ET203B

ET203D

29.3721 96.9119 4403 Granite

28.4731 97.0499 1454 Granite

28.5193 97.0800 1528 Granite

28.5616 97.0852 1644 Granite 59 ± 3

28.5991 97.2496 1896 Deformed granite 133 ± 1

28.5991 97.2496 1896 Deformed granite 133 ± 1

28.6724 97.4698 2319 Granite 133 ± 1

28.4539 97.0314 1524 Granite

28.4539 97.0314 1524 Granite

Major element (wt.%) SiO2 73.05 TiO2 0.32 A12O3 14.20 Fe2O3b 2.30 MnO 0.03 MgO 0.29 CaO 1.34 Na2O 2.63 K2O 5.36 P2O5 0.05 LOI 0.77 Sum 100.34

72.90 0.17 14.56 1.41 0.04 0.12 1.30 3.22 4.68 0.03 0.53 98.96

72.75 0.19 14.33 1.43 0.03 0.09 1.26 2.45 5.47 0.03 0.80 98.83

72.35 0.24 14.25 1.46 0.04 0.35 1.93 2.14 5.23 0.04 0.90 98.93

74.05 0.25 13.79 1.49 0.03 0.16 1.20 2.73 5.06 0.02 0.75 99.53

74.05 0.25 13.79 1.49 0.03 0.16 1.20 2.73 5.06 0.02 0.75 99.53

73.17 0.23 14.45 1.71 0.04 0.33 1.25 2.64 4.72 0.12 0.72 99.38

70.77 0.17 14.90 1.38 0.04 0.12 1.40 3.30 4.94 0.03 0.38 97.43

Trace element (ppm) Sc 17.9 V – Cr 3.36 Mn 279 Co 2.59 Ni 1.74 Cu 4.25 Zn 26.8

12.5 – 5.25 382 0.97 0.63 2.78 39.2

11.5 – 6.13 295 1.03 0.75 6.46 42.9

10.2 – 1.32 340 1.71 2.23 6.61 95.2

7.28 – 3.90 270 1.38 0.61 1.57 4.69

7.94 – 4.55 270 1.31 1.03 2.03 3.84

21.8 – 5.57 367 2.20 2.44 4.26 23.8

3.84 4.88 1.03 358 1.08 0.82 – 52.1

Latitude (°N) Longitude (°E) Altitude (m) Rock type Agea

73–73

73–164

Granite 128 ± 2

Granite

71.14 0.18 14.51 1.40 0.04 0.11 1.35 3.20 4.90 0.03 0.30 97.16

73.33 0.22 14.68 1.80 0.05 0.30 1.20 2.99 4.68 0.16 1.10 100.51

73.61 0.33 14.34 1.93 0.05 0.27 1.52 2.57 5.17 0.08 0.55 100.42

3.95 8.07 3.20 371 1.12 0.67 – 60.2

48.7 18.9 88.8 377 2.69 7.49 – –

36.5 13.3 37.8 359 2.13 4.56 – –

(continued on next page)

136

I-Jhen Lin et al. / Journal of Asian Earth Sciences 53 (2012) 131–150

Table 1 (continued) Sample

Chayu batholith ET107A

ET108B

ET111B

ET113A

ET115F1

ET115F2

ET116B

ET203B

ET203D

Latitude (°N) Longitude (°E) Altitude (m) Rock type Agea

29.3721 96.9119 4403 Granite

28.4731 97.0499 1454 Granite

28.5193 97.0800 1528 Granite

28.5616 97.0852 1644 Granite 59 ± 3

28.5991 97.2496 1896 Deformed granite 133 ± 1

28.5991 97.2496 1896 Deformed granite 133 ± 1

28.6724 97.4698 2319 Granite 133 ± 1

28.4539 97.0314 1524 Granite

28.4539 97.0314 1524 Granite

Ga Rb Sr Y Zr Nb Cs Ba La Ce Pr Nd Sm Eu Gd Tb Dy Ho Er Tm Yb Lu Hf Ta Pb Th U

20.6 330 63.9 44.1 254 16.9 12.7 170 61.0 123 14.2 52.5 10.1 0.62 8.73 1.33 7.00 1.35 3.77 0.56 3.67 0.54 6.82 2.70 38.9 54.4 6.93

20.1 192 179 31.7 173 13.6 8.00 509 26.5 56.1 6.55 26.0 5.51 0.79 5.15 0.85 4.71 0.92 2.58 0.37 2.34 0.34 4.68 1.61 36.9 13.1 2.82

22.8 335 78.3 38.4 192 27.5 7.07 245 77.3 156 17.2 60.8 11.8 0.61 9.63 1.43 7.17 1.30 3.45 0.46 3.01 0.42 6.22 2.69 64.0 47.0 7.75

17.8 226 214 23.3 240 8.82 7.36 355 52.4 108 12.1 46.1 9.38 0.82 7.69 1.04 4.65 0.74 1.78 0.23 1.42 0.21 6.30 0.93 43.1 44.2 2.53

17.7 396 69.7 36.6 208 11.8 15.5 297 52.9 109 11.7 41.3 7.05 0.50 5.87 0.83 4.20 0.82 2.34 0.36 2.38 0.37 4.20 0.85 40.9 38.9 4.65

17.7 402 72.1 37.0 210 11.8 16.5 319 49.6 102 11.1 39.4 6.79 0.48 5.74 0.81 4.11 0.80 2.26 0.34 2.33 0.36 4.10 0.83 41.6 40.1 4.84

22.0 345 81.5 37.1 110 19.5 13.7 301 26.0 53.6 5.97 22.2 5.04 0.58 4.93 0.92 5.41 1.05 2.86 0.42 2.69 0.38 3.18 2.77 48.8 24.1 7.98

19.1 207 163 33.1 193 13.5 7.92 696 29.1 60.6 7.07 26.9 5.80 0.96 5.43 0.93 5.36 1.08 2.97 0.44 2.89 0.41 5.41 1.26 38.1 11.0 2.37

18.8 221 156 31.6 176 13.7 9.33 662 38.8 81.1 9.38 35.8 7.47 0.96 6.40 1.03 5.42 1.02 2.76 0.39 2.47 0.35 4.95 1.28 36.7 15.3 2.36

73–73

73–164

Granite 128 ± 2

Granite

23.0 385 129 38.5 127 25.9 14.7 548 26.7 56.2 6.76 23.8 5.61 0.56 5.85 1.07 6.51 1.29 3.62 0.54 3.38 0.49 4.30 4.01 49.0 24.4 5.49

20.0 306 157 33.9 197 26.0 8.07 747 87.4 165 18.9 64.7 11.6 0.86 8.59 1.30 6.79 1.23 3.36 0.45 2.75 0.40 6.50 2.36 47.4 52.8 7.14

‘‘–’’ Below detection limit or not determined. a Zircon U–Pb age data (Chiu et al., 2009). b Total Fe measured as Fe2O3.

2. Background The Lhasa terrane is widely believed to have dispersed from Gondwanaland during the Permian or Triassic (Allègre et al., 1984; Chang et al., 1986); it was then drifting northward and finally collided with the Qiangtang terrane in the Eurasia during the late Jurassic-early Cretaceous (Kapp et al., 2005a). The Lhasa terrane is confined by the Bangong–Nujiang suture in north and by the Yarlu–Tsangpo suture in south (Fig. 1), with the latter being formed by closure of the Neo-Tethys ocean owing to the continental collision between India and Asia (Yin and Harrison, 2000). The Transhimalayan batholiths, distributing 2500 km throughout the Lhasa terrane, have been conventionally divided into two principal magmatic suites: (1) a southern Gangdese belt represented by the Gangdese Batholith that consists dominantly of Cretaceous to Eocene metaluminous granotoids with I-type geochemical affinities (Debon et al., 1986; Searle et al., 1987; TBGMR, 1993; Wen, 2007; Wen et al., 2008b; Ji et al., 2009b; Wu et al., 2010; Zhang et al., 2010a, 2010b; Guo et al., 2011), and (2) a northern plutonic belt of peraluminous or S-type granitoids such as those exposed in the Nyainqentanghla Range, or the Central Lhasa Subterrane (Zhu et al., 2011), that were emplaced largely during the early Cretaceous (Xu et al., 1985; Harris et al., 1990; Kapp et al., 2005b; Wen, 2007; Chiu et al., 2009; Zhu et al., 2009a, 2011). It is generally consented that the Gangdese Batholith, and associated Linzizong volcanic successions (Fig. 1), are the magmatic products by northward subduction of the Neo-Tethyan oceanic lithosphere under South Asia. However, the petrogenesis of the northern plutonic belt is an issue of long-lasting debates that have yielded different models, including: (1) crustal anatexis during

and/or postdating the continental collision between the Lhasa and Qiangtang terranes (Xu et al., 1985; Pearce and Mei, 1988), (2) high-temperature crustal melting due to upwelling of the asthenosphere after the Lhasa-Qiangtang collision (Harris et al., 1990), (3) a low-angle, or shallow northward subduction of the Neo-Tethyan oceanic lithosphere (Coulon et al., 1986; Ding et al., 2003; Zhang et al., 2004; Kapp et al., 2005a; Chu et al., 2006), and (4) southward subduction of the Bangong–Nujiang oceanic slab and subsequent slab breakoff related to the Lhasa–Qiangtang collision (Zhu et al., 2009a, 2011). Moreover, how do these magmatic suites correlate to the east, and then southeastward around the eastern Himalayan syntaxis to the intrusive bodies in western Yunnan and Myanmar, remains a highly uncertain question because detailed studies had rarely been performed for the eastern Transhimalayan batholiths exposed in regions east of 95°E since the pioneer work by Tu et al. (1982). 3. Samples and previous studies Field excursions were conducted along the main roads in the areas from Bomi to Basu and Chayu (Shama), between 95– 97.5°E and 30–28.5°N, SE Tibet (Fig. 1), through which we collected 80+ samples from three major Transhimalayan batholiths, namely, Azhagong, Demulha and Chayu (Tu et al., 1982). These include granitoids and mafic enclaves; the latter occur only occasionally in the Azhagong batholith. The granitoids are composed mainly of median- to coarse-grained monzogranites, granodiorites and granites that contain rather simple mineral constituents including K-feldspar (40%), plagioclase (30%), quartz (20%), biotite (5–10%) and accessary minerals such as hornblende,

137

I-Jhen Lin et al. / Journal of Asian Earth Sciences 53 (2012) 131–150

muscovite, apatite and opaque phases. More mafic lithologies such as gabbros and diorites are observed in the Azhagong batholith. Twenty-four among these samples had been subjected to in situ zircon U–Pb and Hf isotopic determinations by Liang et al. (2008) and Chiu et al. (2009). The dating results indicate that the Azhagong batholith resulted from two stages of emplacement during 125–109 and 66–59 Ma, respectively, the Demulha batholith was emplaced at 125 Ma, and the Chayu batholith formed also in two periods at 130 and 60 Ma, respectively (Liang et al., 2008; Chiu et al., 2009). These, together with additional zircon U–Pb ages reported by Booth et al. (2004) and Zhu et al. (2009b), suggest that the eastern Transhimalayan magmatism in the studied area occurred largely in the early Cretaceous (133–109 Ma) and subordinately in the Paleocene (66–57 Ma). Thus, there appears to have a magmatic gap or quiescence time in the late Cretaceous. This age pattern makes it difficult to correlate westward to the eastern Gangdese Batholith (Fig. 1), where the late Cretaceous has been repeatedly documented to be a major magmatic stage

(Wen et al., 2008a, 2008b; Ji et al., 2009a, 2012; Zhang et al., 2010a, 2010b; Guo et al., 2011). Besides, we carried out a comparative study of an early Cretaceous (120 Ma) volcanic sequence cropping out in Ranwu area, just off the main road (Fig. 1). Twelve samples were recovered from an 1500 m-thick, volcanic sequence (Fig. 2) that erupted subaerially and now lies unconformably over the late Paleozoic turbidite and Jurassic sedimentary formations (Wu et al., 1999).

4. Analytical methods 4.1. Major and trace element analyses Whole-rock samples were crushed using a jaw crusher, handpicked, and then powdered by corundum mill. Major elements were determined by X-ray fluorescence (XRF) techniques on fused glass beads using a RigakuÒ RIX-2000 spectrometer at Department

Table 2 Major and trace element data of Cretaceous volcanic rocks from Ranwu area, SE Tibet. Sample

a

RAW12

RAW13

RAW15

RAW17

RAW20

RAW22

RAW24

RAW25

RAW26

RAW29

RAW30

Major element (wt.%) SiO2 57.63 TiO2 1.11 Al2O3 15.20 Fe2O3a 6.47 MnO 0.13 MgO 1.57 CaO 4.62 Na2O 3.78 K2O 2.34 P2O5 0.33 LOI 8.11 Sum 101.29

RAW11

55.16 1.14 18.16 6.52 0.14 1.44 4.41 4.02 2.34 0.33 7.56 101.29

60.67 0.99 17.78 6.10 0.09 0.63 2.99 2.46 3.09 0.30 4.40 99.50

52.51 1.56 18.47 8.31 0.13 3.59 6.59 3.14 0.93 0.40 3.32 98.95

68.63 0.48 16.99 2.58 0.06 3.59 1.59 2.37 2.84 0.08 2.22 98.44

51.00 1.36 21.57 7.41 0.11 2.37 5.17 2.74 3.19 0.38 3.32 98.62

53.64 1.43 17.00 7.93 0.13 2.36 4.65 3.18 2.44 0.40 5.97 99.13

55.24 1.48 17.47 7.64 0.14 2.42 5.76 3.20 3.07 0.42 2.63 99.47

50.38 1.52 17.33 8.60 0.12 4.22 5.85 2.85 2.08 0.36 6.64 99.95

51.73 1.45 16.60 8.27 0.13 4.03 6.24 3.87 1.29 0.34 3.91 97.86

54.48 1.45 17.21 8.86 0.13 4.09 5.35 3.60 1.79 0.33 3.24 100.53

45.85 2.13 19.21 11.40 0.11 6.01 4.62 3.49 1.29 0.48 3.85 98.44

Trace element (ppm) Sc 7.51 V 49.5 Cr 4.92 Mn 760 Co 8.56 Ni 3.66 Cu 14.2 Zn 69.2 Ga 17.0 Rb 89.4 Sr 185 Y 35.4 Zr 287 Nb 14.7 Cs 3.89 Ba 214 La 32.6 Ce 67.7 Pr 7.77 Nd 30.7 Sm 6.41 Eu 1.62 Gd 6.37 Tb 1.03 Dy 5.85 Ho 1.22 Er 3.43 Tm 0.50 Yb 3.25 Lu 0.49 Hf 6.78 Ta 1.24 Pb 20.0 Th 13.2 U 2.57

7.64 50.3 4.32 825 9.16 3.98 9.57 68.5 17.6 96.8 146 36.8 284 13.9 4.04 114 32.5 66.5 7.77 30.9 6.59 1.63 6.63 1.07 6.05 1.26 3.53 0.51 3.3 0.50 6.76 1.20 16.8 12.8 2.59

11.9 18.0 1.60 558 3.88 1.33 7.17 57.5 20.2 124 108 45.5 316 20.0 4.89 238 42.4 93.3 10.4 41.3 8.61 2.06 8.50 1.36 7.67 1.57 4.40 0.4 4.12 0.62 7.64 1.51 23.6 12.1 1.90

13.0 110 41.4 777 17.8 26.8 26.6 78.4 20.1 30.7 319 31.6 244 16.2 2.22 148 28.4 60.8 7.19 29.1 6.19 1.76 6.04 0.97 5.42 1.0 3.04 0.43 2.78 0.42 5.67 1.22 12.4 7.22 1.38

5.14 31.2 3.45 348 3.95 2.22 2.99 37.4 14.3 157 64.3 26.9 92.6 8.44 3.75 339 28.1 56.8 6.09 22.4 4.46 0.83 4.40 0.72 4.20 0.88 2.53 0.37 2.45 0.36 2.96 0.83 11.2 18.0 3.22

6.16 96.0 16.3 711 13.2 13.5 34.4 66.2 20.7 40.4 233 24.7 345 18.3 1.34 223 15.8 72.1 5.09 21.3 4.99 1.24 5.11 0.89 5.27 1.11 3.15 0.47 3.07 0.46 7.77 1.38 11.5 5.48 2.38

17.4 123 25.1 1168 17.8 15.8 48.2 117 27.0 134 265 56.2 429 24.9 5.89 203 48.9 109 12.2 48.7 10.3 2.52 10.2 1.63 9.25 1.92 5.42 0.78 5.06 0.77 9.82 1.85 24.8 17.4 3.17

13.6 112 19.3 980 23.32 14.7 8.11 112 21.3 95.6 273 45.1 393 21.1 2.30 324 43.5 91.4 10.5 41.0 8.51 1.91 8.41 1.33 7.50 1.54 4.39 0.63 4.16 0.62 8.93 1.58 17.6 17.8 3.26

16.1 142 51.3 850 23.3 39.6 4.22 82.1 19.2 91.0 223 30.3 230 13.2 5.12 194 27.2 57.7 6.65 26.6 5.67 1.29 5.73 0.91 5.11 1.05 2.94 0.42 2.73 0.41 5.23 1.02 5.39 9.20 1.74

16.3 145 52.9 862 22.7 38.6 4.50 74.0 18.5 57.6 290 30.5 222 12.7 4.58 112 28.5 58.8 6.79 27.3 5.80 1.56 5.90 0.92 5.16 1.05 2.92 0.42 2.67 0.40 5.06 0.99 6.56 9.04 1.84

16.5 137 50.9 892 21.8 37.2 28.7 61.3 17.3 77.5 293 29.8 218 12.4 1.67 231 30.6 61.9 7.08 28.1 5.84 1.64 5.88 0.91 5.01 1.02 2.82 0.40 2.59 0.39 4.93 0.96 7.72 8.93 1.62

18.1 189 46.8 743 41.1 45.6 111 82.7 21.9 69.3 243 42.6 299 17.5 2.70 105 28.6 63.9 7.77 32.2 7.18 1.47 7.29 1.20 6.87 1.42 3.98 0.56 3.64 0.55 6.44 1.22 11.5 9.13 1.74

Total Fe measured as Fe2O3.

138

Table 3 Sr and Nd isotopic data of the eastern Transhimalayan granitoids, SE Tibet. Rb (ppm)

Sr (ppm)

87

Azhagong batholith ET103A Deformed granite ET104B Granite ET105A Granite ET105B Granite ET107A Granite ET117A Granite ET120A Granite ET122A Granodiorite ET125A Deformed granite

119 ± 2 115 ± 2 120 120 120 117 ± 2 109 ± 1 66 ± 2 125 ± 2

770 176 161 240 330 177 204 91.8 181

145 105 163 94.2 63.9 229 230 723 195

Azhagong enclaves ET105G Enclave ET119A Enclave ET120C Enclave ET120D Enclave ET120E Enclave

120 120 109 109 109

58.8 139 55.7 31.1 50.2

Demulha batholith ET106A2 Granite ET219B2 Granite ET220B Granite ET221B Granite ET222B Granite

123 ± 2 125 ± 1 125 125 125

Chayu batholith ET113A Granite ET115F1 Granite ET116B Granite ET203B Granite ET203D Granite 73–73 Granite

59 ± 3 133 ± 1 133 ± 1 60 60 128 ± 2

Rock type

Rb/86Sr

(87Sr/86Sr)m

(87Sr/86Sr)

Sm (ppm)

Nd (ppm)

147

Sm/144Nd

(143Nd/144Nd)m

3.39 4.86 2.86 7.38 14.9 2.24 2.57 0.367 2.69

0.717494 0.716762 0.715423 0.714782 0.741119 0.713866 0.706863 0.711866 0.722641

0.7118 0.7089 0.7106 0.7022 0.7156 0.7101 0.7029 0.7115 0.7179

5.54 2.53 2.90 4.40 10.1 4.20 2.57 0.71 6.92

33.4 1090 0.42 21.9 52.5 2.2 10.95 31.9 37.3

0.100 0.109 0.114 0.121 0.116 0.120 0.8090 0.125 0.112

0.512020 0.512207 0.512171 0.512202 0.512265 0.512215 0.512376 0.512404 0.511925

220 694 546 425 273

0.774 0.580 0.295 0.212 0.532

0.706562 0.706447 0.706237 0.706173 0.706092

0.7052 0.7055 0.7058 0.7058 0.7053

4.83

20.9

0.140

5.71 8.27 4.11

27.1 33.8 17.1

491 644 713 675 658

6.46 8.90 11.5 9.57 9.15

120 210 180 204 208

0.977088 0.974909 0.949798 0.955354 0.960528

(0.5927) (0.6027) (0.6309) (0.5925) (0.5906)

8.22 10.6 11.8 12.6 13.5

226 396 345 207 221 385

214 69.7 81.5 221 156 129

3.06 16.4 12.2 2.71 4.10 8.68

0.716425 0.749173 0.750538 0.707888 0.707959 0.760712

0.7139 0.7181 0.7274 0.7056 0.7045 0.7449

9.38 7.05 5.04 5.80 7.47 5.61

eNd(T)

TDM1(Ga)

TDM2(Ga)

10.6 7.14 7.85 7.36 6.05 7.11 3.61 3.97 12.6

1.52 1.38 1.49 1.56 1.38 1.52 0.95 1.29 1.83

1.77 1.49 1.55 1.51 1.41 1.49 1.20 1.19 1.94

0.512372

4.32

1.60

1.26

0.127 0.148 0.145

0.512454 0.512514 0.512460

2.63 1.74 2.76

1.23 1.47 1.53

1.12 1.05 1.13

0.35 0.25 0.26

25.1 36.6 49.8 52.3 54.7

0.198 0.175 0.143 0.146 0.149

0.512091 0.512038 0.512049 0.512047 0.512054

11.3 11.4 10.6 10.7 10.6

(10.2) (4.34) 2.37 2.46 2.58

1.78 1.82 1.78 1.78 1.78

(0.01) ( 0.11) 0.27 0.26 0.24

46.1 41.3 22.2 27.0 35.8 23.7

0.123 0.103 0.137 0.130 0.126 0.143

0.512070 0.512069 0.512184 0.512533 0.512521 0.511944

10.5 9.52 7.86 1.53 1.74 12.7

1.81 1.49 1.92 1.12 1.09 2.58

1.72 1.70 1.56 0.99 1.01 1.94

0.37 0.48 0.30 0.34 0.36 0.27

All Sr and Nd isotope ratios are reported at the 2r confidence level. Sr/86Sri = 87Sr/86Sr (87Rb/86Sr)  (ekT 1), kRb–Sr = 0.0142 Ga 1, 87Rb/86Sr = (Rb/Sr)  2.8956. 143 Nd/144Ndi = 143Nd/144Nd (147Sm/144Nd)  (ekT 1), kSm–Nd = 0.00654 Ga 1, 147Sm/144Nd = (Sm/Nd)  0.60456. eNd(T) = [(143Nd/144Nd)Sample(T)/(143Nd/144Nd)CHUR(T) 1]  104; (143Nd/144Nd)CHUR(T) = 0.512638–0.1967  (ekT 1). TDM1(Ga) = 1/kSm–Ndx ln{1 + [((143Nd/144Nd)Sample 0.51315)/((147Sm/144Nd)Sample 0.2137)]}
fSm/Nd = (147Sm/144Nd/0.1967) 1. TDM2(Ga) = TDM1 (TDM1 t)((fcc fs)/(fcc fdm)), where fcc = 0.4, fDM = 0.08592, fs = the fSm/Nd values of the sample, t = the emplacement age; CHUR = chondritic uniform reservoir; DM = depleted mantle. 87

fSm/Nd

0.49 0.44 0.42 0.38 0.41 0.39 0.55 0.36 0.43 -0.29

I-Jhen Lin et al. / Journal of Asian Earth Sciences 53 (2012) 131–150

Age (Ma)

Sample no. Granitoids

139

I-Jhen Lin et al. / Journal of Asian Earth Sciences 53 (2012) 131–150

of Geosciences, National Taiwan University. The analytical procedures were the same as those described by Wang et al. (2004), yielding analytical uncertainties generally better than ±5% (2r).

Loss on ignition (LOI) was determined separately by routine procedures. Powdered samples of the Ranwu volcanic rocks weighing 20 mg were dissolved using super-pure HF and HNO3 (1:1)

Table 4 Sr and Nd isotopic data of Cretaceous volcanic rocks from Ranwu area, SE Tibet.

a

Sample no.

Rock type

Rb (ppm)

Sr (ppm)

87

Rb/86Sr

RAW11 RAW12 RAW13 RAW15 RAW17 RAW20 RAW22 RAW24 RAW25 RAW26 RAW29 RAW30

Andesite Basaltic andesite Andesite Basaltic andesite Dacite Basaltic andesite Basaltic andesite Basaltic andesite Basalt Basaltic andesite Basaltic andesite Basalt

89.4 96.8 124 30.7 157 56.6 134 95.6 91.0 57.6 77.5 69.3

185 146 108 319 64.3 279 265 273 223 290 293 243

1.40 1.92 3.31 0.278 7.08 0.588 1.46 1.02 1.18 0.575 0.765 0.827

(87Sr/86Sr)m

(87Sr/86Sr)

Sm (ppm)

Nd (ppm)

147

Sm/144Nd

0.708774 0.709886 0.712819 0.706806 0.717157 0.707451 0.707820 0.707072 0.707405 0.706797 0.706974 0.707362

0.7064 0.7066 0.7072 0.7063 0.7051 0.7064 0.7053 0.7053 0.7054 0.7058 0.7057 0.7060

6.41 6.59 8.61 6.19 4.46 6.76 10.3 8.51 5.67 5.80 5.84 7.18

30.7 30.9 41.3 29.1 22.4 31.5 48.7 41.0 26.6 27.3 28.1 32.2

0.126 0.129 0.126 0.128 0.120 0.130 0.127 0.125 0.129 0.129 0.126 0.135

(143Nd/144Nd)m 0.512557 0.512583 0.512399 0.512607 0.512269 0.512588 0.512578 0.512670 0.512738 0.512582 0.512577 0.512597

eNd(T) 0.50 0.03 3.59 0.44 6.03 0.05 0.10 1.71 2.98 0.06 0.09 0.15

Assumed age = 120 Ma.

Fig. 3. Plots of the alkalis (Na2O + K2O) vs. silica for (a) early Cretaceous and Paleocene granitoids from the eastern Transhimalayan batholiths, and (b) Ranwu volcanic rocks, SE Tibet. Names of the rock types are from Middlemost (1994) and Le Maitre (2002), respectively.

140

I-Jhen Lin et al. / Journal of Asian Earth Sciences 53 (2012) 131–150

mixture in screw-top Teflon beakers for 7–10 days at 100 °C, followed by evaporation to dryness, refluxing in HF and HNO3 (1:1) mixture for >12 h at 100 °C and drying again, and then dissolving the sample cake in 2% HNO3. An internal standard solution of 10 ppb Rh and Bi was added and the spiked dissolutions were diluted with 2% HNO3 to a final sample/solution weight ratio of 1/ 4000. Fused glass beads of the granitoids were powdered, weighing 40 mg, and dissolved using super-pure HF and HNO3 (1:1) mixture in screw-top Teflon beakers for 2 h at 100 °C, followed by evaporation to dryness, refluxed in 2 ml HNO3 (1:2) for >12 h at 100 °C, and then the sample solution was diluted with 2% HNO3. The internal standard solution of 10 ppb Rh and Bi was added and the spiked solution was diluted with 2% HNO3 to a sample/solution weight ratio of 1:1500. The internal standard solution was utilized for monitoring the signal shift during the trace element measurements by the inductively coupled plasma-mass spectrometry (ICP-MS) using an Agilent 7500cx spectrometer at the Dr. Shen-su Sun memorial lab, Department of Geosciences, National Taiwan University, which routinely shows a good stability range of less than 5% variation. The precision of the ICP-MS

measurements was generally better than 3% (2r) using powder and 5% using glass bead for most trace elements, as shown by the statistics on duplicate analyses of USGS standards AGV-2, BHVO-2, and BCR-2 (see Appendix Table A). 4.2. Sr and Nd isotope analyses Powdered samples, weighing 80 mg, were decomposed in 15 ml screw-top SavillexÒ beaker using super-pure HF and HNO3 (1:1) mixture for >5 days at 150 °C until complete digestion, evaporated to dryness, and then dissolved in 2 ml 4 N and 1 N HCl. Sr and REEs were separated from the solution by passing through a cation-exchange column containing AG50W-X8 100– 200 mesh resin, and then Nd was extracted from the REE portion by passing through a column containing Ln Spec resin. Sr and Nd isotope ratios were measured using a Finnigan-Thermo NeptuneÒ MC-ICP-MS (multiple collector-inductively coupled plasma0mass spectrometer) also at the Dr. Shen-su Sun memorial lab. Measured 87 Sr/86Sr and 143Nd/144Nd ratios were normalized to 86Sr/88Sr = 0.1194 and 146Nd/144Nd = 0.7129 for mass fractionation. The mean

Fig. 4. Plots of major elements vs. SiO2 for the studied samples from SE Tibet.

I-Jhen Lin et al. / Journal of Asian Earth Sciences 53 (2012) 131–150

values of standards SRM (NBS) 987 and JNdi-1 during the period of data acquisition were 87Sr/86Sr = 0.710288 ± 20 (n = 65) and 143 Nd/144Nd = 0.512121 ± 20 (n = 40), respectively. For routine analyses of individual unknown samples, the 2r analytical errors are commonly <0.000020 for 87Sr/86Sr and <0.000010 for 143 Nd/144Nd isotopic ratios. More analytical details can be found in Lee et al. (2012). 5. Results Whole-rock major and trace element data of the Transhimalayan batholiths and Ranwu volcanic rocks are listed in Tables 1 and 2, respectively. Their Sr–Nd isotope results are given in Tables 3 and 4, respectively. 5.1. Major elements 5.1.1. The batholiths The samples overall show a wide range in silica contents, owing to granitoids from the Azhagong batholith that contain 51– 74 wt.% SiO2 (Fig. 3a). They are, however, dominantly of granite to granodiorite composition. Plotting together, their TiO2, Al2O3, tFe2O3, MgO, CaO, and P2O5 decrease, and K2O increases, with increasing silica content (Fig. 4). In the ASI discrimination diagram (Fig. 5), the Azhagong granitoids that generally show high alkali contents (Na2O + K2O = 3.4–8.0 wt.%) plot in the strongly to weakly metaluminous field, with A/CNK (i.e., molar ratio of Al2O3/[CaO + Na2O + K2O]) and A/NK (i.e., molar ratio of Al2O3/[Na2O + K2O]) ratios ranging from 0.90 to 1.16 and 1.35 to 2.46, respectively. Most of them reveal the characteristic of I-type granite (Fig. 5). Five samples from the Demulha batholith are exclusively granite (Fig. 3a), characterized by high silica and alkalis (SiO2 = 74– 78 wt.%, Na2O + K2O = 7.1–8.3 wt.%), and lowest TiO2, Al2O3, tFe2O3, MgO, CaO, and P2O5 contents (Fig. 4). They all plot as weakly peraluminous (A/CNK = 1.10–1.15, A/NK = 1.22–1.27), straddling the line that divides I-type and S-type granites (Fig. 5). The Chayu batholith is composed entirely of granite with a rather uniform

141

composition (Fig. 3a), marked also with high silica and alkali contents (SiO2 = 70–74 wt.%, Na2O + K2O = 7.4–8.2 wt.%), plotting within the fields of peraluminous (A/CNK = 1.12–1.23; A/NK = 1.38–1.55) and S-type granite (Fig. 5). We note here that, along with the overwhelming Cretaceous granitoids, there are several younger samples of Paleocene ages. These are sample ET122A, dated at 66 ± 2 Ma (Table 1), a gabbroic diorite from the Azhagong batholith (Fig. 3a), and sample ET113A, dated at 59 ± 3 Ma (Table 1), a granite from the Chayu batholith (Fig. 3a). In addition, Paleocene ages are suggested for two other Chayu granites, ET203B and ET203D (Tables 1 and 3), because a nearby sample ET205 that has been dated at 57 ± 1 Ma (Chiu et al., 2009). Given the uniform geochemical composition observed in the Chayu batholith, these two Paleocene samples are not specifically denoted, as do samples ET122A and ET113A, throughout the figures in this paper for comparison purpose.

5.1.2. Azhagong mafic enclaves We determined five mafic enclaves from the early Cretaceous granitoids, the Azhagong batholith (Table 1). They are gabbro and diorite, with SiO2 varying from 45 to 64 wt.% (Fig. 3a). Their major element characteristics are comparable to those of the Ranwu volcanic rocks (Fig. 4), implying a possible genetic link. In the ASI discrimination diagram (Fig. 5), they plot in the strongly to mildly metaluminous field, with A/CNK ranging from 0.73 to 1.04 and A/ NK from 1.73 to 3.54.

5.1.3. Ranwu volcanics The 12 samples from the Ranwu volcanic succession are basalt to dacite, with SiO2 contents ranging from 45 to 69 wt.% (Fig. 3b), which generally reveal high-K calc-alkaline nature. In the Harker diagram (Fig. 4), these rocks appear to show a magma differentiation trend as their SiO2 has a positive correlation with K2O and negative correlations with Al2O3, tFe2O3, MgO, CaO, Na2O, and P2O5 contents. It is noted that these rocks have high LOI from 8.1 to 2.2 wt.% (Table 2), indicating the effect of sample alteration.

Fig. 5. Plots of A/NK [Al2O3/(Na2O + K2O)] vs. A/CNK [Al2O3/(CaO + Na2O + K2O)] of the samples (after: Maniar and Piccoli, 1989). The molar ratios were calculated after Zen (1986).

142

I-Jhen Lin et al. / Journal of Asian Earth Sciences 53 (2012) 131–150

5.2. Trace elements 5.2.1. The batholiths In the rare earth element (REE) diagram, granitoids from the Azhagong batholith are plotted on the basis of SiO2 contents in two groups, i.e., gabbro–diorite–granodiorite (Fig. 6a) and granite (Fig. 6b). They show highly to moderately LREE-enriched distribution patterns, mostly are coupled with apparent or mild Eu negative anomalies (Eu/Eu = 0.41–1.03). In the spidergram or primitive mantle-normalized multi-element diagram (Fig. 7a and b), all these granitoids are characterized by depletions in the high field strength elements (HFSE; e.g., Ti, Nb, Ta), enrichments in the large ion lithosphere elements (LILE; e.g., K, Rb, Cs, Th) and Pb, similar to arc magmas from modern subduction zones or active continental margins. The granites from the Demulha batholith exhibit markedly different REE patterns (Fig. 6c), with diagnostic features including high HREE (Yb = 7.7–10 ppm), and thus flat patterns [(La/Yb)n

= 1.5–4.9], and significant Eu negative anomalies (Eu/Eu = 0.02– 0.04). These are furthermore associated with the presence of tetrad REE patterns that are often observed in highly differentiated rocks with strong hydrothermal interaction (Bau, 1996; Jahn et al., 2001; Monecke et al., 2002). In the spidergram (Fig. 7c), all these samples show enrichments in the alkalis (e.g., Rb = 419–713 ppm), depletions in Nb, Ta, Ti, Ba (10–46 ppm) and Sr (6–12 ppm), coupled with low Ca, Cr, Co and Ni contents, which are the characteristics of A-type granites (Eby, 1990; Bonin, 2007). In the A-type granite ‘‘discriminant diagram’’ (Fig. 8a), the Demulha samples that contain high alkalis and Ga/Al ratios do plot within the A-type granite field, in contrast to those from the Azhagong and Chayu batholiths that fall essentially in the field of I–S–M type granites. Comparatively, they have similar compositions and plot close to the range of highly fractionated A-type granites from South China (Fig. 8a and b), forming as the initial phase of post-orogenic magmatism related to rapid rollback and breakoff of the subducting slab in middle Jurassic time (Li and Li, 2007).

Fig. 6. Chondrite-normalized REE diagrams of the samples, SE Tibet. Chondrite values are from Sun and McDonough (1989).

I-Jhen Lin et al. / Journal of Asian Earth Sciences 53 (2012) 131–150

143

Fig. 7. Primitive mantle-normalized incompatible element variation diagrams or spidergrams of the samples, SE Tibet. Normalizing values are from Sun and McDonough (1989).

The eleven granites from the Chayu batholith show similar REE patterns (Fig. 6d). They all are characterized by enrichment in LREE, depletion in HREE, and apparent Eu negative anomalies (Eu/Eu = 0.17–0.45), despite sample ET113A has slightly lower HREE abundance. Their spidergram patterns (Fig. 7d), as a whole, are generally comparable to those of granites from the Azhagong betholith (Fig. 7b).

REE abundance, which is observed in a basaltic andesite sample RAW22 (SiO2 = 53.6 wt.%) whose La and Yb concentrations are up to 49 and 5 ppm, respectively (Table 2). In the spidergram (Fig. 7f), all of them are depleted in HFSE, Ba and Sr, and enriched in LILE and Pb.

5.2.2. Azhagong mafic enclaves The mafic enclaves show slightly LREE-enriched patterns (Fig. 6e), some with small Eu negative anomalies, similar to the REE patterns observed in the Ranwu volcanic rocks (see below). In the spidergram (Fig. 7e), all of these enclaves are marked by depletions in HFSE and enrichments in LILE, also similar to the Ranwu volcanics.

5.3.1. The batholiths The granitoids of the Azhagong and Chayu batholiths show heterogeneous Sr–Nd initial isotopic ratios, the former have ISr ratios from 0.702 to 0.717 and eNd(T) values from 1 to 11, and the latter have ISr ratios from 0.704 to 0.745 and eNd(T) values from 1 to 13 (Fig. 9 and Table 3). Among the Azhagong granitoids, the Paleocene sample ET122A reveals a relatively higher eNd(T) value of 4 (Fig. 9), yielding a younger Nd model age (TDM) of 1.3 Ga (Table 3). As for Paleocene granites from the Chayu batholith, sample ET113A shows a relatively lower eNd(T) of 10.5, yielding an older TDM of 1.8 Ga (Table 3), while samples ET203B and ET203D have the highest eNd(T) values of about 1.5 that yield young Nd model ages of 1.1 Ga (Table 3).

5.2.3. Ranwu volcanics The Ranwu volcanic rocks exhibit mildly LREE-enriched patterns (Fig. 6f), and they all display small negative Eu anomalies (Eu/Eu = 0.57–0.87). The dacite sample RAW17 (SiO2 = 68.6 wt.%) has the largest Eu anomaly, but does not have the highest overall

5.3. Sr and Nd isotopes

144

I-Jhen Lin et al. / Journal of Asian Earth Sciences 53 (2012) 131–150

(a)

5.3.3. Ranwu volcanics The Ranwu volcanic rocks show heterogeneous Nd isotopic ratios, with eNd(T) from +3 to 6, and a rather uniform Sr isotopic ratios, with Isr of 0.705–707 (Table 4), thus plotting as a vertical trend in the Sr–Nd isotopic correlation diagram (Fig. 9). The Nd isotopic variation, moreover, correlates in general with SiO2 contents such that a basalt sample RAW25 has the highest eNd(T) value of +3 and the dacite sample RAW17 has the lowest eNd(T) value of 6 (Table 4). 6. Discussion 6.1. Petrogenesis

(b)

Fig. 8. Plots of the eastern Transhimalayan granitoids in the (a) Zc vs. 10,000  Ga/ Al granite discriminant diagram of Whalen et al. (1987) and (b) modified alkali-line index (Na2O + K2O CaO) vs. silica diagram of Frost et al. (2001). The range of Atype granites, South China is after Li et al. (2012).

The Demulha A-type granites have low, or ‘‘radiogenic’’, initial Nd isotopic ratios, with eNd(T) values of about 11 (Table 3). Owing to their flat REE patterns, and elevated Sm/Nd ratios that are too high to obtain reasonable Nd model ages by the one-stage evolution model, these samples were treated with a two-stage model by Keto and Jacobsen (1987) that TDM2 ages of 1.8 Ga in the late Paleoproterozoic (Table 3). Measured 87Sr/86Sr isotopic ratios of these A-type granites are high, varying from 0.950 to 0.977 (Table 3). However, due to their high Rb (>500 ppm) and low Sr (6– 12 ppm), yielding extremely high Rb/Sr elemental ratios (87Rb/86Sr  200; Table 3), which would result in huge uncertainties when calculating initial Sr isotopic ratios (e.g., Wu et al., 2002; Jahn et al., 2004), the ISr ratios are over-corrected and much too low (0.7; Table 3) to be meaningful, and thus will not be used in the following discussion. 5.3.2. Azhagong mafic enclaves The enclaves have rather uniform Sr and Nd isotopic ratios, with Isr ratios of 0.706 and eNd(T) values from 2 to 4 (Table 3), plotting around the highest domain relative to their host granitoids and overlapping the trend delineated by the Ranwu volcanic rocks (Fig. 9).

The overall Sr–Nd isotope compositions of the rocks suggest three source components, or ‘‘end-members’’, involved in the magma genesis (Fig. 9), which are (1) the depleted mantle wedge, as defined by the Gangdese Batholith (Wen, 2007; Wen et al., 2008a; Ji et al., 2009b), (2) the lower continental crust (Miller et al., 1999), and (3) the upper continental crust of the Lhasa terrane (Harris et al., 1988; Wen, 2007). Accordingly, we propose a two-stage petrogenetic model that involves (1) Stage 1: deep-level differentiation of the mantle wedge-derived mafic magmas in association with various amounts of assimilation by the lower continental crust; and (2) Stage 2: additional differentiation and upper crustal contamination when the evolved magmas later rose and installed in the magma chambers at shallow depths. The first stage explains how the Ranwu volcanic rocks and Azhagong mafic enclaves were generated, and the second stage is argued for producing the Azhagong and Chayu batholiths. 6.1.1. Ranwu volcanics and Azhagong enclaves The Sr–Nd isotopic correlation of the Ranwu volcanic rocks (Fig. 9) is best explained by the AFC (assimilation and fractional crystallization) processes that occurred at lower crustal depths. This may be achieved by mantle-derived mafic magmas that intrude/underplate in the lower part of the continental crust around or just above the Moho, as commonly observed in the Andes (Davidson and de Silva, 1992; Petford et al., 1996) and modern subduction zones elsewhere (Tatsumi and Eggins, 1995). If the mantle-lower crust mixing curve #1 is applied (Fig. 9), together with FC processes, various degrees of lower crustal assimilation (10–45%) can produce the vertical isotopic trend delineated by the Ranwu volcanic rocks. Likewise, the Azhagong enclaves may be interpreted as fragments of the mafic intrusions/underplates that were later captured by the evolved magmas eventually forming the batholith at upper crustal depth (see below). 6.1.2. Azhagong and Chayu batholiths In Fig. 9, mixing curves #2 and #3 were drawn to depict the upper crustal contamination. Curve #2, a mixing between the average Azhagong enclaves and the upper continental crust, may broadly account for most granitoids from the Azhagong and Chayu batholiths to support our argument on the petrogenesis at Stage 2. Some Chayu granites show very high ISr ratios, which plot close to or within the upper crust domain (Fig. 9), suggesting substantial amounts of the upper crustal involvement in the magma genesis and consistent with the major element constraints grouping the rocks as highly fractionated, peraluminous S-type granites (Fig. 5). As a whole, these two eastern Transhimalayan batholiths are isotopically comparable to the broadly coeval northern Lhasa plutonic belt (Figs. 9 and 10) that consists mainly of S-type granitoids marked with high ISr and low eNd(T) values yielding Proterozoic Nd model ages. By contrast, the Gangdese Batholith in the southern Lhasa terrane is composed typically of I-type granitoids

I-Jhen Lin et al. / Journal of Asian Earth Sciences 53 (2012) 131–150

145

Fig. 9. Plots of eNd(T) values vs. initial Sr isotope ratios for the samples, SE Tibet. The end-members used for mixing calculations are: (1) a Gangdese gabbro, representing the mantle wedge-derived magma: ISr = 0.7045, eNd(T) = +6, [Sr] = 411 ppm, [Nd] = 11 ppm (Wen et al., 2008a); (2) the lower continental crust: ISr = 0.710, eNd(T) = 12, [Sr] = 300 ppm, [Nd] = 26 ppm (Miller et al., 1999); (3) the upper continental crust: ISr = 0.748, eNd(T) = 12, [Sr] = 400 ppm, [Nd] = 30 ppm (Harris et al., 1988); and (4) average of the Azhagong mafic enclaves: ISr = 0.706, eNd(T) = 3, [Sr] = 400 ppm, [Nd] = 20 ppm. Three curves represent mixing calculations done between end-members (1) and (2) [curve #I], (1) and (3) [curve #II], and (2) and (4) [curve #III]. For comparison, the Lhasa terrane data from Wen (2007) and those of Chayu granites from Zhu et al. (2009b) are also shown.

that exhibit ‘‘unradiogenic’’ Sr–Nd isotope compositions and thus apparently younger Nd model ages (Chung et al., 2005; Mo et al., 2005; Wen et al., 2008a; Ji et al., 2009a, 2009b; Wu et al., 2010). 6.1.3. Demulha A-type granites All five samples from the Demulha batholith are highly fractionated and show uniformly low eNd(T) values around 11, among the lowest in the eastern Transhimalayan granitoids. In the A-type granite discriminant diagram (Fig. 11), they plot in the A2 domain, interpreted as representing magmas from the continental crust or underplated crust that has been through a cycle of continental collision or island-arc magmatism (Eby, 1992). A-type granitoids, in the tectonic discrimination scheme of Pearce et al. (1984), are equivalent to within-plate granites (WPG; Fig. 12). However, the Demulha granites do not plot right in the WPG field, but straddle the boundaries of either WPG/ORG (Fig. 12a) or WPG/post-COLG (Fig. 12b), in contrary to the Azhagong granitoids that plot largely in the VAG (volcanic arc granites) field and the Chayu granites plotting around the transitional ‘‘triple junction’’ (Fig. 12). The classification between I-, S- and A-type granites are sometimes difficult, particularly for highly fractionated rocks (Chappell and White, 1992; King et al., 2001; Bonin, 2007; Wu et al., 2007). All the Demulha granites are extremely evolved rocks, with subordinate amount of biotite as the only mafic constituent, which make a very ‘‘reliable’’ classification even more difficult. In Fig. 8, utilizing the geochemical schemes proposed by Whalen et al. (1987) and Frost et al. (2001), they are compared with the A-type granites (also highly fractionated) from South China, interpreted as the initial phase of post-orogenic magmatism that formed in an extensional regime owing to breakoff and foundering of the subducting slab in the region (Li and Li, 2007; Li et al., 2012). The above-described geochemical diagnostics leads us to favor a classification that rocks from the Demulha batholith are A-type granites that, therefore, may hardly be generated by extreme

magma differentiation from either I- or S-type granites (King et al., 2001; Wu et al., 2007). Many petrogenetic models have been proposed for A-type granites and related rocks, and most imply solely crustal derivation (cf. Bonin, 2007). This may be achieved by low-pressure (P 6 4 kbar) melting of calc-alkaline granitoids (Patino Douce, 1997). Under the framework of the two-stage petrogenetic model described above, we therefore argue that the shallow-level intrusions could have caused low-pressure partial melting of pre-existing country rocks, e.g., those atop the magma chambers, which have calc-alkaline nature and Paleoproterozoic model age, to form the Demulha A-type granites. Consequently, three types of plutonism, producing granitoids of (1) metaluminous I-type (Azhagong), (2) highly fractionated and peraluminous S-type (Chayu), and (3) highly fractionated and A-type (Demulha) geochemical features, took place coevally in early Cretaceous time at this particular part affiliated to the arc to back-arc evolution of the Neo-Tethyan subduction system (see below). 6.2. Regional tectonic implications As shown in Figs. 9 and 10, the Nd isotopic systematics of the eastern Transhimalayan batholiths is comparable to that of the northern Lhasa plutonic belt and different from that of the Gangdese Batholith. This correlation may be even better illustrated by a comparative plot using compiled data of SiO2 contents, eNd(T) values and ISr ratios of the three magmatic suites (Fig. 13). Therefore, the eastern Transhimalayan batholiths are not the eastward equivalent of the Gangdese Batholith, but should be correlated to the northern Lhasa plutonic belt. Using zircon U–Pb and Hf isotopic constraints, the same conclusion has been reached by Chiu et al. (2009). Moreover, the eastern Transhimalayan batholiths can correlate southeastward to the Cretaceous–Paleocene batholiths in the Gaoligong–Tengliang belt, western Yunnan (Yang et al., 2006;

146

I-Jhen Lin et al. / Journal of Asian Earth Sciences 53 (2012) 131–150

Fig. 10. Plots of the eastern Transhimalayan granitoids in terms of (a) eNd(T) vs. intrusive ages, and (b) eNd(T) vs. Nd depleted-mantle model ages. In the latter, TDM2 ages were plotted when the samples have Sm/Nd elemental ratios too high or too low (Jahn et al., 2004). Data of the Gangdese Batholith and northern Lhasa plutonic belt are from Wen (2007).

Xu et al., 2012) and then the Jurassic–Paleocene batholiths in the Shan Scarps province, Burma (Mitchell et al., accepted for publication). The eastward extension of the Gangdese Batholith, instead, may be exposed in areas southeast of the Namche Barwa Syntaxis and immediately north of the Yarlu-Tsangpo suture (Fig. 1), where, unfortunately, is around the China–India border and hardly accessible for any detailed study. However, our most recent work from the southern part of the Lohit batholith, NE India (Lin et al., 2010) suggests that there exists a Gangdese equivalent. Our new results include (1) zircon U–Pb ages of five Lohit granitoid samples from 148 to 96 Ma, (2) zircon Hf isotopes marked with high, positive eHf(T) values from +15 to +10, and (3) calc-alkaline geochemical nature of the rocks, all matching with the Gangdese Batholith dataset (Wen et al., 2008a, 2008b; Ji et al., 2009a, 2009b, 2012; Wu et al., 2010; Zhang et al., 2010a, 2010b; Guo et al., 2011).

While a general consensus has been reached for generating the Gangdese magmatism by northward subduction of the Neo-Tethyan oceanic lithosphere underneath the southern Lhasa terrane, the petrogenesis of the northern Lhasa plutonic belt remains rather debatable. Using a comparative analysis, Xu et al. (2012) recently pointed out that the Cretaceous granitoids in the northern Lhasa plutonic belt show overall geochemical similarities to the North American Cordilleran Interior batholiths that did not form directly in a subduction setting but resulted from an intra-continental collisional setting, in which magma generation occurred in response to crustal thickening followed in some cases by extension (cf. Driver et al., 2000). Therefore, Xu et al. (2012) argued, after an early view of Pearce and Mei (1988), that the northern Lhasa plutonic belt may have formed in a post-collisional regime as result of the late Jurassic-early Cretaceous collision between the Qiangtang

I-Jhen Lin et al. / Journal of Asian Earth Sciences 53 (2012) 131–150

147

Fig. 11. Plots of the Demulha granites in the discriminant diagram for A-type granitoids (Eby, 1992).

and Lhasa terranes. Under this framework, the S-type magmatism that prevails in the northern Lhasa plutonic belt was initiated as a result of collision-induced crustal thickening, which may have capabilities of causing crustal anatexis by itself. Evidence for regional crustal thickening has been reported by Kapp et al. (2005a), which showed a >50% crustal shortening, and thus thickening, in the northern Lhasa terrane before the India–Asia collision. The post-collisional scenario, nevertheless, has some drawbacks (Chiu et al., 2009) as it cannot explain the Jurassic granitoids in the eastern Transhimalayan area (Chiu et al., 2009), nor the Jurassic magmatism in the northern Lhasa plutonic belt (Fig. 1). The latter, though most active in the early Cretaceous (Zhu et al., 2009a, 2011), lasted until late Cretaceous and Paleocene time (Wen et al., 2008b; Chiu et al., 2009). Such longevity of magmatism, also present in the Cordilleran orogenic belts in the central Andes (Allmendinger et al., 1997) and western North America (Wells and Hoisch, 2008), requires a longer-lasting tectonic process, rather than a post-collisional mechanism that would be most likely shorter-lived. By analogy, the northward Neo-Tethyan subduction is suggested to be the long-lasting process that played a key role in the petrogenesis of the northern Lhasa plutonic belt. The new idea of southward subduction of the Bangong–Nujiang oceanic slab (Zhu et al., 2009a, 2011) is not favored as it does not account for

Fig. 12. Plots of the eastern Transhimalayan granitoids in diagrams of (a) Nb vs. Y and (b) Rb vs. (Nb + Y) for granites (after: Pearce et al., 1984). VAG = volcanic arc granites, WPG = within-plate granites. ORG = ocean-ridge granites, COLG = collisional granites.

the late Cretaceous to Paleocene magmatism. While the early Cretaceous granitoids in the northern Lhasa plutonic belt and eastern Transhimalayan batholiths may be interpreted as the main product of collision-induced crustal thickening in the post-collisional regime, we argue the importance of ‘‘far-field’’ interactions with the Neo-Tethyan subduction related processes for the igneous longevity and genesis of specific rock types. For example, back-arc extension (Zhang et al., 2004; Wen et al., 2008a), occurring as a recurrent tectonic process in the arc to retroarc evolution of the Neo-Tethyan subduction system, could have interacted with the post-collisional stress during the early Cretaceous to form the Demulha A-type granites. 7. Concluding remarks (1) This study reports geochemical and Sr–Nd isotopic data of the Cretaceous to Paleocene volcano-plutonic belt, from Bomi to Chayu, in the eastern Transhimalayan region, SE

148

I-Jhen Lin et al. / Journal of Asian Earth Sciences 53 (2012) 131–150

Fig. 13. Comparative histograms of (a) SiO2 contents, (b) eNd(T) values, and (c) ISr ratios of the early Cretaceous to Paleocene granitoids from the easternmost part of the Lhasa terrane, SE Tibet, with data compiled from those of the Gangdese Batholith and northern plutonic belt, the central part of the Lhasa terrane, southern Tibet (Wen, 2007; Xu et al., 2012).

Tibet, including three major batholiths, Azhagong, Demulha, and Chayu, and an early Cretaceous volcanic succession around Ranwu. While the Azhagong batholith consists mostly of metaluminous I-type granitoids that occasionally contain mafic enclaves, the Chayu batholith consists of peraluminous, highly fractionated S-type granites and the Demulha batholith consists of highly fractionated A-type granites. The Ranwu volcanic rocks that range from basalt to dacite compositions are calc-alkaline in nature. All these rocks exhibit geochemical features similar to those of arc magmas from modern subduction zones or active continental margins. (2) Overall speaking, the eastern Transhimalayan granitoids show heterogeneous Sr and Nd isotope ratios, with eNd(T) from 1.5 to 13 and ISr from 0.703 to 0.745, and the Ranwu volcanic rocks have eNd(T) from +3 to 6 and ISr from 0.705 to 0.707. The latter broadly overlaps the isotopic range of the Azhagong mafic enclaves. The isotopic data suggest three magma source components involved in the petrogenesis of this volcanic–plutonic association, which are the mantle wedge, and the lower and upper parts of the Lhasa continental crust.

(3) We propose a two-stage petrogenetic model: (1) deep level differentiation of the mantle wedge-derived mafic magmas associated with assimilation by the lower continental crust of the Lhasa terrane and (2) additional differentiation and upper crustal contamination of the evolved magmas as they rose and installed in shallow-level magma chambers. While the first stage can explain how the Ranwu volcanics and Azhagong enclaves formed, the second stage accounts for the emplacement of the Azhagong and Chayu batholiths. The shallow intrusions, moreover, may have caused lowpressure melting of pre-existing country rocks that have calc-alkaline nature and Paleoproterozoic model age to produce the early Cretaceous (125 Ma) A-type granites in the Demulha batholith, a specific rock type that results scarcely from subduction zone processes but echoes with the notion for a post-collisional tectonic setting that may have interacted with the back-arc evolution in the Neo-Tethyan subduction system. (4) The eastern Transhimalayan batholiths are not the eastward equivalent of the Gangdese Batholith, but should be correlated westward to the northern Lhasa plutonic belt. These can correlate southeastward and then southward to the

I-Jhen Lin et al. / Journal of Asian Earth Sciences 53 (2012) 131–150

Cretaceous–Paleocene batholiths in the Gaoligong–Tengliang belt, western Yunnan and the Jurassic–Paleocene batholiths in the Shan Scarps province, Burma.

Acknowledgments We thank C.-H. Lo, T.-Y. Lee, Mary Yeh, Y.-B. Wang and M.-F. Chu for help in the fieldwork, M.-F. Chu for advise and help with ICP-MS analyses, and Y.-G. Xu for sharing ideas during this study, which was financially supported by the National Science Council, Taiwan, ROC. We are grateful to the critical and constructive comments provided by journal reviewers Zeming Zhang and Yi-Gang Xu, and the editorial handling by Zhidan Zhao, which were of significant help with improving the presentation of the paper. Appendix A. Supplementary material Supplementary data associated with this article can be found, in the online version, at http://dx.doi.org/10.1016/j.jseaes.2012.03.010. References Allègre, C.J. et al., 1984. Structure and evolution of the Himalaya–Tibet orogenic belt. Nature 307, 17–22. Allmendinger, R.W., Jordan, T.E., Kay, S.M., Isacks, B.L., 1997. The evolution of the Altiplano–Puna Plateau of the Central Andes. Annu. Rev. Earth Planet. Sci. 25, 139–174. Bau, M., 1996. Controls on the fractionation of isovalent trace elements in magmatic and aqueous systems: evidence from Y/Ho, Zr/Hf, and lanthanide tetrad effect. Contrib. Mineral Petrol. 123, 323–333. Bonin, B., 2007. A-type granites and related rocks: evolution of a concept, problems and prospects. Lithos 97, 1–29. Booth, A.L., Zeitler, P.K., Kidd, W.S.F., et al., 2004. U–Pb zircon constraints on tectonic evolution of southeastern Tibet, Namche Barwa area. Am. J. Sci. 304, 889–929. Chang, C. et al., 1986. Preliminary conclusions of the Royal Society and Academia Sinica 1985 geotraverse of Tibet. Nature 323, 501–507. Chappell, B.W., White, A.J.R., 1992. I- and S-type granites in the Lachlan Fold Belt. Trans. Roy. Soc. Edinburgh: Earth Sci. 83, 1–26. Chiu, H.-Y., Chung, S.-L., Wu, F.-Y., et al., 2009. Zircon U–Pb and Hf isotopic constraints from eastern Transhimalayan batholiths on the precollisional magmatic and tectonic evolution in southern Tibet. Tectonophysics 477, 3–19. Chu, M.-F., Chung, S.-L., Song, B., et al., 2006. Zircon U–Pb and Hf isotope constraints on the Mesozoic tectonics and crustal evolution of southern Tibet. Geology 34, 745–748. Chu, M.-F., Chung, S.-L., O’Reilly, S.Y., et al., 2011. India’s hidden inputs to Tibetan orogeny revealed by Hf isotopes of Transhimalayan zircons and host rocks. Earth Planet. Sci. Lett. 307, 479–486. Chung, S.-L., Chu, M.-F., Zhang, Y., et al., 2005. Tibet tectonic evolution inferred from spatial and temporal variations in post-collisional magmatism. Earth-Sci. Rev. 68, 173–196. Coulon, C., Maluski, H., Bollinger, C., 1986. Mesozoic and Cenozoic volcanic rocks from central and southern Tibet: 39Ar–40Ar dating, petrological characteristics and geodynamical significance. Earth Planet. Sci. Lett. 79, 281–302. Davidson, J.P., de Silva, S.L., 1992. Volcanic rocks from the Bolivian Altiplano: insights into crustal structure, contamination and magma genesis in the central Andes. Geology 20, 1127–1130. Debon, F., Le Fort, P., Sheppard, S.M.F., Sonet, J., 1986. The four plutonic belts of the Transhimalaya–Himalaya: a chemical, mineralogical, isotopic and chronological synthesis along a Tibet–Nepal section. J. Petrol. 27, 219–250. Ding, L., Kapp, P., Zhong, D., Deng, W., 2003. Cenozoic volcanism in Tibet: evidence from a transition from oceanic to continental subduction. J. Petrol. 44, 1833– 1865. Driver, L.A., Creaser, R.A., Chacko, T., Erdmer, P., 2000. Petrogenesis of the Cretaceous Cassiar batholith, Yukon-British Columbia, Canada: implications for magmatism in the North American Cordilleran Interior. Bull. Geol. Soc. Am. 112, 1119–1133. Eby, G.N., 1990. The A-type granitoids: a review of their occurrence and chemical characteristics and speculations on their petrogenesis. Lithos 26, 115–134. Eby, G.N., 1992. Chemical subdivision of the A-type granitoids: petrogenetic and tectonic implications. Geology 20, 641–644. Frost, B.R., Barnes, C.G., Collins, W.J., Arculus, R.J., Ellis, D.J., Frost, C.D., 2001. A geochemical classification for granitic rocks. J. Petrol. 42, 2033–2048. Guo, L., Zhang, H.F., Harris, N., Pan, F.B., Xu, W.C., 2011. Origin and evolution of multi-stage felsic melts in eastern Gangdese belt: constraints from U–Pb zircon dating and Hf isotopic composition. Lithos 127, 54–67. Harris, N.B.W., Xu, R.-H., Lewis, C.L., Jin, C., 1988. Plutonic rocks of the 1985 Tibet Geotraverse: Lhasa to Golmud. Philos. Trans. Roy. Soc. Lond. A327, 145–168.

149

Harris, N.B.W., Inger, S., Xu, R.H., 1990. Cretaceous plutonism in central Tibet: an example of post-collision magmatism? J. Volcanol. Geotherm. Res. 44, 21–32. Jahn, B.-M., Wu, F.-Y., Capdevila, R., et al., 2001. Highly evolved juvenile granites with tetrad REE patterns: the Woduhe and Baerzhe granites from the Great Xing’an (Khingan) Mountains in NE China. Lithos 59, 171–198. Jahn, B.-M., Capdevila, R., Liu, D., et al., 2004. Sources of Phanerozoic granitoids in Mongolia: geochemical and Nd isotopic evidence, and implications for Phanerozoic crustal growth. J. Asian Earth Sci. 23, 629–653. Ji, W.-Q., Wu, F.-Y., Chung, S.-L., et al., 2009a. Zircon U–Pb chronology and Hf isotopic constraints on the petrogenesis of Gangdese batholiths, southern Tibet. Chem. Geol. 262, 229–245. Ji, W.-Q., Wu, F.-Y., Liu, C.-Z., Chung, S.-L., 2009b. Geochronology and petrogenesis of granitic rocks in Gangdese batholith, southern Tibet. Sci. China (Series D) 52, 1240–1261. Ji, W.-Q., Wu, F.-Y., Liu, C.-Z., Chung, S.-L., 2012. Early Eocene crustal thickening in southern Tibet: new age and geochemical constraints from the Gangdese batholith. J. Asian Earth Sci. (this volume). Kapp, P., Yin, A., Harrison, T.M., Ding, L., 2005a. Cretaceous-Tertiary shortening, basin development, and volcanism in central Tibet. Bull. Geol. Soc. Am. 117, 865–878. Kapp, J.L.D., Harrison, T.M., Kapp, P., et al., 2005b. Nyainqentanglha Shan: a window into the tectonic, thermal, and geochemical evolution of the Lhasa block, southern Tibet. J. Geophys. Res. 110, B08413. Keto, L.S., Jacobsen, S.B., 1987. Nd and Sr isotopic variation of Early Palaeozoic oceans. Earth Planet. Sci. Lett. 84, 7–41. King, P.L., Chappell, B.W., Allen, C.M., White, A.J.R., 2001. Are A-type granites the high-temperature felsic granites? Evidence from fractionated granites of the Wangrah Suite. Aust. J. Earth Sci. 48, 501–514. Lee, H.-Y., Chung, S.-L., Wang, Y., et al., 2007. Age, petrogenesis and geological significance of the Linzizong volcanic successions in the Linzhou basin, southern Tibet: evidence from zircon U–Pb dates and Hf isotopes. Acta Petrol. Sin. 23, 493–500. Lee, H.-Y., Chung, S.-L., Lo, C.-H., et al., 2009. Eocene Neotethyan slab breakoff in southern Tibet inferred from the Linzizong volcanic record. Tectonophysics 477, 20–35. Lee, H.-Y., Chung, S.-L., Ji, J.-Q., et al., 2012. Geochemical and Sr–Nd isotopic constraints on the genesis of the Cenozoic Linzizong volcanic successions, southern Tibet. J. Asian Earth Sci. (this volume). Le Maitre, R.W. (Ed.), 2002. Igneous Rocks: A Classification and Glossary of Terms. Cambridge Uni. Press, 236pp. Liang, Y.-H., Chung, S.-L., Liu, D., et al., 2008. Detrital zircon evidence from Burma for reorganization of the eastern Himalayan river system. Am. J. Sci. 308, 618–638. Li, Z.-X., Li, X.-H., 2007. Formation of the 1300-km-wide intracontinental orogen and postorogenic magmatic province in Mesozoic South China: a flat-slab subduction model. Geology 35, 179–182. Li, Z.-X., Li, X.-H., Chung, S.-L., et al., 2012. Magmatic switch-on and switch-off along the South China continental margin since the Permian: transition from an Andean-type to a Western Pacific-type plate boundary. Tectonophysics 532– 535, 271–290. Lin, I-J., Chung, S.-L., Kumar, A., et al., 2010. The formation, exhumation and tectonic implications of the Lohit batholith, NE India with respect to the India-Asia collision. Abst. to Ann. Conf. on Petrology and Geodynamics, Peking Uni., Beijing. Maniar, P.D., Piccoli, P.M., 1989. Tectonic discrimination of granitoids. Geol. Soc. Am. Bull. 101, 635–643. Middlemost, E.A.K., 1994. Naming materials in the magma/igneous rock system. Earth-Sci. Rev. 37, 215–224. Miller, C., Schuster, R., Kotzli, U., et al., 1999. Post-collisional potassic and ultrapotassic magmatism in SW Tibet: geochemical and Sr–Nd–Pb–O isotopic constraints for mantle source characteristics and petrogenesis. J. Petrol. 40, 1399–1424. Mitchell, A.H.G., Chung, S.-L., Thura, O.O., et al., accepted for publication. Zircon U– Pb ages in Myanmar: magmatic–metamorphic events and the closure of a neoTethys ocean? J. Asian Earth Sci., accepted for publication. Mo, X.X., Dong, G.C., Zhao, Z.D., et al., 2005. Spatial and temporal distribution and characteristics of granitoids in the Gangdese, Tibet and implication for crustal growth and evolution. Geol. J. Chin. Univ. 11, 190–281. Monecke, T., Kempe, U., Monecke, J., et al., 2002. Tetrad effect in rare earth element distribution patterns: a method of quantification with application to rock and mineral samples from granite-related rare metal deposits. Geochim. Cosmochim. Acta 66, 1185–1196. Pan, G.-T., et al. (Eds.), 2004. Guide book of the Geological Map of Qinghai-Xizang (Tibet) and Adjacent Areas: 1:1,500,000. Chengdu Inst. Geol. Mineral Res., China Geol. Surv., Chengdu Cart. Publ. House, 48pp. Patino Douce, A.E., 1997. Generation of metaluminous A-type granites by lowpressure melting of calc-alkaline granitoids. Geology 25, 743–746. Pearce, J.A., Mei, H., 1988. Volcanic rocks of the 1985 Tibet Geotraverse: Lhasa to Golmud. Philos. Trans. Roy. Soc. Lond. A327, 169–201. Pearce, J.A., Harris, N.B.W., Tindle, A.G., 1984. Trace element discrimination diagrams for tectonic interpretation of the granitic rocks. J. Petrol. 25, 956–983. Petford, N., Atherton, M.P., Halliday, A.N., 1996. Rapid magma production rates, underplating and remelting in the Andes: Isotopic evidence from northerncentral Peru (9–11°S). J. South Am. Earth Sci. 9, 67–78. Searle, M.P., Windley, B.F., Coward, M.P., et al., 1987. The closing of Tethys and the tectonics of Himalaya. Geol. Soc. Am. Bull. 98, 678–701.

150

I-Jhen Lin et al. / Journal of Asian Earth Sciences 53 (2012) 131–150

Sun, S.-s., McDonough, W.F., 1989. Chemical and isotopic systematics of oceanic basalts: implications for mantle composition and process. In: Saunders, A.D., Norry, M.J. (Eds.), Magmatism in the Ocean Basins, vol. 42. Geol. Soc. Spec. Publ., pp. 313–345. Tatsumi, Y., Eggins, S., 1995. Subduction Zone Magmatism. Blackwell Sci., 211pp. TBGMR (Tibetan Bureau of Geology and Mineral Resources), 1993. Regional Geology of Xizang (Tibet) Autonomous Region. Geol. Mem. Ser. 1, vol. 31. Geol. Publ. House, Beijing, 699pp (in Chinese with English abstract). Tu, G., Zhang, Y., Wang, Z., et al., 1982. Geochemistry of Granitoids, Southern Tibet. Geol. Publ. House, Beijing, 190pp. Wang, K-L., Chung, S-L., O’Reilly, S.Y., et al., 2004. Geochemical constraints for the genesis of post-collisional magmatism and the geodynamic evolution of the northern Taiwan region. J. Petrol. 45, 975–1011. Wells, M.L., Hoisch, T.D., 2008. The role of mantle delamination in widespread Late Cretaceous extension and magmatism in the Cordilleran orogen, western United States. Geol. Soc. Am. Bull. 120, 515–530. Wen, D.-R., 2007. The Gangdese Batholith, Southern Tibet: Ages, Geochemical Characteristics and Petrogenesis. Unpubl. PhD Thesis, National Taiwan University. Wen, D.-R., Chung, S.-L., Song, B., et al., 2008a. Late Cretaceous Gangdese instrusions of adakitic geochemical characteristics, SE Tibet: petrogenesis and tectonic implications. Lithos 105, 1–11. Wen, D.-R., Liu, D., Chung, S.-L., et al., 2008b. New zircon SHRIMP U–Pb ages of the Gangdese batholith and implications for Neotethyan subduction in southern Tibet. Chem. Geol. 252, 191–201. Whalen, J.B., Currie, K.L., Chappell, B.W., 1987. A-type granites: geochemical characteristics, discrimination and petrogenesis. Contrib. Mineral. Petrol. 95, 407–419. Wu, F.-Y., Sun, D.-Y., Li, H.-M., et al., 2002. A-type granites in Northeastern China: age and geochemical constraints on their petrogenesis. Chem. Geol. 187, 143–173. Wu, F.-Y., Li, X.-H., Yang, J.-H., Zheng, Y.-F., 2007. Discussion on the petrogenesis of granites. Acta Petrol. Sin. 23, 1217–1238 (in Chinese). Wu, F.-Y., Ji, W.-Q., Liu, C.-Z., Chung, S.-L., 2010. Detrital zircon U–Pb and Hf isotopic data from the Xigaze fore-arc basin: constraints on Transhimalayan magmatic evolution in southern Tibet. Chem. Geol. 271, 13–25.

Wu, G., Wang, X., Zhong, D., 1999. Early Cretaceous Andean-type arc volcanic in SE Xizang, China. Acta Petrol. Sin. 15, 422–429 (in Chinese with English abstract). Xu, R.-H., Schärer, U., Allègre, C.J., 1985. Magmatism and metamorphism in the Lhasa block (Tibet): a geochronological study. J. Geol. 93, 41–57. Xu, Y.-G., Yang Q.-J., Lan, J.-B., et al., 2012. Temporal-spatial distribution and tectonic implications of the batholiths in the Gaoligong-Tengliang-Yingjiang area, western Yunnan: constraints from zircon U–Pb ages and Hf isotopes. J. Asian Earth Sci. (this volume). Yang, Q.-J., Xu, Y.-G., Huang, X.-L., Luo, Z.-Y., 2006. Geochronology and geochemistry of granites in the Gaoligong tectonic belt, western Yunnan: tectonic implications. Acta Petrol. Sin. 22, 817–834. Yin, A., Harrison, T.M., 2000. Geologic Evolution of the Himalayan-Tibetan Orogen. An. Rev. Earth Planet. Sci. 28, 211–280. Zen, E., 1986. Aluminum enrichment in silicate melts by fractional crystallization: some mineralogic and petrographic constraints. J. Petrol. 27, 1095–1117. Zhang, H.F., Harris, N., Guo, L., Xu, W.C., 2010a. The significance of Cenozoic magmatism from the western margin of the eastern syntaxis, southeast Tibet. Contrib. Mineral. Petrol. 160, 83–98. Zhang, K.J., Xia, B.D., Wang, G.M., et al., 2004. Early Cretaceous stratigraphy, depositional environments, sandstone provenance, and tectonic setting of central Tibet, western China. Bull. Geol. Soc. Am. 116, 1202–1222. Zhang, Z.M., Zhao, G.C., Santosh, M., Wang, J.L., Dong, X., Shen, K., 2010b. Late Cretaceous charnockite with adakitic affinities from the Gangdese batholith, southeastern Tibet: evidence for Neo-Tethyan mid-oceanic ridge subduction? Gondwana Res. 17, 615–631. Zhu, D.C., Mo, X.X., Niu, Y., et al., 2009a. Geochemical investigation of Early Cretaceous igneous rocks along an east–west traverse throughout the central Lhasa Terrane, Tibet. Chem. Geol. 268, 298–312. Zhu, D.C., Mo, X.X., Wang, L.Q., et al., 2009b. Petrogenesis of highly fractionated Itype granites in the Chayu area of eastern Gangdese, Tibet: constraints from zircon U-Pb geochronology, geochemistry and Sr–Nd–Hf isotopes. Sci. China (Series D). http://dx.doi.org/10.1007/s11430-009-0132-x. Zhu, D.C., Zhao, Z.D., Niu, Y., et al., 2011. The Lhasa terrane: record of a microcontinent and its histories of drift and growth. Earth Planet. Sci. Lett. 301, 241– 255.