Mesoproterozoic rift setting of SW Hainan: Evidence from the gneissic granites and metasedimentary rocks

Precambrian Research 325 (2019) 69–87

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Mesoproterozoic rift setting of SW Hainan: Evidence from the gneissic granites and metasedimentary rocks

T

Limin Zhanga,b, Yuzhi Zhanga,b, , Xiang Cuia,b, Peter A Cawoodc, Yuejun Wanga,b, Aimei Zhangd ⁎

a

Guangdong Provincial Key Lab of Geodynamics and Geohazards, School of Earth Sciences and Engineering, Sun Yat-sen University, Guangzhou 510275, China Southern Laboratory of Ocean Science and Engineering, Zhuhai 519082, China c School of Earth, Atmosphere & Environment, Monash University, Melbourne, VIC 3800, Australia d Third Institute of Oceanography, Ministry of Natural Resource, Xiamen 361005, China b

ARTICLE INFO

ABSTRACT

Keywords: Baoban metasedimentary rocks Baoban gneissic granites Elemental and isotopic compositions Mesoproterozoic rifting Nuna break-up Southwest Hainan

The Mesoproterozoic Baoban Complex, southwest Hainan Island, has played a crucial role in deciphering Nuna (Columbia) supercontinent reconstructions. Metasedimentary rocks in the Baoban Complex are intruded by Mesoproterozoic gneissic granites and mafic rocks. Our new geochemical and geochronological data show that these gneissic granites are monzogranites and granodiorites and crystallized at ∼1430 Ma. Geochemically, they are subdivided into two groups with I- and A-type affinities. The groups show broadly similar εNd (t) values ranging from −2.4 to +0.9, zircon εHf (t) from −5.4 to +7.8 and δ18O values from +5.0 to +8.6‰, suggesting derivation from the same source involving juvenile mafic melt and ‘‘ancient” continental crust components. Metasedimentary rocks have high La/Sc (1.4–5.8) but low Sc/Th (0.6–1.6) and Co/Th (0.3–1.1) ratios, as well as negative εNd (t) of −4.5 to −4.1, indicative of an “ancient” felsic igneous source with a recycled sedimentary component. Detrital zircon grains from the metasedimentary rocks yield three primary age-peaks of ∼1780 Ma, ∼1610 Ma and ∼1440 Ma, with the depositional age synchronous with those of the gneissic granites and metabasites (∼1430 Ma). Our geochemical and geochronological data, along with regional geological constraints, suggest a rift setting. The age populations and hafnium compositions of detrital zircons from the metasedimentary rocks in the Baoban Complex, southwest Hainan are comparable to those igneous zircons from East Antarctica, pointing out a probable affinity between southwest Hainan and East Antarctica in the Nuna supercontinent.

1. Introduction The South China Block (SCB) comprises the Yangtze Block to the northwest and Cathaysia Block to the southeast, separated by the Jiangnan Orogen, along which they were amalgamated (Fig. 1a; Wang et al., 2004, 2007, 2013a, 2014a,b; Ye et al., 2007; Yu et al., 2009; Shu et al., 2011; Xia et al., 2011; Zhang and Wang, 2016). South China is generally thought to occupy either an internal or external location within Rodinia (e.g., Li et al., 1995, 1999, 2002, 2003; Zheng et al., 2007, 2008; Zhou et al., 2004, 2009; Zhao and Cawood, 2012; Wang et al., 2013a, 2014b; Cawood et al., 2013, 2018; Zhang and Wang, 2016 and references therein), although recently, Merdith et al., (2017) suggested a setting where South China was independent from Rodinia on a separate plate. Reports on the Paleo- and Mesoproterozoic units from the northern and western portions of the Yangtze Block and the Mesoproterozoic units in southwest Hainan suggest that the South China

(Yangtze and Cathaysia blocks) might have been involved in the assembly and breakup of the Nuna (Columbia) supercontinent (e.g., Gao et al., 1999; Wilde et al., 2002; Kusky and Li, 2003; Zhai and Liu, 2005; Zhang et al., 2006; Liu et al., 2008; Sun et al., 2009; Zhao et al., 2010; Chen et al., 2013; Fan et al., 2013; Yin et al., 2013; Wang et al., 2015; Han et al., 2017; Yao et al., 2017; Zhang et al., 2018). However, its position in Nuna is poorly constrained (Zhao and Cawood, 1999, 2012; Li and Li, 2007; Shu et al., 2008; Yu et al., 2009, 2012; Liu et al., 2014; Li et al., 2014; Yao et al., 2017; Zhang et al., 2017a, 2018). Hainan Island constitutes the southern exposed extent of the South China Block and is thought to be a part of the Cathaysia Block. It contains Mesoproterozoic metasedimentary and metaigneous rocks in the Baoban Complex, which outcrops in the SW portion of the island (e.g. Yao et al., 2017; Zhang et al., 2018). Previous work within the complex suggests both the metabasites and granitoids were formed at ∼1430 Ma, equivalent to the maximum depositional age of the Baoban

⁎ Corresponding author at: Guangdong Provincial Key Lab of Geodynamics and Geohazards, School of Earth Sciences and Engineering, Sun Yat–sen University, No. 135, Xingang Xi Road, Guangzhou 510275, China. E-mail address: [email protected] (Y. Zhang).

https://doi.org/10.1016/j.precamres.2019.02.013 Received 23 August 2018; Received in revised form 11 February 2019; Accepted 12 February 2019 Available online 13 February 2019 0301-9268/ © 2019 Elsevier B.V. All rights reserved.

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Fig. 1. (a) Tectonic outline of Southeast Asia (after Wang et al., 2017), (b) simplified geological map of Hainan Island showing the distribution of Mesoproterozoic rocks (revised after Guangdong BGMR, 1988) and (c) simplified stratigraphic column of the Mesoproterozoic Baoban Complex (revised after Guangdong BGMR, 1988). Table 1 Summary of sampling locations, zircon U-Pb, in-situ Hf-O, Sr-Nd and ACNK analyses of the Mesoproterozoic gneissic granites and metasedimentary rocks in southwest Hainan. Sample

Lithology

GA-2B

Gneissic granite

13GA-21A

Gneissic granite Gneissic granite

14HN-12B 14HN-12C

Gneissic granite

14HN-13B4

Gneissic granite

16HN-26B

Gneissic granite

14HN-05A

Mica-quartz schist

16HN-27B

Quartz-mica schist

Sample location

Gong'ai area N 18°51.326′; E 108°46.556′ Gong'ai area Gezhen village N 19°12.592′; E 108°58.005′ Gezhen village N 19°11.320′; E 108°58.307′ Gezhen village N 19°10.992′; E 108°58.159′ Chongzuling area N 18°35.366′ E 108°54.743′ Gong'ai area N 18°50.797′ E 108°47.611′ Chongzuling area N 18°35.366′ E 108°54.743′

Zircon U-Pb crystallization age (Ma) Minimum crystallization age (Ma)

inherited zircon U-Pb age (Ma) Peaks (Ma)

1430 ± 12 Ma, n = 17, MSWD = 0.26 1421 ± 17 Ma, n = 10, MSWD = 0.56 1429 ± 12 Ma, n = 18, MSWD = 0.38

1677

1431 ± 12 Ma, n = 15, MSWD = 0.36 1428 ± 10 Ma, n = 21, MSWD = 0.72

1561, 1587

1426 ± 11 Ma, n = 18, MSWD = 0.43 1461 ± 23 Ma, n = 8, MSWD = 1.6 N 18°50.797′; E 108°47.611′ 1457 ± 52 Ma, n = 7, MSWD = 0.16

Grains for Mid-Mesoproterozoic crystallization age εHf (t)

TDM (Ga)

δ18O

εNd (t)

+ 0.8–+5.1

2.13–1.89

6.39–7.89

−1.9

1.03

−0.3–+5.4

2.21–1.86

−0.7

1.09

+ 1.7–+6.6

2.09–1.79

+ 0.7–+4.7

2.19–1.89

7.18–8.62

−1.5

1.05

+ 0.8–+6.9

2.15–1.75

6.14–8.10

−1.3

1.03

− 0.2–+6.2

2.20–1.79

4.96–6.06

0.42

1.08

1.05

∼1445; ∼1610; ∼1780; ∼2475

−4.1

∼1460; ∼1585; ∼1750; ∼2450

−4.8

70

A/CNK

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Fig. 2. Simplified geological maps of the Gezhen (Changjiang) (a), Gong’ai (Ledong) (b) and Chongzuling (Ledong) (c) areas showing the sampling locations (modified from Guangdong BGMR, 1988; Ma et al., 1997)

Wu et al., 2008). Latest Paleo- to Mesoproterozoic sedimentary rocks are sporadically exposed on the southwestern Yangtze Block, including the ca. 1750–1600 Ma Dahongshan Group, the ca. 1750–1500 Ma Dongchuan Group and the ca. 1800–1500 Ma Tong’an Formation, whereas Mesoproterozoic igneous rocks are represented by ca. 1.5 Ga gabbros and 1.1 Ga A-type felsic rocks in the lower Huili Group that occur in the western Yangtze Block (Greentree et al., 2006; Zhang et al., 2006; Greentree and Li, 2008; Sun et al., 2008, 2009; Wu et al., 2008; Zhao et al., 2010; Zhao and Cawood, 2012; Wang et al., 2012; Chen et al., 2013; Fan et al., 2013). Archean basement is not exposed in the Cathaysia Block but has been inferred from the presence of minor inherited and/or xenocrystic zircons in the younger sedimentary sequence (e.g., Zhao and Cawood, 2012). The oldest rocks exposed in the Cathaysia Block are Paleoproterozoic (1890–1830 Ma) high-grade metamorphic schist, gneiss, gneissic granite, quartzite, marble, amphibolite and migmatite, traditionally defined as the Badu Complex, they crop out in the northeastern part of the Cathaysia Block (e.g., Zhao and Cawood, 1999, 2012; Li and Li, 2007; Shu et al., 2008; Yu et al., 2009, 2012; Liu et al., 2014). Mesoproterozoic metaigneous and metasedimentary rocks are absent from the Cathaysia Block on the Chinese mainland but occur on Hainan Island (e.g., Ma et al., 1997; Li et al., 2002, 2014; Yao et al., 2017; Zhang et al., 2017a, 2018). Neoproterozoic rocks are the dominant Precambrian units in the Cathaysia Block, represented by the Mamianshan, Mayuan, Chencai and Longquan groups in eastern Cathaysia, and the Yunkai Group in the western part (e.g., Wan et al., 2007; Shu et al., 2011; Wang et al., 2013a, 2014b, 2018; Zhang and Wang, 2016). Precambrian rocks in southwest Hainan (Fig. 1b) include the Mesoproterozoic Baoban Complex, the Shilu Group and the Shihuiding

metasedimentary rocks which might be related to the breakup of the Nuna supercontinent (e.g.,Xu et al., 2001; Li et al., 2008; Yao et al., 2017; Zhang et al., 2017a, 2018). However, the type and petrogenesis of the granitoids remains controversial (Li et al., 2002; Xu et al., 2001, 2006; Zhang et al., 2017a), and data on the provenance record of metasedimentary rocks within the complex is lacking. Such data has the potential to better constrain the paleogeographic position of the region within Nuna. This paper presents new geochronological, geochemical and Sr-Nd-Hf-O isotopic data from the Baoban gneissic granites and metasedimentary samples in SW Hainan. These data, along with our field observations and the available published data, enable evaluation of the Proterozoic tectonic setting of Hainan Island and further constrain its relationship with other continental blocks within supercontinent Nuna. 2. Geological setting and sampling The Yangtze and the Cathaysia blocks amalgamated along the Jiangnan orogen during latest Meso- to middle Neoproterozoic, overlapping in part with the assembly of Rodinia (Wang et al., 2004, 2007, 2013a, 2014a,b; Ye et al., 2007; Yu et al., 2009; Shu et al., 2011; Xia et al., 2011; Zhang and Wang, 2016). Crystalline basements of the Yangtze and Cathaysia blocks have different compositions. In the Yangtze Block, the oldest crystalline basement is represented by the Archean TTG gneisses with ages from ca. 3.45 to 2.90 Ga outcropped in the northern Yangtze Block and the Paleoproterozoic (2.0–1.9 Ga) metasedimentary rocks that are sparsely exposed in the Kongling, Huangtuling, Houhe areas (Qiu et al., 2000; Zheng et al., 2006; Jiao et al., 2009; Gao et al., 2011, 2014; Zhang et al., 2006; Sun et al., 2008; 71

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Fig. 3. Outcrop sketch of the Baoban Complex (a) and microscopic photographs for the representative granite samples (b–d) and metasedimentary rocks (e–g). Q: Quartz, Hb: Hornblende, Pl: Plagioclase, Kfs: K-feldspar, Mus: Muscovite.

Formation (Chen et al., 1997; Ma et al., 1997). The Shihuiding Formation is dominated by siliciclastic rocks with thickness of ∼125 m (Chen et al., 1997). The Shihuiding Formation unconformably overlies the Shilu Group (e.g., Chen et al., 1997; Li et al., 2008), which consists of greenschist facies shallow marine siliciclastic and carbonate rocks (Yao et al., 1999), and has been interpreted as a Mesoproterozoic or early Neoproterozoic foreland basin deposit (Ma et al., 1997; Li et al., 2008; Wang et al., 2015; Yao et al., 2017; Zou et al., 2017). The Baoban Complex, previously defined as the Baoban Group, is mainly exposed in the Changjiang, Gong’ai and Chongzuling areas in southwest Hainan. It consists of two units, which have previously been referred to as formations. They consist of deformed and metamorphosed igneous and

sedimentary rocks and are herein referred to as assemblages: the greenschist- to amphibolite-facies Gezhencun and Ewenling assemblages (Fig. 1b; Chen et al., 1997; Ma et al., 1997; Wang et al., 1991; Ma et al., 1997; Li et al., 2002, 2008). The Gezhencun assemblage is characterized by granitic gneisses, migmatites, metamorphic volcanic rocks and gneissic granites, and the Ewenling assemblage is dominated by paragneisses, quartz-mica schists, quartzites and amphibolite pods or interlayers and gneissic granites veins (Fig. 1c; Chen et al., 1997; Ma et al., 1997; Li et al., 2002; Yao et al., 2017). In this study, 8 metasedimentary and 17 gneissic granite samples were collected from the Baoban Complex in the Gezhen (Changjiang), Gong’ai and Chongzuling (Ledong) areas. Additionally four gneissic 72

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0.28 0.26

P b / 2 3 8U

0.24

0.30

a gneissic granite

(14HN-12B) Weighted age = 1429±12 Ma n=18, MSWD = 0.38

0.26 1394 Ma

206

0.16

0.18

1440

1100

1400

1360

1320

1320

2.0

2.8

2.4

3.2

3.6

0.14 1.4

1.8

2.6

2.2

3.0

3.4

3.8

4.2

0.28 1650

1500

d gneissic granite

(14HN-13B 4)

0.24

P b / 2 3 8U

1433 Ma 1428 Ma

1520

1360

c gneissic granite

0.27

1300

1480

1440

1400

0.29

1500

n=15, MSWD = 0.36

0.22

1480

0.18

0.14 1.6 0.31

Weighted age = 1431±12 Ma

1411 Ma 1150

1700

(14HN-12C)

1435 Ma

1350

0.22 0.20

b gneissic granite

(GA-2B) Weighted age = 1430±12 Ma n=17, MSWD = 0.26

Weighted age = 1424±10 Ma n=20, MSWD = 0.66

0.25

1200

0.20

1448 Ma 1413 Ma

1417 Ma

1300

1439 Ma

1500

206

1520

0.23

1350

1460 1480

1000

1440

1420

0.16

1400

0.21

1380

1360 1340

1320

0.19 2.2

0.38 0.34

2.6

3.0

3.4

3.8

4.2

0.27

e gneissic granite

P b / 2 3 8U 206

0.26

Weighted age = 1421±17 Ma

1600

n=10, MSWD = 0.56

0.25

1435 Ma 1440 Ma

2.6

2.2

3.0

f gneissic granite

1500

1350

1420 Ma 1443 Ma 1520

0.21

1460

1250

1500 1480 1460 1440

1420

1000

3.4

Weighted age = 1426±11 Ma n=18, MSWD = 0.43

0.23

1500

0.22 0.18

1.8

(16HN-26B)

(13GA-21A)

1800

0.30

0.12 1.4

1420

0.19

1380

0.14

1400 1380

1340

1360 1300

0.10 0.5

1.5

2.5

3.5

4.5

0.17 2.2

5.5

Pb/235U

1340

2.4

2.6

2.8

3.0

3.2

3.4

Pb/235U

207

207

Fig. 4. Zircon U-Pb concordia diagrams with zircon CL images from the gneissic granites in southwest Hainan.

granite samples published in Zhang et al. (2017a) are reanalyzed (Fig. 1b and 2 and Table 1). The gneissic granites are preserved as stocks and lenses in the metasedimentary rocks (Figs. 1–3). The mineral assemblages in the gneissic granites taken from Gong’ai and Gezhen areas are mainly plagioclase (∼20–40%), K-feldspar (∼15–35%), quartz (∼30–55%), biotite (∼5–15%) and hornblende (∼5%) with minor amounts of garnet, apatite, zircon, monazite, and Fe–Ti oxides (Fig. 3b and d). Samples form Chongzuling area are primarily composed of K-feldspar (∼30–40%), plagioclase (20–35%), quartz (30–40%), and minor biotite (Fig. 3f). The metasedimentary rocks are dominated by mica-quartz schists, composed of recrystallized quartz and plagioclase with biotite aligned along the schistosity plane (Fig. 3c, e and g).

Engineering at Sun Yat-sen University. Operating conditions were an accelerating voltage of 15 Kv and a sample current of 10 nA with a beam diameter ranging from 1 to 5 μm. In-situ zircon U, Th and Pb isotopic measurements from gneissic granites (GA-2B, 13GA-21A, 14HN-12B, 14HN-12C, 14HN-13B4 and 16HN-26B) were undertaken on a VG PQ Excel ICPMS equipped with a New Wave Research LUV213 laser ablation system, at the Department of Earth Sciences, the University of Hong Kong (UHK). Zircon U–Pb dating and trace element analyses for detrital zircons from metasedimentary rocks (14HN-05A and 16HN-27B) were performed by laser ablation inductively coupled plasma mass spectrometry (LA-ICP-MS) at the State Key Laboratory of Geological Processes and Mineral Resources, China University of Geosciences in Wuhan, China. The instrumental settings and detailed analytical procedures for the two techniques are described in Xia et al. (2004) and Yuan et al. (2004). The trace element compositions of detrital zircons were calibrated against the National Institute of Standards and Technology Standard Reference Material 610 using Si as the internal standard and NIST SRM 610 as the reference standard. Each analysis consisted of a 20 s background measurement (laser off) followed by 45 s data acquisition. The detailed

3. Analytical methods Zircon grains from metasedimentary and gneissic granite samples were separated by conventional heavy liquid and magnetic techniques and then handpicked under a binocular microscope. Their internal texture was examined by cathodoluminescence (CL) imaging using a scanning electron microprobe at the School of Earth Science and 73

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0.65

0.7

a

0.6

Mica-quartz schist

2476 Ma 1785 Ma

1500

0.2

0.0

1798 Ma 1610 Ma

1173 Ma

18 16

4

c

8

Pb/

235

U

Mica-quartz schist 1780 14HN-05A

14 12

12

14 N=87

8

1435

6

0

4

207

8

12

Pb/ 235U

Quartz-mica schist 1780 16HN-27B

16 N=80

1600

10 8

1450

6

600

e

10

Mica-quartz schist

Sample/Chondrite

3

10

10

1

Th/U

10 2 10

0

10 0 10

10

-1

10

-2

200

Age (Ma)

14HN-05A

10 4

0

1000 1400 1800 2200 2600 3000

metamorphic rims magmatic cores 10

-1

-2

0

Age (Ma) 500 1000 1500 2000 2500

10 4

f

1000 1400 1800 2200 2600 3000

Age (Ma)

Quartz-mica schist 16HN-27B

10 3 10 2

10 1

10

10 0

10 0 10 -1 10

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

5

600

-2

Th/U

200

10 5

Sample/Chondrite

1457 Ma

2

2

10

1609 Ma

1039 Ma

4

4 0

1783 Ma

1344 Ma

d

12

2635 Ma

1798 Ma 1629 Ma 1462 Ma

1500

0.25

16

1610

10

2456 Ma

0.35

0.05 207

2500

0.15

1644 Ma 1443 Ma

1054 Ma 430 Ma

0

1433 Ma

206

0.3

Quartz-mica schist 16HN-27B

0.45

P b / 238U

0.4

0.1

Number

2438 Ma

2500

Number

206

P b / 238U

0.5

b

0.55

14HN-05A

10 -1

metamorphic rims magmatic cores 10

Age (Ma)

-2

0

500 1000 1500 2000 2500

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

Fig. 5. (a, b) Zircon U-Pb concordia diagrams with zircon CL images, (c, d) relative probability vs age diagrams and (e, f) zircon REE patterns with Th/U ratios for the Mesoproterozoic metasedimentary rocks in southwest Hainan.

chondritic ratios of 176Hf/177Hf = 0.282772 and 176Lu/177Hf = 0.0332 (Blichert-Toft and Albarede, 1997) were used for calculating εHf (t) values. The calculated model ages (TDM1) are based on the depleted mantle model described by Griffin et al. (2000). The two-stage model age (TDM2) was also calculated on basis of 176Lu/177Hf = 0.015 for average continental crust (Griffin et al., 2002). Zircon oxygen isotopic analyses were measured using the Cameca 1280 at Institute of Geology and Geophysics, Chinese Academy of Sciences (CAS). The Cs+ ion beam was accelerated to 10 kV, with an intensity of ∼2 nA. The normal incidence electron flood gun was used to compensate for sample charging. Oxygen isotopes were measured in the multi-collector mode with two off-axis faraday cups. Analytical procedures are similar to that described by Li et al. (2010, 2013). The internal precision of a single analysis was generally better than 0.20‰ (1 σ) for 18O/16O ratio. All the zircon U-Pb geochronological dating, trace element and in-situ Hf-O isotopic analyzed results are listed in Supplementary Dataset 1–3. Samples selected for whole-rock elemental and Sr-Nd isotopic analyses were crushed to 200-mesh using an agate mill. Major oxides, trace and REE elements and Sr-Nd isotopic ratios were analyzed at the GIG, CAS. Major oxides were measured by a wavelength X-ray fluorescence spectrometer using a Rigaku ZSX100e instrument, with the relative standard derivations within 5%. Trace elements were analyzed by ICP-

analytical procedures and data plotting follow Ludwig (2003) and Liu et al. (2010). Fractionation correction and associated calculations follow ICPMSDataCal (8.4) (Liu et al., 2010). The errors for individual U-Pb analyses are presented with 1 σ error in data tables and on concordia diagrams. Data reduction for all samples was carried out using the SQUID 1.0 and ISOPLOT program (Ludwig, 2003). In-situ zircon Lu-Hf isotopic analyses were performed by the laser ablation multi-collector inductively coupled plasma mass spectrometry (La-MC-ICPMS) method using a Neptune MC-ICPMS and a Resolution M-50 laser-ablation system at the State Key Laboratory of Isotope Geochemistry at the Guangzhou Institute of Geochemistry (GIG), Chinese Academy of Sciences (CAS). Helium was used as the carrier gas to transport the ablated material. Hf isotopic data was acquired on certain zircon grains following the U-Pb dating, targeting similar domains identified from the CL images. A 45 μm spot was used with a repetition rate of 6 Hz. The instrumental conditions and detailed analytical procedure follow Zhang et al. (2014, 2015). The standard zircon Penglai (4.4 ± 0.1 Ma; Li et al., 2010) was used as a check on data quality and was measured twice between every 5 unknown analyses. Repeated measurements of this standard zircon yielded 176Hf/177Hf ratios of 0.282907 ± 0.000035 (2σ, n = 40), within uncertainty of the known ratios (0.282906; Li et al., 2010). A decay constant for 176Lu of 1.865 ± 0.015 × 10−11/year (Scherer et al., 2001), the present-day 74

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MS and the international standard BCR-1 was chosen to calibrate the element concentrations. Detailed procedures are described by Li et al. (2005, 1996). Sample powders for Sr-Nd isotopic ratios were measured on MC-ICP-MS. The total procedure blank is in the range of 200–500 pg for Sr and < 50 pg for Nd. The mass fractionation corrections for isotopic ratios based on 86Sr/88Sr = 0.1194 and 146Nd/144Nd = 0.7219. The measured 87Sr/86Sr ratios of ten analyses for the (NIST) SRM 987 standard and 143Nd/144Nd ratios of twelve analyses for the La Jolla standard are 0.710265 ± 12 (2σ) and 0.511862 ± 10 (2σ), respectively. The detailed analytical procedures and data plotting follow Liang et al. (2003). 4. Results 4.1. Zircon U-Pb geochronological and in-situ Lu-Hf and O isotopic results Zircon U–Pb, Lu-Hf and O isotopic analytical results are presented in the Supplementary Dataset and Table 1, and are plotted on concordia diagrams (Figs. 4–6). Zircon grains from all of these samples are transparent to translucent and prismatic. CL images (Figs. 4 and 5) show that grains from gneissic granites display internal oscillatory zoning, but those from the Baoban metasedimentary rocks show a core with oscillatory zoning and a rim with bright luminescence. 4.1.1. Gneissic granites Samples 14HN-12B, 14HN-12C and 14HN-13B4 are gneissic granites from the Changjiang area (Fig. 2a). These zircons with oscillatory zoning have Th/U ratios of 0.1–1.3, consistent with their igneous origin. Twenty-three spots from 23 grains of 14HN-12B display apparent 207Pb/206Pb ages ranging from 1450 Ma to 1389 Ma, indicative of Pb loss during solid-state recrystallization (Hoskin and Black, 2000). In the U-Pb concordia diagram, all the 23 analyses yield an upper intercept age of 1428 ± 12 Ma (MSWD = 0.48), and eighteen concordant spots (> 97%) yield a weighted mean age of 1429 ± 12 Ma (MSWD = 0.38) (Fig. 4a). Twenty-three analytical spots from 14HN12C and twenty-six spots from 14HN-13B4 defined discordia intercept ages of 1429 ± 13 Ma (MSWD = 0.86) and 1420 ± 10 Ma (MSWD = 1.05), with weighted mean ages of 1431 ± 12 Ma (MSWD = 0.36, n = 15) and 1424 ± 10 Ma (MSWD = 0.66, n = 20), respectively (Fig. 4b and c). Analysis 14HN-13B4-14 and −18 give older 207Pb/206Pb apparent ages of 1561 ± 33 Ma and 1587 ± 31 Ma. The corresponding εHf(t) values and TDM2 model ages are in the range of +1.7 to +6.6 and 2.1–1.8 Ga for 14HN-12B, +0.7 to +4.7 and 2.2–1.9 Ga for 14HN-12C, and +0.8 to +6.9 and 2.2–1.7 Ga for 14HN13B4 (Fig. 6a). In-situ zircon δ18O values from 14HN-12C and 14HN13B4 range from 7.2‰ to 8.6‰ and 6.1‰ to 8.1‰, respectively (Fig. 6b). Gneissic granites samples GA-2B and 13GA-21A were collected from the Gong’ai area (Fig. 2b). Twenty-three spots from GA-2B yield apparent 207Pb/206Pb ages varying from 1461 ± 25 Ma to 1337 ± 26 Ma and define an upper intercept age of 1435 ± 11 Ma (MSWD = 2.2). Seventeen concordant analyses from 23 analyses from GA-2B give variable Th/U ratios (0.2–0.7) and yield a weighted mean 207 Pb/206Pb age of 1430 ± 12 Ma with MSWD = 0.26 (Fig. 4d). Fifteen spots from 13GA–21A show apparent 207Pb/206Pb ages ranging from 1677 Ma to 1392 Ma and Th/U ratios of 0.1–0.8, with an upper intercept age of 1425 ± 16 Ma (MSWD = 1.18), and ten concordant spots yield a weighted mean age of 1421 ± 17 Ma (MSWD = 0.56) (Fig. 4e). Zircon εHf(t) values for GA-2B range from +0.8 to +5.1 with the corresponding TDM2 model ages of 2.1–1.9 Ga, and zircon δ18O values are in the range of 6.4–7.9 ‰. For 13GA-21A, the zircon εHf (t) and TDM2 model age values are from −0.3 to +5.4 and 2.2 Ga to 1.9 Ga, respectively. Spot 13GA-21A-08 gives an older 207Pb/206Pb apparent age of 1677 ± 80 Ma, interpreted as an inherited grain. For gneissic granite 16HN-26B, from the Chongzuling area (Ledong, Fig. 2c), eighteen concordant analyses on 20 spots have Th/U ratios of

Fig. 6. Plots of (a) zircon U-Pb ages vs. εHf (t), (b) oxygen isotopic compositions for zircon grains and (c) zircon saturation temperatures vs. δ18 O. Also shown for MORB (Eiler et al., 2000), altered upper and lower oceanic crust (Cocker et al., 1982; Gregory and Taylor, 1981), mafic rocks and I-, and S-type granites (Eiler et al., 2000). The depleted mantle and new continental crust evolution lines were extrapolated after Griffin et al. (2000) and Dhuime et al. (2011), respectively. Samples of Group 1 are plotted as solid rectangles and Group 2 are plotted as solid triangles in red. Gneissic granites in Zhang et al. (2017a) are also shown as hollow rectangle in red and felsic rocks in Li et al. (2008) are shown as hollow triangle in gray. (For interpretation of the references to colour in this figure legend, the reader is referred to the web version of this article.)

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Table 2 Major oxides, trace elemental and Sr-Nd isotopic analytical results for the Mesoproterozoic gneissic granites and metasedimentary rocks in southwest Hainan. Representative samples of gneissic granites Samples of Group 1 Samples

GA-1

GA-2B

13GA-21A

13GA-21B

13GA-21C

13GA-22A

13GA-23A

14HN-12B

14HN-12C

14H-13B2

14HN-13B4

15HN13B1

15HN13B3

SiO2 TiO2 Al2O3 FeOT MnO MgO CaO Na2O K2O P2O5 LOI Total Sc V Cr Co Ni 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 87 Rb/86Sr 147 Sm/144Nd 87 Sr/86Sr 2σ 143 Nd/144Nd 2σ 87 Sr/86Sr(i) εNd(t) TDM (Ga) TZr (°C) Source

65.97 0.77 14.98 4.82 0.07 1.62 3.85 2.75 2.81 0.11 1.28 99.56 19.4 98.3 74.4 6.73 11.2 26.0 193 116 42.9 216 15.3 11.0 574 48.0 95.8 10.5 32.4 6.28 1.41 7.34 1.20 7.48 1.58 4.46 0.68 4.44 0.69 5.79 1.26 15.4 17.5 4.10 4.834 0.117 0.809119 10 0.511792 5 0.71 −1.92 2.15 755 This study

66.64 0.76 14.84 4.78 0.08 1.42 3.63 2.78 2.95 0.08 1.38 99.87 18.9 98.4 73.0 10.65 18.6 24.6 192 114 35.2 217 15.0 22.7 574 44.2 87.6 9.49 33.1 6.45 1.32 6.58 1.06 6.12 1.28 3.50 0.54 3.41 0.53 5.90 1.20 19.1 17.0 3.56 4.912 0.118 0.809119 10 0.5118 5 0.708 −1.92 2.16 759 This study

69.82 0.56 13.66 3.98 0.05 1.27 2.02 2.99 3.72 0.06 1.04 99.60 6.39 12.9 4.70 1.71 2.93 16.6 228 124 29.8 116 9.90 3.48 505 27.4 58.1 6.02 22.6 4.94 0.52 4.35 0.78 5.05 1.03 3.00 0.44 2.95 0.42 3.32 1.49 41.0 18.6 2.66 5.331 0.132 0.812631 9 0.511998 4 0.703 −0.66 2.16 710 This study

70.21 0.42 13.70 3.63 0.05 1.21 1.95 3.00 3.69 0.06 1.28 99.60 6.92 12.7 6.67 1.65 4.05 17.2 239 86.1 29.1 117 10.3 4.00 399 23.1 48.2 5.06 18.7 4.20 0.45 4.16 0.72 4.63 1.02 2.89 0.45 2.97 0.43 3.36 1.56 41.1 18.4 2.28

69.71 0.55 13.80 3.95 0.06 1.26 2.01 3.07 3.68 0.06 1.03 99.63 6.75 12.1 9.11 1.65 4.81 16.4 256 82.8 27.0 109 9.63 3.47 411 23.2 47.3 5.02 18.4 4.15 0.46 3.89 0.67 4.33 0.92 2.58 0.40 2.50 0.37 2.99 1.53 35.0 19.3 2.08

66.19 0.61 14.85 4.82 0.09 1.45 3.76 2.76 2.83 0.09 1.61 99.60 14.2 68.3 22.7 9.94 8.65 20.0 112 232 38.5 187 11.4 9.11 632 36.9 72.5 8.07 29.7 5.87 1.12 6.12 1.00 6.47 1.35 3.91 0.59 3.88 0.58 5.35 1.60 44.7 15.6 3.95 1.400 0.120 0.739119 8 0.511846 5 0.710 −1.32 2.12 741 This study

66.05 0.62 14.82 5.30 0.07 1.49 3.69 3.06 3.04 0.10 0.99 99.81 11.2 66.1 19.3 6.71 4.21 17.8 139 217 39.2 144 9.17 5.52 600 33.8 65.0 6.86 24.1 5.18 0.84 6.16 1.04 6.79 1.32 3.60 0.54 3.40 0.50 4.27 0.85 21.5 17.9 4.52

67.86 0.53 14.34 5.33 0.08 1.27 3.47 2.97 2.48 0.08 0.78 99.77 11.6 74.2 17.5 10.1 7.19 18.8 102 261 28.0 154 10.2 5.61 470 27.7 57.8 6.21 22.6 4.87 0.98 4.36 0.73 4.85 0.98 2.84 0.44 2.91 0.45 3.92 0.81 50.8 16.9 5.18

739 This study

68.39 0.50 14.52 4.41 0.07 1.41 3.45 2.72 2.87 0.08 0.93 99.83 13.4 67.0 22.2 10.6 7.38 18.7 77.0 225 27.9 148 9.73 3.98 524 37.6 68.4 7.58 25.9 4.87 0.96 4.56 0.76 4.79 0.97 2.82 0.43 2.91 0.44 4.26 1.07 20.0 14.4 3.71 0.992 0.114 0.733126 8 0.511784 4 0.713 −1.45 2.09 725 This study

68.37 0.52 14.28 4.82 0.11 1.42 3.44 2.81 2.69 0.07 0.76 99.83 14.6 68.8 29.9 10.2 11.4 18.9 113 203 36.7 187 10.7 7.21 371 29.8 57.8 6.96 26.7 6.16 1.14 6.17 1.03 6.27 1.29 3.63 0.55 3.60 0.53 5.19 0.94 34.2 15.5 4.50

704 This study

70.57 0.51 13.63 3.35 0.06 1.15 1.68 3.27 3.94 0.05 1.03 99.60 4.74 16.5 8.68 2.11 9.44 14.7 109 82.4 26.8 144 11.0 2.36 306 29.7 55.4 6.55 24.6 5.21 0.47 4.22 0.70 4.50 0.96 2.72 0.41 2.65 0.40 4.30 1.62 27.2 15.0 2.75 3.835 0.128 0.781983 9 0.511925 5 0.703 −1.36 2.19 731 This study

66.67 0.58 15.15 4.81 0.07 1.42 3.71 2.76 2.96 0.09 1.02 99.78 13.8 69.4 22.3 10.5 8.36 20.0 85.0 244 33.8 178 10.6 6.53 528 37.1 70.5 7.94 29.1 5.87 1.17 5.63 0.91 5.70 1.17 3.37 0.52 3.42 0.53 5.09 0.99 26.9 14.1 4.60 1.010 0.122

714 This study

68.51 0.62 14.12 4.00 0.06 1.46 2.18 3.12 3.99 0.07 1.02 99.59 14.3 66.9 35.0 8.12 19.5 19.5 204 127 32.1 149 13.7 6.39 414 26.9 54.7 6.26 24.2 5.19 0.80 4.55 0.81 5.26 1.11 3.12 0.48 3.18 0.46 4.26 1.58 28.0 18.2 2.67 4.646 0.130 0.801809 9 0.51191 5 0.707 −1.93 2.26 726 This study

706 This study

725 This study

Samples of Group 1

746 This study

Samples of Group 2

Samples

GA-3

GA-4

GA-8D

GA-9

13GA-20A

16HN-26B

16HN-26B10

16HN-26B13

SiO2 TiO2 Al2O3 FeOT MnO MgO CaO Na2O K2O P2O5

69.08 0.61 14.37 4.54 0.06 1.22 0.95 1.85 4.40 0.12

71.01 0.44 14.31 3.03 0.03 0.88 1.04 2.47 4.43 0.10

70.00 0.57 14.11 4.02 0.06 0.96 1.58 2.89 3.62 0.11

69.36 0.57 14.48 4.13 0.04 1.13 1.32 2.52 3.88 0.11

69.20 0.48 13.82 4.38 0.07 1.16 2.68 2.78 3.39 0.05

68.70 0.50 14.25 4.33 0.07 1.35 2.89 2.58 3.38 0.06

70.62 0.46 13.09 3.95 0.08 1.02 1.95 3.11 3.80 0.05

72.74 0.44 12.63 3.51 0.07 0.89 1.61 2.55 3.69 0.04

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Table 2 (continued) Representative samples of gneissic granites Samples of Group 1 Samples

GA-1

GA-2B

13GA-21A

13GA-21B

13GA-21C

13GA-22A

13GA-23A

14HN-12B

LOI Total Sc V Cr Co Ni 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 87 Rb/86Sr 147 Sm/144Nd 87 Sr/86Sr 2σ 143 Nd/144Nd 2σ 87 Sr/86Sr(i) εNd(t) TDM (Ga) TZr (°C) Source

1.82 99.53 11.9 48.6 26.8 6.43 8.42 19.2 212 96.6 30.5 213 12.4 9.86 718 41.7 84.4 10.7 39.0 8.04 1.12 6.71 1.08 6.23 1.28 3.49 0.53 3.51 0.55 6.23 1.14 22.6 17.6 4.97

1.43 99.51 8.35 38.2 21.9 4.42 5.49 16.9 171 132 39.6 177 11.9 5.14 659 37.7 81.3 9.94 37.4 8.24 0.85 7.80 1.29 7.67 1.61 4.44 0.67 4.24 0.62 5.31 1.17 35.4 19.8 7.96

1.14 99.51 12.5 45.4 22.2 5.70 5.77 19.0 215 115 35.0 203 12.7 22.5 501 28.9 62.3 8.19 30.0 6.22 0.94 5.28 0.95 6.05 1.36 3.93 0.62 4.04 0.61 6.07 1.25 37.2 17.8 5.66

1.53 99.53 12.4 46.9 23.9 6.46 8.21 18.6 188 110 26.5 152 11.9 10.4 705 31.1 67.6 8.24 30.9 6.43 1.00 5.73 0.92 5.46 1.11 2.99 0.45 2.84 0.41 4.52 1.06 34.4 15.7 3.62

0.126

0.126

0.511859 4

0.511864 5

0.511849 4

−2.02 2.22 824 Zhang et al. (2017a,b)

−2.06 2.23 787 Zhang et al. (2017a,b)

−2.38 2.26 769 Zhang et al. (2017a,b)

1.03 99.62 6.40 4.43 3.09 2.11 6.78 23.9 203 118 117 728 36.9 36.3 204 77.0 163 19.8 79.1 16.8 3.95 17.7 3.07 19.8 4.09 11.6 1.73 11.1 1.67 18.4 2.64 28.1 29.5 7.99 4.988 0.128 0.816708 12 0.512018 7 0.714 0.42 2.03 922 this study

1.01 99.58 5.09 3.53 10.9 1.66 16.4 22.0 225 108 86.8 588 33.9 38.5 195 60.7 130 15.8 63.6 13.4 2.97 13.3 2.30 14.7 3.11 8.76 1.31 8.49 1.25 14.6 2.42 24.7 27.7 7.67

0.125

1.00 99.50 6.08 3.59 8.84 1.91 16.3 27.8 209 129 108 596 36.6 35.2 318 77.0 161 19.8 73.3 15.7 3.96 16.8 2.88 18.6 3.78 10.8 1.58 10.4 1.53 14.7 2.31 31.2 25.0 8.06 4.704 0.129 0.802614 11 0.511872 6 0.706 −2.58 2.31 890 this study

886 this study

1.05 99.61 5.72 3.93 6.73 1.82 11.6 23.0 215 112 104 608 35.6 37.4 201 69.4 148 18.1 72.5 15.5 3.46 15.5 2.69 17.4 3.57 10.1 1.51 9.66 1.43 15.5 2.51 26.5 28.6 7.90 5.672 0.127 0.820973 13 0.512031 7 0.705 0.86 1.98 920 this study

787 Zhang et al. (2017a,b)

14HN-12C

14H-13B2

14HN-13B4

15HN13B1

15HN13B3

Representative samples of metasedimentary rocks Samles

14HN-05A

14HN-05C

14HN-09A

14HN-09C

14HN-11C

16HN-27B

16HN-28B

16HN-29B

SiO2 TiO2 Al2O3 Fe2O3t MnO MgO CaO Na2O K2O P2O5 Total CIA Sc V Cr Co Ni Cu Zn Ga

68.89 0.59 16.64 3.27 0.02 1.83 0.41 2.03 3.82 0.02 99.30 72.67 8.49 46.5 33.7 5.49 8.29 12.2 35.4 24.3

71.72 0.49 14.66 3.61 0.02 1.98 0.39 1.67 3.65 0.03 99.92 71.95 9.29 37.1 37.1 3.50 10.9 8.15 55.2 20.0

67.37 0.56 14.17 4.29 0.05 3.23 0.71 3.41 3.50 0.03 100.08 65.02 12.9 92.5 64.5 9.03 22.0 4.31 91.5 18.4

72.18 0.42 14.56 3.35 0.03 1.88 0.67 1.94 3.45 0.05 99.68 70.60 8.47 42.8 40.0 5.93 14.4 33.1 46.9 11.6

64.25 0.64 16.46 4.53 0.07 2.12 0.57 2.19 4.97 0.04 100.05 68.06 16.0 72.4 54.0 10.2 17.7 11.5 63.4 17.8

67.97 0.74 14.99 5.32 0.02 2.23 0.51 1.61 3.27 0.04 99.83 73.57 15.5 100 64.5 7.03 24.1 15.0 43.3 19.6

65.62 0.79 15.90 5.85 0.02 2.35 0.51 1.86 3.59 0.05 99.67 72.73 17.4 106 72.8 8.1 25.6 12.9 39.1 21.0

69.70 0.67 14.57 4.34 0.02 2.16 0.52 1.65 3.74 0.03 99.90 71.14 13.1 85.7 58.1 5.71 20.7 8.61 40.6 17.9

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Table 2 (continued) Representative samples of gneissic granites Samples of Group 1 Samples

GA-1

GA-2B

13GA-21A

13GA-21B

13GA-21C

13GA-22A

13GA-23A

14HN-12B

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 143 Nd/144Nd εNd(t) 2σ Source

119 61.6 51.1 298 15.3 5.51 978 49.0 105 12.4 45.7 8.80 1.24 8.48 1.37 8.18 1.80 5.25 0.81 5.19 0.77 8.43 1.15 14.3 14.6 3.15

128 72.5 52.5 278 13.0 10.7 680 42.0 92.7 11.1 43.1 8.64 1.19 8.54 1.38 8.27 1.73 4.98 0.78 5.05 0.73 7.47 1.15 18.8 11.0 3.32 0.511706 −4.07 8 This study

225 103 21.6 183 9.82 11.5 559 17.7 37.8 4.34 15.9 2.99 0.79 2.87 0.45 2.64 0.55 1.63 0.24 1.61 0.24 4.73 0.88 24.1 8.22 2.25 0.511614 −4.45 10 This study

110 117 15.1 233 9.05 5.98 630 22.5 44.1 5.34 19.8 3.40 0.76 3.10 0.49 2.85 0.61 1.81 0.28 1.86 0.29 5.43 0.69 16.3 7.71 1.78

60.8 124 21.1 197 14.9 5.40 653 39.1 80.7 8.83 31.4 5.66 1.29 4.96 0.85 5.09 1.02 3.17 0.47 3.28 0.51 5.54 1.17 24.2 13.5 2.79

122 20.9 18.9 215 13.7 4.48 562 28.4 64.6 7.65 28.6 5.34 1.09 4.67 0.65 3.81 0.76 2.29 0.32 2.27 0.33 5.62 0.99 18.4 11.2 2.06

137 24.4 24.3 199 14.4 5.07 599 35.9 81.0 9.43 35.1 6.65 1.37 6.01 0.81 4.84 0.94 2.80 0.41 2.79 0.40 5.20 1.02 16.7 12.1 2.4

103 42.9 20.4 202 12.5 3.17 522 36.5 80.1 9.33 33.3 5.87 1.18 4.87 0.67 3.82 0.75 2.28 0.33 2.19 0.34 5.14 0.89 14.3 10.6 1.78

This study

This study

This study

This study

This study

This study

14HN-12C

3

b Peraluminous

Metaluminous

2 an

A/NK

Gr ior ite

M on zo granite

od

A

1

P

Peralkaline

0 0.5

0.7

0.9

1.1

1.3

1.5

1.7

14HN-13B4

15HN13B1

15HN13B3

Fig. 7. (a) QAP and (b) Molar Al/ (Ca + Na + K) vs Al/(Na + K) diagrams for Group 1 and Group 2 gneissic granite samples in southwest Hainan. Samples of Group 1 are plotted as solid rectangle, and Group 2 are plotted as solid triangle in red. Gneissic granites in Zhang et al. (2017a) are also shown as hollow rectangle in red and felsic rocks in Li et al. (2008) are shown as hollow triangle in gray. (For interpretation of the references to colour in this figure legend, the reader is referred to the web version of this article.)

Q

a

14H-13B2

1.9

A/CNK

0.3–0.7 and define the 207Pb/206Pb apparent ages ranging from 1456 Ma to 1407 Ma, with a weighted mean age of 1426 ± 11 Ma (MSWD = 0.43 (Fig. 4f). The corresponding εHf(t) values, TDM2 model ages and zircon δ18O values are in the range of −0.2–+6.2, 2.2–1.8 Ga, and 5.0–6.1‰, respectively. The weighted mean ages for all the six samples are similar within the analytical uncertainties and they are consistent with their upper intercept ages, representing their crystallization ages.

∼1500–1430 Ma, with age-peaks at ∼1780 Ma, ∼1600 Ma and ∼1435 Ma (Fig. 5c). Almost all the concordant (> 90%) grains with age-clusters of ∼2700–2000 Ma and ∼1900–1730 Ma have εHf(t) values of −5.7 to +2.9 and −6.5 to +2.6, respectively, and those with the younger age-clusters show εHf(t) values ranging from −6.9 to +8.7 and −2.6 to +4.4, respectively. The fourteen concordant analyses from rims give apparent ages of 550–456 Ma and 1173–922 Ma, with Th/U ratios of less than 0.1 (Fig. 5e). From 16HN-27B sample, eighty-four spots were analyzed on 84 grains, from which eighty analyses are concordant (Fig. 5b). Eight spots exhibit apparent ages from 1344 to 1039 Ma with Th/U of < 0.1 (Fig. 5f) and 10 gains from 2674 Ma to 2010 Ma. The remaining sixtytwo concordant spots yield 207Pb/206Pb apparent ages of ∼1900–1433 Ma, and form three age-clusters of ∼1900–1700 Ma (peak at 1780 Ma), ∼1700–1550 Ma (peak at 1600 Ma) and

4.1.2. Metasedimentary rocks Samples 14HN-05A and 16HN-27B are quartz-mica schists from the Gong’ai and Chongzuling areas, respectively (Fig. 2c). Ninety-two grains from 14HN-05A were analyzed on rims or cores (Fig. 5a). Seventy-three spots on the cores yield four age-clusters of ∼2700–2000 Ma, ∼1900–1730 Ma, ∼1700–1530 Ma and 78

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1000

a

Rock/Primitive Mantle

Rock/Chondrite

1000

100

~1.43Ga granites from Li et al., 2008

100 ~1.43Ga granites from Li et al., 2008

10

10

1

3

0.3

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

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

1000

c

Rock/Primitive Mantle

1000

Rock/Chondrite

b

100 ~1.43Ga granites from Li et al., 2008

10

100

10 ~1.43Ga granites from Li et al., 2008

1

3

d

0.3

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

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

Fig. 8. Chondrite normalized REE patterns (a and c) and primitive mantle normalized multi-element spidergrams (b and d) for the Group 1 and 2 gneissic granites in southwest Hainan. Chondrite values are from Sun and McDonough, (1989) and primitive mantle values are from McDonough and Sun (1995). Gneissic granites in Zhang et al. (2017a) are also shown as hollow rectangle in black. Data of the ∼1.43 Ga A-type granites in Hainan are from Li et al. (2008), and the ∼1.43 Ga granites in west Laurentia are from Frost et al. (1999).

6

ε

Nd

(t)

2

B MOR rray tle a man

10

4.2.1. Gneissic granites Our results, together with the published data for the Baoban gneissic granites (e.g., Li et al., 2008; Zhang et al., 2017a), show they are subdivided into two groups. Group 1 samples have SiO2 contents of 65.97–71.01 wt. %, K2O + Na2O = 5.45–7.35 wt. %, Al2O3 = 13.63–15.15 wt. %, CaO = 0.95–3.85 wt. %, FeOt = 3.03–5.33 wt. %, MgO = 0.88–1.62 wt. %, TiO2 = 0.42–0.77 wt. % and P2O5 = 0.05–0.12 wt. %. They plot in the granodiorite and monzogranite fields in the QAF diagram (Fig. 7a) and show weakly to strongly peraluminous affinity (Fig. 7b). Group 2 samples display variable SiO2 (68.70–72.74 wt%) Al2O3 (12.63–14.25 wt. %), CaO (1.61–2.89 wt. %), P2O5 (0.04–0.06 wt. %) and TiO2 (0.44–0.50 wt. %) contents. They are weakly peraluminous with A/CNK values of 1.02–1.14 and plot in the granodiorite and monzogranite fields on the QAP diagram (Fig. 7a and b). All samples from both groups show right-leaning patterns of rare earth elements (REEs) with different abundances and fractionation degrees (Fig. 8a). Group 1 show more fractionation of light and heavy REEs with the higher (La/Yb) n (n herein refers to chondrite-normalized value) ratios (5.13–9.30) and negative Eu anomalies (δEu = 0.31–0.65). Group 2 samples have lower (La/Yb) n ratios (4.98–5.31) and higher contents of HREEs as well as moderate negative Eu anomalies (δEu = 0.68–0.75). On the primitive mantle normalized spidergram (Fig. 8b and d), both groups are enriched in Rb, K, Th, U, Zr and Hf, and depleted in Nb, Ta, Ti, P, Ba and Sr. Compared with Group 1, Group 2 samples have more abundant high field strength element content. The initial Sr–Nd isotopic ratios for the seven representative samples of Group 1 were back-calculated using their formation ages of 1430 Ma and give 87Sr/86Sr (i) ratios of 0.7030–0.7130 and εNd (t) values for ten samples range from −2.4 to −0.7 with Nd model ages of 2.3–2.1 Ga (Fig. 9), and 87Sr/86Sr (i) ratios, εNd (t) values and Nd model ages for three samples from Group 2 range in 0.7050–0.7140, −2.6– +0.9 and 2.3–2.0 Ga, respectively.

weathering or sea-water alteration

~1430 Ma granites in the Laurentia

-2 -6 -10 -14 0.700 0.705

EMⅡ

EMⅠ

0.710 87

0.715

0.720

0.725

0.730

Sr/ Sr(i) 86

Fig. 9. Initial Sr–Nd isotopic composition for the Group 1 and 2 gneissic granites in southwest Hainan. The symbols are the same as in Fig. 7. The Sr–Nd isotopic fields of the ∼1.43 Ga granites in Laurentia are from Frost et al. (2002).

∼1500–1430 Ma (peak at 1435 Ma; Fig. 5d) with their corresponding εHf(t) values of −6.2 to +4.5, −3.6 to +6.2 and −1.6 to +4.9. 4.2. Geochemical data Elemental and isotopic analytical results of the granitic and metasedimentary samples from SW Hainan are listed in Table 2 and their geochemical characteristics are summarized in Figs. 7–13. 79

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S iO 2 TiO 2 A l 2O F e 2O3 3 MnO MgO CaO N a 2O K 2O P 2O 5 Rb Cs Ba Sr Th U Y Zr Nb Hf Cr Co V Ni Sc

R o c k / PA A S

PASS

0

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

Fig. 10. (a) Upper crust normalized REE patterns for the Mesoproterozoic metasedimentary rocks in southwest Hainan and (b) PAAS-normalized multi-element spidergrams. Chondrite and upper crust-normalized data are from Sun and McDonough (1989) and Rudnick and Gao (2003). 0.9

0.6

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0.6 0.4 67

Ti O 2 ( w t . % )

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Sr (ppm)

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LOI. (wt.%) 0.8

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Fig. 11. Plots (a) of SiO2 vs. MgO, (b) SiO2 vs. TiO2, (c) SiO2 vs. FeOT, (d) SiO2 vs. Al2O3, (e) SiO2 vs. CaO, (f) SiO2 vs. P2O5, (g) LOI. vs. CaO, (h) LOI. vs. Na2O, (i) LOI. vs. A/CNK, (j) LOI. vs. Sr, (k) LOI. vs. Rb and (l) LOI. vs. Th for the Group 1 and 2 Mesoproterozoic gneissic granites in southwest Hainan. The symbols are the same as in Fig. 7.

80

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10 3

a Zr (ppm)

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Fig. 12. Plots of (a) 10,000 * Ga/Al vs. Ce, (b) 10,000 * Ga/Al vs. Zr, (c) Zr + Nb + Ce + Y vs. FeOt/MgO and (d) Zr + Nb + Ce + Y vs. 10,000 * Ga/Al (after Whalen et al.,1987) for Group 1 and 2 Mesoproterozoic gneissic granites in southwest Hainan. The symbols and cited data are the same as in Fig. 7. FG: fractionated granites; OGT: unfractionated I-, S-, and M-type granites.

b

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4.2.2. Metasedimentary rocks Metasedimentary samples display an SiO2 range of 64.25–72.18 wt. %, Al2O3 of 14.17–16.64 wt. %, FeOt of 2.94–5.26 wt. % and MgO of 1.83–3.23 wt. %. TiO2 and K2O correlate positively but CaO and Na2O insignificantly with Al2O3, suggesting influence of aluminous-rich clay minerals (e.g., illite or smectite) and significant provenance weathering (Asiedu et al., 2000; Fedo et al., 1996). Apart from CaO, Na2O and MnO, the other major elements display a negative correlation with SiO2. Compared with the post-Archean Australian average shale (PAAS) (Fig. 10a, Taylor and McLennan, 1985), they display higher SiO2 and Na2O but lower Al2O3, CaO and FeOt contents. Their chondrite-normalized REE patterns are similar to those of the PAAS and NASC (Fig. 10b; Taylor and McLennan, 1985), with (La/Yb)n ranging from 6.0 to 12.0 (average 8.5) and Eu/Eu* from 0.43 to 0.82 (average 0.64). These metasedimentary samples have constant 147Sm/144Nd ratios of 0.114–0.120 and measured 143Nd/144Nd ratios of 0.511614–0.510790. Their corresponding εNd (t = 1450 Ma) values range from −4.8 to −4.1 and Nd isotopic model age of ∼2.3 Ga, slightly lower and older than those of the coeval gneissic granite.

10 4

supported by the depletion in Eu and Sr (Fig. 8b and d). Apatite and FeTi oxides might also have been removed from the magma, as indicated by the negative correlations between SiO2 and FeOt, P2O5 and TiO2 (Fig. 11b–f) as well as the negative P and Ti anomalies (Fig. 8b and d). Based on their high FeOt/(FeOt + MgO) ratios, Li et al. (2008) suggested that the gneissic granites from Baoban Complex are of A-type affinity. However, this classification is complicated by their high A/ CNK ratios, negative εNd values, and presence of garnet and muscovite, based on which, they were considered as S-type granite by Xu et al. (2001) and Zhang et al. (2017a). Experimental results show that garnet and muscovite also may be present in the late stage of fractionation of Itype granite, thus the presence of hornblende and cordierite is more reliable than muscovite and garnet for classifying granite types (Miller, 1985; Wu et al., 2007 and references therein). Gneissic granites from Baoban Complex contain hornblende and lack cordierite. Additionally, except for four samples with higher LOI, Group 1 samples are mostly metaluminous or weakly peraluminous with A/CNK < 1.1. Group 1 samples also show P2O5 decreasing with increasing SiO2 (Fig. 11f), which is considered important criteria by Chappell and White (1992) for a distinction between I-type and S-type granitoids. We therefore interpret Group 1 samples as I-type rather than S-type, and suggest that the several samples with high A/CNK (> 1.1) may have resulted from the loss of CaO and Na2O after emplacement (Fig. 11g-i). With the high ratios of 10,000 * Ga/Al (> 2.6) and FeOt/(FeOt + MgO), high concentration of Nb + Ce + Y + Zr (> 350 ppm) and enrichment in Zr, Ce and Y, Group 2 samples plot in the A-type granite field (Fig. 12), which is consistent with the observed high zircon saturation temperatures (885–921 °C).

5. Discussion 5.1. Petrogenesis of the gneissic granites 5.1.1. I-type, S-type or A- type granite? High field strength elements, such as Th, Ti, Nb, Ta, Zr, Hf, Y and REEs and Nd isotopic compositions are generally considered immobile during alteration or weathering processes (Barnes et al., 1985). Our granite samples display insignificant correlations between LOI and Na2O, CaO, A/CNK, Rb, Sr and εNd (t) values except four samples with higher LOI (1.14–1.82) (Fig. 11). These signatures, together with the subparallel REE and multi-element patterns in Fig. 8, indicate that the behavior of these incompatible elements can be used to trace primary magmatic features (Deniel, 1998). All the gneissic granite samples from the Baoban Complex display linear variations of major element oxides and trace elements (Fig. 11a-f), indicating that crystal fractionation played a significant role during magma evolution. Negative correlations between SiO2 and Al2O3 and CaO suggest fractional crystallization of plagioclase during magma evolution (Fig. 11a and b), which is further

5.1.2. Source characteristics Samples from the two groups show broadly similar Nd-Hf isotopic compositions with variable zircon saturation temperatures (Table 2, Boehnke et al., 2013), which indicate that they originated from a common source, and the P-T conditions of partial melting and fractional crystallization during late stage may have played an important role in dictating their geochemical compositions (Zhao et al., 2015). Petrological and geochemical data indicate that granites can be derived from fractional crystallization of mantle-derived magma or partial melting of pre-existing rocks with mantle magmas involved or not (e.g., Rapp 81

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a

rather than the direct mixing of mantle and ancient crust melts. The Hf isotopic compositions of the ∼1430 Ma gneissic granites correspond to Paleoproterozoic model ages (1800–1750 Ma), suggesting the ∼1430 Ma gneissic granites originated from a hybrid source consisting of both Paleoproterozoic and juvenile crust. The mid-Mesoproterozoic rejuvenation of Paleoproterozoic crust was likely triggered by coeval underplating (Zhang et al., 2018). Compared with Group 1, Group 2 shows lower (La/Yb)n ratios and higher contents of HFSEs (Fig. 8), this suggests that accessory minerals enriched in HREEs and Zr, Y, Nb, Ce contents, such as zircon and xenotime, controlled the behavior of these trace elements during partial melting or fractional crystallization in late stage (Rollinson, 1993; Bea, 1996). All of the whole-rock geochemical and zircon Hf isotopic compositions of the Mesoproterozoic gneissic granites in Baoban Complex are indicative of their formation from the same hybrid source over a range of magma process. Additionally, δ18O values have a wide range for these samples, with 6.1–8.6‰ for Group 1 and 5.0–6.1‰ for Group 2, suggesting they have experienced variable degrees of water-rock interaction at different formation temperatures during magmatic emplacement (Fig. 6c). Group 1 I-type granites formed at relatively low temperatures and experienced low-temperature water-rock interaction, which caused higher δ18O values (6.1–8.6‰). Group 2 A-type granites were generated at higher temperatures and experienced high-temperature water-rock interaction, which resulted in lower δ18O values of 5.0–6.1‰ than normal mantle and cooled down at shallower crust.

Granite

Zirco

n add

ition

Andesite

Basalt

b

Tholeiitic ocean island source

Lower continental crust Andesitic arc source

5.2. Depositional age and provenance characteristics of metasedimentary rocks

Mixed felsix/basic source

UCC

Quartz dilution

Passive margin source

The metasedimentary rocks in the Baoban Complex were described as the oldest exposed metasedimentary unit in Hainan (e.g., Ma et al., 1997). However, previous whole-rock Sm-Nd and Rb-Sr isochron dating for the Baoban metasedimentary rocks yielded a wide range of ages from 1.67 to 0.98 Ga (Tan et al., 1991; Chen et al., 1997; Ma et al., 1997), whereas detrital zircons from the Baoban paragneiss yield the maximum depositional age of 1450 Ma (Yao et al., 2017), thus their timing of deposition is controversial. Detrital zircons from 14HN-05A and 16HN-27B have similar age patterns with the minimum weighted mean ages of 1461 ± 23 Ma and 1457 ± 16 Ma (weighted mean age of youngest concordant zircon cores), respectively. These results are consistent with Yao et al. (2017), which indicates deposition after ca. 1460 Ma (Xia et al., 2006). Metamorphic rims with low Th/U ratio and LREE-enriched REE chondrite-normalized pattern yield apparent ages of 1324–922 Ma, suggesting deposition prior to 1324 Ma (Fig. 5e and f). In addition, field observations show that the metasedimentary rocks were intruded by ∼1430 Ma granitic and mafic plutons (Ma et al., 1997; Zhang et al., 2018). The synthesis of these data indicates the accumulation time of the Baoban sedimentary sequence might be synchronous with the formation of the ∼1430 Ma igneous rocks, indicative of an active magmatic and rapidly subsiding tectonic environment ca. 1460–1430 Ma. Low SiO2/Al2O3 (whole-rock) ratios (3.8–5.2) for the metasedimentary rocks, together with a chemical index of alteration (CIA) of 65–74 and an index of compositional variability (ICV) of 0.72–1.11 (average: 0.89), suggest these samples have undergone moderate chemical weathering (Nesbitt and Young, 1982, 1984; Fedo et al., 1995; Cox et al., 1995). Rare earth elements (REEs) generally behave uniformly during deposition of fine-grained sedimentary rocks and are not significantly affected by weathering, diagenesis, or metamorphism, and thus can be used to infer their source rocks (Taylor and McLennan, 1985). In Fig. 10b, our Baoban metasedimentary samples show LREEenriched chondrite-normalized patterns and negative Eu anomalies, with (La/Yb)n ranging from 6.0 to 12.0 (average 8.5) and Eu/Eu* from 0.43 to 0.82 (average 0.64), similar to sediments from felsic sources and the cratonic upper continental crust (Taylor and McLennan, 1985). They have high Zr/Sc (11.4–35.1 average of 20.0) ratios and show a

Increasing old sediment component

Fig. 13. Plots of (a) Th/Sc vs. Zr/Sc (after McLennan et al., 1993) and (b) La/Th vs. Hf (after Floyd and Leveridge 1987) for the Mesoproterozoic metasedimentary rocks in southwest Hainan. Average compositions of volcanic rocks on plot (a) from Condie (1993).

et al., 1991; Rapp, 1995; Barth et al., 1995; Patñio-Douce and Beard, 1995; Soesoo, 2000; Barbarin, 2005; Yang et al., 2007; Ji et al., 2009). Our samples show significantly lower εNd (t) values and higher incompatible trace element ratios (Nb/Th = 0.51–1.46 and Th/ La = 0.32–0.68) than those of the synchronous mafic rocks (εNd (t) = +5.5 to +6.7, Nb/Th = 4.31–14.86 and Th/La = 0.09–0.13) reported by Zhang et al. (2018). Thus, they cannot be derived from fractional crystallization of the mafic magma, which is also supported by the observation of a greater exposure volume of Mesoproterozoic felsic rocks than the coeval mafic rocks in southwest Hainan (Li et al., 2002, 2008; Xu et al. 2006; Zhang et al., 2017a, 2018). The analyzed samples have a wide range of bulk rock εNd (t)- and zircon εHf (t) values, reflecting a hybrid source at the time of crystallization of zircon. The highest εHf at 1430 Ma (+8) is only marginally lower than that of the coeval mafic rocks (+9 to +13) (Zhang et al., 2018). It is reasonable to infer the involvement of mantle-derived melts (including mantle melt and juvenile crustal melt) in magma genesis. The lower and widely variable εHf values argue for a significant contamination by an isotopically evolved component, which is reinforced by the considerable difference between the emplacement age and calculated model ages (Supplementary dataset 3), and the dominantly negative whole rock εNd (t) (−2.8 to +0.9) values. The high positive εHf values and relatively high SiO2 contents supports mixing of juvenile and ancient crust melts 82

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Fig. 14. (a) Relative probability plots for zircon ages for southwest Hainan, west Laurentia, Tasmania, India and East Antarctica. (b) Comparison of Hf-isotope compositions of detrital zircons between southwest Hainan and representative basement complexes in the Gawler craton, Australia, western Laurentia, East Antarctic and southeastern India. Data in southwest Hainan are from this study and Yao et al. (2017); west Laurentia are from Ross and Villeneuve (2003), Rämö et al. (2003) and Doe et al. (2012); Gawler Craton are from Reid et al. (2008), Reid and Payne (2017) and Howard et al. (2011), southeast India are from Upadhyay et al.(2009) and Henderson et al.(2014), east Antarcica are from Peucat et al. (2002), Zhang et al. (2012), Goodge et al. (2017) and Morrissey et al. (2017).

greater increase in Zr/Sc than in Th/Sc (Fig. 13a). These data point to a contribution from felsic igneous rocks with an input of a recycled sedimentary component (McLennan et al., 1993; Cullers, 2000), which is further supported by the mixing trend between felsic and recycled sedimentary sources (Fig. 13b), as well as their low εNd (1460 Ma) values (−4.5 to −4.1) and Paleoproterozoic Nd isotope model age. In addition, detrital zircons U-Pb ages from the metasedimentary rocks can provide further information about their provenance. Detrital zircons from two samples of the Baoban Complex have similar age distributions dominated by Paleo- and Mesoproterozoic ages with minor Archean ages. Detrital zircons with these ages are also ubiquitous in the age spectra of Proterozoic and Paleozoic strata in Hainan (Wang et al., 2015; Zhou et al., 2015; Zhang et al., 2017b). The rounded morphology of zircons (Fig. 5a and b) suggests long distance transportation and/or multi-cycle sedimentary processing prior to deposition. Furthermore, the absence of Paleo- to early Mesoproterozoic sources in Hainan, suggest the detritus is either from an exotic provenance or is no longer exposed.

5.3. Mesoproterozoic rifting setting and its link with Nuna continents Two incompatible tectonic models have been proposed for the Mesoproterozoic setting of Hainan (Xu et al., 2001; Li et al., 2008; Zhang et al., 2017a, 2018). Zhang et al. (2018) and Li et al. (2008) considered that the Baoban complex formed in a rift setting based on the geochemical signatures of metabasites and the coeval A-type granites. In contrast, Xu et al. (2001) and Zhang et al. (2017a) proposed an active margin setting based on “S-type” granites. However, the gneissic granites at the Changjiang, Gong’ai and Chongzuling areas show both an I- and A-type geochemical affinity rather than S-type. Their positive εHf (t) and high zircon saturation temperatures range from 704 °C to 921 °C (e.g. Boehnke et al., 2013), most likely indicate contributions from mantle-derived magmas. Considering the absence of earlier subduction-related records as well as the lack of abundant mafic and andesitic rocks in southwest Hainan, our data support an extensionrather than a subduction-related setting. Reconstructions of supercontinent Nuna show a core containing 83

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isotopically juvenile source. In Ongole Domain of southeastern India, the exposed charnockite rocks are dated at 1638–1575 Ma (Upadhyay et al., 2009; Henderson et al., 2014). Limited Hf isotopic data from these exposures indicate that they are generally isotopically evolved, indicating derivation from melting of older Archean crust, with εHf values ranging from −12 to −3 (Henderson et al., 2014), significantly more negative than the similar-aged southwest Hainan. Although much of Antarctica is covered with ice, the presence of Mesoproterozoic crustal rocks have been identified, such as ∼1606–1595 Ma felsic volcanic rocks found in moraines of the Terre Adélie Craton (Peucat et al., 2002), 1578 Ma granite clasts from the Transantarctic Mountains (Goodge et al., 2010) and 1486–1404 Ma mafic and felsic rocks observed in Mount Brown (Liu et al., 2016; Paulsen et al., 2017). Igneous zircons in the central East Antarctica yield age-clusters of ∼1450 Ma, ∼1600 Ma and ∼1800 Ma with Hf isotopic compositions similar to those in southwest Hainan (Fig. 14b; Goodge et al., 2010, 2017; Paulsen et al., 2017). Thus, this region might be the main source for detritus in southwest Hainan and west Laurentia during mid-Mesoproterozoic. Additionally, the widespread magmatic and metamorphic rocks with ages of 1.65–1.55 Ga in the Gawler Craton (Fanning et al., 2007; Hand et al., 2007; Reid et al., 2008; Reid and Payne, 2017; Belousova et al., 2009; Howard et al., 2011), which constitutes part of the Mawson Craton extending into Antarctica (Cawood and Korsch, 2008), are an additional potential source for the detritus in southwest Hainan-west Laurentia as shown in Fig. 15.

Yangtze

NAC

ys tha Ca

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WAC

ia

? H

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ai

na

n

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Mawson

~1.45 Ga igneous rocks

East Antarctica

Belt Basin

1.65-1.55 Ga igneous rocks ~1.45 Ga sedimentary sequences

Fig. 15. Configuration of southwest Hainan, west Laurentia, Tasmania and Mawson Continent (South Australia Gawler Craton and Antarctica) during extension of supercontinent Nuna ca. 1450 Ma. Inferred sedimentary provenance links are shown by magenta arrows. Red ellipses circled with dashed line on Mawson Continent depict point sources in East Antarctica and Terre Adélie of unknown extent (For interpretation of the references to colour in this figure legend, the reader is referred to the web version of this article.). (For interpretation of the references to colour in this figure legend, the reader is referred to the web version of this article.)

6. Conclusions

Siberia, Laurentia and Baltica (Evans and Mitchell, 2011), flanked by South America and West Africa, Western Australia and South Africa, East Antarctica, and North China and India (Zhao et al., 2002a,b, 2003a,b). The Mesoproterozoic (∼1430 Ma) metabasites and felsic rocks from the Baoban Complex in SW Hainan have comparable geochronological and geochemical characteristics with those in the BeltPurcell Supergroup, western Laurentia (Anderson and Davis, 1995; Evans et al., 2000; Frost et al., 2002; Goodge and Vervoort, 2006; Li et al., 2008; Yao et al., 2017; Zhang et al., 2018). Additionally, the U-Pb age-populations (∼1440 Ma, ∼1610 Ma, ∼1780 Ma and ∼2400 Ma) and Hf isotopic compositions of detrital zircons from the Baoban Mesoproterozoic metasedimentary rocks, along with their depositional age, resemble those in the lower Belt-Purcell Supergroup and their equivalents (Fig. 14, Ross et al., 1992; Evans et al., 2000; Ross and Villeneuve, 2003; Link et al., 2007; Doe et al., 2012, 2013). Such similarities suggest the potential spatial affinity of SW Hainan with west Laurentia. Nevertheless, it is noted that there is no potential source for the ∼1.6 Ga detrital zircons either in SW Hainan (or the remainder of South China Block) or west Laurentia (e.g., Karlstrom et al., 2001; Duebendorfer et al., 2006; Stewart et al., 2010; Zhao and Guo, 2012; Zheng and Zhang, 2007; Wang et al., 2013b; Yao et al., 2017). In Laurentia, while numerous igneous source rocks are known for the ca.1.70–1.65 Ga and ca. 1.48 to 1.35 Ga periods, a lack of magmatic source rocks occurs between ca. 1.65 and 1.49 Ga (Karlstrom et al., 2001; Duebendorfer et al., 2006; Stewart et al., 2010). Furthermore, paleocurrent data from the Belt-Purcell Supergroup suggest derivation from a westerly source (e.g., Ross et al., 1992; Ross and Villeneuve, 2003). Therefore, it is generally thought an exotic continent with 1.78 Ga, 1.60 Ga and 1.45 Ga crystalline basements was to the west of Laurentia during this time interval. In the Ongole Domain, southeastern India, magmatic and metamorphic rocks with the age of ∼1760 Ma, ∼1600 Ma and ∼1450 Ma (Dobmeier and Raith, 2003; Upadhyay et al., 2009; Kumar et al., 2010; Ratre et al., 2010; Henderson et al., 2014) match the Paleo- to Mesoproterozoic age-peaks of detrital zircons from the Baoban Complex in southwest Hainan and the lower Belt- Purcell Supergroup in western Laurentia (Fig. 14a). Our findings of initial εHf values of −3.6 to +8.7 indicate that ∼1.65–1.55 Ga detrital zircons were largely derived from

Comprehensive zircon U-Pb geochronological, elemental and Sr-NdHf-O- isotopic data for Mesoproterozoic gneissic granites and metasedimentary rocks in the Baoban Complex in SW Hainan indicate the following: (1) Gneissic granites in the Baoban Complex are dominated by I- and Atype granite that originated from a hybridized source of ancient continental materials with a juvenile component. (2) The Baoban metasedimentary sequence accumulated rapidly between 1460 and 1430 Ma, synchronous with gneissic granites and metabasites in the Baoban Complex. (3) The Baoban metasedimentary rocks and gneissic granites formed in an extension setting. (4) Southwest Hainan has a tectonic affinity with East Antarctica at ca. 1430 Ma. Acknowledgments We would like to thank Dr. G-F Zhao for his help during field work and zircon U-Pb analyses. We also thank Prof. Yanhua Zhang for polishing the English. This study was jointly funded by the National Science Foundation of China (U1701641, 41830211, 41506050 and 41672213), Ministry of Science and Technology of China (2016YFC0600303) and Guangdong Province (2018B030312007), to SYSU. Peter A. Cawood acknowledges support from Australian Research Council grant FL160100168. We thank editor-in-chief Prof GC Zhao and two anonymous reviewers for their comments and suggestions on the manuscript. Appendix A. Supplementary material Supplementary data to this article can be found online at https:// doi.org/10.1016/j.precamres.2019.02.013. References Asiedu, D.K., Suzuki, S., Nogami, K., Shibata, T., 2000. Geochemistry of lower Cretaceous sediments, inner zone of southwest Japan: constraints on provenance and tectonic

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