Petrogenesis of ca. 1.95 Ga meta-leucogranites from the Jining Complex in the Khondalite Belt, North China Craton: Water-fluxed melting of metasedimentary rocks

Accepted Manuscript Petrogenesis of ca. 1.95 Ga meta-leucogranites from the Jining Complex in the Khondalite Belt, North China Craton: water-fluxed melting of metasedimentary rocks Luo-Juan Wang, Jing-Hui Guo, Chang-Qing Yin, Peng Peng PII: DOI: Reference:

S0301-9268(16)30569-1 http://dx.doi.org/10.1016/j.precamres.2017.04.036 PRECAM 4753

To appear in:

Precambrian Research

Received Date: Revised Date: Accepted Date:

15 December 2016 9 April 2017 26 April 2017

Please cite this article as: L-J. Wang, J-H. Guo, C-Q. Yin, P. Peng, Petrogenesis of ca. 1.95 Ga meta-leucogranites from the Jining Complex in the Khondalite Belt, North China Craton: water-fluxed melting of metasedimentary rocks, Precambrian Research (2017), doi: http://dx.doi.org/10.1016/j.precamres.2017.04.036

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Petrogenesis of ca. 1.95 Ga meta-leucogranites from the Jining Complex in the Khondalite Belt, North China Craton: water-fluxed melting of metasedimentary rocks

Luo-Juan Wang a,b*, Jing-Hui Guo b,c*, Chang-Qing Yin a, Peng Peng b,c

a

School of Earth Science and Geological Engineering, Sun Yat-Sen University,

Guangzhou 510275, China b

State Key Laboratory of Lithospheric Evolution, Institute of Geology and Geophysics,

Chinese Academy of Sciences, Beijing 100029, China c

University of Chinese Academy of Sciences, Beijing 100049, China

*

Corresponding author 1: Jing-Hui Guo

Tel.: +86 010 82998541; fax: +86 010 62010846 E-mail address: [email protected] Postal address: Institute of Geology and Geophysics, Chinese Academy of Sciences, P.O. Box 9825, Beijing 100029, China *

Corresponding author 2: Luo-Juan Wang

Tel.: +86 18565021356; E-mail address: [email protected] Postal address: School of Earth Science and Geological Engineering, Sun Yat-Sen University, Guangzhou 510275, China

E-mail addresses: Chang-Qing Yin: [email protected] Peng Peng: [email protected]

Abstract

Anatexis occurs in response to changing P-T-fluid conditions during orogenesis, is thus crucial for understanding the tectonic evolution of orogenic belts. Here we report an integrated petrological, geochemical, whole-rock oxygen isotopic and zircon U-Pb-HfO isotopic study of meta-leucogranites from the Jining Complex, North China Craton, to unravel its petrogenesis and constrain the tectonic evolution of the Paleoproterozoic Khondalite Belt. The meta-leucogranites are weakly peraluminous with homogeneous minimum-melt compositions, and are characterized by low Rb contents and Rb/Sr ratios, high Ba and Sr contents and Sr/Y ratios, and moderately fractionated REE patterns without obvious Eu anomalies. These trace-element characteristics differ from that of leucogranites derived from fluid-absent melting. Considering their low wholerock Zr saturation temperatures (746–780℃) and comparable compositions with experimentally generated melts produced by water-fluxed melting, we infer that the meta-leucogranites are low-temperature granites, and were generated by water-fluxed melting of metasedimentary rocks at 6–8 kbar. SIMS zircon U-Pb analyses suggest that the meta-leucogranites were emplaced at ~1.95 Ga or slightly earlier, subsequently were metamorphosed and cut by a pegmatite dike at ~1.92 Ga. The abundant inherited

zircons yield nearly concordant

207

Pb/206Pb ages ranging from 2.24 to 1.98 Ga, which

are consistent with the detrital zircon age spectra of the metasedimentary rocks from the Khondalite Belt. The Hf isotopic compositions of inherited and magmatic zircons (εHf(t) = +0.2–+7.7) closely overlap with the time evolved εHf range of detrital zircons from metasediments in the Khondalite Belt. Different types of zircons (inherited, magmatic and metamorphic zircons) have similar δ18O values of 7.2–9.2‰, which is lower than that of metamorphic zircons (10.0–13.6‰) from surrounding metasediments. Thus, we propose that the meta-leucogranites were formed by water-fluxed melting of metasedimentary rocks from the Khondalite belt at ~1.95 Ga during the prograde upper amphibolite-facies metamorphism.

Keywords: Leucogranite; Crustal anatexis; Geochemistry; Zircon U-Pb-Hf-O isotopic systems; North China Craton

1. Introduction

Crustal anatexis is a fundamental geological process for the evolution and differentiation of the continental crust (Brown and Rushmer, 2006). Partial melting may be triggered by an ingress of H2O-rich fluid phase (termed water-present, water-assisted or water-fluxed melting) or the breakdown of hydrous phases, such as muscovite, biotite, and amphibole (called as fluid-absent hydrate breakdown melting) (Clemens, 2006; Weinberg and Hasalová, 2015). Leucogranites, typical products of crustal

melting, are common in many collisional orogens, such as the Himalayas and Hercynides. They can form by either prograde heating during continental subduction (Groppo et al., 2010, 2012; Prince et al., 2001; Visonà and Lombardo, 2002) or decompression melting during orogenic exhumation (Harris and Massey, 1994; King et al., 2011; Whitney et al., 2004; Zhang et al., 2004). Thus, leucogranites can not only provide insights into the evolution and differentiation of the continental crust, but also reveal the thermal and rheological evolution of orogen.

Khondalites are the dominant component in the Khondalite Belt, North China Craton. Previous studies have revealed a genetic link between granulite-facies metasedimentary rocks and S-type granites in the Khondalite Belt (Dan et al., 2014; Peng et al., 2012; Yin et al., 2009, 2011). In the Jining Complex, voluminous porphyritic garnet granites were generated by nearly in-situ partial melting of metasedimentary rocks under high- to ultrahigh-temperature (UHT) granulite-facies condition associated with underplated mafic intrusions (Peng et al., 2010, 2012). However, there is little known about granitic magmatism related with prograde melting. In this paper, we present whole-rock geochemical and oxygen isotope data and zircon U-Pb-Hf-O isotope data for metaleucogranites from the Liangcheng area within the Khondalite belt of North China Craton. These data are combined to place constraints on water-fluxed melting of the metasedimentary rocks of the Jining Complex during prograde metamorphism.

2. Geological background

It is widely accepted that the North China Craton consists of four ArcheanPaleoproterozoic blocks (i.e., the Longgang, Langrim, Yinshan and Ordos Blocks) amalgamated by three Paleoproterozoic orogenic belts, named the Khondalite Belt, Trans-North China Orogen and Jiao-Liao-Ji Belt (Fig. 1) (Li et al., 2005, 2011a; Zhao et al., 1998, 2003, 2005; Zhao and Zhai, 2013). The Khondalite Belt is proposed to represent a continent-continent collisional belt resulting from the collision between the Yinshan Block to the north and the Ordos Block to the south to form the Western Block at ~1.95 Ga (Zhao et al., 2005; Zhao and Zhai, 2013). It is traditionally subdivided from east to west into Jining Complex, Daqingshan-Wulashan Complex, and QianlishanHelanshan Complex. The predominant rock types in the Khondalite Belt are high-grade sillimanite-garnet gneiss, quartz-garnet gneiss, quartzo-feldspathic gneiss, calc-silicate rock and marble. They are spatially associated with minor tonalite-trondhjemitegranodiorite (TTG) gneisses, mafic granulites, syntectonic charnockites, and S-type granites (Lu et al., 1996). Metamorphic studies suggested that the metasedimentary rocks and associated mafic granulites have experienced medium- or high- pressure granulite facies metamorphism with typical clockwise P-T paths characterized by nearisothermal decompression (Cai et al., 2014; Jiao et al., 2013a; Liu, 1994; Lu and Jin, 1993; Wang et al., 2011a, b; Yin et al., 2014, 2015). UHT granulites have been recognized at several localities in the Jining and Daqingshan Complexes (Jiao and Guo, 2011; Jiao et al., 2011, 2015; Guo et al., 2012; Li and Wei, 2016; Liu et al., 2012; Santosh et al., 2006, 2007a). Based on recent zircon U-Pb isotopic data, the protoliths of

metasedimentary rocks were inferred to be mainly derived from a 2.2–2.0 Ga provenance, deposited during 2.0–1.95 Ga, and then metamorphosed at 1.95–1.85 Ga (Dan et al., 2012; Jiao et al., 2013b; Li et al., 2011b; Wan et al., 2006, 2009; Wang et al., 2015; Xia et al., 2006a, b; Yin et al., 2009, 2011). Although the protoliths of the metasediments were previously considered to have been deposited on a passive continental margin (Condie et al., 1992; Li et al., 2000; Lu et al., 1996), an active continental margin was preferred in recent studies (Dan et al., 2012; Wan et al., 2009; Wang et al., 2015).

The Jining Complex, eastern part of the Khondalite Belt, is characterized by several UHT occurrences, voluminous S-type granites (~40% of the exposure), and widespread small gabbronoritic intrusions (Fig. 2a). The peak metamorphic conditions of UHT granulites were estimated at 900–1000℃ and 8–10 kbar (Jiao and Guo, 2011; Jiao et al., 2011; Li and Wei, 2016; Liu et al., 2012; Santosh et al., 2006, 2007a). The S-type granites are mainly located in the Liangcheng area, and can be subdivided into two types: coarse-grained, massive and porphyritic garnet granites (named the Liangcheng garnet granites) and fine-grained gneissic garnet-bearing leucogranites (named the Anzishan leucogranites). The former is volumetrically dominant and was derived from large-scale melting of the metasedimentary rocks at 1.93–1.92 Ga (Guo et al., 2001; Peng et al., 2012, 2014; Zhai et al., 2003; Zhong et al., 2007). The latter is minor in volume and was previously considered to be high silicic end member of the Liangcheng garnet granites (Peng et al., 2012; Zhong et al., 2006). Our petrographic observation and

temperature estimates reveal that the garnet-bearing leucogranites have experienced UHT metamorphism (Wang, 2016), thus they should be strictly classified as metaleucogranites or leucogranulites. The gabbronoritic intrusions were emplaced at 1.95– 1.92 Ga (~1.93 Ga) as a result of asthenospheric upwelling induced by the slab window during ridge-subduction process (Peng et al., 2010, 2012). They provided additional heat for the coeval UHT metamorphism and extensive partial melting of metasedimentary rocks to produce porphyritic garnet granites (Peng et al., 2010, 2012). In addition, two large-scale ductile shear zones occur in the Jining Complex.

The typical meta-leucogranites crop out as small stocks over areas of c. 2 × 10 km2 in the Liangcheng area (Fig. 2b). They are petrographically homogeneous (Fig. 3a), but contain cm-size clots of Al-rich mineral (grt, sil, spl) and cm- to meter-size irregular schlieren of sil-bi-grt-bearing granulites and spl-grt granulites (Fig. 3b,c,d). In Anzishan village, the meta-leucogranites are intruded by a narrow (15 cm thick) and straight pegmatite dike (Fig. 3e), which is discordant to the foliation of meta-leucogranites and characterized by garnet coronae developed between biotite+quartz aggregates and plagioclase (Fig. 3f). The meta-leucogranites are deformed, and display remarkable foliation and weak lineation. The pegmatite dike shows progressive transition from an undeformed pegmatite in its central part to a fine-medium grained granite with weakly foliation in the outermost part, indicative of its syn-kinematic nature.

3. Petrography of the meta-leucogranites and pegmatites

The meta-leucogranites consist of garnet, mesoperthite, quartz, plagioclase, K-feldspar with minor biotite, sillimanite, spinel, ilmenite and zircon. They are characterized by inequigranular textures and mylonitic fabric (Fig. 4a,b). Large (0.5–2 mm) garnet and mesoperthite porphyroclasts are surrounded by a matrix of fine-grained (0.2–0.5 mm) quartz aggregates and finer-grained (0.05–0.1 mm) two feldspars aggregates (Fig. 4a,b). Garnet grains contain inclusions of quartz, biotite, ilmenite, minor spinel, and rare mesoperthite, and are partially replaced by biotite and/or sillimanite clusters during retrogression (Fig. 4a,c,d). In places, garnet grains are replaced by spinel and quartz, which are either in direct contact or separated by a thin corona of plagioclase (Fig. 4e,f). Mesoperthites show undulose extinction and contain rare spinel inclusions. Quartz exhibit lobate grain boundaries and forms ribbons parallel to the main foliation. The two feldspars display straight boundaries and are interpreted to be the recrystallized products of former exsolved mesoperthites (Fig. 4g). Locally, fine-grained K-feldspars contain exsolution lamellae of plagioclase (Fig. 4h). The fine-grained quartzo-feldspathic matrix indicates that the meta-leucogranites were strongly deformed. The preservation of retrograde biotite on garnet rims and the irradiated sillimanite aggregates in the matrix suggest that retrograde biotite and sillimanite grew during or after ductile shearing. Thus, the strong deformation occurred under relatively high temperature conditions, probably at or above upper amphibolite facies metamorphic condition. The mylonitic deformation of gabbronorite in the Xuwujia area was estimated to occur at granulite facies condition (Guo and Zhai, 1992).

The pegmatites contain 1–3 mm hydrous mafic aggregates within feldspar-rich matrix (Fig. 4h). They comprise predominantly plagioclase, quartz, biotite, garnet with minor K-feldspar, spinel, magnetite, zircon and monazite. The mafic aggregates mainly consist of 0.2–0.5 mm biotite and quartz with minor magnetite and spinel (Fig. 5a,b). Garnet coronae occur between biotite+quartz aggregates and plagioclase, and contain inclusions of quartz and minor biotite, plagioclase, and K-feldspar (Fig. 5c,d). The feldspar-rich matrix is dominated by oligoclase with minor biotite, quartz and Kfeldspar. The mafic aggregates are interpreted as pseudomorphs of earlier orthopyroxenes.

4. Analytical methods

4.1 Whole-rock major and trace elements

Representative samples were crushed and powdered to 200 mesh using a jaw crusher and tungsten carbide swing mill. Glass discs were obtained by fusing the mixtures of rock powders and Li2B4O7 with a Class M4 fluxer. Major element concentrations were determined on fused glass discs by a PANalytical Axios wavelength dispersive X-ray fluorescence spectrometer at the Institute of Geology and Geophysics, Chinese Academy of Sciences (IGGCAS), Beijing. The analytical uncertainties were better than 2% relative. For trace element analyses, rock powders were digested using HF+HNO3 in high-pressure Teflon bombs. Trace element concentrations were analysed by a Bruker Aurora M90 inductively-coupled plasma mass spectrometry (ICP-MS) at Guizhou

Tuopu resource and environmental analysis center. The analytical uncertainties were estimated to be better than 5–10% relative.

4.2 Whole-rock oxygen isotopes

The whole-rock oxygen isotopic analysis was performed at the Stable Isotope Geochemistry Laboratory, IGGCAS. Oxygen was liberated from silicates by standard BrF5 fluorination technique. Isotope ratios were measured on a MAT-252 mass spectrometer.

18

O/16O ratios are expressed by the conventional δ18O value in permil

relative to the Vienna Standard Mean Ocean Water compositions (VSMOW: 18O/16O = 0.0020052). Replicate analyses give uncertainties of less than ±0.2‰.

4.3 Zircon U-Pb dating

Zircon crystals were separated using conventional heavy liquid and magnetic separation techniques. The grains were mounted in epoxy resin and polished down to expose the grain centers. All zircon grains were photographed in transmitted and reflected light and imaged using cathodoluminescence (CL) to find suitable areas for analyses. U-Th-Pb analyses were performed using a Cameca IMS-1280 SIMS at IGGCAS. The operating and data processing procedures were described by Li et al. (2009). The ellipsoidal spots were about 20 × 30 or 10 × 15 µm in size. U-Th-Pb ratios and absolute abundances were determined relative to the standard Plésovice (Sláma et al., 2008). A long-term uncertainty of 1.5% (1 RSD) for

206

Pb/238U measurements of the standard zircons was

propagated to the unknowns (Li et al., 2010a), despite the fact that the measured 206

Pb/238U error in a specific session was generally around 1% (1 RSD) or less.

Common Pb was assumed to be mainly surface-contaminated, and corrections of common Pb were made using measured

204

Pb and average present-day Pb composition

(Stacey and Kramers, 1975). Uncertainties of individual analyses and pooled analyses are reported at 1σ and 2σ level, respectively. Data reduction was carried out using the Isoplot/Ex v. 3.23 program (Ludwig, 2003).

4.4 Zircon oxygen isotopes Zircon oxygen isotopic compositions were also measured by the Cameca IMS-1280 SIMS at IGGCAS, following standard procedures (Li et al., 2010b). The analytical spot size is about 20 µm in diameter. The instrumental mass fractionation factor (IMF) was corrected using the zircon standard Penglai with a δ18O value of 5.3‰ (Li et al., 2010c). Measured 18O/16O ratios were normalized using the VSMOW, and then corrected for the IMF. Uncertainties on single analyses are usually around 0.2‰ (1σ standard error).

4.5 Zircon Lu-Hf isotopes

Lu–Hf isotopic analyses were conducted on the same zircon grains that were previously analyzed for U–Pb dating, using a Thermo Neptune Plus multi-collector ICP-MS equipped with a Geolas-193 laser-ablation system at IGGCAS. Analytical procedures were described by Wu et al. (2006). During analyses, the laser beam of 44 µm with a repetition rate of 8 or 10 Hz was used. GJ-1 and Mud Tank served as the reference materials. For the interference corrections of value of 0.02655,

176

176

Lu and

176

Yb on

176

Hf, the

176

Lu/175Lu

Yb/172Yb value of 0.5887, and mean βYb value obtained during Hf

analysis on the same spot were applied (Chu et al., 2002; Wu et al., 2006). Errors for the

analyses are reported at 2σ level.

5. Results

5.1 Major and trace element geochemistry

The major and trace element compositions of the meta-leucogranites are presented in Table 1. Published data from Peng et al. (2012) and Zhang et al. (2013) are also listed.

The meta-leucogranites have relatively high SiO2 (72.6–73.7 wt.%), Al2O3 (15.0–15.6 wt.%), CaO (1.34–1.46 wt.%) and Na2O (4.47–4.93 wt.%), but low TiO2 (0.17–0.20 wt.%), Fe2O3T + MgO (1.15–1.80 wt.%) and Mg# (33–39). They are weakly peraluminous in terms of their ASI values (1.05–1.10) (ASI = molecular Al2O3/[CaO+Na2O+K2O]) (Fig. 6a). Na2O/K2O ratios are in the range of 1.24–1.42, showing that these meta-leucogranites are slightly Na-rich. In the normative An-Ab-Or ternary diagram (Fig. 6b), they are plotted in the granite field and close to the field of trondhjemite.

The meta-leucogranites have low ∑REE (67–114 ppm). Their REE patterns are characterized by strong LREE enrichments (LaN/YbN = 21–39), nearly flat HREE (HoN/YbN = 1.1–1.4) and weak Eu anomalies (Eu/Eu* = 0.88–1.20) (Fig. 7a). In the primitive mantle-normalized trace element spidergram (Fig. 7b), these metaleucogranites are enriched in most LILE (e.g., Rb, Ba and Sr), but display negative anomalies in Th, Nb, Ta, P and Ti. They have high Sr (607–906 ppm) and Ba (789–1341

ppm) contents, but low Rb (48–69 ppm), Y (3.6–9.0 ppm), Zr (99–133 ppm), Th (0.4– 2.3 ppm) and U (0.5–1.2 ppm) contents. Thus, the meta-leucogranites are characterized by high Sr/Y (90–202) and low Rb/Sr (0.06–0.11) ratios.

5.2 Whole-rock oxygen isotopic compositions

Eight samples representing the major lithologies in the Jining Complex were selected for whole-rock oxygen isotope analysis. The analytical data are given in Table 2. Two meta-leucogranite samples yield δ18O values of 9.5‰ and 10.4‰. Two porphyritic garnet granite samples have higher δ18O values of 11.6‰ and 11.9‰. Four metapelite samples also show higher δ18O values of 11.9–13.7‰.

5.3 Zircon U-Pb geochronology

Four representative samples were selected for SIMS zircon U-Pb dating. The analytical data are presented in Supplementary Table 1 and plotted on concordia diagrams in Fig. 9.

Meta-leucogranites (sample 11WS02, 13AZS11, and 13AZS12): Zircons from meta-leucogranites are classified as subhedral prismatic and subrounded grains in terms of morphology. The former type ranges in size from 100 µm to 200 µm with length-to-width ratios of 1:1 to 3:1, whereas the latter type is relatively small in size (40–100 µm). CL images reveal that some prismatic zircons show core-mantle-rim structures (Fig. 8). The volumetrically significant cores are oscillatory-zoned or unzoned, vary from bright to grey in luminescence, and are sometimes truncated by thin

oscillatory-zoned mantle with low luminescence. In some cases, core-mantle boundaries were marked by bright resorption surface. The zircon cores are interpreted to be inherited origin. The thin mantle show oscillatory zoning, typical of magmatic zircons. The rim is narrow and structureless, indicative of metamorphic origin. Some prismatic grains have no inherited cores and consist of oscillatory-zoned magmatic domains surrounded by thin unzoned metamorphic rim. Subrounded zircons are generally structureless with or without low-luminescent cores, which is either unzoned or weakly oscillatory-zoned (Fig. 8).

Sample 11WS02 (N40º34′3.92″, E112º34′3.54″) Four analyses on inherited cores yield apparent 207Pb/206Pb ages ranging from 2034 Ma to 1997 Ma. The inherited cores have U contents of 148–1499 ppm, Th contents of 50– 645 ppm, and Th/U ratios of 0.27–0.61. Fourteen analyses on magmatic domains are variably discordant, twelve of which yield a discordia with an upper intercept age of 1934 ± 11 Ma (MSWD = 1.30) (Fig. 9a). They have variable U (137–6397 ppm) and Th (28–408 ppm) contents with Th/U ratios of 0.03–0.90. Ten analyses on metamorphic zircons give an upper intercept age of 1918 ± 18 Ma (MSWD = 2.3) (Fig. 9a). They have U contents of 175–2011 ppm, Th contents of 29–306 ppm, and Th/U ratios of 0.08–0.18.

Sample 13AZS11 (N40º32′33.79″, E112º31′50.36″)

Of twelve analyses on inherited cores, eleven analyses give apparent

207

Pb/206Pb ages

scattering between 2238 and 2017 Ma. They have U contents of 100–1009 ppm, Th contents of 41–601 ppm, and Th/U ratios of 0.15–0.83. One analysis yields a significantly younger

207

Pb/206Pb age of 1879 Ma due to partial Pb loss. Twenty-four

analyses on magmatic zircons show a broad age range (1985–1567 Ma) and significant Pb loss, ten of which define a discordia with an upper-intercept age of 1954 ± 18 Ma (MSWD = 1.5) (Fig. 9b). Their U and Th contents vary in a wide range of 261–8245 ppm and 34–3502 ppm, respectively (Th/U = 0.04–0.75). Of eight weakly to highly discordant analyses on metamorphic zircons, seven analyses yield an upper intercept age of 1925 ± 18 Ma (MSWD = 1.09) (Fig. 9b). They have U and Th contents in the range of 540–2937 ppm and 75–436 ppm, respectively (Th/U =0.12–0.20).

Sample 13AZS12 (N40º32′33.79″, E112º31′50.36″)

Five analyses on inherited cores give apparent 207Pb/206Pb ages scattering between 2099 and 1977 Ma. They have U contents of 183–536 ppm, Th contents of 51–592 ppm, and Th/U ratios of 0.28–0.60 (one analysis 1.30). Fifteen analyses on magmatic zircons exhibit significant Pb loss and yield apparent 207Pb/206Pb ages ranging from 1978 Ma to 1655 Ma. They are plotted along a discordant line with an upper intercept age of 1950 ± 26 Ma (MSWD = 2.5) (Fig. 9c). Their U and Th contents range from 404 ppm to 6648 ppm and from 55 ppm to1697 ppm, respectively (Th/U = 0.04–0.69, one analysis 1.22). Of thirteen weakly to highly discordant analyses on metamorphic zircons, twelve

analyses define an upper intercept age of 1916 ± 16 Ma (MSWD = 1.9) (Fig. 9c). They have U contents of 346–2816 ppm, Th contents of 63–360 ppm, and Th/U ratios ranging from 0.05 to 0.28.

Pegmatite (sample 13AZS14, N40º32′35.42″, E112º31′51.98″): Zircons from pegmatite are mostly oval or columnar in shape. They range from 150 µm to 300 µm in length with aspect ratios of 1:1 to 3:1. All zircon grains show weak or no zoning under CL (Fig. 8). Nineteen analyses were performed on nineteen zircon grains. They yield nearly concordant ages with a weighted mean

207

Pb/206Pb age of 1918 ± 3

Ma (MSWD = 1.1) (Fig. 9d). These zircons are characterized by moderate U contents (160–536 ppm) and Th contents (56–182 ppm) with Th/U ratios of 0.16–0.50. This age is interpreted as the crystallization age of the pegmatite dike.

5.4 Zircon O isotopic compositions

In-situ zircon O isotope analyses were conducted on four dated samples. The analytical data are listed in Supplementary Table 2.

Sample 11WS02 The δ18O values of inherited cores are clustered between 7.2‰ and 8.5‰. Magmatic domains have similar δ18O values of 7.2–8.7‰ with an average of 8.0 ± 0.2‰, except for three analyses with lower δ18O values (4.9–6.2‰), which probably result from high U content (2003–6397 ppm) or significant Pb loss. The δ18O values of metamorphic zircons fall between 7.6‰ and 8.6‰ with an average of 8.2 ± 0.3‰, except that one

analysis with high U content (2011 ppm) and significant Pb loss has higher δ18O value of 10.0‰.

Sample 13AZS11 The δ18O values of inherited cores vary from 8.2‰ to 9.0‰, except for one analysis with lower δ18O of 6.6‰, which is the result of high U content (1376 ppm) and significant Pb loss. Most magmatic zircons have δ18O values of 8.1–8.8‰ with an average of 8.5 ± 0.2‰, but two analyses yield δ18O values of 7.3‰. Two analyses on metamorphic zircons with high U content (1367 and 1433 ppm) yield significantly lower δ18O values of 5.7‰ and 6.5‰.

Sample 13AZS12 Different types of zircons from the sample 13AZS12 also show similar δ18O ranges. Inherited cores, magmatic and metamorphic zircons have δ18O values of 7.8–8.7‰, 7.7– 9.1‰ (Mean = 8.3 ± 0.2‰) and 7.7–9.2‰ (Mean = 8.1 ± 0.4‰), respectively. One analysis on a metamorphic zircon with high U content (2816 ppm) yields significantly lower δ18O value of 6.9‰.

Sample 13AZS14 In-situ oxygen isotope analyses were conducted on nineteen dated zircons from the pegmatite sample (13AZS14). The measured δ18O values range from 9.2‰ to 10.3‰, with a mean of 9.7 ± 0.1‰.

5.5 Zircon Hf isotopic compositions

In-situ zircon Hf isotope analyses were conducted on zircons from the sample 11WS02. The analytical data along with the calculated εHf(t) value and Hf model age are listed in Supplementary Table 3. Sample 11WS02 The inherited cores show wide

176

Hf/177Hf range of 0.281575–0.281731, corresponding

to εHf(t = apparent 207Pb/206Pb age) values of +1.4–+7.7 and TDMC ages of 2.17–2.54 Ga. Magmatic zircons have similar

176

Hf/177Hf range of 0.281587–0.281712, corresponding

to εHf(t = 1950 Ma) values of +0.2–+4.8 (average +2.3) and TDM C ages of 2.28–2.57 Ga (average 2.43 Ga). Metamorphic zircons have relatively higher

176

Hf/177Hf ratios of

0.281647–0.281760, corresponding to εHf(t = 1918 Ma) values of +2.0–+6.7 (average +4.4) and TDM C ages of 2.14–2.43 Ga (average 2.28 Ga).

6. Discussion

6.1 Petrogenesis of the meta-leucogranites

Most previous studies proposed that the meta-leucogranites were derived by partial melting of metasedimentary rocks (Peng et al., 2012; Zhai et al., 2003; Zhong et al., 2006, 2007). However, Zhang et al. (2013) suggested that the meta-leucogranites were generated by partial melting of the mafic lower crust rather than metasedimentary rocks on the basis of their adakitic signature (high Sr/Y and LaN/YbN ratios). The geochemistry of crustal melts depends on the composition of the protolith, the H2O

content, and the P-T conditions of melting (Clemens, 2006). These factors are discussed below, in order to constrain the petrogenesis of the meta-leucogranites.

6.1.1 Source rock

Leucogranites can be produced by partial melting of different kinds of crustal rocks, including metasedimentary rocks, felsic orthogneiss, and amphibolites (Atherton and Petford, 1993; Braun et al., 1996; Inger and Harris, 1993; Jung et al., 2009; Li et al., 2014; Patiño Douce and Harris, 1998; Reichardt and Weinberg, 2012; Zeng et al., 2011, 2012). In this study, the meta-leucogranites contain minor sillimanite, spinel, Al-rich mineral clots and schlieren, implying that they have petrogenetic relationship with metasedimentary rocks. The abundant inherited zircons in the meta-leucogranites show a spread of ages from 2.24 Ga to 1.98 Ga with a major peak at 2.03 Ga, consistent with the detrital zircon age spectra of the metasedimentary rocks in the Khondalite Belt (Dan et al., 2012; Li et al., 2011; Wan et al., 2006, 2009; Xia et al., 2006a,b; Yin et al., 2009, 2011). Moreover, εHf(t) values and two-stage Hf model ages of zircons from metaleucogranites are also quite close to those of detrital zircons from the metasediments in the Khondalite Belt (Dan et al., 2012; Xia et al., 2006b, 2008; Yin et al., 2011). It is concluded that the meta-leucogranites were most likely sourced from the metasedimentary rocks in the Khondalite Belt.

Oxygen isotope can help identify supracrustal source, which typically have higher δ18O values because of low temperature interactions with hydrosphere. The δ18O values of

magmatic zircons in the meta-leucogranites fall between 7.2‰ and 9.1‰, similar to that of S-type Hawkins Dacite, Cootralantra Granodiorite, Violet Town Ignimbrite and Strathbogie Granite from the Lachlan Fold Belt (7.5–10.5‰, Kemp et al., 2006). Based on the empirical relationship between composition and ∆18O (Whole-rock–Zircon) (Lackey et al., 2008), the calculated whole rock δ18O values of meta-leucogranites are 10.3–10.5‰, in good agreement with the measured whole-rock δ18O values (9.5‰ and 10.4‰). The high δ18O values of zircon and whole rock further suggest that the metaleucogranites are sourced from metasedimentary rocks (Harris et al., 1997; O’Neil et al., 1977).

However, the whole rock δ18O values of meta-leucogranites (9.5–10.4‰) are distinctly lower than that of the surrounding metasedimentary rocks (11.9–13.7‰) (Table 2). The δ18O values of magmatic zircons (7.2–9.1‰) are also lower than that of metamorphic zircons (10.0–13.6‰) from surrounding HT-UHT metasedimentary rocks and magmatic zircons (9.2–11.6‰) from the parautochthonous Liangcheng garnet granites in the Jining Complex (Dong et al., 2016; Wang, 2016; our unpublished data). The absence of mafic enclaves and high silica contents preclude the contribution of mantle-derived magmas, which commonly have low δ18O values (5.7 ± 0.3‰) (Taylor and Sheppard, 1986). Recently, metasedimentary rocks with low zircon δ18O values have been identified in the Daqingshan-Wulashan Complex (Dong et al., 2016). S-type granites with similar zircon δ18O values were also reported in the Helanshan Complex (7.3– 10.6‰, Dan et al., 2014). Therefore, it is possible that the meta-leucogranites were

derived from unexposed metasedimentary source with relatively low δ18O values in the Jining Complex. The low δ18O characteristic reflects low maturity and clay content of the protoliths of metasedimentary rocks. Alternatively, low δ18O values may result from the influx of externally derived fluids with low δ18O values during melting. There are few metamorphic terranes documenting significant decrease of δ18O values because of the infiltrating fluid during regional metamorphism and partial melting (Cartwright et al., 1995; Wickham and Taylor et al., 1985).

6.1.2 Melting condition and reaction

The meta-leucogranites have high SiO2 contents and low FeO, MgO and TiO2 contents, typical of leucogranites (Clarke et al., 1993; Guillot and Le Fort, 1995; Inger and Harris, 1993; Le Fort, 1981; Liu et al., 2014; Searle et al., 1997). Their compositions are comparable to that of the haplogranitic minimum melt. The minimum melt composition may represent low-degree primary melt or highly fractionated melt. The low Rb and high Sr contents and weak Eu anomalies of meta-leucogranites argue against extensive fractionation process, and thus rule out the possibility of highly fractionated melt. Formation conditions of minimum melt can be estimated by comparison with experimental data. Experimental studies indicated that the melt composition would become richer in albite component with increasing pressure, and have higher orthoclase component with decreasing aH2O (Ebadi and Johannes, 1991; Johannes and Holtz, 1996). The meta-leucogranites are close to H2O-saturated Qz-Ab-Or minimum melt composition at PH2O=5 kbar (Fig. 10a). This suggests that the meta-leucogranites were

formed at high aH2O and moderate pressure.

The melt temperature can be robustly constrained by Zr concentrations in silica melts on the basis of the empirical relationship among zircon solubility, temperature, and melt composition (Watson and Harrison, 1983). The Zr contents in the meta-leucogranites are in the range of 99–133 ppm, corresponding to zircon saturation temperature (TZr) of 746–780 °C. The presence of abundant inherited zircons indicates that the melt was saturated in zircon at source, and that part of whole-rock Zr contents is in inherited zircons rather than melt. Therefore, TZr values should provide a maximum limit for the melt temperatures, suggesting that the meta-leucogranites are low-temperature (cold) granites (Miller et al., 2003).

For metasedimentary rocks, the melting reactions that produce leucogranitic melts include water-present melting reactions, muscovite-dehydration melting reactions and biotite-dehydration melting reactions. Biotite-dehydration melting reactions commonly occur at ~780–950 °C (Vielzeuf and Holloway, 1988; Le Breton and Thompson, 1988; Patiño Douce and Johnston, 1991; Stevens et al., 1997), which is significantly higher than the magma temperature of the meta-leucogranites. Thus, the meta-leucogranites could not have been formed by biotite-dehydration melting. Water-present melting and muscovite-dehydration melting reactions occur at much lower temperatures (< 750 °C) (Johannes and Holtz, 1996; Patiño Douce and Harris, 1998). The two types of melting reactions consume different proportions of plagioclase and muscovite, thereby

producing melts with distinct geochemical features. Experimental studies have shown that water-present melting reactions consume plagioclase in higher abundances than muscovite, since increasing water activity depresses the plagioclase + quartz solidus more strongly than it reduces the stability of micas (Conrad et al., 1988; Patiño Douce and Harris, 1998). Therefore, water-present melting reactions produce trondhjemitic melts with high Na2O/K2O ratios, in contrast with granitic melts with low Na2O/K2O ratios derived by muscovite-dehydration melting（Cruciani et al., 2008; Gao and Zeng, 2014; Gao et al., 2016; King et al., 2011; Prince et al., 2001; Whitney and Irving, 1994; Zeng et al., 2005, 2012）. Furthermore, melts formed by these melting reactions also differ in Rb, Sr, Ba, and Eu concentrations, which are controlled by major reactant phases (mica and feldspar). In metasedimentary rocks, micas are major hosts for Rb, while feldspars hold most proportions of Sr, Ba, and Eu. Thus, melts derived by waterpresent melting are rich in Sr and poor in Rb and Ba with low Rb/Sr and Ba/Sr ratios and positive to no Eu anomalies, whereas melts formed by mica-dehydration melting are enriched in Rb and depleted in Sr and Ba with high Rb/Sr and Ba/Sr ratios and marked negative Eu anomalies (Harris and Inger, 1992; Harris et al., 1993). In this study, the meta-leucogranites are characterized by mildly peraluminous (ASI = 1.05– 1.1), relatively high Na2O/K2O ratios (1.24–1.42), low Rb (48–69 ppm) and high Sr (607–906 ppm) contents, extremely low Rb/Sr ratios (0.06–0.11), and weak negative to positive Eu anomalies. These geochemical characteristics suggest that the metaleucogranites were generated by water-present melting of metasedimentary rocks.

The relative proportions of plagioclase and muscovite in water-present melting are mainly determined by pressure and temperature. With increasing pressure, more plagioclase is consumed, the melt composition becomes richer in albite (Ab) and anorthite (An). With increasing temperature, more muscovite participates the melting reaction, the melt composition becomes richer in orthoclase (Or) (Patiño Douce and Harris, 1998). Although the meta-leucogranites have relatively high Na2O/K2O ratios, they plot in the granite field in the An-Ab-Or diagram (Fig. 10b). Their relative proportions of normative albite, anorthite and orthoclase are similar to those of experimental melts produced by water-fluxed melting of metasediments at 6 kbar, 750 °C, 1–2 wt.% added H2O, and significantly differ from those of melts generated by water-fluxed melting of metasediments at 10 kbar (Fig. 10b) (Patiño Douce and Harris, 1998). Therefore, the meta-leucogranites are suggested to be formed at moderate pressure conditions (6–8 kbar), which is also supported by their composition comparable with minimum melt composition at PH2O = 5 kbar in the haplogranite system, as noted above.

The meta-leucogranites have high Sr/Y (90–202) and LaN/Yb N (21–39) values, which are the most prominent features of adakites (Martin, 1986, 1999; Defant and Drummond, 1990; Martin et al., 2005). We propose that these geochemical features result from water-fluxed melting of metasedimentary rocks rather than high-pressure melting of basaltic rocks. For aluminous crustal sources, high Sr/Y and LaN/YbN melts could be produced within the garnet stability field at moderate pressure (5–10 kbar)

(Moyen, 2009). Garnets could form during subsolidus metamorphism at moderate pressures (5–8 kbar) in metasedimentary rocks (White et al., 2007; Rubatto et al., 2013). Generally, subsolidus garnets have extremely high Y and HREE contents (Otamendi et al., 2002; Pyle and Spear, 1999). During water-fluxed melting, subsolidus garnets survive as residual phase (trapping Y and HREE), whereas large amounts of plagioclase are consumed (releasing Sr), producing leucogranitic melts with high Sr/Y and LaN/Yb N ratios. Water-fluxed melting of granodiorite and diorite in the mid-crust can also generate high Sr/Y and LaN/YbN leucogranitic melts with peritectic hornblende accumulation in the source (Reichardt and Weinberg, 2012; Wang et al., 2013).

6.2 Timing of emplacement, metamorphism, and deformation of the meta-leucogranites

Interpreting zircon U-Pb data of the meta-leucogranites is highly contentious owing to the complex internal structures of zircons resulted from polyphase thermal events. Most previous studies proposed that the meta-leucogranites were formed at 1.92 Ga (Guo et al., 1999; Peng et al., 2014; Zhong et al., 2007), whereas Zhang et al. (2013) argued that the protoliths of meta-leucogranites were emplaced at 2.0 Ga and metamorphosed at 1.95–1.90 Ga. Zhong et al. (2007) described inherited and metamorphic zircons from the meta-leucogranites, and obtained 1933 Ma and 1903 Ma for peak and retrograde metamorphic ages, respectively. Peng et al. (2014) reported a wide apparent

207

Pb/206Pb

age range (2002–1878 Ma) with an upper intercept age of 1922 Ma, which was interpreted as the age of formation and metamorphism of meta-leucogranites. Zhang et

al. (2013) obtained a broader apparent

207

Pb/206Pb age span (2083–1857 Ma) for

magmatic zircons, and considered the upper intercept age of 1993 Ma as the formation age of meta-leucogranites.

The proper interpretation of zircon U-Pb ages relies on full understanding of zircon structures, growth history, and U-Pb isotopic system. In many cases, due to their low magma temperature, leucogranites commonly have abundant inherited zircons and lack new zircon growth, such as Himalayan leucogranites (Liu et al., 2014, 2016; Noble and Searle, 1995; Quigley et al., 2008). The meta-leucogranites from the Jining Complex also contain abundant inherited zircons and have experienced granulite-facies metamorphism, so that their zircons generally exhibit complex structures, comprising inherited cores, magmatic mantles, and metamorphic overgrowths. The inherited zircon core with bright CL response or truncated by unconformable oscillatory-zoned magmatic mantle is easily identified. However, the distinction between inherited zircons and magmatic zircons is sometimes far from straightforward based on CL images (Fig. 8). In this study, except these inherited zircons revealed by CL images, zircons with apparent

207

Pb/206Pb age above 2.0 Ga are also attributed as inherited origin, since that

the source rock (the khondalites) of meta-leucogranites was deposited after 2.0 Ga. Interpreting zircon U-Pb data is further complicated by that magmatic zircons have high U and common Pb contents and experienced recent radiogenic-Pb loss in varying degrees, which have also been reported in previous studies (Guo et al., 1999; Peng et

al., 2014). The magmatic zircons yield apparent 207Pb/206Pb ages ranging from 1985 Ma to 1567 Ma, mostly between 1950 Ma and 1850 Ma. There is a negative correlation between apparent

207

Pb/206Pb age and U content. The younger discordant or concordant

ages are possibly caused by ancient and recent radiogenic-Pb loss and partial recrystallization during later metamorphic event. In particular, the later HT-UHT granulite-facies metamorphism can partially reset the U-Pb system of zircon. In this case, the oldest apparent

207

Pb/206Pb age of magmatic zircons (1.98–1.94 Ga) is

considered to represent the crystallization age. This is consistent with the upper intercept ages of magmatic zircons (1.95 Ga) from two meta-leucogranite samples. In addition, the formation age of meta-leucogranites can be bracketed by the wellestablished geological processes in this region. Firstly, the meta-leucogranites should be formed later than the deposition time of their source (the khondalites), which are constrained between 2.0 Ga and 1.95 Ga. Secondly, the meta-leucogranites should be formed earlier than 1.93–1.92 Ga, since they were low temperature granites and later metamorphosed at HT-UHT granulites-facies conditions during 1.93–1.92 Ga. Therefore, we propose that the meta-leucogranites were formed at 1.95 Ga or slightly earlier.

Metamorphic zircons from three meta-leucogranite samples yield consistent ages of 1925–1916 Ma, indicating that the meta-leucogranites were metamorphosed at ~1.92 Ga. This age has been reported in previous studies (Guo et al., 1999; Peng et al., 2014; Zhang et al., 2013; Zhong et al., 2007). It is consistent with the metamorphic age of HT-

UHT granulite-facies metapelites and mafic granulites in the Jining Complex (Jiao et al., 2013b; Santosh et al., 2007b, 2012, 2013; Wang et al., 2015). The 1.92 Ga regional metamorphic event has been well documented in many recent metamorphic and geochronological studies (Jiao and Guo, 2011; Jiao et al., 2011, 2013b; Li and Wei, 2016; Liu et al., 2012; Santosh et al., 2006, 2007a,b, 2012, 2013).

Mylonitic deformation of meta-leucogranites is inferred to occur after the peak stage of HT-UHT

granulite-facies

metamorphism

from

petrographic

observation

that

porphyroclasts of mesoperthite (peak mineral) have been deformed into fine-grained two feldspars aggregates. Field observation that the pegmatite dike cut the foliation of meta-leucogranites and has been weakly deformed in the external part implies that the pegmatite dike is syn-kinematic. The metamorphic age of meta-leucogranites and the crystallization age of pegmatite dike has been well constrained to be 1.92 Ga. Accordingly, mylonitic deformation of meta-leucogranites is proposed to occur at ~1.92 Ga.

6.3 Crustal anatexis events in the eastern part of Khondalite Belt Crustal melting is a significant process responsible for changing P-T-fluid conditions during orogenesis. In terms of melting mechanism, partial melting can be caused by three processes: prograde heating, fluid influx, and decompression. In terms of melting stage, partial melting mostly occurs by prograde heating in HT-UHT granulite terranes, along the evolution from peak pressure to peak temperature in high-pressure granulite terranes, and during decompression in ultrahigh-pressure metamorphic terranes (Brown

and Korhonen, 2009, and references therein). Recent studies revealed that multiple episodes of crustal melting occurred in some orogenic belts, such as Himalayan orogen and Dabie orogen (Li et al., 2016; Liu et al., 2015; King et al., 2011; Prince et al., 2001; Streule et al., 2010; Zhang et al., 2004).

It is well accepted that Khondalite Belt is a continental-continental collisional orogenic belt as the result of the convergence between Yinshan and Ordos Block (Zhao et al., 2005, 2013), although recent studies question the existence of Ordos Block (Peng et al., 2014; Wan et al., 2013). Multiple crustal melting events have been identified in the Khondalite Belt, mostly producing voluminous S-type granites (Dan et al., 2014; Peng et al., 2012; Yin et al., 2009, 2011; Zhong et al., 2006, 2007). Combined with previous studies, two distinct melting episodes were recognized in the Jining Complex, eastern part of the Khondalite Belt: 1.95 Ga meta-leucogranites and 1.92 Ga porphyritic garnet granites.

The meta-leucogranites represent small-volume, low temperature, primary, nearminimum melts with low REE contents, and are proposed to be formed by water-fluxed melting of metasedimentary rocks during prograde upper amphibolite-facies metamorphism (Fig. 11). Many natural examples of water-fluxed melting have been reviewed in detail by Weinberg and Hasalová (2015). The external fluids may be channeled along shear zone or via the advection of regional metamorphic fluids. Compared with meta-leucogranites, the voluminous porphyritic garnet granites have

relatively higher magma temperature, FeOt+MgO+TiO2 contents, and REE contents. They were generated by biotite-dehydrated melting or higher degree melting of metasedimentary rocks under HT-UHT granulite facies metamorphism (Fig. 11; Peng et al., 2012). This extensive crustal melting was promoted by the contemporaneous underplated mantle-derived magma (Peng et al., 2010, 2012). The porphyritic garnet granites display magma mingling and mixing textures as a result of the interaction between felsic and mafic magma. After the extensive crustal melting under HT-UHT conditions, decompression could hardly trigger melting in the melt-depleted residual terrane.

7. Conclusions

The following conclusions can be drawn from this study: 1. The meta-leucogranites were emplaced at ~1.95 Ga or slightly earlier, subsequently were metamorphosed and cut by a pegmatite dike at ~1.92 Ga. 2. It is inferred that the meta-leucogranites were generated by water-fluxed melting of metasedimentary rocks during prograde upper amphibolite-facies metamorphism. 3. The meta-leucogranites were sourced from the metasedimentary rocks in the Khondalite Belt.

Acknowledgements

We are grateful to Fu Liu, Xudong Ma, Dingding Zhang for their help in the field. We thank Xianhua Li, Qiuli Li, Yu Liu, Guoqiang Tang for assistance with zircon SIMS

U-Pb dating and O isotope analyses, Yueheng Yang for assistance with zircon LAICPMS Lu-Hf analyses, He Li, Liang Qi for assistance with whole rock major and trace elements analyses, Xin Yan and Saihong Yang for assistance with zircon CL imaging. We particularly appreciate Shujuan Jiao for her thoughtful discussion. We would like to thank Yusheng Wan and two anonymous reviewers for their insightful comments, and Editor Guochun Zhao and Guest editor Chaohui Liu for their careful editorial work. This work was financially supported by research grants No. 41602197, 41672190, and 41602184 from the National Nature Science Foundation of China, and Chinese 1000 Young Talents Program.

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Figure captions

Fig.1. Tectonic subdivision map of the North China Craton (after Zhao et al., 2005). Abbreviations of metamorphic complexes: AL: Alashan, GY: Guyang, HL: Helanshan, JN: Jining, QL: Qianlishan, WC:Wuchuan, WD: Wulashan-Daqingshan. Abbreviations in inset: CAOB: Central Asian Orogenic Belt, HO: Himalaya Orogen, NCC: North China Craton, SCC: South China Craton, SLO: Su-Lu Orogen, TC: Tarim Craton,

QDO: Qinling-Dabie Orogen, QO: Qilianshan Orogen.

Fig.2. (a) Geological map of Archean and Paleoproterozoic lithological units in the eastern part of the Khondalite Belt, the North China Craton (after Guo et al., 2001). (b) Geological map showing the distribution of the meta-leucogranites in Liangcheng area. The sample locations are indicated by squares.

Fig.3. Field photographs of the meta-leucogranites. (a) Medium-grained metaleucogranites. (b-c) Schlieren of grt-sil-bi granulites within the meta-leucogranites. (d) Schlieren of grt-spl-mper granulites within the meta-leucogranites. (e) Narrow white pegmatite dike intruded into meta-leucogranites. Sample locality for 13AZS14. (f) Garnet coronae occurring biotite+quartz aggregates and plagioclase.

Fig.4. Photomicrographs and BSE images showing mineral assemblages and textures of the meta-leucogranites. Scales are shown by horizontal bars. (a, b) Photomicrograph showing the dominant mineral assemblage of Grt+Mper+Q with minor Bi + Sil. Garnet and mesoperthite porphyroclasts set in a recrystallized matrix of Qz+Pl+Kfs. Poikiloblastic garnet grains contain inclusions of quartz (plane and crossed polarized light, respectively). (c) Coarse garnet grains contain inclusions of ilmenite. (d) Garnet grain is partially replaced by biotite and sillimanite clusters. (e, f) Garnet grains are replaced by spinel and quartz, which are either in direct contact or separated by a thin corona of plagioclase. (g) Mesoperthite porphyroclasts set in a recrystallized matrix of

Pl+Kfs. (h) Granoblastic texture of recrystallized Pl+Kfs. K-feldspars contain fine-scale plagioclase exsolution lamellae.

Fig.5. Photomicrographs of mineral assemblages and textures in the pegmatite. Scales are shown by horizontal bars. (a, b) The mafic aggregates mainly consist of 0.2-0.5 mm biotite and quartz with minor magnetite and spinel (plane and crossed polarized light, respectively). (c, d) Garnet corona occurs between biotite+quartz aggregates and plagioclase, and contains inclusions of quartz and minor biotite (plane and crossed polarized light, respectively).

Fig.6. (a) Plot of A/NK [molar Al2O3/(Na2O+K2O)]) versus A/CNK [molar Al2O3/(CaO+Na2O+K2O)] demonstrating the weakly peraluminous character of the meta-leucogranites (after Maniar and Piccoli, 1989). (b) Normative An-Ab-Or diagram showing the chemical compositions of the meta-leucogranites (Barker, 1979).

Fig.7. Chondrite-normalized REE patterns (a) and primitive mantle-normalized trace element spidergram (b) of the meta-leucogranites. The chondrite and PM values are from Sun and McDonough (1989).

Fig.8. Representative CL images of zircon grains from the meta-leucogranites (11WS02, 13AZS11, 13AZS12) and pegmatite (13AZS14). Ellipses indicate the in-situ analytical spots of U-Pb and oxygen isotopes by SIMS. The analysis number,

207

Pb/206Pb ages with 1σ error, and oxygen isotopic values are shown.

Fig.9. Concordia diagrams for U-Pb analyses of zircon grains from the metaleucogranites (11WS02, 13AZS11, 13AZS12) and pegmatite (13AZS14). The analyses are plotted at 2σ level.

Fig.10. (a) Normative Qz-Ab-Or contents of the meta-leucogranites (Johannes and Holtz, 1996), compared with water-saturated minimum melt compositions at given pressures. (b) Normative An-Ab-Or contents of the meta-leucogranites (Barker, 1979), compared with that of experimentally melts generated by muscovite dehydration melting and water-fluxed melting from muscovite-biotite schist (Patiño Douce and Harris, 1998).

Fig.11. P-T diagram showing the predicted melting conditions of two crustal anatexis events in the Jining Complex. M1, the first melting event producing the metaleucogranites; M2, the second melting event producing porphyritic garnet granites. The metamorphic P–T paths of representative rocks in the Jining Complex are: 1, metapelite and mafic granulite (first metamorphic event, Lu and Jin, 1993); 2, metapelite and mafic granulite (second metamorphic event, Lu and Jin, 1993); 3, metapelite (Wang et al., 2011a); 4, garnet-bearing mafic granulite (Wang et al., 2011b); 5, garnetite (Jiao et al., 2013a); 6, UHT metapelite (Li and Wei, 2016); 7, UHT metapelite (Santosh et al., 2007a). Metamorphic facies boundaries are modified after Vernon and Clarke (2008).

Table captions

Table 1 Major (wt. %) and trace (ppm) element data of meta-leucogranites.

Table 2 Whole-rock oxygen isotope compositions of representative samples in the Jining Complex. Supplementary tables Supplementary Table 1 SIMS U-Pb data of zircons from meta-leucogranites and pegmatite.

Supplementary Table 2 Oxygen isotopic compositions of zircons from metaleucogranites and pegmatite.

Supplementary Table 3 Lu-Hf isotopic compositions of zircons from the metaleucogranite.

Table 1 Major (wt. %) and trace (ppm) element data of meta-leucogranites Sampl

12WS

12WS

13WS

12AZ

13AZ

13AZ

13AZ

13AZ

YY0 1

YY0

07LC 572

e

M01

M02

M08

S02

S11

S12

S27

S28

07

SiO2

73.7

72.8

73.4

73.5

72.7

72.7

72.9

73.2

73.4

73.0

72.6

TiO2

0.18

0.19

0.20

0.17

0.17

0.19

0.18

0.18

0.19

0.20

0.15

Al2O3

15.0

15.4

15.0

15.2

15.4

15.4

15.0

15.2

15.2

15.2

15.6

1.09

1.10

1.16

1.19

0.85

1.41

1.00

1.04

1.15

1.20

MnO

0.01

0.01

0.01

0.01

0.01

0.01

0.01

0.01

0.02

0.01

0.01

MgO

0.31

0.33

0.32

0.30

0.22

0.39

0.31

0.27

0.36

0.39

0.26

CaO

1.39

1.43

1.37

1.34

1.03

1.46

1.39

1.37

1.38

1.43

1.44

Na2O

4.47

4.70

4.56

4.79

4.55

4.62

4.72

4.77

4.93

4.47

4.85

K2O

3.61

3.72

3.50

3.46

3.60

3.42

3.45

3.36

3.50

3.54

3.69

P2O5

0.05

0.06

0.05

0.06

0.05

0.06

0.05

0.05

0.06

0.06

0.06

LOI

0.24

0.10

0.16

0.22

0.66

0.16

0.14

0.22

0.16

0.18

0.40

100.0

99.9

99.7

100.2

99.3

99.8

99.2

99.6

101.

100.

3

8

99.8

36

37

35

33

34

35

38

34

38

39

37

1.24

1.26

1.30

1.38

1.26

1.35

1.37

1.42

1.41

1.26

1.31

1.09

1.07

1.09

1.08

1.16

1.10

1.07

1.08

1.05

1.10

1.07

Li

36.0

41.5

30.7

4.96

34.7

36.9

40.1

36.5

Be

1.25

1.50

0.57

1.28

1.15

0.99

0.70

1.09

Sc

4.70

4.84

5.44

4.68

3.95

4.94

4.80

2.10

2.87

1.63

V

11.9

12.8

14.5

11.8

12.8

12.5

10.4

10.9

12.6

9.23

Cr

7.00

8.31

8.97

7.37

5.95

5.49

5.45

Co

1.88

1.40

1.47

0.94

1.66

1.32

1.17

Ni

3.26

5.54

2.17

2.99

2.04

2.23

2.02

2.27

Cu

2.26

4.30

2.55

1.88

2.95

3.56

1.21

1.00

Zn

46.7

55.7

36.6

31.0

57.2

44.4

42.2

Ga

19.0

20.1

19.6

18.0

19.1

18.9

20.1

Rb

53.9

63.5

48.3

67.9

60.0

64.7

54.3

Fe2O3 T

TOTA L Mg# Na2O/ K2O A/CN K

08

1

0.89

5.86 17.9

35.0

19.2

1.00

40.9 15.6

68.0

56.0

68.6

Sr

735

797

717

607

755

732

699

672

906

741

Y

5.43

6.17

4.47

5.37

8.39

3.62

5.60

4.93

9.01

3.69

Zr

118

113

127

133

133

118

109

99

104

111

Nb

2.55

3.04

2.93

2.30

2.45

2.27

2.41

2.35

2.57

1.74

Cs

0.16

0.33

0.06

0.09

0.04

0.15

0.16

Ba

846

834

853

970

895

1000

934

789

1341

1012

La

16.7

17.7

16.8

18.1

19.3

20.0

17.0

18.2

29.3

19.4

Ce

28.1

32.5

29.2

31.0

34.6

33.5

30.0

31.1

49.9

34.9

Pr

3.28

3.53

3.32

3.41

3.61

3.86

3.28

3.56

5.54

3.57

Nd

11.7

13.0

11.4

12.0

13.1

13.4

11.7

11.7

19.2

13.1

Sm

1.83

2.18

1.82

1.83

2.12

2.16

1.86

1.89

2.95

2.10

Eu

0.58

0.62

0.55

0.60

0.61

0.60

0.56

0.65

0.76

0.71

Gd

1.59

1.79

1.71

1.56

1.90

1.57

1.41

1.45

2.34

1.45

Tb

0.22

0.25

0.22

0.21

0.31

0.18

0.21

0.19

0.33

0.17

Dy

1.16

1.30

1.01

1.04

1.54

0.77

1.13

0.93

1.70

0.83

Ho

0.23

0.22

0.18

0.18

0.30

0.14

0.21

0.17

0.32

0.14

Er

0.59

0.61

0.43

0.52

0.77

0.38

0.54

0.44

0.82

0.38

Tm

0.08

0.09

0.07

0.07

0.11

0.06

0.07

0.06

0.11

0.06

Yb

0.54

0.57

0.48

0.47

0.65

0.39

0.59

0.40

0.71

0.36

Lu

0.08

0.08

0.08

0.07

0.10

0.05

0.07

0.06

0.10

0.05

Hf

3.55

3.56

3.37

3.81

3.61

3.46

3.25

3.26

3.16

3.29

Ta

0.18

0.19

0.21

0.15

0.16

0.12

0.13

0.17

0.19

0.16

W

7.11

2.58

5.32

4.56

2.77

3.62

0.60

Pb

22.4

26.2

20.7

22.2

30.8

24.7

22.4

21.0

21.6

24.1

Th

1.05

1.24

0.39

2.30

0.98

1.17

0.89

0.77

0.88

1.00

U

0.77

0.86

0.48

1.22

0.64

0.50

0.67

0.69

0.79

0.64

0.12

114. 66.7

74.4

67.3

71.1

79.0

77.0

68.7

70.7

1

77.2

22

22

25

28

21

37

21

33

30

39

1.04

0.96

0.95

1.09

0.92

0.99

1.06

1.20

0.88

1.2

Rb/Sr

0.07

0.08

0.07

0.11

0.08

0.09

0.08

0.10

0.06

0.09

Sr/Y

135

129

160

113

90

202

125

136

101

201

Th/U

1.37

1.44

0.82

1.89

1.52

2.32

1.33

1.12

1.11

1.56

Zr/Hf

33

32

38

35

37

34

34

30

33

34

Nb/Ta

14

16

14

15

15

20

19

14

14

11

764

758

770

780

774

762

757

746

754

ƩREE LaN/Y bN Eu/Eu *

o

TZr( C )

1 data from Zhang et al

757

(2013) 2 data from Peng et al (2012)

Table 2 Whole-rock oxygen isotope compositions of representative samples in the Jining Complex Sample

δ18O (‰)

Meta-leucogranites 12WSM01

9.5

13AZS12

10.4

Porphyritic garnet granites

11DNS03

11.9

11YZ03

11.6

Metapelites 12SHZ08

11.9

12SHZ11

13.1

15TGS04

13.7

15TGS08

13.7

Highlights

A prograde melting event is recognized in the Jining Complex

The meta-leucogranites were generated by water-fluxed melting of metasediments

The meta-leucogranites were emplaced at 1.95 Ga and metamorphosed at 1.92 Ga