Genesis of Leucogranite by Prolonged Fractional Crystallization: a Case Study of the Mufushan Complex, South China

Lithos 206–207 (2014) 147–163

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Genesis of leucogranite by prolonged fractional crystallization: A case study of the Mufushan complex, South China

Lian-Xun Wang a,b,⁎, Chang-Qian Ma a,⁎,ChaoZhangc,Jin-YangZhangd, Michael A.W. Marks b a Faculty of Earth Sciences, China University of Geosciences, 430074 Wuhan, China b FB Geowissenschaften, Mathematisch-Naturwissenschaftliche Fakultät, Universität Tübingen, 72074 Tübingen, Germany c Institut für Mineralogie, Leibniz Universität Hannover, 30167 Hannover, Germany d Faculty of Earth Resources, China University of Geosciences, 430074 Wuhan, China article info abstract

Article history: We present major and trace elemental geochemical data, Sr–Nd–Hf isotopes and zircon U–Pb ages for igneous Received 5 April 2014 rocks of the Mufushan complex (~2400 km2 outcrop area) in South China. The complex intruded episodically Accepted 27 July 2014 from late Jurassic (ca.154 Ma) to early Cretaceous (ca. 146 Ma) with a compositional evolution from diorite Available online 7 August 2014 through granodiorite and biotite-bearing monzogranite to two-mica leucogranite and garnet-bearing leucogranite dykes. Diorites have high Mg# (up to 71), low SiO and high siderophile elements (e.g. Cr, Ni Keywords: 2 and V) resembling sanukite or high-Mg diorite. They display isotopic characteristics similar to those of incident Zircon dating ﬁ – ε − − Sr–Nd–Hf isotopes enriched mantle-derived ma c rocks, such as low ISr(t) (0.7080 0.7085), high Nd(t) ( 4.3 to 4.8) and ε − – Leucogranite Hf(t) ( 2.41 to 0.59). In contrast, felsic rocks show a common crustal signature with higher ISr(t) (0.7115 High-Mg diorite 0.7184), lower εNd(t) (−7.9 to −10.2) and εHf(t) values (−7.73 to −4.04). These felsic rocks display decreas- tot South China ing Al2O3,CaO,FeO , MgO contents and gradually enhanced depletions in Sr, Ba and Ti and Eu with increasing Fractional crystallization SiO2 and decreasing zircon U–Pb age, which implies continuous magmatic evolution towards leucogranites dominated by fractional crystallization. The most evolved SiO2-rich rocks (two-mica leucogranites) are compositionally similar to the Himalaya leucogranites, indicating that prolonged fractional crystallization of metaluminous granitic magma is a feasible mechanism to form peraluminous leucogranitic magma. The differentiation process of the felsic magma lasted from 152 to 146 Ma as indicated by zircon U–Pb dating, which implies that magma differentiation, emplacement and subsequent solidiﬁcation in giant batholiths may proceed on a timescale of several million years. © 2014 Elsevier B.V. All rights reserved.

1. Introduction and of the low density contrasts between minerals and silicate melts (Tartèse and Boulvais, 2010). Nevertheless, several studies proposed Two-mica leucogranites are commonly considered as products fractional crystallization of mafic/intermediate magmas as an important of partial melting of metasediments, as evidenced by classic case studies mechanism to generate leucogranites (e.g. Miller, 1985; Secchi et al., from the Himalayan Orogen (e.g., Le Fort et al., 1987; Zhang et al., 2004) 1991; Teixeira et al., 2012). In order to clarify whether or not fractional and the Hercynian massifs of western Europe (e.g., Bernard-Griffiths crystallization is the dominating cause for silicic magma evolution, sys- et al., 1985; Vidal et al., 1984; Williamson et al., 1996), as well as by tematic geochronology and isotope geochemistry data for leucogranite partial melting experiments on metapelites and metagraywackes and associated mafic and intermediate rocks in multiphase complex (Acosta-Vigil et al., 2006; Annen et al., 2006; Litvinovsky et al., 2000; are required to constrain magma sequences and origins, but such com- Scaillet et al., 1995; Xiong et al., 2002) and other case studies worldwide prehensive studies are relatively rare (Scaillet et al., 1990; Secchi et al., (e.g., Jung et al., 2009, 2012; Paul et al., 2014; VandeFlierdtetal.,2003). 1991). Fractional crystallization is considered relatively difficult in granitic Quantifying the timescales of magma generation, differentiation magmas comparable to mafic magmas, because of their high viscosity and intrusion/eruption is essential to understand and reconstruct the evolution of the lithosphere and the growth rate of the crust (e.g., Hawkesworth et al., 2000, 2004; Schaltegger et al., 2009; Schoene et al., 2012). Recent improvements of analytical techniques ⁎ Corresponding authors. Tel.: +49 7071 29 730 77; fax: +49 7071 29 3060. make it possible to build a temporal framework for magmatic processes E-mail addresses: [email protected] (L.-X. Wang), [email protected] (C.-Q. Ma). and re-attract attentions to chronometers (e.g., Barboni et al.,

2013; Hawkesworth et al., 2004; Schoene et al., 2012). For example, the are genetically associated with economically signiﬁcant W, Sn, Nb–Ta U-series radioactive disequilibria (e.g., 238U, 230Th, 226Ra) provide quan- and REE deposits, which are widespread in South China (e.g., Lu et al., titative constraints for the timing of pre-eruptive activities of recent vol- 2003; Yin et al., 2002; Yuan et al., 2011). Therefore, it is important to canisms (e.g., Chekol et al., 2011; Kuritani et al., 2011; Reagan et al., better understand the petrogenesis of such leucogranites. 2003). However, the short-lived timescale (generally b 1 Ma) is limited In this contribution, we present systematic zircon U–Pb geochronol- and inappropriate for giant granitoid batholiths since the emplacement ogy, geochemical and Sr, Nd and Hf isotopic data of four dominate and evolution rates of granitic magmas are likely to be much slower due rock units (diorite, granodiorite, monzogranite and leucogranite) to their high viscosities, massive volumes, and deep intrusive levels from the Mufushan complex (MFSC) in South China. We intend (Harris et al., 2000). High-precision dating on minerals, in particular zir- (i) to decipher the genesis of the leucogranites and their genetic re- cons, provides absolute ages for mineral growths and has been utilized lationships to the associated rocks and (ii) to estimate the timescale to calibrate the timescale of batholiths construction histories, with an of magma evolution from high-Mg diorite to two-mica leucogranite assumption that zircon crystallization ages are identical to magma in- in the MFSC. trusive ages (e.g., Coleman et al., 2004; Leuthold et al., 2012; Matzel et al., 2006; Schaltegger et al., 2009; Walker et al., 2007). Two-mica 2. Geological setting and petrography leucogranites are extensively exposed in the South China block, especially in the hinterland of some orogenic belts (e.g., L. Wang et al., The South China tectonic plate is surrounded by the North China 2008; Wang et al., 2007; X.L. Wang, 2008; Xiong et al., 2002; Zhou Craton in the north, the Tibetan Plateau in the west and the Philippine and Li, 2000). Unlike the Himalayan leucogranites, these rocks are Sea Plate in the southeast (Fig. 1). It is composed of the Yangtze Craton often accompanied by biotite-bearing granites and intermediate to and the Cathaysia Block, bounded by the Jiangshan–Shaoxing and maﬁc rocks, and in such igneous complexes leucogranites generally Pingxiang–Yushan fault. The Cathaysia Block is characterized by show clear late intrusive contacts towards the other rock units (e.g. L. widespread Mesozoic granitoids, which formed in three main stages: Wang et al., 2008; Sun et al., 2005; Wang et al., 2007; X.L. Wang, (1) 265–205 Ma, Indosinian granitoids; (2) 180–142 Ma, Early 2008; Xiong et al., 2002; Yu et al., 2007). In addition, some leucogranites Yanshanian granitoids and (3) 142–66 Ma, Late Yanshanian granitoids

110 112 114 116 118 120 122 32 32

Dabie Orogen

TARIM NCC QDO Tibet Wuhan 30 30

YC Pacific Ocean CB 900km Jiangshan- This study Shaoxing and Hunnan Province Yangtze Craton Pingxiang- Yushan fault 28 28

NEE-striking granite belt

26 26

Cathaysia Block Shi-Hang Tai Pei

Zone 24 24 265-205 Ma granitoids 180-142 Ma granitoids 142-66 Ma granitoids

Abbreviations

NCC North China Craton 22 22 Hong Kong QDO Qinling-Dabie Orogen 0 50 100 km YC Yangtze Craton CB Cathaysia Block

Fig. 1. Geological sketch map of south China showing the distribution and classiﬁcation of Mesozoic granitic rocks and the location of Mufushan complex (after Zhou et al., 2006). L.-X. Wang et al. / Lithos 206–207 (2014) 147–163 149

(Zhou et al., 2006). The mechanism of these intensive magmatisms porphyritic or coarse-grained, with relatively less muscovite but more has been ascribed to the westward subduction of the paleo- plagioclase. (2) LG2 is rare, occurring as dykes or small stocks, Pacific plate in Mesozoic, which was prevailing in eastern China medium- to fine-grained, rich in alkali feldspar and muscovite and usu- (e.g., Wu et al., 2006; Zhang et al., 2011; Zhou et al., 2006). ally contains garnet. In the Yangtze Craton, relatively less Mesozoic granitoids are ex- The basement of Yangtze Craton is mainly composed of Archaean to posed (Fig. 1), including mainly the Late Yanshanian granitoids Mesoproterozoic meta-sedimentary rocks (Gao et al., 1999; Ma et al., in the northeast (Lower Yangtze region) and the Indosinian and 2000; Qiu et al., 2000; Zhang et al., 2006; Zheng et al., 2008), which early Yanshanian granitoids in the middle part (Middle Yangtze are overlain by Neoproterozoic to Cenozoic strata. The primary part of region). the MFSC intrudes into Mesoproterozoic to early Neoproterozoic low- The MFSC is the largest Mesozoic intrusive complex in the Middle grade metasediments (i.e. the Lengjiaxi Group) except the northeastern Yangtze region, with a total outcrop area of ca. 2400 km2. It consists of part which contacts with Lower Palaeozoic sedimentary rocks (Fig. 2). several individual intrusive units ranging from intermediate (mafic) to felsic rocks (Fig. 2). Field relations (Fig. 3a&b) indicate that the emplace- 3. Analytical methods ment sequence is: (1) diorites (D); (2) granodiorites (GD); (3) biotite- bearing monzogranites (BG) and two-mica leucogranites (LG) (this Concentrations of whole rock major elements for 18 rock samples of study and BGMEHP, 1988; Bureau of Geology and Mineral Exploration the MFSC were determined using a 3080E XRF spectrometer at the An- of the Hunan Province). alytical Institute of the Hubei Bureau of Geology and Mineral Resources Diorites are the most mafic rock type with hornblende and plagio- (Table 1). The relative standard deviations are b5% for the major clase (An42–51) as the major rock-forming minerals (Supp. Table 1; elemental oxides. Trace and Rare Earth Elements (REE) were deter- Fig. 3c). These rocks are exposed over only a few hundred square meters mined for the same samples using inductively coupled plasma

(Fig. 2). Granodiorites consist of predominant plagioclase (An33–49), mass spectrometry (ICP-MS; Agilent 7500a) at the State Key Laboratory alkali-feldspar and quartz as well as minor biotite and amphibole. of Geological Process and Mineral Resources (GPMR) at the China Uni- Maﬁc enclaves (ME) exist occasionally in the granodiorites containing versity of Geosciences (CUG, Wuhan; Table 1). Repeated analysis on ref- abundant biotite. Euhedral magmatic epidote is common and partially erence materials of AGV-1 and GSR-3 shows a relative standard enriched in both MEs and granodiorite (Zou and Wang, 2011; deviation of b5% for REE and 5–12% for other trace elements. Sample Fig. 3d&e). Biotite-bearing monzogranites are composed of alkali feld- preparation and analytical procedures are described in detail by Liu spar, plagioclase (An17–41), quartz, biotite and minor muscovite. Two- et al. (2008b). mica leucogranites (LG) are the most abundant rock type. Besides alkali Whole rock Sr and Nd isotopic ratios for 12 rock samples were feldspar, quartz and albite-rich plagioclase (An14–38), they are charac- obtained by a Finnegan MAT-261 multi-collector mass spectrometer terized by the common presence of primary muscovite (Fig. 3f). Based at GPMR (Table 2). Analyses of NBS987 and La Jolla standards gave on ﬁeld appearance and petrography, two different varieties of 87Sr/86Sr = 0.710289 ± 4 (2σ)and143Nd/144Nd = 0.511845 ± 2 leucogranites can be distinguished: (1) LG1 is widespread, normally (2σ), respectively. Total procedural Sr and Nd blanks were b1 ng and

154Ma 154Ma 148Ma S 500 m 151Ma

146Ma Pt

Diorite Pt Granodiorite Biotitemonzogranite N Q Two- mica leucogranite

Proterozoic mica schist 0 10 km

Fig. 2. Simpliﬁed geological map of the Mufushan complex, showing the major intrusive units and the sample locations dated in this study. Pt = Proterozoic stratum; Q = Quaternary stratum; S = Silurian stratum; = Cambrian stratum. 150 L.-X. Wang et al. / Lithos 206–207 (2014) 147–163

Fig. 3. Filed photographs and microscopic characteristics of the various rocks from the Mufushan complex. (a) Intrusive contact between diorites and biotite-bearing monzogranites. (b) Field photograph of the intrusive contact between biotite-bearing monzogranites and leucogranites. (c) Microphotograph of amphibole in diorite. (d) & (e) Microphotograph of magmatic epidotes in granodiorites and enclosed maﬁc enclaves. (f) Microphotograph of muscovite in the leucogranites. D = diorite; BG = biotite-bearing monzogranite; LG = leucogranite; Am = amphibole; Pl = plagioclase; Ep = epidote; Aln = allanite; Bt = biotite; Mus = muscovite.

b50 pg, respectively. The procedures of chemical separation and deter- used to calibrate the mass discrimination and isotope fractionation mination are given in detail by Gao et al. (1999). and zircon standard 91500 was used as unknown for further certifi- Zircon from 4 rock samples of the MFSC was separated by means of cation of data quality. Details on operating conditions and data ac- heavy liquid and magnetic techniques. Subsequently, representative quisition procedures are given in Liu et al. (2008a). Data processing zircon grains were handpicked, mounted in epoxy resin, polished was carried out using ICPMSDataCal (Liu et al., 2008a)andISOPLOT and coated with film. Afterwards U–Pb dating was performed at 3.0 (Ludwig, 2003). Common Pb was corrected according to the GPMR in CUG. Laser sampling was conducted using an excimer method proposed by Anderson (2002). Uncertainties listed in the laser ablation system. An Agilent 7500a Inductively Coupled Plasma data tables (Supp. Table 2) and plotted on the concordia diagrams at Mass Spectrometry (ICP-MS) instrument was used to acquire ion- the 2σ level. The ages reported here are the weighted means at the signal intensities. The spot size was set to 24 μm to decrease the de- 95% confidence level. Cathodoluminescence (CL) images were taken tection limit and improve data precision. Zircon standard GJ-1 was for all zircons using a JXA 8100 electron microprobe also in the GPMR. L.-X. Wang et al. / Lithos 206–207 (2014) 147–163 151

Table 1 Whole-rock major (wt.%) and trace (ppm) element of Mufushan complex.

DDDGDGDBGBGBGBG

0801-1 0725-2 0725-3 0713-1 0723-1 0701-1 0702-1 730 0733-1

SiO2 50.7 53.4 50.5 65.7 65.2 71.0 71.2 71.4 72.1

TiO2 1.3 1.0 1.0 0.6 0.6 0.3 0.3 0.4 0.3

Al2O3 13.1 12.3 10.7 16.1 16.1 15.0 15.1 14.8 14.7

Fe2O3 2.5 2.3 2.9 1.5 1.1 0.6 0.5 0.4 0.1 FeO 7.2 5.8 6.8 2.7 3.3 1.5 1.4 1.6 1.8 MnO 0.13 0.12 0.15 0.08 0.08 0.04 0.03 0.04 0.04 MgO 10.5 10.7 13.0 1.7 1.9 0.9 0.7 0.8 0.6 CaO 8.2 8.1 9.5 4.1 4.2 2.8 2.6 2.3 2.2

Na2O 2.5 2.7 2.1 3.2 3.0 3.7 3.9 3.6 3.7

K2O 1.7 1.8 1.3 3.2 3.2 3.2 3.3 3.7 3.6

P2O5 0.10 0.20 0.28 0.24 0.25 0.13 0.10 0.13 0.15

H2O+ 1.8 1.3 1.7 0.8 0.8 0.5 0.5 0.6 0.5

CO2 0.3 0.04 0.04 0.02 0.05 0.07 0.07 0.04 0.04 Sum 99.7 99.8 99.8 99.8 99.7 99.7 99.7 99.8 99.8 Mg# 67 71 71 43 45 43 42 43 38 DI 31 33 26 69 67 80 82 83 83 ASI 0.6 0.6 0.5 1.0 1.0 1.0 1.0 1.1 1.1 AR 1.5 1.6 1.4 1.9 1.9 2.3 2.4 2.5 2.5 T* 842 712 705 750 748 750 750 701 737 Sc 33 27 29 12 12 5 4 3 4 V 305 190 193 82 93 34 33 19 21 Cr 490 584 662 19 22 12 8 8 8 Co 57 48 49 10 11 4 4 3 3 Ni 210 205 233 6 7 4 3 2 2 Sn 1.3 1.3 1.1 2.5 2.3 2.1 1.8 2.7 4.8 Rb 58 61 35 128 127 133 131 114 171 Sr 469 440 329 470 476 647 756 187 226 Zr 89 74 71 141 137 148 156 93 148 Ba 620 633 468 907 1170 1184 1443 463 634 Cs 4 5 2 7 8 5 10 19 7 Hf 3 2.7 2.3 4 3.9 4.4 4.5 2.6 4.2 Ta 0.6 0.6 0.6 0.8 0.6 0.5 0.3 0.3 0.5 Nb 11 12 11 10 8 7 5 5 9 Ga 16 16 13 20 20 21 20 12 21 Be 1.1 1.2 1.0 2.6 2.2 3.1 2.5 1.8 2.5 Y 18141418 16 7 6 4 7 Pb 18 15 11 29 27 43 51 24 43 Th 8 8 512 1318171826 U 1.7 2 1.3 2.1 1.8 3.2 4 1.8 2.2 La 29 28 24 33 36 43 42 33 45 Ce 53 61 55 69 78 78 77 60 79 Pr 6.8 7.1 6.5 7.8 8.5 8.4 8.1 5.8 7.4 Nd 27 29 27 31 33 31 29 19 25 Sm 5.7 5.8 5.3 6.2 6.0 5.0 4.8 2.9 3.8 Eu 1.5 1.4 1.3 1.5 1.4 1.2 1.2 0.6 0.8 Gd 4.9 4.3 4.0 4.6 4.3 3.1 2.8 1.8 2.4 Tb 0.7 0.6 0.6 0.7 0.6 0.4 0.3 0.2 0.3 Dy 3.7 3.1 3.0 3.6 3.3 1.6 1.3 0.8 1.4 Ho 0.68 0.54 0.52 0.62 0.58 0.24 0.2 0.13 0.23 Er 1.6 1.3 1.3 1.7 1.7 0.7 0.5 0.3 0.6 Tm 0.21 0.18 0.17 0.24 0.23 0.09 0.07 0.04 0.09 Yb 1.23 1.01 1.05 1.42 1.45 0.53 0.42 0.3 0.54 Lu 0.16 0.15 0.14 0.22 0.21 0.08 0.06 0.05 0.08

LG1 LG1 LG1 LG1 LG2 LG2 LG2 ME MS

0718-1 0705-1 0710-1 0728-1 0727-1 0706-1 0711-1 0803-1 0735-2

SiO2 72.8 74.0 72.6 72.9 75.0 75.1 74.1 50.3 68.2

TiO2 0.2 0.1 0.3 0.2 0.0 0.1 0.1 1.3 0.9

Al2O3 14.7 14.2 14.5 14.5 14.1 13.9 14.6 15.7 14.1

Fe2O3 0.1 0.3 0.3 0.2 0.4 0.2 0.2 3.8 1.0 FeO 1.2 0.7 1.3 1.2 0.1 0.5 0.6 8.5 5.1 MnO 0.04 0.05 0.04 0.04 0.02 0.04 0.08 0.26 0.09 MgO 0.5 0.2 0.5 0.4 0.1 0.1 0.1 5.6 2.0 CaO 1.8 0.8 1.3 0.9 0.9 0.4 0.2 6.1 0.6

Na2O 3.9 3.7 3.3 3.4 3.9 3.6 4.0 2.1 1.4

K2O 4.0 4.8 4.8 5.2 4.6 5.0 4.6 3.8 4.6

P2O5 0.09 0.18 0.17 0.23 0.03 0.12 0.15 0.42 0.11

H2O+ 0.5 0.8 0.8 0.7 0.6 0.8 1.1 1.8 1.7

CO2 0.07 0.05 0.02 0.04 0.04 0.04 0.02 0.11 0.04 Sum 99.8 99.9 99.8 99.9 99.9 99.9 99.9 99.7 99.8 Mg# 41 29 35 32 27 27 22 DI 87 93 88 91 94 95 95 41 75

(continued on next page) 152 L.-X. Wang et al. / Lithos 206–207 (2014) 147–163

Table 1 (continued)

LG1 LG1 LG1 LG1 LG2 LG2 LG2 ME MS

0718-1 0705-1 0710-1 0728-1 0727-1 0706-1 0711-1 0803-1 0735-2

ASI 1.1 1.1 1.1 1.1 1.1 1.2 1.2 0.8 1.7 AR 2.7 3.0 2.4 2.6 3.2 3.0 3.4 1.5 2.4 T* 705 654 711 685 588 579 567 Sc33533216516 V 19 6 18 12 2 3 1 245 109 Cr947532210370 Co31320102914 Ni21221102028 Sn 4.6 13.2 16 10.5 4.5 17.2 17.9 5.6 6.7 Rb 210 381 314 368 279 444 367 203 323 Sr 220 52 95 73 61 16 5 296 112 Zr 103 53 132 97 23 21 17 214 210 Ba 589 179 403 251 41 30 15 487 583 Cs 19 40 27 45 17 27 59 17 17 Hf 3 2 4.1 3.2 1.4 1.3 1.1 5.4 6 Ta 1.1 3.2 2.2 2 1.3 4.2 4 0.3 0.7 Nb71715151119181013 Ga 20 23 24 22 20 24 16 26 19 Be 6.6 8.4 5.9 6.2 3.7 13.5 4.8 3.1 1.7 Y 7 13 15 8 14 8 2 31 30 Pb 45 29 30 34 69 24 11 22 24 Th 24 14 29 27 6 5 3 1 14 U 7.2 15.9 3.1 4.8 2.3 5 1.1 1 2.6 La 40 17 41 28 7 4 3 5 39 Ce 70 37 82 63 14 10 5 13 84 Pr 6.8 4.1 8.7 7.0 1.7 1.1 0.7 2.7 9.5 Nd 22 15 30 26 7 4 2 15 37 Sm 3.4 3.4 5.6 5.6 1.9 1.2 0.7 5.6 7.5 Eu 0.7 0.3 0.6 0.5 0.2 0.1 0.0 1.0 1.0 Gd 2.3 2.7 3.7 3.6 1.9 1.1 0.5 6.5 6.2 Tb 0.3 0.5 0.5 0.5 0.4 0.2 0.1 1.0 1.0 Dy 1.4 2.5 2.8 2.0 2.5 1.4 0.5 5.9 5.8 Ho 0.24 0.43 0.49 0.26 0.45 0.24 0.07 1.13 1.07 Er 0.7 1.2 1.4 0.7 1.2 0.7 0.2 2.8 3.2 Tm 0.09 0.18 0.2 0.09 0.19 0.12 0.05 0.38 0.49 Yb 0.59 1.17 1.22 0.5 1.21 0.84 0.38 2.42 2.91 Lu 0.08 0.18 0.18 0.08 0.18 0.12 0.06 0.36 0.46

Zircon saturation temperature calculation (T*) is according to Watson and Harrison (1983). Abbreviations: D = diorite; GD = granodiorite; BG = biotite-bearing monzogranite; LG1 = two-mica leucogranite; LG2 = garnet-bearing leucogranite; ME = maﬁc enclave; MS = mica schist; DI = differentiation index (Qz + Or + Ab); ASI = alumina saturation index Al2O3 /(Na2O+K2O + CaO) (molar); AR = alkalinity ratio [Al2O3 +CaO+(Na2O+K2O)] / [Al2O3 +CaO− (Na2O+K2O)] (wt.%).

In situ zircon Hf isotope analyses (Supp. Table 3) were carried out 4. Results mostly on the dated spots using a 193 nm laser attached to a Neptune multi-collector ICP-MS (LA-MC-ICPMS) at the Institute of Geology and 4.1. Major and trace element geochemistry Geophysics, Chinese Academy of Sciences. During analyses, spot sizes of 63 μm and a laser repetition rate of 10 Hz at 100 mJ were used. The 4.1.1. Major elements 176 177 176 177 Hf/ Hf and Lu/ Hf ratios of the zircon standard 91500 were Diorites have SiO2 concentrations from 50.5 to 53.4 wt.%, K2O con- 0.282310 ± 15 (2σ, n = 20) and 0.00031, respectively, similar to tents of 1.29–1.75 wt.% and Al2O3 varying from 10.7 to 13.1 wt.%, signif- those measured using the solution method (e.g., 0.282306 ± 9, icantly lower than those of other felsic granitic rocks (Table 1). In

Woodhead et al., 2004). The detailed analytical technique and correc- contrast, their FeO* (total iron), TiO2, MgO, MnO and CaO contents are tion procedure is provided in Wu et al. (2006). much higher than that of the granitic rocks (Table 1). The Mg# [Mg

Table 2 Rb–Sr and Sm–Nd isotopic data for selected samples from the Mufushan complex.

87 86 87 86 87 86 147 144 143 144 Rock type Sample no. Rb Sr Rb/ Sr Sr/ Sr 2σ ( Sr/ Sr)i Sm Nd Sm/ Nd Nd/ Nd 2σεNd(t) D 0725-2 61 440 0.40 0.709340 2 0.7085 5.8 29.0 0.12 0.512315 1 −4.8 D 0725-3 39 371 0.31 0.708655 4 0.7080 5.3 26.7 0.12 0.512340 1 −4.3 GD 0713-1 128 470 0.79 0.714410 4 0.7127 6.2 30.6 0.12 0.512158 3 −7.9 GD 0723-1 127 476 0.78 0.714535 2 0.7129 6.0 32.7 0.11 0.512148 1 −7.9 BG 0701-1 133 647 0.59 0.713717 2 0.7125 5.0 30.7 0.10 0.512113 1 −8.4 BG 0702-1 131 756 0.50 0.712530 10 0.7115 4.8 29.4 0.10 0.512124 1 −8.2 LG1 0718-1 210 220 2.77 0.720397 3 0.7147 3.4 22.4 0.09 0.512082 3 −8.9 LG1 0715-2 162 65 7.19 0.733293 4 0.7184 3.4 11.7 0.17 0.512094 4 −10.2 LG2 0706-1 444 16 82.64 0.870012 5 0.6985 3.4 14.7 0.14 0.512226 3 −7.0 LG2 0711-1 367 5 200.63 1.03432 10 0.6179 0.7 2.3 0.18 0.512206 1 −8.2 ME 0803-1 203 296 1.99 0.717109 4 0.7128 5.6 15.5 0.22 0.512245 1 −8.1 MS 0735-2 323 112 8.41 0.730946 4 0.7135 7.5 36.8 0.12 0.512090 2 −9.3

87 86 Rb, Sr, Sm and Nd concentrations are given in ppm. ( Sr/ Sr)i and εNd(t) were calculated using the ages dated in this study from D to LG, 154 Ma for ME and 150 Ma for the MS. L.-X. Wang et al. / Lithos 206–207 (2014) 147–163 153

Foid number; Mg2+ /(Mg2++Fe*) × 100, with Fe* as Fe2+] of this rock type Syenite a ﬁ Foid is as high as 71. In the modi ed TAS diagram (Middlemost, 1994), Foidolite Syenite 12 Monzo- they plot in the gabbro and gabbroic diorite ﬁelds (Fig. 4a). When syenite plotted in a SiO2 against K2O diagram, these rocks lie at the boundary Foid Monzo- between high-K calc-alkaline and calc-alkaline series rocks (Fig. 4b). diorite Monzonite Quartz Their calculated differentiation index (D.I.) values (26–33, Table 1)

(wt%) Monzonite 8 Foid are similar to the average D.I. value of gabbros (30; Thornton and O Monzo-

2 Gabbro diorite Tuttle, 1960), much lower than that of the diorite (48) given by

Na Granite

+ Monzo- Thornton and Tuttle (1960).

O gabbro 2 The granitic rocks (granodiorite, biotite-bearing monzogranite K 4 and leucogranite) reveal a large variation of SiO2 from 65.2 to Granodiorite 75.1 wt.%. Their MgO concentrations are much lower than those of Diorite

Gabbro the diorites and decrease from granodiorites (1.68–1.94 wt.%) to Diorite Gabbroic leucogranites (0.1–0.5 wt.%). These rocks belong to the high-K calc- 0 alkaline series (Fig. 4b) and are peraluminous to strongly 40 50 60 70 80 peraluminous (Fig. 4c). Their D.I. values (67–95) are similar to the SiO2 (wt%) D.I. values for the granodiorite and granite given by Thornton and Tuttle (1960).Amafic enclave presenting in granodiorites falls into b the monzogabbro field in the modified TAS diagram (Fig. 4a). It is characterized not only by high MgO and FeO* similar to the diorite 5 (Table 1), but also by high K2OandNa2O similar to the felsic rocks (Fig. 4b). 4 Shoshonite series 4.1.2. Trace and rare earth elements (REE) (wt%)

3 Diorites are strongly enriched in siderophile elements (e.g., V, Cr, Co O 2 High K calc-alkaline series and Ni) and high field strength elements (e.g., Sc and Y). Conversely, the K 2 large ion lithophile elements (e.g., Rb and Cs) show an incompatible be- havior (Table 1). In the multielement diagram of trace elements, diorites Calc-alkaline series show negative anomalies for Nb and Ta but a weak negative peak for Sr 1 compared to their neighboring elements (Fig. 5a). Unlike the diorites, series Low K tholeiitic the felsic granitic rocks are relatively enriched in incompatible elements 0 (e.g. Rb and Cs) but depleted in compatible elements (e.g., Cr, Co and Ni; 40 50 55 60 65 70 75 Table 1). Negative Ba and Sr anomalies and a positive Rb anomaly are SiO2 (wt%) enhanced from GD to LG2 in the multielement diagram (Fig. 5b–d). Nb and Ta show strong negative anomalies in GD and BG, which are 2.5 c much less pronounced in LG1 and change into positive ones in most LG2 rocks. The mafic enclave displays different trace elemental patterns, showing negative anomalies for Th and Ta and positive ones for Rb and K(Fig. 5a). 2.0 Peraluminous Chondrite-normalized REE patterns for diorites are characterized by a slight enrichment of LREE over HREE (Fig. 6a). This effect increases Metaluminous from granodiorite to biotite-bearing monzogranite (Fig. 6b). However, 1.5 LG2 exhibits nearly flat REE patterns (Fig. 6d). Throughout the

ANK rock series, a negative Eu anomaly develops from diorites to granodiorites, intensiﬁes towards biotite-bearing monzogranites and two-mica leucogranites, and reaches the most pronounced in LG2 rocks 1.0 (Fig. 6a–d).

Peralkaline 0.5 4.2. Whole rock Sr and Nd isotopes 0.50 0.75 1.00 1.25 1.50 1.75

ACNK Diorites have relatively low 87Rb/86Sr ratios (0.31–0.40), (87Sr/ 86 Sr)i ratios (0.7080–0.7085) and εNd(t) values of − 4.3 to −4.8 Mafic enclave Biotite monzogranite (Table 2). In contrast, the granitic rocks (except LG2) have higher 87 86 – 87 86 – Diorite Two-mica leucogranite and variable Rb/ Sr (0.50 7.19) and ( Sr/ Sr)i ratios (0.7115 0.7184) and more negative εNd(t)valuesof−7.9 to −10.2. The Granodiorite Leucogranite dyke LG2 samples show extremely high 87Rb/86Sr ratios (83–201) and un- 87 86 reasonably low ( Sr/ Sr)i of 0.6179 to 0.6985. Such data may indicate that these rocks are influenced by the interaction with later fluids Fig. 4. Geochemical classification of the major rock units from Mufushan complex. (a) The total alkali (Na2O+K2O) vs. silica (SiO2) (TAS) diagram (Middlemost, 1994); (b) The K2O causing the loss of radiogenic Sr and/or the addition of Rb (e.g., Marks vs. SiO2 diagram with dividing curves from Peccerillo and Taylor (1976); (c) Alumina et al., 2003; Wu et al., 2000). However, the εNd(t) values of these LG2 saturation index shown by ANK vs. ACNK diagram (Maniar and Piccoli, 1989)ANK= samples (εNd(t) from −7.0 to −8.2) are similar to other felsic rocks. Al2O3 /(Na2O+K2O) (molar); ACNK = Al2O3 /(CaO+Na2O+K2O) (molar). In addition, the mafic enclave and a mica schist (Table 2) give a similar 87 86 ( Sr/ Sr)i ratios (0.7128 and 0.7135) and εNd(t) values (−8.1 and −9.3). 154 L.-X. Wang et al. / Lithos 206–207 (2014) 147–163

1000 ab1000 Diorite Granodiorite Mafic enclave 100 100 Biotite monzogranite

10 10

rock / primitive mantle rock / primitive mantle 1 1

0.1 0.1 Rb BaTh U K Ta Nb La Ce Sr Nd P Zr Hf SmTi Y Yb Lu Rb BaTh U K Ta Nb La Ce Sr Nd P Zr Hf SmTi Y Yb Lu

1000 1000 cd

Two-mica leucogranite 100 100 Leucogranite dyke

10 10

rock / primitive mantle 1 rock / primitive mantle 1

0.1 0.1 Rb BaTh U K Ta Nb La Ce Sr Nd P Zr Hf SmTi Y Yb Lu Rb BaTh U K Ta Nb La Ce Sr Nd P Zr Hf SmTi Y Yb Lu

Fig. 5. Primitive mantle normalized trace element diagrams (Sun and McDonough, 1989) for (a) diorites and maﬁc enclaves within granodiorites, (b) granodiorites and biotite-bearing monzogranites, (c) two-mica leucogranites and (d) leucogranite dykes.

4.3. Zircon U–Pb geochronology and Hf isotope data monzogranite sample (07MFS01-1; N 29°18.791′ E 113°40.130′)yield a weighted mean 206Pb/238U age of 148.3 ± 1.4 Ma (MSWD = 1.2; Zircons from a diorite sample (07MFS25-2; N 29°17.463′, Fig. 7c). One additional spot analyzed in the core of a zircon crystal E 113°44.051′) are mostly tabular, subhedral to euhedral and gives an inherited age of 849 ± 15 Ma. Twelve out of sixteen spot 150–300 μm in length, and are distinct relatively to zircons from analyses in zircons from the two-mica leucogranite sample other felsic granitic rocks. Cathodoluminescence imaging of these (07MFS18-1; N 29°13.518′ E113°52.905′) are concordant or nearly zircons displays relatively broad oscillatory zoning (Fig. 7a). These concordant and cluster as a single population, with a weighted zircons show high Th (508–8839 ppm) and U (669–5146 ppm) con- mean 206Pb/238U age of 145.8 ± 0.9 Ma (MSWD = 2.2; Fig. 7d). tents with Th/U ratios ranging from 0.68 to 2.07 (Supp. Table 2). This result agrees well with the previous study (146 Ma; Gilder Among 16 analytical spots, 11 are concordant or nearly concordant et al., 1996). The other 4 spot analyses plot below the concordia and cluster as a single population with a weighted mean 206Pb/238U and may be caused by partial lead inheritance. age of 154.0 ± 1.9 Ma (mean square of weighted deviates [MSWD] = The zircon Hf isotope data (Supp. Table 3; Fig. 8) imply similar com- 2.9). Five outliners, however, give slightly younger ages of approx. positional groups as indicated by the whole rock Sr and Nd isotope data. 146 Ma, which may reflect the effect of metamictization (e.g., Ji et al., The εHf(t) values of diorite zircons are relatively high varying from 2009). −2.41 to +0.59 (mean = −0.9; n = 25). Conversely, the Zircons from granodiorite, biotite-bearing monzogranite and two- εHf(t) values of the zircons from granodiorites, biotite-bearing mica leucogranite are generally euhedral and show dense oscillatory monzogranites and leucogranites largely overlap from −7.73 to zoning (Fig. 7b–d). They have crystal lengths of ~50–200 μm with −4.04, significantly lower than that of the diorites. length-to-width ratios from 2:1 to 3:1. Zircon from the granodiorite sample (07MFS13-1; N 29°09.409′, E 113°53.973′) shows variable U contents 5. Discussion (except for inherited cores) ranging from 1315 to 24319 ppm (Supp. Table 2). Nine out of twelve spot analyses of this sample give a weighted 5.1. Petrogenesis mean 206Pb/238U age of 151.5 ± 1.3 Ma. Two remaining data points lie below the concordia with large discordance (Fig. 7b), possibly caused 5.1.1. Mantle-derived diorite by partial lead loss. Another weakly zoned zircon gives a concordant Diorites of the MFSC show a typical gabbro differentiation index (30; 206Pb/238Uageof844±14Mainthecore,reflecting an inherited zircon Thornton and Tuttle, 1960), high Mg # (67–71), and high contents of age. Sixteen spot analyses in zircons from the biotite-bearing Cr (490–662 ppm), Ni (205–233 ppm) and V (190–305 ppm), requiring L.-X. Wang et al. / Lithos 206–207 (2014) 147–163 155

1000 ab1000 Diorite Granodiorite Mafic enclave Biotite monzogranite 100 100

10 10 rock/chondrite rock/chondrite

1 1

0.1 0.1 La Ce Pr Nd Sm Eu Gd Tb Dy Ho Er Tm Yb Lu La Ce Pr Nd Sm Eu Gd Tb Dy Ho Er Tm Yb Lu

1000 1000 cd

Two-mica leucogranite 100 100 Leucogranite dyke

10 10 rock/chondrite rock/chondrite

1 1

0.1 0.1 La Ce Pr Nd Sm Eu Gd Tb Dy Ho Er Tm Yb Lu La Ce Pr Nd Sm Eu Gd Tb Dy Ho Er Tm Yb Lu

Fig. 6. Chondrite normalized rare earth element (REE) diagrams (McDonough and Sun, 1995) for (a) diorites and maﬁc enclaves enclosed in granodiorites, (b) granodiorites and biotite- bearing monzogranites, (c) two-mica leucogranites and (d) leucogranite dykes.

asigniﬁcantly more maﬁc source than typical diorites (Mg # = 34–42; 5.1.2. Fractionation and magma mixing of the granitic rocks Cr = 35; Ni = 20; Kelemen, 1995; Taylor and Mclennan, 1985). Their The bulk Sr and Nd and zircon Hf isotopic signatures of the granitic high Mg# and the high amounts of Cr, Ni and V are similar to Archaean rocks of the MFSC are different from those of the diorites (Table 2 & high-Mg diorites in the Superior Province of North America (Shirey and Supp. Table 3), which preclude a model that felsic granitic rocks are Hanson, 1984) and Miocene high-Mg andesites (sanukites) from the simply derived by magma differentiation from the dioritic magma. Setouchi volcanic belt of Japan (Fig. 9a&b, Ishizaka and Carlson, 1983; The bulk rock Sr and Nd isotope data of the MFSC granitic rocks are Martin et al., 2005), which were interpreted as being derived from a hy- similar to those of mica schist country rocks and Mesozoic granitic drousmantleperidotite(Tatsumi and Ishizaka, 1982). Isotopically, their rocks in the Middle Yangtze region (Fig. 9c). This implies that the εNd(t) values of around −4.5 is lower than the common depleted felsic granitic rocks (granodiorite, biotite-bearing monzogranite MORB mantle (Zindler and Hart, 1986). This implies that the diorites and two-mica leucogranite) originated from a common (at least of the MFSC might be generated by: (1) melting of an enriched mantle partly) crustally-derived magma which can be further supported

(2) melting of less enriched or even depleted mantle followed by crustal by the high SiO2 and K2O and low MgO, Cr and Ni concentrations of contamination (Yang et al., 2008). these rocks. Meanwhile, fractional crystallization processes in the Cretaceous mafic rocks from the lower Yangtze Craton display an felsic granitic rocks seem likely, based on (i) negative correlations total enriched-mantle affinity (Chen et al., 2001; Li et al., 2008; Q. Wang of Al2O3,CaO,MgO,TiO2 and FeO with SiO2 (Fig. 10), (ii) positive et al., 2006; Wang et al., 2004; X.L. Wang et al., 2006; Xie et al., 2006; correlations of total alkalies with SiO2, (iii) correlations of trace ele- Yan et al., 2008). Chen et al. (2001) demonstrated an enriched and ments such as Cr and Ni with SiO2 (Fig. 9a) and (iv) decreasing zircon highly heterogeneous mantle with a varying εNd(t) from − 1.8 ages with increasing bulk SiO2 concentrations of the three rock- to −9.3 based on the isotopic compositions of the maficrocksin types. Considering that the granitic rocks are temporally later than the southeastern China. Yan et al. (2008)proposed that the mantle diorites, it is likely that the mantle-derived magma, which was in the Lower Yangtze region was metasomatized by slab-derived emplaced as diorite acted as a heat source beneath the crust and trig- fluids/melts, given the 87Sr/86Sr(t) (0.7056 to 0.7071) and gered partial melting of the middle to lower crust and resulted in the εNd(t) values (− 5.3 to −8.3) for the Cretaceous maficrocks.The formation of felsic magmas. Sr–Nd isotopic results of diorites in MFSC (87Sr/86Sr(t) = 0.7080– We performed thermodynamic modeling on major elements using 0.7085; εNd(t) = −4.3 to −4.8) are similar to these data (Fig. 9c) the MELTS program (Ghiorso and Sack, 1995) in order to evaluate po- and might therefore indicate that they are likely derived from an tential fractional crystallization processes in the felsic magmatism. For enriched mantle source. these calculations, the granodiorite sample with the highest MgO 156 L.-X. Wang et al. / Lithos 206–207 (2014) 147–163

180 180 0.028 a Diorite 0.028 b Granodiorite

Mean =154.0± 1.9Ma 170 170 MSWD =2.9, n=11 Mean =151.5± 1.3Ma 0.026 0.026 MSWD =0.82, n=9 160 160 U U 0.024

238 0.024 238 150 150 Pb/ Pb/ 206 206 0.022 140 0.022 140

130 130 0.020 0.020

120 120 0.018 0.018 0.12 0.14 0.16 0.18 0.20 0.12 0.14 0.16 0.18 0.20 207Pb/235U 207Pb/235U

0.032 200 180 0.028 c Biotite Monzogranite d Two-mica Leucogranite 0.030 170 Mean =148.3± 1.4Ma 0.026 180 MSWD =1.2, n=16 0.028 160 U U 0.024 0.026 238 150 238 160 Pb/ Pb/ 0.024 206 206 0.022 140 0.022 140 130 0.020 0.020 Mean =145.8± 0.9Ma 120 120 MSWD =2.2, n=12 0.018 0.018 0.12 0.14 0.16 0.18 0.20 0.12 0.14 0.16 0.18 0.20 0.22 207Pb/235U 207Pb/235U

Fig. 7. Representative cathodoluminescence images and U–Pb Concordia diagrams for zircons from (a) diorite; (b) granodiorite; (c) biotite-bearing monzogranite and (d) two-mica leucogranite.

concentrations and lowest SiO2 contents (sample 0723-1; Table 1)was amaﬁc magma and crustal-derived melts is suggested. Assuming used as the starting composition. As initial conditions we used a range in that dioritic magma and monzogranitic magma are two end- oxygen fugacity (QFM to QFM + 1), water contents (1–5wt.%)and members, the magma mixing process is modeled using selected pressure (1–5 kbar). The liquidus temperature (900–1000 °C) was trace elements (Fig. 11). The results indicate that around 70% calculated by the program. Selected results for the evolution of melt monzogranitic magma and 30% dioritic magma are needed composition during fractional crystallization are shown in Fig. 10. to form the granodioritic magma. The mixing process is also sup-

The evolution of MgO and TiO2 contents closely matches the ported by the following ﬁeld and isotopic observations: (1) grano- whole rock data, when modeled with a pressure of 2 kbar, a water diorites are spatially close to the diorites and contain maﬁc content of 2 wt.% and fO2 at QFM + 1, in which crystallizations of enclaves; (2) granodiorites have a slightly higher εHf(t) value amphibole, biotite, muscovite, feldspar and quartz are considered. than biotite-bearing monzogranite and two-mica leucogranite

However, CaO, Al2O3,Na2O, K2OandFeOdeviatefromtheobserved (Fig. 8). Apart from magma mixing, the felsic magma might also rock compositions especially for the high-SiO2 samples. These dis- be inﬂuenced by assimilation of crustal material as suggested by crepancies could be due to the limitations of the MELTS program the slightly decreasing Nd isotope compositions with increasing when applied to granitoid rocks (Kessel et al., 1998), or might indi- bulk SiO2 contents (Fig. 12). However, because of the relatively cate that besides fractional crystallization, magma mixing and/or small differences in the Sr and Nd isotopic compositions and the ab- country rock assimilation are also involved during the evolution of sence of isotopic data for a potential lower crustal endmember con- the felsic rocks. taminant, further modeling on the possible assimilation is out of Variation diagrams for high ﬁeld strength elements, such as Zr, Hf, Nb the scope of this study. and Ta, and REE (Fig. 11) show that the biotite-bearing monzogranites, two-mica leucogranites and leucogranite dykes are primarily affected 5.1.3. MFSC leucogranite vs. Himalayan leucogranite by fractional crystallization whereas the granodiorites generally fall The Himalayan leucogranites are characterized by high SiO2 and between the trends of fractional crystallization and magma mixing Al2O3 and incompatible elements such as Rb, Ta, and Cs but depleted (with dioritic magma). Therefore, a certain extent of mixing between in CaO, Ba and Sr (e.g., Deniel et al., 1987; Harris and Inger, 1992). L.-X. Wang et al. / Lithos 206–207 (2014) 147–163 157

Zircon U-Pb Age (Ma) 140 145 150 155 160 165 -8 -6 -4 -20 2

Mean = 145.8±0.9 Ma Mean = -6.12±0. 31 Two-mica MSWD = 2.2,n=12 leucogranite n=25

Mean = -6.13±0. 33 Biotite Mean = 148.3±1.4 Ma n=19 monzogranite MSWD=1.2,n=16

Mean = 151.5±1.3 Ma MSWD=0.8,n=9 Mean = -5.55±0. 58 Granodiorite n=16

Diorite Mean = -0.92±0. 34 Mean = 154±1.9 Ma n=25 MSWD = 2.9,n=11

Fig. 8. Weighted average 206Pb/238U ages and initial 176Hf/177Hf ratios of zircons from two-mica leucogranite, biotite-bearing monzogranite, granodiorite and diorite in Mufushan Complex.

Similarly, leucogranites of the MFSC are high in SiO2, Rb, Ta and Cs and high fractionation could be another mechanism to form leucogranitic are strongly depleted in CaO, Ba and Sr (Fig. 13; Table 1). Although magmas. lower than other associated granitic rocks, the Al2O3 contents of the leucogranites are comparable to those of the Himalayan leucogranites 5.2. Timescale of magma differentiation (N14%). Vidal et al. (1984) showed that the Himalayan leucogranites gener- Zircons from diorite, granodiorite, biotite-bearing monzogranite and ally have lower Th/U ratios (0.2–1.4) compared to common igneous two-mica leucogranite are crystallized at 154.0 ± 1.9 Ma, 151.5 ± rocks (3–5). However, Deniel et al. (1987) observed highly variable 1.3 Ma, 148.3 ± 1.4 Ma and 145.8 ± 0.9 Ma, respectively, implying a de- Th/U ratios (0.2–8). The MFSC leucogranites also show variable creasing trend from diorites towards two-mica leucogranites (Fig. 8). Th/U ratios (0.8–9) that are generally lower than other associated These results are consistent with previous K–Ar and Rb–Sr dating data granitic rocks (4–12; Table 1), particularly for LG2 (1–2.7). The (170–134 Ma; Hunan Institute of the Geological Survey) and zircon strongly negative Eu anomalies of MFSC leucogranites are also in U–Pb isotopic age (146 Ma) of the two-mica leucogranite by Gilder good agreement with the Himalayan leucogranites (e.g., Deniel et al. (1996) and indicate that the magma chamber for the MFSC was et al., 1987). potentially active for about 8 Ma. The estimated crystallization temperatures for the MFSC leucogranites However, in situ zircon Hf isotope data suggest that the diorite orig- based on zircon saturation thermometry (Harrison and Watson, inated from a relatively depleted source compared to the felsic granitic 1983; Watson and Harrison, 1983) range between 654 and 715 °C rocks (Fig. 8). Considering its earlier emplacement than other lithologi- except for LG2 which shows much lower temperature (567– cal units, we suggest that the diorites might represent more or less 588 °C; Table 1), similar to the calculated temperature (680 °C) for primitive basaltic magmas derived from the upwelling lithospheric average compositions of High Himalayan two-mica leucogranites mantle, and such mantle-derived magmas are believed to have (Ayres and Harris, 1997; Zhang et al., 2004). Experimental studies been extensively underplating beneath South China crust at the imply that muscovite breaks down at 720–770 °C, and at pressures Late Mesozoic (e.g., Jiang et al., 2008). Conductive heat transport of of 5–10 kbar (Douce and Harris, 1998; Petö, 1976), whereas at these maﬁc magmas triggered crustal anatexis resulting in the 4 kbar the thermal stability of muscovite drops to b700 °C (Scaillet formation of the felsic granitic rocks of the MFSC. The similarity of et al., 1995). Thus, we suggest that the pressure conditions for the zircon Hf isotopes and whole rock Sr and Nd isotopic data for the MFSC leucogranite are b5 kbar, consistent with the modeled felsic granitic rocks (Fig. 9c) suggests a very similar source for magmatism condition by MELTS (2 kbar). these rocks. The decreasing trend of zircon U–Pb ages from granodi- Overall, the MFSC leucogranites are similar to the Himalayan orites towards leucogranites further indicates that fractional crystal- leucogranites particularly in terms of their geochemical compositions. lization lasted for around 6 Ma. The Himalayan leucogranites are typically generated by low degree ThelargeextentrangeofzirconU–Pb ages and their strikingly melting of metasediments or middle crust, however, the MFSC decreasing trend with increasing silica make it possible to constrain leucogranites are the evolved products of prolonged differentiation of the timescale of magma differentiation before intrusion. Previous granitic magmas as particularly evidenced by the REE tetrad effect of estimates of evolution timescale from intermediate to acid, or LG2 (Fig. 6d; Wu et al., 2004 and references therein). This implies that from maﬁc to intermediate magmas in volcanic systems generally 158 L.-X. Wang et al. / Lithos 206–207 (2014) 147–163

10000 a ca. 1.5 Ma time period (42.4–40.9 Ma) for the evolution from gabbro Continental to granodiorite in Adamello batholiths, northern Italy. Additionally, lithospheric – 1000 mantle Walker et al. (2007) demonstrateda~2Ma(17.4 15.3 Ma) history for the Spirit Mountain batholiths (U.S.). Matzel et al. (2006) Upper investigated a plutonic complex with a volume of N1400 km3 and 100 Crust Hig-Mg obtained a crystallization timescale of over ca. 5.4 Ma based on zir- Andesite con U–Pb dating. Although quantitative data of the magma volume

Ni (ppm) 10 and evolution time are lacking, the MFSC rocks record a ~6 Ma Lower time period of magma differentiation from granodiorite to two- Crust mica leucogranite in the N2400 km2 outcrops. This might imply 1 that a large magma body is essential for a prolonged differentiation and crystallization. 0.1 1 10 100 1000 10000 5.3. Geodynamic implications Cr (ppm) Our geochronological data for the MFSC, together with recent zircon 80 b ages for other granitic plutons in the adjacent regions (Jiang et al., 2009; Li et al., 2005, 2009; Zhang and Ma, 2008) suggest that strong magmatic activities are present in the Middle Yangtze region (Fig. 1) at Middle 70 Hig-Mg Jurassic to Early Cretaceous (180–142 Ma). Wang et al. (2007) demon- Andesite strated that the Triassic (250–205 Ma) peraluminous granites from the Middle Yangtze region are formed by collision-related radiogenic 60 Diorite heating and subsequent dehydration melting of the crust, which is sim- Granodiorite SiO2 (wt%) Biotite granites ilar to the interpretation for Himalayan leucogranites. However, the au- Two-mica leucogranite thors also proposed that lithospheric extension has already developed 50 Leucogranite dyke in Yangtze region after ca. 175 Ma (e.g., Wang et al., 2003). Therefore, Mafic enclave Mica schist it is unlikely that the Middle Jurassic to Early Cretaceous granitic rocks in the Middle Yangtze region were formed in a syn-collisional setting. 40 Li et al. (2009) interpreted the late Jurassic to early Cretaceous granitic 10 30 50 70 rocks in Daye region by lithospheric extension, whereas Jiang et al. Mg number (2009) stressed that the late Jurassic felsic and maﬁcrocksinsouthern 10 Hunan are caused by the formation of an intra-arc rift along Shi-Hang c zone in consequence of the roll-back of subducted Palaeo-Paciﬁc slab. Cenozoic basalts Based on the presence of A-type granites, shoshonites, alkaline basalts, 5 from Cathaysia Block K-rich diorites and metamorphic core complexes in the Middle Yangtze, a consensus has been reached on the extension setting for this region at 0 Middle Jurassic to Early Cretaceous (Jiang et al., 2009; Li et al., 1999, Cretaceous mafic rocks 2009; Wang et al., 2003). from Lower Yangtze craton

(t) Indeed, these Middle Jurassic to Early Cretaceous granitic rocks spa-

Nd -5 Mesozoic granitoids

ε tially form a NE-/NEE-striking granitoid belt (Fig. 1)intheMiddle from Middle Yangtze region Yangtze region, which is parallel to the widespread NE-/NEE-fault -10 in Cathaysia Block and consistent with the distributions of the con- temporaneous granitic rocks in the Cathaysia Block as well as the vo- Cretaceous luminous Cretaceous granitic rocks in the coastal region (Fig. 1; Zhou -15 A-type granitoids and Li, 2000 and references therein). Thus, we favor a model where from Lower Yangtze region these granitic rocks were mainly formed in an extensional tectonic -20 setting related to the northwestward subduction of the Paleo- 0.700 0.705 0.710 0.715 0.720 0.725 0.730 0.735 Pacific plate. 87 86 However, whether or not the subducted slab can reach the ( Sr/ Sr)i hinterland of South China (e.g., Hunan province) is highly debated (e.g., Jiang et al., 2009; Li and Li, 2007; Wang et al., 2007; Zhou and Fig. 9. (a) Ni vs. Cr diagram showing the origin of diorite and the fractional crystallization – trend of felsic granitic rocks. The data for upper and lower crust and continental litho- Li, 2000). Zhou and Li (2000) implied that the 800 1000 km Meso- spheric mantle are from Wedepohl (1995) and McDonough (1990), respectively. The zoic igneous rock belt in southeastern China is genetically related to high-Mg andesite field is modified after Tatsumi and Ishizaka (1982). (b) Mg-number Paleo-Pacific plate subduction. Li and Li (2007) further suggested fi fi vs.SiO2 diagram. The high-Mg andesite eld is modi ed after Tatsumi and Ishizaka that the orogenic front related to subduction by late Triassic (1982).(c)εNd(t) vs. initial 87Sr/86Sr diagram for samples from the Mufushan complex, in comparison with isotopic data for Cenozoic basalts from Cathaysia Block (Zou et al., (ca. 210 Ma) can propagate 1300 km away from the trench locality 2000), Cretaceous mafic rocks of the Lower Yangtze craton (Yan et al., 2008), Mesozoic which has already arrived the Yangtze block. Conversely, Wang granitic rocks in central Hunan province (Wang et al., 2005) and Cretaceous A-type et al. (2007) argued that the Triassic magmatisms in northern granitic rocks of the LowerYangtze craton (Chen et al., 2001). Hunan were caused by the collision between the South China Block and the North China Block. More recently, Jiang et al. (2009) pointed out that the presence of late Jurassic Daoxian basalts, Guiyang lamprophyres and Jinjiling and Xishan A-type granites pro- show short residence time periods of tens of thousand years vided evidence for the long-distance subduction of Pacificplate (e.g., Chekol et al., 2011; Reagan et al., 2003). Conversely, ap- which might arrive as far as Shi-Hang zone in southern Hunan proaches on timescale of magma evolution in plutonic batholiths (Fig. 1). Our new data of the late Jurassic high-Mg diorites and are much longer. For example, Schaltegger et al. (2009) reported a other associated felsic granitic rocks in MFSC confirmed the L.-X. Wang et al. / Lithos 206–207 (2014) 147–163 159

a b 2.0 0.6

1.5 0.4 (wt%)

1.0 2 TiO MgO (wt%) 0.2 0.5

0.0 0.0 66 68 70 72 74 76 78 66 68 70 72 74 76 78 SiO2 (wt%) SiO2 (wt%)

18 c d 4 (wt%)

16 3 3 O 2

Al 2

14 CaO (wt%) 1

12 0 66 68 70 72 74 76 78 66 68 70 72 74 76 78

SiO2 (wt%) SiO2 (wt%)

6 e

QFM, 2 wt% H2O, 2kbar 4 QFM+1, 2 wt% H2O, 2kbar (wt%)

QFM+1, 2 wt% H2O, 5kbar total QFM+1, 3 wt% H2O, 2kbar

FeO 2

0 66 68 70 72 74 76 78

SiO2 (wt%)

total Fig. 10. Selected major element data for rocks of the Mufushan complex plotted against SiO2 (Harker diagrams). (a) MgO (b) TiO2 (c) Al2O3 (d) CaO (e) FeO . Modeling lines for fractional crystallization were calculated by MELTS (Ghiorso and Sack, 1995). Symbols as in Fig. 9.

hypothesis by Jiang et al. (2009) and provide new evidence for the of several million years. The two-mica leucogranites, which are the most long-distance subduction of the palaeo-Pacific plate into the hinter- SiO2-rich residual melts formed by fractionation crystallization, are land of South China. compositionally similar to the classic Himalayan leucogranites. This implies that prolonged fractional crystallization could be another feasible 6. Conclusions mechanism to form leucogranitic magmas apart from dehydration melting of metasediments in middle to lower crust. The middle Jurassic Zircon dating of rocks from the Mufushan complex implies a de- to early Cretaceous magmatism in Middle Yangtze region indicates that creasing trend of zircon U–Pb ages from high-Mg diorites through the subduction effects of the palaeo-Pacific plate can far reach the hin- granodiorites and biotite-bearing monzogranites to two-mica terland of South China. leucogranites (from 154 Ma to 146 Ma). Whole rock Sr–Nd and zircon Hf isotopes imply that the diorite originated from enriched upper man- Acknowledgments tle material, whilst the granitic rocks originated from a common crustally-derived source. Elemental geochemical data indicate a contin- Yong-Sheng Liu, Fu-Yuan Wu and Rui-Chun Duan are acknowledged uous evolution from granodiorite towards leucogranites dominated by for their help during zircon U–Pb dating, and zircon Hf isotope and fractional crystallization. This felsic magmatism lasted for about 6 Ma, whole rock Sr–Nd isotope analyses. Special thanks to Yuan-Yuan Liu, which indicates that magma differentiation, intrusion and subsequent Jin-Song Liu, Yan Wang and Hui-Juan Zou for their help in the field cooling and solidification in giant batholiths may proceed on a timescale work. Gregor Markl is acknowledged for the helpful improvement of 160 L.-X. Wang et al. / Lithos 206–207 (2014) 147–163

200 Assumed Anatectic Magma b a Fractional crystallization (FC) 5 150 10% 4 30% Mixing with dioritic magma 100 50% 3 Zr (ppm) Hf (ppm)

50 2

0 1 50 60 70 50 60 70 SiO2 (wt%) SiO2 (wt%)

c d 4 15

3 10 2 Nb (ppm) Ta (ppm) 5 1

0 0 50 60 70 50 60 70 SiO2 (wt%) SiO2 (wt%)

60 e 2.0 f

1.5 40

1.0 La (ppm) Eu (ppm) 20 0.5

0 0.0 50 60 70 50 60 70

SiO2 (wt%) SiO2 (wt%)

Fig. 11. Selected trace element contents vs. SiO2 contents showing the effects by fractional crystallization and magma mixing. (a) Zr (b) Hf (c) Nb (d) Ta (e) La (f) Eu. The monzogranite (sample 0701-1) is used as the initial composition for magma mixing modeling. Symbols as in Fig. 9. this manuscript. We are also very grateful for the detailed reviews by Nature Science Foundation of China (grants 41272079, 90814004 and Stefan Jung and another anonymous reviewer as well as for the editorial 40334037) and China Geological Survey (grant 1212011121270). The handling by Nelson Eby. This study is ﬁnancially supported by the China Scholarship Council program (2010641006) is also appreciated for providing scholarships to the ﬁrst author.

-4 Appendix A. Supplementary data

-6 Supplementary data to this article can be found online at http://dx. doi.org/10.1016/j.lithos.2014.07.026.

(t) -8 Nd ε References

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