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Authors requiring further information regarding Elsevier’s archiving and manuscript policies are encouraged to visit: http://www.elsevier.com/authorsrights Author's personal copy Journal of Asian Earth Sciences 72 (2013) 178–189 Contents lists available at SciVerse ScienceDirect Journal of Asian Earth Sciences journal homepage: www.elsevier.com/locate/jseaes Delineation of the ca. 2.7 Ga TTG gneisses in the Zanhuang Complex, North China Craton and its geological implications ⇑ Chonghui Yang a, , Lilin Du a, Liudong Ren a, Huixia Song a, Yusheng Wan a,b, Hangqiang Xie a,b, Yuansheng Geng a a Institute of Geology, Chinese Academy of Geological Sciences, Beijing 100037, China b Beijing SHRIMP Center, Beijing 100037, China article info abstract Article history: Through detailed studies we have delineated a suite of banded TTG gneisses from the Zanhuang Complex. Available online 16 October 2012 The protolith of the gneisses, predominantly tonalite, has undergone intensive metamorphism, deforma- tion and anatexis and in a banded structure is intimately associated with melanocratic dioritic gneiss and Keywords: leucocratic trondhjemitic veins. SHRIMP Zircon U–Pb data show that the tonalite was formed ca. TTG gneisses 2692 ± 12 Ma ago. The tonalitic gneiss has the features of high SiO2 (67.76–73.31%), high Al2O3 (14.38– ca. 2.7 Ga 15.83%), rich in Na2O (4.48–5.07%) and poor in K2O (0.77–1.93%). The gneiss is strongly fractioned in Geochemistry REE ((La/Yb) = 12.02–24.65) and shows a weak positive Eu anomaly (Eu/Euà = 1.05–1.64). It has high Zanhuang Complex N contents of Ba (199–588 ppm) and Sr (200–408 ppm), low contents of Yb (0.32–1.00 ppm) and Y North China Craton (3.41–10.3 ppm) with high Sr/Y ratios (21.77–96.77) and depletion in HFSE Nb, Ta and Ti. These charac- teristics are similar to those of the high-Si adakitic rocks. The melanocratic dioritic gneiss has low SiO2 (59.81%), high MgO (6.34%), high Al2O3 (14.02%) contents, rich in Na2O (3.7%) and poor in K2O (1.79%), with high Mg index (Mg# = 67). REE and trace elements are on the whole similar to that of the tonalitic gneiss, but compatible element abundances V (116 ppm), Cr (249 ppm), Co (37 ppm) and Ni (179 ppm) are higher. The leucocratic felsic bands (approximating trondhjemite in composition) have major oxides similar to that of the TTG gneisses but the REE and compatible elements are extremely low, which are indicative of the products of anatexis. The tonalitic gneiss has positive eNd(t) (2.37–3.29) and low initial Sr (0.69719–0.70068) values with depleted mantle Nd model age of ca. 2.8 Ga, suggesting its generation from partial melting of mantle-derived juvenile crust. The dioritic gneiss was also derived from subduc- tion environment, but has undergone significant metasomatism of mantle wedge. The delineation of the ca. 2.7 Ga TTG gneisses in the Zanhuang Complex further proves that the North China Craton experienced large-scale continental crustal accretion in early Neoarchean, and gives new constraints on the subdivi- sion of the early blocks and greenstone belts of the craton. Ó 2012 Elsevier Ltd. All rights reserved. 1. Introduction et al., 1992; Jahn et al., 1998), the Pilbara and Yilgarn Cratons in Western Australia (Nelson, 1997; Bateman et al., 2001; Rasmussen ca. 2.7 Ga tectonothermal events have been recorded world- et al., 2005; Said et al., 2010), the Kaapvaal and Zimbabwe Cratons wide from the Archean Cratons, e.g. the Superior Craton in southern Africa (Kröner et al., 1999; Matthew et al., 1999; Poujol (Beakhouse et al., 1999; Henry et al., 2000; Polat and Kerrich, et al., 2003; Hofmann et al., 2004; Taylor et al., 2010), and the 2000, 2002; Percival et al., 2001; Polat and Münker, 2004), the Dharwar Craton in India (Nutman et al., 1996; Manikyamba and Wyoming Craton (Carlson and Irving, 1994; Rino et al., 2004), the Kerrich, 2011). The ca. 2.7 Ga events are recognized as a large-scale western Canada Shield (Wyman, 1999; Sandeman et al., 2006) tectonothermal event in the Earth’s history, responsible for the ra- and the southern West Greenland Craton (Friend et al., 1996; pid accretion of the continental crust in a short time span, mani- Thrane, 2002; Steenfelt et al., 2005; Friend and Nutman, 2005; festing the formation of voluminous extrusive and intrusive rocks Polat et al., 2010) in North America, the Baltic Shield in Europe (Condie, 2000; Condie et al., 2009; Condie and Aster, 2010; Barley (Bibikova et al., 2005; Balagansky et al., 2011; Heilimo et al., et al., 2005; Zhai and Santosh, 2011; Wan et al., 2011a). In the 2011; Mikkola et al., 2011) and the Aldan Shield in Siberia (Nutman North China Craton (referred to as NCC hereafter), the most distin- guished magmatic event was at ca. 2.5 Ga, as also recorded in the Pilbara Craton, the Dharwar Craton, the West Greenland Craton ⇑ Corresponding author. Tel.: +86 10 68999708; fax: +86 10 68997803. as well as in the East Antarctic Shield (Jayananda et al., 2000; Shen E-mail address: [email protected] (C. Yang). 1367-9120/$ - see front matter Ó 2012 Elsevier Ltd. All rights reserved. http://dx.doi.org/10.1016/j.jseaes.2012.09.031 Author's personal copy C. Yang et al. / Journal of Asian Earth Sciences 72 (2013) 178–189 179 et al., 2005; Condie et al., 2009; Nutman et al., 2010; Wan et al., Group in the northwest, are in tectonic contact with the Guandu 2011b). Though well-manifested in the xenocrystic/inherited or Group in the east, while in the southwest the boundary has not detrital zircon U–Pb data and Hf model ages of the North China yet been delineated due to discontinuous outcroups (Fig. 1). The Craton (Shen et al., 2005; Geng et al., 2011), the ca. 2.7 Ga event banded gneisses consist mainly of tonalitic gneiss and melanocrat- is discerned there merely in a few areas within the craton, e.g. ic dioritic gneiss with common occurrence of amphibolite enclaves. the western Shandong terrane (Cao, 1996; Zhuang et al., 1997; This suite of gneisses is distinguished by the development of leuc- Jahn et al., 1988; Du et al., 2003, 2010; Lu et al., 2008; Wang ocratic felsic bands which can be subdivided into two generations. et al., 2009; Wan et al., 2011b), the Jiaodong–Qixia region (Jahn Bands of the earlier generation are parallel to the foliation, 1–2 cm et al., 2008) in Shandong Province and the Huoqiu area in northern in width, dominated by fine-grained plagioclase and quartz Anhui Province (Wan et al., 2010). In the Fuping Complex, Taihang (Fig. 2a); bands of the later generation are wider, 5–20 cm, lying Mts., enclaves of ca. 2.7 Ga hornblende gneiss are found in the TTG generally parallel to, but locally discordant to, the foliation gneisses (Guan et al., 2002), and in Lushan county in western He- (Fig. 2b), composed mainly of medium-to-coarse-grained plagio- nan Province, vestiges of the earlier ca. 2.8 Ga magmatism have clase and quartz. In most cases the bands have straight boundaries been recorded (Kröner et al., 1988; Sun et al., 1994; Liu et al., (Fig. 2a) but sometimes sigmoidal folds occur (Fig. 2c). The bands 2009a; Diwu et al., 2010). Other Archean TTG gneisses of the are heterogeneously distributed and where least developed more NCC are predominantly at 2.5–2.6 Ga. In this paper we delineate protolith features are preserved (Fig. 2d and e). well-exposed ca. 2.7 Ga banded TTG gneisses from the Zanhuang The samples collected are as follows: Z07-6 (Fig. 2e), Z09-1 Complex of the central NCC (Fig. 1). On the basis of petrographical, (Fig. 2d), Z87-1 (Fig. 2f) and Z88-1 (Fig. 2g) for banded tonalitic geochemical, zircon SHRIMP dating and Sr–Nd isotope studies, we gneiss; Z88-4 (Fig. 2g and h) for melanocratic dioritic gneiss, discuss the formation age, magma source, origin and dynamic set- Z88-2 for fine-grained gneissic trondhjemitic veins (Fig. 2g) and ting of the TTG gneisses in an attempt to give new constraints on Z88-3 for medium-coarse-grained trondhjemitic (granitic) veins the basement subdivision and tectonic evolution of the NCC. (Fig. 2g). The banded tonalitic gneiss (samples Z07-6, Z09-1, Z87-1 and Z88-1) is gray, medium-grained and granoblastic in texture. Major 2. Regional geology minerals are biotite, plagioclase and quartz, with minor epidote, muscovite and chlorite, accessory zircon, apatite and magnetite. The Zanhuang Complex occurs in the southern Taihang In some samples, quartz grains are rectangularly shaped and dis- Mountains and belongs to the middle eastern segment of the tributed like ribbons, suggesting static recrystallization after Trans-North China Orogen as delineated by Zhao et al. (2005). mylonitic quartz ribbons. The complex is mainly composed of deformed and metamorphosed Dioritic gneiss (Z88-4) is banded, or lenticular in occurrence and early Precambrian TTG gneisses, monzonitic and potassic granite, in intimate association with tonalitic gneiss (Fig.