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Discovery of Hadean–Mesoarchean Crustal Materials in the Northern

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Discovery of Hadean–Mesoarchean Crustal Materials in the Northern Precambrian Research 271 (2015) 118–137 Contents lists available at ScienceDirect Precambrian Research jo urnal homepage: www.elsevier.com/locate/precamres Discovery of Hadean–Mesoarchean crustal materials in the northern Sibumasu block and its significance for Gondwana reconstruction ∗ Gongjian Li, Qingfei Wang , Yuhan Huang, Fuchuan Chen, Peng Dong State Key Laboratory of Geological Processes and Mineral Resources, China University of Geosciences, Beijing 100083, China a r t i c l e i n f o a b s t r a c t Article history: The micro-continental blocks in SE Asia are thought to be derived from the East Gondwana which has a Received 28 June 2015 basement as old as Hadean–Mesoarchean. However, such old crustal materials have not been found any- Received in revised form where in SE Asia. In this paper, we report the occurrence of the Hadean–Mesoarchean crustal materials 25 September 2015 in the northern Sibumasu block, SW China. Our finding is based on inherited zircon U–Pb ages and Hf Accepted 7 October 2015 isotope model ages of co-magmatic zircon crystals from early-Paleozoic S-type granitoids in the north- Available online 17 October 2015 ernmost Sibumasu. LA-ICP-MS zircon U–Pb isotopic analysis reveals that some S-type granitoids in this region formed between 468 Ma and 447 Ma. These rocks are strongly peraluminous, with high A/CNK Keywords: ratios > 1.2 and normative corundum content >2 wt%, and have low CaO/Na2O ratios <0.3, which indi- Hadean crust cates that they formed by anatexis of metapelitic crustal rocks. The ca. 470–450 Ma S-type granitoids Zircon age ∼ ε Zircon Hf isotopes contain inherited zircon crystals as old as Mesoarchean ( 3.1 Ga). The Hf(t) values of zircon crystallized − − − Palinspastic reconstruction from the magmas of these rocks vary from 49 to +16, with major peaks approximately at 46, 35 Sibumasu and −27. The corresponding model ages for the formation of the source crust are ∼4.39 Ga, ∼3.62 Ga and Gondwana ∼ 3.12 Ga. This, together with the discovery of ∼3.1 Ga inherited zircon in the granitoids, indicates that the northern Sibumasu block has Hadean–Mesoarchean crustal materials. A Gondwana-wide comparison of crustal formation time data reveals that these Hadean–Mesoarchean crustal materials show similar age distribution with the crusts of the Pilbara and Yilgarn Cratons, Western Australia. Their derivation analysis provides a new line of evidence for the majority view that the Sibumasu block was attached to NW Australia before its breakup from Gondwana. © 2015 Elsevier B.V. All rights reserved. 1. Introduction and Torsvik, 2013) and many other researchers (e.g., Ueno, 2003; Metcalfe, 2006, 2013; Ferrari et al., 2008) proposed that the Sibu- The mainland SE Asia is a collage of micro-continental blocks, masu block was an integral constituent of East Gondwana until volcanic arcs, and suture zones that contain the remnants of the the opening of the Meotethys Ocean in the Early Permian. Despite Tethyan Oceans. These continental blocks rifted from East Gond- decades of deliberation based on results from multi-disciplinary wana and subsequently accreted to the Eurasia in the Paleozoic studies such as paleomagnetics (Ali et al., 2013; Xu et al., 2015), and Mesozoic (e.g., Metcalfe, 2006, 2011; Cocks and Torsvik, 2013). faunal/floral distribution (Burrett et al., 1990; X.D. Wang et al., Tracing the origin of individual micro-continental block in SE Asia is 2013; Metcalfe and Aung, 2014), tectonostratigraphy (Stauffer and important in Gondwana reconstruction (e.g., Cawood and Buchan, Lee, 1989; Ampaiwan et al., 2009), zircon age-dating of crustal 2007; Metcalfe, 2013). basement (Guynn et al., 2012), paleoenvironmental reconstruction The Sibumasu block is one of the largest continental blocks in (Waterhouse, 1982; Dopieralska et al., 2012) and detrital zircon SE Asia (Fig. 1a). Cocks and Torsvik (2002) suggested that this block provenance (Burrett et al., 2014; Cai et al., 2015), the exact location was separated from the rest of East Gondwana in the early Paleo- of the Sibumasu block in the East Gondwana before its breakup in zoic. More recently, these authors (Torsvik and Cocks, 2009; Cocks early Paleozoic remains controversial (see summary in Ali et al., 2013). Crustal evolution studies have witnessed increased interest ∗ in the recent years on the vestiges of extremely old crustal Corresponding author at: State Key Laboratory of Geological Processes and components preserved in the Gondwana-derived continents (e.g., Mineral Resources, China University of Geosciences, No. 29, Xueyuan Road, Beijing Harrison et al., 2005, 2008; Nelson, 2008; Jayananda et al., 2013; 100083, China. Tel.: +86 10 82322301; fax: +86 10 82322301. E-mail address: [email protected] (Q. Wang). Van Kranendonk et al., 2013). A number of recent reports on Hadean http://dx.doi.org/10.1016/j.precamres.2015.10.003 0301-9268/© 2015 Elsevier B.V. All rights reserved. G. Li et al. / Precambrian Research 271 (2015) 118–137 119 Fig. 1. (a) Distribution of the principal continental blocks and suture zones of mainland SE Asia emphasizing the lineament of Sibumasu in which the Baoshan block is located (modified after Sone and Metcalfe, 2008). (b) Simplified geological map showing the regional tectonic relationships of the Baoshan, Tengchong and Simao blocks, and the distribution of the major strata, igneous rocks and faults in the Baoshan block (modified after Burchfiel and Chen, 2012; Deng et al., 2014a,b; Li et al., 2015a). materials from mircoblocks in the western Australia and southern the middle, to Sumatra in the south (Fig. 1a) (e.g., Ueno, 2003; India, which are important constituents of the Gondwana, have pre- Metcalfe, 2011). It is widely accepted that the Sibumasu block is sented in the literature (e.g., Wilde et al., 2001; Harrison et al., 2005, a Gondwana-derived continental fragment (e.g., Metcalfe, 2006, 2008; Tessalina et al., 2010; Santosh et al., 2014). This arouses our 2013; Ampaiwan et al., 2009; Ridd, 2009; Ali et al., 2013; Burrett interest to look for ancient crustal material, especially the Hadean et al., 2014). It was separated from Gondwana in Early Permian and record, which has not been found anywhere in SE Asia (Metcalfe, accreted to Indochina after the Paleotethys Ocean was closed in the 2013; Deng et al., 2014a), in the Sibumasu block. In this study, Middle–Late Triassic (Sone and Metcalfe, 2008). we use samples from S-type granitoids in northmost Sibumasu The Baoshan block is the northern tip of the Sibumasu block (e.g., that formed by crustal anataxis and contain both inherited and co- Metcalfe, 2011; Burchfiel and Chen, 2012). It is separated from the magmatic zircon crystals. The U–Pb ages and Hf isotopes of these Simao block by the Changning-Menglian Paleotethys suture zone to two types of zircon together are used to determine the nature of the the east and from the Tengchong block by the Gaoligongshan shear source crust (e.g., Horie et al., 2010; Qiao et al., 2015). This approach zone to the west (Fig. 1b; Burchfiel and Chen, 2012; Deng et al., has proven to be a powerful tool to study the origin and evolu- 2014a). The Baoshan block consists of an outcropped Late Neo- tion of the Earth’s crust (e.g., Harrison et al., 2005; Kemp et al., proterozoic to Cambrian basement which is mainly composed of 2010). The results provided the first evidence for the occurrence of low-grade metamorphosed siliciclastic and carbonate rocks, locally Hadean–Mesoarchean crust material in Sibumasu, which is further intercalated with volcanic rocks in the upper part (BGMRY, 1990; utilized to locate the Sibumasu block in the East Gondwana before Yang et al., 2012), and a Paleozoic to Mesozoic sedimentary cover its breakup in early Permian. which is mainly composed of carbonates and clastic rocks, with minor Early Permian volcanic rocks (Burchfiel and Chen, 2012). The meta-basalt from the basement yields zircon U–Pb age of ∼499 Ma 2. Geological background and samples (Yang et al., 2012). Early Paleozoic and Late Cretaceous to Paleocene granitoids are the main magmatic rocks present in the Baoshan The Sibumasu continental block is an elongated belt stretch- block (Fig. 1b; e.g., Dong et al., 2013a,b; Li et al., 2015b). The early ing from southwestern Yunnan in the north, through Thailand in 120 G. Li et al. / Precambrian Research 271 (2015) 118–137 Table 1 Whole-rock major and trace element of the early Paleozoic peraluminous granites in the Shuangmaidi area, northern Baoshan block, SW China. Samples Drill core ZK7-1 G01 G02 G03 G04 Major element (wt%) SiO2 75.38 75.29 74.44 73.73 TiO2 0.24 0.22 0.27 0.24 Al2O3 13.24 13.39 13.27 13.71 Fe2O3 0.21 0.42 0.59 0.32 FeOT 1.74 1.58 2.23 2.09 MnO 0.03 0.02 0.03 0.04 MgO 0.62 0.85 0.53 0.72 CaO 1.24 0.55 0.46 0.46 Na2O 4.18 3.45 2.57 2.63 K2O 1.90 2.59 4.62 4.78 P2O5 0.18 0.18 0.18 0.19 LOI 1.05 1.62 1.10 1.19 Total 99.80 99.74 99.70 99.78 CIPW normative mineral (wt%) Q 39.49 42.71 39.19 37.25 An 5.03 1.66 1.18 1.15 Ab 35.22 29.36 21.64 22.13 Or 11.18 15.39 27.17 28.09 C 2.45 4.33 3.59 3.76 Hy 3.77 4 3.74 4.17 Il 0.45 0.43 0.5 0.45 Mt 2.0 1.7 2.57 2.57 Ap 0.42 0.42 0.42 0.43 DI 85.89 87.46 88.00 87.47 Trace element (ppm) Sc 4.46 4.67 4.85 4.51 V 15.3 17 17 17.1 Cr 9.84 11.9 11.1 10.9 Fig.
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