Gondwana Research 27 (2015) 1270–1282 Contents lists available at ScienceDirect Gondwana Research journal homepage: www.elsevier.com/locate/gr The Alashan Terrane was not part of North China by the Late Devonian: Evidence from detrital zircon U–Pb geochronology and Hf isotopes Wei Yuan a,b, Zhenyu Yang c,d,a,⁎ a School of Earth Sciences and Engineering, Nanjing University, Nanjing 210093, China b Wuxi Research Institute of Petroleum Geology, SINOPEC, Wuxi, Jiangsu 214126, China c Key Laboratory of Paleomagnetism and Tectonic Reconstruction, Ministry of Land and Resource, Beijing 100081, China d Institute of Geomechanics , Chinese Academy of Geological Sciences, Beijing, 100081, China article info abstract Article history: The relationship between the Alashan Terrane and North China is a contentious issue given the discovery of al- Received 9 July 2013 lochthonous detrital zircons in Middle Ordovician flysch sandstones from the southwestern Ordos Margin and Received in revised form 8 November 2013 the large differences in palaeolatitudes between the North China and Tarim cratons. We have collected a suite Accepted 8 December 2013 of Middle to Late Devonian sedimentary rocks from the Niushoushan Mountains at the southeastern margin of Available online 28 December 2013 the Alashan Terrane, adjacent to the western margin of the Ordos Basin of the North China Craton (NCC). U–Pb – – Handling Editor: Z.M. Zhang dating and Lu Hf isotopic studies were carried out on detrital zircons from these rocks. The zircon U Pb ages de- fine five age populations: 0.4–0.7 Ga (peak at 488 Ma), 1.0–1.3 Ga (peaks at 1001 and 1152 Ma), 1.5–1.8 Ga, Keywords: 2.4–2.8 Ga (prominent peak at 2506 Ma and secondary peaks at 2668 and 2796 Ma) and N3.0 Ga (peak at Alashan Terrane 3332 Ma). One detrital zircon yielded a Hadean age of 4022 ± 17 Ma. Zircons with U–Pb age spectra of North China Craton 2.4–2.7 and N3.0 Ga and their corresponding εHf(t) values are significantly different from those in the NCC, indi- East Gondwana cating that these detrital zircons are not from the NCC, which implies that the Alashan Terrane was not part of Middle to Late Devonian North China until the Middle to Late Devonian. U–Pb age spectra of zircons dated at 1.0–1.3 Ga, 2.4–2.7 Ga, – Zircon U Pb dating and Hf isotopes and N3.0 Ga, and their corresponding Hf isotope data, have a strong similarity with zircons from East Gondwana and the South China Craton. © 2013 International Association for Gondwana Research. Published by Elsevier B.V. All rights reserved. 1. Introduction these have improved our understanding of the regional geology of these areas. Given its different Precambrian basement The continental crust of China is a mosaic of Precambrian cratonic and Neoproterozoic geological processes, the existence of the Sino– cratons and terranes separated by orogenic belts, in which the Tarim, Korean–Tarim Craton (Li et al., 1982) has been called into question North China, and Yangtze cratons constitute the basic tectonic on the basis of geological and palaeomagnetic results that suggest framework of China (Lu et al., 2009; Zheng et al., 2013,)(Fig. 1A). The the Tarim Craton had collided with Kazakhstan and Siberia by the Alashan Terrane that bridged the southern Central Asian Orogenic Belt end-Permian, whereas the NCC and Mongolian Orogenic Belt were and the Tarim, Qaidam, and North China Craton (NCC), is considered distant from Siberia during the Permian–Triassic (Enkin et al., as the key region in understanding the tectonic evolution of Northern 1992; Yang and Besse, 2001; Xiao et al., 2008, 2010). As such, deter- China. In recent decades, numerous geological and palaeomagnetic mining the affinity of the Alashan Terrane with these two cratons studies have been conducted in the Qilian Orogenic Belt, Hexi corridor, during the Early Palaeozoic might shed light on the tectonic evolution Alashan Terrane, and NCC (e.g., Yang et al., 1992, 1996, 1998; Yang of Northern China. For example, supposed the Alashan Terrane was and Besse, 2001; Geng et al., 2002; Yang et al., 2002, 2004; Zhao et al., the westernmost part of NCC during the Early Palaeozoic, Xiao et al. 2004, 2005; Geng et al., 2007; Xiao et al., 2009; Zhao, 2009; Geng and (2009) proposed the multiple subduction systems that the Alashan Zhou, 2010; Liu et al., 2010; Dan et al., 2012; Liu et al., 2013; Song Terrane and its cover sequence were underthrust southward beneath et al., 2013; Tang et al., 2013; Yang et al., 2014; Zhai and Santosh, the coherent Qilian arc at a low angle, which led to final amalgamation 2013; H.F. Zhang et al., 2013; Zhao and Zhai, 2013; Zheng et al., 2013; between the Alashan Terrane (NCC), Qilian Orogenic belt and Qaidam Zhou and Wilde, 2013; Wang et al., 2013; Zheng et al., 2014), and block in the Late Devonian. However, Ge et al. (2009) argued that a tectono-stratigraphic comparison prior to the Mesozoic between the NCC and Alashan Terrane suggests that suturing between these two ⁎ Corresponding author at: Key Laboratory of Paleomagnetism and Tectonic cratons occurred during the Late Hercynian–Indosinian (Late Triassic) Reconstruction, Ministry of Land and Resource, Beijing 100081, China. Tel.: +86 10 68422348; fax: +86 1068422326. in a zone buried under the Tengger Desert. The assumed linkage between E-mail address: [email protected] (Z. Yang). the Alashan Terrane and the NCC in the early Palaeozoic has also been 1342-937X/$ – see front matter © 2013 International Association for Gondwana Research. Published by Elsevier B.V. All rights reserved. http://dx.doi.org/10.1016/j.gr.2013.12.009 W. Yuan, Z. Yang / Gondwana Research 27 (2015) 1270–1282 1271 Fig. 1. (A) Sketch maps of the tectonic elements of Northern China. (B) Simplified geological map of the study area and adjacent regions in the Niushoushan Mountains at the southeastern margin of the Alashan Terrane. The star symbol denotes the sampled section. questioned on the basis of the detrital zircon geochronology of Ordovi- not connected with the NCC prior to the Middle Ordovician. Based on cian clastic sediments in the Alashan Terrane (J. Zhang et al., 2011; X.J. field observations, Li et al. (2012) also concluded that amalgamation of Zhang et al., 2011). These results suggest that the Alashan Terrane was the NCC with the Alashan Terrane took place between the Late 1272 W. Yuan, Z. Yang / Gondwana Research 27 (2015) 1270–1282 Ordovician and Early Devonian. Thus, the relationship between the NCC red beds intercalated with sparse limestones and marly sandstones. and Alashan Terrane requires further clarification. Vertebrate fossil assemblages that include Remigolepis microcephala The robustness of the zircon U–Pb dating technique, coupled with Pan (sp. Nov.), R. major Pan (sp. nov.), Remigolepis zhongweiensis Pan (sp. Lu–Hf isotope investigations of zircon (Kinny et al., 1991; Kinny and nov.), Remigolepis xiangshanensis Pan (sp. nov.), and Sublepidodendron Maas, 2003; Yang et al., 2006), has led to many studies using these mirabile (Nath.) Hirmer (Pan et al., 1987) indicate a Middle Devonian methods to study supercontinent cycles and the growth of continental age. The Shixiagou Formation is unconformably overlain by the Dadaigou crust (e.g., Condie and Aster, 2013). Moreover, combined U–Pb dating Formation. The Upper Devonian Zhongning Formation conformably and Hf isotope analysis of zircons can be used to constrain the prove- overlies the Upper Devonian Dadaigou Formation and is, in turn, nance of clastic sediments that, in turn, may enable the reconstruction disconformably overlain by the Lower Carboniferous Chouniugou of the tectonic evolution of continental cratons (Hoskin and Ireland, Formation. Sediments of the Zhongning Formation comprise grey to 2000; Fedo et al., 2003). grey–yellow, medium-bedded, fine-grained, quartzo-feldspathic sand- We have carried out a zircon U–Pb geochronological and Hf isotope stone with minor glutenite layers, which contain fossil fish such as study of detrital zircons in Middle to Upper Devonian sediments from Bothriolepis niushoushanensis, Quansipetalichthys haikouensis Liu,and the Niushoushan Mountains at the southeastern margin of the Alashan Bothriolepis niushoushanensis (BGMRGS, Bureau of Geology and Mineral Terrane (Fig. 1B), which is located adjacent to the western margin of the Resources of Gansu Province, 1990). Ordos Basin of the NCC. These data are used to constrain the relationship Five sandstone samples were collected for detrital zircon analysis between the Alashan Terrane and the NCC. from the Middle Devonian Shixiagou Formation and Upper Devonian Zhongning Formation in the Niushoushan Mountains of the Ningxia 2. Geological setting and sampling Autonomous Region at the southeastern margin of the Alashan Terrane (Fig. 1B). Sample SX-1 was collected from the Shixiagou Formation, and The Alashan Terrane is a triangle-shaped terrane that has long been the other four samples were taken from the Zhongning Formation (from considered the western part of the NCC, which sutured to the Qilian Oro- lower to upper: SX-3, SX-4, SX-6, and SX-7). These five samples are genic Belt in the Devonian (Li et al., 1982; Xiao et al., 2009; Zhao, 2009; purple red medium-coarse grained sandstones. Based on microscopic Song et al., 2013; Zheng et al., 2013). Xiao et al. (2009) suggested that observations, sample SX-1 is a medium grained sandstone, composing the Qilian Orogenic Belt has recorded multiple subduction–accretion pro- of 76% quartz, 13% feldspar, 9% lithic fragments and 2% dolomite. Sample cesses between the Alashan and Qaidam blocks during the Early to Middle SX-3 has a composition of 78% quartz, 5% feldspar, 10% lithic fragments Palaeozoic. The Alashan Terrane is bounded to the east by the NCC (across and 7% calcite cement (dolomite).