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Giant Radiating Mafic Dyke Swarm of the Emeishan Large Igneous Province: Identifying the Mantle Plume Centre

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Giant Radiating Mafic Dyke Swarm of the Emeishan Large Igneous Province: Identifying the Mantle Plume Centre doi: 10.1111/ter.12154 Giant radiating mafic dyke swarm of the Emeishan Large Igneous Province: Identifying the mantle plume centre Hongbo Li,1,2 Zhaochong Zhang,1 Richard Ernst,3,4 Linsu L€u,2 M. Santosh,1 Dongyang Zhang1 and Zhiguo Cheng1 1State Key Laboratory of Geological Processes and Mineral Resources, China University of Geosciences, Beijing 100083, China; 2Geologi- cal Museum of China, Beijing 100034, China; 3Department of Earth Sciences, Carleton University, Ottawa, ON K1S 5B6, Canada; 4Ernst Geosciences, 43 Margrave Avenue, Ottawa, ON K1T 3Y2, Canada ABSTRACT In many continental large igneous provinces, giant radiating and recognized six dyke sub-swarms, forming an overall dyke swarms are typically interpreted to result from the arri- radiating dyke swarm and converging in the Yongren area, val of a mantle plume at the base of the lithosphere. Mafic Yunnan province. This location coincides with the maximum dyke swarms in the Emeishan large igneous province (ELIP) pre-eruptive domal uplift, and is close to the locations of have not received much attention prior to this study. We high-temperature picrites. Our study suggests that the Yon- show that the geochemical characteristics and geochronologi- gren area may represent the mantle plume centre during the cal data of the mafic dykes are broadly similar to those of peak of Emeishan magmatism. the spatially associated lavas, suggesting they were derived from a common parental magma. Based on the regional geo- Terra Nova, 27, 247–257, 2015 logical data and our field observations, we mapped the spa- tial distribution patterns of mafic dyke swarms in the ELIP, ridge by a continent (Gower and swarms and their distributions pro- Introduction Krogh, 2002), edge-driven enhanced vide an opportunity to further test Large igneous provinces (LIPs) are mantle convection (King and Ander- the plume model for the ELIP. the product of anomalously high son, 1995, 1998; Anderson, 1998), In general, giant radiating dyke melt production rates, and thus have slab steepening and breakoff (Ke- swarms (defined to be >300 km in been linked to the arrival of a mantle skin, 2003), and meteorite impacts radius) are typically considered to starting plume at the base of the (Jones, 2005). result from the arrival of a mantle lithosphere (e.g. Richards et al., The Emeishan LIP (ELIP) has plume at the base of the lithosphere; 1989; Campbell and Griffiths, 1990; been the focus of several recent geo- they are thought to converge towards Coffin and Eldholm, 1994; Maruy- chronological, geochemical and geo- the mantle plume centre and feed ama, 1994; Kerr et al., 2000; Courtil- physical studies (e.g. Shellnutt, 2014; associated flood basalts, which are lot et al., 2003; Ernst and Buchan, and references therein). Key evidence often present only as erosional rem- 2003; Ernst et al., 2005; Saunders has been proposed to support a man- nants (May, 1971; Halls, 1982; Fah- et al., 2005; Ernst, 2014). According tle plume origin, such as the presence rig, 1987; LeCheminant and to this model, the plume centre of high magnesian picrites (Zhang Heaman, 1989; Heaman et al., 1992; region should have associated high- et al., 2006a,b) and domal uplift Ernst et al., 1995a,b, 2001; Baragar temperature picrites generated along shortly before volcanism (He et al., et al., 1996; Ernst and Buchan, the higher temperature plume axis, 2003, 2006, 2010, 2011), among other 1997b; Wilson and Head, 2002; Ernst be the locus of domal uplift shortly features. However, Ukstins-Peate and Bleeker, 2010; Ernst, 2014). before the onset of volcanism and be and Bryan (2008, 2009) recognized Therefore, a giant radiating dyke the focus of a giant radiating dyke voluminous mafic hydromagmatic swarm can be used to identify and swarm feeding the volcanism. Some deposits and submarine extrusions, locate a mantle plume centre (e.g. alternative models of LIP formation indicative of emplacement at or Fahrig, 1987; Ernst et al., 1995b, have also been proposed (e.g. Foul- below sea-level, at Daqiao and 2001; Ernst and Buchan, 1997a,b; ger et al., 2005; Foulger and Jurdy, Binchuan, which are immediately Ray et al., 2007; Ernst, 2014; Wang 2007; see discussion in Ernst, 2014), adjacent to the ‘inner’ (maximum et al., 2014), such as the 200 Ma such as lithospheric delamination uplift) zone of the ELIP (defined by Central Atlantic Magmatic Province (e.g. Elkins-Tanton and Hager, He et al., 2003). Their observations (swarm radius >2000 km) associated 2000), over-riding of a spreading have cast doubt on the existence of with the opening of the central any pre-eruptive uplift, and even on Atlantic ocean, the 1270 Ma Mac- > Correspondence: Zhaochong Zhang, State the Emeishan mantle plume model, kenzie LIP (swarm radius 2000 km) Key Laboratory of Geological Processes although the presence of associated with the plume centre located on the and Mineral Resources, China University rifting, and local down-dropping of northern side of the Canadian shield, of Geosciences, 100083, China. Tel.: blocks, could explain their observa- and the Matachewan LIP (swarm +0086 10 82322195; fax: +0086 10 tions (e.g. He et al., 2011; see later radius >800 km) with the plume 82322176; e-mail: [email protected] discussion). The trends of dyke centre located on the southern side © 2015 John Wiley & Sons Ltd 247 Mafic dyke swarm of the Emeishan Large Igneous Province • H. Li et al. Terra Nova, Vol 27, No. 4, 247–257 ............................................................................................................................................................. of the Superior craton. Evidence low-grade metasedimentary rocks these faults (Chung et al., 1998; from Venus and Mars also supports interbedded with felsic and mafic Polyakov et al., 1998; Xiao et al., a primary radiating geometry of metavolcanic rocks. The basement is 2003a, 2004b; Hanski et al., 2004, dyke swarms (Grosfils and Head, overlain by a thick sequence of late 2010; Fan et al., 2008; Lai et al., 1994; Ernst et al., 1995b, 2001). Neoproterozoic (~600 Ma) to Perm- 2011). Field observations and mag- In the case of the ELIP, the colli- ian clastic, carbonate and metavolca- netostratigraphic data suggest that sion of Greater India and Eurasia nic rocks (BGMRSP, 1991; Yan the bulk of the ELIP was formed caused Cenozoic uplift (Leloup et al., et al., 2003). The ELIP, particularly within 1–2 Ma (Huang and Opdike, 1995; Chung et al., 1998). Conse- the Panxi region, experienced tec- 1998; Ali et al., 2002). Recent iso- quently, the lava sequence is deeply tonic uplift and denudation during tope chronological data give more eroded and numerous mafic dykes the Himalayan impingement (Zhang precise constraints on the duration of are exposed (Fig. 1a). Although the et al., 1990; Courtillot et al., 1999; the eruption as 260–257 Ma, with geochronology, geochemistry and Liu et al., 2001; Wu and Zhang, voluminous eruption at ~260 Ma petrogenesis of some mafic dykes 2012). (e.g. Wang and Zhou, 2006; Zhou associated with the ELIP have been The extensive Emeishan flood bas- et al., 2006, 2008; He et al., 2007; investigated (Guo et al., 2004; Zhou alts are exposed over an area of Fan et al., 2008; Xu et al., 2008; Li et al., 2006; Zi et al., 2008; Han ~3.0 9 105 km2 and represent a late et al., 2012; Shellnutt et al., 2012; et al., 2009; Shellnutt et al., 2008; Permian continental food basalt Zhong et al., 2014). Shellnutt and Jahn, 2011; Shellnutt event (Xu et al., 2001; Ali et al., Mafic dykes in the western part of et al., 2012; Li et al., 2012), the spa- 2005). The volcanic sequence has a the Yangtze craton can be generally tial distribution patterns of the mafic thickness ranging from several hun- grouped into three major episodes dyke swarms in the ELIP are poorly dred metres to 5 km and contains pi- based on field relations (BGMRYP, understood. In this study, we present crites, tholeiites and andesitic basalts 1990; BGMRSP, 1991) and isotopic the spatial pattern of the giant dyke (Chung and Jahn, 1995; Song et al., ages of Neoproterozoic, Palaeozoic swarms in the ELIP, and discuss the 2001; Xu et al., 2001; Xiao et al., (late Permian) and Cenozoic. The geometric characteristics and the 2004a; Zhang et al., 2006a). As men- Neoproterozoic dykes are predomi- implications for the postulated Emei- tioned above, the distribution of nantly exposed in the Kangding-Pan- shan mantle plume. units belonging to the ELIP has been zhihua area. Here, the host rocks, subsequently affected by Mesozoic dominated by granites, granodiorites and Cenozoic post-emplacement and tonalites, are cut by minor Geological background faulting associated with the develop- mafic-ultramafic bodies and mafic The ELIP is located to the east of ment of the Songpan-Ganze terrane dykes (Zhu et al., 2008). These dykes the Tibetan plateau and near the and the Indo-Eurasian collision have narrow widths of 1–10 m and western margin of the Yangtze (Chung and Jahn, 1995), such as the trend NE, NW or E–W. They Block, SW China (Fig. 1a). The Jinshajiang-Ailaoshan-Red River intrude the Proterozoic basement basement rocks for the ELIP locally strike-slip fault (or suture zone, Liu and show crystallization ages comprise the Palaeoproterozoic et al., 2015). Recent studies have between 792 and 752 Ma (Li et al., Kangding Complex, composed of suggested that basalts and mafic 2003; Lin et al., 2007; Zhu et al., granulite-amphibolite facies meta- complexes exposed in the Songpan- 2008; Ren et al., 2013). The late morphic rocks, the Palaeo–Mesopro- Ganzi terrane, the Qiangtang terrane, Permian mafic dykes (Emeishan- terozoic Huili Group or its the Simao basin and in northern related) will be discussed in more equivalents, and the Yanbian or Vietnam might form part of an detail below.
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