Geochronological and geochemical studies of the OIB-type Baiyanghe dolerites: implications for the existence of a mantle plume in northern West Junggar (NW China)

Abstract

In this paper, zircon U–Pb geochronology, major and trace elements, and Sr–Nd isotope geochemistry of the Baiyanghe dolerites in northern West Junggar of NW China are presented. The U–Pb dating of zircons from the dolerites yielded ages of 272.2±4 Ma and 276.7±6.2 Ma, which indicate the emplacement times. The dolerites are characterized by minor variations in SiO2(46.89 to 49.07 wt%), high contents of Al2O3(13.60 to 13.92 wt%) and total Fe2O3(11.14 to 11.70 wt%), and low contents of MgO (2.67 to 3.64 wt%) and total alkalis (Na2O+K2O, 5.1 to 5.97 wt%, K2O/Na2O = 0.37–0.94), which indicate affinities to metaluminous tholeiite basalt. The REE pattern ((La/Sm)N= 2.25–2.34, (La/Yb)N= 7.42–8.36), V–Ti/1000 and 50*Zr–Ti/50–Sm discrimination diagrams show that these rocks are OIB-type. The high contents of Zr and Ti indicate a within-plate tectonic setting, and samples plot in the ‘plume source’ field shown on the Dy/Yb(N)versus Ce/Yb(N)diagram. The positive εNd(t) values (+7.09 to +7.48), high initial87Sr/86Sr ratios (0.70442 to 0.70682) and depletions of Nb and Ta elements in the samples can be explained by the involvement of subducted sediments. In summary, it is possible that the Baiyanghe dolerites were derived from an OIB-like mantle source and associated with a mantle plume tectonic setting. Therefore, our samples provide the youngest evidence for the existence of a mantle plume, which may provide new insights into the Late Palaeozoic tectonic setting of West Junggar.

Genesis of the volcanic-related Be-U-Mo Baiyanghe deposit, West Junggar (NW China), constrained by mineralogical, trace element and U-Pb isotope signatures of the primary U mineralisation

“…The West Junggar region then experienced a postorogenic stage (Choulet et al, 2012(Choulet et al, , 2011; Fig. 10) associated with intraplate magmatism and marked by multiple events of dyke intrusions until the late Triassic (Miao et al, 2019;. In the Baiyanghe area, the late Devonian felsic volcanic and pyroclastic rocks of the Tarbagatay Group, and the late Carboniferous Yangzhuang granite porphyry represent the U source rocks for the mineralisation in the Baiyanghe deposit proposed in previous studies (Li et al, 2015;Mao et al, 2014;Shabaga et al, 2013;Zhang et al, 2019Zhang et al, , 2020.…”

“…Lithofacies paleogeographical studies and paleomagnetic research revealed that a remnant oceanic basin still existed in the northern West Junggar region until 300 Ma ago (Choulet et al, 2011;Wang, 2006;Wang et al, 2007), which strongly argues in favour of an ocean ridge subduction model to interpret the extensive late Carboniferous magmatism in West Junggar (Geng et al, 2011(Geng et al, , 2009Tang et al, 2010aTang et al, , 2010bTang et al, , 2009Yang et al, 2012;Yin et al, 2011Yin et al, , 2010. The northern West Junggar region then entered in a post-orogenic stage (Choulet et al, 2012(Choulet et al, , 2011 associated with intraplate magmatism characterised by multiple events of dyke intrusions during the early Permian-middle Triassic (Miao et al, 2019;Yi et al, 2014), including diorite porphyry (290±18 Ma, 222±18 Ma), dolerite (277±6 Ma, 272±4 Ma), diabase (255 Ma), and alaskite (255±2 Ma, 246±1 Ma).…”

“…These volcano-sedimentary units were then intruded by the late Carboniferous Yangzhuang granite porphyry and a series of dykes emplaced during the early Permian-late Triassic (Figs. 1B and 1C;Li et al, 2015;Miao et al, 2019;Yi et al, 2014;Zhang et al, 2019). The Be-U-Mo mineralisation is mainly hosted within the Yangzhuang granite porphyry and the late Devonian rhyolite and rhyolitic tuff of the Tarbagatay Group (Figs.…”

Direct evidence for the source of uranium in the Baiyanghe deposit from accessory mineral alteration in the Yangzhuang granite porphyry, Xinjiang Province, northwest China

“…2a). They were emplaced during the Early Permian to Late Triassic (Ma et al 2010;Miao et al 2019). Miao et al (2019) suggested that the diabase dykes in the Baiyanghe deposit were probably derived from an ocean-island basalts (OIB)-like mantle source and associated with a mantle plume tectonic setting.…”

“…The geochronological framework that includes the magmatism and U-Be mineralization in the Baiyanghe deposit. The data are from:Ma et al 2010, Zhang and Zhang 2014, Yi 2016Miao et al 2019, Xia 2019 …”