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

AbstractIn 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.