2115 Ma Haicheng Igneous Province unveils extensive plume-lithospheric interaction during the Great Oxidation event (GOE)

Abstract

The 2115 Ma Haicheng Igneous Province (HIP) distributes across the Eastern North China Craton. As one representative large igneous provinces coincident with the Great Oxidation Event (GOE), it is important to know whether such an igneous province is plume-originated or not. Synthetic petrology, geochronology and geochemistry study on the plumbing system of the HIP, especially the mafic sills in the Fanhe-Liaohe basins are performed to seek further constraints. The sills intruding the carbonates of the Sanchazi Group (2.2–2.1 Ga) in the Fanhe basin have thicknesses of about 20 m. They mainly consist of clinopyroxene, plagioclase, and minor Fe-Ti oxides, with greenschist-faices metamorphic overprinting of actinolite/chlorite, albite and quartz, as well as secondary epidote and uralite. Precise Pb-Pb SIMS dating of baddeleyite from the Yunpangou sill, the one with the highest MgO content identified by this study in the Fanhe basin, yields a ²⁰⁷Pb/²⁰⁶Pb average age of 2115 ± 6 Ma, which is the same as others of the HIP. The Yunpangou sill is doleritic and tholeiitic, with low SiO₂ content (44.8–48.2 wt.%) but high MgO (5.3–10.9 wt.%), TFe₂O₃ (total iron: 16.0–19.7 wt.%) and TiO₂ contents (2.0–2.8 wt.%). It shows slightly enriched trace elements, distributed within patterns of E-MORB and OIB. Its Sr-Nd isotopes are quite primitive (⁸⁷Sr/⁸⁶Sr_(t) = 0.702–0.703; ε_Nd(t) = +2.7–+3.4). However, its dramatically varying internal compositions comprise an inverted C-shaped pattern, in which the samples with the highest MgO (8.0–11.0 wt.%) in the center represent the least differentiated component. Its high-Mg content, OIB-affinitive patterns and primitive Sr-Nd isotopes favor a plume source. The mafic units of the HIP show wide compositional variations, with SiO₂ of 45.8–55.5 wt.%, ⁸⁷Sr/⁸⁶Sr_(t) of 0.702–0.709, and ε_Nd(t) of −2.8-+3.9; while the felsic units with SiO₂ of 63.0–80.0 wt.%, ⁸⁷Sr/⁸⁶Sr_(t) of 0.707–0.73, and ε_Nd(t) of -1.5–-0.7. These largely varied compositions and the bimodal feature are resulted from the involving of different melts from sub-continental lithospheric mantle, a paleo-plume, as well as the crust. The HIP represents an extensive plume-lithospheric interaction across much of the craton during the late-stage of GOE.