Age, geochemistry and zircon Hf isotope of the alkaline basaltic rocks in the middle section of the Yan-Liao aulacogen along the northern margin of the North China Craton: New evidence for the breakup of the Columbia Supercontinent

Abstract

In this contribution, we reported geochemistry, zircon U-Pb ages and Lu-Hf isotopes of the alkali basalt (Dahongyu and Tuanshanzi formations) and mafic dyke (Chuanlinggou Formation) from the Early Mesoproterozoic Changchengian System in Yan-Liao aulacogen along the northern margin of the North China Craton (NCC). Together with regional geology and previous research, we discuss the time, source and geodynamic regime of these basic rocks. The SHRIMP zircon U-Pb ages of alkaline basalt and mafic dyke are coeval, 1624 ± 9Ma and 1620 ± 9Ma respectively. All the studied basic rocks share similar geochemical feature: alkaline, high Zr content (94 × 10-6 ∼ 196 × 10-6), enrichment in light rare earth elements (LREE) ((La/Yb)N =10.63 ∼21.97) and large ion lithophile element (LILE); insignificant Eu anomaly, trace element characteristics resemble those of oceanic island basalt (OIB-like). Zircon εHf(t) values range from -0.6 to 3.8, indicating slightly depleted signature. The primitive magma of these basic rocks were derived from low-degree partial melting (2% ∼3%) of asthenospheric mantle source with minor involvement of lithospheric mantle materials and insignificant crust contamination, intensive crystal fractionation took place before eruption and emplacement. The alkaline magmatism eruption in Yan-liao aulacogen initiated at ca. 1635Ma and peaked at ca. 1625Ma. Thus, the depositional age of the Dahongyu Formation was younger than ca. 1635Ma. Comparing with the other continents around world at that time, the Mesoproterozoic igneous activity in the Yan-Liao aulacogen were most possibly related with the break-up of the Columbia Supercontinent.