Quaternary volcanic activities in the Weizhou Island, Beibu Gulf: Constraints on their eruption styles and mantle source affinities

<p indent="0mm"> The Weizhou Island in the Beibu Gulf is the largest and youngest volcanic island in China. In this paper, we have discussed the form of volcanic activities and properties of mantle source of the erupted magmas, in order to provide constraints for the most recent tectonic-magmatic processes in South China and the South China Sea. The early to middle Pleistocene <sc>(1.42‒0.49 Ma)</sc> volcanic activities in the Weizhou Island are dominated by the effusive eruption. Their lava flows were spread out from the Henglushan crater, forming a shield volcano cone which is the main body of the Weizhou Island. The late Pleistocene (36‒<sc>13 ka)</sc> volcanic activities, characterized with the magma-emanation eruption, formed the Nanwan maar type caldera. The final episodic magmtic materials, erupted from the Eyushan crater, formed the current geological and geomorphological pattern of the Weizhou Island. The early to middle Pleistocene olivine basalt and the late Pleistocene basanite both belong to the alkaline series and have similar Sr-Nd-Pb isotopic compositions. However, the former one (olivine basalt) has relatively high SiO₂ contents but relatively low Mg^# values, indicating that it had undergone a certain degree of magmatic crystallization differentiation of minerals such as olivine and clinopyroxene. The chemical composition of the late Pleistocene basanite is relatively close to that of the parent magma which could be originated from the low-degree partial melting of the mantle sourced materials. The mantle source of the Weizhou Island volcanic rocks could be the mixing result of the depleted MORB-type mantle and enriched EM2-type mantle by possible influence of the South China Sea mantle plume which has controlled the tectonic-magmatic processes in the South China Sea since the Pleistocene.