Periods of volcanic activity and magma evolution of Holocene in North Hainan Island
琼北火山活动分期与全新世岩浆演化

Volcanic activity of North Hainan Island started in Eocene. Eogene volcanic rocks hidden in different sedimentary strata in type of intermediate layer. Here we present six K-Ar ages of basalt and two Th ages of sandstone xenolith in the basalt. The new age data provide the evidence of Holocene volcanic activity in North Hainan Island. Volcanic rocks exposed on the earth's surface in North Hainan Island can be divided into six periods according to times, namely Penglai Period (Miocene), Jinniuling Period (Pliocene), Duowenling Period (Early Pleistocene), Dongying Period (Middle Pleistocene), Daotang Period (Late Pleistocene) and Leihuling Period (Holocene). Leihuling Period can be divided into two sub-periods: Leihuling Sub-period and Ma' anling Sub-period, respectively. Volcanic rocks of Leihuling Sub-period belong to olivine tholeiite, whereas, volcanic rocks of Ma' anling Sub-period are quartz tholeiite. The REE, trace elements and Sr, Nd, Pb isotopes characteristics reveal that the magma comes from a mixing source of DMM and enriched lithosphere or DMM and ocean crust subduction. Olivine tholeiite magma is relatively primitive magma in the mantle. Quartz tholeiite could have been formed by about 10% olivine crystal fractionation of olivine tholeiite magma. No evidence shows the crust contamination during the uplift of magma.