关键词: 第四纪火山, 喷发方式 , 喷发时代 , 琼北火山群 , 峨蔓

Abstract: As one of the largest Quaternary volcanic clusters in China, the volcanic activities of Qiongbei are characterized by multi-stage and multi-cycle, however, the eruption era of Eman volcanic rock located in the northwest of Qiongbei volcanic cluster is still controversial. Here, we present a comprehensive study of volcanic geology and geomorphology, whole-rock major elements, K-Ar geochronology of volcanic rocks and 14C geochronology of conch, in order to revel the epoch of volcanic activity and eruption characteristics of Eman volcanic field. There are many craters, such as Bijialing, Chunliling, Bingmajiao, Longmenjilang, Longmen pharos, and Zhangwu. The main types of volcanic eruption are effusive eruptions, phreatomagmatic explosive eruptions and weakly magmatic explosive eruptions. Lava flows almost cover the entire volcanic field, with an area of about 26.3km2. However, base-surge deposits, spattering deposits and scoria are only distributed in the vicinity of Longmenjilang-Wucaiwan and Zhangwu Village. The composition of Eman volcanic rocks varies greatly and is generally intermediate, which is mainly composed of basaltic andesite, basaltic trachyandesite and trachyandesite, and experiences fractional crystallization of olivine and clinopyroxene in the process of magmatic evolution. we based on the weathering degree of volcanic rocks (spherical weathering, red clay layer), volcanic geology and geomorphology (cone morphology, slope), petrology and petrogeochemistry (difference of major elements, olivine phenocryst alteration), K-Ar age of volcanic rocks (0.12~0.44 Ma) and 14C age of conch (43.27±0.67 ka.BP), it is concluded that the eruption era in Eman volcanic field belongs to the Middle and Late Pleistocene.

Key words: Quaternary volcano, eruption type, eruption era, Qiongbei volcanic clusters, Eman