广西涠洲岛南湾火山喷发特征

涠洲岛是北部湾内的一座火山岛,火山熔岩构筑了该岛的基底,岛南端的南湾火山喷发物形成了涠洲岛现代火山地貌．南湾火山喷发以岩浆喷发和射气岩浆喷发交替进行为特征,火山碎屑岩和基浪堆积物向岛北延伸,覆盖了大半个涠洲岛．选取了鳄鱼嘴和猪仔岛2个典型剖面,对南湾火山喷发活动进行详细的观察和描述,发现了诸如爬升层理、大型低角度交错层理和板状层理等射气岩浆喷发成因的基浪堆积物中特有的构造,并且观察到射气岩浆作用的指相物质——增生火山砾．所有这些现象都反映了南湾火山是射气与岩浆交替喷发成因的复合火山,其中射气岩浆喷发占据重要地位,而喷发中心位于南湾海中．

Nanwan Volcano Eruption Features on Weizhou Island, Guangxi

Weizhou island is a volcanic island, which is located in Beibu Bay. The base of Weizhou island is constituted by lava. The Nanwan volcano effusive mass forms modern volcanic physiognomy of Weizhou island. Pycroclastics and base surge extend to the north island, covering more than half of the island. Eyuzui and Zhuzidao are two typical sections, which are selected in order to observe and describe the volcanic activity of Nanwan volcano in detail. Special structures were found that belong to the base surge, including large-scale and low-angle cross-bedding, slaty-bedding, climb-bedding, and distal facies accretionary lappili. These structures prove that Nanwan volcano is a multiplex volcano caused by alternation of magma e-ruption and phreatomagmatic eruption. Phreatomagmatic eruption plays an important role in the formation of Nanwan volcano. The eruptive center is located in the Nanwan sea.