Tephra evidence for the most recent eruption of Laoheishan volcano, Wudalianchi volcanic field, northeast China

Abstract

Wudalianchi volcanic field (WDLC) is one of the youngest intracontinental monogenetic volcanic fields in China. The 1719–1721 CE Laoheishan-Huoshaoshan eruption, and the 1776 CE Laoheishan eruption are the latest eruptions in WDLC based on the local historical records. However, most of the recent explosive eruptive products around WDLC are attributed to the 1719–1721 CE Laoheishan-Huoshaoshan eruption while less attentions were paid on the 1776 CE Laoheishan eruption. There are two types of scoria fall deposits around Laoheishan volcano, i.e. the upper light grey high vesicular scoria deposit (US) and below dark low vesicular scoria deposit (BS). Most of the glass shards from US exhibit >4% Na2O while BS show <4% Na2O. In addition, US presents two different glass composition clusters, indicating a complex magma batch feeding the eruption. Broadly, all of these eruptive products from WDLC have extreme high potassium (usually >5%) content with trachyandesitic to tephriphonolitic in composition that can be clearly distinguished from those from other nearby volcanic regions, such as Nuomin (~150km to Nangelaqiushan lake (NGLQ)), Arxan-Chaihe (~450km to NGLQ), Longgang (~700km to NGLQ) and Jingbohu (~550km to NGLQ). A cryptotephra layer is clearly revealed as a distinct peak in magnetic susceptibility measurements from NGLQ~8km northwest to Laoheishan volcano. Glass composition of the cryptotephra layer recorded in NGLQ is similar to the proximal US around Laoheishan volcano. On basis of historical records and field observations, we ascribed US to the 1776 CE Laoheishan eruption and BS to the 1719–1721 CE Laoheishan-Huoshaoshan eruption. Consequently, historical records assigned a precise age (1776 CE) for the tephra recorded in NGLQ, and thus can be used to refine the age model of these lacustrine sediments.