IAVCEI 2013 Scientific Assembly - July 20 - 24, Kagoshima, Japan
Forecasting Volcanic Activity - Reading and translating the messages of nature for society

3W_3C-P29

Date/Time: July 23 Poster

Volcanic geology, geochronology and geochemistry information provided by the Halaha
River and Chaoer River volcanic field in Daxing’an Mountain Range
YongWei ZHAO, QiCheng FAN
Institute of Geology, China Earthquake Administration, China
E-mail: zilongzhao1981@yahoo.com.cn

34 Quaternary volcanoes, which scattered along a Quaternary NE strike fault, are found in the area of Halaha Riverand Chaoer River, middle of Daxing’an Mountain Range. Quaternary volcanic rocks in this area, mainly alkaline
basalt, cover an area of ca. 400 km2 . Both magmatic eruptions and phreatomagmatic eruptions are found in thisarea. The magmatic eruptions form a series of products, including scoria cones, tephra fallout deposits, and manykinds of lava (e.g. aa lava, pahoehoe lava and block lava). Typical fumarolic cones and lava hillocks are found in
the lava. The phreatomagmatic eruptions have typical base surge deposits, which are characterized by parallel
bedding and staggered bedding. Volcanic activity in this area form many volcanogenic lakes. According to thedifference of lake forming, they are divided into four types: crater lake, maar lake, volcanic dammed lake, collapse
lava lake (Zhao et al., 2008).
Based on studies on the volcanic field characteristics, in conjunction with geological dating by K-Ar, it is identified
that the volcanism occurred in four periods: Early Pleistocene, Middle Pleistocene, Late Pleistocene and Holocene.
Basalts of Early Pleistocene, mostly mantled by the later volcanic rocks, are distributed in the margin and valleysof the volcanic field. Middle Pleistocene, the most volcanic active period in this area, witnessed the formationof more than half of Quaternary volcanoes and lava spreading. Moderate volcanism occurred in Late Pleistocene
which produced a small amount of volcanic deposits. Volcanic activities are strengthened again in Holocene Period,
characterized by strongly explosive explosion, widespread lava flow and well-keeping lava landforms features (Fanet al., 2011).
The volcanic rocks, dominated by alkali olivine basalts in sodium series, is characterized by relative enrichment inlarge ion lithophile elements and light rare earth elements. The fractionation of rare earth element of the basalts isweak((La/Yb)N =8-12).They resemble alkali basalts in Datong, as shown by trace elements distribution patterns, andgenerally exhibit OIB-like characteristics. The basalts show nearly homogeneous Sr-Nd-Pb isotopic composition
similar to MORB source and present depleted mantle characteristics. All data show that basalts of HC have agarnet lherzolite mantle source, low degree partial melting(8%-15%)in which results in the primitive magma. Crystal
fractionation of olivine and pyroxene from the magma is weak and seldom contamination by the crust rocks happens
during the magma ascending, which resulting the volcanic rocks with high MgO content(>9wt%), Ni content andMg value(60-70).Regional extension triggers asthenospheric upwelling, which may lead to the genesis of magmaand subsequent volcanism (Zhao and Fan, 2012).
Supported by NSFC 41172305.

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