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

3W_3C-P30

Date/Time: July 23 Poster

Origin of Cenozoic basaltic magmatism at Changbaishan volcanic field, northeast China
Takeshi Kuritani1 , Jun-Ichi Kimura2 , Eiji Ohtani3
1Osaka City University, Japan, 2 Japan Agency for Marine-Earth Science and Technology, Japan,
3Tohoku University, Japan
E-mail: kuritani@sci.osaka-cu.ac.jp

In NE China, Cenozoic intraplate basalts are widely distributed, and Changbaishan is one of the largest volcanic
fields. This intraplate magmatism is unique because the stagnant slab of the subducted Pacific plate is present
in the mantle transition zone (MTZ). Therefore, the geodynamic and geochemical processes in relation to thestagnant slab and their effects on the magmatism have received considerable attention (e.g., Zou et al., 2008;
Ohtani and Zhao, 2009). This paper summarizes the results of our recent studies on the Cenozoic basalts inNE China (Kuritani et al., 2009, 2011, 2013), and integrates them toward understanding the origin of the basaltic
magmatism at Changbaishan.
A prominent low-velocity anomaly with a plume-like shape was imaged in the upper mantle beneath Changbaishanby P-wave tomography, and was suggested as an upwelling of wet materials from the MTZ (Zhao et al., 2009). We
have compiled geochemical data of Quaternary basalts from Changbaishan and the surrounding volcanic fields(e.g., Jingbohu and Kuandian), and found a spatial correlation between the basalt chemistry and the distribution of
the low-velocity zone. Namely, the Ba/Th and Pb/U ratios of the basalts tend to decrease with increasing distancefrom Changbaishan. Furthermore, the basalts from Changbaishan have Sr, Nd, and Pb isotopic ratios similar tothe EM1 endmember and the rests are from more depleted source.
One possible source of the EM1-like component is the lower part of the sub-continental lithospheric mantle (SCLM).
However, this is unlikely because the lower part of the SCLM beneath NE China formed in Cenozoic times,
precluding prolonged isotopic ingrowth. Alternatively, the component was proposed to be derived from the MTZ.
In the subducted materials, K-hollandite in metamorphosed sediments can be a major reservoir of incompatible
elements such as Sr, Ba, and Pb. Elements released by breakdown of sedimentary K-hollandite would behigh-Ba/Th and Pb/U, and thus, a suitable metasomatic agent to form EM1-like mantle in the MTZ (Rapp et al.,2008). Because the formation of the EM1 isotopic signature requires a timescales of >1 Ga, sediments in an
ancient stagnant slab, as well as those in the Pacific plate stagnant slab, may have been involved in the source
materials for the Changbaishan basalts.
Assuming that the age of the ancient slab sediment is 1.5 Ga, the isotopic ratios of the Changbaishan basalts canbe explained by mixing of a depleted mantle with a 0.5% sediment component which consists of a 1:2 to 1:3 mixtureof the recent and the ancient sediments. The MTZ beneath NE China is remarkably hydrous, as evidenced fromthe electrical conductivity observations (Kelbert et al., 2009). Therefore, it is plausible that a hydrous mantle plumeascended from the hydrated MTZ, and that partial melting occurred in the ascending plume in the asthenosphericmantle, leading to the basaltic magmatism at Changbaishan and its surrounding volcanic fields.

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