The last volcanic eruptions at the intraplate Wudalianchi volcanic field in northeast China were ~300 yr ago. Recent ambient noise tomography (ANT) imaged a potential magma chamber beneath one of its volcanoes, the Weishan volcano, which last erupted at ca. 50 ka. To image the spatial distribution of the magmatic system and estimate the melt fractions beneath the Weishan volcano, we use a dense magnetotelluric (MT) network (average site spacing of ~1 km) around the Weishan cone to image a three-dimensional (3-D) resistivity structure beneath the volcano. For the first time, 3-D MT inversion illuminates the high-resolution spatial distribution of a very low-resistivity body of ~0.3–3 Ω·m at depth of ~2–15 km beneath the Weishan volcano. From the 3-D resistivity model, it can be deduced there exists a magma chamber in the upper and middle crust. From both low-velocity anomalies from ANT and low-resistivity anomalies from MT imaging, melt fractions of magma reservoirs are reliably estimated to be >~15%. From the morphology of magma reservoirs and the shallow magma chamber, the Weishan volcano can be best described by the model of transcrustal magmatic system. Considering the significant melt fractions and active earthquakes and tremors occurring around magma reservoirs, the Weishan volcano is likely in an active stage with magma recharging. Therefore, it needs more active monitoring for better forecasting of its potential future eruptions.
The Wudalianchi Volcano Field (WDF) is a typical intraplate volcano in northeast China with generation mechanism not yet well understood. As its last eruption was around 300 years ago, the present risk for volcano eruption is of particular public interest. We have carried out a high‐resolution ambient noise tomography to investigate the location of magma chambers beneath the volcanic cones with a dense seismic array of 43 seismometers and ~ 6 km spatial interval. Significant low‐velocity anomalies up to 10% are found at 7–13 km depth under the Weishan volcano, consistent with the pronounced high electrical‐conductivity anomalies from previous magnetotelluric survey. We propose these extremely low velocity anomalies can be interpreted as partial melting in a shallow magma chamber with volume at least 200 km3 which may be responsible for most of the recent volcanic eruptions in WDF. Therefore, this magma chamber may pose a serious hazard for northeast China.
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