Analysis of Deformation Characteristics and Uplift Mechanism in the Longgang Volcanic Field, China

The Longgang volcanic field (LVF), one of the most active volcanic areas in Northeast China, is a continental monogenetic volcanic zone located about 100 km west of the Tianchi volcano in the Changbaishan volcanic field. Since the Early Pleistocene, the LVF has experienced multiple eruptive episodes from several centers, forming over 160 spatter cones, scoria cones, and maar lakes. The most recent eruption occurred around 1,700 years ago at the Jinhongdingzi (JLDZ) volcano, which produced a subplinian-style eruption. The LVF is bounded by the NNE-trending Dunhua-Mishan and Yalyjiang faults, with the Hunjiang fault also transecting the area.

The region exhibits significant seismic activity and rapid surface uplift, particularly in its northeastern part. Seismicity has been shallowing over time, suggesting a potential link to deep magmatic processes.

Using GNSS and leveling data, we investigated three-dimensional crustal movements. Horizontal velocities relative to the Eurasian plate are generally below 10 mm/year toward the southeast. Stations east of the Dunhua-Mishan fault show postseismic effects from the 2011 Tohoku earthquake. The fault currently displays extensional behavior. Vertical motion has been dominantly uplift over the past 60 years, consistent with InSAR observations from 2014–2019 in the Jingyu area.

Magnetotelluric profiling reveals a crustal high-resistivity structure beneath the LVF, interpreted as solidified magma. These bodies vary in depth: >18 km in the west, shallowest beneath JLDZ, >40 km in the central region (early volcanic centers), and >20 km near Fusong in the east. A large-scale low-resistivity zone beneath these high-resistivity bodies is interpreted as a mid-to-lower crustal magma system. Notably, a low-resistivity anomaly below 10 km beneath JLDZ likely represents a magma conduit connected to the deeper system. The eastern magma source is relatively shallow (~30 km). We propose that mantle upwelling and intermittent magma migration contribute to the observed uplift and seismicity in the LVF.