A Narrow Magma Conduit of the Changbaishan Volcano Revealed by High-Resolution Receiver Function Imaging

The Changbaishan volcano (CBV) is the largest Cenozoic intraplate stratovolcano in Northeast China. Although many seismic imaging studies have been conducted in the CBV area during the past two decades, the detailed crustal structure beneath the Tianchi caldera is still poorly understood due to the sparse seismic observations limited by the harsh natural conditions. In this study, we deployed dense linear seismic arrays along three slopes of the Changbaishan-Tianchi volcanic area for the first time to obtain unprecedented high-resolution images of the crustal structure by using the teleseismic receiver-function imaging technique. Our results reveal detailed variations of crustal interface characteristics beneath the Tianchi caldera and adjacent areas. Several intracrustal interfaces are clearly revealed that correspond well to geological bodies, which might indicate boundaries of consolidated igneous bodies related to the primitive magmatic activities. A continuous Moho discontinuity at ∼37 km depth is revealed, whereas a weak Moho zone with a vertical offset of ∼4 km appears directly beneath the Tianchi caldera, which shows a clear positive correlation with the average crustal Vp/Vs ratio. We deem that the prominent crustal thickening and the higher Vp/Vs ratio beneath the Tianchi caldera might be closely associated with the complicated mantle-derived mafic materials underplating at the crust-mantle boundary. The joint effect of the multilevel magmatic plumbing system and a narrow magma conduit beneath the Tianchi caldera could account for the distinctive bimodal volcanic eruption history of the CBV.