Seismic Structure of the Changbai Intraplate Volcano in NE China From Joint Inversion of Ambient Noise and Receiver Functions

Abstract

We study the detailed 3-D crustal and upper mantle structure beneath the active Changbai intraplate volcano in Northeast China by conducting a trans-dimensional Bayesian inversion of teleseismic receiver functions and Rayleigh-wave group velocity dispersions from ambient noise. More than 12,000 teleseismic receiver functions recorded at 78 seismic stations and 1,573 group velocity dispersions are used in this study. Receiver-function H-κ stacking measurements reveal a thick crust (~40 km) with a high Vp/Vs ratio (~1.8) beneath the Changbai volcano. Our joint inversion results show a heterogeneous crustal structure in the study region. A low-velocity body at depths of 8-15 km is revealed directly beneath the Changbai volcano, which has a lateral extent of~100 km in the north-south direction and may reflect a large magma chamber in the midcrust. Our results also reveal a 5-10 km depressed Moho and a low-velocity anomaly in the uppermost mantle beneath the Changbai volcano. These features may indicate an upwelling channel of the asthenospheric material with a high mafic composition, and the mafic intrusion attaches to the bottom of the crust and thus deepens the Moho beneath the volcano. Our results support the notion that the Changbai volcanism is caused by hot and wet mantle upwelling associated with subductiondriven corner flow in the big mantle wedge above the stagnant Pacific slab in the mantle transition zone.

Distribution of Partial Melt Beneath Changbaishan/Paektu Volcano, China/Democratic People's Republic of Korea

“…To date, no geophysical survey has imaged or shown evidence for a shallow magmatic system linked to the evolved commendite storage, suggesting it is small and/or cool. However, this study and past geophysical surveys do show evidence for an anomalous deeper region of low velocities(Hetland et al, ; Kyong‐Song et al, ; Liu et al, ; Song et al, ; Wu et al, ; Yang et al, ; Zhu et al, ; Zhang et al, ), attenuation (Wu et al, ), and conductivity (Choi et al, ; Tang et al, ).…”

“…They base this on relatively low Poisson ratios estimated from their RFs along with heat flow measurements from hot springs around CMP (Ehara et al, ). However, the prevalence of geophysical evidence such as high conductivities (Choi et al, ; Tang et al, ), strong velocity reduction (this study, (Zhang et al, ; Zhu et al, ), and strong attenuation (Wu et al, ) directly beneath the volcano suggest the presence of significant partial melt is likely. An exception to this is the study of Kim et al (), who find little evidence for a velocity reduction with depth in the crust beneath CMP.…”

“…However, the multiple magma chambers suggested by Zhang et al () are more likely explained by a distributed region of partial melt throughout the crust, as suggested by petrological studies at CMP (Andreeva et al, ; Pan et al, ) and similar to magma plumbing systems beneath other volcanoes (Annen et al, ; Cashman et al, ; Christopher et al, ; Sparks et al, ; Schmandt et al, ). More recently, a joint RF and surface wave study using data in China showed evidence for a significant low S wave velocity zone in the midcrust (∼3.0 km/s), with high P wave to S wave ratio (> 1.8) directly beneath CMP, supporting evidence for the presence of a magma reservoir beneath the volcano (Zhu et al, ).…”

Intraplate Volcanism and Regional Geodynamics in NE Asia Revealed by Anisotropic Rayleigh‐Wave Tomography

“…In contrast, a prominent middle‐lower crustal low‐velocity anomaly beneath the CBV is imaged by Fan and Chen () and interpreted to be the main magma chamber that may feed the surface volcanism and hydrothermal activities. Differences among existing seismic images complicate our interpretations, such as whether the lower crust of the CBV is characterized by cooled materials with low temperature (Kim et al, ; Zhu et al, ) or a magma chamber with high thermal state (Fan & Chen, ; Ri et al, ; Tang et al, ).…”

“…For example, Kim et al () imaged a middle‐lower crustal anomaly with relatively high Vs beneath the CBV, which is attributed as a consequence of compositional partitioning by mafic underplating and overlying cooled felsic layers as a result of fractional crystallization. However, Zhu et al () resolved a low‐velocity body at depths of 8–15 km under the CBV and interpreted it to be a middle crustal magma chamber, whereas the underlying lower crust is characterized by relatively high velocity that reflects cooled intrusive mafic material. In contrast, a prominent middle‐lower crustal low‐velocity anomaly beneath the CBV is imaged by Fan and Chen () and interpreted to be the main magma chamber that may feed the surface volcanism and hydrothermal activities.…”