Shear wave velocity structure beneath Northeast China from joint
inversion of receiver functions and Rayleigh wave group velocities:
Implications for intraplate volcanism
Abstract
A high-resolution 3-D crustal and upper-mantle shear-wave velocity model
of Northeast China is established by joint inversion of receiver
functions and Rayleigh wave group velocities. The teleseismic data for
obtaining receiver functions are collected from 107 CEA permanent sites
and 118 NECESSArray portable stations. Rayleigh wave dispersion
measurements are extracted from an independent tomographic study. Our
model exhibits unprecedented detail in S-velocity structure.
Particularly, we discover a low S-velocity belt at 7.5-12.5 km depth
covering entire Northeast China (except the Songliao basin), which is
attributed to a combination of anomalous temperature, partial melts and
fluid-filled faults related to Cenozoic volcanism. Localized crustal
fast S-velocity anomaly under the Songliao basin is imaged and
interpreted as late-Mesozoic mafic intrusions. In the upper mantle, our
model confirms the presence of low velocity zones below the Changbai
mountains and Lesser Xing’an mountain range, which agree with models
invoking sub-lithospheric mantle upwellings. We observe a positive
S-velocity anomaly at 50-90 km depth under the Songliao basin, which may
represent a depleted and more refractory lithosphere inducing the
absence of Cenozoic volcanism. Additionally, the average
lithosphere-asthenosphere boundary depth increases from 50-70 km under
the Changbai mountains to 100 km below the Songliao basin, and exceeds
125 km beneath the Greater Xing’an mountain range in the west.
Furthermore, compared with other Precambrian lithospheres, Northeast
China likely has a rather warm crust (~480-970 °C) and a
slightly warm uppermost mantle (~1200 °C), probably
associated with active volcanism. The Songliao basin possesses a
moderately warm uppermost mantle (~1080 °C).