Preliminary magnetotelluric investigation of crustal magma plumbing system beneath the Wulanhada volcanic field, northern China: Implications for the Magma reservoir and pathway

The Wulanhada Volcanic Field (WVF) in northern China consists of a few tens of well-preserved monogenetic volcanoes, where Holocene eruptions have occurred, but is rarely known. Understanding the internal structure of the crustal magma plumbing system beneath the WVF is of great significance for the study of volcanic eruption mechanisms and the assessment of volcanic risks and hazards. We present the crustal electrical resistivity models across the WVF obtained from two-dimensional (2-D) and three-dimensional (3-D) inversion of magnetotelluric profile data, which show some robust and meaningful features. Two high-resistivity anomalies (>1000 Omega center dot m) occupy almost the entire upper and middle crust. They may serve as an impermeable barrier to impede the ascent of deep magmatic fluids and/or melts. However, there is also a sub-vertical anomaly with moderate resistivity separating two high-resistivity anomalies. We inferred that it may represent a crustal-scale buried fault that provided a pathway for magma ascent during past eruptions and controlled the spatial distribution of the Holocene volcanic group in the WVF. A remarkably high-conductivity anomaly (3-10 Omega center dot m) in the middle-lower crust is explained to be the presence of similar to 0.8-7.5% partial melts. It may represent a magma reservoir that exists as a crystal-rich mush zone. Considering the presence of the magma reservoir and pathway beneath the WVF, the volcanic risks and hazards of future eruptions should not be ignored. The results shed light on the structure of the buried volcanic edifice in the WVF and need to be verified by more specific work in the future.