Electrical Structure Beneath Jingpohu Volcano Area And Its Magmatic Dynamic Significance

Jingpohu volcanic area is located in the middle of the Dunhua-Mishan volcanic eruption belt in Eastern China.Volcanoes were active for a long time,and took place in the Cenozoic Tertiary and Quaternary.At present,Jingpohu volcano is an active volcano in the state of dormancy.At the same time,the volcanic mechanism of Jingpohu volcano is not clear,and there are still some controversials on the origin of the volcano,so it is very necessary to study the underground structure and volcanic mechanism of Jingpohu volcano systematically.We carried out wide-band magnetotellurite observations in and around Jingpohu area,with a total of 44 effective observation stations,with a distance of about 40 km.The observation time of each station was more than 20 hours.After the original time series data were processed into the standard EDI format with the software provided by the instrument,we conducted phase tensor analysis on all stations,and the results show that the stations in the fault and volcanic area show strong 3d properties,so it is reasonable to choose 3d inversion.After the trial calculation of different inversion methods and parameters,the three dimensional electrical results which are more consistent with geology and geophysics are selected.At the same time,in order to verify the reliability of the inversion results,we also carried out replacement verification for two deep low-resistivity anomalies,which proved the existence of the low-resistivity anomalies.The resistivity results show that there is a low resistivity anomaly D at the bottom of the crust 30-100 km in the Jingpohu area,and the root of the anomaly reaches the bottom of the lithosphere.There is a small low resistivity stratiform C2 in the middle and upper crust.At the same time,a smaller low resistivity body C1 was found about 5 km below the Dunhua-Mishan Fault.This low resistivity body is thedisplay of the sedimentary layer of the Ning'an Basin.According to the analysis of petrophysics,D anomaly is partially molten magma,the melting proportion is about10%-20%,C2 anomaly is saline fluid,and the rock porosity within this range is estimated to be about 1%.It is further speculated that the volcanic mechanism of the Jingpohu volcano,because the Pacific plate stayed in the mantle transition zone of Northeast China and continued dehydration,it partially melted on the top of the mantle transition zone when the plate retreated,eventually,it reached the bottom of the crust in the Jingpohu area to form a magma room.Under the control of the Dunhua-Mishan Deep Fault,the magma continued to rise,condensed and consolidated while releasing the salt-containing fluid in the middle and upper crust,and distributed horizontally in layers.At the same time,the Ning'an Basin next to the Jingpohu volcano was controlled by faults and volcanoes.After undergoing uplift and denudation and volcanic eruption during the Cenozoic period,it formed the current large-scale basalt-covered landform.