Reconstruction of Ancient Volcanic Edifices Using Magnetotellurics: A Case Study from Carboniferous Zhibo Iron Deposit in Western Tianshan Metallogenic Belt in China

Volcanoes are the main pathway to the surface for the heat and material within the Earth. It is the window into the Earth because they provide and record many clues to what is going on in the subsurface. Active and potentially active volcanoes greatly affected the course of human history and are closely related to the present tectonics of the Earth. As a result, a great number of active volcanoes have experienced comprehensive geophysical studies. However, understanding to the internal structure of the ancient volcano complexes remains very poor. We propose a new approach to study the structure of the ancient volcano complexes based on the comparison of the magnetotelluric (MT) observation from Zhibo (ZB) ancient volcano and the active mid-oceanic ridges volcanoes from Iceland and intracontinental volcanoes from north China. MT responses of magma chambers from active volcanoes shows very close resistivity values. Based on these observations, we assumed that the ancient active volcano chambers have similar resistivity as current active volcanoes. We then reconstruct the ancient Carboniferous volcanoes complex in ZB using the ratio of the lower portion of the MT responses from ZB and active volcanoes. The results imply the existence of the fossil magma chambers at some 5 km in depth. It serves as the critical indication for a volcanic center and confirms the magmatic origin of the ZB volcanic rock-hosted iron deposits.