Magnetotelluric Image of Transcrustal Magmatic System Beneath the Tulu Moye Geothermal Prospect in the Ethiopian Rift. Issue 23 (14th December 2018)

• Record Type: Journal Article
• Authors: Samrock, Friedemann; Grayver, Alexander V.; Eysteinsson, Hjalmar; Saar, Martin O.
• Is Part Of: Geophysical research letters. Volume 45:Issue 23(2018)
• Page Start: 12, 847
• Page End: 12, 855
• Publication Date: 2018-12-14
• Subjects: magnetotellurics -- hydrothermal systems -- volcano monitoring -- geothermal energy -- volcanic unrest; Geophysics -- Periodicals; Planets -- Periodicals; Lunar geology -- Periodicals; 550
• DOI: 10.1029/2018GL080333
• Languages: English
• ISSNs: 0094-8276

Abstract

Abstract: Continental rifting is initiated by a dynamic interplay between tectonic stretching and mantle upwelling. Decompression melting assists continental breakup through lithospheric weakening and enforces upflow of melt to the Earth's surface. However, the details about melt transport through the brittle crust and storage under narrow rift‐aligned magmatic segments remain largely unclear. Here we present a crustal‐scale electrical conductivity model for a magmatic segment in the Ethiopian Rift, derived from 3‐D phase tensor inversion of magnetotelluric data. Our subsurface model shows that melt migrates along preexisting weak structures and is stored in different concentrations on two major interconnected levels, facilitating the formation of a convective hydrothermal system. The obtained model of a transcrustal magmatic system offers new insights into rifting mechanisms, evolution of magma ascent, and prospective geothermal reservoirs. Plain Language Summary: The Earth's continental plates can be broken apart by tectonic forces to form rift systems that may extend over thousands of kilometers. Continental rifts are often associated with numerous volcanoes that are fed by magma, which forms deep in the Earth's mantle and rises up along pathways of the fractured tectonic plate. A detailed understanding of the volcanic systems is important for hazard assessment and for geothermal energy production. We analyzed geophysical data that were measured at a volcanic field in the Ethiopian Rift Valley. The data consist of time series of the natural electric and magnetic fields. These fields are sensitive to the electrical conductivity structure of the Earth and can be used to image the subsurface electrical properties down to depths of many kilometers. Magma, for example, has typically very high electrical conductivities, which is why this method is ideal to detect melt reservoirs in the Earth's crust. Our obtained model shows, in great detail, how magma is transported through the crust and how it is stored below the volcanic system. Therefore, it provides new insights into rift‐associated volcanism, risk assessment, and geothermal energy production. Key Points: Magmatic system in continental rift setting extends over entire crust Shallow crustal partial melt zone drives convective hydrothermal system Three‐dimensional magnetotelluric phase tensor inversion is an ideal tool for imaging volcanic systems and for geothermal exploration