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Since the Quaternary, extension and magmatism in the Main Ethiopian Rift (MER) have been mainly focused into narrow magmatic segments that have numerous volcanic centers and caldera collapses that offer favorable conditions for the occurrence of geothermal resources. However, the subsurface structure of the volcanic systems (0–10 km) and their link to the distribution of shallow geothermal resources remain unclear. To investigate the role of subsurface structures on the occurrence of these resources, we conducted gravity and magnetic studies combined with geological constraints within the Tulu Moye Geothermal Prospect (TMGP), one of the current geothermal prospects in the central MER associated with caldera collapses. Gravity data from the Global Gravity Model plus (GGMplus 2013) and ground magnetic data transformed into residual and derivative maps reveal that shallow magmatic intrusions occur under the volcanic centers (Tulu Moye, Bora, and Bericha). Our interpretation along with recent magnetotelluric model suggests that only the intrusion beneath Tulu Moye is currently magmatically active and includes partial melt, consistent with it being a primary heat source for the geothermal system. A new caldera formation model is proposed where the TMGP hosts an older large caldera (about 25 km diameter) within which there are several smaller nested caldera systems associated with the Bora, Bericha, and Tulu Moye volcanoes. Along with existing geologic, seismic, and magnetotelluric studies, our gravity and magnetic analysis indicate the interaction between NNE-SSW (rift-parallel) and NW-SE (cross-rift) trending faults, along with shallow magmatic intrusions and caldera systems, suggesting that such a large geothermal system is possible under these conditions.

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The Cauvery sedimentary basin of India, a part of the Eastern Continental Margin of India (ECMI), has evolved as a consequence of its breakup from East Antarctica in the early Cretaceous. This study covers approximately 10,000 km2 in the southern part of the Cauvery basin. A total of 5,161 gravity-magnetic observations were made in an area bounded by 78°–79°E longitude and 9°–10°N latitude. The gravity anomaly map shows a dominant NE-SW trend with a total relief of 83 mGal from −77 mGal to 6 mGal. The map reveals very prominent NE-SW trending linear gravity high bands and two circular/elliptical gravity lows around Madurai and Ramanathapuram, respectively. The residual gravity map reveals NE-SW trending alternative bands of gravity highs and lows, revealing a ridge-depression structure. The gravity modeling shows the presence of underplated material, which may be related to magmatic activity during the Cretaceous. The magnetic map reveals two prominent E-W trending linear structures, which probably represent the disposition of a shear zone under the Cauvery Basin. Based on the filtered magnetic and gravity map, we have prepared an interpreted basement geology map. The magnetic map and residual gravity map suggest that the basement rock of the basin is crystalline (granite/gneiss) and may not comprise a high-grade metamorphic rock Eastern Ghat Orogeny.

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Frontiers in Earth Science

Exploring Near-Surface Geophysics and Tectonics: From Conventional Modeling to AI Solutions
Edited by Ashutosh Chamoli, Luciano Telesca, Sanjit Kumar Pal
Deadline
14 May 2025
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