La Palma island (Spain) geothermal system revealed by 3D magnetotelluric data inversion

Federico Di Paolo,Juanjo Ledo,Nemesio M Pérez,Iván Cabrera-Pérez,Katarzyna Ślęzak,David Martínez Van Dorth

doi:10.1038/s41598-020-75001-z

Abstract

The study of geothermal systems is nowadays a topic of great importance because of the huge amount of energy that could be converted in electricity for human consumption from such sources. Among the various geophysical methods employed to study geothermal reservoirs, the magnetotelluric (MT) method is capable to reveal the internal structures of the subsurface and interpret the geological structures from the electrical resistivity. We present the first 3D resistivity model of La Palma (Canary archipelago, Spain) obtained from a dataset of 44 broadband magnetotelluric soundings distributed around the island. Our results highlight the presence of resistivity anomalies, spatially coinciding with density anomalies present in literature. In the north of the island, a high resistivity anomaly can be interpreted as the signature of an old intrusive body beneath the Taburiente caldera. In the south, a complex resistivity structure around the Cumbre Vieja volcanic ridge could be indicative of presence of an active geothermal system. In particular, low-resistivity anomalies, located in a high-fractured zone, have values compatible with clay alteration caps (illite and illite–smectite). Such a result suggests the presence of hot rocks, or a dike system, heating fluids in the interior of Cumbre Vieja volcanic system.

Highlights

The use of geophysics to map the presence of magmatic/geothermal reservoirs beneath the surface of volcanic islands has been successfully employed not just for scientific purposes and as a first step to evaluate the possibility of exploration and exploitation of the geothermal r esources[1]
The geological evolution of the island, connected to the most significant visible volcanic edifices, can be summarized as[10]: (i) the old basal complex comprising a Pliocene seamount sequence and a plutonic complex, uplifted and tilted by subsequent intrusions, currently outcropping only inside the Taburiente caldera thanks to an extensive erosion; (ii) a volcanic series (1.7 to 0.4 Ma), including the Garafía volcano, the Taburiente shield volcano and Cumbre Nueva and Bejenado edifices, covering the northern part of the island; and (iii) the Cumbre Vieja series (123 ka to present), a ridge system having rift, faults and volcanic vents aligned along its N–S crest and whose volcanic products cover the southern part of the island
Such volcanic units are shown in Fig. 1: visible are the depressions of the Cumbre Nueva landslide and the Taburiente caldera, and the Cumbre Vieja ridge

Summary

Introduction

The use of geophysics to map the presence of magmatic/geothermal reservoirs beneath the surface of volcanic islands has been successfully employed not just for scientific purposes and as a first step to evaluate the possibility of exploration and exploitation of the geothermal r esources[1]. 4 to 3 Ma) comprising a Pliocene seamount sequence and a plutonic complex, uplifted and tilted by subsequent intrusions, currently outcropping only inside the Taburiente caldera thanks to an extensive erosion; (ii) a volcanic series (1.7 to 0.4 Ma), including the Garafía volcano, the Taburiente shield volcano and Cumbre Nueva and Bejenado edifices, covering the northern part (more than a half in surface) of the island; and (iii) the Cumbre Vieja series (123 ka to present), a ridge system having rift, faults and volcanic vents aligned along its N–S crest and whose volcanic products cover the southern part of the island. A shallow intrusive sills and dikes complex has been suggested to be present beneath Cumbre Vieja v olcano[14]

Methods

Discussion

Conclusion