ASSESSING FRACTURE NETWORKS THAT CONTROL GEOTHERMAL FLUIDS IN THE NORTH REGION OF THE MALAWI RIFT ZONE

Most geothermal systems in the Malawi Rift Zone (MRZ) are structurally-controlled with no evidence of magmatic sources. However, structurally-controlled systems are poorly understood along the Western Branch of the East African Rift System. The lack of knowledge about fracture networks, which act as pathways of the geothermal fluids and favorable structural settings that enhance permeability, increase the risk of drilling non-productive wells in the first stages of exploration.

This study aims to quantify the relationship between complex fracture networks and geothermal fluids in the two regions with the highest heat flow of the MRZ: The Karonga and Nkhata basins in the northern part of the rift. Here the term “complexity” means fracture networks that show a wider range of orientations and higher intensity than other areas. The guiding hypothesis of this study is that the interconnected regional joints, inherited reactivated structures, and Quaternary faults comprise a complex fracture network that controls the geothermal fluid pathways and storage in geothermal systems in the Karonga and Nkhata regions.

We used digital elevation models to map structures, density of fracture intensity, and topology characterization to identify connectivity at the surface. Moreover, we used high-resolution aeromagnetic data to identify possible conductive structures at depth and the relationship between Precambrian structures and geothermal systems.

The initial results show that most of the hot springs in the Karonga area are located in Permian-Triassic and Quaternary basins with ~NNW-SSE fault trends. Also, hot springs are focused in a region of higher fracture intensity with a favorable setting related to terminations of ~NNW-SSE faults and intersections with reactivated Precambrian foliations (NW-SE). The Chiweta hot spring, the highest reservoir temperature in Malawi, is located in an intersection between NE-SW, N-S, and NW-SE faults. The aeromagnetic data shows that most of the hot springs are aligned with the deep conductive structures ~NW-SE of the Karonga Fault Zone (KFZ). The KFZ has been associated with the reactivation of the Precambrian Mughese Shear Zone.Further results will provide a better understanding of structurally-controlled geothermal systems and advance the development of geothermal energy in this region.