Magmatic Processes in the Naibor Soito Distributed Volcanic Field, Tanzania Constrained from Satellite Geodesy and Seismicity

Active rifts are regions of lithospheric extension that experience a complex interplay between volcanic activity, magmatism, seismicity, and faulting. An ideal setting to study magmatic-tectonic interactions in a young active rift is the Naibor Soito distributed volcanic field, Tanzania, which represents a 50 by 50 km2 section of the East African rift system. The area hosts a distributed volcanic field of monogenetic cones bounded by Gelai, a shield volcano that has not erupted in the past 10,000 years, and Ol Doinyo Lengai, the only active volcano in the world that erupts carbonatite lava. Although Gelai is dormant, the volcano experienced a magma-driven earthquake swarm and dike intrusions from July to September 2007. A graben formed on the southern flank of Gelai after the largest earthquake in the sequence struck in mid-July. According to geodetic studies, land subsidence continued over the following weeks as a result of dike emplacement, which was likely related to the explosive eruption phase of Ol Doinyo Lengai in 2007-2008. Evidently, the volcanoes at the Naibor Soito distributed volcanic field are connected by an underground network of magmatic conduits. However, constraining the 3-D structure of the magma plumbing system and corresponding magmatic processes require further investigation. This study involves the analysis of a temporally dense COSMO-SkyMed SAR dataset spanning the period 2013-2014 for which a seismic catalog of microseismicity is available. In the absence of detectable deformation at the Naibor Soito distributed volcanic field, the USGS Coulomb 3.4 software was used to determine the extent of growth that magma sources can attain without causing detectable deformation. For instance, a sill at a depth of 10 km needs to undergo a tensile opening of at least 15 m in order for the surface above to have a vertical displacement of 1.5 cm, the value of the smallest displacement that the COSMO-SkyMed satellite system can likely detect. Coulomb input parameters such as seismicity and faulting can also provide insights into magmatic processes. Ultimately, geodetic and seismic datasets are used to constrain published models of magma sources. The results have implications for characterizing the magma plumbing system and more broadly, improving forecasts of eruptions and earthquakes at rift systems.