Seismicity of ultraslow spreading mid-ocean ridges at local, regional and teleseismic scales: A case study of contrasting segments

• Main Author: Läderach, Christine
• Format: Thesis
• Language: unknown
• Published: 2012
• Subjects: Arctic; Indian
• Online Access: https://epic.awi.de/id/eprint/25874/; https://hdl.handle.net/10013/epic.38794

Of the global mid-ocean ridge system, ultraslow spreading ridges represent a different class of spreading mechanism. Below a full spreading rate of 20 mm y-1, the melt supply per increment of plate boundary drastically decreases resulting in a ridge morphology which is different from the morphology of faster spreading ridges. The main representatives of ultraslow spreading ridges, the Arctic Ridge System (ARS) and the Southwest Indian Ridge (SWIR), are located in remote areas which is the reason for the few number of case studies conducted at these ridges compared to manifold studies performed at faster spreading ridges. Nevertheless, several studies of the ARS and the SWIR have revealed that these ridges are composed of magmatic and amagmatic segments which represent different styles of crustal accretion. At the magmatic segments, the presence of basalt at the seafloor and a continuous positive magnetic anomaly at the ridge axis (CMA) indicate robust magmatism. At amagmatic segments, volcanic activity seems to be absent or to be concentrated on isolated volcanic centres where magma accumulates. Away from these volcanic centres, the seafloor is mainly composed of peridotite and lacks a CMA. Spreading at such segments is interpreted to take place by extension and thinning of the crust along normal faults or detachment faults exposing mantle material to the seafloor. At the ARS, the perennial ice cover limits ship operation including seismic profiling and the deployment of ocean bottom instrumentation. Similarly, the SWIR is located in latitudes with stromy weather limiting local studies accordingly. Thus, it is not well understood how spreading takes place at these ridges and what factors lead to the formation of volcanic centres. In order to learn more about spreading processes at ultraslow spreading mid-ocean ridges, seismicity can be monitored as earthquakes indicate active processes and give information about the mechanical and thermal state of the lithosphere. This project includes two case studies at an ...