Magmatic versus amagmatic : a study of local seismicity and lithospheric structure at two contrasting Southwest Indian Ridge segments

• Main Author: Schmid, Florian
• Other Authors: Bach, Wolfgang, Schlindwein, Vera, Grevemeyer, Ingo
• Format: Doctoral or Postdoctoral Thesis
• Language: English
• Published: Universität Bremen 2017
• Subjects: Mid-ocean ridge; seismicity; local earthquake tomography; lithosphere; magmatism; 550; 550 Earth sciences and geology; ddc:550; Arctic; Southern Ocean; Arctic Ocean; Indian; Gakkel Ridge
• Online Access: https://media.suub.uni-bremen.de/handle/elib/1326; https://nbn-resolving.org/urn:nbn:de:gbv:46-00106232-10

New sea oor is constantly being created at the global spanning system of mid-ocean ridges (MOR). Over a wide range of spreading rates is the produced oceanic crust of surprisingly uniform thickness and composition. An exception are ridges with spreading rates slower than 15-20 mm yra 1, so-called ultraslow spreading MORs, at which the crustal thickness and composition drastically change. A totally different mode of sea oor spreading occurs, with discontinuous crustal accretion along-axis. Entire sections of the ridge axis lack an igneous crust and the neighbouring volcanoes receive more melt than the regional average. The Gakkel Ridge in the ice-covered Arctic Ocean and the Southwest Indian Ridge (SWIR) in the stormy Southern Ocean are the main representatives of the ultraslow spreading ridges. At present, the processes of lithosphere formation at ultraslow spreading rates are still poorly understood. The investigation of microearthquakes, with networks of ocean bottom seismometers (OBS) or hydrophones, has signi cantly progressed our understanding of the lithosphere accretion processes at faster spreading ridges. Until recently, the rough environmental conditions prevented the long-term deployment of OBSs at the main representatives of ultraslow ridges. This thesis makes use of the rst one-year long records from two OBS networks with comparable extent that had been placed at different sections of the SWIR from 2012 to 2013. The chosen sites are characterized by contrasting crustal thickness, lithology and morphology. The Oblique Supersegment network was deployed near 13Adegree30a E where peridotites are the dominant sea oor lithology and a typical igneous crust is absent. The Segment 8 network was deployed near 65Adegree30a E around the volcanic center of the SWIR Segment 8 where the crust is locally thickened and the sea oor consists exclusively of basalts. I picked and located the microearthquakes for the Oblique Supersegment network and compiled an 11-month long catalogue that contains 2000 microearthquakes. ...