Crustal structure beneath the Malawi and Luangwa Rift Zones and adjacent areas from ambient noise tomography |
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| Institution: | 1. Geology and Geophysics Program, Missouri University of Science and Technology, Rolla, MO 65409, USA;2. Laboratory of Seismology and Physics of Earth''s Interior, School of Earth and Space Sciences, University of Science and Technology of China, Hefei 230026, China;1. Department of Geosciences, Biogeology, University of Tübingen, Hölderlinstrasse 12, 72074 Tübingen, Germany;2. Senckenberg Research Centre for Human Evolution and Paleoenvironment, University of Tübingen, Hölderlinstrasse 12, 72076 Tübingen, Germany;3. Instituto de Investigaciones Arqueológicas y Paleontológicas del Cuaternario Pampeano (INCUAPA-CONICET), Universidad Nacional del Centro de la provincia de Buenos Aires, Del Valle 5737, B7400JWI Olavarría, Buenos Aires, Argentina;4. Museo Municipal de Ciencias Naturales Pachamama, Santa Clara del Mar, Argentina;5. Universidad Nacional de Mar del Plata, Argentina;6. Div. Paleontología Vertebrados, Museo de La Plata, Paseo del Bosque, 1900 La Plata, Argentina;7. Centro Regional de Investigaciones Científicas y Transferencia Tecnológica de La Rioja (CRILAR), Provincia de La Rioja, UNLaR, SEGEMAR, UNCa, CONICET, Entre Ríos y Mendoza s/n, 5301 Anillaco, La Rioja, Argentina;1. Department of Earth and Environmental Sciences, National Chung Cheng University, 62102 Chia-Yi, Taiwan;2. State Key Laboratory of Geological Processes and Mineral Resources, Institute of Geophysics and Geomatics, China University of Geosciences, Wuhan, Hubei 430074, China;3. Hubei Subsurface Multi-scale Imaging Lab, Institute of Geophysics and Geomatics, China University of Geosciences, 388, Lumo Rd., Wuhan, Hubei 430074, China;1. Massachusetts Institute of Technology-Woods Hole Oceanographic Institution Joint Program in Oceanography/Applied Ocean Science and Engineering, Woods Hole, MA 02543, USA;2. Department of Geology and Geophysics, Woods Hole Oceanographic Institution, Woods Hole, MA 02543, USA;3. Boone Pickens School of Geology, Oklahoma State University, Stillwater, OK 74078, USA;4. Dublin Institute for Advanced Studies, Dublin, Ireland;5. Geological Survey Department of Zambia, P.O. Box 50135, Lusaka, Zambia |
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| Abstract: | Crustal shear wave velocity structure beneath the Malawi and Luangwa Rift Zones (MRZ and LRZ, respectively) and adjacent regions in southern Africa is imaged using fundamental mode Rayleigh waves recorded by 31 SAFARI (Seismic Arrays for African Rift Initiation) stations. Dispersion measurements estimated from empirical Green's functions are used to construct 2-D phase velocity maps for periods between 5 and 28 s. The resulting Rayleigh wave phase velocities demonstrate significant lateral variations and are in general agreement with known geological features and tectonic units within the study area. Subsequently, we invert Rayleigh wave phase velocity dispersion curves to construct a 3-D shear wave velocity model. Beneath the MRZ and LRZ, low velocity anomalies are found in the upper-most crust, probably reflecting the sedimentary cover. The mid-crust of the MRZ is characterized by an ~3.7% low velocity anomaly, which cannot be adequately explained by higher than normal temperatures alone. Instead, other factors such as magmatic intrusion, partial melting, and fluid-filled deep crustal faults might also play a role. Thinning of the crust of a few kilometers beneath the rifts is revealed by the inversion. A compilation of crustal thicknesses and velocities beneath the world's major continental rifts suggests that both the MRZ and LRZ are in the category of rifts beneath which the crust has not been sufficiently thinned to produce widespread syn-rifting volcanisms. |
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