Integrated geophysical mapping of the Ifewara transcurrent fault system,Nigeria |
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| Institution: | 1. Department of Cardiology, Papworth Hospital, Cambridge, UK;2. Department of Cardiology, Royal Brompton Hospital, London and Biomedical Research Unit, Royal Brompton and Harefield NHS Trust and Imperial College London, UK;3. Department of Cardiology, Mayo Clinic, 200 First St. SW, Rochester, MN 55905, USA;4. Department of Cardiac Physiology, Papworth Hospital, Cambridge, UK;1. Tianjin Key Laboratory of Ionic-Molecular Function of Cardiovascular disease, Department of Cardiology, Tianjin Institute of Cardiology, Second Hospital of Tianjin Medical University, Tianjin 300211, People''s Republic of China;2. Key Laboratory of Hormones and Development (Ministry of Health), Department of Diabetes and Gout, Metabolic Disease Hospital & Tianjin Institute of Endocrinology, Tianjin Medical University, Tianjin 300070, People''s Republic of China;1. Department of Cardiovascular Research, King''s College London, James Black Centre, 125 Coldharbour Lane, London SE5 9NU, United Kingdom;2. Kings College Hospital NHS Foundation Trust, Denmark Hill, London SE5 9RS, United Kingdom |
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| Abstract: | Integrated geophysical methods involving magnetic and dipole–dipole resistivity (DDR) were conducted across a prominent zone of weakness clearly observable in Landsat MSS and SLAR images in the Precambrian basement complex of southwestern Nigeria. Up till now, the location and existence of this megascopic structure have not been confirmed using geophysical methods. With the objective of delineating this weak zone and its structural attributes, three traverses were established at 500 m intervals across it, and geophysical measurements were made at 10 m intervals along these traverses. Qualitative interpretation of the magnetic data obtained shows a diagnostic signature of a near-vertical fault, trending along a NNE–SSW direction. Also, the quantitative interpretation of the data using the non-linear least-squares regression technique indicates that the width of the magnetic anomaly ranges from 90 to 150 m, its dip angle varies between 75° and 85°; the anomaly is concealed by a regolith of approximately 15 m thickness. Furthermore, a 2D resistivity inversion of the field resistivity data reveals a three-layer model, representing thin resistive topsoil underlain by weathered bedrock, resistive bedrock with a distinct low resistivity zone located within the bedrock. The most plausible explanation for this low resistivity zone is that it was formed by shearing activities during Late Precambrian times. Conclusively, the integrated approach employed in this research confirms the existence of the supposed Ifewara shear zone (ISZ). |
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