Earth Sciences 2015; 4(2): 80-88 Published online April 9, 2015 (http://www.sciencepublishinggroup.com/j/earth) doi: 10.11648/j.earth.20150402.13 ISSN: 2328-5974 (Print); ISSN: 2328-5982 (Online) Global Mid-Ocean Ridges Mantle Tomography Profiles Desiderius Cyril Patrick Masalu University of Dar es Salaam, Institute of Marine Sciences, Zanzibar, Tanzania Email address: masalu@ims.udsm.ac.tz (D. C. P. Masalu) To cite this article: Desiderius Cyril Patrick Masalu. Global Mid-Ocean Ridges Mantle Tomography Profiles. Earth Sciences. Vol. 4, No. 2, 2015, pp. 80-88. doi: 10.11648/j.earth.20150402.13 Abstract: We have studied mantle tomography profiles of global mid-ocean ridges to investigate their depth of origin and other characteristics. The Mid-Atlantic and the South West Indian Ridges are deep rooted ridges that extend as far down in the mantle to 250-300 km. The Central Indian Ridge, South East Indian Ridge, Antarctica Nazca, Pacific Antarctica, Pacific Nazca and Juan de Fuca are shallow rooted ridges that extend down in the mantle only to 100 km. The deep rooted ridges appear to be characterized by a weak low velocity ridge anomaly while the shallow rooted ridges are characterized by strong low velocity ridge anomaly. This may be due to the variations of the geochemistry of the ridges due to the fractionation process during magma ascent. Furthermore, despite the three ridges that make the Indian Rodriguez Triple Junction having different characteristics, all the three sections of the ridges that make the Triple Junction are characterized by strong low velocity ridge anomaly and extended down to only 100 km. This is particularly typical for the length of nine to ten degrees from the Triple Junction which makes it appear as an independent system. Keywords: Mid-Ocean Ridges, Mantle Tomography, Hotspot, Triple Junction 1. Introduction Global tomography is a technique which involves the interpretation of observed seismic wave field in terms of seismic properties at depth to image the interior of the solid earth [1, 2]. The technique emerged about three decades ago. Tomography is used in global imaging to study the interior of the earth for various geophysical investigations, for example, mantle convection [3], mantle heterogeneities [4, 5], plumes [6], detection of subducted and folded lithosphere [7] and so on. Several digital global mantle tomography models have been developed and published [e.g. 5, 8-12]. These models are used to study the earth’s interior and investigate geophysical processes. Mantle profiles along global mid-ocean ridges were investigated in order to study the depth of origin of mid-ocean ridges and other characteristics of the profiles. This information would assist in the detail understanding and/or quantification of the various studies on mid-ocean ridges such as mid-ocean ridge basalt chemical systematics [e.g. 13, 14], correlation with kinematic parameters [e.g., 15], mid-ocean ridge tectonics [e.g., 16-18] and other geophysical and geochemical studies. 2. Methods Several available models of global mantle tomography [5, 8-12] were assessed for use in this study. With the exception of the Zhang & Tanimoto [12] model all other models were obtained from the REM webpage [19]. However, all these models except only for the Zhang & Tanimoto [12] model were found to have no suitable resolutions for this study which focuses on the top 600 km of the earth. Models from the REM webpage [19] are 4 by 4 degrees maps at depth intervals ranging from 89 to 130 km in the top 650 km of the earth. These models have trouble imaging narrow, shallow features like mid-ocean ridges. On the other hand, the Zhang & Tanimoto [12] model is a 2 by 2 degrees horizontally and for the first 90 km has four depth intervals ranging from 8 to 28 km starting at 10 km depth, and from 90 km to 650 km depth intervals of 20 km. Furthermore, this model uses surface waves and so it is better able to resolve shallow structures/features. The Zhang & Tanimoto [12] model was therefore chosen and used in this study as it offered relatively better resolution both horizontally and vertically that could image mid-ocean ridges. A Fortran program was coded to read the Zhang & Tanimoto [12] model and output the tomographic profile along a given segment of a mid ocean ridge. The mid-ocean ridge mantle profiles were plotted using the GMT