| Author: | Rathnayake Mudiyanselage, Samurdhika P R |
| Title: | Geophysical investigation of the lithospheric structure beneath the Indian Ocean |
| Advisors: | Tenzer, Robert (LSGI) Chen, Wu (LSGI) |
| Degree: | Ph.D. |
| Year: | 2022 |
| Subject: | Lithosphere Indian Ocean Hong Kong Polytechnic University -- Dissertations |
| Department: | Department of Land Surveying and Geo-Informatics |
| Pages: | xiii, 234 pages : color illustrations |
| Language: | English |
| Abstract: | The investigation of the lithospheric structure and processes is important for a better understanding of various natural geographical phenomena, such as plate tectonics, orogeny or isostasy. In this study, the particular attention is given to the study area covering the Indian Ocean and its surrounding continental regions. The lithospheric structure beneath the Indian Ocean is probably the most complicated, but at the same time, the least understood among world's oceans. Results of tomographic, geochemical, magnetic and other surveys provide the evidence of its complex geological history. Seismic surveys have been a primary source of information about the lithospheric structure beneath the Indian Ocean, but these experiments are mainly concentrated at locations of a high geophysical interest. Marine gravity data obtained from processing the satellite-altimetry measurements, on the other hand, deliver a detailed image of the whole seafloor relief, advancing further the knowledge about its formation, tectonism and volcanism. Due to the limited observed data in the Indian Ocean, this research investigates the geological and lithospheric structure by using gravimetric forward and inverse modelling methods together with other heterogeneous data. It continues with the Moho depth computation by using various gravimetric methods that assume either local or regional/global compensation mechanisms, particularly involving the Airy's theory of isostasy and the solution to the Vening Meinesz-Moritz inverse problem of isostasy, and two other approaches based on the direct gravity inversion. Lastly, an emphasis is also given to estimate the effective elastic thickness of the oceanic and continental lithosphere of that area. A better understanding of the effective elastic thickness is geologically important when investigating the mechanical strength of the lithosphere. The results presented in this work indicate that Bouguer and mantle gravity maps together with gravity gradient maps can effectively be used to identify major geological and tectonic features within the oceanic lithosphere that are spatially correlated with crustal thickness variations and a thermal signature of the lithospheric mantle. The comparison of various methods for a Moho modelling indicates that the Vening Meinesz-Moritz inverse method provides slightly more realistic result beneath the Indian Ocean than other three investigated methods. It is also demonstrated that the elastic thickness of the oceanic lithosphere is mainly controlled by its thermal state and isostatic rebalance of the oceanic lithosphere due to conductive cooling. Newertheleess, it is concluded that existing gravimetric methods for modelling of the elastic thickness of the ocenic lithosphere as well as for a Moho determination under the oceanic crust are not fully optimal. This requires development of more advanced methods that integrate various geophysical data and geological, geochemical, geothermal and geotectonic information. |
| Rights: | All rights reserved |
| Access: | open access |
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