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|Title:||The isotopic evolution of the northern East African Orogen|
|Author:||Blades, Morgan Lee|
|School/Discipline:||School of Physical Sciences|
|Abstract:||The Neoproterozoic era saw some of the most important events in the evolution of the planet. These events notably include the emergence of complex life and climatic extremes that involved widespread, possibly global glaciation. This era also saw the demise of the supercontinent Rodinia and formation of the supercontinent Gondwana, which likely played a fundamental role in the recorded events. Thus, to better understand these events there is a need to have rigorous models that describe the plate reconfiguration occurring during the Neoproterozoic. The East African Orogen (EAO) is a Neoproterozoic to early Cambrian mobile belt that reflects the collision between India and the African continents. It is the major collisional orogeny that formed as central Gondwana coalesced and the Mozambique Ocean closed. The evolution of the northern East African Orogen is well documented in the Arabian Nubian Shield (ANS). However, much less is known about the development of the orogen to the west (Chad, Sudan, Ethiopia) and east (Oman) of the ANS. This thesis provides new evidence from a number of Mesoproterozoic to Neoproterozoic basement exposures from western Ethiopia, Sudan, Chad and Oman to further constrain the evolution of the northern East African Orogen and subsequent effects on surrounding terranes. The Western Ethiopian Shield (WES) sits within the transition between the Arabian Nubian Shield and the Mozambique Belt. The shield is defined by three main phases of magmatism ca. 850– 810 Ma, 780–700 Ma and 620–550 Ma, with no evidence for pre-Neoproterozoic crust. The rocks have a supra-subduction related geochemical signature suggesting formation from fractional crystallisation and assimilation of mantle derived parental magmas. Post tectonic magmatism within the Western Ethiopian Shield occurs at ca. 572 Ma, defining the cessation of subduction within the area. To the west of the WES lies the Sahara Metacraton, a tract of pre-Neoproterozoic continental crust that is bound by suture zones. The effects of the collisional events that create these suture zones, can be seen in the form of deformation, emplacement of igneous bodies (ca. 1000–1100 Ma and 600–560 Ma), as well as localised episodes of crust formation due to rifting. Butana to the east of the Sahara Metacraton, preserves three main phases of magmatism and deformation at; ca. 987 Ma, 862 Ma and 764 Ma. The youngest pulse at ca. 764 Ma has been interpreted to represent the collision or accretion of Butana onto the Sahara Metacraton, therefore constraining the timing of terrane amalgamation in Sudan. In Oman, a small number of basement exposures offer an insight into its relationship to the Arabian Nubian Shield. Geochronological data suggest that the basement rocks of Oman formed between ca. 1000–750 Ma. The cessation of magmatism occurred by ca. 700 Ma, this was followed by the deposition of passive margin sequences. Lu–Hf isotope data suggest the progressive development of arc rocks away from a continental source, starting from the older eastern exposures to the more juvenile exposures in west Oman. Detrital data suggest that the Omani basement accreted on the margin of Neoproterozoic NW India, sourcing Palaeoproterozoic–Neoarchaean zircons, possibly from the Kabul Block. These data help to further constrain present reconstruction models for the Neoproterozoic, elucidating the continual remobilization of the Sahara Metacraton as a result of the Neoproterozoic orogenesis. These data can be used to place the terranes of the Arabian Nubian Shield in context with the rest of Gondwana and emphasise the importance of the migration of India towards the amalgams of Africa.|
|Advisor:||Collins, Alan Stephen|
Foden, John David
|Dissertation Note:||Thesis (Ph.D.) (Research by Publication) -- University of Adelaide, School of Physical Sciences, 2018|
|Keywords:||East African Orogen|
Research by Publication
|Provenance:||This thesis is currently in process. To enquire about access to this thesis please email firstname.lastname@example.org|
|Appears in Collections:||Research Theses|
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