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Title: Constraining the temporal and spatial extent of the Indian Ocean-MORB composition: A Study of Rheic Ocean Ophiolites
Authors: Band, Adrian Robert
Supervisors: Barry, Tiffany
Zalasiewicz, Jan
Award date: 1-Jul-2016
Presented at: University of Leicester
Abstract: The depleted mantle producing mid-ocean ridge basalt (MORB) can be divided into chemical domains through variations in its radiogenic isotope compositions. Through performing whole-rock ¹⁴³Nd/ ¹⁴⁴Nd and ¹⁷⁶Hf/ ¹⁷⁷Hf analyses of MORB-like material in Rheic Ocean ophiolites, the range of the Indian Ocean-type mantle domain has been spatially and temporally traced. Isotope results presented in this study extend the known range of Indian Ocean-type mantle by highlighting its existence since c. 480 Ma, and documenting its pervasive distribution through Europe in the Devonian (c. 410 Ma to c. 390 Ma). Ophiolites from the Rheic Ocean generally contain radiogenic ¹⁴³Nd/ ¹⁴⁴Nd and ¹⁷⁶Hf/ ¹⁷⁷Hf, above estimates for the depleted mantle (DM) at the time of formation. These values indicate a history of melt depletion in the mantle pre-dating formation of the Rheic Ocean and depletion model ages (TDM) suggest this occurred throughout the Neoproterozoic-Cambrian. Highly radiogenic ¹⁷⁶Hf/ ¹⁷⁷Hf in the Careón ophiolite, NW Galicia, extend the known range of εHft in MORB from <+25-30 up to +39. The generally decoupled isotope compositions and increased ¹⁷⁶Hf/¹⁷⁷Hf common in the Rheic Ocean ophiolites is inconsistent with a model of mantle depletion, storage and re-melting. Instead, isotope compositions may highlight a complex history of mantle depletion, re-fertilisation, and mixing. Specifically, the isotope compositions may be reproduced by mixing Pacific Ocean-type mantle with anciently depleted and subsequently re-fertilised sub-continental lithospheric mantle. This modelling indicates that the Indian Ocean-type compositions in the Rheic Ocean ophiolites may have been produced by shallow contamination of the mantle, and likewise, the Indian Ocean-type mantle signature may also be a shallow mantle feature. The appearance of Indian Ocean-type mantle in the incipient Rheic Ocean preserved in the Pulo de Lobo ophiolite, S. Iberia (c. 480 Ma), coupled with a lack of such material in the coeval Ballantrae Complex from the Iapetus Ocean, suggests that the signature may be intrinsically related to Gondwana.
Type: Thesis
Level: Doctoral
Qualification: PhD
Rights: Copyright © the author. All rights reserved.
Appears in Collections:Leicester Theses
Theses, Dept. of Geology

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