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Title: The nature of the chemically enriched components of the Iceland mantle plume
Author: Williams, Alice Josiane
Awarding Body: University of Edinburgh
Current Institution: University of Edinburgh
Date of Award: 2005
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The main intentions of this research are to identify and characterise enriched components in the sub-Icelandic mantle and to determine their origins and relationships with other mantle components. Helium, strontium, neodymium and lead isotope data, in conjunction with major and trace element data, allow the characterisation of enriched mantle sources in the flank-zones. Postglacial olivine- and pyroxene-bearing basalt samples have been collected from each of three flank-zones. Pyroxene 3He/4He may have been affected by pre- or post-eruptive addition of radiogenic 4He, but olivine 3He/4He represent the time-integrated 3He/(U+Th) of the mantle source. Published oxygen isotope data indicate that the flank-zone basalts have not been affected by crustal contamination. Coherent trends in He-Sr-Nd-Pb isotope co-variation diagrams allow the identification of three distinct enriched components in the North Atlantic mantle. Each enriched component is characterised by lower 3He/4He (< 6 Ra) and 143Nd/ 144Nd and more radiogenic Pb and Sr isotope ratios than the depleted mantle components sampled in the rift-zones and along the MAR. One enriched component, EIl, is most prevalent in the mantle beneath the SFZ. It is distinguished from the other enriched components by its extreme Pb isotope composition (206Pb/204Pb > 19.4). It is probably derived from recycled oceanic crust (a young-HIMU-like component). The second enriched component, EI2, is only sampled at Öræfajökull (EFZ), and is distinguished by its extreme 87Sr/86Sr (> 0.7037) and positive D7/4. Its isotopic composition most likely has its origins in recycled pelagic or terrigenous sediments. The third enriched component, E13, dominates the Jan Mayen (North Atlantic) and Snæfell (EFZ) mantle sources. It has similar Sr, Nd and He isotopic compositions to EIl, but is characterised by less-radiogenic Pb isotope ratios ( 206Pb/204Pb ~ 18.6). It is also most likely derived from young recycled oceanic crust. Enriched mantle beneath Snæfellsnes appears to be derived from mixing of EIl and EI3. Two depleted components (DI1 and DI2) are required to explain negative trends in He-Sr, He-Nd or He-Pb co-variation diagrams. They have similar Sr, N d and Pb isotopic compositions to each other, but can be distinguished on the basis of 3He/4He. DI1 is characterised by 3He/4He ~45 Ra and represents the depleted Iceland plume component. DI2 is characterised by lower 3He/4He (7-9 Ra) and represents the depleted component in the N-MORB mantle. Only a very small contribution of DI1 can change the 3He/4He of a source without affecting its Sr; Nd or Pb isotopic composition. A mixing model is presented which enables plume-derived enriched components to be distinguished from those present in the shallow asthenospheric mantle. Only EIl appears to be intrinsic to the plume, whereas EI2 and EI3 are upper-mantle heterogeneities.
Supervisor: Not available Sponsor: Not available
Qualification Name: Thesis (Ph.D.) Qualification Level: Doctoral
EThOS ID:  DOI: Not available