The Halogen Composition of the Proto-Iceland Plume Source Mantle
APPROVED The study of halogens in mantle-derived melts is allowing for new and unique insights into mantle geodynamics (e.g. Kendrick et al., 2017). The current dataset of mantle halogens record the compositions of both the depleted MORB mantle and the major re-enriched OIB deep mantle reservoirs (E...
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| Other Authors: | , |
| Format: | Thesis |
| Language: | English |
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Trinity College Dublin. School of Natural Sciences. Discipline of Geology
2018
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| Online Access: | http://hdl.handle.net/2262/82826 http://people.tcd.ie/dofarre |
| Summary: | APPROVED The study of halogens in mantle-derived melts is allowing for new and unique insights into mantle geodynamics (e.g. Kendrick et al., 2017). The current dataset of mantle halogens record the compositions of both the depleted MORB mantle and the major re-enriched OIB deep mantle reservoirs (EMI, EMII and HIMU). However our understanding of the halogen geochemical cycle suffers from a major limitation; the lack of a direct and measurable constraint on the Bulk Silicate Earth halogen composition of the Earth. Without this constraint in place, it is impossible to assess properly, the overall mass balance of halogens between the major geochemical reservoirs. This study has aimed to address this issue by characterising the halogen composition of the primordial ?undegassed? mantle reservoir. This ?undegassed? high 3He/4He mantle is sampled in the Vaigat formation; the oldest rocks of the 62-58Ma Baffin Island-West Greenland lavas; products of the ancestral Iceland plume (Stuart et al., 2003; Starkey et al., 2009). Based on tungsten isotopic measurements in lavas from the same locality; the formation of this reservoir is time constrained to the first fifty million years of solar system history (Rizo et al., 2016). It records primordial compositions with respect to Pb and Nd (Jackson et al., 2010); and has previously elucidated the primordial water content of the Earth (Hallis et al., 2015). As such characterising the halogen composition of this reservoir represents a unique opportunity to assess the halogen inventory of the earliest Earth. Modelling for crustal contamination revealed that none of the inclusions studied display any evidence of having been obviously crustally contaminated. The most primitive inclusions, yielded near-chondritic trace element compositions, while more enriched inclusions, record comparative light-ion lithophile element enrichment consistent with their respective whole rock?s more radiogenic Sr-Nd composition. Cl/K ratios suggest that only one of the inclusions studied records ... |
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