Tracing mantle structure and chemical evolution using noble gas isotopes
The mantle is the largest reservoir of many of the Earth's volatile species. Detailed isotopic studies of noble gases within the mantle volatiles have demonstrated that they are of a primordial origin, which have been trapped in the mantle since the Earth's accretion. This original volatil...
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| Format: | Doctoral or Postdoctoral Thesis |
| Language: | English |
| Published: |
2015
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| Online Access: | https://research.manchester.ac.uk/en/studentTheses/a231d757-1535-4edd-899c-b2ecff0accf9 https://pure.manchester.ac.uk/ws/files/54564500/FULL_TEXT.PDF |
| Summary: | The mantle is the largest reservoir of many of the Earth's volatile species. Detailed isotopic studies of noble gases within the mantle volatiles have demonstrated that they are of a primordial origin, which have been trapped in the mantle since the Earth's accretion. This original volatile signature has continually evolved over time, due to the production of in situ radiogenic isotopes and through the recycling of surface volatiles back into the mantle (Lupton and Craig, 1975; Holland and Ballentine, 2006). The study of noble gases within magmatic samples has enabled the composition and structure of the mantle to be determined and has distinguished the multiple volatile reservoirs (primordial, crustal, marine etc.) that have contributed to the mantle composition sampled. Together with the halogens (Cl, Br and I) they represent key tracers of volatile transport processes in the Earth. Therefore a combined analytical approach including the halogens and noble gases is not only be able to track the influx of surface volatile into the mantle, but also provide a greater understanding to the fundamental controls of transport, storage and partitioning of volatiles within the mantle.A combined noble gas and halogen study was undertaken on three different geological samples sets to determine how surface volatiles interact with the mantle on a variety of different scales. Firstly continental xenoliths from the Western Antarctic Rift were analysed to establish the role of subduction volatiles in the creation of the rifts volcanic products. The xenoliths have 3He/4He ratios of 7.5RA indicating that the rift is dominated by the rising asthenospheric mantle. However the Br/Cl and I/Cl ratio and heavy noble gases within the xenoliths indicate that marine derived volatiles have been incorporated into the mantle beneath the rift and may have provided and fundamental control on the formation of the rift itself.Secondly the role of surface contamination on mantle samples has been evaluated. A transect along a MOR pillow basalt has ... |
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