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Rare earth elements in mud-rich sediments and their use as provenance indicators

Alexander, Jane Louise; (1998) Rare earth elements in mud-rich sediments and their use as provenance indicators. Doctoral thesis (Ph.D), UCL (University College London). Green open access

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Abstract

Rare earth element (REE) patterns play a key role in understanding the provenance of mudrocks. However, there is uncertainty about the extent to which REE are mobile in sediments, and the effect this has on the provenance signal. This study focuses on Miocene to Pliocene hemipelagic mudrocks from Ocean Drilling Program (ODP) Site 808, drilled in the toe of the Nankai accretionary prism, SE Japan. A second mudrock suite from the Amatsu Formation, Boso Peninsula, Japan, was studied as a comparison. Mudrocks from the Nankai accretionary prism all have intermediate provenance, while those from the Amatsu Formation on the Boso Peninsula trend from intermediate provenance in the lower part of the sequence to mafic provenance in the upper part. There is a correlation between REE fractionation and provenance, which holds for both mudrock suites. Mudrocks with intermediate provenance have more fractionated REE patterns and higher concentrations of the light REE than those with mafic provenance. Some samples do not conform to this trend. Those from the Boso Peninsula appear to have had mixed sediment sources. The anomalous samples from the Nankai accretionary prism are related to fluid- rock interactions at the décollement zone, which have altered the provenance signature. Most have REE, trace and major element concentrations similar to the other hemipelagic mudrocks, despite being brecciated. However, there is a heavy REE enrichment in some samples from the décollement that are close to breaks in core recovery. They are associated with an enrichment in calcium, in the form of calcite. The enrichment of heavy REE in otherwise typical mudrocks suggests that they have been transported to the decollement in fluids, where they were co-precipitated with calcite. A potential source for these REE is a series of umbers and hydrothermal deposits, from where heavy REE may be preferentially leached.

Type: Thesis (Doctoral)
Qualification: Ph.D
Title: Rare earth elements in mud-rich sediments and their use as provenance indicators
Open access status: An open access version is available from UCL Discovery
Language: English
Additional information: Thesis digitised by ProQuest.
Keywords: Earth sciences; Rare earth elements
URI: https://discovery.ucl.ac.uk/id/eprint/10101190
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