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    The Cenozoic evolution of the South Vietnam margin of the South China Sea and the origin of coastal placer deposits

    Nguyen, Hiep Huu (2019) The Cenozoic evolution of the South Vietnam margin of the South China Sea and the origin of coastal placer deposits. Doctoral thesis, Birkbeck, University of London.

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    Abstract

    Vietnam mineral reserves contribute significantly to its economy and South Vietnam is especially rich in these resources. Whilst this region is well known as a source of oil and gas, extracted from offshore basins it is also an exporter of titanium ore extracted from coastal sands rich in heavy minerals. Despite decades of exploitation there remain fundamental questions about the origins of these resources that form the aims of this thesis. Specifically, 1) Where did the titanium bearing mineral known as ilmenite found in the heavy mineral sands come from? 2) How is the sedimentation history of the hydrocarbon basins connected to the uplift and erosion history of South Vietnam? To answer these questions an extensive set of rock and sand samples were collected from across the region and analysed using a combination of detrital zircon geochronology, petrology, geochemistry and apatite thermochronometry. In answer to question one results showed that the placer sands along coastal southern Vietnam came from local river catchments rich in outcrops of Cretaceous granites. The geochemical and petrological data also showed ilmenite titanium contents increased to the south, explained by a wider continental shelf that increased exposure to weathering during glacial sea-level lowstands before rising sea- levels remobilised the sand. Question two was answered by apatite thermochronometry data that detected increased rock uplift between 25-15 Ma across most of South Vietnam. This timing is significant as local marine basins also show inversion and a regional unconformity at the Oligocene/Miocene boundary. Following inversion basins subsided under the load of thick sands produced by erosion of the onshore region. These data provide the first solid link between basin sedimentation and onshore erosion. The cause of uplift is likely related to a change in regional stress field linked to ocean spreading in the South China Sea.

    Metadata

    Item Type: Thesis
    Additional Information: Date of PhD award confirmed as 2019 by registry
    Copyright Holders: The copyright of this thesis rests with the author, who asserts his/her right to be known as such according to the Copyright Designs and Patents Act 1988. No dealing with the thesis contrary to the copyright or moral rights of the author is permitted.
    Depositing User: Acquisitions And Metadata
    Date Deposited: 13 May 2019 13:07
    Last Modified: 19 Jun 2021 08:27
    URI: https://eprints.bbk.ac.uk/id/eprint/40385

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