School of Earth Sciences - Theses

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End date: 2019 × Subject: Neogene × Author: SHIN, JAERYUL ×

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    Neogene vertical motions in intraplate settings: case studies from Australia and Korea
    SHIN, JAERYUL ( 2012)
    The lithosphere is dynamically linked with the large-scale dynamics in the convective mantle beneath. While the horizontal lithospheric movements are now well understood in a framework of plate tectonics, it is still a challenge to explain the vertical motions of the Earth’s surface, especially in intraplate regions. Such movements may arise from a variety of causes, such as upper mantle flow and lithospheric responses to plate boundary forces. This thesis explores the unique records of vertical motion in two settings. In Southeast Australia, tectonic modes and rates during the Late Neogene are established from uplifted marine terraces and other geomorphic constraints. Uplift of southern Victoria has occurred at rates of up to ~55 m Myr-1 during the Quaternary, and the rate of uplift has increased progressively since the Middle Pliocene. Non-uniform uplift of coastal Tasmania varies from ~40 m Myr-1 to ~112 m Myr-1. Spatial variations of vertical motions in southern Victoria and Tasmania is order 100’s kms, and is largely explicable in terms of lithospheric flexure, in response to contemporary plate boundary forces coupled with localised lithospheric failures, superimposed on a longer wavelength dynamic topography. The eastern margin of NE Asia, including Korea, sits in the back-arc setting to the Western Pacific Subduction Zone, in the vicinity of a complex trench triple junction of the Philippine, Pacific, and Eurasian plate. Geochronology of the Quaternary marine terraces and fission track dating results of upper Cretaceous granites imply maximum uplift rates of 45.3±1.1 m Myr-1 during the Neogene and 168±16 m Myr-1 in the Late Quaternary. Maximum uplift rates correspond in a general sense with a belt of Quaternary mafic intraplate volcanism suggesting the uplift can be attributed to asthenospheric upwelling around the edges of the sinking Western Pacific slab. The edges of the subducting slab are currently located beneath the eastern margin of the peninsula at a depth of 600 km. In addition, plate boundary forces arising from interactions between the Pacific, Asian and Philippine plate contribute to lithospheric failure relating with faulting movements in the peninsula since the Late Neogene. This research on the long- term vertical deformation field of the continents provides new insights into the way in which the internal dynamics of the Earth modify the surface with the various scales driven by both lithospheric and sub-lithospheric processes.