Abstract
Asia is a key natural laboratory for the study of active intra-continental deformation in far-field response to the ongoing collision ofIndiaandEurasia. The resulting tectonic processes strongly depend on the thermo-mechanical structure of the lithosphere. This lithosphere can be separated into crustal and lithospheric mantle parts. Since crustal heterogeneities tend to mask underlying upper mantle heterogeneities a reliable crustal model is required before the lithospheric mantle can be assessed. Therefore, a new methodology is proposed to obtain crustal models in areas such asAsia, where data is sometimes sparse and data spreading is inhomogeneous.
First the depth to the Moho discontinuity is assessed. Starting from the original observations, the isostatic topographic effect is removed, leading to residual observations. This greatly reduces the variance in depth between the observations. Then the residual, rather than original, observations are interpolated using Ordinary Kriging, which one average reduces the uncertainty of the interpolation by 30%. Finally, the removed isostatic topographic effect is restored to the interpolated Moho depth, leading to the full interpolated depth to Moho. Large parts of the resulting model have an estimated 1σ-accuracy (of the interpolation) of less than 2km. Regions with lower accuracy are characterised by lack of data (Arabian Peninsula, Afghanistan and Pakistan, Mongolia and far east Russia), or by abrupt, large lateral variations in Moho depth (e.g. western China).
Secondly crustal velocities have been estimated by fitting a three-layer velocity-depth curve through available data at each interpolation location.Three major regions with a characteristic average P-wave velocity (vp) range can be identified: northern and western Asia (vp ~ 6.6-6.8km/s), south-east Asia (vp ~ 6.3-6.4km/s), and the Tibetan region (vp ~ 6.2km/s). The average coefficient of determination is 66.5% but varies substantially throughout the research area.
Thirdly, using the crustal model, the crustal gravity anomaly signal can be removed from observed gravity anomalies derived from satellite missions and field campaigns. The residual anomalies are attributed to density heterogeneities in the uppermost mantle and together with seismic tomography data, these allow for an integrative study of the uppermost mantle. This reveals the presence of a cold lithospheric mantle root beneath the Siberian Craton and the East European Platform, up to a depth of 150km and 200km, respectively. The cold root of the Indian Craton is less thick (up to 100km). The Sino-Korean Craton seems to lack any cold lihospheric mantle root. The mantle beneath the Alpine-Himalayan convergence zone is warmer than ambient, most pronounced at depths of 100km and 150km. Uncertainties in the thermal modelling are of the order of 100°C and inaccuracies in the composition could add at most 100°C to this uncertainty.
The full 3-D model of the lithosphere thus obtained can be used to assess for example the strength of the lithosphere. Important spatial variations in the lithospheric strength are thus predicted throughout the study area. In the crust, this heterogeneity is largely related to variations in crustal thickness, while in the mantle, the mantle temperature is of primary importance.
Original language | English |
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Qualification | Doctor of Philosophy |
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Award date | 9 Sept 2013 |
Place of Publication | Utrecht |
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Print ISBNs | 978-90-6266-331-6 |
Publication status | Published - 9 Sept 2013 |