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Australia: The Land Where Time Began |
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Mantle Flow on a Large Scale Revealed by
Global Dynamic Topography Observations to Have a Limited Influence
A fraction of the topography of the surface of the Earth that varies
with space and time is maintained by convective circulation of the
mantle. It is shown by most predictive models that this dynamic
topography has peak amplitudes of about ± 2 km, dominated by wavelengths
of 104 km. In this study Haggard, White & Al-Attar tested
these models against their comprehensive observational database of 2,120
spot measurements of dynamic topography that had been determined by
analysing oceanic seismic surveys. These accurate measurements, the
robustness of which has been carefully tested and benchmarked, have
typical peak amplitudes of ± 1 km and wavelengths of approximately 103
km, and generate a global spherical harmonic model when combined with
limited continental constraints. It
was revealed by their power spectral analysis that there were
significant discrepancies between observed and predicted topography.
Observed dynamic topography has peak amplitudes of about ± 500 m at
longer wavelengths, such as 104 km. Significant dynamic
topography is still observed at shorter wavelengths, such as 103
km. In this study it was shown that these discrepancies can be explained
if short-wavelength dynamic topography is generated by density
anomalies, which are temperature driven, within a sub-plate
asthenospheric channel. It is shown by stratigraphic observations from
adjacent continental margins that these dynamic topographic signals
evolve quickly over time. On the surface of the Earth more rapid
temporal and spatial changes in vertical displacement have direct
consequences for fields as diverse as mantle flow, oceanic circulation
and climate changes over the long term.
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Author: M.H.Monroe Email: admin@austhrutime.com Sources & Further reading |