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| Titel |
Cenozoic Uplift, Erosion and Dynamic Support of Madagascar |
| VerfasserIn |
Simon Stephenson, Nicky White |
| Konferenz |
EGU General Assembly 2016
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| Medientyp |
Artikel
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| Sprache |
en
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| Digitales Dokument |
PDF |
| Erschienen |
In: GRA - Volume 18 (2016) |
| Datensatznummer |
250130713
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| Publikation (Nr.) |
 EGU/EGU2016-11009.pdf |
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| Zusammenfassung |
| The physiography of Madagascar is characterised by high-elevation but low-relief
topography; 42% of the landscape is above 500 m in elevation. Eocene (marine) nummulitic
(marine) limestones at elevations of ∼400 m above sea level and newly dated, emergent 125
ka coral reefs suggest that Madagascar has experienced differential vertical motions during
Cenozoic times. Malagasy rivers are often deeply incised and contain steepened reaches,
implying that they have responded to changes in regional uplift rate. However, low
temperature thermochronology and 10Be derived erosion rates suggest that both Cenozoic
and Recent average denudation rates have been low. Extensive laterite-capped, low-relief
surfaces also suggest that there have been long periods of tectonic quiescence. In contrast, the
modern landscape is characterised by erosional gullies (i.e. lavaka), with very high local
erosion rates. To bridge the gap between this disparate evidence, we inverted 2566
longitudinal river profiles using a damped non-negative, least-squares linear inversion to
determine the history of regional uplift. We used a simplified version of the stream power
erosional law. River profiles were extracted from the 3 arc-second Shuttle Radar
Topography Mission (SRTM) digital elevation model. Calibration of the stream power
erosional law is based upon Cenozoic limestones and new radiometrically dated
marine terraces. The residual misfit between observed and calculated river profiles
is small. Results suggest that Malagasy topography grew diachronously by 1–2
km over the last 15–20 Ma. Calculated uplift and denudation are consistent with
independent observations. Thus drainage networks contain coherent signals that record
regional uplift. The resultant waves of incision are the principal trigger for modern
erosional processes. Admittance calculations, the history of basaltic volcanism
and nearby oceanic residual age-depth measurements all suggest that as much as
0.8—1.1 km of Cenozoic uplift in Madagascar is supported by mantle processes. |
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