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| Titel |
Cenozoic vertical motions of the western continental margin of Peninsular India |
| VerfasserIn |
Fred Richards, Mark Hoggard, 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 |
250129031
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| Publikation (Nr.) |
 EGU/EGU2016-9093.pdf |
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| Zusammenfassung |
| Despite the cessation of rifting at ∼65 Ma and its remoteness from active convergence, the
topography of Peninsular India is dominated by a dramatic, high-elevation escarpment along
its western margin: the Western Ghats (∼1 – 1.5 km amsl). Inland of the escarpment, South
Indian topography exhibits a long-wavelength (>1000 km), low-angle (∼0.1∘) eastward tilt
down to the Krishna-Godavari and Cauvery deltas on the eastern continental margin.
Offshore, oceanic residual depth measurements show an identical long-wavelength
asymmetry from highs of +1 km in the Arabian Sea to lows of -1.2 km in the Bay of
Bengal.
Strong evidence from margin stratigraphy, dated palaeosurfaces, thermochronology,
cosmogenic nuclides and marine terraces combine to suggest that, following a period
of relative quiescence from 50 Ma – 25 Ma, the present-day topography evolved
in response to Neogene uplift and erosion along the western Indian margin. By
jointly inverting 530 longitudinal river profiles for uplift rate and calibrating our
inversions against these geological constraints, we successfully place this Cenozoic
landscape evolution into a more complete spatio-temporal framework. The results
demonstrate slow growth of the eastward tilt from 50 Ma – 25 Ma (≤0.02 mm
a−1), preceding a phase of increasingly rapid development – initiating in the south
– from 25 Ma onwards (≤0.2 mm a−1). The onset of rapid uplift pre-dates the
initial intensification of the Indian monsoon by >15 Ma, suggesting that rock uplift
and not climate change is primarily responsible for the modern-day relief of the
peninsula.
Previous studies have aimed to explain this topographic evolution by invoking flexural
isostatic mechanisms involving denudation, sediment loading and/or underplating. However,
seismological constraints show that South Indian topography deviates significantly from
crustal isostatic expectations, while the 9.8−2.2+3.8 km effective elastic thickness of the
region generates ∼125 km flexural wavelengths; considerably shorter than required for a
purely flexural driving mechanism. Instead, the ∼1 km amplitude, ∼2000 km wavelength
and long-timescale (∼25 Ma) growth of the western Indian margin topographic
anomaly are diagnostic of dynamic topography. This implication is confirmed by
the excellent spatial correlation between upper mantle shear wave anomalies and
residual depth measurements. The western Indian margin is one of several elevated
passive margins that abut regions of anomalously elevated ocean floor, suggesting that
mantle-derived vertical motions may be the major control on modern-day margin topography. |
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