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| Titel |
Deciphering post-Deccan weathering and erosion history of South Indian Archean rocks from cryptomelane 40Ar-39Ar dating |
| VerfasserIn |
Nicolas Bonnet, Nicolas Arnaud, Anicet Beauvais, Dominique Chardon |
| Konferenz |
EGU General Assembly 2015
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| Medientyp |
Artikel
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| Sprache |
Englisch
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| Digitales Dokument |
PDF |
| Erschienen |
In: GRA - Volume 17 (2015) |
| Datensatznummer |
250109221
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| Publikation (Nr.) |
 EGU/EGU2015-9114.pdf |
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| Zusammenfassung |
| Since the extrusion of Deccan traps ~ 63 Ma ago, weathering and erosion processes have
shaped the landscapes of this Peninsula India. This resulted in pervasive bauxitic
weathering on traps and deep lateritic weathering of their basement on either side of the
Western Ghats Escarpment, which separates a coastal lowland from an East-dipping
highland plateau. Mn-rich lateritic profiles formed by supergene weathering of Late
Archean manganiferous protores in the different greenstone belts are exposed on relict
paleosurfaces, which are preserved at different elevations on the highland plateau
and in the coastal lowland, allowing for direct comparison of paleosurfaces and
geomorphological processes across one of the most prominent relief in the Indian
peninsula.
Detailed petrological and geochemical investigations of samples collected in the
different Mn-rich lateritic profiles allowed for precise characterization of cryptomelane
[Kx Mn8-xIV MnxIII O16, nH2O], a Mn-oxide suitable for 40Ar-39Ar dating.
The ages obtained document major weathering periods at ~ 53-50 Ma, ~ 40-32
Ma, and ~ 30-23 Ma in the highland profiles, and ~ 47-45 Ma, ~ 24-19 Ma and
a younger age at ~ 9 Ma in the coastal lowland profiles. The age clusters are in
good agreement with major regional and global Cenozoic paleoclimatic events,
e.g., the Eocene climatic optimum and the early beginnings of Asian monsoons
at ~ 40 Ma. The old ages obtained both in the coastal lowland and high plateau
indicate synchronous lateritic (mostly bauxitic) weathering on both sides of the
escarpment. The ages also indicate that most of the incision and dissection of plateau
landsurfaces must have taken place during successive periods after 45, 32 and 23 Ma,
while the coastal lowland surface was only weakly incised after 19 Ma. Our results
thus document post-Eocene divergent erosion and weathering histories across the
escarpment since it was formed at least 47 Ma ago, suggesting installation of a dual
climatic regime on either sides of this escarpment after the Eocene greenhouse peak. |
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