Jean, Amandine, Beauvais, Anicet, Chardon, Dominique, Bonnet, Nicolas, Jayananda, Mudlappa, Janwari, Shazia, Mathe, P.-E., Aix Marseille Université (AMU), Institut de Recherche pour le Développement (IRD), Centre National de la Recherche Scientifique (CNRS), Centre européen de recherche et d'enseignement des géosciences de l'environnement (CEREGE), Institut de Recherche pour le Développement (IRD)-Aix Marseille Université (AMU)-Collège de France (CdF (institution))-Institut national des sciences de l'Univers (INSU - CNRS)-Centre National de la Recherche Scientifique (CNRS)-Institut National de Recherche pour l’Agriculture, l’Alimentation et l’Environnement (INRAE), Géosciences Environnement Toulouse (GET), Institut de Recherche pour le Développement (IRD)-Université Toulouse III - Paul Sabatier (UT3), Université de Toulouse (UT)-Université de Toulouse (UT)-Institut national des sciences de l'Univers (INSU - CNRS)-Observatoire Midi-Pyrénées (OMP), Université de Toulouse (UT)-Université de Toulouse (UT)-Institut national des sciences de l'Univers (INSU - CNRS)-Centre National d'Études Spatiales [Toulouse] (CNES)-Centre National de la Recherche Scientifique (CNRS)-Météo-France -Institut de Recherche pour le Développement (IRD)-Institut national des sciences de l'Univers (INSU - CNRS)-Centre National d'Études Spatiales [Toulouse] (CNES)-Centre National de la Recherche Scientifique (CNRS)-Météo-France -Centre National de la Recherche Scientifique (CNRS), Université de Rennes (UR), Géosciences Rennes (GR), Université de Rennes (UR)-Institut national des sciences de l'Univers (INSU - CNRS)-Observatoire des Sciences de l'Univers de Rennes (OSUR), Université de Rennes (UR)-Institut national des sciences de l'Univers (INSU - CNRS)-Université de Rennes 2 (UR2)-Centre National de la Recherche Scientifique (CNRS)-Institut National de Recherche pour l’Agriculture, l’Alimentation et l’Environnement (INRAE)-Institut national des sciences de l'Univers (INSU - CNRS)-Université de Rennes 2 (UR2)-Centre National de la Recherche Scientifique (CNRS)-Institut National de Recherche pour l’Agriculture, l’Alimentation et l’Environnement (INRAE)-Centre National de la Recherche Scientifique (CNRS), University of Hyderabad, and Centre for Earth and Space Sciences [Hyderabad]
International audience; Cenozoic topographic rejuvenation of divergent continental margins and their cratonic hinterland is a matter ofdebate. For instance, continental scale tilt has been advocated as a cause of Late Cenozoic relief growth of theIndian Peninsula. Our work aims at providing independent geomorphological constraints to test such assertions.The western margin of the Peninsula bears theWestern Ghats Escarpment (WGE), which carves both Precambrianrocks and 65 Ma old Deccan Traps. The escarpment separates a narrow coastal lowland plain drained to the ArabianSea from a highland plateau drained towards the Bengal Sea. Alternating and coupled chemical weatheringand erosion led to formation and dissection of lateritic paleolandscapes preserved both sides of the WGE. In thehighland, the relicts of three distinctive lateritic surfaces are recognized. They formed successively from 53Ma to 23 Ma on the basis of ages obtained by Ar-Ar dating of K-rich manganese oxides [1]. The first surfaceis topped by a duricrust rich in Al (bauxite) forming mesas at altitudes of 960 to 1400 m. The second surfacecalled "Intermediate" is mantled by a ferricrete, whose relicts remain 100 m below the bauxite at altitudes of 850 to 1250 m. The third surface corresponds to the relicts of a lateritic pediment, which may be capped by aferricrete at altitudes of 600 to 900 m. Three lateritic surfaces have been documented in the lowland. The Ar-Arages obtained indicate common lateritic weathering in both the highland and the lowland between at 53-45 Ma,then a divergence later on [1]. The oldest remnants of lateritic surface in the lowland are preserved at maximumelevation of 400-500 m close to the WGE and correspond to a pediment. This ancient landform was re-altered at24-19 Ma to form residual hills of the “Intermediate” relief (ca. 350-200 m). A younger pediment formed aroundthe residual hills and is preserved at ca. 150-50 m elevation.Relicts’ elevations of the three surfaces have been retrieved in both the lowland and the highland to reconstructsuccessive topographies across the WGE and estimate relief evolution and erosion budgets for major time steps.The results suggest that the denudation did not exceed 10 m/my in the Highland since 45 Ma, and is less than 11m/my since mitigation of chemical weathering ca. 23 Ma ago. In the lowland, denudation was limited to 5 m/mysince 45 Ma and less than 6 m/my since 19 Ma, implying negligible reworking of the WGE, which stabilizedat least 50 Ma ago [2]. These results have major implications for relief evolution of South India. They implyvery low relief growth since the Eocene and do not require a tilt of the Peninsula. They further put constraints onsedimentary supplies to both margins of the Peninsula over the last 50 Ma.[1] Bonnet et al., 2016, Chemical Geology 446, 33-53.[2] Beauvais et al., 2016, Geology 44, 299-302.