![]() ![]() In the elevated plateaus, the ongoing surface uplift, disconnection with general baselevel and the loose of drainage area due the escarpment advance, have led to local-relief and erosion rates decreasing, as well as to the weathering profile deepening. These rates point to the mobility capacity of the escarpments which have migrated against the low-relief plateaus during Miocene times. The erosion map shows that modern erosion is focused on the current escarpments and the incised rivers with rates as high as the long-term ones. From Late Cretaceous and along Cenozoic, Precambrian shear zones and transfer zones seem to exert control in long/short-time denudation rates and delimitates the start position of escarpments. Thermal modeling, together with the published AFT ages, indicate widespread denudation following the Atlantic rift and a peak at Late Cretaceous associated with the alkaline magmatic intrusions and a high-relief extended proto Serra do Mar. Indeed, we performed a model for modern erosion rates based on the relationship of 10 Be-derived erosion rates and topographic and climatic parameters. In order to understand how the landscape has been evolving from these events, we integrated new apatite U-Th-Sm/He (AHe) data to a broad apatite fission track (AFT) dataset. These mountains record fast rock uplift episodes tens of millions of years after the Early Cretaceous continental rifting which are correlated to high sediment influx to the offshore basins. The passive margin of southeastern Brazil is characterized by two coast-parallel mountain ranges, Serra do Mar and Serra da Mantiqueira, separated by valleys partially covered with Cenozoic basins. ![]() These very long wavelength deformations record mantle dynamics, with a sharp increase of mantle upwelling around 34 Ma and an increase of the wavelength of the deformation and then of mantle convection around 10–3 Ma. Some long wavelength deformations (several 100 km) also occurred with (1) the low-elevation Central African Rise since 34 Ma and (2) the Atlantic Bulge since 20–16 Ma. (iii) The present-day topography of Central Africa is younger than 40–30 Ma and records very long wavelength deformations (1000–2000 km) with (1) the growth of the Cameroon Dome and East African Dome since 34 Ma, (2) the Angola Mountains since 15–12 Ma increasing up to Pleistocene times and (3) the uplift of the low-elevation (300 m) Congo Basin since 10–3 Ma. Restoration of this surface in Central Africa suggests very low-elevation planation surfaces adjusted to the Atlantic Ocean and Indian Ocean with a divide located around the present-day eastern branch of the East African Rift. (ii) Central Africa is an extensive etchplain-type weathering surface – called the African Surface – from the uppermost Cretaceous (70 Ma) to the Middle Eocene (45 Ma) with a paroxysm around the Early Eocene Climatic Optimum. This stepping of landforms records a local base level fall due to a local tectonic uplift. These planation surfaces are stepped along plateaus with different elevations. (i) The African relief results from two major types of planation surfaces, etchplains (weathering surfaces by laterites) and pediplains/pediments. Our objective is here (1) to present a new method of characterization of the very long and long wavelength deformations using planation surfaces with an application to Central Africa and (2) to reconstruct the growth of the very long wavelength relief since 40 Ma, as a record of past mantle dynamics below Central Africa. characteristic of lithospheric and mantle deformations respectively. Both plateaus and plains are characterized by large erosional surfaces, called planation surfaces that display undulations with middle (several tens of kilometres) to very long (several thousands of kilometres) wavelengths, i.e. There are two types of emerged relief on the Earth: high elevation areas (mountain belts and rift shoulders) in active tectonic settings and low elevation domains (anorogenic plateaus and plains) characteristic of the interior of the continents i.e. ![]()
0 Comments
Leave a Reply. |
AuthorWrite something about yourself. No need to be fancy, just an overview. ArchivesCategories |