New insights from low-temperature thermochronology into the tectonic
and geomorphologic evolution of the south-eastern Brazilian highlands
and passive margin
-
Abstract
The South Atlantic passive margin along the south-eastern Brazilian highlands exhibits a complex
landscape, including a northern inselberg area and a southern elevated plateau, separated by the Doce
River valley. This landscape is set on the Proterozoic to early Paleozoic rocks of the region that once was
the hot core of the Araçuaí orogen, in Ediacaran to Ordovician times. Due to the break-up of Gondwana
and consequently the opening of the South Atlantic during the Early Cretaceous, those rocks of the
Araçuaí orogen became the basement of a portion of the South Atlantic passive margin and related southeastern
Brazilian highlands. Our goal is to provide a new set of constraints on the thermo-tectonic history
of this portion of the south-eastern Brazilian margin and related surface processes, and to provide a
hypothesis on the geodynamic context since break-up. To this end, we combine the apatite fission track
(AFT) and apatite (UeTh)/He (AHe) methods as input for inverse thermal history modelling. All our AFT
and AHe central ages are Late Cretaceous to early Paleogene. The AFT ages vary between 62 Ma and
90 Ma, with mean track lengths between 12.2 mm and 13.6 mm. AHe ages are found to be equivalent to
AFT ages within uncertainty, albeit with the former exhibiting a lesser degree of confidence. We relate
this Late CretaceousePaleocene basement cooling to uplift with accelerated denudation at this time.
Spatial variation of the denudation time can be linked to differential reactivation of the Precambrian
structural network and differential erosion due to a complex interplay with the drainage system. We
argue that posterior large-scale sedimentation in the offshore basins may be a result of flexural isostasy
combined with an expansion of the drainage network.We put forward the combined compression of the
Mid-Atlantic ridge and the Peruvian phase of the Andean orogeny, potentially augmented through the
thermal weakening of the lower crust by the Trindade thermal anomaly, as a probable cause for the
uplift.
-
-