Identifying the reactivation of ancient shear zones in Sul-rio-grandense/Uruguayan shield (South America) using geomorphological index

Cratonic/shield regions are usually considered tectonically quiescent. Fluvial geomorphology analysis has demonstrated that these areas may face continuous deformation. This study proposes the use of anomalous $k_{sn}$ values, related to fluvial geomorphology, to infer recent deformation in these cratonic/shield regions. This approach is validated by the joint integration of $k_{sn}$ anomalies with other geomorphological indexes such as knickpoints and $\chi$, available uplift rates, and analysis of satellite images. Our methodology was tested in the Sul-rio-grandense/Uruguayan shield, a region formed during the Neoproterozoic, and its surrounding areas, which potentially hold evidence of neotectonism. Our findings reveal that $k_{sn}$ anomalies coincide with tectonic-related knickpoints and follow a preferential NE-trend in the northern of the study area. In the south, several $k_{sn}$ anomalies are associated with elevated $\chi$ values and extend to the Quaternary sediments. In general, the NE trend observed in our joint methodology fits well with mapped Neoproterozoic shear zones and potentially reflects ongoing deformation along these ancient shear zones. Potential causes for this neotectonism include far-field stresses associated with the Andean Orogeny and tectonic plate adjustments related to the Atlantic opening, as observed in other places along the Brazilian coast. The relationship between anomalous $k_{sn}$ values and other geomorphological indexes supports that our methodology could be a reliable approach for mapping neotectonism at regional scales.