Dynamic Topography of the Borborema Province, South America

Change log
Santana, Ana Patricia 

The Borborema Province is located in the northeast corner of the Brazilian Shield. It is characterized by a positive long-wavelength free-air gravity anomaly of ∼ +30 mGal, which is consistent with sub-crustal dynamic support. This inference is corroborated by the presence of positive residual depth anomalies of 100s of meters which are observed along the abutting continental margin. Onshore, regional uplift is manifest by Albian marine limestones, which crop out at 700 m within the Araripe basin, and by emergent Oligo-Miocene marine coastal terraces. It is inferred that sub-plate mantle convective processes play a significant role in generating and maintaining this elevated topography. Crustal velocity structure is constrained using a combination of legacy seismic wide-angle experiments and receiver function analyses. By exploiting a global compilation of rock physics measurements of velocity and density, residual topography anomalies are calculated for the onshore region. These anomalies have amplitudes of up to ∼ 1 km, consistent with offshore residual depth measurements. Finally, the temporal evolution of this domed region is investigated by analysing fluvial drainage patterns and legacy thermochronologic measurements. An inventory of more than 2, 200 longitudinal river profiles is assembled and inverted to recover uplift rate as a function of time and space, subject to independent calibration and validation. Results suggest that regional uplift commenced in Upper Cretaceous times and continued to the present day at an average rate of 0.005 mm yr−1. This history is consistent with inverse modeling of legacy apatite fission track samples. Rapid cooling events are recorded by samples located at the base of escarpments of the Borborema Plateau. Denudation of ∼ 1 km is estimated to have occurred during Miocene times. In conclusion, regional elevation of this region is youthful and maintained by a sub-lithospheric thermal anomaly that is manifest through a combination of slow shear-wave velocity anomalies, a lithospheric mantle shadow zone, and Neogene volcanism.

White, Nicholas
Dynamic Topography, Borborema Province, Residual Topography
Doctor of Philosophy (PhD)
Awarding Institution
University of Cambridge