The NE “corner” of South America, known among geologists as the Borborema province, is penetrated by beautiful transcurrent shear zone networks, with the largest ones being several tens of kilometers wide and extending for hundreds of kilometers, now limited by the Atlantic Ocean in the east and the Phanerozoic Parnaiba Basin in the west. They continue under the Parnaiba basin to form the Transbrasiliano lineament, and to the NE into the African continent as part of a shear zone system that is thousands of kilometers long. I have been lucky enough to visit the region several times and hope to continue to study some aspects of these intriguing shear zones.
In Brazil the largest shear zones separate blocks of Precambrian basement of somewhat different ages and characteristics, but it is uncertain whether they represent sutures or just intracontinental shear zones formed during the late Neoproterozoic.
Magnetic maps nicely portray the extraordinary shear zone pattern in this area:
In outcrop, some of the shear zone system formed at high temperatures with melt generation, while other parts formed under lower temperatures. Outcrop pictures shown below.
Small-scale structures are abundant, as shown here from mylonites of the S part of the Patos Shear Zone. Click images for higher resolution.
A huge strike-slip duplex is well developed in the western part of the Patos Shear Zone, also showing up nicely on the magnetic map:
In summary, this shear zone system is one of the largest in the world and display the anastomosing patterns of shear zone systems at scales from 1000 km down to that of a thin section. It contains many hidden secrets, and definitely deserves more attention.
Read more about shear zones in:
Fossen, H. & Cavalcante, G. C. G. 2017. Shear zones – A review. Earth-Science Reviews 171, 434-455.