Cataclastic deformation bands affecting alkaline volcaniclastics along an emerged island in oceanic fracture zone: the Paredão Volcano, Trindade Island

The presence of deformation bands (DBs) associated with porous volcaniclastic rocks, it is ubiquitous but poorly described. In Trindade Island, the Paredão Volcano's lapilli tuffs are deposited during the Middle Pleistocene, and several deformation bands are associated with conjugate pairs geometry. To analyze the structural geometry and mineral phase of host rocks, we employed a multiscale approach that included regional fracture and geometry studies in the field, microtectonics with a support of scanning electron microscopy (SEM-EDS), and 2D petrophysical properties analysis. The analysis revealed that the deformation bands result from two mechanisms. The first is a granular flow mechanism characterized by grain rotation and matrix reorganization. This mechanism is also associated with fluid flow and matrix zeolitization. The second mechanism is a cataclastic flow marked by crystal fragmentation and the formation of a fine-grained matrix. It is observed that the pre-existence of mineral cleavages and fractures facilitates these mechanisms. The combination of these two mechanisms, driven by fluid flow, leads to the development of cataclastic bands characterized by the loss of porosity, matrix reorganization, and distinct geometric patterns. Those mechanisms are suggested to be developed in a transtensional context related to the Vitória-Trindade Fracture Zone.