Feições de dissolução em inselbergs graníticos: primeiras considerações

Abstract

Inselbergs are landforms shaped by a number of erosion processes. They can be characterized either by a predominance of dissolution features or fracturing, and occasionally exhibit massive slopes. In this study, it will be demonstrated the primary structural mechanisms driving the formation of dissolution features, such as gnammas (pits). In granitic rocks, mafic ellipsoidal enclaves can act as a starting point for differential erosion. The enclaves and their orientation control the early stages of dissolution features (ellipsoidal microcavities and gnammas). In the Pedra do Cruzeiro inselberg, located in Quixadá, northeastern Brazil, 99 enclaves were analyzed in a 230m SW-NE transect in the inselberg hillslope. The data show that the primary trend of enclave orientation coincides with the orientation of dissolution features in their first and second stages. 97% of these features follow the main strike (86E) of the enclaves. In advanced erosion stages, mega karren are developed and not controlled by the preexisting structural patterns, attesting to the superimposition of the local drainage network over the structure (e.g., magmatic foliation and mafic enclave orientation).