New insights into the geology and formation of the Araguainha impact structure, Brazil, from morphological and structural analysis

Recent roadworks across the 40-km-wide Araguainha impact structure (AIS) provided new, extensive exposures for mapping and structural analysis. We present an updated geological map of the AIS, highlighting Passa Dois Group Blocks (PDGBs) and the central uplift geology. Mapping indicates that faults outside the AIS likely result from pre-impact regional tectonics. The most prominent structural features in the AIS are primarily linked to the excavation and modification stages of cratering, with strain likely accommodated through detachments along interfaces between lithologic units with different rheologies. The outer rim and intermediate sections of the structure exhibit similar structural frameworks, where large, fault-bounded blocks dominate. PDGBs generally have quasi-centripetal structural vergences. In the outer rim region, PDGBs resemble gravity-driven complex slumps. There is no consistent evidence for the previously referred kilometer-scale concentric rings in the outer parts of the AIS, which had been surmised as evidence for a peak-ring configuration. PDGBs occur only between 10 km and 20 km from the structure’s center as a result of concurrent central uplift formation and crater rim collapse. The central uplift diameter is estimated at up to 20 km, and there is evidence for its asymmetric collapse. Besides rare injections of impact melt rock, the northern core comprises three types of impact breccia (suevite and polymict lithic breccia). The core can be divided into a structurally diverse megablock zone that overlies a seemingly coherent but folded and faulted crater floor of (meta)sedimentary basement. The AIS exhibits structural asymmetry that may be controlled, in part, by pre-impact anisotropy of the target.