Abstract
Araguainha is a mid-sized complex impact structure formed in sedimentary and underlying basement rocks of the Paraná Basin, Brazil. The structure has strongly deformed sedimentary strata surrounding a granitic core. The central uplift is a region of high geological complexity, comprising different types of sedimentary, igneous (granite) and metamorphic lithologies, plus breccias and impact melt sheets. New ground gravity data was collected to produce a Bouguer anomaly map and to perform a 3-D inversion in order to obtain a 3-D density model of the central uplift. This 3-D density model is consistent with iSALE numerical modeling results, which shows that the rocks in the innermost portion became brecciated and/or melted after undergoing pressure/temperature peaks. The positive anomaly of Furnas and Ponta Grossa formations associated with the numerical model shows that the central uplift is ~16 km wide. Thus, the granite's uplift caused the uplift of the entire stratigraphic package, from its Devonian-aged units to the Permian ones, forming a bull's eye pattern around the granitic core. The results also indicate that Araguainha was formed by a 3 km diameter impactor, and the rocks of the granitic basement rocks were uplifted by ~2 km.
Highlights
Impact structures are found on all solid planetary bodies, and play an important role in the formation and evolution of planetary landscapes
Some features are exclusively formed under high pressure conditions, such as shatter cones, planar fractures, tectosilicates with planar features, high-density minerals ranging from quartz to graphite, and transformation of minerals into amorphous phases, such as glass/lechatelierite (Melosh 1989, French 1998, Crósta et al 2019)
The residual Bouguer anomaly map for the central uplift (CU) does not show a circular pattern which is typically observed in impact structures (Figure 2)
Summary
Impact structures are found on all solid planetary bodies, and play an important role in the formation and evolution of planetary landscapes. Understanding the processes through which impact structures are formed helps to reveal how the planet evolved over geological time, its shallower layers. As the Earth is one of the most geologically active planetary bodies among all terrestrial objects in the solar system, impact structures are often poorly preserved and difficult to identify due to processes such as erosion, sedimentation, and tectonic movements that obliterate the geological record of impact events (Reimold et al 2018, Crósta et al 2019). Most of the known impact structures on Earth are partially eroded and/or covered by post-impact sedimentary rocks. This is usually the case of the seven impact structures found in Brazil, formed in the Phanerozoic Paraná Basin
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