Antonio Zeoli

Evolution, pattern, and partitioning of deformation during oblique continental rifting: Inferences from lithospheric‐scale centrifuge models

Oblique rifting is investigated through centrifuge experiments that reproduce extension of a continental lithosphere containing a preexisting weakness zone. During extension, this weakness localizes deformation, and different rift obliquity is obtained by varying its trend with respect to the stretching direction. Model results show that deformation is mostly controlled by the obliquity angle a (defined as the angle between the orthogonal to the rift trend and the extension direction). For low obliquity (alpha 45 degrees), no boundary faults form, and the extensional deformation affects the rift depression since early stages of extension. Dominance of the strike-slip motion over extension leads to the development of oblique-slip and nearly pure strike-slip faults, oblique to both the rift trend and the orthogonal to the extension direction, with no strain partitioning between the margins and the rift floor. These results suggest that oblique reactivation of preexisting weaknesses plays a major role in controlling rift evolution, architecture, and strain partitioning, findings that have a significant relevance for natural oblique rifts.

The Kamil Crater in Egypt

An unusually well-preserved 45-meter-diameter crater provides ground truth for small-scale meteorite impacts on Earth. We report on the detection in southern Egypt of an impact crater 45 meters in diameter with a pristine rayed structure. Such pristine structures are typically observed on atmosphereless rocky or icy planetary bodies in the solar system. This feature and the association with an iron meteorite impactor and shock metamorphism provides a unique picture of small-scale hypervelocity impacts on Earth’s crust. Contrary to current geophysical models, ground data indicate that iron meteorites with masses of the order of tens of tons can penetrate the atmosphere without substantial fragmentation.

Kamil Crater (Egypt): Ground truth for small-scale meteorite impacts on Earth

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Ice-flow dynamics and meteorite collection in Antarctica

Abstract Typical targets for meteorite searches in Antarctica are blue ice fields in front of major bedrock obstacles, where the meteorite-bearing ice slows down, is uplifted and exhumed by ablation. However, in some areas collection occurs in the lee of topographic barriers, as documented in the downstream side of the Frontier Mountain, a major emerged bedrock barrier. In this study we present an analogue modelling study of ice flow at Frontier Mountain, which has been chosen as example study area because an exceptionally complete set of glaciological data is available to investigate the causes leading to meteorite concentration. Results of modelling show how the boundary conditions (mainly the bedrock topography) control ice flow and how this flow, coupled to high ablation, may give rise to a stable meteorite trap downstream of major topographic obstacles. Modelling results support the contention that, as erosion is not a mountain builder, ablation does not represent a driving force in ice-flow dynamics, although it plays a significant role in shaving stranding surfaces and exhuming meteorites.