Large Meteorite Impacts and Planetary Evolution VI
This volume represents the proceedings of the homonymous international conference on all aspects of impact cratering and planetary science, which was held in October 2019 in Brasília, Brazil. The volume contains a sizable suite of contributions dealing with regional impact records (Australia, Sweden), impact craters and impactites, early Archean impacts and geophysical characteristics of impact structures, shock metamorphic investigations, post-impact hydrothermalism, and structural geology and morphometry of impact structures—on Earth and Mars. Many contributions report results from state-of-the-art investigations, for example, several that are based on electron backscatter diffraction studies, and deal with new potential chronometers and shock barometers (e.g., apatite). Established impact cratering workers and newcomers to the field will appreciate this multifaceted, multidisciplinary collection of impact cratering studies.
Shock metamorphism in samples from the Shili impact structure (Kazakhstan) and discussion of its size and age
*corresponding author: [email protected]
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Published:August 02, 2021
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CiteCitation
Ludovic Ferrière*, Siddharth Rajpriye, Pavel Sapozhnikov, Baurzhan Baimagambetov, 2021. "Shock metamorphism in samples from the Shili impact structure (Kazakhstan) and discussion of its size and age", Large Meteorite Impacts and Planetary Evolution VI, Wolf Uwe Reimold, Christian Koeberl
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ABSTRACT
Four impact structures are known from the Republic of Kazakhstan, most of which have been poorly studied. This includes the Shili impact structure, an ~1.5-km-wide circular feature visible in satellite imagery. It is located in the western part of Kazakhstan, in the Aktobe Region, where the structure is centered at 49°10.5′N and 57°50′E. While the structure was first considered to be a salt diapir, its impact origin was confirmed in 1989 based on the findings of rare shocked quartz grains and a few poorly developed “shatter cones.” In this contribution, we report the results of a field campaign and a detailed petrographic investigation of 15 quartz sandstone samples. We confirm the presence of rare shocked quartz grains with planar fractures (PFs) and planar deformation features (PDFs). The characterization of shocked quartz allows us to not only confirm the impact origin of the structure, but also to estimate a shock pressure of at least 16 GPa (with a local peak-shock pressure of at least 20 GPa) for some of the rocks now outcropping at the surface. Signs of postimpact hydrothermal alteration include the decoration of many of the PDFs and the occurrence of fractures filled with secondary silica in a few samples. The name and some statistics commonly reported for this structure are also discussed. We suggest the structure be referred as “Shili,” after the name of a nearby river and also that of a phytonym. The minimum original diameter of the Shili impact crater is estimated at ~4–5 km based on a minimum central uplift diameter of 1 km. An early Eocene to Pliocene age for the formation of the Shili impact structure is inferred based on stratigraphy.
- Asia
- Cenozoic
- Central Asia
- clastic rocks
- Commonwealth of Independent States
- Eocene
- field studies
- framework silicates
- hydrothermal alteration
- impact craters
- impact features
- Kazakhstan
- metamorphism
- metasomatism
- Neogene
- Paleogene
- planar deformation features
- Pliocene
- quartz
- sandstone
- sedimentary rocks
- shock metamorphism
- silica minerals
- silicates
- Tertiary
- Shili impact structure