Dissertation
Monturaqui meteorite impact crater, Chile: a terrestrial analog for small craters on Mars
University of Iowa
Doctor of Philosophy (PhD), University of Iowa
Summer 2020
DOI: 10.17077/etd.005565
Abstract
Meteorite impact cratering is a ubiquitous and important geological process across the solar system. Small craters (<1 km diameter), the most abundant type, are underrepresented and understudied on Earth because they are rapidly eroded away or buried by active geological processes.
Monturaqui Crater is a small (370 x 350 m) and well-preserved simple crater located south of the Salar de Atacama in the Atacama Desert of northern Chile. It was formed 663 ka by the impact of a c.15 m diameter asteroid in a simple target lithology consisting of Ordovician monzogranite unconformably overlain by Pliocene ignimbrite and cut by mafic and felsic dikes. The impact resulted in extensive ejecta deposits around the crater that have been subsequently eroded by eolian, mass wasting, and fluvial processes.
The Atacama Desert has commonly been used as a terrestrial analog for Mars due to its hyperarid climate and volcanic geology. Thus, Monturaqui Crater is an ideal terrestrial analog crater to better understand how similar features form on other solid bodies in the solar system. It also is an ideal location for study the local effects of the impacts the size of the one that produced Monturaqui Crater.
Studying small craters on Mars requires a satellite-based remote sensing approach to characterize a site and construct a reasonable geologic interpretation. Monturaqui was used as a test site to evaluate this methodology. This was done by using satellite imagery from IKONOS and ASTER to map the lithology and ejecta deposits of the site and estimate erosion by identifying likely erosional pathways and characterizing the overall shape of the crater. Estimates of original ejecta thickness and erosion rates were also made. This was followed up by ground-truthing through field work, which resulted in a high resolution geologic map of the target rocks and ejecta deposits. The field work also led to the discovery of the remnants of a fold hinge at the rim, and collection of impactite samples. Samples of impact melt rock were studied in detail to characterize their morphology and textures to identify specific processes that the samples underwent during ejection, transport, and deposition and to constrain the shock pressures during the impact event.
The ability of the remote sensing approach to distinguish lithology was limited because it required assumptions to be made, such as the degree of preservation of the crater. In addition, there were several sub-meter features observed in the field that were below the resolution threshold of the remote sensing methods used, resulting in a significant change in the geologic interpretation of the site. Monturaqui is relatively well-preserved, but the rim has experienced significant erosion, perhaps as much as 35 m. Ejecta deposits are preserved only in the continuous ejecta zone and are concentrated within one crater radius of the rim. Meteoritic- and melt-bearing impact products were recovered from the site and are clustered on the south-southeast crater rim, which provides additional evidence supporting an impact direction from the north-northwest. Structural measurements indicate the presence of a fold hinge on the northwest and east rims, the remnants of the original overturned rim sequence. Sub-meter field observations suggest a more complicated history than the one suggested by remote sensing.
Resolution is a limiting factor in studying ejecta at small craters and becomes increasingly problematic as crater size decreases. Remote sensing can be used to construct basic geologic interpretations for small craters but details below the available resolution can significantly change the interpretation of a site. Increasing resolution can help mitigate this problem.
Details
- Title: Subtitle
- Monturaqui meteorite impact crater, Chile: a terrestrial analog for small craters on Mars
- Creators
- Kathryn Christine Rathbun
- Contributors
- Mark K Reagan (Advisor)C. Tom Foster (Advisor)Raymond R Anderson (Committee Member)Bradley D Cramer (Committee Member)Cornelia Lang (Committee Member)
- Resource Type
- Dissertation
- Degree Awarded
- Doctor of Philosophy (PhD), University of Iowa
- Degree in
- Geoscience
- Date degree season
- Summer 2020
- DOI
- 10.17077/etd.005565
- Publisher
- University of Iowa
- Number of pages
- xx, 284 pages
- Copyright
- Copyright 2020 Kathryn Christine Rathbun
- Language
- English
- Description illustrations
- color illustrations, color maps
- Description bibliographic
- Includes bibliographical references (pages 209-220).
- Public Abstract (ETD)
Meteorite impact cratering is a ubiquitous and important geologic process in the solar system. It has modified the surfaces of all planetary bodies we have thus far observed. Impact cratering also is a significant threat to human society, with a particular threat posed by both relatively small (0.05-0.1 km diameter) and relatively large (> 2 km diameter) impactors (National Research Council 2010. Defending Planet Earth: Near-Earth-Object Surveys and Hazard Mitigation Strategies. Washington, DC: The National Academies Press. https://doi.org/10.17226/12842). Preservation, particularly of small impact craters on Earth, is rare. Other planetary bodies in the Solar System preserve craters better, but studying these craters requires sending expensive manmade machines there to collect data and to create maps.
A purpose of this research is to study one well preserved small crater on Earth: Monturaqui Crater, located in the Atacama Desert in northern Chile. One goal is to better understand the local effects of the impact. Studying ejecta deposits, which is the material thrown out of a crater when it is formed, and creating a geological map of the crater and its surroundings can provide a detailed understanding of the crater process and its subsequent erosion. Another goal is to test the methodologies used to study small craters on Mars by using the same methodologies on Earth. The Atacama Desert is an ideal location to conduct a Mars analog study because its climate is hyperarid like Mars.
A geologic interpretation was made using satellite-based study methods and then compared to observations made in the field. The satellite-based method was able to identify basic characteristics about the crater, such as the rock types present, but was unable to identify important details because the image resolution was too coarse. Details that are smaller than the image resolution are important because they can lead to a significantly better understanding of a crater’s history. At Monturaqui, the crater is preserved but eroded, and the ejecta deposits reveal a complex history of erosion at the site. The satellite-based methodology has significant limitations at small craters due to their size and a thorough understanding of a site requires field-based observations.
- Academic Unit
- Earth and Environmental Sciences
- Record Identifier
- 9983987894802771
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