Dating terrestrial impact structures
Skip to main content. Log In Sign Up. Eric Tohver. A combination of two plateau ages and one isochron age, with a weighted Available online xxxx Editor: Sotin mean of
(U-Th)/He dating of terrestrial impact structures: The Manicouagan example
E-mail address: Use the link below to share a full-text version of this article with your friends and colleagues. Learn more. However, the timing and magnitude of such events remain difficult to constrain. Recent studies have focused on zircon within impactites as recorders of impact events. Zircon ZrSiO 4 occurs as a common accessory mineral in a variety of rock types and geologic environments, including terrestrial impactites.
It is widely used for geochemical and isotopic studies because of its capacity to retain trace elements, including actinides, lanthanides, and radiogenic daughter products under extreme conditions. The preferential incorporation of U and Th into zircon coupled with its highly refractory nature, often surviving multiple geologic cycles, has made zircon the premier terrestrial geochronometer [ Finch and Hanchar , ].
Although zircon is currently being used to date impact events, the crystallization of zircon within impact melts and the response of radiogenic elements to shock and heating associated with impacts remain poorly understood and need to be further refined if zircons are to accurately record impact events. Thus, chronometers used to date zircons from the target rocks, directly below the melt sheet can be compared to the known age of the impact event to asses which systems record the age of the impact.
The sample location is also consistent with the hot shock zone [ Moser et al. Shock features such as multiple planar deformation features PDF in quartz and pebbles of the underlying basement have been identified previously [ Hart et al. As the majority of the sample was used to extract the relatively few zircons used, shock features have not been investigated within this sample; however, we presume it to be equally shocked.
Mineral separates were obtained from bulk rocks samples by standard heavy liquid separation procedures. Analytical procedures for depth profiling zircons were broadly similar to those outlined by Abbott et al. We centered the secondary ion image within a small contrast diaphragm and field aperture prior to each analysis to better restrict transmission to ions originating from the crater bottom. All analyses were carried out on single grains.
U and Th concentrations were determined by isotope dilution inductively coupled plasma mass spectrometry analysis. These grains are used to establish an accurate impact age for Morokweng, however are not the focus of this study. Some grains appear fractured, although no evidence for internal planar deformation features [ Wielicki et al. These young ages may have been affected by sampling issues discussed above; nevertheless, this would imply that the grains are even younger than reported.
This appears to contradict recent studies [ Moser et al. We note that Abramov et al. Although a few reset zircons have been reported from Vredefort [ Kamo et al. Recrystallization of these grains may also be responsible for apparent impact ages, as noted by Moser et al. However, it appears that the unshocked model [ Abramov et al. The lack of any identifiable epitaxial overgrowths in depth profiles of Morokweng zircon, and the seemingly few reports in terrestrial impactites, suggests that the formation of such rims requires specific conditions that may not be present in the majority of recent impact events, possibly suggesting an alternative mechanism for the formation of rims on Jack Hills zircons [ Trail et al.
As Vredefort is significantly older than Morokweng, it is not surprising that these grains have experienced more postimpact thermal events and thus no longer record the timing of the Vredefort impact. This may provide another tool with which to identify impact events, when no crater has yet been identified but ejecta exists or possibly to date large ejecta blankets from future sample return missions.
Many terrestrial craters do not have melt sheets preserved e. The lack of epitaxial overgrowth rims suggests unique conditions of formation that may occur in relatively few recent impact events, possibly determined by impactor energy and target composition. To our knowledge, no epitaxial overgrowth rims have thus far been identified in terrestrial impactites; however, more detailed studies of inherited zircons are needed to gain insights into the occurrence of this phenomenon.
We also would like to acknowledge Patrick Boehnke University of California, Los Angeles for the support with modeling simulated impacts. Lastly, we would like to thank Aaron J. Cavosie and Oleg Abramov for their insightful reviews of this manuscript. Please note: The publisher is not responsible for the content or functionality of any supporting information supplied by the authors.
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Figure 1 Open in figure viewer PowerPoint. Figure 2 Open in figure viewer PowerPoint. Modified after Hart et al. Figure 3 Open in figure viewer PowerPoint. Figure 4 Open in figure viewer PowerPoint. Depth profiles of Morokweng basement zircon to identify the presence of epitaxial overgrowth rims coincident with the impact. No evidence of rims with Morokweng impact ages was observed on Archean target zircon cores. References Abbott, S. Google Scholar.
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Jun 10, Due to planetary resurfacing and the inherent difficulties in dating complex, impact‐derived samples, fewer than 10% of all‐known craters, can. Request PDF on ResearchGate | Dating terrestrial impact structures. In Impact! Bolides, craters, and catastrophes, edited by Jourdan F. and Reimold W. U.
Andrew Glikson does not work for, consult, own shares in or receive funding from any company or organisation that would benefit from this article, and has disclosed no relevant affiliations beyond their academic appointment. Republish our articles for free, online or in print, under Creative Commons licence. Following the Late Heavy Bombardment , which pummelled the inner solar system around 3. All this changed in the late s, when Walter and Louis Alvarez discovered the million-year-old K-T Cretaceous-Tertiary boundary asteroid impact event.
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Terrestrial impact craters: Their spatial and temporal distribution and impacting bodies
Rocks from space are constantly bombarding the Earth. When they do, they leave behind an impact crater. On the pesky matter of terminology: In the rare case that an impact crater is preserved, water can fill the depression, creating a lake. In other cases, when the water that has collected is unconnected, impact crater lakes can provide a valuable geologic and fossil record by preserving ancient sediment.
List of impact craters on Earth
Natural Disasters Tulane University Prof. Stephen A. Nelson Meteorites, Impacts, and Mass Extinction. On February 15, a meteor exploded in the sky over Chelyabinsk, southern Russia. Although the Chelyabinsk meteorite probably weighed about 12,—13, metric tonnes, and measured 17 to 20 m in diameter before it exploded, sientists were quick to point out that it was very small compared to other objects that could potentially hit the earth. The explosion released energy estimated at about kilotons of TNT about 20 to 30 times more energy than the Hiroshima atomic bomb. A Meteorite is a piece of rock from outer space that strikes the surface of the Earth. A Meteoroid is a meteorite before it hits the surface of the Earth.
Pre dating Method for the St. Martin crater: A type of naturally occurring glass having the composition of plagioclase series feldspar, created by the vitrification of plagioclase by shock melting in meteorites and meteorite impacts.
There's a second impact crater under Greenland
Fred Jourdan, W. Elements ; 8 1: Hypervelocity impacts of asteroids and comets have played a key role in the evolution of the Solar System and planet Earth. Geochronology, the science that investigates the ages of rocks, has become a preponderant tool for dating impact events and for assessing whether they are related in time to mass extinctions on Earth. Impact events are instantaneous compared to other geological processes and, in theory, represent easy targets for multitechnique geochronology. Yet, only a few terrestrial impact events are accurately and precisely dated. A dating campaign is urgently needed if we are to fully understand the role of impacts in Earth history. Shibboleth Sign In. OpenAthens Sign In. Institutional Sign In. Sign In or Create an Account. User Tools.
ST. MARTIN IMPACT STRUCTURE
Biren, Brian D. Monteleone, Jahandar Ramezani, John G. Spray, Lucy M. Research output: The accurate dating of meteorite impact structures on Earth has proven to be challenging.
Earth has about known impact craters, but surely our planet has endured more bashing than that in its history. All the other terrestrial planets and moons in our solar system are covered by impact craters. But since two-thirds of Earth is covered by water, any asteroid impacts occurring in the oceans are difficult to find. In fact, a geologist recently discovered an impact crater using Google Earth! It is approximately kilometers in diameter and is thought to to be about two billion years old.
Until recently, impacts by extraterrestrial bodies were regarded as an interesting but, perhaps, not an important phenomenon in the spectrum of geological process affecting the Earth. Our concept of the importance of impact processes, however, has been changed radically through planetary exploration, which has shown that virtually all planetary surfaces are cratered from the impact of interplanetary bodies. It is now clear from planetary bodies that have retained portions of their earliest surfaces that impact was a dominant geologic process throughout the early solar system. For example, the oldest lunar surfaces are literally saturated with impact craters, produced by an intense bombardment which lasted from 4. The Earth, as part of the solar system, experienced the same bombardment as the other planetary bodies.