40Ar/39Ar ages of impacts involving ordinary chondrite meteorites
Timothy D. Swindle, D. A. Kring, J. R. Weirich, 2014. "40Ar/39Ar ages of impacts involving ordinary chondrite meteorites", Advances in 40Ar/39Ar Dating: From Archaeology to Planetary Sciences, F. Jourdan, D. F. Mark, C. Verati
Download citation file:
Impact ages have now been determined for c. 100 ordinary chondrites, providing information about impacts in the asteroid belt throughout the history of the Solar System. Most notably, there is evidence for (a) impact events in the first 100 Ma of Solar System history, during the accretion of material; (b) an increase in impact ages produced between 3500 and 4100 Ma, presumably related to the suspected ‘lunar cataclysm’; (c) many L chondrites being degassed during the disruption of their parent body slightly less than 500 Ma ago; and (d) at least one younger event in the H chondrites. There are no 40Ar/39Ar ages that clearly match the cosmic ray exposure ages of any meteorites, which means that the collisions that liberated the fragments we now have as meteorites did not produce time–temperature histories capable of degassing radiogenic 40Ar. Since there is no way to know a priori whether an ordinary chondrite impact melt is the result of a recent or ancient event, much of the progress will continue to come from reconnaissance studies of shocked ordinary chondrites.
Figures & Tables
Advances in 40Ar/39Ar Dating: From Archaeology to Planetary Sciences
Decoding the complete history of Earth and our solar system requires the placing of the scattered pages of Earth history in a precise chronological order, and the 40Ar/39Ar dating technique is one of the most trusted dating techniques to do that. The 40Ar/39Ar method has been in use for more than 40 years, and has constantly evolved since then. The steady improvement of the technique is largely due to a better understanding of the K/Ar system, an appreciation of the subtleties of geological material and a continuous refinement of the analytical tools used for isotope extraction and counting. The 40Ar/39Ar method is also one of the most versatile techniques with countless applications in archaeology, tectonics, structural geology, orogenic processes and provenance studies, ore and petroleum genesis, volcanology, weathering processes and climate, and planetary geology. This volume is the first of its kind and covers methodological developments, modelling, data handling, and direct applications of the 40Ar/39Ar technique.