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Dating terrestrial impact structures: U‐Pb depth profiles and (U‐Th)/He ages of zircon
Author(s) -
Wielicki Matthew M.,
Harrison T. Mark,
Stockli Daniel
Publication year - 2014
Publication title -
geophysical research letters
Language(s) - English
Resource type - Journals
SCImago Journal Rank - 2.007
H-Index - 273
eISSN - 1944-8007
pISSN - 0094-8276
DOI - 10.1002/2014gl060757
Subject(s) - zircon , geology , radiogenic nuclide , geochemistry , thermochronology , geochronology , paleontology , mantle (geology)
We investigate the presence of epitaxial overgrowth rims and “reset” zircon, complete loss of radiogenic lead (Pb*), from terrestrial impactites to constrain the occurrence of such phenomenon in impact environments and their possible use in dating impact events. We also explore (U‐Th)/He dating of zircon to evaluate this geochronometer in accurately identifying impact ages, particularly when no dateable melt sheet exists. Our results show that (U‐Th)/He ages of zircon from the brecciated, and presumably shocked target, can accurately date an impact event and provides another tool to determine impact ages when no melt sheet exists, an alternative to problematic interpretations of commonly used apparent 40 Ar/ 39 Ar plateau ages. No evidence of epitaxial overgrowth rims and/or reset zircon was observed, suggesting that zircons within shocked impactites have remarkably slow Pb diffusion and possibly explaining the relatively few reset grains reported in terrestrial impactites.