Main Geochemical Signatures Related to Meteoritic Impacts in Terrestrial Rocks: A Review

Abstract

The chemical composition of impact melt rocks, breccias and ejecta layers is dominated mainly by the proportions and composition of target rocks. However, small quantities of vaporized and molten meteorite material mixed with them significantly alter the concentrations and ratios of certain elements and isotopes. The identification of this meteoritic signature is used to propose an impact formation for structures of uncertain origin, as well as a possible criterion for infemng the impactor type. The most common criteria applied to these studies are the detection of a positive siderophile element anomaly, the Re-Os isotopic

Armouring effect on Sr-Nd isotopes during disequilibrium crustal melting: the case study of frozen migmatites from El Hoyazo and Mazarron, SE Spain

“…the whole rock (e.g., Bea et al, 1994;Ayres & Harris, 1997;Förster, 1998;Muñoz-Espadas et al, 2000;Pyle et al, 2001), determining a balancing effect in terms of Nd isotope composition in the analysed glass and mineral phases, including the HCl-leachates and the single grains phosphatic inclusions (Fig. 7).…”

“…The shape of HREE pattern (Fig. 6b) could also indicate a minor contribution of xenotime (e.g., Förster, 1998;Pyle et al, 2001), which has been detected in the El Hoyazo xenoliths (Muñoz-Espadas et al, 2000), to the accessory phosphate population. Minor contributions from the hosting mineral or melt inclusions to the HCl-leachates cannot be excluded considering other trace Table 4) and Eu anomaly is positive in biotite leachates from El Hoyazo, which, again, is not typical of apatite, monazite or xenotime (Bea et al, 1994;Ayres & Harris, 1997;Förster, 1998).…”

Extraterrestrial chromite in the resurge deposits of the early Late Ordovician Lockne crater, central Sweden

“…Physical pieces of projectile material have, with a few exceptions such as the Eltanin impact event [3], only been found at small (b 1.5 km in diameter) impact craters [4][5][6]. Larger projectiles are believed to be totally vaporized upon impact, leaving only a small amount of recondensed projectile vapour mixed in with the target rocks (e.g., [7]). Factors that can affect the survival extent are the impact velocity [8], angle of impact [9], the type of impactor and impact target material.…”

“…Factors that can affect the survival extent are the impact velocity [8], angle of impact [9], the type of impactor and impact target material. Pieces of meteorites have a low resistance towards weathering and diagenesis; most meteorites do not survive more than between a few thousand years to a couple of hundred of thousand years on the Earth surface [7,10]. Attempts to identify the type of impactor have previously focused on the geochemistry of the impact rocks hosting the recondensed fraction.…”

Impact cratering — fundamental process in geoscience and planetary science

“…The number of confirmed impact structures on Earth, thereafter, has slowly increased further, standing now at about 170, with several others proposed but not unequivocally confirmed yet. It is important to emphasize that while geophysical observations or remote sensing have been very successful in pinpointing the locations of a number of impact structures, the acceptance of such discoveries as confirmed impact structures has, in all cases, to come from the study of shock-deformed rocks and minerals, or the recognition of traces of a meteoritic projectile in impact melt rock (e.g., Montanari and Koeberl 2000;Muñoz-Espadas et al 2003;Koeberl 2004).…”