Magnetic fines from the Kaali impact-site (Holocene, Estonia): Preliminary SEM investigation

Abstract

The Kaali crater field (1 sq. kilometre, 9 craters) offers a unique opportunity to recover large amounts of magnetic fines still partly preserved from late-stage weathering. SEM studies of these materials reveal an unusually wide spectrum of derivatives from the initial iron meteorite body, including minor amounts of marched metal fragments, and an abundance of more evolved products resulting from primary oxidation processes. Most of these products are sprays and splashes of liquid iron oxides, and some particles may be ascribed to oxide condensates from a vapor phase, as a result of both atmospheric ablation and vaporization upon impact. This wide range reflects varied impact conditions, due to variable masses and velocities of fragments after atmospheric disruption of the original meteoritic body. The large spectrum of magnetic fines from Kaali should provide an excellent probe into the chemical- and isotopic-fractionation of elements over a range of impact processes, from atmospheric entry to post-impact alteration. Magnetic fines from other sites of multiple impacts may have the same potential, and deserve more systematic attention. © 2004 by The Geochemical Society of Japan.