Australian Asteroid Ejecta/Fallout Units

Andrew Y. Glikson, Franco Pirajno

Research output: Chapter in Book/Conference paperChapter

Abstract

Geochronological U-Pb zircon dates are increasingly indicative of an episodic nature of the evolution of lithosphere and crust, including tectonic and thermal episodes associated with large asteroid impacts. Documented Archaean and early Proterozoic impacts at similar to 3.47, similar to 2.63, similar to 2.57, similar to 2.56, similar to 2.48, similar to 2.023 Ga (Vredefort) and 1.85 Ga (Sudbury) are considered to represent a minimum impact incidence due to gaps in stratigraphic sequences and the difficulty in identifying impact ejecta/fallout units. Evidence for major dynamic and thermal effects of large impact clusters on the early Precambrian crust is provided by ejecta/fallout units associated with: unconformities, tsunami boulder debris, compositional contrasts between supracrustal sequences that underlie and overlie ejecta units; including an onset of iron-rich sedimentation; and near-contemporaneous intrusion of granitoid magmas. A prime example is a similar to 3.26-3.24 Ga impact cluster whose fallout units, documented in the Barberton greenstone belt, South Africa, are associated with unconformities. The unconformities constitute abrupt breaks between underlying mafic-ultramafic volcanic sequences and overlying continental sediments which include granitoid detritus, representing granite felsic igneous activity. Geocronologically correlated unconformities and olistostrome mega-breccia are observed in the Pilbara Craton, Western Australia. In these terrains a > 300 Malong period of greenstone-granite evolution is abruptly terminated by unconformities overlain by impact ejecta, turbidite and banded iron-formation and associated with major faulting, uplift, erosion, and the onset of high-energy sedimentation including detrital components derived from contemporaneous and older granites. Onset of iron-rich sedimentation, including banded iron-formation, in the wake of these impacts is indicative of weathering and soluble transport of ferrous oxide under low-oxidation atmosphere and hydrosphere conditions, likely representing mafic volcanic activity triggered by the impacts. Depending on the site of the similar to 2.48 Ga impact, extensive injection of mafic dykes during similar to 2.48-2.42 Ga (Matachewan, Scourie, Karelian, Widgiemooltha, Bangalore, Antarctica dykes) may have been related to deep crust/mantle fractures triggered by mega-impacts.

Original languageEnglish
Title of host publicationASTEROIDS IMPACTS, CRUSTAL EVOLUTION AND RELATED MINERAL SYSTEMS WITH SPECIAL REFERENCE TO AUSTRALIA
EditorsYildirim Dilek, Franco Pirajno, Brian Windley
PublisherSpringer
Chapter2
Pages31-59
Number of pages29
Volume14
ISBN (Print)9783319745442
DOIs
Publication statusPublished - 2018

Publication series

NameModern Approaches in Solid Earth Sciences
PublisherSPRINGER
Volume14
ISSN (Print)1876-1682

Cite this

Glikson, A. Y., & Pirajno, F. (2018). Australian Asteroid Ejecta/Fallout Units. In Y. Dilek, F. Pirajno, & B. Windley (Eds.), ASTEROIDS IMPACTS, CRUSTAL EVOLUTION AND RELATED MINERAL SYSTEMS WITH SPECIAL REFERENCE TO AUSTRALIA (Vol. 14, pp. 31-59). (Modern Approaches in Solid Earth Sciences; Vol. 14). Springer. https://doi.org/10.1007/978-3-319-74545-9_2