DARWIN Glass and DARWIN Crater Revisited. Multiple Impacts in the Australasian Strewn Field?

Details DARWIN Glass and DARWIN Crater Revisited. Multiple Impacts in the Australasian Strewn Field? DARWIN Glass and DARWIN Crater Revisited. Multiple Impacts in the Australasian Strewn Field?

Sep 1995

adsabs.harvard.edu/cgi-bin/nph-data_query?bibcode=1995metic..30q.545m&link_type=abstract

Meteoritics, vol. 30, no. 5, page 545-545

Other

Argon-Argon Ages, Craters, Impacts, Indochinites, Shock Effects, Tektites

Scientific paper

Darwin glass, an impact glass occurring in South West Tasmania, has been found at least since human beings reached Tasmania ca. 40 k.y. ago. Darwin glass, although in the proximity of the Australasian tektites strewn field, has never been counted as part of it. Darwin Crater was recognized about 30 years ago. Still, the existence of an impact structure in Tasmania has been neglected and does not show up in most compilations of known impact craters. Age determinations on Darwin Glass from the early 70's revealed a combined K-Ar and fission track age of 0.73 +/- 0.04 m.y. [1]. The most recent and most precise estimate for Australites and Indochinites yields 0.784 +/- 0.012 m.y. [2]. The two ages are indistinguishable from each other. This contemporaneity lead to the hypothesis that impact on Earth producing australites also formed Darwin Crater as a primary and/or secondary crater (Gentner et al., 1973). If one believes that all tektites of the Australian strewn field were produced by one impact in or near Indochina, then a special case is required to also form Darwin Crater, which is at least 5000 km away. Atmospheric breakup of a planetary body is a very unlikely possibility, because the distance travelled after breakup is too small to account for the dispersion. Double craters on Earth are always close to each other (e.g., Kara and Kara Ust). A more likely scenario could be an impact of an asteroidal body with an accompanying small moon (e.g., Ida and Gaspra). If one believes in multiple impacts for the formation of Muong Nong-type or layered tektites in the Australasian strewn field, then a collision of an asteroidal body with another body shortly before impact on Earth is required. In this case, an impact on Earth a large distance away (i.e., Tasmania) is realistic. To address the problem of crater recognition and possible simultaneous impact events, a new multidisciplinary investigation is currently underway. We intend to determine the age of three Darwin Glasses with the 40Ar-39Ar technique at the University of Bern. We thus hope to obtain a precise age which will permit or deny verification of multiple impacts large distances apart. New samples, taken from the country rock of the proposed Darwin Crater site, are currently being studied for microscopic impact features. Mathematical calculations will be performed to test possible impact scenarios for the likelihood of contemporaneity of multiple impact events in the Australasian strewn field area. References: [1] Gentner W. et al. (1973) EPSL, 20, 204-210. [2] Kunz J. et al. (1995) LPS XXVI, 809.

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