New sites of Australasian microtektites in the central Indian Ocean: Implications for the location and size of source crater

Abstract

[1] We have identified 15 new Australasian microtektite sites along a transect roughly N-S in the central Indian Ocean. These locations, in addition to the existing 46 sites, total to 61 microtektite sites in the oceans. We carried out regression analysis of a selected area between 12-26°N and 98-112°E, at 0.5°intervals using three microtektite data sets separately: 41 sites, 46 sites (number of sites known up to the years 1994 and 2006, respectively), and the entire data set of 61 sites. This area was chosen because, on the basis of various lines of evidence, several investigators suggested impact craters for the strewn field within this broad area. The 41 site data set defines an impact site at about 12°N and 106°E. Whereas the contours joining the highest values of the square of the correlation coefficient by using 46 site and 61 site data sets define an area located in NE Thailand-central Laos, the center of this site is at 18°N and 104°E. Therefore with progressive increase in microtektite data the location of the impact site seems to get defined more rigorously. On the basis of the equations for the concentration of the ejecta and the distance from the source region, the calculated crater size has a diameter range between 33 and 120 km. Interestingly, the lower size limit of 33 km has been found closer to ground truth by verification from the microtektite data of the Ivory Coast strewn field.

Transantarctic Mountain microtektites: Geochemical affinity with Australasian microtektites

“…The margin of the Australasian tektite/microtektite strewn field would be shifted southward by approximately 3000 km (Fig. 1b), thereby bringing the maximum distance of microtektite distribution from the putative parent impact site in Indochina (e.g., Glass and Pizzuto, 1994;Lee and Wei, 2000;Ma et al, 2004;Glass and Koeberl, 2006;Prasad et al, 2007) to more than 10,000 km in a southeastward direction. This would emphasize its asymmetry and the paradox that the parent crater of the largest (more than 10 percent of the Earth's surface) and youngest tektite strewn field discovered on Earth is still unidentified.…”

“…The latter is outlined by tektite finds on land and microtektite finds in cored deep-sea sediments. The gray area marks the region where the hypothetical source crater of the Australasian tektites is likely located according to Glass and Pizzuto (1994), Glass and Koeberl (2006) and Prasad et al (2007).…”

Correlation of the oldest Toba Tuff to sediments in the central Indian Ocean Basin

“…This strewn microtektite field encompasses most of the Indian Ocean, the southwestern Pacific Ocean and the landmasses of Indochina, Malaysia, Philippines and Australia. So far, Australasian microtektites have been found in 75 locations in the Indian and Pacific Oceans (Prasad et al 2007).…”

“…Glass shards from the coarse fraction were separated using bromoform liquid, then washed with water and cleaned ultrasonically. The method followed in isolating the microtektites is described by Prasad et al (2007). Morphology of microtektites and glass shards was observed using a JEOL JSM-5800LV Scanning Electron Microscope at the National Institute of Oceanography, Goa.…”

Changes in abundance and nature of microimpact craters on the surfaces of Australasian microtektites with distance from the proposed source crater location

“…Tektite and especially microtektite strewn fields come with an inherent advantage of being distributed over vast geographic areas as demonstrated in three of the four strewn fields (Glass 1990; Koeberl 1994). Microtektites belonging to the Australasian tektite strewn field have been found in 75 locations so far (Prasad et al. 2007).…”