Source of the Australasian Tektite Strewn Field: A possible off‐shore impact site

Abstract

Although there is a preponderance of evidence that tektites were formed by asteroid impacts on the Earth, no source crater has been found for the largest and youngest of the strewn fields‐the Australasian strewn field. We have examined a combined Seasat/Geos 3 altimeter data set of sea surface heights in the northern portion of the Australasian strewn field for negative gravity anomalies on the continental shelf and slope which might be related to the source crater for these tektites. A large negative anomaly, which we call the Qui Nhon Slope Anomaly, is a sea surface depression of approximately 1.5 meters over an area of 100 km diameter, centered at 13° 47′N latitude and 110° 37′ E longitude. It corresponds to a gravity anomaly of about −50 mgal. A surface‐ship gravimeter track across most of the structure confirms the satellite measurements. This site is on the continental slope in 1 to 3 km of water. A sea floor topographic depression of more than 200 meters occurs in the southeast quadrant of the anomaly. The center of the structure is 175 km offshore and is less than 300 km from the Muong Nong substrewn field and the prolific Dalat site, perhaps the largest concentration of tektites within the Australasian field. Due to its location, size, and magnitude we propose this anomaly may be due to the impact structure that produced the Australasian strewn field.