THE THEORY OF JETTING - APPLICATION TO THE ORIGIN OF TEKTITES

Jetting is a phenomenon that may occur when surfaces of objects converge obliquely. Whether jetting occurs depends on the velocity and angle of convergence as well as on the material properties of the colliding objects. Jetting has long been proposed as an explanation for the terrestrial impact origin of tektites. The well-developed theory of jetting during the collision of thin plates is extended to the case of the impact of a sphere on a half-space. Asteroidal impacts are modeled, using the equation of state for dunite, for impact velocities of 10 to 30 km/sec and impact angles ranging from 0° (normal impact) to 75°. The initial, most highly shocked portions of the jet are vapor, followed later by melt. It is postulated that the vapor portion of the jet blows away the atmosphere ahead of it so that the melt is ejected into a much rarified atmosphere. This inhibits the breakup of the melt and may thus allow the melt to travel long distances without being broken up into a fine spray. The jet, however, is roughly half projectile material and half target material. Because tektites in general do not have any measurable siderophile contamination from projectile material, jetting cannot explain the terrestrial impact origin of tektites. Jetting may, however, have produced the early Archean silicate spherule beds recently found in South Africa and Australia, which do show extreme enrichment in Ir and other siderophile elements. © 1993 Academic Press. All rights reserved.