Airesites: a New Class of Late Miocene Tektites from Argentina

Introduction: We report the discovery of two tektites (Fig. 1A) collected in the vicinity of Bahía Blanca, Buenos Aires Province (BPA), Argentina. The smaller tektite (T2) has an elongate, teardrop form ~2 mm long. The larger one (T1) appears to be a classic disc-shaped tektite ~2 mm in diameter. Both are black in reflected light and exhibit the grooved and pitted surface sculpting common to tektites[1]. We propose that the name “airesites” be applied to these tektites and any bona fide tektites subsequently found in BAP. Unlike other tektites, T1 and T2 were discovered attached to a ~2 cm long piece of impact glass (Fig. 2B). The impact glass (BB-T) is typical of the 5.28 Ma melt breccias that occur in Miocene-Pliocene sediments over a large region of southern BAP [2]. We are aware of no other tektites that have been found so intimately associated with proximal impact melt. The tektites appear to have collided with BB-T while both were still molten, and the bottom of T2 flowed almost 2mm into BB-T (Fig. 1C) Because of their unique chemistry and association with the proximal melt, these airesites provide some rare opportunities to gain insights into the nature and location of the impact and into the formation and distribution of all tektites. Major Element Composition: One thin section was made from T1 while T2 was sacrificed to produce 60 μm thick wafers for FTIR. The tektite glass is brownish-yellow in transmitted light (Fig. 2). Electron microprobe analyses were carried out for T1 on a Cameca Camebax using the silica glass routine described by [3]. The average normalized composition of 13 points is given in Table 1. The composition of the proximal melt is also reported.