Fig. 2.

The Bolaven volcanic field covers much of the Bolaven Plateau and spills over its kilometer-high flanks to the floodplain of the Mekong River. The perimeter cliffs of the plateau expose nearly flat-lying Mesozoic sandstones and mudstones like those inferred from tektite composition to be the dominant target rocks of the Australasian impactor. ⁴⁰Ar-³⁹Ar ages on lavas appear as dots colored according to age. Squares are previously published ages (35). See SI Appendix, Table S1 and Ar-Ar Metadata_Dataset S3 (25) for details on geochronology and SI Appendix, Fig. S2 for a much more detailed geological map of the region.