A small outcrop of pumice-like rocks in northern Cáceres province (Extremadura, Spain) is totally unrelated to Cenozoic volcanism in the whole lberian Peninsula. Microscope petrography, SEM-EDX, and XRD studies reveal a highly-vesiculated glass with abundant quartz, and minor amounts of orthopyroxene and ringwoodite, a high-pressure polyrnorph of olivine. According to this evidence, we interpret this rock as a result of a hypervelocity impact of a small meteorite. Under this preliminary interpretation, glass and vesicles resulted from melting and vaporization of the target metasedimentary clastic rocks and pore water, quartz grains are unrnelted relics of quartz from the target rock, and ringwoodite originated from a Mg-bearing mineral phase during and irnmediately after shock-wave passage. The reduced size and geological uniqueness of the outcrop rnerits its highest protection as part of the geological heritage of meteorite impacts in Spain, and any extraction of material from the site should be restricted and strictly controlled.

Este estudio es una contribución al Programa IMPACT de la European Science Foundation, y forma parte del proyecto «Estudio del registro geológico de impactos meteoríticos en España)) del Laboratorio de Geoplanetología del Centro de Astrobiología (INTA-CSIC).

4 páginas, 2 figuras, 1 tabla.-- Trabajo presentado a la 30ª Sesión Científica, El Enciso, La Rioja, 2001.

Peer reviewed