Petrology and shock metamorphism of Pampa del Infierno chondrite

Pampa del Infierno, an L6 chondrite, displays strong evidence of impact metamorphism. Rare chondrules and two types of dark-colored clasts occur in a light-colored matrix. Granular clasts are similar in mineralogy and chemistry to the host meteorite, but display shock metamorphic features, produced mainly by deformation, such as mosaicism, undulatory extinction, and fracturing. Partial melting in the granular clasts is manifested by the presence of selvages of mafic glass with troilite-iron eutectic intergrowths around remnants of low-Ca pyroxene and plagioclase glass with skeletal poikilitic inclusions of olivine. Clasts with spinifex texture are believed to have crystallized from a supercooled, impact-generated, ultramafic melt of the host chondrite or a chondritic source of similar composition. The light-colored matrix mainly displays evidence of shock metamorphism under subsolidus conditions as manifested by kinking and deformation twinning in pyroxene; high-pressure phase transitions of olivine and low-Ca pyroxene to ringwoodite and majorite, respectively; and lineation that still preserves the deformation features in the different mineral phases. Pertinent shock-wave data used to interpret the metamorphic history of the Pampa del Infierno chondrite suggest metamorphism by impact at a minimum peak pressure greater than 300 kbar.