Minerals of a soil developed in the meteoritic crater of Carancas, Peru, and evidences of phase changes on the impact event

We report studies about the phase transformations in the soil of the Carancas meteoritic crater located in an inhabited area near the town of Carancas, in the Region of Puno, about 1,300 km southeast of Lima, Peru. The studies by energy dispersive X-ray fluorescence, X-ray diffractometry and transmission Mössbauer spectroscopy (at RT and 77 K) reveal that the sample consists mainly of quartz, albite and impactites such as coesite and stishovite (SiO₂) that have experienced phase metamorphism or alterations, related to high pressures and temperatures, forming their corresponding polymorphs. The occurrence of these phases, with high content of SiO₂, in the soil of the crater strengthens the hypothesis of its origin by metamorphism induced by impact; we observed also a magnetic sextet on the Mössbauer pattern, assigned to the Fe^{3 +} in hematite, and three paramagnetic doublets, two of them associated with structural Fe^{3 +} and Fe^{2 +} cations, respectively, in illite and/or montmorillonite, and a third one due to an unidentified Fe^{3 +} site.