Chondrite Shock Metamorphism History Assessed by Non-Destructive Analyses on Ca-Phosphates and Feldspars in the Cangas de Onís Regolith Breccia

Abstract

The Cangas de Onís regolith breccia is an H5-H6 ordinary chondrite that fell to Earth in 1866. It is constituted by 60% H6-H5 clasts within an H5 clastic matrix. All clasts are affected by intense fissuration, with an intricate pattern filled by kamacite and troilite, shock metamorphism of plagioclase into maskelynite. The chondrite is composed of low-Ca pyroxene, olivine and plagioclase as the main silicate phases, with two types of phosphates, taenite-kamacite blebs and troilite. The specimen was studied by micro-Raman spectroscopy, Fourier-transform infrared spectrophotometry (FTIR), spectral cathodoluminescence and computer tomography. The ease with which the specimens can be prepared for analysis using these techniques, and the speed with which relevant information can be obtained, make them excellent tools for the study of non-replaceable materials. Moreover, the Raman and FTIR results offer enough resolution to reveal heterogeneities in the shocked metamorphism throughout the specimen. The obtained results showed that the extent of the metamorphic conditions within the studied sample is heterogeneous, which leads us to believe that the last accretionary event that took place in this regolithic breccia was not significant enough to allow for overall homogenization.