The Pecora Escarpment (PCA) 91020 EL3 chondrite and deformation on the EL3 asteroid

Y. Boleaga, M. K. Weisberg, J. M. Friedrich, D. S. Ebel

Meteoritics & Planetary Science
Version of Record online: 24 November 2021


“We present the results of our study of two thin sections of Pecora Escarpment (PCA) 91020, a heavily shocked EL3 chondrite, to characterize the sizes, shapes, orientations, and mineral compositions of its chondrules and opaque nodules. We also studied the mildly shocked Queen Alexandra Range (QUE) 94594 EL3 chondrite for comparison. PCA 91020 appears to show the evidence of deformation throughout the meteorite in both the chondrules and the opaque (metal–sulfide) nodules. Aspect ratios of the chondrules in PCA 91020 are greater than in the mildly shocked QUE 94594. Aspect ratios of the more ductile metal grains are higher than those of the chondrules in both sections of PCA 91020 and in QUE 94594. The data suggest that the chondrules and metal-rich nodules in PCA 91020 were elongated (flattened) to a greater degree and show a preferred orientation in comparison to objects in typical EL3 chondrites such as QUE 94594. The chondrule and metal-rich nodule deformation and foliation in PCA 91020 were likely produced by an impact on the EL3 asteroid. However, there are some inconsistencies in reconciling an impact hypothesis with all of the observations. Scenarios of hot accretion and/or overburden compaction during progressive (potentially rapid, hot) accretion to explain the deformation cannot be completely ruled out. Also, heavily shocked E3 chondrites, like PCA 91020, are relatively rare, suggesting the impacts that may have compacted chondrites, although potentially frequent, were of weak magnitude.”