Variably shock‐compacted chondrites: Deformation–thermal histories, large differences in mineral deformation response, and implications for lithification

Abstract Eight different H, L, and LL chondrites with 11 lithologies were studied and show good evidence for progressive shock effects and compaction. In weakly shocked chondrites (Baszkόwka, Bjurböle, Saratov, NWA 7298 Lithology A and C), silicates were dominantly fractured, troilite and metal were more deformed than olivine and fluidized, and estimated stresses were ~4–7 GPa. In strongly shocked chondrites (NWA 7298 Lithology B, NWA 11315 Lithology A and B, Alfianello, NWA 8709, NWA 4860), olivine grains display more plastic deformation than in weakly shocked chondrites and were ultimately recrystallized; troilite, some metal, and some bulk areas were melted; and estimated stresses were >7 GPa. Three settings for lithification are inferred: (A) initial lithification during accretion of warm chondrule aggregates, (B) later lithification in warm, metamorphosing parent bodies that were being affected by mainly low‐velocity collisions, and (C) final lithification in cool parent bodies after the waning of metamorphic heat that were being affected by higher velocity collisions. Thus, collisions together with heat of different types (accretionary, metamorphic, and shock‐related) were probably the main ways in which unmelted planetesimals were lithified. Impact‐fluidized metal and troilite may have acted as important lithification binding agents even in weak shock events.