High‐pressure phase preservation in ordinary L‐chondrite melt veins: Evidence for control by post‐shock thermal evolution

Abstract This study investigates the petrography and mineralogy of three L‐type ordinary chondrite meteorites: Northwest Africa (NWA) 4137 (L6), Homestead (L5), and Kunashak (L6). We studied the shock‐related deformation features in the matrix and the characteristics of the melt veins, including the presence or absence of high‐pressure (HP) phases. Our goal is to constrain the shock history of these meteorites, including constraints on peak shock conditions and on post‐shock thermal histories. All three studied meteorites are strongly shocked, with textural evidence indicating shock stages up to S4 and development of melt veins. However, NWA 4137 is the only one of these meteorites in which HP phases were observed; we identified wadsleyite, majorite, albitic jadeite, tuite, and xieite within melt veins, indicating peak shock pressure in the range of 11–23 GPa. In contrast, the investigated melt veins in Homestead and Kunashak lack any HP phases despite indicators of comparable shock intensity to that observed in NWA 4137. The absence of HP phases in these two meteorites is attributed to a high post‐shock temperature that favored back‐transformation into low‐P minerals during decompression over preservation of HP phases. These case studies testify to the importance of the full pressure ( P )–temperature ( T )–time ( t ) path experienced by meteoritic samples during shock events in determining their ultimate mineralogy.