A thermoluminescence study of experimentally shock‐loaded oligoclase and bytownite

Abstract

The thermoluminescence (TL) of samples of terrestrial oligoclase and bytownite shock‐loaded to 10.5–45 GPa have been measured. The TL sensitivities of both feldspars decreased 10‐fold after shock‐loading to 25–32 GPa and, for the oligoclase, 25‐fold after shock‐loading to greater pressures. The shock‐induced changes for oligoclase are very similar to those of the Kernouve meteorite, in which the TL phosphor is oligoclase, after similar shock‐loading. The data indicate that ordinary chondrites of shock facies d‐f have suffered shock pressures over 25 GPa, consistent with petrographic estimates. Petrographic studies on the shocked samples suggest that the lowering of TL sensitivity is caused by maskelynization (and, at the highest pressures, melting). The oligoclase samples shocked above 34 GPa showed changes in their glow curve shapes similar to those produced by annealing Amelia albite and a type 3.4 ordinary chondrite above 700°C; the dominant peak moves from 132 ± 8°C to 230 ± 12°C. Changes in the glow carve shape for bytownite resembled those produced by annealing certain shergottites. In addition to a major peak at 138 ± 3°C, a peak appeared at 178 ± 8°C. For albite, the changes were shown to be associated with small degrees of disordering, and we suggest that shock‐induced disordering, or some process closely associated with the onset of disordering, is occurring in the trace amounts of feldspar that survive maskelynization after shock‐loading to pressures >34 GPa.