Thermoluminescence and the origin of the dark matrix of Fayetteville and similar meteorites

The induced thermoluminescence properties and carbon contents of the dark matrix and light clasts of 6 regolith breccias have been measured. The TL sensitivity of the matrix (normalized to that of the clasts) decreases from ~0.8 to ~0.3 with increasing inert gas content, increasing abundances of highly volatile elements and carbon, and decreasing amounts of interstitial, grain-boundary glass. For meteorites with the highest inert-gas contents (Fayetteville and Leighton), the matrix samples have broader TL peaks (by ~ 10°C) and lower peak temperatures (by ~ 10°C) than the light clasts, whereas meteorites with low inert-gas contents ( e.g. Pantar) do not show this difference in the TL properties of the two lithologies. It is argued that the data are consistent with the formation of the dark matrix by comminution of the light clasts with the addition of a component, perhaps CM-like chondrites, with TL properties distinct from those of ordinary chondrites. The present data are inconsistent with the matrix being a new “primitive” material akin to type 3 ordinary chondrites, or with the dark matrix being related to the clasts by purely thermal processes.