The sensitisation of quartz extracted from andesite

Abstract

Low quartz sensitivities have been reported in several studies in Iran, and in part this is presumed to be a result of the volcanic provenance of many of the sediments in the study areas. In this study we test experimentally whether a quartz sample, extracted from an andesitic rock and showing an insensitive fast component in the Optically Stimulated Luminescence (OSL) signal, can be sensitised using optical and thermal methods.The luminescence characteristics of quartz extracted from a rock sample from a landslide in Iran (Rudbar-Manjil) are compared to those of a well-characterised quartz sample. We find that very few of aliquots prepared from extracted quartz grains show any sensitivity of the most easily stimulated part of the OSL signal, but that ∼23% of aliquots give detectable initial signals after repeated dosing and bleaching. Surprisingly, a large fraction of the most easily stimulated quartz OSL is removed by infra-red stimulation, even though there is no significant IRSL signal in the UV. However thermal annealing at 700 °C gives rise to a test-dose response that is unaffected by IR. This annealing sensitises all aliquots to some degree and induces a signal which is stable up to 260 °C, in contrast to that following optical sensitisation, which begins to decrease when heated to 140 °C. The implications of these observations are discussed, both in terms of luminescence process and potential for dating.