Palaeomagnetic cleaning strategies

摘要: Abstract Cleaning is a term used in palaeomagnetism to refer laboratory methods designed demagnetize preferentially the less stable components of magnetization. Although diversity suggests that there wide choice available, this illusory. Except simple cases, wrong cleaning strategy may yield misleading results. include thermal, magnetic (alternating field or a.f.), low-temperature, chemical, shock and microwave cleaning. A involves one more applied specific sequence. The design made easier with priori knowledge mineralogy granulometry, other words, rock properties. not substitute for experiments, variation low-field susceptibility temperature ( k − T ) only provides information on but it also draws attention chemical alteration occur during thermal Apart from rapid, though reversible, decrease associated Curie temperatures, diagnostic features low-temperature (about −140°C) peak typical multidomain (MD) magnetite, high-temperature (Hopkinson) fine-grained magnetite (and minerals) classic lepidocrocite-maghemite-haematite profile, which irreversible. Examples are given where remanence caused by lightning can be effectively eliminated applying a.f. low (LT) pre-treatment. Such an isothermal remanent magnetization (IRM), combination IRM anhysteretic (ARM). As unblocking relatively low-coercivity MD grains extend high-temperature, often desirable suppress remanence. An example palaeointensity determination, without LT nature transition briefly addressed light rare double peak, reflect both isotropic point Verwey transition.