Nanocracks upon Fracture of Oligoclase

Abstract—The spectrum of fractoluminescence (FL) upon fracture of the surface of oligoclase is obtained. The analysis of the spectrum has shown that fracture of crystals leads to the formation of electronically excited free radicals ≡Si−O• and Fe3• ions as well as electron traps. FL consisted of a set of the signals with the intensities varying by an order of magnitude. The duration of the signals was ~50 ns and the time interval between them varied from ~0.1 to 1 μs. Each signal contained four maxima associated with the destruction of barriers preventing the motion of dislocations along the sliding planes. These breakthroughs cause the formation of the smallest (“primary”) cracks. All other, larger cracks are formed by the coalescence of the “primary” cracks. The sizes of “primary” cracks range from ~10 to 20 nm and the time of their formation is 16 ns. The distribution of cracks by size (surface areas of crack walls) is power law with the exponent –1.9.

The Properties of Thermochemical Remanent Magnetization Acquired by Slow Laboratory Cooling of Titanomagnetite-Bearing Basalt Samples from Different Temperatures and the Results of the Thellier Method

Abstract—The experiments have been carried out on the acquisition of thermochemical remanent magnetization (TCRM) in basalt samples containing titanomagnetite (TM) with the Curie temperature Тс ~200°C by their rapid heating to maximum temperatures Т* from 450 to 530°C followed by slow cooling in the laboratory magnetic field Blab. At different stages of the preliminary thermal treatment of the initial samples, a set of magnetomineralogical studies including electron microscopy, X-ray diffraction and thermomagnetic analyzes, and measurements of magnetic hysteresis parameters were performed. It is shown that as early as the very beginning of the cooling process, all samples demonstrate explosive growth of TCRM corresponding to the stage of rapid single-phase oxidation of the initial titanomagnetite fraction of basalt, and that TCRM is acquired by the increase of Тс and volume of single-phase oxidized parts of TM grains as well as by the growth of the volume of Ti-depleted (relative to the initial TM) cells of microstructure of the subsequent oxidative exsolution. The Arai–Nagata diagrams for the samples carrying TCRM have a form of a broken line consisting of two linear segments. The low-temperature interval T < Т* corresponds to a mixture of thermochemical and thermoremanent (TRM) magnetizations and gives a slightly overestimated Blab because of the effect of a low cooling rate during the acquisition of TCRM and TRM. The high-temperature interval corresponds to pure TCRM and the Blab strength determined from this interval is underestimated by 20–27%. It is recommended to reject samples whose Araii–Nagata diagram has two or more linear segments against the background single-component NRM.