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31.
High-T torsion experiments on lizardite + chrysotile serpentinites produced mineralogical and micro/nanostructural changes,
with important implications in rheological properties. High-resolution TEM showed that specimens underwent ductile [by microkinking
and (001) interlayer glide] and brittle deformation (by microfracturing), together with dehydration and break-down reactions.
Lizardite is affected by polytypic disorder and microkinking [kink axial planes at high angle with respect to (001) planes],
that were not present in the initial ordered 1T-lizardite. Chrysotile fibres are deformed, resulting in elliptical cross-sections,
with strong loss of interlayer cohesion. Both lizardite and chrysotile break down to a fine intergrowth of olivine (up to
200 nm), talc (up to 30 nm) and poorly-crystalline material. Lizardite-out reaction preferentially occurs at kink axial planes,
representing sites of preferential strain and enhanced reactivity; conversely, chrysotile break-down is a bulk process, resulting
in large healed olivine aggregates, up to micrometric in size. Overall observations suggest that dehydration and break-down
reactions are more advanced in chrysotile than in lizardite. 相似文献
32.
Laboratory verification of submicron magnetite production in pseudotachylytes: relevance for paleointensity studies 总被引：2，自引：0，他引：2
Pseudotachylytes generally possess stable remanent magnetizations but the processes by which pseudotachylytes are magnetized remain poorly understood. Magnetic hysteresis and scanning electron microscope studies reveal that experimental frictional melting of granites produces dispersed submicron inclusions of weakly interacting pseudo-single-domain (PSD) magnetite, in artificial pseudotachylyte. The magnetite inclusions are absent in the undeformed granite protolith and result from oxidation of Fe in melt-susceptible mafic minerals during the melt-quenched event. The pseudotachylytes acquired a stable thermal remanence in fine-grained PSD magnetites during the rapid cooling of the melt, implying that fine-grained magnetite has the potential for paleointensity determinations of contemporaneous magnetic fields with co-seismic faulting in granitoids. 相似文献
33.
Measurements of perturbations in the atmospheric potential gradient around volcanic plumes at multiple (from two to five) sites, and measurements of the charge-mass ratio of ash particles falling from volcanic plumes, were carried out at Sakurajima Volcano, Japan. Results from 28 and 29 October 1995, show that the nature of the perturbations depends on the intensity of plume activity. Although plume activity was vigorous on 28 October, negative perturbations were predominant. As plume activity peaked, the magnitude of negative perturbations decreased just below the plume and increased at an off-axis site. During the peak period, positively charged ash particles fell out from the plume. This suggests that the active plume dominantly contained negatively charged materials, and that positively and negatively charged materials were added to the lower and upper parts of the plume, respectively, during the peak period. On the other hand, as plume activity became less vigorous on 29 October, the perturbations were characterized by a positive anomaly followed by a negative anomaly. Because wind velocity increased with altitude that day, we infer that positive and negative charges were distributed in the upper and lower parts of the plume, respectively. The differences in perturbations observed on 28 and 29 October suggest that volcanic plumes are generally composed of three parts: an upper part with positively charged gas and aerosol, a middle part with negatively charged fine ash particles, and a lower part with positively charged coarse ash particles. The compilation of present and previous results from Sakurajima and other volcanoes indicates that the effect of the negative charge in the middle part was predominant in most cases, although positive perturbations caused by the upper part were observed around some weak plumes. The effect of positively charged particles in the lower part was observable only when plume activity was sufficiently strong because positively charged coarse particles tended to fall out near the vent. 相似文献
34.
Anthony John Parsons Yuichi Onda Takehiro Noguchi Jeremy Patin James Cooper John Wainwright Naoki Sakai 《地球表面变化过程与地形》2014,39(12):1693-1696
In this paper, we examine the use of radio frequency identification (RFID) tags for studying soil erosion. Surrogate soil particles were created by coating RFID tags with silicone clay and bronze powder to give them an overall density similar to that of quartz particles. The particles were between 2.5 mm and 4.0 mm in diameter and had specific weights of 2.5 to 3.0. These tagged particles were deployed on two plots: first, in a proof‐of‐concept laboratory study and secondly in a field study, the latter involving repeated surveys after rainfall events. Seven surveys under natural rainfall over four months yielded recovery rates averaged 56%. RFIDs are shown to provide useful insights into the movement of individual soil particles during erosion processes. As RFID technology advances, further miniaturization is likely to occur enabling the movement of a greater range of soil particles to be studied, and we may anticipate improvements to the signal detection so that recovery does not rely wholly on visual identification. Copyright © 2014 John Wiley & Sons, Ltd. 相似文献
35.
The mixing of mafic and silicic magmas in a squeezed conduit is simulated by fluid dynamics experiments using glue and dilute glycerin in a squeezed vinyl tube. Lighter and more viscous glue initially stably overlies dilute glycerin in a tube. As the tube is squeezed downward by a roller, the glue and dilute glycerin axisymmetrically circulate in the tube. The stable density stratification overturns due to the circulative motion. Because of viscosity contrast between the two liquids, the convective motion becomes unsteady and chaotic, which leads to efficient mixing of two liquids, even when the tube is squeezed very slowly. It is suggested that magma mixing in a squeezed conduit may explain some occurrences of natural mixed lavas with nearly homogeneous groundmass. 相似文献