EXPERIMENTAL STUDY ON DEFORMATION FABRICS OF QUARTZ AND CALCITE IN SHEAR ZONE

Frictional experiments of samples with quartz and calcite sandwich have been operated under certain confining pressures, strain rate and different temperatures. Samples deformed and undeformed have been studied by means of microscope, TEM, and U-Stage. On the basis of this, changes of deformation micro-structures and fabrics of quartz and calcite aggragates with temperatures under condition of simple shear have been analyzed     

Eolian dust deposition on the Giara di Gesturi basalt plateau,Sardinia

Mineralogical study of samples from depression fills on an isolated basalt plateau in Central Sardinia showed that, although the basalt is free of quartz and mica, fair amounts of these minerals occur in the finer fractions. Results from X-ray analyses of silt fractions and morphoscopical analyses of sand fractions indicate that the bulk of the quartz and mica is of eolian origin. The eolian quartz is predominantly of medium and coarse silt size and, in the upper 10 cm of the depression fills, constitutes about 20 per cent of the soil mass (approx. 20 kg/m²). Eolian mica is present in smaller amounts and is of medium silt or smaller size. The provenance of the eolian material could not be established with certainty, although a local origin can be excluded.     

Development of quartz ribbons in quartzofeldspathic granulites

In high-grade (granulite facies) quartzofeldspathic rocks the progressive development of a fabric records contrasting deformation behaviour of quartz and feldspar. Feldspar has undergone deformation mainly by recrystallization-accommodated dislocation creep and produced smaller recrystallized grains progressively in the course of deformation. Quartz has not deformed solely by dislocation creep but also by a diffusion-controlled mechanism. Dislocation climb is important in the dislocation creep of quartz. In contrast to feldspar, quartz grains have not recrystallized into smaller grains at any stage of deformation. Rather, they have transformed initially to short monocrystalline ribbons and ultimately to long polycrystalline ribbons. This textural change of quartz is a continuous process and has taken place in the course of bulk textural change of the rocks during the deformation.     

青海尕科合含铜银砷矿床成矿地质特征及矿床成因浅析

笔者在系统研究尕科合银砷矿床成矿地质背景和矿床地质特征的基础上，重新厘定了矿区赋矿地层层序，探讨了尕科合石英闪长岩体与矿化的关系。     

Devensian glacial events in Buchan (NE Scotland): A progress report on new OSL dates and their implications

Optically stimulated luminescence (OSL) dating of a series of glaciofluvial/glaciodeltaic sediments in central Buchan and Aberdeen has recently been undertaken. The aims of this project are to test the chronological model proposed by the most recent regional review and the suggestion that parts of Buchan may have remained ice-free during the last glacial maximum (late marine isotope stage (MIS) 3 and MIS 2 29–15 ka). The preliminary results indicate that during the Devensian (ca. 116–12 ka), extensive areas of Buchan may have been glaciated earlier than previously believed (possibly during MIS 4, 72–60 ka), but parts of the region show no depositional evidence of later glaciation. Some waterlain sediments from the Ugie Valley have yielded OSL ages indicating deposition during MIS 5d to MIS 5a (116–72 ka). We discuss whether the absence of overlying glaciogenic sediments at these locations raises questions about the reliability of the OSL ages or about existing models of the Devensian glaciation of Buchan.     

OSL dating of sediments from deserts in northern China

Aeolian samples from deserts in northern China were studied using the optically stimulated luminescence (OSL) of quartz and potassium (K) feldspar separates. K-feldspar has shown advantages over quartz for dating samples younger than 100 years, due to its more homogeneous equivalent dose (D_e) values, higher internal dose rate and higher luminescence sensitivity to dose. Without additional measurements, the luminescence characteristics of quartz obtained in D_e determination procedures can be used to reveal the source material and/or quartz thermal history for the deserts in northern China. The results indicated that the duration of paleosol formation in desert areas reflects regional paleoenvironments.     

Quartz Rheology and Short-time-scale Crustal Instabilities

We present numerical results of thermal-mechanical feedback in crustal quartz rheology and contrast this behavior to the vastly different character of an olivine mantle. In the numerical experiments quartz is found to have a very strong tendency for short-time-scale instabilities, while our numerical experiments show that olivine has a decisive tendency for a stable thermally lubricated slip. At the same time, olivine can also go through a transitional period of creep bursts, which are physically caused by multiple interacting ductile faults at various length and time scales which collocate quickly into a major shear zone. Since olivine has this strong propensity to self organize in a large apparently stable fault system, it lacks the dynamics of interacting ductile faults evident in other minerals. Quartz behaves totally different and keeps its jerky slip behavior for prolonged deformation. An example is shown here in which a 30 × 50 km piece of a wet quarzitic crust is extended for about 2 Ma. The associated total displacement field clearly shows the unstable slipping events, which have a characteristic time frame of one to several years, In contrast, olivine is very stable and has a much longer time scale for thermal instability of 100 kyrs.     

Dating of Japanese Quaternary tephras by ESR and luminescence methods

Electron spin resonance (ESR) and red thermoluminescence (RTL) methods were applied to quartz of eight Japanese Quaternary tephras ranging from 30 to 900 kyr, which have independent ages from other dating methods. The ESR ages were consistent for younger samples, while those from the Ti–Li center are older than those for the Al center for older samples. RTL ages are consistent with the age references and are roughly consistent with Al center ages. The dose response of the Ti–Li center after heating at 260 °C for 15 min implies that thermally unstable component is created in Ti–Li center by irradiation, leading to possible overestimations in the dose values.     

Hornblende etching and quartz/feldspar ratios as weathering and soil development indicators in some Michigan soils

Weathering can be used as a highly effective relative age indicator. One such application involves etching of hornblende grains in soils. Etching increases with time (duration) and decreases with depth in soils and surficial sediments. Other variables, related to intensity of weathering and soil formation, are generally held as constant as possible so as to only minimally influence the time-etching relationship. Our study focuses on one of the variables usually held constant—climate—by examining hornblende etching and quartz/feldspar ratios in soils of similar age but varying degrees of development due to climatic factors. We examined the assumption that the degree of etching varies as a function of soil development, even in soils of similar age. The Spodosols we studied form a climate-mediated development sequence on a 13,000-yr-old outwash plain in Michigan. Their pedogenic development was compared to weathering-related data from the same soils. In general, soils data paralleled weathering data. Hornblende etching was most pronounced in the A and E horizons, and decreased rapidly with depth. Quartz/feldspar ratios showed similar but more variable trends. In the two most weakly developed soils, the Q/F ratio was nearly constant with depth, implying that this ratio may not be as effective a measure as are etching data for minimally weathered soils. Our data indicate that hornblende etching should not be used as a stand-alone relative age indicator, especially in young soils and in contexts where the degree of pedogenic variability on the geomorphic surface is large.