Symplectitic augite: evidence for discontinuous precipitation as an exsolution mechanism in Ca-rich clinopyroxene

Abstract Part of the augite in the Artfjället gabbro consists of symplectitic intergrowths between augite and blebs or lamellae of orthopyroxene. Mineral compositions are consistent with formation of these symplectites by exsolution of orthopyroxene from magmatic augite at a temperature of ca . 900–1000°C. The microstructures indicate that the exsolution mechanism is discontinuous precipitation, whereby the boundary of an augite grain sweeps through a neighbouring augite, leaving the symplectite in its wake. The formation of this symplectitic augite is catalysed by the presence of an intergranular water-rich fluid phase, which promotes grain boundary mobility.     

Nonequilibrium thermodynamics of pressure solution

This paper is concerned with the thermodynamic theory of solution and precipitation processes in wet crustal rocks and with the mechanism of steady pressure-solution slip in contact zones, such as grain-to-grain contacts, fracture surfaces, and permeable gouge layers, that are infiltrated by a mobile aqueous solution phase. A local dissipation jump condition at the phase boundary is fundamental to identifying the thermodynamic force driving the solution and precipitation process and is used here in setting up linear phenomenological relations to model near-equilibrium phase transformation kinetics. The local thermodynamic equilibrium of a stressed pure solid in contact with its melt or solution phase is governed by Gibbs's relation, which is rederived here, in a manner emphasizing its independence of constitutive assumptions for the solid while neglecting surface tension and diffusion in the solid. Fluid-infiltrated contact zones, such as those formed by rough surfaces, cannot generally be in thermodynamic equilibrium, especially during an ongoing process of pressure-solution slip, and the existing equilibrium formulations are incorrect in overlooking dissipative processes tending to eliminate fluctuations in superficial free energies due to stress concentrations near asperities, defects, or impurities. Steady pressure-solution slip is likely to exhibit a nonlinear dependence of slip rate on shear stress and effective normal stress, due to a dependence of the contact-zone state on the latter. Given that this dependence is negligible within some range, linear relations for pressure-solution slip can be derived for the limiting cases of diffusion-controlled and interface-reaction-controlled rates. A criterion for rate control by one of these mechanisms is set by the magnitude of the dimensionless quantityk/2C _pD, wherek is the interfacial transfer coefficient, is the mean diffusion path length,C _p is the solubility at pressurep, andD is the mass diffusivity.     

A CASE OF MESOSCALE CONVECTIVE COMPLEX EVOLVING INTO A VORTEX

A case of mesoscale convective complex(MCC)which evolved into a vortex is documented in this paper.As theMCC entered into the dissipating phase,a well-defined spirally banded structure became visible in the satellite image.The blackbody temperature(TBB)of the residual cold-cloud-shield indicates the vortex existed in the layer from 400 to250 hPa.According to the upper air analysis,the upper level vortex was an anticyclone.The MCC-generated vortex wasvisualized in the satellite images because it was located in the subtropical high where the wind field was very weak.     

1989年7月川东大暴雨中尺度对流系统分析

使用气象卫星资料，分析了１９８９年７月发生在四川东部的４个中尺度对流系统的特征，第一个系统是由３个对流云团合并而成，生成后快速向前移动，第二个为向后传播。第三个系统生成后，系统的西南部不断生成新的对流单体，使之维持准静止状态，最后一个系统的初期呈胞状结构，后与冷锋结合，成为冷锋云系的一部分，这４个系统都是西南低涡暖切变形势下的产物，随着形势演变，其大尺度环境略有差异。     

东北地区中尺度对流复合体的卫星云图特征

通过１０年（１９８３－１９９２年）卫星云图资料的分析，综合归纳了东北地区中尺度对流复合体（ＮＭＣＣ）的基本特征及其发展演变过程，由于受地理条件的影响，ＮＭＣＣ与美国大平原以及我国西北和华北平原上的ＭＣＣ有明显差别，作为一类特殊的对流性天气系统，ＮＭＣＣ与一般中尺度对流云图特征有明显差异。     

归一化植被指数与降水量、土壤湿度的关系

归一化植被指数是描述植被绿度及生长状况的指数，由于植被生长依赖于环境条件因此ＮＤＶＩ与环境参量的关系是应用ＮＤＶＩ监测环境状况的基础。分别应用位于中国北部的干旱及半干旱地区的降水量资料对ＮＤＶＩ与降水量之间的关系地分析，结果表明仅在干旱半干旱地区生长季末的累积降水量与累积ＮＤＶＩ存在着显著的非线性关系，相关系数为０．７８。     

A CASE OF MESOSCALE CONVECTIVE COMPLEX EVOLVING INTO A VORTEX*

A case of mesoscale convective complex(MCC) which evolved into a vortex is documented in this paper.As the MCC entered into the dissipating phase,a well-defined spirally banded structure became visible in the satellite image.The blackbody temperature(TBB) of the residual cold-cloud-shield indicates the vortex existed in the layer from 400 to 250 hPa.According to the upper air analysis,the upper level vortex was an anticyclone.The MCC-generated vortex was visualized in the satellite images because it was located in the subtropical high where the wind field was very weak.     

中国西北C-3植物的碳同位素组成与年降雨量关系初探

 本文对不同年降雨量环境下生长的藜、独行菜、魁蓟和平车前这4种常见C-3植物的δ¹³C进行了分析,发现这4种C-3植物的δ¹³C组成都表现出随年降雨量减少而变重的趋势,其中藜和独行菜的碳同位素组成对降水变化的响应相对要较其它2种植物强烈得多。藜、独行菜和魁蓟的δ¹³C组成与年降雨量有显著的线性关系,平车前碳同位素组成与年降雨量没有显著的相关性,表明藜、独行菜和魁蓟的δ¹³C组成可作为年降雨量的替代性指标,平车前的δ¹³C组成不能作为年降水的替代性指标。     

The Relative Impact of Regional Scale Land Cover Change and Increasing CO2 over China

A series of 17-yr equilibrium simulations using the NCAR CCM3 (T42 resolution) were performed to investigate the regional scale impacts of land cover change and increasing CO2 over China. Simulations with natural and current land cover at CO2 levels of 280,355, 430, and 505 ppmv were conducted. Results show statistically significant changes in major climate fields (e.g. temperature and surface wind speed) on a 15-yr average following land cover change. We also found increases in the maximum temperature and in the diurnal temperature range due to land cover change. Increases in CO2 affect both the maximum and minimum temperature so that changes in the diurnal range are small. Both land cover change and CO2 change also impact the frequency distribution of precipitation with increasing CO2 tending to lead to more intense precipitation and land cover change leading to less intense precipitation-indeed, the impact of land cover change typically had the opposite effect versus the impacts of CO2. Our results provide support for the inclusion of future land cover change scenarios in long-term transitory climate inodelling experiments of the 21st Century. Our results also support the inclusion of land surface models that can represent future land cover changes resulting from an ecological response to natural climate variability or increasing CO2. Overall, we show that land cover change can have a significant impact on the regional scale climate of China, and that regionally, this impact is of a similar magnitude to increases in CO2 of up to about 430 ppmv. This means that that the impact of land cover change must be accounted for in detection and attribution studies over China.