Salt weathering: influence of evaporation rate,supersaturation and crystallization pattern     

Carlos Rodriguez-Navarro  Eric Doehne 《地球表面变化过程与地形》1999,24(3):191-209

Micro- and macroscale experiments which document the dynamics of salt damage to porous stone have yielded data which expose weaknesses in earlier interpretations. Previously unexplained differences are found in crystal morphology, crystallization patterns, kinetics and substrate damage when comparing the growth of mirabilite (Na₂SO₄. 10H₂O) and thenardite (Na₂SO₄) versus halite (NaCl). The crystallization pattern of sodium sulphate was strongly affected by relative humidity (RH), while a lesser RH effect was observed for sodium chloride. Macroscale experiments confirmed that mirabilite (crystallizing at RH > 50 per cent) and thenardite (crystallizing at RH < 50 per cent) tend to form subflorescence in highly localized areas under conditions of constant RH and temperature. This crystallization pattern was more damaging than that of halite, since halite tended to grow as efflorescence or by filling the smallest pores of the stone in a homogeneous fashion, a result which contradicts Wellman and Wilson's theoretical model of salt damage. Low RH promoted rapid evaporation of saline solutions and higher supersaturation levels, resulting in the greatest damage to the stone in the case of both sodium sulphate and sodium chloride crystallization. At any particular crystallization condition, sodium chloride tended to reach lower supersaturation levels (resulting in the crystallization of isometric crystals) and created negligible damage, while sodium sulphate reached higher supersaturation ratios (resulting in non-equilibrium crystal shapes), resulting in significant damage. ESEM showed no damage from sodium sulphate due to hydration. Instead, after water condensation on thenardite crystals, rapid dissolution followed by precipitation of mirabilite took place, resulting in stone damage by means of crystallization pressure generation. It is concluded that salt damage due to crystallization pressure appears to be largely a function of solution supersaturation ratio and location of crystallization. These key factors are related to solution properties and evaporation rates, which are constrained by solution composition, environmental conditions, substrate properties, and salt crystallization growth patterns. When combined with a critical review of salt damage literature, these experiments allow the development of a model which explains variations in damage related to combinations of different salts, substrates and environmental conditions. Copyright © 1999 John Wiley & Sons, Ltd.  相似文献   

喜马拉雅淡色花岗岩结晶分异机制概述   总被引：8，自引：5，他引：3  

刘志超  吴福元  刘小驰  王建刚 《岩石学报》2020,36(12):3551-3571

近年来,喜马拉雅淡色花岗岩的高分异成因得到了学术界的高度关注。另外,有调研工作发现,喜马拉雅淡色花岗岩具有良好的稀有金属成矿潜力,是未来矿产勘探的重点靶区。稀有金属元素的富集过程应与岩浆的结晶分异作用密切相关。但是,目前我们对喜马拉雅淡色花岗岩的岩浆分异演化过程缺乏深入的了解,因而也难以对其成矿效应进行有效评估。针对该问题,本文选择喜马拉雅带中两个颇具代表性的、明显发生稀有金属矿化现象的岩体（特提斯喜马拉雅带中的然巴淡色花岗岩和高喜马拉雅带中的告乌淡色花岗岩）开展系统野外地质、岩相学、矿物学、岩石学和地球化学调查研究,就喜马拉雅淡色花岗岩的结晶分异机制进行初步探讨。综合近年来有关花岗岩结晶分异作用的研究进展,我们认为喜马拉雅淡色花岗岩的结晶分异过程可以划分为原地结晶分异和岩浆侵位运移过程中流动分异两种主要机制,大部分的喜马拉雅淡色花岗岩应是两种机制共同作用的产物。  相似文献   

滇西晚始新世高镁富钾火山岩的地球化学特征及其岩石成因机制探讨   总被引：11，自引：0，他引：11  

黄小龙  徐义刚  杨启军  邱华宁 《地球化学》2007,36(2):120-138

40Ar/39Ar同位素定年分析显示滇西新生代高镁富钾火山岩均形成于始新世晚期(约36 Ma),富含MgO(＞9%)和K2O(3.07%～7.28%),绝大部分K2O/Na2O比值大于2,均属超钾质系列岩石.较高的Cr、Ni含量和较低的Sc(＜30 μg/g)、TiO2(＜1%)含量暗示了源区为尖晶石相方辉橄榄岩;高镁富钾火山岩与区内同时代的粗面岩具相似的地球化学组成特征,均富集LILE和LREE,亏损高场强元素Nb-Ta和Ti等,具有极低的Nb/La比值(0.2～0.3)、较高的87Sr/86Sr初始值(0.7056～0.7072)、负的εNd初始值(-0.97～-4.87)和相对较高的206pb/204Pb(18.556～18.695)、207pb/204Pb(15.609～15.630)比值,具有明显的岛弧型钾质火山岩的性质.高镁富钾火山岩来源于受古特提斯俯冲带流体交代的尖晶石相方辉橄榄岩的部分熔融岩浆,并在深部岩浆房经历了橄榄石的结晶分异和堆晶作用,而粗面岩则还在相对浅部岩浆房经历了较大程度的长石与单斜辉石的分离结晶.  相似文献   

稀有金属伟晶岩过度冷却与侵位之关系——基于野外地质观察及年代学的思考     

凤永刚  梁婷  雷如雄  鞠明辉  张忠利  高景刚  周义  吴昌志 《地球科学与环境学报》2021,(1):100-116

稀有金属伟晶岩的结晶过程是认识其成矿作用的重要方面.前人利用冷却模型所推测出的侵入变质围岩的伟晶岩冷却时间为几天至几千年,但对侵位于花岗岩中伟晶岩的结晶过程缺乏相关研究.基于此,对新疆大喀拉苏及镜儿泉地区稀有金属伟晶岩的野外地质观察及年代学研究显示,两处伟晶岩的侵位模式不同,侵位时花岗岩围岩的温度有别.大喀拉苏1号伟晶...  相似文献