The effects of stress on reactions in the Earth: Sometimes rather mean,usually normal,always important          下载免费PDF全文

John Wheeler 《Journal of Metamorphic Geology》2018,36(4):439-461

Stress affects chemical processes on all scales in the Earth but the magnitude of its effect is debated. Here, I give a new synthesis of the theory that describes the effects of stress on chemistry, elaborating upon work in Materials Science which is built from fundamental thermodynamic laws, and show its significance in Earth Science. There are separate but compatible relationships describing what happens (1) at interfaces and (2) within grains. (1) The main chemical effects of stress in the Earth are due to variations in normal stress along grain interfaces and between interfaces with different orientations. For reactions involving diffusion these variations give effects on mineral stability broadly equivalent to pressure changes of (molar volume)/(molar volume change during reaction) × (stress variation). The volume ratio is generally large and so the effects of normal stress variations are always important since all stressed rocks have interfaces supporting different normal stresses. There is no global chemical equilibrium in a stressed system, so reaction kinetics contribute to ongoing evolution until stresses relax: this evolution can include deformation by diffusion creep and pressure solution, possibly with new mineral growth. These effects are relevant for predicting the conditions for reactions involving fluids, such as serpentinite formation and breakdown (relevant for the Earth's volatile cycles) and for other reactions such as ringwoodite breakdown (relevant for understanding the 660 km mantle discontinuity). (2) Within stressed solid solution grains it is not possible to define chemical potentials of all chemical components since one has to be specified as “immobile.” The chemical potential of a “mobile” component such as an exchange vector can be defined. It depends on the “partial molar strain,” a second rank tensor defining the variation in unit cell geometry with composition. In cubic crystals the partial molar strain is isotropic and the chemical potential of a mobile component depends on mean stress. In other crystal systems the partial molar strain is anisotropic and the chemical potential depends on a “weighted” mean stress; orientation as well as magnitude of stress has an influence. I propose “chemical palaeopiezometry”—the possibility of measuring past stress levels via chemistry. Examples show that stress variations in hundreds of MPa to GPa are required to produce 2% variations in composition but high stresses and/or precise chemical analyses will allow this proposal to be tested. High stresses around inclusions and dislocations could be targeted. So, the weighted mean stress inside grains has an effect which is relatively minor although potentially valuable in explaining chemical variations; the normal stress at interfaces plays the main role in chemical processes and its effects are of significant magnitude.  相似文献   

Th/U ratios in metamorphic zircon   总被引：2，自引：0，他引：2       下载免费PDF全文

Chris Yakymchuk  Christopher L. Kirkland  Chris Clark 《Journal of Metamorphic Geology》2018,36(6):715-737

The Th/U ratios of zircon crystals are routinely used to help understand their growth mechanism. Despite the wide application of Th/U ratios in understanding the geological significance of zircon U–Pb ages, the main controls on the Th/U ratio in metamorphic zircon are poorly understood. Here, phase equilibria modelling coupled with solubility expressions for accessory minerals are used to investigate the controls on the Th/U ratios of suprasolidus metamorphic zircon in an average amphibolite facies metapelite composition. We also present a new database of metamorphic Th/U ratios in zircon from Western Australia. Several factors affecting the Th/U ratio are investigated, including the bulk rock concentrations of Th and U, the amount of monazite in the system, and open v. closed system behaviour. Our modelling predicts that the main controls on the Th/U ratio of suprasolidus metamorphic zircon are the concentrations of Th and U in the system, and the breakdown and growth of monazite in equilibrium with zircon. Furthermore, the relative timing of zircon and monazite growth during cooling and melt crystallization has an important role in the Th/U ratio of zircon. Early grown zircon near the peak of metamorphism is expected to have elevated Th/U ratios whereas zircon that grew near the solidus is predicted to have relatively low Th/U ratios, which reflects the coeval growth of monazite during cooling and melt crystallization. Our modelling approach aims to provide an improved understanding of the main controls of Th/U in metamorphic zircon in migmatites and hence better apply this geochemical ratio as a tool to assist in interpretation of the genesis of metamorphic zircon.  相似文献   

盐类对甲烷水合物稳定性影响研究进展     

刘唯一  陈勇  王淼  张韩静 《岩矿测试》2018,37(2):111-120

甲烷水合物稳定性主要控制着甲烷水合物稳定带的厚度,温度、压力、孔隙水盐度和气体组分等因素影响着水合物稳定带的厚度。甲烷水合物的形成与地层水关系密切,而地层水中的各种盐离子(Cl~-、Na~+、Mg~(2+)、SO_4(~2-)、Ca~(2+))以及过渡金属(Fe、Mn、Cu、Co、Ni等)会影响天然气水合物的形成和分解条件。因此,研究盐类对甲烷水合物的稳定性认识有助于更加深入了解天然气水合物的成藏条件。本文分析了氯化物、硫酸盐、碳酸盐三大盐类对甲烷水合物稳定性的影响:同一盐类不同盐度条件下,随着盐度的增加,甲烷水合物相平衡曲线向低温高压偏移。总结了不同盐类和阴阳离子对甲烷水合物的抑制作用大小:在相同浓度、不同盐类条件下,盐类浓度在1.0~1.5 mol/L时盐类对甲烷水合物的抑制作用大小为MgCl_2CaCl_2Na ClKCl,盐类浓度大于1.5 mol/L时CaCl_2的抑制作用较强;阴离子对甲烷水合物的抑制作用大小争议较大,阳离子中Mg~(2+)对甲烷水合物的抑制作用最强。从目前的研究成果来看,已有数据与实际地质条件还存在一定差距,需要在真实实验条件下加强氯化物-硫酸盐-碳酸盐-甲烷-水体系的详细研究。本文提出,将高压可视反应腔与显微激光拉曼技术相结合,有望准确获取天然气水合物稳定形成时的温压条件,明确盐类和阴阳离子的抑制作用大小,以及盐类和离子特性如何影响水合物的形成和稳定,以便为未来的水合物勘探开发提供参考。  相似文献   

Permo-Triassic high-pressure metamorphism in the central western Korean Peninsula,and its link to Paleo-Tethyan Ocean closure: Key issues revisited     

Hyeong Soo Kim  Sanghoon Kwon  Sung Won Kim  M.Santosh 《地学前缘(英文版)》2018,9(5):1325-1335

Permo-Triassic high-pressure(HP) mafic granulites, together with the Bibong retrogressed eclogite,preserved along the central western Korean Peninsula provide important insights into the Late Permian to Triassic collisional orogeny in northeast Asia. The metamorphic pressureetemperatureetime(P-T-t)paths of these rocks, however, remain poorly constrained and even overestimated, owing to outdated geothermobarometers and inaccurate isopleth techniques. Here we evaluate the metamorphic Pe T conditions of Triassic HP mafic granulites including those in Baekdong, Sinri and Daepan and the Bibong Triassic retrogressed eclogite in the Hongseong area, and the Permo-Triassic Samgot mafic granulite in the Imjingang Belt of the central western Korean Peninsula through the application of modern phase equilibria techniques. The Baekdong and Samgot mafic granulites and the Bibong retrogressed eclogite yield a range of 12.0 -16.0 kbar and 800 -900℃, representing HP granulite facies conditions. The Sinri and Daepan granulites from the Hongseong area show relatively lower grade metamorphic conditions between HP granulite and normal granulite facies, and are characterized by sub-isothermal decompression during exhumation. The similarities in the metamorphic ages and the post-collisional igneous activity from the central western Korean Peninsula indicate that the Triassic ages represent the retrograde stage of the metamorphic Pe T paths. In contrast, the Late Permian metamorphic ages, which are older than protolith ages of the post-collisional igneous rocks, correspond to the possible prograde stage of metamorphism. The P-T-t paths presented in this paper, together with the metamorphic ages and post-orogenic igneous events reported from these areas suggest trace of the subduction, accretion and exhumation history, and indicate a tectonic linkage among the northeast Asian continents during the Paleo-Tethyan Ocean closure.  相似文献   

Comparison of the compositions of crystalline aluminosilicate rocks and their minerals in a planar triangular projection     

Z.F. Golitsyna  S.V. Banushkina  N.V. Surkov 《Russian Geology and Geophysics》2018,59(3):257-267

The problem of comparison of the composition of crystalline rocks with the composition of the constituent minerals of these rocks is considered. It is proposed to present the composition of rocks and the compositions of the constituent minerals in the form of a triangle on the plane. The experience of presentation of compositions in phase diagrams was taken as a basis for the construction. Analysis of the crystallochemical characteristics of clinopyroxenes and garnets has shown that three parameters are enough for depicting the compositions of these and other minerals. For this purpose, similar composition components of rocks and their minerals are summarized in molecular proportions and are plotted on the triangle DO-1/2(R₂O3)-XO₂, where DO = (MgO + CaO + FeO + MnO + NiO + ...) + 1/4(Na₂O + Al₂O₃) + 1/4(K₂O + Al₂O₃), 1/2(R₂O₃) = 1/2(Al₂O₃ + Fe₂O₃ + Cr₂O₃ + ...) - (1/4(Na₂O + Al₂O₃) + 1/4(K₂O + Al₂O₃)), and XO₂ = SiO₂ + TiO₂. The compositions of minerals are expressed as the sums of their components: Ol = Fo + Fa + Lar + Neph + ..., Px = Di + En + Wol + Ged + Gip + Jd + Eg + ..., Ga = Pyr + Gross + Alm + Spe + Ski + Knr + Mj + ..., etc. A step-by-step calculation algorithm is proposed, which permits evaluation of the contents of bi- and trivalent iron during probe microanalyses of garnets and pyroxenes. Comparison of the compositions of deep-seated rocks and their minerals shows their good consistency. The proposed schematic projection permits a visual comparison of the compositions of rocks with low contents of carbonates and water, from ultrabasic (e.g., dunites) to acid (e.g., granites) ones.  相似文献   

辽河(岩)群变形期次再讨论     

仲米山  王海鹏  鲁红峰  郭洪方 《地质与资源》2018,27(3):218-223

辽河（岩）群在辽宁省为十分重要的地层,不仅蕴藏着丰富的矿产,还存在诸多有争议的问题,变形期次就是其中重要问题之一.辽河（岩）群中最主要的构造形迹就是东西向展布的区域上透入性面理,它是纵向置换作用形成的,在微观上残留了较多置换过程的痕迹.从辽河（岩）群的的原岩建造来看,它至少经历了类似"大西洋阶段"和"太平洋阶段",不会是夭亡的裂谷.通过全方位构造解析认为,洋盆闭合挤压造山过程是一个漫长的递进变形过程,在这一漫长的递进变形过程中形成的所有构造形迹皆属同一期构造,即辽河（岩）群可归纳为一期构造.  相似文献   

西藏松多地区晚白垩世末期弧岩浆岩岩石成因及构造意义     

刘金恒  解超明  范建军  王明  罗安波  高忠维  王斌  曾孝文 《地质通报》2018,37(8):1477-1491

新特提斯洋在晚白垩世末期(68Ma左右)的构造演化一直饱受争议。西藏松多地区晚白垩世末期弧岩浆岩包括花岗斑岩和二长花岗岩。锆石定年结果显示,二长花岗岩和花岗斑岩年龄均为68Ma。松多花岗斑岩和二长花岗岩的Si O_2含量为68.5%~80.6%,K_2O含量为4.1%~6.5%,P2O5含量为0.011%~0.058%。花岗斑岩Mg#值较低,为11.3~19.0,二长花岗岩Mg~#值为24.2~43.5。花岗斑岩和二长花岗岩样品均显示轻稀土元素富集、重稀土元素亏损和明显的Eu(δEu=0.15~1.21)负异常。两者均富集大离子亲石元素Rb、Th、U、K、Pb等,亏损高场强元素Nb、Ta、Ti。花岗斑岩εHf(t)值为-0.9~+2.9,二阶段模式年龄T_(DM)~C在955~1196Ma之间;二长花岗岩εHf(t)值为-17.1~+7.9(只有1个点为负值),二阶段模式年龄在633~2219Ma之间。最终认为,松多地区晚白垩世末期二长花岗岩和花岗斑岩岩浆源区为新生下地壳,但花岗斑岩更靠近古老下地壳。结合区域资料,认为新特提斯洋在晚白垩世末期68Ma左右属于洋脊俯冲结束阶段。  相似文献   

基于极化相干层析技术的森林垂直剖面重建研究     

曹先革  杨金玲  刘江  孟祥来 《测绘与空间地理信息》2015,(8):19-21

极化相干层析技术作为极化干涉合成孔径雷达的一个重要应用方向,在林业遥感方面应用广泛。在分析极化相干层析技术原理的基础上,基于仿真数据从10 m,18 m和22 m三种森林高度以及Deciduous,Pine(2)和Hedge三种树型分别对极化相干层析技术构建森林垂直结构剖面的精度进行了验证,研究结果表明,该方法能够有效构建垂直结构剖面,森林高度和树型对估算结果影响较小,该方法对不同树型和不同高度均具有良好的适应性。  相似文献   

FY-3A/MERSI海上沙尘天气气溶胶光学厚度反演   总被引：1，自引：1，他引：0  

周永波  白洁  周著华  齐琳琳 《遥感学报》2014,18(4):771-787

利用FY-3A/MERSI资料,结合MODIS C005算法的海上气溶胶模型,研究了中国渤海、黄海以及东海海域沙尘天气气溶胶光学厚度反演方法。通过MERSI反演的气溶胶光学厚度与MODIS C005气溶胶光学厚度产品(MOD04)对比,发现MERSI气溶胶光学厚度反演结果存在较大偏差。分析认为,这种偏差是由MODIS C005算法的海上气溶胶模型对MERSI气溶胶光学厚度反演不完全适用造成的。鉴于此,本文研究引进了一种沙尘气溶胶模型,并将其与MODIS C005算法的粗粒子气溶胶模型按照一定比例混合,形成了改进的气溶胶模型。利用改进气溶胶模型再次反演海上沙尘天气气溶胶光学厚度,反演结果与MOD04一致性较好,说明改进气溶胶模型能有效地提高MERSI定量反演沙尘气溶胶的能力。  相似文献   

GNSS天线相位中心偏差检定及不确定度分析     

刘智超  张则宇  庞飞 《测绘信息与工程》2014,(3):19-23

GNSS天线相位中心偏差是GNSS天线接收卫星信号的电气中心与其机械几何中心之差。相位偏差具有一定的稳定性,呈现系统误差性质。现行规程将相位偏差按限差要求加以检测,而没有按系统误差加以检定并进行改正,本文对规程的检定方法加以改进,定量检定天线相位偏差半径r和偏差角a,并依据r值的大小,给出相位偏差在GNSS测量中的采用原则,对两种改进方法进行了测量不确定度分析。  相似文献