砂岩侵入体系模拟及形成机理分析

砂岩侵入体系是一种普遍的地质现象,近些年来越来越受到地学界的重视,但对其形成机理探讨较少。作者及研究团队通过设计一套室内模拟实验装置,来简化模拟3层地层结构中砂岩侵入体系的形成和演化过程。在之前模拟实验(实验变量为顶层沉积物的厚度、进水管的结构)结果的基础上,进一步考察了地形坡度对实验结果的影响,并对砂岩侵入体系的形成机理进行了分析。实验过程中,共观察到7种不同形态不同样式的管道,并对实验过程中压力变化进行了测试。对实验结果分析认为:盖层厚度越大,压力下降的速度越慢,越不利于压力的释放;随着实验的继续进行,砂岩侵入体最终会转化为砂岩喷出体并喷出地表;不稳定的地形有利于触发疏松沉积物发生变形。实验表明,超压是砂岩侵入体发生的最重要条件之一, 沉积盆地中的压实不均衡和生烃作用是可独立产生大规模超压的2种主要机制。     

内蒙古大桦背I型花岗岩地球化学特征及其成因意义

在大桦背花岗岩体区域地质和岩石学研究的基础上,运用X射线荧光光谱分析样品主量元素,采用电感耦合等离子体质谱对其样品进行了微量、稀土元素分析.同时结合前人的锆石年龄和Pb同位素数据,认为大桦背花岗岩为I型花岗岩,主要为古亚洲洋板块向华北板块多期俯冲过程中,中下地壳、成熟岛弧和大洋岛弧大面积部分熔融的产物,伴有少量地幔与未知含量的海洋沉积物及早期造山作用产物等物质的不同程度混合作用.     

2014年2月12日于田7.3级地震序列震源机制特征分析

基于新疆及西藏区域数字地震台网的宽频带资料,采用CAP方法反演了2014年2月12日于田7.3级地震的前震、主震及早期MS≥3.5余震序列的震源机制解。结果显示,此次7.3级强震为带有正断分量的走滑型地震,结合震源区的构造和余震分布,节面I走向241°/倾角90°/滑动角-22°,判定该节面代表了主震的发震断层面。主震主压力轴方位为194o,与该区历史中强震主压应力P轴方位近NS向较为接近。其5.4级前震和主震震源机制解具有较高的一致性。18次余震中有10次为走滑型地震,其中6次为正断型,2次为逆断型,且70%的地震具有近SN向的P轴方位。此次7.3级地震序列震源深度范围5~28km,而大部分地震为15~20km,略大于本文计算得到的主震震源深度10km。     

2013年洱源M_S5.5地震序列M_L≥3.4地震的震源机制解研究

利用云南省地震台网的宽频带数据,采用CAP方法计算了2013年3月3日洱源MS5.5地震前后共10次ML≥3.4地震的震源机制解,分析了洱源MS5.5地震前后震源机制解的一致性变化特征,结合精定位结果、震后现场灾害评估报告及震区地质构造情况,判定维西—巍山断裂以西的苍山西麓炼铁盆地东缘主边界断裂带为洱源MS5.5地震的发震构造,震源机制解节面Ⅱ(走向160°、倾角48°、滑动解-99°)为其发震断层面。     

Mechanism of mineralization in the Changjiang uranium ore field,South China: Evidence from fluid inclusions,hydrothermal alteration,and H–O isotopes

The Changjiang uranium ore field, which contains >10,000 tonnes of recoverable U with a grade of 0.1–0.5%, is hosted by Triassic two-mica and Jurassic biotite granites, and is one of the most important uranium ore fields in South China. The minerals associated with alteration and mineralization can be divided into two stages, namely syn-ore and post-ore. The syn-ore minerals are primarily quartz, pitchblende, hematite, hydromica, chlorite, fluorite, and pyrite; the post-ore minerals include quartz, calcite, fluorite, pyrite, and hematite. The fluid inclusions of the early syn-ore stage characteristically contain O₂, and those of the late syn-ore and post-ore stage contain H₂ and CH₄. The fluid inclusions in quartz of the syn-ore stage include H₂O, H₂O–CO₂, and CO₂ types, and they occur in clusters or along trails. Homogenization temperatures (T_h) for the H₂O–CO₂ and two-phase H₂O inclusions range from 106 °C to >350 °C and cluster in two distinct groups for each type; salinities are lower than 10 wt% NaCl equiv. The ore-forming fluids underwent CO₂ effervescence or phase separation at ∼250 °C under a pressure of 1000–1100 bar. The U/Th values of the altered granites are lowest close to the ore, increase outwards, but subsequently decrease close to unaltered granites. From the unaltered granites to the ore, the lowest Fe₂O₃/FeO values become lower and the highest values higher. The REE patterns of the altered granites and the ores are similar to each other. The U contents of the ores show a positive correlation with total REE contents but a negative correlation with LREE/HREE ratios, indicating the pitchblende is REE-bearing and selectively HREE-rich. The δEu values of the ore show a positive correlation with U contents, indicating the early syn-ore fluids were oxidizing. The δCe values show a negative correlation, indicating the later mineralization environment became reducing. The water–rock interactions of the early syn-ore stage resulted in oxidization of altered granites and reduction of the ore-forming fluids, and it was this reduction that led to the uranium mineralization. During alteration in the early syn-ore stage, the oxidizing fluids leached uranium from granites close to faults, and Fe₂O₃/FeO ratios increased in the alteration zones. The late syn-ore and post-ore alteration decreased the Fe₂O₃/FeO ratios in the alteration zones. The δ¹⁸O_W–SMOW values of the ore-forming fluids range from −1.8‰ to 5.4‰, and the δD_W–SMOW values range from −104.4‰ to −51.6‰, suggesting meteoric water. The meteoric water underwent at least two stages of water–rock interaction: the first caused the fluids to become uranium-bearing, and the second stage, which was primarily associated with ore-bearing faults, led to uranium deposition as pitchblende, accompanied by CO₂ effervescence.     

Geochemical characteristics of mud volcano fluids in the southern margin of the Junggar basin,NW China: implications for fluid origin and mud volcano formation mechanisms

Mud volcanoes can provide important information about the underlying strata, hydrocarbon accumulation, and recent neotectonic movements in an area. The fluids erupting from mud volcanoes provide important information about their formation and evolution. The ion concentration and the hydrogen and oxygen isotopes of the fluids that were erupted from the three mud volcano groups, Baiyanggou, Aiqigou, and Dushanzi, and nearby rivers in the southern margin of the Junggar basin, northwestern China, are studied. The concentrations of Na and Cl in mud volcano fluids are clearly elevated, displayed as the Na-Cl type. The δD and δ18O values of the fluids are similar between the Baiyanggou and Dushanzi mud volcanoes, which are mainly from ancient sedimentary pore water. However, the Aiqigou mud volcano is depleted in dissolved Cl and shows lower δ18O values with mixed sources, including deep pore and local meteoric water. Two types of mud volcanoes are proposed in this study. One type is low-energy mud volcanoes with a low volume of fluid of deep origin on the hillcrest, which display as mud pool/pie/hole. The other type is high-energy mud volcanoes having mixed fluid origin in the valley and formed in the shape of a mud cone (dome).     

山东谢家沟金矿床流体包裹体研究及成矿机制的探讨

谢家沟金矿床位于胶东隆起西北缘的焦家断裂带和招平断裂带之间。矿床赋存在中生代玲珑花岗岩体中,矿体主要受NNE向和NNW向断裂构造控制,主要呈脉状或透镜状产出。矿石矿物主要有黄铁矿、黄铜矿、方铅矿、闪锌矿、自然金、银金矿以及少量的碲银矿和辉银矿。围岩蚀变主要有钾长石化、硅化、黄铁绢英岩化、绿泥石化和碳酸盐化等。成矿作用从早到晚可划分为4个阶段:石英-黄铁矿阶段(Ⅰ)、石英-绢云母-黄铁矿阶段(Ⅱ)、石英-多金属硫化物阶段(Ⅲ)、碳酸盐-萤石阶段(Ⅳ)。流体包裹体显微测温和激光拉曼成分分析表明,成矿早期流体温度为308~377℃,盐度为6.29%~8.55%,压力为350 MPa,属于H_2O-CO_2-NaCl流体体系;主成矿期的流体温度为226~331℃,盐度为4.87%~10.29%,压力为280~300 MPa,属于H_2O-CO_2-NaCl±CH_4流体体系。包裹体显微测温及岩相学观察发现,主成矿期的成矿流体发生了不混溶作用,这可能是导致金矿化的主要原因之一。硫同位素研究表明,谢家沟金矿床主成矿期黄铁矿的δ34S值接近或略低于胶东典型金矿床成矿期黄铁矿的δ34S值,暗示这些金矿床的成矿物质可能来自相同的源区;氢、氧同位素对比研究表明,谢家沟金矿床成矿流体表现出较明显的岩浆水特征,可能有大气降水的参与,但参与程度较弱。大气降水与岩浆水混合引起的温度降低、挥发分含量的降低可能是导致金矿化的另一原因。     

Hybrid finite-discrete element modelling of dynamic fracture and resultant fragment casting and muck-piling by rock blast

A state-of-the-art review is conducted to highlight the fracture mechanism in rock blast and advantages and limitations of various methods in modelling it. A hybrid finite-discrete element method (FEM-DEM) is implemented to simulate rock fracture and resultant fragment muck-piling in various blasting scenarios. The modelled crushed, cracked and long radial crack zones are compared with those in literatures to calibrate the hybrid FEM-DEM. Moreover, the hybrid modelling reproduces the rock fragmentation process during blasting. It is concluded that the hybrid FEM-DEM is superior to continuous and discontinuous methods in terms of modelling dynamic fracture of rock under blast-induced impact load.     

应用FTIR-SEM研究一类合成欧珀的微结构及其变彩成因机制

近些年来,相关人工合成欧泊的研究工作主要聚焦于天然与合成欧泊的鉴别与筛选,而相关合成欧泊的微结构、变彩机制及其中水的赋存状态的深入研究鲜见报道。本文通过傅里叶变换红外光谱(FTIR)、场发射扫描电镜(FE-SEM)对一类合成欧泊的微结构、结构缺陷进行较系统的研究。同时,结合对样品的热处理就该合成欧泊体色、变彩机制及其中水的赋存状态作了初步探讨。结果表明:该样品的红外光谱中,在约2900 cm~(-1)、1737 cm~(-1)处出现合成欧泊特征吸收,且在4000~6000 cm-1波段,合成欧泊相比天然欧泊的吸收峰更为复杂。合成欧泊的颜色由体色与变彩两者共同构成,该体色与存在于其微结构中准球状、粒径约205 nm的二氧化硅颗粒的间隙填充物直接关联,且在热处理条件下随着间隙物的析出而渐退。同时,该类合成欧泊的变彩归因于结构致色并由其内部SiO_2颗粒周期性排列而构成的三维的光子带隙结构所致。此外,在欧泊的微观结构发生重构前,变彩所呈现的颜色主要由准球状二氧化硅颗粒粒径与间隙填充物决定。     

Active and passive arching stresses in c′-ϕ′ soils: A sensitivity study using computational limit analysis

Vertical soil arching, commonly known as the “trapdoor mechanism,” is a pervasive phenomenon in various geotechnical applications that can be evaluated through a variety of analytical and numerical approaches, most of which exist due to a variety of proposed arching mechanisms, many of which are focused on either purely frictional or cohesive soils. This study investigates the realized arching mechanisms and associated loads for trapdoors under both active and passive arching conditions in c′-ϕ′ soils through a series of dimensionless charts using both upper and lower bound limit analyses. An associated sensitivity analysis demonstrates that arching loads are highly dependent on collapse mechanism, a function of not only geometry, but soil shear strength, with cohesion affecting the realized mechanism and arching loads.