The imprint of basalt on the geochemistry of silicic magmas

We propose that the fluid mechanics of magma chamber replenishment leads to a novel process whereby silicic magmas can acquire an important part of their chemical signatures. When flows of basaltic magma enter silicic magma chambers, they assume a ‘fingered' morphology that creates a large surface area of contact between the two magmas. This large surface area provides an opportunity for significant chemical exchange between the magmas by diffusion that is enhanced by continuous flow of silicic liquid traversing the basalt through thin veins. A quantitative analysis shows that a basaltic magma may thereby impart its trace-element and isotopic characteristics to a silicic magma. Depending on concentration differences and diffusion coefficients for the given components, this new mechanism may be as important as crystal fractionation and assimilation in producing the compositional diversity of silicic magmas. It may explain concentration gradients in silicic ash-flow tuffs and should be considered when interpreting the isotopic signatures of silicic rocks, even in the overt absence of mixing. For example, we show that, for several well studied, compositionally graded ash-flow tuffs, the concentrations and isotopic ratios of important geochemical tracers such as strontium could be largely due to this flow-enhanced diffusion process.     

Assessment of connectivity in a water‐stressed wetland (Kaabar Tal) of Kosi‐Gandak interfan,north Bihar Plains,India

Landscape elements respond to the processes acting on them, and this response connects with neighboring landscape units. The propagation, superposition, and interference of these responses are functions of the connectivity among the landscape units. Such landscape units are referred to as ‘Connectivity Response Units’ or CRUs that are in turn influenced by topography and landuse/landcover (LULC). The CRUs are obtained by the application of diffusion‐kernel based smoothing technique over the connectivity potential maps. A framework has been designed using the CRUs to understand the impacts of changing LULC on the connectivity structure in a relatively flat terrain under pre‐ and post‐monsoon scenarios. The proposed framework has been applied to a water‐stressed wetland occurring in an interfan setting in north Bihar plains, eastern India. It has also been demonstrated that CRUs can be used as a viable option for understanding the seasonal and temporal dynamics of connectivity structure in and around such wetlands and for guiding a rehabilitation strategy for such fragile ecosystems. Copyright © 2017 John Wiley & Sons, Ltd.     

INFLUENCE OF PRESSURE HEAD CHANGE AND ITS CHANGE RATE ON RESERVOIR TRIGGERED SEISMICITY -A CASE STUDY OF ZIPINGPU RESERVOIR

For analyzing the role that reservoir impounding plays in triggering earthquake, the process of diffusion of pore pressure and its mechanism of action should be understood firstly. The temporal distribution of seismicity, which occurred before the M_S8.0 Wenchuan earthquake, following the impoundment of Zipingpu reservoir is studied in this paper. Then the mechanisms of the occurrence and development of reservoir triggered seismicity are discussed. A comparative analysis of the temporal distribution of seismicity and the submerged area by reservoir impounding is carried out firstly. Then the influence of various factors on modeling is analyzed in detail. After calculating, the pore pressure change by the Zipingpu reservoir impoundment is obtained. The following observations are made:(1)Conspicuous swarms of earthquakes, of which the sources are located on the same fault of the M_S8.0 Wenchuan earthquake, occurred orderly with the impoundment of Zipingpu reservoir.(2)Because of the influences of the terrain and the medium, the range of effect of pore pressure change by the impoundmemt is limited and anisotropic. Hydraulic diffusivities(D)of 0.7 and 0.35m²/s along the fault strike and the fault dip are reached respectively by a semi-quantitative assessment. Of course, the qualitative pressure constraints on the surface are also applied for the modeling.(3)The calculation results show that the temporal distribution of seismicity near the Zipingpu reservoir is related with the pore pressure change. After the pore pressure reached the threshold of triggering earthquake, whether the pressure head change is high or not, the change rate of pressure head change plays a key role in the decrease or increase of seismicity. It means that the triggered seismicity by pore pressure is a dynamic triggering process.     

Comparing the behaviour of spherical beads and natural grains in bedload mixtures

It is common to use idealised materials to study the dynamics of granular transport in fluid flows, but the impact of this choice upon sediment behaviour has not been extensively explored. To tackle this research gap, two experiments were undertaken to explore the influence of a finer grain input to a channelized coarser granular flow driven by a shallow fluid flow. The first set of runs was undertaken using spherical glass beads, and the second set with natural fluvial sediment. The transport system approximates a narrow slice through the bedload at the bottom of a river. In the runs with natural grains, the infiltration of fine sediment into the bed was similar to the spherical glass beads, but with reduced infiltration capacity. We ascribe this behaviour to irregular and variable pore shapes and sizes in the natural material. The behaviour of the bedload in the natural material runs matched that of the bead runs only when the feed contained a high content of fines. When the feed contained a low content of fines the transport of natural grains was more complex, including the emergence of migrating collections of grains. However, the overall changes in bed and water slope due to the finer grain input were comparable in both sets of experiments. We conclude that artificial, idealised materials qualitatively represent sedimentary phenomena, but that quantitative differences in the outcomes must be expected. © 2020 John Wiley & Sons, Ltd.     

同球向双球面减隔震支座关键部件力学参数影响因素分析

以同球向双球面减隔震支座中的剪力销与减震榫耗能器为研究对象,针对减隔震支座剪力销和减震榫力学参数的影响因素及其规律进行研究。通过反应谱分析和有限元数值模拟的方法讨论了墩高和场地类型变化对剪力销剪断力的影响和减震榫几何参数对减震榫力学性能的影响,同时分析了减震榫在屈服荷载和极限荷载作用下的应力应变分布情况。结果表明,支座剪力销剪断力受墩高和场地条件的影响较大,不能简单地取支座竖向力与某一百分数的乘积设置剪力销的剪断力;减震榫的力学性能主要受d₀、L₁和L3个几何参数控制,本文给出的几何参数对减震榫力学性能的影响规律为减震榫力学参数的初步设置提供了参考。     

洞庭湖湿地洪水期甲烷扩散和气泡排放通量估算及水环境影响分析

水体甲烷（CH₄）主要通过气泡和扩散传输排放到大气,这两种途径在CH₄总排放中的相对贡献及环境影响因子目前关注较少.本文以洞庭湖湿地3种生境类型（光滩、苔草、芦苇）为研究对象,通过静态箱法和扩散模型法估算洪水期CH₄总排放通量、扩散排放通量和气泡排放通量,并分析其水体环境因子影响.结果表明：苔草地CH₄总排放量最高,为6.49±3.12 mg（C）/（m²·h）.在3个生境中,CH₄扩散排放占总排放通量的1.34%~3.91%,气泡排放占96.09%~98.66%.扩散排放通量受水体pH、电导率和水温的影响,而CH₄的总排放和气泡排放主要受水温的影响.当水温低于11.7℃时,水体CH₄以扩散排放为主,但当水温高于11.7℃时,水体CH₄主要通过气泡排放.但这一温度阈值是否同样适用于其他类型湿地还需要更多实验验证.本研究对于揭示中低纬度内陆湖泊水体CH₄排放过程有重要意义.     

岩溶湿地表层水体CO2分压时空分布特征及其扩散通量

为揭示岩溶湿地表层水体二氧化碳分压(pCO₂)的时空分布规律及其扩散通量,以我国最大的岩溶湿地贵州威宁草海为研究对象,分别于2019年7月(丰水期)和12月(枯水期)通过网格布点法,系统采集草海表层湿地水体,测定水样理化指标和离子组成,利用PHREEQCI软件计算水体pCO₂,并基于Cole提出的气体扩散模型估算水-气界面二氧化碳(CO₂)的扩散通量.结果表明:草海湿地表层水体丰水期pCO₂的变化范围为0.44~645.65μatm,平均值为(55.94±124.73)μatm;枯水期变化范围为35.48~707.95μatm,平均值为(310.46±173.54)μatm;丰水期水体整体pCO₂低于枯水期,空间上两期水体均呈现东部区域及河流入湖口处pCO₂较高,而中西部区域pCO₂欠饱和的特征.水-气界面CO₂的扩散通量在丰水期变化范围为-43.27~27.16 mmol/(m²·d),平均值(-34.49±12.93)mmol/(m²·d),枯水期变化范围为-33.36~28.15 mmol/(m²·d),平均值(-8.02±15.85)mmol/(m²·d),与其他岩溶湖库相比,水生植物丰富的草海在两个极端水文期CO₂扩散通量相对较低,总体表现为大气CO₂的汇.     

结合改进的降斑各向异性扩散和最大类间方差的SAR图像水体提取

利用遥感成像技术获取地面水体信息对水资源调查、自然灾害评估、流域规划和生态环境监测等具有重要意义,其中SAR成像作为大范围地面监测的可靠数据源,拥有全天时、全天候、广覆盖等光学遥感系统所不具有的优点,在水体提取中得到了广泛的应用。但由于受SAR图像相干斑噪声的影响,现有水体提取方法难以迅速、精确提取SAR图像中复杂精细的自然水体结构。为此,提出一种结合改进的降斑各向异性扩散和最大类间方差的SAR图像水体提取方法。首先,利用降斑各向异性扩散滤波SAR图像,在迭代滤波过程中通过计算图像间平均结构相似度自适应控制迭代过程,使其同时保持精细边缘和纹理结构;然后,以类间方差最大为准则,自适应确定阈值,实现滤波结果图像二值化分割。在二值化分割结果中,搜索具有相同像元值且位置相邻的前景像元点组成的连通区域,使每个单独的连通区域形成一个被标识的块,通过获取这些块的几何参数来消除图像的误分割,精确划定真实的水体区域,以实现SAR图像水体提取。为了验证提出方法的准确性,将本文方法提取的水体边界与人工绘制的水体边界叠加,结果表明二者可较好吻合。同时,从视觉、提取精度和运行时间对本文方法与目前常用3种SAR图像水体提取算法的结果进行比较分析,其中本文方法的运行时间满足实时应用的要求,提取结果的边界在2个像元评级区重叠度均达到80%,明显优于其他方法且本文方法提取结果在边界及细节信息等视觉方面也更加显著。对结果的定性及定量评价表明本文方法的优越性。     

乡村产业振兴背景下台商“西进”的空间路径演变——以福建省为例

本研究以西进参与福建省乡村产业振兴的2980家乡村台企为研究对象,采用GIS空间分析方法和空间扩散模型,揭示台商“西进”的空间路径演变。研究发现：① 国际经济形势和海峡两岸政治关系变化促成了泉州的晋江市和石狮市、厦门的海沧区和同安区、漳州的龙海市形成台商“西进”的高密度聚集区,以及福州的闽侯县和福清市、莆田的涵江区形成中密度聚集区;② 在企业内部因素的主导下,台商“西进”轨迹呈现近“S”形增长态势,并形成以沿海福州和厦门城市群的郊区县（市）为核心,向内陆地区扩展扩散的格局;③ 空间扩散路径模拟显示,当前台商“西进”已达到数量扩散的阈值,未来台商“西进”路径将由反“E”字型向“日”字形转变,沿海地区仍是空间扩散的主要方向。