Study on Physical Mechanism of Influence on Atmospheric Boundary Layer Depth in the Arid Regions of Northwest China

Using the sounding data of wind, temperature, and humidity in the boundary layer and micrometeorological data on the earth's surface observed in the same period in Dunhuang arid region of Northwest China,this paper researches characteristics of potential temperature, wind, and humidity profiles, confirms the structure and depth of thermodynamic boundary layer in Dunhuang region, and analyzses the relationship of depth of thermodynamic boundary layer with surface radiation, buoyancy flux as well as wind speed and wind direction shear in the boundary layer. The results show that the maximum depth of diurnal convective boundary layer is basically above 2000 m during the observational period, many times even in excess of 3000 m and sometimes up to 4000 m; the depth of nocturnal stable boundary layer basically maintains within a range of 1000-1500 m. As a whole, the depth of atmospheric boundary layer is obviously bigger than those results observed in other regions before. By analyzing, a preliminary judgement is that the depth of atmospheric thermodynamic boundary layer in Dunhuang region may relate to local especial radiation characteristics, surface properties (soil moisture content and heat capacity) as well as wind velocity shear of boundary layer, and these properties have formed strong buoyancy flux and dynamic forcing in a local region which are fundamental causes for producing a super deep atmospheric boundary layer.     

深厚淤泥爆破挤淤堤坝沉降计算与分析

爆破挤淤技术在海洋围垦和潮汐电站等工程堤坝建设中发挥着重要作用,随着海洋工程的不断推进,堤坝修建需要处理淤泥(软基)厚度在逐渐加深,在超过12 m的深厚淤泥中往往采用“悬浮式”堤坝结构,对该种堤坝结构开展沉降计算与分析有着重要的意义和应用价值。以惠州港兴盛油库护岸工程为工程实例,分别采用传统沉降计算方法、基于多孔介质渗透理论的考虑浮力作用沉降计算方法及数值模拟方法,对其爆破挤淤形成的“悬浮式”堤坝开展沉降计算,并与实际监测结果对比验证,分析几种沉降计算方法的适用性和合理性。研究表明,传统沉降计算方法得到的沉降值比实际监测值明显偏大,不适合于“悬浮式”堤坝沉降计算;考虑浮力作用方法和数值模拟方法的计算结果较为接近实际监测值,可用于“悬浮式”堤坝沉降计算。     

非常规油气藏的形成及其分布特征*

非常规油气领域是目前油气勘探和开发的热点领域, 也是石油工业的发展趋向, 非常规油气的成藏研究对非常规油气勘探具有重要指导意义。非常规油气与常规油气成藏的最本质区别在于非常规油气是非浮力驱动聚集, 这主要是由于致密储集层中微纳米级孔隙发育导致毛细管阻力较大, 同时缺乏提供强大浮力的有利条件。根据烃源岩演化与非常规油气成藏的关系, 将非常规油气资源分为油页岩、页岩油、致密油、页岩气、致密气和煤层气6种类型。油页岩、页岩油、煤层气和页岩气的源储组合特征都是“源储一体”, 而致密油气源储组合有2种类型：一种是源储叠置的临源型致密油气, 另一种是与常规油气藏类似的源储不相临、但距离不远的近源型致密油气。成藏动力学上的差异使非常规油气藏在地质上表现为大面积分布、局部富集、油气赋存具有明显的“滞留”或短距运移特征、没有明显的圈闭边界和无统一的油水界面等特点。     

Effects of buoyancy and mechanical layering on collisional deformation of continental lithosphere: Results from physical modeling

We use two suites of lithospheric-scale physical experiments to investigate the manner in which deformation of the continental lithosphere is affected by both (1) variations of lithospheric density (quantified by the net buoyant mass per area in the lithospheric mantle layer, M_B), and (2) the degree of coupling between the crust and lithospheric mantle (characterized by a modified Ampferer ratio, Am). The dynamics of the experiments can be characterized with a Rayleigh–Taylor type ratio, _CLM. Models with a positively buoyant lithospheric mantle layer (M_B > 0 and _CLM > 0) result in distributed root formation and a wide deformation belt. In contrast, models with a negatively buoyant lithospheric mantle layer strongly coupled to the crust (M_B < 0, 0 > _CLM > ≈ − 0.2, and Am > ≈ 10^{− 3}) exhibit localized roots and narrow deformation belts. Syncollisional delamination of the model lithospheric mantle layer and a wide deformation belt is exhibited in models with negatively buoyant lithospheric mantle layers weakly coupled to the crust (M_B < 0, _CLM < 0, and Am < ≈ 10^{− 3}). Syncollisional delamination of the continental lithosphere may initiate due to buoyancy contrasts within the continental plate, instead of resulting from wedging by the opposing plate. Rayleigh–Taylor instabilities dominate the style of deformation in models with a negatively buoyant lithospheric mantle layer strongly coupled to the crust and a slow convergence rate (M_B < 0 and _CLM > ≈ − 0.2). The degree of coupling (Am) between the model crust and lithospheric mantle plays a lesser role in both the style of lower-lithospheric deformation and the width of the crustal deformed zone with increasing density of the lithospheric mantle layer.     

Richardson number profiles in laboratory experiments applied to shallow seas

Abstract

A unified analysis is given of the critical conditions for the onset of stratification due to either a vertical or a horizontal buoyancy flux, with tidal or wind stirring.

The critical conditions for the onset of stratification with a horizontal buoyancy flux are found to be of the form of ratios of the tidal slope, or wind setup, to the equivalent surface slope due to the lateral density gradient. These ratios, which are easily determined from sea data, indicate that the profiles of critical flux Richardson Number, averaged over the stirring cycle, are similar to those inferred from the laboratory experiments of Hopfinger and Linden (1982) in which there is zero mean shear turbulence with a stabilising buoyancy flux, and also that the efficiency for the conversion of kinetic energy to potential energy for tidal stirring is similar to that for wind stirring.

The observed much greater efficiency for wind stirring, compared with tidal stirring with a vertical buoyancy flux, is also consistent with the existence of flux Richardson Number profiles in the sea similar to those occurring in the corresponding laboratory experiments. Using the solution of the turbulent kinetic energy equation for the water column, the relative importance of the production of turbulent kinetic energy, and its diffusion by turbulence are assessed, and the critical conditions for the onset of stratification with a vertical buoyancy flux are shown to reduce the classical Simpson—Hunter form.     

Ascent of migmatites of a high-temperature metamorphic complex due to buoyancy beneath a volcanic arc: a mid-Cretaceous example from the eastern margin of Eurasia

ABSTRACT

Mixtures of melt and residue in a high-T metamorphic complex have a lower density and viscosity than the surrounding host crust, and the mixtures should ascend due to buoyancy. The mixtures are recognized as migmatites in the high-T metamorphic complex. To confirm ascent of migmatites, we conducted numerical simulations of ascent of a model migmatite (buoyant viscous fluid). The numerical simulations show that the model migmatite could rise to shallow levels of a model crust so long as it is continuously produced at the bottom of the model crust. Otherwise it ceases to rise at depth due to loss of buoyancy by cooling. The numerical simulations also show that the model migmatite experiences vertical thinning during the ascent. The ascent mechanism proposed in this paper requires the continuous production of partially melted rocks at the base of the crust, which is provided by a continuous input of energy into the crust from the mantle. Given that high-T metamorphic complexes are associated with igneous activity beneath a volcanic arc, the igneous activity reflects the energy input into the lower crust from the mantle. A high-grade part (migmatites) of a high-T metamorphic complex in the Omuta district of northern Kyushu, southwest Japan, experienced thinning during ascent. Large amount of igneous rocks, such as plutonic and volcanic rocks, are also distributed in northern Kyushu. Zircon U–Pb ages of igneous rocks from northern Kyushu reveal that igneous activity continued from 115 to 93 Ma, and that peak igneous activity at 110–100 Ma was synchronous with the ascent of migmatites of the high-T metamorphic complex in northern Kyushu. Therefore, the numerical simulations may provide an appropriate model of the ascent of migmatites of the high-T metamorphic complex beneath a volcanic arc, at the eastern margin of Eurasia in the mid-Cretaceous.     

流体孔隙剪切变形与岩石圈层状运动机理

在岩石圈层状滑移系统中,如大陆地壳俯冲叠置构造、逆冲推覆断层、拆离断层、滑坡等系统,近于水平的断裂带上存在许多有一定压力的流体孔隙。如果这些流体孔隙是密闭的,便可看成液压千斤顶的液缸。那么,断层面以上滑移体的重量S_T不仅被断裂带上的固体支撑,也受孔隙液体举托力F_f支撑。设F_f与S_T之比为R,那么R就是一个描述滑移体滑移运动难易程度的重要参数。R值越大,滑移体越容易被移动（推动）。而岩石圈中层状滑移系统滑脱面的剪切变形可以显著地改变该参数的大小,从而对层状滑移运动产生深刻的影响。设剪切面上孔隙流体平均压强初始值为P₀,剪切角为α,剪切变形后的平均压强为P（α）,R（α）-α间存在下式的函数关系:R（α）=（R₀P（α））/（P₀cosα）由此可见,R（α）与P（α）正相关,与剪切角α也正相关。P（α）与剪切角α的函数关系目前还难以给出,但剪切过程中,流体孔隙压强保持不变的恒压过程是常见的,即P（α）=P₀。将该等式代入上式（1）,即可获得下式:R（α）=（R₀）/（cosα）,[P（α）=P₀,即恒压过程]由此作出恒压剪切过程的R（α）-α图解。从而发现,恒压剪切过程中,只要滑脱面上密闭流体孔隙存在初始压强,即R₀>0,那么,R（α）随α增长,当剪切角α达到一定程度,R（α）迅速超过1;R₀越大,实现R（α）>1所需的α值越小;反之,所需的α值越大。由此证明,密闭流体孔隙经过恒压剪切变形,导致R（α）>1的基本规律。非恒压过程总体规律不变。R（α）>1意味着层状滑移体完全被孔隙流体的浮托力支持。从而揭示岩石圈俯冲——推覆体及拆离机理和滑坡爆发的可能机制。