一种非板块深俯冲快折返的柯石英形成新机制——评析“石英—柯石英相变研究中若干问题讨论”一文

本文分析评论了嵇少丞等(2010)发表的"石英—柯石英相变研究中若干问题讨论"一文。指出他们对柯石英非俯冲折返新机制的一些误解,对某些热力学、物理学概念,及其在地学问题中的解释理解的不同。分析了机械球磨的作用机制;论证了机械球磨作用本质与构造挤压剪切作用本质的同一性。分析了岩石糜棱岩化过程的两个阶段;讨论了地震波形成柯石英机制的可能性。围绕比较标准问题,论证了高能机械球磨(预处理)能大大降低α-石英转变成柯石英的压力、温度和合成时间,促进柯石英的形成。用小尺度不均匀局域高压微区模型解释了人工合成柯石英的规律性、南极洲天然矿物的行为,柯石英的寄生矿物、岩石——锆石、榴辉岩包裹体、非包裹体的形成。列举事例澄清了"球磨引进的Fe杂质提高柯石英形成压力迟缓合成"的说法;讨论了第二相存在对石英—柯石英转变的影响和"应变禁区"边界区的应力梯度相变驱动力可以形成柯石英问题。指出了机械球磨石英原料预处理和静高压合成柯石英后处理两步法,是一种实验室研究柯石英形成规律的有效物理方法;小尺度不均匀局域高压微区模型和无需板块深俯冲快折返的柯石英形成机制,是一种有希望的柯石英形成新机制。     

Mesozoic and early Cenozoic tectonic convergence-to-rifting transition prior to opening of the South China Sea

We have investigated Mesozoic geological problems around the South China Sea (SCS) based on gravimetric, magnetic, seismic, and lithofacies data. Three-dimensional analytical signal amplitudes (ASA) of magnetic anomalies clearly define the inland tectonic boundaries and the residual Mesozoic basins offshore. The ASA suggest that the degree of magmatism and/or the average magnetic susceptibility of igneous rocks increase southeastwards and that late-stage A-type igneous rocks present along the coast of southeast China possess the highest effective susceptibility. The geophysical data define Mesozoic sedimentary and tectonic structures and reveal four major unconformities [Pz/T–J, T–J/J, J/K, and Mesozoic/Cenozoic (Pz, Palaeozic; T, Triassic; J, Jurassic; K, Cretaceous)], corresponding to regional tectonic events revealed by nine palaeogeographic time slices based on prior geological surveys and our new fieldwork. Showing both sedimentary and volcanic facies and regional faults, our palaeogeographic maps confirm an early Mesozoic northwestward-migrating orogeny that gradually obliterated the Tethyan regime, and a middle-to-late Mesozoic southeastward migration and younging in synchronized extension, faulting, and magmatism. Three major phases of marine deposition developed but were subsequently terminated by tectonic compression, uplift, erosion, faulting, rifting, and/or magmatism. The tectonic transition from the Tethyan to Pacific regimes was completed by the end of the Middle Triassic (ca. 220 Ma), reflecting widespread Mesozoic orogeny. The transition from an active to a passive continental margin occurred at the end of the Early Cretaceous (ca. 100 Ma); this was accompanied by significant changes in sedimentary environments, due likely to an eastward retreat of the palaeo-Pacific subduction zone and/or to the collision of the West Philippine block with Eurasia. The overall Mesozoic evolution of southeast China comprised almost an entire cycle of orogenic build-up, peneplanation, and later extension, all under the influence of the subducting palaeo-Pacific plate. Continental margin extension and rifting continued into the early Cenozoic, eventually triggering the Oligocene opening of the SCS.     

A Comparison of Precipitation Distribution of Two Landfalling Tropical Cyclones during the Extratropical Transition

The precipitation distributions associated with two landfalling tropical cyclones(TCs) during extratropical transition(ET) were examined in this study.Their distinction is that the bulk of precipitation fell to the left of the TC track in one TC and to the right in the other.The analyses indicate that,for the TC Haima(2004) case,accompanied by the approach of a deep midlatitude trough throughout the depth of the troposphere,the warm and moist air advection by the southeasterly flow north of TC was favorable for warm advection and frontogenesis to the northwest of the TC.Due to the steepening of equivalent potential temperature(θ e),the air-parcel uplift along the θ e surface,in collaboration with thermally direct circulation related to frontogenesis,led to enhanced precipitation northwest of the TC.In contrast,for TC Matsa(2005) embedded within a moister environment,a weak midlatitude trough was situated at the mid-upper level.The convection was triggered by the conditional instability at the lower level and then sustained by dynamic forcing at the mid-upper level so that the heavy precipitation occurred to the northeast of TC.For the two TC cases,the precipitation enhancement was also linked to the upper-level anomalous divergence associated with the jet-related forcing on the right side of the jet entrance.From the quasigeostrophic perspective,the advection of geostrophic absolute vorticity by the thermal wind most likely served as an indication reflecting the displacement of the vertical motion relative to the center of the TC.     

中平流层环流转型日期气候及异常特征

利用NCEP/NCAR北半球1958—1997年40a中平流层（10～70 hPa）逐日位势高度场再分析资料,计算出其余弦球函数～YC20的系数A20。根据A20稳定由负转正的日期,确定了中平流层各层环流由气旋型转换为反气旋型的日期。结果表明：1）由冬入夏,20 hPa环流最先由气旋型转换为反气旋型,平均为4月24日;6月17日向下传播到70hPa,历时54d,此时整个中平流层进入盛夏。2）50、70hPa环流转型日期具有明显的年代际变化特征。分析表明,50、70hPa环流转型日期与低纬平流层纬向风准两年振荡存在显著正相关关系。     

Imaging the mantle transition zone beneath eastern and central China with CEArray receiver functions

We analyzed a total of 37 427 receiver-function data recorded by national and regional broadband seismic networks of the China Earthquake Administration to study the mantle transition zone beneath eastern and central China.Significant topography on both the 410-km and 660-km discontinuities was clearly imaged in the 3D volume of CCP (common-conversion-point) stacked images that cover an area of 102.5 E-122.5 E and 22.0 N-42.0 N.3D crustal and mantle velocity models were used in computing the Ps time moveout...     

Evolution of an advancing gravel front: observations from Vedder Canal,British Columbia

Channelization of the lowermost part of Vedder River in 1922 initiated a natural experiment relevant to the unresolved question of how abrupt gravel–sand transitions develop along rivers. The new channel (Vedder Canal) had a fine bed and a much lower slope than the gravel‐bed river immediately upstream. Changes in morphology and sedimentology as gravel advanced into and along the Canal are documented using air photos, historical surveys, and fieldwork. The channel aggraded and steepened until stabilized by occasional gravel extraction in recent decades. The deposited material fines progressively along the Canal but the gravel front has retained an abrupt appearance because it has advanced by the sequential development of discrete gravel tops on initially sandy alternate bars. Near the gravel front the bed is highly bimodal and there is a sharper drop in the extent of gravel‐framework surface facies than in bulk gravel content. Ahead of the front, gravel is restricted to thin ribbons which often become buried by migrating sand. Calculations show that even though the gravel bed at the head of the Canal is almost unimodal, size‐selective transport during floods can account for the strong bimodality farther downstream. Copyright © 2011 John Wiley & Sons, Ltd.     

构造-岩性油藏油水微观分布规律与主控因素探讨

在对油水接触面形态和油水过渡带厚度的分布规律进行定量分析的基础上,以苏北盆地花17断块为例,结合油井生产动态特征分析了构造-岩性油藏中油水分布规律,并探讨了其影响因素.结果表明,在实际油藏中油水接触面是一个呈波状起伏的面,其在自由水面以上的高度随残余油饱和度下的毛管压力增大而抬高;油水过渡带厚度仅与束缚水饱和度和残余油...     

Small-Scale Mineralogical Heterogeneity from Variations in Phase Assemblages in the Transition Zone and D Layer Predicted by Convection Modelling

Small-scale heterogeneity in the deep mantle is concentrated in the upper-mantle transi-tion zone(TZ),in the depth range 410-660 km and also at the bottom 250 km D region.This encour-ages a more detailed investigation of the potential for seismic reflectivity imaging by modelling hetero-geneous structures in mantle convection models including phase transitions of the TZ and D regions.We applied finite elements with variable spacing near the boundary layers in 2-D cylindrical geometry that allow for sufficie...     

A study of extratropical transition and re-intensification of Typhoon Mindulle (2004)

In this study,the fifth-generation Pennsylvania State University-National Center for Atmospheric Research (PSU-NCAR) Mesoscale Model (MM5) is used to simulate Typhoon Mindulle (2004) at high resolution (3-km grid size).The data from measurements show that in the upper atmosphere the existence of an upper jet is important to the transition cyclone.When Mindulle moved to the area of the upper jet entrance,where high-altitude divergence existed, the pumping of the high-altitude divergence would enhance the vertical motion and low-level cyclone convergence. The enhanced vertical motion was confirmed by the simulation results and indicated that the existence of upper divergence enhanced the vertical motion which was favorable for the maintenance of Typhoon Mindulle.The process of extratropical transition (ET) and re-intensification always accompanies the process of cold air invasion. This process enhances the baroclinicity of the atmosphere and the formation of front at high altitudes, which converts baroclinic potential energy into kinetic energy and strengthens the cyclone vortex.The distributions of equivalent potential temperature (θe) and temperature anomalies show that the warm-core of the typhoon at the tropopause aids the re-intensification of the system. As the typhoon reenters the ocean, latent heat flux (LHF) increases in the north and west and the strong reflectivity and vertical motion occur in the east and southeast,and the west.With the re-intensification of the typhoon the wind field evolves from an oval to a circle at the lower atmosphere, the area coverage by high winds increases, and the distribution of the tangential wind shows an asymmetric pattern.     

Finite element analysis on impact of foundation treatment in bridgehead transition section upon bridge piles

In order to decrease relative settlement, foundation treatment plays an extremely important role in bridgehead transition section, especially, the situation of building the bridge piles firstly, and th...