Tectonometamorphic evolution of an intracontinental orogeny inferred from P–T–t–d paths of the metapelites from the Rehamna massif (Morocco)

New petrographic and microstructural observations, mineral equilibria modelling and U/Pb (monazite) geochronological studies were carried out to investigate the relationships between deformation and metamorphism across the Rehamna massif (Moroccan Variscan belt). In this area, typical Barrovian (muscovite to staurolite) zones developed in Cambrian to Carboniferous metasedimentary rocks that are distributed around a dome‐like structure. First assemblages are characterized by the presence of locally preserved andalusite, followed by prograde evolution culminating at 6 kbar and 620 °C in the structurally deepest staurolite zone rocks. This Barrovian sequence was subsequently uplifted to supracrustal levels, heterogeneously reworked at greenschist facies conditions, which was followed locally by static growth of andalusite, indicating heating to 2.5–4 kbar and 530–570 °C. The ²⁰⁶Pb/²³⁸U monazite age of 298.3 ± 4.1 Ma is interpreted as minimum age of peak metamorphic conditions, whereas the ages of 275.8 ± 1.7 Ma and 277.0 ± 1.1 Ma date decompression and heating at low pressure, in agreement with previous dating of Permian granitoids intruding the Rehamna massif. The prograde metamorphism occurred during thickening and associated horizontal flow in the deeper crust (S1 horizontal schistosity). The horizontally disposed metamorphic zones were subsequently uplifted by a regional scale antiform during ongoing N–S compression. The re‐heating of the massif follows late massive E–W shortening, refolding and retrograde shearing of all previous fabrics coevally with regionally important intrusions of Permian granitoids. We argue that metamorphic evolution of the Rehamna massif occurred several hundred kilometres from the convergent plate boundaries in the interior of continental Gondwanan plate. The tectonometamorphic history of the Rehamna massif is put into Palaeozoic plate tectonic perspective and Late Carboniferous reactivation of (Devonian)–Early Carboniferous basins formed during stretching of the north Gondwana margin and formation of the Palaeotethys Ocean. The inherited heat budget of these magma‐rich basins plays a role in the preferential location of this intracontinental orogen. It is shown that rapid transition from lithospheric stretching to compression is characterized by specific HT type of Barrovian metamorphism, which markedly differs from similar Barrovian sequences along Palaeozoic plate boundaries reported from Variscan Europe.     

用于图像重建的波前法射线追踪

本文给出一种基于Huygens-Fresnel原理的射线追踪方法--波前法.该方法精度高、计算速度快,不仅可给出波从源点传播到接收点的透射走时和射线路径,而且可给出任何时刻的波阵面,为层析成像提供了一种有效的射线追踪方法.     

考虑溢流条件下的核电厂址风暴潮模拟与研究

基于ADCIRC建立了三门湾风暴潮模型,模型模拟结果与实测数据吻合较好。以可能最大热带气旋参数为基础构建了多种假想台风路径来计算三门核电厂址处的可能最大风暴潮增水。结果表明,NW向登陆且距离核电厂址左侧为R(最大风速半径)时的假想台风使得三门核电厂址处的增水达到最大,风暴潮增水最大值为4.58 m。将可能最大风暴潮增水叠加天文高潮位进行计算,厂址前沿处水位达到了7.75 m,而三门湾顶附近的最高水位已经达到9 m,超出了三门湾沿岸海堤高程。将三门湾沿岸陆地依照高程概化为计算区域进行漫堤计算,当天文高潮位叠加可能最大风暴潮水位时,三门湾沿岸会发生漫堤溢流现象,淹没范围最严重的区域出现在湾顶处,最大淹没面积达到了120 km2。此时厂址前沿最高潮位为7.25 m,与不溢流相比下降了0.50 m。本研究可为三门核电厂址的安全防护提供科学依据。     

Garnet growth during crustal thickening in the Cascades Crystalline Core,Washington, USA

Garnet Sm–Nd and zircon U–Pb ages, and pressure–temperature–time paths elucidate Late Cretaceous crustal thickening which occurred within magmatic arc rocks of the Insular Superterrane. Voluminous tonalitic magma of the Mount Stuart batholith intruded at <3 kbar into upper crustal sedimentary rocks between 96 and 91 Ma, with initial intrusion prior to garnet growth in the metasedimentary rocks. Arc plutonism then shifted northward as crustal thickening commenced. Initial garnet growth, locally with kyanite and staurolite replacing andalusite, at c. 91 Ma was directly associated with intrusion of granodiorite to tonalite sheets at 7 kbar, north of the Mount Stuart batholith, within the Nason Ridge Migmatitic Gneiss. Subsequent heating and garnet growth, which postdates emplacement of large plutons, occurred between 88 and 86 Ma. This late garnet growth occurred at pressures of 6–8 kbar. The history of garnet growth and intrusion indicates that initial garnet zone and higher temperature metamorphism was restricted to contact aureoles. However, later widespread garnet growth at higher pressure probably resulted from heating as the orogenic wedge approached thermal equilibrium after crustal thickening. We conclude that metasedimentary rocks outside narrow contact aureoles remained at temperatures significantly below those of garnet growth and that the growth of garnet lasted <6 Myr. Heating to temperatures that stabilized garnet after pluton emplacement is compatible with intrusion of arc plutons into an accretionary wedge (Chiwaukum Schist) which was tectonically thickened and/or overthrust causing loading and thermal relaxation.     

The characteristics of sea fog with different airflow over the Huanghai Sea in boreal spring

Using the observations from ICOADS datasets and contemporaneous NCEP/NCAR reanalysis datasets during 1960-2002, the study classifies the airflows in favor of sea fog over the Huanghai (Yellow) Sea in boreal spring (April-May) with the method of trajectory analysis, and analyzes the changes of proportions of warm and cold sea fogs along different paths of airflow. According to the heat balance equation, we investigate the relationships between the marine meteorological conditions and the proportion of warm and cold sea fog along different airflow paths. The major results are summarized as follows. (1) Sea fogs over the Huanghai Sea in spring are not only warm fog but also cold fog. The proportion of warm fog only accounts for 44% in April, while increases as high as 57% in May. (2) Four primary airflow paths leading to spring sea fog are identified. They are originated from the northwest, east, southeast and southwest of the Huanghai Sea, respectively. The occurrence ratios of the warm sea fog along the east and southeast airflow paths are high of 55% and 70%, while these along the southwest and northwest airflow paths are merely 17.9% and 50%. (3) The key physical processes governing the warm/cold sea fog are heat advection transport, longwave radiation cooling at fog top, solar shortwave warming and latent heat flux between airsea interfaces. (4) The characteristics of sea fog along the four airflow paths relate closely to the conditions of water vapor advection, and the vertical distribution of relative humidity.     

基于卫星高度计资料的黑潮入侵南海流径的时间变化规律研究

黑潮入侵南海对南海的温盐平衡、环流、涡旋和局地气候等具有重要作用。基于吕宋海峡处黑潮不同流径的识别方法,对1993～2021年的卫星高度计资料进行识别,获取黑潮不同流径的发生时间,探究黑潮入侵南海流径的时间变化规律。结果表明:(1)黑潮主要以流套(Looping)和分支(Leaking)两种流径入侵南海,Leaking流径发生的时长(710周)和概率(46.9%)要远高于Looping流径(时长218周,概率14.4%)。(2) Looping流径和Leaking流径均可将高温高盐的西北太平洋水带入南海,Looping流径下的平均吕宋海峡上层通量(6.3×10⁶ m³/s)略大于Leaking流径(5.6×10⁶ m³/s)Looping和Leaking流径在4×10⁶ m³/s～6×10⁶ m³/s区间发生时间最长。(3)季节变化上,Looping流径主要发生在冬季,Leaking流径在冬半年均较强,夏季二者发...     

福建热带气旋风雨空间分布特征及风险评估

根据1961—2010年热带气旋资料,按登陆地段或移动路径将登陆影响福建的热带气旋分为11种路径,分析各种路径的致灾因子空间分布特征,结果表明:热带气旋雨灾最严重的区域位于北部和中部沿海,风灾最严重的是南部沿海;从路径来看,降水强度最强是登台入闽北路径,强风区域最大的是直接登陆闽南路径和登台入闽中部路径,风力最强的是登台入闽南路径。采用相关系数客观赋权法建立了致灾因子风险评估模型,分析不同热带气旋路径致灾因子风险等级,登台入闽中和登台入闽北路径风险最大,其次是直接登陆闽南和登陆珠江口及以东路径;高风险区域 (包括次高危险和高危险区) 集中在沿海地区、闽西和闽北的局部。     

干湿路径影响粉土小应变剪切模量的试验研究

天然土尤其是地表浅层土常处于非饱和状态,其小应变剪切模量是预测地基变形及土工结构物动力反应的一个重要参数。通过对非饱和压实粉土三轴样进行弯曲元试验,研究了吸力和干湿路径对其小应变剪切模量的影响。试验结果表明,非饱和压实粉土样的小应变剪切模量各向异性忽略不计;小应变剪切模量G0(vh)、G0(hh)和G0(hv)均随吸力增大而非线性增大;同一吸力下不同干湿路径上的土样,饱和度不同,其小应变剪切模量随饱和度升高而减小,主要原因是土的平均骨架应力和土中毛细水的作用。根据试验结果对非饱和土小应变剪切模量的半经验公式进行了改进,同时考虑了吸力与饱和度的作用。     

甘肃某生活垃圾填埋场地下水污染特征及污染途径分析

依据实际调查数据,采用单因子污染指数分析法确定了生活垃圾填埋场地下水中主要污染物、污染程度和污染范围,并进行了土壤和地下水污染耦合性分析,研究结果表明：该生活垃圾填埋场地下水污染物主要为氨氮、总氮、高锰酸盐、锰、挥发酚和氟化物,其污染指数最大值分别为1 407.24、745.00、137.12、97.50、3.60和1.68,污染区总面积0.168 km²;填埋场下游沟谷纵向上,总氮、锰两项指标在土壤中的含量与地下水中浓度变化趋势一致;其污染途径主要为库区防渗层破损,渗滤液垂向沿基岩风化裂隙进入地下含水层,以连续渗漏的方式不断污染地下水,污染物在地下水径流作用下向拦挡坝下游不断迁移。