Accelerated continental-scale snowmelt and ecohydrological impacts in the four largest Siberian river basins in response to spring warming

River runoff from the four largest Siberian river basins (the Ob, Yenisei, Lena, and Kolyma) considerably contributes to freshwater flux into the Arctic Ocean from the Eurasian continent. However, the effects of variation in snow cover fraction on the ecohydrological variations in these basins are not well understood. In this study, we analysed the spatiotemporal variability of the maximum snow cover fraction (SCF_max) in the four Siberian river basins. We compared the SCF_max from 2000 to 2016 with data in terms of monthly temperature and precipitation, night-time surface temperatures, the terrestrial water storage anomaly (TWSA), the normalised difference vegetation index (NDVI), and river runoff. Our results exhibit a decreasing trend in the April SCF_max values since 2000, largely in response to warming air temperatures in April. We identified snowmelt water as the dominant control on the observed increase in the runoff contribution in May across all four Siberian river basins. In addition, we detected that the interannual river runoff was predominantly controlled by interannual variations in the TWSA. The NDVI in June was strongly controlled by the timing of the snowmelt along with the surface air temperature and TWSA in June. The rate of increase in the freshwater flux from the four Siberian rivers decreased from 2000 to 2016, exhibiting large interannual variations corresponding to interannual variations in the TWSA. However, we identified a clear increase trend in the freshwater flux of ~4 km³/year when analysing the long-term 39-year historical record (1978–2016). Our results suggest that continued global warming will accelerate the transition towards the earlier timing of snowmelt and spring freshwater flux into the Arctic Ocean. Our findings also highlight the effects of earlier snowmelt on ecohydrological changes in the Northern Hemisphere.     

New apatite fission track evidence from the northern Qiangtang terrane reveal two‐phase evolution of central Tibet

The growth of central Tibet remains elusory, albeit important in evaluating different topographic growth models accounting for the Tibetan Plateau development. Thermochronological records in the northern Qiangtang terrane (QT) provide valuable information for investigating the cooling and exhumation history in central Tibet. New apatite fission track data, assisted by inverse thermal modelling, reveal two stages of accelerated cooling. The Early Cretaceous cooling is related with refrigeration of the QT and exhumation probably induced by crustal shortening. The Eocene‐Oligocene renewed cooling reflects the far‐field contraction after the onset of the India‐Asia collision and Cenozoic crustal shortening deformation in the QT, coupled with thermal relaxation and transient lithospheric removal. Our data support models indicating that Cretaceous crustal shortening produced a thickened crust in the QT, whereas the present‐day elevation was established during Eocene‐Oligocene due to crustal shortening, continental subduction and lithospheric delamination.     

Impact Analysis for Safety Prevention and Control of Special-Shaped Shield Construction Closely Crossing Multiple Operational Metro Tunnels in Shallow Overburden

Geotechnical and Geological Engineering - With the improvement of the urban rail transit network, crossing construction has become an inevitable situation in the construction of subway tunnels. The...     

贵州红粘土的孔隙特征及区域性分布规律

本文通过红粘土电镜资料研究贵州红粘土微观结构,印证了其微结构是复杂的二重空间结构,并运用SPSS数据分析软件,对贵州七个地区1858组土工实验数据进行统计分析,研究红粘土的孔隙性指标在水平方向上的分布规律及深度方向上的变化规律,得出贵州红粘土孔隙性指标在水平横向的总趋势为由西向东逐渐减小;水平纵向孔隙指标北部由北向南孔隙指标呈现减小趋势,南部由北向南孔隙指标亦呈现减小趋势;而在剖面深度方向孔隙性指标由上至下呈增大的趋势。     

双碳背景下地下工程永临结构一体化技术实践

永临结构一体化就是在设计施工过程中,将临时降止水结构和临时支护结构同永久结构结合起来一体化设计和一体化施工,以最大程度地发挥临时结构的作用,或者最大程度地减少临时结构的浪费。作者首次提出了地下工程永临结构一体化的建造理念,并结合作者近年来所做的科研工作,系统梳理了国内在永临结构一体化方面所做的科学尝试和技术实践,提出在双碳背景下应该大力倡导地下工程永临结构一体化,以减少材料浪费,降低对周边环境的影响,加快施工速度。     

莺歌海盆地东斜坡超高压气田天然气地球化学特征差异与成因

近年来,在南海北部莺歌海盆地东斜坡南部勘探取得重大进展,发现了超高压高温L气田。但针对该气田内部天然气地球化学特征差异及其成因等问题研究较少,制约了本区勘探的进展。文章基于天然气地球化学数据,结合区域石油地质条件、烃源岩特征及包裹体分析等资料初步揭示天然气的类型和气藏差异成因。从天然气地球化学特征上看,L气田中L1、L2和L3气藏天然气地球化学特征在天然气干燥系数及重烃碳同位素值组成等方面差异较大。尽管天然气均为煤型气,但可依据甲烷、乙烷及丙烷碳同位素值及δ13C1-δ13C2等参数细分为M型和S型,M型主要与梅山组烃源岩有关,S型主要来自三亚组;从不同类型天然气的分布看,从近凹中的L1气藏至近隆的L3气藏,天然气类型由既有M型也有S型转变为以S型为主,这一差异与烃源岩生烃过程、气藏的空间位置及垂向充注过程密切相关;从气藏形成过程看,凹陷斜坡南部梅山组和三亚组烃源岩在全新世进入高过成熟阶段;近凹一侧梅山组和三亚组烃源岩生成的天然气沿断裂进入黄流组成藏,形成L1气藏,近隆一侧三亚组天然气进入梅山组二段成藏形成L3气藏。     

福建余朋—南口火把山萤石矿地质特征及成因

笔者总结了福建余朋—南口地区火把山萤石矿床的地质特征, 并通过萤石的微量元素及稀土元素地球化学特征, 探讨了矿床的成因及成矿物质、流体来源。萤石矿石的微量元素及稀土元素结果显示: 火把山萤石呈中等Eu负异常及弱Ce异常, 稀土元素配分模式具有轻稀土富集型及轻稀土弱亏损的平缓型等两种曲线型式。根据萤石矿石特征、微量元素、稀土元素等特征及Y/Ho-La/Ho图解, 可知萤石存在至少三期成矿地质作用。依据M?ller的Tb/La-Tb/Ca成因判别图解, 结合常口萤石矿床的萤石及围岩的稀土元素特征, 认为火把山萤石成矿流体一方面与常口大型萤石矿床受同一成矿流体场控制, 并在有利的部位富集成矿; 另一方面, 成矿热液流体流经下峰岩组发生了淋滤、萃取、交换作用, 形成了不同地球化学特征的另一成矿期次的萤石。综合分析认为, 火把山萤石矿床为受断裂控制的大气降水成因的中低温热液充填矿床。     

基于泊松方程的空间波数混合域二度体磁异常数值模拟

正演数值模拟是反演成像的基础。为了实现磁法勘探精细化反演成像与定量解释,本文利用把一个大问题分解为多个小问题的思路,提出一种基于泊松方程的高效、高精度空间波数混合域二度体磁异常数值模拟方法。该方法利用傅里叶变换把二度体磁位偏微分方程转换为一维常微分方程,并采用基于二次插值的一维有限单元法求解该方程,进而通过反傅里叶变换得到空间域磁异常。在模型算例中,分别设计截面为矩形的常磁化率和变磁化率二度体模型,针对本文算法的计算精度和计算效率进行了验证。模型算例结果表明：该算法计算精度高,相对误差绝对值均小于1%;计算速度快,网格节点剖分2 501×2 501的模型模拟时间为4.18 s;适用于任意复杂地形模型。