Multi‐temporal scale changes of streamflow and sediment load in a loess hilly watershed of China

Global climate change and diverse human activities have resulted in distinct temporal–spatial variability of watershed hydrological regimes, especially in water‐limited areas. This study presented a comprehensive investigation of streamflow and sediment load changes on multi‐temporal scales (annual, flood season, monthly and daily scales) during 1952–2011 in the Yanhe watershed, Loess Plateau. The results indicated that the decreasing trend of precipitation and increasing trend of potential evapotranspiration and aridity index were not significant. Significant decreasing trends (p < 0.01) were detected for both the annual and flood season streamflow, sediment load, sediment concentration and sediment coefficient. The runoff coefficient exhibited a significantly negative trend (p < 0.01) on the flood season scale, whereas the decreasing trend on the annual scale was not significant. The streamflow and sediment load during July–August contributed 46.7% and 86.2% to the annual total, respectively. The maximum daily streamflow and sediment load had the median occurrence date of July 31, and they accounted for 9.7% and 29.2% of the annual total, respectively. All of these monthly and daily hydrological characteristics exhibited remarkable decreasing trends (p < 0.01). However, the contribution of the maximum daily streamflow to the annual total progressively decreased (?0.07% year^?1), while that of maximum daily sediment load increased over the last 60 years (0.08% year^?1). The transfer of sloping cropland for afforestation and construction of check‐dams represented the dominant causes of streamflow and sediment load reductions, which also made the sediment grain finer. Copyright © 2015 John Wiley & Sons, Ltd.     

Lake sedimentary processes and vegetation changes over the last 45k cal a bp in the uplands of south-eastern Amazonia

This study addresses paleoclimate influences in a southern Amazonia ecotone based on multiproxy records from lakes of the Carajás region during the last 45k cal a bp. Wet and cool environmental conditions marked the initial deposition in shallow depressions with detrital sediments and high weathering rates until 40k cal a bp. Concomitantly, forest and C3 canga plants, along with cool-adapted taxa, developed; however, short drier episodes enabled expansion of C4 plants and diagenetic formation of siderite. A massive event of siderite formation occurred approximately 30k cal a bp under strong drier conditions. Afterwards, wet and cool environmental conditions returned and persisted until the Last Glacial Maximum (LGM). The LGM was marked by lake-level lowstands and subaerial exposure. The transition from the LGM to the Holocene is marked by the onset of oscillations in temperature and humidity, with an expansion of forest and canga plants. Cool taxa were present for the last time in the Carajás region ~ 9.5–9k cal a bp. After 10k cal a bp , shallow lakes became upland swamps due to natural infilling processes, but the current vegetation types and structures of the plateaus were acquired only after 3k cal a bp under wetter climatic conditions.     

内蒙古敖汉旗七家金矿闪长玢岩锆石U-Pb年代学、地球化学及地质意义

内蒙古敖汉旗七家金矿构造位置上处于兴蒙造山带与华北克拉通北缘的结合部位, 靠近兴蒙造山带一侧, 是近年来新发现的石英脉型金矿床.区内岩脉以闪长玢岩为主, 且与石英脉型矿体空间关系密切.根据岩脉与矿体的穿插关系, 将其分为成矿前闪长玢岩和成矿后闪长玢岩.LA-ICP-MS锆石U-Pb年代学表明, 成矿前闪长玢岩加权平均年龄为166.3±3.4 Ma, 成矿后闪长玢岩加权平均年龄为128.6±4.5 Ma, 与区域上两期构造-岩浆活动时间(分别为160 Ma左右和128 Ma左右)近似吻合.主量元素特征显示: 二者均属于准铝质, 高钾钙碱性系列; 微量元素特征显示: 二者均富集轻稀土元素、大离子亲石元素(Rb、K)和活泼的不相容元素(U、Pb), 相对亏损重稀土元素和高场强元素(Nb、Ta、Ti), 反映出岩浆来源具壳源特征.主微量元素特征均显示出二者具有岛弧岩浆岩的地球化学属性.另外, 成矿后闪长玢岩有较高的Nb/Ta(18.66~20.27)和Zr/Hf(37.16~39.23)比值, 暗示其岩浆来源具明显的幔源特征.岩石地球化学特征表明, 成矿前闪长玢岩可能起源于太平洋板块俯冲导致的下地壳部分熔融岩浆; 成矿后闪长玢岩可能起源于俯冲流体交代的地幔楔熔融岩浆, 并在其演化侵位过程中伴有地壳物质的混染.结合闪长玢岩成岩时代、岩石成因及区域构造演化, 反映出七家金矿的形成与太平洋板块的西向俯冲密切相关, 矿床在地壳由挤压增厚向伸展减薄的转换过程中形成.     

新元古代扬子—华夏陆块拼合带：来自华南重磁异常的启示

扬子和华夏两大陆块是构成华南大陆的最基本单元, 但它们的拼合带位置（尤其是西延位置）是人们长期争论的焦点。本文以国家专项“深部探测技术与实验研究”探测得到的深反射地震剖面以及华南大陆的地质资料为约束, 对重、 磁异常作地壳构造融合解译, 追踪扬子—华夏陆块拼合带。由于华南大陆广泛发育具有剩磁多期、 多类的火山—侵入岩, 本文将磁异常换算为受剩磁影响小的解析信号作构造解译, 减小剩磁造成的地质解释偏差。研究认为, 扬子与华夏两陆块的拼合带东界为鹰潭—萍乡—衡阳—贺州—北海一线, 而西界为宜昌—张家界—铜仁—都匀—百色一线, 鹰潭以东和以北的拼合带位置因为受大规模岩浆岩的干扰而不清。     

西藏拿若铜(金)矿床隐爆角砾岩流体包裹体研究

隐爆角砾岩是西藏拿若矿床的重要组成部分,赋存厚大的铜矿体。笔者将隐爆角砾岩中流体分成两个主要期次,并对这两期流体开展包裹体研究。通过包裹体岩相学和显微测温认为:角砾中的石英(早期)包裹体形状均匀呈椭圆形,大小主要在2~5μm;胶结物中石英(晚期)包裹体形状可见椭圆状、长条状和近方形,大小主要在2~7μm。早期流体的包裹体可分为两个阶段,均一温度分别为早阶段280~368℃和晚阶段208~305℃,盐度分布为(4.65~12.73)%Na Cleq。晚期流体的包裹体同样可分为两个阶段,其均一温度分别为早阶段309~588℃和晚阶段232~335℃,盐度变化为(3.55~12.51)%Na Cleq,两个阶段的流体分别属于高温、中低盐度和中高温、中低盐度流体。L-V型包裹体激光拉曼分析显示:包裹体中气泡成分主要为气态H2O和少量CO2。拿若矿床至少经历两次隐爆作用,由晚期沸腾热液引起,并未成矿。成矿作用发生于隐爆角砾岩形成之后。     

Mesoscale numerical simulation study of warm fog dissipation by salt particles seeding

Based on the dynamic framework of WRF and Morrison 2-moment explicit cloud scheme, a salt-seeding scheme was developed and used to simulate the dissipation of a warm fog event during 6–7 November 2009 in the Beijing and Tianjin area. The seeding effect and its physical mechanism were studied. The results indicate that when seeding fog with salt particles sized 80 μm and at a quantity of 6 gm~(-2) at the fog top, the seeding effect near the ground surface layer is negative in the beginning period, and then a positive seeding effect begins to appear at 18 min, with the best effect appearing at 21 min after seeding operation. The positive effect can last about 35 min. The microphysical mechanism of the warm fog dissipation is because of the evaporation due to the water vapor condensation on the salt particles and coalescence with salt particles.The process of fog water coalescence with salt particles contributed mostly to this warm fog dissipation. Furthermore, two series of sensitivity experiments were performed to study the seeding effect under different seeding amounts and salt particles sizes. The results show that seeding fog with salt particles sized of 80 μm can have the best seeding effect, and the seeding effect is negative when the salt particle size is less than 10 μm. For salt particles sized 80 μm, the best seeding effect, with corresponding visibility of 380 m, can be achieved when the seeding amount is 30 g m~(-2).