Zircon U-Pb Ages of Quaternary Loess-Paleosol Sequences from the Luochuan Section: Implication for Sediment Provenance

<正>Objective The sediment provenances of the thick Quaternary Loess-Paleosol sequences of the Chinese Loess Plateau can provide clues to the evolution of the paleoclimate and paleoenvironment in East Asia.Furthermore,based on the proposed sediment sources and transport routes,the evolution of the East Asian monsoon can be evaluated.     

Petrogenesis of I-type granites from Yuqikapa granite pluton of the western Kunlun orogen: Deformation-driven filter-pressing differentiation

<正>1 Introduction The western Kunlun orogen,located in the northwest Tibet Plateau,and is a conjunction between the Pan-Asian and the Tethys tectonic domains.From north to south,the Western Kunlun orogen includes four     

黔东南金矿与圈定的黔湘桂新元古代火山构造特征及地质意义

黔东南金矿地质勘查及找矿研究程度低,为之利用区域重磁资料,研究深部成矿环境,圈定区内可能存在一处大型的中心式喷发火山环形构造或隐伏岩浆岩体分布群。岩体异常北东向分布,覆盖面积广,组合形态复杂,分带特征明显,跨越黔湘桂三省区,主体异常在贵州,部分在湖南和广西,并受控于3条深大断裂,见中心环带、内环带、过渡环带、外环带,4带发育齐全,火山岩相配套出现,岩体异常分枝发育。研究发现天柱—锦屏—黎平及丹寨—三都与湘西会同—怀化等地区金矿,极有规律地分布于相应构造环带和地表背斜区及有利赋矿地层内,由内环向外环依次出现石英脉型、蚀变岩型、微细粒浸染型金矿。所圈定的潜火山构造或隐伏岩体群,将对黔湘桂交界地区地质特征及金矿成矿规律产生新的认识,具有重要的地质意义。     

SHRIMP Zircon U-Pb Ages of the Wajilitag Igneous Complex: Constraints on the Origin of A-type Granitoids in the Tarim Large Igneous Province, NW China

<正>Objective Large igneous provinces(LIPs)are sites of spatially contiguous,rapidly emplaced magmatic rocks,which represent the physical and chemical transfer of material from the mantle to the crust.Exposed within some continental LIPs are felsic and mafic plutonic and volcanic rocks.Although their volumes are minor compared to the flood basalts,the plutonic rocks of continental LIPs are     

突发水污染事故中污染物输移主导水动力识别——以深圳湾为例

河口地区感潮河段水动力过程复杂,为在突发水污染事故中合理制定精细化应急方案,基于环境流体水动力模型（EFDC）从水动力学角度对不同水文条件下深圳河口水域突发水污染事故的影响范围、时间及程度进行了数值模拟分析,提出了一种判断河口海湾地区主导水动力因素的分析方法。采用基于傅里叶变换的频谱分析法对事故中污染物输移扩散的主要影响因子进行了准确识别,并采用单因变量多因素方差分析法进行了印证。结果表明,潮流是感潮河段水动力过程的主要驱动因素,但在突发水污染事故中,深圳河各断面特征污染物浓度变化与陆地径流关系密切,径流是感潮河段内突发事故中特征污染物输移的主导动力因素。     

稳健总体最小二乘Helmert方差分量估计

对于总体最小二乘而言,经常需要处理不同精度或者不同类型的观测数据,根据先验方差来定权往往不准确,同时观测数据中可能含有粗差。针对这两个问题,提出稳健总体最小二乘Helmert方差分量估计,将稳健估计和Helmert方差分量估计同时应用于总体最小二乘中。最后通过两个实验的计算结果表明,该方法是可行的、有效的。     

Tracing environmental lead sources on the Ao mountain of China using lead isotopic composition and biomonitoring

Atmospheric lead(Pb) and other trace metals can transport over long distance and deposit on remote alpine ecosystems. In this work, the soil profiles, litter and dominant mosses along a large altitude were collected on Ao Mountain, Central China, to obtain the spatial distributions of Pb in these materials, decipher the possible factors controlling the distribution, and quantitatively distinguish the natural versus anthropogenic sources of Pb through the Pb isotopic tracing and biomonitoring. The results show that soil Pb concentrations(mg/kg) decreased significantly with depth, and they were markedly higher in the O(42.6± 2.7) and A(36.4 ± 2.2) horizons than in the litter(7.20 ± 1.9) and mosses(28.0 ± 3.9). The Pb enrichment in the surface soils(O and A horizons),litter and mosses existed in the relatively high altitudes, which was attributed to the influences from atmospheric wet deposition, plants, soil physicochemical properties and human activity. ThePb isotopic ratios identified the Pb sources as originating mainly from Chinese coal combustion,mining and smelting. Atmospheric Pb from southeastern, southwestern and northwestern regions could be deposited in the alpine ecosystem by long distance atmospheric transport. The anthropogenic Pb reached over 50% in the O and A horizons, and over 70% in the litter and mosses, which corresponded to the concentrations of 26.9, 17.7, 5.92 and 21.2 mg/kg, respectively. The results indicate that the mutual effects of climate and regional human activity could increase the Pb accumulation in remote alpine ecosystems.     

Formation and evolution of Emeishan basalt saprolite in vadose zones of Touzhai landslide source rockmass

In order to explain the formation process of slope hazards, and to identify the key factors leading to instability of a slope, Emeishan basalt saprolite in vadose zones of the Touzhai landslide in Zhaotong, Yunnan, was studied. The formation and evolution of Emeishan basalt saprolite was examined using, amongst other techniques, field investigations, thin section analysis, scanning electron microscopy (SEM) observations, chemical analysis, physical and water-physical property tests of rock masses. Field observations revealed that the majority of the weathered rock blocks were presented as a concentric layer structure in which an internal corestone was enveloped with several layers of external saprolized crust. Chemical and mineralogical analysis identified that iron was the most sensitive element and that the weathering progress usually started with the oxidation of Fe²⁺ to Fe³⁺ in rock blocks. Alkaline elements such as Si, Ca, Mg, Na and K were also dissolved and Fe and Al were concentrated in saprolized crusts. Results indicated that loss on ignition (LOI) also increased significantly. SEM results showed that the weathering intensity of the basalt blocks decreased gradually from the outside to the inside, and the mineral morphology significantly differed on both sides of the weathering front. The saprolized crusts presented cellular microstructure features due to the generation of micropore and clay minerals. Thin section analysis showed that plagioclase was relatively more stable than pyroxene and chlorite during weathering. With a centripetal propagation of the weathering front, saprolized crusts became thicker and corestones became smaller; fresh Emeishan basalt blocks gradually turned into saprolized blocks. Due to the loose structure and low strength of saprolite, the quality of the Emeishan basalt mass significantly deteriorated, this being a potentially important factor which caused the Touzhai landslide to occur.     

Dating for Jifanggou metamorphic complex in central Jilin and its tectonic implications

Based on the results of four regional geological surveys of 1: 50000 including Shulan County map in Jilin,taking Shulan area as the study area,the authors re-delineated the rock type assemblages,e.g. metamorphic rhyolite,metamorphic tuffaceous breccia lava,sericite-quartz schist and tremolite altered rock,etc.,and the structural contacts between them. With the help of in-situ LA-ICP-MS U-Pb dating for zircons,it is concluded that the zircon crystallization ages of the metamorphic rhyolite,the metamorphic andesitic tuff breccia lava and the tremolite altered rock are 339. 1 ± 1. 3 Ma( n = 27,MSWD = 0. 78),351. 8 ± 1. 7 Ma( n = 21,MSWD = 0.82),and 362.0±1.8 Ma( n = 43,MSWD = 2.2) respectively. The metamorphic complex is actually a set of tectonic melange which comprises the rocks in different types,sources,times,or tectonic settings,and was formed by tectonism.     

Effects of Density and Viscosity in Modeling Heat as a Groundwater Tracer

Decoupled simulation of groundwater flow and heat transport assuming constant fluid density and viscosity is computationally efficient and simple. However, by neglecting the effects of variable density and viscosity, numerical solution of heat transport may be inaccurate. This study investigates the conditions under which the density and viscosity effects on heat transport modeling can be neglected without any significant loss of computational accuracy. A cross-section model of aquifer-river interactions at the Hanford 300 Area in Washington State was employed as the reference frame to quantify the role of fluid density and viscosity in heat transport modeling. This was achieved by comparing the differences in simulated temperature distributions with and without considering variable density and viscosity, respectively. The differences between the two sets of simulations were found to be minor under the complex field conditions at the Hanford 300A site. Based on the same model setup but under different prescribed temperature gradients across the simulation domain, a series of heat transport scenarios were further examined. When the maximum temperature difference across the simulation domain is within 15°C, the mean discrepancy between the simulated temperature distributions with and without considering the effects of variable density and viscosity is approximately 2.5% with a correlation coefficient of above 0.8. Meanwhile, the speedup in runtime is roughly 225% when the maximum temperature difference is at 15°C. This work provides some quantitative guidelines for when heat transport may be simulated by assuming constant density and viscosity as a reasonable compromise between accuracy and efficiency.