Predominance of parallel‐ and cross‐predation in anglerfish

Several studies in the last 20 years have revealed that morphological asymmetry in fish can be characterized as ‘antisymmetry’. Antisymmetry is a lateral dimorphism in which each population consists of individuals with well‐developed left sides (lefties) and well‐developed right sides (righties). This dimorphism influences predator–prey interactions. In some piscivorous fishes, it has been found that predators can catch more prey of the opposite morphological type to themselves (cross‐predation) than of the same morphological type (parallel‐predation). Our previous work clarified that the predominance of cross‐predation is caused by lateralized behaviors of predators and prey that correspond to their morphological antisymmetry. Moreover, based on the results of our behavioral observations, we hypothesized that parallel‐predation can predominate when predators encounter the potential prey frontally. To test this hypothesis, in the present study we investigated the relationship between lateral morphological types of anglerfish (Lophiomus setigerus) and those of the prey fishes found in their stomachs. Anglerfish attract potential prey using their first dorsal fin (illicium) as a lure, and their frontal encounters with potential prey fishes were photographed in situ and observed in an aquarium. The results of a stomach contents analysis indicated that parallel‐predation predominated in five benthopelagic prey fish species (perches and eels). By contrast, five benthic prey fishes (gobies and weevers) exhibited the predominance of cross‐predation. These results not only demonstrate the predominance of parallel‐predation in a natural fish community, but also suggest that the relationship between morphological types of predator and prey species can be reversed depending on the lifestyle of prey.     

黑潮延伸体上游中尺度涡场的年代际振荡及其相关机制

黑潮延伸体上游区域的中尺度涡场的涡动能和涡特征尺度存在显著地年代际振荡,和黑潮延伸体路径的年代际变化有很好的相关性。当黑潮延伸体路径比较稳定时,其上游区域涡动能比较高,涡特征尺度比较大,反之相反。通过对黑潮延伸体上游区域的中尺度涡场进行集合分析发现:当黑潮延伸体处于稳定状态时,上游涡场几乎是各向均匀地,有轻微的径向伸长;而当黑潮延伸体处于不稳定状态时,上游的中尺度涡场有显著地纬向伸长。对与中尺度涡场的产生相关的线性斜压不稳定和正压不稳定进行了计算分析,结果显示,线性斜压不稳定不是控制中尺度涡场年代际变化的机制,而正压不稳定对中尺度涡场的年代际变化有积极的贡献。不稳定产生的中尺度涡之间存在非线性涡-涡相互作用。     

西北太平洋浪流相互作用对有效波高的影响研究

西北太平洋强流区会对海浪的特征和分布产生显著的影响,尤其是研究台风过程中海流与海浪的相互作用具有重要的研究意义。本文以ROMS海洋模式和SWAN海浪模式为基础,构建了浪流耦合模式系统,对2013年10月6-17日间的台风“丹娜丝”、“百合”、“韦帕”过程中西北太平洋浪流相互作用中海流对有效波高的影响进行了研究。通过对比模式模拟有效波高与浮标观测资料,发现耦合后的有效波高比非耦合结果更接近观测值,耦合模式中海流的存在对有效波高的分布有明显的影响。研究表明,特别是在有效波高峰值处,海流引起的有效波高增大最大可达1 m。海浪浪向及流向的空间分布以及中国近海浮标处浪向与流向的时间序列表明,流向与浪向反向时,海流的影响造成有效波高增大;二者同向时,有效波高减小。海流对有效波高的调整会沿着海浪传播的方向传播相当一段距离。在西北太平洋的海浪场计算中,引入海流的耦合模式计算结果对改善强流区海浪预报具有重要意义,并且海流的模拟精度对于高精度的海浪预报非常重要。     

Hydrothermal Fluid Sources of the Fengjia Barite–fluorite Deposit in Southeast Sichuan,China: Evidence from Fluid Inclusions and Hydrogen and Oxygen Isotopes

The Fengjia barite–fluorite deposit in southeast Sichuan is a stratabound ore deposit which occurs mainly in Lower Ordovician carbonate rocks. Here we present results from fluid inclusion and oxygen and hydrogen isotope studies to determine the nature and origin of the hydrothermal fluids that generated the deposit. The temperature of the ore‐forming fluid shows a range of 86 to 302 °C. Our detailed microthermometric data show that the temperature during mineralization of the fluorite and barite in the early ore‐forming stage was higher than that during the formation of the calcite in the late ore‐forming stage. The salinity varied substantially from 0.18% to 21.19% NaCl eqv., whereas the density was around 1.00 g/cm³. The fluid composition was mainly H₂O (>91.33%), followed by CO₂, CH₄ and traces of C₂H₆, CO, Ar, and H₂S. The dominant cation was Na⁺ and the dominant anion Cl^‐, followed by Ca²⁺, SO₄^2‐, K⁺, and Mg²⁺, indicating a mid–low‐temperature, mid‐low‐salinity, low‐density NaCl–H₂O system. Our results demonstrate that the temperature decreased during the ore‐forming process and the fluid system changed from a closed reducing environment to an open oxidizing environment. The hydrogen and oxygen isotope data demonstrate that the hydrothermal fluids in the study area had multiple sources, primarily formation water, as well as meteoric water and metamorphic water. Combined with the geological setting and mineralization features we infer that the stratabound barite–fluorite deposits originated from mid–low‐temperature hydrothermal fluids and formed vein filling in the fault zone.     

板翼动力锚沉贯深度模型试验研究

板翼动力锚是依靠自重完成安装并靠自重和海床土的抗力来锚固的新型动力锚。板翼动力锚高速(15~25 m/s)贯入地基过程中涉及到高应变率、流固耦合、土体软化和大变形等难题,模型试验可避免上述计算困难,能直接得出不同的贯入速度所对应的沉贯深度。本文首先推导了模型相似关系,然后在常规重力条件下,进行了两组26个工况的板翼动力锚在均质黏土中动力安装过程的模型试验,根据试验结果确定了率效应参数的取值范围,并研究了每一项受力对沉贯深度的影响。最后提出了在均质黏土中预测板翼动力锚沉贯深度的经验公式。     

Geochemical Constraints on the Origin of Banded Iron Formation‐Hosted Iron Ore from the Archaean Ntem Complex (Congo Craton) in the Meyomessi Area,Southern Cameroon

Banded iron formations (BIFs) are the most significant source of iron in the world. In this study, we report petrographic and geochemical data of the BIF from the Meyomessi area in the Ntem Complex, southern Cameroon, and discuss their genesis and the iron enrichment process. Field investigations and petrography have revealed that the studied BIF samples are hard; compact; weakly weathered; and composed of magnetite, subordinate quartz, and geothite. The geochemical composition of the whole rock reveals that iron and silica represent more than 98 wt% of the average composition, whereas Al₂O₃, TiO₂, and high‐field strength elements (HFSE) contents are very low, similar to detritus‐free marine chemical precipitates. The total iron (TFe) contents range from 48.71 to 65.32 wt % (average of 53.29 wt %) and, together with the low concentrations of deleterious elements (0.19 wt % P on average), are consistent with medium‐grade iron ores by global standards. This interpretation is confirmed by the SiO₂/Fe₂O_3total versus (MgO + CaO + MnO)/Fe₂O_3total discrimination plot in which most of the Meyomessi BIF samples fall in the field of medium‐grade siliceous ore. Only one sample (MGT94) plots in the high‐grade magnetite–geothite ore domain. The high Fe/Ti (376.36), Fe/Al (99.90), and Si/Al (29.26) ratios of the sample are consistent with significant hydrothermal components. The rare earth elements (REE) contents of the studied BIF samples are very low (∑REE: 0.81–1.47 ppm), and the Post‐Archaean Australian Shale (PAAS)‐normalized patterns display weak positive Eu anomalies (Eu/Eu*: 1.15–1.33), suggesting a syngenetic low‐temperature hydrothermal solutions, similar to other BIF worldwide. However, the Meyomessi BIFs show high Fe contents when compared to the other BIFs. This indicates an epigenetic mineralization process affected the Meyomessi BIF. From the above results and based on the field and analytical data, we propose that the genetic model of iron ores at the Meyomessi area involves two stages of the enrichment process, hypogene enrichment of BIF protore by metamorphic and magmatic fluids followed by supergene alteration as indicated by the presence of goethite in the rocks.     

Calibration of cyclic constitutive models by oscillating functions

Most structures are subjected to more cyclic loads during their life time than static loads. These cyclic action could be a result of either natural or man-made activities and may lead to soil failure. In order to understand the response of the foundation and its interaction with these complex cyclic loadings, various researchers have over the years developed different constitutive models. Although a lot of research is being carried out on these relatively new models, little or no details exist in literature about the model-based identification of the cyclic constitutive parameters which to a large extent govern the quality of the model output. This could be attributed to the difficulties and complexities of the inverse modeling of such complex phenomena. A variety of optimisation strategies are available for the solution of the sum of least-squares problems as usually done in the field of model calibration. However, for the back analysis (calibration) of the soil response to oscillatory load functions, this article gives insight into the model calibration challenges and also puts forward a method for the inverse modeling of cyclic loaded foundation response such that high-quality solutions are obtained with minimum computational effort.     

Origin of natural sulfur-metal chimney in the Tangyin hydrothermal field,Okinawa Trough: constraints from rare earth element and sulfur isotopic compositions

For the first time, we present the rare earth element (REE) and sulfur isotopic composition of hydrothermal precipitates recovered from the Tangyin hydrothermal field (THF), Okinawa Trough at a water depth of 1206 m. The natural sulfur samples exhibit the lowest ΣREE concentrations (ΣREE= 0.65×10^–6–4.580×10^–6) followed by metal sulfides (ΣREE=1.71×10^–6–11.63×10^–6). By contrast, the natural sulfur-sediment samples have maximum ΣREE concentrations (ΣREE=11.54×10^–6–33.06×10^–6), significantly lower than those of the volcanic and sediment samples. Nevertheless, the δEu, δCe, (La/Yb)_N, La/Sm, (Gd/Yb)_N and normalized patterns of the natural sulfur and metal sulfide show the most similarity to the sediment. Most hydrothermal precipitate samples are characterized by enrichments of LREE (LREE/HREE=10.09–24.53) and slightly negative Eu anomalies or no anomaly (δEu=0.48–0.99), which are different from the hydrothermal fluid from sediment-free mid-oceanic ridges and back-arc basins, but identical to the sulfides from the Jade hydrothermal field. The lower temperature and more oxidizing conditions produced by the mixing between seawater and hydrothermal fluids further attenuate the leaching ability of hydrothermal fluid, inducing lower REE concentrations for natural sulfur compared with metal sulfide; meanwhile, the negative Eu anomaly is also weakened or almost absent. The sulfur isotopic compositions of the natural sulfur (δ³⁴S=3.20‰–5.01‰, mean 4.23‰) and metal sulfide samples (δ³⁴S=0.82‰–0.89‰, mean 0.85‰) reveal that the sulfur of the chimney is sourced from magmatic degassing.     

辽宁赛马碱性岩体异性石化学成分特征及其蚀变组合对碱性岩浆-热液演化的指示意义

辽宁赛马碱性岩体早年因产铀矿而闻名,该岩体主要由响岩、霞石正长岩和异霞正长岩组成,其中铀、锆和稀土等元素矿化主要集中于异霞正长岩岩浆阶段。异性石是异霞正长岩中特征的锆-稀土矿物,主要分为两期,晚期异性石表现出更加富集Nb、REE等高场强元素的特点。早期异性石经历了一系列的热液蚀变,根据蚀变强弱程度,蚀变矿物组合可分为:(1)异性石+钠锆石+霓石±钠沸石;(2)异性石+钠锆石+锆石+钠沸石±霓石;(3)异性石假晶,假晶主要由残余异性石+钠锆石+锆石+钠沸石+霓石+钾长石+铈硅磷灰石组成。相比于岩浆锆石,蚀变组合中次生锆石具有富Ca、Al、Fe的特点,与异性石本身化学成分和流体性质密切相关。通过对异性石及其蚀变组合的精细矿物学研究,我们得知假晶的形成可能是异性石"溶解-再沉淀"的结果,致使假晶形成的流体至少包括:(1)占主导的富Na(±K)、Al、F的自交代流体;(2)少量晚期富Ca流体。假晶中次生锆石和铈硅磷灰石的结晶说明了Zr和REE等高场强元素的热液活动性,自交代碱性流体和富Ca流体在此过程中起到"搬运"和"提纯"的作用,这对认识碱性岩稀有、稀土成矿机制具有重要的指示意义。     

Hydrothermal Dolomite: A Review and PerspectiveEI北大核心CSCD

Hydrothermal dolomite commonly closely associates with oil-gas reservoirs and sediment-hosted Pb-Zn deposits, the Mississippi Valley-type (MVT) Pb-Zn deposits in particular. Host rocks of MVT deposits usually experienced extensive dolomitization, and indeed, hydrothermal dolomite is considered as a useful prospective indicator for MVT mineralization. However, genetic link between the hydrothermal dolomitization and MVT Pb-Zn mineralization is a matter of debate. This paper briefly reviewed the nomenclature and research history of hydrothermal dolomite, introduced the major geological, geochemical characteristics, and distribution of hydrothermal dolomite, spatial and possibly genetic relationship between hdyrothermal dolomite and hdyrothermal ore deposits and oil-gas reservoirs based on case studies including the occurrence of hydrothermal dolomites in MVT deposits in Southwest China. The temporal and genetic relationships between dolomitizaiton and thermal sulfate reduction, sulfide precipitation and thus the location of ore mineralization well worthy more attention, and comprehensive geological and isotope geochemical and state of art in situ techniques will contribute to understanding of the genesis of hydrotherml dolomite and the spatially related ore deposits and oil-gas reservoirs. © 2018, Science Press. All right reserved.