动态古地貌再造: Badlands软件在盆地分析中的应用*

近几年来的研究发现,当存在较强的构造活动时,古地理特征变化将会加快,而常规方法很难对这一构造活动过程中的古地理和古地貌进行有效的恢复和研究。Basin and Landscape Dynamics(Badlands)软件正是基于前人的研究工作而开发的一款数值模拟软件,用于模拟各种空间和时间尺度的地貌演化。它可用于研究地表演化过程、预测侵蚀和沉积速率并评估沉积物通量,从而实现对古地理和古地貌进行更为精细化的研究。笔者介绍了Badlands软件的基本原理和方法,并将此方法应用于东海陆架盆地南部中生代地貌及地质演化过程的研究: 首先利用研究区域内现有的地震剖面、测井、平衡剖面等资料获得中生代早期的古地形;再通过恢复的古地形构建数值模型,并加载降雨量、岩石侵蚀性、海平面变化、动力地形调整和地壳弹性层厚度等相关参数进行模拟研究,以分析强烈的构造运动对盆地地貌演化的影响;最后对比模拟结果与已知的中生代的地貌特征和沉积分布,并据此进一步分析中生代盆地演化过程中的沉积物分布规律以及三维古地理和古地貌演化特征。该方法可以为沉积盆地充填过程分析和能源矿产勘探提供有益的思路。     

吉林省和龙地区鸡南BIF型铁矿床含矿建造地球化学特征及形成时代

鸡南铁矿床位于吉林省和龙地区,地处华北克拉通北缘与兴蒙造山带接壤的龙岗地块北部,是东北地区发现较早的BIF型铁矿床之一。该矿床铁矿体主要呈层状、似层状、扁豆状赋存于鞍山群鸡南组上段中部层位,含矿岩石以黑云斜长片麻岩、角闪黑云斜长片麻岩、黑云角闪斜长片麻岩及斜长角闪岩为主,为角闪岩相的中低级区域变质岩系;主要矿石类型为条带状磁铁石英岩型和块状磁铁角闪岩型。为确定该矿床含矿建造的原岩、变质时代及构造背景,重点对含矿岩系中的斜长角闪岩进行了岩石地球化学和锆石U-Pb年代学研究。结果表明：斜长角闪岩的地球化学特征表现为富集大离子亲石元素、轻微富集重稀土元素;主量元素质量分数与中性-基性岩类基本相似,结合原岩恢复图解,判断其原岩类型为亚碱性玄武岩（拉斑玄武岩）,形成于弧后盆地背景;LA-ICP-MS锆石U-Pb年代学研究中,2个较老的锆石测点年龄分别为（2 468±15）和（2 469±9）Ma,代表区内峰期变质年龄（约2 460 Ma）,26个锆石测点的测年数据较为集中,加权平均年龄为（2 275±25）Ma,代表区内退变质年龄。通过与国内外典型BIF型铁矿床的对比研究认为,区内的鸡南铁矿与官地铁矿同属Algoma型铁矿床。     

LA-ICP-MS原位分析白钨矿稀土元素

白钨矿是各类矿床中较为常见的副矿物,通过分析白钨矿的稀土元素质量分数及其标准化配分模式图,可为矿床成矿流体特征及演化提供重要的判别依据。本文对东北地区羊鼻山矽卡岩型矿床和杨金沟热液脉型矿床两个典型钨矿床的白钨矿样品中的稀土元素进行了激光剥蚀-电感耦合等离子体质谱（LA-ICP-MS）原位分析。其中：羊鼻山矽卡岩型矿床白钨矿LA-ICP-MS分析方法所获得的稀土元素配分曲线模式与前人用传统的溶液-ICP-MS分析方法所获得的结果完全吻合,表明采用剥蚀束斑44 μm和剥蚀频率7 Hz的193 nm ArF激光器,NIST 610作外部标样,Ca作内标元素,对基体效应影响最小,所获数据可靠,方法可行;而杨金沟热液脉型矿床白钨矿溶液-ICP-MS分析方法与LA-ICP-MS分析法所获得结果既具有相似性又具有差异性。原因在于羊鼻山白钨矿的成因类型为矽卡岩型、粒度较小且形成时间短,因此不同矿物颗粒间、同一矿物不同部位间稀土元素的配分模式一致;而杨金沟白钨矿的成因类型属于热液脉型、粒度较大、沉淀结晶时间长,因此同一矿物不同部位的稀土元素的配分模式因成矿流体早晚阶段不同而不同。基于以上对比研究发现,无论是在取样和测试过程方面,还是数据准确度方面,相比传统溶液-ICP-MS分析法,LA-ICP-MS原位分析法均具有明显的优势,主要表现在样品形式简单、粒度和质量分数要求低、测试周期短、费用低且结果精确度高;同时其可对不同成矿阶段或白钨矿不同部位成分进行精细测定,从而得出不同成矿阶段或白钨矿不同部位的稀土元素质量分数,以及在更高的空间分辨率下获得更详细准确的数据信息。此外,对白钨矿（尤其是无明显环带者）进行LA-ICP-MS原位分析时,既可采用电子探针微量分析（EPMA）准确测定Ca的质量分数,也可直接采用标准化学式计算Ca的质量分数,分析所得数据同样可以获得合理的地质解释。     

Neural network–based prediction methods for height of water-flowing fractured zone caused by underground coal mining

Low-Ca clinopyroxene crystal of pigeonite composition has been discovered in the Tchabal Mbabo volcano massif of the Cameroon Volcanic Line (CVL), a long a     

Estimation of tensile strength of sandy soil from soil–water characteristic curve

Acta Geotechnica - During heavy rainfalls, the surface soil on a slope may be eroded and the erosion is much dependent on the tensile strength of soil. In addition, the tensile strength of soil is...     

Laboratory testing and numerical simulation of properties and thermal-induced cracking of Eibenstock granite at elevated temperatures

The knowledge about thermo-mechanical properties of granite is still limited to some extent. Individual measurements are necessary to obtain reliable properties for specific granite types. A reliable numerical model of thermal cracking behaviours of granite exposed to extreme high temperatures (e.g. 800–1000 °C) is missing. In this study, the impact of temperature up to 1000 °C on physical, mechanical, and thermal properties as well as thermo-mechanical coupled behaviour of Eibenstock granite was investigated by laboratory testing and numerical simulations. The physical properties including mineral composition, density, P-wave velocity, and open porosity are measured to be temperature dependent. Uniaxial compression and Brazilian tests were carried out to measure uniaxial compressive strength (UCS), Young’s modulus, stress–strain relationship, and tensile strength of Eibenstock granite before and after thermal treatment, respectively. Thermal properties including specific heat, thermal conductivity, thermal diffusivity, and linear thermal expansion coefficient are also measured and found to be temperature dependent, especially the expansion coefficient which shows a steep increase around 573 °C as well as at 870 °C. The numerical simulation code FLAC^3D was used to develop a numerical scheme to simulate the thermal-induced damage of granite at high temperatures. Statistical methods combined with real mineral composition were used to characterize the heterogeneity of granite. The numerical model is featured with reliable temperature-dependent parameters obtained from laboratory tests. It can well reproduce the laboratory results in form of thermal-induced micro- and macrocracks, as well as the stress–strain behaviour and the final failure pattern of Eibenstock granite after elevated temperatures up to 1000 °C. The simulation results also reveal that the thermal-induced microcracks are randomly distributed across the whole sample. Although most thermal-induced damages are tensile failures, shear failure begins to develop quickly after 500 °C. The obvious UCS reduction in granite due to heating is mainly caused by the increase in shear failure. The simulation also shows that the dominant impact of α–β quartz transition is widening pre-existing cracks rather than the formation of new microcracks.

     

风场对鄱阳湖丰水期表层蓝藻密度的影响

目前,在风场对蓝藻的影响研究方面,国内针对太湖、滇池、巢湖等浅水湖泊的研究较多,针对鄱阳湖的研究则多集中于蓝藻群落特征及其与营养盐之间的关系。近年来,作为长江流域重要的通江湖泊,处于轻度富营养化状态的鄱阳湖水体蓝藻水华在局部库湾和部分水域出现,风场如何影响鄱阳湖表层蓝藻密度是一个值得探讨的问题。2019-2021年,在鄱阳湖布设13~49个采样点,于平水期、丰水期和枯水期现场采集各个点位表层水样、藻类、风场和流场数据,分析风场对鄱阳湖丰水期表层蓝藻密度的影响。结果表明,2019-2021年鄱阳湖丰水期风速与表层蓝藻密度呈显著正相关性,风场对水体的充分混合及驱动水体形成的风生流是促进蓝藻生长的原因之一。在流速较高(>0.05 m/s)的区域,无论风速高于还是低于临界风速(3~4 m/s),鄱阳湖表层蓝藻密度的空间分布受流场的影响更大;在流速较低(<0.05 m/s)的区域,风速在临界风速以下时,鄱阳湖表层蓝藻密度的空间分布受风场影响更大。2019-2021年鄱阳湖丰水期蓝藻密度超过水华暴发的阈值,但在高风速高流速的共同作用下未能发生大范围的蓝藻水华,仅能在风速适宜(<3~4 m/s)、流速较低(<0.05 m/s)的内湾、尾闾区等区域发生小面积的蓝藻水华。鄱阳湖丰水期水体处于长江顶托的低流速且微风条件下时,发生大面积蓝藻水华的概率可能会明显上升。     

Scattering process of internal waves propagating over a subcritical strait slope onto a shelf region

The scattering process, which means the redistribution of energy fluy in modenumber space, is analyzed for internal waves propagating from the abyssal ocean onto a subcritical strait slope and then a shelf region. In light of Wunsch＇s work, the waves are analytically expressed as superimposition of eigensolutions distribution of energy flux in the shelf region： one is the ratio of water depth in and the other is the ratio of the slope of the internal tide rays to the topographic energy flux distribution： the energy flux is focused around one modenumber or case, the range of modenumbers where energy flux is distributed is narrow. Two parameters have evident effects on the the shelf region to that in the abyssal ocean slope. Generally, there are two patterns of focused around two modenumbers. In any case, the range of modenumbers where energy flux is distributed is narrow.     

1961—2006年内蒙古年平均气温突变分析

利用内蒙古70个气象站1961—2006年年平均气温资料,分析了近46年来内蒙古气温变化趋势。采用滑动t检验、Mann-Kendall和累积距平曲线3种检验方法对全区年平均气温进行检验分析,揭示了在50年时间尺度上,内蒙古气温存在明显的增暖突变的事实,突变点在1987年。并指出:气温突变后内蒙古气候显著变暖,与突变前相比有明显差异。     

Trophic structure and functioning in a eutrophic and poorly flushed lagoon in southwestern Taiwan

Tapong Bay, a eutrophic and poorly flushed tropical lagoon, supports intensive oyster culture. Using the Ecopath approach and network analysis, a mass-balanced trophic model was constructed to analyze the structure and matter flows within the food web. The lagoon model is comprised of 18 compartments with the highest trophic level of 3.2 for piscivorous fish. The high pedigree index (0.82) reveals the model to be of high quality. The most-prominent living compartment in terms of matter flow and biomass in the lagoon is cultured oysters and bivalves, respectively. The mixed trophic impacts indicate that phytoplankton and periphyton are the most-influential living compartments in the lagoon. Comparative analyses with the eutrophic and well-flushed Chiku Lagoon and non-eutrophic tropical lagoons show that high nutrient loadings might stimulate the growth and accumulation of phytoplankton and periphyton and therefore support high fishery yields. However, net primary production, total biomass, fishery yields per unit area, and mean transfer efficiency of Tapong Bay were remarkably lower than those of Chiku Lagoon. The lower transfer efficiency likely results from the low mortality of cultured oysters and invasive bivalves from predation or the lower density of benthic feeders constrained by the hypoxic bottom water as a result of poor flushing. This might therefore result in a great proportion of flows to detritus. However, the hypoxic bottom water might further reduce the recycling of the entering detritus back into the food web. In contrast to many estuaries and tropical lagoons, poor flushing of this eutrophic tropical lagoon might induce a shift from detritivory to herbivory in the food web.