The Paleoproterozoic North Hebei Orogen: North China craton's collisional suture with the Columbia supercontinent

Understanding the geologic history and position of the North China craton in the Paleoproterozoic Columbia supercontinent has proven elusive. Paleoproterozoic orogenic episodes (2.00–1.85 Ga) are temporally associated with ultimate stabilization of the North China craton (NCC), followed by the development of extensive craton-wide rift systems at 1.85–1.80 Ga. The age difference between the sedimentary cover and the metamorphic basement is up to 500–700 Ma, suggesting that uplift and doming of cratonic basement occurred in the latest Paleoproterozoic. Mafic dike swarms (1.80–1.77 Ga) and anorogenic magmatism (1.80–1.70 Ga) record the extensional breakup and dispersal of the North China craton during this stage. The late Paleoproterozoic tectonic framework and geological events documented provide important constraints for reconstruction of the NCC within the Late Paleoproterozoic supercontinent of Columbia.An east-west striking thousand kilometer long belt of khondalites (granulite facies metapelites) stretches along the northern margin of the North China craton, on the cratonward side of the Northern Hebei orogenic belt. This granulite belt includes Mg–Al (sapphirine bearing) granulites that reached ultrahigh-temperature “peak” metamorphic conditions of  1000 °C at 10 kbars at 1927 ± 11 Ma. Following peak ultrahigh-temperature conditions, the rocks underwent initial isobaric cooling and subsequent isothermal decompression, and these trajectories are interpreted to be part of an overall anti-clockwise P-T evolution indicating that the northern margin of the craton experienced continental collision at 1.93–1.92 Ga. The position of the khondalite belt south of the Northern Hebei orogenic belt makes it analogous to Tibet, a continental collision-related plateau characterized by double crustal thicknesses and granulite facies metamorphism at depth. We suggest that the tectonic evolution of the NCC during this period was closely related to the assembly and break-up of the Columbia supercontinent, and that the NCC was adjacent to the Baltic and Amazonian cratons in the period 2.00–1.70 Ga. Craton-wide extension occurred within 100–150 Ma of collision along the northern margin of the craton at 1.93–1.92 Ga. It is concluded that mantle upwellings are chiefly responsible for the breakup of the NCC from the Paleoproterozoic supercontinent.     

Placement Optimization Method of FPSO Gas Detectors Based on Leakage Risk

As the first step of the fire/gas-detection systems of floating production storage and offloading(FPSO)units is to iden-tify leakage accidents,gas detectors play an important role in controlling the leakage risk.To improve the leakage scenario detection rate and reduce the cumulative risk value,this paper presents an optimization method of the gas detector placement.The probability density distribution and cumulative probability density distribution of the leakage source variables and environmental variables were calculated based on the Offshore Reliability Data and the statistical data of the relevant leakage variables.A potential leakage sce-nario set was constructed using Latin hypercube sampling.The typical FPSO leakage scenarios were analyzed through computational fluid dynamics(CFD),and the impacts of different parameters on the leakage were addressed.A series of detectors was deployed according to the simulation results.The minimization of the product of effective detection time and gas leakage volume was the risk optimization objective,and the location and number of detectors were taken as decision variables.A greedy extraction heuristic algo-rithm was used to solve the optimization problem.The results show that the optimized placement had a better monitoring effect on the leakage scenario.     

山西地区6次MS≥4.5地震前地震活动异常总结

系统梳理了2000年以来山西地区6次M_S≥4.5地震前地震活动异常,结果表明,地震空区/平静、地震条带、显著地震/震群、大同地震窗“开窗”活动等异常在地震发生前具有一定普遍性,且异常基本围绕在震中及附近地区分布,特别是在地震平静/空区、地震条带等异常发展后期出现的显著地震/震群活动,对未来地震发生的地点和时间具有较好的预测意义。异常持续时间与发震间隔统计表明：异常多出现在主震发生前6个月以内,显著地震/震群、大同地震窗“开窗”对未来主震的发生具有短临预测意义。此外,随着区域应力水平的不断增强,在特定敏感地区会发生成组极微震密集活动,监视跟踪这些有别于正常活动背景的极微震活动,对地震短临预测具有一定意义。     

植草沟滞蓄城市道路雨水的试验及模拟

为定量分析植草沟的水文性能,优化其设计参数取值,通过植草沟滞蓄城市道路雨水的试验设施开展模拟径流试验,验证了SWMM （storm water management model）模型模拟植草沟滞蓄效果的可行性,通过模型情景分析提出了设施的优化设计参数,评估了设施对提高道路排水标准和长期径流削减的影响。研究结果表明:SWMM模型对模拟植草沟水文性能具有较好的精度,对较小的降雨重现期和边坡比,较大的滞蓄深度、植被覆盖率和面积负荷比,植草沟的滞蓄能力更强,建议其设计降雨重现期不超过10年,滞蓄深度为10 cm以上,边坡比至少为3,植被覆盖率为0.5以上,面积负荷比为5%以上。模拟北京某城市道路采用植草沟设施后,可将3年、5年、10年的排水标准分别提高到15年、20年、30年,在长达64年的运行中,植草沟几乎可消纳自身及汇水区域内所有径流,可为道路植草沟的设计和应用提供参考。     

Characteristics of Holocene Loess-Palaeosol Particle Size Composition and Paleoclimatic Significance in East Guanzhong,Shaanxi Province

This paper made an end-member analysis of particle size data collected from 150 samples based on the continuous Holocene Loess-Paleosol profile (Yaohecun profile) in east Guanzhong, Shaanxi Province. Wavelet analysis was also performed for the EMs along the time scale of depth.The result shows that three end members can be separated from different sediment particle sizes. Based on comparative analysis of magnetic susceptibility and geochemical index, it was considered that the End-member 1 might indicate the weathering and pedogenic remoulding after sediment deposition under the east Asian summer monsoon. The End-member 2 might indicate dynamic effect of dust storm accumulation under the influence of northwest monsoon, representing typical component characteristics of aeolian loess.The End-member 3 indicated the stronger transporting force for coarse components, which should belong to the northeasterly winds for the coarse-grained near-source sediments from the Yellow River flood plain. Results of wavelet analysis show that each EM has different periodic characteristics at 1.5 ka, 3.0 ka and 4.5 ka scales.The End-element analysis method has a good effect in indicating the sedimentary environment and provenance characteristics of sediments. The combination characteristics of each End-member can reflect the characteristics of sedimentary dynamics combination and can well reflect the Holocene dynamic change course. At the same time, it hasreference significance to reconstruct the paleoclimate on the longer time scale.The wavelet analysis method provides significant results in terms of inversion cycles and trends of dynamics change of sedimentary particle size within each EM.     

Chemical and Sr-Nd compositions and 40Ar/39Ar ages of NW-trending dolerite dikes of Burkina Faso: Evidence for a Mesoproterozoic magmatism in the West African Craton

The Paleoproterozoic basement of the northeastern part of the Leo-Man craton is intruded by generally NW-trending dikes. These regional scale dikes extend over 1000 km in Burkina Faso, Mali and Niger. We present chemical and Sr-Nd isotope compositions, as well as ⁴⁰Ar/³⁹Ar ages of these dikes with the following strikes N98°–N112°, and N114°–N124° in NE Burkina Faso. Field relationships show that the dikes are posterior to all other rock types dated between 2.26 Ga and 2.0 Ga. Chemical data indicate that the dikes are continental flood basalts and composed of low-Ti (TiO₂ ≤ 2 wt.%) sub-alkaline basalts and andesites. They exhibit a minor negative Europium anomaly (0.86–0.99) and slightly fractionated REE patterns ((La/Yb)_N = 2.5–9.1; Yb_N = 9.5–19.9). The ratios of Th/Ta (1.3–11.4) and Ce/Pb (5.2–58.5) suggest a varying crustal assimilation of the dike magmas during ascent in the continental crust for all studied samples. Calculated P-T conditions indicate that the magma reached temperatures of 1285 °C (calculated from olivine compositions) and pressures of 6.9 kbar (calculated for pyroxene minerals). Calculated initial ⁸⁷Sr/⁸⁶Sr (0.70040–0.70260) and ɛ_Nd(t) = +2.1 to −3.5 at 1575 Ma, also point to a crustal contamination with the most primitive samples showing T_DM values of 1946 Ma and 2154 Ma. The low values of La/Ba (<0.2) and Nb/La (<1.0), contrast with the low Th/Nb (<0.9), and suggest a lithospheric mantle or subduction-modified mantle as possible source for the dikes. Sr-Nd data, Mg# and Nb-Ta-Zr-Y-Th-Tb-Yb compositions further suggest that the most primitive samples were emplaced in a none orogenic setting and their magmas were subjected to variable crustal contaminations. Literature and the present whole rock ⁴⁰Ar/³⁹Ar age determinations show that the dikes were emplaced during a widespread Mesoproterozoic magmatism between 1.6 Ga and 1.2 Ga, and were affected by a thermal event causing the argon systematics resetting, best constrained by the date of sample KK1 (1236 ± 20 Ma, ⁴⁰Ar/³⁶Ar = 294 ± 13, MSWD = 2.2). Contemporaneous 1590–1570 Ma extensive magmatism is reported in other crustal blocks in Baltica (Sveconorw-Goth, svecofennian) NW Laurentia (Slave craton, Yukon), and Australia (Gawler craton), and together with the 1575 studied dikes, are related to the breakup of the supercontinent Nuna.     

智能优化LSSVM算法的混沌时间序列边坡变形预测模型

边坡变形序列存在一定混沌特征,本文将混沌分析方法应用到边坡变形预测中。为解决标准LSSVM模型中惩罚参数和核函数参数因任意给定或经验给定带来的非最优问题,将遗传算法和粒子群算法引入LSSVM模型,根据变形序列建立GA-LSSVM和PSO-LSSVM预测模型,与标准LSSVM混沌预测模型和基于神经网络的混沌预测模型进行比较。结果表明,GA-LSSVM和PSO-LSSVM模型预测中误差分别为0.73 mm和0.77 mm,LSSVM,BP,RBF三种模型中误差分别为0.90 mm,0.80 mm和0.75 mm;因此,本文提出的预测模型用于边坡变形预测比其他几种模型具有更高的精度。     

航空摄影测量生产作业流程优化方法

传统的航空摄影测量生产作业流程存在着内业、外业相对独立,采编与图库相互分离等许多缺点。这样,导致较长的生产周期难以提供实时的测量结果,在经济发展快的地区表现得更加严重。本文通过新技术的应用和工作经验总结,进行了生产作业流程优化方法的关键技术讨论,实现了缩短生产周期,提高了生产作业效率。最后,结合应用实例进行效果评价。     

基于有限元分析的松原震群与日本大地震的关系探讨

日本3·11大地震之后,我国松原地区发生了多次4级以上地震,两者之间存在的关系是本文探讨的重点。利用有限元方法,构造两个有限元模型,从库仑应力变化的角度研究日本3·11大地震对位于郯庐断裂带北段第二松花江断裂的影响。模拟结果表明,日本大地震对我国东北部地区影响大,第二松花江断裂带的位移最大达到20 mm。整个研究区的静态库仑应力均为正值,表明该断层处于危险阶段。考虑到实际地壳介质对应变传递的延迟效应,日本3·11大地震对我国东北地区的实际影响会有一个滞后,因此松原震群与日本3·11大地震存在密切相关性。     

一种优化的自由网平差及其在变形监测中的应用研究

主要介绍使用序贯平差与秩亏自由网平差联合的方法对自由网平差进行优化,此优化方法能集合自由网平差无控制点约束的特点和序贯平差处理大数据量的高效率特点.最后通过工程实例具体阐述了将该优化的自由网平差方法应用于变形监测中.