龙门山南段飞来峰构造变形及形成演化

龙门山前山构造带中分布着大量的飞来峰。为了解其构造演化过程,主要通过分析研究龙门山南段白石-苟家飞来峰和金台山飞来峰内部及下覆地层的构造变形特征,确定出其至少经历了5个构造变形序列,并结合前人资料讨论龙门山南段飞来峰的形成和演化。     

Geochemistry and SHRIMP geochronology of alkaline rocks of the Zijinshan massif in the eastern Ordos basin, China

Characteristics of geology, petrology, and geochemistry of the Zijinshan massif were studied in the eastern part of the Ordos basin. Geochemical analysis shows that the massif is characterized by high alkali, relatively high Fe, and low Mg and Ca contents. The rocks are undersaturated in SiO₂, rich in REE (with no Eu anomaly) and belong to the alkaline-peralkaline series. The geologic history of the Zijinshan massif consists of several stages of magmatism. The obtained isotope-geochronological (U-Pb SHRIMP) data show that the magmatic activity climaxed in the interval 150–110 Ma, while the age of 16 zircon grains fitted a narrower interval, 132–125 Ma, i.e., the Early Cretaceous. The younger age corresponds to the middle and late stages of the evolution of the Ordos basin and agrees with a large Early Cretaceous tectonothermal event in North China. This event led to the large-scale uplift of the eastern flank of the Ordos basin, rise of the Lüliang asthenosphere, and to the formation of a large west-sloping monocline. The U-Pb SHRIMP studies have also revealed magmatic zircons of Carboniferous–Permian age, which evidences the multistage character of the thermal process.     

Massively parallel spatial point pattern analysis: Ripley’s K function accelerated using graphics processing units

This study presents a massively parallel spatial computing approach that uses general-purpose graphics processing units (GPUs) to accelerate Ripley’s K function for univariate spatial point pattern analysis. Ripley’s K function is a representative spatial point pattern analysis approach that allows for quantitatively evaluating the spatial dispersion characteristics of point patterns. However, considerable computation is often required when analyzing large spatial data using Ripley’s K function. In this study, we developed a massively parallel approach of Ripley’s K function for accelerating spatial point pattern analysis. GPUs serve as a massively parallel platform that is built on many-core architecture for speeding up Ripley’s K function. Variable-grained domain decomposition and thread-level synchronization based on shared memory are parallel strategies designed to exploit concurrency in the spatial algorithm of Ripley’s K function for efficient parallelization. Experimental results demonstrate that substantial acceleration is obtained for Ripley’s K function parallelized within GPU environments.     

锆石对地球早期地壳演化和构造体制转换的启示

锆石是研究早期地球演化的重要矿物之一,它的U-Pb年龄结合其微量元素以及同位素成分是反演寄主岩石成因乃至地球动力学背景的重要手段.本文从锆石矿物包裹体、微量元素、U-Pb同位素体系、Lu-Hf同位素、O同位素以及Si、Zr和Ti同位素这6个方面综述了近10年来前人取得的主要研究成果,总结了次生矿物包裹体可能产生的方式以...     

The bedform morphology of Chinese sturgeon spawning sites in the Yangtze River

Quantitative measures of the relationships between channel morphology and the habitat use of Chinese sturgeon(Acipenser sinensis) can help management and regulatory agencies to quantify potential spawning habitats and develop recovery goals in view of the decreasing area of sturgeon spawning habitat.This study determined the specific bedform types at the pool-riffle scale and evaluated the slopes,aspects and bed load gradation composition of Chinese sturgeon spawning areas in the Yangtze River,China.A bedform differencing technique was used to objectively quantify the longitudinal riverbed profile into four distinct pool-riffle units that were independent of discharge.The vertical location of thalweg points within these units was quantified with a riffle proximity index.Chinese sturgeon spawning areas were mapped and correlated with the pool-riffle units,slopes and aspects.The results indicate that Chinese sturgeon spawning areas occur primarily in riffles.The majority of Chinese sturgeon spawning occurred at elevations greater than 75%of the difference in elevation between the nearest riffle crest and the pool bottom.The slope of spawning sites was distributed between 0.05 and 6.36,and the average aspects were 219.92 and 207.63,respectively.The bed load is mainly composted of gravel and pebble,sediment diameter concentrated on 50-500mm.These analyses of bedform morphology will assist regional fish managers in quantifying existing and potential Chinese sturgeon spawning habitats and will provide a quantitative framework for evaluating general ecological implications of channel morphology in the Yangtze River.     

张家口万全断裂特征研究

万全断裂是河北省张家口市万全县西边的一条第四纪控盆断裂,构造上位于山西断陷带与燕山断隆交汇部位,地貌上为低山丘陵与山前冲洪积平原分界,地质上为中生代地层与新生代地层分界。断裂走向NE,倾向SE,分为南、北2段。其东北端与张家口断裂相交,西南端与洗马林断裂相汇,共同控制着万全盆地的发展演化。本文从断裂附近地形地貌宏观显示、隐伏段地球物理探测及地质地貌调查等多方面,对该断裂的特征进行分析,最终给出万全断裂的构造特征及具体空间展布形态,填补了该条断裂的研究空白,为开展大城市活断层探测与研究,进行合理的城市规划和抗震设防提供依据。     

Paleomagnetic constraints on Miocene rotation in the central Japan Arc

We present new Middle Miocene paleomagnetic data for the central Japan Arc, and discuss their implications for Miocene rotation. To obtain a refined paleodirection, we made magnetic measurements on basaltic to andesitic lavas and intrusive rocks from 12 sites in the Tsugu volcanic rocks (ca 15 Ma) in the northern part of the Shitara area, Japan. Significant secondary magnetizations in samples with strong magnetic intensities are interpreted as lightning‐induced components. Mean directions carried by magnetite and/or titanomagnetite were determined for all sites. An overall mean direction with a northerly declination was obtained from dual‐polarity site means for nine sites. This direction is indistinguishable from the mean direction for coeval parallel dikes in the northern part of the Shitara area, and also indistinguishable from the Miocene reference direction derived from the paleopole for the North China Block in the Asian continent. These comparisons suggest little or no rotation or latitudinal motion in the study area with respect to the North China Block since 15 Ma. We obtained a refined early Middle Miocene paleodirection (D = 9.7°, I = 52.5°, α₉₅ = 4.8°; 30 sites) and paleopole (82.0°N, 230.8°E, A₉₅ = 5.6°) for Shitara by combining data from the Tsugu volcanic rocks and a coeval dike swarm. An anomalous direction found at three sites could be a record of an extraordinary field during a geomagnetic polarity transition or excursion. Paleomagnetic data from Shitara suggest that: (i) the western wing of the Kanto Syntaxis, a prominent cuspate geologic structure in central Honshu, underwent a counterclockwise rotation with respect to the main part of the southwestern Japan Arc between ca 17.5 Ma and 15 Ma; (ii) collision between the Japan and Izu–Bonin (Ogasawara) Arcs began prior to 15 Ma; and (iii) clockwise rotation of the entire southwestern part of the Japan Arc had ceased by 15 Ma.     

Soil bentonite wall protects foundation from thrust faulting: analyses and experiment

When seismic thrust faults emerge on the ground surface,they are particularly damaging to buildings,bridges and lifelines that lie on the rupture path.To protect a structure founded on a rigid raft,a thick diaphragm-type soil bentonite wall(SBW) is installed in front of and near the foundation,at sufficient depth to intercept the propagating fault rupture.Extensive numerical analyses,verified against reduced–scale(1 g) split box physical model tests,reveal that such a wall,thanks to its high deformability and low shear resistance,"absorbs" the compressive thrust of the fault and forces the rupture to deviate upwards along its length.As a consequence,the foundation is left essentially intact.The effectiveness of SBW is demonstrated to depend on the exact location of the emerging fault and the magnitude of the fault offset.When the latter is large,the unprotected foundation experiences intolerable rigid-body rotation even if the foundation structural distress is not substantial.     

夏垫断裂带深部构造特征与第四纪活动性讨论

利用重力、浅层地震和高密度电阻率法物探工作成果,由深及浅垂向上“接力拼接”的方式,结合钻探等手段,把夏垫断裂带分解为基岩断裂带和第四纪断裂带2个部分进行研究,结果表明:1)夏垫断裂带的基岩断裂带由主干断裂和次级断裂构成.其北段(马坊-西集一带)较窄,由2条主干断裂构成.其南段(西集-凤河营一带)较宽,由3条主干断裂构成.2)第四纪断裂带是基岩断裂带向上延伸的部分,是断裂带最新活动的直观表现,并受控于基岩断裂带.夏垫第四纪断裂带同样由主干和次级断裂构成,北段(马坊-西集一带)由2条主干断裂和分布于北端尾部次级断裂构成,与基岩断裂带一一对应关系较好.2条主干断裂产状差异较大,最新活动时间均为全新世.而南段(西集-凤河营一带)断裂分布不连续,很难分清主次断裂,同基岩断裂带的对应关系较差,推测为基岩断裂中夏垫断裂的活动.这些主、次级断裂产状均较为陡立,最新活动时间为晚更新世晚期-全新世早期.3)夏垫断裂带内上、下两盘全新世沉积底界垂向累积位错量为1.7 ～4.8m,晚、中、早更新世以来则分别为6 ～ 26m、26 ～ 167m和44 ～ 330m,其中最大累积位错量位于夏垫地区,向南、北逐渐减小.4)以张家湾断裂为界把夏垫断裂带划分为南、北2段.北段第四纪活动性强,中强震及微小地震时有发生,而南段第四纪活动性弱,仅发生微小地震.     

小江断裂带中段和南段井水位变化与形变分析

应用井孔-裂隙、微裂隙(孔隙)水流交换产生的潮汐水位-固体潮的位相差和振幅变化理论,结合井水位变化,分析小江断裂带中段和南段的形变特征.裂隙承压含水层条件下,地震波和构造应力引起的形变能够引起潮汐水位分波位相差和振幅的变化.地震波引起含水层与井孔之间水流交换增大,疏通裂隙而使渗透率增大,震后井水位潮汐分波相位差提前,其后裂隙内沉积物重新堵塞裂隙,渗透率降低,位相差逐渐下降.位相差的长期趋势性变化反映出含水层在构造应力作用下的应变信息.小江断裂带中段和南段形变变化不同.断裂带中段地区,观测井位相差和振幅趋势性下降,表明该区段不仅有走滑特性,并且具有挤压特征.小江断裂带与红河断裂带交会地区观测井振幅和位相差稳定,表明该区域没有受到明显的挤压,形变不明显.