Palaeomagnetism of igneous rocks of the Lake District (Caledonian) terrane,Northern England: palaeozoic motions and deformation at a leading edge of Avalonia

The Lake District terrane of northern England comprises Upper Cambrian–Silurian sediments and volcanics accumulated at the northern margin of the Avalonian Plate during growth and demise of the Iapetus Ocean. Ocean closure and suturing resulted in Late Ordovician and Acadian tectonism and were accompanied by emplacement of a large regional batholith. Palaeomagnetic study of intrusive igneous rocks, including application of thermal demagnetization, field tests and principal component analysis, identifies a history of Ordovician to Devonian magnetization. Late plutons (Shap and Skiddaw granites and/or aureoles) record a shallow dipolar (A3) axis (mean declination/inclination (D/I=278/+17°) dating from emplacement in late Early Devonian times (c. 395 Ma). Although this axis is recorded as a sporadic overprint in older rocks, no pervasive remagnetization is attributable to batholith emplacement. Instead, the Carrock Fell Complex Layered Gabbros have a mid- to late Ordovician (A1) remanence (D/I)=17·4/−58·1°, 36 samples, α₉₅=4·8°) predating regional F2 folding. Later events in this igneous complex comprise the Carrock Fell Granophyre with a post-folding Ordovician remanence, and Round Knott Dolerite with a remanence linked to hydrothermal alteration late in the Ordovician magmatic episode. A Late Ordovician (Ashgill) palaeofield is also defined by remanence (A2) in the Threlkeld–St John's Microgranite and aureole (438 Ma, D/I=236·5/63·3°, 41 samples, α₉₅=4·7°). Other intrusions carrying a remanence predating the Acadian deformation include the Great Cockup Picrite (458 Ma, D/I=43·2/−31·8°, 31 samples, α₉₅=7·7°) and basic intrusives in the aureole of the Eskdale Granite (429 Ma, D/I=174·5/25·8°, 32 samples, α₉₅=8·8°). Collectively the palaeomagnetic data from this terrane identify a hairpin in the apparent polar wander path during Late Ordovician (Caradoc–Ashgill) times corresponding to ‘soft’ closure of the Iapetus suture and accompanying deformation. The same motion is recognized in contemporaneous data from the Welsh Caledonides where declinations are rotated by c. 55° relative to contemporaneous results from the Lake District. Adjustment for this (probable late Acadian) rotation beings fold trends of the Paratectonic Caledonides into alignment and identifies a parallel mid- to late Ordovician destructive plate margin comprising forearc (Lake District) and backarc (North Wales). This arc was oriented latitudinally in mid-southerly latitudes during formation and the bulk of the magmatism occurred during a single normal-polarity chron. The relationships between magnetization and folding in both the Lake District and Welsh Borderlands identify the importance of Late Ordovician deformation along this arc during collision of Avalonia and Laurentia. Arc-related volcanism was succeeded in Silurian times by parallel foreland basins embracing the Welsh Basin and southern Lake District as the Laurentian Plate overrode the Avalonian Plate. © 1997 John Wiley & Sons, Ltd.     

Fingerprinting upland sediment sources: particle size‐specific magnetic linkages between soils,lake sediments and suspended sediments

Accelerated erosion of fine‐grained sediment is an environmental problem of international dimensions. Erosion control strategies and targeting of mitigation measures require robust and quantitative identification of sediment sources. Here, we use magnetic ‘fingerprinting’ to characterize soils, and examine their affinity with and contribution to suspended sediments transported within two subcatchments feeding Bassenthwaite Lake, northwest England. A high‐resolution soil magnetic susceptibility survey was made using a field susceptometer (ZH Instruments, SM400 probe). Combining the spatial and vertical (down‐profile) soil magnetic data, a subset of soil profiles was selected for detailed, laboratory‐based magnetic remanence analyses. The magnetic properties of the catchment soils are highly particle size‐dependent. Magnetic analyses were performed on the 31–63 µm fraction, for particle size‐specific comparison both with the suspended sediments and lake sediments. Fuzzy cluster analysis groups the soil magnetic data into six clusters, apparently reflecting variations in parent material and horizon type, with three magnetically hard soils as unclassified outliers. Examination of the cluster affinity of the soils, suspended sediments and lake sediments indicates that topsoils of the upper Newlands Valley and subsoils around Keskadale Beck are a major source of the Newlands Beck suspended load, and the recent (post‐nineteenth century) sediments in the deep lake basin. Older lake sediments show strong affinity with a small number of the Derwent suspended sediments and one of the Glenderamackin soils. A large number of Derwent suspended sediments show no affinity with any of the soils or lake sediments, instead forming a coherent, discrete and statistically unclassified group, possibly resulting from mixing between the magnetically hard subsoils of the medium to high‐altitude Glenderamackin and Troutbeck areas and softer, lower altitude Glenderamackin soils. The lack of any affinity of these suspended sediments with the lake sediments may indicate deposition along the Derwent flood plain and/or in the shallow delta of Lake Bassenthwaite. Particle size‐specific magnetic fingerprinting is thus shown to be both highly discriminatory and quantitatively robust even within the homogeneous geological units of this catchment area. Such a methodological approach has important implications for small–large scale catchment management where sources of sediment arising from areas with uniform geology have been difficult to determine using other approaches, such as geochemical or radionuclide analyses. Copyright © 2009 John Wiley & Sons, Ltd.     

Space-time variations of the frequency-energy relation for mining-induced seismicity in the Ostrava-Karviná mining district

The values of parameters of the relation logN=a–b logE characterize in general the level of seismicity of individual regions. In the present paper, a detailed analysis ofb values of the frequency-energy distributions was carried out with the aid of a database of seismic events recorded by the seismological networks in the Ostrava-Karviná Coal Mine District (Czech Republic), using the least squares regression and maximum likelihood method, as well. The determination ofb value was performed for a relatively large number of regions investigated and for different time series of observations. Special attention has been paid to induced seismic events statistics for the vicinity of one of the coalfaces in the Lazy Mine. It could be generally stated that lowerb values correspond to a higher level of induced seismic activity, while the higher ones correspond to a low and a moderate seismic activity.     

山东地区长水准与跨断层短水准资料变化特征分析

本文利用山东地区跨同一断层长水准与短水准的观测资料,结合历史主要震例,根据其变化特证,进行断层垂直形变特征与异常分析。结果显示,山东内陆长水准和跨断层短水准资料所反映的断层活动基本一致。     

兰州区域数字地震遥测台网常用近震定位程序的定位效果分析

对兰州台网2002年1月1日至2002年10月31日网内、网缘共100次2.0≤ML≤4.3以上地震事件的Hypo81、Genetic、NearLoc三种定位程序的定位结果作了研究分析,结果表明:NearLoc程序的定位效果明显优于其它两种定位程序,其使用范围广,对网内、网缘以及网外1 000 km以内的地震都有较好的定位效果。     

A mass balance approach to quantifying Pb storage and fluxes in an upland catchment of the Peak District,north‐central England

A mass balance model of the main Pb stores and fluxes for a typical organic‐rich upland catchment in the Peak District, UK, has been produced. The model, based on the Howden reservoir catchment, reveals that the majority of Pb in the catchment is stored within the soil (approximately 8·63 t km^?2). Soil Pb levels are extremely high and can only be explained as the result of centuries of atmospheric Pb deposition from surrounding urban–industrial conurbations, and mining and smelting activity within the Peak District National Park. The atmospheric Pb flux onto the Howden catchment is approximately 107 kg a^?1. The aquatic Pb flux is estimated at between 29·9 and 71·7 kg a^?1; thus, at present, catchment soils are acting as a sink for Pb pollution. The Howden reservoir acts as a secondary store for Pb eroded and leached from catchment soils, with approximately 80% re‐deposited in its sediments. It is estimated that 2·3% of the catchment soil Pb pool has been retained in the reservoir sediments over its 91 year lifespan. Although the catchment is currently acting as a Pb sink, the rate of change in the soil Pb pool is very small. Future change in climate or deposition chemistry could, however, transform catchment soils into a significant source of Pb to the aquatic environment and water supply. Copyright © 2008 John Wiley & Sons, Ltd.     

南沙东部海域裂陷结束不整合面时空迁移规律及构造意义

南沙东部海域构造位置特殊,油气资源丰富,其构造过程对认识南海形成演化意义重大.由于地质条件复杂、资料分布不均,其地层系统和主要构造变革面属性认识尚不清楚,尤其具有断坳转换性质的裂陷结束不整合面地质时代和意义存在诸多争议.本文在综合国内外地层划分方案的基础上,运用连井剖面对比、地震相类比方法,对该海域多道地震资料进行系统的构造-地层综合解释,重点厘定了T7、T6和T5三个与裂陷结束相关的不整合面.研究表明,裂陷结束不整合面具有抬升剥蚀、断块掀斜、挠曲变形、拆离滑脱、沉积相突变等特征,且具有东北早西南晚,南侧靠陆早、北侧近洋晚的带状时空迁移规律.结合南海构造演化、地层岩性和沉积环境变化分析裂陷结束不整合面的构造含义,认为该界面是南海岩石圈破裂、洋脊跃迁、挠曲前隆、陆陆碰撞、扩张停止等一系列构造事件在不同构造位置单次或多次叠加的构造-沉积响应.

     

阳泉矿区3#煤煤层气解吸特性的研究

实验测定了阳泉矿区3#煤煤层气的解吸特性。利用煤粒中吸附煤层气扩散微分方程式计算出煤层气的解吸时间,并用作图法确定出3#煤煤层气的解吸时间,为阳泉矿区3#煤煤层气的开发和利用提供了重要的参数。      

基于Landsat TM和OLI数据的30年间土地利用变化及生态敏感性研究——以西安市秦岭段鄠邑区为例

对位于关中平原南缘的西安市秦岭段鄠邑区,采用Landsat TM和OLI数据,分析1990~2021年土地利用及景观格局变化特征,并选取高程、坡度、坡向、土地利用类型、植被覆盖度和水系缓冲距离6个敏感性因子,结合层次权重决策分析法（AHP法）评价生态敏感性,识别了不同生态环境敏感区空间分布格局。结果表明：1）在1990~2021年间西安市秦岭段鄠邑区土地利用变化为林地和建设用地面积分别增加了39.31 km²和4.01 km²;耕地、水域、草地和未利用土地的面积分别缩减了41.29 km²、1.16 km²、0.79 km²和0.04 km²;30年间该区土地利用变化速率较大,土地利用程度综合指数从208.48降至204.21,与退耕还林政策的实施及城市建设紧密相关。2）在斑块类型水平上,耕地和建设用地破碎化程度高,分布趋于集中连片;林地和耕地的景观主导性不断降低。在景观水平上,整体格局趋于破碎和离散,景观形状不规则性强,总体异质性和均衡性降低,说明大力发展城乡建设推动了区域景观格局的动态变化,在人为干预和规划下,当地生态环境有所恢复。3）生态敏感性由城市向外围逐渐增加,高敏感区分布在山区和水域区,低敏感区位于城镇规划区周围,不敏感区在城镇中心,是人类活动区,说明生态敏感性和环境抗压能力受人类活动的影响。本研究结果旨在为秦岭区域土地资源可持续利用、生态环境保护提供科学依据,有效防止城市建设的无序蔓延和人类活动的过度干扰,对最大限度保持自然本底具有指导意义。     

遥感技术在鸡西合作区煤层气综合评价中的应用研究

根据鸡西合作区煤系及煤岩曾有过的成烃和聚气过程,寻找其遥感影像、地球化学及放射性能谱特征,从而总结出该区煤层气的综合地质特征,进而研究其周边地区聚气成烃的可能性,为扩大寻找煤成气提供可应用的资料。