赣西南下奥陶统樟木曲组笔石带的修正和补充

本文在对笔石作系统研究的基础上,对樟木曲组的笔石带进行了补充和修正。由原来的9个笔石带划分为11个笔石带,厘定了各笔石带的范围和笔石群的总体面貌,并逐带与国内外进行了对比。文内还涉及到宁国阶的顶界、上下两层下垂时笔石以及关于肿笔石与心笔石混生的问题。     

Tectonique transpressive en terre Adélie au Paléoprotérozoı̈que (Est Antarctique)Palaeoproterozoic transpression in Terre Adélie (East Antarctica)

The Palaeoproterozoic units of Terre Adélie show two types of structural domains associated with HT–LP metamorphic conditions: domes and NS–N340° striking vertical shear zones. Shear zones reflect dextral transpressive motions. Domes reflect sub-vertical shortening and principal stretching subparallel to shear zones. They could partly result from longitudinal flow coeval with transpression. Deformations are comparable to those described along the eastern and western boundaries of the Archean Gawler Craton (South-East Australia), which underlines the continuity between these two areas before opening of the Austral Ocean. To cite this article: A. Pelletier et al., C. R. Geoscience 334 (2002) 505–511.     

Use of the magnetic,geochemical, and sedimentary records in establishing paleoclimate change in the environment of Sebkha: Case of the Sebkha Mhabeul in southeastern Tunisia

In this study, we explored the evidence of late Holocene climate changes in southern Tunisia, examining extreme events of flood and sandstorm sedimentary succession records, in Sebkha Mhabeul. A sediment-derived climatic proxy was inferred from a 93.5-cm-deep core (Mh1), whose dating by tephrochronology has already been achieved in previous works. Multiple geochemical, sedimentological, magnetic susceptibility, and quartz grain microtexture proxies were used to determine the shifts in regional climatic conditions. The Sebkha core captured sensitive changes in the precipitation/evaporation (P/E) balance by adjustments in salinity, and is especially valuable for reconstructing variability over centennial timescales. The Sebkha Mhabeul area showed higher salinity during the Roman Warm Period (RWP: 2100–1400 cal yr BP), the Medieval Warm Period (MWP: 1000–600 cal yr BP) and the present era, and generally lower salinity during the Dark Ages (DA: 1400-1000 cal yr BP) and the Little Ice Age (LIA: 600-200 cal yr BP).In southeastern Tunisia, the hydrological behavior was sometimes consistent with the flood activities in the eastern Mediterranean, and sometimes contemporaneous with the flood pulsations of the western Mediterranean.     

珠江三角洲农业土壤磁化率空间分布特征及其影响因素分析

在珠江三角洲范围内选取300件农业土壤样品进行磁化率及频率磁化率分析。结果表明,300件土壤样品的磁化率在1.29×10-8~185.89×10-8m3/kg范围内变动,平均值为31.20×10-8m3/kg。珠江三角洲农业土壤磁化率具有明显的空间分异特征,呈南高北低、中心区高东西两翼低的空间分布格局; 全区具4个明显的磁化率高值区,分布在: 珠海、深圳、惠阳及顺德。因子分析结果表明灌溉方式、土地利用类型和母岩与母质、土壤类型对农业土壤磁化率高低起主要作用。同时,重金属污染对农业土壤的磁性具有明显的增强作用。     

The recognition of former melt flux through high‐strain zones

High‐strain zones are potential pathways of melt migration through the crust. However, the identification of melt‐present high‐strain deformation is commonly limited to cases where the interpreted volume of melt “frozen” within the high‐strain zone is high (>10%). In this contribution, we examine high‐strain zones in the Pembroke Granulite, an otherwise low‐strain outcrop of volcanic arc lower crust exposed in Fiordland, New Zealand. These high‐strain zones display compositional layering, flaser‐shaped mineral grains, and closely spaced foliation planes indicative of high‐strain deformation. Asymmetric leucosome surrounding peritectic garnet grains suggest deformation was synchronous with minor amounts of in situ partial melting. High‐strain zones lack typical mylonite microstructures and instead display typical equilibrium microstructures, such as straight grain boundaries, 120° triple junctions, and subhedral grain shapes. We identify five key microstructures indicative of the former presence of melt within the high‐strain zones: (a) small dihedral angles of interstitial phases; (b) elongate interstitial grains; (c) small aggregates of quartz grains with xenomorphic plagioclase grains connected in three dimensions; (d) fine‐grained, K‐feldspar bearing, multiphase aggregates with or without augite rims; and (e) mm‐ to cm‐scale felsic dykelets. Preservation of key microstructures indicates that deformation ceased as conditions crossed the solidus, breaking the positive feedback loop between deformation and the presence of melt. We propose that microstructures indicative of the former presence of melt, such as the five identified above, may be used as a tool for recognising rocks formed during melt‐present high‐strain deformation where low (<5%) volumes of leucosome are “frozen” within the high‐strain zone.     

Magnetic and Gravity Investigations of Lisan Peninsula-Dead Sea(Jordan)

The Lisan Peninsula is located within the Dead Sea basin which represents the plate boundary between African and Arabian plates. This basin constitutes a good example of a pull-apart basin because of its large dimensions, its structural simplicity and its active subsidence . The gravity data reveal that the Dead Sea basin can be divided into segments, each of them about 30 km long in N-S direction , where the Lisan Peninsula represents the deepest one (9 km thick Pleistocene sediments ), overlying about 6 km thick Mesozoic sediments . In addition , 20 km of extension was predicted along the Dead Sea basin, which indicates that the Dead Sea basin should be about 3.3 Ma in age . Furthermore, the Precambrian basement under the Lisan area is characterized by high susceptibility contrast that is related to continuous tectonic activity in the region.     

宁沪高速公路句容段两侧土壤磁化率异常与重金属元素的关系研究

高速公路两侧土壤的磁化率从路中央向两侧具有逐渐降低的特征,相对应的样品中的重金属Cu、Pb、Zn、N i、Cr、Fe等元素的含量也具有从路中心向两侧逐渐降低的现象。相关分析表明,土壤磁化率与土壤中的Cu、Pb、Zn、N i、Cr、Fe的相关性显著,因而可以利用磁化率异常来指示高速公路两侧土壤的重金属污染状况。元素的赋存形态分析表明铁锰氧化物态与残渣态是Cu、Pb、Zn、N i、Cr、Fe的主要赋存形式;各元素的形态分析结果与土壤磁化率的相关统计分析表明,高速公路两侧土壤的磁化率与可交换态中的Cu、Pb、Zn、铁锰氧化物态中的Fe、Pb、Zn、有机还原态中的Cu、Cr、Fe、Zn和残渣态中的Cu、Pb、Zn、Cr、Co、N i具有明显的相关性。     

Kinematics of throughgoing fractures in jointed rocks

Throughgoing fractures play a major role in subsurface fluid flow yet the kinematics of their formation, which directly impact rock flow properties, are often difficult to establish. We investigate throughgoing fractures in the Monterey Formation of California that developed by the coalescence of pre-existing joints. At Lompoc Landing, throughgoing fractures fall into three main groups: linked, linked with aperture, and breccia zones. The segmented nature of their walls provides numerous piercing points to firmly establish the sense of displacement. Analysis of displacement vectors derived from piercing points demonstrates that the NW–SE trending throughgoing fractures, often interpreted as strike–slip faults, are in fact extensional structures in origin. We suggest that this method may be applied to throughgoing fractures that form by the same mechanism in other geologic settings. Establishing kinematics of throughgoing fractures will lead to a better understanding of their contribution to subsurface fluid flow.     

基于专家经验值的滑坡易发性评价——以四川平武高坪铺库区为例

滑坡灾害的易发性评价方法和模型有很多,不同的学者又对其进行了不同的改进,形成了不同的方法。究竟哪种方法更好,还需要结合实际进行方法的比较分析。论文应用基于专家经验值的二元统计法分析了四川平武高坪铺库区(约32 km2)高程、岩性、与居民点距离、与河流距离、坡度和坡向6种因素对滑坡灾害影响,并在此基础上进行了滑坡易发性评价。