高频电磁测深法在钼矿采空区探测中的应用

采空区给人类生产生活带来危害,采空区的探测已成为重要研究课题.针对采空区的特点,合理选择物探方法、灵活运用物探方法是准确探测采空区的关键.本文介绍了高频电磁测深法的原理、特点和工作方法,通过分析已知采空区与未知采空区的测量结果,说明高频大地电磁测深是探测采空区的有效手段.通过某钼矿采空区探测中的实例,验证了此方法在钼矿...     

EH4高频电磁测深在断层构造探测中的应用研究——以川藏路高尔寺山隧道为例

将EH4高频大地电磁测深法应用于高原特长隧道—高尔寺山隧道构造、岩性的勘察,通过与钻探及地质调绘的资料对比,EH4音频大地电磁法可以在宏观上查明深埋隧道地层岩性分界、地质构造及其赋水性,为钻孔布置及隧道设计、施工提供地球物理依据,在高原地区深埋隧道勘查中能达到较为理想的效果。     

10KV高压电线对EH4观测的影响特征分析及噪声压制

在农村或乡镇周围进行EH4工作时经常会遇到10 KV高压输电线,距离高压线较近时,50 Hz及其谐波的能量较强,对观测的影响较大,EH4工作应尽量远离高压线.经实验研究,距高压线约150 m和200 m的EH4信号强度变化不明显,此时通过快速傅里叶变换,选择合适的阈值进行去噪,可有效地对50 Hz及其谐波引起的噪声进行...     

花岗岩地区深部地热构造电磁法探测研究——以福建龙海地区为例

为探查福建龙海花岗岩区深部地热构造,试验音频大地电磁法(AMT)在此类地区的应用效果,在该区域布设了数条AMT测线.经过一系列的数据处理及反演,得到研究区的各条测线的电阻率深度剖面图及电阻率分布平面切片图.该测区AMT研究成果反映了地下2 km深度范围内的地质构造分布基本情况,指示了可能的深部地热构造位置,为深部构造探测提供了良好的地球物理基础资料.结果表明,音频大地电磁法在探测花岗岩地区深部地热构造方面是有效的.     

高频大地电磁测深在断层构造探测中的应用研究

各种大型工程中测区范围内的断层及破碎带构造，都将对施工产生安全隐患，阐述采用EH-4电导率成像系统的高频大地电磁法能够准确快速的探测一定深度范围内的断层及破碎带等地质构造，对施工区的断层及破碎带等地质构造的赋存状态进行超前的宏观预测，并将野外的成功实例进行分析。     

AMT方法在鳌山卫花岗岩地区深部地热构造勘探中的应用

作为我国最近规划的中国蓝谷海洋高科技开发区,对能源结构有着较高要求.目前,地热资源的直接利用是最经济最方便的绿色能源途径.鳌山卫研究区,是中国蓝谷的核心区之一,根据地质资料和温泉露头情况推测,该研究区内有可观的地热资源潜力.为探测鳌山卫花岗岩地区的深部地热构造,搜集已有的地质地球物理资料,在该区布设了10条AMT测线.通过资料采集、预处理、反演,得到了研究区地下2000 m以浅的电性结构的空间展布形态.勘探结果显示,研究区发育一条走向为N30°E的断裂构造F1,深度约1500 m;同时确定了构造低阻异常中心位置,为下一步钻孔布设提供依据.本次花岗岩区AMT探测,克服了城市人文干扰和高压输电线引起的各种电磁干扰,为类似地区深部地热构造探测工作提供了实践经验,是一次成功的深部地热构造探测.     

音频大地电磁法在探测地下水中的应用——以湛江南木水为例

本文通过在广东省湛江市省级生态农业示范区——南木水地区进行地下水探测拟解决当地的生活用水问题.该区域主要为燕山期花岗岩,本文采用了音频大地电磁法(AMT)勘探方法,从构造分析出发,选择三个有利区域(分别为A、B、C、区),布设了10条AMT勘探线,共166个测点,进行野外数据.对野外数据进行了一系列预处理、反演和电阻率成像得到各线的剖面图.分析研究剖面图和切片图,确定了三个可能含水的低阻带以及三口钻井的位置.其中C区已经打井取水,出水50 m~3/h,很好地验证了AMT方法在硬岩地区进行地下水探测的实用性和有效性.     

CSAMT法在高速公路长大深埋隧道勘察中的应用研究

CSAMT法是一套综合了MT和AMT各自优点的电磁自动采集和处理系统.本文介绍了CSAMT的原理、特点、工作方法和资料处理.该系统首次运用于高速公路长大深埋隧道勘察中，结合其它手段，成功解译出了隧道的软弱层、地下水及断层破碎带的位置，为划分隧道围岩类别提供了较好的依据，同时也为高速公路长大深埋隧道提供了一种新的勘察方法.     

AMT和高密度电法结合探测稻城LHAASO项目区隐伏断层和基岩埋深

高海拔花岗岩区裸露基岩丘与多成因沉积物盆垄显示地质条件变化较大,给高海拔宇宙射线观测站(LHAASO)工程建设带来挑战.地质调查和物探相结合,对场区大范围勘察以求规划避让断层,中心区WCDA小范围精细探测以刻画基岩顶面起伏变化,便于地基设计.采用音频大地电磁法(AMT)和高密度电法相结合,在场区和中心区布网探测.结果发现,在避开区域断层后,不同规模断层在场区依然存在,与区域断裂构造NNE走向和节理走向不完全一致,影响到局部坳陷盆地规模走向和沉积物分布.场区基岩埋深20～60 m,变化较大.受第四纪冰川和现代河流作用,堆积了厚达30 m冰碛物和60 m冲洪积物,分布在场区约4 km2范围内,而靠近较大规模断层破碎带的堆积物厚达100多米.分析结果被后期钻探验证,为工程规划设计提供了科技支撑.     

瞬变电磁法及EH-4在钼矿采空区探测中的应用

地下采空区的存在严重威胁着人们正常的生产生活,选取有效的方法对采空区探测有着重大的现实意义.本文探讨了瞬变电磁法和EH-4电导率成像法的方法技术以及在某钼矿采空区的应用效果.瞬变电磁法观测的是纯二次场,所以分辨率高,特别是对低阻异常体反应灵敏.EH-4电导率成像系统探测深度大,适用于各种复杂地形,可以有效的减少地形的影响,因此结合这两种方法对采空区进行综合探测,可以相互补充,提高对采空区评价的准确性.     

Weathering of granitic rocks by chlorides: effect of the nature of the solution on weathering morphology

Five granites from NW Spain were subjected to two salt‐spray weathering tests under controlled atmospheric conditions. Granite samples were exposed to a sodium chloride solution in the first test and to a complex solution (sea water) in the second. Subsequent examination of the rocks by light and petrographic microscopy clearly demonstrated the development of different weathering morphologies in each test. The distribution of dissolved ions in samples taken at different depths from the weathered surfaces at the end of the experiments, and the changes in weight of the samples during the tests, also differed. In our opinion, these results were determined by the nature of the solution used; although sodium chloride is the predominant salt in sea water, the presence of other ions modifies its solubility, thereby varying the dynamics of mobility and precipitation and thus the weathering morphology that develops. Copyright © 2003 John Wiley & Sons, Ltd.     

Frost weathering and the saturation of coastal rocks

Measurements were made of the water content in coastal rocks, by simulating tidal oscillations in the laboratory, and by field measurement in eastern Canada. If rapid freezing takes place upon exposure to the air, saturation levels may be high enough to permit frost weathering in fine grained rocks in the lower portions of the intertidal zone. Near the high tidal level, however, it may be dependent upon a supply of water from the ice foot and from melting snow. If freezing is slow, frost action may be inhibited by desorption of the rocks while they are exposed by the ebb tide. There was no evidence of a level of permanent sea water saturation within the intertidal zone. Ambient temperature and humidity may affect the rate of rock desorption.     

Weathering of granite in Antarctica: I. Light penetration into rock and implications for rock weathering and endolithic communities

Where rocks are composed of translucent minerals, light penetrates the rock and, in so doing, impacts on the thermal conditions. Where minerals are not translucent all the heat transformation must be at the rock surface, and steep thermal gradients can occur. Where light does penetrate, a component of the incoming radiation is transformed to heat at differing depths within the rock, thereby decreasing the thermal gradient. Equally, light transmissive minerals facilitate endolithic communities, which can also play a role in rock weathering. The attribute of light transmission within rock and the impact this has on the resulting thermal conditions has not been considered within rock weathering studies. An attempt was made to monitor the amount of light penetrating the outer 2 mm of coarse granite under Antarctic summer conditions and to evaluate the thermal impact of this. It was found that the amount of light penetration at this site exceeded modeled or postulated values from biological studies and that it could significantly impact the thermal conditions within the outer shell of the rock. Although the resulting data highlighted a number of flaws in the experimental procedure, sufficient information was generated to provide the first assessment of the range of thermal responses due to light transmissive minerals in rock. Copyright © 2007 John Wiley & Sons, Ltd.     

Sr isotope evolution during chemical weathering of granites -- impact of relative weathering rates of minerals

The Sr isotopic systematics in the weathering profiles of biotite granite and granite porphyry in southern Jiangxi Province were investigated. The results showed that during the chemical weathering of granites, remarked fractionation occurred between Rb and Sr. During the early stages of chemical weathering of granites, the released Sr/Si and Sr/Ca ratios are larger than those of the parent rocks, and the leaching rate of Sr is higher than those of Si, Ca, K, Rb, etc. Dynamic variations in relative weathering rates of the main Sr-contributing minerals led to fluctuation with time in 87Sr/86Sr ratios of inherent and released Sr in the weathering crust of granite. Successive weathering of biotite, plagioclase and K-feldspar made 87Sr/86Sr ratios in the weathering residues show such a fluctuation trend as to decrease first, increase, and then decrease again till they maintain stable. This work further indicates that when Sr isotopes are used to trace biogeochemical processes on both the catchment and global scales, one must seriously take account of the prefer-ential release of Sr from dissolving solid phase and the fluctuation of 87Sr/86Sr ratios caused by the variations of relative weathering rates of Sr-contributing minerals.     

The influence of solar‐induced thermal stresses on the mechanical weathering of rocks in humid mid‐latitudes

The role of solar‐induced thermal stresses in the mechanical breakdown of rock in humid‐temperate climates has remained relatively unexplored. In contrast, numerous studies have demonstrated that cracks in rocks found in more arid mid‐latitude locations exhibit preferred northeast orientations that are interpreted to be a consequence of insolation‐related cracking. Here we hypothesize that similar insolation‐related mechanisms may be efficacious in humid temperate climates, possibly in conjunction with other mechanical weathering processes. To test this hypothesis, we collected rock and crack data from a total of 310 rocks at a forested field site in North Carolina (99 rocks, 266 cracks) and at forested and unforested field sites in Pennsylvania (211 rocks, 664 cracks) in the eastern United States. We find that overall, measured cracks exhibit statistically preferred strike orientations (47° ± 16), as well as dip angles (52° ± 24°), that are similar in most respects to comparable datasets from mid‐latitude deserts. There is less variance in strike orientations for larger cracks suggesting that cracks with certain orientations are preferentially propagated through time. We propose that diurnally repeating geometries of solar‐related stresses result in propagation of those cracks whose orientations are favorably oriented with respect to those stresses. We hypothesize that the result is an oriented rock heterogeneity that acts as a zone of weakness much like bedding or foliation that can, in turn, be exploited by other weathering processes. Observed crack orientations vary somewhat by location, consistent with this hypothesis given the different latitude and solar exposure of the field sites. Crack densities vary between field sites and are generally higher on north‐facing boulder‐faces and in forested sites, suggesting that moisture‐availability also plays a role in dictating cracking rates. These data provide evidence that solar‐induced thermal stresses facilitate mechanical weathering in environments where other processes are also likely at play. Copyright © 2015 John Wiley & Sons, Ltd.     

Thermal weathering of granite spheroidal boulders in a dry‐temperate climate,Northern Dobrogea,Romania

Weathering microforms associated with exfoliation were investigated on 40 granitic spheroidal boulders identified on Pricopan Ridge (M?cin Mountains) in order to establish a spatial distribution pattern. Continuous thermal monitoring allowed the frequency and intensity distribution assessment of short‐term temperature changes triggered by summer storms, of intense day–night amplitudes and frost cycles across a uniform rounded boulder. Rock strength estimated by Schmidt hammer tests differentiates a significantly weaker resistance on the southern face of the boulders (rebound values of 27 to 33) in comparison with the northern face (43–50). The lowest resistance of the north–south cross‐boulder profile corresponds to the southern gentle slopes (0°–45°) thus defining the most susceptible area to exfoliation and other weathering processes. It is argued that this low‐resistant sector fits well with the maximum frequency and intensity of thermal processes recorded on the low and mid slopes (0°–45°) of the boulders south side, with small differences from one process to another, whilst the sector of 20° to 30° south corresponds to the peak activity of all. In accordance, the overlay map of exfoliated surfaces places the high frequency area on a spherical cap developed similarly (between 5° north and 45° south). The smallest exfoliated surfaces normally appear around 30° south and are inferred to extend in time both to the boulder top and downslope. The correlations between the frequency/intensity maps of thermal processes and the frequency map of exfoliated surfaces point to a complementary action in the exfoliated surfaces development of the short‐term temperature changes and diurnal cooling and heating due to the directional insolation effect, as similarly inferred in the development of meridional cracks. Copyright © 2016 John Wiley & Sons, Ltd.     

Rock temperatures as an indicator of weathering processes affecting rock art

To aid rock art conservation, rock temperatures have been monitored at different depths and at low (30 min) and high (1 min) acquisition rates in a painted rock shelter in the uKhahlamba‐Drakensberg Park (South Africa). Preliminary data for winter (cold and dry) show that in that season cryoclasty is unlikely to occur (rare subzero thermal events and probable reduced moisture availability) and thermal shocks are improbable (highest measured ΔT/Δt < 2 °C min^?1). High amplitude (about 30 °C) rock temperature cycles accompanied by reversals of the thermal gradient have been observed to occur almost daily and hint at the possibility of thermal stress fatigue. Copyright © 2006 John Wiley & Sons, Ltd.     

Some observations on the chemical weathering of the Dartmoor granite

The majority of geomorphological papers about Dartmoor have been essentially speculative, particularly when discussing weathering processes and the evolution of the Dartmoor landscape. In contrast, this article presents a synthesis of several experimental investigations aimed at studying the chemical weathering of Dartmoor granite through the systematic analysis of soil and water samples. This involved the computation of a geochemical budget to determine the amount of erosion in the catchment, as well as more detailed mineralogical investigations within a soil profile. The annual output of solutes due to weathering was 116 kg ha^?1 a^?1 of which the majority was silica (93 kg ha^?1 a^?1). From an examination of the soil mineralogy, it was calculated that these solutes were derived from the dissolution of approximately 200 kg ha^?1 a^?1 plagioclase, 90 kg ha^?1 a^?1 biotite, and 40 kg ha^?1 a^?1 orthoclase. As well as the weathering of granite, there was also the production of kaolinite (150 kg ha^?1 a^?1) and gibbsite (0.02 kg ha^?1 a^?1). Analysis of the soil water chemistry confirmed that kaolinite was the stable mineral phase in the regolith, although in areas where interflow was the dominant mode of water movement, the solute composition was in equilibrium with both kaolinite and gibbsite. Examination of the clay mineralogy confirmed these results. The microtexture of quartz grains was examined by the scanning electron microscope as another means of investigating the hydrochemical environment in the soil. Silica was found precipitated on all the grains examined but the maximum amount occurred in the Bs horizon. This evidence showed that, firstly, the dissolution of aluminosilicate minerals is greater than that calculated by the chemical budget and, secondly, that models of granite weathering must take localized weathering in the soil profile into account. The final part of the paper highlights the limitations of calculating denudation rates for an entire catchment and stresses the need to consider weathering as a highly localized phenomenon, particularly where there are high volumes of interflow at hill crest sites. Observations on granite decomposition in the future should be quantitative in approach and be related to the local site conditions.     

Deterioration processes affecting prehistoric rock art engravings in granite in NW Spain

Prehistoric rock art sites are endangered despite conservation efforts. The lack of scientific documentation regarding weathering agents affecting rock art and the absence of specific diagnostic protocols hinder the development of conservation strategies. The aim of this research was to investigate active deterioration processes in a granite petroglyph site located in Mougás (Galicia, NW Spain) by characterizing the granite, conducting a geotechnical study of the outcrop and describing and analysing the main weathering processes. Two main deterioration factors were identified. First, water favours block disjunction at the massif scale and causes pitting and surface erosion at the millimetre scale that affects the readability of the engravings. Second, high temperatures associated with wildfires cause mineral transformations that increase the susceptibility of the rock to weathering. Identifying deterioration factors is a first step in developing appropriate preventive conservation measures, which should aim to reduce rock contact time with water (technically affordable in the short term) and to reduce the probability of wildfire occurrence (technically more complex and possibly with longer‐term results). Copyright © 2018 John Wiley & Sons, Ltd.     

Incipient weathering rind development on introduced machine‐polished granite discs in an Arctic alpine environment,northern Scandinavia

Weathering rinds, zones of alteration on the exterior surfaces of rock outcrops and coarse unconsolidated surficial debris are widely used by geomorphologists and Quaternary geologists as indicators of the relative age of landforms and landscapes. Additionally they provide unique insights into the earliest stages of rock and mineral weathering, yet the origin of these alteration zones is relatively poorly understood. This lack of understanding applies especially to the initial stages of rind formation. The study reported in this paper has two principal objectives. The first is to use lightly polished granite discs inserted in soil profiles under several different plant communities in an Arctic alpine environment for a period of four or five years to investigate the nature of incipient weathering rind development. The second is to investigate the factors responsible for spatial variability in the nature and rates of rind formation. Incipient weathering rind development on the outer edges of the granite discs is observable and measurable over a period of time as short as four years in the mild Arctic alpine environment of Swedish Lapland. The earliest stages of rind development involve the development of a porous structure consisting of a combination of pits and fractures which have been solutionally enlarged and modified. Solution appears to be preferentially concentrated on the surfaces of feldspars and, to a lesser extent, quartz. In addition, iron oxides are present along grain boundaries and in grain interiors and are interpreted to have been derived from the oxidation of ferromagnesian minerals. Spatial variability in weathering rind development appears to be particularly driven by differences in moisture but is not related to soil pH. Copyright © 2005 John Wiley & Sons, Ltd.