Magnetostratigraphy and environmental magnetism in a Pleistocene sedimentary sequence, Marcos Paz, Argentina     

Juan Carlos Bidegain  S. Jurado  M. A. E. Chaparro  M. Gómez Samus  S. Zicarelli  A. V. Parodi 《Environmental Earth Sciences》2013,68(3):749-763

The deterioration of groundwater quality, particularly due to salinization, because of the overexploitation of groundwater in the Lower Central Plain of Thailand remains a major concern. With increasing demand for water there is a growing need for sustainable management of the resource, which would benefit from an improved understanding of the sources of chloride contamination. Thus, a hydrochemical and isotopic study was carried out to chemically characterize groundwater and to investigate possible sources of salinization, and in particular of chloride contamination, in the multi-layered Bangkok aquifer system. Groundwater samples were taken from four topmost aquifers (Bangkok, Phra Pradaeng, Nakhon Luang, and Nonthaburi). Additionally, short-term rainwater sampling, as well as river and seawater sampling was performed and later analyzed for ionic composition and stable water isotopes. Ionic and isotopic data indicate at least three different recharge sources for groundwater. The major recharge source is rainwater. The influence of seawater is limited to the coastal region and tidally influenced areas of the two main rivers (Chao Phraya and Tha Chin). Bromide data also suggest the influence of saline water in deeper aquifers due to trapped water. Most importantly, although the influence of seawater on groundwater is recognizable, the surrounding geology contributes a significant number of dissolved ions detected in the groundwater.  相似文献   

Criterion for flow liquefaction instability     

José E. Andrade  Alfonso M. Ramos  Arcesio Lizcano 《Acta Geotechnica》2013,8(5):525-535

This study describes a general liquefaction flow instability criterion for elastoplastic soils based on the concept of loss of uniqueness. We apply the criterion to the general case of axisymmetric loading and invoke the concepts of effective stresses and loss of controllability to arrive at a general criterion for the onset of liquefaction flow. The criterion is used in conjunction with an elastoplastic model for sands to generate numerical simulations. The numerical results are compared with experimental evidence to give the following insights into predicting liquefaction. (1) The onset of liquefaction flow is a state of instability occurring under both monotonic and cyclic tests, and coincides with loss of controllability. (2) The criterion proposed herein clearly and naturally differentiates between liquefaction flow (instability) and cyclic mobility. (3) Flow liquefaction not only depends on the potential of the material to generate positive excess pore pressures, but more importantly, it also depends on the current state of the material, which is rarely predicted by phenomenology.  相似文献   

大别地块东南缘变质P-T条件及锆石U-Pb年代学研究     

石永红  王娟  康涛  徐旭峰 《岩石学报》2013,29(5):1540-1558

大别山东南缘高压-超高压地块一直为研究的热点地区,人们普遍认同其是由2个具有不同变质级别的单元构成,并以此为基点探讨大别造山带的俯冲、折返机制.然而,由于工作程度所限,对于大别山腹地店前-寺前-罗溪地区一直缺乏详细的资料,对其确实的变质属性及年龄并不清晰,限制了人们对该地区客观的结构单元划分的准确理解.本次通过区域变质岩石学和年代学的研究,详实地分析了该地块的结构构成.研究显示,大别山东南缘高压-超高压地块由2个超高压单元和1高压单元构成,并呈岩石-构造岩片形式相互叠置,其变质P-T条件分别为:(1)单元-Ⅰ:-T=723±22℃和-P=3.90±0.43GPa(金刚石稳定域);(2)单元-Ⅱ:-T=630 ±45℃和P=3.10 ±0.23GPa(柯石英稳定域);(3)单元-Ⅲ:-T=545±24℃和-P=2.48±0.11GPa(石英稳定域).锆石U-Pb年龄表明这三个单元具有穿时性,形成于不同的时间段,自单元-Ⅰ、单元-Ⅱ至单元-Ⅲ,年龄分别为226.4±2.6Ma→230.1±3.5Ma→235.2±4.2Ma年龄(徐旭峰等,2013).在空间分布上自北向南,总体的峰期变质P-T条件逐渐降低,年龄则逐渐变老.但由于风化剥蚀作用,在马龙-石马一线的单元-Ⅰ以构造窗形式产出,致使P-T条件呈现跳跃性的变化.石永红等:大别地块东南缘变质P-T条件及锆石U-Pb年代学研究  相似文献   

郯庐断裂东侧肥东地块变质属性及年代学研究   总被引：5，自引：5，他引：0  

康涛  刘晓燕  王娟  聂峰  石永红 《岩石学报》2013,29(9):3142-3158

肥东地块是郯庐断裂带中段的一个极为重要的变质地块,其变质属性和构造归属的精确标定对探究郯庐断裂的形成与演化极为关键。然而,直至目前对于该地块的区域性的变质岩石学研究极为匮乏,制约了人们对于该断裂的深入理解。为此,本研究对肥东地块进行了较为系统的野外地质调查、区域变质岩石学、岩相学、热力学和年代学的分析。研究显示,肥东地块自西向东主要由单元-I、II和III构成,主要岩石类型为花岗片麻岩、黑云斜长片麻岩、角闪斜长片麻岩,其间含少量的石榴黑云斜长片麻岩和斜长角闪岩。P-T条件评价显示,肥东地块的变质高峰期温压条件为610~690℃、0.61~0.81GPa,平均P-T条件分别656±25℃、0.71±0.06GPa,变质峰期属于角闪岩相。锆石U-Pb定年则显示肥东地块的原岩形成年龄为809.2±6.7Ma,表明该地块属于扬子板块。结合前人构造地质学的研究及相关年龄数据,推测肥东地块与宿松变质杂岩应为相当层,它们目前的P-T差异可能是由于郯庐断裂的同俯冲平移错断所致。  相似文献   

宝鸡市簸箕山滑坡特征及治理对策     

王佳武  程增强  吕娟  王仲孝 《陕西地质》2013,(2):81-85

文中分析了宝鸡市簸箕山滑坡特征,提出了滑坡防治对策和治理措施.  相似文献   

综合地球物理方法在阜新市四合地区地热资源普查中的应用     

雷晓东  何祎  李娟 《城市地质》2013,(4):48-52

阜新市四合地区是地热资源勘查开发的空白区,为查明其地热资源赋存状况,采用了综合地球物理方法（重力勘探、磁力勘探、可控源音频大地电磁测深、大地电场岩性探测）,推断了断裂构造位置、热储层顶板埋深及温度范围,确定了工作区南部为勘探靶区,设计了勘探井位,为下一步钻探工作的开展,提供了重要依据。  相似文献   

Platinum-group elements, S, Se and Cu in highly depleted abyssal peridotites from the Mid-Atlantic Ocean Ridge (ODP Hole 1274A): Influence of hydrothermal and magmatic processes   总被引：1，自引：0，他引：1  

Claudio Marchesi  Carlos J. Garrido  Jason Harvey  José María González-Jiménez  Károly Hidas  Jean-Pierre Lorand  Fernando Gervilla 《Contributions to Mineralogy and Petrology》2013,166(5):1521-1538

Highly depleted harzburgites and dunites were recovered from ODP Hole 1274A, near the intersection between the Mid-Atlantic Ocean Ridge and the 15°20′N Fracture Zone. In addition to high degrees of partial melting, these peridotites underwent multiple episodes of melt–rock reaction and intense serpentinization and seawater alteration close to the seafloor. Low concentrations of Se, Cu and platinum-group elements (PGE) in harzburgites drilled at around 35–85 m below seafloor are consistent with the consumption of mantle sulfides after high degrees (>15–20 %) of partial melting and redistribution of chalcophile and siderophile elements into PGE-rich residual microphases. Higher concentrations of Cu, Se, Ru, Rh and Pd in harzburgites from the uppermost and lowest cores testify to late reaction with a sulfide melt. Dunites were formed by percolation of silica- and sulfur-undersaturated melts into low-Se harzburgites. Platinum-group and chalcophile elements were not mobilized during dunite formation and mostly preserve the signature of precursor harzburgites, except for higher Ru and lower Pt contents caused by precipitation and removal of platinum-group minerals. During serpentinization at low temperature (<250 °C) and reducing conditions, mantle sulfides experienced desulfurization to S-poor sulfides (mainly heazlewoodite) and awaruite. Contrary to Se and Cu, sulfur does not record the magmatic evolution of peridotites but was mostly added in hydrothermal sulfides and sulfate from seawater. Platinum-group elements were unaffected by post-magmatic low-temperature processes, except Pt and Pd that may have been slightly remobilized during oxidative seawater alteration.  相似文献   

Geochemical evidence for melting of carbonated peridotite on Santa Maria Island, Azores     

Christoph Beier  João Mata  Ferdinand Stöckhert  Nadine Mattielli  Philipp A. Brandl  Pedro Madureira  Felix S. Genske  Sofia Martins  José Madeira  Karsten M. Haase 《Contributions to Mineralogy and Petrology》2013,165(5):823-841

The islands of the Azores archipelago emerge from an oceanic plateau built on lithosphere increasing in age with distance from the Mid-Atlantic Ridge from 10 to 45 Ma. Here, we present the first comprehensive major and trace element and Sr–Nd–Pb isotope data from Santa Maria, the easternmost island of the archipelago, along with published data from the other Azores islands situated much closer to the Mid-Atlantic Ridge axis. We can show that the distinctively more variable and more enriched trace element ratios at Santa Maria combined with a relatively small range in Sr–Nd–Pb isotope ratios are the result of low degrees of partial melting of a common Azores mantle plume source underneath thicker lithosphere. This implies that melt extraction processes and melting dynamics may be able to better preserve the trace element mantle source variability underneath thicker lithosphere. These conclusions may apply widely for oceanic melts erupted on relatively thick lithosphere. In addition, lower Ti/Sm and K/La ratios and SiO₂ contents of Santa Maria lavas imply melting of a carbonated peridotite source. Mixing of variable portions of deep small-degree carbonated peridotite melts and shallow volatile-free garnet peridotite could explain the geochemical variability underneath Santa Maria in agreement with the volatile-rich nature of the Azores mantle source. However, Santa Maria is the Azores island where the CO₂-rich nature of the mantle source is more evident, reflecting a combination of a smaller extent of partial melting and the positioning at the edge of the tilted Azores mantle plume.  相似文献   

Granite emplacement by crustal boudinage: example of the Calmayo and El Hongo plutons (Córdoba,Argentina)     

Fernando D'Eramo  José M. Tubía  Lucio Pinotti  Néstor Vegas  Jorge Coniglio  Manuel Demartis  Aitor Aranguren  Miguel Basei 《地学学报》2013,25(5):423-430

This study deals with the structure and emplacement of the Calmayo and El Hongo trondhjemite plutons (Famatinian belt of Córdoba, Argentina). It provides structural data from the granites and the country rocks and a study of the magnetic fabric in the plutons. New U/Pb geochronological data yield intrusion ages of 512.1 ± 3.4 Ma and 500.6 ± 4.5 Ma for the Calmayo and El Hongo plutons respectively. The El Hongo massif and the southern part of the Calmayo trondhjemite preserve magmatic structures, whereas the northern domain of Calmayo shows the imprint of solid‐state deformation. The main foliation in the country rocks outlines a boudin‐like pattern at the map scale and the granites are located along boudin necks, suggesting that the emplacement of these trondhjemite plutons was linked to large‐scale boudinage of the country rocks.  相似文献   

2002年广东沿海赤潮与海洋水文气象关系的研究   总被引：2，自引：0，他引：2  

吴迪生  王文娟  俞胜宾  周水华  张娟 《热带气象学报》2011,27(2):271-277

根据2001年1月—2002年12月广东沿海赤潮实况与海洋水文气象要素的实测资料,分析了广东沿海赤潮发生与海洋水文气象关系。结果表明：在大万山海域出现六级强风的情况下仍然可以发生赤潮;中肋骨条藻(Skeletonema costatum,斜体表示拉丁文,下同)和无纹环沟藻(Gyrodinium instriatum)最大增殖速率的发生环境为：海水温度27.51～29.81 ℃、盐度20.06‰～31.94‰、气温22.7～30.4 ℃、风速0.3～12.0 m/s、气压995.9～1 002.0 hPa、相对湿度72%～98%;风速减弱、气压下降、水温和盐度升高、降水偏少是诱发赤潮大爆发的海洋环境因素。另外,2002年赤道太平洋发生的El Ni?o事件,导致中国东南沿海的水温、盐度、风速、相对湿度、气压及广东降水量发生异常变化,对赤潮的形成和发展有重要影响。  相似文献