The Alpine-Carpathian-Dinaridic orogenic system: correlation and evolution of tectonic units   总被引：8，自引：0，他引：8  

Stefan M. Schmid  Daniel Bernoulli  Bernhard Fügenschuh  Liviu Matenco  Senecio Schefer  Ralf Schuster  Matthias Tischler  Kamil Ustaszewski 《Swiss Journal of Geoscience》2008,101(1):139-183

  相似文献   

The contribution of lateritization processes to the formation of the kaolin deposits from eastern Amazon     

Marcondes Lima da Costa  Daniel José Lima Sousa  Rômulo Simões Angélica 《Journal of South American Earth Sciences》2009,27(2-3):219-234

The eastern region of the Amazon is home to the most important kaolin bauxite producing district in Brazil, referred to as the Paragominas-Capim kaolin bauxite district, which has a reserve of at least 1.0 billion tons of high-quality kaolin used in the paper coating industry. The kaolin deposits are closely related to sedimentary rocks of the Parnaíba basin and their lateritic cover. Two large deposits are already being mined: IRCC (Ipixuna) and PPSA (Paragominas). The geology of the IRCC mine is comprised of the kaolin-bearing lower unit (truncated mature laterite succession derived from the Ipixuna/Itapecuru formation) and the upper unit (immature lateritized Barreiras formation). The lower kaolin unit is characterized by a sandy facies at the bottom and a soft (ore) with flint facies at the top. It is formed by kaolinite, quartz, some iron oxi-hydroxides, mica and several accessories and heavy minerals. The <2 μm kaolinite crystallites only correspond to 41.3–58.3% of the soft kaolin, and large booklets of 15–300 μm are common. The degree of structure order of kaolinite decreases towards the flint kaolin. The chemical composition of the soft kaolin is similar to the theoretical chemical composition of kaolinite, with low iron content, and can be well correlated to most kaolin deposits in the region. The distribution pattern of chemical elements from sandy to flint kaolin (lower unit) suggests a lateritic evolution and erosive truncation. This is quite distinct from the upper unit, which has a mineralogical and chemical pathway relating it to a complete immature lateritic profile. The geological evolution of the IRCC kaolin is similar to that of other deposits in the eastern Amazon region, being comprised of: parent rocks formed in an estuarine marine and fluvio-laccustrine environment during the early Cretaceous; establishment of mature lateritization with the formation of kaolin in the Eocene; marine transgression and regression – (Pirabas and Barreiras formation) with kaolin profile erosion and forward movement of deferruginization and flintization during the Miocene after partial mangrove covering; and immature lateritization – partial kaolin ferruginization during the Pleistocene.  相似文献   

Annealing of far infrared photoconductors with infrared diode lasers     

U. Schießl  M. Tacke  J. Wolf  D. Lemke 《Experimental Astronomy》1991,2(3):139-148

High sensitivity infrared detectors made from extrinsic semiconductors are used for astronomical applications on satellite missions in the earth orbit. High energy radiation reduces the sensitivity and changes the calibration of these photoconductors drastically. This process is reversible through on board annealing. Laser emission of mid infrared diode lasers was used for efficient annealing with low power dissipation.  相似文献   

Saturated permeability measurements on pumice and welded-tuffaceous materials     

Reda  Daniel C.  Hadley  G. Ronald 《Environmental Geology》1986,8(3):137-145

Fluid flows in consolidated porous media of volcanic origin are being investigated to support such diverse efforts as the modeling of thermal/outgassing phenomena at Mount St. Helens and the hydrological modeling of tuffaceous rocks in support of the Department of Energy’s (DOE) Nevada Nuclear Waste Storage Investigations Project An experimental apparatus was designed and built to allow water-saturated permeabilities as low as 10⁻¹⁸ m² to be measured on cores of diameter 5 cm and length 10 cm under steady-state flow conditions. This same apparatus can also be utilized in a transient (pressure-decay) mode in order to measure permeabilities several orders of magnitude lower than the steady-state limit. Tests were conducted on samples of pumice, fractured welded tuff, and welded tuff, representing a permeability range of seven orders of magnitude Pumice was found to have a permeability of ∼3×10⁻¹² m², sufficiently high to allow the complete Darcy-to-Ergun regime to be investigated Welded (unfractured) tuff was tested in the transient mode, yielding a permeability of ∼5×10⁻¹⁹ m². Two, long-time-scale, steady-flow experiments were conducted on a core of welded tuff containing a single, through-going fracture. For the first experiment, the core was an integral cylinder containing a naturally occurring fracture. For the second experiment, the core was separated into two pieces along the existing fracture plane, then rejoined. Effects of essentially constant, as well as rapidly varied, circumferential stress were studied in both tests. Results showed core permeability to decay to 2×10⁻¹⁸ m² in both cases, independent of the initial fracture state (closed versus open). With a naturally occurring fracture, core permeability decreased by a factor of 2 over a 200-h test period. With an initially open fracture, core permeability decreased by a factor of 4 under the influence of a comparable 200-h load-time history, after 700 h of testing, core permeability was reduced by an order of magnitude from its initial level. Final effective hydraulic fracture aperture was calculated to be 10⁻⁶ m, corresponding to a calculated effective fracture permeability of 10⁻¹³ m² Fracture flow was thus estimated to account for 80% of the total flow rate through this core under final test conditions.  相似文献   

Patterned fen development in northern Scotland: Hypothesis testing and comparison with ombrotrophic blanket peats     

Daniel J. Charman 《第四纪科学杂志》1995,10(4):327-342

Patterned fens are part of the diverse Holocene peatland landscape of the Flow Country, northern Scotland. Their present vegetation and morphology allies them with boreal systems in Scandinavia and North America. However, previous work has shown that their mode of formation is rather different and has suggested a developmental model in which the poor fens have formed only recently and have arisen as a result of local hydrological change. These ideas are tested here by morphological, stratigraphical and macrofossil studies on three additional patterned fens covering a wider geographical and ecological range. Two sites corroborate the hypotheses of the earlier study, and one site which refutes the earlier findings can be shown to be dependent on different topographic controls. A comparison of two patterned fens with an ombrotrophic mire site in the same area shows that hydroseral processes dominate the early development of individual components of the mire complex. The time of initiation of patterned fens coincides with increasing surface wetness on the ombrotrophic mire. This may be due to climatic change and/or the coalescence of the constituent parts of the present integrated blanket mire system. The hydrological changes arising from this led to the emergence of the springs that currently supply the patterned fens with their water and elevated nutrient levels. The study supports the idea that landscape-scale research and conservation are essential for the understanding and hydrological integrity of blanket mire landscapes such as the Flow Country.  相似文献   

New clues on the calcium underabundance in early-type galaxies     

Daniel Thomas  Claudia Maraston  Ralf Bender 《Monthly notices of the Royal Astronomical Society》2003,343(1):279-283

  相似文献   

The clustering of luminous red galaxies in the Sloan Digital Sky Survey imaging data     

Nikhil Padmanabhan  David J. Schlegel  Uro&#; Seljak  Alexey Makarov  Neta A. Bahcall  Michael R. Blanton  Jonathan Brinkmann  Daniel J. Eisenstein  Douglas P. Finkbeiner  James E. Gunn  David W. Hogg  &#;eljko Ivezi&#;  Gillian R. Knapp  Jon Loveday  Robert H. Lupton  Robert C. Nichol  Donald P. Schneider  Michael A. Strauss  Max Tegmark  Donald G. York 《Monthly notices of the Royal Astronomical Society》2007,378(3):852-872

  相似文献   

Age constraints on the evolution of the Austroalpine basement to the south of the Tauern Window   总被引：1，自引：0，他引：1  

Siegfried Siegesmund  Till Heinrichs  Rolf L. Romer  Daniel Doman 《International Journal of Earth Sciences》2007,96(3):415-432

The Austroalpine basement to the south of the Tauern Window once was part of the northern margin of Gondwana. It includes the “Altkristallin” and the phyllitic Thurntaler Complex. In the Altkristallin (AMU, MPU), suites of arc-related metamafic sequences occur together with calc-alkaline metagranite. SHRIMP U–Pb dating of zircon from calc-alkaline metagranite associated with an eclogitic amphibolite give an age of 470 ± 3 Ma interpreted as the age of protolith emplacement. In the Thurntaler Complex, metaporphyroids occur together with tholeiitic as well as alkaline within-plate basalt-type metabasite. The metaryholites of this association give a crystallization SHRIMP age of 477 ± 4 Ma, which suggests contemporaneity of arc-related and extensional settings in the Austroalpine basement units. The age data demonstrate widespread magmatic activity associated with the Early-Ordovician amalgamation at the end of the 550–470 Ma subduction–accretion–collision cycle. The Pb–Pb and U–Pb systematics of step-wise leached staurolite and kyanite from the peak-metamorphic assemblage of the Altkristallin indicate that (1) step-wise leaching of staurolite and kyanite yields the age of inclusions rather than the host; (2) zircon inclusions in staurolite suggest an Ordovician or older age for the precursor of the staurolite-schists; (3) the weighted average of the ²⁰⁶Pb/²³⁸U data of the various leaching steps yields a Variscan age for the inclusions (ilmenite, biotite, and andesine). Since these inclusions are part of the metamorphic mineral assemblage, this age provides a minimum estimate for staurolite growth, i.e., metamorphism. Thus, the Pb–Pb and U–Pb systematics of staurolite provide evidence for a Variscan metamorphism of the Austroalpine basement, e.g., MPU, AMU and Thurntaler Complex, to the south of the Tauern Window.  相似文献   

Evolution of the Peak Hill high-sulfidation epithermal Au–Cu deposit,eastern Australia     

Richard J. Squire  Walter Herrmann  Daniel Pape  D. Ian Chalmers 《Mineralium Deposita》2007,42(5):489-503

The early Palaeozoic Macquarie Arc, southeastern Australia, hosts a variety of major late Ordovician to earliest Silurian subduction-related deposits (e.g., Cadia East, Ridgeway, Cadia Hill, Cowal and Northparkes). However, there is uncertainty about whether coeval high-sulfidation epithermal deposits, which occur in intra-oceanic metallogenic belts elsewhere in the West Pacific, (e.g., Lepanto and Chinkuashih), are also present in the Macquarie Arc. This has led to suggestions that their absence may be due to the poor preservation potential of deposits that form at relatively shallow crustal levels in ancient rocks. We present here an interpretation for evolution of the Peak Hill Au–Cu deposit based on the distribution of alteration facies, sulfur isotope data from several textural forms of pyrite and barite, and an assessment of the regional volcanic and sedimentary facies architecture. These data show that the Peak Hill deposit displays a distinct sub-vertical zoning with a pyrophyllite and vuggy-quartz core, that today extends about 350 m east–west and at least 550 m north–south, which grades out through paragonite+muscovite, kaolinite to a chlorite+epidote alteration zone at the margin. The alteration zoning reflects both lower temperatures and neutralisation of acid fluids with increasing distance from the core, which represents the conduit along which hot acidic hydrothermal fluids were channelled. Several temporally overlapping events of silicification, bladed-quartz-pyrite veining, brecciation and pyrite veining occurred during the last stages of hydrothermal alteration, although most appear to predate mineralisation. Au–Cu mineralisation was associated with late quartz-pyrite-barite veins, and the highest gold grades occur mainly in microcrystalline-quartz-altered rocks in the paragonite+muscovite alteration zone, generally within 50 m outward from the boundary of the pyrophyllite and vuggy-quartz core. Sulfur- and lead-isotope data, and the characteristic zoning of ore minerals and alteration assemblages support a magmatic source for the hydrothermal fluids. Similarities in many of the isotopic signatures between Peak Hill and deposits such as Northparkes support generation of the high-sulfidation mineralisation during the Late Ordovician to earliest Silurian (possibly ca. 440 Ma) metallogenic event. The Late Ordovician to Early Silurian volcanic and sedimentary facies associations at Peak Hill are consistent with alteration and mineralisation occurring in rocks deposited in a submarine setting.  相似文献   

Geochemistry of lead contaminated wetland soils amended with phosphorus     

Daniel G. Strawn  Patrick Hickey  Andrew Knudsen  Leslie Baker 《Environmental Geology》2007,52(1):109-122

To remediate Pb contaminated soils it is proposed that phosphorus can be amended to the soils to transform the Pb into poorly soluble Pb-phosphate mineral phases. However, remediation strategies must account for variable Pb speciation and site-specific factors. In this study soil mineralogy and Pb speciation in soils from P-amended field trials at sites within the Coeur d’Alene River Basin in Idaho, USA were investigated. The soils are contaminated from mining activities and are enriched with Fe and Mn. Selective extraction of the soils indicated that the Fe oxides are poorly crystalline. XRD of the soil clay size fractions identified quartz, muscovite, kaolinite, siderite, lepidocrocite, and chlorite minerals. Amendment with P fertilizer dissolved the siderite. No Pb–phosphate minerals were detected by XRD. Electron microprobe analysis showed direct correlations between Pb, Fe, and Mn in the unamended soils, and negative correlations between Pb and Si. Lead and Mn were strongly correlated. In the amended soils Fe and P were strongly correlated. Results indicate that the Pb is associated with poorly crystalline Fe and Mn oxides, and that added P is primarily associated with Fe oxide phases. Comparisons of pore water Pb concentrations with chloropyromorphite and plumbogummite solubility suggest that in the phosphate-amended soils the pore waters are undersaturated in these phases, whereas several of the control soil pore waters were oversaturated, indicating the added phosphate suppressed the Pb solubility. Results from this research provide insight into the geochemistry occurring in the P-remediated soils that will help in making management and remediation decisions.  相似文献