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The Neogene quartz andesites from the Oa? and Gutâi Mountains (Romania) are mid-K calc-alkaline rocks and contain plagioclase-orthopyroxene-clinopyroxene-amphibole-magnetite phenocrysts as well as quartz crystals. They are associated with a volcanic sequence ranging from basalts and basaltic andesites to dacites and rhyolites, but form a separate magma group, mostly in respect to the trace elements. Based on the geochemical data combined with inferences from complex zoning patterns in plagioclase and pyroxene, the evolution of quartz andesites is interpreted in terms of fractional crystallization, AFC and magma mixing. A parental magma deriving from a MORB- or OIB-type source modified by fluids and melts originating from sediments is envisaged. 相似文献
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Influence of anthropogenic land‐use change on hillslope erosion in the Waipaoa River Basin,New Zealand 
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下载免费PDF全文 European settlement of the Poverty Bay Region resulted in deforestation and conversion of > 90% of the landscape to pastureland. The resulting loss of vegetation triggered a rapid increase in hillslope erosion as widespread landslide complexes and gully systems developed on weak lithologic units in the Waipaoa Basin. To quantify the rate and volume of historic hillslope degradation, we used a 1956–2010 sequence of aerial photographs for a ~16 km2 catchment to map temporal changes in the spatial extent of active landslides. Then we created a ‘turf index’ based on the extent and style of pastoral ground disruption, which correlates with downslope velocity. Based on the movement of trees and other features, we assigned average velocities to the turf classes as follows: (1) minimal disrupted ground: 0.6 m/yr, (2) a mix of disrupted ground and intact blocks: 3.4 m/yr, and (3) no intact blocks or vegetation: > 6 m/yr. We then calculated the average annual sediment flux using these turf‐derived velocities, the width of the landslide‐channel intersection, and an average toe depth of 4.4 ± 1.3 m (mean ± standard deviation [SD]) from 37 field measurements. The resulting catchment averaged erosion rates are (mean ± SD): 29.9 ± 12.9 mm/yr (1956), 28.8 ± 13.7 mm/yr (1969), 13.4 ± 4.9 mm/yr (1979), 17.0 ± 6.2 mm/yr (1988), and 9.9 ± 3.6 mm/yr (2010). Compared with long‐term (post‐18 ka) erosion rates (1.6 mm/yr) and the long‐term uplift rate (~1 mm/yr) for this site, the 50‐year anthropogenically‐driven rate is an order of magnitude larger (~20 mm/yr). Previously, we measured an increase in erosion over the past 3.4 kyr (2.2 mm/yr), and here, we demonstrate this increase could be primarily due to human land‐use change – showing that a century of rapid erosion superimposed on the background geologic rate can profoundly skew the interpretation of erosion rates. Copyright © 2016 John Wiley & Sons, Ltd. 相似文献
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Dengsheng Lu Guiying Li Emilio Moran Mateus Batistella Corina C. Freitas 《ISPRS Journal of Photogrammetry and Remote Sensing》2011,66(6):798-808
This research explored the integrated use of Landsat Thematic Mapper (TM) and radar (i.e., ALOS PALSAR L-band and RADARSAT-2 C-band) data for mapping impervious surface distribution to examine the roles of radar data with different spatial resolutions and wavelengths. The wavelet-merging technique was used to merge TM and radar data to generate a new dataset. A constrained least-squares solution was used to unmix TM multispectral data and multisensor fusion images to four fraction images (high-albedo, low-albedo, vegetation, and soil). The impervious surface image was then extracted from the high-albedo and low-albedo fraction images. QuickBird imagery was used to develop an impervious surface image for use as reference data to evaluate the results from TM and fusion images. This research indicated that increasing spatial resolution by multisensor fusion improved spatial patterns of impervious surface distribution, but cannot significantly improve the statistical area accuracy. This research also indicated that the fusion image with 10-m spatial resolution was suitable for mapping impervious surface spatial distribution, but TM multispectral image with 30 m was too coarse in a complex urban–rural landscape. On the other hand, this research showed that no significant difference in improving impervious surface mapping performance by using either PALSAR L-band or RADARSAT C-band data with the same spatial resolution when they were used for multi-sensor fusion with the wavelet-based method. 相似文献
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János Kovács Szabolcs Á. Fábián Gábor Varga Karoly Németh Corina Risso Francisco Nullo Gabor Kereszturi Titusz Bugya Szabolcs Á. Fábián Noémi L. Görcs István P. Kovács Bertalan Radvánszky Gabriella Barta Rudolf Musil Alice Ghiselli Marzio Merazzi Andrea Strini Roberto Margutti Michele Mercuriali Rauf Gardashov Daria Gushchina Boris Dewitte Martin Michálek Marián Putiš Christoph A. Hauzenberger Jindřich Šancer Martin Štrejbar Aneta Maleňáková George Migiros George D. Bathrellos Hariklia D. Skilodimou Theodoros Karamousalis 《Central European Journal of Geosciences》2011,3(2):229-229
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Gernot Arp Andreas Reimer Klaus Simon Sebastian Sturm Jakob Wilk Corina Kruppa Lutz Hecht Bent T. Hansen Jean Pohl Wolf Uwe Reimold Thomas Kenkmann Dietmar Jung 《Meteoritics & planetary science》2019,54(10):2448-2482
The 26 km diameter Nördlinger Ries is a complex impact structure with a ring structure that resembles a peak ring. A first research drilling through this “inner crystalline ring” of the Ries was performed at the Erbisberg hill (SW Ries) to better understand the internal structure and lithology of this feature, and possibly reveal impact‐induced hydrothermal alteration. The drill core intersected the slope of a 22 m thick postimpact travertine mound, before entering 42 m of blocks and breccias of crystalline rocks excavated from the Variscan basement at >500 m depth. Weakly shocked gneiss blocks that show that shock pressure did not exceed 5 GPa occur above polymict lithic breccias of shock stage Ia (10–20 GPa), with planar fractures and planar deformation features (PDFs) in quartz. Only a narrow zone at 49.20–50.00 m core depth exhibits strong mosaicism in feldspar and {102} PDFs in quartz, which are indicative of shock stage Ib (20–35 GPa). Finally, 2 m of brecciated Keuper sediments at the base of the section point to an inverse layering of strata. While reverse grading of clast sizes in lithic breccias and gneiss blocks is consistent with lateral transport, the absence of diaplectic glass and melt products argues against dynamic overthrusting of material from a collapsing central peak, as seen in the much larger Chicxulub structure. Indeed, weakly shocked gneiss blocks are rather of local provenance (i.e., the transient crater wall), whereas moderately shocked polymict lithic breccias with geochemical composition and 87Sr/86Sr signature similar to Ries suevite were derived from a position closer to the impact center. Thus, the inner ring of the Ries is formed by moderately shocked polymict lithic breccias likely injected into the transient crater wall during the excavation stage and weakly shocked gneiss blocks of the collapsing transient crater wall that were emplaced during the modification stage. While the presence of an overturned flap is not evident from the Erbisberg drilling, a survey of all drillings at or near the inner ring point to inverted strata throughout its outer limb. Whether the central ring of the Ries represents remains of a collapsed central peak remains to be shown. Postimpact hydrothermal alteration along the Erbisberg section comprises chloritization, sulfide veinlets, and strong carbonatization. In addition, a narrow zone in the lower parts of the polymict lithic breccia sequence shows a positive Eu anomaly in its carbonate phase. The surface expression of this hydrothermal activity, i.e., the travertine mound, comprises subaerial as well as subaquatic growth phases. Intercalated lake sediments equivalent to the early parts of the evolution of the central crater basin succession confirm a persistent impact‐generated hydrothermal activity, although for less time than previously suggested. 相似文献
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Corina Vogt Petrik Galvosas Norbert Klitzsch Frank Stallmach 《Journal of Applied Geophysics》2002,50(4)
The self-diffusion of water and hexadecane in medium and coarse sands from glacial sand deposits in central Germany were investigated by pulsed field gradient nuclear magnetic resonance (PFG NMR). Due to the restriction of the diffusion path at the pore/grain interface, the measured apparent self-diffusion coefficients (D(Δ)) in the pore space depend on the observation time (Δ) in the PFG NMR experiment. Although the bulk self-diffusion coefficients of water and hexadecane differ by about one order of magnitude, the apparent self-diffusion coefficients in the pore space obey the same characteristic time-behaviour, which depends only on geometrical properties of the pore system. Using the “short-time diffusion” model, surface-to-volume (S/V) ratios and inherent self-diffusion coefficients (D0) of the pore fluids were extracted from these diffusion measurements. The S/V ratios obtained are independent of the pore fluid used and agree with known geometrical properties of the sand grains. Moreover, the D0 values are consistent with the corresponding bulk self-diffusion coefficients measured separately. In contrast to these results of PFG NMR, simultaneous investigations of longitudinal (T1) nuclear magnetic relaxation reveal that the relaxation time of the pore fluid is a less suitable parameter for a quantitative estimation of geometrical properties of the pore/grain interface in these unconsolidated sediments since it depends on chemical properties of the fluid/grain interface. 相似文献
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The aim of this work was to evaluate the Salamanca Formation greensands as an alternative potassium fertilizer to KCl. Glauconitic pellets from this formation tend to naturally concentrate in 600–250 μm (BS 250) and 250–125 μm (BS 125) fractions. After dry sieving and magnetic separation, these fractions were used for chemical, lixiviation, and specific surface analyses and agronomic evaluations. Two concentrated products were obtained: GL250c (600–250 μm) and GL125c (250–125 μm) representing 40.9 % of total sample. GL250c contains 2.97 % K2O, and GL125c contains 4.05 % K2O, representing 27 and 60 % increase in K-content compared to the bulk sample. Grain size of both concentrates decreased significantly through lixiviation tests. Potassium release curves from lixiviation waters show that K-liberation from GL250c was more effective in the first 15 days but decreased after that whereas liberation from GL125c continued to increase after 15 days probably due to higher K-content (36 % higher than GL250c). Specific area could have influenced liberation rates because after leaching it increased 27 % for the finer fraction and by only 16 % for the coarser one. From agronomic assays, measured over 75 days with five harvests, the first four harvests yield best results from KCl probably due to fast K-liberation rates from the salt. However, after overall harvests, fertilization efficiency using either GL250c or GL125c was very similar to and slightly higher than KCl fertilization. As equivalent results were found using either GL250c or GL125c, sieving to obtain these fractions seems not necessary. The results indicate that greensands from the Salamanca Formation are effective slow release alternative K source for fertilizers with low cost of production and treatment compared to operation costs required for mining K soluble salts at depth. 相似文献
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Lorella Montrasio Roberto Valentino Angela Corina Lauro Rossi Roberto Rudari 《Natural Hazards》2014,74(2):1263-1290
In the last decades, physically based distributed models turned out rather promising to achieve the space–time assessment of shallow landslides at large spatial scale. This technical note deals with the application of a physically based stability model named Shallow Landslides Instability Prediction (SLIP), which has been adopted by the Department of National Civil Protection of Italy as a prototype early warning system for rainfall-induced shallow landslides on national scale. The model is used as a main methodology to create space–time shallow landslide susceptibility maps based on a simple deterministic slope-stability approach, combined with high-resolution rainfall information and geographic information system-based geospatial datasets. The safety factor as an index to measure slope instability is modeled as function of topographic, geologic, geotechnical and hydrologic variables. Although the main aim of this work was to prove the operational viability of such model on a nationwide domain and some simplification are adopted at this stage, hind cast tests on some relevant case histories of shallow landslides occurred between October 2009 and October 2011 showed that the model has skill in representing both timing and location of those shallow landslides. 相似文献
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M.J. Orgeira L.N. Castro G.A. Goldmann C.B. Prezzi E. Sileo D.R. Vega C. Franzosi R.D. Acevedo O. Martínez J. Rabassa J.F. Ponce O.R. Tófalo 《地学前缘(英文版)》2017,8(1):137-149
The Quaternary infilling of a circular structure located in Bajada del Diablo, Chubut Province, Argentina has been proposed as a crater strewn field in previous studies. Here we report the finding of about 65 microspherules collected in a trench excavated in the center of the structure. The majority of hand-picked specimens are single, but some of them exhibit compound forms. The single specimens are spherical with a mean size of 137 μm, whereas the more complex samples show peduncles and drop shapes. Dendritic crystal growth is recognized in the internal structure of some broken microspherules. Preliminary chemical composition from the surface and center of microspherules was determined by energy dispersive spectrometry employing EDS. Quantitative EMPA and XRD analysis indicate that the microspherules are mainly composed of Fe and O with magnetite, Fe0 with subordinate wüstite. Following consideration of possible anthropogenic and volcanic origins, these spherulites are ascribed to an extraterrestrial input. An accumulation rate of 47 microspherules per m2/yr is estimated for the studied sediments. This value is two orders of magnitude higher than the reference flux for cosmic dust estimated for the last 1 Ma in the Transantarctic Mountains. The microspherules might have been generated as a byproduct of asteroid entry in the atmosphere. 相似文献