Structure of volcanic glasses from the NMR-EPR perspective: a preliminary application to the Neapolitan Yellow Tuff     

R. Petrini  C. Forte  G. Contin  C. Pinzino  G. Orsi 《Bulletin of Volcanology》1999,60(6):425-431

Glass samples from alkali-trachytic pumice of the Lower Member (LM, level LM1) and Upper Member (UM) of the Neapolitan Yellow Tuff at Campi Flegrei Caldera were studied by nuclear magnetic resonance (NMR) and electron paramagnetic resonance (EPR) spectroscopy. The EPR data show that the relative occupancy of the different iron sites varies in samples from the Lower Member LM1 and Upper Member of the eruptive sequence. The LM1 glasses are characterized by a more homogeneous distribution of the cationic site population of iron compared with UM and by a different Fe³⁺/Al³⁺ substitution in the C_2v symmetrical sites of the silicate framework. ²⁹Si MAS NMR spectra on glasses indicate that LM1 glasses are more depolymerized than UM glasses, indicating the existence of structurally distinct magma batches. ²⁷Al MAS NMR spectra indicate the occurrence in UM glasses of aluminum in both tetrahedral and octahedral coordination; the observed Al^VI is believed to be a primary feature of the glass, since ²⁷Al CP-MAS NMR experiments do not reveal detectable esa-hydrated Al. The Al in sixfold coordination could be ascribed either to the more abundant alkali–OH terminations in UM, in which alkalies would be extracted from their charge-balance role for Al, thus altering its fourfold structural position, or to permanent compaction during fast cooling and decompression of high-pressure melts. ²³Na CP-MAS NMR experiments indicate the existence of Na–OH groups in both LM1 and UM glasses, relatively more abundant in the latter. Although preliminary, the results indicate the possible application of atomic-scale studies to variables that determine the regimes of explosive volcanism. Received: 1 July 1998 / Accepted: 1 October 1998  相似文献   

Quaternary drainage network reorganization in the Colombian Eastern Cordillera plateau     

Lucía Struth  Emanuele Giachetta  Sean D. Willett  Lewis A. Owen  Eliseo Tesón 《地球表面变化过程与地形》2020,45(8):1789-1804

Dramatic drainage reorganization from initial longitudinal to transversal domains has occurred in the Eastern Cordillera of Colombia. We perform a regional analysis of drainage basin geometry and transformed river profiles based on the integral form of the slope-area scaling, to investigate the dynamic state of drainage networks and to predict the degree of drainage reorganization in this region. We propose a new model of drainage rearrangement for the Eastern Cordillera, based on the analyses of knickpoint distribution, normalized river profiles, landforms characteristic of river capture, erosion rates and palaeodrainage data. We establish that the oldest longitudinal basin captured by the Magdalena River network was the Suárez Basin at ≈409 ka, inferring the timing of abandonment of a river terrace using in situ produced cosmogenic beryllium-10 (¹⁰Be) depth profiles and providing a first estimation of incision rate of 0.07 mm/yr. We integrate published geochronologic data and interpret the last capture of the Sabana de Bogotá, providing a minimum age of the basin opening to the Magdalena drainage at ≈38 ka. Our results suggest that the Magdalena basin Increased its drainage area by integrating the closed basins from the western flank of the Eastern Cordillera. Our study also suggests that the Magdalena basin is an aggressor compared to the basins located in the eastern flank of the orogen and provides a framework for examining drainage reorganization within the Eastern Cordillera and in similar orogenic settings. The results improve our understanding of headward integration of closed basins across orogenic plateaux. © 2020 John Wiley & Sons, Ltd.  相似文献   

Performance evaluation of automated approaches to building detection in multi-source aerial data     

Kourosh Khoshelham  Carla Nardinocchi  Emanuele Frontoni  Adriano Mancini  Primo Zingaretti 《ISPRS Journal of Photogrammetry and Remote Sensing》2010,65(1):123-133

Automated approaches to building detection in multi-source aerial data are important in many applications, including map updating, city modeling, urban growth analysis and monitoring of informal settlements. This paper presents a comparative analysis of different methods for automated building detection in aerial images and laser data at different spatial resolutions. Five methods are tested in two study areas using features extracted at both pixel level and object level, but with the strong prerequisite of using the same training set for all methods. The evaluation of the methods is based on error measures obtained by superimposing the results on a manually generated reference map of each area. The results in both study areas show a better performance of the Dempster-Shafer and the AdaBoost methods, although these two methods also yield a number of unclassified pixels. The method of thresholding a normalized DSM performs well in terms of the detection rate and reliability in the less vegetated Mannheim study area, but also yields a high rate of false positive errors. The Bayesian methods perform better in the Memmingen study area where buildings have more or less the same heights.  相似文献