Crystal fractionation,magma step ascent,and syn-eruptive mingling: the Averno 2 eruption (Phlegraean Fields,Italy)     

Céline Fourmentraux  Nicole Métrich  Antonella Bertagnini  Mauro Rosi 《Contributions to Mineralogy and Petrology》2012,163(6):1121-1137

The 3.7 ka year-old Averno 2 eruption is one of the rare eruptions to have occurred in the northwest sector of the Phlegraean Fields caldera (PFc) over the past 5 ka. We focus here on the fallout deposits of the pyroclastic succession emplaced during this eruption. We present major and trace element data on the bulk pumices, along with major and volatile element data on clinopyroxene-hosted melt inclusions, in order to assess the conditions of storage, ascent, and eruption of the feeding trachytic magma. Crystal fractionation accounts for the evolution from trachyte to alkali-trachyte magmas; these were intimately mingled (at the micrometer scale) during the climactic phase of the eruption. The Averno 2 alkali trachyte represents one of the most evolved magmas erupted within the Phlegraean Fields area and belongs to the series of differentiated trachytic magmas erupted at different locations 5 ka ago. Melt inclusions record significant variations in H₂O (from 0.4 to 5 wt%), S (from 0.01 to 0.06 wt%), Cl (from 0.75 up to 1 wt%), and F (from 0.20 to >0.50 wt%) during both magma crystallization and degassing. Unlike the eruptions occurring in the central part of the PFc, deep-derived input(s) of gas and/or magma are not required to explain the composition of melt inclusions and the mineralogy of Averno 2 pumices. Compositional data on bulk pumices, glassy matrices, and melt inclusions suggest that the Averno 2 eruption mainly resulted from successive extrusions of independent magma batches probably emplaced at depths of 2–4 km along regional fractures bordering the Neapolitan Yellow Tuff caldera.  相似文献   

Long‐term presence and habitat use of Cuvier's beaked whale (Ziphius cavirostris) in the Central Tyrrhenian Sea          下载免费PDF全文

Antonella Arcangeli  Ilaria Campana  Luca Marini  Colin D. MacLeod 《Marine Ecology》2016,37(2):269-282

Cuvier's beaked whale (Ziphius cavirostris, G. Cuvier 1823) is a poorly known species and many international agreements have asked for a better understanding of its biology for conservation purposes. In the present study, systematic cetacean surveys were carried out from ferries along a trans‐regional fixed transect in the Central Tyrrhenian Sea (Civitavecchia, Latium – Golfo Aranci, Sardinia), just outside the southeastern border of the Pelagos Sanctuary. This research provided long‐term, consistent data on Cuvier's beaked whale during two research periods (1990–1992 and 2007–2011). The objective of the research was to compare the presence, distribution and habitat use of Cuvier's beaked whale between the two investigated periods. Summer data (June–September) from the two periods were compared in terms of frequency of sightings, group size and spatial distribution related to the main ecogeographical features. A presence‐absence model (generalized additive modelling) was performed to predict habitat suitability in the two study periods. The results highlight long‐term site fidelity of Cuvier's beaked whale in the Central Tyrrhenian Sea with encounter rates comparable to the ones reported for other key areas. Separate suitability models based on 1990s and 2000s data appeared to work for each individual time period but differences were evident between the two periods, indicating changes in habitat selection over time. Our findings of the study appear to expand the definition of suitable beaked whale habitat and underline how the temporal scale of the analysis can affect the results in habitat studies. Moreover, this research highlights the importance of the Central Tyrrhenian Sea marine region for Cuvier's beaked whale and the ability of continuous monitoring to identify changes in cetacean frequency and distribution, necessary for adaptive conservation management approaches.  相似文献   

Comparison of pumping at constant head and at a constant rate for determining the sustainable yield of a well     

Antonella Baiocchi  Francesca Lotti  Simone M. Piacentini  Vincenzo Piscopo 《Environmental Earth Sciences》2014,72(4):989-996

Determining the yield of a production well remains one of the main problems in hydrogeological studies. Starting from the results of a 3-year-long monitoring of a continuously exploited well functioning at constant head (i.e., at a variable discharge rate), a new pumping style has been examined using numerical models. The objective is to control the impact of pumping on the aquifer in accordance with the principle of sustainability. Different models were developed in a transient state and were calibrated using discharge data of the well during the recession periods. Successively, the trends of the residual outflow from the aquifer system with the well operating at variable discharge and at constant discharge were simulated. The results indicate that the ratio of the volume of water pumped from the well to the volume of residual outflow is a significant indicator of the sustainability of groundwater withdrawals. Modeling confirms that a constant discharge rate can be derived from the information gained through a preliminary production phase of a well at constant head. This approach appears to be particularly useful when the problem is determining the sustainable yield of a single well from aquifers with low hydraulic diffusivity.  相似文献   

Seismicity of Eastern Algeria: a revised and extended earthquake catalogue   总被引：1，自引：0，他引：1  

Assia Harbi  Antonella Peresan  Giuliano F. Panza 《Natural Hazards》2010,54(3):725-747

A new revised earthquake catalogue for Eastern Algeria [22°N-38°N–4°E-9.5°E], from 419 to 2008, has been compiled as a starting point for a catalogue dealing with the whole country. The re-evaluation is based on a critical method, and formal criteria are adopted in the parameterization of the earthquake catalogue. Two digital versions are produced: (a) a basic version, presented here, including all the compiled data, the authors of each quoted parameter and the quality rank of the macroseismic information; (b) a second version, obtained after removing doubtful events and parameters, is produced in order to carry out statistical analyses. The newly compiled earthquake catalogue provides a more reliable picture of the seismicity in Eastern Algeria than the previous ones as shown by the comparison of the recent catalogues over the common territory and time span. This catalogue can be easily updated and adapted to the needs of the user.  相似文献