1980–1990: Ten years of geochemical investigation at Phlegrean Fields (Italy)     

Marino Martini  Luciano Giannini  Antonella Buccianti  Franco Prati  Paola Cellini Legittimo  Paolo Iozzelli  Bruno Capaccioni 《Journal of Volcanology and Geothermal Research》1991,48(1-2)

A systematic geochemical investigation on the thermal manifestations of the volcanic area of Phlegrean Fields started in 1980, with the aim of obtaining useful information about the changes possibly occurring at the same time of vertical ground movements, termed as “bradyseismic”, which frequently interested this area.The attention was initially given to the fumaroles and the boiling pools of Solfatara and Pisciarelli, then subsequently extended to thermal springs, dug wells, and crater lakes.Analytical data pertaining to a period preceding the last crisis of 1982–1984 were then available, as well as other data collected during the previous crisis of 1970; a comprehensive picture of the variations observed before, during and after the acceleration of vertical movement has been drawn.According to the results obtained, the intrusion of a magmatic body as the trigger of the observed ground deformation is considered unrealistic. The whole area appears now in a quiet stage, and no further perturbation is expected without previous significant tectonic activity; chemical precursors appear suitable for an early detection of changes occurring at depth, to forecast possible consequences to be expected in the surface environment.  相似文献   

Composition of hydrothermal fluids during the bradyseismic crisis which commenced at Phlegraean Fields in 1982     

M. Martini  P. Cellini Legittimo  G. Piccardi  L. Giannini 《Bulletin of Volcanology》1984,47(2):267-273

A systematic geochemical surveillance on the fumaroles of Solfatara and the boiling pools of Pisciarelli was carried out by discontinuous monitoring of the chemical composition of the emitted fluids during the Phlegraean Fields bradyseismic crisis which has begun in 1982. The fluids are considered to be produced by the ebullition of shallow aquifers receiving a convective gaseous inflow from the underlying magma chamber.Increased water vapor concentrations at a constant temperature of about 155 °C throughout the investigated period, along with the occurrence of ground deformations and seismic phenomena, are interpreted as resulting from an increased heat supply to the boiling water bodies.Dissolution processes and reactions with the confining rocks can alter the chemical composition of fluids escaping from magma to a large extent. Therefore it does not appear correct to consider the absolute values of any chemical constituent for geochemical surveillance without taking this modifying factor into account. Acid gases will be preferably absorbed by the above mentioned aquifers, while other species like H₂, N₂, O₂, CH₄, will instead increase their relative concentrations. Because of this, water vapour concentrations and the ratios H₂S/CO₂ and H₂/CH₄ in surface thermal manifestations appear to reflect better the varying extent of the observed phenomenon.On the basis of these parameters, and of both the upheaval rate and the intensity of seismic events, maximum values in the convective input of magmatic origin are estimated to have occurred at the beginning of the crisis and in September–October 1983.As long as water bodies at shallow depth are able to buffer the convective flow both thermally and chemically, no important volcanic activity can develop. When the absorbing capacity of these aquifers is exhausted, the increasing temperature and the changing characteristics of fluids towards a magmatic composition will indicate a higher probability of eruptive phenomena.CNR —Centro di studio per la mineralogia e la geochimica dei sedimenti.  相似文献   

Marine geology of the Medriff Corridor, Mediterranean Ridge   总被引：1，自引：0，他引：1  

Nicoetta  Fusi  Giovanni Aloisi  de Larderel Ada  Borelu  Ottavio  Amelio  Davide  Castradori  Alessandra  Negri    Bianca  Rimoldi  Rossella  Sanvoisin  Paola  Tarbini  Maria B.  Cita 《Island Arc》1996,5(4):420-439

Abstract Thirty-one piston and/or gravity cores not exceeding 10 m in length were raised in selected areas of a 300 km-long transect (Medriff Corridor) crossing the Mediterranean Ridge, an accretionary complex subject to continent/continent collision, containing an important evaporitic body (Messinian evaporites), in order to ground-truth the geological make-up. Core location, very accurate with reference to a complex bottom configuration, was preceded by swathe mapping, seismic profiling and side-scan sonar investigations. Most sediment cores have a pelagic facies, with biogenic marls as dominant lithology, and sapropels and tephras as minor, isochronous lithologies. A combination of isochronous lithologies and calcareous plankton biochronology permits high resolution stratigraphic correlations. Pelagic facies sediments are Middle Pleistocene to Holocene in age. Two cores associated with mounds located along thrusts contain a matrix-supported mud breccia of deep provenance, Burdigalian-Langhian in age, similar to that characteristic of the Mediterranean Ridge diapiric belt (Cita et al. 1995 ). Three new brine-filled anoxic basins (Urania, l'Atalante and Discovery) were discovered. The brines originated from submarine dissolution of Messinian evaporites and are different in the various basins. The sedimentary record strongly differs from basin to basin. These brine lakes are very young (35 000 years or less). A drastic change in sedimentation rate recorded in the Discovery Basin suggests that basin collapse was sudden and followed by progressive development of basin anoxia. Some cores were analyzed with a prototype multisensor for P-wave velocity, magnetic susceptibility and density. Sapropels show up as abrupt decreases in P-wave velocity and density, and tephra as sudden increases in magnetic susceptibility. Mud breccia displays P-wave velocities greater than pelagic marls, with peaks related to lithic clasts. Anoxic sediments have high P-wave velocities; peaks are associated with gypsum crystals.  相似文献   

Columnar joints in the Patino Formation sandstones, Eastern Paraguay： a dynamic interaction between dyke intrusion, quartz dissolution and cooling-induced fractures     

Victor Fernandez Velazquez Paulo Cesar Fonseca Giannini Claudio Riccomini Alethea Ernandes Martins Sallun Jorge Hachiro Celso de Barros Gomes 《《幕》》2008,31(3):302-308

The Patiho Formation sandstones, which crop out in Aregud neighborhood in Eastern Paraguay and show columnar joints near the contact zone with a nephelinite dyke, have as their main characteristics the high pro- portion of syntaxial quartz overgrowth and a porosity originated from different processes, initially by dissolu- tion and later by partial filling and fracturing. Features like the presence of floating grains in the syntaxial cement, the transitional interpenetrative contact between the silica-rich cement and grains as well as the intense fracture porosity are strong indications that the cement has been formed by dissolution and reprecipita- tion of quartz from the framework under the effect of thermal expansion followed by rapid contraction. The increase of the silica-rich cement towards the dyke in association with the orthogonal disposition of the columns relative to dyke walls are indicative that the igneous body may represent the main heat source for the interstitial aqueous solutions previously existing in the sediments. At macroscopic scale, the increasing of inter- nal tensions in the sandstones is responsible for the nucleation of polygons, leading to the individualization of prisms, which are interconnected by a system of joints, formed firstly on isotherm surfaces of low tem- perature and later on successive adjacent planes towards the dyke heat source.  相似文献   

Using historical maps to analyze two hundred years of land cover changes: case study of Sorrento peninsula (south Italy)     

Stefania Pindozzi  Elena Cervelli  Alessandra Capolupo  Collins Okello 《制图学和地理信息科学》2016,43(3):250-265

Historical maps are effective sources of geographical information and useful for historical and territorial research. In this study, the examination of landscape dynamics on the basis of historical maps over a period of more than 200 years was conducted. The study area is Sorrento peninsula and part of the near Sarno river basin in South Italy. This study provides a general framework for the assessment of the overall quality and accuracy of historical maps. The application of the methodology used in this specific case study can contribute to a better understanding of the dynamics of the landscape in the long term. The derived knowledge can be applied in the planning of the landscape in order to implement correct conservation strategies. The comparison was made on four maps 1817, 1875, 1960, and 2006. Geodetic accuracy of the sheet maps of 1817 and 1875 offer a right basis for a macro analysis of land cover dynamics, evaluating conversion from one land cover category to another. Main transformation, identified in the period between 1875 and 1960, was the disappearance of vineyards, which covered 25% of the total study area in 1875. Agricultural areas increased in this period to cover 57% of the total area.  相似文献   

Earthquake-induced reactivation of landslides under variable hydrostatic conditions: evaluation at regional scale and implications for risk assessment     

Giannini  Leonardo Maria  Varone  Chiara  Esposito  Carlo  Marmoni  Gian Marco  Scarascia Mugnozza  Gabriele  Schilir&#;  Luca 《Landslides》2022,19(8):2005-2019

Landslides - Earthquake-induced landslides represent a significant seismic hazard since they can largely increase the damage and losses due to a seismic event, an issue that must be considered in...  相似文献   

Weighting of Parts in Compositional Data Analysis: Advances and Applications     

Hron  Karel  Menafoglio  Alessandra  Palarea-Albaladejo  Javier  Filzmoser  Peter  Talská  Renáta  Egozcue  Juan José 《Mathematical Geosciences》2022,54(1):71-93

Mathematical Geosciences - It often occurs in practice that it is sensible to give different weights to the variables involved in a multivariate data analysis—and the same holds for...  相似文献   

The contrasting geochemical message from the New Caledonia gabbronorites: insights on depletion and contamination processes of the sub-arc mantle in a nascent arc setting     

Arianna?Secchiari  Alessandra?MontaniniEmail author  Delphine?Bosch  Patrizia?Macera  Dominique?Cluzel 《Contributions to Mineralogy and Petrology》2018,173(8):66

The New Caledonia ophiolite hosts one of the rare examples of crust-mantle sections built in a nascent arc environment, providing the unique opportunity to investigate the first stages of arc magmatism in a subduction setting. The sequence consists of refractory harzburgites, overlain by ultramafic (dunites and wehrlites) and mafic lithologies (gabbronorites). The gabbronorites occur in the upper part of the sequence as decimetre to metre-size sills. They are mainly formed (??55 to 70 vol%) of Ca-rich plagioclase (An up to 96 mol%) and high Mg# (88–92), Al₂O₃-poor (1.5–2.4 wt%) clinopyroxene (8–20 vol%), often rimmed by interstitial or poikilitic orthopyroxene (6–27 vol%). Mg-rich olivine (3–15 vol%, Fo?=?87–89 mol%) occurs as anhedral, resorbed crystals. Whole rock (WR) compositions exhibit high Mg# (86–92) and strikingly low trace element contents. They own LREE-depleted patterns, with nearly flat (0.82?≤?Dy_N/Yb_N?≤?1.00) and low HREE (Yb_N?=?0.2–0.9) and positive Eu anomalies. Clinopyroxene trace element chemistry mirrors the extreme depletion of the WR. By contrast, FME enrichments are observed for WR and clinopyroxene. Geochemical models show that the gabbronorites crystallized from primitive, ultra-depleted melts bearing evidence of fluid contamination processes, but with significantly different geochemical signatures compared to boninitic rocks worldwide, i.e. lower LREE-MREE, and absence of Nb depletion and Zr–Hf enrichments. Nd isotopes (+?8.2?≤?εNd_i?≤?+?13.1), together with radiogenic Pb isotopic ratios, support an origin from a DMM source variably modified by slab fluids. We propose that the geochemical signature of the New Caledonia gabbronorites reflect emplacement of primitive, non-aggregated, magma batches in the lower fore-arc crust, during the first phases of arc formation.  相似文献   

The impact of coastal urbanization on the structure of phytobenthic communities in southern Brazil     

Martins CD  Arantes N  Faveri C  Batista MB  Oliveira EC  Pagliosa PR  Fonseca AL  Nunes JM  Chow F  Pereira SB  Horta PA 《Marine pollution bulletin》2012,64(4):772-778

The anthropogenic pressures on coastal areas represent important factors affecting local, regional, and even global patterns of distribution and abundance of benthic organisms. This report undertakes a comparative analysis of the community structure of rocky shore intertidal phytobenthos in both pristine like environments (PLE) and urbanized environments (UBE) in southern Brazil, characterizing variations on different spatial scales. Multivariate analysis of variance indicated that the PLE is characterized by a larger number of taxa and an increased occurrence of Rhodophyta species in relation to UBE. In contrast, UBE were dominated by opportunistic algae, such as Cladophora and Ulva spp. Significance tests further indicated higher species richness and Shannon-Wiener diversity on the PLE in relation to UBE. Here we provide data showing the magnitude of seaweed biodiversity loss and discuss direct and indirect consequences of unplanned urbanization on these communities.  相似文献   

Phytoplankton community in the tropical lake of Lagoa Santa (Brazil): Conditions favoring a persistent bloom of Cylindrospermopsis raciborskii   总被引：2，自引：0，他引：2  

Cleber Cunha Figueredo  Alessandra Giani 《Limnologica》2009,(4):264-272

This study presents data on seasonal changes of the phytoplanktonic community of a small tropical lake, Lagoa Santa, in the Brazilian cerrado. Temporal variation in the community structure was small and we observed a permanent dominance of the cyanobacteria Cylindrospermopsis raciborskii. This dominance could be associated to the stability of several environmental conditions. Especially water temperature, always within the optimal growth range for C. raciborskii, and the constant mixed water column may have been important factors driving to the long term dominance of this species in the lake. Remarkable seasonal variation in rainfall, as well as the occasional and non-seasonal variation in nutrient concentrations, were important to explain changes in environmental and biological variables, but were not related to the dominance of C. raciborskii. Pearson's correlation and PCA could just in part explain the stable dominance of this cyanobacterium. Meteorological and chemical factors seem to have no clear control on the variability of the phytoplankton dynamics in Lagoa Santa. The weak relationship between C. raciborskii abundance and environmental variables points to additional intrinsic factors associated to this species that may be important in structuring the phytoplankton assemblage.  相似文献