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1.
Geological, geodetic and seismological data have been analyzed in order to frame the Lipari–Vulcano complex (Aeolian archipelago, southern Italy) into the geodynamic context of the southeastern Tyrrhenian Sea. It is located at the northern end of a major NNW–SSE trending right-lateral strike-slip fault system named “Aeolian–Tindari–Letojanni” which has been interpreted as a lithospheric discontinuity extending from the Aeolian Islands to the Ionian coast of Sicily and separating two different tectonic domains: a contractional one to the west and an extensional one to the north-east. Structural field data consist of structural measurements performed on well-exposed fault planes and fractures. The mesostructures are mostly represented by NW–SE striking normal faults with a dextral-oblique component of motion. Minor structures are represented by N–S oriented joints and tension gashes widespread over the whole analyzed area and particularly along fumarolized sectors. The analyzed seismological dataset (from 1994 to 2013) is based on earthquakes with magnitude ranging between 1.0 and 4.8. The hypocenter distribution depicts two major alignments corresponding to the NNW–SSE trending Aeolian–Tindari–Letojanni fault system and to the WNW–ESE oriented Sisifo–Alicudi fault system. GPS data analysis displays ∼3.0 mm/yr of active shortening between the two islands, with a maximum shortening rate of about 1.0 × 10−13 s−1, between La Fossa Caldera and south of Vulcanello. This region is bounded to the north by an area where the maximum values of shear strain rates, of about 0.7 × 10−13 s−1 are observed. This major change occurs in the area south of Vulcanello that is also characterized by a transition in the way of the vertical axis rotation. Moreover, both the islands show a clear subsidence process, as suggested by negative vertical velocities of all GPS stations which exhibit a decrease from about −15 to −7 mm/yr from north to south. New data suggest that the current kinematics of the Lipari–Vulcano complex can be framed in the tectonic context of the eastward migrating Sisifo–Alicudi fault system. This is dominated by transpressive tectonics in which contractional and minor extensional structures can coexist with strike-slip motion. 相似文献
2.
Lastarria volcano (25°10′ S, 68°31′ W; 5,697 m above sea level), located in the Central Andes Volcanic Zone (northern Chile),
is characterized by four distinct fumarolic fields with outlet temperatures ranging between 80°C and 408°C as measured between
May 2006–March 2008 and April–June 2009. Fumarolic gasses contain significant concentrations of high temperature gas compounds
(i.e., SO2, HCl, HF, H2, and CO), and isotopic ratios (3He/4He, δ13C–CO2, δ18O–H2O, and δD–H2O) diagnostic of magmatic gas sources. Gas equilibria systematics, in both the H2O-H2-CO2-CO-CH4 and alkane–alkene C3 system, suggest that Lastarria fumarolic gasses emanate from a superheated vapor that is later cooled and condensed at relatively
shallow depths. This two-stage process inhibits the formation of a continuous aquifer (e.g., horizontal liquid layer) at relatively
shallow depth. Recent developments in the magmatic gas system may have enhanced the transfer and release of heat causing shallow
aquifer vaporization. The consequent pressure increase and aquifer vaporization likely triggered the inflation events beginning
in 2003 at the Lastarria volcano. 相似文献
3.
Antonio Montalto 《Bulletin of Volcanology》1994,56(3):220-227
Since the last eruption (1888–1890) volcanism at Vulcano, Aeolian Archipelago, southern Tyrrhenian Sea, has taken the form of persistent fumarolic activity. The gas-vapour phases of the geothermal systems are mainly discharged within two restricted areas about 1 km apart from each other, in the northern part of the island. These areas are La Fossa crater, and the beach fumaroles of the Baia di Levante. Fluids released at the two main fumarolic fields display quite different chemical and temperature characteristics, implying different origins. The local seismicity essentially takes the form of discrete shocks of shallow origin (depth1 km) at La Fossa, usually with energy < 1013
ergs. They are thought to be related to the uprise of pressurized hot gases and vapours discharged at the crater fumaroles. The present investigation points to the existence of two principal categories of seismic events (called M-shocks and N-shocks). These are short events (normally < 10 s). M-type shocks are thought to be due to resonance vibrations within the interior of the volcano, probably driven by the excitation of shock-waves within cavities deeply affected by deposition and alteration of self-sealant hydrothermal minerals. N-type events display features that resemble those of volcano-tectonic earthquakes, but have no recognizable S-phases. Here they are tentatively attributed to microfracturing of rocks which have been extensively hydrothermally altered. Results of the present study permit a preliminary conceptual model of the local shallow seismic processes in the framework of geochemical modelling of fumarolic activity and geological inferences from geothermal drilling. 相似文献
4.
Mount Rainier is one of the most seismically active volcanoes in the Cascade Range, with an average of one to two high-frequency
volcano-tectonic (or VT) earthquakes occurring directly beneath the summit in a given month. Despite this level of seismicity,
little is known about its cause. The VT earthquakes occur at a steady rate in several clusters below the inferred base of
the Quaternary volcanic edifice. More than half of 18 focal mechanisms determined for these events are normal, and most stress
axes deviate significantly from the regional stress field. We argue that these characteristics are most consistent with earthquakes
in response to processes associated with circulation of fluids and magmatic gases within and below the base of the edifice.Circulation
of these fluids and gases has weakened rock and reduced effective stress to the point that gravity-induced brittle fracture,
due to the weight of the overlying edifice, can occur. Results from seismic tomography and rock, water, and gas geochemistry
studies support this interpretation. We combine constraints from these studies into a model for the magmatic system that includes
a large volume of hot rock (temperatures greater than the brittle–ductile transition) with small pockets of melt and/or hot
fluids at depths of 8–18 km below the summit. We infer that fluids and heat from this volume reach the edifice via a narrow
conduit, resulting in fumarolic activity at the summit, hydrothermal alteration of the edifice, and seismicity.
Received: 10 February 1999 / Accepted: 26 June 1999 相似文献
5.
A. Di Roberto M. Rosi A. Bertagnini M.P. Marani F. Gamberi A. Del Principe 《Journal of Volcanology and Geothermal Research》2008
A 4.8 m long gravity core was recovered on a relative topographic high in the northern part of the Marsili Basin (southern Tyrrhenian Sea) at a water depth of 3200 m. The core was taken in order to decipher the sedimentary record of the past volcanic events of the nearby Aeolian arc. A succession of thin (2 cm to 5 cm thick) fine-grained turbidites, mainly of volcaniclastic origin, topped by hemipelagic mud layers and a number of primary tephra layers were recovered by the core. The most prominent turbidite occurs in the lower part of the core at 385 cm. It consists of a 20 cm-thick, thinning-upward, pebble to sand-sized bed. 相似文献
6.
The Baoshan Cu–Pb–Zn deposit, located in the central part of the Qin–Hang belt in South China, is closely related to the granodiorite-porphyry. However, the characteristics and the source of the ore-forming fluid are still ubiquitous. According to the crosscutting relationships between veinlets and their mineral assemblages, three stages of hydrothermal mineralization in this deposit were previously distinguished. In this contribution, two different colored fluorites from the major sulfide miner... 相似文献
7.
Eugenio Nicotra Marco Viccaro Rosanna De Rosa Marco Sapienza 《Bulletin of Volcanology》2014,76(8):1-24
Critical to understanding explosive eruptions is establishing how accurately representative pyroclasts are of processes during magma vesiculation and fragmentation. Here, we present data on densities, and vesicle size and number characteristics, for representative pyroclasts from six silicic eruptions of contrasting size and style from Raoul volcano (Kermadec arc). We use these data to evaluate histories of bubble nucleation, coalescence, and growth in explosive eruptions and to provide comparisons with pumiceous dome carapace material. Density/vesicularity distributions show a scarcity of pyroclasts with ~65–75 % vesicularity; however, pyroclasts closest to this vesicularity range have the highest bubble number density (BND) values regardless of eruptive intensity or style. Clasts with vesicularities greater than this 65–75 % “pivotal” vesicularity range have decreasing BNDs with increasing vesicularities, interpreted to reflect continuing bubble growth and coalescence. Clasts with vesicularities less than the pivotal range have BNDs that decrease with decreasing vesicularity and preserve textures indicative of processes such as stalling and open system degassing prior to vesiculation in a microlite-rich magma, or vesiculation during slow ascent of degassing magma. Bubble size distributions (BSDs) and BNDs show variations consistent with 65–75 % representing the vesicularity at which vesiculating magma is most likely to undergo fragmentation, consistent with the closest packing of spheres. We consider that the observed vesicularity range may reflect the development of permeability in the magma through shearing as it flows through the conduit. These processes can act in concert with multiple nucleation events, generating a situation of heterogeneous bubble populations that permit some regions of the magma to expand and bubbles to coalesce with other regions in which permeable networks are formed. Fragmentation preserves the range in vesicularity seen as well as any post-fragmentation/pre-quenching expansion which may have occurred. We demonstrate that differing density pyroclasts from a single eruption interval can have widely varying BND values corresponding to the degree of bubble maturation that has occurred. The modal density clasts (the usual targets for vesicularity studies) have likely undergone some degree of bubble maturation and are therefore may not be representative of the magma at the onset of fragmentation. 相似文献
8.
On 28 December 2002, new vents opened on the flanks of Stromboli, just below the summit craters, interrupting the persistent
activity of the volcano with a 7-month-long effusive eruption. We here report on the plagioclase size distribution (PlgSD)
in lava samples collected following the chronology of the 2002–2003 eruption. Data reveal a linear PlgSD similar to that found
in samples of normal Stromboli activity, indicating that the switch from Strombolian explosive to effusive activity is not
associated with changes in texture. Nevertheless, the crystal size distribution slopes and intercepts exhibit slight sinusoidal
temporal variations that are here ascribed to a magma supply mechanism able to induce “resonance” in the crystal size distribution,
with an amplitude that depends on the supply rate. 相似文献
9.
《Earth and Planetary Science Letters》2003,205(3-4):309-324
High-precision Nb, Ta, Zr, Hf, Sm, Nd and Lu concentration data of depleted mantle rocks from the Balmuccia peridotite complex (Ivrea Zone, Italian Alps) were determined by isotope dilution using multiple collector inductively coupled plasma mass spectrometry (MC-ICPMS) and thermal ionisation mass spectrometry (TIMS). The Zr/Hf ratios of all investigated samples from the Balmuccia peridotite complex are significantly lower than the chondritic value of 34.2, and the most depleted samples have Zr/Hf ratios as low as 10. Correlated Zr/Hf ratios and Zr abundances of the lherzolites preserve the trend of a mantle residue that has been depleted by fractional melting. This trend confirms experimental studies that predict Hf to behave more compatibly than Zr during mantle melting. Experimentally determined partition coefficients imply that the major Zr and Hf depletion most likely occurred in the spinel stability field, with (DZr/DHf)cpx≈0.5, and not in the garnet stability field, where (DZr/DHf)grt is probably close to one. However, minor amounts of melting must have also occurred in a garnet facies mantle, as indicated by low Sm/Lu ratios in the Balmuccia peridotites. The Nb/Ta ratios of most lherzolites are subchondritic and vary only from 7 to 10, with the exception of three samples that have higher Nb/Ta ratios (18–24). The overall low Nb/Ta ratios of most depleted mantle rocks confirm a higher compatibility of Ta in the mantle. The uniform Nb/Ta ratios in most samples imply that even in ‘depleted’ mantle domains the budget of the highly incompatible Nb and Ta is controlled by enrichment processes. Such a model is supported by the positive correlation of Zr/Nb with the Zr concentration. However, the overall enrichment was weak and did barely affect the moderately incompatible elements Zr and Hf. The new constraints from the partitioning behaviour of Zr–Hf and Nb–Ta provide important insights into processes that formed the Earth’s major silicate reservoirs. The correlation of Zr/Hf and Sm/Nd in depleted MORB can be assigned to previous melting events in the MORB source. However, such trends were unlikely produced during continental crust formation processes, where Sm/Nd and Zr/Hf are decoupled. The different fractionation behaviour of Zr/Hf and Sm/Nd in the depleted mantle (correlated) and the crust (decoupled) indicates that crustal growth by a simple partial melting process in the mantle has little effect on the mass budget of LREE and HFSE between crust and mantle. A more complex source composition, similar to that of modern subduction rocks, is needed to fractionate the LREE, but not Zr/Hf and the HREE. 相似文献
10.
Systematic measurements of the height of the summit crater rim on the active Karymskii Volcano showed that the variation of that parameter has been greater during its last eruption, lasting, with short intermissions, from January 1, 1996 until now (October 2007) compared with the earlier eruptions. The periodic increases in the height of Karymskii Volcano were due to explosion discharges of unconsolidated pyroclastic material, with most of this falling on the volcano’s cone. The increased seismicity of Karymskii Volcano intensified the slope movement processes, resulting in a comparatively flat area forming periodically on the crater rim; during separate, not very long, periods the height of the volcanic cone was increasing in discrete steps and at a greater rate. The periodic decrease in the height of Karymskii Volcano is due to compaction of pyroclastic material and, to a much greater extent, after violent explosions which expand the crater by removing its nearsummit circumference. The other contributing factor consists in sagging of the magma column due to partial emptying of the peripheral magma chamber, which makes the internal crater slope steeper, hence causes cone collapse and the cone lower. These occurrences are generally similar to the processes of crater and caldera generation described by previous investigators for other volcanoes of the world. 相似文献
11.
Rosa Anna Corsaro Lucia Civetta Valeria Di Renzo Lucia Miraglia 《Bulletin of Volcanology》2009,71(7):781-793
Following the 2001 and 2002–2003 flank eruptions, activity resumed at Mt. Etna on 7 September 2004 and lasted for about 6 months.
This paper presents new petrographic, major and trace element, and Sr–Nd isotope data from sequential samples collected during
the entire 2004–2005 eruption. The progressive change of lava composition allowed defining three phases that correspond to
different processes controlling magma dynamics inside the central volcano conduits. The compositional variability of products
erupted up to 24 September is well reproduced by a fractional crystallization model that involves magma already stored at
shallow depth since the 2002–2003 eruption. The progressive mixing of this magma with a distinct new one rising within the
central conduits is clearly revealed by the composition of the products erupted from 24 September to 15 October. After 15
October, the contribution from the new magma gradually becomes predominant, and the efficiency of the mixing process ensures
the emission of homogeneous products up to the end of the eruption. Our results give insights into the complex conditions
of magma storage and evolution in the shallow plumbing system of Mt. Etna during a flank eruption. Furthermore, they confirm
that the 2004–2005 activity at Etna was triggered by regional movements of the eastern flank of the volcano. They caused the
opening of a complex fracture zone extending ESE which drained a magma stored at shallow depth since the 2002–2003 eruption.
This process favored the ascent of a different magma in the central conduits, which began to be erupted on 24 September without
any significant change in eruptive style, deformation, and seismicity until the end of eruption. 相似文献
12.
The benthic fluxes (diffusive and with chambers) of dissolved inorganic carbon (DIC), dissolved oxygen (DO) and total alkalinity (TA) have been calculated in summertime in the estuary system formed by the mouths of the Tinto and Odiel rivers (SW of Spain). An increase of DIC in interstitial water with depth was found for all stations showing values of up to 28 mM at a depth of 5 cm. The diffusive fluxes of DIC and TA obtained ranging between 1.8–7.8 and 1.5–7.3 mmol m−2 d−1, respectively. These intervals are in agreement with those found for other coastal systems. Considering the plots of DIC vs. alkalinity (ΔDIC/ΔTA) in the first 30 cm of interstitial water, it was deduced that sulphate reduction and the oxidation of sulphides seem to have special relevance in the sediments of the stations studied. The benthic fluxes of inorganic carbon and DO measured by benthic chambers were variable, presenting elevated values (309–433 mmol DIC m−2 d−1 and 50–120 mmol DO m−2 d−1). The most elevated fluxes of DIC were seen at the stations with high anthropogenic influence (close to populated areas and industrial discharges). A great proportion of these fluxes are due to CaCO3 dissolution processes, which constitute an estimated 49% of total DIC flux. DIC and DO benthic flux quotients were far in excess of unity, indicating the significance processes of anaerobic degradation of organic material at the stations studied. 相似文献
13.
Flank instability and collapse are observed at many volcanoes. Among these, Mt. Etna is characterized by the spreading of its eastern and southern flanks. The eastern spreading area is bordered to the north by the E–W-trending Pernicana Fault System (PFS). During the 2002–2003 Etna eruption, ground fracturing along the PFS migrated eastward from the NE Rift, to as far as the 18 km distant coastline. The deformation consisted of dextral en-echelon segments, with sinistral and normal kinematics. Both of these components of displacement were one order of magnitude larger (~1 m) in the western, previously known, portion of the PFS with respect to the newly surveyed (~9 km long) eastern section (~0.1 m). This eastern section is located along a pre-existing, but previously unknown, fault, where displaced man-made structures give overall slip rates (1–1.9 cm/year), only slightly lower than those calculated for the western portion (1.4–2.3 cm/year). After an initial rapid motion during the first days of the 2002–2003 eruption, movement of the western portion of the PFS decreased dramatically, while parts of the eastern portion continued to move. These data suggest a model of spreading of the eastern flank of Etna along the PFS, characterized by eruptions along the NE Rift, instantaneous, short-lived, meter-scale displacements along the western PFS and more long-lived centimeter-scale displacements along the eastern PFS. The surface deformation then migrated southwards, reactivating, one after the other, the NNW–SSE-trending Timpe and Trecastagni faults, with displacements of ~0.1 and ~0.04 m, respectively. These structures, along with the PFS, mark the boundaries of two adjacent blocks, moving at different times and rates. The new extent of the PFS and previous activity over its full length indicate that the sliding eastern flank extends well below the Ionian Sea. The clustering of seismic activity above 4 km b.s.l. during the eruption suggests a deep décollement for the moving mass. The collected data thus suggests a significant movement (volume >1,100 km3) of the eastern flank of Etna, both on-shore and off-shore.Editorial responsibility: R. Cioni 相似文献
14.
The main goal of this study is to provide moment tensor solutions for small and moderate earthquakes of the Matese seismic sequence in southern Italy for the period of December 2013–January 2014. We estimate the focal mechanisms of 31 earthquakes with local magnitudes related to the Matese earthquake seismic sequence (December 2013–January 2014) in Southern-Central Italy which are recorded by the broadband stations of the Italian National Seismic Network and the Mediterranean Very Broadband Seismographic Network (MedNet) run by the Istituto Nazionale di Geofisica e Vulcanologia (INGV). The solutions show that normal faulting is the prevailing style of seismic deformation in agreement with the local faults mapped out in the area. Comparisons with already published solutions and with seismological and geological information available allowed us to properly interpret the moment tensor solutions in the frame of the seismic sequence evolution and also to furnish additional information about less energetic seismic phases. Focal data were inverted to obtain the seismogenic stress in the study area. The results are compatible with the major tectonic domain of the area. 相似文献
15.
We derive S-wave attenuation characteristics, earthquake source parameters and site amplification functions at seismic stations
used for earthquake early warning in the Irpinia–Basilicata region, using non-parametric spectral inversion of seismograms
from 49 local events with M
L = 1.5–3.1. We obtain relatively low Q values (Q
0 = 28 at a frequency of 1 Hz) in conjunction with a strong frequency-dependence (close to linear). The source spectra can
be satisfactorily modeled using the omega-square model, with stress drops ranging between 0.01–2 MPa, and in the narrow magnitude
range available for analysis, the source spectra seem to scale self-similarly. The local magnitude M
L shows a linear correlation with moment magnitude M
W, however with a systematic underestimation by about 0.5-magnitude units. The results obtained in this work provide important
insights into the ground-motion characteristics that are required for appropriate seismic hazard assessment and are of practical
relevance for a suite of applications, such as the calibration of ground-motion prediction equations or the correction for
site amplification in earthquake early warning and rapid calculation of shake-maps for seismic emergency management. 相似文献
16.
G. Melián F. Tassi N. Pérez P. Hernández F. Sortino O. Vaselli E. Padrón D. Nolasco J. Barrancos G. Padilla F. Rodríguez S. Dionis D. Calvo K. Notsu H. Sumino 《Bulletin of Volcanology》2012,74(6):1465-1483
The present work reports the results of 15 studies of diffuse CO2 degassing performed at Teide Volcano crater (Canary Island, Spain) and the chemical and isotopic compositions of fluids discharged from a fumarolic field located at the top of the volcano as measured between 1991 and 2010. A higher contribution of magmatic gases accompanied by enhanced total diffuse CO2 emissions were observed in relation with a seismic crisis that occurred in Tenerife Island between 2001 and 2005, with the main peak of seismic activity between April and June 2004. A significant pulse in total diffuse CO2 emission was observed at the crater of Teide (up to 26.3?t day?1) in 2001. In December 2003, the chemical composition of the Teide fumarole changed significantly, including the appearance of SO2, an increase in the HCl and CO concentrations and in the C2H6/C2H4 and C3H8/C3H6 ratios, and a decrease in the H2S, CH4, and C6H6 concentrations and in the gas/steam ratio. A few months after a drastic decrease in seismic activity, the SO2, HCl, and CO concentrations and the C2H6/C2H4 and C3H8/C3H6 ratios strongly decreased, whereas the CH4 and C6H6 concentrations and the gas/steam ratios increased. According to the trends shown by both the geochemical parameters and the seismic signals late in the observation period, the risk of a rejuvenation of volcanic activity at Teide is considered to be low. The associated temporal changes in seismic activity and magmatic degassing indicate that geophysical and fluid geochemistry signals in this system are related. Future monitoring programs aimed at mitigating volcanic hazard on Tenerife Island should involve coupled geophysical and geochemical studies. 相似文献
17.
Corrado Di Martino Maria Luce Frezzotti Federico Lucchi Angelo Peccerillo Claudio A. Tranne Larryn W. Diamond 《Bulletin of Volcanology》2010,72(9):1061-1076
Fluid inclusion studies together with volcanological and petrochemical data allow reconstruction of the magma feeding system
of basaltic-andesitic to andesitic activity during the oldest and intermediate stages of development of Lipari Island (223–81 ka).
A major magma storage zone is active during the overall investigated time span at depths of 22 km, close to the crust-mantle
Moho transition, at which mantle-derived mafic magmas tend to accumulate due to neutral buoyancy conditions. Beneath central-type
volcanoes (M. Mazzacaruso, M. S.Angelo, M. Chirica-Costa d’Agosto), a shallower magma reservoir is located within the upper
crust at 5.5–3.5 km, associated with a major lithological discontinuity. For fissural-type volcanoes (Timpone Ospedale, Monterosa,
M. Chirica), tectonic structures are suggested to influence further magma ascent and storage at mid-crustal depths (∼14 km),
with no ponding at shallower levels. Partial crustal melting processes at the roofs of the deep magma reservoirs (∼17 km)
are invoked to explain the origin of cordierite-bearing lavas beneath M. S.Angelo and M. Chirica-Costa d’Agosto volcanoes,
which were active during the intermediate stages of development of Lipari (105–81 ka). The generation of felsic anatectic
melts in the lower crust could have created density and rheologic barriers to impede the passage of mafic melts and promote
their ponding, with influence on the subsequent evolution of Lipari volcano. 相似文献
18.
Antonio Eff-Darwich Olivier Grassin José Fernández 《Pure and Applied Geophysics》2008,165(6):1049-1070
Continuous monitoring of ground deformation in the volcanic island of Tenerife, Canary Islands, is based on GPS networks,
since there are as yet no tiltmeter stations installed on the island. However, there is a world-class astronomical observatory
on the island, the El Teide Observatory, where four tiltmeters, two aligned in the North-South and the other two in the East-West,
are monitoring the movements of the solar telescope THEMIS. THEMIS (Heliographic Telescope for the Study of Solar Magnetism
and Instabilites) is among the three largest solar telescopes in the world. Since THEMIS is located a few kilometers from
the main volcanic structures of the island, in particular the El Teide-Pico Viejo stratovolcano, and the precision of the
inclinometers is comparable to those used in geophysical studies, we carried out the analysis of the tilt measurements for
the period 1997–2006. The tiltmeters at THEMIS are placed in the seventh floor of a tower, hence their sensitivity to geological
processes is reduced compared to geophysical installations. However, THEMIS measurements are the only terrestrial data available
in Tenerife for such a long period of observations, which include the sustained increase in seismic activity that started
in 2001. In this sense, a significant change was found in the East-West tilt of approximately 35 μ-radians between the years
2000 and 2002. Some theoretical models were calculated and it was concluded that such tilt variation could not be due to dike
intrusions, nor a volcanic reactivation below the El Teide-Pico Viejo volcano. The most likely explanation comes from dislocations
produced by a secondary fault associated to a major submarine fault off the eastern coast of Tenerife. In any case, taking
into account the nearly permanent data recording at THEMIS, they could be considered as a complement for any ground deformation
monitoring system in the island. 相似文献
19.
New Sr and Nd isotope data for whole rocks, glasses and minerals are combined to reconstruct the nature and origin of mixing
end-members of the 200 km3 trachytic to phonolitic Campanian Ignimbrite (Campi Flegrei, Italy) magmatic system. The least-evolved magmatic end-member
shows equilibrium between host glass and the majority of the phenocrysts and is less radiogenic in Sr and Nd than the most-evolved
magma. On the contrary, only the Fe-rich pyroxene from the most-evolved erupted magma is in equilibrium with the matrix glass,
while all other minerals are in isotopic disequilibrium. These magmas mixed prior to and during the Campanian Ignimbrite eruption
and minerals were freely exchanged between the magma batches. Combining the results of the geochemical investigations on magma
end-members with geophysical and geological data, we develop the following scenario. In stage 1, a parental, less differentiated
magma rose into the middle crust, and evolved through combined crustal assimilation and crystal fractionation. In stage 2,
the differentiated magma rose to shallower depth, fed the pre-Campanian Ignimbrite activity and evolved by further open-system
processes into the most-evolved and most-radiogenic Campanian Ignimbrite end-member magma. In stage 3, new trachytic magma,
isotopically distinct from the pre-Campanian Ignimbrite magmas, rose from ca. 6 km to shallower depth, recharged the most-evolved
pre-Campanian Ignimbrite magma chamber, and formed the large and stratified Campanian Ignimbrite magmatic system. During the
course of the Campanian Ignimbrite eruption, the two layers were tapped separately and/or simultaneously, and gave rise to
the range of chemical and isotopic values displayed by the Campanian Ignimbrite pumices, glasses and minerals. 相似文献
20.
D. Rouwet Y. Taran S. Inguaggiato N. Varley J.A. Santiago Santiago 《Journal of Volcanology and Geothermal Research》2008
El Chichón volcano (Chiapas, Mexico) erupted violently in March–April 1982, breaching through the former volcano–hydrothermal system. Since then, the 1982 crater has hosted a shallow (1–3.3 m, acidic (pH ∼ 2.2) and warm (∼ 30 °C) crater lake with a strongly varying chemistry (Cl/SO4 = 0–79 molar ratio). The changes in crater lake chemistry and volume are not systematically related to the seasonal variation of rainfall, but rather to the activity of near-neutral geyser-like springs in the crater (Soap Pool). These Soap Pool springs are the only sources of Cl for the lake. Their geyser-like behaviour with a long-term (months to years) periodicity is due to a specific geometry of the shallow boiling aquifer beneath the lake, which is the remnant of the 1983 Cl-rich (24,000 mg/l) crater lake water. The Soap Pool springs decreased in Cl content over time. The zero-time extrapolation (1982, year of the eruption) approaches the Cl content in the initial crater lake, meanwhile the extrapolation towards the future indicates a zero-Cl content by 2009 ± 1. This particular situation offers the opportunity to calculate mass balance and Cl budget to quantify the lake–spring system in the El Chichón crater. These calculations show that the water balance without the input of SP springs is negative, implying that the lake should disappear during the dry season. The isotopic composition of lake waters (δD and δ18O) coincide with this crater lake-SP dynamics, reflecting evaporation processes and mixing with SP geyser and meteoric water. Future dome growth, not observed yet in the post-1982 El Chichón crater, may be anticipated by changes in lake chemistry and dynamics. 相似文献