1,720,990 research outputs found
Influence of pre-existing nuclei on the crystallization kinetics of primitive alkaline magmas: insights on the deep feeding system of the campi flegrei Volcanic district
Full text linkAiming to evaluate the influence of pre-existing nuclei on the clinopyroxene crystallization kinetics, time-series experiments were performed using both natural and vitrified starting materials. Experiments were carried out at pressure of 0.8 GPa, temperatures between 1220 and 1250 °C, and dwell times ranging from 0.16 to 12 h. Clinopyroxene growth rates of the runs performed using the natural starting material containing pre-existing nuclei (~2 × 10−7 to ~6 × 10−8 cm∙s−1) are higher than those of the runs performed using the vitrified one (~3 × 10−7 to ~2 × 10−8 cm∙s−1). In both cases the growth rates decrease with increasing time. Conversely, clinopyroxene nucleation rates are lower in the experiments performed using the natural powder (102 and 10 mm−3 s−1) compared to those performed with the glassy starting material (105 and 103 mm−3∙s−1). The nucleation rates tend to decrease increasing dwell time in all the series up to ~3 h, after which it remains nearly constant. Finally, the combination of the obtained clinopyroxene growth rates with the crystal size analysis of natural clinopyroxenes, allowed to estimate the magma ascent rate and the recharge rate of the Campi Flegrei Volcanic District deep reservoir
High-Mg basalts at Capo Marargiu (Sardinia, Italy): experimental constrains on amphibole stability
No full textHigh pressure experiments on kinetic and rheological properties of primitive alkaline magmas: constraints on deep magmatic processes at the Campi Flegrei Volcanic District
Full text linkDefining the timescales of magma storage and ascent beneath active volcanoes is a fundamental tool in volcanological investigation of the last decade to constrain pre-eruptive magmatic processes and magma chamber dynamics, since it is able to provide the basis for volcanic hazard assessment. This Ph.D. project focuses on the investigation of the deep portion of the Campi Flegrei Volcanic District plumbing system (crustal-mantle boundary; ~25 km of depth), in correspondence of which the presence of a possible crystallization zone has been hypothesized on the basis of melt inclusion studies, seismic data interpretations, gravimetric and petrological modelling and experimental data. The Campi Flegrei Volcanic District, which includes the Campi Flegrei and the islands of Ischia and Procida, represents one of the most active volcanic areas in the Mediterranean region and one of the most dangerous volcanic complexes on Earth owing to the intense urbanization of the area. Many petrological, geochemical and geophysical surveys were carried out in the Campania Active Volcanic Area that have helped to define the main architecture and the development of the sub-volcanic system. Nevertheless, the dynamic processes that operate during the earliest, deepest differentiation steps of primitive magmas that fed all Campi Flegrei eruptions are yet poorly constrained. The knowledge of the dynamics and residence and ascent timescales of magma at deep levels, indeed, may be the key to understand the triggering mechanisms of volcanic eruptions, and are essential for understanding the rates at which magmas are supplied to volcanic complexes. In this thesis, the investigation of the kinetic and rheological properties of a K-basaltic magma at Moho depth, together with the partitioning of trace elements between crystal and melts, has allowed to fill some gaps relative to the knowledge of the deep portion of the Campi Flegrei Volcanic District plumbing system, providing magma residence time and ascent timescales, and models for deep magmatic differentiation processes
Amphibole growth from a primitive alkaline basalt at 0.8 GPa: Time-dependent compositional evolution, growth rate and competition with clinopyroxene
No full textAmphibole growth rates were experimentally determined at hydrous (3.3-4.2 wt% H2O), isobaric (0.8 GPa) conditions, variable temperature (1030 and 1080 °C) and dwell time (0.25, 3, 6, and 9 h), using as starting material a primitive alkaline basalt from Procida island (Campi Flegrei Volcanic District, south Italy). Amphibole growth rates decrease from 1.5·10-7 to 2.9·10-8 cm·s-1 as the duration of our experiments increase from 0.25 to 9 hours. Moreover, increasing both temperature and water content leads to similar growth rate increase at constant dwell time. The comparison between amphibole and clinopyroxene growth rates determined at the same experimental conditions reveals for amphibole a faster growth relatively to the coexisting clinopyroxene, regardless of the dwell time. Furthermore, the experimental time appears to be a critical parameter for the composition of synthetic amphiboles; specifically, edenite is the dominant composition in short experiments (≤3 h), particularly, at low temperature (1030 °C), whereas the magnesiohastingsitic amphibole becomes progressively more important shifting towards longer duration and higher temperature run conditions. The magnesiohastingsite, on the basis of the amphibole-liquid Fe-Mg exchange coefficient values, results to be the compositional term representative of amphibole-melt equilibrium at the investigated P-T-H2O conditions. Finally, experimental growth rates from this study have been used to investigate the crystallization time of natural amphiboles and clinopyroxenes from the Oligo-Miocene cumulates of north-western Sardinia (i.e. Capo Marargiu Volcanic District, Italy), yielding crystallization times of 1.46-3.12 yr
Clinopyroxene growth rates at high pressure. Constraints on magma recharge of the deep reservoir of the Campi Flegrei volcanic district (south Italy)
No full textClinopyroxene growth rates were experimentally determined in a K-basaltic rock from Campi Flegrei Volcanic District (south Italy). The primary objective was to provide constraints on the clinopyroxene crystallization kinetics at high pressure: we carried out a series of experiments at 0.8 GPa, 1030–1250 °C, 1 ≤ H2O ≤ 4 wt.%, with durations of 0.25, 3, 6 and 9 h. Overall, growth rate reaches a maximum value in the shortest experiments (~ 3·10−7 cm·s−1), decreasing to ~ 1·10−8 cm·s−1 in the longest duration runs. Temperature and water content do not seem to significantly affect the growth rate. Moreover, partition coefficients based on the crystal-liquid exchange show that mineral chemistry progressively approaches equilibrium with increasing run duration. Furthermore, to estimate the magma recharge of the deep reservoirs, we combined the determined growth rates with data from thermobarometry and from crystal size distribution analyses of clinopyroxenes in the most primitive scoria clasts of the Campi Flegrei Volcanic District (CFVD). We obtained a minimum residence time of ~ 5 months for the larger clinopyroxene population, and an ascent velocity of ~ 0.5·10−4 m·s−1 for the CFVD K-basaltic magma. The smaller clinopyroxene phenocrysts and microlite populations, however, suggest that the late stage of Procida magma crystallization took place in disequilibrium conditions
Experimental time constraints on the kinetic and chemistry of amphibole at deep crustal levels
No full textAiming to improve the current knowledge about amphibole growth kinetics at deep crustal levels, new amphibole growth rate data are provided. Our findings, indeed, may be useful to correctly interpret the textural features of amphibole-bearing mafic cumulates and rocks, and for a better constraining of the timescales of magmatic processes at upper mantle-lower crustal depths. Experiments were performed to determine the amphibole growth rates in a primitive alkaline basalt from Procida island (Campi Flegrei Volcanic District, southern Italy) at the following conditions: temperature of 1030 and 1080 °C, pressure of 0.8 GPa, water content in the range 3.3-4.2 wt%, and variable dwell time from 0.25 to 9 h. Amphibole growth rates range from 1.5·10-7 to 2.9·10-8 cm·s-1 with increasing the duration of the experiments. It is observed that, keeping a constant dwell time, an increase of the experimental temperature or of the water content results in comparable growth rate increase. Coexisting synthetic amphibole and clinopyroxene show a faster growth rates in favour of amphibole regardless of the dwell time, since the chemical and structural similarities of these minerals cause kinetic competition. Moreover, the chemical composition of amphibole is influenced mainly by the experimental time; in detail, in the shortest (≤3 h) and low temperature runs edenite is the prevailing composition whereas the magnesiohastingsitic term becomes dominant at higher temperature and longer run duration. Based on the interpretation of the Fe-Mg exchange coefficient values between amphibole and coexisting liquid, the magnesiohastingsitic amphibole is considered to be the stable term at the investigated run conditions. Finally, the resulting growth rates have been applied to constrain the crystallization time of natural amphiboles and clinopyroxenes from the Oligo-Miocene cumulates of north-western Sardinia (i.e., Capo Marargiu Volcanic District, Italy), yielding crystallization times in the range 1.46-3.12 yr
Experimental re-melting of a continental crust:probing the deep storage zone of Campi Flegrei and Vesuvius magmas
Full text linkMantle magmas interact with surrounding rocks during their ascent and storage in the continental crust, leading to open system processes as wall rock partial melting. In this study, we have experimentally investigated the reactions between a leucosome depleted migmatite and a primitive K-basaltic of Campi Flegrei (Italy). Experiments were carried out at pressure of 0.8 GPa temperatures from 1250 °C to 1050 °C and constant temperature and thermal gradient conditions. The experimental products consist of biotite-free migmatite, glass and crystals of clinopyroxene, olivine, plagioclase and Cr-spinel with proportions that vary as a function of temperature. Open system isothermal experiments indicate that the chemistry of melts and phase relationships are controlled by the high Al2O3 content of leucosome depleted migmatite with the glass composition shifting from K-trachybasalt towards shoshonite as the temperature decreases from 1200 °C to 1125 °C. At temperatures 1150°C, migmatite assimilation is not exclusively due to the assimilation fractional crystallization process because evidence of mingling and mixing is observed. T-gradient experiment shows melt composition ranging from shoshonite to phono-tephrite moving from the slightly crystalline zone (T = 1250 –1210 °C) at the bottom of the capsule towards the highly crystalline zone (T = 1160 –1140 °C). This SiO2-constant trend indicates that at temperature below the basalt solidus, the assimilation of leucosome depleted crust is represented almost exclusively by the biotite breakdown, leading to the increase in Al, Mg, Fe, Ti, and K activities in the system. The shoshonitic composition obtained in our experiments could represent the parental magma for both Campi Flegrei volcanic district and Vesuvius magmatic systems, indicating modification in a deep storage zone through mixing with the partial melts derived from restitic continental crust.</p
Magma residence time, ascent rate and eruptive style of the November ash-laden activity during the 2021 Tajogaite eruption (La Palma, Spain)
Full text linkWe combined compositional analyses, crystal size distributions and geothermobarometry of tephra erupted during the 2021 Tajogaite eruption (La Palma, Spain), focusing on samples collected in November 2021 associated with a period of abundant ash emission characteristic of the second half of the eruption (from October onwards). Magma erupted in November exhibits a more primitive basanitic composition than the earlier magma. Crystallization temperatures range between ~1100-1160 °C (H2O = 1-3 wt.%) for phenocrysts and microphenocrysts, with corresponding pressures indicating depths from ~10 to ~30 km. Crystal size distribution analysis reveals short (minutes) residence times for plagioclase. Finally, magma ascent velocities (~0.01-0.3 m/s) suggest acceleration and fragmentation in the shallowest part of the conduit. Our results suggest that the trigger of the November explosive activity can be attributed to complex feedback between gas emission rates, changes in conduit geometry, and magma ascent rate
Rheology of primitive alkaline basalts: constraints on the pre-eruptive system of Campi Flegrei (Naples, Italy)
No full textThe knowledge of the rheology of magmas at high
pressure and temperature is of fundamental importance to
model their mobility, ascent rate and volcanic activity at
surface. In this study, we determined the viscosity and the
atomic structure of the nominally anhydrous APR16 alkali
basalt representative of the least-evolved magmas of
Phlegrean Volcanic District (Phlegrean Fields, Italy;
Bonechi et al., 2017). The sample is a lithic fragment
belonging to the Solchiaro hydromagmatic tuff of Procida
island, characterized by a porphyritic texture (P.I. 12%
volume) with phenocrysts of olivine (Fo85-80),
occasionally hosting Cr-spinel grains (Cr# ~0.50), and
clinopyroxene (Wo46-48 En46-31 Fs6-23), and a
groundmass made of olivine, clinopyroxene, plagioclase
(An79-52), Ti-magnetite (Usp4.1-4.4). The APR16 has
[Mg/(Mg+Fe)] 0.66, 49 wt% SiO2, 4.4 wt% of total alkali
(Na2O+K2O) and ~12 wt% of CaO. The anhydrous glass
was prepared at Bayerisches Geoinstitut by using a gasmixing
furnace. The rock powder was melted at 1400 °C
for 15 minutes at atmospheric pressure and oxygen
fugacity buffered at Nickel-Nickel Oxide level using a
CO/CO2 gas mixture. The viscosity of glassy APR16 was
determined by the in situ falling sphere technique at P of
0.7-2.5 GPa and T of 1335-1700°C using the Paris-
Edinburgh press available at the 16BMB beamline at the
Advanced Photon Source (Argonne National Lab, Illinois,
USA). The falling velocity of the Pt probing spheres was
measured by X-ray imaging using a high-speed camera
recording 500 frames per second. In addition, analyses of
the melt structure were performed by using multi-angle
energy dispersive X-ray diffraction technique. Preliminary
data show the viscosity being in the range of 0.1-1 Pa·s at
the target P and T. These viscosity values can be used to
model the mobility and ascent velocity of primitive alkali
basalts considered to be parental magmas at Campi Flegrei
with important implications for the volcanic hazard of the
area over time
- …
