1,721,062 research outputs found
Rare element minerals’ assemblage in El Quemado pegmatites (Argentina): insights for pegmatite melt evolution from gahnite, columbite-group minerals and tourmaline chemistry and implications for minerogenesis
Full text linkThe pegmatite district of El Quemado (NW Pampean Ranges, NW Argentina) hosts several Ordovician pegmatite bodies of theLCT (Li, Cs, Ta) type. We present paragenetic assemblages for a set of samples from two of the El Quemado pegmatite groups,Santa Elena and Tres Tetas, and mineral chemistry analyses for gahnite, columbite-group minerals, tourmaline, micas, albite,microcline, and discuss the relation between their major element composition and the degree of evolution of pegmatite melts. Thechemical composition of rare element minerals allows recognizing an evolutive trend reaching highly differentiated compositions, with complex paragenetic assemblages including Li-, Zr-, U-, Zn-, P-, Mn- and Ta-bearing minerals. The temperature ofcrystallization during the magmatic phase was below 400 °C. Non-pervasive hydrothermal alteration, testified by a moderatepresence of phyllosilicates, affected the pegmatite bodies. Chlorite geothermometry indicates that the circulation of postmagmatic hydrothermal fluids occurred at a temperature ranging between 200 °C and 250 °C. The mineralogical featuresrecognized in the El Quemado pegmatite rocks have implications for the metallogenesis of the region, suggesting that thepegmatites potentially contributed to the genesis of Ta-Nb oxide placer mineralizations.Fil: López, Vanina Lucrecia. Consejo Nacional de Investigaciones Científicas y Técnicas. Centro Científico Tecnológico Tucumán. Instituto Superior de Correlación Geológica. Grupo Vinculado al INSUGEO- Centro de Estudios Geológicos Andinos; ArgentinaFil: Fulignati, Paolo. Universita Degli Studi Di Pisa. Dipartimento Di Scienze Della Terra; ItaliaFil: Gioncada, Anna. Universita Degli Studi Di Pisa. Dipartimento Di Scienze Della Terra; ItaliaFil: Azarevich, Miguel Basilio. Consejo Nacional de Investigaciones Científicas y Técnicas. Centro Científico Tecnológico Tucumán. Instituto Superior de Correlación Geológica. Grupo Vinculado al INSUGEO- Centro de Estudios Geologicos Andinos; Argentin
Fluid inclusion evidence on the direct exsolution of magmatic brines from a granite intrusion beneath the eastern sector of Larderello geothermal field (Italy)
Full text linkThis work is based on a fluid inclusion investigation on two core samples (sampled at 3017m and 4150m of depth) of a granite intrusion drilled by the Travale 1 sud geothermal well, in the eastern sector of Larderello geothermal field. Fluid inclusion data demonstrate that the earliest fluids circulating in the intrusion were high-temperature brines exsolved directly from the crystallizing magma during its ascent in the shallow crust. The progressive release of magmatic fluids from the crystallizing granitic magma probably occurred under confining lithostatic pressure of about 200 MPa.
Two phase fluid inclusions represent the hydrothermal meteoric water-dominated fluids that penetrated in the granite after opening of the system, induced by cooling and consequent transition from ductile behaviour to brittle fracturing. Type 1b two phase fluid inclusions, having temperature of homogenization that agree well with down-hole measured temperatures, may be considered to approximate the fluid that is actually circulating in the granite in recent times
Hydrothermal fluid evolution in the "Botro ai Marmi" quartz-monzonitic intrusion (Campiglia Marittima, Tuscany, Italy). Evidence from a fluid inclusion investigation
Full text linkAbstract:
The quartz-monzonitic intrusion of "Botro ai Marmi" (Tuscany, Italy) can be considered to be a typical example of an intrusion-centered magmatic hydrothermal system. The evolution of hydrothermal fluids in the "Botro ai Marmi" intrusion was investigated using fluid inclusion analyses to provide suitable physico-chemical constraints on the fluids involved in the late- to postmagmatic hydrothermal activity that affected the intrusion, providing inferences on their origin and variations of temperature and pressure with time.
This work demonstrates that the earliest fluids circulating in the "Botro ai Marmi" intrusion were high-temperature brines exsolved directly from the crystallizing magma. This fluid circulated in the intrusion under lithostatic conditions (P > 90 MPa, T > 540°C). A second evolutionary stage of the magmatic hydrothermal system is marked by the transition from lithostatic (>90 MPa) to
hydrostatic dominated conditions (50 to 10 MPa). In this stage the fluids are also interpreted to be mainly orthomagmatic in origin but unmixed in a high-salinity brine and in a low-salinity vapor aqueous phase, at a temperature ranging from about 500°C to 300°C. These fluids were responsible for the potassic alteration facies. At a later stage of hydrothermal evolution, abundant meteoric dominated fluids entered the system and are associated with propylitic alteration. This event marks the transition from a magmatic-hydrothermal system to a typical hydrothermal (“geothermal”) system, which can be assumed to be similar to some extent to the nearby active high-enthalpy geothermal system of Larderello. Low-temperature and low-salinity meteoric water-dominated fluids characterize the latest stage of the "Botro ai Marmi" hydrothermal system
Tracing volatile exsolution within the 472 AD "Pollena" magma chamber of Vesuvius (Italy) from melt inclusion investigation
No full textThis paper reports the volatile contents of melt inclusions from juvenile (Lc-phonolite to phonotephrite) and cognate xenoliths
from the 472 AD eruption of Vesuvius. This enables us to infer on pre-eruptive volatile content of magmas that fed the eruption and
to trace the volatile behavior in the chamber and at its peripheral parts. Different types of inclusions were identified within both
juvenile fragments and cognate xenoliths and subsequently analyzed for major elements and volatile contents. The water contents
of melt inclusions from juvenile fractions indicate trapping pressures of about 95 MPa, corresponding to a magma chamber at
approximately 3.5–4.5 km depth.
The degassing of H2O, Cl, and S from melt within the 472 AD magma chamber is highlighted by the compositions of melt
inclusions. In contrast, F was not partitioned into volatile phases and was instead concentrated in melts within the upper portions
and periphery (solidification front) of the chamber.
The chemistry of melt inclusions from the solidification front of the magma chamber indicates that the system was saturated
with a hydrous chloride phase that directly exsolved from melt as a hypersaline aqueous fluid phase
Presence of native gold and tellurium in the active high sulfidation system of La Fossa volcano (Vulcano, Italy)
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