Search results for " Magma"

Active geodynamic in the central Mediterranean: Transfer of mantle fluids across the eastern Sicily

2018

Institutions, Symbolic Networks and Transindividual.

2017

The paper introduces a fundamental topic of actual debate in philosophy of institutions: the linguistic dimension of political praxis. In order to analyze such topic, we mention some theoretical points of this debate: a) the actual status of the concept of institution; b) the notion of social imaginary; 3) the notion of semogenesis.

Volatiles in pantellerite magmas: A case study of the Green Tuff Plinian eruption (Island of Pantelleria, Italy)

2013

Abstract The Green Tuff (GT) Plinian eruption, the largest in magnitude at Pantelleria, erupted 3 to 7 km3 DRE of pantellerite magma and a small volume of trachyte. Fifty-nine anorthoclase-hosted melt inclusions from the two basal pumice members were analyzed by FT-IR spectroscopy in order to assess the pre-eruptive H2O content in the pantellerite melt. Microanalytical methods were used to determine major element, Cl, F and S contents. Melt inclusions and glassy groundmasses have a nearly homogeneous pantelleritic composition (peralkaline index = 1.9-2.2) and variable water contents ranging from 1.4 to as high as 4.2 wt %, i.e. much higher than the 1.4 wt % of earlier published studies. The…

Geochemical characteristics of Cretaceous carbonatites from Angola

1999

Abstract The Early Cretaceous (138–130 Ma) carbonatites and associated alkaline rocks of Angola belong to the Parana-Angola-Etendeka Province and occur as ring complexes and other central-type intrusions along northeast trending tectonic lineaments, parallel to the trend of coeval Namibian alkaline complexes. Most of the Angolan carbonatite-alkaline bodies are located along the apical part of the Mocamedes Arch, a structure representing the African counterpart of the Ponta Grossa Arch in southern Brazil, where several alkaline-carbonatite complexes were also emplaced in the Early Cretaceous. Geochemical and isotopic (C, 0, Sr and Nd) characteristics determined for five carbonatitic occurren…

Hydrogen emissions from Erebus volcano, Antarctica

2012

International audience; The continuous measurement of molecular hydrogen (H2) emissions from passively degassing volcanoes has recently been made possible using a new generation of low-cost electrochemical sensors. We have used such sensors to measure H2, along with SO2, H2O and CO2, in the gas and aerosol plume emitted from the phonolite lava lake at Erebus volcano, Antarctica. The measurements were made at the crater rim between December 2010 and January 2011. Combined with measurements of the long-term SO2 emission rate for Erebus, they indicate a characteristic H2 flux of 0.03 kg s-1 (2.8 Mg day-1). The observed H2 content in the plume is consistent with previous estimates of redox cond…

Evolution of the magma system of Pantelleria (Italy) from 190 ka to present

2022

The eruptive history of Pantelleria has been marked by the eruption of nine peralkaline ignimbrites, with inter-ignimbrite episodes from small, local volcanic centres. New whole-rock geochemical data are presented for seven ignimbrites and used with published data for younger units to track compositional changes with time. From»190 ka, silicicmagmatismwas dominated by comenditic trachyte to comendite compositions, evolving along generally similar liquid lines of descent (LLOD). The final ignimbrite, the Green Tuff (»46 ka), was tapped from a compositionally zoned pantelleritic upper reservoir to a trachytic mush zone. Younger (20–7 ka) silicic magmatism has been relatively small scale, with…

Water solubility in trachytic and pantelleritic melts: an experimental study

2021

International audience; Solubility experiments were performed on a trachyte and a pantellerite from Pantelleria. The trachyte has SiO 2 = 65.2 wt%, Al 2 O 3 = 15.2 wt% and a peralkaline index (P.I. = molar[(Na 2 O + K 2 O)/Al 2 O 3 ]) ∼ 1 while the pantellerite has SiO 2 = 72.2 wt%, Al 2 O 3 = 11 wt% and a P.I. = 1.3. Solubility experiments were performed in the pressure range of 50-300 MPa at T = 950°C for the trachyte and 50-200 MPa at T = 850°C for the pantellerite. The water content of experimental glasses was determined by Karl Fischer titration, elemental analyser and FT-IR spectroscopy. Water content appears similar in both compositions for analogous pressure conditions, varying from…

Experimental and thermodynamic constraints on mineral equilibrium inpantelleritic magmas

2020

Abstract Crystallization experiments on two pantellerites from Pantelleria, Italy, provide new evidence for the relationships between mineral phases in pantelleritic rocks as well as the influence of temperature and redox conditions on mineral assemblages. Experiments were performed at 1 kbar with temperature ranging between 750–900°C, and fluid saturation conditions with XH2O (=H2O/H2O+CO2) between 0 and 1. Redox conditions were fixed at, or slightly below, the FMQ buffer. Results show that at temperature of 900 °C pantelleritic magmas are well above the liquidus regardless their water content; we also observed a decrease in liquidus temperature (800°C) with increasingly reducing condition…

Cooling and crystallization recorded in trachytic enclaves hosted in pantelleritic magmas (Pantelleria, Italy): Implications for pantellerite petroge…

2015

Abstract This study focuses on the comenditic trachyte enclaves hosted in pantelleritic lava and pumices emplaced during one of the most recent eruptive events at Pantelleria (~ 6 ka). Enclaves range from mm-sized fragments to dm-sized blocks with spheroidal to amoeboid shapes and characteristic globular surfaces; they are crystal-rich with ~ 30 vol% large anorthoclase, less abundant Fe-rich olivine, clinopyroxene and Fe–Ti oxides. Vesicles ranging from a few mm to 1–2 cm in size are distributed throughout the enclave and are commonly filled with microlite-free vesicular glass. The groundmass presents spectacular textures, including fine to coarse spherulites and hopper and skeletal microli…

Potassic and sodic igneous rocks from eastern Paraguay: their origin from the lithospheric mantle and genetic relationships with the associated Paran…

1997

3 DIPARTIMENTO DI SCIENZE DELLA TERRA, UNIVERSITY OF TRIESTE, VIA E. WEISS 8, I-34127 TRIESTE, ITALY 4 INSTITUTO DE GEOCIENCIAS, UNIVERSIDADE DE SAO PAULO, C.P. 30627, 01051 SAO PAULO, SP, BRAZIL 5 DIPARTIMENTO DI SCIENZE DELLA TERRA, ‘LA SAPIENZA’ UNIVERSITY, PIAZZALE ALDO MORO 5, I-00185, ROME, ITALY 6 ISTITUTO DI MINERALOGIA, PETROGRAFIA E GEOCHIMICA, UNIVERSITY OF PALERMO, VIA ARCHIRAFI 36, I-90100,