1,721,031 research outputs found
Manganese bearing fluids in composite vein systems in the braunite deposit from Molinello Mine (Val Graveglia, Notrthern Apennine, Italy)
No full textAlteration of braunite ores from Eastern Liguria (Italy) during syntectonic veining processes: mineralogy and fluid inclusions.
No full textTransmission electron microscopy applied to fluid inclusion investigation
No full textThe transmission electron microscope (TEM) allows a detailed characterization of textural and chemical features of fluid inclusions (shape inner compositions and inner textures), a: a resolution higher than that attainable with an optical microscope (OM). TEM investigation indicates that most fluid inclusions appear as perfectly euhedral negative crystals, with variable shape (from prismatic to equant) and size (typically from <0.02 to 0.15 μ). Inner texture (fluid phase/melt distribution) and composition are variable as well. Different kinds of negative crystals may coexist in the same trail of inclusions, possibly indicating locally variable trapping conditions. A critical feature, revealed by TEM, is that inclusions are often connected to structural defects (in particular, to dislocation arrays), which are undetected by optical microscopy. The identification of these hidden nanostructures should be taken into account for the correct petrological interpretation of microthermometric results, particularly when controversial data have been obtained. In fact, these nanostructures may represent a possible path for fluid phase leakage, thus modifying the original composition and/or density of the inclusions. © 2001 Elsevier Science B.V. All rights reserved
Fluid inclusion evidence for progressive folding in metasediments of the Voltri Group (Western Alps, Italy).
No full textRe-equilibration of glass and fluid inclusions in xenolith olivines: a tem study
No full textCO2-rich fluid inclusions were observed in olivine from mantle xenoliths from the Island of Tenerife, Canary Islands. Inclusions that are present in deformed olivine porphyroclasts consist of CO2 fluids + minor high-alkali, silica-rich glass ± Ni-Fe sulfides. Homogenization temperature distributions reveal that most of the inclusions (originally trapped at mantle conditions) re-equilibrated to lower density values. Transmission electron microscope (TEM) studies indicate that most fluid inclusions appear as perfectly euhedral negative crystals, with variable shape (from prismatic to equant), size (from <0.02 to 0.15 μm), and inner texture. Different kinds of negative crystals may coexist in the same trail of inclusions. Inclusions are commonly connected to structural defects (dislocation arrays formed after fracture healing), which represent a possible path for leakage of the fluid phase. These microstructures, undetectable by optical microscopy, could have modified the original composition and/or density of the inclusions through CO2 diffusion; consequently, they should be taken into account for the correct interpretation of microthermometric results
Carbonate metasomatism and CO2 lithosphere-asthenosphere degassing beneath the Western Mediterranean: An integrated model arising from petrological and geophysical data
No full textWe present an integrated petrological, geochemical, and geophysical model that offers an explanation for the present-day anomalously high non-volcanic deep (mantle derived) CO2 emission in the Tyrrhenian region. We investigate how decarbonation or melting of carbonate-rich lithologies from a subducted lithosphere may affect the efficiency of carbon release in the lithosphere-asthenosphere system. We propose that melting of sediments and/or continental crust of the subducted Adriatic-Ionian (African) lithosphere at pressure greater than 4 GPa (130 km) may represent an efficient mean for carbon cycling into the upper mantle and into the exosphere in the Western Mediterranean area. Melting of carbonated lithologies, induced by the progressive rise of mantle temperatures behind the eastward retreating Adriatic-Ionian subducting plate, generates low fractions of carbonate-rich (hydrous-silicate) melts. Due to their low density and viscosity, such melts can migrate upward through the mantle, forming a carbonated partially molten CO2-rich mantle recorded by tomographic images in the depth range from 130 to 60 km. Upwelling in the mantle of carbonate-rich melts to depths less than 60-70 km, induces massive outgassing of CO2. Buoyancy forces, probably favored by fluid overpressures, are able to allow migration of CO2 from the mantle to the surface, through deep lithospheric faults, and its accumulation beneath the Moho and within the lower crust. The present model may also explain CO2 enrichment of the Etna active volcano. Deep CO2 cycling is tentatively quantified in terms of conservative carbon mantle flux in the investigated area. © 2009 Elsevier B.V. All rights reserved
Diamond-bearing COHS fluids in the mantle beneath Hawaii
No full textWe apply Raman microspectroscopy to exceptionally high-density CO2 (+H2O+H2S) fluid inclusions containing nanocrystalline diamonds, which are present in garnet pyroxenites from Salt Lake Crater from Oahu (Hawaii), and show for the first time the presence of free diamond-bearing carbonate-rich fluids/melts, originated within the asthenospheric mantle at depths greater than 150 km, in the diamond stability field. We argue that these fluids can migrate, generate compositional and rheological modifications to form small-scale fluid-rich regions beneath Hawaii, which are easily melted to give enriched basaltic magmas at normal mantle temperatures
Gradual and selective trace-element enrichment in slab-released fluids at sub-arc depths
No full textThe geochemical signature of magmas generated at convergent margins greatly depends on the nature of fluids and melts released during subduction. While major- and trace-elements transport capacity of ultrahigh pressure (UHP) hydrous-silicate melts has been investigated, little is known about solute enrichment and fractionation in UHP (>3.5–4 GPa) solute-rich aqueous fluids released along colder geothermal gradients. Here, we performed in situ LA-ICP-MS trace-element analyses on selected UHP prograde-to-peak fluid inclusions trapped in a kyanite-bearing quartzite from Sulu (China). The alkali-aluminosilicate-rich aqueous fluid released from the meta-sediments by dehydration reactions is enriched in LILE, U, Th, Sr, and REE. Inclusions trapped at increasing temperature (and pressure) preserve a gradual and selective trace-element enrichment resulting from the progressive dissolution of phengite and carbonate and the partial dissolution of allanite/monazite. We show that, at the investigated P-T conditions, aqueous fluids generated by dissolution of volatile-bearing minerals fractionate trace-element distinctly from hydrous-silicate melts, regardless of the source lithology. The orogenic/post-orogenic magmas generated in a mantle enriched by metasomatic processes involving either solute-rich aqueous fluids or hydrous-silicate melts released by the slab at UHP conditions can preserve evidence of the nature of these agents
- …
