69 research outputs found
The crystal-chemistry of okanoganite-(Y): an example of (sims+empa+sref) multi-analytical approach to solve a complex problem.
No full textThe crystal structure of piergorite-(Ce), Ca8Ce2(Al0.5 Fe3+0.5) Σ 1(□,Li,Be)2Si6B8O36(OH,F)2: A new borosilicate from Vetralla, Italy, with a modified hellandite-type chain
No full textPiergorite-(Ce) is a new mineral found at Tre Croci, Vetralla, Italy with simplified formula Ca8Ce2 (Al0.5Fe0.53+)∑1(□,Li,Be)2Si6B8O36(OH,F)2. It occurs as strong intergrowths of small crystals, colorless to pale yellow, associated with sanidine, mica, magnetite, rutile, titanite, and other Th-U-REE bearing minerals, in miarolitic cavities of a syenitic ejectum. Piergorite-(Ce) is biaxial negative, nα = 1.717 (1), nβ = 1.728 (1), and nγ = 1.735 (1), 2Vmeas = 68(2)°, X = b, and Z ^ c = 7(1)°. Crystals show tabular habit and a very good {010} cleavage; twinning along the (30-1) plane produces “L” forms. The three strongest lines in the simulated powder diffraction pattern (dobs, I, hkl) are: 2.65 Å, 100.0, (213, -413); 1.91 Å, 48.3, (223, -423, 821); 2.90 Å, 44.9, (-603, -612). The structure was solved by Patterson synthesis from X-ray diffraction data [monoclinic, space group P2/a, a = 28.097(3) Å, b = 4.777(1) Å, c = 10.236(2) Å, β = 96.81(1)°, V = 1364.2(7) Å3, Z = 2] and was refined to a final Robs = 0.059 for 6480 Fo with Io > 3σ (Io). The structure shows similarities with the hellandite group because Si and B tetrahedra form chains along c. Hellandite structure is characterized by a single chain of five-membered rings, whereas piergorite-(Ce) shows a double chain of five-membered rings interconnected by a single octahedral site to form a three-dimensional framework containing five independent eightfold-coordinated M sites and a partly occupied T-cavity
The crystal chemistry of piergorite, (Ca8REE2)10 (Al0.5Fe0.5) (vac, Li,Be)2Si6B8O36(OH,F)2: a new REE-borosilicate from Tre Croci, Vetralla, Italy.
No full textWater, lithium and trace element compositions of olivine from Lanzo South replacive mantle dunites (Western Alps): New constraints into melt migration processes at cold thermal regimes
No full textNew perspectives on the origin of olivine-rich troctolites and associated harrisites from the Ligurian ophiolites (Italy)
No full textDetails of the analytical techniqu
Water-rich basalts at mid-ocean-ridge cold spots
No full textAlthough water is only present in trace amounts in the suboceanic upper mantle, it is thought to play a significant role inaffecting mantle viscosity, melting and the generation of crust atmid-ocean ridges. The concentration of water in oceanic basaltshas been observed to stay below 0.2wt%, except for water-richbasalts sampled near hotspots and generated by ‘wet’ mantle plumes. Here, however, we report unusually high water contentin basaltic glasses from a cold region of the mid-ocean-ridgesystem in the equatorial Atlantic Ocean. These basalts aresodium-rich, having been generated by low degrees of meltingof the mantle, and contain unusually high ratios of light versusheavy rare-earth elements, implying the presence of garnet in the melting region. We infer that water-rich basalts from suchregions of thermal minima derive from low degrees of ‘wet’melting greater than 60 km deep in the mantle, with minor dilution by melts produced by shallower ‘dry’ melting—a viewsupported by numerical modelling. We therefore conclude thatoceanic basalts are water-rich not only near hotspots, but also at‘cold spots’
Recupero e valorizzazione storico-urbanistico-ambientale della Piazza del Duomo
No full textPubblicato in:
Forma Urbis/Forma Agri. Residenza e spazio pubblico a Cerignola/Residence and public space in Cerignola in Aa.Vv., Community / architecture. Documents from the Festival Architettura 5 2009-2010, a cura di E. Prandi, Festival Architettura Edizioni, Parma, 2010.
Esposto in mostra in occasione del Festival dell’Architettura 5 2009-2010, Parma, Reggio Emilia Modena, 26 novembre-12 dicembre 2010
The fate of B, Cl and Li in the subducted oceanic mantle and in the antigorite breakdown fluids
No full textWe present an inventory of B, Cl and Li concentrations in (a) key minerals from a set of ultramafic samples featuring the
main evolutionary stages encountered by the subducted oceanic mantle, and in (b) fluid inclusions produced during high-pressure breakdown of antigorite serpentinite. Samples correspond to (i) nonsubducted serpentinites (Northern Apennine and Alpine ophiolites), (ii) high-pressure olivine-bearing antigorite serpentinites (Western Alps and Betic Cordillera), (iii) high-pressure olivine–orthopyroxene rocks recording the subduction breakdown of antigorite serpentinites (Betic Cordillera). Two main dehydration episodes are recorded by the sample suite: partial serpentinite dewatering during formation of metamorphic
olivine, followed by full breakdown of antigorite serpentine to olivine + orthopyroxene + fluid. Ion probe and laser ablation ICPMS (LA ICP-MS) analyses of Cl, B and Li in the rock-forming minerals indicate that the hydrous mantle is an important carrier of light elements. The estimated bulk-rock B and Cl concentrations progressively decrease from oceanic serpentinites (46.7 ppm B and 729 ppm Cl) to antigorite serpentinites (20 ppm B and 221 ppm Cl) to olivine–orthopyroxene rocks (9.4 ppm B and 45 ppm Cl). This suggests release of oceanic Cl and B in subduction fluids, apparently without inputs from external sources.
Lithium is less abundant in oceanic serpentinites (1.3 ppm) and the initial concentrations are still preserved in high-pressure antigorite serpentinites. Higher Li contents in olivine, Ti-clinohumite of the olivine–orthopyroxene rocks (4.9 ppm bulk rock Li), as well as in the coexisting fluid inclusions, suggest that their budget may not be uniquely related to recycling of oceanic Li, but may require input from external sources.
Laser ablation ICP-MS analyses of fluid inclusions in the olivine–orthopyroxene rocks enabled an estimate of the Li and
B concentrations in the antigorite breakdown fluid. The inclusion compositions were quantified using a range of salinity
values (0.4–2 wt.% NaClequiv) as internal standards, yielding maximum average fluid/rock DB = 5 and fluid/rockDLi = 3.5. We also performed model calculations to estimate the B and Cl loss during the two dehydration episodes of serpentinite subduction. The first event is characterized by high fluid/rock partition coefficients for Cl (f100) and B (f60) and by formation of a fluid with salinity of 4–8 wt.% NaClequiv. The antigorite breakdown produces less saline fluids (0.4–2 wt.% NaClequiv) and is characterized by lower partition coefficients for Cl (25–60) and B (12–30). Our calculations indicate that the salinity of the subduction fluids decreases with increasing depths. Fluid/rockDB/fluid/rockDCl<1 ( about 0.5) indicates that Cl
preferentially partitions into the evolved fluids relative to B and that the B/Cl of fluids progressively increases with
increasing depths and temperatures.
Despite light element release in fluids, appreciable B, Cl and Li are still retained in chlorite, olivine and Ti-clinohumite
beyond the antigorite stability field. This permits a bulk storage of about 10 ppm B, 45 ppm Cl and 5 ppm Li, i.e.,
concentrations much higher than in mantle reservoirs. Chlorite is the Cl repository and its stability controls the Cl and H2O budget beyond the antigorite stability; B and Li are bound in olivine and clinohumite. The subducted oceanic mantle thus retains light elements beyond the depths of arc magma sources, potentially introducing anomalies in the upper mantle
Geochemistry of basic magmatism of Western Antarctic Rift: implications for volatiles storage and recycling in the mantle
No full textNo abstract available
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