1,115 research outputs found
Emerging technologies in solid drug delivery: An interview with Nadia Passerini
No full textNadia Passerini is interviewed by Hannah Makin, Commission Editor. Nadia Passerini is Associate Professor of Pharmaceutical Technology at the University of Bologna (Bologna, Italy). She obtained the degree in Pharmaceutical Chemistry and Technology at the University of Bologna in 1992 and the PhD in Pharmaceutical Science in 1997. Her research focuses on the study of drug delivery systems, developing new technologies and new apparatus for the production of solid dosage forms (microparticles, granules and tablets), which can optimize the bioavailability of drugs according to the specific needs of the therapy. Furthermore, she is interested in the solid-state characterization of the produced delivery systems in order to correlate their physicochemical properties to the in vitro release of the drugs. Currently, her research focuses in particular on the production and characterization of microparticles produced by the spray congealing technology. She is author of over 50 international peer-reviewed publications and over 50 contributions (poster and oral presentations) to national and international conferences
The “W-type” LILE signature of deep subduction zone fluids
No full textSubduction zones are the Earth’s environments where fluids or melts released by the
slab recycle elements into the mantle wedge, triggering partial melting and arc volcan-
ism. Despite the recent advancements in understanding the nature and composition of
the fluid phase released from the subducted slab, the interaction of this fluid with the
overlying mantle wedge remains poorly constrained. Information on the geochemical
exchange processes between suduction fluids and sub-arc mantle can be gained by
the study of metasomatised UHP ultramafic rocks in continental basements. A rele-
vant case study is represented by garnet orthopyroxenites from the Maowu Ultramafic
Complex, Dabie Shan, China. Such pyroxenites are locally bounded by phlogopite-
rich layers and are hosted by garnet-coesite gneisses. They contain orthopyroxene
(Opx2 ) + garnet (Grt2 )
± clinopyroxene which form at the expense of a previous
ultramafic olivine + garnet bearing paragenesis. Grt2 includes core clusters of primary
polyphase inclusions corresponding to a solute-rich aqueous fluid enriched in LILE
and LREE (Malaspina et al., 2006a). Textural and geochemical data demonstrate that
the Maowu Ultramafic Complex consists of metasomatic layers produced after the
reaction of mantle peridotites with a hydrous granitic melt (or a solute-rich supercrit-
ical liquid) sourced by the associated crustal rocks at UHP conditions (4.0-6.0 GPa,
700-750 ̊C). This hydrous metasomatic fluid phase likely loses elements such as SiO2 ,
Al2 O3 and K2 O during the reactive flow in the mantle peridotites, forming phlogopite-
rich layers and garnet orthopyroxenites. On the other hand, the H2 O component of the
hydrous solute-rich agent evolves into a residual aqueous fluid which concentrates the
incompatible LILE and LREE.
The trace element pattern of this fluid shows a peculiar “W-type” LILE signature char-
acterised by positive spikes of Cs, Ba, and Pb relative to Rb and K, thereby suggesting
selective enrichment in some LILE. Previous works on K-Rb-Cs partitioning between
phlogopite and fluid at 2.0 and 4.0 GPa (Melzer and Wunder, 2001) indicate that phl-
ogopite preferentially retains Rb and K with respect to Cs. They also demonstrate
that with increasing phlogopite crystallisation, the Cs/Rb ratio in the coexisting fluid
continuously increases. Formation of phlogopite layers bounding the Maowu orthopy-
roxenites may play an important role on the partitioning of incompatible elements,
resulting in a selective LILE enrichment of the residual crustal metasomatic fluid. The
mantle phases pyroxene and olivine do not incorporate large amounts of LILE (Ay-
ers et al., 1997). Moreover, absence of amphibole at P>3.0 GPa enables the residual
aqueous fluid to transfer the W-shaped signature (positive spikes of Cs, Ba, Pb, and
negative anomalies of Rb, K) to the locus of sub-arc partial melting, once it escapes the
metasomatic slab-mantle interface. An important aspect of this filtering process is that
the trace element fingerpint of other slab lithologies in Dabie Shan (Malaspina et al.,
2006b), as well as of wedge-type Alpine amphibole + garnet peridotites (Ulten Zone,
Italian Alps) is similar to the one of such residual fluid (Scambelluri et al., 2006). This
indicates that the “W-type” slab fluids are able to transfer their trace element signature
within the slab and to the locus of fluid-assisted mantle melting.
Malaspina et al. 2006a, EPSL 249, 173–187; Melzer and Wunder 2001, Lithos 59, 69-
90; Ayers et al. 1997, EPSL 150, 371-398; Malaspina et al. 2006b, Lithos 90, 19-42;
Scambelluri et al. 2006, CMP 151, 372-394
Fluid/mineral interaction in UHP garnet peridotite
No full textWe present two case studies of metasomatised garnet peridotite from the Sulu (Zhimafang) and of garnet orthopyroxenite from the Dabie Shan (Maowu) ultrahigh-pressure terranes (Eastern China). The mantle-derived peridotite from Zhimafang shows two ultrahigh-pressure (UHP) mineral assemblages. The older one is made of porphyroclastic garnet rich in inclusions (Grt1), coarse exsolved clinopyroxene (Cpx1) and coarse phlogopite flakes (Phl1). The younger paragenesis consists of fine-grained olivine + clinopyroxene (Cpx2) + orthopyroxene ± magnesite ± Phl2 equilibrated with neoblastic garnet (Grt2). The inclusions inside porphyroclastic Grt1 are polyphase secondary inclusions related to microfractures cutting the garnet core. They display irregular shapes and contain microcrystals of calcic-amphibole, chlorite, phlogopite and rare talc, associated with pyrite and/or spinel. The low Al2O3 content ( 5.0 GPa). The microtextural identification of pseudosecondary inclusions in the porphyroclastic garnet core and their geochemical characterisation indicate that an incompatible element- and silicate-rich fluid subsequently metasomatised the garnet peridotite and equilibrated with the newly formed Cpx2 probably during Triassic UHP metamorphism.
Ultramafic metasomatic layers at Maowu Ultramafic Complex (Dabie Shan) consist of layered websterite and orthopyroxenite which preserve an old olivine + orthopyroxene (Opx1) + garnet (Grt1) ± Ti-clinohumite paragenesis, overgrown by poikilitic Opx2. Grt2 is associated with Opx2 + phlogopite along the foliation, and fine-grained idiomorphic clinopyroxene also occurs. Grt2 cores contain disseminated primary polyphase inclusions. The textural and geochemical analyses of the primary polyphase inclusions indicate that they derive from a homogeneous fluid characterised by high LILE concentrations with spikes in Cs, Ba, Pb and high U/Th. These inclusions are interpreted as remnants of the LILE- and LREE-enriched residual fluid produced when a crust-derived Si-rich metasomatic agent reacted with a previous harzburgite to form garnet orthopyroxenite. The in-situ trace element analyses of the major phases garnet, clinopyroxene and phlogopite that formed at the same time as the polyphase inclusions at Maowu, permit the determination of empirical mineral/fluid partitioning at pressures relevant for element recycling in subduction zones. Our estimated DCpx/fluid suggests that all LILE are highly incompatible, Th and U are moderately incompatible, Pb is close to unity and Sr is moderately compatible. Phlogopite preferentially incorporates Rb and K with respect to Ba and Cs, and Th with respect to U.
The similarity between the residual Maowu fluid with the secondary inclusions in the UHP wedge-type garnet peridotite from Sulu, indicates that the fluids produced from reactions at the slab–mantle interface may be effective metasomatic agents in the mantle wedge. Such reactions may produce phlogopite, which plays an important role in controlling the LILE characteristics of the slab-derived fluid in subduction zones
Strain localization in pseudotachylyte veins at lower crustal conditions
No full textViscous shearing in the dry and strong lower crust often localizes in pseudotachylyte veins (i.e. quenched molten
rocks formed by the frictional heat released during seismic slip), and it has been suggested that brittle (coseismic)
grain-size reduction and fluid infiltration in the fractured domains are necessary to weaken the anhydrous granulitic
lower crust. However, the deformation mechanisms responsible for the associated strain weakening and viscous
shear localization in pseudotachylytes are yet to be explored.
This study investigates the deformation microstructures of mylonitized pseudotachylytes in anorthosites from Nus-
fjord, northern Norway, where ductile shear zones invariably nucleate in pseudotachylyte veins. Thus, pseudotachy-
lytes are weaker than the host rock during superposed ductile deformation.
Pristine pseudotachylytes contain microlites of plagioclase, clinopyroxene, amphibole and orthopyroxene, flow
structures, and chilled margins. Some pseudotachylytes have lost the pristine microstructure and have recrystallized
into a fine-grained (
<
10
μ
m) mixture of plagioclase, amphibole, clinopyroxene, biotite, quartz
±
K-feldspar
±
orthopyroxene. Thus, the fine grain size in the mylonites (
<
20
μ
m) is not the product of progressive grain-size
reduction with increasing strain, but is an initial characteristic of the shear zone (pseudotachylyte) precursor. The
stable mineral assemblage in the mylonitic foliation consists of plagioclase, hornblende, clinopyroxene
±
quartz
±
biotite
±
orthoclase. Geothermobarometry and thermodynamic modelling indicate that pristine pseudotachylytes
and their mylonitized equivalents formed at ca. 700 ̊C and 0.6-0.9 GPa. Diffusion creep and grain boundary sliding
were identified as the main deformation mechanisms in the mylonite on the basis of the lack of crystallographic
preferred orientations, the high degree of phase mixing, and the nucleation of hornblende in dilatant sites.
In contrast with common observations that fluid infiltration is required to trigger viscous deformation, thermody-
namic modelling indicates that a limited amount of fluid (0.4 wt%, similar to the bulk fluid content measured in the
host rock) is sufficient to stabilize the mineral assemblage in the mylonite. This suggests that cosesimic grain size
reduction resulted in fluid redistribution into the fractured domains and not necessarily in fluid infiltration. Recent
experiments suggest that very small amount of water (tens of ppm) are effective in facilitating mineral reactions
if sufficient porosity in present. Coseismic fracturing and creep cavitation in the mylonitized pseudotachylytes en-
hance the porosity of the shear zone and result in nucleation of new phases in dilatant sites. This process keeps the
grain size of the polymineralic aggregate in the grain-size sensitive creep field, thereby stabilizing strain localiza-
tion in the mylonitized pseudotachylytes.
This study highlights that pseudotachylytes caused by brittle faulting can be precursors of viscous, weak shear
zones in the dry lower crust, indicating lower crustal earthquakes as agents of rheological change from strong,
brittle lower crust, to strong lower crust with embedded fine grained, weak viscous shear zones
Selected Songs of Nadia Boulanger: Formal Analysis and Adaptation for Brass Chamber Music
No full textWorth can be a difficult thing to understand and define, even under the best of circumstances. Nadia Boulanger is known to have told her teacher, Gabriel Fauré, that “if there is one thing of which I am certain, it is that my music is worthless.” As a teacher, Boulanger empowered her students to listen for the internal logic present in the pieces of art that she considered valuable. This document will apply Nadia Boulanger’s teachings to her compositions to demonstrate that her music does have worth. To that end, these analyses will compile data to discern the internal logic in her pieces.
As a performer, Nadia Boulanger coupled her analytical beliefs to her performance practice; her concerts were shaped by and carefully crafted to present her analyses. Her formal classes included an informal ticket to hear her commentaries in action. Therefore, in addition to analytical validation, the author intends to demonstrate the value of Nadia Boulanger’s music through the arrangement and performance of her compositions as brass chamber music. as brass chamber music
Multistage metasomatism in ultrahigh-pressure mafic rocks from the North Dabie Complex (China)
No full textRelease of metamorphic fluids within the slab and/or from the slab to the mantle wedge in subduction environments can produce important metasomatic effects. Ultrahigh-pressure (UHP) metasomatised rocks represent ideal materials to study the element exchange at pressures corresponding to sub-arc depths in subduction zones. We present a petrologic and geochemical study of eclogites (s.l.) from the Dabie Mountains (China). The investigated samples were collected in the North Dabie Complex, where eclogite-facies rocks are significantly overprinted by granulite-facies metamorphism and partial melting. The studied eclogites are included in meta-lherzolitic bodies, which are in turn hosted by leucocratic gneisses. The textural relations among the various rock-forming minerals enabled us to identify several re-crystallisation stages. The peak (UHP) paragenesis consists of
garnet, clinopyroxene and rutile. UHP garnet and clinopyroxene display oriented inclusions of polycrystalline rods of rutile + ilmenite and of albite, K–Ba-feldspar and quartz, respectively. Garnet and clinopyroxene are both rimmed by an inclusion free zone that formed after the peak, still at high-pressure conditions. Such optical zoning does not correspond to a difference in major element concentrations between garnet core and rim. This observation provides evidence that the major element composition of garnet was reset during exhumation, thus preventing thermobarometric determination of peak metamorphic conditions. Further
decompression is documented by the formation of limited ilmenite+amphibole and granulite-facies coronas consisting of
clinopyroxene, orthopyroxene, plagioclase and amphibole around garnet. In order to investigate the stability of observed mineral parageneses, a series of reconnaissance piston cylinder synthesis experiments were carried out in an identical bulk composition.
The experimental study indicates that the peak metamorphic paragenesis is stable at P∼3.5 GPa and T≥750–800 °C. The
petrological study, combined with bulk-rock and mineral trace element analyses, provides evidence of intense metasomatism
affecting these eclogites. The bulk-rock major and trace element compositions indicate that the eclogites derive from basaltic protoliths with MORB and E-MORB affinity. Compared with such basalts, the studied rocks show strong depletion in SiO2 and alkalis and enrichment in MgO and FeO. These features likely derive from element exchange with ultramafic rocks prior to subduction, possibly related with the influx of Si-depleted and Mg-enriched fluids produced during the serpentinisation of the associated lherzolitic rocks. On the other hand, the trace element bulk-rock compositions show strong enrichment in Cs, Ba and Pb. The same characteristic enrichment and fractionation is recorded by peak metamorphic clinopyroxene but not in retrograde amphibole. Therefore, influx of crustal fluids transporting LILE and light elements must have occurred during subduction at UHP conditions. This stage likely records the tectonic coupling of the mafic–ultramafic rocks with the associated crustal rock units and provides evidence of LILE mobility between different slab components
Serpentinite Subduction: Implications for Fluid Processes and Trace-Element Recycling
No full textSerpentinites are important components of the oceanic lithosphere and are viewed as major water sources in subduction zones. Study of a set of ultramafic rocks equilibrated at increasing subduction depths (oceanic and high-pressure antigorite serpentinites, olivine-orthopyroxene rocks), shows that these rocks can act as carriers of Cl, B, Sr, Rb, Cs, and alkalis. Serpentinization of the oceanic mantle produces enrichment in Sr, Cl, B, and alkalis. The subduction path within the stability field of antigorite serpentine is accompanied recycling of oceanic Cl, B, Sr, and alkalis into variably saline fluids (4-8 wt% NaClequiv based on mass balance calculations; 10 to 50 wt% NaClequiv based on fluid inclusion analysis). Fluids are produced during a first (olivine-in) dehydration reaction releasing a maximum amount of 2 wt% H2O. The oxygen isotope compositions of the high-pressure antigorite serpentinites largely mirror those of the pre-subduction protoliths. This is interpreted as a lack of re-equilibration due to limited fluid production and mobility during high-pressure metamorphism Breakdown of the antigorite serpentinites to olivine-orthopyroxene rocks releases 6.5 wt% H2O with formation of a low salinity fluid (0.4-2 wt% NaClequiv based on mass balance calculations). The salt contents of subduction fluids appear to decrease with increasing depth: a "differentiation" in the Cl content of fluids can thus be expected, with shallower saline fluids being followed by deeper, less saline, solutions. Primary fluid inclusions in olivine-orthopyroxene rocks represent remnants of the antigorite-breakdown fluid. Their trace-element compositions are enriched in several LILE (Rb, Sr, Cs, Pb), Li, B, and alkalis and are depleted in HFSE; their trace-element patterns are similar to those of many present-day arc lavas. Oxygen isotope compositions of olivine-orthopyroxene rocks are rather homogeneous, and are suggestive of larger fluid mobility during dehydration. The antigorite breakdown reaction appears to produce a mobile fluid that can play a role in the metasomatism of sub-arc mantle. Serpentinized oceanic mantle thus represents a valuable candidate reservoir for fluids and incompatible elements: consequently, its role in the overall element cycle in subduction settings should be re-evaluate
Deciphering the tectonometamorphis history of the Anarak Metamorphic Complex, Central Iran.
No full textDynamics of mineral crystallization from precipitated slab-derived fluid phase: first in situ synchrotron X-ray measurements
No full textPolyphase inclusions in garnet–orthopyroxenite (Dabie Shan, China) as monitors for metasomatism and fluid-related trace element transfer in subduction zone peridotite
No full textThe ultrahigh-pressure (UHP) Maowu Ultramafic Complex (Dabie Shan, China) is hosted by coesite-bearing gneisses. Textural and geochemical data demonstrate that garnet-orthopyroxenites within the ultramafic complex derive from garnet-harzburgite precursors that have been metasomatised at peak UHP conditions (4.0 ± 1.0 GPa, 750 ± 50 °C) by the addition of a silica- and incompatible trace element-rich fluid phase (hydrous melt), sourced from the associated crustal rocks. This metasomatism produced poikilitic orthopyroxene with high LREE and Ni contents and inclusion-rich garnet porphyroblasts. Solid polyphase primary inclusions within peak metamorphic garnet display negative crystal shapes and constant volume ratios of infilling mineral phases. Experimental homogenisation of these inclusions at conditions close to the estimated metamorphic peak demonstrates that the polyphase inclusions derive from trapped solute-rich aqueous fluids. The trace element characteristics of the experimentally re-homogenised inclusions include high LREE contents, a pronounced enrichment in LILE, with spikes of Cs, Ba, Pb and high U/Th. The investigated UHP garnet-orthopyroxenites from Maowu represent a natural laboratory to constrain the trace element transfer from the subducted crust to the mantle wedge at sub-arc depths. The observed textures and chemical characteristics provide evidence for the infiltration of a felsic hydrous melt into garnet-peridotite, a circumstance comparable to expected interaction of sediment-derived melts with mantle wedge peridotites in subduction zones. The SiO2 and Al2O3 component of the hydrous melt reacted with olivine to form replacive orthopyroxene and new garnet. The neoblastic orthopyroxene is able to accommodate some of the LREE, whereas the H2O and LILE component of the melt were partitioned into a residual aqueous fluid phase. Remnants of such an aqueous fluid were trapped in the garnet and formed the polyphase inclusions. The trace element pattern of these inclusions is very similar to the incompatible element enrichment observed in arc lavas. We suggest that the residual fluid produced by the peridotite/hydrous melt reaction is able to transfer the characteristic LILE signature from the subducted sediments to the locus of partial melting in the mantle wedge. Moreover, this study provides evidence that polyphase inclusions are important tools for constraining the nature and composition of UHP fluid
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