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Transition from protomylonite to ultramylonite in the variscan leucogranite from Monte Grighini Complex, West-Central Sardinia: Preliminary data
No full textContinuous vs. discontinuous garnet growth in mylonitic micaschists from northeastern Sardinia, Italy: Evidence from LA-ICPMS trace element mapping
Full text linkGarnet with complex, discontinuous zoning is a common occurrence in metamorphic terrains, and the rela tionship between major and trace element zoning can provide insight into the metamorphic evolution of the host rock. Mylonitic micaschists along the Posada-Asinara Shear Zone in the Axial Zone of the Sardinia Variscan chain contain garnet porphyroblasts, enveloped by the S2 schistosity, with distinct core and rim domains. A large garnet porphyroblasts was investigated by laser ablation-inductively coupled plasma-mass spectrometry (LA ICPMS) mapping. The major element compositional variation follows a bell-shaped zoning, with Ca and Mn contents progressively decreasing, and Fe and Mg increasing, from the core to the outer rim. LA-ICPMS mapping revealed a thin and sharp annular enrichment zone in Y, Sc, Dy, Ho, Er, Tm at the mantle-rim boundary. The trace element (TE) compositional profiles show a central enrichment area for HREE (Tm, Yb, Lu). This enrich ment decreases progressively, as a function of atomic number, for Er, Ho and Dy. Elements with even lower atomic number (Tb, Gd, Eu and Sm), are depleted in this central domain, but their content increases in broad shoulders towards the garnet rim. The position of these lateral shoulders migrates progressively rimwards with decreasing atomic number. The REE distribution, trend and behavior in the growth zones of the garnet is an example of TE control during a continuous growth ruled by diffusion-limited REE uptake. The Y + HREE annular enrichment zone, interpreted as resulting from a decrease in the garnet growth rate, reflects a short-lived episode in the garnet growth history
Geochemical characterization of migmatized orthogneiss from Porto Ottiolu (NE Sardinia, Italy) and its inferences on partial melting process
No full textPetrophysical properties of a granite-protomylonite-ultramylonite sequence: insight from the Monte Grighini shear zone, central Sardinia, Italy
No full textThe Monte Grighini intrusive complex (central-west Sardinia) has been affected by a 1.5 km wide late-Variscan shear
zone; microstructures and deformation fabrics indicate that high strain domains resulted in sharp transitions among protomylonite to
ultramylonite. A representative geological cross section of the shear zone has been sampled, as well as samples from outside the
mylonitic belt for use as slightly deformed protolith reference samples. Physical and mechanical analyses were performed on each
group in order to evaluate a possible correlation between petrophysical properties (density, porosity and mechanical strength) and the
degree of mylonitic deformation. Ultramylonites are generally characterized by a higher solid-phase density (2.82–2.85 g/cm3) than
less deformed protomylonites and mylonites (2.73–2.79 g/cm3), testifying to the formation of high-density minerals with an increase
in deformation. Conversely, bulk density tends to decrease as deformation increases (from 2.52–2.57 g/cm3 to 2.47–2.48 g/cm3) due
to the total porosity increase occurring during mylonitization. The mean values of total porosity range from 6.33 to 9.27 % in
protomylonites and mylonites and from 12.01 to 12.85 % in ultramylonites. The relatively high value of porosity in more deformed
ultramylonites is the result of the sum of closed micropores and open pores produced by different processes. Mechanical strength
measurements show a noticeable anisotropy, with higher strength values measured applying the load perpendicular to foliation
(Z axis) and lower values obtained parallel to it (X,Y axes). In the Monte Grighini mylonite the anisotropy is due to the distribution of
pores and to the preferred orientation of new minerals, as highlighted by the correlation between scalar physical properties (solid, real
and bulk densities, porosity) and vector properties (resistance to punching or uniaxial compressive strengths). The results show that
the degree of deformation of mylonitic rocks can be characterized by petrophysical properties, in order to shed light on the tectonic
processes experienced at depth
METODO DI SINTESI DELLA MOLECOLA OTTACALCIO FOSFATO
Full text linkL’invenzione è relativa ad un processo per la produzione di Ottacalcio fosfato a partire da carbonato di calcio e acido ortofosforico in cui il carbonato di calcio e l’acido ortofosforico sono posti a reagire in acqua secondo un rapporto molare compreso nell’intervallo 1,25-1,41, la massa di carbonato di calcio essendo compresa nell’intervallo 0,1-20 g per litro d’acqua, la temperatura di reazione essendo compresa nell’intervallo 55-85°C e la reazione essendo condotta per un intervallo di tempo fra 3 e 16 ore. Al termine della reazione, si recupera l’Ottacalcio fosfato dalla sospensione acquosa per filtrazione o decantazion
Petrophysical properties of a granite-protomylonite-ultramylonite sequence: insight from the Monte Grighini shear zone, central Sardinia, Italy
No full textThe Monte Grighini intrusive complex (central-west Sardinia) has been affected by a 1.5 km wide late-Variscan shear
zone; microstructures and deformation fabrics indicate that high strain domains resulted in sharp transitions among protomylonite to
ultramylonite. A representative geological cross section of the shear zone has been sampled, as well as samples from outside the
mylonitic belt for use as slightly deformed protolith reference samples. Physical and mechanical analyses were performed on each
group in order to evaluate a possible correlation between petrophysical properties (density, porosity and mechanical strength) and the
degree of mylonitic deformation. Ultramylonites are generally characterized by a higher solid-phase density (2.82–2.85 g/cm3) than
less deformed protomylonites and mylonites (2.73–2.79 g/cm3), testifying to the formation of high-density minerals with an increase
in deformation. Conversely, bulk density tends to decrease as deformation increases (from 2.52–2.57 g/cm3 to 2.47–2.48 g/cm3) due
to the total porosity increase occurring during mylonitization. The mean values of total porosity range from 6.33 to 9.27 % in
protomylonites and mylonites and from 12.01 to 12.85 % in ultramylonites. The relatively high value of porosity in more deformed
ultramylonites is the result of the sum of closed micropores and open pores produced by different processes. Mechanical strength
measurements show a noticeable anisotropy, with higher strength values measured applying the load perpendicular to foliation
(Z axis) and lower values obtained parallel to it (X,Y axes). In the Monte Grighini mylonite the anisotropy is due to the distribution of
pores and to the preferred orientation of new minerals, as highlighted by the correlation between scalar physical properties (solid, real
and bulk densities, porosity) and vector properties (resistance to punching or uniaxial compressive strengths). The results show that
the degree of deformation of mylonitic rocks can be characterized by petrophysical properties, in order to shed light on the tectonic
processes experienced at dept
Passive structural control on skarn ore mineralization: the case study of the Rosas shear zone in the fold-and-thrust belt of SW Sardinia (Italy)
No full textGeothermobarometry of Al-silicate-bearing migmatites from the Variscan chain of NE Sardinia, Italy: a P-T pseudosection approach
No full textThis paper investigates Al-silicate-bearing migmatite from NE Sardinia by using the P-T pseudosection approach with the aim to determine the P-T conditions of partial melting and those of melt crystallization. P-T pseudosections were calculated in the NCKFMASH system within the P-T range 500-800°C, 0.1-1.5 GPa by using the average compositions of metapelitic greywacke, average mesosome and average trondhjemitic leucosome, respectively. The P-T pseudosections calculated for the average metapelitic greywacke and for the average mesosome, contoured for melt volume %, Si/Al and Na/K molar ratios in melt point to P–T conditions 700-740°C, 1.1-1.3 GPa which are indicative of partial melting. The P-T pseudosection calculated for the average composition of trondhjemitic leucosomes, contoured for kyanite and biotite modal content and for XMg ratio in biotite indicates P-T conditions of 660-730°C, 0.75-0.90 GPa for the crystallization of the melt. The comparison between the Na/K and Si/Al ratios in leucosomes, and the same ratios modeled for the anatectic melt by an haplogranitic melt model is thus a powerful tool for the reconstruction of P-T conditions of partial melting also in pelitic rocks, provided that leucosomes represent pure melts and are not contaminated by restitic phases or feldspar cumulates
Potential recovery of metal from plants: a combined XRD-Thermal study on Juncus acuts
No full textIn the Arburese mine district (SW Sardinia, Italy), centuries of mine exploitation addressed to the extraction
of Zn and Pb from sulphides and non-sulphides (calamine) deposits, left a widespread metal pollution. The
Juncus acutus, a halophyte pioneer plant, was able to adapt in this extreme environment and to affect metal
mobility thanks to its capacity to stabilize them in the external roots and rhizosphere.
A method for evaluating the potential of reuse of biomasses for economic purposes is here presented starting
from the specific case study of Juncus acutus. For this purpose, plants and rhizospheres, collected from the
banks of two streams (Rio Naracauli and Rio Irvi) impacted by past mining activity, were used to perform
Thermogravimetry and Differential Thermal analyses combined with X-ray Diffraction (XRD) carried out on
raw samples and on samples heated ex-situ (by a conventional diffractometer) or in-situ (by synchrotron-based
diffraction).
Results showed the presence of mainly quartz, phyllosilicates, and feldspars with minor amounts of
sulphides, sulphates, and Fe, Pb, and Zn carbonates concentrated in the rhizosphere of raw samples. The
mineral phases, Zn and Fe oxides and willemite, detected in internal roots and stems samples after heating,
indicated the presence of metals in the plant tissues. The ex-situ heating was found to be useful in determining
the occurrence of metal-bearing phases in plants especially if combined with thermal analyses in order to
reveal the temperature stages at which the significant reactions occur. Despite the high resolution proper of
a synchrotron light source, the in-situ heating resulted less effective in revealing minor phases in organic
samples, maybe due to the scarcity of oxygen within the sample holder that avoid sulphides oxidation and the
degradation of organic compounds (Fancello et al., 2019).
This method, if further developed, could be a useful tool in different application fields. The recognition
of metals in plant tissues, and the mineralogical form in which they transform after thermal treatment, is
an essential information for phytomining by hyperaccumulator plants. Likewise, biochar production from
vegetal masses would benefit from the knowledge of the mineral assemblage attainable under different thermal
conditions, to find the optimum temperature
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