Room-temperature equation of state of Li<Subscript>2</Subscript>VOSiO<Subscript>4</Subscript> up to 8.5 GPa

High-pressure single-crystal X-ray diffraction measurements of lattice parameters of the compound Li₂VOSiO₄, which crystallises with a natisite-type structure, has been carried out to a pressure of 8.54(5) GPa at room temperature. Unit-cell volume data were fitted with a second-order Birch-Murnaghan EoS (BM-EoS), simultaneously refining V ₀ and K ₀ using the data weighted by the uncertainties in V. The bulk modulus is K ₀ = 99(1) GPa, with K′ fixed to 4. Refinements of third order equations-of-state yielded values of K′ that did not differ significantly from 4. The compressibility of the unit-cell is strongly anisotropic with the c axis (K ₀(c) = 49.7 ± 0.5 GPa) approximately four times more compressible than the a axis (K ₀(a) = 195 ± 3 GPa).     

Garnet and spinel in fertile and depleted mantle: insights from thermodynamic modelling

We performed thermodynamic calculations based on model and natural peridotitic compositions at pressure and temperature conditions relevant to the Earth’s upper mantle, using well-established free energy minimization techniques. The model is consistent with the available experimental data in Cr-bearing peridotitic systems and can therefore be used to predict phase relations and mineral compositions in a wide range of realistic mantle compositions. The generated phase diagrams for six different bulk compositions, representative of fertile, depleted and ultra-depleted peridotitic mantle, shown that the garnet + spinel stability field is always broad at low temperatures and progressively narrows with increasing temperatures. In lithospheric sections with hot geotherms (ca. 60 mW/m²), garnet coexists with spinel across an interval of 10–15 km, at ca. 50–70 km depths. In colder, cratonic, lithospheric sections (e.g. along a 40 mW/m² geotherm), the width of the garnet–spinel transition strongly depends on bulk composition: In fertile mantle, spinel can coexist with garnet to about 120 km depth, while in an ultra-depleted harzburgitic mantle, it can be stable to over 180 km depth. The formation of chromian spinel inclusions in diamonds is restricted to pressures between 4.0 and 6.0 GPa. The modes of spinel decrease rapidly to less than 1 vol % when it coexists with garnet; hence, spinel grains can be easily overlooked during the petrographical characterization of small mantle xenoliths. The very Cr-rich nature of many spinels from xenoliths and diamonds from cratonic settings may be simply a consequence of their low modes in high-pressure assemblages; thus, their composition does not necessarily imply an extremely refractory composition of the source rock. The model also shows that large Ca and Cr variations in lherzolitic garnets in equilibrium with spinel can be explained by variations of pressure and temperature along a continental geotherm and do not necessarily imply variations of bulk composition. The slope of the Cr# [i.e. Cr/(Cr + Al)mol] isopleths in garnet in equilibrium with spinel changes significantly at high temperatures, posing serious limitations to the applicability of empirical geobarometric methods calibrated on cratonic mantle xenoliths in hotter, off-craton, lithospheric mantle sections.     

Detecting the stepwise propagation of the Eastern Sicily thrust belt (Italy): insight from thermal and thermochronological constraints

An extensive dataset of vitrinite reflectance, FTIR parameters on organic matter, illite content in mixed layers illite‐smectite, apatite fission tracks and U‐Th/He dating has been used to reconstruct the stepwise propagation of the Eastern Sicily fold‐and‐thrust belt during Late Palaeogene and Neogene times. The results indicate that the fold‐and‐thrust belt is divisible into two levels of thermal maturity. These levels consist of a less evolved level of thermal maturity that records limited sedimentary burial and minor heating, and a more evolved level of thermal maturity that indicates tectonic burial and exhumation at different times. Deformation and exhumation of shallowly buried units are linked to wedge forward propagation by low‐angle thrusts, whereas the evolution of deeply buried units is associated with tectonic imbrications by duplex formation and steep thrusts. The two tectonic styles alternate during evolution of the fold‐and‐thrust belt under low erosion rates.     

Natural and anthropogenic sources of total suspended particulate and their contribution to the formation of black crusts on building stone materials of Catania (Sicily)

Blackening and disaggregation of exposed surfaces of stone monuments are well-known effects of stone decay taking place in polluted urban environments all over the world. This paper aims to assess the contribution of natural and anthropogenic sources of total suspended particulate (TSP) causing permanent damage (black crusts) to the stone monuments of Catania (Sicily), one of the most popular ??cities of art?? of southern Italy. Atmospheric pollution of Catania, a typical Mediterranean coastal town, is mainly contributed by vehicle exhaust emissions rather than industrial ones. Episodically, the city also suffers gaseous and ash emissions (plumes) from the nearby Mount Etna volcano. Thus, to discriminate between natural and anthropogenic contributions to stone decay on Catania monuments, black crusts and TSP were sampled within the urban area and subjected to specific analytical procedures (optical microscopy, X-ray powder diffraction, Fourier transformed infrared spectroscopy, scanning electron microscopy equipped with energy dispersive spectrometry, ionic chromatography and dual inlet mass spectrometry). Mineralogical, chemical and isotopic characterization of black crusts and TSP provided new insights concerning the partition of sulfate sources in this particular urban context. The influence of Mount Etna emissions on both TSP and black crusts compositions was shown. Nevertheless, the key role of anthropogenic sources in the total sulfate budget was confirmed, while sea spray and volcanic emissions were found to make subordinate contributions. Quantitative data useful for the identification of the threshold pollution levels for preventive conservation of Catania monuments were obtained.     

Geomorphological and historical changes on the Argentina delta,Ligurian coast,Italy

A preliminary investigation of the geomorphological evolution of the small delta of the Argentina river (Riviera di Ponente, Italy) shows that it has largely been affected by anthropic processes. Erosion is undermining land and structural developments not only in the delta, but also along the nearby shores and a thorough knowledge of them seems necessary prior to management applications. In fact, processes affecting the evolution of the investigated area could well be regarded as a good example of the evolution of many other deltaic areas in the Northern Mediterranean.     

Syn-thrust deformation across a transverse zone: the Grem–Vedra fault system (central Southern Alps, N Italy)

The lateral continuity of the E?CW trending thrust sheets developed within the Lower to Middle Triassic cover of the central Southern Alps (Orobic belt) is disturbed by the occurrence of several N?CS trending transverse zones, such as the poorly known Grem?CVedra Transverse Zone (GVTZ). The GVTZ developed during the emplacement of the up to six S-verging thrust sheets consisting of Lower to Middle Triassic units, occurring immediately south of the Orobic Anticlines. The transverse zone, active during thrust emplacement related to the early Alpine compressions which pre-date the Adamello intrusion, includes three major vertical shear zones, the Grem, Pezzel and Zuccone faults. The major structure of the transverse zone is the dextral Grem fault, forming a deep lateral ramp between thrust sheets 3 and 5. A similar evolution also occurred along the Zuccone and Pezzel faults, which show a left-lateral displacement of syn-thrust folds. The Grem fault was later reactivated as an oblique tear fault during the emplacement of the Orobic Anticlines, due to back-thrusting along out-of-sequence thrust surfaces (Clusone fault). Transpressional deformations along the fault zone are recorded by the rotation of major syn-thrust folds, which also suggest a horizontal offset close to 0.5?km. Records of the first stage of evolution of the Grem fault are better preserved along its northern segment, and structural relationships suggest that it propagated southward and downward in the growing thrust stack. The study of the meso and megascopic structures developed along the GVTZ constrains the evolution of the transverse zone, illustrating the complex deformational phenomena occurring in a transpressional regime. The GVTZ probably reflects the existence of pre-existing tectonic lineaments with a similar orientation. Evidence of pre-existing structures are not preserved in the exposed units, nevertheless the N?CS extensional fault systems that characterize the Norian to Jurassic rifting history of the Lombardian basin are valid candidates.