Gabriele Lanzafame

Monte guardia sequence: a late-pleistocene eruptive cycle on Lipari (Italy)

This paper documents a complex sequence of interbedded lapilli-fall, base-surge, and pyroclastic-flow deposits, here named the Monte Guardia sequence, that erupted from volcanic centers in the southern part of Lipari (Aeolian Island Arc). Radiocarbon data from ash-flow tuffs above and below this sequence bracket its eruption between 22,600 and 16,800 years ago. Geologic evidence, however, suggests that this single eruptive cycle had a more restricted duration of years to tens-of-years.The basis for our interpretations comes from data measured at 38 detailed sections located throughout the island. The Monte Guardia sequence rests on a series of lower rhyolitic endogenous domes in the southern part of Lipari and it covers the oldest lavas, lahars, and pyroclastic flows in the north. Only in the northeast part of the island is it covered by younger deposits which there consist of lapilli tuffs and lavas of the Monte Pilato rhyolitic cycle. The deposit ranges in thickness from more than 60 m surrounding the vents in the south to less than a few decimeters at 10 km distance in the north. Throughout most of the island the Monte Guardia sequence overlies a thin andesitic lapilli-fall layer which is a key bed for correlation. This lapilli tuff probably erupted from a volcanic center on another island of the Aeolian Arc (possibly Salina).The principal activity of the Monte Guardia sequence started with an explosion that formed a continuous breccia blanket covering most of the island. Some pumiceous blocks within this breccia are composed of alternating bands of acidic and andesitic composition suggesting that the initiation of pyroclastic activity could have been triggered by magma mixing. Typical Monte Guardia sequence consists of explosive products that grade from magmatic (pumice-fall) to phreatomagmatic (base-surge) character. The eruptive cycle is characterized by a number of energy decreasing megarhythms that start with a lapilli-fall bed and end with a base-surge set that progresses through sand-wave, massive, and planar beds. Isopach maps of the fall and surge deposits indicate that both types were directed to the northwest by prevailing winds. Existing topographic relief was an additional factor that affected the emplacement of surge products. At the end of the cycle andesitic pyroclastic flows and rhyolitic endogenous domes were emplaced above the Monte Guardia deposits near the vent.

Solidification and Turbulence (Non-laminar) during Magma Ascent: Insights from 2D and 3D Analyses of Bubbles and Minerals in an Etnean Dyke

Solidification, emplacement and fluid dynamics of a sub-volcanic rock at Mt Etna have been investigated through two-dimensional (2D) and three-dimensional (3D) textural analyses of the hosted bubbles and minerals. This rock is a 4 3 m thick aphyric dyke (DK) that solidified at a depth of 100–300 m, below the pristine surface level. Seven samples from the dyke rim (DK1) to core (DK7) have been analysed in two dimensions by using a high-resolution scanner, a transmission optical microscope and scanning electron microscopy imaging with back-scattered electrons, and in three dimensions by microfocus X-ray computed tomography. Field observations and mesoscopic polished rock surfaces show bubble-rich, -poor and -free patches even in rock pieces of a few cubic centimetres, with changes in sizes and shapes; even so, their shapes and spatial arrangement can never be attributed to high degrees of strain. In parallel, the amount of bubbles irregularly varies from dyke rim to core, whereas plagioclase (plg), clinopyroxene (cpx), titanomagnetite (timt), and olivine (ol) show only limited variations. The fabric of bubbles retrieved by 3D orientation of their maximum length (i.e. elongation) is invariably random in space for each DK sample. These bubble features have been attributed to transitional to turbulent flows; that is, non-laminar regimes (Reynolds number> 1000), predicted for a long time from numerical models and that occurred before the crystallization of minerals. Water solubility, volume of bubbles, magma density and viscosity models indicate that, at pressure higher than 10 MPa, 1 wt % H2O was dissolved in the original trachybasaltic magma, which, in turn, was close to its liquidus temperature. As the pressure decreased at very shallow levels, the magma significantly degassed and volatile exsolution induced marked crystallization (mostly plg followed by cpx). The viscosity of the system increased, decelerating and halting the magmatic suspension. The textures and fabrics of bubbles were suddenly frozen in, despite crystals continuing to grow under the effect of cooling rate variables from the inner (DK7) to outer (DK1) dyke portions. Fluid-dynamic computations suggest that the DK trachybasaltic magma ascended with a velocity of few metres per second in a transitional to turbulent regime, before the growth of minerals.

A quantitative analysis of 3D-cell distribution in regenerating muscle-skeletal system with synchrotron X-ray computed microtomography

One of the greatest enigmas of modern biology is how the geometry of muscular and skeletal structures are created and how their development is controlled during growth and regeneration. Scaling and shaping of vertebrate muscles and skeletal elements has always been enigmatic and required an advanced technical level in order to analyse the cell distribution in 3D. In this work, synchrotron X-ray computed microtomography (µCT) and chemical contrasting has been exploited for a quantitative analysis of the 3D-cell distribution in tissues of a developing salamander (Pleurodeles waltl) limb – a key model organism for vertebrate regeneration studies. We mapped the limb muscles, their size and shape as well as the number and density of cells within the extracellular matrix of the developing cartilage. By using tomographic approach, we explored the polarity of the cells in 3D, in relation to the structure of developing joints. We found that the polarity of chondrocytes correlates with the planes in joint surfaces and also changes along the length of the cartilaginous elements. Our approach generates data for the precise computer simulations of muscle-skeletal regeneration using cell dynamics models, which is necessary for the understanding how anisotropic growth results in the precise shapes of skeletal structures.

A compact and flexible induction furnace for in situ X-ray microradiograhy and computed microtomography at Elettra: design, characterization and first tests

A compact and versatile induction furnace for in situ high-resolution synchrotron and laboratory hard X-ray microradiography and computed microtomography is described. The furnace can operate from 773 to 1723 K. Its programmable controller enables the user to specify multiple heating and cooling ramp rates as well as variable dwell times at fixed temperatures allowing precise control of heating and cooling rates to within 5 K. The instrument can work under a controlled atmosphere. Thanks to the circular geometry of the induction coils, the heat is homogeneously distributed in the internal volume of the graphite cell (ca. 150 mm3) where the sample holder is located. The thermal gradient within the furnace is less than 5 K over a height of ca. 5 mm. This new furnace design is well suited to the study of melting and solidification processes in geomaterials, ceramics and several metallic alloys, allowing fast heating (tested up to 6.5 K s-1) and quenching (up to 21 K s-1) in order to freeze the sample microstructure and chemistry under high-temperature conditions. The sample can be held at high temperatures for several hours, which is essential to follow phenomena with relatively slow dynamics, such as crystallization processes in geomaterials. The utility of the furnace is demonstrated through a few examples of experimental applications performed at the Elettra synchrotron laboratory (Trieste, Italy).