Experimental study of vibro-acoustic response of stiffened cylindrical shells

Vibrational response of stiffened cylindrical shell to reverberant acoustic field

U and Th content in the Central Apennines continental crust: a contribution to the determination of the geo-neutrinos flux at LNGS

The regional contribution to the geo-neutrino signal at Gran Sasso National Laboratory (LNGS) was determined based on a detailed geological, geochemical and geophysical study of the region. U and Th abundances of more than 50 samples representative of the main lithotypes belonging to the Mesozoic and Cenozoic sedimentary cover were analyzed. Sedimentary rocks were grouped into four main "Reservoirs" based on similar paleogeographic conditions and mineralogy. Basement rocks do not outcrop in the area. Thus U and Th in the Upper and Lower Crust of Valsugana and Ivrea-Verbano areas were analyzed. Based on geological and geophysical properties, relative abundances of the various reservoirs were calculated and used to obtain the weighted U and Th abundances for each of the three geological layers (Sedimentary Cover, Upper and Lower Crust). Using the available seismic profile as well as the stratigraphic records from a number of exploration wells, a 3D modelling was developed over an area of 2^{\circ}x2^{\circ} down to the Moho depth, for a total volume of about 1.2x10^6 km^3. This model allowed us to determine the volume of the various geological layers and eventually integrate the Th and U contents of the whole crust beneath LNGS. On this base the local contribution to the geo-neutrino flux (S) was calculated and added to the contribution given by the rest of the world, yielding a Refined Reference Model prediction for the geo-neutrino signal in the Borexino detector at LNGS: S(U) = (28.7 \pm 3.9) TNU and S(Th) = (7.5 \pm 1.0) TNU. An excess over the total flux of about 4 TNU was previously obtained by Mantovani et al. (2004) who calculated, based on general worldwide assumptions, a signal of 40.5 TNU. The considerable thickness of the sedimentary rocks, almost predominantly represented by U- and Th- poor carbonatic rocks in the area near LNGS, is responsible for this difference.Comment: 45 pages, 5 figures, 12 tables; accepted for publication in GC

Decadal to monthly timescales of magma transfer and reservoir growth at a caldera volcano

International audienceCaldera-forming volcanic eruptions are low-frequency, highimpact events capable of discharging tens to thousands of cubic kilometres of magma explosively on timescales of hours to days, with devastating effects on local and global scales1. Because no such eruption has been monitored during its long build-up phase, the precursor phenomena are not well understood. Geophysical signals obtained during recent episodes of unrest at calderas such as Yellowstone, USA, and Campi Flegrei, Italy, are difficult to interpret, and the conditions necessary for large eruptions are poorly constrained2,3. Here we present a study of pre-eruptive magmatic processes and their timescales using chemically zoned crystals from the 'Minoan' caldera-formingeruption of Santorini volcano,Greece4, which occurred in the late 1600s BC. The results provide insights into how rapidly large silicic systems may pass from a quiescent state to one on the edge of eruption5,6. Despite the large volume of erupted magma4 (40-60 cubic kilometres), and the 18,000-year gestation period between the Minoan eruption and the previous major eruption, most crystals in the Minoan magma record processes that occurred less than about 100 years before the eruption. Recharge of the magma reservoir by large volumes of silicic magma (and some mafic magma) occurred during the century before eruption, and mixing between different silicicmagmabatches was still taking place during the final months. Final assembly of large silicic magma reservoirs may occur on timescales that are geologically very short by comparison with the preceding repose period, with major growth phases immediately before eruption. These observations have implications for the monitoring of long-dormant, but potentially active, caldera systems

Impact responses and classifications of motor vehicle structural system - a survey.

National Highway Safety Bureau, Washington, D.C.Mode of access: Internet.COP: 2COP: 3Author corporate affiliation: Wyle Laboratories, Huntsville, Ala.Subject code: DECSubject code: DGSubject code: D

Petrology, mineralogy and geochemistry of a mafic dyke from Monte Castello, Elba Island, Italy

A mafic dike is intruded into two SW-NE trending normal faults, and crosscuts the Mt. Alpe Cherts and the Nisportino Fm. in the Monte Castello area, Elba Island, Tuscan Archipelago. The dike is dark grey to brownish in colour, it has a porphyritic texture with phenocrysts of plagioclase + clinopyroxene + olivine, and seldom xenocrysts of large k-feldspar. The original mineralogy is strongly altered and replaced by secondary minerals. Clinopyroxene and plagioclase in some cases are still preserved, whereas olivine is entirely replaced by smectite aggregates. Euhedral Mg-chromite inclusions occur in the olivine ghosts. In the freshest samples the groundmass is made up of clinopyroxene, k-feldspar, plagioclase, magnetite and apatite. Large k-feldspar xenocrysts probably scavenged from a monzogranite are also present. No olivine analyses are available due to strong weathering. Mg-chromites hosted by olivine ghosts have a mild residual character with a Cr# between 0.40 and 0.65. Plagioclases range in composition from An75 to An65, although those enclosed in the k-feldspar xenocrysts have a compositional range from An39 to An35. Clinopyroxenes are mainly sub-calcic diopside (augite) with an Mg# ranging from 0.88 to 0.83. Step-heating 40Ar/39Ar dating was performed on the k-feldspar-rich groundmass of the less altered sample. The result establishes a date of 5.83±0.14 Ma (~70% of the released 39Ar), although the slightly radiogenic initial Ar isotopic composition and the scatter observed during the release of Ar at low temperature make the result only indicative of the age. Secondary minerals are ubiquitous even in the freshest samples, the whole rock compositions indicate that the parental magma has a shoshonitic composition, with a clear alkaline-potassic affinity. Mineral chemistry of k-feldspar and clinopyroxene crystals indicate that the magma belongs to the Italian Potassic Suites, with a strong resemblance to the potassic rocks cropping out at the Capraia Island and in the Southern Tuscany. The presence of olivine ghosts with euhedral Mg-chromite inclusions suggest that the magma has a strong primitive composition, with an alkaline character. Initial Sr-isotope values are in the range between 0.70878-0.70900, which indicate that the parental magma of the dike has not been contaminated with the monzogranite but the radiogenic Sr has been diluted by small scale magma-wall rock interaction. The presence of xenocrysts from a monzogranite, and lack of reaction paragenesis clearly indicates that the mafic magma intruded the monzogranite successively to its cooling. The 5.8 Ma age of this dike constitutes a very important datum: in fact it indicates that block tectonics should began in the Island before this date, and could be contemporaneous or also older of the gravitational detachments triggered by the Monte Capanne pluton uplift

Isotope geochemistry (Sr-Nd-Pb) and petrogenesis of leucite-bearing rocks from “Colli Albani” volcano, Roman Magmatic Province, Central Italy: inferences on volcanic evolution

The “Colli Albani” composite volcano is made up of strongly silica-undersaturated leucite-bearing rocks. Magmas were erupted during three main periods, but a complex plumbing system dominated by regional tectonics channelled magmas into different reservoirs. The most alkali-rich magmas, restricted to the caldera-forming period (pre-caldera), are extremely enriched in incompatible trace elements and display more radiogenic Sr (87Sr/86Sr = 0.71057–0.71067), with slightly less radiogenic Pb with respect to those of the post-caldera period. Post-caldera volcanic activity was concentrated in three different volcanic environments: external to the caldera, along the caldera edge and within the caldera. The post-caldera magmas produced melilite- to leucitite-bearing, plagioclase-free leucitites. In contrast to the pre-caldera lavas, they are characterised by lower incompatible trace element abundances and less radiogenic Sr ( 87 Sr / 8 6Sr = 0. 71006–0. 71039) . Magmas evolved through crystal fractionation plus minor crustal assimilation in a large magma chamber during the pre- caldera period. The multiple caldera collapses dissected and partially obliterated the early magma chamber. During the post-caldera stage, magmas were channelled through several pathways and multiple shallow-level magma reservoirs were established. A lithospheric mantle wedge previously depleted in the basaltic component and subsequently enriched by metasomatic slab-derived component is suggested as the mantle source of Colli Albani parental magmas. Two different parental magmas are recognised for the pre- and post-caldera stages. The differences may be related to the interplay between smaller degrees of melting for the pre-caldera magmas and more carbonate-rich recycled subducted lithologies in the post-caldera magmas