Petrology and major element geochemistry of basaltic glasses from the Blanco Trough, northeast Pacific

The original electron microprobe analyses of suite of basaltic glasses recovered in 1968 by W.G. Melson and co-workers from the Blanco Trough have extremely unusual characteristics. Their compositions plot in a region of the normative Ol-Di-Pl-SiO2 tetrahedron which suggests that they represent liquids in equilibrium with an upper mantle assemblage of olivine + orthopyroxene at 10-15 kb. Given the present state of controversy surrounding the composition and depth of origin of primary MORB, natural examples of such liquids would be very important. The major element variations observed in the suite imply that the dominant phases are olivine and an iron-aluminum rich spinel. The crystal/melt partitioning data are consistent with an unusually large Fe2O3 component in the melt, which could help to explain the variation in liquidus phases, and thus the suite\u27s position in Ol-Di-Pl-SiO2 space. New analyses of the original samples, performed on the microprobe at Rensselaer Polytechnic Institute, have failed to reproduce the original anomalies. The R.P.I. data does show that the glasses are slightly enriched in FeO* giving them unusually low Mg/(Mg + Fe) ratios for otherwise primitive looking mid-ocean ridge tholeiites. The new analyses plot near the Ol-Di join when projected from PI onto the Ol-Di-SiO2 plane, a region not uncommon for primitive MORB. The disagreement between the two data sets appears to be the result of a transposition of the FeO* and CaO abundances in the Smithsonian analyses prior to their publication by Melson et al. (1977), in addition to minor differences in calibration between the two laboratories. All of the Blanco Trough glasses that were studied in thin section contain olivine, while 61.5% are saturated in chromian spinel. Some of the olivines display deformation bands and possible fluid inclusions, indicating that they are probably cumulate xenocrysts. In contrast with most other MORB suites, plagioclase is a major phenocryst phase in only one sample and is absent completely from 38.5% of the thin sections. Based on petrography, the first phase to appear is olivine, followed by assemblages of olivine + chromian spinel, olivine + chromian spinel + plagioclase and olivine + plagioclase. Although the appearance and disappearance of phenocryst phases agrees very well with the phase equilibria in the system An-Fo-Di, no simple relationship exists between the Mg/(Mg + Fe) ratio of the liquid and the phenocryst assemblage. Least-squares mixing models show that the primitive and evolved ends of the suite cannot be related simply by the fractional crystallization of an assemblage of olivine + chromian spinel + plagioclase. The best fit is obtained if clinopyroxene is added to the crystallizing assemblage, although it is not found as a phenocryst phase in any of the samples. The problem of needing to crystallize significant amounts of clinopyroxene to explain a suite of MORB which does not contain clinopyroxene is not unique to this study, but has been recognized by other workers for a number of years. The petrogenesis of the suite appears to involve several stages, in addition to fractional crystallization of olivine, chromian spinel and plagioclase in a shallow level magma chamber. Polybaric crystallization of several batches of parental magma, followed by homogenization during episodes of magma-mixing seems likely

Finite element modelling of masonry cross vaults: considerations on block interlocking and interface properties

Masonry cross vaults had been used for centuries in the roofing of European buildings, palaces and churches, representing nowadays an integral part of national cultural heritage. In this regard, a sound knowledge of the structural response of cross vaults under vertical and horizontal loads is fundamental for planning accurate and compatible conservation programs. Whereas a certain consensus on the static behavior of the cross vault under gravitational loads has been reached, still more efforts are requested for assessing its seismic capacity. In the present work, the finite element approach has been implemented with a particular attention to the block interlocking and interface elements. On the one hand, an appreciable accommodation between the real block arrangement and computational effort is shown. On the other hand, modelling the blocks with rigid-infinitely resistant elements leads the interface as the only source of physical nonlinearities. Paralleling recent works on the seismic behavior of masonry arches, the influence of the mechanical parameters of the interface elements is discussed. Comparisons between numerical and experimental results available in literature are presented in terms of ultimate strength capacity and failure mechanisms.- (undefined

Experimental determination of Pb partitioning between sulfide melt and basalt melt as a function of P, T and X

© The Author(s), 2016. This is the author's version of the work and is distributed under the terms of the Creative Commons Attribution License. The definitive version was published in Geochimica et Cosmochimica Acta 185 (2016): 9-20, doi:10.1016/j.gca.2016.01.030.We have measured the partition coefficient of Pb (KdPb) between FeS melt and basalt melt at temperatures of 1250–1523 °C, pressures of 1.0–3.5 GPa and oxygen fugacities at iron–wustite and wustite–magnetite. The total observed range of KdPb is 4.0–66.6, with a strong negative dependence on pressure and a strong negative dependence on FeO of the silicate melt (Fe+2 only). The FeO control was constrained over a wide range of FeO (4.2–39.5%). We found that the effect of oxygen fugacity can be subsumed under the FeO control parameter. Prior work has established the lack of a significant effect of temperature (Kiseeva and Wood, 2015; Li and Audétat, 2015). Our data are parameterized as: KdPb = 4.8 + (512 − 119*P in GPa)*(1/FeO − 0.021). We also measured a single value of KdPb between clinopyroxene and basalt melt at 2.0 GPa of 0.020 ± 0.001. This experimental data supports the “natural” partitioning of Pb measured on sulfide globules in MORB (Patten et al., 2013), but not the low KdPb of ∼3 inferred from sulfides in abyssal peridotites by Warren and Shirey (2012). It also quantitatively affirms the modeling of Hart and Gaetani (2006) with respect to using sulfide to buffer the canonical Nd/Pb ratio for MORB and OIB (Hofmann, 2003). For the low FeO and pressure of segregation typical of MORB, KdPb ∼ 45, and the Nd/Pb ratio of erupted basalts will be the same as the Nd/Pb ratio of the mantle source. The remaining puzzle is why MORB and OIB have the same Nd/Pb when they clearly have different FeO and pressure of melt segregation.This work would not have been done without the support of NSF, through Grant EAR-0635530.2017-02-1

Shock Tube Flows Past Partially Opened Diaphragms

Unsteady compressible flows resulting from the incomplete burst of the shock tube diaphragm are investigated both experimentally and numerically for different initial pressure ratios and opening diameters. The intensity of the shock wave is found to be lower than that corresponding to a complete opening. A heuristic relation is proposed to compute the shock strength as a function of the relative area of the open portion of the diaphragm. Strong pressure oscillations past the shock front are also observed. These multi-dimensional disturbances are generated when the initially normal shock wave diffracts from the diaphragm edges and reflects on the shock tube walls, resulting in a complex unsteady flow field behind the leading shock wave. The limiting local frequency of the pressure oscillations is found to be very close to the ratio of acoustic wave speed in the perturbed region to the shock tube diameter. The power associated with these pressure oscillations decreases with increasing distance from the diaphragm since the diffracted and reflected shocks partially coalesce into a single normal shock front. A simple analytical model is devised to explain the reduction of the local frequency of the disturbances as the distance from the leading shock increases

Serpentinite-derived slab fluids control the oxidation state of the subarc mantle

© The Author(s), 2021. This article is distributed under the terms of the Creative Commons Attribution License. The definitive version was published in Zhang, Y., Gazel, E., Gaetani, G. A., & Klein, F. Serpentinite-derived slab fluids control the oxidation state of the subarc mantle. Science Advances, 7(48), (2021): eabj2515, https://doi.org/10.1126/sciadv.abj2515.Recent geochemical evidence confirms the oxidized nature of arc magmas, but the underlying processes that regulate the redox state of the subarc mantle remain yet to be determined. We established a link between deep subduction-related fluids derived from dehydration of serpentinite ± altered oceanic crust (AOC) using B isotopes and B/Nb as fluid proxies, and the oxidized nature of arc magmas as indicated by Cu enrichment during magma evolution and V/Yb. Our results suggest that arc magmas derived from source regions influenced by a greater serpentinite (±AOC) fluid component record higher oxygen fugacity. The incorporation of this component into the subarc mantle is controlled by the subduction system’s thermodynamic conditions and geometry. Our results suggest that the redox state of the subarc mantle is not homogeneous globally: Primitive arc magmas associated with flat, warm subduction are less oxidized overall than those generated in steep, cold subduction zones.Y.Z. acknowledges funding from the National Science Foundation of China (91958213), the Chinese Academy of Sciences (XDB42020402), and the Shandong Provincial Natural Science Foundation, China (ZR2020QD068). This study was supported in part by the U.S. National Science Foundation NSF EAR 1826673 to E.G. and G.A.G. and OCE 1756349 to E.G

Experimental and numerical analyses of a masonry arch under base impulse excitation

Considering the long-lasting history of the masonry arch theory, the investigation of its dynamic behavior is a relatively recent issue, which is mostly focused on the analytical formulation of the SDOF four-link rigid block mechanism. With the aim of better understanding the seismic response of vaulted masonry structures, the present study is focused on the performance of a scaled arch assembled by dry-joint 3D printed voussoirs. Due to the susceptibility of rigid bodies to base impulse excitation, the tests accounted for a set of windowed sine impulses that allowed computing a failure curve in the frequency-amplitude domain. In order to track the in-plane motion of selected points, a feature tracking based measuring technique was employed. The results have been compared with a finite element model with voussoirs assumed infinitely rigid and friction interface elements, showing an appreciable match. Eventually, the outcomes of impulse base motion tests available in literature were examined, highlighting the differences in terms of failure mechanisms and seismic capacity.(undefined

Experimental investigations of differentiation processes in the terrestrial planets

Thesis (Ph. D.)--Massachusetts Institute of Technology, Dept. of Earth, Atmospheric, and Planetary Sciences, 1996.Includes bibliographical references.by Glenn Allan Gaetani.Ph.D

Factors affecting B/Ca ratios in synthetic aragonite

Author Posting. © The Author(s), 2015. This is the author's version of the work. It is posted here for personal use, not for redistribution. The definitive version was published in Chemical Geology 437 (2016): 67-76, doi:10.1016/j.chemgeo.2016.05.007.Measurements of B/Ca ratios in marine carbonates have been suggested to record seawater carbonate chemistry, however experimental calibration of such proxies based on inorganic partitioning remains limited. Here we conducted a series of synthetic aragonite precipitation experiments to evaluate the factors influencing the partitioning of B/Ca between aragonite and seawater. Our results indicate that the B/Ca ratio of synthetic aragonites depends primarily on the relative concentrations of borate and carbonate ions in the solution from which the aragonite precipitates; not on bicarbonate concentration as has been previously suggested. The influence of temperature was not significant over the range investigated (20 – 40°C), however, partitioning may be influenced by saturation state (and/or growth rate). Based on our experimental results, we suggest that aragonite B/Ca ratios can be utilized as a proxy of [CO32-]. Boron isotopic composition (δ11B) is an established pH proxy, thus B/Ca and δ11B together allow the full carbonate chemistry of the solution from which the aragonite precipitated to be calculated. To the extent that aragonite precipitation by marine organisms is affected by seawater chemistry, B/Ca may also prove useful in reconstructing seawater chemistry. A simplified boron purification protocol based on amberlite resin and the organic buffer TRIS is also described.This work was supported by the Australian Research Council (ARC) Centre of Excellence for Coral Reef Studies. Research conducted at WHOI was supported by NSF grant OCE-1338320. M.H. was supported by an ARC Super Science Fellowship and an NSF International Postdoctoral Fellowship. T.D. was supported by a NSF Graduate Research Fellowship. M.M. was supported by a Western Australian Premiers Fellowship and an ARC Laureate Fellowship

A Prosthetic Limb Managed by Sensors-Based Electronic System: Experimental Results on Amputees

Taking the advantages offered by smart high-performance electronic devices, transradial prosthesis for upper-limb amputees was developed and tested. It is equipped with sensing devices and actuators allowing hand movements; myoelectric signals are detected by Myo armband with 8 ElectroMyoGraphic (EMG) electrodes, a 9-axis Inertial Measurement Unit (IMU) and Bluetooth Low Energy (BLE) module. All data are received through HM-11 BLE transceiver by Arduino board which processes them and drives actuators. Raspberry Pi board controls a touchscreen display, providing user a feedback related to prosthesis functioning and sends EMG and IMU data, gathered via the armband, to cloud platform thus allowing orthopedic during rehabilitation period, to monitor users’ improvements in real time. A GUI software integrating a machine learning algorithm was implemented for recognizing flexion/extension/rest gestures of user fingers. The algorithm performances were tested on 9 male subjects (8 able-bodied and 1 subject affected by upper-limb amelia), demonstrating high accuracy and fast responses