Age of the magma chamber and its physicochemical state under Elbrus Greater Caucasus, Russia using zircon petrochronology and modeling insights.

Mount Elbrus, Europe's tallest and largely glaciated volcano, is made of silicic lavas and is known for Holocene eruptions, but the size and state of its magma chamber remain poorly constrained. We report high spatial resolution U-Th-Pb zircon ages, co-registered with oxygen and hafnium isotopic values, span ~ 0.6 Ma in each lava, documenting magmatic initiation that forms the current edifice. The best-fit thermochemical modeling constrains magmatic fluxes at 1.2 km3/1000 year by hot (900 °C), initially zircon-undersaturated dacite into a vertically extensive magma body since ~ 0.6 Ma, whereas a volcanic episode with eruptible magma only extends over the past 0.2 Ma, matching the age of oldest lavas. Simulations explain the total magma volume of ~ 180 km3, temporally oscillating δ18O and εHf values, and a wide range of zircon age distributions in each sample. These data provide insights into the current state (~ 200 km3 of melt in a vertically extensive system) and the potential for future activity of Elbrus calling for much-needed seismic imaging. Similar zircon records worldwide require continuous intrusive activity by magmatic accretion of silicic magmas generated at depths, and that zircon ages do not reflect eruption ages but predate them by ~ 103 to 105 years reflecting protracted dissolution-crystallization histories.

Enhancing covalent mechanochemistry in bulk polymers using electrospun ABA triblock copolymers.

The mechanochemical activation of covalent bonds in bulk polymers is often characterized by low conversions. Here we report that the activation of gem-dibromocyclopropane (gDBC) mechanophores embedded in a poly(1,4-butadiene) (PB) is enhanced when a central gDBC-PB block is flanked by two polystyrene (PS) end blocks in an ABA-type triblock architecture. Electrospinning the PS-(gDBC)PB-PS leads to even greater activation in aligned fiber mats under tension.

Solving the Martian meteorite age conundrum using micro-baddeleyite and launch-generated zircon.

Invaluable records of planetary dynamics and evolution can be recovered from the geochemical systematics of single meteorites. However, the interpreted ages of the ejected igneous crust of Mars differ by up to four billion years, a conundrum due in part to the difficulty of using geochemistry alone to distinguish between the ages of formation and the ages of the impact events that launched debris towards Earth. Here we solve the conundrum by combining in situ electron-beam nanostructural analyses and U-Pb (uranium-lead) isotopic measurements of the resistant micromineral baddeleyite (ZrO2) and host igneous minerals in the highly shock-metamorphosed shergottite Northwest Africa 5298 (ref. 8), which is a basaltic Martian meteorite. We establish that the micro-baddeleyite grains pre-date the launch event because they are shocked, cogenetic with host igneous minerals, and preserve primary igneous growth zoning. The grains least affected by shock disturbance, and which are rich in radiogenic Pb, date the basalt crystallization near the Martian surface to 187 ± 33 million years before present. Primitive, non-radiogenic Pb isotope compositions of the host minerals, common to most shergottites, do not help us to date the meteorite, instead indicating a magma source region that was fractionated more than four billion years ago to form a persistent reservoir so far unique to Mars. Local impact melting during ejection from Mars less than 22 ± 2 million years ago caused the growth of unshocked, launch-generated zircon and the partial disturbance of baddeleyite dates. We can thus confirm the presence of ancient, non-convecting mantle beneath young volcanic Mars, place an upper bound on the interplanetary travel time of the ejected Martian crust, and validate a new approach to the geochronology of the inner Solar System.

Shapes and dimensional characteristics of polyethylene wear particles generated in vivo by total knee replacements compared to total hip replacements.

Periprosthetic tissue was obtained at revision surgery from 10 posterior cruciate retaining total knee replacement cases (five different manufacturers). The tissues were hydrolyzed and polyethylene particles were isolated from each case. Individual particles were analyzed by scanning electron microscopy combined with computerized image analysis. For comparison, periprosthetic tissues from 10 total hip replacement cases (six different manufacturers) were processed and analyzed simultaneously with identical methods. The morphologies of the isolated polyethylene particles from total knee specimens were distinctly different. There was more variety of size, shape, and texture in the total knee particles. Submicron granules were less prevalent than in hip specimens. Larger flake-shaped particles, some measuring several microns in length and width, were commonly seen in knee specimens but not hip specimens. The overall average area of particles from the total knees (1.2 microns2) was twice that of total hips (0.61 micron2) (p = 0.049). The average perimeter (p = 0.026) and length (p = 0.026) of total knee particles was also greater than the total hip particles. The proportion of the smallest polyethylene particles (those averaging 0.2 micron2) in the total knee specimens was significantly less than that in total hip specimens (p < 0.0001). Although the large flake-shaped particles were visually striking, it is important to note that the majority of the wear particles from the total knee cases were also submicron. These differences in wear particle morphology and size are due to differences in the wear mechanisms of total knees and total hips. Size is only one parameter in wear particle bioreactivity. Other factors include particle shape, surface area, and possibly size/shape variability, as well as surface chemistry and particle concentration. Polyethylene wear particles are not unidimensional; they have complex and variable shapes. The combination of morphologic description and quantitative image analysis used in this study defines several differences in polyethylene wear particles from different sources.

Responses of photosynthetic O2 evolution to PPFD in the CAM epiphyte Tillandsia usneoides L. (Bromeliaceae).

Past studies of the effects of varying levels of photosynthetic photon flux density (PPFD) on the morphology and physiology of the epiphytic Crassulacean acid metabolism (CAM) plant Tillandsia usneoides L. (Bromeliaceae) have resulted in two important findings: (1) CAM, measured as integrated nocturnal CO2 uptake or as nocturnal increases in tissue acidity, saturates at relatively low PPFD, and (2) this plant does not acclimate to different PPFD levels, these findings require substantiation using photosynthetic responses immediately attributable to different PPFD levels, e.g., O2 evolution, as opposed to the delayed, nocturnal responses (CO2 uptake and acid accumulation). In the present study, instantaneous responses of O2 evolution to PPFD level were measured using plants grown eight weeks at three PPFD (20-45, 200-350, and 750-800 µmol m(-2)s(-1)) in a growth chamber, and using shoots taken from the exposed upper portions (maximum PPFD of 800 µmol m(-2)s(-1)) and shaded lower portions (maximum PPFD of 140 µmol m(-2)s(-1)) of plants grown ten years in a greenhouse. In addition, nocturnal increases in acidity were measured in the growth chamber plants. Regardless of the PPFD levels during growth, O2 evolution rates saturated around 500 µmol m(-2)s(-1). Furthermore, nocturnal increases in tissue acidity saturated at much lower PPFD. Thus, previous results were confirmed: photosynthesis saturated at low PPFD, and this epiphyte does not acclimate to different levels of PPFD.