Petrogenesis of shield volcanism from the Juan Fernández Ridge, Southeast Pacific: Melting of a low-temperature pyroxenite-bearing mantle plume

The Juan Fernández Ridge (JFR) is an age-progressive volcanic chain (∼800 km long) related to a fixed mantle plume in the Southeast Pacific offshore central Chile. The high 3He/4He ratio (up to 18 times higher than that of the atmosphere) and spatiotemporal 40Ar/39Ar geochronology suggest that the source material of the JFR is derived from the lower mantle and transferred to the surface by a relatively stationary plume. We used new whole-rock geochemical data (major-element, trace-element, and Sr–Nd–Pb isotopic data) for representative samples from the shield-stage of volcanism in the JFR (from O’Higgins Guyot, Alpha Seamount, Robinson Crusoe Island, and Alejandro Selkirk Island) to develop a petrogenetic model with the goal of understanding the temporal and spatial evolution of magmatism along the JFR. The shield-building lavas of JFR consist primarily of tholeiitic to alkalic basalts. Their compositional differences are explained by the fractional crystallization of olivine and clinopyroxene ± plagioclase, magmatic recharge, melt mixing, and olivine accumulation. Radiogenic Sr–Nd–Pb isotopes show a narrow field within the compositional range of the common FOZO mantle. The 206Pb/204Pb and 207Pb/204Pb ratios of JFR lavas are similar to those of other islands on the Nazca Plate (e.g., San Félix and San Ambrosio). However, the JFR lavas are more radiogenic and show a narrower compositional range compared to the Easter Seamount Chain. The low CaO content at a given MgO content, moderate Ti–Ta–Nb ‘TITAN' anomaly, fractionated heavy rare earth element values, and isotopic composition of JFR lavas are consistent with the presence of pyroxenite (recycled oceanic crust) in the mantle source. To estimate source parameters, we used OBS1 software (Kimura and Kawabata, 2015) to calculate the potential temperature (1316°C–1412°C), total degree of melting (3.4–19.2 wt%), and pyroxenite fraction (0.6–18.4 wt%) of the mantle beneath JFR. The temporal changes in the thermal, compositional, and lithologic characteristics of the source material can explain the chemical differences observed between different JFR volcanoes. We propose that shield-stage volcanism in JFR is largely generated by the melting of pyroxenite in a relatively low-temperature mantle plume. As a result, this weak plume containing low mantle He is difficult to image using seismic tomography

Understanding the open circuit voltage in organic solar cells on the basis of a donor-acceptor abrupt (p-n++) heterojunction

By using electrical characterization and classical solid state semiconductor device theory, we demonstrate that the open circuit voltage (V oc ) in organic solar cells based on non-intentional doped semiconductors is fundamentally limited by the built-in potential (V bi ) originated at a donor-acceptor abrupt (p-n ++ ) heterojunction in case of selective contacts. Our analysis is validated using P3HT:PCBM devices fabricated in our research group. We also demonstrate that such a result can be generalized using data already reported in literature for fullerene-based solar cells. Finally, we show that the dependence of V oc on the device contacts can be understood in terms of the potential barriers formed by the Fermi level alignment of semiconductors at the heterojunction and at the Schottky junctions

Turbulent cross-field transport of non-thermal electrons in coronal loops: theory and observations

<p><b>Context:</b> A fundamental problem in astrophysics is the interaction between magnetic turbulence and charged particles. It is now possible to use Ramaty High Energy Solar Spectroscopic Imager (RHESSI) observations of hard X-rays (HXR) emitted by electrons to identify the presence of turbulence and to estimate the magnitude of the magnetic field line diffusion coefficient at least in dense coronal flaring loops.</p> <p><b>Aims:</b> We discuss the various possible regimes of cross-field transport of non-thermal electrons resulting from broadband magnetic turbulence in coronal loops. The importance of the Kubo number K as a governing parameter is emphasized and results applicable in both the large and small Kubo number limits are collected.</p> <p><b>Methods:</b> Generic models, based on concepts and insights developed in the statistical theory of transport, are applied to the coronal loops and to the interpretation of hard X-ray imaging data in solar flares. The role of trapping effects, which become important in the non-linear regime of transport, is taken into account in the interpretation of the data.</p> <p><b>Results:</b> For this flaring solar loop, we constrain the ranges of parallel and perpendicular correlation lengths of turbulent magnetic fields and possible Kubo numbers. We show that a substantial amount of magnetic fluctuations with energy ~1% (or more) of the background field can be inferred from the measurements of the magnetic diffusion coefficient inside thick-target coronal loops.</p&gt

New Age and Geochemical Data from the Southern Colville and Kermadec Ridges, SW Pacific: Insights into the recent geological history and petrogenesis of the Proto-Kermadec (Vitiaz) Arc

Highlights • Age and petrogenesis of the Miocene-Pleistocene proto Kermadec arc: the Kermadec and Colville Ridge • Complex interplay between element flux from the subducting Pacific Plate and heterogenous mantle wedge • New insights into the recent tectonic history of the Kermadec arc system Abstract The intra-oceanic Kermadec arc system extends ~1300 km between New Zealand and Fiji and comprises at least 30 arc front volcanoes, the Havre Trough back-arc and the remnant Colville and Kermadec Ridges. To date, most research has focussed on the Kermadec arc front volcanoes leaving the Colville and Kermadec Ridges virtually unexplored. Here, we present seven 40Ar/39Ar ages together with a comprehensive major and trace element and Sr-, Nd-, and Pb-isotope dataset from the Colville and Kermadec Ridges to better understand the evolution, petrogenesis and splitting of the former proto-Kermadec (Vitiaz) Arc to form these two remnant arc ridges. Our 40Ar/39Ar ages range from ~7.5–2.6 Ma, which suggests that arc volcanism at the Colville Ridge occurred continuously and longer than previously thought. Recovered Colville and Kermadec Ridge lavas range from mafic picro-basalts (MgO = ~8 wt%) to dacites. The lavas have arc-type normalised incompatible element patterns and Sr and Pb isotopic compositions intermediate between Pacific MORB and subducted lithosphere (including sediments, altered oceanic crust and serpentinised uppermost mantle). Geochemically diverse lavas, including ocean island basalt-like and potassic lavas with high Ce/Yb, Th/Zr, intermediate 206Pb/204Pb and low 143Nd/144Nd ratios were recovered from the Oligocene South Fiji Basin (and Eocene Three Kings Ridge) located west of the Colville Ridge. If largely trench-perpendicular mantle flow was operating during the Miocene, this geochemical heterogeneity was likely preserved in the Colville and Kermadec sub arc mantle. The Colville and Kermadec Ridge data therefore highlight the complex interplay between pre-existing mantle heterogeneities and material fluxes from the subducting Pacific Plate. The new data allow us to present a holistic (yet simplified) picture of the tectonic evolution of the late Vitiaz Arc and northern Zealandia since the Miocene and how this tectonism influences volcanic activity along the Kermadec arc at the present

Increasing organic solar cell efficiency with polymer interlayers

We demonstrate how organic solar cell efficiency can be increased by introducing a pure polymer interlayer between the PEDOT:PSS layer and the polymer: fullerene blend. We observe an increase in device efficiency with three different material systems over a number of devices. Using both electrical characterization and numerical modeling we show that the increase in efficiency is caused by optical absorption in the pure polymer layer and hence efficient charge separation at the polymer bulkheterojunction interface