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The Pacific Northwest (PNW) has a complex tectonic history and over the past ~17 Ma has played host to several major episodes of intraplate volcanism. These events include the Steens/Columbia River flood basalts (CRB) and the striking spatiotemporal trends of the Yellowstone/Snake River Plain (Y/SRP) and High Lava Plains (HLP) regions. Several different models have been proposed to explain these features, which variously invoke the putative Yellowstone plume, rollback and steepening of the Cascadia slab, extensional processes in the lithosphere, or a combination of these. Here we integrate seismologic, geodynamic, geochemical, and petrologic results from the multidisciplinary HLP project and associated analyses of EarthScope USArray seismic data to propose a conceptual model for post-20 Ma mantle dynamics beneath the PNW and the relationships between mantle flow and surface tectonomagmatic activity. This model invokes rollback subduction as the main driver for mantle flow beneath the PNW beginning at ~20 Ma. A major pulse of upwelling due to slab rollback and upper plate extension and consequent melting produced the Steens/CRB volcanism, and continuing trench migration enabled mantle upwelling and hot, shallow melting beneath the HLP. An additional buoyant mantle upwelling is required to explain the Y/SRP volcanism, but subduction-related processes may well have played a primary role in controlling its timing and location, and this upwelling likely continues today in some form. This conceptual model makes predictions that are broadly consistent with seismic observations, geodynamic modeling experiments, and petrologic and geochemical constraints., National Science Foundation (U.S.) (Continental Dynamics Program Grant EAR-0507486)

The Pacific Northwest (PNW) has a complex tectonic history and over the past ∼17 Ma has played host to several major episodes of intraplate volcanism. These events include the Steens/Columbia River flood basalts (CRB) and the striking spatiotemporal trends of the Yellowstone/Snake River Plain (Y/SRP) and High Lava Plains (HLP) regions. Several different models have been proposed to explain these features, which variously invoke the putative Yellowstone plume, rollback and steepening of the Cascadia slab, extensional processes in the lithosphere, or a combination of these. Here we integrate seismologic, geodynamic, geochemical, and petrologic results from the multidisciplinary HLP project and associated analyses of EarthScope USArray seismic data to propose a conceptual model for post‐20 Ma mantle dynamics beneath the PNW and the relationships between mantle flow and surface tectonomagmatic activity. This model invokes rollback subduction as the main driver for mantle flow beneath the PNW beginning at ∼20 Ma. A major pulse of upwelling due to slab rollback and upper plate extension and consequent melting produced the Steens/CRB volcanism, and continuing trench migration enabled mantle upwelling and hot, shallow melting beneath the HLP. An additional buoyant mantle upwelling is required to explain the Y/SRP volcanism, but subduction‐related processes may well have played a primary role in controlling its timing and location, and this upwelling likely continues today in some form. This conceptual model makes predictions that are broadly consistent with seismic observations, geodynamic modeling experiments, and petrologic and geochemical constraints.

Systematic variations in 54Cr/52Cr ratios between meteorite classes (Qin et al., 2010a; Trinquier et al., 2007) point to large scale spatial and/or temporal isotopic heterogeneity in the solar protoplanetary disk. Two explanations for these variations have been proposed, with important implications for the formation of the Solar System: heterogeneous seeding of the disk with dust from a supernova, or energetic-particle irradiation of dust in the disk. The key to differentiating between them is identification of the carrier(s) of the 54Cr anomalies. Here we report the results of our recent NanoSIMS imaging search for the 54Cr-rich carrier in the acid-resistant residue of the CI chondrite Orgueil. A total of 10 regions with extreme 54Cr-excesses ({\delta}54Cr values up to 1500 %) were found. Comparison between SEM, Auger and NanoSIMS analyses showed that these 54Cr-rich regions are associated with one or more sub-micron (typically less than 200 nm) Cr oxide grains, most likely spinels. Because the size of the NanoSIMS primary O- ion beam is larger than the typical grain size on the sample mount, the measured anomalies are lower limits, and we estimate that the actual 54Cr enrichments in three grains are at least 11 times Solar and in one of these may be as high as 50 times Solar. Such compositions strongly favor a Type II supernova origin. The variability in bulk 54Cr/52Cr between meteorite classes argues for a heterogeneous distribution of the 54Cr carrier in the solar protoplanetary disk following a late supernova injection event. Such a scenario is also supported by the O-isotopic distribution and variable abundances in different planetary materials of other presolar oxide and silicate grains from supernovae.

Chemical evolution of planetary bodies, ranging from asteroids to the large rocky planets, is thought to begin with differentiation through solidification of magma oceans many hundreds of kilometres in depth. The Earth's Moon is the archetypical example of this type of differentiation. Evidence for a lunar magma ocean is derived largely from the widespread distribution, compositional and mineralogical characteristics, and ancient ages inferred for the ferroan anorthosite (FAN) suite of lunar crustal rocks. The FANs are considered to be primary lunar flotation-cumulate crust that crystallized in the latter stages of magma ocean solidification. According to this theory, FANs represent the oldest lunar crustal rock type. Attempts to date this rock suite have yielded ambiguous results, however, because individual isochron measurements are typically incompatible with the geochemical make-up of the samples, and have not been confirmed by additional isotopic systems. By making improvements to the standard isotopic techniques, we report here the age of crystallization of FAN 60025 using the207 Pb-206 Pb,147 Sm- 143 Nd and146 Sm-142 Nd isotopic systems to be 4,360±3 million years. This extraordinarily young age requires that either the Moon solidified significantly later than most previous estimates or the long-held assumption that FANs are flotation cumulates of a primordial magma ocean is incorrect. If the latter is correct, then much of the lunar crust may have been produced by non-magma-ocean processes, such as serial magmatism.

Helium is a powerful tracer of primitive material in Earth’s mantle. Extremely high 3He/4He ratios in some ocean-island basalts suggest the presence of relatively undegassed and undifferentiated material preserved in Earth’s mantle. However, terrestrial lavas with high 3He/4He ratios have never been observed to host the primitive lead-isotopic compositions that are required for an early (roughly 4.5 Gyr ago) formation age1,2. Here we show that Cenozoic-era Baffin Island and West Greenland lavas, previously found to host the highest terrestrial-mantle 3He/4He ratios3,4,5, exhibit primitive lead-isotope ratios that are consistent with an ancient mantle source age of 4.55–4.45 Gyr. The Baffin Island and West Greenland lavas also exhibit 143Nd/144Nd ratios similar to values recently proposed for an early-formed (roughly 4.5 Gyr ago) terrestrial mantle reservoir6,7. The combined helium-, lead- and Nd-isotopic compositions in Baffin Island and West Greenland lavas therefore suggest that their source is the most ancient accessible reservoir in the Earth’s mantle, and it may be parental to all mantle reservoirs that give rise to modern volcanism.

Putting data into the public domain is not the same thing as making those data accessible for intelligent analysis. A distinguished group of editors and experts who were already engaged in one way or another with the issues inherent in making research data public came together with statisticians to initiate a dialogue about policies and practicalities of requiring published research to be accompanied by publication of the research data. This dialogue carried beyond the broad issues of the advisability, the intellectual integrity, the scientific exigencies to the relevance of these issues to statistics as a discipline and the relevance of statistics, from inference to modeling to data exploration, to science and social science policies on these issues., Comment: Published in at http://dx.doi.org/10.1214/10-STS320 the Statistical Science (http://www.imstat.org/sts/) by the Institute of Mathematical Statistics (http://www.imstat.org)

High precision measurements of 226Ra–230Th–238U disequilibria and Ba concentrations are reported for samples from two chemically zoned trachyte deposits from Fogo volcano, São Miguel, Azores. High-precision U-series disequilibria measurements by plasma ionization multicollector mass spectrometry were performed on pumice lapilli and volcanic glass separates from Fogo 1563 A.D. (∼ 0.14 km3) and the ∼ 4.7 ka Fogo A (∼ 0.7 km3) deposits in order to quantify the time scales of magmatic processes. Observed (226Ra)/Ba–(230Th)/Ba relationships in Fogo 1563 are compatible with a conventional instantaneous fractional crystallization model and a pre-eruptive magma residence time of ∼ 50 y. However, the Fogo A data cannot be explained by instantaneous fractional crystallization, and require a prolonged crystallization history. Continuous differentiation models better explain the observed 226Ra–230Th variations within the Fogo deposits and may be more realistic in general. Such models suggest magma residence times prior to eruption of ∼ 50–80 years for Fogo 1563, and ∼ 4.7 ka for the larger volume Fogo A eruption. These time scales represent liquid residence ages rather than the crystallization ages documented in most previous magmatic time scale studies, and allow constraints to be placed on the time scales necessary for the development of chemical zonation within the Fogo magma chamber. Our results indicate that calculated time scales are relatively insensitive to the precise nature of the continuous differentiation models, and further indicate that meaningful magma differentiation time scales can be obtained despite open system behavior, because the Ra–Th disequilibria are overwhelmingly controlled by feldspar fractionation. Calculated time scales are, however, extremely sensitive to DRa/DBa ratios. We therefore emphasize the crucial importance to better constrain the relative partitioning of Ra and Ba when employing Ra–Th disequilibrium data to constrain the rates and time s