Compositional signatures of subducted crust in the deep-mantle sources of ocean island volcanoes in the Atlantic Ocean but not the Pacific reveal that plate motions on Earth's surface influence the characteristics of Earth's deepest interior.

Continental flood basalts are more prone to compositional modification from passage through thicker and (or) more felsic crust in comparison to their oceanic counterparts. The Steens Basalt in southeast Oregon (similar to 17 Ma) is among the oldest and most mafic members of the Columbia River Basalt Group and provides a record of the early stages of flood basalt volcanism. We evaluate the balance of mantle sources in time during the onset of Columbia River Basalt Group magmatism and assess the effect of crustal passage using stratigraphically controlled Sr, Nd, Pb, Hf, Os, and O isotopic compositions, as well as whole rock major and trace element data.

The principles governing ionization techniques used in thermal ionization mass spectrometers are relatively well understood and have remained largely unchanged for many decades. Though significant advances have been made in ion signal quantification for isotope ratio measurements, particularly for analyses of small samples by using multiple detector systems and low-noise amplifiers, the fundamental approach to sample ionization has received little focus. Modern TIMS techniques attempting to achieve parts-per-million level isotope ratios precisions are realizing limits imposed by the physics of the ionization source. A type of high-ionization efficiency thermal source employed in nuclear physics communities for decades is the so-called cavity thermal ionization source. Here, we provide a proof-of-concept study that shows cavity sources may provide a path forward to achieve a new level of precision in isotope ratio measurements from solid samples. We document our new, simple, cavity ion source design, show preliminary results from Nd isotope measurements, and discuss these new data in the context of current precision limits imposed during traditional thermal ionization methods. We show that, within the limits of our testbed mass spectrometer, mass fractionation within the cavity ion source appears similar to that from filament ion sources. We also demonstrate that oxide-versus-metal ion production plays a significant role in cavity ionization processes for Nd. Cavity ion sources may provide a viable path forward to achieving isotope ratios precisions at the sub-ppm precision level.

Detection of Hadean isotopic signatures within modern ocean island basalts (OIB) has greatly influenced understanding of Earth's earliest history and long-term dynamics. However, a relationship between two isotopic tools for studying early Earth processes, the short-lived Sm-146-Nd-142 and Hf-182-W-182 systems, has not been established in this context. The differing chemical behavior of these two isotopic systems means that they are complementary tracers of a range of proposed early Earth events, including core formation, magma ocean processes, and late accretion. There is a negative trend between Nd-142/Nd-144 and W-182/W-184 ratios among Reunion OIB that is extended by Deccan continental flood basalts. This finding is contrary to expectations if both systems were affected by silicate differentiation during the lifetime of Hf-182. The observed isotopic compositions are attributed to interaction between magma ocean remnants and Earth's core, coupled with later assimilation of recycled Hadean mafic crust. The effects of this scenario on the long-lived Nd-143-Hf-176 isotopic systematics mirror classical models invoking mixing of recycled trace-element enriched (sedimentary) and depleted (igneous) domains in OIB mantle sources.

Komatiites and sedimentary rocks sampled during the International Continental Drilling Program (BARB1-2-3-4-5) in the Barberton greenstone belt, South Africa, were analyzed for Sm-146-Nd-142 systematics. Resolved negative mu Nd-142 values (down to -7.7 +/- 2.8) were identified in komatiites from the 3.48 Ga Komati Formation and this signature correlates with low Hf/Sm ratios measured in these samples. The negative mu Nd-142 point to a source with subchondritic Sm/Nd ratio which formed during the Hadean. No analytically resolvable Nd-142 anomalies were measured in crustal detritus-rich, Si-rich, Ca-Fe-rich sediments and cherts from the Buck Reef (3.42 Ga) and the Fig Tree Group (3.23-3.28 Ga). Our new measurements are incorporated into a larger set of Sm-147-Nd-143 and Lu-176-Hf-176 data to better understand the Nd-142,Nd-143-Hf-176 isotope signatures in the mantle source at the time of komatiite crystallization. Our calculations show that the Nd-142,Nd-143-Hf-176 isotope signatures and Hf/Sm ratios cannot be produced by recycling into the komatiite source of detrital sediments like those sampled in the Barberton area. Only cherts have the required trace element characteristics - low Hf/Sm, radiogenic epsilon Hf-176 -but the trace element concentrations in the cherts are so low that unrealistic amounts of chert would need to be added.

Globally distributed kimberlites with broadly chondritic initial Nd-143-Hf-176 isotopic systematics may be derived from a chemically homogenous, relatively primitive mantle source that remained isolated from the convecting mantle for much of the Earth's history. To assess whether this putative reservoir may have preserved remnants of an early Earth process, we report W-182/W-184 and Nd-142/Nd-144 data for "primitive" kimberlites from 10 localities worldwide, ranging in age from 1,153 to 89 Ma. Most are characterized by homogeneous mu W-182 and mu Nd-142 values averaging -5.9 +/- 3.6 ppm (2SD, n = 13) and +2.7 +/- 2.9 ppm (2SD, n = 6), respectively. The remarkably uniform yet mod-estly negative mu W-182 values, coupled with chondritic to slightly suprachondritic initial Nd-143/Nd-144 and Hf-176/Hf-177 ratios over a span of nearly 1,000 Mya, provides permissive evidence that these kim-berlites were derived from one or more long-lived, early formed mantle reservoirs. Possible causes for negative mu W-182 values among these kimberlites include the transfer of W with low mu W-182 from the core to the mantle source reservoir(s), creation of the source reser-voir(s) as a result of early silicate fractionation, or an overabundance of late-accreted materials in the source reservoir(s). By contrast, two younger kimberlites emplaced at 72 and 52 Ma and characterized by distinctly subchondritic initial Hf-176/Hf-177 and Nd-143/Nd-144 have mu W-182 values consistent with the modern upper mantle. These isotopic compositions may reflect contamination of the ancient kimberlite source by recycled crustal components with mu W-182 >= 0.

A mission to unexplored lunar territory has returned the youngest volcanic samples collected so far. The rocks highlight the need to make revisions to models of the thermal evolution of the Moon.

The short-lived Sm-146-Nd-142 isotope system traces key early planetary differentiation processes that occurred during the first 500 million-years of the solar system history. The variations of Nd-142/Nd-144 in terrestrial samples, typically within a range of +/- 20 ppm, are determined using high-precision mass spectrometry that requires quantitative separation of Nd from all other elements in the sample, including the neighboring lanthanides. Recent improvements in mass spectrometry have pushed the analytical precision of Nd-142/Nd-144 measurements down to similar to 2 ppm. Non-mass-dependent isotope fractionation produced during Nd separation, however, is a major factor limiting the quality of the Nd-142 data. Popular chemical separation methods using Ln resins have unpredictable nuclear field shift effects that generate anomalous Nd isotope ratios. In order to solve this problem and potentially resolve small Nd-142/Nd-144 variations within +/- 5 ppm, in this study, we present a new two-step column separation method that effectively removes the isobaric interferents of Ce, Pr and Sm, with a recovery rate of Nd greater than 98%. JNdi-1 standard solutions doped with these interfering elements and geological reference materials are tested to document the performance of this method. A set of titanite samples from the Pilbara Craton in western Australia were also investigated to test the potential isotope fractionation effects. The same samples were processed using our method and the widely used Ln method. In contrast to the nuclear field shift effects observed from the samples using the Ln method, the results based on our new method show no detectable isotope fractionation, which further confirms the reliability of this new column chemistry scheme that is optimized for ppm-level precision Nd isotope ratio measurement, especially for resolving small variations in Nd-142/Nd-144 caused by the decay of Sm-146.

A commonly held view in the turbomachinery community is that finite element methods are not well-suited for very large-scale thermomechanical simulations. We seek to dispel this notion by presenting performance data for a collection of realistic, large-scale thermomechanical simulations. We describe the necessary technology to compute problems with O(10(7)) to O(10(9)) degrees-of-freedom, and emphasise what is required to achieve near linear computational complexity with good parallel scaling. Performance data is presented for turbomachinery components with up to 3.3 billion degrees-of-freedom. The software libraries used to perform the simulations are freely available under open source licenses. The performance demonstrated in this work opens up the possibility of system-level thermomechanical modelling, and lays the foundation for further research into high-performance formulations for even larger problems and for other physical processes, such as contact, that are important in turbomachinery analysis.