Major and trace element and radiogenic isotopic characteristics of primitive mafic Pleistocene and Holocene lavas from Newberry Volcano, Oregon, define two groups. The first consists of dry tholeiitic high-alumina olivine basalts that are slightly enriched in highly incompatible elements. The second group consists of calc-alkaline basalts that contained 2-4 wt % H2O prior to eruption and shows strong enrichment in the light rare earth elements, Ba, and Sr, and deficits in Nb, Ta, Hf, and Zr. The tholeiitic basalts reflect 6-11% anhydrous adiabatic decompression melting of spinel peridotite. The calc-alkaline basalts derived from compositionally distinct sources with strong LIL enrichment and relative depletion in HFSE, but with Sr, Nd, Hf, and Pb isotopic composition only slightly distinct from the sources of the tholeiitic magmas. Radiogenic Os correlates with LREE enrichment in the calc-alkaline magmas, which indicates that their source materials include a contribution from a mafic component that was melted in the garnet stability field. The calc-alkaline magmas were derived by melting of peridotite metasomatized by a fluid/melt that originated by melting of a mixture of the sediment plus MORB basalt/mantle in the underlying subducting oceanic plate. While the trace element characteristics of the calc-alkaline magmas were determined by the subduction component, their isotopic characteristics were modified during transit through the mantle by interaction with the highly magmatically processed mantle wedge beneath Newberry Volcano that, without the slab component, serves as the source of the tholeiitic magmas.

In order to apply the vanadium (V) stable isotope system for studies of planetary accretion and evolution in the solar system and redox variations in terrestrial magmatic processes, the V isotope composition of the Bulk Silicate Earth (BSE) needs to be precisely constrained. Previous studies have shown that fertile peridotites have systematically higher V-51/V-50 ratios than MORB. This, however, is in conflict with the theoretical prediction that mantle melting residues should be enriched in V-50 rather than V-51. To address these issues, a more precise estimate of the V isotope composition of the BSE is required. This study presents delta V-51 data for eleven peridotite xenoliths from two late Cenozoic eruption centers at Tariat in central Mongolia, ten komatiites from five localities ranging in age between 3.48 and 2.41 Ga, and four 1.98 Ga picrites from the Onega Plateau in Fennoscandia. The mean delta V-51 for fertile spinel lherzolites is -0.91 +/- 0.06 parts per thousand (2SD, n = 8). They show no resolvable difference in V isotope compositions compared to three moderately to highly refractory peridotite xenoliths analyzed, with a mean 5 51 V of -0.93 +/- 0.01 parts per thousand (2SD, n = 3). The mean delta V-51 for the komatiites is -0.91 +/- 0.05 parts per thousand (2SD, n = 10), which is identical to that for the fertile peridotites. Based on the V isotope compositions of the peridotites and komatiites analyzed in this study, the mean delta V-51 of the BSE is estimated to be -0.91 +/- 0.09 parts per thousand (2SD, n = 18).

The analysis of lunar samples returned to Earth by the Apollo and Luna missions changed our view of the processes involved in planet formation. The data obtained on lunar samples brought to light the importance during planet growth of highly energetic collisions that lead to global-scale melting. This violent birth determines the initial structure and long-term evolution of planets. Once past its formative era, the lunar surface has served as a recorder of more than 4 billion years of interaction with the space environment. The chronologic record of lunar cratering determined from the returned samples underpins age estimates for planetary surfaces throughout the inner Solar System and provides evidence of the dynamic nature of the Solar System during the planet-forming era.

Substantial quantities of sediments are known to enter the deep lithosphere at subduction zones, but the extent to which sediments melt and the process involved in sediment contribution to the deep lithosphere are inadequately understood. Vigorous debate continues about whether the subducted sediment component is terrigenous or pelagic and transported as a hydrous melt, an aqueous fluid, or bulk sediment. In this contribution, we conduct an integrated study on a variety of deep-seated xenoliths in the Neogene Hannuoba basalts from the northern margin of the North China Craton. Among these xenoliths, clinopyroxenite xenoliths are compositionally and isotopically distinct. Mineral chemistry shows that the clinopyroxenite xenoliths come from a depth near the MOHO, rather than from the mantle as suggested previously. The clinopyroxenite xenoliths have extremely evolved Sr-Nd-Hf isotopic compositions and are interpreted to have a late Archean protolith age. The extremely low contents of Cr and Ni for the clinopyroxenite xenoliths preclude a magmatic origin. Instead, a metasomatic origin is suggested, which is strongly supported for the clinopyroxenites by the occurrence of hydrous minerals and high contents of large-ion-lithophile elements (K, Rb, Ba, Th and Sr) and light rare earth elements, as well as elevated delta O-18 (9.9-11.3 parts per thousand) and light delta Mg-26 (-1.04 parts per thousand to 1.42 parts per thousand) isotopic compositions. Furthermore, their high high-field-strength element (Nb, Ta, Zr and Hf) contents indicate that the metasomatic agent is a hydrous melt, rather than an aqueous fluid. The metasomatic melts are considered to be derived from a mixed source of sedimentary carbonates and ancient, felsic continental materials. A combination of zircon ages and oxygen isotope data for the clinopyroxenite xenoliths further restricts the timing of metasomatism to the late Paleozoic. Considering the regional tectonic setting, the sediments most likely came from the subducted Paleo-Asian oceanic slab. Thus the Hannuoba clinopyroxenite xenoliths provide direct evidence for melting of the subducted Paleo-Asian oceanic slab sediment and its interaction with the deep lithosphere. The data show that melting of subducted sediments can take place at a much shallower depth than commonly thought and place an independent constraint on future models of slab geotherms. (C) 2019 Elsevier Ltd. All rights reserved.

To constrain the deformation, thermal evolution, and seismic properties of the mantle lithosphere beneath the Hangay Dome, we have analyzed the microstructures, crystal preferred orientations (CPO), and hydrogen concentrations of olivine and pyroxenes of 50 mantle xenoliths carried up by Cenozoic basalts from Zala, Haer, and Shavaryn-Tsaram from Tariat, Mongolia. Most xenoliths are medium- to coarse-grained spinel-lherzolites, but four contain garnet + spinel. Coarse granular, highly annealed microstructures predominate. The microstructures are associated with well-developed CPO, typical of deformation under high temperature, moderate pressure, and dry conditions. The hydrogen concentrations in olivine, orthopyroxene, and clinopyroxene are low and range around 5, 75, and 147 ppm H2O wt, respectively. Together, microstructures and CPO indicate that ductile deformation was followed by static recrystallization, which has annealed the microstructures but preserved the CPO and, hence, the anisotropy of physical properties. Lack of correlation between annealing and equilibrium temperatures suggest that the annealing is due to a long quiescence episode since the last deformation episode. Here, there is not evidence that the formation of Hangay Dome is associated with recent deformation in the lithospheric mantle. Calculated seismic properties show moderate seismic anisotropy, with fast propagation of P waves and polarization of S waves parallel to the flow direction and low birefringence for S waves propagating obliquely to the flow plane. The results are consistent with weak P wave anomalies but not with the strong low S wave velocity anomalies predicted by some tomographic models or with the high conductivity inferred from magnetotelluric data for the lithospheric mantle beneath the Hangay Dome.

The Mn-53-Cr-53 short-lived radionuclide decay system is a powerful tool to investigate the timescales of early solar system processes. A complication arises, however, from the fact that spallation and thermal/epithermal neutron capture processes induced by cosmic rays can significantly alter Cr-53/Cr-52 ratios in solar system objects that have long exposure ages and high Fe/Cr ratios. Quantifying these cosmogenic effects helps constrain the cosmic ray exposure history of extraterrestrial samples. The isotopic shifts produced by cosmic ray irradiation also need to be corrected before the Cr isotope systematics can be used as a dating tool and as a tracer of nucleosynthetic provenance. To investigate the impact of cosmogenic production on Cr, the Cr isotopic compositions of 25 samples from 16 iron meteorites belonging to nine different chemical groups were measured. The measurements show that exposure to cosmic rays can cause large coupled excesses in epsilon Cr-53 (up to +268.29 +/- 0.14; 2SE) and epsilon Cr-54 (up to +1053.78 +/- 0.72; 2SE) with a best fit line of epsilon Cr-54 = (3.90 +/- 0.03) x epsilon Cr-53. The magnitude of Cr isotope production is controlled by various factors including the exposure age, the chemical composition (i.e., Cr concentration and Ni/Fe ratio) and shielding conditions. Nevertheless, the correlation of epsilon Cr-53 and epsilon Cr-54 is independent of these factors, which provides an effective method to evaluate the cosmogenic contribution to Cr-53 by monitoring the cosmogenic variations in epsilon Cr-54 in meteoritic irons. The results are compared with modeling results that yield a slightly shallower slope of 3.6 +/- 0.2. Modeling results for the olivine in stony meteorites yield a higher slope (similar to 5.4). However, the previous estimated results for lunar samples (stony targets for comic ray irradiation) exhibit an observably shallower slope (similar to 2.62). The reason for the different slopes is that the production rates of different cosmogenic Cr isotopes in iron meteorites and lunar samples are in different proportions. The differences may not be completely controlled by the higher thermal and epithermal neutron fluencies in lunar samples than in iron meteorites, but instead may largely reflect different radiation geometry between the two. More studies are needed to solve this open question. (C) 2019 Published by Elsevier Ltd.