A new allotrope of nitrogen in which the atoms are connected to form a novel N-6 molecule is predicted to exist at ambient conditions. The N-6 molecule is a charge-transfer complex with an open-chain structure containing both single and triple bonds. The charge transfer induces ionic characteristics in the intermolecular interactions and leads to a much higher cohesive energy for the predicted crystal compared to solid N-2. The N-6 solid is also more stable than a previously reported polymeric solid of nitrogen. Because of the kinetic stability of the molecules and strong intermolecular interactions, the N-6 crystal is shown by metadynamics simulations to be dynamically stable around room temperature and to only dissociate to N-2 molecules above 700 K. The N-6 crystal can likely be synthesized under high-pressure high-temperature conditions, and the considerable metastability may allow for an ambient pressure recovery of the crystal. Because of the large energy difference between the single and triple bonds, the dissociation of the N-6 crystal is expected to release a large amount of energy, placing it among the most efficient energy materials known today.

Using global structure searches, We have explored the structural, stability of CaB3N3, a compound analogous to CaC6, under pressure. There are two high-pressure phases with space groups R3c and Amm2 that were found to be stable between 29 and 42 GPa, and above 42 GPa, respectively. The two phases show different structural frameworks, analogous to graphitic CaC6. Phonon calculations confirm that both structures are also dynamically stable at high pressures. The electronic Structure calculations show that the R3c phase is a semiconductor With a band gap of 2.21 eV and that the Amm2 phase is a semimetal. These findings help advance our understanding of the Ca-B-N ternary system.

Recent hydrodynamic simulations and observations of radio jets have shown that the surrounding environment has a large effect on their resulting morphology. To investigate this, we use a sample of 50 Extended Radio Active Galactic Nuclei (ERAGN) detected in the Observations of Redshift Evolution in Large-Scale Environments survey. These sources are all successfully cross-identified to galaxies within a redshift range of 0.55 <= z <= 1.35, either through spectroscopic redshifts or accurate photometric redshifts. We find that ERAGN are more compact in high-density environments than those in low-density environments at a significance level of 4.5 sigma. Among a series of internal properties under our scrutiny, only the radio power demonstrates a positive correlation with their spatial extent. After removing the possible radio power effect, the difference of size in low- and high-density environments persists. In the global environment analyses, the majority (86%) of high-density ERAGN reside in the cluster/group environment. In addition, ERAGN in the cluster/group central regions are preferentially compact with a small scatter in size, compared to those in the cluster/group intermediate regions and fields. In conclusion, our data appear to support the interpretation that the dense intracluster gas in the central regions of galaxy clusters plays a major role in confining the spatial extent of radio jets.

Solar-induced chlorophyll fluorescence (SIF) shows enormous promise as a proxy for photosynthesis and as a tool for modeling variability in gross primary productivity and net biosphere exchange (NBE). In this study, we explore the skill of SIF and other vegetation indicators in predicting variability in global atmospheric CO2 observations, and thus global variability in NBE. We do so using a 4-year record of CO2 observations from NASA's Orbiting Carbon Observatory 2 satellite and using a geostatistical inverse model. We find that existing SIF products closely correlate with space-time variability in atmospheric CO2 observations, particularly in the extratropics. In the extratropics, all SIF products exhibit greater skill in explaining variability in atmospheric CO2 observations compared to an ensemble of process-based CO2 flux models and other vegetation indicators. With that said, other vegetation indicators, when multiplied by photosynthetically active radiation, yield similar results as SIF and may therefore be an effective structural SIF proxy at regional to global spatial scales. Furthermore, we find that using SIF as a predictor variable in the geostatistical inverse model shifts the seasonal cycle of estimated NBE and yields an earlier end to the growing season relative to other vegetation indicators. These results highlight how SIF can help constrain global-scale variability in NBE.

Defining the age of the Moon has proven to be an elusive task because it requires reliably dating lunar samples using radiometric isotopic systems that record fractionation of parent and daughter elements during events that are petrologically associated with planet formation. Crystallization of the magma ocean is the only event that unambiguously meets this criterion because it probably occurred within tens of millions of years of Moon formation. There are three dateable crystallization products of the magma ocean: mafic mantle cumulates, felsic crustal cumulates, and latestage crystallization products known as urKREEP (uniform residuum K, rare earth elements, and P). Although ages for these materials in the literature span 200 million years, there is a preponderance of reliable ages around 4.35 billion years recorded in all three lunar rock types. This age is also observed in many secondary crustal rocks, indicating that they were produced contemporaneously (within uncertainty of the ages), possibly during crystallization and overturn of the magma ocean.

The nature of Earth's first crust and the processes that formed it are poorly constrained due to limited exposures of >3.7 billion-year-old (Ga) rocks. Here we report the discovery of a new Eoarchean terrane named the Muzidian gneiss complex in the Yangtze craton of central China where rocks as old as 3.81 Ga are preserved. In this study, we characterized six samples (including five TTGs and an amphibolite) through zircon U-Pb age, Hf isotope and bulk-rock 146,147Sm-142,143Nd isotope compositions. The subchondritic zircon initial Hf isotope compositions and the negative mu 142Nd values for the 3.81 - 3.65 Ga samples reveal that these rocks were most likely reworked from >4.3 Ga mafic crust. The 2.5 - 2.4 Ga rocks in the same complex are the youngest felsic rocks on Earth with deficits in 142Nd, highlighting the long-lived role of Hadean crustal components in the building of a stable continent. The 147Sm-143Nd isotopic systematics of these rocks are disturbed. The currently available data for global Eoarchean rocks suggest two distinct lineages for > 3.6 Ga Eoarchean crustal blocks, one produced by reworking of Hadean mafic crust with the isotopic signature of coupled negative epsilon Hf(t) and mu 142Nd, and the other by melting of incompatible-element-depleted mantle sources residual to Hadean crust formation characterized by positive mu 142Nd and near chondritic epsilon Hf(t). The Eoarchean samples of the Muzidian gneiss complex in the present study, along with >3.6 Ga rocks in the Acasta, Napier and Nuvvuagittuq regions imply a Hadean crustal source distinct from the products expected for magma ocean crystallization.(c) 2023 Elsevier B.V. All rights reserved.

The Tuli Basin represents one of the larger erosional remnants of the rift-related sequences of the Karoo continental flood basalts (CFB) of southern Africa. We present previously unpublished bulk-rock major and trace element analyses for 787 high-Ti picrites and basalts, including both surface and drill core samples, as well as SrNd-Hf-Pb-Os isotope compositions and rare earth element (REE) abundances for selected samples. Due to the identification of previously unrecognised basaltic sub-types, a new classification scheme for the high-Ti basalts and picrites of the Tuli Basin is proposed where they are divided into three types based on Zr/Nb and Ce/Y ratios: HZN-1, HZN-2, and LZN. The HZN-1 picrites/basalts occur at the base of the lava sequence and are overlain by the HZN-2 basalts, which, in turn, are overlain by the LZN basalts. We show that crustal assimilation is not the dominant process in influencing basalt and picrite petrogenesis. Using the Magma Chamber Simulator (MCS) program, the HZN-1 basalts are shown to have evolved over a range of pressure, whereas the HZN-2 and LZN basalts evolved at shallow depths. The HZN-1 and LZN picrites are highly enriched in LILE, HFSE, and LREE and are characterised by variable Zr/Y with high values at the base of the lava sequence that gradually decrease upward. This upwards decrease is shown to be related to increasing degrees of partial melting in the source with time. Compared to the picrites, the basalts have relatively low Zr/Y, indicating that evolution of basalt from a picritic parent began only after achieving higher degrees of partial melting in the source. The HZN-1 picrites and basalts have relatively radiogenic 87Sr/86Sri (0.7048 to 0.7059), low ENdi (-7.2 to -9.8), low EHfi (-8.9 to -14.2), and variable gamma Osi (-14.0 to +10.8), and are clearly distinguishable from HZN-2 and LZN basalts that have less radiogenic (87Sr/86Sr)i (-0.7045), higher ENdi (-1.2 to -4.5), EHfi (-0.1), and gamma Osi (-1.6 and +3.9). We show that the mantle source of southern African Karoo high-Ti basalts comprises at least three components with a dominant sub-continental lithospheric mantle (SCLM) signature. Each basalt type is shown to represent a temporally distinct episode of mantle melting and each of the three mantle components are progressively exhausted in the source with time. The possible presence of a sub-lithospheric component is only significantly reflected in the composition of the LZN basalts and picrites; the final phase of eruption.

Temporal variations in lava chemistry at active submarine volcanoes are difficult to decipher due to the challenges of dating their eruptions. Here, we use high-precision measurements of 226Ra-230Th disequilibria in basalts from Kama`ehuakanaloa (formerly LiVihi) to estimate model ages for recent eruptions of this submarine Hawaiian pre-shield volcano. The ages range from ca. 0 to 2300 yr (excluding two much older samples) with at least five eruptions in the past similar to 150 yr. Two snapshots of the magmatic evolution of Kama`ehuakanaloa (or "Kama`ehu") are revealed. First, a long-term transition from alkalic to tholeiitic volcanism was nearly complete by ca. 2 ka. Second, a systematic short-term fluctuation in ratios of incompatible elements (e.g., Th/Yb) for summit lavas occurred on a time scale of similar to 1200 yr. This is much longer than the similar to 200-yr-long historical cycle in lava chemistry at the neighboring subaerial volcano, Kilauea. The slower pace of the variation in lava chemistry at Kama`ehu is most likely controlled by sluggish mantle upwelling on the margin of the Hawaiian plume.

Isotope dilution W whole-rock data, coupled with data for other trace elements in 42 peridotite xenoliths from Tariat (Mongolia), Yangyuan and Hannuoba (China), and Letlhakane (Botswana) are used to constrain the W abundance and behavior in the continental lithospheric mantle. Tungsten concentrations are >11 ng g-1, even in the most depleted peridotites, and higher than the W abundance estimate of the bulk silicate Earth (BSE) in all but one sample. Combined W-Th-U systematics reveal fractionation of W from Th and U with increasing degree of melt depletion, while incompatible element-enriched samples display no such fractionation. Integrated melt reactions and degrees of melt depletion are estimated based on either residual Th or residual Yb abundances for each sample, relative to a BSE precursor. This allows modelling of different partial melting scenarios that consider maximized trace element retention (Th-based model; where measured Th contents are decoupled from Al2O3 contents) or correction for metasomatic trace element contributions (Yb-based model; where measured Yb contents are well-coupled with Al2O3 contents). Modelled residual W concentrations reveal W excesses of 11-19 ng g-1, even when correcting for metasomatic W contributions. Combined with available in situ trace element mineral data for the rock-forming silicates and spinel, which all display W abundances much higher than ex-pected, these findings suggest that either (i) W is less incompatible than previously thought, or that (ii) the peridotites experienced W metasomatism after the last melt depletion event with subsequent re-equilibration. The latter is unlikely, as similar geochemical patterns are observed for oceanic lithospheric mantle based on published data, requiring such W metasomatism to be a global phenomenon. We thus conclude that W is not as incompatible as Th and U during upper mantle melting and potential W-Th-U fractionation mechanisms are examined to explain near-constant W/Th and W/U in mantle melts. We propose revised W concentrations for the BSE of 27 +/- 16 ng g-1 to 31 +/- 14 ng g-1 and for the depleted mantle of 22 +/- 13 ng g- 1.

Tungsten and helium isotope ratios in lavas derived from deeply rooted mantle plumes are tracers of lower mantle compositional heterogeneity or core-mantle exchange. We measured the tungsten isotopic compositions of lavas with exceptionally high-He-3/He-4 ratios that erupted above the head of the Iceland plume on Baffin Island. These lavas have W-182/W-184 ratios that are indistinguishable from the convecting upper mantle, unlike younger lavas in Iceland that have lower W-182/W-184 ratios. This implies that only the Iceland plume tail was infused with low W-182/W-184 material, likely from the core. If high-He-3/He-4 helium also comes from the core, then diffusion across the core-mantle boundary may stratify plume-source mantle domains, with elevated He-3/He-4 travelling farther into the lower mantle than W-182/W-184 anomalies. Over Earth history, tungsten diffusion from the core can explain the decline of W-182/W-184 in the convecting mantle. We speculate that the uneven pace of this decline corresponds with evolving lower mantle dynamics.