Rejuvenation Events Research Articles

Apatite Textures, Elemental and Isotopic Compositions Unmask the Homogenizing Process in Silicic Magma Chambers

AbstractSilicic magmas are the most viscous of all magmas, however some granitic plutons display remarkably homogeneous compositions, which contradicts the hypothesis that mechanical mixing is the main homogenizing process in the magma chamber. Thus much remains controversial about the mechanisms responsible for the homogeneities of silicic plutons. Here, we present textural observations, elemental mapping, and in situ elemental and Nd‐O isotopic data of apatites from the compositionally homogeneous Late Permian Yuanyang A‐type granitic pluton (SW Yunnan, South China). Apatite grains display oscillatory chemical zonation and resorption‐precipitation texture, suggesting incremental growth dominated by co‐genetic magma batches injection. The intra‐/inter‐grain core to rim elemental and Nd‐O isotopic variations imply crystal transfer and crystallization from different melt domains within the crystal mush. We propose that rejuvenation events associated with hotter cogenetic intermediate magma batch injection has induced crystal mush reactivation and convective stirring in silicic magma chambers, thereby homogenizing the entire reservoir.

EXPLORING THE BIOLOGICAL AGING DYNAMICS IN A RENAL DEVELOPMENT ORGANOID MODEL

Abstract Aging clocks emerge have emerged as promising molecular estimators of biological age based on DNA methylation or transcriptomic profiles. Among other insights, they revealed “ground zero” of aging during mouse embryogenesis characterized by the lowest biological age. To model the biological age dynamics during human embryogenesis, we established a differentiation culture system that mimics embryonic kidney development from human iPSCs. We then applied multiple aging clocks to the samples from hiPSC to kidney organoid stages. This analyses revealed the lowest biological age around the intermediate mesoderm stage, indicating a potential rejuvenation event at an early stage of renal development. A principal component analysis suggested that development in this system may comprise two processes with distinct contributions to aging, with one process increasing monotonically during development, while the other increasing at primitive streak and decreasing after the mesoderm phase. We further examined the relationship between these two processes and our previously-established transcriptomic signatures of aging and reprogramming. Interestingly, the former process may represent mostly age-related genes, while the latter process reprogramming-related genes. These findings suggest the occurrence of “ground zero” in a cell culture model of early embryonic development and characterize it in the context of molecular pathways and transcriptomic signatures.

EPIGENETIC AGE DYNAMICS AND EMBRYONIC MORTALITY POINT TO GASTRULATION AS AGING GROUND ZERO IN XENOPUS LAEVIS

Abstract Recent studies on embryonic development revealed a natural rejuvenation event followed by epigenetic aging. Here, we developed a frog aging clock based on the DNA methylation profile in the African clawed frog Xenopus laevis. Application of this clock to Xenopus laevis early embryonic development identified a decrease in epigenetic age during early embryogenesis, with the minimal epigenetic age reached around gastrulation. We further examined the individual developmental trajectories of 6,457 embryos and found that this minimum age is also accompanied by a higher incidence of disrupted development. Taken together, our data point to gastrulation as a critical stage for aging and natural rejuvenation, characterized by the lowest epigenetic age and increased mortality, defining aging ground zero as the basepoint where rejuvenation ends and the aging process begins.

HINOTORI I: The nature of rejuvenation galaxies

Abstract We present the HINOTORI (Star Formation History Investigation To Find Rejuvenation) project to reveal the nature of rejuvenation galaxies (RGs), which are galaxies that restarted their star formation after being quiescent. As the first step of HINOTORI, we construct the largest RG sample with 1071 sources. We select these RGs from 8857 MaNGA (Mapping Nearby Galaxies at APO) survey galaxies by reconstructing their star formation histories with the Prospector spectral energy distribution fitting code. Both optical spectral data and UV to IR photometric data are used for the fitting. Using mock data, we confirm that our method can detect weak rejuvenation events that form only about $0.1$% of the total stellar mass with high completeness. The RGs account for ${\sim}10$% of the whole sample, and rejuvenation events contribute on average only about $0.1$% of the total stellar mass in those galaxies but $17$% of the cosmic star formation rate density today. Our RGs have a similar mass distribution to quiescent galaxies (QGs). However, the morphology of the RGs is more disk-like than QGs, suggesting that rejuvenation may occur selectively in disk-like QGs. Our results also suggest the possibility of multiple-time rejuvenation events in a single galaxy. Further spatially resolved analyses of integral field unit data and radio observations and comparisons to simulations are needed to identify the mechanism and the role of rejuvenation in galaxy evolution.

Intersection clock reveals a rejuvenation event during human embryogenesis.

Recent research revealed a rejuvenation event during early development of mice. Here, by examining epigenetic age dynamics of human embryogenesis, we tested whether a similar event exists in humans. For this purpose, we developed an epigenetic clock method, the intersection clock, that utilizes bisulfite sequencing in a way that maximizes the use of informative CpG sites with no missing clock CpG sites in test samples and applied it to human embryo development data. We observed no changes in the predicted epigenetic age between cleavage stage and blastocyst stage embryos; however, a significant decrease was observed between blastocysts and cells representing the epiblast. Additionally, by applying the intersection clock to datasets spanning pre and postimplantation, we found no significant change in the epigenetic age during preimplantation stages; however, the epigenetic age of postimplantation samples was lower compared to the preimplantation stages. We further investigated the epigenetic age of primed (representing early postimplantation) and naïve (representing preimplantation) pluripotent stem cells and observed that in all cases the epigenetic age of primed cells was significantly lower than that of naïve cells. Together, our data suggest that human embryos are rejuvenated during early embryogenesis. Hence, the rejuvenation event is conserved between the mouse and human, and it occurs around the gastrulation stage in both species. Beyond this advance, the intersection clock opens the way for other epigenetic age studies based on human bisulfite sequencing datasets as opposed to methylation arrays.

Compact jets dominate the continuum emission in low-luminosity active galactic nuclei

Low-luminosity active galactic nuclei (LLAGN) are special among their kind due to the profound structural changes that the central engine experiences at low accretion rates (≲ 10−3 in Eddington units). The disappearance of the accretion disc – the blue bump – leaves behind a faint optical nuclear continuum whose nature has been largely debated. This is mainly due to serious limitations on the observational side imposed by the starlight contamination from the host galaxy and the absorption by hydrogen, preventing the detection of these weak nuclei in the infrared (IR) to ultraviolet (UV) range. We addressed these challenges by combining multi-wavelength sub-arcsecond resolution observations – able to isolate the genuine nuclear continuum – with nebular lines in the mid-IR, which allowed us to indirectly probe the shape of the extreme UV continuum. We found that eight of the nearest prototype LLAGN are compatible with pure compact jet emission over more than ten orders of magnitude in frequency. This consists of self-absorbed synchrotron emission from radio to the UV plus the associated synchrotron self-Compton component dominating the emission in the UV to X-ray range. Additionally, the LLAGN continua show two particular characteristics when compared with the typical jet spectrum seen in radio galaxies: (i) a very steep spectral slope in the IR-to-optical/UV range (−3.7 < α0 < −1.3; Fν ∝ να0); and (ii) a very high turnover frequency (0.2–30 THz; 1.3 mm–10 μm) that separates the optically thick radio emission from the optically thin continuum in the IR-to-optical/UV range. These attributes can be explained if the synchrotron continuum is mainly dominated by thermalised particles at the jet base or the corona with considerably high temperatures, whereas only a small fraction of the energy (∼20%) would be distributed along the high-energy power-law tail of accelerated particles. On the other hand, the nebular gas excitation in LLAGN is in agreement with photo-ionisation from inverse Compton radiation (αx ∼ −0.7), which would dominate the nuclear continuum shortwards of ∼3000 Å, albeit a possible contribution from low-velocity shocks (< 500 km s−1) to the line excitation cannot be discarded. No sign of a standard hot accretion disc is seen in our sample of LLAGN, nevertheless, a weak cold disc (< 3000 K) is detected at the nucleus of the Sombrero galaxy, though its contribution to the nebular gas excitation is negligible. Our results suggest that the continuum emission in LLAGN is dominated at all wavelengths by undeveloped jets, powered by a thermalised particle distribution with high energies, on average. This is in agreement with their compact morphology and their high turnover frequencies. This behaviour is similar to that observed in peaked-spectrum radio sources and also compact jets in quiescent black hole X-ray binaries. Nevertheless, the presence of extended jet emission at kiloparsec scales for some of the objects in the sample is indicative of past jet activity, suggesting that these nuclei may undergo a rejuvenation event after a more active phase that produced their extended jets. These results imply that the dominant channel for energy release in LLAGN is mainly kinetic via the jet, rather than the radiative one. This has important implications in the context of galaxy evolution, since LLAGN probably represent a major but underestimated source of kinetic feedback in galaxies.

Long-term spatiotemporal dynamics in a mountain birch (Betula pubescens ssp. czerepanovii) forest in south-east Norway.

Mountain birch forest covers large areas in Eurasia, and their ecological resilience provides important ecosystem services to human societies. This study describes long-term stand dynamics based on permanent plots in the upper mountain birch belt in SE Norway. We also present forest line changes over a period of 70 years. Inventories were conducted in 1931, 1953, and 2007. Overall, there were small changes from 1931 up to 1953 followed by a marked increase in biomass and dominant height of mountain birch throughout the period from 1953 to 2007. In addition, the biomass of spruce (Picea abies) and the number of plots with spruce present doubled. The high mortality rate of larger birch stems and large recruitment by sprouting since the 1960s reveal recurrent rejuvenation events after the earlier outbreak of the autumnal moth (Epirrita autumnata). Our results demonstrate both a high stem turnover in mountain birch and a great ability to recover after disturbances. This trend is interpreted as regrowth after a moth attack, but also long-term and time-lagged responses due to slightly improved growth conditions. An advance of the mountain birch forest line by 0.71 m year-1 from 1937 to 2007 was documented, resulting in a total reduction of the alpine area by 12%. Most of the changes in the forest line seem to have taken place after 1960. Regarding silviculture methods in mountain birch, a dimension cutting of larger birch trees with a cutting interval of c. 60 years seems to be a sustainable alternative for mimicking natural processes.

Thermal storage conditions and origin of compositional diversity of plagioclase crystals in magmas from the 1980 and 2004-2005 eruptions of Mount Saint Helens

Abstract The thermal histories of upper crustal magma reservoirs place important constraints on the formation, evolution, and remobilization of crustal magmas, yet quantifying thermal histories remains challenging. We report new in-situ plagioclase trace-element data, Sr in plagioclase diffusion timescales, and plagioclase 238U-230Th-226Ra disequilibria data from Mount Saint Helens (MSH) 1980 cryptodome and 2004-2005 dacite domes to evaluate the thermal storage conditions and compositional diversity of recent MSH magmas. This approach allows us to more directly link the thermal (and therefore physical) conditions within the MSH magma reservoir to timescales of storage, thereby constraining the fraction of time 1980-2005 MSH magmas have spent in a mobile state. Plagioclase trace-element data and U-series characteristics reveal a compositionally heterogenous magmatic system beneath MSH and also require multi-stage plagioclase growth histories. The data also show that 2004-05 dacites contain a different plagioclase population relative to the 1980 cryptodome dacite, comprised of either a compositionally (and possibly temporally) distinct plagioclase component or composed of the same plagioclase components but in significantly different proportions. Discordant plagioclase 238U-230Th and 230Th-226Ra apparent ages require a mixture of young (likely eruption related) and old (>20-40 ka) plagioclase crystals in both 1980 and 2004-05 dacites. The low (230Th)/(232Th) in all measured 1980 and 2004-05 plagioclase requires a significant fraction (>10-30%) of the plagioclase to be old (>10s kyr). Maximum modeled Sr diffusion timescales at 750oC range from decades to centuries for both eruptions, with a maximum of ~600 years found in 1980 cryptodome plagioclase. However, partially equilibrated Sr in the innermost exposed parts of some crystals found in both 1980 and 2004-05 plagioclase indicate that a fraction (>20%) of plagioclase may have experienced a total of >10 kyrs at temperatures ≥750oC. Coupling Sr diffusion timescales with U-series measurements indicates that significant fraction (at least ~40%) of modeled MSH plagioclase spent <5% of their storage time at temperatures ≥750oC and thus in an easily mobilized rheological state. In contrast, the fraction of partially equilibrated plagioclase possibly spent >25-50% of their storage time at hotter conditions. Our data combined with data from other arc magmatic systems (e.g., Mt. Hood) imply that the process of remobilizing magma in arc systems towards successive eruptions requires thermally rejuvenating largely crystalline material, as opposed to sequential tapping of a persistent liquid-dominated magma body, even if successive eruptions are spaced closely in time (decades). In addition, rejuvenation events responsible for successive eruptions may sample spatially localized, but potentially overlapping, portions of the broader magma reservoir.

Profiling Epigenetic Age in Single Cells

Abstract DNA methylation of a defined set of CpG dinucleotides emerged as a critical and precise biomarker of the aging process. Multi-variate machine learning models, known as epigenetic clocks, can exploit quantitative changes in the methylome to predict the age of bulk tissue with remarkable accuracy. However, intrinsic sparsity and digitized methylation in individual cells have so far precluded the assessment of aging in single cell data. We developed scAge, a probabilistic approach to determine the epigenetic age of single cells, and validated our results in mice. scAge tissue-specific and multi-cell type single cell clocks correctly recapitulated the chronological age of the original tissue, while uncovering the inherent heterogeneity that exists at the single-cell level. The data suggested that while cells in a tissue age in a coordinated fashion, some cells age more or less rapidly than others. We showed that individual embryonic stem cells exhibit an age close to zero, that certain stem cells in a tissue showed a reduced age compared to their chronological age, and that early embryogenesis is associated with the reduction of epigenetic age in individual cells, the latter supporting a natural rejuvenation event during gastrulation. scAge is both robust against the low coverage that is characteristic of single cell sequencing techniques and is flexible for studying any cell type and mammalian organism of interest. We demonstrate the potential for accurate epigenetic age profiling at single-cell resolution.

Profiling epigenetic age in single cells.

DNA methylation dynamics emerged as a promising biomarker of mammalian aging, with multivariate machine learning models ('epigenetic clocks') enabling measurement of biological age in bulk tissue samples. However, intrinsically sparse and binarized methylation profiles of individual cells have so far precluded the assessment of aging in single-cell data. Here, we introduce scAge, a statistical framework for epigenetic age profiling at single-cell resolution, and validate our approach in mice. Our method recapitulates the chronological age of tissues, while uncovering heterogeneity among cells. We show accurate tracking of the aging process in hepatocytes, demonstrate attenuated epigenetic aging in muscle stem cells, and track age dynamics in embryonic stem cells. We also use scAge to reveal, at the single-cell level, a natural and stratified rejuvenation event occurring during early embryogenesis. We provide our framework as a resource to enable exploration of epigenetic aging trajectories at single-cell resolution.

Epigenetic clocks reveal a rejuvenation event during embryogenesis followed by aging.

The notion that the germ line does not age goes back to the 19th-century ideas of August Weismann. However, being metabolically active, the germ line accumulates damage and other changes over time, i.e., it ages. For new life to begin in the same young state, the germ line must be rejuvenated in the offspring. Here, we developed a multi-tissue epigenetic clock and applied it, together with other aging clocks, to track changes in biological age during mouse and human prenatal development. This analysis revealed a significant decrease in biological age, i.e., rejuvenation, during early stages of embryogenesis, followed by an increase in later stages. We further found that pluripotent stem cells do not age even after extensive passaging and that the examined epigenetic age dynamics is conserved across species. Overall, this study uncovers a natural rejuvenation event during embryogenesis and suggests that the minimal biological age (ground zero) marks the beginning of organismal aging.

Petrological insights on the last 1000 years of explosive activity at La Soufrière volcano, St. Vincent (Lesser Antilles)

The petrological features of scoria samples and enclosed holocrystalline xenoliths from the last ~1000 years of activity of the La Soufrière volcano of St. Vincent (Lesser Antilles) are described in detail here. The products of the investigated prehistoric eruptions (pre-1440, 1440, 1580 CE) are relatively homogeneous basaltic andesites (with a paragenesis consisting of plagioclase, clinopyroxene, orthopyroxene and opaques) commonly hosting gabbroic xenoliths. Scoria samples from the historical eruptions (1718–1812 and 1902–03 CE) are mostly similar to the former in terms of whole-rock composition, mineral chemistry and types of xenoliths, but include also a mafic-rich scoria type (plagioclase + clinopyroxene + olivine) in the products of the 1902–03 eruption that is less evolved in composition and encloses ol-gabbro and ultramafic xenoliths. Both scoria types were likely affected by crystal contamination and accumulation processes, as indicated by their moderately to strongly porphyritic textures and large compositional variation of the crystal populations. Recycling of xenocryst, protocryst and/or antecryst phases, however, did not significantly modify the original magma composition, as suggested by the overall consistency of whole-rock differentiation trends with petrography, mineral chemistry, xenolith types and glass compositions (within both inclusions and the groundmass) and experimental petrology observations, crystal fractionation therefore still appearing as the main evolutionary process. Most of the gabbro and ol-gabbro xenoliths have mineral compositions in line with that of the coexisting phenocrysts and textural features consistent with an intrusive origin, i.e., representing fully-crystallised melt aliquots. Conversely, ultramafic, troctolitic and noritic xenoliths (plus some ol-gabbro) are likely representing cumulitic assemblages, i.e., mineral phases removed from the magma by crystal fractionation. The typical association of An-rich plagioclase and relatively Fo-poor olivine of the troctolite (and ol-gabbro) cumulates is ascribed to crystallisation from a hydrous (H2O ~4.5–6 wt%) high-Al2O3 basalt/basaltic andesite magma crystallising at shallow depths (~0.2 GPa, i.e., at ~7 km). On the other hand, the ultramafic cumulitic xenoliths are thought to derive from a less hydrous basalt magma stalling at deeper levels (~0.4 GPa, ~13 km). The tapping of such magma could mark a major rejuvenation event, which is the process that likely triggered the 1902–03 eruption.

Early Science with the Large Millimeter Telescope: Constraining the Gas Fraction of a Compact Quiescent Galaxy at z = 1.883

Abstract We present constraints on the dust continuum flux and inferred gas content of a gravitationally lensed massive quiescent galaxy at z = 1.883 ± 0.001 using AzTEC 1.1 mm imaging with the Large Millimeter Telescope. MRG-S0851 appears to be a prototypical massive compact quiescent galaxy, but evidence suggests that it experienced a centrally concentrated rejuvenation event in the last 100 Myr. This galaxy is undetected in the AzTEC image but we calculate an upper limit on the millimeter flux and use this to estimate the H2 mass limit via an empirically calibrated relation that assumes a constant molecular-gas-to-dust ratio of 150. We constrain the 3σ upper limit of the H2 fraction from the dust continuum in MRG-S0851 to be M H 2 / M ⋆ ≤ 6.8 % . MRG-S0851 has a low gas fraction limit with a moderately low sSFR owing to the recent rejuvenation episode, which together result in a relatively short depletion time of <0.6 Gyr if no further H2 gas is accreted. Empirical and analytical models both predict that we should have detected molecular gas in MRG-S0851, especially given the rejuvenation episode; this suggests that cold gas and/or dust is rapidly depleted in at least some early quiescent galaxies.

Multiple rejuvenation episodes of a silicic magma reservoir at the origin of the large diatreme-dome complex and porphyry-type mineralization events at Cerro de Pasco (Peru)

The Cerro de Pasco district in central Peru hosts one of the world largest porphyry-related epithermal polymetallic deposits. The district is centered onto a large diatreme-dome complex crosscut by numerous dacite to rhyodacite bodies showing domal structures and quartz-monzonite dykes. Three temporally distinct high-temperature porphyry-type mineralization events have been recognized (PM1, PM2, and PM3). Dating of the latter by molybdenite Re-Os and by zircon U-Pb (LA-ICP-MS and CA-ID-TIMS) geochronology complements the already available dataset of zircon U-Pb ages of the subvolcanic and volcanic rocks mostly dacitic in composition occurring in the district and shows the existence of successive short-lived episodes (<100 kyr) of shallow magmatic activity and porphyry-type mineralization. The new geochronology data indicate that the magmatic system was active during more than 400 kyr, spanning from 15.59 ± 0.12 Ma to 15.16 ± 0.04 Ma, punctuated by three porphyry-type mineralization events that are precursors (maximum gap of 0.9 Myr) of the last stage of epithermal polymetallic mineralization at Cerro de Pasco. Detailed petrographic and geochemical (whole rock and minerals) studies have been performed and silicate melt inclusions hosted in quartz phenocrysts from the subvolcanic and volcanic rocks emplaced between and after the different porphyry-type mineralization events have been analyzed by LA-ICP-MS. Our results suggest that prior to their emplacement at shallow level, magmas were stored at depth with a high degree of crystallinity (>50%) at pressures between 0.9 and 3.4 kbar and at temperatures between ~680 °C and ~725 °C. At such conditions, magma is beyond the point of rheological lock-up and is not eruptible. The emplacement of the mostly dacitic subvolcanic and volcanic rocks has required a series of rejuvenation events of the upper crustal high-crystallinity silicic magma reservoir. Field relationships and geochronology indicate that emplacement of the subvolcanic and volcanic rocks is preceded each time by high-temperature (>600 °C) quartz-pyrite-magnetite ± chalcopyrite and quartz-molybdenite veining forming the three recognized porphyry-type mineralization events. Hydrothermal quartz of these veins host silicate melt inclusions, a rare feature in hydrothermal veins. Their composition determined by LA-ICP-MS analysis indicates that the mineralizing fluids, potentially sourced from intermediate magma recharges, have circulated in a magma reservoir in which the residual interstitial melt was more evolved than the melt trapped as inclusions in the magmatic quartz. The combined geochemical and geochronological data obtained show that several episodes of rejuvenation of a highly crystallized upper-crustal silicic magma reservoir, probably triggered by intermediate magma recharges and by circulation of CO2- and S-rich fluids exsolved from them, are at the origin of the large diatreme-dome complex and porphyry-type mineralization events at Cerro de Pasco.

Clues on the history of early-type galaxies from SDSS spectra and GALEX photometry

ABSTRACT Stellar population studies of early-type galaxies (ETGs) based on their optical stellar continuum suggest that these are quiescent systems. However, emission lines and ultraviolet photometry reveal a diverse population. We use a new version of the starlight spectral synthesis code and state-of-the-art stellar population models to simultaneously fit Sloan Digital Sky Survey spectra and Galaxy Evolution Explorer photometry for a sample of 3453 galaxies at z &amp;lt; 0.1 with near ultraviolet (NUV) − r &amp;gt; 5 that are classified as elliptical by Galaxy Zoo. We reproduce far ultraviolet (FUV) magnitudes for 80 per cent of UV upturn galaxies selected using criteria from the literature, suggesting that additional stellar population ingredients such as binaries and extreme horizontal branch stars may have a limited contribution to the UV upturn. The addition of ultraviolet data leads to a broadening of the distributions of mean stellar ages, metallicities, and attenuation. Stellar populations younger than $1\,$ Gyr are required to reproduce the ultraviolet emission in 17 per cent of our sample. These systems represent 43 per cent of the sample at 5 &amp;lt; NUV − r &amp;lt; 5.5 and span the same stellar mass range as other ETGs in our sample. ETGs with young stellar components have larger H α equivalent widths (WH α) and larger dust attenuation. Emission line ratios and WH α indicate that the ionizing source in these systems is a mixture of young and old stellar populations. Their young stellar populations are metal-poor, especially for high-mass galaxies, indicating recent star formation associated with rejuvenation events triggered by external processes, such as minor mergers.

Relative Abundance and Compositional Variation of Silicates, Oxides and Phosphates in the W-Sn-Rich Lodes of the Panasqueira Mine (Portugal): Implications for the Ore-Forming Process

Panasqueira is a world-class W-Sn-Cu lode-type deposit located in Portugal. It consists of a dense swarm of subhorizontal quartz lodes criss-crossed by several ENE–WSW and N–S fault zones, bordering Late Variscan granite and hosted in Late Ediacaran—Early Cambrian metasediments. The relative abundance and compositional variation (assessed with EPMA) of the main silicates, oxides and phosphates forming the quartz lodes and their margins were examined, aiming to explore: (i) mineral and geochemical zonation at the mine scale; and (ii) some conclusions on the chemical nature of prevalent fluid inflows and T-conditions of mineral deposition. Quartz lodes nearby or far from the known greisen-granite cupola display significant differences, reflecting multiple fluid influxes of somewhat distinct composition related to various opening and closing events extending for several My, ranging from an early “oxide–silicate stage” (OSS) to a “main sulfide stage” (MSS), and further on to a post-ore carbonate stage (POCS); however, a rejuvenation event occurred after MSS. The onset of OSS was placed at ca. 299 ± 5 Ma and the rejuvenation event at ca. 292 Ma. The OSS was confined to ≈500 ≤ T ≤ 320 °C, following rutile and tourmaline growth under ≈640 ≤ T ≤ 540 °C (depending on aSiO2). The rejuvenation event (≈440–450 °C) preceded a late chlorite growth (≈250–270 °C) and the progression towards POCS.

A detailed look at the stellar populations in green valley galaxies

ABSTRACT The green valley (GV) represents an important transitional state from actively star-forming galaxies to passively evolving systems. Its traditional definition, based on colour, rests on a number of assumptions that can be subjected to non-trivial systematics. In Angthopo, Ferreras &amp; Silk (2019), we proposed a new definition of the GV based on the 4000 Å break strength. In this paper, we explore in detail the properties of the underlying stellar populations by use of ∼230 thousand high-quality spectra from the Sloan Digital Sky Survey (SDSS), contrasting our results with a traditional approach via dust-corrected colours. We explore high-quality stacked SDSS spectra, and find a population trend that suggests a substantial difference between low- and high-mass galaxies, with the former featuring younger populations with star formation quenching, and the latter showing older (post-quenching) populations that include rejuvenation events. Subtle but measurable differences are found between a colour-based approach and our definition, especially as our selection of GV galaxies produces a cleaner ‘stratification’ of the GV, with more homogeneous population properties within sections of the GV. Our definition based on 4000 Å break strength gives a clean representation of the transition to quiescence, easily measurable in the upcoming and future spectroscopic surveys.

Ca isotopes record rapid crystal growth in volcanic and subvolcanic systems

Kinetic calcium isotope effects can be used as growth-rate proxies for volcanic and subvolcanic minerals. Here, we analyze Ca isotopic compositions in experimental and natural samples and confirm that large kinetic effects (>2‰) can occur during magmatic plagioclase crystallization. Experiments confirm theoretical predictions that disequilibrium isotope effects depend mainly on the rates for crystal growth relative to liquid phase Ca diffusivity (R/D). Plagioclase phenocrysts from the 1915 Mount Lassen rhyodacite eruption, the ∼650-y-old Deadman Creek Dome eruption, and several mafic subvolcanic orbicules and plagioclase comb layers from Northern California have disequilibrium Ca isotopic compositions that suggest rapid crystal growth rates (>1 cm/y to 15 cm/y). The Ca isotope results, combined with complementary crystal-size distribution analyses, suggest that magmatic rejuvenation (and eruption) events, as reflected in crystal growth times, can be as short as ∼10-3 y. Although mafic systems are predicted to have shorter magmatic rejuvenation periods, we find similarly short timescales in both mafic and silicic systems. These results are consistent with a growing body of evidence suggesting that dominantly crystalline volcanic magma reservoirs can be rapidly reactivated by the injection of fresh magma prior to eruption. By focusing on a common mineral such as plagioclase, this approach can be applied across all major magmatic compositions, suggesting that Ca isotopes can be used as a tool for investigating the dynamics and timing of volcanic eruptions.

Rejuvenation in z ∼ 0.8 Quiescent Galaxies in LEGA-C

Abstract We use reconstructed star formation (SF) histories of quiescent galaxies at z = 0.6–1 in the Large Early Galaxy Astrophysics Census survey to identify secondary SF episodes that, after an initial period of quiescence, moved the galaxies back to the star-forming main sequence (blue cloud). 16 ± 3% of the z ∼ 0.8 quiescent population has experienced such rejuvenation events in the redshift range of 0.7 &lt; z &lt; 1.5 after reaching quiescence at some earlier time. On average, these galaxies first became quiescent at z = 1.2, and those that rejuvenated, remained quiescent for ∼1 Gyr before their secondary SF episode, which lasted ∼0.7 Gyr. The stellar mass attributed to rejuvenation is on average 10% of the galaxy stellar mass, with rare instances of an increase of more than a factor of 2. Overall, rejuvenation events only contribute ∼2% of the total stellar mass in z ∼ 0.8 quiescent galaxies and we conclude that rejuvenation is not an important evolutionary channel when considering the growth of the red sequence. However, our results complicate the interpretation of galaxy demographics in color space: the galaxies with rejuvenation events tend to lie in the so-called “green valley,” yet their progenitors were quiescent at z ∼ 2.

Insights into magma histories through silicate-oxide crystal clusters: Linking the Hiltaba Suite intrusive rocks to the Gawler Range Volcanics, Gawler Craton, South Australia

The Roxby Downs Granite (RDG), host to the supergiant Olympic Dam deposit, and the Gawler Range Volcanics (GRV) in South Australia, both contain clusters of touching silicate and oxide minerals. Here we report on the geochemistry and petrography of these rocks and their contained mineral clusters, before comparing them to similar occurrences elsewhere in the world to gain a better understand of their genesis and the links between the RDG (and other members of the Hiltaba Suite) and the GRV. Crystal clusters in the RDG comprise magnetite + apatite ± titanite ± biotite ± zircon which are typically enveloped in a plagioclase crystal-matrix. In the GRV, crystal clusters comprise pyroxene + titanomagnetite ± plagioclase ± apatite ± zircon, display variably glomeroporphyritic, equigranular, poikilitic, and loosely packed habits, and are enclosed by texturally varied groundmass. Of the GRV lavas studied, pyroxenes and titanomagnetite show systematic trends in major and trace element compositions conformable with the stratigraphic position of their hosts. This suggests the lavas are related through differentiation in the upper crust and represent the inversion of a normally zoned reservoir. There are no compositional contrasts between phenocrysts and crystals in GRV clusters, and Mg# of pyroxenes are consistent with those predicted from whole-rock compositions, implying that all analysed crystals (including those in clusters) were formed within, or were at least equilibrated to, the host lavas’ precursors. Rather than entire histories as isolated crystal clusters entrained by melt flow, intergrowth textures and mafic magmatic enclaves suggest that the majority of GRV crystal clusters were liberated from closely packed crystal masses through magma rejuvenation and associated crystal resorption. Consistent Fe-Ti oxide + apatite + zircon + plagioclase assemblages and textures in both the GRV and RDG suggest a shared genetic scenario, although an extended model is needed to account for the transformation of GRV-type to HS-type crystal clusters. For hot and dry magmas such as those that formed the GRV and RDG, cooling causes pyroxene + Fe-Ti oxide + plagioclase in GRV-type crystal clusters to react with each other and the melt, forming HS-type magnetite + titanite + biotite + feldspar crystal clusters. Rejuvenation events implicated in the liberation of GRV-type crystal clusters may be important drivers of magmatic-hydrothermal iron-oxide deposit formation.