43 research outputs found
40Arā39Ar ages and isotope geochemistry of Cretaceous basalts in northern Madagascar: Refining eruption ages, extent of crustal contamination and parental magmas in a flood basalt province
The Madagascar Cretaceous igneous province exposed in the Mahajanga basin is represented by basalt and basaltic andesite lavas. New 40Arā39Ar plateau ages (92.3 Ā± 2.0 Ma and 91.5 Ā± 1.3 Ma) indicate that the magmatism in the Mahajanga basin started about 92 Ma ago. Four geochemically distinct magma types (Groups AāD) are present. Group A and C rocks have low to moderate TiO2 (1.2ā2.6 wt%), Nb (3ā9 Ī¼g gā1) and Zr (82ā200 Ī¼g gā1), and show large variations in ÉNdi (+0.1 to ā10.8), 206Pb/204Pb (15.28 to 16.33) and Ī³Os (+11.4 to +7378). The large isotopic variations, particularly in Os, Nd and Pb isotopic compositions, are likely due to crustal contamination. The low Pb isotope ratios observed in the Group A and C rocks suggest involvement of continental crust with low Ī¼ (238U/204Pb). Group B and D rocks have moderate to high TiO2 (2.2ā4.9 wt%), Nb (8ā24 Ī¼g gā1) and Zr (120ā327 Ī¼g gā1). Age-corrected isotopes of Group B and D lavas show a small range in ÉNdi (+1.0 to +4.0) and a wide range in Ī³Os (+128 to +1182). Values of 207Pb/204Pb are within the range for Groups A and C, but the Group D 206Pb/204Pb (16.52ā17.08) and 208Pb/204Pb (37.51ā38.01) values are higher, indicating a different crustal contaminant. Pb isotopic values of the Group B rocks seem to reflect the isotopic features of their mantle source. The magma groups of Mahajanga display a wide range of trace element and isotopic compositions that cannot be explained only by open-system crystallization processes but, rather, by distinct mantle sources
A Study of the Residual 39Ar Content in Argon from Underground Sources
The discovery of argon from underground sources with significantly less 39Ar
than atmospheric argon was an important step in the development of
direct-detection dark matter experiments using argon as the active target. We
report on the design and operation of a low background detector with a single
phase liquid argon target that was built to study the 39Ar content of the
underground argon. Underground argon from the Kinder Morgan CO2 plant in
Cortez, Colorado was determined to have less than 0.65% of the 39Ar activity in
atmospheric argon.Comment: 21 pages, 10 figure
Geo-neutrinos and the Radioactive Power of the Earth
Chemical and physical Earth models agree little as to the radioactive power
of the planet. Each predicts a range of radioactive powers, overlapping
slightly with the other at about 24 TW, and together spanning 14-46 TW.
Approximately 20 % of this radioactive power (3-8 TW) escapes to space in the
form of geo-neutrinos. The remaining 11-38 TW heats the planet with significant
geo-dynamical consequences, appearing as the radiogenic component of the 43-49
TW surface heat flow. The non-radiogenic component of the surface heat flow
(5-38 TW) is presumably primordial, a legacy of the formation and early
evolution of the planet. A constraining measurement of radiogenic heating
provides insights to the thermal history of the Earth and potentially
discriminates chemical and physical Earth models. Radiogenic heating in the
planet primarily springs from unstable nuclides of uranium, thorium, and
potassium. The paths to their stable daughter nuclides include nuclear beta
decays, producing geo-neutrinos. Large sub-surface detectors efficiently record
the energy but not the direction of the infrequent interactions of the highest
energy geo-neutrinos, originating only from uranium and thorium. The measured
energy spectrum of the interactions estimates the relative amounts of these
heat-producing elements, while the intensity estimates planetary radiogenic
power. Recent geo-neutrino observations in Japan and Italy find consistent
values of radiogenic heating. The combined result mildly excludes the lowest
model values of radiogenic heating and, assuming whole mantle convection,
identifies primordial heat loss. Future observations have the potential to
measure radiogenic heating with better precision, further constraining
geological models and the thermal evolution of the Earth.Comment: 48 pages, 11 figures, 8 table
Kimberlites reveal 2.5-billion-year evolution of a deep, isolated mantle reservoir
The widely accepted paradigm of Earth's geochemical evolution states that the successive extraction of melts from the mantle over the past 4.5 billion years formed the continental crust, and produced at least one complementary melt-depleted reservoir that is now recognized as the upper-mantle source of mid-ocean-ridge basalts1. However, geochemical modelling and the occurrence of high 3He/4He (that is, primordial) signatures in some volcanic rocks suggest that volumes of relatively undifferentiated mantle may reside in deeper, isolated regions2. Some basalts from large igneous provinces may provide temporally restricted glimpses of the most primitive parts of the mantle3,4, but key questions regarding the longevity of such sources on planetary timescalesāand whether any survive todayāremain unresolved. Kimberlites, small-volume volcanic rocks that are the source of most diamonds, offer rare insights into aspects of the composition of the Earthās deep mantle. The radiogenic isotope ratios of kimberlites of different ages enable us to map the evolution of this domain through time. Here we show that globally distributed kimberlites originate from a single homogeneous reservoir with an isotopic composition that is indicative of a uniform and pristine mantle source, which evolved in isolation over at least 2.5 billion years of Earth historyāto our knowledge, the only such reservoir that has been identified to date. Around 200 million years ago, extensive volumes of the same source were perturbed, probably as a result of contamination by exogenic material. The distribution of affected kimberlites suggests that this event may be related to subduction along the margin of the Pangaea supercontinent. These results reveal a long-lived and globally extensive mantle reservoir that underwent subsequent disruption, possibly heralding a marked change to large-scale mantle-mixing regimes. These processes may explain why uncontaminated primordial mantle is so difficult to identify in recent mantle-derived melts
Analytical evaluation and systematization of technologies for extraction of rare metals from production waste
The article is a message containing systematized information on resource-saving technologies as the basic for involving metal-containing secondary raw materials in the economic turnover. The set of independent technologies arranged in a certain sequence that solve the problems of resource saving allows us to compare the specific features and effectiveness of the use of each of them, the details and features of the processes. It is shown that the following can be the main sources of rare metals and REE: phosphogypsum (REE, Sr); ash and slag waste from TPPs, ash and slag waste (REE, Ti, Sc); metallurgical slags (Ge, Be, Se, Te, V); sulfuric acid dust (Se, Te); alumina production waste - red mud (Sc, REE); liquid waste from sulphate production of titanium dioxide (Sc, Ti); refinery dust bins (Se, Te); wastes from production of permanent magnets (Nd, Sm). It is noted that the technology uses beneficiation methods, acid leaching and ion-exchange concentration, biotechnology, electrolysis, heat treatment, a combination of different methods. To assess the quality of man-made raw materials and their suitability for complex processing and utilization, the article uses the methodology of analytical research of a set of patented technological solutions (technological samples were taken from real man-made deposits)
Simultaneous Transcriptional and Epigenomic Profiling from Specific Cell Types within Heterogeneous Tissues InĀ Vivo
Epigenomic mechanisms direct distinct gene expression programs for different cell types. Various inĀ vivo tissues have been subjected to epigenomic analysis; however, these studies have been limited by cellular heterogeneity, resulting in composite gene expression and epigenomic profiles. Here, we introduce āNuTRAP,ā a transgenic mouse that allows simultaneous isolation of cell-type-specific translating mRNA and chromatin from complex tissues. Using NuTRAP, we successfully characterize gene expression and epigenomic states of various adipocyte populations inĀ vivo, revealing significant differences compared to either whole adipose tissue or inĀ vitro adipocyte cell lines. We find that chromatin immunoprecipitation sequencing (ChIP-seq) using NuTRAP is highly efficient, scalable, and robust with even limited cell input. We further demonstrate the general utility of NuTRAP by analyzing hepatocyte-specific epigenomic states. The NuTRAP mouse is a resource that provides a powerful system for cell-type-specific gene expression and epigenomic profiling
Adipocytes fail to maintain cellular identity during obesity due to reduced PPARĪ³ activity and elevated TGFĪ²-SMAD signaling
Objective
Obesity due to overnutrition causes adipose tissue dysfunction, which is a critical pathological step on the road to type 2 diabetes (T2D) and other metabolic disorders. In this study, we conducted an unbiased investigation into the fundamental molecular mechanisms by which adipocytes transition to an unhealthy state during obesity.
Methods
We used nuclear tagging and translating ribosome affinity purification (NuTRAP) reporter mice crossed with Adipoq-Cre mice to determine adipocyte-specific 1) transcriptional profiles (RNA-seq), 2) promoter and enhancer activity (H3K27ac ChIP-seq), 3) and PPARĪ³ cistrome (ChIP-seq) profiles in mice fed chow or a high-fat diet (HFD) for 10 weeks. We also assessed the impact of the PPARĪ³ agonist rosiglitazone (Rosi) on gene expression and cellular state of adipocytes from the HFD-fed mice. We integrated these data to determine the transcription factors underlying adipocyte responses to HFD and conducted functional studies using shRNA-mediated loss-of-function approaches in 3T3-L1 adipocytes.
Results
Adipocytes from the HFD-fed mice exhibited reduced expression of adipocyte markers and metabolic genes and enhanced expression of myofibroblast marker genes involved in cytoskeletal organization, accompanied by the formation of actin filament structures within the cell. PPARĪ³ binding was globally reduced in adipocytes after HFD feeding, and Rosi restored the molecular and cellular phenotypes of adipocytes associated with HFD feeding. We identified the TGFĪ²1 effector protein SMAD to be enriched at HFD-induced promoters and enhancers and associated with myofibroblast signature genes. TGFĪ²1 treatment of mature 3T3-L1 adipocytes induced gene expression and cellular changes similar to those seen after HFD in vivo, and knockdown of Smad3 blunted the effects of TGFĪ²1.
Conclusions
Our data demonstrate that adipocytes fail to maintain cellular identity after HFD feeding, acquiring characteristics of a myofibroblast-like cell type through reduced PPARĪ³ activity and elevated TGFĪ²-SMAD signaling. This cellular identity crisis may be a fundamental mechanism that drives functional decline of adipose tissues during obesity
Impact-induced changes in source depth and volume of magmatism on Mercury and their observational signatures
Mantle partial melting produced the volcanic crust of Mercury. Here, the authors numerically model the formation of post-impact melt sheets and find that mantle convection was weak at around 3.7ā3.8āGa and that the melt sheets of Caloris and Rembrandt may contain partial melting of pristine mantle material