Jadeitite formed during subduction: In situ zircon geochronology constraints from two different tectonic events within the Guatemala Suture Zone

Jadeitite is a rare rock type associated with high-pressure–low-temperature blocks within serpentinite matrix mélanges. Models of formation involve precipitation from subduction-zone aqueous fluids veining the overlying mantle wedge (P-type), or metasomatism of igneous and/or sedimentary protoliths previously emplaced into the mélange (R-type). Age determinations of mélange lithologies provide constraints on the timing of “peak metamorphism” and subsequent exhumation. The timing of jadeitite formation, particularly in the rich source of the Guatemala Suture Zone (GSZ), is a controversial subject needing further attention. Over 80 in situ zircon crystals from three jadeitites and two mica–albite rocks from the North Motagua Mélange and one phengite jadeitite from the South Motagua Mélange of the GSZ were studied for age and trace-element determination. Most of these zircons are characterized by low Th/U ratios, depleted chondrite-normalized REE patterns relative to zircons from oceanic gabbros, and contain fluid and mineral inclusions that reflect the primary mineralogy (i.e., jadeite) and context (i.e., crystallization from an aqueous fluid) of the host rock, and thus formed during jadeitite crystallization. The SHRIMP-RG and LAM-ICP-MS U–Pb dates from zircon indicate that jadeitites and mica–albite rocks from the GSZ were formed through vein precipitation at ~98−80 and ~154–158 Ma, respectively. These data show (a) older ages that indicate jadeitite crystallization occurred ~10–30 Ma before the preserved subduction-zone peak metamorphism (e.g., exhumed eclogite), and (b) a second group of ages slightly younger than, or similar to, exhumation ages given by Ar–Ar dates from micas. Similar relationships occur at other jadeitite occurrences, such as the Syum-Keu ultramafic complex in the Polar Urals (Russia) and the serpentinite mélanges of the Río San Juan complex (Dominican Republic). The data argue for formation of jadeitite within the mantle wedge during active subduction. Thus, jadeitite provides a record of fluid introduction into the mantle wedge during subduction rather than during exhumation

Metamorphic reworking of a high pressure–low temperature mélange along the Motagua fault, Guatemala: A record of Neocomian and Maastrichtian transpressional tectonics

The Guatemala suture zone is a major east–west left-lateral strike slip boundary that separates the North American and Caribbean plates in Guatemala. The Motagua fault, the central active strand of the suture zone, underwent two major collisional events within a system otherwise dominated by strike–slip motion. The first event is recorded by high-pressure/low temperature (HP/LT) eclogites and related rocks that occur within serpentinites both north and south of the Motagua fault. Lawsonite eclogites south of the fault are not significantly retrograded and give 40Ar/39Ar ages of 125–116 Ma and Sm–Nd mineral isochrons of 144–132 Ma. Eclogites north of the fault give similar Sm–Nd isochron ages (131–126 Ma) but otherwise differ in that they are strongly overprinted by a lower pressure assemblage and, along with associated HP/LT rocks, give much younger 40Ar/39Ar ages of 88–55 Ma indicating a later amphibolite facies metamorphic event. We propose therefore that all serpentinite hosted eclogites along the Motagua fault formed at essentially the same time in different parts of a laterally extensive Lower Cretaceous forearc subduction system, but subsequently underwent different histories. The southern assemblages were thrust southwards (present coordinates) immediately after HP metamorphism whereas the northern association was retrograded during a later collision that thrust it northward at ca. 70 Ma. They were subsequently juxtaposed opposite each other by major strike slip motion. This model implies that the HP rocks on opposing sides of the Motagua fault evolved along a plate boundary that underwent both dip slip and strike slip motion throughout the Late Cretaceous as a result of oblique convergence. The juxtaposition of a convergent and strike slip system means that HP/LT rocks within serpentinites can be found at depth along much of the modern Guatemala suture zone and its eastward extension into the northern Caribbean. Both sets of assemblages were exhumed relatively recently by the uplift of mountain ranges on both sides of the fault caused by movement along a restraining bend. Recent exhumation explains the apparently lack of offset of surface outcrops along a major strike slip fault

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Percutaneous Cell Delivery Into the Heart Using Hydrogels Polymerizing In Situ

Heart disease is the leading cause of death in the US. Following an acute myocardial infarction, a fibrous, noncontractile scar develops, and results in congestive heart failure in more than 500,000 patients in the US each year. Muscle regeneration and the induction of new vascular growth to treat ischemic disorders of the heart can have significant therapeutic implications. Early studies in patients with chronic ischemic systolic left ventricular dysfunction (SLVD) using skeletal myoblasts or bone marrow-derived cells report improvement in left ventricular ejection function (LVEF) and clinical status, without notable safety issues. Nonetheless, the efficacy of cell transfer for cardiovascular disease is not established, in part due to a lack of control over cell retention, survival, and function following delivery. We studied the use of biocompatible hydrogels polymerizable in situ as a cell delivery vehicle, to improve cell retention, survival, and function following delivery into the ischemic myocardium. The study was conducted using human bone marrow-derived mesenchymal stem cells and fibrin glue, but the methods are applicable to any human stem cells (adult or embryonic) and a wide range of hydrogels. We first evaluated the utility of several commercially available percutaneous catheters for delivery of viscous cell/hydrogel suspensions. Next we characterized the polymerization kinetics of fibrin glue solutions to define the ranges of concentrations compatible with catheter delivery. We then demonstrate the in vivo effectiveness of this preparation and its ability to increase cell retention and survival in a nude rat model of myocardial infarction

SI methane hydrate confined in C8-grafted SBA-15: A highly efficient storage system enabling ultrafast methane loading and unloading

Confinement of water and methane in mesopores of hydrophobized SBA-15 is demonstrated to promote methane hydrate formation. In comparison to as-synthesized SBA-15, hydrophobization by C8 grafting accelerates the kinetics of methane storage in and delivery from the hydrate. C8 grafting density was determined at 0.5 groups nm-2 based on TGA and quantitative NMR spectroscopy. Multinuclear 1H-1H DQSQ and 1H-1H RFDR NMR provided spectroscopic evidence for the occurrence of C8 chains inside the mesopores of SBA-15, by showcasing close spatial proximity between the grafted C8 chains and pore-intruded water species. X-ray diffraction demonstrates formation of Structure I hydrate on SBA-15 C8. At 7.0 MPa and 248 K, the water-to-hydrate conversion on hydrophobized SBA-15 C8 reaches 96 pct. as compared to only 71 pct. on a pristine SBA-15 sample with comparable pore size, pore volume and surface area. The clathrate loading amounted to 14.8 g g-1. 2D correlation NMR spectroscopy (1H-13C CP-HETCOR, 1H-1H RFDR) reveals hydrate formation occurs within pores of SBA-15 C8 as well as in interparticle volumes. Following the initial crystallization of SBA-15 C8-supported methane hydrate taking several hours, a pressure swing process at 248 K allows to desorb and re-adsorb methane from the structure within minutes and without thawing the frozen water structure. Fast loading and unloading of methane was achieved in 19 subsequent cycles without losses in kinetics. The ability to harvest the gas and regenerate the structure without the need to re-freeze the water represents a 50 pct. energy gain with respect to melting and subsequently recrystallizing the hydrate at 298 K and 248 K, respectively. After methane desorption, a small amount of residual methane hydrate in combination with an amorphous yet locally ordered ice phase is observed using 13C and 2H NMR spectroscopy

Redox, haem and CO in enzymatic catalysis and regulation

The present paper describes general principles of redox catalysis and redox regulation in two diverse systems. The first is microbial metabolism of CO by the Wood–Ljungdahl pathway, which involves the conversion of CO or H2/CO2 into acetyl-CoA, which then serves as a source of ATP and cell carbon. The focus is on two enzymes that make and utilize CO, CODH (carbon monoxide dehydrogenase) and ACS (acetyl-CoA synthase). In this pathway, CODH converts CO2 into CO and ACS generates acetyl-CoA in a reaction involving Ni·CO, methyl-Ni and acetyl-Ni as catalytic intermediates. A 70 Å (1 Å=0.1 nm) channel guides CO, generated at the active site of CODH, to a CO ‘cage’ near the ACS active site to sequester this reactive species and assure its rapid availability to participate in a kinetically coupled reaction with an unstable Ni(I) state that was recently trapped by photolytic, rapid kinetic and spectroscopic studies. The present paper also describes studies of two haem-regulated systems that involve a principle of metabolic regulation interlinking redox, haem and CO. Recent studies with HO2 (haem oxygenase-2), a K+ ion channel (the BK channel) and a nuclear receptor (Rev-Erb) demonstrate that this mode of regulation involves a thiol–disulfide redox switch that regulates haem binding and that gas signalling molecules (CO and NO) modulate the effect of haem.National Institutes of Health (U.S.) (NIH grant GM69857)National Institutes of Health (U.S.) (NIH grant GM39451)National Institutes of Health (U.S.) (NIH grant HL 102662)National Institutes of Health (U.S.) (NIH grant GM65440)National Institutes of Health (U.S.) (NIH grant GM48242)National Institutes of Health (U.S.) (NIH grant Y1-GM- 1104)National Institutes of Health (U.S.) (NIH grant GM065318)National Institutes of Health (U.S.) (NIH grant AG027349)National Science Foundation (U.S.) (grant number CHE-0745353)United States. Dept. of Energy. Office of Biological and Environmental ResearchHoward Hughes Medical Institute (Investigator

A Dedicated Promoter Drives Constitutive Expression of the Cell-Autonomous Immune Resistance GTPase, Irga6 (IIGP1) in Mouse Liver

Background: In general, immune effector molecules are induced by infection. Methodology and Principal Findings: However, strong constitutive expression of the cell-autonomous resistance GTPase, Irga6 (IIGP1), was found in mouse liver, contrasting with previous evidence that expression of this protein is exclusively dependent on induction by IFNc. Constitutive and IFNc-inducible expression of Irga6 in the liver were shown to be dependent on transcription initiated from two independent untranslated 59 exons, which splice alternatively into the long exon encoding the full-length protein sequence. Irga6 is expressed constitutively in freshly isolated hepatocytes and is competent in these cells to accumulate on the parasitophorous vacuole membrane of infecting Toxoplasma gondii tachyzoites. Conclusions and Significance: The role of constitutive hepatocyte expression of Irga6 in resistance to parasites invading from the gut via the hepatic portal system is discussed

PG-Keys: Keys for Property Graphs

International audienceWe report on a community effort between industry and academia to shape the future of property graph constraints. The standardization for a property graph query language is currently underway through the ISO Graph Query Language (GQL) project. Our position is that this project should pay close attention to schemas and constraints, and should focus next on key constraints. The main purposes of keys are enforcing data integrity and allowing the referencing and identifying of objects. Motivated by use cases from our industry partners, we argue that key constraints should be able to have different modes, which are combinations of basic restriction that require the key to be exclusive, mandatory, and singleton. Moreover, keys should be applicable to nodes, edges, and properties since these all can represent valid real-life entities. Our result is PG-Keys, a flexible and powerful framework for defining key constraints, which fulfills the above goals. PG-Keys is a design by the Linked Data Benchmark Council's Property Graph Schema Working Group, consisting of members from industry, academia, and ISO GQL standards group, intending to bring the best of all worlds to property graph practitioners. PG-Keys aims to guide the evolution of the standardization efforts towards making systems more useful, powerful, and expressive. CCS CONCEPTS • Information systems → Integrity checking; • Theory of computation → Data modeling; Database constraints theory