Sensitive high-resolution ion microprobe U-Pb dating of prograde and retrograde ultrahigh-temperature metamorphism as exemplified by Sri Lankan granulites

Ultrahigh-temperature (UHT) granulites of the central Highland Complex, Sri Lanka, underwent some of the highest known peak temperatures of crustal metamorphism. Zircon and monazite U-Pb systems in granulites near Kandy, the highest grade region (similar to 1050 degrees C; 0.9 GPa), preserve both a record of the timing of prograde and retrograde phases of UHT metamorphism and evidence for the ages of older protolith components. Zircon grains from a quartz-saturated granulite containing relics of the peak UHT assemblage have remnant detrital cores with dates of ca. 2.5-0.83 Ga. Date clusters of ca. 1.7 and 1.04-0.83 Ga record episodes of zircon growth in the source region of the protolith sediment. Two generations of overgrowths with contrasting Th/U record metamorphic zircon growth at 569 +/- 5 and 551 +/- 7 Ma, probably in the absence and presence of monazite, respectively. The age of coexisting metamorphic monazite (547 +/- 7 Ma) is indistinguishable from that of the younger, low-Th/U zircon overgrowths. Zircon from a quartz-undersaturated monazite-absent UHT granulite with a mainly retrograde assemblage is mostly metamorphic (551 +/- 5 Ma). The ca. 570 Ma zircon overgrowths in the quartz-saturated granulite probably record partial melting just before or at the metamorphic peak. The ca. 550 Ma zircon in both rocks, and the ca. 550 Ma monazite in the quartz-saturated sample, record post-peak isothermal decompression. A possible model for this pressure-temperature-time evolution is ultrahot collisional orogeny during the assembly of Gondwana, locally superheated by basaltic underplating, followed by fast extensional exhumation.

Evidence for Permo-Triassic collision in Far East Asia: The Korean collisional orogen

Eclogites from paragneiss in the Korean Peninsula are characterized by a peak pressure assemblage of garnet + omphacite + quartz + rutile, that is overprinted by multiphase symplectites involving augite, amphibole, orthopyroxene, ilmenite and plagioclase and by a similar high-pressure assemblage with a pronounced absence of the omphacite component in clinopyroxene formed during the peak and orthopyroxene in the retrograde stage. Eclogites were metamorphosed at a minimum pressures of not, vert, similar 20–23 kbar at temperatures of not, vert, similar 840–1000 °C, equivalent to a crustal depth of not, vert, similar 70–75 km, whereas high-pressure granulite in Late Paleozoic rocks underwent metamorphic conditions of not, vert, similar 18–19 kbar at not, vert, similar 950 °C with a minimum crustal depth of not, vert, similar 60–65 km. The presence of the eclogites and high-pressure granulite suggests deep-seated subduction of crustal complexes with metamorphism at different crustal levels. The eclogites were exhumed quickly resulting in near- isothermal decompression. On the other hand, the multistage exhumation of the high-pressure granulites suggests retrograde overprinting after initial decompression. The similarity of these petrological characteristics, metamorphic conditions and also the regional structural styles with those of the Sulu belt (China) strongly suggests the existence of a Permo-Triassic Alpine-type “Korean collision belt” in Far East Asia. This model provides a better understanding of the paleogeograpic evolution of Permo-Triassic East Asia, including a robust tectonic correlation of the Korean collision belt with the Qinling–Dabie–Sulu collision belt.

Counterclockwise exhumation of a hot orogen: The Paleoproterozoic ultrahigh-temperature granulites in the North China Craton

Regional metamorphic belts provide important constraints on the plate tectonic architecture of orogens. We report here a detailed petrologic examination of the sapphirine-bearing ultra-high temperature (UHT) granulites from the Jining Complex within the Khondalite Belt of the North China Craton (NCC). These granulites carry diagnostic UHT assemblages and their microstructures provide robust evidence to trace the prograde, peak and retrograde metamorphic evolution. The P–T conditions of the granulites estimated from XMgGrt(Mg/Fe + Mg) − XMgSpr isopleth calculations indicate temperature above 970 °C and pressures close to 7 kbar. We present phase diagrams based on thermodynamic computations to evaluate the mineral assemblages and microstructures and trace the metamorphic trajectory of the rocks. The evolution from Spl–Qtz–Ilm–Crd–Grt–Sil to Spr–Qtz–Crd–Opx–Ilm marks the prograde stage. The Spl–Qtz assemblage appears on the low-pressure side of the P–T space with Spr–Qtz stable at the high-pressure side, possibly representing an increase in pressure corresponding to compression. The spectacular development of sapphirine rims around spinel enclosed in quartz supports this inference. An evaluation of the key UHT assemblages based on model proportion calculation suggests a counterclockwise P–T path. With few exceptions, granulite-facies rocks developed along collisional metamorphic zones have generally been characterized by clockwise exhumation trajectories. Recent evaluation of the P–T paths of metamorphic rocks developed within collisional orogens indicates that in many cases the exhumation trajectories follow the model subduction geotherm, in accordance with a tectonic model in which the metamorphic rocks are subducted and exhumed along a plate boundary. The timing of UHT metamorphism in the NCC (c. 1.92 Ga) coincides with the assembly of the NCC within the Paleoproterozoic Columbia supercontinent, a process that would have involved subduction of passive margins sediments and closure of the intervening ocean. Thus, the counterclockwise P–T path obtained in this study correlates well with a tectonic model involving subduction and final collisional suturing, with the UHT granulites representing the core of the hot or ultra-hot orogen developed during Columbia amalgamation.

Retrogressed eclogite (20 kbar, 1020 °C) from the Neoproterozoic Palghat–Cauvery suture zone, southern India

The Palghat–Cauvery suture zone in southern India separates Archaean crustal blocks to the north and the Proterozoic Madurai block to the south. Here we present the first detailed study of a partially retrogressed eclogite (from within the Sittampundi anorthositic complex in the suture zone) that occurs as a 20-cm wide layer in a garnet gabbro layer in anorthosite. The eclogite largely consists of an assemblage of coexisting porphyroblasts of almandine–pyrope garnet and augitic clinopyroxene. However, a few garnets contain inclusions of omphacite. Rims and symplectites composed of Na–Ca amphibole and plagioclase form a retrograde assemblage. Petrographic analysis and calculated phase equilibria indicate that garnet–omphacite–rutile–melt was the peak metamorphic assemblage and that it formed at ca. 20 kbar and above 1000 °C. The eclogite was exhumed on a very tight hairpin-type, anticlockwise P–T path, which we relate to subduction and exhumation in the Palghat–Cauvery suture zone. The REE composition of the minerals suggests a basaltic oceanic crustal protolith metamorphosed in a subduction regime. Geological–structural relations combined with geophysical data from the Palghat–Cauvery suture zone suggest that the eclogite facies metamorphism was related to formation of the suture zone. Closure of the Mozambique Ocean led to development of the suture zone and to its western extension in the Betsimisaraka suture of Madagascar.

High P-T granulite relicts from the Imjingang belt, South Korea:Tectonic significance

This study presents a detailed description on crustal metamorphic signatures of garnet-clinopyroxene-quartz-rutile-bearing high P-T granulites, Samgot unit, Imajingang belt, northwestern Korean Peninsula that formed during Permo-Triassic regional metamorphism related to the amalgamation of East Asian continental fragments. Lenses and blocks of high P-T granulites and garnet-bearing leucosomes occur within mafic metamorphic rocks (mainly amphibolites). The mafic blocks comprise relicts of granoblastic garnet and clinopyroxene with medium-grained quartz and rutile. These relict mineral assemblages are confined to local micro-domains and constitute remnants of peak metamorphism. Plagioclase and amphibole form only as retrograde phases in medium ton coarse-grained moats that rim grain boundaries between relict peak mineral assemblages. This microstructure represents the reaction between garnet, clinopyroxene, quartz and rutile in the presence of melt to form amphibole, plagioclase and titanite with minor biotite. The leucosome domains consist of euhedral garnets within the quartz-K feldspar-plagioclase (granitic) matrix, probably representing peritectic garnet growth along with melting. The rare earth element (REE) composition of minerals also support the peritectic garnet growth with a positive Eu/Eu* (positive Eu anomaly), while the relict garnet shows a slight negative anomaly typical for high-grade granulites. The peak-metamorphic conditions calculated from thermodynamic modeling and compositional isopleths indicate a temperature around c. 900 degrees C at a pressure around c. 20 kbar. The present P-T path indicates a clear multi-stage decompression history with initial decompression and cooling followed by a stage of decompression during hydration possibly during Late Triassic exhumation. The results from this study together with the presence of eclogites from the Hongsung area suggest that the Imjingang area and the western Gyeonggi massif likely resided at crustal levels deeper than those of the eastern and southern part of the Gyeonggi massif. (C) 2009 International Association for Gondwana Research. Published by Elsevier B.V. All rights reserved.

Quality assessment of CdZnTe (Zn similar to 4 %) crystals

We have studied the as grown and annealed CdZnTe (Zn similar to 4 %) crystals for the assessment of their crystalline quality. As grown crystals suffer from tellurium precipitates and cadmium vacancies, which are inherent, due to retrograde solid solubility curve in the phase diagram. This is reflected in the Fourier transform infrared (FTIR) spectra over the 400 - 4500 cm(-1) range by a strong absorption around 2661 cm(-1) which corresponds to the band gap of tellurium confirming their presence, where-as a monotonic decrease in the transmission with the decrease in wave number indicates the presence of cadmium vacancies. Obviously the presence of Cd vacancies lead to the formation of tellurium precipitates confirming their presence. Annealed samples under cadmium + zinc ambient at 650 degrees C for 6 hours show an improvement in the transmission over the same range. This can be attributed to thermo-migration of tellurium precipitates and hence bonding with Cd or Zn to form CdZnTe. This is further supported by the reduced full width at half maximum in the X-ray diffraction rocking curve of these CdZnTe crystals. Cadmium annealing although can passivate Cd vacancy related defects and reduce the Te precipitates, as is observed in our low temperature Photoluminescence (PL) spectra, alone may not be sufficient possibly due to the loss of Zn. Vacuum annealing at 650 degrees C for 6 hours further deteriorated the material quality as is reflected in the low temperature PL spectra by the introduction of a new defect band around 0.85 eV and reduced IR transmission.

The slowing down of galaxy disks in dissipationless minor mergers

We have investigated the impact of dissipationless minor galaxy mergers on the angular momentum of the remnant. Our simulations cover a range of initial orbital characteristics, and the system consists of a massive galaxy with a bulge and disk merging with a much less massive (one-tenth or one-twentieth) gasless companion that has a variety of morphologies (disk-or elliptical-like) and central baryonic mass concentrations. During the process of merging, the orbital angular momentum is redistributed into the internal angular momentum of the final system; the internal angular momentum of the primary galaxy can increase or decrease depending on the relative orientation of the orbital spin vectors (direct or retrograde), while the initially nonrotating dark matter halo always gains angular momentum. The specific angular momentum of the stellar component always decreases independently of the orbital parameters or morphology of the satellite, the decrease in the rotation velocity of the primary galaxy is accompanied by a change in the anisotropy of the orbits, and the ratio of rotation speed to velocity dispersion of the merger remnant is lower than the initial value, not only because of an increase in the dispersion but also of the slowing-down of the disk rotation. We briefly discuss several astrophysical implications of these results, suggesting that minor mergers do not cause a "random walk" process of the angular momentum of the stellar disk component of galaxies, but rather a steady decrease. Minor mergers may play a role in producing the large scatter observed in the Tully-Fisher relation for S0 galaxies, as well as in the increase of the velocity dispersion and the decrease in upsilon/sigma at large radii as observed in S0 galaxies.

Sequestration of the abrin A chain to the nucleus by BASP1 increases the resistance of cells to abrin toxicity

Abrin, a type II ribosome-inactivating protein, comprises A and B subunits wherein the A subunit harbours toxin activity and the B subunit has a galactose-specific lectin activity. The entry of the protein inside the cell is through the binding of the B chain to cell surface glycoproteins followed by receptor-mediated endocytosis and retrograde transport. A previous study from our laboratory showed that different cell lines exhibited differences of as great as similar to 200-fold in abrin toxicity, prompting the present study to compare the trafficking of the toxin within cells. Observations made in this regard revealed that the abrin A chain, after being released into the cytosol, is sequestered into the nucleus through interaction with a cellular protein of similar to 25 kDa, BASP1 (brain acid-soluble protein 1). The nuclear localization of the A chain is seen predominantly in cells that are less sensitive to abrin toxicity and dependent on the levels of BASP1 in cells. The sequestration by BASP1 renders cells increasingly resistant to the inhibition of protein synthesis by abrin and the nucleus act as a sink to overcome cellular stress induced

Angular momentum transport and evolution of lopsided galaxies

The surface brightness distribution in the majority of stellar galactic discs falls off exponentially. Often what lies beyond such a stellar disc is the neutral hydrogen gas whose distribution also follows a nearly exponential profile at least for a number of nearby disc galaxies. Both the stars and gas are commonly known to host lopsided asymmetry especially in the outer parts of a galaxy. The role of such asymmetry in the dynamical evolution of a galaxy has not been explored so far. Following Lindblad's original idea of kinematic density waves, we show that the outer part of an exponential disc is ideally suitable for hosting lopsided asymmetry. Further, we compute the transport of angular momentum in the combined stars and gas disc embedded in a dark matter halo. We show that in a pure star and gas disc, there is a transition point where the free precession frequency of a lopsided mode, Omega - kappa, changes from retrograde to prograde and this in turn reverses the direction of angular momentum flow in the disc leading to an unphysical behaviour. We show that this problem is overcome in the presence of a dark matter halo, which sets the angular momentum flow outwards as required for disc evolution, provided the lopsidedness is leading in nature. This, plus the well-known angular momentum transport in the inner parts due to spiral arms, can facilitate an inflow of gas from outside perhaps through the cosmic filaments.

Solubilities of n-Butyl Esters in Supercritical Carbon Dioxide

The solubilities of butyl stearate and butyl laurate were determined in the temperature range of 308 K to 323 K and 313 K to 328 K, respectively, at pressures of 10 MPa to 16 MPa. The solubility of butyl laurate was higher than that of butyl stearate by almost an order in magnitude. Retrograde behavior was observed throughout the investigated pressure range. Semiempirical models such as Mendez-Teja, Chrastil, and other density-based models were used to correlate the experimental data of our work as well as several other liquid solutes.

Solubilities of 10-undecenoic acid and geraniol in supercritical carbon dioxide

The solubilities of 10-undecenoic acid and geraniol in supercritical carbon dioxide were measured at 308, 313,323 and 333K, and at pressures of 10-18 MPa. Solubilities (in mole fraction),ranged from 0.4 x 10(-3) to 17.4 x 10(-3) for 10-undecenoic acid and 2.7 x 10(-3) to 25 x 10(-3) for geraniol, respectively. The AARD was around 11% and 5% for these models for 10-undecenoic acid and geraniol, respectively. The solubilities of both compounds showed retrograde behavior wherein the solubilities decrease with temperature at isobaric conditions. The solubility of geraniol was higher than 10-undecenoic acid at all investigated temperatures and pressures. The data were found to be self consistent based on the Mendez-Santiago model. New models based on association theory using van Laar and Margules activity coefficient models for solute in liquid phase were derived, and used to correlate the solubilities. (C) 2015 Elsevier B.V. All rights reserved.

Botulinum neurotoxin type-A enters a non-recycling pool of synaptic vesicles

Neuronal communication relies on synaptic vesicles undergoing regulated exocytosis and recycling for multiple rounds of fusion. Whether all synaptic vesicles have identical protein content has been challenged, suggesting that their recycling ability may differ greatly. Botulinum neurotoxin type-A (BoNT/A) is a highly potent neurotoxin that is internalized in synaptic vesicles at motor nerve terminals and induces flaccid paralysis. Recently, BoNT/A was also shown to undergo retrograde transport, suggesting it might enter a specific pool of synaptic vesicles with a retrograde trafficking fate. Using high-resolution microscopy techniques including electron microscopy and single molecule imaging, we found that the BoNT/A binding domain is internalized within a subset of vesicles that only partially co-localize with cholera toxin B-subunit and have markedly reduced VAMP2 immunoreactivity. Synaptic vesicles loaded with pHrodo-BoNT/A-Hc exhibited a significantly reduced ability to fuse with the plasma membrane in mouse hippocampal nerve terminals when compared with pHrodo-dextran-containing synaptic vesicles and pHrodo-labeled anti-GFP nanobodies bound to VAMP2-pHluorin or vGlut-pHluorin. Similar results were also obtained at the amphibian neuromuscular junction. These results reveal that BoNT/A is internalized in a subpopulation of synaptic vesicles that are not destined to recycle, highlighting the existence of significant molecular and functional heterogeneity between synaptic vesicles.

Experimental solubilities of two lipid derivatives in supercritical carbon dioxide and new correlations based on activity coefficient models

The solubilities of two lipid derivatives, geranyl butyrate and 10-undecen-1-ol, in SCCO2 (supercritical carbon dioxide) were measured at different operating conditions of temperature (308.15 to 333.15 K) and pressure (10 to 18 MPa). The solubilities (in mole fraction) ranged from 2.1 x 10(-3) to 23.2 x 10(-3) for geranyl butyrate and 2.2 x 10(-3) to 25.0 x 10(-3) for 10-undecen-1-ol, respectively. The solubility data showed a retrograde behavior in the pressure and temperature range investigated. Various combinations of association and solution theory along with different activity coefficient models were developed. The experimental data for the solubilities of 21 liquid solutes along with geranyl butyrate and 10-undecen-1-ol were correlated using both the newly derived models and the existing models. The average deviation of the correlation of the new models was below 15%.