High Pressure Low Temperature Research Articles

High‐Pressure Synthesis of Amorphous Si3N4 and SiBN‐Based Monoliths without Sintering Additives

Amorphous Si3N4 and SiBN monoliths without sintering additives are successfully prepared by high‐pressure–low‐temperature (HPLT) sintering using the single‐source‐precursor‐derived amorphous Si3N4 and SiBN powders as raw materials. The microstructural evolution and crystallization behavior of the as‐prepared samples are investigated using scanning electron and transmission electron microscopy and X‐ray powder diffraction, respectively. The results show that the incorporation of boron in the Si–N network enhances the crystallization temperature up to 1200 °C. The Vickers’ hardness of the HPLT‐sintered Si3N4 sample amounts ≈11.6 GPa whether prepared at 1000 or 1200 °C, while the maximum hardness of the SiBN sample is up to 16.3 GPa. The fracture toughness of amorphous Si3N4 and SiBN5 samples is almost identical (around 2.5 MPa m1/2) whether prepared at 1000 or 1200 °C, and SiBN2 and SiBN5 samples show an improved fracture toughness. In addition, the oxidation resistance of the as‐prepared samples is investigated at temperatures up to 1000 °C. A comparison between amorphous Si3N4 and SiBN monoliths demonstrates a positive effect of the presence of boron on their oxidation resistance.

Electrical Conductivity of Subsurface Ocean Analogue Solutions from Molecular Dynamics Simulations.

Investigating the habitability of ocean worlds is a priority of current and future NASA missions. The Europa Clipper mission will conduct approximately 50 flybys of Jupiter's moon Europa, returning a detailed portrait of its interior from the synthesis of data from its instrument suite. The magnetometer on board has the capability of decoupling Europa's induced magnetic field to high precision, and when these data are inverted, the electrical conductivity profile from the electrically conducting subsurface salty ocean may be constrained. To optimize the interpretation of magnetic induction data near ocean worlds and constrain salinity from electrical conductivity, accurate laboratory electrical conductivity data are needed under the conditions expected in their subsurface oceans. At the high-pressure, low-temperature (HPLT) conditions of icy worlds, comprehensive conductivity data sets are sparse or absent from either laboratory data or simulations. We conducted molecular dynamics simulations of candidate ocean compositions of aqueous NaCl under HPLT conditions at multiple concentrations. Our results predict electrical conductivity as a function of temperature, pressure, and composition, showing a decrease in conductivity as the pressure increases deeper into the interior of an icy moon. These data can guide laboratory experiments at conditions relevant to icy moons and can be used in tandem to forward-model the magnetic induction signals at ocean worlds and compare with future spacecraft data. We discuss implications for the Europa Clipper mission.

Comparison of fatigue life behavior between 4-point and uniaxial loading for L-PBF Ti–6Al–4V after HIP treatments

The present study investigated the effects of Hot Isostatic Pressing (HIP) on the fatigue performance of Laser Powder Bed Fusion (L-PBF) Ti–6Al–4V alloy under both 4-point bending and uniaxial testing. Three HIP-cycles were examined: standard, low temperature/high pressure (LTHP), and super beta. Moreover, an annealed heat treatment group was incorporated to compare against the HIP groups. The material microstructure was analyzed and compared across the heat treatments during the study, which showed the presence of α′ martensites, α+β Widmanstätten, and coarse equiaxed grains. Similarly, tensile and hardness testing were implemented to study the mechanical properties, where due to the effects of the HIP treatments, higher ductility but lower hardness values were recorded. Furthermore, fracture morphologies and stress-life (cycles-to-failure) (S–N) curves of the Ti–6Al–4V specimens concerning the fatigue behavior were analyzed. The HIP treatment groups behaved similarly during 4-point bending and uniaxial testing, with the LTHP obtaining a superior fatigue life behavior, followed by the standard and super beta HIP groups. In addition, the efficacy of HIP to reduce pores showed better results in the 4-point bending specimens, leading to few defects as fatigue initiators in contrast to the uniaxial specimens. Fractography results suggested that defects and microstructural features acting as fatigue crack initiators (FCI) govern the fracture behavior of uniaxial specimens. In contrast, only the presence of microstructural features controls the 4-point bending failure behavior.

High pressure salt water and low temperature effects on the material performance characteristics of additive manufacturing polymers

The effects of salt water exposure at deep ocean depth pressures when coupled with low temperatures on the material characteristics of three unique additively manufactured polymers has been investigated through a detailed experimental approach. The polymers in the study were manufactured utilizing both Vat Photopolymerization and Material Extrusion printing techniques. The Material Extrusion process was utilized to produce material specimens of Stratasys ULTEM 9085 and Markforged Onyx while the Vat Photopolymerization process was used to produce specimens of Accura ClearVue. The ULTEM 9085 and Markforged Onyx are filament based polymers and the ClearVue is a liquid based resin. The specimens were first submerged in a high pressure, salt water bath of 3.5% NaCl solution at 34.5 MPa (5000 lb/in2) for a total exposure time of 60 days to determine the water absorption characteristics. Subsequent to the salt water exposure at high pressure, the specimens were evaluated to determine changes in tension, compression, flexure, and in-plane fracture properties. To determine the effects of water saturation and low temperature coupling, the mechanical testing was performed at temperatures of 20 °C, 0 °C and −20 °C in both dry and saturated conditions. Additionally, non-destructive testing in the form of TeraHertz and FIRT imaging was conducted to analyze the physical material changes through the thickness of the material due to the saline water absorption. To quantify the change in material storage and loss moduli properties, Dynamic Mechanical Analysis (DMA) characterization was performed on each of the AM polymers in dry and saturated states. The DMA testing also quantified changes in the Glass Transition Temperature because of salt water exposure. In summary, The current study investigates the effects of coupled long term/high pressure salt water exposure with low temperatures on the mechanical and material characteristics of three unique AM polymers by: (1) immersing the materials in a salt water solution at 34.5 MPa for 60 days, (2) Conducting post exposure mechanical testing on the materials at 0 °C and −20 °C with comparisons to 20 °C testing on dry specimens, and quantifies changes in material properties through DMA experiments. The results from all testing in the study show that high pressure salt water exposure when coupled with low temperatures has unique effects on each of the materials considered in the study and careful consideration to each parameter must be given based on the material type when components will be employed in marine operations.

Coherent underplating of HP–LT blueschist packages and basement during Hellenic subduction recorded by zircon U–Pb data, Pelion, Greece

Studies of HP–LT metamorphic complexes are crucial in advancing our understanding of subduction processes, such as underplating, metamorphism and exhumation. Detailed new U–Pb zircon data of blueschist facies metasedimentary units at Pelion indicate two distinct stratigraphically upright and coherent structural slices: (1) the South Pelion slice consisting of strata with Permian–Late Cretaceous zircon maximum depositional ages; and (2) the North Pelion slice consisting of strata with Triassic–Late Cretaceous zircon maximum depositional ages. Both slices have Late Cretaceous strata at the top of the section with cosmopolitan detrital zircon signatures. The ages from zircon U–Pb rim overgrowths correlate with existing constraints from subduction metamorphism during the Paleocene–Eocene, with a possible second stage recorded during basal underplating in the Late Eocene–Oligocene. Detrital zircon provenance data and multi-dimensional scaling comparisons demonstrate a tectono-metamorphic linkage between the Pelion rocks and the Cycladic Blueschist Unit, and between the southern Pelion basement and the Cycladic basement. Protolith deposition for Pelion blueschist facies rocks occurred during Permo-Carboniferous intra-arc extension and Adria–Pindos rifting. Our results show that the Pelion blueschist facies rocks, representing lateral equivalents of the Cycladic Blueschist Unit, consist of two separate, coherent upper crustal slivers that were underplated and metamorphosed during Hellenic subduction beneath the Pelagonian margin. Thematic collection: This article is part of the Ophiolites, melanges and blueschists collection available at: https://www.lyellcollection.org/topic/collections/ophiolites-melanges-and-blueschists Supplementary material: Detailed methodology, further provenance and maximum depositional age methods and descriptions, sample location coordinates (Supplementary Table 1), and zircon U–Pb data (Supplementary Table 2). These data are available at https://doi.org/10.5281/zenodo.8300635 and https://doi.org/10.6084/m9.figshare.c.7008123

High-pressure low-temperature densification of NASICON-based LATP electrolytes for solid-state lithium batteries

Ceramic oxides are promising solid electrolytes for Lithium metal solid-state batteries (SSBs) because of their high ionic conductivity and stability under ambient conditions. Nonetheless, the need for high-temperature densification approaches challenges their processability towards upscaling and their implementation into practical SSB devices. Here, we investigate a High-Pressure Low-Temperature (HPLT) processing technique for the densification of NASICON-based Li1+xAlxTi2-x(PO4)3 (LATP) solid electrolyte, providing an understanding of several key parameters such as temperature, pressure and time. Our results show that nanometric LATP can be densified using the HPLT technique at 200°C within 2 min delivering an ionic conductivity of 6.15×10−5 Scm−1, which is the highest reported value at this temperature without the addition of solvents. On the other hand, by combining HPLT with a short post-heat treatment at 700 or 800 °C for 1 hour, highly dense pellets with an ionic conductivity of 10−4 Scm−1 can be obtained. This represents a reduction of the densification temperature of 400°C compared to conventional high-temperature sintering and shows the potential of HPLT to overcome current densification constraints derived from the use of very high temperatures.

New evidence for the presence of the Inner Tauride Ocean: Lithological, geochronological and P-T correlations with the Tavşanlı and Afyon zones of Central Anatolia (Türkiye)

The Tavşanlı and Afyon zones, which are well defined in western Türkiye, represent high pressure-low temperature (HP-LT) metamorphic rocks formed in a subduction zone. The Korumaz and Hınzır mountains (northeast of Kayseri) between the Central Anatolian Crystalline Complex and the Eastern Tauride Belt are represented by a HP-LT metamorphic sequence, which is thought to have formed between the Carboniferous and the Cretaceous. Here we present 40Ar/39Ar data from white micas within the Lower-Middle Triassic calc-phyllites from Korumaz Mountain, which yielded an age of 87 ± 2 Ma. Therefore, based on new mineralogical and geochronological data we suggest that this low-grade (HP-LT) metasedimentary sequence correlates with the Afyon Zone. Tectonically emplaced on-top of the HP-LT metasedimentary units of the Korumaz and Hınzır mountains is a meta-accretionary complex consisting of serpentinite, listvenite, marble, phyllite, calc-phyllite, metabasite, and meta-plagiogranite. Petrographic and mineral chemical studies show that the meta-accretionary complex was subjected to metamorphism under the HP-LT conditions that are similar to those of the Tavşanlı Zone in western Türkiye. Zircon Hf isotopic compositions from the meta-plagiogranite in the Korumaz and Hınzır mountains exhibit a depleted mantle signature with positive epsilon Hf(t) values of +5.6 to +13.1, and yielded a U-Pb crystallization age of 101.14 ± 0.84 Ma, which is the oldest age determined in oceanic crustal rocks of the ophiolites from the Tauride Belt. Geochemically, the metabasites and meta-plagiogranites from the meta-accretionary complex show subduction-related characteristics. White micas from phyllites and listvenite, which dominate the matrix of the meta-accretionary complex, yielded 40Ar/39Ar metamorphic ages ranging from 78 to 60 Ma. Our new geological and geochronological data suggest that metamorphic units of the Korumaz and Hınzır mountains are the eastern continuation of the Afyon and Tavşanlı zones. This indicates that the Inner Tauride Ocean, the existence of which has been controversial in the literature, was indeed present between the Central Anatolian Crystalline Complex and the Eastern Tauride Belt.

Spectroscopic characterization of yellow gem quality CVD diamond

CVD (chemical vapor deposition) diamond in the gem market today is dominated by colorless and pink material. However yellow CVD material is also found and it is concluded that all the yellow CVD diamonds found in the gem market have been post growth HPHT (high pressure high temperature) processed. This study shows that HPHT and LPHT (low pressure high temperature) treatments are essential for removal of the brown and gray color associated with as grown CVD material. The distinguishing temperatures and conditions of these treatments can be determined from the spectroscopic study of vacancy-related optical centers.

Sensitivity of Listeria innocua to high hydrostatic pressure at low temperature in Ringer's solution and milk

The research was performed to investigate the effect of high hydrostatic pressure low temperature (HHPLT) on Listeria innocua in Ringer's solution (RS) and raw milk (RM). The physicochemical properties of RM were studied at 300 MPa and 10 °C. Compared with the control, protein and lipase activities were reduced at HHPLT in RM. The L-values (luminance) of LHPLT applied RM were significantly (P < 0.05) decreased for colour Pressure application at 300 MPa for 90 min totally inactivated L. innocua at –20 °C in both RS and RM. L. innocua showed resistance to low pressure (200 MPa) in RM. Overall, increasing the pressure with applications at –20 and –30 °C resulted in a higher (P < 0.05) inactivation of L. innocua than at 10 and 20 °C. HHPLT applications to frozen RM resulted in the retention of textural characteristics.

Synthesis of fluorinated copolymers and their applications as pressure‐responsive materials

AbstractPressure‐sensitive paints (PSPs) have been demonstrated to be very important for aerodynamics research. In order to improve the pressure sensitivity and adhesion ability of PSP, herein, a series of fluorine‐containing copolymers compositing of an oxygen and pressure‐responsive probe derived from platinum(II)‐5,10,15,20‐tetrakis‐(2,3,4,5,6‐pentafluorophenyl)‐porphyrin (PtTFPP) named as poly[(tBs)a‐co‐(TFEM)b‐co‐(PtTFPP‐1MA)c] were synthesized and investigated as PSPs. These PSPs were constructed with different fluorine ratios for the investigation of the effect of fluorine contents on PSPs. Especially, PSP (F0.33) with the trifluoroethyl methacrylate (TFEM) molar ratio of 33% in the copolymers could adhere well to the surface of an aircraft model. F0.33 showed high oxygen sensitivity (I0/I100 = 32.87), reasonable response time to oxygen (44 s), high pressure sensitivity (SP = 0.75%/kPa at 20°C) and low temperature response (ST = −0.77%/°C at 100 kPa). F0.33 was further sprayed on the surface of a delta wing of an aircraft model and its pressure response was verified in a wind tunnel. The data from F0.33 film at the same wind speed and position were close to the pressure data measured by using traditional method using open pressure holes, showing the potential application of these PSPs.

Accretion and subduction mass transfer processes: Zircon SHRIMP and geochemical insights from the Carboniferous Western Series, Central Chile

ABSTRACT In the region of Pichilemu (Central Chile), the exhumed roots of the Carboniferous paleo-accretionary wedge developed during subduction of an oceanic realm underneath the western Gondwana margin are exposed. We focus on the areas of Infiernillo beach and Punta de Lobos: the former representing a well-characterized transitional blueschist-facies coherent stack of metabasitic lithologies interlayered at the centimetre- to metre-scale within metasedimentary rocks and glaucophanites, whereas the latter corresponds to a massive, up to hundreds of metres thick, strained metapillow lavas edifice surrounded (not interlayered) by metasedimentary rocks. We provide new field, geochemical, Raman thermometry and zircon SHRIMP U-Th-Pb geochronology on the lithologies forming the Infiernillo-Punta de Lobos complex aiming at characterizing the sedimentary sources and the extent of mechanical mixing. Field observations suggest that the Infiernillo-Punta de Lobos complex can be considered as part of the same successions, subducted and basally accreted almost coherently at high pressure-low temperature (HP-LT) conditions. The geochemistry signal in metasedimentary rocks and maximum deposition ages point to a marked forearc source for all the metasedimentary and glaucophanite lithologies, whereas massive metapillow lavas and greenschists might represent volcanic products and oceanic roughnesses erupted near the trench when the oceanic material approached the Gondwana margin at c. 329 Ma. It is suggested that the interlayering now observed in the field is mostly the consequence of sedimentary and/or volcanic processes close to the trench environment, with minor tectonic reworking of the pre-subduction structures (e.g. lithological contacts). Our results suggest that the Punta de Lobos edifice is closely related to the subduction of large volumes of continent-derived, trench-filling sediments towards HP-LT conditions. Thus, in line with previous experimental and numerical simulations, we emphasize the potential role of oceanic roughness as stress perturbations that could contribute to the subduction of thick sedimentary sequences, and discuss their implications for seismogenesis.

Lithium pegmatite of anatectic origin – A case study from the Austroalpine Unit Pegmatite Province (Eastern European Alps): Geological data and geochemical modeling

There is an ongoing debate as to whether rare element pegmatite is always related to fractional crystallization of huge fertile granite bodies or whether it can also form directly from limited portions of enriched anatectic melt. In this contribution, we present a case study from the Eastern European Alps, showing the continuous evolution from melt generation in staurolite bearing micaschist to spodumene (LiAlSi2O6) bearing pegmatite. The investigated Austroalpine Unit Pegmatite Province formed during Permian lithospheric extension and all levels of the Permian crust are now accessible in a Cretaceous nappe stack. This nappe stack is mapped in detail, subdivided lithostratigraphically and the internal tectonic structure is well understood. It is clear that the described pegmatites are neither spatially nor genetically related to large fertile granite bodies. A review of geochronological data proofs that emplacement of pegmatite and leucogranite is broadly contemporaneous with high temperature-low pressure metamorphism of the country rocks. Field observations give clear evidence of a genetic link between simple pegmatite, leucogranite, evolved pegmatite and albite-spodumene pegmatite, on the one hand, and the subsolidus or suprasolidus metasediment hosting them on the other hand. These relations are underpinned by geochemical major and trace element investigations on all types of rock and the minerals therein. As source rock an Al-rich metapelite enriched in Li (70–270 ppm) with respect to the average upper continental crust is identified. The main Li-carrier is staurolite with up to 3000 ppm Li. The pegmatite and leucogranite originate in anatectic melts that formed between 0.6 and 0.8 GPa and 650–750 °C, corresponding 18–26 km depth. During melt formation staurolite was consumed by sillimanite forming reactions. Subsequently, the melts were enriched in Li by fractional crystallization of quartz and feldspar during their ascent to higher crustal levels. While simple pegmatite and inhomogeneous leucogranite formed in lower and intermediate levels, evolved and albite-spodumene pegmatite crystallised at high levels at conditions between 0.3 and 0.4 GPa and 500–570 °C, corresponding to about 12 km depth. Based on these data we develop a geochemical model for showing that Li can be transferred from a metasediment into an anatectic melt if staurolite is stable or metastable at the onset of melting. Such a melt can contain between 200 and 1000 ppm Li and the melt can be further enriched with up to 5000 to 10000 ppm Li through fractional crystallization of quartz and feldspar, allowing crystallization of spodumene. Estimated fractionation degrees vary between 81 and 99 %, depending on the protolith composition, the melting scenario and the partitioning coefficients. Li-Al-rich metasediments are therefore a rich source of certain rare elements when they first melt. However, the spectrum of elements contained in the melt depends on a wide variety of conditions. This anatectic model provides an alternative explanation for the formation of Li-rich pegmatite if no fertile parent granite can be identified.

Metamorphism and Deformation on Subduction Interfaces: 1. Physical Framework

AbstractA thermal and mechanical framework is presented for analysis of pressure‐temperature (P‐T) data and structural observations from high‐pressure‐low‐temperature (HPLT) terrains. P‐T data from 281 HPLT rocks exhibit two regimes separated at a pressure of ∼1.5 GPa, which corresponds to the modal maximum depth of thrust faulting in subduction zones. At pressures ≲1.5 GPa, interpreted as recording conditions on the plate interface, temperatures increase at about 350°C/GPa and are consistent with conditions calculated for shear stresses of ∼30–100 MPa on the interface. Such shear stresses are high enough to carry several kilometers' thickness of sediment at least to the base of the plate interface. Burial of material on plate interfaces occurs predominantly during large‐to‐great earthquakes; the exhumation phase involves contrasts in ascent rates of adjacent units, because of their differing buoyancies and strengths. In consequence, juxtaposition of unrelated rock types is expected to be ubiquitous, during both descent and ascent. The scarcity of temperatures higher than ∼650°C at pressures ≳1.5 GPa may reflect loss of material from the wedge‐slab interface by buoyant ascent. Exhumation of rocks in the subduction interface requires substantial reduction in shear stress, most plausibly by (near‐)cessation of subduction. During prograde metamorphism temperatures increase smoothly with depth in the plate interface, with almost isothermal compression in the wedge‐slab interface. Following cessation of subduction, rocks rising along the wedge‐slab interface are likely to heat slightly during decompression. Within the plate interface, temperatures drop following the cessation of shear heating, and rocks follow counter‐clockwise hairpin PT paths.

Thermochronometry of metamorphic rock complexes on the SE Peloponnese, Greece, using thermoluminescence (TL): preliminary experiments

Here, we report preliminary results from thermoluminescence (TL) measurements on metamorphic quartz from the SE Peloponnese, Greece, and we discuss its potential for thermometric and, possibly, thermochronometric applications over longer geological periods. Extensive high pressure/low temperature (HP/LT) schists associated with a 24 Ma metamorphic age, and with cooling ages ranging between 6-14 Ma (based on fission-track and (U-Th)/He thermochronometry), encompass sizable quartzite outcrops associated with substantially low radiation (U, Th, K concentrations below the analytical detection limits), allowing TL signal to grow on longer geological timescales. Although deeper TL traps (&gt;360°C) appeared saturated as expected, geologically stable traps lying between around 360°C were found to be far from saturation. Once higher analytical resolution is achieved in the determination of the radioelement concentrations the recovered equivalent doses will be combined with the respective dose rates to explore the suitability of TL from quartz for longer-range thermochronometry in extremely low-radiation geological environments.

Evaluating the defects in CVD diamonds: A statistical approach to spectroscopy

Laboratory-grown diamonds produced by chemical vapor deposition (CVD) can have similar sizes and colors to natural diamonds, and their color can be enhanced by post-growth treatment. Despite considerable published research on CVD diamond growth, post-growth treatment remains difficult to detect in some CVD diamonds. To improve the detection of post-growth treatment, we apply multivariate statistics to photoluminescence (PL) emission spectra and surface fluorescence images from 11,606 gem-quality CVD diamonds within the D-Z color range. Unsupervised statistics indicate as-grown CVD diamonds commonly have 3H defects, with zero-phonon line (ZPL) at 503.5 nm, and relatively intense PL peaks at 467.6 nm. These features are absent or minor in diamonds treated under high-pressure, high-temperature (HPHT) conditions. HPHT-treated CVD diamonds tend to exhibit the H3 system (with ZPL at 503.2 nm) as well as larger 491.9 nm and 566.6 nm peak areas. A subset of CVD diamonds showing the H3 system could have experienced treatment at low-pressure high-temperature (LPHT) conditions (including inside the reactor during or after CVD growth).

Lithospheric extension of the accretionary wedge: An example from the Lanling high-pressure metamorphic terrane in Central Qiangtang, Tibet

Deciphering the exhumation mechanism of high-pressure−low-temperature (HP-LT) metamorphic rocks can provide important insights into the tectonic evolution of oceanic subduction zones at active continental margins. Here, we present a multidisciplinary study examining the exhumation tectonics of the Permo−Triassic eclogite-bearing HP-LT terranes of the Central Qiangtang metamorphic belt (CQMB) in the central Tibetan Plateau. Field geological relations and microscopic observations show that the HP-LT rocks in the Lanling area are separated from the epimetamorphic late Paleozoic ophiolite mélange of the hanging wall by low-angle detachment faults and primarily exhibit five stages of deformation. The HP-LT terranes were exhumed as a metamorphic core complex and show pervasive synexhumation top-to-the-SW and -S shear structures. The results of the petrological and mineralogical analysis and pseudosection modeling of retrograde eclogites indicate that these rocks are characterized by synexhumation mineral growth pulses with hairpin-type decompressional pressure-temperature trajectories. A compilation of previous geochronological data and our 40Ar/39Ar dating results of synexhumation minerals and shear bands in HP-LT rocks indicate continuous exhumation at ca. 244−215 Ma prior to the continental collision between the North Qiangtang Block (NQB) and South Qiangtang Block. Moreover, the CQMB is likely an autochthonous accretionary wedge resulting from northward subduction of the Paleo-Tethys Ocean beneath the NQB. Combined with ca. 243−230 Ma mantle upwelling to the north of Lanling, we infer that the CQMB, namely, the accretionary wedge of the Paleo-Tethys Ocean, experienced Middle−Late Triassic lithospheric extension in the NW-SE direction.

The Moglio-Testico Unit (Ligurian Alps, Italy) as Subducted Metamorphic Oceanic Fragment: Stratigraphic, Structural and Metamorphic Constraints

Along the Western Alps, the oceanic units showing blueschists to eclogite facies metamorphic imprint are classically regarded as fragments of the Ligurian-Piedmont Ocean. These units recorded a strongly deformation related to their subduction, accretion and subsequent exhumation into the Alpine wedge, developed during the convergence between the Europa and Adria Plates. However, some of these units, for example the Moglio-Testico Unit, are less pervasively deformed, providing evidence of their sedimentary evolution as well as the tectono-metamorphic history. Therefore, we present original stratigraphic, structural and thermo-barometric data to characterize the tectono-metamorphic history and the sedimentary evolution of the Moglio-Testico Unit, performing different techniques including fieldwork, structural analysis and chlorite-phengite multiequilibrium thermobarometry. Our dataset indicates that the Moglio-Testico Unit can be considered as a fragment of oceanic cover whose sedimentary evolution reflects that of a portion of oceanic lithosphere approaching to the subduction zone. Structural analysis combined with the thermobarometry indicate that this unit recorded a polyphase deformation history developed under High Pressure-Low Temperature metamorphic conditions (D1: 1.2–1.0 GPa and Tpeak: 330–260 °C; D2: 0.4–0.7 GPa and 230–170 °C) during its underthrusting, accretion into the Alpine wedge and subsequent exhumation up to the shallower crustal levels.

Characterization of metastable high pressure phase transition positions and its influence on the behavior of microbial destruction

Effect of perturbation factors on phase transition metastable positions of whole milk (4% fat content) and their influence on microbial destruction characteristics of non-pathogenic Escherichia coli inoculated in milk subjected to high pressure low temperature treatment were evaluated using a specially developed high pressure (HP) cooling system. Initially, the phase transition data of milk transitioning through the metastable phases were obtained and fitted successfully using Simon-like models as done in previous studies and polynomial formulas with R2 of 0.997 & 0.996 for ice I, and 0.989 & 0.989 for ice III, respectively. The phase transition position of milk was explored with 5% and 10% sodium chloride solution as perturbation sources, respectively. Results showed that the 5% sodium chloride solution can reduce the transition pressure of milk by 43 MPa and increase the transition temperature by 4.1 °C, so that the milk can achieve phase transition at lower pressure and higher temperature. Phase transition microbial destruction was characterized by discontinuity, mutation and segmentation when the phase transition pressure interval 250– 300 MPa was carefully refined. The inactivation amount of E. coli before the phase transition (250 MPa) was 1.11 log and the phase transition process itself brought an additional 1.26 log destruction of E. coli population in milk. Industrial relevanceHigh pressure low temperature (HPLT) phase change kinetics were employed to enhance microbial destruction. HPLT was established based on a self-cooling unit positioned inside conventional HP chamber offering opportunities for scale up and commercialization. The effectiveness of HPLT phase transition for Escherichia coli destruction was demonstrated. The related research in metastable state provides a reference point for commercial application of high-pressure-low-temperature technology for microbial destruction and quality enhancement.

Investigating the microbial inactivation effect of low temperature high pressure carbon dioxide and its application in frozen prawn (Penaeus vannamei).

During the pandemic of coronavirus disease 2019, the fact that frozen foods can carry the relevant virus raises concerns about the microbial safety of cold-chain foods. As a non-thermal processing technology, high pressure carbon dioxide (HPCD) is a potential method to reduce microbial load on cold-chain foods. In this study, we explored the microbial inactivation of low temperature (5-10 °C) HPCD (LT-HPCD) and evaluated its effect on the quality of prawn during freeze-chilled and frozen storage. LT-HPCD treatment at 6.5 MPa and 10 °C for 15 min could effectively inactivate E. coli (99.45%) and S. aureus (94.6%) suspended in 0.85% NaCl, SARS-CoV-2 Spike pseudovirus (>99%) and human coronavirus 229E (hCoV-229E) (>1-log virus tilter reduction) suspended in DMEM medium. The inactivation effect of LT-HPCD was weakened but still significant when the microorganisms were inoculated on the surface of food or package. LT-HPCD treatment at 6.5 MPa and 10 °C for 15 min achieved about 60% inactivation of total aerobic count while could maintain frozen state and quality of prawn. Moreover, LT-HPCD treated prawn exhibited significant slower microbial proliferation and no occurrence of melanosis compared with the untreated samples during chilled storage. A comprehensive quality investigation indicated that LT-HPCD treatment could maintain the color, texture and sensory of prawn during chilled or frozen storage. Consequently, LT-HPCD could improve the microbial safety of frozen prawn while maintaining its original quality, and could be a potential method for food industry to improve the microbial safety of cold-chain foods.

Low temperature eclogite facies rocks discovered in the Eastern Himalayan Syntaxis: Poly‐cyclic metamorphic evolution and implications

AbstractWe report the first occurrence of poly‐cyclic high‐pressure low‐temperature (HP‐LT) rocks from the easternmost Indus‐Yarlung suture zone, formed during subduction of Neo‐Tethyan oceanic lithosphere. Petrology, mineral composition and P–T pseudosection modelling reveal two low‐temperature eclogite facies metamorphic events with an initial high‐pressure P–T condition of 16.4–18.7 kbar and 510–520°C, exhumation to 10.5–12.0 kbar and 580–590°C and a subsequent second high‐pressure P–T condition of ~16 kbar and ~560°C and exhumation to ≤9 kbar and ≤600°C. This history implies a complex ‘yo‐yo type’ P–T path. In situ monazite dating and textural relationships show that late‐stage exhumation, cooling and garnet breakdown occurred at c. ~25–22 Ma. We interpret the first burial event to represent subduction of the Neo‐Tethys Ocean at the eastern Indus‐Yarlung suture zone. Initial exhumation, reburial and final exhumation represent material transport in a large‐scale convective circulation system in the subduction channel. Convective overturn in the subduction channel evidently serves both as a mechanism to produce poly‐cyclic metamorphism and to exhume LT eclogite facies rocks.