Decompression Stage Research Articles

Biportal endoscopic en bloc removal of the ligamentum flavum for spinal stenosis: nuances for the "butterfly" technique.

The introduction of endoscopic spine surgery has led to a paradigm shift in the treatment of spinal disorders. In particular, biportal endoscopic surgery has gained traction for its wider visual field and improved the maneuverability of instruments, familiar anatomy, and costeffectiveness. In this study, we describe our en bloc removal of the ligamentum flavum using a "butterfly" technique. This approach had several advantages: (1) The flavum serves as a protective barrier for the dura during drilling. (2) There is less epidural bleeding, which provides (3) better visualization. (4) In an inadvertent durotomy, this usually occurs later in the procedure, which is more manageable than the early stages of decompression. Biportal decompression for spinal stenosis can be performed using an en bloc ligamentum flavum removal technique that is safe, reproducible, and efficient. A systematic approach will help early adopters overcome the steep learning curve.

Post–peak petrochronology and C–O–H fluid influx in the lower crust: A case study of garnet–orthopyroxene granulites from the Rauer Islands, East Antarctica

Garnet–orthopyroxene granulites from the Rauer Islands (East Antarctica) provide a spectacular example to investigate the late fluid evolution, metamorphic duration, and behavior of monazite and zircon in response to metamorphic reactions and fluid–rock interaction. Here, we characterize the secondary fluid inclusions in peritectic garnet and orthopyroxene, which occur as multiphase inclusions along micro–fractures. Inclusions are composed of siderite, pyrophyllite, calcite, quartz and residual CO2, representing stepdaughter phases resulting from the interactions between C–O–H fluid and its hosts at variable temperatures during retrogression. Zircon grains show clear core–rim structure, which yield 206Pb/238U ages of 540–507 Ma and 527–490 Ma, respectively. Index inclusions and internal structures suggest that the cores document the timing of peak and post–peak decompression while the growth of rims corresponds to melt crystallization during the final cooling. The UPb systems in zircons are considered to have not been obviously affected by fluid or melt–mediated modification. The unusual formation of monazites in garnet–orthopyroxene granulites may be linked with the elevated phosphorus budget as a result of apatite dissolution during the prograde melting of the rocks. Detailed investigations suggest that the crystallization of monazites occurred both at peak and post–decompression stages, whose isotopic systematics has been completely reset due to melt–mediated dissolution–precipitation. The spurious dates for monazites (522–495 Ma) are highly coinstantaneous with the dating results for zircon rims, further supporting this view. Therefore, we conclude that the late carbonic fluid influx cannot result in marked U(Th)–Pb resetting in zircon and monazite. Instead, anatectic melt may have played an important role in the disturbance of isotopic systematics in monazites, especially for long–lived high–grade metamorphic terranes. Combined with previously published data, we propose that the Pan–African metamorphic event in the Rauer Islands may have reached the peak at around ∼540 Ma, followed by a protracted post–peak evolution that lasted for at least ∼50 Myr. This study highlights the importance of an integrated investigation of fluid and index mineral inclusions, as well as the chemical signatures of zircon and monazite, to interpret chronological data correctly.

Efficient protein structure archiving using ProteStAr.

The introduction of Deep Minds' Alpha Fold 2 enabled the prediction of protein structures at an unprecedented scale. AlphaFold Protein Structure Database and ESM Metagenomic Atlas contain hundreds of millions of structures stored in CIF and/or PDB formats. When compressed with a general-purpose utility like gzip, this translates to tens of terabytes of data, which hinders the effective use of predicted structures in large-scale analyses. Here, we present ProteStAr, a compressor dedicated to CIF/PDB, as well as supplementary PAE files. Its main contribution is a novel approach to predicting atom coordinates on the basis of the previously analyzed atoms. This allows efficient encoding of the coordinates, the largest component of the protein structure files. The compression is lossless by default, though the lossy mode with a controlled maximum error of coordinates reconstruction is also present. Compared to the competing packages, i.e. BinaryCIF, Foldcomp, PDC, our approach offers a superior compression ratio at established reconstruction accuracy. By the efficient use of threads at both compression and decompression stages, the algorithm takes advantage of the multicore architecture of current central processing units and operates with speeds of about 1 GB/s. The presence of Python and C++ API further increases the usability of the presented method. The source code of ProteStAr is available at https://github.com/refresh-bio/protestar.

Tectono-metamorphic evolution of the Central Bundelkhand Craton, India from geochemistry and bulk composition modelling of amphibolite enclaves

The Bundelkhand Craton (BuC) represents a significant Archean terrane within the northern Indian Craton and yet its tectono-metamorphic evolutionary history remains relatively understudied. Our investigation involves detailed petrography, geochemistry, and bulk composition modeling of both garnet-bearing and garnet-absent amphibolites with a two-fold objective: (i) to constrain the protolithic nature and tectonic settings involved in the genesis of these rocks, and (ii) to propose a tectono-metamorphic evolutionary history for the BuC. The BuC amphibolites originate from basalt and andesitic-basalt protoliths. Their trace element compositions reveal negative anomalies in Nb, Ta, and Ti, while their rare earth element (REE) normalized patterns indicate enrichment in light REEs over heavy REEs. The basaltic protolith is interpreted to have formed during orogeny in a compressional tectonic regime at the active margins of island arcs in a subduction-related setting. This interpretation is supported by various discrimination plots for amphibolites, such as Nb/Th vs Zr/Nb, Zr vs Zr/Y, and Th/Nb vs Ce/Nb, as well as high Th/Yb and low Nb/Yb contents— all of which suggest an island arc setting influenced by subduction. These amphibolites have undergone three distinct phases of metamorphism, as evidenced by petrography, mineral chemistry, and bulk composition modeling. This interpretation is further supported by geochemical discrimination diagrams which indicate that a subduction tectonic setting was active during peak metamorphism. During the pre-peak phase, the garnet-bearing amphibolites experienced pressure and temperature conditions ranging from 6.25 to 6.5 kbar and 580 to 590ºC, while the garnet-absent amphibolites underwent conditions from 5.0 to 5.8 kbar and 400 to 450ºC. Peak metamorphism was observed at pressures ranging from 6.8 to 7.4 kbar and temperatures from 760 to 805ºC for the garnet-bearing amphibolites, and at pressures from 7.0 to 7.4 kbar and temperatures from 785 to 810ºC for the garnet-absent amphibolites. The metamorphic retrograde conditions for the garnet-bearing amphibolites are defined by P-T conditions ranging from 4.45 to 4.75 kbar and 585 to 615ºC, while for the garnet-absent amphibolites, it ranges from 3.1 to 4.0 kbar and 620 to 710ºC. The mineral assemblages and P-T conditions delineate a clockwise P-T path for both, garnet-bearing and garnet-absent amphibolites from the Babina and Mauranipur regions. This suggests that the rocks underwent a burial process amid subduction tectonic settings in an arc-related environment, followed by a decompression stage that brought them to the surface.

A new model to predict the small-hole decompression process of long CO2 pipeline

CO2 pipeline transportation is considered as an economical and safe way of moving large quantities of CO2 in Carbon Capture Utilization and Storage (CCUS) projects. However, design and planning of CO2 pipelines passing through populated areas require careful risk assessment of accidental pipeline failure scenarios leading to CO2 pipeline decompression. In this study, a new zero-dimensional multi-stage outflow model describing transient decompression of CO2 is developed. The model accounts for the experimentally observed liquid level variation along the pipeline and uses the liquid volume fraction threshold parameter (αt) to mark the end of the saturated liquid flow decompression stage. Besides, the Lee model is applied to describe the mass transfer in gas-liquid phases. The model was validated against experimental data obtained large-scale pipeline decompression tests and can be recommended for simulation of outflow of supercritical and liquid CO2 from pipelines longer than 258 m and the orifice-to-pipeline diameter ratios smaller than 0.21. The advantage of this model lies in its use of the relatively simple Vessel Blowdown Model (VBM) to accurately model the depressurization process. It addresses the inconvenience posed by the heavy computational burden of high-dimensional models when predicting long-duration leakages in large-capacity pipelines.

Reconciling petrologic magma ascent speedometers for the June 12th, 1991 eruption of Mt. Pinatubo, Philippines

We investigate whether decompression rates derived from three often-disparate petrologic techniques (microlites, bubbles, and melt embayments) can be reconciled or integrated for a more complete understanding of magma ascent in the conduit. We focus on the well-studied and -documented earliest Plinian eruptions (June 12, 1991) of Mount Pinatubo. Using a newly developed two-stage decompression-diffusion model, volatile profiles in quartz-hosted embayments reveal an initial stage of decompression nearly two orders of magnitude slower than final rates. In applying time-integrated models of microlite and bubble nucleation and growth, initial decompression rates from embayments are supported by microlite modeling results, whereas final rates are in close agreement with bubble number densities. This consistency and continuity between speedometers supports the sensitivity of different petrologic recorders to specific regions of the conduit system and highlights the fidelity of embayments as recorders of decompression throughout the entire conduit. Ascent timescales derived from Pinatubo embayments range from hours to days, coinciding with the visual onset of lava effusion leading to explosive activity.

End‐to‐End Compressed Meshlet Rendering

AbstractIn this paper, we study rendering of end‐to‐end compressed triangle meshes using modern GPU techniques, in particular, mesh shaders. Our approach allows us to keep unstructured triangle meshes in GPU memory in compressed form and decompress them in shader code just in time for rasterization. Typical previous approaches use a compressed mesh format only for persistent storage and streaming, but must decompress it into GPU memory before submitting it to rendering. In contrast, our approach uses an identical compressed format in both storage and GPU memory. Hence, our compression method effectively reduces the in‐memory requirements of huge triangular meshes and avoids any waiting times on streaming geometry induced by the need for a decompression stage on the CPU. End‐to‐end compression also means that scenes with more geometric detail than previously possible can be made fully resident in GPU memory. Our approach is based on a novel decomposition of meshes into meshlets, i.e. disjoint primitive groups that are compressed individually. Decompression using a mesh shader allows de facto random access on the primitive level, which is important for applications such as selective streaming and fine‐grained visibility computation. We compare our approach to multiple commonly used compressed meshlet formats in terms of required memory and rendering times. The results imply that our approach reduces the required CPU–GPU memory bandwidth, a frequent bottleneck in out‐of‐core rendering.

Autological bone marrow concentrate for the treatment of early stages of femoral head avascular necrosis (literature review)

Relevance. In the treatment of the early stages of the femoral head osteonecrosis core decompression is widely used, which reduces intraosseous pressure and increases blood flow to the femoral head. To increase the efficiency of the core decompression the use of various bioadjuvants, including concentrate of autologous bone marrow cells is needed, the appropriateness of which is actively discussed.Purpose of the systematic review: evaluation of the effectiveness of autologous bone marrow cells in core decompression in the treatment of the early stages of the femoral head osteonecrosis according to the literature.Material and methods. Articles with clinical data in full text in English or Russian available in the Internet (PubMed and elibrary databases) were included in the study. Articles containing actual data on the stage of osteonecrosis, the number of femoral heads operated on, the use of autologous bone marrow cells as an adjunct to the core decompression of the femoral head, the number of ineffective surgical interventions after which total hip arthroplasty was required were included.Results. Sixteen original articles (2011–2022) were analyzed, and the results of 1135 femoral heads treatment (892 with autologous bone marrow cells, 243 without autologous bone marrow cells, control group) were evaluated. Patient follow-up periods ranged from 9 to 120 months, averaging 45 months. When using autologous bone marrow cells, the need for total hip arthroplasty was observed in 168 of 892 patients (18.8 %); when core decompression was used without autologous bone marrow cells, the rate of total hip arthroplasty was 27.2 % (p > 0.05). Only 2 articles out of 16 authors did not consider autologous bone marrow cells to be reasonable in the core decompression of femoral head.Conclusion. The use of autologous bone marrow cells concentrate as a bioadjuvant in the core decompression slows the progression of osteonecrosis. According to the overwhelming number of authors, the core decompression using autologous bone marrow cells is highly effective, significantly reducing the intensity of pain syndrome and improving the function of the hip joint. The results will be more encouraging with the further development of regenerative medicine, which will provide new samples of cellular preparations for bone tissue structure restoration.

Reactions in UHT calc-silicate granulites from the In Ouzzal terrane (Western Hoggar, South Algeria): Implication for pressure-temperature-fluid evolution

Calc-silicate granulites constitute a relatively small part of the whole granulitic material outcrops characterizing the In Ouzzal terrane (NW Hoggar, South Algeria). However, these rocks preserve a number of spectacular reaction textures that could be effectively used to infer their pressure-temperature-fluid history. These textures are interpreted using P-T and T-XCO2 grids in the simplified CaO-Al2O3-SiO2-Vapor system. In this process, sequences of reactions have been subdivided into two distinct stages: (i) the early prograde stage that was accompanied by significant rise of temperature from about 800 °C up to 1050 °C at around10 kbar followed by (ii) the decompression stage from about 9 to 6 kbar. During the prograde stage, coarse grained wollastonites were produced according to the reaction calcite + quartz → wollastonite + CO2. Furthermore, in the peak pressure temperature stage, the reaction producing wollastonite + scapolite from coarse primary garnet consumes CO2 with temperature increasing from 850 °C to 1000 °C according to the reaction 3grossular + 3CO2 → 3wollastonite + 2calcite + scapolite. The latest reactions have been occurred during the decompression stage from about 10 kbar to 5 kbar and cooling from 1000 °C to 800 °C. The growth of calcite + quartz around wollastonite besides to garnet coronas between wollastonite, calcite and scapolite are explained by the reaction: calcite + quartz → wollastonite + CO2 and 3wollastonite + scapolite +2calcite → 3grossular + 3CO2. The appearance of anorthite around scapolite occurs following a decrease of temperature independently to the fluids according to the reaction scapolite → 3anorthite + calcite. All reactions took place at CO2 low pressure which was estimated between 0.04 and 0.55.

Thermophysical evolution during different decompression of N2‐containing S‐CO2 pipelines

AbstractPipelines transporting impure supercritical carbon dioxide in the carbon capture, utilization, and storage (CCUS) chain exhibit varying decompression characteristics due to engineered emissions or accidental leakage, resulting in diverse temperature drops and heat transfer mechanisms in the media and pipe walls. Therefore, studying heat transfer characteristics during slow and instantaneous decompression is crucial to investigating pipeline operational risks. In this work, supercritical CO2 pipeline valve release and rupture disc release experiments were performed with a 1.5% molar ratio of N2 content in an experimental pipeline (16 m long, 100 mm inner diameter). The evolution of the medium and pipe wall's physical properties was measured and discussed. Two methods of depressurization were employed to analyze the phase changes and heat transfer processes in the pipe. The instantaneous decompression process has a shorter decompression time and undergoes fluctuating and stable decompression stages. The slow decompression process has a slower temperature drop rate, but the wall during the process can reach a lower minimum temperature. Both release methods cause a larger temperature drop and Nusselt number at the bottom of the pipe wall due to evaporation heat transfer compared to the middle and top. The slow decompression process demonstrates a higher peak Nusselt number at the bottom, resulting in superior heat transfer efficiency compared to the instantaneous decompression process. © 2023 Society of Chemical Industry and John Wiley & Sons, Ltd.

Pre-Alpine prograde evolution of the Upper Alpujarride (Betic-Rif belt) reveals a Paleotethys-related collision

ABSTRACT Medium and high grade kyanite-bearing graphitic metapelites of the basement of the Torrox Unit (Upper Alpujarride, Western Mediterranean) show kyanite-andalusite-kyanite replacements and coexisting garnet types with complex compositional zoning and growth-dissolution stages. This allows inferring two clockwise P-T paths associated with contrasted orogenic cycles of latest Carboniferous – earliest Permian and Eocene(?)-Miocene age, respectively. Dated (306 ± 77 Ma) prograde medium grade garnet cores with relatively low to moderate Ca content indicates pre-Alpine barrovian metamorphism in the kyanite stability field (ca. 600°C, 0.7–0.8 GPa). This implies a prograde pressurization of the sequence followed by decompression, as inferred from andalusite replacements after kyanite. Deeper in the sequence, anatectic granitic orthogneisses contain high-grade graphitic kyanite-bearing metapelitic restitic enclaves. Dating of rutile (with inclusions of kyanite) and monazite (shielded in biotite) from the pelitic enclaves provided pre-Alpine ages (ca. 300 Ma) rejuvenated due to Alpine overprint. Such pressurization event is not consistent with a late Variscan stage, commonly identified with a tectonic scenario characterized by orogenic collapse and decompression at ca. 300 Ma. Instead, we propose a post-Variscan collision event related to the closure of the western Paleotethys. On the other hand, Ca-rich cores of garnet porphyroblasts in the medium-grade metapelites formed at 1.1–1.2 GPa, 500°C, implying a metamorphic gradient of ca. 11.5°C/km related to Eocene (?) subduction. Kyanite+phengite replacements after andalusite are related to this stage. Late Mg-rich Ca-poorer overgrowths in garnet porphyroblasts document increasing temperature during the first stage of decompression (down to 0.9 GPa at ca. 650°C) with increasing thermal gradient up to ca. 20°C/km. These two complete metamorphic cycles of pressurization and heating followed by decompression allow reconciling previous contradictory conclusions about the paragenetic and thermal gradient development during the Paleotethyan and Alpine cycles in different units of the Betic-Rif belt.

Omphacite breakdown, symplectite formation and carbonate metasomatism in a retrograded continental eclogite: Implications for the exhumation of the Tso Morari Crystalline Complex (Trans-Himalaya, NW India)

The India-Eurasia collision zone in eastern Ladakh, India, is marked by the Tso Morari Crystalline Complex (TMCC), which underwent continental subduction, eclogite grade metamorphism, and rapid exhumation during the Himalayan orogeny. The TMCC is characterized by eclogitic enclaves, metamorphic evolution of which has been extensively studied in the past. Detailed petrography, mineral chemistry, Raman spectroscopy, and P-T-X pseudosection modelling of two such eclogite samples from the core and western margin of TMCC were carried out to address the differences and discrepancies from previous studies. Our study suggests peak metamorphism at ∼2.75 ± 0.1 GPa and ∼550 ± 50 °C, followed by a decompression stage at ∼1.50 ± 0.1 GPa and ∼580 ± 50 °C and subsequent high-temperature overprint at ∼0.85 ± 0.1 GPa and ∼680 ± 50 °C. Fine-grained grain boundary omphacite + garnet + amphibole symplectite colonies indicate exhumation along with fluid infiltration. The transition of omphacite into a more calcic variety and its subsequent replacement with amphibole are also observed. Presence of diopside + plagioclase symplectite indicates post-peak decompression and fluid infiltration. Carbonates in the matrix as veins and within fractures indicate late-stage fluid infiltration and metasomatism. Our study shows that lawsonite and/or Na-amphibole have not played any significant role in the metamorphic evolution of TMCC. In contrast to most of the previous studies carried out in TMCC, we opine that omphacite breakdown and metasomatism through externally derived carbonaceous fluids played a vital role in the exhumation and retrogression. We further opine that our mineral chemistry data and metamorphic modelling resemble a continental eclogite and mark differences from oceanic eclogites.

Soliton solutions of the equations of hydrodynamics in describing collisions and oscillations of atomic nuclei

The hydrodynamic approach was used to find an analytical solution of the hydrodynamic equations in the soliton approximation for layer collisions in the one- and two-dimensional cases. The compression stage, the decompression stage, and the expansion stage are considered within the framework of a single formula for layers with energies on the order of ten MeV per nucleon. Our generalization to the two-dimensional case leads to the idea of the formation of a rarefied bubble region at the stage of expansion. The approach can be used in other fields for calculations of the nonlinear dynamics of oscillations of complex systems.

Metamorphic evolution and tectonic significance of Neoarchean high-pressure mafic granulites in the Central Limpopo Belt, South Africa

ABSTRACT The Sand River area is in the northeastern part of the Central Zone (CZ) of the Limpopo Belt, and represents a key terrane to reveal early Precambrian tectonic processes in southern Africa. Based on petrology, U–Pb zircon ages, and major and trace element data of high-pressure (HP) mafic granulites from the Sand River area, the tectonic evolution of the Central Zone of the Limpopo Belt is re-evaluated here that allows revision of previous interpretations. The protoliths of the HP mafic granulites and amphibolites are sub-alkaline tholeiitic basalts similar to those formed at a mid-ocean ridge and intruded at 2.8 Ga. Based on the distinct mineral assemblages, three metamorphic stages (M1–M3) are recognized in the studied samples: (1) a peak HP granulite facies stage M1 (~1.17–1.32 GPa/~825–870°C), (2) a post-peak near-isothermal decompression stage M2 (~0.70–0.73 GPa/~835–880°C), and (3) a later, independent metamorphic stage M3 (~0.53–0.69 GPa/~793–801°C). M1 and M2 define together a clockwise P–T path. It reveals important information related to the Neoarchean collisional orogeny, and its later overprinted by an independent orogeny with subsequent exhumation and cooling. U–Pb zircon dating of two mafic granulites samples yielded protolith formation of the mafic granulites is prior to ~2.72 Ga, and the two metamorphic age peaks of ~2.72 (M1) and ~2.0 Ga (M3), which present the peak and post-peak cooling stages, respectively. The metamorphic evolution of HP mafic granulites in the Sand River area as reconstructed in this study suggests the Neoarchean collision of the Kaapvaal and Zimbabwe cratons and a discrete Paleoproterozoic orogenic overprint followed by post-orogenic exhumation and cooling.

Experimental Investigation on Deformation and Permeability of Clayey–Silty Sediment during Hydrate Dissociation by Depressurization

The sediments in the South China sea are mainly composed of clayey silt, characterized by weak cementation, low strength, and poor permeability. These characteristics lead to slow gas and water transport and low gas production efficiency in the production process, which is not conducive to reservoir stability. Therefore, this paper studied the influence of different factors on the displacement and permeability of hydrate-bearing sediments by using remolded cores from the South China Sea. It was found that, when the depressurization method was used for hydrate decomposition, the displacement change in sediments could be divided into three stages: depressurization stage, decomposition stage, and creep stage. During the decompression stage, sediment deformation was rapid and displacement was small. During the decomposition process of hydrates, sediment deformation was slow and displacement was maximum. The creep stage had the slowest deformation and the smallest displacement. The displacement increased with the increase in initial porosity, hydrate saturation, effective pressure, and depressurization amplitude. The permeability of the sediments was lower than that of the original sediments after hydrate decomposition. This permeability damage increased with the increase in the sediment porosity, hydrate saturation, depressurization range and effective pressure. Furthermore, the displacement of sediments was positively correlated with the permeability damage.

Urea-Formaldehyde Resin Removal in Medium-Density Fiberboards by Steam Explosion: Developing Nondestructive Analytical Tools

The cascading recycling of wood waste is currently a hot topic. Medium-density fiberboard (MDF) is a material whose consumption has been increasing worldwide for several decades. However, current wood waste treatment processes do not allow for efficient recycling. The potential of steam explosion (SE) treatment was investigated for stripping off the urea-formaldehyde (UF) resin and producing clean fibers from MDF. Hot liquid water during the hydrothermal stage and water expansion during the decompression stage of SE provoked the (1) hydrolytic breakdown of UF and removal of >80% of resin from the fibers and (2) efficient defibration of MDF producing ≈67% of fibers with similar morphological features when compared with MDF fibers. Near infrared spectroscopy (NIRS), nitrogen quantification, and confocal laser scanning microscopy/scanning electron microscopy-wavelength dispersive spectroscopy were used to evaluate the SE effect on UF removal from MDF fibers. The sample clusters obtained by principal component analysis of NIRS spectra were correlated with the nitrogen content and processing conditions used. This work brings versatile solutions based on hydrothermal treatments, namely SE, for diverse low environmental impact and valorization routes of MDF waste. We showed that MDF processing treatment must be chosen wisely according to the future valorization of the MDF targeted.

Repeated Caledonian burial and ultrafast cooling and exhumation of high‐pressure granulite facies rocks from the Blåhø Nappe on the island of Fjørtoft, Western Gneiss Region, Norway

AbstractThe allochthonous Blåhø Nappe in the Nordøyane ultra high pressure (UHP) domain, Western Gneiss Region in Norway, acts as a window to examine geological processes occurring in continent–continent collisional zones, but many aspects regarding its tectonometamorphic evolution remain debated and elusive. In this contribution, an integrated study including major‐ and trace‐element zoning in garnet, phase equilibrium modelling and the simulation of cation diffusion in garnet was conducted on two high‐pressure (HP) granulite facies rocks from the Blåhø Nappe on the island of Fjørtoft. The results shed new light on the complex geodynamic processes that act in continent–continent collisional zones and finally shape collisional orogens. Phengite, biotite, amphibole, zoisite‐allanite and low‐Zr rutile enclosed in garnet likely attest to a prograde eclogite facies metamorphism for the studied rocks. Pressure–temperature (P–T) conditions of ~1.5–1.6 GPa and 615–670°C were retrieved for this stage. An extensive re‐equilibration under peak HP granulite facies conditions of ~1.5 GPa and 925 ± 50°C followed. Subsequently, the rocks were cooled and reburied to eclogite facies conditions of ~1.8–1.9 GPa and 805–825°C. This was followed by a final stage of decompression and cooling to amphibolite facies conditions of ~650–780°C and 0.5–1.0 GPa. Cooling and exhumation rates of >400°C/Ma and >75 km/Ma, respectively, indicating an ultrafast temperature and pressure decrease are estimated for this stage from simulations of cation diffusion in garnet. The anticlockwise P–T path obtained here is relatively complete and compatible with a repeated burial history during the Caledonian orogeny but not with UHP conditions proposed for the Blåhø Nappe. Our model proposes that the rocks later forming the Blåhø Nappe were buried to lower crustal depths of approximately 55 km equating to a geothermal gradient of ~13°C/km during the early Caledonian orogeny. Subsequent heating of these rocks to HP granulite facies conditions was likely driven by slab break‐off and hot mantle upwelling. Baltica underthrusting during the Scandian continent–continent collision cooled and transported the Blåhø Nappe to greater depths. The obtained cooling and exhumation rates indicate ultrafast exhumation, presumably in an exhumation channel.

Boron isotope compositions of coexisting kornerupine and tourmaline in high-grade metabasic rocks: an example from Akarui Point, Lützow-Holm Complex, East Antarctica

Boron isotope compositions were measured in kornerupine and tourmaline from lenses consisting primarily of kornerupine, plagioclase and corundum. The lenses occur within hornblende-gneiss or along the boundary between this gneiss and an amphibolite lens at Akarui Point in the Lützow-Holm Complex, Prince Olav Coast, East Antarctica. The peak metamorphic conditions have been estimated to be ~ 800-900 oC and ~ 8-11 kbar. The δ11B compositions of kornerupine, which is interpreted to have been a stable phase at the metamorphic peak, are -11.6 ± 0.4 to -7.8 ± 0.5 ‰ and -9.8 ± 0.3 to -6.1 ± 0.2 ‰ in two different samples. Grains of prograde tourmaline included in kornerupine and corundum yielded δ11B = -2.1 ± 0.3 to +0.6 ± 0.3 ‰, and the secondary tourmaline replacing kornerupine yielded δ11B = -4.6 ± 0.2 to -3.7 ± 0.2 ‰. Therefore, the isotopic fractionation between kornerupine and tourmaline, △11BTur–Krn (= δ11BTur - δ11BKrn), of the average prograde tourmaline and average host kornerupine is +6.7 ± 1.5 ‰, which is interpreted to indicate isotopic equilibrium at the metamorphic peak on the basis of previous studies of isotope fractionation between tourmaline and minerals of the kornerupine-prismatine series. The δ11B values obtained on prograde tourmaline are between whole rock δ11B of MORB and mantle rocks and of some sedimentary rocks, and are similar to the δ11B of blackwall tourmalines that crystallized during the decompression stage following high-pressure metamorphism. We infer that the syn-metamorphic B-bearing fluid present in the kornerupine-plagioclase-corundum lens is likely sourced from a mixture of sedimentary, mafic and ultramafic lithologies in a subduction setting. The metabasic and meta-ultramafic lenses found in Akarui Point could be interpreted as the remnant of mixing zone of Ediacaran to Cambrian subduction channel.

The metabasites from the Texel Unit (Austroalpine nappe stack): markers of Cretaceous intracontinental subduction and subsequent collision

Abstract Eclogites in the Texel Unit (Austroalpine nappe stack; Eastern Alps, South Tyrol, Italy) represent the westernmost out-crops of the E-W striking Eoalpine High-Pressure Belt (EHB). East of the Tauern Window, the EHB forms part of a Cretaceous intracontinental south-dipping subduction/collision zone. The impetus of this contribution is to extend the geothermo-barometric data of the eclogites from the EHB using conventional geothermobarometry and multi-equilibrium calculations as well as Zr-in-rutile/titanite geothermometry and to put the P-T results of eclogites and amphibolites from the Texel Unit into the geodynamic framework. The investigated samples of this study are from the Spronser- and the Saltaus valleys (S-Tyrol) in the Austroalpine Texel Unit. The Texel Unit is composed mainly of paragneisses with minor intercalations of micaschists, orthogneisses, amphibolites and subordinately eclogites. The amphibolites from the Spronser valley contain the mineral assemblage amphibole + plagioclase + garnet + clinozoisite/epidote + quartz + titanite ± ilmenite ± rutile ± apatite ± calcite. Chemical zoning in plagioclase and amphibole shows two main growth stages: an older P-dominated stage (e.g. albite and barroisite cores) and a younger amphibolite-facies stage. The core of the amphiboles shows barroisite composition, the rim can be chemically classified as hornblende, edenite, tschermakite and pargasite. Geothermobarometric calculations with multi-equilibrium geothermobarometry (THERMOCALC v.3.21) yield temperatures of 600–654°C and pressures of 0.98–1.17 GPa for the same samples. The eclogites from the Saltaus valley contain the peak mineral assemblage omphacite + amphibole + garnet + clinozoisite/epidote + muscovite + quartz + titanite ± ilmenite ± rutile. Thermobarometric calculations, were performed in the system CaO-FeO-MgO-Na2O-Al2O3-FeO-SiO2-H2O with the assemblage clinopyroxene + garnet + amphibole + clinozoisite/epidote + muscovite + quartz ± H2O. The calculations involved an H2O-absent invariant point (mode-1 calculation) as well as two types of average P-T mode-2 calculations. The obtained average P-T H2O-absent mode 1 P-T conditions are 1.89 ± 0.18 GPa and 578 ± 60°C. Using the average P-T mode-2 two types of calculations were done: (1) calculations without amphiboles but with H2O present, which yield mean P-T conditions of 1.95 ± 0.28 GPa and 601 ± 55°C and (2) calculations with amphiboles but without H2O, which yield mean P-T conditions of 1.95 ± 0.26 GPa and 666 ± 77°C. Calculations using THERMOCALC v.3.33 yield similar results with slightly higher pressures of 0.3 GPa. Based on the present geothermobarometric data in conjunction with available mineral ages the eclogites represent the Eoalpine intracontinental subduction stage whereas the amphibolites reflect the subsequent, P-accentuated stage of decompression associated with the subsequent Eoalpine collisional stage.

Surgical Aspects of Treatment of Hilar Cholangiocarcinoma

Introduction. Treatment of hilar cholangiocarcinoma remains one of the most complicated issues of surgical hepatology. As known, hilar cholangiocarcinoma is resistant to chemotherapy and radiation therapy, and only a surgical option is an effective way to improve patient survival.The aim of the study was to improve clinical outcomes of patients with cholangiocarcinoma by evaluating the efficiency of various options for resection and reconstructive and restorative stages of surgical treatment.Methods. The study involved clinical findings and outcomes of 68 patients with hilar cholangiocarcinoma. Biliary decompression was performed in 61 (89.7%) cases. Radical surgical interventions were performed in 35 (51.4%) cases, and palliative surgical interventions were performed in 33 (48.6%) cases.Results. Specific complications at the stage of biliary decompression were noted in 4 (6.5%) cases, inadequate drainage of the biliary tract occurred in 5 (8.2%) cases. The syndrome of "rapid decompression of the biliary tract" was recorded in 14 (23.0%) cases, cholangitis - in 12 (19.7%). Intraoperative complications were noted in 2 (15.3%) cases, postoperative - in 6 (17.1%) cases. Mortality rate was 8.5%. In the long-term period, stenosis of the biliodigistic anastomosis was recorded in 11.4% of cases, tumor recurrence occurred in 28.6% of cases. The five-year survival rate was 17.0%.Conclusion. Resection of the bile ducts combined with hemihepatectomy is an operation accompanied by high risks, especially at the height of jaundice and in the elderly patients. Performing a sparing hiatal resection of the liver and bile ducts provides an acceptable survival rate. The proposed method to form a biliodigistic anastomosis is effective in terms of preventing insolvency and stenosis of the anastomosis.