Entrapment Conditions Research Articles

Experimental constraints on the nature of multiphase solid inclusions and their bearing on mantle wedge metasomatism, Bohemian Massif

This study tests experimentally the hypothesis that calculated bulk compositions of multiphase solid inclusions present in minerals of ultrahigh pressure rocks, can be equated to the composition of the former trapped fluids. We investigated samples from the ultrahigh pressure garnet peridotites of the Bohemian Massif, spatially associated with ultrahigh pressure crustal rocks and representing a former subduction interface environment. Inclusions present in garnets, composed of amphibole + Ba-mica kinoshitalite + carbonates (dolomite + magnesite + norsethite), were taken to their entrapment conditions of c. 4.5 GPa and 1075 ºC. They (re)crystallized into a garnet fringe at the boundary between inclusion and host garnet, kinoshitalite ± olivine, carbonatite melt, and a hydrous fluid. Although the latter may have exsolved from the carbonatite melt upon quenching, microstructures suggest it was present at trapped conditions, and mass balance indicates that it corresponds to a Na-K-Cl-F-rich saline aqueous fluid (brine). Experiments demonstrate the stability of kinoshitalite at 4.5 GPa and 1075 ºC, and suggest that Ba-rich mica + carbonatite melt + brine coexisted at near-peak conditions. Barium is compatible in the carbonatite melt and mica with respect to the brine, with a partition coefficient between carbonatite melt and mica of ≈ 2.5–3. The garnet fringe formed from incongruent reaction of the former inclusion assemblage due to reversing the fluid(s)-host garnet reaction that occurred upon natural cooling/decompression. Loss of H2 or H2O from the inclusions due to volume diffusion through garnet and/or decrepitation, during geological timeframes upon decompression/cooling, may have prevented rehomogenization to a single homogeneous fluid. Our study shows that great care is needed in the interpretation of multiphase solid inclusions present in ultrahigh pressure rocks.

Trends and impact of comorbidities on Guyon's Canal release for the treatment of Guyon's Canal syndrome: A decade long nationwide analysis

BackgroundGuyon's Canal Syndrome (GCS) is a rare nerve entrapment condition with limited studies exploring the trends of GCS patients undergoing Guyon's Canal release. The aim of this study is to examine the trends associated with GCS: (1) Guyon's Canal release procedures performed; (2) surgically relevant comorbidities; (3) 90-day readmissions; and (4) same-day and 90-day reimbursement. MethodsA retrospective query was performed on the PearlDiver Mariner Database from 2010 to 2020 by CPT code 64719 to identify patients who underwent Guyon's Canal release. A total of 33,3764 patients were identified. Linear regression models were used to analyze trends in procedures performed, comorbidities, readmission, and reimbursement over this period. A P-value less than 0.05 was considered statistically significant. ResultsBetween 2010 and 2020, there was an overall significant decreasing trend in the number of Guyon's Canal release procedures performed (RC, −127.50; p < 0.001). There was an increase in number of GCS patients that had undergone Guyon's Canal release who drink alcohol (RC, 0.33; p < 0.001), are obese (RC, 0.81; p < 0.001), and use tobacco (RC, 0.56; p < 0.004), and decrease number of GCS patients with a history of diabetes (RC, −0.82; p < 0.001), hypothyroidism (RC, −0.56; p < 0.001), PVD (RC, −0.71; p < 0.001), and RA (RC, −0.33; p < 0.001). We also found an overall increasing trend in 90-day readmissions (RC, 0.09; p = 0.019) and increased same-day (RC, 68.09; p < 0.001) and 90-day average reimbursement (RC, 257.15; p < 0.001) from 2010 to 2020. ConclusionThe study demonstrated a decreasing trend in Guyon's Canal release performed in GCS patients but increasing cost of care implicated by the increased 90-day readmissions and same day and 90-day reimbursement. This may be attributed to the comorbidities present in GCS patients undergoing Guyon's Canal release. Therefore, it is imperative when consulting GCS patients with surgically relevant comorbidities to weigh the risk and benefits of the procedure.

A brief history of solid inclusion piezobarometry

Abstract. Solid inclusion piezobarometry is the determination of the entrapment conditions of solid inclusions in a host by measurement and interpretation of the residual pressure of the inclusion. The development over the past two centuries of the concepts, analytical tools and measurement techniques of inclusion piezobarometry is reviewed, and potential future developments are outlined for the special issue of the European Journal of Mineralogy devoted to the study of mineral and melt inclusions.

Thermoelastic Properties of Fe3+‐Rich Jeffbenite and Application to Superdeep Diamond Barometry

AbstractJeffbenite (Mg3Al2Si3O12) is a tetragonal phase found in so far only in superdeep diamonds, and its thermoelastic parameters are a prerequisite for determining entrapment pressures as it is regarded as a potential indicator for superdeep diamonds. In this study, the thermoelastic properties of synthetic Fe3+‐jeffbenite were measured up to 33.7 GPa and 750 K. High‐temperature static compression data were fitted, giving (∂KT0/∂T)P = −0.0107 (4) GPa/K and αT = 3.50 (3) × 10−5 K−1. The thermoelastic properties and phase stability are applied to modeling isomekes, or P‐T paths intersecting possible conditions of entrapment in diamond. We calculate that under ideal exhumation, jeffbenite entrapped at mantle transition zone conditions will exhibit a high remnant pressure at 300 K (Pinc) of ∼5.0 GPa. Elastic geobarometry on future finds of jeffbenite inclusions can use the new equation of state to estimate entrapment pressures for this phase with still highly uncertain stability field in the mantle.

Enzyme Entrapment and Cross-Linking of Psychrophilic Lipase from Serratia marcescens VT 1

Immobilization has gained importance in industrial biotechnology as an efficient approach for modifying the characters ensuring the reusability of biocatalysts. The current study focuses on the potential application of entrapment and crosslinking techniques to immobilize the lipase from Serratia marcescens VT 1 (SMVT 1). Purified SMVT 1 lipase was immobilized by entrapment onto calcium alginate beads and cross-linking with glutaraldehyde. The effect of different factors affecting entrapment and cross-linking was determined. Further, the immobilized lipase was subjected to characterization and reusability studies. The calcium alginate entrapment and glutaraldehyde cross-linking resulted in an immobilization yield of 65.72% and 77.19% respectively. Optimal conditions for entrapment were 3% sodium alginate, 3 M calcium chloride (CaCl2), and an immobilization time of 45 min, while, for cross-linking it was 0.4% glutaraldehyde and a cross-linking time of 45 min. Characterization and reusability studies highlighted cross-linking as superior with enhanced activity and stability at higher temperatures, a shift in optimum pH to 8, good stability in basic pH, and 58.5% residual activity after eight cycles of reactions. Fourier transform infrared spectroscopy analysis provided insights into the bond formations during calcium alginate entrapment and glutaraldehyde cross-linking. Cross-linking was identified as an ideal mode of immobilization for SMVT 1 lipase

Exploring the potential of immobilized phytase to enhance phosphorus uptake by Catharanthus roseus

The current study was designed to establish stable phytases, using poly-(acrylamide-co-acrylic acid) hydrogels as an entrapment matrix, for their application in the promotion of plant growth. Different production parameters were optimized to gain the maximum enzyme yield of 14.3 ± 0.41 U/g and a protein content of 0.7 ± 0.03 mg/ml from Rhizopus oligosporus under solid-state fermentation. For plants, phytase is a source of phosphorus, an essential nutrient for their growth. The study outlined the standardized conditions for the physical entrapment of phytase within polyhydrogel as; 1.5 ml APS, 0.25 ml enzyme, and a 12-minute procurement period. Moreover, the optimal temperature and pH for the partially purified immobilized enzyme were recorded as 50 ºC and 7.5, respectively, under the optimized conditions. The immobilized enzyme has shown enhanced stability over the free enzyme at 70 °C and a wide pH range. During the study, the maximum enzyme activity achieved by partially purified free and immobilized phytase was 7.65 ± 0.43 and 9.12 ± 0.28 U/g. Furthermore, the characterization of the poly-hydrogel revealed that it contains a rough and porous 3-D structure, with abundant cross-linking channels. In a pot experiment, phytase-entrapped poly-(acrylamide-co-acrylic acid) hydrogel was applied to the soil and displayed a positive impact upon different growth parameters as well as phosphorus content of the C. roseus than free enzyme and control groups. The phosphorus-status of the soil having entrapped phytase, increased up to 1.69 and 2.17-fold compared to the plants of free enzyme and control. The study has shown that immobilized phytase was effective to deliver phytate-P to Catharanthus roseus as it significantly increased its rate of photosynthesis (25.9 ± 1.4 µ mol m−2s−1), shoot length (36.1 ± 1.3 cm), and leaf chlorophyll content (56.7 ± 2.8) as compared to the other experimental groups. Overall, the work declares the considerable potential of phytases in phosphorus uptake and plant growth-promoting activities.

Elasticity of mixtures and implications for piezobarometry of mixed-phase inclusions

Abstract. Elastic thermobarometry (or piezobarometry) is the process of determining the P (pressure) and T (temperature) of entrapment of inclusions from their pressure, stress or strain measured when their host mineral is at room conditions. The methods and software used for piezobarometry are currently restricted to inclusions consisting of single phases. In this contribution we describe the theory of the elasticity of mixtures of different phases and combine it with the existing isotropic analysis of the elastic interactions between single-phase inclusions and their hosts to calculate the inclusion pressures of mixed-phase inclusions. The analysis shows that the reliability of calculated entrapment conditions for mixed-phase inclusions, including those containing fluid plus minerals, depends in a complex way upon the contrasts between the elastic properties of the host and the phases in the inclusion. The methods to calculate the entrapment conditions of mixed-phase inclusions have been incorporated into the EosFit7c program (version 7.6) that is available as freeware from http://www.rossangel.net.

High-temperature behavior of quartz-in-garnet system revealed by in situ Raman spectroscopy

Quartz is one of the most abundant minerals in the Earth crust and therefore quartz inclusions in garnet are of great interest for elastic geobarometry, an approach that exploits the elastic properties of the mineral pair to back-calculate the conditions of inclusion entrapment. However, the high-temperature behavior of quartz inclusions close to the alpha–beta transition boundary has not been studied experimentally. We have therefore performed in situ high-temperature Raman spectroscopy on a quartz-in-garnet system up to 1000 K, and have also collected an improved reference data set for the temperature dependence of the Raman scattering of free quartz. Our results show that the alpha-to-beta phase transition is hindered by the stress imposed by the host on the quartz inclusion, resulting in a thermosalient effect of the whole host-inclusion system or a mechanical cracking of the host mineral.

Estimation of P-T entrapment conditions of a subduction fluid using elastic thermobarometry: A case study from Cabo Ortegal Complex, Spain

Estimation of P-T entrapment conditions of a subduction fluid using elastic thermobarometry: A case study from Cabo Ortegal Complex, Spain

Quartz-in-garnet (QuiG) under pressure: insights from in situ Raman spectroscopy

Elastic geothermobarometry relies on the contrast between the thermal expansion and compressibility of a mineral inclusion and its surrounding host, leading to a residual pressure in the inclusion (Pinc) that may differ significantly from the external pressure. Quartz-in-garnet (QuiG) inclusion-host systems are widely used in elastic geothermobarometry to estimate the inclusion entrapment conditions and thus the rock petrogenesis. To elucidate the behaviour of QuiG at elevated pressures, we have applied in situ high-pressure Raman spectroscopy on three QuiG samples having Pinc close to 0 GPa at room temperature. We demonstrate that upon pressure increase, the garnet host acts as a shield to the softer quartz inclusion. Consequently, the Pinc increases with a smaller rate compared to that of the external pressure. Up to 2.5 GPa, the evolution of Pinc calculated from the Raman data agrees very well with prediction from the equations of state. Furthermore, the behaviour of a quartz inclusion in a relatively thin host specimen was explored up to external pressures of 7 GPa. Our results indicate that the shielding effect of the host (even if only partial because of the insufficient distance between the inclusion and the host surface) can keep the quartz inclusions thermodynamically stable up to about 2 GPa above the equilibrium quartz–coesite phase boundary. In addition, the partial shielding leads to the development of anisotropic symmetry-breaking stresses and quartz inclusions undergo a reversible crossover to a lower symmetry state. Given that the presence of non-hydrostatic stress may influence the quartz-to-coesite phase boundary, especially at elevated temperatures relevant for entrapment conditions, our results emphasize the importance of elastic anisotropy of QuiG systems, especially when quartz inclusion entrapment occurs under conditions close to the coesite stability field.

Elastic Thermobarometry

Upon exhumation and cooling, contrasting compressibilities and thermal expansivities induce differential strains (volume mismatches) between a host crystal and its inclusions. These strains can be quantified in situ using Raman spectroscopy or X-ray diffraction. Knowing equations of state and elastic properties of minerals, elastic thermobarometry inverts measured strains to calculate the pressure-temperature conditions under which the stress state was uniform in the host and inclusion. These are commonly interpreted to represent the conditions of inclusion entrapment. Modeling and experiments quantify corrections for inclusion shape, proximity to surfaces, and (most importantly) crystal-axis anisotropy, and they permit accurate application of the more common elastic thermobarometers. New research is exploring the conditions of crystal growth, reaction overstepping, and the magnitudes of differential stresses, as well as inelastic resetting of inclusion and host strain, and potential new thermobarometers for lower-symmetry minerals.▪A physics-based method is revolutionizing calculations of metamorphic pressures and temperatures.▪Inclusion shape, crystal anisotropy, and proximity to boundaries affect calculations but can be corrected for.▪New results are leading petrologists to reconsider pressure-temperature conditions, differential stresses, and thermodynamic equilibrium.

Relatively oxidized conditions for diamond formation at Udachnaya (Siberia)

Abstract. Thanks to the physical strength of diamonds and their relatively unreactive chemical nature, their mineral inclusions may remain exceptionally preserved from alteration processes and chemical exchanges with surrounding minerals, fluids and/or melts following diamond formation. Cr-bearing spinels are relatively common inclusions found in peridotitic diamonds and important oxybarometers providing information about the oxygen fugacity (fO2) of their source mantle rocks. Here, we investigated a magnesiochromite–olivine touching pair in a diamond from the Udachnaya kimberlite (Siberia) by in situ single-crystal X-ray diffraction and energy-domain synchrotron Mössbauer spectroscopy, aiming to constrain the physical–chemical conditions of diamond formation and to explore the redox state of this portion of the Siberian craton when the diamond was formed. The P–T–fO2 entrapment conditions of the inclusion pair, determined by thermo- and oxybarometric analyses, are ∼ 5.7(0.4) GPa and ∼ 1015(50) ∘C (although entrapment at higher T and re-equilibration during subsequent mantle storage are also possible) and fO2 near the enstatite–magnesite–olivine–diamond (EMOD) buffer. The determined fO2 is similar to, or slightly more oxidized than, those of xenoliths from Udachnaya, but whilst the xenoliths last equilibrated with the surrounding mantle just prior to their entrainment in the kimberlite at ∼ 360 Ma, the last equilibration of the inclusion pair is much older, occurring at 3.5–3.1, ∼ 2 or ∼ 1.8 Ga before final encapsulation in its host diamond. Hence, the similarity between xenoliths and inclusion fO2 values indicates that the modern redox state of this portion of the Siberian lithosphere was likely attained relatively early after its formation and may have persisted for billions of years after diamond formation, at least at the local scale. Moreover, the oxygen fugacity determination for the inclusion pair provides direct evidence of diamond formation near the EMOD buffer and is consistent with recent models suggesting relatively oxidized, water-rich CHO fluids as the most likely parents for lithospheric diamonds.

Resetting of zircon inclusions in garnet: Implications for elastic thermobarometry

Abstract Elastic thermobarometry of host-inclusion systems for back-calculating pressure (P) and temperature (T) conditions of inclusion entrapment relies on the assumption that the hostinclusion rheology is purely elastic. In this study, we have explored both the elastic and non-elastic behavior of zircon-in-garnet (ZiG) systems by in situ Raman spectroscopy at high T and ambient P. We show that upon heating, plastic relaxation takes place immediately after the zircon inclusions experience tensile stress conditions with respect to a free crystal at the same T. On subsequent cooling, the inclusions develop a new stress state, and thus the inclusion pressures have been reset from those corresponding to their original entrapment. Resetting of inclusion pressures therefore strongly depends on the exhumation P-T path. This explains why elastic thermobarometry using ZiG systems is reliable when applied to low-P high-T rocks where the cooling path after inclusion entrapment passes quickly into the compression domain of the inclusion. On the other hand, high-P rocks exhumed along quasi-isothermal paths take zircon inclusions into the tensile domain where they are reset until significant cooling commences at low P. ZiG systems in ultrahigh-P rocks therefore commonly indicate pressures on clockwise exhumation paths instead of the conditions of original entrapment.

Lubrication, Flow Visualization, and Multiphase CFD Modeling of Ball Bearing Cage

The objective of this study was to experimentally and analytically investigate the lubrication condition and visualize the fluid flow in a ball bearing cage under various operating conditions. To achieve the experimental aspects of this investigation, a test apparatus incorporating a transparent cage was designed and developed. The transparent cage was manufactured based on the original geometry of the bearing cage. The transparent cage was positioned in the test rig relative to the ball using a precision XYZ table. This allowed for critical observation and examination of air and oil entrapment conditions within the cage. A high-speed camera was utilized to capture the fluid flow and air distribution inside the cage. To address the analytical aspects of this study, Ansys Fluent computational fluid dynamics (CFD) software was used to develop a multiphase lubrication model simulating the same conditions as the test apparatus. Lubricant and air distribution within the cage were investigated for various operating speeds and cage positions relative to the ball. Results from the experimental and analytical studies were corroborated and found to be in good agreement. The results demonstrate that as the cage was moved closer to the ball, lubrication conditions changed and fluid striated over the ball surface, resulting in greater air entrapment within the cage. The CFD model predicted similar trends and results. Increasing ball speed promoted starvation of lubricant supply to the cage. The CFD model confirmed that lubricant surface tension plays a key role in the striation patterns over the ball surface.

The role of symmetry-breaking strains on quartz inclusions in anisotropic hosts: Implications for Raman elastic geobarometry

Raman elastic geobarometry for mineral host-inclusion systems is used to determine the strains acting on an inclusion still entrapped in its host by measuring its Raman wavenumber shifts which are interpreted through the phonon-mode Grüneisen tensors of the inclusion phase. The calculated inclusion strains can then be used in an elastic model to calculate the pressure and temperature conditions of entrapment. This method is applied frequently to host inclusion systems where the host is almost elastically isotropic (e.g. garnet) and the inclusion is elastically anisotropic (e.g. quartz and zircon). In this case, when the entrapment occurs under hydrostatic conditions the host will impose isotropic strains on the inclusion which in turn will develop non-hydrostatic stress. In this scenario the symmetry of the inclusion mineral is preserved and the strains in the inclusion can be measured via Raman spectroscopy using the phonon-mode Grüneisen tensor approach. However, a more complex situation arises when the host-inclusion system is fully anisotropic, such as when a quartz inclusion is entrapped within a zircon host, because the symmetry of the inclusion can be broken due to the external anisotropic strain field imposed on the inclusion by the host, which in turn will modify the phonon modes. We therefore calculated the strain states of quartz inclusions entrapped in zircon hosts in multiple orientations and at various geologically relevant pressure and temperature conditions. We then performed ab initio Hartree-Fock/Density Functional Theory (HF/DFT) simulations on α-quartz in these strain states. These HF/DFT simulations show that the changes in the positions of the Raman modes produced by strains that are expected for symmetry broken quartz inclusions in zircon are generally similar to those that would be seen if the quartz inclusions remained truly trigonal in symmetry. Therefore, the use of the trigonal phonon-mode Grüneisen tensor to determine the inclusion strains does not lead to geologically significant errors in calculated quartz inclusion entrapment pressures in zircon. • Mineral inclusions in anisotropic hosts can be subject to symmetry-breaking strains. • Symmetry-breaking strains modify the Raman spectrum of quartz. • Applicability of the trigonal Grüneisen tensor to symmetry-broken quartz is tested. • Entrapment pressures from the isotropic elastic model are in error by <0.185 GPa. • Entrapment pressures from the anisotropic elastic model are in error by <0.034 GPa.

Garnet EoS: a critical review and synthesis

All available volume and elasticity data for the garnet end-members grossular, pyrope, almandine and spessartine have been re-evaluated for both internal consistency and for consistency with experimentally measured heat capacities. The consistent data were then used to determine the parameters of third-order Birch–Murnaghan EoS to describe the isothermal compression at 298 K and a Mie–Grüneisen–Debye thermal-pressure EoS to describe the PVT behaviour. In a full Mie–Grüneisen–Debye EoS, the variation of the thermal Grüneisen parameter with volume is defined as gamma = {gamma }_{0}{left(frac{V}{{V}_{0}}right)}^{q}. For grossular and pyrope garnets, there is sufficient data to refine q which has a value of q = 0.8(2) for both garnets. For other garnets, the data do not constrain the value of q and we therefore refined a q-compromise version of the Mie–Grüneisen–Debye EoS in which both γ/V and the Debye temperature θ D are held constant at all P and T, leading to left( {{raise0.7exhbox{{partial C_{{text{V}}} }} !mathord{left/ {vphantom {{partial C_{{text{V}}} } {partial P}}}right.kern-nulldelimiterspace} !lower0.7exhbox{{partial P}}}} right)_{{text{T}}} = 0, parallel isochors and constant isothermal bulk modulus along an isochor. Final refined parameters for the q-compromise Mie–Grüneisen–Debye EoS are: PyropeAlmandineSpessartineGrossularV0 (cm3/mol)a113.13115.25117.92125.35K0T (GPa)169.3 (3)174.6 (4)177.57 (6)167.0 (2)K^{prime}_{{0{text{T}}}}4.55 (5)5.41 (13)4.6 (3)5.07 (8)θ D0771 (28)862 (22)860 (35)750 (13)γ01.185 (12)1.16 (fixed)1.18 (3)1.156 (6)for pyrope and grossular, the two versions of the Mie–Grüneisen–Debye EoS predict indistinguishable properties over the metamorphic pressure and temperature range, and the same properties as the EoS based on experimental heat capacities. The biggest change from previously published EoS is for almandine for which the new EoS predicts geologically reasonable entrapment conditions for zircon inclusions in almandine-rich garnets.

Impact of superhydrophobic sphere onto a pool covered by oil layer

We experimentally investigate the impact of a millimetric superhydrophobic sphere on a water pool covered by a thin oil layer, with the aim of seeking the critical conditions for sphere entrapment at the interfaces. The interfacial tension and viscosity of the thin oil layer are found to have a significant effect on the fate of the impacting spheres that are denser than the liquids: sinking or floating. For the oil layer of low viscosity, the impact dynamic is dominated by the capillary force, and the sphere experiences more or less uniform acceleration after the impact, which is similar to a sphere impacting onto a pure water pool. For the oil layer of relatively high viscosity, the viscous dissipation inside the thin oil layer greatly hinders the descending of the sphere, and thus, it is the viscosity of the oil layer that dictates the acceleration process of the spheres at the early stage of impact. At the late stage, the sphere moves very slowly under water (particularly at the onset of sinking), and the competition between the oil–water interfacial tension and buoyancy determines whether the sphere would eventually sink or float. We then conduct the theoretical analysis of the dynamic processes of the impacting sphere and give the theoretical predictions of the respective critical conditions, which agree well with the experimental observations.

Early carbonatite magmatism at Oldoinyo Lengai volcano (Tanzania): carbonatite–silicate melt immiscibility in Lengai I melt inclusions

Carbonatites are unusual C-rich alkaline magmas that have been reported throughout the geological record. Nevertheless, there is only one currently active carbonatite system on Earth: Oldoinyo Lengai stratovolcano in northern Tanzania (God’s mountain in Maasai culture). Present-day Lengai carbonatites are natrocarbonatites, peculiar Na-rich carbonatites that, under atmospheric conditions, alter and leach to compositions similar to the more common Ca-carbonatites within weeks, preventing any long-term geological record of such Na-rich magmas. It follows that the oldest report of natrocarbonatites at Oldoinyo Lengai dates to the 19th century. Here, by using samples from the Lengai I cone (>11 ka), we show that immiscible silicate–carbonatite melts were already present at reservoir conditions at that time. Measurements of three-phase (carbonatite + silicate + gas) melt inclusions from Lengai I highlight that their chemical compositions were similar to those of immiscible melts recently present in the reservoir. Alkaline carbonatites in melt inclusions from both Lengai I and historical explosive eruptions are enriched in Ca relative to those historically effused at the surface and likely record higher equilibrium temperatures (>1100 °C). We also report chemical maps that qualitatively document elemental partitioning between immiscible silicate–carbonatite melts. We show that at the melt inclusions’ entrapment conditions Si, Fe, K, Na, and Cl are compatible with the silicate phase when C, Ca, P, Sr, Ba, and F are compatible with the carbonate phase.

Estimation of P-T Entrapment Conditions of a Subduction Fluid Using Elastic Thermobarometry: A Case Study from Cabo Ortegal Complex, Spain

Estimation of P-T Entrapment Conditions of a Subduction Fluid Using Elastic Thermobarometry: A Case Study from Cabo Ortegal Complex, Spain

Entrapment history of aqueous fluids in Archean cherts from the Barberton Greenstone Belt, South Africa

We performed fluid inclusion microthermometric analyses of four cherts and one silicified anhydrite from various successions of the Mesoarchean Barberton Greenstone Belt, South Africa, and constrained the entrapment conditions and provenance of fluids that were incorporated during different magmatic or tectono-thermal events. Major saline aqueous fluid inclusion assemblages in cherts from the 3.2 Ga old Mendon Formation (Barite Valley Syncline, Power Line Road) and from the 3.42–3.45 Ga old uppermost Hooggenoeg Formation (Buck Reef Chert) correspond to fluids incorporated during metamorphism. Their documented P-T conditions compare well with reported petrologic constraints. In Buck Reef chert we also found a distinctive suite of inclusions with high salinities and low homogenization temperatures (61–118 °C). This is in agreement with a hydrothermal formation of these fluids at subseafloor conditions. Finally, we investigated quartz in a silicified anhydrite and its sandstone host from the Stolzburg Syncline (Moodies Group, ca. 3.2 Ga). One major inclusion assemblage in the evaporite and in adjacent quartz within the embedding sandstone share the P-T range observed for the cherts from the Mendon Fm. Its incorporation is postdating the silicification process. We also found two higher temperature inclusion types that favor a magmatic origin. In particular, one of these inclusion suites is only observed in quartz within the matrix and likely mirrors trapping of brines associated with magmatic fluids predating sedimentation of the sandstone, e.g., from the potential magmatic source region of the quartz. Our results indicate the presence of coexisting aqueous fluids in cherts derived from distinct source environments, spanning an age range of several 100 Ma on a grain scale. The earliest hydrothermal aqueous inclusions were documented in a Buck Reef chert (3.42–3.45 Ga), whereas the majority of aqueous fluids are metamorphic in origin and likely related to the documented 3.23 Ga and 3.1 Ga tectono-thermal events. Our findings demonstrate that constraining environmental conditions by the volatile record of Archean cherts requires analyses on inclusion, not grain scale.