Exsolutions of Diopside and Magnetite in Olivine from Mantle Dunite,Luobusa Ophiolite,Tibet,China

The exsolutious of diopside and magnetite occur as intergrowth and orient within olivine from the mantle dunite, Luobusa ophiolite, Tibet. The dunite is very fresh with a mineral assemblage of olivine （〉95%） ＋ chromite （1%-4%） ＋ diopside （〈1%）. Two types of olivine are found in thin sections： one （Fo = 94） is coarse-grained, elongated with development of kink bands, wavy extinction and irregular margins; and the other （Fo = 96） is fine-grained and poly-angied. Some of the olivine grains contain minor Ca, Cr and Ni. Besides the exsolutions in olivine, three micron-size inclusions are also discovered. Analyzed through energy dispersive system （EDS） with unitary analytical method, the average compositions of the inclusions are： Na20, 3.12%-3.84%; MgO, 19.51%-23.79%; Al2O3, 9.33%-11.31%; SiO2, 44.89%-46.29%; CaO, 11.46%-12.90%; Cr2O3, 0.74%-2.29%; FeO, 4.26%- 5.27%, which is quite similar to those of amphibole. Diopside is anhedral f＇dling between olivines, or as micro-inclusions oriented in olivines. Chromite appears euhedral distributed between olivines, sometimes with apparent compositional zone. From core to rim of the chromite, Fe content increases and Cr decreases; and A! and Mg drop greatly on the rim. There is always incomplete magnetite zone around the chromite. Compared with the nodular chromite in the same section, the euhedral chromite has higher Fe3O4 and lower MgCr2O4 and MgAI2O4 end member contents, which means it formed under higher oxygen fugacity environment. With a geothermometer estimation, the equilibrium crystalline temperature is 820℃-960℃ for olivine and nodular chromite, 630℃-770℃ for olivine and euhedral chromite, and 350℃-550℃ for olivine and exsoluted magnetite, showing that the exsolutions occurred late at low temperature. Thus we propose that previously depleted mantle harzburgite reacted with the melt containing Na, Al and Ca, and produced an olivine solid solution added with Na^＋, Al^3＋, Ca^2＋, Fe^3＋, Cr^3＋. With temperature decreasing, the olivine solid solution decomposed; and Fe^3＋, Cr^3＋ diffused into magnetite and Ca^2＋ and Na^＋ into clinopyroxene, both of which formed intergrowth textures. A few Fe^3＋ and Cr^3＋ entered interstitial chromite. Through later tectonism, the peridotite recrystallized and formed deformational coarse grained olivine, fine grained and poly-angled olivine, and euhedral grained chromite. Due to the fast cooling rate of the rock or rapid tectonic emplacement, the exsolution textures in olivine and compositional zones of chromite are preserved.

Enhancing layered perovskite ferrites with ultra-high-density nanoparticles via cobalt doping for ceramic fuel cell anode

Nanoparticles anchored on the perovskite surface have gained considerable attention for their wide-ranging applications in heterogeneous catalysis and energy conversion due to their robust and integrated structural configuration.Herein,we employ controlled Co doping to effectively enhance the nanoparticle exsolution process in layered perovskite ferrites materials.CoFe alloy nanoparticles with ultra-high-density are exsolved on the(PrBa)_(0.95)(Fe_(0.8)Co_(0.1)Nb_(0.1))2O_(5+δ)(PBFCN_(0.1))surface under reducing atmosphere,providing significant amounts of reaction sites and good durability for hydrocarbon catalysis.Under a reducing atmosphere,cobalt facilitates the reduction of iron cations within PBFCN_(0.1),leading to the formation of CoFe alloy nanoparticles.This formation is accompanied by a cation exchange process,wherein,with the increase in temperature,partial cobalt ions are substituted by iron.Meanwhile,Co doping significantly enhance the electrical conductivity due to the stronger covalency of the Cosingle bondO bond compared with Fesingle bondO bond.A single cell with the configuration of PBFCN_(0.1)-Sm_(0.2)Ce_(0.8)O_(1.9)(SDC)|SDC|Ba_(0.5)Sr_(0.5)Co_(0.8)Fe_(0.2)O_(3−δ)(BSCF)-SDC achieves an extremely low polarization resistance of 0.0163Ωcm^(2)and a high peak power density of 740 mW cm^(−2)at 800℃.The cell also shows stable operation for 120 h in H_(2)with a constant current density of 285 mA cm^(−2).Furthermore,employing wet C_(2)H_(6)as fuel,the cell demonstrates remarkable performance,achieving peak power densities of 455 mW cm^(−2)at 800℃and 320 mW cm^(−2)at 750℃,marking improvements of 36%and 70%over the cell with(PrBa)_(0.95)(Fe_(0.9)Nb_(0.1))_(2)O_(5+δ)(PBFN)-SDC at these respective temperatures.This discovery emphasizes how temperature influences alloy nanoparticles exsolution within doped layered perovskite ferrites materials,paving the way for the development of high-performance ceramic fuel cell anodes.

Nanoparticle Exsolution on Perovskite Oxides:Insights into Mechanism,Characteristics and Novel Strategies

Supported nanoparticles have attracted considerable attention as a promising catalyst for achieving unique properties in numerous applications,including fuel cells,chemical conversion,and batteries.Nanocatalysts demonstrate high activity by expanding the number of active sites,but they also intensify deactivation issues,such as agglomeration and poisoning,simultaneously.Exsolution for bottomup synthesis of supported nanoparticles has emerged as a breakthrough technique to overcome limitations associated with conventional nanomaterials.Nanoparticles are uniformly exsolved from perovskite oxide supports and socketed into the oxide support by a one-step reduction process.Their uniformity and stability,resulting from the socketed structure,play a crucial role in the development of novel nanocatalysts.Recently,tremendous research efforts have been dedicated to further controlling exsolution particles.To effectively address exsolution at a more precise level,understanding the underlying mechanism is essential.This review presents a comprehensive overview of the exsolution mechanism,with a focus on its driving force,processes,properties,and synergetic strategies,as well as new pathways for optimizing nanocatalysts in diverse applications.

Quartz and clinoenstatite exsolutions in clinopyroxene of garnet-pyroxenolite from the North Dabie Mountains,eastern China

The exsolution lamellae of quartz and clinoen-statite are idenfied in diopside of garnet-pyroxenolite from the North Dabie Mountain by transmission electron microscopy, which is interpreted that the lamellae are originally exsolved from a former ultra-high-pressure clinopyroxene due to decreasing of pressure. Study of petrography shows that there is compositional zoning hi the diopside itself. It is implied that the garnet-pyroxenolite had undergone intensive high-temperature granulite fades and high-amphibolitic fades retrogressive metamorphism, while the peridotite (the garnet-pyroxenolite’s host rock) emplaced the

Exsolved materials for CO_(2)reduction in high-temperature electrolysis cells

Electrochemical reduction of CO_(2)into valuable fuels and chemicals has become a contemporary research area,where the heterogeneous catalyst plays a critical role.Metal nanoparticles supported on oxides performing as active sites of electrochemical reactions have been the focus of intensive investigation.Here,we review the CO_(2)reduction with active materials prepared by exsolution.The fundamental of exsolution was summarized in terms of mechanism and models,materials,and driven forces.The advances in the exsolved materials used in hightemperature CO_(2)electrolysis were catalogued into tailored interfaces,synergistic effects on alloy particles,phase transition,reversibility and electrochemical switching.

Petrogenetic characterization of the host rocks of the Sanaga iron ore prospect,southern Cameroon

The Sanaga iron ore prospect is a recent discovery in the Nyong Series with a resource estimated at 82.9 Mt at 32.1%Fe and whose origin remains debatable.The mineralization occurs as NE-SW oriented discontinuous lenticular bodies of magnetite-bearing pyroxenegneisses(MPG)hosted by ortho-derived gneisses.Rare amphibolites are observed.The MPG mineral assemblage consists of quartz-magnetite-orthopyroxene-garnet-tremolite/actinolite exhibiting a granoblastic texture,which is characteristic of granulite facies metamorphism.The granodioritic gneisses show compositional features of the tonalite-trondhjemite-granodiorite association.Their trace and REE element geochemistry indicate their protolith melt resulted from the partial melting of a subducted oceanic slab,with interaction with the overlying mantle wedge during ascent.The amphibolites show enrichment in LILE with negative Ta–Nb and Zr–Hf indicating arc-related magmas generated by partial melting of a sub-continental lithospheric mantle source with metasomatism by subduction-related fluids.The MPG exhibits oxidation-exsolution features characterized by ilmenite lamellae,with hematite fracture-fillinginmagnetite,andlacksfeatures characteristic of typical BIF such as LREE depletion relative to HREE,positive Eu,La,and Y anomalies.Based on the results of this study,we interpret the Sanaga MPG as a possible skarn-type mineralization formed by the metamorphism/metasomatism of a possible BIF protolith.The results of this study compare with similar magnetite-rich mineralization in the Sa o Francisco craton in northeastern Brazil and enhance the correlation of pre-drift reconstructions of the Sa o Francisco–Congo Cratons.

The solution and exsolution characteristics of natural gas components in water at high temperature and pressure and their geological meaning

The processes of solution in, and exsolution from, formation water influence the component content of natural gas by contrasting the relative contents of components before the natural gas dissolves in water and those after exsolving from water under different conditions of high temperatures and pressures. Compared with the composition of original natural gas, the relative content of methane and nitrogen increased after the natural gas dissolved in water. The increase of nitrogen content exceeds that of methane, but the content of ethane, propane, pentane etc reduced. At the same temperature and with pressure increasing the content of methane increased and that of heavier hydrocarbons reduced. At the same pressure the content of methane increased quickly from 90~C to 120~C, and the content of heavier hydrocarbons reduced. But at even higher temperatures, the increase of methane slowed down and the content of heavier hydrocarbons increased slightly. At the same temperature and different pressures, heavier hydrocarbons reduced much more with increasing carbon atom number, while with temperature increasing the content difference of heavier hydrocarbons reduced. Therefore, the influence of the solution and exsolution should be considered in the study of the migration and accumulation mechanism of natural gas.

Mineralogical Characteristics of Exsolved Spinel in the Panzhihua V-Ti Magnetite Deposit, Sichuan: Implications for the Mineralization Process

Spinel exsolution is widespread in titanomagnetite from the Fe-Ti oxide gabbro of the Panzhihua intrusion, Emeishan Large Igneous Province, SW China. However, little research has been conducted into the implications of patterns in the mineralogical characteristics of the spinel for spatial variation in the controls on the exsolution mechanism and, hence, the formation process of the ore deposit. This study selected the Lanjiahuoshan Ore Block in the Panzhihua V-Ti magnetite deposit to explore this issue, systematically studying exsolution textures in the titanomagnetite through petrographic observation and the integrated use of in-situ microanalysis. The results show that the exsolved spinel gradually becomes finer-grained and less abundant from the center to edge and the bottom to top of the ore bodies. Compositionally, there is an inverse correlation between the size of exsolved spinel grains and their Mg# value. In addition, there is compositional zonation in the spinel interiors, with a gradual increase in the Mg content and decrease in Fe content from the core to the rim. The analysis suggests that fractional crystallization of ferrotitanium magma with a high oxygen fugacity in a shallow magma chamber caused compositional differences in the primary magnetite solid solution in different parts of the Panzhihua intrusion. Additionally, the thermal evolution of the magnetite solid solution differed in different parts of orebody, bringing about variations in spinel development. Together, these effects resulted in spatial variation in the abundance, grain size, and morphology of spinel in different parts of the orebody and intrusion that follows an identifiable distribution law. Furthermore, the compositional zonation of exsolved spinels reflects the rapid growth of exsolution features in a high-temperature environment. Thus, the size, morphology, abundance, and composition of spinel exsolution features in titanomagnetite provide a valuable petrogenetic tool for estimating the maturity and formational environment of the deposit.

The Discovery of Phlogopite Exsolution Lamellae in Garnets of Eclogite Inclusions, Liaoning Province

In No. 50 kimberlite pipe of Fuxian County, Liaoning Province, an eclogite inclusion(nodule), which is extremely rare in kimberlites, was discovered and phlogopite exsolutionlamellae were found in garnets of the inclusion. Microscopic, TEM and energy spectral observa-tions and studies confirmed that these lamellae are phlogopite. They are colourless and acicularin section, generally 0.5-5μm in width and 10-100μm in length. Nevertheless, fine lamellae,0.05-0.1μm wide and 1-2μm long, are also well developed. Along [111] of the garnet, three setsof phlogopite lamellae show oriented arrangement approximately at angles of 60°-70°, indi-cating that these lamellae might be the product of exsolution from garnet as a result ofpressure-release when eclogite ascended from the relatively deep level to the relatively shallowlevel of the mantle. Tiny acicular exsolution minerals (or inclusions) are commonly found ingarnet and pyroxene in eclogite inclusions of kimberlites all over the world and it has been re-ported that the identified exsolution minerals include pyroxene and rutile. This is the first timethat phlogopite exsolution lamillae were found in eclogite inclusions in the world.

Raman Spectrum Study on Quartz Exsolution in Omphacite of Eclogite and Its Tectonic Significances

The studies on ultra microstructure characteristics of quartz exsolution in eclogite and coesite in UHP eclogite of several localities are done with the appliance of laser Raman spectroscopy and U stage. Research results show that the phase transformation of coesite quartz in garnet and/or omphacite is a continuous process. Topological relationship is present between quartz exsolution in omphacite and its host mineral which shows orientations of two long axes of quartz exsolution parallel to (100) and (-101) of omphacite. At present, some scholars suggest that the quartz exsolution in omphacite of eclogite is the evidence of UHP metamorphism. However, temperature and pressure condition and the exsolution mechanism of oriented needlelike quartz in omphacite still remain unclear. Therefore, further study should be enhanced on experimental research on exsolution mechanism of super silicate clinopyroxene, which could provide experimental quantitative constraint on quartz exsolution as UHP indicator.

Pressure and Temperature Conditions Recorded by the Beni-Bousera Ultramafic Body and the Overlying Lower-crustal Rocks(Rif,Morocco)

The Beni Bousera massif(Rifean belt,northern Morocco)is predominantly composed of spinel lherzolite with subordinate garnet pyroxenite and garnet peridotite layers.It formed an antiformal dome which was overlain by graphite-sillimanite-garnet gneisses(kinzigites)equilibrated at around 1 GPa and 750℃.Within these kinzigites,kyanite-bearing basic granulites record somewhat higher PT conditions of around 1.6-2.0 GPa and 760-820℃.Garnet clinopyroxenite(either graphite-bearing or graphi-

Iron isotope fractionation during fenitization:a case study of carbonatite dykes from Bayan Obo,Inner Mongolia,China

As a powerful tracer in high-temperature geochemistry,Fe isotopes have been studied for their behaviour during fl uid exsolution and evolution related to felsic magma system,but that for carbonatite magma system remains unknown.Here we study the Fe isotope fractionation behaviour during fenitization–processes that widely occur associated with carbonatite or alkaline intrusions.Nine fenite/carbonatite samples from carbonatite dykes at Bayan Obo area are analyzed for their Fe isotope compositions as well as elemental compositions.Combined with previous reported carbonatite δ^(56)Fe data,the results show that carbonatites range from-0.35‰to 0.28‰,with an average of-0.10‰in δ^(56)Fe values,while fenites range from-0.17‰to 0.30‰,with an average of 0.11‰in δ^(56)Fe values.This indicates that fenitizing fl uids exsolved from carbonatite melts are enriched in heavier Fe isotopes.Such a Fe isotope fractionation trend is diff erent from that for fl uid exsolution from felsic magmatism.δ^(56)Fe values in fenites are negatively correlated with indicators of fenitization intensity such as(Na+K),Ti,Ba,Th,Nb,U or Pb abundances,likely refl ecting that Fe isotopes fractionate during the evolution of the fenitizing fl uids.Thus,Fe isotopes are a valuable tool for tracing fl uid exsolution and evolution relevant to carbonatite magmatism and related metal mineralization.

Mineral Components, Texture, and Forming Conditions of Hydrothermal Chimney on the East Pacific Rise at 9°-10°N

To characterize the hydrothermal processes of East Pacific rise at 9°-10°N, sulfide mineral compositions, textural, and geochemical features of chimney ores were studied using ore microscope,scanning electron microscope, X-ray diffraction analysis, and electron microprobe techniques. Results show that there are three mineral assemblages for the hydrothermal chimney ores, namely：（i） anhydrite ＋ marcasite ＋ pyrite, （ii） pyrite ＋ sphalerite ＋ chalcopyrite, and （iii） chalcopyrite ＋ bornite ＋ digenite ＋ covellite. Mineral assemblages, zonational features, and geochemical characteristics of the ore minerals indicate that ore fluid temperature changed from low to high then to low with a maximum temperature up to 400 ℃. The chimney is a typical black smoker. The initial structure of the chimney was formed by the precipitation of anhydrites, and later the sulfides began to precipitate in the inner wall.

Silver Exsolution-Enhanced Electrical Properties of Lanthanum-Based Perovskites

The effect of silver(Ag)exsolution on the electrical conductivity of strontium-doped lanthanum manganite(La1-x-ySrxAgyMnO3-δ,LSAM)and ferrite(La1-x-ySrxAgyFeO3-δ,LSAF)perovskites was investigated.The single-phase Ag-doped materials formed at 800℃ using modified Pechini method and revealed thermal stability in oxidizing atmosphere up to sintering temperature of the materials at 1,200℃.The exsolution of the metallic Ag nanoparticles was performed at 420-500℃ in reducing atmosphere of 5%H2/N2.Scanning electron microcopy results exhibited the metallic Ag phase nanoparticles on the surface of the oxide backbone with a good contact of Ag to the surface of the perovskite after exsolution.The electrical conductivity of the materials was investigated in the temperature range of 50-900℃ in air and isothermally in 5%H2/N2 at 420 and 500℃ by means of four probe DC measurement method,and reached 80-230 S·cm^-1 for undoped and Ag-doped LSF and LSM.The electrical conductivity results showed improving conductivity in Ag-doped single-phase and Ag nanoparticle decorated perovskites after Ag exsolution.The results revealed the dependence of electrical conductivity on the atmosphere,temperature and Ag exsolution time.

The first observation of Ni nanoparticle exsolution from YSZ and its application for dry reforming of methane

Ni nanocatalysts produced through exsolution have shown strong resistance to particle sintering and carbon coking in a beneficial dry reforming of methane(DRM)reaction utilizing greenhouse gases such as CH_(4)and CO_(2).However,most of the existing oxide supports for exsolution have been limited to perovskite oxide,while studies on fluorite support have been rarely conducted due to the limited solubility despite its excellent redox stability.Here we demonstrate that 3 mol%Ni can be successfully dissolved into the yttria-stabilized zirconia(YSZ)lattice and be further exsolved to the surface in a reducing atmosphere.The YSZ decorated with exsolved Ni nanoparticles shows enhanced catalytic activity for DRM reaction compared to the conventional cermet type of bulk Ni-YSZ.Moreover,the catalytic activity is extremely stable for about 300 h without significant degradation.Overall results suggest that the YSZ-based fluorite structure can be utilized as one of the support oxides for exsolution.

Dynamic tracking of exsolved PdPt alloy/perovskite catalyst for efficient lean methane oxidation

Supported Pd based catalysts are considered as the efficient candidates for low-carbon alkane oxidation for their outstanding capability to break C-H bond. Whereas, the irreversible deactivation of Pd based catalysts was still frequently observed. Herein, we reinforced the extruded Pd nanoparticles with quantitive Pt to assemble the evenly distributed Pd Pt nanoalloy onto ferrite perovskite(Pd Pt-LCF) matrix with strengthened robustness of metal/oxide support interface. We further co-achieved the enhanced performance, anti-overoxidation as well as resistance of vapor-poisoning in durability measurement. The operando X-ray photoelectron spectroscopy(O-XPS) combined with various morphology characterizations confirms that the accumulation of surface deep-oxidation species of Pd^(4+) is the culprit for fast activity loss in exsolved Pd system, especially at high temperature of 400 ℃. Conversely, it could be completely suppressed by in-situ alloying Pd with equal amount of Pt, which helps maintain the metastable Pd^(2+)/Pd shell and metallic solid-solution core structure. The density function theory(DFT) calculations further buttress that the dissociation of C–H was facilitated on alloy/perovskite interface which is, on the contrary, resistant toward O–H bond cleavage, as compared to Pd/perovskite. Our work suggests that the modification of exsolved metal/oxide catalytic interface could further enrich the toolkit of heterogeneous catalyst design.

Femtosecond laser ultrafast photothermal exsolution

Exsolution,as an effective approach to constructing particle-decorated interfaces,is still challenging to yield interfacial films rather than isolated particles.Inspired by in vivo near-infrared laser photothermal therapy,using 3 mol%Y_(2)O_(3)stabilized tetragonal zirconia polycrystals(3Y-TZP)as host oxide matrix and iron-oxide(Fe3O4/γ-Fe_(2)O_(3)/α-Fe_(2)O_(3))materials as photothermal modulator and exsolution resource,femtosecond laser ultrafast exsolution approach is presented enabling to conquer this challenge.The key is to trigger photothermal annealing behavior via femtosecond laser ablation to initialize phase transition from monoclinic zirconia(m-ZrO_(2))to tetragonal zirconia(t-ZrO_(2))and induce t-ZrO_(2)columnar crystal growth.Fe-ions rapidly segregate along grain boundaries and diffuse towards the outmost surface,and become‘frozen’,highlighting the potential to use photothermal materials and ultrafast heating/quenching behaviors of femtosecond laser ablation for interfacial exsolution.Triggering interfacial iron-oxide coloring exsolution is composition and concentration dependent.Photothermal materials themselves and corresponding photothermal transition capacity play a crucial role,initializing at 2 wt%,3 wt%,and 5 wt%for Fe3O4/γ-Fe_(2)O_(3)/α-Fe_(2)O_(3)doped 3Y-TZP samples.Due to different photothermal effects,exsolution states of ablated 5 wt%Fe_(3)O_(4)/γ-Fe_(2)O_(3)/α-Fe_(2)O_(3)-doped 3Y-TZP samples are totally different,with whole coverage,exhaustion(ablated away)and partial exsolution(rich in the grain boundaries in subsurface),respectively.Femtosecond laser ultrafast photothermal exsolution is uniquely featured by up to now the deepest microscale(10μm from 5 wt%-Fe_(3)O_(4)-3Y-TZP sample)Fe-elemental deficient layer for exsolution and the whole coverage of exsolved materials rather than the formation of isolated exsolved particles by other methods.It is believed that this novel exsolution method may pave a good way to modulate interfacial properties for extensive applications in the fields of biology,optics/photonics,energy,catalysis,environment,etc.

Promoting catalysis activity with optimizable self-generated Co-Fe alloy nanoparticles for efficient CO_(2)electrolysis performance upgrade

Stable and flexible metal nanoparticles(NPs)with regeneration ability are critical for long-term operation of solid oxide electrolysis cells(SOECs).Herein,a novel perovskite electrode with stoichiometric Pr_(0.4)Sr_(0.6)Co_(0.125)Fe_(0.75)Mo_(0.125)O_(3)−δ(PSFCM)is synthesized and studied,which undergoes multiple redox cycles to validate its structural stability and NPs reversibility.The Co-Fe alloy has exsolved from the parent bulk under reducing atmosphere,and is capable of reincorporation into the parent oxide after re-oxidation treatment.During the redox process,we successfully manipulate the size and population density of the exsolved NPs,and find that the average particle size significantly reduces but the population density increases correspondingly.The electrode polarization resistance of the symmetric cell remains stable for 450 h,and even activates after the redox cycling,which may be attributed to the higher quantity and larger specific surface area of the regenerated Co-Fe alloy NPs.Moreover,the electrochemical performance towards carbon dioxide reduction reaction(CO_(2)RR)is evaluated,and the CO_(2)electrolyzer consisting of CoFe@PSCFM-Ce_(0.8)Sm_(0.2)O_(1.9)(SDC)dual-phase electrode exhibits an excellent current density of 1.42 A·cm^(−2)at 1.6 V,which reaches 1.7 times higher than 0.83 A·cm^(−2)for the pristine PSCFM electrode.Overall,with this flexible and reversible high-performance SOEC cathode material,new options and perspectives are provided for the efficient and durable CO_(2)electrolysis.

Ultrahigh pressure (>7 GPa) gneissic K-feldspar (-bearing) garnet clinopyroxenite in the Altyn Tagh, NW China: Evi- dence from clinopyroxene exsolution in garnet

The exsolution of clinopyroxene and rutile in coarse-grain garnet is found in the gneissic K-feldspar(-bearing) garnet clinopyroxenite from Yinggelisayi in the Altyn Tagh, NW China. The maximum content of the exsolved clinopyroxene in the garnet is up to >5% by volume. The reconstructed precursor garnet (Grt1) before exsolution has a maximum Si content of 3.061 per formula uint, being of supersilicic or majoritic garnet. The peak-stage metamorphic pressure of >7 GPa is estimated using the geobarometer for volume percentage of exsolved pyroxene in garnet and the Si-(Al+Cr) geobarometer for majoritic garnet, and the temperature of about 1000℃ using the ternary alkali-feldspar geothermometer and the experimental data of ilmen- ite-magnetite solid solution. The protoliths of the rocks are intra-plate basic and intermediate ig- neous rocks, of which the geochemical features indicate that they are probably the products of the evolution of basic magma deriving from the continental lithosphere mantle. The rocks are in outcrops associated with ultrahigh pressure garnet-bearing lherzolite and ultrahigh pressure garnet granitoid gneiss. All of these data suggest that the ultrahigh pressure metamorphic rocks in the Altyn Tagh are the products of deep-subduction of the continental crust, and such deep- subduction probably reaches to >200 km in depth. This may provide new evidence for further discussion of the dynamic mechanism of the formation and evolvement of the Altyn Tagh and the other collision orogenic belts in western China.

Pore-scale visualization on a depressurization-induced CO2 exsolution

The pore-scale behavior of the exsolved CO_2 phase during the depressurization process in CO_2 geological storage was investigated.The reservoir pressure decreases when the injection stops or when a leaking event or fluid extraction occurs.The exsolution characteristics of CO_2 affect the migration and fate of CO_2 in the storage site significantly.Here,a micromodel experimental system that can accommodate a large pressure variation provides a physical model with homogeneous porous media to dynamically visualize the nucleation and growth of exsolved CO_2 bubbles.The pressure decreased from 9.85 to 3.95 MPa at different temperatures and depressurization rates,and the behavior of CO_2 bubbles was recorded.At the pore-scale,the nuclei became observable when the CO_2 phase density was significantly reduced,and the pressure corresponding to this observation was slightly lower than that of the severe expansion pressure region.The lower temperature and faster depressurization rate produced more CO_2 nuclei.The exsolved CO_2 bubble preferentially grew into the pore body instead of the throat.The progress of smaller CO_2 bubbles merging into a larger CO_2 bubble was first captured,which validated the existence of the Ostwald ripening mechanism.The dispersed CO_2 phase after exsolution shows similarity with the residually trapped CO_2.This observation is consistent with the low mobility and high residual trapping ratio of exsolved CO_2 measured in the core-scale measurement,which is considered to be a self-sealing mechanism during depressurization process in CO_2 geological storage.