The effect of iron on the sound velocities ofδ-AlOOH up to 135 GPa

δ-(Al,Fe)OOH is considered to be one of the most important hydrous phases on Earth,remaining stable under the extreme conditions throughout the mantle.The behavior ofδ-(Al,Fe)OOH at high pressure is essential to understanding the deep water cycle.δ-(Al_0.956Fe_0.044)OOH crystals synthesized at 21 GPa and 1473 K were investigated by high-pressure Brillouin light scattering spectroscopy and synchrotron X-ray diffraction up to 135.4 GPa in diamond anvil cells.The incorporation of 5 mol%FeOOH increases the unit-cell volume ofδ-AlOOH by~1%and decreases the shear-wave velocity(VS)by~5%at 20–135 GPa.In particular,the compressional(V_P)and shear(VS)wave velocities ofδ-(Al_0.956Fe_0.044)OOH are 7%–16%and 10%–24%greater than all the major minerals in the mantle transition zone including wadsleyite,ringwoodite,and majorite.The distinctly high sound velocities ofδ-(Al_0.956Fe_0.044)OOH at 20–25 GPa may contribute to the seismic anomalies observed at~560–680 km depths in the cold and stagnant slab beneath Izu-Bonin and/or Korea.Furthermore,the VS ofδ-(Al_0.956Fe_0.044)OOH is about 10%and 4%–12%lower than iron-bearing bridgmanite Mg_0.96Fe_0.05Si_0.99O3and ferropericlase(Mg_0.92Fe_0.08)O,respectively,under the lowermost mantle conditions,which might partially contribute to the large low-shear-velocity provinces and ultralow velocity zones at the bottom of the lower mantle.     

Reassessment of the Distribution of Mantle CO2 in the Bohai Sea, China: The Perspective from the Source and Pathway System

Research on the distribution of mantle CO₂should involve comprehensive analysis from CO₂source to accumulation.The crust-mantle pathway system is the key controlling factor of the distribution of mantle CO₂,but has received little attention.The pathway system and controlling factors of CO₂distribution in the Bohai Sea are analyzed using data on fault styles and information on the mantle and lithosphere.The relation between volcanic rocks and the distribution of mantle CO₂is reassessed using age data for CO₂accumulations.The distribution of mantle CO₂is controlled by uplift of the asthenosphere and upper mantle,magma conduits in the mantle and fault systems in the crust.Uplifted regions of the asthenosphere are accumulation areas for CO₂.The area with uplift of the Moho exhibits accumulation of mantle CO₂at depth.CO₂was mainly derived from vertical migration through the upper mantle and lower crust.The fault style in the upper crust controls the distance of horizontal migration and the locations of CO₂concentrations.The distribution of mantle CO₂and volcanic rocks are not the same,but both probably followed the same pathways sometimes.Mantle CO₂in the Bohai Sea is concentrated in the Bozhong sag and the surrounding area,particularly in a trap that formed before 5.1 Ma and is connected to crustal faults(the Bozhang faults)and lithospheric faults(the Tanlu faults).     

Stability and band gap engineering of silica-confined lead halide perovskite nanocrystals under high pressure

SiO₂is the major mineral substance in the upper mantle of the earth.Therefore,studies of the silica-coated materials under high-pressure are essential to explore the physical and chemical properties of the upper mantle.The silica-confined CsPbBr₃nanocrystals(NCs)have recently attracted much attention because of the improved photoluminescence(PL)quantum yield,owing to the protection of silica shell.However,it remains considerable interest to further explore the relationship between optical properties and the structure of CsPbBr₃@SiO₂NCs.We systemically studied the structural and optical properties of the CsPbBr₃@SiO₂NCs under high pressure by using diamond anvil cell(DAC).The discontinuous changes of PL and absorption spectra occurred at~1.40 GPa.Synchrotron X-ray diffraction(XRD)studies of CsPbBr₃@SiO₂NCs under high pressure indicated an isostructural phase transformation at about 1.36 GPa,owing to the pressure-induced tilting of the Pb-Br octahedra.The isothermal bulk moduli for two phases are estimated about 60.0 GPa and 19.2 GPa by fitting the equation of state.Besides,the transition pressure point of CsPbBr₃@SiO₂NCs is slightly higher than that of pristine CsPbBr₃NCs,which attributed to the buffer effect of coating silica shell.The results indicate that silica shell is able to enhance the stabilization without changing the relationship between optical properties and structure of CsPbBr₃NCs.Our results were fascinated to model the rock metasomatism in the upper mantle and provided a new‘lithoprobe’for detecting the upper mantle.     

Low Mantle Perovskite: Solid Solution,Spin State of Iron and Water Solubility

Silicate perovskites((Mg, Fe)SiO 3 and CaS iO 3) are believed to be the major constituent minerals in the lower mantle. The phase relation, solid solution, spin state of iron and water solubility related to the lower mantle perovskite are of great effect on the geodynamics of the Earth's interior and on ore mineralization. Previous studies indicate that a large amount of iron coupled with aluminum can incorporate into magnesium perovskite, but this is discordant with the disproportionation of(Mg,Fe)SiO 3 perovskite into iron-free MgS i O3 perovskite and hexagonal phase(Mg0.6Fe0.4)SiO 3 in the Earth's lower mantle. MnS iO 3 is the first chemical component confirmed to form wide range solid solution with Ca SiO 3 perovskite and complete solid solution with MgS i O3 perovskite at the P-T conditions in the lower mantle, and addition of Mn Si O3 will strongly affects the mutual solubility between Mg Si O3 and CaS iO 3. The spin state of iron is deeply depends on the site occupation of the Fe3+or Fe2+, the synthesis and the annealing conditions of the sample. It seems that the spin state of Fe2+ in the lower mantle perovskite can be settled as high spin, however, the existence of intermediate spin or low spin state of Fe2+ in perovskite has not been clarified. Moreover, different results have also been reported for the spin state of Fe3+ in perovskite. The water solubility of the lower mantle perovskite is related with its composition. In pure Mg SiO 3 perovskite, only less than 500 ppm water was reported. Al–Mg Si O3 perovskite or Al–Fe–MgS iO 3 perovskite in the lower mantle accommodates water of 1100 to 1800 ppm. Further experiments are necessary to clarify the detailed conditions for perovskite solid solution, to reliably analyze the valence and spin states of iron in the coexisting iron-bearing phases, and to compare the water solubility of different phases at different layers for deeply understanding the geodynamics of the Earth's interior and ore mineralization.     

A geochemical study of the peat and soft-brown coal from the Zhenan basin,Western Yunnan,China

Little is known about the geochemistry of peat and soft-brown coal The analytical chemical dataof forty eight samples have been obtained for the peat and soft-brow n coal in the 7henan basin, western Yunnan. njection of continental detritus into theswamp is favourable for the degradation of plant remains and thefor-oration of humic acid. The oxide compositions of the ash of the peat and soft一)rown coal and their distribution-typeshave indicated that the continental detritusome from two kinds of parent rocks.The Al₂O₃ and SiO₂have a positive correlation with humic acid(Hmz)，showing that the organic matter is ad-vantageous to the formation of aluminosilic;ate mineral(mainly kaolinite, authigenic organic clay minerals). The TiO₂ enrichment is mainly related to mineral materials. The Ge content in the peat and soft-brown coalranges from 0. 2- 2.6×10-6, and it is mainly bound to those minerals with Al₂O₃and organic matters. The GaContent is from 2. 3- 19.1×10-6，and it is associated with minerals that are MgO一Baring aluminosilicate minerals.The uranium (0.3- 4.9×10-6) is mainly bound in the Ca-and Mg-bearing minerals. They are not enriched andnot related to organic matter.     

http://www.sciencedirect.com/science/article/pii/S1674987110000034

<正>We synthesize significant recent results on the deep structure and origin of the active volcanoes in mainland China.Magmatism in the western Pacific arc and back-arc areas is caused by dehydration of the subducting slab and by corner flow in the mantle wedge,whereas the intraplate magmatism in China has different origins.The active volcanoes in Northeast China(such as the Changbai and Wuda-lianchi) are caused by hot upwelling in the big mantle wedge(BMW) above the stagnant slab in the mantle transition zone and deep slab dehydration as well.The Tengchong volcano in Southwest China is caused by a similar process in the BMW above the subducting Burma microplate(or Indian plate). The Hainan volcano in southernmost China is a hotspot fed by a lower-mantle plume which may be associated with the Pacific and Philippine Sea slabs' deep subduction in the east and the Indian slab's deep subduction in the west down to the lower mantle.The stagnant slab finally collapses down to the bottom of the mantle,which can trigger the upwelling of hot mantle materials from the lower mantle to the shallow mantle beneath the subducting slabs and may cause the slab—plume interactions.     

浙江桐庐火山侵入杂岩的地球化学特征

The Tonglu volcano-intrusive complex belongs to a calci-alkalic rock series. The geochemistry of major and minor elements in the rocks is characteristic of the differentiation and the evolution of the calci-alkalic series. The rare-earth distribution patterns in the rocks and minerals indicate that rhyolitic, rhyodacitic and quartz ttachyandesitic magmas responsible for the volcano-intrusive complex are comagmatic. The Rb-Sr isotopic relationship in the rocks suggests that the earliest volcanic activity in western Zhejiang may commence at Middle Jurassic. The magma responsible for the Tonglu volcano-intrusive complex originated from partil melting of the lower crust. The derivation of upper mantle material was introduced upwards through deep faults, which would accelerate partial melting of the lower crust.This magma seems to have been contaminated slightly by upper crustal material during the process of upward intrusion.     

Aluminum solubility in bridgmanite up to 3000 K at the top lower mantle

The temperature dependence of the Al2O3 solubility in bridgmanite has been determined in the system MgSiO3–Al₂O₃at temperatures of 2750–3000 K under a constant pressure of 27 GPa using a multi-anvil apparatus.Bridgmanite becomes more aluminous with increasing temperatures.A LiNbO3-type phase with a pyrope composition(Mg₃Al₂Si₃O₁₂)forms at 2850 K,which is regarded as to be transformed from bridgmanite upon decompression.This phase contains 30 mol%Al₂O₃at 3000 K.The MgSiO3 solubility in corundum also increases with temperatures,reaching 52 mol%at 3000 K.Molar volumes of the hypothetical Al₂O₃bridgmanite and MgSiO₃corundum are constrained to be 25.95
0.05 and 26.24±0.06 cm³/mol,respectively,and interaction parameters of non-ideality for these two phases are 5.6±0.5 and 2.2±0.5 KJ/mol,respectively.The increases in Al²O³and MgSiO³contents,respectively,in bridgmanite and corundum are caused by a larger entropy of Al₂O₃bridgmanite plus MgSiO₃corundum than that of MgSiO₃bridgmanite plus Al₂O₃corundum with temperature,in addition to the configuration entropy.Our study may help explain dynamics of the top lower mantle and constrain pressure and temperature conditions of shocked meteorites.     

Geochemistry of core sediments from the southeastern Bay of Bengal:Inferences on weathering and early diagenetic changes

A sediment core(ABP24/05),collected at a water depth of 3520 m from the southeastern Bay of Bengal was studied to determine the change in chemical weathering during the last glacial to deglacial periods and the factors of sedimentary environment which controlled earliest diagenetic changes in the sediment after its deposition.High ratios of K/Rb,Ti/Al and Zr/Rb during~45 to~18 cal kyr B.P.in the core sediments may be attributed to the stronger physical erosion and turbidity currents activity during this period.This might have brought a higher quantity of unaltered minerals to the study area.Low ratios of K/Rb,Zr/Rb,and Ti/Al and increase of SiO₂/TiO₂,Rb/Al and Cs/Al from~18 cal kyr B.P.to present may be indicating an increase in the rate of chemical weathering during this period.The time of increased chemical weathering in the study area is consistent with deglaciation warming in the tropical Indian Ocean and strengthening of river runoff into the Andaman Sea.Climate change during the interglacial period by increased solar insolation thereby strengthened the summer monsoon which might have led to intensified chemical weathering in the source region since~18 cal kyr B.P.The low organic carbon(OC),high Mn/Al,Fe/Al and the Mn-oxides minerals precipitation indicate prevailing of oxic conditions during~11 cal kyr B.P.in the core sediments,which is contradictory to suboxic conditions developed in the deep ocean sediments in the western Bay of Bengal and the equatorial Indian Ocean.The low terrigenous influx and export of less OC to the bottom sediments might have created a favorable condition for the formation of Mn-oxides in the study area during Holocene.     

In-situ Moissanite in Dunite: Deep Mantle Origin of Mantle Peridotite in Luobusa Ophiolite, Tibet

We report the discovery of an in-situ natural moissanite as an inclusion in the Cr-spinel from the dunite envelope of a chromitite deposit in Luobusa ophiolite, Tibet. The moissanite occurs as a twin crystal interpenetrated by two quadrilateral signal crystals with sizes of 17 μm× 10 μm and 20 μm× 7 μm, respectively. The moissanite is green with parallel extinction. The absorption peaks in its Raman spectra are at 967-971 cm-1, 787-788 cm-1, and 766 cm-1. The absorption peaks in the infrared spectra are at 696 cm-1, 767 cm-1, 1450 cm-1, and 1551 cm-1, which are distinctly different from the peaks for synthetic silicon carbide. Moissanites have been documented to form in ultra-high pressure, high temperature, and extremely low fO2 environments and their 13C-depleted compositions indicate a lower mantle origin. Combined with previous studies about other ultra-high pressure and highly reduced minerals in Luobusa ophiolite, the in-situ natural moissanite we found indicates a deep mantle origin of some materials in the mantle sequence of Luobusa ophiolite. Further, we proposed a transformation model to explain the transfer process of UHP materials from the deep mantle to ophiolite sequence and then to the supra-subduction zone environment. Interactions between the crown of the mantle plume and mid-ocean ridge are suggested to be the dominant mechanism.     

Degassing of primordial major energy source for hydrogen and helium as the internal terrestrial processes

Examples of the mightiest energy releases by great earthquakes and volcanic eruptions and hypotheses providing explanations for them are analyzed along with the results of some recently published researches and visualizations.The emerging conclusions are that the mechanism of the strong earthquake is a chemical explosion;that volcanic eruption is a special type of earthquake wherein the hypocenter rises to the earth-surface;and that there is an association between the seismic-volcanic processes and mantle "fluids" and the lack of energy for mantle plumes.A conceptual system of hypotheses is put forward to explain the conservation of energy during Earth’s accretion,its quasi-stable release by primordial H- and He-degassing and of the crucial role of the energy of degassing-comprisingreactions in endogenic processes.Specific mechanisms and chemical processes are proposed for the gas-liquid mantle plumes melting through the solid mantle using heat-energy released in reactions of their metamorphic and chemical transformation under gradual decrease of pressure and temperature;volcanic gases are put forward as energy carriers.He performance as a unique measuring transformer correlative to the internal heat flow was used for calculation of energy release by degassing;it equals to 5.12×10²⁰ J/yr.an amount of energy five-fold greater than the entire energy loss involved in earthquake and volcanic activity.The hypotheses proposed are objectively testable.     

Joint Inversion of the 3D P Wave Velocity Structure of the Crust and Upper Mantle under the Southeastern Margin of the Tibetan Plateau Using Regional Earthquake and Teleseismic Data

The special seismic tectonic environment and frequent seismicity in the southeastern margin of the Qinghai–Tibet Plateau show that this area is an ideal location to study the present tectonic movement and background of strong earthquakes in mainland China and to predict future strong earthquake risk zones. Studies of the structural environment and physical characteristics of the deep structure in this area are helpful to explore deep dynamic effects and deformation field characteristics, to strengthen our understanding of the roles of anisotropy and tectonic deformation and to study the deep tectonic background of the seismic origin of the block's interior. In this paper, the three-dimensional(3D) P-wave velocity structure of the crust and upper mantle under the southeastern margin of the Qinghai–Tibet Plateau is obtained via observational data from 224 permanent seismic stations in the regional digital seismic network of Yunnan and Sichuan Provinces and from 356 mobile China seismic arrays in the southern section of the north–south seismic belt using a joint inversion method of the regional earthquake and teleseismic data. The results indicate that the spatial distribution of the P-wave velocity anomalies in the shallow upper crust is closely related to the surface geological structure, terrain and lithology. Baoxing and Kangding, with their basic volcanic rocks and volcanic clastic rocks, present obvious high-velocity anomalies. The Chengdu Basin shows low-velocity anomalies associated with the Quaternary sediments. The Xichang Mesozoic Basin and the Butuo Basin are characterised by lowvelocity anomalies related to very thick sedimentary layers. The upper and middle crust beneath the Chuan–Dian and Songpan–Ganzi Blocks has apparent lateral heterogeneities, including low-velocity zones of different sizes. There is a large range of low-velocity layers in the Songpan–Ganzi Block and the sub–block northwest of Sichuan Province, showing that the middle and lower crust is relatively weak. The Sichuan Basin, which is located in the western margin of the Yangtze platform, shows high-velocity characteristics. The results also reveal that there are continuous low-velocity layer distributions in the middle and lower crust of the Daliangshan Block and that the distribution direction of the low-velocity anomaly is nearly SN, which is consistent with the trend of the Daliangshan fault. The existence of the low-velocity layer in the crust also provides a deep source for the deep dynamic deformation and seismic activity of the Daliangshan Block and its boundary faults. The results of the 3D P-wave velocity structure show that an anomalous distribution of high-density, strong-magnetic and high-wave velocity exists inside the crust in the Panxi region. This is likely related to late Paleozoic mantle plume activity that led to a large number of mafic and ultra-mafic intrusions into the crust. In the crustal doming process, the massive intrusion of mantle-derived material enhanced the mechanical strength of the crustal medium. The P-wave velocity structure also revealed that the upper mantle contains a low-velocity layer at a depth of 80–120 km in the Panxi region. The existence of deep faults in the Panxi region, which provide conditions for transporting mantle thermal material into the crust, is the deep tectonic background forthe area's strong earthquake activity.     

Evidence for the Lower Continental Crustal Origin of the Xihuashan Granite

The Xihuashan granite is typically representative of the tungsten-bearing granites widespread in theNanling area of South China. It was considered in the past to have been formed by partial melting of the upper continental crust, with its source rocks most probably of the Sinian or Cambrian. However, detailed REE analyses, studies of the Rb-Sr isotopic system and melting experiments of metasedimentary rocks all argue against this idea. Moreover, stable isotopic data also indicate a deep source origin for S, C, H and O. The authors thus propose a genetic concept of the lower continental crustal source of the Xihuashan granite, and point out further that tungsten deposits related to this kind of granite are linked in some way to deep-seated structure and concentrated along NNE-NE- and ENE-striking major deep fault belts above the transitional zone between mantle uplift and mantle depression.     

Characteristics of crustal variation and extensional break-up in the Western Pacific back-arc region based on a wide-angle seismic profile

The marginal sea and back-arc basins in the Western Pacific Ocean have become the focus of tectonics due to their unique tectonic location.To understand the deep crustal structure in the back-arc region, we present a 545-kmlong active-source ocean bottom seismometer(OBS) wide-angle reflection/refraction profile in the East China Sea.The P wave velocity model shows that the Moho depth rises significantly, from approximately 30 km in the East China Sea shelf to approximately 16 km in the axis of the Okinawa Trough.The lower crustal high-velocity zone(HVZ) in the southern Okinawa Trough, with V_p of 6.8–7.3 km/s, is a remarkable manifestation of the mantle material upwelling and accretion to the lower crust.This confirms that the lower crustal high-velocity mantle accretion is developed in the southern Okinawa Trough.During the process of back-arc extension, the crustal structure of the southern Okinawa Trough is completely invaded and penetrated by the upper mantle material in the axis region.In some areas of the southern central graben, the crust may has broken up and entered the initial stage of seafloor spreading.The discontinuous HVZs in the lower crust in the back-arc region also indicate the migration of spreading centers in the back-arc region since the Cenozoic.The asthenosphere material upwelling in the continent-ocean transition zone is constantly driving the lithosphere eastward for episodic extension, and is causing evident tectonic migration in the Western Pacific back-arc region.     

The effect of oxygen fugacity on ionic conductivity in olivine

The oxygen fugacity(f_O2) may affect the ionic conductivity of olivine under upper mantle conditions because Mg vacancies can be produced in the crystal structure by the oxidization of iron from Fe²⁺ to Fe3+. Here we investigated olivine ionic conductivity at 4 GPa, as a function of temperature, crystallographic orientation, and oxygen fugacity, corresponding to the topmost asthenospheric conditions. The results demonstrate that the ionic conductivity is insensitive to f_O2 under relatively reduced conditions(f_O2 below Re-ReO₂ buffer), whereas it has a clear f_O2-dependence under relatively oxidized conditions(f_O2 around the magnetite-hematite buffer). The ionic conduction in olivine may contribute significantly to the conductivity anomaly in the topmost asthenosphere especially at relatively oxidized conditions.     

Can HHe+exist at high pressure:Exploration of high pressure induced HF–He compounds

HHe⁺is considered as the strongest acid and most powerful proton donor known to human.Whether HHe⁺exists at planetary high pressure environment is a quite important problem in physics,chemistry and planetary sciences.Here,using the ab initio evolutionary algorithm USPEX package,we searched HF–He system,which was reported as the most possible candidate to contain HHe⁺.The calculation proved HHe⁺cannot form at pressure<1000 GPa,due to a conflict between the covalent component in symmetric hydrogen bond and ionic HHe⁺.Although He atoms have no chemical bonding with other elements,they can supply a chemical pressure,leading to two new phases He2(HF)4 and He(HF).With coplanar(HF)₄rings,He₂(HF)₄have an aromaticity-like electronic behavior while He(HF)has a new type of chiral HF chain.The formation of He₂(HF)₄and He(HF)prove that the chemical pressure from He,on par with external pressure,have ability to control the structural and electronic configuration and induce some new familiars of compounds include H and He elements which are fundamental planetary materials in giant planets.     

Adsorption behavior of CO2 in magnesite micro-pores at high temperature and pressure

The fluid inclusions in mantle rocks and melt indicated that a large amount of CO₂fluid exists in the deep earth,which is of great significance for understanding the deep carbon cycle and the composition of mantle.However,it was also suggested that carbonate minerals were likely to be the main host of mantle carbon.At the same time,the distribution and behavior of carbon in the mantle still remain a puzzle.In this paper,the adsorption behavior and occurrence characteristics of supercritical CO₂in magnesite(MgCO3)pores were studied by the Grand Canonical Monte Carlo method(GCMC)under the different conditions of CO₂pressures(0–100 MPa),temperatures(350–1500 K)and the pore sizes(7.5–30?).The simulated results showed that the adsorption of CO₂in magnesite was a physical adsorption,which was mainly controlled by the intermolecular force.The gas adsorption became more stable when the adsorption site shifted from the high energy site to the low energy site with increasing pressure(P)and decreasing temperature(T)and pore size.At the same time,the variations of excess adsorption amounts of CO₂in the pores of magnesite(Nexcess)under the different conditions were quantitatively calculated.It was found that the Nexcess decreased with increasing T,but increased with increasing P and pore size.The results favor understanding the CO₂migration,seismic precursor observations,and heat transfer process in the deep earth.     

On the Chemical Evolution of Upper Mantle of the Early Earth—An Experimental Study on Melting of the Silicate Phase in Jilin Chondrite at High Pressures

Relatively old ages of chondrites(normally around 4.5Ga)suggest that their parent bodies did not experience any mely-fractionation under high temperature and high pressure conditions pertaining to the interior of terrestrial plaets.Therefore,it is reasonable to take chondrites as starting materials in the study of the chemical evolution of the early earth.The sillicate phase in the Jilin chondrite (H5)was chosen for this purpose because it possesses a chemical composition similar to that of the primitive mantle.The melting experiment was carried out at 20-30 k bar and has rsulted in a product which contains1-5% melts in addition to solid cryustal phase.The chemical composition of the melt phases and the partitioning of various elements between the coexisting silicate melts are geochemically similar to those of anatectic rocks on the earth.This can thus serve as the basis for discussing the chemical evolution of the early upper mantle.     

http://www.sciencedirect.com/science/article/pii/S1674987112000394

High-grade dehydration of amphibolite-facies rocks to granulite-facies is a process that can involve partial melting,fluid-aided solid-state dehydration,or varying degrees of both.On the localized meter scale,solid-state dehydration,due to CO₂-rich fluids traveling along some fissure or crack and subsequently outwards along the mineral grain boundaries of the surrounding rock,normally is the means by which the breakdown of biotite and amphibole to orthopyroxene and clinopyroxene occur.Various mineral textures and changes in mineral chemistry seen in these rocks are also seen in more regional orthopyroxene-clinopyroxene-bearing rocks which,along with accompanying amphibolite-facies rocks, form traverses of lower crust.This suggests that solid-state dehydration during high-grade metamorphism could occur on a more regional scale.The more prominent of these fluid-induced textures in the granulitefacies portion of the traverse take the form of micro-veins of K-feldspar along quartz grain boundaries and the formation of monazite inclusions in fluorapatite.The fluids believed responsible take the form of concentrated NaCl- and KC1- brines from a basement ultramafic magma heat source traveling upwards along grain boundaries.Additional experimental work involving CaSO₄ dissolution in NaCl-brines. coupled with natural observation of oxide and sulfide mineral associations in granulite-facies rocks,have demonstrated the possibility that NaCl-brines,with a CaSO₄ component,could impose the oxygen fugacity on these rocks as opposed to the oxygen fugacity being inherent in their protoliths.These results, taken together,lend credence to the idea that regional chemical modification of the lower crust is an evolutionary process controlled by fluids migrating upwards from the lithospheric mantle along grain boundaries into and through the lower crust where they both modify the rock and are modified by it. Their presence allows for rapid mass and heat transport and subsequent mineral genesis and mineral reequilibration in the rocks through which they pass.     

Variation and dispersal of PM10 and PM2.5 during COVID-19 lockdown over Kolkata metropolitan city,India investigated through HYSPLIT model

The higher concentration of PM₁₀ and PM_2.5 in the lower atmosphere is severely harmful for human health and it also makes visibility diminution along with weather and climate modifications.The main objective is to find out the spatiotemporal variation and dispersal of PM₁₀ and PM_2.5 along with COVID-19 infection in the dusty city Kolkata.The consecutive two years PM₁₀ and PM_2.5 data of different stations have been obtained from State Pollution Control Board,Govt.of West Bengal.Forward trajectory analysis has been done through HYSPLIT(Hybrid Single Particle Lagrangian Integrated Trajectory)model to find the path and direction of air particles.The result showed that the various meteorological or environmental factors(such as temperature,relative humidity,wind,wind speed,pressure and gusty wind)and geographical location regulate the spatiotemporal variation of PM₁₀ and PM_2.5.These factors like high temperature with relative humidity and strong wind influence to disperse the particulate matters from north to south direction from city to outside during summer in Kolkata metropolitan city.During summer(both pre and lockdown years),the height of particles is extended up to 1000 m owing to active atmospheric ventilation whereas in winter it is confined within 100 m.The HYSPLIT model clearly specified that the particles dispersed from south,south-west to north and north east direction due to strong wind.The constant magnification of PM₁₀ and PM_2.5 in the lower atmosphere leads to greater frequency of COVID-19 infections and deaths.In Kolkata,the one of the crucial reasons of high infection and deaths(COVID-19)is co-morbidity of people.