In situ high-temperature crystal structure analysis of natural heulandite with the chemical composition (Na1.14K0.40Ca3.64Sr0.21)(Al9.21Si26.88)O72·25.2H2O from Maharastra, India was conducted up to 300 °C. The room-temperature and high-temperature X-ray diffraction intensities of a single crystal were measured using an imaging plate detector coupled with a U-shaped high-temperature furnace. At room temperature, the sample was monoclinic, with C2/m symmetry [a = 17.716(4) Å, b = 17.880(3) Å, c = 7.438(2) Å, and β = 116.43(1)°]. Structural refinement of the data set at room temperature yielded a final R value of R = 0.049 and Rw = 0.115 for 1663 independent reflections. The crystal structures of the partially dehydrated states at elevated temperatures (100 °C, 150 °C, 200 °C, 250 °C and 300°C) were refined using C2/m space group. The loss of H2O and the accompanying migration of cations caused a change in the cell parameters: a- and c-axes and the β angle remained invariant, but the b axis decreased, leading to a reduction of the cell volume. Channels A and B became elongated and compressed, respectively, with increasing degree of dehydration. Dehydration began with the loss of H2O coordinated to the Ca1 site in Channel A, defined by 10-membered tetrahedral rings. At 150 °C, the water coordinated to the Ca1 site was expelled radically, and it caused the Ca1 site to migrate to the cavity wall, forming a stronger bond with a tetrahedral framework, whereas the Ca2 site-coordinated water molecules remained in the 8-membered tetrahedral rings with full occupancy. The loss of water at 250 °C from Channel B triggered a structural change: Part of the structure transformed into a heat-collapsed heulandite structure with new T-O-T connections.
We report here monazite geochronology on a newly discovered high pressure (HP) and ultrahigh-temperature (UHT) granulite locality at Thoppur within the Palghat-Cauvery Shear Zone system in southern India. In situ dating of monazites associated with the UHT minerals using electron probe technique yielded PbO vs. ThO2* apparent isochron age of 544 ± 5 Ma. This is the first study from southern India where older monazite cores or complex age patterns are virtually absent, and all the monazite population in the studied samples crystallized/recrystallized during a single thermal maximum which we correlate with the timing of extreme crustal metamorphism during the final assembly of the Gondwana supercontinent.
The conventional focused ion beam (FIB) sample preparation technique “lift-out method” was modified for the reliable analysis of a laser-heated diamond anvil cell (LHDAC) sample. Box-shaped grooves were prepared in the LHDAC specimen in order to recover a block using a gallium ion beam in the vicinity of the area to be characterized by transmission electron microscope (TEM). The recovered block was fixed on the stage of a copper (or molybdenum) grid and thinned by the gallium ion beam in order to obtain a TEM foil. Our modified lift-out method allows us to thin the entire vertical section (from the upper anvil surface to the lower anvil surface) of the LHDAC sample.
Microthermometry and micro-Raman spectroscopy are performed on fluid inclusions within lenticular quartz veins elongated parallel to the main foliation of a pelitic schist of the Sanbagawa metamorphic belt, Saganoseki, Kyushu, Japan. The fluid inclusions are isolated or are arranged along the planes, which are developed subparallel (∼ 20°) to the main foliation of the quartz veins. Both types of fluid inclusions show similar homogenization temperatures and compositions in the H2O-NaCl-CH4 system. The trapping P-T conditions of the isolated fluid inclusions are determined to be 3.7-6.5 kbar and 320-450 °C by combining microthermometry and the pressure dependence of CH4 Raman shift. The estimated P-T range is consistent with the peak metamorphic conditions of the host rock (6-8 kbar, 300-400 °C) or bit lower, suggesting that the fluid inclusions are primary or secondary ones trapped at a relevant depth and they are potential evidence on the fluid composition derived from metamorphic reactions at 10-20 km depths.
Synthetic end-members Mg2SiO4, Fe2SiO4, Mn2SiO4, and Co2SiO4 and natural samples of forsterite-fayalite series, tephroite and monticellite, are investigated using Raman spectroscopy. The Raman spectra of the olivine-group minerals have a characteristic set of two intense lines of the Si-O asymmetric stretching band (wavenumber κ1) and Si-O symmetric stretching band (κ2). The κ1 and κ2 values of the Mg2SiO4-Ca(Mg, Fe)SiO4 series, in which the M2 site is occupied by nontransition elements, vary from 847 cm−1 to 857 cm−1 and from 815 cm−1 to 825 cm−1, respectively, and their ω (= κ1 − κ2) value is fairly constant around 32 cm−1. On the other hand, fayalite, tephroite, and other olivine-group minerals in which transition elements exist in the M2 site have a fairly constant κ1 (836-839 cm−1) value and variable κ2 (808-819 cm−1) and ω (20-32 cm−1) values. The ω value of the forsterite-fayalite series systematically increases with Mg#[= Mg/(Mg + Fe)] and is useful for determining their chemical compositions.
The Raman spectroscopy of more than 2000 SiO2 inclusions in zircon separates from Gföhl migmatitic gneisses in the Nové Dvory area shows that most of the SiO2 inclusions are composed of quartz with clear and intense peaks at 464, 393, 266, 207 and 125 cm−1. It also reveals that a few SiO2 inclusions have a weak but clear peak at 521 cm−1, which is the most fundamental vibration of coesite, along with typical quartz vibrations mentioned above. The Raman spectrum is composed of the intense vibrations of quartz at 464, 393 and 266 cm−1 of quartz and the weak vibration of coesite at 521 cm−1 is obtained from the quartz proximal to the relict coesite inclusion in the pyrope of ultra-high-pressure (UHP) rocks in Dora Maira Massif. A similar Raman spectrum has been obtained for quartz transformed from coesite in UHP rocks recovered from the CCSD drillhole of the Sulu belt, eastern China. Therefore, we propose that the SiO2 phase whose Raman spectrum shows a weak vibration at 521 cm−1 existed as coesite in the past.
In order to study physicochemical states of water in a chalcedony, thin sections were heated from room temperature (RT) to 400 °C at 50 °C intervals under an infrared (IR) microscope. A sharp IR absorption band due to hydroxyls (Si-OH) shifts linearly from 3585 cm−1 at RT to 3599 cm−1 at 400 °C (1.8 cm−1/50 °C). A broad band due to H2O shifts also linearly from 3425 cm−1 at RT to 3535 cm−1 at 400 °C (15 cm−1/50 °C). These reversible band shifts, without dehydration, of hydroxyl and H2O can be explained by the increasing hydrogen bond distance and the decreasing coordinating numbers of water molecules, respectively. The in-situ IR spectra of the chalcedony thin sections during the isothermal heating at 550 °C showed a decrease of the total water band area. The RT spectra quenched from 550 °C indicated the major decrease of 3585 cm−1 absorbance due to Si-OH with the minor decrease of the 3425 cm−1 absorbance due to H2O. These results suggest the dominant dehydration of Si-OH species from the microcrystalline quartz and the certain stability of liquid-like H2O against dehydration in pores and grain boundaries.
We have predicted a new high-pressure phase of InOOH by first principles density functional calculations, which stabilizes at ∼ 15 GPa under the static 0 K condition. The structure obtained at 15 GPa has a pyrite-type InO2 framework with the interstitial asymmetric hydrogen bonds, which is assigned to the space group P213 (No. 198). The cell parameters and internal atomic coordinates optimized at 15 GPa are a = 5.265 Å, Inx = 0.005, O1x = 0.367, O2x = 0.633, and Hx = 0.487. Relative enthalpies also indicate that the dehydration of this phase into In2O3 + H2O is unlikely to occur at least up to 50 GPa under the static condition. To our knowledge, this is the first report on the high-pressure isochemical phase transition of oxyhydroxide compounds to the pyrite-type structure. The new phase of InOOH has been identified in an experiment, as reported in detail in a separate paper. We have also found that the low-pressure-type asymmetric hydrogen bond in the new pyrite-type phase changes to the symmetric hydrogen bond over 30 GPa. The present results suggest that a similar phase relation is expected in other group IIIB oxyhydroxides such as AlOOH and GaOOH.
We report the first fluid inclusion data on Palaeoproterozoic basement rocks in Bangladesh for the characterization of magmatic fluid compositions and determination of the crystallization pressure and temperature of the host rock. Fluid inclusions are present as primary and pseudosecondary types in quartz grains within pegmatite and aplite, which occur as veins in dioritic rocks. Both primary CO2-rich and H2O-rich inclusions are present, even in the same inclusion cluster, probably reflecting a single stage of fluid activity during the crystallization of the veins. The melting temperature (Tm) and homogenization temperature (Th) of the dominant carbonic inclusions are in the ranges of −56.6 °C to −58.1 °C and −6.8 °C to +30 °C, respectively; the Th values translate into densities of 0.59-0.97 g/cm3. Rare aqueous fluid inclusions have a final Tm value in the range of 0 °C to −10.8 °C and a Th value in the range of +209.8 °C to +405.5 °C, which corresponds to bulk densities of 0.52-0.97 g/cm3. Isochores of the inclusions and temperatures obtained from the zircon saturation thermometry of pegmatite indicate that the veins crystallized at ∼ 4.8 kbar and 660-670 °C (depth of ∼ 14 km). The results of this study will be useful in understanding the magmatism and metallogeny of felsic igneous rocks of Bangladesh, which are related to the formation of the Columbia supercontinent.
The elastic wave velocities of MORB glass were measured up to 18.7 GPa at 27 °C using an ultrasonic technique combined with in situ high-pressure X-ray diffraction and imaging. High-pressure Raman spectroscopy using a diamond anvil cell was also employed to study the local structure of the glass sample up to 20 GPa. Both the elastic wave velocities and Raman frequency at ∼ 1600 cm-1 show significant changes in their pressure dependences at ∼ 10 GPa. The pressure derivatives of the P-wave and bulk sound velocities gradually increase with pressure above ∼ 10 GPa, whereas the S-wave velocity is almost constant below 10 GPa, above which it increases significantly. The plot of apparent change in the Raman frequency shift versus pressure suggests that these notable changes in elastic properties may be attributed to the local structural changes in the MORB glass. Our observations demonstrate that both the density and adiabatic bulk modulus of the MORB glass increase continuously at pressures above ∼ 10 GPa. These apparently conflicting tendencies can be reasonably explained if the zero-pressure density is increased continuously above ∼ 10 GPa accompanied by structural modification. Since the fundamental structure of silicate glass is analogous to that of melt, the results are important and aid in understanding the elastic properties of silicate melt at high pressures.
Framboidal pyrite in mudstone is known to be a reservoir of arsenic, yet few studies have conducted quantitative analyses of framboidal pyrite with ppm-level sensitivity. In this study, we used micro-PIXE to measure the concentrations of heavy metals in framboidal pyrite from drill-core samples of mudstone from the Late Cretaceous Hakobuchi Group, central Hokkaido, Japan. Pyrite framboids that occur in polyframboids can be divided into two types based on framboid diameter (D) and the average diameter of microcrystals within framboids (d): type 1, being relatively small grains; and type 2, being relatively large grains. Higher concentrations of As are observed in most type 2 framboids than in type 1 framboids. High concentrations of Pb generally occur as isolated islands within type 1 framboids, concentrated along the rims of polyframboids. It could be concluded that contrasting formation processes among different framboids led to the observed changes in heavy metal concentrations.
The EPMA analysis of a pelitic sample from the Besshi district, central Shikoku, in the Sambagawa metamorphic belt reveals that two types of garnet porphyroblasts with different sizes and chemical compositions are present within a single thin section. One type consisting of medium-sized (d ∼ < 1 mm) grains has a high Mn content at the core and shows a pyrope-rich profile. The other type is comparatively larger in size (d ∼ 2 mm). The rim compositions of both types are different. The influence of the initial bulk rock chemistry on the garnet is calculated by the forward model. A comparison of the observations with the calculated results indicates that the difference between the two types of garnet grains is attributed to the initial Fe/Mg ratio of the local bulk rocks.
Zn-bearing beaverite occurs as a secondary mineral in an oxidized zone of a quartz vein in the hydrothermal Cu-Zn-Pb ore deposit of the Mikawa mine, Niigata Prefecture, Japan. The Zn-bearing beaverite is dark brown in color with streaks and the associated minerals are quartz, galena, sphalerite, pyrite, anglesite, beaverite, orthoclase, and osarizawaite. The empirical formula of the mineral based on EPMA is Pb0.95(Fe1.88Al0.10)Σ1.98(Zn0.83Cu0.30)Σ1.13(SO4)2[O0.38(OH)5.36]Σ5.74 for S = 2, which leads to the ideal formula Pb(Fe2Zn)(SO4)2(OH)6. The crystal structure is refined by Rietveld analysis in the space group R3m. Using powder XRD data obtained by the combined use of a Gandolfi camera and monochromatic synchrotron radiation, the following values are obtained: a = 7.3028(2), c = 17.0517 (4) Å, V = 787.56(4) Å3, and Dcalc = 4.25 g/cm3.
The crystal chemistry of ZnS minerals formed as high-temperature volcanic sublimates from Iwodake volcano, Satsuma-Iwojima, Japan, has been studied by means of single-crystal X-ray diffraction (XRD), electron microprobe (EMP), micro-XRD, and micro-Raman scattering analyses. These minerals were identified as sphalerite and matraite by using a four-circle automated X-ray diffractometer. However, these two minerals were virtually the same in XRD pattern, chemical composition and micro Raman-scattering spectrum. A close examination of the observed reflections for the matraite sample revealed that all of them can be identified as reflections diffracted from (001)-twinned matraite. Moreover, all the reflections from (001)-twinned matraite were completely identical with those from (111)-twinned sphalerite. Consequently, it is evident that matraite is not a distinct mineral species but can be treated as (111)-twinned sphalerite. Occurrences of this twinned sphalerite may be characteristic of high-temperature volcanic sublimates.
We performed high-pressure and high-temperature X-ray diffraction experiments on InOOH using laser heated diamond anvil cells. After heating at 1300 K, pyrite-type InOOH was formed at 14 GPa and it was stable up to at least 30 GPa. Pyrite-type InOOH partially transformed back to distorted rutile-type InOOH after recovery. The lattice constant and unit-cell volume of pyrite-type InOOH were determined to be a0 = 5.3151(8) Å and V0 = 150.15 (7) Å3 at ambient conditions, respectively. The density difference between pyrite-type and distorted rutile-type InOOH was 5% at ambient condition.
The crystal structure of sibirskite (CaHBO3) was solved by the Monte Carlo simulation using powder X-ray diffraction data and confirmed by the Rietveld refinement. The mineral sibirskite is monoclinic with space group P21/a and cell constants of a = 8.643(6), b = 9.523(2), c = 3.567(3) Å, and β = 119.23(3)°. The unit cell consists of independent atoms such as calcium, boron, hydrogen, and three oxygen atoms. The calcium atom is surrounded by six oxygen atoms in an octahedral coordination, and a symmetrical pair of edge-shared CaO6 octahedra forming a double chain elongates the crystallographic c axis. The CaO6 double chains are not directly connected to each other. The BO3 triangles are linked to one vertical and two shared oxygen atoms in three CaO6 double chains to form the sibirskite structure. Sibirskite is isostructural with nahcolite (NaHCO3), which consists of NaO6 double chains and CO3 triangles.
Northwest Africa 1232 (NWA 1232) is a carbonaceous chondrite consisting of two lithologies (A and B) that are separated by a sharp boundary. A petrographic and mineralogical study indicates that both lithologies can be classified as type CO3. However, olivine in lithology B chondrules is more enriched in Fe than in lithology A, whereas olivine in lithology B matrix is more depleted in Fe than in lithology A. Chondrules and Ca-Al-rich inclusions (CAIs) in lithology B show a higher degree of nephelinization than those in lithology A. These differences can be explained by that lithology B has gone through a higher degree of thermal metamorphism than lithology A. These two lithologies probably represent rocks that have been thermally metamorphosed at different locations within a single CO parent body and later mixed to form the present combined rock during a brecciation process.