•We report the structural characteristics of Proterozoic organic-walled microfossils using Raman spectroscopy in North China.•CM in Ruyang and Liulaobei microfossils experienced low-grade ...metamorphism with apparent peak metamorphic temperatures of ~200 °C.•Heterogeneities in structural characteristics exist among different subcellular structures of S. macroreticulatum and different taxa of the same stratigraphic horizon.
Raman spectroscopy is a minimally intrusive and minimally destructive technique that has played an important role in analyzing Precambrian carbonaceous microfossils and microstructures. Previous studies have shown that heterogeneities in structural order of carbonaceous material (CM) as revealed by Raman spectroscopy can be preserved in Proterozoic silicified cyanobacterial fossils. However, such heterogeneities have not been documented in Proterozoic eukaryotic microfossils preserved as carbonaceous compressions. In this study, we used Raman spectroscopy to investigate the structural characteristics of organic-walled microfossils, including eukaryotes preserved as carbonaceous compressions, from the late Paleoproterozoic Ruyang Group and the early Neoproterozoic (Tonian) Liulaobei Formation in the North China Craton. Raman geothermometers indicate that CM experienced low-grade metamorphism with apparent peak metamorphic temperatures of ~200 °C for both the Ruyang and Liulaobei microfossils. Heterogeneities in structural characteristics of CM in eukaryotic microfossils were found among different subcellular structures of Shuiyousphaeridium macroreticulatum and among different taxa from the same stratigraphic horizon. We suggest that these heterogeneities can be attributed to differences in precursor organic compounds; thus, the importance of organic precursors should be considered in CM Raman geothermometry studies, especially in environments where heating events occurred quickly. The Raman data presented here are also consistent with hypotheses that the Ruyang microfossils Dictyosphaera delicata and S. macroreticulatum are biologically conspecific taxa with their vesicle walls having similar CM Raman features, and that the Liulaobei microfossils Leiosphaeridia jacutica and L. tenuissima are distinct taxa despite their similarities in morphologies other than vesicle wall thickness. Although more data are needed to verify the consistency of interspecies, intraspecies, and intraspecimen variability, this study indicates that Raman spectroscopy may have the potential to provide an independent test of early eukaryote taxonomy, which has been traditionally based only on morphological features, and to reveal heterogeneities of CM of early eukaryotic organisms.
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GEOZS, IJS, IMTLJ, KILJ, KISLJ, NLZOH, NUK, OILJ, PNG, SAZU, SBCE, SBJE, UILJ, UL, UM, UPCLJ, UPUK, ZAGLJ, ZRSKP
Fluid inclusion petrography and vein mineral textures indicative of boiling have been characterized in 855 samples from epithermal precious metals deposits along the Veta Madre at Guanajuato, Mexico. ...Mineral textures and fluid inclusions characteristic of fluid immiscibility or boiling, including colloform quartz, plumose/feathery/flamboyant quartz, lattice-bladed calcite and lattice-bladed calcite replaced by quartz, as well as coexisting liquid-rich and vapor-rich fluid inclusions and assemblages of vapor-rich only inclusions, have been identified in mineralized samples from the Veta Madre. Most samples studied were assayed for Au, Ag, Cu, Pb, Zn, As and Sb, and were divided into ore grade and sub-economic samples based on the gold and silver concentrations. For silver, samples containing >100ppm were classified as ore grade, and ore grade gold samples contained >1ppm Au. The feature that is most closely associated with ore grades of both gold and silver is colloform quartz that was originally precipitated as amorphous silica, and this feature also shows the largest difference in average grade between samples that show colloform texture (178.8ppm Ag and 1.1ppm Au) and those that do not exhibit this texture (17.2ppm Ag and 0.2ppm Au). Statistical analysis of the data confirmed the petrographic observations that indicated that colloform quartz is the feature that has the greatest predictive power for distinguishing between ore grade and sub-economic samples. For both Ag and Au, there is no significant difference in average grade of samples containing coexisting liquid-rich and vapor-rich fluid inclusions or assemblages of vapor-only inclusions and those that do not, suggesting that fluid inclusion evidence for boiling is not correlative with ore grades. This result is consistent with the fact that most forms of silica that are precipitated during boiling do not trap useful fluid inclusions. The results of this study suggest that mineral textures and fluid inclusions provide complementary information that should both be used in exploration for epithermal precious metal deposits.
Metal grades and boiling intensity of samples collected along a traverse perpendicular to the Veta Madre and above known economic mineralization are both low at relatively short distances away from the vein and increase as the vein is approached. This suggests that mineralogical and fluid inclusion evidence for boiling are restricted to the immediate vicinity of, and increase in the direction of, mineralized veins and may be used in exploration to establish vectors towards vein systems that may host precious metal mineralization. Previous studies of epithermal systems show that the Ag and Au mineralization zone is most often located at or above the bottom of the boiling zone. In this regard, the presence of abundant evidence for boiling that is observed in the deepest levels of the Veta Madre that have been sampled suggests that additional precious metal mineralization may be present beneath the deepest levels that have been explored.
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►Mineral textures and fluid inclusions identify boiling in epithermal Au–Ag deposits. ►Colloform texture silica is best guide to high gold and silver grades. ►Boiling intensity increases towards mineralization. ►Highest gold and silver grades occur above the deepest boiling levels.
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GEOZS, IJS, IMTLJ, KILJ, KISLJ, NUK, OILJ, PNG, SAZU, SBCE, SBJE, UL, UM, UPCLJ, UPUK
The Raman spectral behavior of N2, CO2, and CH4 in ternary N2–CO2–CH4 mixtures was studied from 22°C to 200°C and 10 to 500 bars. The peak position of N2 in all mixtures is located at lower ...wavenumbers compared with pure N2 at the same pressure (P)–temperature (T) (PT) conditions. The Fermi diad splitting in CO2 is greater in the pure system than in the mixtures, and the Fermi diad splitting increases in the mixtures as CO2 concentration increases at constant P and T. The peak position of CH4 in the mixtures is shifted to higher wavenumbers compared with pure CH4 at the same PT conditions. However, the relationship between peak position and CH4 mole fraction is more complicated compared with the trends observed with N2 and CO2. The relative order of the peak position isotherms of CH4 and N2 in the mixtures in pressure–peak position space mimics trends in the molar volume of the mixtures in pressure–molar volume space. Relationships between the direction of peak shift of individual components in the mixtures, the relative molar volumes of the mixtures, and the attraction and repulsion forces between molecules are developed. Additionally, the relationship between the peak position of N2 in ternary N2–CO2–CH4 mixtures with pressure is extended to other N2‐bearing systems to assess similarities in the Raman spectral behavior of N2 in various systems.
The Raman spectra of N2, CO2, and CH4 in ternary N2–CO2–CH4 gas mixtures were analyzed from 10 to 500 bars and 22 to 200°C. A qualitative model relating molar volume of gases with differences in the Raman peak position of a given component in one mixture relative to another or pure system is presented. Finally, a ternary N2–CO2–CH4 gas barometer was developed using only N2 peak position and composition and was tested on various multicomponent systems.
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BFBNIB, FZAB, GIS, IJS, KILJ, NLZOH, NUK, OILJ, SBCE, SBMB, UL, UM, UPUK
A 2 to 4 °C warming episode, known as the Latest Maastrichtian warming event (LMWE), preceded the Cretaceous-Paleogene boundary (KPB) mass extinction at 66.05 ± 0.08 Ma and has been linked with the ...onset of voluminous Deccan Traps volcanism. Here, we use direct measurements of melt-inclusion CO
concentrations and trace-element proxies for CO
to test the hypothesis that early Deccan magmatism triggered this warming interval. We report CO
concentrations from NanoSIMS and Raman spectroscopic analyses of melt-inclusion glass and vapor bubbles hosted in magnesian olivines from pre-KPB Deccan primitive basalts. Reconstructed melt-inclusion CO
concentrations range up to 0.23 to 1.2 wt% CO
for lavas from the Saurashtra Peninsula and the Thakurvadi Formation in the Western Ghats region. Trace-element proxies for CO
concentration (Ba and Nb) yield estimates of initial melt concentrations of 0.4 to 1.3 wt% CO
prior to degassing. Our data imply carbon saturation and degassing of Deccan magmas initiated at high pressures near the Moho or in the lower crust. Furthermore, we find that the earliest Deccan magmas were more CO
rich, which we hypothesize facilitated more efficient flushing and outgassing from intrusive magmas. Based on carbon cycle modeling and estimates of preserved lava volumes for pre-KPB lavas, we find that volcanic CO
outgassing alone remains insufficient to account for the magnitude of the observed latest Maastrichtian warming. However, accounting for intrusive outgassing can reconcile early carbon-rich Deccan Traps outgassing with observed changes in climate and atmospheric pCO
.
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BFBNIB, NMLJ, NUK, PNG, SAZU, UL, UM, UPUK
Raman spectroscopy yields information about the internal vibrational modes of covalently bonded molecules, which are sensitive to the local molecular environment. As such, Raman spectra of a gas ...composed of covalently bonded molecules collected at different temperatures and/or pressures show variations in band positions and other spectral features, reflecting molecular‐scale interactions (attraction and repulsion) among gas particles associated with the local physical and chemical environment. Because the molecules interact, gases are nonideal, and fugacity is the fundamental thermodynamic quantity that describes partial pressures of gases, adjusted to account for the nonideality. The fugacity of a substance is generally obtained from thermodynamic calculations rather than by direct analysis or measurement and, as such, is conceptually nebulous. Here, we perform spectroscopic analyses of a gas mixture of known composition at variable and known pressures and couple these results with thermodynamic calculations of gas fugacities. We show that Raman peak shifts in gas mixtures are directly correlated to fugacities of the component gas species. Our results thus provide experimental evidence that fugacities of gases can be estimated from Raman spectra collected in situ. By this approach, the thermodynamic quantities fugacity and the related thermodynamic property activity are linked directly with underlying molecular‐scale phenomena, according to the vibrational properties of molecular species. This represents a tractable method to efficiently obtain large datasets on thermodynamic properties of gas mixtures, and with some adjustments, may lead to a viable method for developing nonideal mixing rules for other substances, such as crystalline solid solutions, aqueous ions, and electrolytes.
Raman spectra of gases show variations in band positions reflecting molecular‐scale interactions. Because molecules in gases interact, gases are nonideal and the fugacities of components in the gas describe the nonideality. Here, we show that fugacities of gases can be obtained in situ and at elevated pressure directly from spectroscopic data. This discovery illustrates a link between the spectroscopic and thermodynamic properties of materials, while also providing a straightforward method to extract thermodynamic properties of gases from spectroscopic data.
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BFBNIB, FZAB, GIS, IJS, KILJ, NLZOH, NUK, OILJ, SBCE, SBMB, UL, UM, UPUK
We report the first experimental characterization of isomerically pure and pristine C120 fullertubes, 5,5 C120-D5d(1) and 10,0 C120-D5h(10766). These new molecules represent the highest aspect ratio ...fullertubes isolated to date; for example, the prior largest empty cage fullertube was 5,5 C100-D5d(1). This increase of 20 carbon atoms represents a gigantic leap in comparison to three decades of C60–C90 fullerene research. Moreover, the 10,0 C120-D5d(10766) fullertube has an end-cap derived from C80-Ih and is a new fullertube whose C40 end-cap has not yet been isolated experimentally. Theoretical and experimental analyses of anisotropic polarizability and UV–vis assign C120 isomer I as a 5,5 C120-D5d(1) fullertube. C120 isomer II matches a 10,0 C120-D5h(10766) fullertube. These structural assignments are further supported by Raman data showing metallic character for 5,5 C120-D5d(1) and nonmetallic character for C120-D5h(10766). STM imaging reveals a tubular structure with an aspect ratio consistent with a 5,5 C120-D5d(1) fullertube. With microgram quantities not amenable to crystallography, we demonstrate that DFT anisotropic polarizability, augmented by long-accepted experimental analyses (HPLC retention time, UV–vis, Raman, and STM) can be synergistically used (with DFT) to down select, predict, and assign C120 fullertube candidate structures. From 10 774 mathematically possible IPR C120 structures, this anisotropic polarizability paradigm is quite favorable to distinguish tubular structures from carbon soot. Identification of isomers I and II was surprisingly facile, i.e., two purified isomers for two possible structures of widely distinguishing features. These metallic and nonmetallic C120 fullertube isomers open the door to both fundamental research and application development.
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IJS, KILJ, NUK, PNG, UL, UM
The Dominion Range 2010 howardite pairing group contains an evolved lithic clast of dacite composition. The dacite contains an assemblage of plagioclase, quartz, and augite, with minor pigeonite, ...troilite, ilmenite, FeNi metal, K‐feldspar, and phosphates. Primary augite occurs as >1 mm oikocrysts enclosing plagioclase. Quartz is abundant, comprising approximately 30% of the clast. Textural and geochemical characteristics support the hypothesis that the dacite is a primary igneous lithology, and represents a partial melt of the eucritic crust. Numerical modeling (MELTS) suggests 10–20% partial melting of a Juvinas source could have produced the dacite lithology; quantitative trace element modeling further supports crustal partial melting as the magma source for the dacite. The dacite likely formed as evolved‐melt pockets, and thus represents a volumetrically minor lithology in the Vestan crust, although its formation provides direct support for a genetic relationship between Stannern and residual trend eucrites, and is the first identification of residual eucrite complementary melts. We propose the dacite clast is the first characterized sample of tertiary crust on Vesta.
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BFBNIB, FZAB, GIS, IJS, KILJ, NLZOH, NUK, OILJ, SBCE, SBMB, UL, UM, UPUK
Extensive research efforts of strained germanium (Ge) are currently underway due to its unique properties, namely, (i) possibility of band gap and strain engineering to achieve a direct band gap, ...thus exhibiting superior radiative properties, and (ii) higher electron and hole mobilities than Si for upcoming technology nodes. Realizing lasing structures is vital to leveraging the benefits of tensile-strained Ge (ε-Ge). Here, we use a combination of different analytical tools to elucidate the effect of the underlying InGaAs/InAlAs and InGaAs overlaying heterostructures on the material quality and strain state of ε-Ge grown by molecular beam epitaxy. Using X-ray analysis, we show the constancy of tensile strain in sub-50 nm ε-Ge in a quantum-well (QW) heterostructure. Further, effective carrier lifetime using photoconductive decay as a function of buffer type exhibited a high (low) defect-limited carrier lifetime of ∼68 ns (∼13 ns) in 0.61% (0.66%) ε-Ge grown on an InGaAs (InAlAs) buffer. These results correspond well with the measured surface roughness of 1.289 nm (6.303 nm), consistent with the surface effect of the ε-Ge/III–V heterointerface. Furthermore, a reasonably high effective lifetime of ∼78 ns is demonstrated in a QW of ∼30 nm 1.6% ε-Ge, a moderate reduction from ∼99 ns in uncapped ε-Ge, alluding to the surface effect of the overlying heterointerface. Thus, the above results highlight the prime quality of ε-Ge that can be achieved via III–V heteroepitaxy and paves a path for integrated Ge photonics.
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IJS, KILJ, NUK, PNG, UL, UM
We present phase equilibria modeling, combined with fluid inclusion microthermometry and textural observations, to constrain the composition and relative timing of subduction zone fluid-rock ...interaction during exhumation of two garnet-bearing blueschists from the northern part of the island of Sifnos, Greece. Water (H2O) from seawater was incorporated into the mafic lithologies by low-temperature water-rock interaction to produce hydrous phases, and was subsequently released during the subduction and exhumation cycle. Coupled phase equilibria modeling and textural observations suggest that fluid release resulted from the breakdown of the hydrous phases epidote and glaucophane, and some of the fluid was trapped as fluid inclusions in quartz. Homogenization temperatures and isochores of fluid inclusions are consistent with petrographic observations that suggest fluid inclusions were trapped during exhumation. Constructed isochores cross the inferred P-T path for Sifnos exhumation at pressures of ~0.3–1.0 GPa (~10–30 km depth) and temperatures of ~440–540 °C, suggesting fluid entrapment during the late stages of exhumation and cooling from peak subduction depths of ~70 km. The fluid inclusions have salinities of ~30–35 wt% NaCl equivalent, likely resulting from a multi-stage process that involves an increase in salinity during formation of hydrous minerals during subduction, leaving high salinity fluids and/or halide salts sequestered in pores. This is followed by the partial release of H2O during subsequent breakdown of high-pressure metamorphic phases, with later incorporation of H2O into newly forming retrograde phases. Portions of this fluid that interacted with earlier-formed saline fluids are now preserved as inclusions trapped in quartz. This interpretation suggests that fluid-rock interaction in the northern part of Sifnos occurred in a closed system, with a low water to rock mass ratio (~0.03 to ~0.05) and little to no infiltration of externally-derived lower salinity fluids. The closed system behavior is consistent with the observation that the blueschist unit is bounded by impermeable marble layers that limited exchange with external fluids during burial and/or exhumation.
•Fluid inclusions trapped in exhuming blueschists from Sifnos, Greece.•High salinities result of multi-stage process deriving from internal fluids.•Fluid-rock interaction existed in a closed system with a low water to rock ratio.
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GEOZS, IJS, IMTLJ, KILJ, KISLJ, NLZOH, NUK, OILJ, PNG, SAZU, SBCE, SBJE, UILJ, UL, UM, UPCLJ, UPUK, ZAGLJ, ZRSKP
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•Graphite discs from Cryogenian Nantuo Formation in Shennongjia area of South China.•Nantuo Graphite discs are detrital in origin.•They were likely sourced from metamorphic basement ...of Kongling terrane.•Shennongjia and Kongling terranes were both parts of Yangtze block by Cryogenian.
The tectonic history of the Yangtze block of South China prior to the Ediacaran Period has been a matter of debate. In particular, the tectonic history of the Shennongjia terrane in the central-northern margin of the Yangtze block is poorly understood, and the tectonic relationship between the Shennongjia terrane and the Huangling massif (exposed in the Huangling anticline) is unclear. Previous researchers have reported U-Pb dates of detrital zircons and Nd isotopic compositions of clastic rocks from Cryogenian successions in the Shennongjia terrane to identify ancient crustal remnants and the provenance of clastic sediments, and to constrain the age and crustal evolution of the Yangtze block. Here, we describe abundant graphite discs from silty mudstone of the Cryogenian Nantuo Formation in the Shennongjia area of the Yangtze block. These graphite discs are opaque, ∼23–171 μm in size, and highly reflective. Most are abraded or rounded, although some show hexagonal crystalline morphology. Their Raman spectra are distinct from those of indigenous carbonaceous material (CM) in the sedimentary matrix from the Nantuo Formation at the same locality. Raman CM geothermometric analysis indicates that graphite discs experienced a maximum metamorphic temperature of nearly 600 °C, which is inconsistent with the relatively low metamorphic grade of the host rock. These observations indicate that the graphite discs are of detrital origin, most likely derived from high-grade metamorphic rocks in the basement of the Yangtze block (e.g., the Archean-Paleoproterozoic Kongling terrain in the core of the Huangling anticline), consistent with the hypothesis that the Shennongjia region was a part of Yangtze block by the end of the Cryogenian Period.
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GEOZS, IJS, IMTLJ, KILJ, KISLJ, NLZOH, NUK, OILJ, PNG, SAZU, SBCE, SBJE, UILJ, UL, UM, UPCLJ, UPUK, ZAGLJ, ZRSKP
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