Search

We report the occurrence of microscopic inclusions of shocked quartz plus a Zr phase and trace of Fe oxide crystallites in Australasian microtektites recovered from deep-sea sediment cores within 2000 km of Indochina. The shocked quartz and the Zr phase are interpreted as relicts of the target rock. Furthermore, the internal homogeneity of Australasian microtektites in terms of abundance of relict mineral inclusions, vesicles, and schlieren increases with distance from Indochina. This finding strengthens the current hypothesis that the source crater of the largest and youngest tektite strewn field on Earth is located in the Indochina region, as internal heterogeneity characterizes normal impact glass found in or near the source crater. This finding also indicates that the Australasian microtektites with the longest trajectories underwent the highest temperatures or were heated longer. The definition of microtektites should include the possible occurrence of microscopic relict inclusions as an indication of proximity to the source crater. doi: 10.1130/G30512.1

The anion skeleton of quartz is a distorted body-centered cubic (BCC) arrangement. A hypothetical ideal BCC crystal structure for quartz has been derived and used to locate and describe the unoccupied tetrahedral sites, quantify the distortion of the quartz anion arrangement from ideal BCC, and characterize the role oftetrahedral distortion and O-O interactions in the compression of quartz. Quartz has eight crystallographically nonequivalent tetrahedra, one occupied by silicon and seven unoccupied. These tetrahedra completely fill space, something that cannot be done using only regular tetrahedra. In ideal BCC quartz, the nonequivalent tetrahedra are identical in size and shape with a unique geometry and are referred to as Sommerville tetrahedra. In reality, the unoccupied tetrahedra of quartz are very distorted from both regular and Sommerville tetrahedra. Changes in the unoccupied tetrahedra are responsible for most of the compression in quartz with pressure, as the volume of the Si tetrahedron decreases by Keywords: Quartz, high pressure, body-centered cubic, packing DOI: 10.2138/am.2010.3241

A protein molecule is an intricate system whose function is highly sensitive to small external perturbations. However, no examples that correlate protein function with progressive subangstrom structural perturbations have thus far been presented. To elucidate this relationship, we have investigated a fluorescent protein, citrine, as a model system under high-pressure perturbation. The protein has been compressed to produce deformations of its chromophore by applying a high-pressure cryocooling technique. A closely spaced series of x-ray crystallographic structures reveals that the chromophore undergoes a progressive deformation of up to 0.8 [Angstrom] at an applied pressure of 500 MPa. It is experimentally demonstrated that the structural motion is directly correlated with the progressive fluorescence shift of citrine from yellow to green under these conditions. This protein is therefore highly sensitive to subangstrom deformations and its function must be understood at the subangstrom level. These results have significant implications for protein function prediction and biomolecule design and engineering, because they suggest methods to tune protein function by modification of the protein scaffold. fluorescence | high-pressure x-ray crystallography | protein engineering | protein structure-function | yellow fluorescent protein

High-resolution electron microprobe maps show the distribution of Ti, Al, Ca, K, and Fe among quartz growth zones revealed by scanning electron microscope-cathodoluminescence (SEM-CL) from 12 hydrothermal ore deposits formed between ~100 and ~750 [degrees]C. The maps clearly show the relationships between trace elements and CL intensity in quartz. Among all samples, no single trace element consistently correlates with variations in CL intensity. However in vein quartz from five porphyry-Cu (Mo-Au) deposits, CL intensity always correlates positively with Ti concentrations, suggesting that Ti is a CL activator in quartz formed at >400 [degrees]C. Ti concentrations in most rutile-bearing vein quartz from porphyry copper deposits indicate reasonable formation temperatures of In quartz from most deposits formed at 2000 ppm, but in high-temperature quartz, Al concentrations are consistently in the range of several hundred ppm. Aluminum concentrations in quartz reflect the Al solubility in hydrothermal fluids, which is strongly dependent on pH. Aluminum concentrations in quartz therefore reflect fluctuations in pH that may drive metal-sulfide precipitation in hydrothermal systems. Keywords: quartz, vein, cathodoluminescence, trace elements, hydrothermal, microprobe.

Laser-ablation inductively coupled-plasma mass spectrometry (LA-ICPMS) is an established method of analyzing the elemental composition of individual fluid inclusions in minerals. While the method affords good spatial control of ablation pits, we have found that stray light from the UV (193 nm) laser may permanently modify the gas species in adjacent fluid inclusions. We have used Raman spectroscopy to analyze natural fluid inclusions in quartz before and after ablating test pits. New molecular species (CO, [H.sub.2], and [O.sub.2]) appeared in the vapor phases of inclusions near the pits, resulting in complex, disequilibrium gas mixtures (e.g., [CO.sub.2]-[CH.sub.4]-[H.sub.2]O-CO-[H.sub.2]-[O.sub.2]) and formation of iron oxyhydroxides in brine inclusions. Ablation for 40 s with a laser fluence of ~24 J/[cm.sup.2] on the sample produced the new gas species in inclusions at various distances up to 210 [micro]m from the pits, depending on pit diameter. We attribute the changes in gas speciation to molecular photodissociation induced by stray UV-laser light. We have no evidence that this artifact changes the bulk elemental composition or density of the affected inclusions. The problem for fluid inclusion analysis is that phase-transition temperatures (e.g., clathrate hydrate dissociation, partial homogenization of the carbonic phases, and total homogenization) are highly sensitive to the mixture of gas species present. This means that parameters such as gas compositions, bulk salinity, and minimum entrapment temperatures are likely to be misinterpreted if inclusions are analyzed by microthermometry or Raman spectroscopy in samples that have already undergone laser ablation. Keywords: Fluid inclusion, Raman spectroscopy, laser ablation ICP-MS, microthermometry, gas, speciation

Due to an expected increase in radiation damage under super-LHC conditions, we propose to substitute the scintillator tiles in the original design of the hadronic endcap (HE) calorimeter with quartz plates. Quartz is shown to be radiation hard. Using wavelength shifting fibers, it is possible to collect efficiently the Cerenkov fight generated in quartz plates. This paper summarizes the results from various test beams, bench tests, and Geant4 simulations done on methods of collecting light from quartz plates, as well as radiation hardness tests on quartz material. Index Terms--Cerenkov detectors, Cerenkov radiation, quartz.

The formation of sillimanite, under metastable conditions, relative to corundum and quartz has been defined experimentally, approximately 700 to 800 MPa inside the kyanite stability field thereby allowing for the approximate location of the metastable Sil = Cnd + Qtz equilibrium to be outlined in P-T space from 600 to 800 [degrees]C. Experiments involved using a NaCl assembly with a graphite furnace in a two-piston-cylinder apparatus. The thermocouple tip was in direct contact with the flat-lying, folded Pt capsule thereby minimizing thermal gradients to Keywords: Sillimanite, kyanite, corundum, quartz, rate of reaction, experimental petrology, Rietveld refinement, aluminosilicates

Upheaval Dome is a unique circular structure on the Colorado Plateau in SE Utah, the origin of which has been controversially discussed for decades. It has been interpreted as a crypto volcanic feature, a salt diapir, a pinched-off salt diapir, and an eroded impact crater. While recent structural mapping, modeling, and analyses of deformation mechanisms strongly support an impact origin, ultimate proof, namely the documentation of unambiguous shock features, has yet to be successfully provided. In this study, we document, for the first time, shocked quartz grains from this crater in sandstones of the Jurassic Kayenta Formation. The investigated grains contain multiple sets of decorated planar deformation features. Transmission electron microscopy (TEM) reveals that the amorphous lamellae are annealed and exhibit dense tangles of dislocations as well as trails of fluid inclusions. The shocked quartz grains were found in the periphery of the central uplift in the northeastern sector of the crater, which most likely represents the cross range crater sector. Keywords: impact craters, shock metamorphism, quartz, TEM data.

A Laser Raman microspectrometry method was applied to metamorphic quartz in quartz-eclogite-, epidote-amphibolite-, and amphibolite-facies rocks to assess the quantitative correlation between the Raman frequency shift and metamorphic pressure. Quartz crystals sealed in garnet and other phases have a higher frequency shift than those in the matrix. Furthermore, the quartz inclusions show a frequency shift specific to the individual host crystals in eclogites (garnet [approximately equal to] kyanite > omphacite [approximately equal to] epidote). These observations imply that the residual pressures retained by quartz inclusions depend on elastic parameters of the host Crystals, as discussed by previous researchers. The Raman frequency shift of quartz inclusions in garnet systematically increases with increasing peak metamorphic pressures from the amphibolite facies (0.30-0.55 GPa/470-570 [degrees]C), through the epidote-amphibolite facies (0.8-1.1 GPa/470-635 [degrees]C) to the quartz-eclogite facies (2.1-2.5 GPa/660-710 [degrees]C). Calibrations based on experimental work suggest that the measured Raman frequency shifts signify residual pressures of 0.1-0.2, 0.4-0.6, and 0.8-1.0 GPa for these three groups of metamorphic rocks, respectively. Normal stresses (internal pressures) of quartz inclusions in garnet, numerically simulated with an elastic model, and inferred pressure-temperature conditions at peak metamorphic stage are compatible with the residual pressures estimated from the frequency shifts. Laser Raman microspectroscopic analysis of quartz is a simple and effective method for (1) comparison of pressure conditions in metamorphic rocks formed under various pressure-temperature conditions, and (2) detection of a higher-pressure signature in metamorphic rocks extensively recrystallized during the subsequent exhumation and hydration stage. Keywords: Raman shift, quartz, residual pressure, metamorphism, elastic model

Titanium is one of many trace elements to substitute for silicon in the mineral quartz. Here, we describe the temperature dependence of that substitution, in the form of a new geothermometer. To calibrate the 'TitaniQ' thermometer, we synthesized quartz in the presence of ruffle and either aqueous fluid or hydrous silicate melt, at temperatures ranging from 600 to 1,000[degrees]C, at 1.0 GPa. The Ti contents of quartz (in ppm by weight) from 13 experiments increase exponentially with reciprocal T as described by: Log ([X.sup.qtz.sub.Ti]) = (5.69 [+ or -] 0.02) - (3765 [+ or -] 24)/T(K). Application of this thermometer is straightforward, typically requiring analysis of only one phase (quartz). This can be accomplished either by EPMA for crystallization temperatures above 600[degrees]C, or by SIMS for temperatures down to at least 400[degrees]. Resulting temperature estimates are very precise (usually better than [+ or -] 5[degrees]C), potentially allowing detailed characterization of thermal histories within individual quartz grains. Although calibrated for quartz crystallized in the presence of rutile, the thermometer can also be applied to rutile-absent systems if Ti[O.sub.2] activity is constrained.

Laser-ablation ICP-MS data of hydrothermal vein quartz with zonation in scanning electron microscope cathodoluminescence reveal two groups of trace elements, one that co-varies in concentration with luminosity and another that remains uniform throughout. Bright luminosity correlates with a high total abundance of trace elements in early quartz, including AI (up to 410 [micro]g/g), Ti (up to 240 [micro]g/g), K (up to 330 [ micro]g/g), Li (up to 8 [micro] g/g), Na (up to 36 [micro]g/g), and Fe (up to 20 [micro]g/g). Up to 20 times lower concentrations of these elements are associated with dark luminosity in late quartz. Concentrations of P (21 [micro]g/g), Ga (~0.3 [micro]g/g), Ge (~1.3 [micro]g/g), Sn (~1.5 [micro]g/g), Cu (~0.3 [micro]g/g), and Ag (~0.1 [micro]g/g) demonstrate no relationship with luminosity. Charge balance cannot be achieved for bright luminescent quartz unless the presence of up to 6 [micro] g/g H+ (not analyzed by LA-ICPMS) or interstitial [A1.sup.3+] is invoked. Interestingly, the inferred ~6 [micro]g/g H+ remains constant for quartz containing more than 10 [micro]mol total trace elements and might represent the solubility of H+ in hydrothermal quartz at temperatures between 450 and 700 [degrees]C. LA-ICPMS results indicate that the fluid chemistry determines the quartz trace-element pattern, which may serve as a monitor for the chemical environment from which quartz crystallized. Ratios of Na/Al and Ti/Al are uniform, whereas K/Al evolves toward lower values with decreasing luminosity. Combined evidence, including quartz vein textures, silica solubility data, and estimates of the temperature of quartz growth, suggest that early quartz crystallized fast but late quartz grew more slowly at 350 to 425 [degrees]C. It is speculated that the higher the quartz growth rate is, the more trace elements are incorporated into quartz, besides the temperature dependence known from the literature. Clearly, growth rate, temperature and fluid chemistry are important parameters affecting luminosity: however, their relative importance may vary from case to case.

Metastable coesite is an important pressure indicator tier ultrahigh-pressure rocks. However, in many cases coesite does not survive exhumation, but reacts back to quartz. Although it was shown experimentally that incorporation of H in coesite increases with increasing pressure, most coesite relics found in nature are essentially dry (i.e., OH concentrations are below detection limit,

Effects of heat treatment on absorption bands in fused quartz produced by melting natural quartz powder containing 2 x 10(super 17) cm(super -3) (sample I) and 1.3 x 10(super 19) cm(super -3) of OH (sample II) are studied. The origin of other absorption bands is also discussed.

A minor error in calculation of geobarometric estimates from laser Raman microspectrometry of quartz inclusions in garnet appears in Enami et al. (2007). Correction of this error eliminates anomalous results for grossular-rich garnet, inspiring greater confidence in the validity and applicability of this geobarometric technique. Keywords: Geobarometry, Raman spectrometry, quartz, garnet, elastic model