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1.
The fine structure of the region of formation of a protostar in the dense molecular cloud OMC-1 of the Orion Nebula was studied during a period of enhanced activity in 1998–1999, with an angular resolution of 50 μas and a velocity resolution of Δv = 0.053 km/s. Inclusions of ice granules in the bipolar outflow were detected and identified. The velocity of the outflow reaches ∼50 km/s, while that of the granules is <5 km/s. The outflow sublimates and accelerates H2O molecules, thereby exciting the maser emission. As a result, their relative velocity and, accordingly, pumping level decrease. The maser emission of the outflow is observed at distances out to ρ < 3 mas, or <1.5 AU. However, in the distant part (ρ > 5 mas), bullets corresponding to maser emission excited by the outflow in the surrounding medium are observed. The emission is amplified by the external medium at a velocity of v LSR = 7.65 km/s in the bandwidth Δ v ≈ 0.5 km/s. The sources of pumping are clusters of infrared sources. The bipolar outflow is inclined at a small angle to the plane of the sky. The acceleration of the maser inclusions also increases the longitudinal component of the velocity, reducing amplification of the emission. The brightness temperature of the components decreases: T b ∼ ρ −0.8±0.1. The activity terminates with the exponential decline of the maser emission, F ∼ exp(−0.5t 2); in the saturated mode this is determined by a decrease in the optical depth, τ ∼ t 2. The material of the surrounding space, including the ice granules, is drawn into the disk, moves along spirals toward the nozzle, and is ejected as a highly collimated bipolar flow. The density of material in the outflow exceeds the surrounding density by three to four orders of magnitude. The accretion of the surrounding material and ejection of the bipolar outflow are a unified process accompanying the initial phase of formation of protostars. The counter motion of material at the center stimulates the formation of a central massive object, whose gravitational field accelerates the process and stabilizes the system. The ratio of the durations of periods of high and low activity is determined by the rates of ejection and disk replenishment, and is ∼1:10. The rotating bipolar flow is self-focused.  相似文献   

2.
Similarity solutions are derived for wedge-shaped hydraulic fractures driven by a constant inlet pressure P0 into a permeable medium under a uniform confining stress σ. These results describe the seepage-dominated regime in which most of the injected fluid is lost into the permeable walls of the fracture; they complement previous results for the capacitance-dominated regime in which seepage is negligible. Fracture propagation velocity is obtained as an analytical function of fracture length, driving pressure, confining stress, material properties and a single separation constant or eigenvalue which is determined numerically. Self-similar profiles of pressure, opening displacement and fluid velocity along the fracture are presented, together with the self-similar isobars of the two-dimensional pressure field within the permeable medium. Comprehensive results are reported for laminar or turbulent flow of a constant-compressibility liquid or an ideal gas driven by overpressures (P0?σ)/σ ranging from 10?2 to 102.  相似文献   

3.
 The empirical linear relation between volume and logarithm of bulk modulus of a material, discovered by Grover, Getting and Kennedy is taken as the basis for our equation of state. Using the latest experimental information on the adiabatic bulk modulus, the equation of state is applied to the three polymorphs of Mg2SiO4 to develop a consistent dataset of their thermodynamic properties in the temperature range of 200–2273 K and a pressure range of 0.1 MPa–30 GPa. The results imply that the bulk sound velocity contrast (v β−v α)/v α increases with temperature along the α–β phase boundary and reaches the value 8.9% at 13.5 GPa, a pressure equivalent to 410 km depth in the Earth. The bulk sound velocity contrast (v γ−v β)/v β decreases with temperature along the β–γ phase boundary and becomes less than 0.7% at temperatures and pressures equivalent to those associated with the 520-km seismic discontinuity in the Earth. Received: 1 August 2000 / Accepted: 1 March 2001  相似文献   

4.
The gradient flux technique, which measures the gas transfer velocity (k), and new observational techniques that probe turbulence in the aqueous surface boundary layers were conducted over a tidal cycle in the Plum Island Sound, Massachusetts. Efforts were aimed at testing new methods in an estuarine system and to determine if turbulence created by tidal velocity can be responsible for the short-term variability ink. Measurements were made during a low wind day, at a site with tidal excursions of 2.7 m and a range in tidal velocity of nearly 1 m s−1. Estimates ofk using the gradient flux technique were made simultaneously with the Controlled Flux Technique (CFT), infrared imagery, and high-resolution turbulence measurements, which measure the surface renewal rate, turbulent scales, and the turbulent dissipation rate, respectively. All measurements were conducted from a small mobile catamaran that minimizes air- and water-side flow distortions. Infrared imagery showed considerable variability in the turbulent scales that affect air-water gas exchange. These measurements were consistent with variation in the surface renewal rate (range 0.02 to 2 s−1), the turbulent dissipation rate (range 10−7 to 10−5 W kg−1), andk (range 2.2 to 12.0 cm hr−1). During this low wind day, all variables were shown to correlate with tidal speed. Taken collectively our results indicate the promise of these methods for determining short-term variability in gas transfer and near surface turbulence in estuaries and demonstrate that turbulent transport associated with tidal velocity is a potentially important factor with respect to gas exchange in coastal systems.  相似文献   

5.
Bacterial metal reduction is an important biogeochemical process in anaerobic environments. An understanding of electron transfer pathways from dissimilatory metal-reducing bacteria (DMRB) to solid phase metal (hydr)oxides is important for understanding metal redox cycling in soils and sediments, for utilizing DMRB in bioremedation, and for developing technologies such as microbial fuel cells. Here we hypothesize that the outer membrane cytochromes OmcA and MtrC from Shewanella oneidensis MR-1 are the only terminal reductases capable of direct electron transfer to a hematite working electrode. Cyclic voltammetry (CV) was used to study electron transfer between hematite electrodes and protein films, S. oneidensis MR-1 wild-type cell suspensions, and cytochrome deletion mutants. After controlling for hematite electrode dissolution at negative potential, the midpoint potentials of adsorbed OmcA and MtrC were measured (−201 mV and −163 mV vs. Ag/AgCl, respectively). Cell suspensions of wild-type MR-1, deletion mutants deficient in OmcA (ΔomcA), MtrC (ΔmtrC), and both OmcA and MtrC (ΔmtrC–ΔomcA) were also studied; voltammograms for ΔmtrC–ΔomcA were indistinguishable from the control. When the control was subtracted from the single deletion mutant voltammograms, redox peaks were consistent with the present cytochrome (i.e., ΔomcA consistent with MtrC and ΔmtrC consistent with OmcA). The results indicate that OmcA and MtrC are capable of direct electron exchange with hematite electrodes, consistent with a role as terminal reductases in the S. oneidensis MR-1 anaerobic respiratory pathway involving ferric minerals. There was no evidence for other terminal reductases operating under the conditions investigated. A Marcus-based approach to electron transfer kinetics indicated that the rate constant for electron transfer ket varies from 0.025 s−1 in the absence of a barrier to 63.5 s−1 with a 0.2 eV barrier.  相似文献   

6.
The dynamic response due to a spherical source of radius a embedded in an elastic and viscoelastic full-space is investigated at a distance R from the source. Previous solutions to the elastic case are extended to incorporate realistic source pressure functions. The elastic solution is then cast in a scale independent form in order to generalize the application. The results show that the near-field of the spherical source may be defined by R/a < 5. For this region the particle velocity and displacement decrease as R?2, and the risetime decreases as R?1. However. in the far-field region (R/a > 5) the particle velocity and displacement decrease as R?1, and the risetime is independent of R. A non-constant Q model is developed to model viscoelastic attenuation and a complete analytical solution for wave propagation is obtained by cascading the separate mechanisms of geometric attenuation and viscoelastic attenuation. A comparison of our analytical model with the results of dynamic finite element modelling shows excellent agreement. This suggests that the method of cascading the separate transfer functions is a valid approach for wave propagation in viscoelastic media.  相似文献   

7.
Experimental determination of the pressure and temperature controls on Ti solubility in quartz provides a calibration of the Ti‐in‐quartz (TitaniQ) geothermometer applicable to geological conditions up to ~ 20 kbar. We present a new method for determining 48Ti mass fractions in quartz by LA‐ICP‐MS at the 1 μg g?1 level, relevant to quartz in HP‐LT terranes. We suggest that natural quartz such as the low‐CL rims of the Bishop Tuff quartz (determined by EPMA; 41 ± 2 μg g?1 Ti, 2s) is more suitable than NIST reference glasses as a reference material for low Ti mass fractions because matrix effects are limited, Ca isobaric interferences are avoided, and polyatomic interferences at mass 48 are insignificant, thus allowing for the use of 48Ti as a normalising mass. Average titanium mass fraction from thirty‐three analyses of low temperature quartz from the Czech Erzgebirge is 0.9 ± 0.2 μg g?1 (2s) using 48Ti as a normalising mass and Bishop Tuff quartz rims as a reference material. The 2s average analytical uncertainty for individual analyses of 48Ti is 8% for 50 μm spots and 7% for 100 μm spots, which offers much greater accuracy than the 21–41% uncertainty (2s) incurred from using 49Ti as an analyte.  相似文献   

8.
Internal Wave (IW) characteristics and the impact of IW on acoustic field have been studied utilizing the hourly time series of temperature and salinity data collected at a coastal site off Paradeep (north Bay of Bengal) during 24–25 October 2008. The IW characteristics, viz. period (t per ), velocity (C vel ), wavelength (L), and wave numbers (k), are found to be 2.133–34.72 h, 0.135 km h−1, 0.37–6.2 km and 2.70–0.16 cycles km−1, respectively. The semi-diurnal tidal forces are predominant than diurnal as well as at other frequencies and its contribution is about 64% towards the total potential energy (E 0 = 3.34 J m−2). Sound velocity perturbations with space and time in the presence of IW field are examined from Garrettt-Munk (GM) model. Transmission loss anomaly for optimized source-receiver configuration at the depth of 53 m and range of 9 km has been computed from acoustic modelling. The loss in the acoustic transmission is found to be 38.4 dB in the presence of low-frequency IW field.  相似文献   

9.
ZAI-JIN YOU  †  BAOSHU YIN† 《Sedimentology》2006,53(5):1181-1190
A unified criterion is developed for initiation of non‐cohesive sediment motion and inception of sheet flow under water waves over a horizontal bed of sediment based on presently available experimental data. The unified threshold criterion is of the single form, Uo = 2πC[1 + 5(TR/T)2]?1/4, where Uo is the onset velocity of sediment motion or sheet flow, T is wave period, and C and TR are the coefficients. It is found that for a given sediment, Uo initially increases sharply with wave period, then gradually approaches the maximum onset velocity Uo = 2πC and becomes independent of T when T is larger. The unified criterion can also be extended to define sediment initial motion and sheet flow under irregular waves provided the significant wave orbital velocity and period of irregular waves are introduced in this unified criterion.  相似文献   

10.
Thirty‐three samples, including 22 eclogites, collected from the Dabie ultrahigh‐pressure (UHP) metamorphic belt in eastern China, have been studied for seismic properties. Compressional (Vp) and shear wave (Vs) velocities in three mutually perpendicular directions under hydrostatic pressures up to 1.0 GPa were measured for each sample. At 1.0 GPa, Vp (7.5–8.4 km s?1), Vs (4.2–4.8 km s?1), and densities (3.2–3.6 g cm?3) in the UHP eclogites are higher than those of UHP orthopyroxenite (7.3–7.5 km s?1, 4.1–4.3 km s?1, 3.2–3.3 g cm?3, respectively) and HP eclogites (7.1–7.9 km s?1, 4.0–4.5 km s?1, 3.1–3.5 g cm?3, respectively). Kyanitites (with 99.5% kyanite) show extremely high velocities and density (9.37 km s?1, 5.437 km s?1, 3.581 g cm?3, respectively). The eclogites show variation of Vp‐ and Vs‐anisotropy up to 9.70% and 9.17%, respectively. Poisson’s ratio (σ) ranges from 0.218 to 0.278 (with a mean of 0.255) for eclogites, 0.281–0.298 for granulites and 0.248 to 0.255 for amphibolites. The σ values for serpentinite (0.341) and marble (0.321) are higher than for other lithologies. The elastic moduli K, G, E of kyanitite were obtained as 163, 102 and 253 GPa, respectively. The Vp and density of representative UHP metamorphic rocks (eclogite & kyanitite) were extrapolated to mantle depth (15 GPa) following a reasonable geotherm, and compared to the one dimension mantle velocity and density model. The comparison shows that Vp and density in eclogite and kyanitite are greater than those of the ambient mantle, with differences of up to ΔVp > 0.3 km s?1 and Δρ > 0.3–0.4 g cm?3, respectively. This result favours the density‐induced delamination model and also provides evidence in support of distinguishing subducted high velocity materials in the upper mantle by means of seismic tomography. Such ultra‐deep subduction and delamination processes have been recognized by seismic tomography and geochemical tracing in the postcollisional magmatism in the Dabie region.  相似文献   

11.
Reported here are results from new flume experiments examining deposition and entrainment of inert, silt‐sized particles (with spherical diameters in the range from 20 to 60 μm) to and from planar, impermeable and initially starved beds underlying channel flows. Bed surfaces comprised smooth or fixed sand‐size granular roughness and provided hydraulically smooth to transitionally rough boundaries. Results of these experiments were analysed with a simple model that describes the evolution of vertically averaged concentration of suspended sediment and accommodates the simultaneous delivery to and entrainment of grains from the bed. The rate of particle arrival to a bed diminishes linearly, and the rate of particle entrainment increases by the 5/2 power, as the value of the dimensionless Saffman parameter S = u*3/g’ν approaches a threshold value of order unity, where u is the conventional friction velocity of the turbulent channel flow, g’ is the acceleration due to gravity adjusted for the submerged buoyancy of individual particles and ν is the kinematic viscosity of the transporting fluid. This transport behaviour is consistent with the notion that non‐cohesive, silt‐sized particles can neither reach nor remain on an impermeable bed under flow conditions where mean lift imposed on stationary particles in the viscous sublayer equals or exceeds the submerged weight of individual particles. Within the size range of particles used in these experiments, particle size and the characteristic size of granular roughness, up to that of medium sand, did not affect rates of dimensionless arrival or entrainment to a significant degree. Instead, a new but consistent picture of fine‐particle transport is emerging. Silt‐sized material, at least, is subject to potentially significant interaction with the bed during intermittent suspension transport at intermediate flow speeds greater than the value required for initiation of transport (ca 20 cm sec?1) but less than the value (ca 50 cm sec?1) required by the Saffman criterion ensuring transport in fully passive suspension or, equivalently, ‘wash‐load’.  相似文献   

12.
Vp and Vs values have been measured experimentally and calculated for granulite-facies lower crustal xenoliths from central Ireland close to the Caledonian Iapetus suture zone. The xenoliths are predominantly foliated and lineated metapelitic (garnet–sillimanite–K-feldspar) granulites. Their metapelitic composition is unusual compared with the mostly mafic composition of lower crustal xenoliths world-wide. Based on thermobarometry, the metapelitic xenoliths were entrained from depths of c. 20–25 ± 3.5 km and rare mafic granulites from depths of 31–33 ± 3.4 km. The xenoliths were emplaced during Lower Carboniferous volcanism and are considered to represent samples of the present day lower crust.Vp values for the metapelitic granulites range between 6.26 and 7.99 km s− 1 with a mean value of 7.09 ± 0.4 km s− 1. Psammite and granitic orthogneiss samples have calculated Vp values of 6.51 and 6.23 km s− 1, respectively. Vs values for the metapelites are between 3.86 and 4.34 km s− 1, with a mean value of 4.1 ± 0.15 km s− 1. The psammite and orthogneiss have calculated Vs values of 3.95 and 3.97 km s− 1, respectively.The measured seismic velocities correlate with density and with modal mineralogy, especially the high content of sillimanite and garnet. Vp anisotropy is between 0.15% and 13.97%, and a clear compositional control is evident, mainly in relation to sillimanite abundance. Overall Vs anisotropy ranges from 1% to 11%. Poisson's ratio (σ) lies between 0.25 and 0.35 for the metapelitic granulites, mainly reflecting a high Vp value due to abundant sillimanite in the sample with the highest σ. Anisotropy is probably a function of deformation associated with the closure of the Iapetus ocean in the Silurian as well as later extension in the Devonian. The orientation of the bulk strain ellipsoid in the lower crust is difficult to constrain, but lineation is likely to be NE–SW, given the strike-slip nature of the late Caledonian and subsequent Acadian deformation.When corrected for present-day lower crustal temperature, the experimentally determined Vp values correspond well with velocities from the ICSSP, COOLE I and VARNET seismic refraction lines. Near the xenolith localities, the COOLE I line displays two lower crustal layers with in situ Vp values of 6.85–6.9 and 6.9–8.0 km s− 1, respectively. The upper (lower velocity) layer corresponds well with the metapelitic granulite xenoliths while the lower (higher velocity) layer matches that of the basic granulite xenoliths, though their metamorphic pressures suggest derivation from depths corresponding to the present-day upper mantle.  相似文献   

13.
We present multitechnique U‐Pb geochronology and Hf isotopic data from zircon separated from rapakivi biotite granite within the Eocene Golden Horn batholith in Washington, USA. A weighted mean of twenty‐five Th‐corrected 206Pb/238U zircon dates produced at two independent laboratories using chemical abrasion‐isotope dilution‐thermal ionisation mass spectrometry (CA‐ID‐TIMS) is 48.106 ± 0.023 Ma (2s analytical including tracer uncertainties, MSWD = 1.53) and is our recommended date for GHR1 zircon. Microbeam 206Pb/238U dates from laser ablation‐inductively coupled plasma‐mass spectrometry (LA‐ICP‐MS) and secondary ion mass spectrometry (SIMS) laboratories are reproducible and in agreement with the CA‐ID‐TIMS date to within < 1.5%. Solution multi‐collector ICP‐MS (MC‐ICP‐MS) measurements of Hf isotopes from chemically purified aliquots of GHR1 yield a mean 176Hf/177Hf of 0.283050 ± 17 (2s, n = 10), corresponding to a εHf0 of +9.3. Hafnium isotopic measurements from two LA‐ICP‐MS laboratories are in agreement with the solution MC‐ICP‐MS value. The reproducibility of 206Pb/238U and 176Hf/177Hf ratios from GHR1 zircon across a variety of measurement techniques demonstrates their homogeneity in most grains. Additionally, the effectively limitless reserves of GHR1 material from an accessible exposure suggest that GHR1 can provide a useful reference material for U‐Pb geochronology of Cenozoic zircon and Hf isotopic measurements of zircon with radiogenic 176Hf/177Hf.  相似文献   

14.
Boron isotopes in marine carbonates are increasingly used to reconstruct seawater pH and atmospheric pCO2 through Earth’s history. While isotope ratio measurements from individual laboratories are often of high quality, it is important that records generated in different laboratories can equally be compared. Within this Boron Isotope Intercomparison Project (BIIP), we characterised the boron isotopic composition (commonly expressed in δ11B) of two marine carbonates: Geological Survey of Japan carbonate reference materials JCp‐1 (coral Porites) and JCt‐1 (giant clam Tridacna gigas). Our study has three foci: (a) to assess the extent to which oxidative pre‐treatment, aimed at removing organic material from carbonate, can influence the resulting δ11B; (b) to determine to what degree the chosen analytical approach may affect the resultant δ11B; and (c) to provide well‐constrained consensus δ11B values for JCp‐1 and JCt‐1. The resultant robust mean and associated robust standard deviation (s*) for un‐oxidised JCp‐1 is 24.36 ± 0.45‰ (2s*), compared with 24.25 ± 0.22‰ (2s*) for the same oxidised material. For un‐oxidised JCt‐1, respective compositions are 16.39 ± 0.60‰ (2s*; un‐oxidised) and 16.24 ± 0.38‰ (2s*; oxidised). The consistency between laboratories is generally better if carbonate powders were oxidatively cleaned prior to purification and measurement.  相似文献   

15.
Sulfur isotope measurements in three sulfide (two pyrite and one pyrrhotite) samples on two epoxy mounts showed that the mount‐to‐mount variation of raw δ34S values was negligible when secondary ion mass spectrometry (SIMS) analytical settings remained stable. In consequence, an off‐mount calibration procedure for SIMS sulfur isotope analysis was applied in this study. YP136 is a pyrrhotite sample collected from northern Finland. Examination of thin sections with a polarising microscope, backscattered electron image analyses and wavelength dispersive spectrometry mapping showed that the sample grains display no internal growth or other zoning. A total of 318 sulfur isotope (spot) measurements conducted on more than 100 randomly selected grains yielded highly consistent sulfur isotope ratios. The repeatability of all the analytical results of 34S/32S was 0.3‰ (2s, n = 318), which is the same as that of the well‐characterised pyrite reference materials PPP‐1 and UWPy‐1. Its δ34S value determined by gas mass spectrometry was 1.5 ± 0.1‰ (2s, n = 11), which agrees with the SIMS data (1.5 ± 0.3‰, 2s) calibrated by pyrrhotite reference material Po‐10. Therefore, YP136 pyrrhotite is considered a candidate reference material for in situ sulfur isotope determination.  相似文献   

16.
This article reported a wind tunnel test of sediment transport related to surface moisture content and wind velocity using sands from tropical humid coastal area. A 1 mm-thick portion of surface sand was scraped using a self-made sediment sampler, and the gravimetric moisture content was determined. Sand transport was measured via a standard vertical sand trap with a 60 cm height. The result shows that the sand transport profile above the wet surface can be expressed with an exponential equation. In general, the influence of moisture content on sand transport profile mainly focuses on the bottom of the blowing sand cloud. Meanwhile, with moisture content increased, total sand transport dropped, and a relatively larger proportion is transported at greater heights. The vertical movement of particles on higher moisture surface (0.587% < M < 1.448%) is more sensitive to moisture content variation as compared to those on low wet surface (M < 0.587%), total sand transport rate tends to be rather low (0.99 g cm−1 s−1) when M > 1.448%. The total sand transport rate varying with moisture content is divided into three regions of differing gradient at the moisture contents of 0.587 and 1.448%. The gradient of the curve reflected the different influences of the various water forms in surface sediments. The higher moisture surface (M > 1.448%) merely functions as a transport plain for the saltation material. Surface moisture content was the dominant control factor for saltation activity between the moisture contents of 0.587 and 1.448%, wind velocity could resume control saltation after the surface dried to the extent (M < 0.587%).  相似文献   

17.
To evaluate the homogeneity of geological reference material BIR‐1a (basalt; United States Geological Survey, USGS) for Re‐Os isotopic studies at the 0.2–1.0 g test portion size level, sixty‐three precise measurement results of Re and Os mass fractions and isotope amount ratios were obtained over an 18‐month period. These data reveal that the reference material has higher Re (0.691 ± 0.022 ng g?1, 2s, n = 63) and lower Os mass fractions (0.343 ± 0.089 ng g?1, 2s, n = 63) than UB‐N (serpentinite, CRPG) and is homogeneous in 187Os/188Os isotope amount ratio (0.13371 ± 0.00092, 2s, n = 63) at the 0.2–1.0 g test portion size level. The results are essentially consistent with previous views indicating that BIR‐1a gives precise measurement results for Re‐Os isotope amount ratio measurements at the 1 g test portion size level (Ishikawa et al., Chemical Geology, 2014, 384, 27–46; Meisel and Horan, Reviews in Mineralogy and Geochemistry, 2016, 81, 89–106). Based on these new Re‐Os data and previous studies, we propose BIR‐1a as a useful reference material that can be used in method validation and quality control and interlaboratory comparisons for studies dealing with mafic geological samples at test portion sizes of > 0.4 g.  相似文献   

18.
We propose a method for quantifying the in situ heterogeneity of solid materials at the picogram test portion scale, illustrating its use by investigating the oxygen isotope ratio (18O?/16O?) of four quartz samples. Using secondary ion mass spectrometry, we could estimate the intrinsic heterogeneity using a large number (~ 100) of closely spaced duplicated measurements. An analysis of variance was then applied to these large data sets to extract the measurement repeatability (typically 0.10–0.15‰, 1s) from the total variability, thereby revealing a variability ranging from 0.18‰ to 2.3‰, which can be attributed to the genuine isotope ratio heterogeneities. A small proportion of outlying values were either rejected manually after inspection, or were accommodated using robust statistics. We also evaluated two distinct approaches for estimating and correcting instrumental drift; the use of a sub‐area of the test material (if shown to have sufficiently low heterogeneity) is judged to be preferable to using a piece of unrelated silicate glass that we believe to be homogeneous. We also compared three approaches for estimating measurement repeatability, from which we show that the ‘duplicate method’ applied to the reference material is preferable to using other methods based either on the drift monitoring material or on assessing residuals of the drift monitoring material after drift correction. Finally, here we propose a strategy for predicting the number of measurements on individual fragments of a material that would be required to achieve a specified target uncertainty.  相似文献   

19.
New zircon reference materials for in situ zircon radiogenic Hf isotope and stable Zr isotopic determinations made by laser ablation multi-collector inductively coupled plasma-mass spectrometry (LA-MC-ICP-MS) are required due to high data productivity and consequently high reference material consumption rate. This study examines a new natural zircon for Zr isotope ratios by double spike thermal ionisation mass spectrometry (TIMS), and for Hf isotopes by bulk solution nebuliser (SN)-MC-ICP-MS with both Zr and Hf determined by LA-MC-ICP-MS. A total of five zirconium isotope measurements from drilled zircons, determined by TIMS, yield a mean δ94/90ZrIPGP-Zr value of -0.09 ± 0.06‰ (2s). Five and eight hafnium isotope measurements for powders from the drilled zircons and Ban-1-4 by SN-MC-ICP-MS, yield mean 176Hf/177Hf ratios of 0.282985 ± 0.000011 (2s) and 0.282982 ± 0.000007 (2s), respectively. The mean δ94/90ZrIPGP-Zr value and 176Hf/177Hf ratio determined by LA-MC-ICP-MS analyses are -0.06 ± 0.09‰ (2s, n = 504) and 0.282985 ± 0.000035 (2s, n = 327), respectively. The isotopic homogeneities suggest that the Ban-1 zircon is a suitable reference material for microbeam Zr and Hf isotopic measurements.  相似文献   

20.
The compressional wave velocities (Vp), pressure derivatives (Vp′) and anisotropy (A) of three types of eclogites and country rocks from the Dabie–Sulu ultrahigh-pressure (UHP) metamorphic belt, China, have been measured under confining pressures up to 800 MPa. Type-1 eclogites, which are coarse-grained and subjected to almost no retrograde metamorphism, experienced recovery-accommodated dislocation creep at peak metamorphic conditions (in the diamond stability field). Type-2 eclogites are fine-grained reworked Type-1 materials that experienced recrystallization-accommodated dislocation creep under quartz/coesite boundary conditions during the early stage of exhumation. Type-3 eclogites are retrogressed samples that were overprinted by significant amphibolite facies metamorphism during a late stage of exhumation within the crust. Type-1 eclogites are richer in Al2O3 and MgO but poorer in SiO2 and Na2O than Type-2 and Type-3 eclogites. Anisotropy of Type-1 and Type-2 eclogites is generally low (<4%) because volumetrically important garnet is elastically quasi-isotropic, while Type-3 eclogites can exhibit high anisotropy (>10%) due to the presence of strongly anisotropic retrograde minerals such as amphibole, plagioclase and mica. The transition of the pressure dependence of velocity from the poroelastic to elastic regimes occurs at a critical pressure (Pc), which depends mainly on the density and distribution of microcracks and in turn on the exhumation history of rocks. The Vp–pressure relationship can be expressed by Vp=a(lnP)2+blnP+c (P≤Pc) and Vp=V0+DP (P≥Pc), where P is the confining pressure, a and b are constants describing the closure of microcracks below Pc, c is the velocity when P is equal to one (MPa), V0 is the projected velocity of a crack-free sample at room pressure, and D is the intrinsic pressure derivative above Pc. When data are curve-fit, pressure derivatives and anisotropy as functions of pressure are determined. The average Vp of the eclogites in the linear regime is 8.42+1.41×10−4P for Type-1, 7.80+1.58×10−4P for Type-2, and 7.33+2.04×10−4P for Type-3, where Vp is in km/s and P in MPa. The decrease in V0 and increase in D from Type-1 to Type-3 eclogites are attributed to a decrease in garnet content and an increase in retrograde minerals. The NE–SW trending, NW-dipping, slab-like high Vp anomaly (8.72 km/s at a depth of 71 km) which extends from the Moho to at least 110 km beneath the Dabie–Sulu region, can be interpreted as the remnant of a subducted slab which is dominated by Type-1 eclogites and has frozen in the upper mantle since about 200–220 Ma. Such relic crustal materials, subducted and preserved as eclogite layers intercalated with felsic gneiss, garnet–jadeite quartzite, marble and serpentinized peridotite, could be responsible for regionally observed seismic reflectors in the upper mantle.  相似文献   

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