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1.
Large-scale streaming is analyzed using a sample of 983 thin, edge-on galaxies from the FGC catalog with radial velocities cz<18000 km s?1. The catalog covers the entire sky and contains galaxies with apparent axial ratios a/b>7 and angular diameters a>0.6 arcmin. The distances to the galaxies were determined using a multi-parameter “rotation amplitude-linear diameter” relation, which is similar to the Tully-Fisher relation and takes into account surface brightness, morphological type, and other global parameters. The bulk motion of the galaxy sample with respect to the frame of the microwave background radiation can be described by a dipole solution with amplitude V B =300±75 km s?1 in the direction (l=328°, b=+7°)±15°. The apex parameters for the FGC galaxies agree well with the amplitude and direction of the bulk motion for the Mark III compiled catalog, although the two samples have no objects in common. The dipole solution provides only a rough approximation to the smoothed peculiar-velocity field of the FGC galaxies. Areas of maxima and minima on the V pec map are not correlated with the locations of known nearby clusters and voids. A comparison of nearby and distant subsamples shows that the amplitude of the bulk motion with respect to the 3K reference frame does not decrease with distance. The observed large-scale galaxy streaming could be due to the Shapley concentration of rich clusters (311°, +30°), which is located within 2σ of the apex.  相似文献   

2.
Quantitative estimates of themaximumallowed totalmasses and sizes of the dark-matter halos in groups and associations of dwarf galaxies—special types of metagalactic populations identified in recent astronomical observations with the Hubble Space Telescope—are presented. Dwarf-galaxy systems are formed of isolated dark-matter halos with a small number of dark galaxies embedded in them. Data on the sizes of these systems and the velocity dispersions of the embedded galaxies can be used to determine lower limits on the total dark-halo masses using the virial theorem. Upper limits follow from the conditions that the systems immersed in the cosmic dark-energy background be gravitationally bound. The median maximum masses are close to 1012 M ⊙ for both groups and associations of dwarf galaxies, although the median virial masses for these two types of systems differ by approximately a factor of ten.  相似文献   

3.
The Dashuigou tellurium deposit, located on the western margin of the Yangtze platform, is unique. The deposit is hosted by Triassic metabasalt 50 to 80 meters thick. The orebodies occur as a group of NNE-striking parallel veins. Mineralization developed in three stages: Stage I— pyrrhotite-pyrite, Stage II—tetradymite, and Stage III—chalcopyrite-pyrite. Stage II is the principal tellurium mineralization stage and the tellurium-bearing minerals are mainly tetradymite, tsumoite, tellurbismuth, joseite, calaverite, stuetzite, and native tellurium. The general ore grade of the tellurium in Stage II ranges from 0.2 to 5 wt%, and it reaches 15 to 25 wt% for the massive ores. The dominant gangue minerals are calcite and dolomite, with minor biotite, muscovite, albite, quartz, and chlorite.

Fluid-inclusion studies of calcite, dolomite, and quartz from Stages I, II, and III yield homogenization temperatures of 356° to 260° C (mean = 320° C), 295° to 198° C (mean = 240°), and 235° to 152° C (mean = 170° C), respectively. Salinities of primary fluid inclusions in all three stages are 1.5 to 5.8 wt% NaCl equivalent, 9 to 15.2 wt% NaCl equivalent, and 2.8 to 3.0 wt% NaCl equivalent, respectively.

Isotopic studies show that δ34 values of sulfides range from -2.2 to +2.8 per mil. δ13C values of calcites and dolomites in the ore veins range from -5.3 to -7.42 per mil, and δ18O values range from +10.9 to +13.1 per mil, which are quite different from the δ13C values of+1.0 to +2.8 per mil and δ18O values of +16.8 to +28.5 per mil for the calcites from the Triassic carbonates in the deposit. The δD and δ18O values of muscovite and quartz were measured to be -61 to -54 per mil and +9.9 to +13.0 per mil, respectively. Values of δ18Owater computed from fluid-inclusion trapping temperatures are +3.9 and +7 per mil.

A date of 93 Ma was obtained through measurement of muscovite from the No. 12 ore vein. Sulfur-, oxygen-, carbon-, and hydrogenisotope data indicate that the ore-forming substances of the Dashuigou tellurium deposit were derived from deep-seated sources, and the mineralizations probably are associated with Late Mesozoic alkaline or alkaline granitic magmatism. The estimated sulfur fugacities (fs2) are 10?16.7 for Stage I and 10?14 to 1015.5 for Stage II, whereas the tellurium fugacities (fTe2) are 10?15 to 10?14 and 10?11.2 to 10?10.5, respectively.  相似文献   

4.
A new class of metagalactic system—wide triple systems of galaxies with characteristic scale lengths of ～1 Mpc—are analyzed. Dynamical models of such systems are constructed, and the amount of dark mass contained in them is estimated. In principle, kinematic data for wide triplets allow two types of models: with individual galactic halos and with a common halo for the entire system. A choice between the two models can be made based on X-ray observations of these systems, which can determine whether clustering and hierarchical evolution continues on scales of ～1 Mpc or whether systems with such scale lengths are in a state of virial quasi-equilibrium.  相似文献   

5.
The structure and evolution of triple galaxy systems in the presence of the cosmic dark-energy background is studied in the framework of the three-body problem. The dynamics of wide triple systems are determinedmainly by the competition between the mutual gravitational forces between the three bodies and the anti-gravity created by the dark-energy background. This problem can be solved via numerical integration of the equations of motion with initial conditions that admit various types of evolutionary behavior of the system. Such dynamical models show that the anti-gravity created by dark energy makes a triple system less tightly bound, thereby facilitating its decay, with a subsequent transition to motion of the bodies away from each other in an accelerating regime with a linear Hubble-law dependence of the velocity on distance. The coefficient of proportionality between the velocity and distance in this asymptotic relation corresponds to the universal value HΛ = 61 km s?1 Mpc?1, which depends only on the dark-energy density. The similarity of this relation to the large-scale recession of galaxies indicates that double and triple galaxies represent elementary dynamical cells realizing the overall behavior of a system dominated by dark energy on their own scale, independent of their masses and dimensions.  相似文献   

6.
Observational data on the evolution of quasars and galaxies of various morphological types and numerical simulations carried out by various groups are used to argue that low-redshift (z < 0.5) quasars of types I and II, identified with massive elliptical and spiral galaxies with classical bulges, cannot be undergoing a single, late phase of activity; i.e., their activity cannot be “primordial,” and must have “flared up” at multiple times in the past. This means that their appearance at low z is associated with recurrence of their activity—i.e., with major mergers of gas-rich galaxies (so-called wet major mergers)—since their lifetimes in the active phase do not exceed a few times 107 yrs. Only objects we have referred to earlier as AGN III, which are associated with the nuclei of isolated, late-type spiral galaxies with low-mass, rapidly-rotating “pseudobulges,” could represent primordial AGNs at low z. The black holes in such galaxies have masses M BH < 107 M ⊙, and the peculiarities of their nuclear spectra suggest that they may have very high specific rotational angular momenta per unit mass. Type I narrow-line (widths less than 2000 km/s) Seyfert galaxies (NLSyIs) with pseudobulges and black-hole masses M BH < 107 M ⊙ may be characteristic representatives of the AGN III population. Since NLSyI galaxies have pseudobulges while Type I broad-line Seyfert galaxies have classical bulges, these two types of galaxies cannot represent different evolutionary stages of a single type of object. It is possible that the precursors of NLSyIs are “Population A” quasars.  相似文献   

7.
A new phase of AlOOH (tentatively called δ-AlOOH) was synthesized at 21?GPa and 1000?°C and its crystal structure was identified by a powder X-ray diffraction method. Rietveld refinement revealed that this aluminum oxide hydroxide has an orthorhombic unit cell, a?=?4.7134(1) Å, b?=?4.2241(1) Å, c?=?2.83252(8) Å, V?=?56.395 (5) Å3, and Z?=?2 in the space group of P21?nm. A calculated density is 3.533?g?cm?3, which is about 4.48 and 15.04% denser than that of diaspore and boehmite, respectively. The δ-[Al0.86Mg0.07Si0.07]OOH is also stable at 21?GPa and 1000?°C, coexisting with majorite and phase egg, and its cell parameters are a?=?4.710(1) Å, b?=?4.215(1) Å, c?=?2.839(1) Å, and V?=?56.37(1) Å3.  相似文献   

8.
The behavior of the gravitational potential outside the region where the main spiral arms of galaxies are located is investigated. The characteristic features of this behavior include nearly circular extensions of the main arms, which typically have an angular extent of 90°. It is natural to interpret these quarter-turn spirals as the response of the galactic disk to the gravitational potential of the main spiral arms. The theoretical models are supported by observational data for the brightness distributions in both normal (NGC 3631) and barred (NGC 1365) galaxies.  相似文献   

9.
The dating of fluid inclusions of quartz yields an Ar-Ar isochrone age of 320.4±6 Ma. Three types of fluid inclusions have been identified with the homogenization temperature ranging from 157℃ to 362℃. The homogenization temperature consists of two groups. The first group varies from 157℃ to 166℃, and the second from 232℃ to 362℃. Their chemical composition is dominated by Na+-Ca2+-Mg2+ and Cl-. The relative concentration of ions is characteristic by Na+>Ca2+>K+>Mg2+ and C1->SO42-> F-. The δD and δ18O values indicate that the ore-forming fluid originates from mixing of multi-source water. The Sarkobu gold deposit has experienced two mineralization stages: gold was enriched during the volcanic-exhalative-sedimentary process in the early stage, while the gold deposit was finally formed under compression-shearing during the orogenic period.  相似文献   

10.
Carbonaceous units commonly host or are closely related to lode-gold mineralization in the mesothermal Fazenda Maria Preta (FMP) and Fazenda Canto (FC) deposits of the Paleoproterozoic Rio Itapicuru greenstone belt of northeastern Brazil. In these deposits, the carbonaceous matter occurs mainly as: (1) straight to anastomosing seams (Type I) along or transecting the rock fabric, or as stylolitic structures in quartz veins; (2) single grains composed of an agglomerate of highly anisotropic subgrains (Type II); or (3) single grains with a homogeneous internal texture (Type III), which are either enclosed in Type-I carbonaceous seams or disseminated in the rock matrix. Type-I carbonaceous matter commonly hosts or is overgrown by the gold-related sulfide paragenesis, particularly arsenopyrite, whereas both Type I and Type II enclose crystals of arsenopyrite or occur as inclusions and in sharp contact with the sulfide phases.

The three morphological types of carbonaceous matter exhibit similar Raman spectral characteristics, with distinct D and O peaks at wave numbers between 1351 cm?1 and 1357 cm?1, and 1585 cm?1 and 1598 cm?1, respectively. In contrast to the FMP deposit, the carbonaceous matter of the FC deposit shows D peaks of higher intensities than the O peaks. The O peaks are accompanied by an additional disorder-induced band on the high wave number side (≈ 1622 cm?1), and the O/D peak intensity ratios are higher and the half-height O-peak widths smaller. These spectral parameters indicate that the carbonaceous matter in both deposits corresponds to some form of microcrystalline disordered graphitic material and defines a graphitization trend from the FMP to the FC deposit.

The carbonaceous matter of the FMP deposit is isotopically lighter (δ13C = ?23.3‰ to ?30.8‰; x = ?27.4 ± 1.8‰ relative to PDB) than the carbonaceous material of the FC (δ13C = ?18.5‰ to ?21.0‰, x = ?19.7 ± 0.9‰). These δ13C values, together with the geologic evidence, point toward a primarily biogenic organic origin for the carbonaceous matter. The marked differences in the Raman spectral parameters and the δ13C values are interpreted as resulting from different degrees of thermal maturation of carbonaceous matter attained during the regional greenschist metamorphism and granite intrusions of the Rio Itapicuru greenstone belt.

The δ13C compositions of CO2 resulting from the oxidation or hydrolysis of the carbonaceous matter, calculated by applying the equilibrium CO2-graphite fractionation, fall within the range ?9.7‰ to ?18.8‰ at 360 to 420°C (FMP deposit) and ?6.0° to ?10.0° at 390 to 455°C (FC deposit). These calculated δ13C values are lower than those obtained from primary fluid-inclusion CO2 in gold-bearing veins (?6.0° to ?10.2° for the FMP deposit; ?2.8° to ?4.9° for the FC deposit) and imply that the thermal maturation process of the carbonaceous matter contributed little to changes in the chemistry and isotopic composition of the ore fluid. The presence of the carbonaceous matter may have been an important factor in gold deposition during fluid-carbon interaction, acting: (1) as a chemical trap, by reducing the f(O2) of the ore fluids or enhancing fluid immiscibility by adding small quantities of CH4 and N2 to the fluid phase; and/or (2) as a physical barrier, by adsorbing gold on its surface as activated carbon.  相似文献   

11.
The aim of the present work is to compile and update a catalogue of the instrumentally recorded earthquakes in Egypt, with uniform and homogeneous source parameters as required for the analysis of seismicity and seismic hazard assessment. This in turn requires a detailed analysis and comparison of the properties of different available sources, including the distribution of events with time, the magnitude completeness, and the scaling relations between different kinds of magnitude reported by different agencies. The observational data cover the time interval 1900–2004 and an area between 22°–33.5° N and 25°–36° E. The linear regressions between various magnitude types have been evaluated for different magnitude ranges. Using the best linear relationship determined for each available pair of magnitudes, as well as those identified between the magnitudes and the seismic moment, we convert the different magnitude types into moment magnitudes M W, through a multi-step conversion process. Analysis of the catalogue completeness, based on the M W thus estimated, allows us to identify two different time intervals with homogeneous properties. The first one (1900–1984) appears to be complete for M W ≥ 4.5, while the second one (1985–2004) can be considered complete for magnitudes M W ≥ 3.  相似文献   

12.
The Martabe Au–Ag deposit, North Sumatra Province, Indonesia, is a high sulfidation epithermal deposit, which is hosted by Neogene sandstone, siltstone, volcanic breccia, and andesite to basaltic andesite of Angkola Formation. The deposit consists of six ore bodies that occurred as silicified massive ore (enargite–luzonite–pyrite–tetrahedrite–tellurides), quartz veins (tetrahedrite–galena–sphalerite–chalcopyrite), banded sulfide veins (pyrite–tetrahedrite–sphalerite–galena) and cavity filling. All ore bodies are controlled by N–S and NW–SE trending faults. The Barani and Horas ore bodies are located in the southeast of the Purnama ore body. Fluid inclusion microthermometry, and alunite‐pyrite and barite‐pyrite pairs sulfur isotopic geothermometry show slightly different formation temperatures among the ore bodies. Formation temperature and salinity of fluid inclusions of the Purnama ore body range from 200 to 260 C and from 6 to 8 wt.% NaCl equivalent, respectively. Formation temperature and salinity of fluid inclusions of the Barani ore body range from 200 to 220 °C and from 0 to 2.5 wt.% NaCl equivalent and those of the Horas ore body range from 240 to 275 °C and from 2 to 3 wt.% NaCl equivalent, respectively. The Barani and Horas ore bodies are less silicified and sulfides are less abundant than the Purnama ore body. A relationship between enthalpy and chloride content indicates mixing of hot saline fluids with cooler dilute fluids during the mineralization of each of the ore bodies. The δ18O values of quartz samples from the southeast ore bodies exhibit a wide range from +4.2 to +12.9‰ with an average value of +7.0‰. The δ18O values of H2O estimated from δ18O values of quartz, barite and calcite confirm the oxygen isotopic shift to near meteoric water trend, which support the incorporation of meteoric water. Salinity of the fluid inclusions decrease from >5 wt.% NaCl equivalent in the Purnama ore body to <3 wt.% NaCl equivalent in the Barani ore body, indicating different fluid systems during mineralization. The δ34S values of sulfide and sulfate in Purnama range from ? 4.2 to +5.5‰ and from +1.2 to +26.7‰, those in the Barani range from ? 4.3 to +26.4‰ and from +3.9 to +18.5‰ and those in the Horas ore body range from ? 11.8 to +3.5‰ and from +1.4 to +25.7‰, respectively. The δ34S of total bulk sulfur in southeastern ore bodies (Σδ34S) was estimated to be approximately +6‰. The estimated sulfur fugacity during formation of the Purnama and Horas ore bodies is relatively high. It was between 10?4.8 and 10?10.8 atm at 220 to 260 °C. Tellurium fugacity was between 10?7.8 and 10?9.5 atm at 260 °C and between 10?9 and 10?10.6 atm at 220 °C in the Purnama ore body. The Barani ore body was formed at lower fS2, lower than about 10?14 atm at 200 to 220 °C based on the presence of arsenopyrite and pyrrhotite in the early stage, and between 10?14 and 10?12 atm based on the existence of enargite and tennantite in the last stage. © 2016 The Society of Resource Geology  相似文献   

13.
《Quaternary Science Reviews》2004,23(3-4):245-260
In Arctic and sub Arctic seas, shell growth and/or secondary calcite overgrowth of Neogloboquadrina pachyderma (left coiled)—Npl—occur along the pycnocline, and their δ13C and δ18O-values are size and weight dependent. However, whereas the Npl 18O data from the NW Atlantic indicate near-equilibrium conditions with ambient waters and a positive relationship between shell weight and 18O-content, assemblages from box-cored sediments of the Chukchi Sea (western Arctic) are depleted by ∼2‰ with respect to equilibrium values with modern conditions, and depict a negative relationship between shell weight and its δ18O-value (−0.15±0.03‰/μg on VPDB scale). A similar feature is also depicted by the dextral form of N. pachyderma (Npd). We associate the reverse shell-size or weight vs. δ18O relationship to the reverse temperature gradient observed along the thermocline between the surface cold and dilute water layer, and the underlying near 3°C-warmer saline North Atlantic water mass. The analysis of two late to post-glacial sedimentary sequences from the Chukchi Sea indicates that such a water mass stratification with a reverse thermocline persisted throughout the Holocene, thus reflecting an early onset of the modern-like linkage between the Arctic Ocean and the North Atlantic. Moreover, lower δ18O-values in both Npl and Npd together with larger δ18O-gradients between the different shell sizes at ca 9–7 ka BP suggest ∼3°C higher temperatures in the upper North Atlantic water mass, in comparison with the present (approximately +1°C, at the study site), thus likely a higher inflow rate of this water mass during the early Holocene.  相似文献   

14.
The δ13C values of dissolved HCO3? in 75 water samples from 15 oil and gas fields (San Joaquin Valley, Calif., and the Houston-Galveston and Corpus Christi areas of Texas) were determined to study the sources of CO2 of the dissolved species and carbonate cements that modify the porosity and permeability of many petroleum reservoir rocks. The reservoir rocks are sandstones which range in age from Eocene through Miocene. The δ13C values of total HCO3? indicate that the carbon in the dissolved carbonate species and carbonate cements is mainly of organic origin.The range of δ13C values for the HCO3? of these waters is ?20–28 per mil relative to PDB. This wide range of δ13C values is explained by three mechanisms. Microbiological degradation of organic matter appears to be the dominant process controlling the extremely low and high δ13C values of HCO3? in the shallow production zones where the subsurface temperatures are less than 80°C. The extremely low δ13C values (< ?10 per mil) are obtained in waters where concentrations of SO42? are more than 25 mg/l and probably result from the degradation of organic acid anions by sulfate-reducing bacteria (SO42? + CH3COO? → 2HCO3? + HS?). The high δ13C values probably result from the degradation of these anions by methanogenic bacteria (CH3COO? + H2OaiHCO3? + CH4).Thermal decarboxylation of short-chain aliphatic acid anions (principally acetate) to produce CO2 and CH4 is probably the major source of CO2 for production zones with subsurface temperatures greater than 80°C. The δ13C values of HCO3? for waters from zones with temperatures greater than 100°C result from isotopic equilibration between CO2 and CH4. At these high temperatures, δ13C values of HCO3? decrease with increasing temperatures and decreasing concentrations of these acid anions.  相似文献   

15.
Two samples from the Eclogite Micaschist Complex (EMC) and the Seconda Zona Diorito–Kinzigitica (IIDK) of the Sesia Zone have been studied using a high-spatial resolution laser probe 40Ar/39Ar technique with the aim of investigating the complexities of argon behaviour in metamorphic rocks and comparing their thermal histories. Data from a single large phengite grain from the EMC show a range of ages from mid-Jurassic to Upper Cretaceous. These ‘apparent age’ variations are spatially related to both location within the grain and to intragrain microstructure. Modelling of the data shows that the profile formed by the diffusion of an excess argon component into the grain, parallel to the mica cleavage. Profile asymmetry is explained by temporal variations in microstructural development enabling excess argon to enter the grain at different times in different places. The temperatures of the initiation of deformation and the possible time-scales for the deformation can be calculated as a function of cooling rate. All estimates suggest deformation at greenschist facies, in accord with the observed retrograde mineral assemblage. Absolute temperature estimates for deformation vary by less than 22 °C for different cooling rates of 10 and 30 °C Ma?1 but vary by 80 °C with different estimates of diffusion parameters. The duration of deformation was for at least 2 Ma at 10 °C Ma?1 or 0.7 Ma at 30 °C Ma?1. Biotites from the IIDK sample record a Permian to Upper Cretaceous age range that correlates with grain size, the smallest grain sizes yielding the youngest ages. This relationship is best explained by a partial resetting of biotites during an Alpine thermal event initiated not more than 70 Ma ago. Modelling of these data suggest that the sample never exceeded 300 °C during the Alpine. The profoundly different thermal histories of the two units—the EMC recrystallized at 550 °C whilst the IIDK remained below 300 °C—suggests that they may not have been juxtaposed until much later than the eclogite facies metamorphism.  相似文献   

16.
We analyze the propagation of light in a universe with density inhomogeneities, which, as was first demonstrated by Zel’dovich, systematically affect the angular sizes and apparent magnitudes of distant objects. The Zel’dovich effect can be represented in terms of an effective curvature, which is proportional to the magnitude of the inhomogeneities. We estimate the effective curvature, radius of curvature, and mean distance between conjugate points for the cases when the density inhomogeneities are taken to be stars in the Galaxy, galaxies, and clusters of galaxies. We discuss the possibility of detecting the Zel’dovich effect using modern astronomical data.  相似文献   

17.
Based on the available observational data on the diffuse X-ray emission from hot gas in virialized systems (the central regions of clusters of galaxies or the coronas of spherical galaxies) and the masses of the central objects in these systems (the central galaxies in clusters or massive compact objects—supermassive black holes—in the galactic nuclei), we show that the X-ray luminosity is proportional to the square of the mass of the central object. This is consistent with the dependence obtained earlier between X-ray luminosities of systems and the square of their optical luminosities (i.e., the luminosity of stars in these systems). The existence of such dependences for virialized systems on various scales may provide evidence that they are all formed by a single mechanism, such as hierarchical gravitational clustering. Although the times to achieve hydrostatic equilibrium between the gaseous and stellar components in systems on various scales differ, the relation between certain internal parameters of these systems may remain the same. This enables us to estimate certain parameters of virialized systems in terms of others, in particular, to estimate the masses of their central objects based on the diffuse X-ray luminosity of their coronas.  相似文献   

18.
We propose a new method for estimating the HI deficiency in galaxies. The method is based on a semi-empirical relationship between the total mass of HI and specific angular momentum of isolated galaxies. The atomic-hydrogen deficiency is estimated for nearby spiral galaxies and for spiral galaxies in the Virgo and Coma clusters. The mean HI deficiencies determined for these samples using our method are similar to those obtained with conventional methods, although there are considerable differences in some cases. The HI deficiency in nearby galaxies does not depend on their degree of isolation, and there is no systematic discrepancy between their HI and “normal” masses. Significant HI deficiencies are observed in the Virgo and Coma clusters, out to distances of 1.5 and 3–4 Mpc from the cluster centers, respectively. At such distances, the ram pressure is too small to sweep a considerable amount of gas from the galactic disks. Either these galaxies have passed through the dense cluster center, or their gas deficiency is due to the fact that the halo had stopped accreting onto the disk when the galaxy entered the cluster.  相似文献   

19.
Hydrogen and oxygen isotopic compositions of cherts (δD for hydroxyl hydrogen in the chert, δ18O for the total oxygen) have been determined for a suite of samples from the central and western United States. When plotted on a δD-δ18O diagram, Phanerozoic cherts define domains parallel to the meteoric water line which are different for different periods of geologic time. The elongation parallel to the meteoric water line suggests that meteoric waters were involved in the formation of many cherts.The existence of different chert δ-values for different geologic times indicates that once the granular microcrystalline quartz of cherts crystallizes its isotopic composition is preserved with time. An explanation for the change with time of the isotopic composition of cherts involving large changes with time in the isotopic composition of ocean water is unlikely since δ18O of the ocean would have had to decrease by about 3‰between Carboniferous and Triassic time and then increase about 5%.` from Triassic to Cretaceous time. Such isotopic changes cannot be accounted for by extensive glaciation, sedimentation of hydrous minerals, or input of water from the mantle into the oceans.The variation with time of the chert δ-values can be satisfactorily explained in terms of past climatic temperature fluctuations if the chert-water isotope fractionation with temperature is approximated by 1000 lnα = 3.09 × 106T?2 – 3.29. Crystallization temperatures so inferred suggest that the average climatic temperatures for the central and western U.S. decreased from about 34 to 20°C through the Paleozoic, increased to 35–40°C in the Triassic, and then decreased through the Mesozoic to Tertiary values of about 17°C. A few data for the Precambrian suggest the possibility that Earth surface temperatures may have reached about 52°C at 1.3 b.y. and about 70°C at 3 b.y.  相似文献   

20.
The differentiated Mesozoic alkali dolerite Prospect Intrusion contains a wide range of secondary minerals, including carbonates (primarily calcite), laumontite, prehnite and heulandite, whose stability relationships imply a formation temperature of <200°C. The δ18O data for carbonates define a higher temperature (160 – 195°C) suite, and a lower temperature (51 – 73°C) suite. The δ13C, δ18O and 87Sr/86Sr isotope systematics for these carbonates suggest derivation of the higher temperature group from magmatic fluids, whereas the other group had a major meteoric component that probably originated from porewater in the country rock. Source fluids for prehnite were meteoric rather than magmatic in origin based on their δD and δ18O ratios. Early in the intrusion's emplacement, CO2-rich hydrothermal fluids formed a carbonate rind sealing the upper part of the hydrothermal system and produced the higher temperature carbonates (calcite) and laumontite. Later, cooler fluids with a meteoric component infiltrated vesicles and fractures, depositing the lower temperature carbonates (calcite, aragonite), heulandite and prehnite.  相似文献   

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