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1.
The structure and kinematics of the ISM in an extended vicinity of the star WR 139 is analyzed using the results of original Hα interferometric observations together with radio and infrared data. A CO cavity with a size of up to 40′ has been detected around the star at velocities of V LSR ∼ 2.5–10 km/s; the cavity is bounded to the North by a shell radiating in the optical. Ionized hydrogen emits at the systematic velocities V LSR ∼ 6–14 km/s toward the CO cavity, and at V LSR ≃ 4–11 km/s toward the shell. High-velocity motions of ionized hydrogen inside the cavity testify to the probable expansion of gas that has been swept out by the stellar wind of WR 139 at velocities of up to 60–80 km/s.  相似文献   

2.
The conditions under which gold and arsenic are enriched separately during mineralization in gold deposits in southwestern Guizhou Province were described and the thermodynamic calculations gave: 200–150°C at 400 × 10−6 -300 × 106 Pa (corresponding to a depth between 1.6 km and 1.2 km); lgf o2,−40 to -35 Pa; lgf s2, -20 to−16 Pa; pH 5.0 -4.2 and Eh -0.53 V. This project was jointly supported by the National Natural Science Foundation of China and the Open Lab. of Ore Deposit Geochemistry, Institute of Geochemistry, Chinese Academy of Sciences.  相似文献   

3.
 Shallow, anaerobic groundwater near a former manufactured-gas plant (MGP) in Charleston, South Carolina, USA, contains mono- and polycyclic aromatic hydrocarbons (MAHs and PAHs, respectively). Between 1994 and 1997, a combination of field, laboratory, and numerical-flow and transport-model investigations were made to assess natural attenuation processes affecting MAH and PAH distributions. This assessment included determination of adsorption coefficients (K ad ) and first-order biodegradation rate constants (K bio ) using aquifer material from the MGP site and adjacent properties. Naphthalene adsorption (K ad =1.35×10–7 m3/mg) to aquifer sediments was higher than toluene adsorption (K ad =9.34×10–10 m3/mg), suggesting preferential toluene transport relative to naphthalene. However, toluene and benzene distributions measured in January 1994 were smaller than the naphthalene distribution. This scenario can be explained, in part, by the differences between biodegradation rates of the compounds. Aerobic first-order rate constants of 14C-toluene, 14C-benzene, and 14C-naphthalene degradation were similar (–0.84, –0.03, and 0.88 day–1, respectively), but anaerobic rate constants were higher for toluene and benzene (–0.002 and –0.00014 day–1, respectively) than for naphthalene (–0.000046 day–1). Both areal and cross-sectional numerical simulations were used to test the hypothesis suggested by these rate differences that MAH compounds will be contained relative to PAHs. Predictive simulations indicated that the distributions of toluene and benzene reach steady-state conditions before groundwater flow lines discharge to an adjacent surface-water body, but do discharge low concentrations of naphthalene. Numerical predictions were "audited" by measuring concentrations of naphthalene, toluene, and benzene at the site in early 1997. Measured naphthalene and toluene concentrations were substantially reduced and the areal extent of contamination smaller than was both observed in January 1994 and predicted for 1997. Measured 1997 benzene concentrations and distribution were shown to be relatively unchanged from those measured in 1994, and similar to predictions for 1997. Received: 26 June 1997 · Accepted: 25 August 1997  相似文献   

4.
Results of numerical simulations of a collision of the gaseous components of two identical disk galaxies during a head-on collision of the galaxies in the polar direction are presented. When the relative velocity of the galaxy collision is small, their gaseous components merge. At high relative velocities (100–500 km/s), the massive stellar components of the galaxies (M g = 109 M ⊙) pass through each other nearly freely, leaving behind the gaseous components, which are decelerated and heated by the collision. If the overall gaseous component of the colliding galaxies is able to cool to the virial temperature during the collision, a new galaxy forms. At velocities V ≥ 500 km/s, the gaseous component does not have time to cool, and the gas is scattered into intergalactic space, supplying it with heavy elements produced in supernovae in the colliding galaxies. High-velocity (V ≥ 100 km/s) collisions of identical low-mass galaxies (M g ≤ 109 M ⊙) whose mass is dominated by the mass of gas lead to the disruption of their stellar components. The overall gaseous component forms a new galaxy when V ≤ 500 km/s, and is scattered into intergalactic space if the velocity becomes higher than this. A galaxy collision increases the star-formation rates in the disk galaxies by nearly a factor of 100. Rotation of the colliding galaxies in the same direction increases the changes of the disruption of both the stellar and gaseous components of the galaxies. The merger of galaxies during their collision can explain the presence of gaseous disks rotating opposite to the rotation of the stellar component in some ordinary elliptical galaxies. Moreover, galaxy mergers can help explain the origin of a comparatively young stellar population in some elliptical galaxies.  相似文献   

5.
By using data on the 1:100 000 aeromagnetic anomalies of the Sulu orogenic belt, we designed three simulated geotraverses, in which deep seismic reflection and other geophysical investigations have been completed. Based on the features of magnetism of the three profiles, and under the constraints of deep seismic reflection data, together with the magnetism of the core petrology at the Chinese Continental Scientific Drilling (CCSD) pilot-hole and areal geology, the three inversions of magnetic anomalies are carried out. The characteristics of terrane structure are presented: the rocks are mostly composed of eclogite, marble, and gneiss at the depth of 5 km. At the depth between 5 and 7 km under the surface, inverse magnetic bodies are mainly the ultra high pressure metamorphic (UHPM) rock slices containing a lot of coesite-bearing eclogite. At the depth between 7 km and the bottom of upper crust are the rocks of the gneiss, granite and granite diorite that underwent ultra high pressure metamorphic process. Middle crust (10–19 km) is mostly composed of UHPM gneiss and granite that intruded later. The rocks of acid and basic granulite dominate the lower crust. Based on the inversed results of the three simulated geotraverses, we know that the UHPM rock slices of the three profiles are dipping north, stacking each other and being uplifted to the earth’s surface, which may be the result of the North China craton’s subduction and exhumation in the Triassic. Translated from Geological Science and Technology Information, 2007, 26(2): 107–112 [译自: 地质科技情报]  相似文献   

6.
Based on shipboard and satellite observations, the characteristics of upwelling in Lake Baikal in the period of direct temperature stratification have been determined for the first time. Coastal upwellings appear annually under the effect of run-down and alongshore winds and are traced along the coast to a distance of up to 60–100 km and up to 250 km in North Baikal. Analogous to the way it occurs in seas, water rises from the depths of 100–200 m (350 m as a maximum) at the velocity of 0.1 × 10−2−6.5 × 10−2 cm/s. Divergence in the field of intràbasin cyclonic macrovortices produces upwelling in the Baikal pelagic zone and downwelling in the vicinity of shores; this lasts from 7 to 88 days and covers the depth interval of 80–300 m in August and up to 400–800 m in early-mid November. The area of upwellings occupies up to 20–60% of the separate basins of the lake. Vertical circulation of water in the field of pelagic upwellings leads to intensification of coastal currents and to formation of the thermobar with a heat inert zone in the central part of the lake in November, and this thermobar is not observed in other lakes, at that.  相似文献   

7.
Summary The low-pressure emplacement of a quartz diorite body in the metapelitic rocks of the Gennargentu Igneous Complex (Sardinia, Italy) produced a contact metamorphic aureole and resulted in migmatisation of part of the aureole through partial melting. The leucosome, formed by dehydration melting involving biotite, is characterised by granophyric intergrowth and abundant magnetite crystals. A large portion of the high temperature contact aureole shows petrographic features that are intermediate between quartz diorite and migmatite s.s. (i.e. hybrid rocks). A fluid inclusion study has been performed on quartz crystals from the quartz diorite and related contact aureole rocks, i.e. migmatite sensu stricto (s.s.) and hybrid rocks. Three types of fluid inclusions have been identified: I) monophase V inclusions, II) L + V, either L-rich or V-rich aqueous saline inclusions and III) multiphase V + L + S inclusions. Microthermometric data characterised the trapped fluid as a complex aqueous system varying from H2O–NaCl–CaCl2 in the quartz diorite to H2O–NaCl–CaCl2–FeCl2 in the migmatite and hybrid rocks. Fluid salinities range from high saline fluids (50 wt% NaCl eq.) to almost pure aqueous fluid. Liquid-vapour homogenisation temperatures range from 100 to over 400 °C with an average peak around 300 °C. Temperatures of melting of daughter minerals are between 300 and 500 °C. Highly saline liquid- and vapour-rich inclusions coexist with melt inclusions and have been interpreted as brine exsolved from the crystallising magma. Fluid inclusion data indicate the formation of fluid of high iron activity during the low-pressure partial melting and a fluid mixing process in the hybrid rocks.  相似文献   

8.
Using the results of our Hα interferometric observations and observational data on the 21 cm and CO lines, we have analyzed the structure and kinematics of the interstellar medium in the extended vicinity of the star WR 137 and the supernova remnants CTB 87 and G73.9+0.9. A shell structure with a radius of up to 40′ observable in optical lines has been discovered around WR 137. The high-velocity motions of ionized hydrogen inside this shell can be interpreted as expansion of the gas swept out by the wind of WR 137 at velocities of up to 60 km/s. The ionized hydrogen near WR 137 emits at the systematic velocity V LSR ∼ 6–18 km/s. The expansion ofG73.9+0.9 at a velocity of up to 55 km/s has been confirmed. The systematic velocities of the ionized hydrogen toward this supernova remnant are V LSR ≃ −14…+14 km/s. An HI shell around G73.9+0.9 has been detected at velocities V LSR≃−14…−8 km/s. A very faint optical shell of CTB 87 with a size of about 20′ has also been detected. Evidence that CTB 87 is located in the Cygnus Arm is presented.  相似文献   

9.
Hydraulic properties of the crystalline basement   总被引：1，自引：1，他引：1  
Hydraulic tests in boreholes, up to 4.5 km deep, drilled into continental crystalline basement revealed hydraulic conductivity (K) values that range over nine log-units from 10−13−10−4 m s−1. However, K values for fractured basement to about 1 km depth are typically restricted to the range from 10−8 to 10−6 m s−1. New data from an extended injection test at the KTB research site (part of the Continental Deep Drilling Program in Germany) at 4 km depth provide K=5 10−8 m s−1. The summarized K-data show a very strong dependence on lithology and on the local deformation history of a particular area. In highly fractured regions, granite tends to be more pervious than gneiss. The fracture porosity is generally saturated with Na–Cl or Ca–Na–Cl type waters with salinities ranging from <1 to >100 g L−1. The basement permeability is well within the conditions for advective fluid and heat transport. Consequently, fluid pressure is hydrostatic and a Darcy flow mechanism is possible to a great depth. Topography-related hydraulic gradients in moderately conductive basement may result in characteristic advective flow rates of up to 100 L a−1 m−2 and lead to significant advective heat and solute transfer in the upper brittle crust. An erratum to this article can be found at  相似文献   

10.
This method pertains to oil and gas geology and to geology of sedimentary basins prospective for oil and gas. It includes identifying catagenesis zones in drilled areas within the sedimentary cover of the basin based on assay results for drill cores and cuttings using the standard methods. Analysis is primarily made in order to determine rock catagenesis based on the optical characteristics of vitrinite. A correlation between catagenesis zones and layer seismic velocities obtained from regional and exploration seismic data is made for a drilled area. Both the layer seismic velocities and the degree of rock catagenesis increase with depth under the influence of increasing rock density. Correlations between layer velocities and the degree of rock catagenesis have been established. The following ratios have been determined for the Scotian shelf, Canada, and the Barents shelf, Russia: a protocatagenesis zone (the cap) corresponds to layer seismic velocities (V lay) of 1.5–3.3 km/s, a mesocatagenesis zone (the principal hydrocarbon generation area) corresponds to V lay of 3.3–5.0 km/s, and an apocatagenesis zone (an area with a very low hydrocarbon potential) corresponds to V lay of over 5.0 km/s. An advantage of the new method of identification of catagenesis zones is that it can be used prior to drilling. Its conceptual originality and cost efficiency lie precisely in this.  相似文献   

11.
Origin and evolutionary history of the Cuddapah Basin in SE India has remained a subject of considerable speculation whether it was evolved through vertical tectonic movements, extentional stretching or even cometary impact. Based on detailed seismic and other geophysical studies (Gravity, magnetotelluric and heat flow), we have delineated signatures of a possible deep seated mantle plume below southwestern part of the Cuddapah Basin, which may have been responsible for the 1.1 Ga kimberlitic magmatism in the eastern part of the Dharwar craton (EDC). The thermal anomaly associated with this mantle plume appears to have resulted into 15–20 km thick magmatic underplating (Vp: 7.10–7.30 km/s; density 3.07–3.16 g/cm3) below the Parnapalle region of the southwestern Cuddapah Basin, which also coincides with the high gravity and high conductivity anomaly. The massive underplating led to thickening of the crust to about 40–44 km below southwestern part of the Cuddapah Basin, compared to about 34± 2 km in the surrounding regions of EDC, indicating thermal restructuring of the crust / mantle boundary. This plume, which was apparently active in an area of about 500 km radius, may have also affected the Closepet granitic region, which is ∼100 km west of Cuddapah Basin.  相似文献   

12.
Palaeoclimate and palaeoecological study was carried out using palynological and thecamoebian evidences buried in ∼4 m vertically exposed sediment section (12 km inland from the present shoreline) of Late Holocene age along the banks of Gautami-Godavari River and from three shallow cores from its Nilarevu tributary, Andhra Pradesh. Inferred climatic periods include (1) a basal cold/arid period (∼3000-2000 yrs BP) with dominance of Botryococcus and other fresh water algal remains coupled with abundance of 25 species of thecamoebians indicating shallow and lentic ecosystem during most of the period and (2) a relatively warm/wet conditions (since ∼2000 yrs BP) reveal lotic fresh water ecosystem characterized by the evidences of tree palynotaxa and low percentage of thecamoebians. The three shallow cores (0.5–1 m) near the mouth (∼8 km stretch) of the Nilarevu tributary reveal fluvio-marine deposition in the top 50–80 cm sediment unlike the deeper fresh water depositional environment suggesting sea water ingression in the recent decades. The study illustrates that the Gautami-Godavari River delta gradually prograded since ∼3000 yrs BP until 100–150 yrs unlike the intermittent relative sea level rise and fall recorded during the same period in the contemporary south-east deltaic areas.  相似文献   

13.
Using powder X-ray diffraction of heated solids to pressures reaching 68 GPa, the pressure-volume-temperature (PVT) data on corundum Al2O3 and ɛ-Fe were determined with the following results: *Corundum,*Iron, *Al2O3*ɛ-Fe Isothermal bulk*258 (2)*164 (3)  modulus K'300, 1 (GPa) Pressure derivative K300, 1*4.88 (4)*5.36 (16) Temperature derivative*–0.020 (2)*–0.043 (3)  (∂K T,1 /∂T) P (GPa/K) Molar volume V300,1*25.59 (2)*6.76 (2)  (cm3/mol) Isobaric thermal expansion at 1 atm (0.101 MPa) is given by (K–1): α T =2.6 (2) 10–5+1.81 (9) 10–9 T–0.67 (6)/T 2 for corundum, and α T =5.7 (4) 10–5+4.2 (4) 10–9 T–0.17 (7)/T 2 for iron ɛ-Fe. Received: 1 March 1997 / Revised, accepted: 21 August 1997  相似文献   

14.
The paper presents data on naturally quenched melt inclusions in olivine (Fo 69–84) from Late Pleistocene pyroclastic rocks of Zhupanovsky volcano in the frontal zone of the Eastern Volcanic Belt of Kamchatka. The composition of the melt inclusions provides insight into the latest crystallization stages (∼70% crystallization) of the parental melt (∼46.4 wt % SiO2, ∼2.5 wt % H2O, ∼0.3 wt % S), which proceeded at decompression and started at a depth of approximately 10 km from the surface. The crystallization temperature was estimated at 1100 ± 20°C at an oxygen fugacity of ΔFMQ = 0.9–1.7. The melts evolved due to the simultaneous crystallization of olivine, plagioclase, pyroxene, chromite, and magnetite (Ol: Pl: Cpx: (Crt-Mt) ∼ 13: 54: 24: 4) along the tholeiite evolutionary trend and became progressively enriched in FeO, SiO2, Na2O, and K2O and depleted in MgO, CaO, and Al2O3. Melt crystallization was associated with the segregation of fluid rich in S-bearing compounds and, to a lesser extent, in H2O and Cl. The primary melt of Zhupanovsky volcano (whose composition was estimated from data on the most primitive melt inclusions) had a composition of low-Si (∼45 wt % SiO2) picrobasalt (∼14 wt % MgO), as is typical of parental melts in Kamchatka and other island arcs, and was different from MORB. This primary melt could be derived by ∼8% melting of mantle peridotite of composition close to the MORB source, under pressures of 1.5 ± 0.2 GPa and temperatures 20–30°C lower than the solidus temperature of “dry” peridotite (1230–1240°C). Melting was induced by the interaction of the hot peridotite with a hydrous component that was brought to the mantle from the subducted slab and was also responsible for the enrichment of the Zhupanovsky magmas in LREE, LILE, B, Cl, Th, U, and Pb. The hydrous component in the magma source of Zhupanovsky volcano was produced by the partial slab melting under water-saturated conditions at temperatures of 760–810°C and pressures of ∼3.5 GPa. As the depth of the subducted slab beneath Kamchatkan volcanoes varies from 100 to 125 km, the composition of the hydrous component drastically changes from relatively low-temperature H2O-rich fluid to higher temperature H2O-bearing melt. The geothermal gradient at the surface of the slab within the depth range of 100–125 km beneath Kamchatka was estimated at 4°C/km.  相似文献   

15.
A new mineral species has been discovered at the calc-skarnoid occurrence near the mouth of the Tashelga River, Kuznetsky Alatau, Gorny Shoria, Russia, and named after the locality of its discovery. Associated minerals are calcite, hibonite, grossular, vesuvianite, hercynite, magnetite, corundum, perovskite, scapolite, diopside, and apatite. The new mineral occurs as prismatic or finely fibrous crystals up to 1.5–2.0 mm in length, their parallel intergrowths, and felty aggregates as large as 10 mm across. Tashelgite is bluish green, translucent to transparent, with vitreous luster; D calc = 3.67 g/cm3. The IR spectrum does not contain bands of OH groups. Tashelgite is biaxial (−), with α = 1.736(2), β = 1.746(2), γ = 1.750(2); 2V meas = −20(2)°. Dispersion is strong, r < ν. Pleochroism is distinct: X (blue-green) > Y (yellowish green) > Z (almost colorless). Chemical composition (electron microprobe, average of five-point analyses, Fe2O3 is estimated from the ratio of intensities I(FeKb5 )/I(FeKb1 )I(Fe_{K\beta _5 } )/I(Fe_{K\beta _1 } ) in the X-ray spectrum, H2O was determined as a weight loss on heating in vacuum up to 1000°C), wt %: 7.98 CaO, 6.75 MgO, 0.45 MnO, 11.32 FeO, 1.40 Fe2O3, 70.70 Al2O3, 1.8(2) H2O, 100.40 in total. The empirical formula calculated on the basis of 17 oxygen atoms is H1.27Ca0.90Mg1.06Mn0.04 Fe1.002+Fe0.113+Al8.80O17.00. The idealized formula is CaMgFe2+Al9O16(OH). According to single-crystal X-ray structural data, tashelgite is monoclinic, pseudoorthorhombic, space group Pc; unit cell parameters are: a = 5.6973(1), b = 17.1823(4), c = 23.5718(5)?; β = 90.046(3)°; V = 2307.5(1)?3, Z = 8. The crystal structure of tashelgite is unique and characterized by ordering of all cations; Al occupies sites with octahedral and tetrahedral coordination. The cation ordering has also been confirmed by IR spectroscopy. The strongest lines of the X-ray powder diffraction pattern (d, ?]-I[hkl] are: 11.79–48 [002], 2.845–43 [061], 2.616–100 [108], 2.584–81 [146], 2.437–44 [163], 2.406–61 [057], 2.202–72 [244]. The type specimen of tashlegite has been deposited at the Fersman Mineralogical Museum of the Russian Academy of Sciences, Moscow, Russia.  相似文献   

16.
To estimate the behavior of Au, Pd, REE, and Y in magmatic and postmagmatic processes, a series of experimental studies on the solubility of noble metals and REE in magma, magmatic fluid, and hydrothermal solutions has been performed in wide temperature and pressure ranges (300–400°C, 860–1350°C; 1–14 kbar). The coefficients of Au and Pd partitioning (D F/L) between fluid and tholeiitic melt have been determined. Depending on P, T, and the composition of the system, they vary from 1 to 11 for Au and 0.02 to 1 for Pd. The phase solubility technique was used to determine Au and Pd solubility in hydrothermal fluid. The effects of temperature, composition, and fluid acidity on Au and Pd solubility have been estimated. The high solubility of these metals in aqueous chloride solutions has been established for both Au (28–803 mg/kg at T = 300°C, 305–1123 mg/kg at T = 350°C, and 330–1400 mg/kg at T = 400°C) and Pd (40–126 mg/kg at T = 300°C, 62–152 mg/kg at T = 350°C, and 20–210 mg/kg at T = 400°C). The coefficients of REE and Y partitioning (D F/L) between fluid and tholeiitic or alkaline melts have been determined. They vary from 0.00n to 2 depending on P, T, and fluid composition. The experimental data on Au and Pd solubility in solutions and magmatic fluids and the wide variation of REE D F/L between fluid and melt show that magmatic and hydrothermal fluids are efficient agents of Au, Pd, and REE transfer and fractionation. The obtained experimental data were used for elucidating sources of fluids and their role in the genesis of Au-Pd-REE occurrences in the Subpolar Urals.  相似文献   

17.
The Geological Survey of India (GSI) established a twelve-station temporary microearthquake (MEQ) network to monitor the aftershocks in the epicenter area of the Bhuj earthquake (M w7.5) of 26th January 2001. The main shock occurred in the Kutch rift basin with the epicenter to the north of Bhachao village, at an estimated depth of 25 km (IMD). About 3000 aftershocks (M d ≥ 1.0), were recorded by the GSI network over a monitoring period of about two and half months from 29th January 2001 to 15th April 2001. About 800 aftershocks (M d ≥ 2.0) are located in this study. The epicenters are clustered in an area 60 km × 30 km, between 23.3‡N and 23.6‡N and 70‡E and 70.6‡E. The main shock epicenter is also located within this zone. Two major aftershock trends are observed; one in the NE direction and other in the NW direction. Out of these two trends, the NE trend was more pronounced with depth. The major NE-SW trend is parallel to the Anjar-Rapar lineament. The other trend along NW-SE is parallel to the Bhachao lineament. The aftershocks at a shallower depth (<10km) are aligned only along the NW-SE direction. The depth slice at 10 km to 20 km shows both the NE-SW trend and the NW-SE trend. At greater depth (20 km–38 km) the NE-SW trend becomes more predominant. This observation suggests that the major rupture of the main shock took place at a depth level more than 20 km; it propagated along the NE-SW direction, and a conjugate rupture followed the NW-SE direction. A N-S depth section of the aftershocks shows that some aftershocks are clustered at shallower depth ≤ 10 km, but intense activity is observed at 15–38 km depth. There is almost an aseismic layer at 10–15 km depth. The activity is sparse below 38 km. The estimated depth of the main shock at 25 km is consistent with the cluster of maximum number of the aftershocks at 20–38 km. A NW-SE depth section of the aftershocks, perpendicular to the major NE-SW trend, indicates a SE dipping plane and a NE-SW depth section across the NW-SE trend shows a SW dipping plane. The epicentral map of the stronger aftershocksM ≥ 4.0 shows a prominent NE trend. Stronger aftershocks have followed the major rupture trend of the main shock. The depth section of these stronger aftershocks reveals that it occurred in the depth range of 20 to 38 km, and corroborates with a south dipping seismogenic plane.  相似文献   

18.
The Upper Rhine Graben (URG) is the most perceptible part of the European Cenozoic Rift System. Uplifted Variscan basement of the Black Forest and the Vosges forms the flanks of the southern part of the graben. Apatite and zircon fission-track (FT) analyses indicate a complex low-temperature thermal history of the basement that was deciphered by inverse modelling of FT parameters. The models were tested against the observed data and independent geological constraints. The zircon FT ages of 28 outcrop samples taken along an E–W trending transect across the Black Forest and the Vosges range from 136 to 312 Ma, the apatite FT ages from 20 to 83 Ma. The frequency distributions of confined track lengths are broad and often bimodal in shape indicating a complex thermal history. Cooling below 120°C in the Early Cretaceous to Palaeogene was followed by a discrete heating episode during the late Eocene and subsequent cooling to surface temperature. The modelled time–temperature (t–T) paths point to a total denudation of the flanks of URG in the range of 1.0–1.7 km for a paleogeothermal gradient of 60°C/km, and 1.3–2.2 km for a paleogeothermal gradient of 45°C/km since the late Eocene.  相似文献   

19.
This work focuses on a rigorous analysis of the physical–chemical, compositional and textural relationships of amphibole stability and the development of new thermobarometric formulations for amphibole-bearing calc-alkaline products of subduction-related systems. Literature experimental results (550–1,120°C, <1,200 MPa, −1 ≤ ΔNNO ≤ +5), H2O–CO2 solubility models, a multitude of amphibole-bearing calc-alkaline products (whole-rocks and glasses, representing 38 volcanoes worldwide), crustal and high-P (1–3 GPa) mantle amphibole compositions have been used. Calcic amphiboles of basalt-rhyolite volcanic products display tschermakitic pargasite (37%), magnesiohastingsite (32%) and magnesiohornblende (31%) compositions with aluminium number (i.e. Al# = [6]Al/AlT) ≤ 0.21. A few volcanic amphiboles (~1%) show high Al# (>0.21) and are inferred to represent xenocrysts of crustal or mantle materials. Most experimental results on calc-alkaline suites have been found to be unsuitable for using in thermobarometric calibrations due to the high Al# (>0.21) of amphiboles and high Al2O3/SiO2 ratios of the coexisting melts. The pre-eruptive crystallization of consistent amphiboles is confined to relatively narrow physical–chemical ranges, next to their dehydration curves. The widespread occurrence of amphiboles with dehydration (breakdown) rims made of anhydrous phases and/or glass, related to sub-volcanic processes such as magma mixing and/or slow ascent during extrusion, confirms that crystal destabilization occurs with relatively low T–P shifts. At the stability curves, the variance of the system decreases so that amphibole composition and physical–chemical conditions are strictly linked to each other. This allowed us to retrieve some empirical thermobarometric formulations which work independently with different compositional components (i.e. Si*, AlT, Mg*, [6]Al*) of a single phase (amphibole), and are therefore easily applicable to all types of calc-alkaline volcanic products (including hybrid andesites). The Si*-sensitive thermometer and the fO2–Mg* equation account for accuracies of ±22°C (σest) and 0.4 log units (maximum error), respectively. The uncertainties of the AlT-sensitive barometer increase with pressure and decrease with temperature. Near the P–T stability curve, the error is <11% whereas for crystal-rich (porphyritic index i.e. PI > 35%) and lower-T magmas, the uncertainty increases up to 24%, consistent with depth uncertainties of 0.4 km, at 90 MPa (~3.4 km), and 7.9 km, at 800 MPa (~30 km), respectively. For magnesiohornblendes, the [6]Al*-sensitive hygrometer has an accuracy of 0.4 wt% (σest) whereas for magnesiohastingsite and tschermakitic pargasite species, H2Omelt uncertainties can be as high as 15% relative. The thermobarometric results obtained with the application of these equations to calc-alkaline amphibole-bearing products were finally, and successfully, crosschecked on several subduction-related volcanoes, through complementary methodologies such as pre-eruptive seismicity (volcano-tectonic earthquake locations and frequency), seismic tomography, Fe–Ti oxides, amphibole–plagioclase, plagioclase–liquid equilibria thermobarometry and melt inclusion studies. A user-friendly spreadsheet (i.e. AMP-TB.xls) to calculate the physical–chemical conditions of amphibole crystallization is also provided.  相似文献   

20.
Numerical simulations, using empirical interatomic potentials within the framework of lattice dynamics and quasi-harmonic approximation, have been carried out to model the behaviour of the structure and of some thermoelastic properties of pyrope at high pressure and high temperature conditions (0–50 GPa, 300–1500 K). Comparison with observed data, available as a function either of P or of T, suggests that the pressure effects are satisfactorily modelled, whilst the effect of T on the simulations is underestimated. The cell edge, bond lengths and polyhedral volumes have been studied as a function of P along five isotherms, spaced by 300 K steps. These isotherms tend to converge at high pressure, which demonstrates that the pressure effects become dominant compared to those of thermal origin in affecting the structural properties far from ambient conditions. The cell parameter, bond distances, and other structural and thermoelastic quantities determined through simulations have been parametrised as a function of P and T by polynomial expansions. Bulk modulus and thermal expansion have been discussed in the light of the high-temperature-Birch-Murnaghan and of the Vinet P – V – T equations of state. The predictions of the bulk modulus versus P and T from the present calculations and from the Vinet-EOS agree up to 10 GPa, but they differ at higher pressure. Received: 23 October, 1998 / Revised, accepted: 23 April, 1999  相似文献   

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