首页 | 本学科首页   官方微博 | 高级检索  
相似文献
 共查询到20条相似文献，搜索用时 31 毫秒
1.
Our objective is to look for deep paths of Cenozoic volcanism and migration routes of active mantle volatiles through the lithosphere of the western Bohemian Massif. We show that the rejuvenated junction of three mantle domains, delimited by different orientation of seismic anisotropy and belonging to originally separated microplates — the Saxothuringian (ST), Moldanubian (MD) and Teplá-Barrandian (TB) — can provide the easiest upward routes of fluids through the deep lithosphere. Geographic distribution of mantle-fluid escapes at the surface suggests fluid migration through the ductile lower crust and through partly open faults in the rigid upper crust, which is locally detached and shifted from its lower part and from the mantle lithosphere. Present-day escapes of mantle-derived helium and CO2 concentrate mainly in two tectonically different crust edifices — in the Cheb Basin (CHB) and in an allochtonous block called the Mariánské Lázně Complex (MLC). Crystalline basement of the CHB developed above the Variscan ‘triple junction’ of the mantle lithosphere domains. The basement was extended during the Cenozoic and dissected by systems of faults into small partly sunken blocks. Thanks to buoyancy the mantle fluids migrate upwards along the lithosphere junction into the faulted basement of the CHB. The highest CO2 flow and the highest 3He/4He ratios are observed at intersections of major normal faults and along the southern boundary of the Smrčiny (Fichtelgebirge) granite Pluton. The fluid escapes are separated from the earthquake swarm epicentres. Routes of the fluids to the MLC are longer and more complicated. Surface escapes tap the mantle fluids mainly from the Mariánské Lázně Fault (MLF) and from the tectonic boundaries along which the MLC block of the TB lower crust was thrust over the ST complexes. Hypocentres of earthquake swarms of the two major focal areas at Novy Kostel and Lazy, located mainly at depths of 6–13 km, reside either in granite or in underlying gneiss, while the escapes of mantle fluids follow major faults or boundaries of crystalline units outside the Smrčiny and Karlovy Vary granite Plutons. We suggest that primarily those parts of faults in the upper crust, which is strengthened by granite magmatism and rigid enough to selectively accumulate stresses, are seismoactive. On the other hand, other parts of the faults tapping ascending mantle volatiles are ‘lubricated’ by the fluids and secondary mineralogical changes, and thus they cannot accumulate sufficient stresses to be released by earthquakes. A comparison of the most probable paths of the mantle fluids with the space-time distribution of the Novy Kostel hypocentres does not seem to support the model of the earthquake swarms triggered by pressurized fluids of mantle origin.  相似文献   

2.
《Journal of Geodynamics》2008,45(3-5):149-159
Locations of the Eger Rift, Cheb Basin, Quaternary volcanoes, crustal earthquake swarms and exhalation centers of CO2 and 3He of mantle origin correlate with the tectonic fabric of the mantle lithosphere modelled from seismic anisotropy. We suggest that positions of the seismic and volcanic phenomena, as well as of the Cenozoic sedimentary basins, correlate with a “triple junction” of three mantle lithospheres distinguished by different orientations of their tectonic fabric consistent within each unit. The three mantle domains most probably belong to the originally separated microcontinents – the Saxothuringian, Teplá-Barrandian and Moldanubian – assembled during the Variscan orogeny. Cenozoic extension reactivated the junction and locally thinned the crust and mantle lithosphere. The rigid part of the crust, characterized by the presence of earthquake foci, decoupled near the junction from the mantle probably during the Variscan. The boundaries (transitions) of three mantle domains provided open pathways for Quaternary volcanism and the ascent of 3He- and CO2-rich fluids released from the asthenosphere. The deepest earthquakes, interpreted as an upper limit of the brittle–ductile transition in the crust, are shallower above the junction of the mantle blocks (at about 12 km) than above the more stable Saxothuringian mantle lithosphere (at about 20 km), probably due to a higher heat flow and presence of fluids.  相似文献   

3.
Locations of the Eger Rift, Cheb Basin, Quaternary volcanoes, crustal earthquake swarms and exhalation centers of CO2 and 3He of mantle origin correlate with the tectonic fabric of the mantle lithosphere modelled from seismic anisotropy. We suggest that positions of the seismic and volcanic phenomena, as well as of the Cenozoic sedimentary basins, correlate with a “triple junction” of three mantle lithospheres distinguished by different orientations of their tectonic fabric consistent within each unit. The three mantle domains most probably belong to the originally separated microcontinents – the Saxothuringian, Teplá-Barrandian and Moldanubian – assembled during the Variscan orogeny. Cenozoic extension reactivated the junction and locally thinned the crust and mantle lithosphere. The rigid part of the crust, characterized by the presence of earthquake foci, decoupled near the junction from the mantle probably during the Variscan. The boundaries (transitions) of three mantle domains provided open pathways for Quaternary volcanism and the ascent of 3He- and CO2-rich fluids released from the asthenosphere. The deepest earthquakes, interpreted as an upper limit of the brittle–ductile transition in the crust, are shallower above the junction of the mantle blocks (at about 12 km) than above the more stable Saxothuringian mantle lithosphere (at about 20 km), probably due to a higher heat flow and presence of fluids.  相似文献   

4.
springerlink.com Studies of mantle fluids are currently one of the hot topics in the earth science, greatly contributing to re-vealing origins and evolutions of fluids. In general, the concept of mantle fluids refers to their active compo-nents, such as CO2, H2O, N2, etc., while the noble gases inert in chemical properties belong to another research system. Due to their marked differences in various fluid sources of the Earth[1], the isotopic sig-natures of He and Ar have been widely used a…  相似文献   

5.
The H2O, CO2 and H2S outputs at the Solfatara of Pozzuoli have been measured and a map of the exhaling areas has also been made. The energy released at the surface by the fluids has been estimated to be 1019 ergs/day.The presence of aquifers at Phlegraean Fields increases the phreatic and phreatomagmatic explosion risk.Our results suggest that even if an uprising magma may interact with water at depth, an explosion could occur only at the shallow levels of a few hundred meters. Since the transfer of energy toward the surface is favoured by the presence of fractures, a detailed analysis of the deep fracture network would help to evaluate the risk levels of the various areas of Phlegraean Fields.  相似文献   

6.
Mantle-derived volatiles in continental crust: the Massif Central of France   总被引：1，自引：0，他引：1  
CO2-rich gases and groundwaters from springs and boreholes originating within the basement of the Massif Central have variable3He/4He ratios with correspondingR/Ra values ranging from 0.8 to 5.5 and 0.3 to 2.8 respectively, indicating the presence of a significant component of mantle helium. Molar concentrations of rare gases in the CO2-rich gases are approximately 5 orders of magnitude greater than in the waters and suggest that a near-surface Henry's Law fractionation has occurred between exsolving CO2 and water.δ13C values of the CO2-rich gases are in the range −4.2 to −6.1‰, i.e. in that range normally attributed to mantle carbon, but which could also represent an average crustal composition and therefore do not discriminate between mantle and crustal sources.C/3He ratios show 4 orders of magnitude variation from 1.4 × 1012 to 5 × 108 and, compared to a mantleC/3He ratio of 109, indicate that either a complex fractionation has occurred between mantle helium and mantle CO2 or more likely that mantle rare gases have been diluted by large quantities of CO2 with an average crustal carbon isotope composition. The regional distribution of3He and C does not show any obvious relationship to age or proximity of volcanic centres or major faults, suggesting that mantle-derived C and He components decoupled from their silicate melt sources at some depth.The results from this area of active fluid circulation suggest that C-isotope data derived from metamorphic terrains should be interpreted with great caution, but that input of some mantle-derived carbon is expected to accompany crustal extension.  相似文献   

7.
The gold contents of 59 samples of mantle-derived xenoliths, along with 85 samples of sulfide assem-blages in them, of Cenozoic basalt from eight districts in eastern China are analyzed. The gold contents of mantle xenoliths usually fall in the range of 10-9―10-8, whereas those of the sulfide assemblages fall in the range of 10-4―10-2. This implies that the latter are several hundred thousand times higher than the former, and thus that Au in the mantle is concentrated mostly in sulfide assemblages. Gold con-tents of both mantle-derived xenoliths and sulfide assemblages in them are inhomogeneous spatially, but their distribution rules are similar. Except the samples from Hainan Province, either the mantle xenoliths with high gold content or sulfide assemblages of the mantle-derived xenoliths with high gold content are distributed mostly on the north and south margins of the North China platform (Hannuoba of Hebei Province and Linqu, Changle of Shandong Province), corresponding to districts with concen-trated gold deposits in northwest Hebei Province and Jiaodong Peninsula of Shandong Province. This may reflect the correlativity in age, nature and composition between the continental crust and the un-derlying lithospheric mantle. The underlying lithospheric mantle of the North China platform is an an-cient gold-rich lithospheric mantle. The gold-rich lithospheric mantle may be the material source of later activation, enrichment, transportation and mineralization of gold by auriferous CO2 mantle fluids.  相似文献   

8.
Diffuse CO<Subscript>2</Subscript> degassing at Vesuvio,Italy   总被引：1，自引：0，他引：1  
At Vesuvio, a significant fraction of the rising hydrothermal–volcanic fluids is subjected to a condensation and separation process producing a CO2–rich gas phase, mainly expulsed through soil diffuse degassing from well defined areas called diffuse degassing structures (DDS), and a liquid phase that flows towards the outer part of the volcanic cone. A large amount of thermal energy is associated with the steam condensation process and subsequent cooling of the liquid phase. The total amount of volcanic–hydrothermal CO2 discharged through diffuse degassing has been computed through a sequential Gaussian simulation (sGs) approach based on several hundred accumulation chamber measurements and, at the time of the survey, amounted to 151 t d–1. The steam associated with the CO2 output, computed assuming that the original H2O/CO2 ratio of hydrothermal fluids is preserved in fumarolic effluents, is 553 t d–1, and the energy produced by the steam condensation and cooling of the liquid phase is 1.47×1012 J d–1 (17 MW). The location of the CO2 and temperature anomalies show that most of the gas is discharged from the inner part of the crater and suggests that crater morphology and local stratigraphy exert strong control on CO2 degassing and subsurface steam condensation. The amounts of gas and energy released by Vesuvio are comparable to those released by other volcanic degassing areas of the world and their estimates, through periodic surveys of soil CO2 flux, can constitute a useful tool to monitor volcanic activity.Editorial responsibility: H. Shinohara  相似文献   

9.
A case study of the influx of upper mantle fluids into the crust   总被引：2，自引：0，他引：2  
Geochemical and geophysical investigations in the Bohai Gulf and adjacent areas, China, indicate that uplift of the high-conductivity layer in the lithosphere coincides with the area of high heat flow. In this area are distributed abundant oil and gas fields in a Tertiary fault basin and also large quantities of basaltic rocks. Gas fields, mostly CO2 bearing, occur at the basin margins, where a widespread alkaline olivine basalt has high contents of gold. Geochemical prospecting of the surface (soil and soil gas) in the area indicates that there is an anomaly zone of large-scale gold mineralization, and large gold deposits have been found in this area. Isotopic study demonstrates that CO2 in the volcanic rocks and in the CO2-bearing gas deposits are all derived from the mantle. Experiments show that Au- and CO2-bearing hydrothermal fluids separated into vapor phase and liquid phases respectively due to a reduction of pressure and temperature over the temperature range from 250 to 290°C and at 22 M Pa. Au appears in the vapor phase rich in CO2. That proves that it is possible that CO2-bearing aqueous fluids (in gas phase) can carry gold and transport it from deeper parts of lithosphere to the surface.  相似文献   

10.
Contents of H2O, CO2 and Cl in well discharges from six explored geothermal systems of the Taupo Volcanic Zone, New Zealand, point to the existence of two distinct source fluids. The fluid present in discharges from systems along the eastern boundary is characterised by high CO2 contents, 1.6 ± 0.5 , at mole ratios of 3.9 ± 1.5. High (0.06) and (12) weight ratios in these waters suggest that all four constituents are derived from associated andesitic rock. Geothermal discharges in the western parts of the TVZ, dominated by rhyolitic magmatism, are characterised by low CO2 contents, 0.12 ± 0.05 , and low (0.14 ± 0.1) ratios. Again, relative Cl, B, Li and Cs contents agree with those of this potential source rock. High and ratios in the east are typical of fluids affected by the addition of volatiles released from subducted marine sediments. For the western systems, these ratios resemble more closely those expected for mantle-derived volatiles. The isotopic compositions of all deep waters point to the presence of variable amounts of a magmatic component, some 14 ± 5% in the eastern and 6 ± 2% in the western systems. The observed variations are explained in terms of interaction of volatiles released from the subducted sediments with material of the mantle wedge to form a volatile-charged, high-alumina basalt. Its convective rise, in a direction opposite to that of the down-going slab, leads to high enrichment in volatiles of the magmas generated beneath the eastern parts of the TVZ and increases their ability to intrude the continental crust. Further fractional crystallisation and assimilation leads to the formation of volatile-rich andesitic melts, partly extruded to form the volcanoes of the andesitic arc, partly intruded to act as source rocks for the high-gas geothermal systems. Batches of high-alumina basalt, depleted in subducted volatiles, travel farther west to pond beneath a zone of crustal extension. Following extensive fractionation, highly siliceous melts, carrying predominantly mantle-type volatiles, rise beneath the western part of the TVZ to supply both heat and volatiles to the geothermal systems there.  相似文献   

11.
It has long been recognized that the Kii Peninsula in the southwest Japan arc is peculiar in a non-volcanic region, indicated by the presence of high temperature hot springs, high terrestrial heat flow and high 3He content in hot spring gases. Geophysical and geochemical studies were carried out to understand the geotectonic environment in the southern part of the Kii Peninsula. Most of the measured 3He / 4He ratios are similar or higher than air, indicating wide spread incorporation of mantle-derived helium into meteoric water. A region with rather high 3He / 4He ratios (> 4 RA) on the west side of the Omine Mountains coincides with the occurrence of high temperature hot springs. A deep crustal resistivity structure across the Omine Mountains was imaged by wide-band magnetotelluric soundings. A 2-D inversion with N–S strike using both TM and TE modes reveals two conductors, one in the upper (3–7 km depth) and the other in lower crust (25–35 km depth) to the west of the Omine Mountains. The distribution of microearthquakes and low-frequency tremors, and the existence of seismic reflectors indicate that the large conductor in the lower crust is related to aqueous fluids derived from the Philippine Sea plate. The upper-crustal conductive zone may also reflect the aqueous fluids trapped in the upper crust, which are presumably derived from the subducting slab. Considering the occurrence of seismic events in the subducting slab beneath the southern Kii Peninsula, the aqueous fluids generated by dehydration of the slab mantle could plausibly include MORB-type helium derived from the residual lithospheric mantle. Therefore, the high temperature hot springs and high 3He emanations in hot spring gases and other geotectonic events in the southern Kii Peninsula may be due to heat flux and mantle-derived helium discharged from aqueous fluid in the upper crust.  相似文献   

12.
This paper deals with the chemical and isotopic compositions of escaped gases from the Rehai geothermal area in Tengchong county of Yunnan Province. Results indicate that there is the mantle-derived magmatic intrusion in shallow crust at this area. Modern mantle-derived magmatic volatiles are being released currently in a steady stream by way of active faults. The escaped gases are mostly composed of CO2, together with subordinate amounts of H2S, N2, H2, CH4, SO2, CO and He. At the studied area, the north-south directed fault is the deepest, and it may be interlinked with the deep-seated thermal reservoir that would be directly recharged by the mantle-derived magmatic volatile. The He, C isotopic evidence reveals that the modern active magma beneath Rehai area may originate from the historical mantle-derived magma which caused the latest eruptive activity of volcanoes in that region.  相似文献   

13.
Na–HCO3–CO2-rich thermomineral waters issue in the N of Portugal, within the Galicia-Trás-os-Montes region, linked to a major NNE-trending fault, the so-called Penacova-Régua-Verin megalineament. Along this tectonic structure different occurrences of CO2-rich thermomineral waters are found: Chaves hot waters (67 °C) and also several cold (16.1 °C) CO2-rich waters. The δ2H and δ18O values of the thermomineral waters are similar to those of the local meteoric waters. The chemical composition of both hot and cold mineral waters suggests that water–rock reactions are mainly controlled by the amount of dissolved CO2 (g) rather than by the water temperature. Stable carbon isotope data indicate an external CO2 inorganic origin for the gas. δ13CCO2 values ranging between ? 7.2‰ and ? 5.1‰ are consistent with a two-component mixture between crustal and mantle-derived CO2. Such an assumption is supported by the 3He/4He ratios measured in the gas phase, are between 0.89 and 2.68 times the atmospheric ratio (Ra). These ratios which are higher than that those expected for a pure crustal origin (≈ 0.02 Ra), indicating that 10 to 30% of the He has originated from the upper mantle. Release of deep-seated fluids having a mantle-derived component in a region without recent volcanic activity indicates that extensive neo-tectonic structures originating during the Alpine Orogeny are still active (i.e., the Chaves Depression).  相似文献   

14.
Seismic monitoring of sequestered carbon dioxide (CO2) in underground deposits is a matter of growing importance. The subsurface monitoring of this greenhouse gas is possible due to the marked contrast between the physical properties of natural reservoir fluids and those of carbon dioxide after the injection. This technique makes necessary the investigation of appropriate seismic indicators to link seismic attributes to petrophysical properties, composition and state of the rock as well as pore-fluid type and in-situ physical conditions. With this motivation in mind, we use a Biot–Gassmann formulation to model the theoretical P-wave amplitude reflection coefficients vs. angle of incidence in the seismic range when a planar P-wave strikes the interface between a caprock and a porous sandstone which has its pore space saturated by a mixture of CO2 with brine or oil at different states (supercritical, liquid and gas). The effects of dissolution of CO2 in oil and the existence of a saturation threshold, above which a free CO2 phase develops, are included in the computations. Attention is particularly focused on the sensitivity of the classic best-fit amplitude variations with angle coefficients, to different degrees of CO2 saturation. We conclude from this analysis that the changes in seismic AVA attributes between 30 and 40 degrees can be useful to infer bounds on the CO2 saturation degree, to detect the presence of immiscible CO2 phase and, in some cases, to infer the physical state of the accumulations.  相似文献   

15.
The northwestern flank of the Colli Albani, a Quaternary volcanic complex near Rome, is characterised by high pCO2 values and Rn activities in the groundwater and by the presence of zones with strong emission of gas from the soil. The most significant of these zones is Cava dei Selci where many houses are located very near to the gas emission site. The emitted gas consists mainly of CO2 (up to 98 vol%) with an appreciable content of H2S (0.8–2%). The He and C isotopic composition indicates, as for all fluids associated with the Quaternary Roman and Tuscany volcanic provinces, the presence of an upper mantle component contaminated by crustal fluids associated with subducted sediments and carbonates. An advective CO2 flux of 37 tons/day has been estimated from the gas bubbles rising to the surface in a small drainage ditch and through a stagnant water pool, present in the rainy season in a topographically low central part of the area. A CO2 soil flux survey with an accumulation chamber, carried out in February–March 2000 over a 12 000 m2 surface with 242 measurement points, gave a total (mostly conductive) flux of 61 tons/day. CO2 soil flux values vary by four orders of magnitude over a 160-m distance and by one order of magnitude over several metres. A fixed network of 114 points over 6350 m2 has been installed in order to investigate temporal flux variations. Six surveys carried out from May 2000 to June 2001 have shown large variations of the total CO2 soil flux (8–25 tons/day). The strong emission of CO2 and H2S, which are gases denser than air, produces dangerous accumulations in low areas which have caused a series of lethal accidents to animals and one to a man. The gas hazard near the houses has been assessed by continuously monitoring the CO2 and H2S concentration in the air at 75 cm from the ground by means of two automatic stations. Certain environmental parameters (wind direction and speed; atm P, T, humidity and rainfall) were also continuously recorded. At both stations, H2S and CO2 exceeded by several times the recommended concentration thresholds. The highest CO2 and H2S values were recorded always with wind speeds less than 1.5 m/s, mostly in the night hours. Our results indicate that there is a severe gas hazard for people living near the gas emission site of Cava dei Selci, and appropriate precautionary and prevention measures have been recommended both to residents and local authorities.  相似文献   

16.
On 27 February 2007, a new eruption occurred on Stromboli which lasted until 2 April. It was characterized by effusive activity on the Sciara del Fuoco and by a paroxysmal event (15 March). This crisis represented an opportunity for us to refine the model that had been developed previously (2002–2003 eruption) and to improve our understanding of the relationship between the magmatic dynamics of the volcano and the geochemical variations in the fluids. In particular, the evaluation of the dynamic equilibrium between the volatiles (CO2 and SO2) released from the magma and the corresponding fluids discharged from the summit area allowed us to evaluate the level of criticality of the volcanic activity. One of the major accomplishments of this study is a 4-year database of summit soil CO2 flux on the basis of which we define the thresholds (low–medium–high) for this parameter that are empirically based on the natural volcanological evolution of Stromboli. The SO2 fluxes of the degassing plume and the CO2 fluxes emitted from the soil at Pizzo Sopra la Fossa are also presented. It is noteworthy that geochemical signals of volcanic unrest have been clearly identified before, during and after the effusive activity. These signals were found almost simultaneously in the degassing plume (SO2 flux) and in soil degassing (CO2 flux) at the summit, although the two degassing processes are shown to be clearly different. The interpretation of the results will be useful for future volcanic surveillance at Stromboli.  相似文献   

17.
A new method of reconstruction of the temperature profile in the lunar mantle from the velocities of seismic P- and S-waves for different models of chemical composition is developed. The procedure of the solution of an inverse problem is realized with the help of the minimization of the Gibbs free energy and the equations of state of a mantle substance, taking into account phase transformations, anharmonicity, and the effects of inelasticity. The geophysical and geochemical constraints on composition and temperature distribution in Moon’s mantle are established. The upper mantle can be composed of olivine pyroxenite, depleted by low-volatile oxides (∼2 wt % of CaO and Al2O3). On the contrary, the lower mantle must be enriched by low-volatile oxides (∼4–6 wt % of CaO and Al2O3). Its composition can be represented by a mineral association of the olivine + clinopyroxene + garnet or olivine + orthopyroxene + clinopyroxene + garnet type, which is close in composition to pyrolite. The temperature distribution at depths 50–1000 km are approximated by the equation: T(°C) = 351 + 1718[1–exp (−0.00082H)]. The constraints inferred make it possible to conclude that the published values of the velocities of P- and S-waves for the lunar mantle, obtained by processing the data of seismic experiments of the Apollo lunar mission are inconsistent with each other at depths below 300 km. Otherwise, the variations in the velocities of P- and S-waves disturb the symmetry between the petrological model (composition), the temperature profile, and the seismic profile.  相似文献   

18.
Step heating experiments on ultra-high pressure (UHP) mcks from the Dabie Mountain shows a majority of CO2 in fluid inclusion (excluding H2O); CO is also a significant component, with a small content of N2 and CH4. Carbon isotopic composition of CO2 in fluid of metamorphic climax stage (-25%0- -30%0) is different from that of mantle carbon, indicating that UHP rocks did not experience obvious transformation by mantle fluids despite their subduction depth. CO2 was derived from carbon matter in the pmtoliths of UHP rocks in a relatively confined system, showing that the UHP rocks subsided quickly and uplifted quickly from the mantle. Current organization: Research Institute of Petroleum Exploration and Development, Beijing 100083, China.  相似文献   

19.
The Main Endeavour Field, northern Juan de Fuca Ridge, experienced intense seismic activity in June 1999. Hydrothermal vent fluids were collected from sulfide structures in September 1999 and July 2000 and analyzed for the abundance of H2, H2S, CH4, CO2, NH3, Mg and Cl to document temporal and spatial changes following the earthquakes. Dissolved concentrations of CO2, H2, and H2S increased dramatically in the September 1999 samples relative to pre-earthquake abundances, and subsequently decreased during the following year. In contrast, dissolved NH3 and CH4 concentrations in 1999 and 2000 were similar to or less than pre-earthquake values. Aqueous Cl abundances showed large decreases immediately following the earthquakes followed by increases to near pre-earthquake values. The abundances of volatile species at the Main Endeavour Field were characterized by strong inverse correlations with chlorinity. Phase separation can account for 20-50% enrichments of CO2, CH4, and NH3 in low-chlorinity fluids, while temperature- and pressure-dependent fluid-mineral equilibria at near-critical conditions are responsible for order of magnitude greater enrichments in dissolved H2S and H2. The systematic variation of dissolved gas concentrations with chlorinity likely reflects mixing of a low-chlorinity volatile-enriched vapor generated by supercritical phase separation with a cooler gas-poor hydrothermal fluid of seawater chlorinity. Decreased abundances of sediment-derived NH3 and CH4 in 1999 indicate an earthquake-induced change in subsurface hydrology. Elevated CO2 abundances in vent fluids collected in September 1999 provide evidence that supports a magmatic origin for the earthquakes. Temperature-salinity relationships are consistent with intrusion of a shallow dike and suggest that the earthquakes were associated with movement of magma beneath the ridge crest. These data demonstrate the large and rapid response of chemical fluxes at mid-ocean ridges to magmatic activity and associated changes in subsurface temperature and pressure.  相似文献   

20.
We model the internal structure of the Moon, initially homogeneous and later differentiated due to partial melting. The chemical composition and the internal structure of the Moon are retrieved by the Monte-Carlo inversion of the gravity (the mass and the moment of inertia), seismic (compressional and shear velocities), and petrological (balance equations) data. For the computation of phase equilibrium relations and physical properties, we have used a method of minimization of the Gibbs free energy combined with a Mie-Gr@uneisen equation of state within the CaO-FeO-MgO-Al2O3-SiO2 system. The lunar models with a different degree of constraints on the solution are considered. For all models, the geophysically and geochemically permissible ranges of seismic velocities and concentrations in three mantle zones and the sizes of Fe-10%S core are estimated. The lunar mantle is chemically stratified; different mantle zones, where orthopyroxene is the dominant phase, have different concentrations of FeO, Al2O3, and CaO. The silicate portion of the Moon (crust + mantle) may contain 3.5–5.5% Al2O3 and 10.5–12.5% FeO. The chemical boundary between the middle and the lower mantle lies at a depth of 620–750 km. The lunar models with and without a chemical boundary at a depth of 250–300 km are both possible. The main parameters of the crust, the mantle, and the core of the Moon are estimated. At the depths of the lower mantle, the P and S velocities range from 7.88 to 8.10 km/s and from 4.40 to 4.55 km/s, respectively. The radius of a Fe-10%S core is 340 ± 30 km.  相似文献   

设为首页 | 免责声明 | 关于勤云 | 加入收藏

Copyright©北京勤云科技发展有限公司  京ICP备09084417号