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1.
The hydrothermal vent in Area A(37.78°S,49.65°E)is the first active hydrothermal vent discovered on the Southwest Indian Ridge(SWIR).Heat source and adequate bulk permeability are two necessary factors for the formation of a hydrothermal vent.Along the SWIR 49.3°E to 51.2°E,the gravity-derived crustal thickness is up to 9.0 km,much thicker than the average thickness of the global oceanic crust.This characteristic indicates that the magma supply in this area is robust,which is possibly affected by a hotspot.The large-scale residual mantle Bouguer anomalies(RMBA)reveal prominent negative-gravity anomalies between the first-order ridge segment(from Indomed to Gallieni,46.0°E to 52.0°E)and the Marion-Del Cano-Crozet region.These anomalies indicate the channel of the hotspot-ridge interaction.The tomography data corrected with theoretical thermal model indicate that the low-velocity anomalies corresponding to this channel can reach the base of the lithosphere.Near the hydrothermal vent area,the topography and crustal thickness at the off-axis area are extremely asymmetrical.South of the SWIR,the high topography corresponds to the thinning crustal thickness.The residual isostatic topography anomalies indicate that Area A is a deviation from the local isostatic equilibrium,similar to the characteristics of the transform fault inside corner.The forward profiles of the magnetic data indicate that the thinning magnetic layer at the south side of Area A corresponds to the shallow,high-velocity area revealed by the OBS,which is the result of tectonic extension of a detachment fault.The active tectonic processes in Area A can provide sufficient crustal permeability to the hydrothermal circulation and may form massive sulfide deposits.  相似文献   

2.
This is the first of two papers that describes a regional tomography investigation,which combines P-wave arrival times of both regional and teleseismic earthquakes to obtain 3D mantle structures of East Asia up to 1 000 km depth.The most important findings of this tomography study are reported in this paper as follows.(1) No fast P-wave velocity anomalies can be related to subducted oceanic slabs beneath the 660 km discontinuity;instead the subducted oceanic slabs become flattened and stagnant within the transition zone.(2) The high velocity anomalies in the transition zone extend up to 1 500 km to the westward of the active trenches,which is a unique feature in the worldwide subduction systems.(3) Slow P-wave velocity anomalies are visible up to ～250 km underneath most of the East Asia on the east of 115°E,similar to the area of the stagnant slabs.These observations have important implications for the geodynamic process at depths beneath the East Asia,which might in turn control the widespread Cenozoic volcanism and associated extensional tectonics seen at the Earth's surface.  相似文献   

3.
The interactions of seafloor hydrothermal fluid with igneous rocks can result in leaching elements from the rocks,creating potential ore-forming fluids and influencing the chemical compositions of near-bottom seawater.The hydrothermal alteration of plagioclase microphenocrysts and basaltic glass in the pillow basalts from one dredge station(103°57.62′′W,12°50.55′N,water depth 2480 m)on the East Pacific Rise(EPR)near 13°N were analyzed using a scanning electron microscope(SEM)and energy dispersive X-ray spectrometry(EDS).The results show that the edges of the plagioclase microphenocrysts and the basaltic glass fragments are altered but the pyroxene and olivine microphenocrysts in the interior of the pillow basalts appear to be unaffected by the hydrothermal fluids.In addition,our results show that the chemical alteration at the rims of the plagioclase microphenocrysts and the edges of basaltic glass fragments can be divided into separate types of alteration.The chemical difference in hydrothermal alteration of the plagioclase microphenocrysts and the basaltic glass indicate that different degrees of hydrothermal fluid-solid phase interaction have taken place at the surface of the pillow basalts.If the degree of hydrothermal fluid-solid phase interaction is relatively minor,Si,Al,Ca and Na diffuse from the inside of the solid phase out and as a result these elements have a tendency to accumulate in the edge of the plagioclase microphenocrysts or basaltic glass.If the degree of hydrothermal fluid-solid phase interaction is relatively strong,Si,Al,Ca and Na also diffuse from the inside of solid phase out but these elements will have a relatively low concentration in the edge of the plagioclase microphenocrysts or basaltic glass.Based on the chemical variation observed in the edges of plagioclase microphenocrysts and basaltic glass,we estimate that the content of Si,Al and Fe in the edges of plagioclase microphenocrysts can have a variation of 10.69%,17.59%and 109%,respectively.Similarly,the Si,Al and Fe concentrations in the edges of basaltic glass can have a variation of 9.79%,16.30%and 37.83%,respectively,during the interaction of hydrothermal fluids and seafloor pillow basalt.  相似文献   

4.
The Diyanqinamu Mo deposit, a newly discovered porphyry deposit in the northern-central part of the Great Xing'an Range, Inner Mongolia, China, is characterized by widely distributed fluorite. It is important to note that almost all the fluorite that is paragenetic with molybdenite is purple. The Tb/Ca–Tb/La ratios of these purple fluorite samples show that they have a hydrothermal origin.The unidirectional solidification texture at the apex of the aplitic granite and the low F contents in the andesite suggest that most of F in fluorite was derived from granitic melts. These observations suggest that the fluorite was related to the magmatic-hydrothermal fluids. All the fluorite separates have consistent total REE contents with LREE-depleted, HREE-enriched, negative Eu anomaly,unapparent Ce anomaly and positive Y anomaly. These characteristics are significantly different than those of country granite, andesite and tuff whole-rock. The positive Y anomaly of the fluorite separates implies that the hydrothermal fluids migrated a long distance, as suggested by the fact that the fluorite-molybdenite veins were mostly hosted in andesite and tuff, far from the Mo ore-forming granites. The features of LREE-depleted and HREE-enriched fluorite are due to the REE-complex in the F-enriched fluids during migration. The stronger negative Eu anomaly of fluorite than those of country rocks suggests that the Eu anomaly of the original hydrothermal fluid was enhanced by the high temperature(generally above 200 or250 °C). The widespread magnetite in the studied deposit indicates that the magmatic-hydrothermal fluid was oxidized at early stage. On the other hand, the pyrite was also paragenetic, with the molybdenite and unapparent Ce anomaly implying that the hydrothermal fluid probably experienced oxygen fugacity decreasing during migration,which is important for Mo mineralization.  相似文献   

5.
The mineralogical and geochemical characteristics of Fe-oxyhydroxide samples from one dredge station (long. 103°54.48'W, lat. 12°42.30'N, water depth 2655 m) on the East Pacific Rise near lat 13°N were analyzed by XRD, ICP-AES, and ICP-MS. Most Fe-oxyhydroxides are amorphous, with a few sphalerite microlites. In comparison with Fe-oxyhydroxides from other fields, the variable ranges in the chemical composition of Fe-oxyhydroxide samples are very narrow; their Fe, Si, and Mn contents were 39.90%, 8.92%, and 1.59%, respectively; they have high Cu (0.88%―1.85%) and Co (65×10?6―704×10?6) contents, and contain Co Cu Zn Ni> 1.01%. The trace-element (As, Co, Ni, Cu, Zn, Ba, Sr) and major-element (Fe, Ca, Al, Mg) contents of these samples are in the range of hydrothermal sulfide from the East Pacific Rise near 13°N, reflecting that this type of Fe-oxyhydroxide constitutes a secondary oxidation product of hydrothermal sulfide. The Fe-oxyhydroxide samples from one dredge station on the East Pacific Rise near 13°N are lower in ΣREE (5.44×10?6―17.01×10?6), with a distinct negative Ce anomaly (0.12 ― 0.28). The Fe-oxyhydroxide samples have similar chondrite-normalized rare-earth-element (REE) patterns to that of seawater, and they are very different from the REE composition characteristics of hydrothermal plume particles and hydrothermal fluids, showing that the REEs of Fe-oxyhydroxide are a major constituent of seawater and that the Fe-oxyhydroxides can become a sink of REE from seawater. The quick settling of hydrothermal plume particles resulted in the lower REE content and higher Mn content of these Fe-oxyhydroxides, which are captured in part of the V and P from seawater by adsorption. The Fe-oxyhydroxides from one dredge station on the East Pacific Rise near 13°N were formed by secondary oxidation in a low temperature, oxygenated environment. In comparison with the elemental (Zn, Cd, Pb, Fe, Co, Cu) average content of hydrothermal sulfide samples from the East Pacific Rise near 13°N, the Zn, Cd, and Pb contents of the Fe-oxyhydroxides are lower, and their Fe, Co, and Cu contents are higher.  相似文献   

6.
The salinity of fluid inclusions is an important pa-rameter, which gives scientists the ability to under-stand paleo-fluid chemistry, the forming of deposit and petroleum as well as the evolution in geological his-tory[1]. Generally, the parameter is estimated to roughly represent the natural frame of geological fluid using the ice melting temperature and first melting temperature from microthermometry apparatus, be-cause fluid inclusion is so small (<100 μm in size) that the fluid in inclusio…  相似文献   

7.
Abundant natural gas inclusions were found in calcite veins filled in fractures of Central Fault Belt across the centre of Ordos Basin. Time of the calcite veins and characteristics of natural gas fluid inclusion were investigated by means of dating of thermolum luminescence (TL) and analyzing stable isotope of fluid inclusion. Results show that natural gas inclusion formed at 130―140℃ with salinity of 5.5 wt%―6.0 wt% NaCl. It indicates that natural gas inclusion is a kind of thermal hydrocarbon fluid formed within the basin. Method of opening inclusion by heating was used to analyze composition of fluid inclusion online, of which the maximal hydrocarbon gas content of fluid inclusion contained in veins is 2.4219 m3/t rock and the maximal C1/Σci ratio is 91%. Laser Raman spectroscopy (LRS) was used to analyze chemistry of individual fluid inclusion in which the maximal hydrocarbon gas content is 91.6% compared with little inorganic composition. Isotope analysis results of calcite veins show that they were deposited in fresh water, in which the δ13CPDB of calcite veins is from -5.75‰ to 15.23‰ andδ18OSMOW of calcite veins is from 21.33‰ to 21.67‰. Isotope results show thatδ13C1 PDB of natural gas fluid inclusion is from -21.36‰ to -29.06‰ and δDSMOW of that is from -70.89‰ to -111.03‰. It indicates that the gas of fluid inclusion formed from coal source rocks and it is the same as that of natural gas of Mizhi gas reservoir. Results of TL dating show that time of calcite vein is (32.4±3.42)×104 a, which is thought to be formation time of gas inclusion. It indicated that natural gas inclusion contained in calcite veins recorded natural gas leakage from Mizhi gas reservoir through the Central Fault Belt due to Himalayan tectonic movement.  相似文献   

8.
With a detailed study on petrology, mineralogy and geochemistry of some important Ordovician carbonate well core samples in Tazhong uplift of Tarim Basin, the distinguishing symbols of hydrothermal karstification are first put forward as the phenomena of rock hot depigmentation, hot cataclasm and the appearance of typical hydrothermal minerals such as fluorite, barite, pyrite, quartz and sphalerite. The main homogenization temperatures of primary fluid inclusions in fluorite are from 260 to 310℃, indicating the temperature of hydrothermal fluid. The fluid affected the dissolved rocks and showed typical geochemistry features with low contents of Na and Mg, and high contents of Fe, Mn and Si. The ratio of 3He/4He is 0.02Ra, indicating the fluid from the typical continental crust. The hydrothermal fluid karstification pattern may be described as follows the hot fluid is from the Permian magma, containing dissolving ingredients of CO2 and H2S, and shifts along fault, ruptures and unconformity, and dissolves the surrounding carbonates while it flows. The mechanism of hydrothermal karstification is that the mixture of two or more fluids, which have different ion intensity and pH values, becomes a new unsaturated fluid to carbonates. The hydrothermal karstification is an important process to form hypo-dissolved pinholes in Ordovician carbonates of Tazhong uplift of Tarim Basin, and the forming of hydrothermal minerals also has favorable influence on carbonate reservoirs.  相似文献   

9.
Syenogranitic dykes in the north of Egypt's Eastern Desert are of geological and economic interest because of the presence of magmatic and supergene enrichment of radioactive mineralization. Zircon crystal morphology within the syenogranitic dykes allows precise definition of sub-alkaline series granites and crystallized at mean temperature of about 637 °C. The growth pattern of the zircons suggest magmatic and hydrothermal origins of radioactive mineralization. Hydrothermal processes are responsible for the formation of significant zircon overgrowth; high U-zircon margins might have occurred contemporaneously with the emplacement of syenogranitic dykes which show anomalous uranium(e U) and thorium(e Th) contents of up to 1386 and 7330 ppm, respectively.Zircon chemistry revealed a relative increase of Hf consistent with decreasing Zr content, suggesting the replacement of Zr by Hf during hydrothermal activity.Visible uranium mineralization is present and recognized by the presence of uranophane and autunite.  相似文献   

10.
To investigate the relationship between velocity structure and earthquake activity on the southeastern front of the Tibetan Plateau, we make use of continuous observations of seismic ambient noise data obtained at 55 broadband stations from the regional Yunnan Seismic Network. These data are used to compute Rayleigh wave Green's Functions by cross-correlating between two stations, extracting phase velocity dispersion curves, and finally inverting to image Rayleigh wave phase velocity with periods between 5 and 34 s by ambient noise tomography. The results show significant lateral variations in crustal and uppermost mantle structures in the studied region. Phase velocity anomalies at short periods(5–12 s) are closely related to regional tectonic features such as sediment thickness and the depth of the crystalline basement. The Sichuan-Yunnan rhombic block, enclosed by the Honghe, Xiaojiang and Jianchuan faults, emerges as a large range of low-velocity anomalies at periods of 16–26 s, that inverts to high-velocity anomalies at periods of 30–34 s. The phase velocity variation in the vicinity of the Sichuan-Yunnan rhombic block suggests that the low-velocity anomaly area in the middle-lower crust may correspond to lower crustal channelized flow of the Tibetan Plateau. The spatial distribution of strong earthquakes since 1970 reveals that the Yunnan region is inhomogeneous and shows prominent characteristics of block motion. However, earthquakes mostly occur in the upper crust, with the exception of the middle-Yunnan block where earthquakes occur at the interface zone between high and low velocity as well as in the low-velocity zones, with magnitudes being generally less than 7. There are few earthquakes of magnitude 5 at the depths of 15–30 km, where gather earthquakes of magnitude 7 or higher ones which mainly occur in the interface zone between high and low velocities with others extending to the high-velocity abnormal zone.  相似文献   

11.
Rayleigh wave phase velocities of South China block and its adjacent areas   总被引：2，自引：0，他引：2  
Using records of continuous seismic waveforms from 609 broadband seismic stations in the South China Block and its adjacent areas in 2010–2012, empirical Green's functions of surface waves were obtained from cross-correlation functions of ambient noise data between these stations. High quality phase velocity dispersion curves of Rayleigh waves were obtained using time-frequency analysis. These interstation dispersion curves were then inverted to build Rayleigh wave phase velocity maps at periods of 6–50 s. The results of phase velocity maps indicate that phase velocities at 6–10 s periods are correlated with the geological features in the upper crust. Major basins and small-scale grabens and basins display slow velocity anomalies; while most of the orogenic belts and the fold belts display high velocity anomalies. With the gravity gradient zone along Taihang Mountain to Wuling Mountain as the boundary for the phase velocity maps at period of 20–30 s, the western area mainly displays low velocity anomalies, while the eastern side shows high velocity anomalies. Phase velocities in the eastern South China Block south to the Qinling-Dabie orogenic belt is higher than that in the eastern North China Block to the north, which is possibly due to the differences of tectonic mechanisms between the North China Craton and the South China Block. The phase velocities at periods of40–50 s are possibly related to the lateral variations of the velocity structure in the lower crust and upper mantle: The low-velocity anomalies in the eastern part of the Tibetan Plateau are caused by the thick crust; while the Sichuan Basin and the southern part of the Ordos Basin display distinct high-velocity anomalies, reflecting the stable features of the lithosphere in these blocks. The lateral variation pattern of phase velocities in the southern part of the South China Block is not consistent with the surface trace of the block boundary in the eastern Yunnan Province and its vicinities. The phase velocities in the Sichuan Basin are overall slow at short periods and gradually increase with period from the central part to the edge of the basin, indicating the features of shallower basement in the center and overall stable lithospheric mantle of the basin. The middle and upper crust of the southern Ordos Basin in the North China Block is heterogeneous, while in lower crust and the uppermost mantle the phase velocities mainly exhibit high anomalies. High-velocity anomalies are widespread at the middle of the Qinling-Dabie orogenic belt, as well as the areas in southeastern Guangxi with Caledonian granite explosion, but its detailed mechanism is still unclear.  相似文献   

12.
In this paper, we show that supercritical fluids have a greater significance in the generation of pegmatites,and for ore-forming processes related to granites than is usually assumed. We show that the supercritical melt or fluid is a silicate phase in which volatiles; principally H_2O are completely miscible in all proportions at magmatic temperatures and pressures. This phase evolves from felsic melts and changes into hydrothermal fluids, and its unique properties are particularly important in sequestering and concentrating low abundance elements, such as metals. In our past research, we have focused on processes observed at upper crustal levels, however extensive work by us and other researchers have demonstrated that supercritical melt/fluids should be abundant in melting zones at deep-crustal levels too. We propose that these fluids may provide a connecting link between lower and upper crustal magmas,and a highly efficient transport mechanism for usually melt incompatible elements. In this paper, we explore the unique features of this fluid which allow the partitioning of variouselements and compounds, potentially up to extreme levels,and may explain various features both of mineralization and the magmas that produced them.  相似文献   

13.
Analysing characteristics of geomagnetic anomalies before MS≥5 earthquakes in recent years in Gonghe basin and at middle east section of Qilian mountains and space-time distribution of the anomalies,geomagnetic short-term prediction indexes before strong earthquakes in northwestern China are studied.The results indicate that various degrees of anomalies of magnetic storm,geomagnetic low-value displacement and correlation coefficients of geomagnetic vertical component between stations appeared before strong earthquakes.Interval from beginning of geomagnetic low-value displacement anomalies to origin time is 10～40 days.Interval from magnetic storm to origin time is three days before and after the dates which are multiple of nine.Coming earthquakes are located at near line of demarcation of the low-value displacement anomalies,or in the anomalous area.If duration of the correlation coefficient anomalies is over 5 months,it is possible that MS≥5 earthquake occurs in anomalous area.  相似文献   

14.
The Emeishan large igneous province(ELIP) in SW China is interpreted to be associated with an ancient mantle plume. Most of the constraints on the role of mantle plume in the generation of the Emeishan flood basalts were provided by geological and geochemical methods, but the geophysical investigation is very limited. In order to better understand the deep structure and features of ELIP, we have studied the crustal velocity structure using the data acquired from the Lijiang-Panzhihua-Qingzhen wide-angle seismic profile. This profile crosses the three sub-zones of the ELIP(the inner, intermediate, and outer zones), divided based on the differential erosion and uplift of the Maokou limestone. The results provided by the active source seismic experiment demonstrate:(1) The average depth of the crystalline basement along the profile is about 2 km.(2) The middle crust in the Inner Zone is characterized by high-velocity anomalies, with the average velocity of 6.2-6.6 km/s, which is about 0.1– 0.2 km/s higher than the normal one. The velocity of the lower crust in the inner zone is 6.9-7.2 km/s, higher than those observed in the intermediate and outer zones(6.7-7.0 km/s). Relatively low velocity anomalies appear in the upper, middle and lower crusts near the junction of the inner zone and intermediate zone, probably due to the effect of the Xiaojiang fault(XJF).(3) The average velocity of the crust is comparatively low on both sides of XJF, especially on the east side, and the average velocity of the consolidated continental crust is also low there. This may suggest that the XJF extends at least down to 40 km deep, even beyond through the crust.(4) The depth to the Moho discontinuity decrease gradually from 47-53 km in the inner zone, via 42-50 km in the intermediate zone to 38-42 km in the outer zone. In the inner zone, the Moho uplifts locally and the(consolidated) crust is characterized by high-velocity anomalies, which are likely related to intensive magma intrusion and underplating associated with melting of plume head. Overall the crustal velocity structure in the study area recorded the imprint left by the Permian Emeishan mantle plume.  相似文献   

15.
Lushan MS7.0 earthquake occurred in Lushan county, Ya’an city, Sichuan province of China, on 20 April 2013, and caused 196 deaths, 23 people of missing and more than 12 thousand of people injured. In order to analyze the possible seismic brightness temperature anomalies which may be associated with Lushan earthquake, daily brightness temperature data for the period from 1 June 2011 to 31 May2013 and the geographical extent of 25°E–35°N latitude and 98°E–108°E longitude are collected from Chinese geostationary meteorological satellite FY-2E. Continuous wavelet transform method which has good resolution both in time and frequency domains is used to analyze power spectrum of brightness temperature data. The results show that the relative wavelet power spectrum(RWPS) anomalies appeared since 24 January 2013 and still lasted on 19 April. Anomalies firstly appeared at the middle part of Longmenshan fault zone and gradually spread toward the southwestern part of Longmenshan fault. Anomalies also appeared along the Xianshuihe fault since about 1 March. Eventually, anomalies gathered at the intersection zone of Longmenshan and Xianshuihe faults. The anomalous areas and RWPS amplitude increased since the appearance of anomalies and reached maximum in late March. Anomalies attenuated with the earthquake approaching. And eventually the earthquake occurred at the southeastern edge of anomalous areas. Lushan earthquake was the only obvious geological event within the anomalous area during the time period, so theanomalous changes of RWPS are possibly associated with the earthquake.  相似文献   

16.
The Shanxi rift zone, located in the Trans-North China Orogen(TNCO) of the North China Craton(NCC), is wellknown for hosting large intraplate earthquakes in continental China. The TNCO is a suture zone formed by the amalgamation of the eastern and the western blocks of the NCC. After its formation, it was reactived and deformed by later tectonic activities,which result in complex lithospheric heterogeneities. Thus, the detailed crustal structure of the Shanxi rift zone is critical for understanding the tectonics and seismogenic mechanism in this area, which will shed new lights on the formation and dynamic evolution of the NCC. In this study, we applied ambient noise tomography based on 18 months continuous records from 108 seismic stations located in Shanxi and its surroundings, in order to constrain its detailed crustal structure. We measured 4437 Rayleigh wave phase velocity dispersion curves in the period of 5–45 s from the cross-correlation functions. Next, a surface wave direct inversion algorithm based on surface-wave ray tracing was used to resolve a 3-D S-wave velocity model in the upper 60 km with lateral resolution of ～50–80 km. The tomographic images show that the sedimentary thickness of the Taiyuan Basin is less than 5 km. At depth of 0–10 km, we observe a good correlation between the imaged structural variations with geological and topographic features at the surface. For example, the center of rift shows low-velocity anomalies and the uplifting areas on both sides are characterized by high velocity anomalies. The western and eastern boundaries of the slow materials coincide with the faults that control the basin. The slow material extends from the shallow surface to depth of about 15 km but it getting smaller in shape at deeper depth. For the Taiyuan Basin, Linfen Basin, and Yuncheng Basin in the central and southern parts, the structure is dominant by slow materials in the upper crust but changes to strong high-velocity anomalies in the lower crust and the uppermost mantle at depth deeper than 25 km. We interprete these high-velocity anomalies to be associated with the cold remnant of the underplated basalt in the lower crust that were formed in early Tertiary before the basin was stretched. We also observe the low-velocity anomaly beneath the Datong volcanic area, which extends from the uppermost mantle to a depth of20 km vertically and migrates from west to east laterally. It may reflect the upwelling channel of the magmatic material in Datong. Moreover, the strong low-velocity anomalies presented north of 38°N could be related to the heated crustal materials with paritial melting as a result of the intensive magmatic activities of the Datong Volcano since the Cenozoic. In our study region, seismicity mainly concentrates in the depth range of 5–20 km and we find that most earthquakes appear to occur in places where velocity changes from high to low rapidly, with slight higher concentration in the faster material areas. In summary, our high-resolution 3-D crustal velocity model provides important seismological constraints to understand the tectonic evolution and seismicity across the Shanxi rift zone.  相似文献   

17.
Yttrium(Y) is a critical metallic element that is used widely in modern scientific,technological,and industrial applications.Phosphorites in the Zhijin area of Guizhou Province,China,are famous for Y enrichment,but the enrichment characteristics and sources remain unclear.Previous studies suggested that the sources of rare earth elements(REEs,La-Lu) and Y(REYs,La-Lu+Y)were related to hydrothermal deposition.However,this study presents evidence refuting that hypothesis,with major and trace elemental data collected with quadrupoleinductively coupled plasma-mass spectrometry(Q-ICPMS) analysis.These data show that Y in Zhijin REYscontaining phosphorites has a normal distribution and is particularly enriched relative to other REYs.The Y enrichment degree is different at different ∑REY intervals.Specifically,the Y enrichment degree is higher at lower ∑REY values and lower at higher ∑REY values.The REYs-containing phosphorites show features of primary phosphorites.Both REEs and Y have good correlations with P_2 O_5 in the phosphorites with low REYs contents(total REYs 535 ppm),whereas at high REYs contents(total REYs 535 ppm),REEs have a good correlation with P_2 O_5 but Y does not.Inconsistent enrichment processes of REYs are suggestive of complex sources of Y.Thus,seafloor hydrothermal fluids were not the direct source of Y.Normal seawater mixed with terrestrial sources might have contributed to the origin of Y here.This study could lead to improvements in Y mineral resource explorations and the situation involving the global REYs supply crisis.  相似文献   

18.
The genetic relationship between different types of granite is critical for understanding the formation and evolution of granitic magma. Fluid-rock interaction experiments between two-mica leucogranite and boron-rich fluids were carried out at 600–700°C and 200 MPa to investigate the effects of boron content in fluid and temperature on the reaction products. Our experimental results show that tourmaline granite can be produced by reactions between boron-rich fluid and two-mica granite.At 700°C, the addition of boron-rich fluid resulted in partial melting of two-mica granite and crystallization of tourmaline from the boron-rich partial melt. Increasing boron concentration in fluid promotes the melting of two-mica granite and the growth of tourmaline. No melt was produced in experiments at 600°C, in which Fe, Mg and Al released from biotite decomposition combined with boron from the fluid to form tourmaline under subsolidus conditions. The Na required for tourmaline crystallization derived from Na/K exchange between feldspar and the K released by biotite decomposition. The produced tourmaline generally has core-rim structures, indicating that the composition of melt or fluid evolved during tourmaline crystallization.Based on the experimental results, we propose that tourmaline granite veins or dikes can be formed by the reactions between boron-rich fluids, presumably produced by devolatilization of boron-bearing granitic magma, and incompletely crystallized granite at the top of the magma chamber. This "self-metasomatism" involving boron-rich fluid in the late stage of magma crystallization could be an important mechanism for the formation of tourmaline granite.  相似文献   

19.
Successive waveforms of the vertical component recorded by 888 broadband seismic stations in the China Seismography Network from January,2010 to June,2011 are used to investigate the temporal and spatial distribution of ambient noise intensity,and the images of ambient noise intensity at the period of 10 s in the Chinese Mainland are obtained. The temporal variation of ambient noise intensity shows some seasonal and periodic characteristics. The maximum ambient noise intensity occurred from January,2011 to March,2011. The spatial distribution images of ambient noise intensity show obvious zoning features,which doesnt correlate with surface geology,suggesting that the noise field is stronger than the site factors. The strength in southeastern coastal areas reaches its maximum and generally decreases toward to inland areas,and arrives at the minimum in the Qinghai-Tibetan Plateau. The zonal intensity distribution is probably correlated with ocean tides from the Philippine Ocean and the Pacific Ocean. It also shows that the influence from the Indian Ocean seems small. However, the ambient noise intensity increases to a certain degree in the Xinjiang area,indicating that the main source of ambient noise in the western area of the Chinese Mainland is not derived from the East and South China Sea,but rather from the deep interior of the Eurasian continent. The ambient noise intensity obtained in this study can supply reference for seismology research based on ambient noise correlation. Moreover,it can supply basic data for attenuation research based on ambient noise, and thus help achieve the object of retrieving the attenuation of Rayleigh waves from ambient noise.  相似文献   

20.
We applied a season-reliant empirical orthogonal function(S-EOF) analysis based on the results of the Community Earth System Model, version 1-Biogeochemistry, to seasonal mean air-sea CO_2 flux over the western North Pacific(WNP)(0°–35°N, 110°E–150°E). The first leading mode accounts for 29% of the total interannual variance, corresponding to the evolution of the El Ni-Southern Oscillation(ENSO) from its developing to decaying phases. During the ENSO developing phase in the summer and fall, the contribution of surface seawater CO_2 partial pressure anomalies is greater than that of gas transfer/solubility anomalies, which contribute to increasing oceanic CO_2 uptake over the WNP. During the ENSO mature phase in the winter, the anomalous southwesterly northwest of the western North Pacific anticyclone(WNPAC) reduces the surface wind speed in the China marginal sea and thus decreases oceanic CO_2 uptake by reducing the gas transfer coefficient. In the subsequent spring, the WNPAC maintains with an eastward shift in position. The anomalous southwesterly warms sea surface temperatures in the China marginal sea by reducing evaporation and thus decreases oceanic CO_2 uptake by enhancing surface seawater CO_2 partial pressure. This process, rather than the effect of decreasing gas transfer coefficient, dominates CO_2 flux anomalies in the spring.  相似文献   

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