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1.
To reveal the petrogenesis of rhyolite from the southwestern Okinawa Trough, the mineral chemistry of plagioclase, orthopyroxene, amphibole, quartz and Fe-Ti oxide phenocrysts were analyzed using an electron microprobe, and in suit Sr and Ba contents of plagioclase analysed by LA-ICPMS were chosen for fingerprinting plagioclases of different provenances. Results indicate an overall homogeneous composition for each of the mineral phases except for plagioclase phenocrysts which have a wide range of composition(An=39~88). Plagioclase crystals characterized by An contents of 70 are not in equilibrium with their whole-rock compositions, and coarse-sieved plagioclase phenocryst interiors record high An contents(70) and Sr/Ba ratios(7), which are similar to the those of plagioclase crystals in basalt. Therefore, these crystals must have been introduced to the rhyolitic magma from a more mafic source. Equilibrium temperatures estimated using orthopyroxene-liquid, iron–titanium oxide, titanium-in-quartz and amphibole geothermometers show consistent values ranging from 792 to 869℃. The equilibrium pressure calculated using amphibole compositions is close to 121 MPa which corresponds to an approximate depth of 4 km. The fO_2 conditions estimated from Fe-Ti oxides and amphiboles plot slightly above the NNO buffer, which indicates that the rock formed under more oxidized conditions. Our results suggests that petrogenesis of the rhyolite due to basaltic magma ascend with the high An and Sr/Ba plaigoclases from deep magma chamber into the shallow chamber where the fractional crystallization and crustal assimilation happened. It also indicates that a two-layer magma chamber structure may occur under the southwestern Okinawa Trough.  相似文献   

2.
The Okinawa Trough is a very active tectonic zone at the margin of the Northwest Pacific and is typical of back-arc rifting at the young stage of tectonic evolution. Many scientists from Japan,China, Germany, France, the U. S.A. and Russia have done a lot of geologic and geophysical investigations there. It is well known that the Okinawa Trough is an active back-arc rift with extremely high heat flow, very strong hydrothermal circulation, strong volcanic and magmatic activity, frequent earthquakes,rapid subsidence and rifting, well-developed fault and central graben. But up to now, there are still some important tectonic problems about the Okinawa Trough that require clarification on some aspects such as the type of its crust, its forming time, its tectonic evolution, the distribution of its central grabens, the relationship between its high heat flow and tectonic activity. Based on the data obtained from seismic sur-vey, geomagnetic and gravity measurements, submarine sampling and heat flow measurements in the last 15 years, the author discusses the following tectonic problems about the Okinawa Trough: (1) If the Okinawa Trough develops oceanic crust or not. (2) Is the South Okinawa Trough tectonically more active than the North Okinawa Trough with shallower water and few investigation data on it. (3) The formation time of the Okinawa Trough and its tectonic evolution. The Okinawa Trough has a very thin continental crust. Up to now, there is no evidence of oceanic crust in the Okinawa Trough. The North, Middle and South Okinawa Trough are all very strongly active areas. From 6 Ma B.P. , the Okinawa Trough began to form. Since 2 Ma, the Okinawa Trough has been very active.  相似文献   

3.
The nature of the crust of the Okinawa Trough is different from that of the continental shelf in the East China Sea. The crust beneath the Trough is in transformation from continental to oceanic and the depth of MOHO in the northern section of the Trough is deeper than in the southern section. Thick sedimentary strata of Neogene and Pleistocene ages are deposited in the Okinawa Trough, and divided into three layers: the upper horizontal layer, the middle layer lightly folded and the lower deformed layer. They were formed in Pleistocene, Pliocene, and Miocene to Paleogene, respectively. The tectonic movement in the southern section is stronger than that in the northern section. Somevolcanic seamounts appear on the bottom of the Trough. On both slopes of the Trough are developed many normal faults and the intrusive igneous rocks. The Okinawa Trough, the back-arc basin,, is an embryonic marginal basin in rifting and spreading. The formation of the Okinawa Trough started in the early Pliocene. The transform  相似文献   

4.
MAGMATIC EVOLUTION OF OKINAWA TROUGH DURING ITS EARLY SPREADING STAGE   总被引：2，自引：0，他引：2  
The Okinawa Trough is different from other typical backarc spreading basins because the acidic vol-canic rock(pumice)is extensively distributed in it.Systematic mineralogical and petrochemical study on arepresentative core(Z14—5)to characterize the magmatic evolution of the Trough during its early spreading stage showed that the pumice magma was originally from the mantle,but underwent full crystallizationdifferentiation and was possibly contaminated by crust-derived material.With time,the acidic volcanic ac-tivities of the Okinawa Trough have an evolutional tendency of shifting to relatively basic magma activity.With further spreading of the Trough the magmatic activity will be intensified and the crust of the Troughwill develop from the transitional type to the oceanic type.  相似文献   

5.
Zeng  Zhigang  Chen  Zuxing  Zhang  Yuxiang  Li  Xiaohui 《中国海洋湖沼学报》2020,38(4):985-1007
Seafloor hydrothermal vent fields(SHVFs) are located in the mid-ocean ridge(MOR),backarc basin(BAB),island arc and hot-spot environments and hosted mainly by ultramafic,mafic,felsic rocks,and sediments.The hydrothermal vent fluids of SHVFs have low oxygen,abnormal pH and temperature,numerous toxic compounds,and inorganic energy sources,such as sulfuric compounds,methane,and hydrogen.The geological,physical,and chemical characteristics of SHVFs provide important clues to understanding the formation and evolution of seafloor hydrothermal systems,leading to the determination of metal sources and the reconstruction of the physicochemical conditions of metallogenesis.Over the past two decades,we studied the geological settings,volcanic rocks,and hydrothermal products of SHVFs and drawn new conclusions in these areas,including:1) the hydrothermal plumes in the Okinawa Trough are affected by the Kuroshio current;2) S and Pb in the hydrothermal sulfides from MOR are mainly derived from their host igneous rocks;3) Re and Os of vent fluids are more likely to be incorporated into Fe-and Fe-Cu sulfide mineral facies,and Os is enriched under low-temperature(200℃) hydrothermal conditions in global SHVFs;4) compared with low-temperature hydrothermal sulfides,sulfates,and opal minerals,high-temperature hydrothermal sulfides maintain the helium(He) isotopic composition of the primary vent fluid;5) relatively low temperature(116℃),oxygenated,and acidic environment conditions are favorable for forming a native sulfur chimney,and a "glue pudding" growth model can be used to understand the origin of native sulfur balls in the Kueishantao hydrothermal field;and 6) boron isotope from hydrothermal plumes and fluids can be used to describe their diffusive processes.The monitoring and understanding of the physical structure,chemical composition,geological processes,and diverse organism of subseafloor hydrothermal systems will be a future hot spot and frontier of submarine hydrothermal geology.  相似文献   

6.
The Ryukyu trench-arc system can be divided into two types according to its subduction model. The normal subduction in the northern part of the Philippine Sea plate creates a hinge sedimentary wedge with large deformation at the collision front, while the oblique subduction in the southern part gives rise to a smaller accretion with small deformation than that in the northern part. The mechanisms that cause the distinction between these two types have been analysed and calculated by using gravity data based on the lithosphere rheology and the stress state of the lithosphere in the subduction boundary. The two types of subduction model are associated with the internal extension in the southern Okinawa Trough and the small extension in the northern part. The difference of the stress state between the two types of subduction model is also manifested in other tectonic features, such as topography, volcanic activity and crust movement. Modeling bathymetric and gravity data from this area suggests that the oblique subduction of low angle, together with smooth geometry of the overlying plate crust, results in small stress released on the south of the trench by the subduction plate. The intraplate faults in the southern Okinawa Trough behind the trench stand in surplus intensive stress. On the other hand, the normal subduction of high angle, together with strong undulation geometry of the overlying crust, results in more intensive stress released in the northern Ryukyu Trench than that in the south. The intraplate faults in the northern Okinawa Trough behind the northern Ryukyu Trench stand in small stress.  相似文献   

7.
This paper reports on our research on the gravity data around the Ryukyu T-A-BA system, and presents the results obtained and the calculation methods, such as, Moho calculation, spectrum analysis, smooth filtering, analytic extension, horizontal derivation, correlative analysis, etc. used in this study. In contrast to the information obtained from seismic profiles, the analyses show that oceanic and continental crusts demarcated by the Ryukyu T-A-BA system are very different in gravitational and tectonic characteristics. The structures in the T-A-BA region are very complicated and linearity of the gravity field and structure is very obvious. The Okinawa Trough with its two groups of fault structures in their respective NW and NNE strikes is an active neo-spreading back are basin whose development and evolution is greatly influenced by faulting.  相似文献   

8.
The Okinawa Trough is a natural laboratory for the study of air-sea interaction and paleoenvironmental change. It has been demonstrated that present offshore export of particles in the bottom nepheloid layer occur primarily with downwelling from the northeast winter monsoon, which is inhibited by a transverse circulation pattern in summer. This current system was very different during the Last Glacial Maximum owing to low sea level(-120 m) and exposure of a large shelf area. We collected sediment core Oki01 from the middle Okinawa Trough during 2012 using R/V K exue No. 1 to elucidate the timing and cause of the current system transition in the East China Sea. Clay mineral, dry density, and elemental(Ti, Ca) composition of core Oki01 was analyzed. The results indicate that clay minerals derived mainly from the Huanghe(Yellow) and the Changjiang(Yangtze) Rivers during 16.0–11.6 ka, and the modern current system in the East China Sea formed beginning in the early Holocene. Therefore, mixing of East China Sea continental shelf, Changjiang River and partially Taiwan Island sediment are the major contributors. The decrease of log(Ti/Ca) and alternating provenance since the early Holocene indicate less sediment from the East China in summer because of resistance of the modern current system, i.e., a "water barrier" and upwelling. Conversely, sediment delivery persists in winter and log(Ti/Ca) indicates the winter monsoon signal since the early Holocene. Our evidence also suggests that sediment from Taiwan Island could be transported by the Kuroshio Current to the middle Okinawa Trough, where it mingles with winter monsooninduced export of sediment from the Changjiang River and East China Sea continental shelf. Although the present research advances understanding of the evolutionary history of paleoenvironmental change in the Okinawa Trough, more sediment cores should be retrieved over wide areas to construct a larger scenario.  相似文献   

9.
Methane-rich fluids were recognized to be hosted in the reservoir volcanic rocks as primary inclusions. Samples were collected from core-drillings of volcanic gas reservoirs with reversed δ^13C of alkane in the Xujiaweizi depression of the Songliao Basin. The volcanic rocks are rhyolite dominant being enriched in the more incompatible elements like Cs, Rb, Ba, Th, U and Th with relative high LREE, depleted HREE and negative anomalies of Ti and Nb, suggesting a melt involving both in mantle source and crustal assimilation. Primary fluids hosted in the volcanic rocks should have the same provenance with the magma. The authors concluded that the enclosed CH4 in the volcanics are mantle/magma-derived alkane and the reversed δ^13C of alkane in the corresponding gas reservoirs is partly resulted from mixture between biogenic and abiogenic gases.  相似文献   

10.
Biomarkers including brassicasterol, dinosterol and alkenone in sediments are used as indicators to reconstruct changes to the phytoplankton community in surface and sub-aerial sediments of Prydz Bay, Antarctica. The results indicate that the bio- marker records in surface and core sediment samples changed with time and space. The total content of phytoplankton biomarkers ranges from 391.0--1 470.6 ng.g-l. The phytoplankton biomass has increased in Prydz Bay over the past 100 years. This variation may be mainly related with climate change in the region. The total biomarker contents in surface sediments from 5 stations in Prydz Bay are in the range of 215.8--1 294.3 ng.g4. The phytoplankton biomass in Prydz Bay is higher than that outside of the bay. This is similar to the distributions of chlorophyll a, organic carbon and biogenic silica in surface waters determined through in situ investigation. Such consistency indicates a coupling between the bottom of the ocean and biogeochemical processes in the upper water.  相似文献   

11.
The Xiong’ershan area,as a part of a metallogenic province in cetral China,contains substantial Leimengou porphyry molybdenite deposit,Qiyugou breccia gold deposits and vein gold deposit occurred in fault zone,as well as previously refer to as orogenic gold deposit.Around or nearby the Mesozoic porphyry granite,the typical porphyry deposit,much more breccia pipes and breccia gold deposit are developed in the area.In this paper we focus on reporting preliminary results obtained from field,petrographic work on the Leimengou porphyry molybdenite and the Qiyugou breccia gold deposit,as well as laser Raman microspectroscopy and microprobe analyses carried out on samples from the Au-bearing Qiyugou breccia pipes.An adularia-calcite assemblage is reported in these breccia gold deposits.Two stages of hydrothermal alteration,pervasive and vein,are identified.The first stage consists of the alteration of the breccia clasts and rock flour by actinolite,green biotite,epidote,chlorite and minor sericite.This hydrothermal activity is likely to relate to the molybdenite mineralisation episode.The second stage is characterised by quartz veining and adularia and calcite filling open-spaces.Vein ores associated with quartz,sericite,and minor calcite alteration occur in NE-trending fault that cut the first stage of alteration.The adularia-calcite alteration is genetically associated with gold mineralization.The adularia-calcite assemblage in the area suggest that the Qiyugou pipes are of low-sulphidation epithermal in nature.The Qiyugou breccia pipes are coeval and spatially associated with the nearby Leimengou porphyry Mo deposit,which together conform to an alkalic mineralising system.We propose a model for the development and evolution of the breccia pipes in conjunction with a model that describes the genesis of the porphyry Mo and auriferous breccia pipes as a unified magmatic-hydrothermal system,which is linked with transition from collisional compressional to extensional geodynamic regime.  相似文献   

12.
The reorganization of the global production network and the increased mobility of urban-rural elements have accelerated the differentiation of rural spaces, resulting in a trend towards specialization in rural areas. This paper focuses on the concept of specialization, and takes a renowned bonsai specialized village in Guangzhou City, China as a typical case to explore its transformation and development process, action logic and coupling mechanism with the social governance. The results show tha...  相似文献   

13.
The major aim of this study is to put forwad a valid model to explain the-gravity anomalies observed over the Okinawa Trough which the crustal structure and a reasonable model of the downgoing slab themselves cannot explain. The result of inversion indicates that the lithosphere above the center of the trough thins out to 45% of the normal thickness (63 km) of the lithosphere of the East China Sea.Further, the originations of lithospheric force are discussed. The tensional stress of about 160 bar arising from density contrast in the Okinawa Trough is recognized to be the most important causative factor in the stretching of the trough.  相似文献   

14.
Along the Czech-German border there are four national parks, two Czech and two German, arranged in cross-border ‘pairs'. This article focuses on the southern ‘pair' formed by the parks of ?umava and Bayerischer Wald(Bavarian Forest). The aim is to evaluate and compare tourism organization in their areas, taking into account selected aspects of management: the network of hiking trails with its related infrastructure, transport accessibility, a typology of tourist centers, as well as directions and destinations of tourist movements. Based on the results, it can be concluded that the availability of geographical space for tourists is much greater in the German than in the Czech national park, and the tourism infrastructure is clearly more extensive there, including the network of tourist trails. This is mainly due to the longer and fairly uninterrupted development of tourism in this area. ?umava National Park can be identified as a model in terms of how to adjust the directions of tourist movements and the layout of the tourist trail network to the needs of natural environment. On the basis of observations in both national parks, it is possible to indicate various solutions that, after appropriate adaptation, may bring benefits to other protected areas.  相似文献   

15.
The morphology and toxicity of Pseudo-nitzschia strain PP0201-01, isolated near the estuary of Changjiang （Yangtze） River in Year 2002 and tentatively identified as Pseudo-nitzschia pungens, were studied. The strain was identified morphologically as P. pungens using scanning electronic microscope （SEM）. The analytical results of LC-PDA （liquid chromatography with photodiode array detector）, LC-MS （liquid chromatography with mass detector）, and the toxicity data from mouse bioassay, showed that no domoic acid was produced by the strain. However, the mechanism of domoic acid production by Pseudo-nitzschia species is complicated. More works are needed to assess the toxic species and to evaluate the potential risk of amnesic shellfish poisoning （ASP） in China.  相似文献   

16.
On the basis of elastic-plastic damage model of cement consolidated soil, the authors took organic contents into reasonable damage variable evolution equation in order to seek relation between the organic contents and parameters in the equation, and established the elastic-plastic damage model of cement consolidated soil considering organic contents. The results show that the parameters change correspondingly with difference of the organic contents. The higher the organic contents are, the less the valves of the parameters such as elastic modulus （E）, material parameters （K, n） and damage evolution parameter （ε） become, but the larger strain damage threshold value （εd） of the sample is. Meanwhile, the calculation results obtained from established model are compared with the test data in the condition of common indoors test, which is testified with reliability.  相似文献   

17.
The X-ray fluorescence(XRF) core scanning method is widely applied in studies of sedimentary paleoenvironments due to its convenient pretreatment, nondestructive characteristics, fast execution, continuous scanning, and high resolution. XRF core scanning for sediments is commonly used in the studies on the South China Sea. This study compares XRF-scanned intensities and measured inductively coupled plasma(ICP) elemental contents of core CS11 in the northeast South China Sea deep basin. The results show that the analyzed elements can be separated into three classes. Class I includes elements with high correlation coefficients, such as Ca, Sr, and Zr; Class II contains elements with average correlation coefficients, such as Fe, Mn, Ti, and Cu; and Class Ⅲ comprises elements with low correlation coefficients, such as K, Ni, Zn, Rb, and Al. In the South China Sea deep basin, pore water,compaction, and grain size have weak effects on the elemental intensities and contents of short core sediments. Hence, for elements with high correlation coefficients, a linear relationship model can be established by the least-squares method, in which the converted XRF intensities are approximately equal to the measured ICP contents. Based on the established log-ratio calibration model, the resulting ln(K/Ca), ln(Ti/Ca), ln(Fe/Ca), and ln(Zr/Ca) values generally display the same variation trends as the measured curves. The elemental contents and ratios produced by the linear model via the least-squares method and the log-ratio calibration model are expected to provide high-resolution data support for future paleoenvironmental research on the South China Sea deep basin.  相似文献   

18.
Hydrothermal barite is a typical low-temperature mineral formed during the mixing of hydrothermal fluid and seawater. Because of its extremely low solubility, barite behaves as a close system after crystallization and preserves the geochemical fingerprint of hydrothermal fluid. In this study, the elemental contents and Sr isotope compositions of hydrothermal barites from the Yonaguni IV were determined using electron microprobe and LA-MC-ICP-MS respectively. On these bases, the fluid/sediment interaction during the hydrothermal circulation and physicochemical condition of barite crystallization were discussed. Results show that the 87 Sr/86 Sr values of hydrothermal barites from the Yonaguni IV are apparently higher than those of the seawater and associated volcanic rocks, indicating the sufficient interaction between the hydrothermal fluid and overlying sediment. Monomineral Sr abundance shows large variations, reflecting the changes in barite growth rate during the fluid mixing. The mineralization condition in the Yonaguni IV was unstable. During the crystallization of barite, hydrothermal fluid and seawater mixed in varying degrees, with the pro-portions of hydrothermal fluid varied from 36% to 72%. The calculated crystallization temperatures range from 109 to 220℃. Sediment plays a critical role during the mineralization process in the Yonaguni IV and incorporation of sediment component into hydrothermal system was prior to barite crystallization and sulfide mineralization.  相似文献   

19.
A comprehensive study of the data profiles, including the 2D seismic data, single channel seismic data, shallow sections, etc., reveals that gas hydrates occur in the East China Sea. A series of special techniques are used in the processing of seismic data, which include enhancing the accuracy of velocity analysis and resolution, estimating the wavelet, suppressing the multiple, preserving the relative amplitude, using the DMO and AVO techniques and some special techniques in dealing with the wave impedance. The existence of gas hydrates is reflected in the subbottom profiles in the appearance of BSRs, amplitude anomalies, velocity anomalies and AVO anomalies, etc. Hence the gas hydrates can be identified and predicted. It is pointed out that the East China Sea is a favorable area of the gas hydrates resource, and the Okinawa Trough is a target area of gas hydrates reservoir.  相似文献   

20.
The South Narimalahei area is located on the north side of the Middle Kunlun fault in the eastern section of the East Kunlun composite orogenic belt. The ore body is veined and controlled by structures and se-condary fissures, which occurs in the structural alteration fracture zone in the Late Triassic granodiorite. In this deposit, copper mineralization is closely related to silicification and sericification. The formation process of the deposit includes hydrothermal mineralization and supergene oxidation. In this paper, the fluid inclusion minera-logy, microscopic temperature measurement and stable isotope studies have been carried out for ore of the main mineralization stage. The results show that the primary gas-liquid two-phase inclusions and a small amount of single-liquid inclusions are mainly developed in the quartz in the main mineralization stage. The results of microscopic temperature measurement show that the ore-forming fluid which has low temperature(151.7℃--205.8℃), low salinity(2.06 wt%--4.94 wt%NaCl), low density(0.86--0.92 g/cm~3) and shallow formation(1.5--3.0 km) is a hydrothermal solution of NaCl-H_2O system. Hydrogen and oxygen isotope results show that the ore-forming fluids mainly come from atmospheric precipitation, with a small amount of magmatic fluids participating. It is preliminarily determined that the South Narimalahei copper polymetallic deposit is a low-temperature hydrothermal vein deposit.  相似文献   

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