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.
Throughy studies of P-T-t paths and decompressive retrograde metamorphic textures of metamorphic rocks in the East Qinling-Dabieshan region,the authors determined the Mesozoic crust rapid uplifting age,and then inferred that in the East Qinling-Dabieshan region lithosphere delamination occurred from T3 to J1.The Yanshanian granites produced by delamination are developed well in the East Qinling-Dabieshan region.But due to the Gondwana plate effect,magmatism in the region caused by delamination lagged until J3 when the northern Tibet terrane and the Eurasian plate completely amalgamated.Additionally,due to western Pacific plate subducting underneath the Eurasian plate,in the East Qinling-Dabieshan region the stress state was transformed from compression to extension.So in the region from J3 to K2 magmatism was most intensive,and liberalization was also relatively strong.Geophysical data reflect that in the East Qinling-Dabieshan region the asthenosphere rose to the shallow level,the Moho is flat with no mountain root,and the crustal thickness is less than 40 km on average. These features agree with those of collisional orogenes in which delamination has occurred.Through contrastin differences in surface and interior depth between east and west Qinling we believe that elamination proceeded from east to west.  相似文献   

2.
Presented in this paper are Sm-Nd isotope and major, trace and rare-earth element analyses of bimodal volcanic rocks of the Shilu Group and other stratigraphic units in northwestern Hainan Is-land ,South China. It is shown that there are some N-MORB-type basalts(spilites) in the western part of the bimodal volcanic belt, in addition to some E-MORB-type and initial rift-type tholeiites (IRT) in th emiddle and eastern parts.Sm-Nd model ages of these basalts range from 545 Ma to 460Ma .The other extremes of the bimodal volcanics are porphyritic quartz rhyolites, which are characteristic of crustal material source.Sm-Nd model ages of the rhyolites range from 1562 Ma to 1371 Ma .The bimodal volcanic rocks are almost distributed in fifts or faulted depressions,as well as in the Upper Paleozoic rift of Hainan Island.Tholeiites of the Shilu Group can be compared with Cenozoic basalts in the middle and south-ern parts of the Red Sea Rift Belt in petrology, elemental geochemistry and Sm-Nd isotope geology. Shilu iron ores are closely associated with N-MORB-type basalts located in the western bimodal vol-canic belt.It is very interesting to note that the Shilu Fe-Co-Cu deposit can also be compared with Atlantis II Deep in the Red Sea Rift Belt.Therefore ,the present authors believe that the Shilu depos-it is a kind of hydrothermal deposit related to ocean volcanic belt ,where the geotectonic setting be-longs to initial extensional rifts in the oceanic crust.On the other hand, the largest Fe-Co-Cu ore de-posit in China used to be influenced by Hercynian granites after mineralization ,as is clearly observed on both εNd(T)-1/Nd and εNd(T)-^147Sm/^144Nd diagrams.  相似文献   

3.
The dissipative structure is an ordered structure.When a ssyterm is far from reaching equilibrium in the condition of non-equilibrium and exchanges some energy and material with the surroundings,this structure will be formed and preserved.Starting with the analysis of practical data,we attempt to use this theory to discuss the tectono-geochemical problems of some rock and ore-forming systems in faults.1.Ordered structure:Under the geological condition,due to the opening of a system in which energy and material are involved in geochemical action,the entropy tends to reduce gradually and substances evolve from non-ordered to ordered in structure.In the processes of formation of rocks and ores in faults,various layer-bands will be formed in rocks.2.Functional action:The physico-chemical activities which include pressure-creeping and thermal-diffusion as well as liquid diffusion have been shown.3.Fluctuating cycle:In the process of metamorphism,various changes in pressure,temperature and liquid are of fluctuation and periodicity.These may play an important role in the formation of rocks and minerals and the occurrence of ordered structures in fault zones.A few examples of mineral deposits in the middle and lower Yangtze River Valley are presented here,and the dissipative activities of rock-forming minerals and mineral-forming elements have been preliminarily established.  相似文献   

4.
The Campanian-Maastrichtian phosphatic deposits in Egypt,called the Duwi Forma-tion,comprise a part of the extensive Middle East to North African phosphogenic province of Late Cretaceous to Paleogene age.The province holds the greatest accumulation of phosphorites in the geological history,possibly in excess of 70 billion metric tons.The phosphate resources in Egypt alone exceed 3 billion metric tons.Two-third of these three billions occur only in the Abu-Tartur area.Among the phosphorite deposits in Egypt,the phosphorites of the Abu-Tartur area are characterized by high contents of iron ranging from 3% to 7% with an average of 5%.The detailed mineralogical and geochemical studies on the Abu-Tartur phosphorites revealed that iron is found in the form of pyrite,ankerite,clay minerals,microinclusions,and iron oxide.Pyrite,which is the major fraction,occurs as filling cement and partial to complete teplacement of phosphatic grains and confined to the fresh phosphorites while iron oxide occurs as cryp-tocrystalline aggregates of red to brown particles and is confined to the weathered outcrops.Ex-clusive relations between pyrite in the fresh phosphorite samples inside the Abu-Tartur mine and iron oxide in the equivalent horizon of the weathered exposure indicated that iron oxide was formed by the oxidation of pyrite as a result of weathering.All of these forms harm the quality of ore,manufacturing processes,and the produced phosphoric acid and fertilizers.  相似文献   

5.
The discovery of abrupt paleo-climate change events and the prediction of environmental changes in the future time have raised an urgent request for high-resolution paleo-environmental records.This paper reviews the progress made in hronology and paleo-environment of stalagmites from karst caves in China and presents some of the results of TIMS-U-series dating of stalagmites composed of secondary carbonates,taken from the Dongge,Longquan and Yamen karst caves in Libo County and the Qixing karst cave in Duyun,Guizhou Province,on a MAT-262 mass spectrometer.  相似文献   

6.
Cenozoic volcanic rocks widespread in eastern China constitute an important part of the circum-Pacific volcanic belt.This paper presents more than 150K-Ar dates and a great deal of petrochemical analysis data from the Cenozoic volcanic rocks distributed in Tengchong,China‘s southeast coast,Shandong,Hebei,Nei Monggol and Northeast China.An integrated study shows that ubiquitous but uneven volcanic activities prevailed from the Eogene to the Holocene,characterized as being multi-eqisodic and multicycled.For example,in the Paleocene(67-58Ma),Eocene(57-37.5Ma),Miocene(22-18,16-19Ma),Pliocene(8-3Ma),and Early Pleistocene-Middle Pleistocene(1.2-0.5Ma) there were upsurges of volcanism,while in the Oligocene there was a repose period.In space,the older Eogene volcanic rocks are distributed within the region or in the central part of the NE-NNE-striking fault depression,while the younger Neogene and Quaternary volcanic rocks are distributed in the eastern and western parts.Petrologically,they belong essentially to tholeiite-series and alkali-series basalts,with alkalinity in the rocks increasing from old to youg.The above regularities are controlled by both global plate movement and regional inherent tectonic pattern.  相似文献   

7.
There are three types of gold deposits in the Jiaodong gold metallogenetic domain.The strata-bound gold deposits are a new type,which occur in a hydrocarbon-dled double-source bed enriched in gold(Au 174ng/g) and organic carbon(0.007-4.225%),At diagenetic a d hydrotherrmal stages water and oil were simultaneously activated and the stratabound gold deposits were formed from interactions between water ,oil and rocks.In the late Yanshanian period,gold oreboides were enriched and enlarged in response to tectonmoagmatism and action of complex ore-forming hydrothermal solutions.As a results,it is highly expected to find suparlarge gold deposits and the Yanzi area is expected to be a perspective target area.  相似文献   

8.
Nd model ages(TDM) of the Pre-Mesozoic crustal rock samples from Southeast China range from 1.2 to 3.5Ga.Two age peaks of 1.4Ga and 1.8 Ga are observed in the histogram of TDM model ages.Available U-Pb zircon inheritance ages are concentrated around 1.2-1.4Ga,1.8Ga and 2.5Ga,respectively.The combined use of Sm-Nd and U-Pb zircon inheritance ages suggests that the formation of the Precambrian curst is of episodic character.The oldest crustal nucleus may have been formed during the Late Archean(2.5Ga or older?).A rapid production of the crust took place 1.8 Ga ago,consistent with the global crust formation event at 1.7-1.9Ga.Another important episode of the addition of juvenile crustal material from the mantle in Southeast China took place 1.2-1.4Ga ago,during which the pre-existing crust was strongly reworked and/or remelted.  相似文献   

9.
The pertochemistry and Sm-Nd isotopic compositions and the geochemical characteristics of REE,U,Th,etc..in the Late Proterozoix and Early Palaeozoic strata in northwestern Jiangxi and western Zhejiang provinces are described in this paper.It seems to be sure that the middle Proterozoic strata of southeastern China are low in the degree of matrration .The strata contain much mantle-derived material.At the end of Late Proterozoic there was an abrupt turn with respect to the crustal geochemical evolution of the eastern part of South China .Since then ,the geochemical environment has undergone a change from a simple reducing environment to a complex oxidizing-reducing environ-ment, which would be geochemically beneficial to the formation of Late Sinian to Early Cambrian U-bearing formations.  相似文献   

10.
The occurrences and characteristics of the association of Au-Sb-As-W are summarized.An interpretation of the association is given according to the fact that the content of reduced sulfur in the ore-forming solution is much high relative to Cl in this kind of ore deposits especially for the Au-Sb-As with W,using the data on their complexes and solubility,The high dfineness of gold and the separation of gold from the base metals Cu,Pb,Zn,and sometimes from Ag in this kind of ore deposits are also interpreted.  相似文献   

11.
In the Inner Mongolia axis and Jiaoliao anteclise along the northern margin of the North China Platform.it has been found that the strata formerly considered as Archaean and Proterozoic are in fact an ophiolite suitesimilar to the Early Palaeozoic Ondor Sum Group in the Northern Geosyncline region of China. The stratahave been named in northern Liaoning as the Qinghezhen Group. The emphasis of this paper is on the discus-sion of the simall shelly fossils found in the siliceous rocks in the upper part of the Qinghezhen Group. Thisophiolite suite stretches in an E-W direction for about 1000 km along the northern margin of the North ChinaPlatform. in which 15 fossil localities with stable stratigraphic horizons have been discovered. In this paper. 4types. 7 genera (including 5 new ones) and 10 species (including 8 new ones and 1 new subspecies) aredescribed, which are collectively referred to as the Qinghezhen Fauna. The characteristics of these fossils are:shell form simple. the maximum length not exceeding 4 mm. with obvious shell wall and wall ornaments. TheQinghezhen Fauna is comparable in shell structure of some genera and species with the Meishucun Fauna inSouth China, but differs from the latter in having only monotonous fossil groups developed in a distinctly va-ried ecological environment. The two faunas may belong to the same evolutionary stage of the Early Cambrianbut have developed parallelly in different regions. The existence of the Qinghezhen Fauna represents an impor-tant biological event in the Early Cambrian in the Northern Geosyncline region of China. The discovery of theQinghezhen Fauna will bring new knowledge and profound influence to a series of problems on basic geologyand mineral deposit prospecting such as the Cambrian faunas. biogeographical povincialism in China and thegeotectonic features of the northern margin of the North China Platform.  相似文献   

12.
The Raman spectra of the natural end members of the garnet-group minerals,which include pyrope, almandine and spessarite of Fe-Al garnet series and grossularite ,andradite and uvarovite of Ca-Fe garnet series, have been strdied.Measured Raman spectra of these minerals are reasonably and qualitatively assigned to the internal modes, translational and rotatory modes of SiO4 tetrahedra, as well as the translational motion of bivalent cations in the X site.The stretch and rotatory A1g modes for the Fe-Al garnet series show obvious Raman shifts as compared with those for the Ca-Fe garnet series ,owing to the cations residing in the Xsite connected with SiO4 tetrahedra by sharing the two edges.The Raman shifts of all members within either of the series are attributed mainly to the properties of cations in the X site for the Fe-Al garnet series andin the Y site for the Ca-Fe garnet series.  相似文献   

13.
The characters of organic matter in rocks and ores in the Fankou and Dabaoshan deposits are systematically studied with regard to their implications for mineralization.The results show that kerogens in this area faaa mainly into the plutonism field in Van Krevelen‘s diagram.Reflectivity of the organic substance was measured to be 3.06%(Fankou)and 1.67%(Dabaoshan),corresponding to the paleo-geotemperatures of 232℃ and 184℃ respectively.The same types of porphyrins and hydrocarbons were recognized in the rocks and ores and hydrocarbon-bearing inclusions are widespread in quartz and calcite,particularly in Dabaoshan,It is thought that the orgain matter must have played a critical role in diagenesis and metallization in these deposits and that the hydrothermal solution was most likely to be the type of water-oil hot brine.  相似文献   

14.
By PVT fractionation experiments to model phase-controlled and gaw-washing fractionations during the formation of petroleum reservoirs,the authors measured the physical and chemical properties of products formed in different fractionation staes and made a correlative analysis of the influence of depressurization and gas washing on oil/gas molecular composition and the rule of fractionation.The analytical results showed that gas washing is an important factor affecting the physical properties of crude oils.and also can be regarded as a good genetic interpretation of marine wax-high oils in the Tarim region,Xinjiang,China.Phase-controlled and gaw-washing fractionations can lead to the formation of condensates and their differences in chemical composition from crude oils are a direct reflection of evaporating fractionation.Phasecontrolled and gaw-washing fractionations have a great influence on the composition of molecular compounds and relevant parameters.So phase-controlled and gas-washing fractionations during the formation of petroleum reservoirs are not only favorable to identifying different processes of formation of petroleum reservoirs,but also to the scientific application of routine geochemical parameters.  相似文献   

15.
Long-and short-term climatic curves were preliminarily established based on the comprehensive analysis of geochemical information since the Late Cenozoic in the Qinghai Xizang(Qinghai-Tibet)Plateau.The curves show that the climate in the plateau was alternatively dry-warm and cold-wet during the period of 30-3.4 Ma when the plateau was not uplifted to an enough altitude and the monsoon was not completely formed either,In the period of 3.4-0.73 Ma.the climate fluctuated between dry-cold and wet-warm when the plateau was rapidly uplifted and the Asian monsoon was consequently formed.Since 0.73 Ma.the climate became even drier when the plateau continuously rose.In the Holocene period.the climate alternatively changed with a complex model of being cool-dry,warm-wet and cold-wet.  相似文献   

16.
Data on the hydrolysis of Th （Ⅳ） and solubility of ThO2 in the presence of organic ligands are of critical importance to the safe disposal and treatment of high-level nuclear waste. Such data are required to predict reliably thorium behaviour in high-level waste repositories where organic anions may be present. In addition, recent studies of the performance of thorium-based fuels report that these fuels can be used to reduce concerns related to potential proliferation of nuclear weapons and disposal of the current uranium dioxide fuel waste. Because several reactor concepts based on thorium fuel cycles are under consideration, it is important to have thermodynamic data to predict how such fuel and its waste form will behave in the environment. To establish the effect of pH and organic ligands on the hydrolysis of Th （Ⅳ）, experiments on the solubility of hydrous ThO2 in aqueous solution at room temperature were performed, covering a wide range of pH （pH=3.0 to 12.0） in 0.1 molal NaNO3 solutions. Experiments also were conducted in the presence of citrate, EDTA and oxalate with a concentration range 100 to 500 μmol. Approach to equilibrium was from supersaturation. Slopes of straight lines fit to plots of log mTh vs. pH were approximately -4 at the acidic region and near 0 at neutral and alkaline region for experiments conducted at constant ionic strength （I=0.1）, implying that the dominant Th species should be Th4^＋ and Th （OH）4（aq） The←→Th^4＋＋2H2O ThO2＋2H2O←→Th （OH）40 as follows： ThO2＋4H^＋ solubility of ThO2 decreases with increasing pH （pH 3 -6） and remains near the detection limit of ICP-MS （in the order of 10^-9 M to 10^1- M） in the range of pH 6-12. These values are in accordance with data in the literature.  相似文献   

17.
The platinum group elements(PGE)in the mafic-ultramafic suite in the Xinjie layered intrusion and associated basalts and syenites were analyzed using neutron activation techniques after fire-assay preconcentration.On this basis,the geochemistry of the platinum group during the magmatic stage is discussed.With respect to PGE distribution,the Xijie layered intrusion is similar to the Bushveld ferruginous ultramafic series and is distinct from komatiite and Alpine-type peridotite.It is also similar to the Emeishan basalt in PGE characteristics,implying that the original magmas of them may be of the same type.  相似文献   

18.
The formation of the Tongyu gold deposit, controlled by regional polyphase deformation-metamorphism.is closely related to the regional composite antiform-shear slip fracture zone. Late-stage reworking of theTaihua Group accounts for the enrichment of ore substances. It is a typical syntectonic gold deposit. The formation and evolution of the deposit involved four stages: (Ⅰ) the state of preparation of ore sub-stances, in which primary source beds originated: (Ⅱ) the stage of remobilization of ore substances, in whichregional progressive metamorphism and migmatization and thermodynamic-chemical differentiation led toremobilization of gold and its initial local concentration: (Ⅲ) the stage of gold deposit formation, in which re-gional folding produced concordant and cross shear-slip fractures and under the dynamic action gold was sepa-rated and migrated in a certain direction and concentrated to form a gold deposit: (Ⅳ) the stage ofsuperpositon, reworking and exposure of orebodies, in which the block uplifted and the deposit againunderwent reworking through faulting and mechanical differentiation.Thermodynamic mineralization played adominant role in the formation of the deposit.  相似文献   

19.
After the establishment of the global stratotype section and point (GSSP) of the Permian-Triassic boundary (PTB), the definition of the accessory section and point (ASP) of the terrestrial Permian-Triassic boundary (TPTB) is now on the agenda. However, all good TPTB sections so far known have the following shortcoming:(1) the exact TPTB horizon is difficult to define paleontologically with high-resolution, and (2) accurate correlation between marine and terrestrial PTBs in hard to attain. In order to enhance the understanding of the nature of the global life crisis in both the marine and terrestrial environments across the Paleozoic-Mesozoic transition, these shortcomings need to be addressed. In western Guizhou and eastern Yunnan, Southwest China, some fossiliferous PTB sections which include marine, paralic and terrestrial are well-developed, allowing bed-to-bed correlation of the PTB sequences. Fortunately, the marine PTB sequence in this area is almost the same as found at the Meishan Section, where the GSSP of the PTB is located, which may provide a reliable auxiliary marker for high-resolution demarcation of the TPTB. These features fund in estern Guizhou and eastern Yunnan make this area a good place to study the ASP of the TPTB, so we propose to study the ASP of the TPTB in this area.  相似文献   

20.
Developed in the southeast coast of te East Shandong Peninsula,the Mesozoic fault-magma belt consists of five rock series:the syenite series;the monzonite series;the megaporphyritic monzogranite series;the biotite-granite series;and the alkali granite seres.Based on their Rb-Sr isochron ages(122-220Ma),these rock series may be divided into three magma subcycles dated at Triassic,Late Jurassic and Early Cretaceous.The initial ^87Sr/^86Sr ration in these rock series range from 0.70436 to 0.7155.The starting points of the Rb-Sr isochrons exhibit four different distribution trends on the(^87Sr/^86Sr)i-^87Rb/^86Sr diagram.These characteristics show that the multiple granitic rock series are different in genesis and derivation.The syenite series might be derived from the combination of mantle-derived magma and crustal material,and the others could be derived from granulite-facies and amphibilite-facies rocks in the deep crust.  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