Table of Content

20 September 2004, Volume 10 Issue 3

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Article

The Study of Granitic Rocks in South China:Looking Back and Forward

WANG De-zi

2004, 10(3):  305-314. 

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The past half a century has witnessed three stages in the study of granitic rocks in South China.Stage 1 began in the 1960s,focusing on the temporal and spatial distribution of granitic rocks.Based on geological evidence and isotopic dating,it was verified that there exist polycyclic granitic rocks in South China,including late Protemzoic,Caledonian,Hercynian-Indosinian and Yanshanian granitoids.It was recognized that different orogenic cycles were accompanied by corresponding granitic rocks.Generally,the age of granitic rocks tends to be younger and younger from northwest to southeast(towards the ocean side).Stage 2 was from the 1970s to the 1980s,concentrating on the petrogenic material sources of granitic rocks.Granitic rocks were classified into four types (types M,I,S and A)in terms of the mechanisms of their formation.During this period researchers also studied the tectonic environments in which various genetic types of granitic rocks were formed,as well as their petrogeochemical criteria.Stage 3 began in the 1990s and is still making progress.The research in this stage has been focusing on the relationships between crust-mantle interaction and the formation of granitic rocks,such as that between the underplating of basaltic magma and the genesis of granitic rocks,and that between magma mingling and the variation of granitic composition.The future research in this field should focus mainly on the following three topics:1.the relationships between crust-mantle interaction and the genesis of A-type granitoids;2.the mechanisms of formation of intracontinental granitic magma(metamorphic core complexes,granitic domes,and composite granitic plutons);and 3.the genesis of the great granitic provinces in South China.

Structural Elements Association of Yanshan Orogenic Belt,North China

DENG din-fu, SU Shang-guo, ZHAO Guo-chun, LIU Cui

2004, 10(3):  315-323. 

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Using the concept of structural elements association of orogenic belt.we studied the evolution of Yanshan orogenic belt.The structural elements association characteristics of each stage of Yanshan orogenic belt are as follows:During the pre-and initial orogenic episode(J1),in the earlier stage of Early Jurassic,it is preorogenic extension.The structural elements associations are:triple junction rift, intraplate basalt,coal-bearing sedimentary formation;In the later stage of Early Jurassic.it is incipient orogenic compression.The structural elements associations are: northward verging fold and thrust, Jiulongshan molasse-like formation,chloritoid-staurolite-kyanite low temperature, middle-high pressure metamorphic belt.During the early orogenic episode(J2),in earlier stage of Middle Jurassic.it is syn-orogenic extension. Structural elements associations are: volcanic basins and intrusive rocks with lithosphere uplift and extension,linear distribution of volcanic rocks;In the later stage of Middle Jurassic, it is compression regime.Structural elements associations are:thrusting and folding,molasse formation.syn-tectonic intrusive rocks and am phibole facies metamorphiesm;During the peak orogenic episode(J3),in the earlier stage of Late Jurassic,it is syn-orogenic extension. Structural elements associations are:volcanic basins and intrusive rocks with lithosphere uplift and extension, planar distribution of vo1canic rocks,high-pressure trachyte,voluminous rhyolite;in the later stage of late Jurassic,it is compression structure, Structural elements associations are:thrusting and folding, molasse formation, syn-tectonic intrusive rocks and amphibole facies metamorphism,high-pressure syenite;During the earlier stage of Early Cretaceous,it is late-orogenic episode.Structural elements associations are:local compression structure,lake facies sedimentary formation,peralkaline quartz syenite,miarolitic granite,komatiitic gabbro;During the later stage of Early Cretaceous,it is post-orogenic extension episode. Structural elements associations are:normal faulting,metamorphic core complex,bimodal dikes,typical peralkaline granite and coal-bearing sedimentary formation.

Lithospheric Thinning Beneath North China:A Temporal and Spatial Perspective

Xu Yi-gang

2004, 10(3):  324-331. 

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This paper reviews geochronological and geochemical data on Mesozoic -Cenozoic magmatism in North China.It is suggested that the temporal variation in geochemistry of Mesozoic-Cenozoic mafic rocks is coupled with lithospheric thinning process in this region. Consequently,the duration of magmatism(180～90 Ma)provides a first-order estimation for the timescale of lithospheric thinning in this region.The relatively long timescale(～100 Ma)suggests that thermomechanical erosion by convective mantle is the main mechanism of lithospheric thinning. Contrasting magmatic evolution trends in western and eastern North China craton suggest that lithospheric thining may have proceeded in diachronous manner.

Discovery of Gabbroic Xenoliths from Early Cretaceous Intrusions in Tongling,Anhui Province,China and Its Geological Significance

DU Yang-song1 2, LEE Hyun-koo3

2004, 10(3):  332-342. 

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Three gabbroic xenoliths have been found for the first time from Early Cretaceous intrusions of quartz monzonitic dioritic to pyroxene monzonitic dioritic composition in Tongling,Anhui Province,China.This paper presents new petrographic observations and microprobe analyses,as well as petrochemical and geochemical analyses on the xenoliths and their hosts,and provides new insight into their formation process and tectonic setting.Two types of gabbroic xenoliths have been identified in these intrusions based on their texture:one with "porphyritic"texture,and the other with gabbro texture.The gabbroic xenoliths are lower in ω(A1203)(13.12％～13.13％),but higher in ω(MgO)(11.28％～11.66％) and alkali co(K20+Na20 =5.50％ ～5.81％).They ale rich in Cr(169.9～186.9 tm／g),Co(19.2 tm／g)and Ni(299.4～356.7 ug／g),and have smaller LREE to HREE ratios(4.43～5.94) with enrichment in Y(22.92～23.56 tc／g).Their initial 87Sr/86Sr ratios range from 0.706 3 to 0.7069,with epsilon Nd(t)= -4.9～-8.8.These data indicate that the gabbroic xenoliths have characteristics consistent with those of alkaline basalt formed in continental rift,and support extension in the regional tectonic regime during their formation.The crystallization temperatures of the minerals in the xenoliths with gabbro texture and the"matrix"in the xenoliths with "porphyritic"texture were determined in the range of 1049℃ and 910～933℃,respectively,using the amphibole-plagioclase and Al-in-amphibole geothermometers.The pressures determined based on electron microprobe analyses of these phases and the"phenocryst"in the xenoliths with "porphyritic" texture indicate that they were formed at the depths of 26 km,8～10 km,and 13 km.These temperatures and depths represent the conditions of magmatic crystallization corresponding to a deep-level magma chamber and a shallow-level magma chamber,respectively.The depth of the deep-level magma chamber is correlated to the depth of the lower sima crust of the lithosphere,and the depth of the shallow-level magma chamber is at the depth between the Arehean Group- Lower Proterozoic Series of hypometamorphic rocks and the Middle-Upper Proterozoic Series of epimetamorphic rocks.Based on the facts mentioned above,it may be inferred that a continent- continent collision between the Yangtz and North China Cratons in the Triassic followed by a continental extension led to the transformation of the regional tectonic regime from early (T2-T3) compression to late(J3一K1)extension and fault depression,and resulted in a regional magma activity of alkaline basalts.The alkaline basaltic magma was derived from upper mantle,and underplated at the depth of 26km± at about 140Ma.After this,crystallization of the underplated alkaline basaltic magma attributed to the formation of the xenoliths with gabbro texture in the deep-level magma chamber at the depth of 26km±.The relevant Sr and Nd isotope results and petrological and mineralogical data are consistent with assimilation of the underplated alkaline basaltic magma with the lower sima crest in the formation of the derived magma with gabbroic composition in the deep-level magma chamber,and support formation of the magma with dioritic composition in the shallow-level magma chamber at the depth of 8～13 km by assimilation of the derived magma from the deep-level magma chamber with the metamorphic rocks.Crystallization fractionation of the dioritic magma in the shallow-level magma chamber Was responsible for formation of the"phenocrysts"in the xenoliths with "porphyritic" texture.and crystallization of the derived magma intruding from the deep-level magma chamber into the shallow-level magma chamber resulted in formation of the"ma trix"around the earlier "phenocrysts" in the xenoliths with "porphyritic"texture.

Geochemistry of the Xilingele Complex,Inner Mongolia: A Historic Record from Rodinia Accretion to Continental Collision after Closure of the Paleo-Asian Ocean

ZHU Yong-Feng1, SUN Shi-hua2, MAO Qian2, ZHAO Guang1

2004, 10(3):  343-355. 

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The metamorphic rocks in Xilingele complex mainly consist of biotite gneisses with plagioclase amphibolite lenses.The gneisses show medium fractionated LREE-enriched pattern with obvious negative Eu anomalies.Their incompatible trace element concentrations are similar to the average continental crust but with depletions of Ba and Sr.One Sm-Nd isochron for amphibolites yields an age of 1 202±64 Ma with εNd(t)value of+6.8.The Rb-Sr isochron for amphibolites yields an isochron age of 393±14 Ma with an initial 87Sr／86Sr ratio of 0.703 79.This Rb-Sr isochron age is consistent with the Ar-Ar age(～383 Ma)of the blueschists in this region,and is～40 Ma younger than the Rb-Sr isochron age of Hegenshan ophiolite.It probably recorded the metamorphism caused by the continental collision after the closure of the Paleo-Asian Ocean ,which finally led to the continental collision of the north China craton with the Siberian craton.The Rb-Sr isoehmn for the gneisses yields an age of 279±6.4 Ma with an initial 87Sr／S86Sr ratio of 0.708 51.which is consistent with the age of volcanic rocks(～277 Ma)most-widely distributed in this region.Such coincidence probably implies that the metamorphism recorded in the studied gneisses was caused by magmatic processes during Early Permian.The geochemistry of the Xilingele complex thus recorded not only the Rodinia accretion processes,but also the closure event of the Paleo-Asian Ocean (～430 Ma),continental collision(～390 Ma)and post-collisional magmatism(～280 Ma)by comparing the ophiolites and magmatic rocks in this region.

Electron-Microprobe Dating of Monazite and Metamorphic Age of Wutai Group,Wutai Mountains

LIU Shu.wen1, SHU Gui-ming1, PAN Yuan-ming2, DANG Qing-ning1

2004, 10(3):  356-363. 

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Electron-microprobe Th-U-Pb chemical age determination of monazite is a new in-situ geochronological method developed over the last few years.Its basic permises are that monazite contains a negligible amount of common lead and that the Th／U／Pb values are not affected by any processes excepting Th and U radioactive decay.Therefore,Th-U-total Pb chemical age of monazite Can be obtained by high-precision determination of mother and daughter elements and statistical analysis.Using the intemational standards of Th02,U metal,PbCrO4 and YAG as standards,we carried out systematic evaluation of experimental conditions and analyses for Th-U-total Pb chemical dating of monazite on a JEOL JXA-8 100 electron microprobe .Application of this electron-microprobe chemical dating of monazite from a metasedimentary rock of the Jingangkou formation,Wutai Group,Wutai Mountains yielded three distinct isochron ages:2 172±37 Ma(n=4),1 922±24 Ma (n=40), and 1 847±62 Ma(n=6).The 2 172 ± 37 Ma age.in agreement with SHRIMP U-Pb zircon ages for granitoid magnmtism in the Wutai group, appears to represent an early thermotectonic event.The 1 922±24 Ma age is within the analytical uncertainty of the metamorphic age of 1 911±38 Ma, detemfined by an internal Sm-Nd isochron of whole-rock and metamorphic minerals.Also, the 1 847 ±62 Ma age is similar to the 1 850 Ma SHRIMP metamorphic zircon ages in neighbouring Hen~han and Fuping complexes.These geologically significant results from the Wutai Group indicate that this electron-microprobe Th-U-total Pb chemical dating of monazite has obvious advantages over other geochronological methods.

Mineralogical Characteristics and Origin of Garnet-Bearing I-type Granitoids in Southeastern Fujian Province

YU Jin-hai, ZHAO Lei, ZH0U Xuan

2004, 10(3):  364-377. 

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I-type granites,aplites and pegmatites outcropping in Mesozoic metamorphic belt of the southeastern coast of Fujian Province contain commonly magmatic garnets and primary muscovites.The garnets are characterized by high Mn,Fe and low Mg,Ca,up to 40～50％ spessartite component.The btotites in the granites also have high MnO and A1203 contents-up to 0.84～1.25％ and 16.04～18.03％ respectively.Primary muscovites exhibit high Fe and low A1 and Na.T-P calculations indicate that these Al-rich minerals crystallized at 750～600％ and 0.3～0.2 GPa.Both petrographic features and the geochemical modeling also show that they are the late-stage crystallization phases.Earlier crystallization of felsic minerals than biotite and garnet is related with much lower crystallization pressure.Phase diagram analyses demonstrate that week peraluminity and high Mn／(Mg+Fe) ratio (>0.060)are two key factors for the formation of garnet in the granitoids.Granitic magma with Mn／(Mg+Fe)>0.06O may produce bt+grt or bt+ rt+ins,and that with Mn／(Mg+Fe)<0.055 only forms bt or bt+ins.Grt+ins assemblage is the ultimate products of strongly evolved magma.Garnet and primary muscovite from these I-type granites have similar composition to those from S-type granites, therefore they cannot be simply used for classifying granite types.

Characteristics of Zircons for Dating from Daping Mylonitized Alkaline Granite in Yunnan and Their Geologic Implications

ZHANG Yu-quan, XIA Bin, LIANG Hua-ying, LIU Hong-ying, LIN Qing-cha

2004, 10(3):  378-384. 

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The Daping mylonitized riebeckite-aegirine granite is located in the southern part of the Ailaoshan-Jinshajiang Cenozoic alkaline magmatic rock belt.The zircons for dating form this granite are of two types:the metamorphic zircons and the metamorphic composite zircons which have old cores and new shells.Their crystal morphology is irregular and／or rounded.Th e high-degree concentration and layering of zircons are observed in rock thin sections.The results of dating are as following:the old core U-Th-Pb age is 247 Ma by using ELA-ICP-MS and the new shell U-Pb age is 145 Ma by using SHRIMP in metamorphic composite zircons.At the same time,there was a regional metamorphic process before mylonitization.In the weakly mylonitized segments the rocks have prism-granular blastic texture and granoblastic texture.The rocks have clear layering,which suggests a sedimentary-metamorphic genesis of this granite.

Mechanism of Interaction between Palygorskite and Copper Ion in an Aqueous Suspended System

CHEN Tian-hu1, SHI Xiao-li1, PENG Shu-chuan1, HUANG Chuan-hui1, XU Hui-fang2

2004, 10(3):  385-392. 

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Investigating adsorption mechanism and ability of the heavy metal ions on minerals is important for correct understanding properties of mineral adsorption,application of environmental mineral materials,behavior of environmental chemistry of heavy metal ions.It is commonly accepted that palygorskite is an important environmental mineral materia1.On the basis of preparing pure palygorskite sample,experiments of copper ion adsorption on palygorskite were carried out under single effecting factor.Meanwhile,pH values of solution were tested and surface structure of palygorskite was investigated before and after adsorption experiments.The results indicate that mechanism of removing copper ion by palygorskite was mainly contributed to copper ion hydrolysis by palygorskite inducement and interaction between copper hydroxide(positive charge colloid)and palygorskite(negative charge colloid)although the removal efficients of copper ion is related to oscillating rate,adsorption time,initial pH value and amount of adsorbent.Strictly speaking,this mechanism is different from adsorption of mineral interface.Because palygorskite has nanometer crystals and is active in surface chemistry.its surface hydrolysis behaves alkaline in the aqueous suspended system of palygorskite-water.It leads the pH value of solution to be increased,at which the copper ion could be basically wholly hydrolysed.

Post-Collision Tectonism and Basin-Range Evolution in the Tianshan Belt

SHU Liang-shu1, GUO Zhao-jie2, ZHU Wen-bin1, LU Hua-fu1, WANG Bo1

2004, 10(3):  393-404. 

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The sub-E-W-striking Tianshan belt was built in the late stage of Paleozoic.evidenced by Permian foreland molasses of regional scale which indicate the uplifting of Tianshan belt and formation of foreland basin.During Triassic,this orogenic belt was peneplaned,and the basins parallel to orogenic belt were further developed.In the interval of Jurassic Paleogene,extensional tectonic activity withinplate split the peneplaned Tianshan region into a series of sub-E-W-striking extensional basins.Since Neogene,a collision between Indian and Eurasian plates took place in the southem side of Tianshan belt,causing a strong intra-continental deformation characterized by thrusting and folding. This event led to coupling of ranges and basins,yielding a mosaic basin-range landform of present time.The strong thrusting influenced the orogenic belt in the hinterland.The Mesozoic-Cenozoic brittle deformation superposed on the ductile deformed Paleozoic rocks,and the transpression structures and listric faults were strongly developed.The thrusting flakes moving toward basins are very common. The distinct kinematic features occur throughout different geological units.At the same time,ranges were strongly reuplifted,and the extensional basins were converted into compression basins. Some Mesozoic coal-bearing basins in the ranges were violently uplifted to 4 000 m high,and the altitude difference between basins and ranges was increased.The step-type thrust faults and related fault folds were developed commonly in the basins. Strong fold-thrust structures occurred in the connecting zone between basins and ranges, accompanied with local sub-E-W-striking strike slip faulting.In the Tianshan region.thrusting deformation is an important basin-range coupling mechanism.The folding and faulting of Mesozoic sedimentary rocks,active faulting,Jurassic coal layer self-ignition and formation of sintered rocks were resulted from Cenozoic tectonism.

Analysis on Features and Origins of the Mesozoic and Cenozoic Faults in Zhanhua Sag

Wu Zhi-ping, LI Wei, Zheng De-shun, Lü Hong-bo

2004, 10(3):  405-417. 

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Based on the quantative analysis of faults activity with faults activity velocity, the development episodes, combination characteristics and formation mechanisms of faults in Zhanhua Sag since the Indonesian movement were studied and discussed.The results show that the development of Zhanhua Sag in Mesozoic and Cenozoic was mainly controlled by the convergence of Siberia plate, Yangtze plate and North China plate in Eurasian tectonic system and the activity of Tanlu fault zone of circum-Pacific tectonic system.The development of NW-trending reverse faults in Late Triassic was the local extrusion adjustment result of convergence of North China plate and Yangtze plate.The reversion of NW-trending faults in late Jurassic and Cretaceous was the result of sinistral shear of Tanlu fault zone under the level stretching background caused by the ascending of mantle.which was the result of subduction of Pacific plate.In the interim of Yanshan-Himalayan stage,the transition from sinistral to dextrorotation of Tanlu fault zone resulted in the transition of faults from NW-trending to NE(NEE)-trending in Zhanhua Sag.

Current Study on Genesis and Formation Conditions of Stromatolites

WEN Zhi-feng, ZHONG Jian-hua, LI Yong, GUO Ze-qing, GAO Jian-bo, XU Xiao-lin

2004, 10(3):  418-428. 

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Stromatolites are organic-sedimentary structures,built mainly by microbes through trapping,binding of coarse-grained sediment and in-situ precipitation,and may potentially preserve direct evidence evolution of life on the Earth.During the 20 years hitherto,many new viewpoints on genesis and formation models of stramatolites have been proposed.In this paper,the recent progress in study on stromatolites genesis is generalized,including stromatolites types,constituents and internal structures of microbialmats,relationship between formation of stromatolites with microbial photosynthesis, sulfate reduction etc.,as well as their basic formation processes and conditions.Based on the comparison with modern stromatolites analogues,the necessary and particular requirements with respect to deposition,water bodies and biogenie conditions are also viewed briefly.

Sedimentary Facies and Their Evolution Characteristics in Jialingjiang Formation of Qianwei Area,Southwest Sichuan Basin

CAO Jian1, TAN Xiu-cheng2 3, CHEN Jing-shan2

2004, 10(3):  429-439. 

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Based on sophisticated observations on cores,thin sections and analysis on logging curves,combined with through study on sedimentary characteristics,such as lithologic types and associations,palaeobiologic fossils and textures,sedimentary structures,and considering regional sedimentary background,it is recognized that Jialingjiang Formation in Qianwei area is characterized by semi-restricted to restricted marine platform deposits.Five sedimentary subfacies could be subdivided:the mixing tidal flat subfacies, the peritidal bank subfacies.the semi-restricted subfacies,the restricted lagoon subfacies, and the evaporate tidal flat subfacies.With the above results,and through the study on facies correlation of three well sections and facies distribution of three key reservoir formations,it is pointed out that the sedimentary environment evolution of Jialingjiang Formation from the botteom upwards is from mixing deposit. Through subtidal deposit with low energy,to supratidal evaporate deposit.This history formed a complete developing cycle from marine transgression to regression.It is quite possible that the peritidal bank subfacies with grain rock type and evaporate tidal flat subfacies with dolomite reek type could be favorable reservoir layers.

The Estimation of the Erosion Thickness of Es4 and Ek in Jiyang Depression,Bohai Bay Basin

HAN Yong-bing, WANG Liang-shu, LIU Shao-wen

2004, 10(3):  440-450. 

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Recovering the erosion thickness of the formation is one of the foundations for basin quantitative analysis.Here we estimated the erosion thickness of the Es4(the fourth member of the Shahejie Formation)and Ek(Kongdian Formation)strata in the Jiyang Depression by means of computer modeling,based on the improved sonic time difference principles,and combined with the optimizing porosity algorithm.The stratigraphic contrast method on seismic profiles is combined to estimate the erosion thickness for the places where the sedimentation regularities of removed formation are destroyed heavily.This traditional method is also improved in this paper.The final erosion thickness of formation is obtained by the weighted average of variously calculated results abtained by using multi-perspective stratigraphic contrast method,so that the calculation errors could be significantly reduced.Our results show that the erosion exists pervasively in the Es4 and Ek strata of the oilfield with a relatively smaller intensity,and the relatively larger erosion is found in the fringe of the sag.The erosion amount of the Es4 ranges of 50～300 meter,with the average of 150 meter;The largest one exists in the edge of western sag of the Luxi Uplift reaching a value of approximately 1000 meter, but localized in a relatively small area.The erosion amount of Ek is relatively larger than that of the Es4,usually varying from 150 to 400 meter,with the average of 250 meter.The largest one is found in the northeast rim of the Huiming sag,with the value of 800 meter.

History of the Earth:Core-Mantle Mill Theory

ZHANG Yi-kun

2004, 10(3):  451-462. 

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In this paper,the author advocates a new dynamical theory of the Earth,attempting to unify plate tectonics and plume theories.Although the new dynamical theory may be judged as based on two unusual hypotheses to be verified by further observations,it is still possible that a consistent model of how the planet works may have been unveiled.The new theory admits the Earth's inner core to be a ferromagnet.The ferromagnetism of inner core is supported by observed anisotropic property of inner core in transmitting seismic waves.Since the torque caused by the magnetic interaction between the Earth and Jovian planets only acts on the iron cole,the core behaves as a rotating engine,tending to change both the rate and axis of Earth's rotation,while the mantle is the resistant to any change of Earth's rotation due to its inertia.The interplay between the two leads to the formations of fluid outer core,basalt magmas,oceanic crust,and differential rotation between the inner core and mantle.Rock materials at the core, mantle boundary are ground into basalt magmas due to the differential rotation between the inner core and mantle.Mid-ocean ridge systems are interpreted as the huge dike systems rooted in some principal magma chambers in the core-mantle boundary layer.The new theory assumes that the driving force of global tectonic movement comes from the external space.Tectonic movements in both continental crust and oceanic crust are the phenomena of surface difusion,which are influenced by the Earth's background radiation and by the matter distribution in the Earth's crust.The anisotropy of background radiation in the polar directions determines the geometric pattems of mid-ocean ridge systems on the Earth's surface and global tectonic movement of the Earth's crust. The Earth currently sufers stronger radiation on to the South Pole than on to the North Pole.The blowing force caused by the anisotropic radiation in the polar directions drives the continents drifting toward the North Pole.The current anisotropy of background radiation in the polar directions moreover results in the pear-shaped Earth with the tensile deformation of Earth developed in the southern hemisphere and the compressive deformation of Earth developed in the northern hemisphere.The asymmetrical Earth deformation produces the present geometric patterns of mid-ocean ridge systems (as the dikes always take the orientation perpendicular to the minimum compressive stress)and determines the modes of sea-floor spreading.History of the Earth is featured by three stages:that without the oceanic crust(before 2.7 Ga),creation of the oceanic crust(2.7～2.25 Ga)and growth of the continental crust(after 2.25 Ga).

A Feasibility Study on CO2 Injection for Enhancing the Coalbed Methane Recovery

Wu Jian-guang1 2, YE Jian-ping2, TANG Shu-hen3

2004, 10(3):  463-467. 

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The adsorption-desorption behavior of carbon dioxide and methane gases in coal samples were experimentally studied.The replacement experiments of methane by carbon dioxide for simulating the proeess of "CH4 production-C02-injection-CH4 production"were also made in order to enhance the coalbed methane recovery.The C02 and CH4 composition.variation and phase separation curves were obtained.The results show that with the proceeding time of experiments,the competition rate of adsorption for C02 decrease, while that for CH4 increases.However,the reverse results were obtained for competition rate of desorption for these gas phases.It indicates that the adsorption of CO2 is prior to that of CH4. If the amount of injected C02 and／or the C02 concentration is higher,the rate of CH4 desorption and C02 adsorption would be higher.The results of our experiments are significant to commercial production of coalbed methane.

A Discussion on Characteristics and Genesis of Salt Deposit in Pukou Formation of Late Cretaceous ,Huaiyin Depression

ZHAO Yan-yan1, LIN Ghun-ming1, WGNG Ya-jun2, MU Rong2, ZHANG Hao-dong2

2004, 10(3):  468-476. 

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The PuKou Formation in Huaiyin depression is composed of cyclothemes of salt rocks,mudstones and shales,which formed saline-lake sedimentary assemblage of more than 1000 m thick.During the aggradation of PuKou formation。the Huaiyin area was a wide lake which consisted of alluvial fans,littoral facies, shallow-lake facies and semi-deep-water facies.The saline sediments were formed in the semi-deep-water saline lake.In this paper,based on the geologic,seismic,geochemical,and palaeobiogical data, the sedime ntation environment of PuKou Formation and the genesis of saline sediments a discussed. Nowadays, there a three viewpoints on the formation of saline substances: (1)the saline substances from the marine transgression, in association with arid or semi-arid climate,and precipitated as saline deposits.(2)in the high-mountain-deep-basin environments, the saline substances from the weathering and leaching rocks such as carbonates, gypsolytes or other salinastones.(3)the saline substances derived mainly from the deep sources which were evidently related with faults or volcanism of the tectonic zone.In this paper, the author agrees with the third point.The reason are as follows:①the sedimentary characteristics:the saline deposits mainly belong to sodium-sulfate-chloride type.The sediments are cyclothems of saline rocks,mudstones and shales. ②the depositional conditions:many faults developed in Huaiyin depression during the formation of the saline deposits.③the asymmetry of salinity.④the palaeontological characteristics.All above- mentioned proofs show that the salt in deep strata was the major source and the deep fractures were the oaths through which the salt substances entered into the depression.