Table of Content

20 June 2003, Volume 9 Issue 2

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Article

Mafic-Ultramafic Rocks at Shacun and Jiaoziyan in North Dabie

ZHAO Zi-fu, ZHENG Yong-fei, WEI Chun-sheng, WU Yuan-bao

2003, 9(2):  139-162. 

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Zircon U-Pb dating， major and trace elements of whole-rocks，oxygen isotope compositions of mineral separates，and carbon concentrations and isotope compositions of apatite and whole-rocks were determined for Mesozoic mafic-ultramafic intrusions at Shacun and Jiaoziyan in the Dabie Mountains．The results show that these mafic-ultramafic rocks are characterized by strong LI E enrichment，negative HFSE anomalies(Nb，Zr and Ti)，and positive anomalies of Pb and Ba．Zircon U-Pb dating yields the Early Cretaceous(122 to 128Ma)magma crystallization ages and also the younger post-magmatic hydrothertmal overgrowth ages (105 to 116 Ma)．There is a large variation in oxygen isotope ratios of minerals and their host rocks(whole rock：1．1‰ ～6．6 ‰ ，clinopyroxenite：3．85 ‰ ～ 5．7 ‰ ，plagioc lase ：2．8 ‰ ～ 7．3 ‰ ，zircon：3．85 ‰ ～6．04 ‰ ． Most zircons have O values different from normal mantle zircon． Equilibrium fractionations of oxygen isotopes among minerals have been preserved for some samples ，but for the others obvious disequilibriaum of oxygen isotope s is detected ，indicating alteration by postmagmatic subsolidus water-rock interactions．Carbon concentrations and isotope compositions vary widely from 0．03 ％ to 0．18 ％ and from -27．0 ‰ to -5．8 ‰ ．respectively．Comparison of element and isotope data for Mesozoic mafic-ultramafic rocks with eclogites from the Dabie Mountains shows that they share many common geochemical features ，and thus there should be genetic links between them ． Protholiths of these ecologites are considered mafic rocks，corresponding to rift magmatism in the northern margin of the Yangtze plate related to Neoproterozoic rifting tectonics．Partial melting of old lithosphere mantle and overlying crust is considered to produce these early Cretaceous mafic-ultramafic rocks．

U-Pb Ages and Oxygen Isotope Compositions of Zircons from Post-Collisional Volcanic Rocks of Dabieshan

XIA Qun-ke1, ZHENG Yong-fei1, Deloule Etienne2

2003, 9(2):  163-171. 

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The internal texture of zircons from post-collisional basalt and andesite in Dabieshan have been investigated by cathodoluminescence(CL) imaging，and their U-Pb ages and oxygen isotope compositions have been determined by SIMS(Cameca 1270)．A1l zircons from the basalt give U-Pb ages of 130±2 Ma(1σ) and low δ18O values of(4．1±0．2)‰ ．Magmatic zircons from the andesite yield ages of 133±3 Ma(1σ)and 8180 values of(5．1±0．1)‰ ，and inherited zircons from the andesite show ages in two groups of 768～ 805 Ma and 1 827～ 1 873 Ma,but the Same δ18O values of(6．9±0．1)‰ ．It appears that the post-collisional volcanic rocks in Dabieshan were all crystallized at 130 M a．The chemical compositions ，trace element pattern, Sr-Nd isotopic ratios and zircon ages of post-collisional volcanic rocks from Dabieshan are similar to the intrusive rocks，so that these rocks may possibly share the same source and petrogenesis．Moreover，the same ages of both basalt and andesite imply their possible petrogenetic connections ．Some zircons from the andesite display retrograde zoning，which are considered to be the relict zircons from the protolith．Their inherited ages correspond to characteristic age signatures from the Yangtze Block and the North China Bloc k, respectively．The lowδ18O zircons from the basalt suggest that the source of basalt magma might contain recycled component like low δ18O protolith of the Dabieshan eclogites ．Therefore，the suture of the Yangtze Bloc k an d the North China Block at depth is probably located in the Beihuaiyang region

The Relation between Rb-Sr，Ar-Ar Geochronometers and Oxygen Isotopic Equilibrium of Intrusions from Eastern Anhui Province，China

CHEN Jiang-feng1, XIE Zhi1, ZHENG Yong-fei1, GONG Bing1, CHEN Wen2, ZHOU Tai-xi1, Zhang Xun1

2003, 9(2):  172-184. 

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In order to relate the thermodynamic equilibrium of oxygen isotopes of the minerals and the validity of the Rb-Sr mineral isochron age for granitoids，oxygen，and Rb-Sr isotopic ratios of mineral and whole rock samples，as well as Ar-Ar ages of hornblendes and biotites were determined for two quartz monzonites from eastern Anhui province．The Tuncang and Hengshan bodies gave quartz (Q)-homblende (Hb1) oxygen isotopic temperature of 545±25℃ and 530±25℃ ，Q-biotite(Bt)temperature of 460±20℃ and 390±15℃ and Q-plagioclase(P1)temperature of 385±40℃ and 285±35℃ ．The relation of 0 isotopic temperatures suggested a retrograde equilibrium among minerals during cooling of the granitoids． Meanwhile，geologically meaningful Rb-Sr isochron ages were obtained ．The Tunchavg intrusion gave whole rock (w．r．)-Hbl-Pl Rb-Sr isochron age of 128．4±4．7 Ma．identical to the Hbl Ar-Ar plateau age of 125.51±0.55 Ma，and w．r．-P1-Hbl-Bt age of 120.3±2.6 M a，identical to the Bt At-At plateau age of 118.0±0.1 M a within uncertainty．For the Hengshan intrusion。the w．r．-Hbl-Pl Rb-Sr isoehron age of 108±15 M a is significantly younger than the Hbl Ar-Ar plateau age of 125.7±1.8 Ma, and the w ．r．-Hbl-Pl-Bt age of 118.6±1.2 Ma younger than the Bt Ar-Ar plateau age of 120.0±0.2 Ma．The young Rb-Sr isoehron ages with large uncertainties are due to alteration of the feldspar and small variation in Rb/Sr ratios in the rock．Therefore．we conclude that the equilibrium state of the oxygen isotope systems is a prerequisite for the geologically meaningful Rb-Sr isochron ages of the granitoids ．However，detailed mineralogical investigation is needed for obtaining a good isoehron．The cooling rate of about 10～20℃ ／Ma obtained by cooling curve built using oxygen isotope temperatures is 10～15℃ ／Ma lower than that of 20～35℃ ／Ma estimated by blocking temperatures，the reason for it merits further investigation

Zircon U-Pb Dating on Mesozoic Granitoids at Wulian，Shangdong Province

ZHOU Jian-bo1 2, ZHENG Yong-fei2, ZHAO Zi-fu2

2003, 9(2):  185-194. 

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Zircon U-Pb dating was carried out for four granitoid plutons at Wulian in the north-western part of the Sulu orogenic belt，whose intrusion ages were not known for a long time and thus were often confused with adjacent granitoids of Neoproterozoic age． The present dating yields concordant ages of 123±4 Ma for amphibole monzonite at Dadian, 126±3 Ma for pyroxene monzonite at Qibaoshan，116±4 Ma for miraolitic granite at Wulianshan．and 115±1 Ma for monzonitic granite at Maershan．The results show the occurrence of Early Cretaceous intru sions at～ 115 Ma and ～ 125 Ma in the Sulu orogenic belt，being consistent with those coeval magmatic activity in the Dabie orogenic belt an d the northeastern part of the Sulu orogenic belt．Although these Yanshanian granitoids occur in the Triassic collisional orogen between the Yangtze and North China plates，they belong to post-collisional magmatism and were produced by partial melting of the subducted continental crust．

Pb Isotopic Characteristics of Late Mesozoic Marfic Rocks from the Lower Yangtze Region：Evidence for Enriched Mantle

YAN Jun, CHEN Jiang-feng, YU Gang, QIAN Hui, ZHOU Tai-xi

2003, 9(2):  195-206. 

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Mafic rocks from the eastern Lower Yangtze region， including Luzong ， Huaining ，Fanchang，Tongling and Ningwu areas，belong to alkaline series and are characterised by high U and Th concentrations(averaging 2.90 and 10.01 x 10-6)and with average Th／Pb and U／Pb ratios of 0.635 and 0.184，respectively．The least contaminated samples show initial Pb isotopic ratios of 206Pb/204 Pb= 17. 65～ 18.60，207Pb／204Pb= 15.42～ 15.50 and 208pb／204Pb=37.67～38.04．The initial basaltic magma came from the enriched lithospheric mantle．which is dominated by EM II component，and subordinated by EM I component．Since the Pb isotopic ratios of the studied rocks are lower than those of basalts from southwestern Dabie and western part of the Lower Yangtze region，but the U／Pb and Th/Pb ratios of the studied mafic rocks are higher than those of the latter region，it is inferred that the Mesozoic lithoshperic mantle beneath the eastern Lower Yangtze region suffered metasomatism by fluid from subducted slab．EM I-type enriched mantle is commonly observed in the North China block。and EM II-type isotope signature appears to dominate the South China bloc k in the late Mesozoic Era．This was closely related to deep subduction of Yangtze block in the Triassic time．Although the Cenozoic basalts from eastern China show depleted characteristics because of large scale lithospheric thinning ，the residue of Mesozoic lithospheric mantle is still kept in the Cenozoic mantle，shown by their Pb isotope signature．

Emei Mantle Plume-Subcontinental Lithosphere Interaction：Sr-Nd and 0 Isotopic Evidences from Low-Ti and High-Ti Basalts

XIAO Lon1 2, XU Ying1, HE Bin1

2003, 9(2):  207-217. 

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The Emeishan flood basalts have high 87Sr／86Sr ratios and low εNd(t)values，suggesting that they were generated from a enriched mantle source．The diversity of Sr and Nd isotopes between early stage low—Ti(LT)and late stage high—Ti(Hr)basalts implies that they were generated from distinct mantle source and experienced different crustal contamination or assimilation．The earliest formed LTi basalts have highest 87Sr／86Sr ratios (0.7063～0.7078) and lowestεNd (t) values(-6．74～ -0．34)，while late stage HT basalts have lowest 87Sr／86Sr ratios(0.7049～0.7064)and highestεNd (t)values(-0.71～1.5)．Along with oxygen isotopes of clinopyrxene from the LT basalts ranging from 6.2 ‰ to 7.86 ‰ , higher than oceanic island basalts(5.4‰ )，this study suggests that The Emeishan flood basalts well recorded the interaction processes in both temporal an d spatial aspects．The early stage form ed low-Ti basalts mainly distributed in the western division of Emeishan large igneous province contain many crustal material signatures．The metasomatized subcontinental lithospheric mantle might be the major source for its generation．Late stage form ed high-Ti basalts occurring mainly in the middle and eastern divisions show some plume signatures and little crustal contamination or assimilation．These factors suggest that the interaction between plume head and the enriched subcontinental lithospheric mantle played an important role in the formation of the low-Ti basalts．However，it was less important for the generation of high-Ti basalts at later stage．

O-Nd-Pb Isotopic Systems in Eclogite Minerals at Jinheqiao in Dabieshan and Constraints on Their Relative Diffusivity

LI Qiu-li, LI Shu-guang, ZHENG Yong-fei, GONG Bing, HONG Ji-an

2003, 9(2):  218-226. 

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Sm—Nd isochron dating and O isotope an alysis were carried out for minerals from eclogite at Jinheqiao in Dabieshan．Garnet+omphacite Sm-Nd line gives an age of 210±3 Ma．and garnet+ rutile， 237 ± 4 Ma． Amphibole occurs as corona around omphacite， indicating significant retrograde reaction during exhumation． Correspondingly， O and Sm-Nd isotopic disequilibria were observed between omphacite and garnet，resulting in an unreasonably low Sm-Nd isochorn age of 210±3 M a．Mineral-pair O isotope thermometers yielded a temperature of 695±35℃ for a quartz-garnet pair and 460±15℃ for a quartz-rutile pair．Sm-Nd isochron defined by garnet + futile with an age of 237±4 M a records the eclogite-facies prograde metamorphic time，which is considerably higher than rutile U—Pb age of 218.2 ± 1.2 Ma from the same sample．A1l these data suggest that the rate of 0 diffusion in garnet is slower than，or close to that of Nd diffusion in garnet，wheress the rates of 0 and Pb diffusion in rutile are faster than those of Nd diffusion in rutile．0 isotope an alysis on different grains of rutile gave consistent results within an alytical uncertainty；the O isotope temperature defined by the quartz-rutile pair is in agrement with a closure temperature of 470±50℃ for Pb diffusion in futile as estimated from the futile U—Pb isochron dating ． These indicate that O an d Pb isotopic homogenization was achieved among different grains of rutile in the scale of han d specimen during the eclogite-facies metamorphism ，and that the rates of 0 an d Pb diffusion in rutile are similar to each other during eclogite cooling ．

Effects of Retrograde-Zoning of Garnet in Eclogite on Nd and O Isotopic Equilibrium between High-Pressure Minerals

LI Shu-guang1, LlU Yi-can1 2, XU Shu-tong2, ZHENG Yong-fei1, GONG Bin1

2003, 9(2):  227-236. 

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Compositional zoning of garnet was observed in a strongly deformed eclogite associated with a foliated peridotite at Raobazhai in North Dabie． CaO concentration of garnet decreases from core to rim ，whereas its MnO concentration increases，suggesting a retrograde origin of such Ca-Mn zoning and a fast rate of Ca and Mn diffusion in garnet．The tie line of garnet + omphacite from this eclogite gave a Sm-Nd age of 187±5 Ma，which is significantly less than Sm-Nd isoehron ages of 221±5 Ma to 228±3 Ma and 210±6 Ma to 214±6 Ma for ultrahigh-pressure eclogites in South Dabie and North Dabie，respectively．This younger Sm-Nd age is interpreted to be resulted from a decrease in 143Nd/144Nd ratio of the retrograde rim in garnet．Oxygen isotope an alysis of omphacite and garnet shows less fractionation values than equilibrium fractionation values between them at temperature of 500 to 900℃ ．suggesting a oxygen isotope disequilibrium． This study demonstrates that the retrograde zoning of garnet in eclogite could result in significant disequilibrium of Nd and O isotopes between omphacite and garnet．

Evolution 0f Eclogite at Tiquishan，Northern Jiangsu Province：Isotopic Evidence

WANG Yin-xi1 2, LI Hui-ming1 2, GU Lian-xing2, CHEN Dao-gong3, YANG Jie-dong1 2， SHEN Ya-qian1 2, ZHAO Lin-xi4, LI Jian-hua5

2003, 9(2):  237-243. 

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Sm-Nd isotope ages of 221.6±8.4 Ma，213.6±9.2 Ma and 216.6±8.1 Ma，respectively，have been obtained for three eclogite bodies in the Tiqiushan region，northern Jiangsu Province．One of the Tiqiushan eclogite bodies is dated by a Rb-Sr isochron at 201±21 Ma．The Sm-Nd age could be interpreted to record recrystallization of the Tiqiushan eclogite body at high pressure eclogite facies during exhumation of the subducted plate，whereas the Rb-Sr age may correspond to initial amphibolite-facies retrograde metamorphism of the same eclogite body．Collision between the Sino-Korean and Yangtze plates occurred around the late Triassic time．

Strontium Isotope Geochemistry of Fluorites from Qinglong Antimony Deposit in Guizhou Province

PENG Jian-tang, HU Rui-zhong, JIANG Guo-hao

2003, 9(2):  244-251. 

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The Qinglong antimony deposit in southwestern Guizhou is an important Sb-producer in South China．Despite previous detailed investigations，no agreement has been reached on the source of ore-forming materials．Sr isotope ratios of fluorites from the Qinglong antimony deposit are in the range of 0.70776 to 0.70932．These are significantly higher than Sr isotope ratios for host sedimentary an d igneous rocks of 0.70672 to 0.70821 for the Permian Maokou limestone and of 0.70441～0.70638 for the Emeishan basalt, respectively．It appears that the ore-forming fluid is relatively enriched in radiogenic 87Sr, suggesting an exterior origin(probably deeper sedimentaly or basement rocks)rather than the country rocks, and an open system of Sb-F mineralization．Because the Sr isotope ratios of the ore-forming fluid ale significaly higher than those of the Emeishan basalt，it is not appropriate to ascribe the Sb-F mineralization in Qinglong deposit to magmatic-hydrothermal process associated with the basaltic eruption．The Sr isotope ratios of the fluorites are also higher than those of the Permian limestone an d coeval seawater，so it is impossible that the ore-forming fluid could be derived only from the Permian seawater．Consequently a genetic model of submarine volcanic sedex is also not suitable for this antimony deposit．This conclusion coincides with our previous result deduced from REE geochemistry ． Existing hydrogen and oxygen isotope studies of ore-forming fluid indicate an origin of highly evolved meteroric water (by reaction with host rocks) rather than seawater．Considering that the ore-forming fluid and the metallogenic materials such as F an d Sb were not simply derived from the host rocks，the Sb-F mi neralization at Qinglong district was not resulted from in-situ remohilization as expected ．

Geochemical Kinetics of Oxygen Isotope Exchange During Fluid-Rock Interactions：A Review

NI Huai-wei, ZHENG Yong-Fei, ZHA0 Zi-Fu

2003, 9(2):  252-267. 

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Oxygen isotope studies play an important role in tracing the time-integrated fluxes (or fluid／rock ratio)，flow directions and sources of fluid during fluid-rock interactions．Based on the principle of mass balance，oxygen isotope exchange models ale built for“closed”systems and open systems The ”closed” systems ale classified into closed， batch volatilization and Rayleigh volatilization systems ．Rayleigh volatilization results in more 18O depletion of rock than batch volatilization，but there is no significant difference between them in geological practice．Mechanisms of oxygen isotope transport in continuum mechanic models of open systems include diffusion／dispersion and advection．Peclet number，defined by the rates of fluid flow to diffusion/dispersion， determines relative contribution of the above two mechanisms to oxygen isotope transport on some scales ．Fluid-rock exchange is controlled by surface kinetics．When exchange rate is faster than fluid flow，equilibrium in oxygen isotope fractionation between fluid and rock is achieved，otherwise the equilibrium will not be attained ．Damkohler number，defined by the rates of fluid flow to fluid-rock exchange，determines the extent of reaction towards equilibrium ．If more than one mineral is considered 88 a monitoring phase，the inner-mineral fractionations may distinguish these two models． This article reviews geochemical kinetics of oxygen isotope exchange during fluid-rock interactions，whose principles an d models can also be extended to studies on other elements．

Tapiolite from the Koktokay No.3 Rare Metal Granitic Pegmatite Dyke，Altai，Xinjiang Autonomous Region

ZHANG Ai-cheng, WANG Ru-cheng, HU Huan

2003, 9(2):  268-272. 

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Tapiolite is a rather rare Ta mineral occurring particularly in highly differentiated granitic pegmatites． The occurence of tapiolite from the Koktokay No.3 granitic pegnmtite dyke，Altai，Xinjiang Autonomous Region，is reported in this paper．The tapiolite，as anhedral crystals，is associated with manganotantalite(including manganotantalite I and manganotantalite II)and uranmierolite，forming Nb-Ta mineral aggregate．The manganotantalite I is the main component of the aggregate，whereas the tapiolite associated with the manganotantalite II occurs typically in the rim of the aggregate．RTa[RTa=Ta/(Nb+Ta)]of tapiolite varies between 0.96 and 0.99，while RMn[RMn=Mn/Fe+Mn]]ranges between 0.10 and 0.21．Based on assemblage and compositional feature of Nb-Ta minerals．it is suggested that tapiolite was a product of exsolution from the metastable phase which was the remnant of manganotantalite I crystallization under disequilibrium condition．

Application of XAFS and Mossbauer Spectroscopy in Studying the Mode of Occurrence of Arsenic and Iron in High-As Coals from Southwest Guizhou Province

DING Zhen-hua1 2, ZHENG Bao-shan1, R B Finkelmam3, H E Belkin3, HU Tian-dou4, LIU Tao4

2003, 9(2):  273-278. 

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Some small coal mines in Southwest Guizhou Province have high arsenic content，sometimes up to 3.5％ ．The application of high As-bearing coals has ca used about 3，000 people in arsenic poisoning in several villages．Coal samples from endemic arsenosis areas have been analyzed with instrument neutron activation analysis(INAA)，X-ray absorption fine structure(XAFS)，and Mossbauer spectroscopy．The modes of occurrence of arsenic and iron in high As-coals are discussed．Arsenic has different modes of occurrence in different samples ． XAFS show that arsenic mainly exists in the form of As5+．The arsenic XANES spectra．with a main peak and a shou1der，indicate the presence of at least two different arsenic forms in each sample，with the possible exception of sample J1-As6-97A．The radial structure functions (RSFs)show one major peak at about 0.125 nm，corresponding to the As -O distance in the AsO43- anion unit，and a small peak at around 0.27 nm，corresponding to As2O3．For sample J1-As6-97A，the RSF peak at 0.125 nm is more intense ，and arsenate is the dominant species of arsenic．Except for sample J1-As6-97A，the Mossbauer spectra show that 60％～91％ of iron is in the form of pyrite．For sample J1-As6-97A all iron is present as paramagnetic or superparamagnetic goethite(α-FeOOH )．The results demonstrate that arsenic exists mainly in the form of high valence，while the As203 ，arsenic pyrite and other sulfides comprise only a small fraction．Iron exists mainly in the form of pyrite(60％～91％)and jarosite (9％～40％)with one exception where all iron is present as paramagnetic or superparamegnetic goethite(α—FeOOH)．The difference between XAFs results and Mossbauer spectra indicates that arsenic and iron initially existed in different forms．It should be emphasized that in interpreting the results of XAFs spectroscopy other analytical results should also be considered．

Geochemistry，Series Subdivision and Petrogenetic Interpretati0n of Cenozoic Volcanic Rocks in Northern Tibet

LIU Shen1 2, HU Rui-zhong1, CHI Xiao-guo3, LI Cai3, FENG Cai-xia1 2

2003, 9(2):  279-292. 

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Based on the ages determined by K-Ar and Ar-Ar dating methods，the Cenozoic volcanic rocks in the studied region，from early to late，can be subdivided into three series．They are high-K calc-alkaline series (40～30Ma)，leucite basanite-phonolite series (29～ 24Ma) and shoshonite series (1.5Ma)，respectively．The Cenozoic volcanic rocks in northern Tibet，mainly studied by petrochemical and isotope methods，have the characteristics of both WPAB (within plate alkali basalt)and IAB(Inland-arc basalt)．For these three series of rocks，the difference exists not only in their geneses ．but also in their sources ．We interprete that high-K calc-alkaline series was generated by partial melting of crust due to underplating of the basaltic magma from enriched mantle，and underwent the process of crust’s AFC． However， the leucite basanitephonolite series and shoshonite series were evolved from an old enriched mantle related to ancient subduction，and their geneses are attributed to the fractional crystallization in different degrees．From this study，it is clear that the depth of the sources for the Cenozoic volcanic rocks in this area gradually be comes deeper and newer from south to north．

Fluid Inclusion Study Related to Cabonatitic Magmatic Process

ZHOU din, NI Pei, DING dun-ying, ZHU Xiao-ting

2003, 9(2):  293-301. 

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Carbonatite is a light grey or offwhite igneous rock rich in carbonate minerals(calcite，dolomite，ankerite etc．，above 50％)．It is often associated with ultramafic and alkaline Intrusives, being located in the centers of the ring intrusions； or is associated with alkaline extrusives as ring complexes． During its intrusions or extrusions ， there often happens fenitization，a type of alkali-rich (Na or K)wall rock alteration between carbonatite and wall rocks． By studying the fluid inclusions in carbonatites ，we can obtain much rock-forming and ore-forming information， such as temperature，pressure， fluid density， fluid compositions and fluidevolution etc． Fluid inclusions study is an effective means to acquire information related tocharacteristics of volatiles in Carbonatites ，immiscibility features ，viscosity，density an d origin ofcarbonatite magmas etc． Results of fluid inclusion studies indicate that：(1)Carbonatite can he formed at magmatic to hydrothermal conditions． (2)CO2 is the most abundant component of volatiles．At the later stage of carbonatitic magma evolution，CH4 may appear as one of the major components of volatiles．(3)Immiscibility between carbonatite melt and silicate melt has been identified by fluid inclusion study which implies existence of independent carbonatitic magma．(4)Carbonatitic magma has low viscosity and density，which enables its easy propagation at shallow crustal levels through fissures and veins． Fluid inclusion study plays an important role in the study of carbo natite petrology and metallog enesis．It can provide unique data to help US to get better understanding of carbonatitic magmatic process and related mineralization．

Gray Classification of Preferred Faults Based on Experience

XU Bao-tian, YAN Chang-hong, WANG Xin-jian

2003, 9(2):  302-306. 

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Based on experience，the preferred faults controlling the regional stability of large engineering can be classified by using the gray correlation degree an analysis method．According to the recognition rule of the biggest correlation degree this method determines the grade of preferred faults by referring to the preferred indices which includes time index(RT)，dimension index(RL)，distance index(RD)，activity period index and activity history index(RR)and comprehensive index(RZ)． The old evaluation methods are more complicated and the boundaries between two preferred indices are not dear．The present analysis method overcomes the above-mentioned shortcoming and can be used in the evaluation of preferred faults and expert system of preferred plane．