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1.
The total rare-earth element values(ΣREE)of loess in the Xinjiang region vary over a range of 128-200 ppm ,with an average of 153ppm .The average REE content of loess lies between the earth‘s crust (155ppm) and sedimentary rocks(151ppm).The Xinjiang loess,with the REE distribu-tion patterns characterized by negative slopes ,is rich in the Ce-family elements, and has a distribu-tion pattern characteristic of sedimentary rocks.The North Xinjiang loess is relatively depleted in Tb,but rich in Yb and Lu.The South Xinjiang loess is relatively rich in light rare-earth elements.This is full proof that the Xinjiang loess comes partly from weathered materials(clay rock,sandstone)in the region studied.The REE distribution patterns in the Xinjiang loess are similar to those in the precipitated dust and Aeolian sand,indicating the same material source.The REE distribution pat-terns in the Xinjiang loess are also similar to those in loess from the middle Yellow River Valley,China and Taskent,the former USSR.This implies that loesses of the three locations(Xinjiang,the mid-dle Yellow River Valley and Taskent) come from a common material source.But the REE patterns in the Xinjiang loess are different from those in wall rocks (volcanic rock,K-bearing volcanic rock).Generally ,LREE/HREE,Eu/Eu* and Ce/Ce* ratios reflect the features of parent materials of loess,indicating that the parent rocks were probably in the early stage of alkaline weathering and the weathered materials existed in an oxidation environment with basic mediums under arid-climatic conditions before transport.As a result,the migration ability of the REE is weak.  相似文献   

2.
陕西洛川黄土剖面中的稀土元素   总被引：4，自引：0，他引：4  
The ∑REE in Ioesses of different ages in the Luochuan section shows a narrow range of variation, indicating the homogeneity of materials in chemical composition. The REE in loess are concentrated mainly in silt.sized detrital minerals. Loesses of different ages and paleosols all are relatively enriched in rare-earth elements of the Ce family, and show similar REE distribution patterns. The fractinnatlon among various REEs in the loess is different from that in morainic, marine and lacustrine sediments,but is similar to that in sand samples from deserts in Northwest China. The ratios of Ce/Ce^* and Eu/Eu^* reflect that the provenance of loessic materials and their accumulating area are all in an oxidation environment with weakly basic mediums under arid or sub-arid climate.  相似文献   

3.
Nineteen volcanic and magmatic rock samples were collectecd from the Jinding leadzinc deposit and its surrounding areas in Yunnan.The ICP and AES analyses,feferred to the previous results,show that the metal minerals and altered rocks in the Jinding lead-zinc deposit display a decreasing trend of ∑REE from the early to late stages of mineralization,and similarities in REE distribution patterns,indicating that the ore fluids are characterized by high LREE enrichment,markedly negative δCe anomaly and slight δEu anomaly.These REE distribution paterns exhibit striking similarities to those of the Pliocene trachyte in the study area,both of which are similar in ∑REE,LREE/HREE ratio,δEu and δCe.The ore fluids besides the basin fluids in the deposit are also closely related to those associated with Pliocene trachyte magmas.  相似文献   

4.
Four types of apatite have been identified in the Ningwu region.The first type of apatite is widely distributed in the middle dark colored zones(i.e.iron ores) of individual deposits.The assemblage includes magnetite,apatite and actinolite(or diopside).The second type occurs within magnetite-apatite veins in the iron ores.The third type is seen in magnetite-apatite veins and (or) nodules in host rocks(i.e.gabbro-diorite porphyry or gabbro-diorite or pyroxene diorite).The fourth type occurs within apatite-pyrite-quartz veins filling fractures in the Xiangshan Group.Rare earth elements (REE) geochemistry of apatite of the four occurrences in porphyry iron deposits is presented.The REE distribution patterns of apatite are generally similar to those of apatites in the Kiruna-type iron ores,nelsonites.They are enriched in light REE,with pronounced negative Eu anomalies.The similarity of REE distribution patterns in apatites from various deposits in different locations in the world indicates a common process of formation for various ore types,e.g. immiscibility.Early magmatic apatites contain 3031.48-12080×10~(-6) REE.Later hydrothermal apatite contains 1958×10~(-6) REE,indicating that the later hydrothermal ore-forming solution contains lower REE.Although gabbro-diorite porphyry and apatite show similar REE patterns,gabbro-diorite porphyries have no europium anomalies or feeble positive or feeble negative europium anomalies, caused both by reduction environment of mantle source region and by fractionation and crystallization(immiscibility) under a high oxygen fugacity condition.Negative Eu anomalies of apatites were formed possibly due to acquisition of Eu~(2+) by earlier diopsite during ore magma cooling. The apatites in the Aoshan and Taishan iron deposits yield a narrow variation range of ~(87)Sr/~(86)Sr values from 0.7071 to 0.7073,similar to those of the volcanic and subvolcanic rocks,indicating that apatites were formed by liquid immiscibility and differentiation of intermediate and basic magmas.  相似文献   

5.
http://www.sciencedirect.com/science/article/pii/S1674987110000125   总被引：3，自引：0，他引：3  
<正>Carbonatites are commonly related to the accumulation of economically valuable substances such as REE.Cu,and P.The debate over the origin of carbonatites and their relationship to associated silicate rocks has been ongoing for about 45 years.Worldwide,the rocks characteristically display more geochemical enrichments in Ba,Sr and REE than sedimentary carbonate rocks.However,carbonatite's geochemical features are disputed because of secondary mineral effects.Rock-forming carbonates from carbonatites at Qinling.Panxi region,and Bayan Obo in China show REE distribution patterns ranging from LREE enrichment to flat patterns.They are characterized by a Sr content more than 10 times higher than that of secondary carbonates.The coarse- and fine-grained dolomites from Bayan Obo H8 dolomite marbles also show similar high Sr abundance,indicating that they are of igneous origin.Some carbonates in Chinese carbonatites show REE(especially HREE) contents and distribution patterns similar to those of the whole rocks.These intrusive carbonatites display lower platinum group elements and stronger fractionation between Pt and Ir relative to high-Si extrusive carbonatite.This indicates that most intrusive carbonatites may be carbonate cumulates.Maoniuping and Daluxiang in Panxi region are large REE deposits.Hydrothermal fluorite ore veins occur outside of the carbonatite bodies and are emplaced in wallrock syenite.The fiuorite in Maoniuping has Sr and Nd isotopes similar to carbonatite.The Daluxiang fiuorite shows Sr and REE compositions different from those in Maoniuping.The difference is reflected by both the carbonatites and rock-forming carbonates,indicating that REE mineralization is related to carbonatites.The cumulate processes of carbonate minerals make fractionated fluids rich in volatiles and LREE as a result of low partition coefficients for REE between carbonate and carbonatite melt and an increase from LREE to HREE.The carbonatite-derived fluid has interacted with wallrock to form REE ore veins.The amount of carbonatite dykes occurring near the Bayan Obo orebodies may support the same mineralization model,i.e.that fluids evolved from the carbonatite dykes reacted with H8 dolomite marble,and thus the different REE and isotope compositions of coarse- and fine-grained dolomite may be related to reaction processes.  相似文献   

6.
Loess of China, regardless of its ageexhibites similarity in the surface textures of silt quartz grains, all of them having conchoidal fractures, flat cleavage planes(or plates) and mechanical cracks, and having been rewrked by silica precipitation and chemical dissolution. Silica precipitation an different-degree chemical etching and dissolution are commonly found on thes silt quartz grains indicating that they would be separated from source rocks, such as granite, gneiss, etc. ; or they might have been subjected to relatively long weathering in situ before transported to loessic accumulation areas; or they probably underwent diagenesis when brought into the sedimentation system, followed by weathering and erosion, and then transported to loess accumulation areas. It is evident from the relationship between loess of China, deserts and Gobi, loessic cimposition and its regional distribution that MesozoicCenozoic land detrital sediments widely spreaded in the Ordos and Alxa regions are the principal material source of loessic materials in China.  相似文献   

7.
我国台湾浅滩海底沉积物稀土元素地球化学   总被引：12，自引：0，他引：12  
吴明清 《地球化学》1983,(3):303-313
REE geochemistry of sea-floor sediments from the Taiwan Shallow has been studied.∑ REE of 76 samples from the Taiwan Shallow was determined by chemical extraetion-spectrophotometry, of which 7 samples were analyzed for 15 rare earth elements by XRF. The analytical results show that ,∑ REE of the samples increases gradually with a decrease in grain size. The average REE contents are 60 ppm for coarse-grained sediments,82 ppm for medium-coarse-grained ones, 145 ppm for fine-grained ones, and 211 ppm for silt. The REE content of the samples is controlled mainly by the grain size and mineralogical composition of sediments. The ehondrite-normalized REE distribution patterns in sediments from the Taiwan Shallow are similar to those in granites in Fujian Province, China, which show a negative Eu anomaly and a positive Ce anomaly. The distribution curves are negative in slope. It is considered that based on REE geochemical characteristics, mineralogical composition and related oceanographic information, the Taiwan Shallow sediments seem to be largely residual deposits of ancient littoral facies from various types of continental rocks during Pleistocene glacial period. These sediments have also been reworked by modern sedimentatoion.  相似文献   

8.
黄河中游全新世黄土   总被引：9，自引：0，他引：9  
郑洪汉 《地球化学》1984,(3):237-246
Holocene loess in the Middle Huanghe Valley can be subdivided into 3 formations which are composed commonly of upper loess and lower dark loessial soil (a kind of paleosol) : the Xifeng Formation of Late Holocene, the Longxi Formation of Middle Holocene and the Luochuan Formation of Early Holocene. The layers of dark loessial soil at similar stratigraphic levels in different localities show such a change in age that samples from south are older than those from north, indicating a northward shift of the climate, belt during pedogenesis.  相似文献   

9.
REE geochemical studies of surficial sediment samples from the Yellow Sea of China have shown:(1)The average content of RE2O3 in the Yellow Sea sediments is 175 ppm,close to that in the East China Sea sediments.The REE distribution patterns in the Yellow Sea sediments are also similar to anomalies.These REE characteristics are typical of the continental crust.(2)The contents of REE are controlled mainly by the sediment grain size,i.e.,REE contents increase gradually with decreasing sediment grain size.REE are present mainly in clay minerals.In addition,REE contents are controlled obviously by heavy minerals.REE abundances in heavy minerals are much greater than those in light minerals.(3)Correlation analysis shows that REE have a close relationship with siderophile elements,especially Ti,which has the largest correlation coefficient relative to REE.Terrigenous clastic materials subjected to weathering and transport are suggested to be the main source of REE in the Yellow Sea sediments.  相似文献   

10.
The aim of this paper is to study the REE geochemistry of the Shenzhen Bay (SZB) and Dapeng Bay(DPB) modern sediments, discuss their REE distribution patterns, reveal the REE geochemical difference between the two bays which share the same material source but are deposited in different sedimentary environments, and expound their dynamic changes.It can be concluded that the SZB and DPB sediments are essentially of continental source.Their REE distribution patterns are quite different from those of Pacific pelagic sediments, but are very similar to those of South Chi-na granites.Because of different sedimentary environments prevailing in the SZB and DPB, some REE fractionation would have taken place in the sediments of the two bays.  相似文献   

11.
Thick loess is deposited on the platform in the piedmont zone of Muling-Xingkai Plain(Muxing Plain), but the genesis of the Muxing loess is still unclear. The aims of this study are to analyze the grain size characteristics of Muxing loess collected from the cores of a typical borehole(ZK1) in the piedmont zone of Muxing Plain, and to verify its genesis. The Muxing loess is mainly composed of the particles with diameter less than 50 μm, with an average content of 92.48%. The coarse silt particles with diameter of 10-50 μm are the basic composition of aeolian sediments, and their average content is 44.34% for the Muxing loess, which is the mode class among the particles with different diameters. The grain size parameters and frequency curves are similar to those of the typical aeolian sediments. The distribution characteristic of the Muxing loess in the C-M scatter diagram is consistent with that of the Xi Feng loess. In addition, the discriminant analysis shows the Muxing loess mostly consists of aeolian sediments. Therefore, it can be concluded that the Muxing loess mainly resulted from aeolian deposition based on the grain size characteristics. Muxing Plain is dominated by the monsoon climate, and the wind-blown dusts are gradually deposited after being transported over long distances.  相似文献   

12.
TL ages of 56 loess samples collected from Xinjiang and the middle reaches of the Yellow River were determined by using fine-grained quartz and man-made light source bleaching techniques.The results indicate that :1.The well-preserved loess sections in Xinjiang began depositing 400000 a ago.The loess/paleosol series may be comparable with that observed in the middle reaches of the Yellow River but the depositing time was probably delayed by 30000-50000a.2.The bottom boundary age of the Malan loess varies from one place to another.The TL dates can be divided into two group:70000-130000 a and 30000-50000 a.The TL data are con-sistent with the appearance of two warmer climate periods since the Pleistocene,indicating obvious regional differences in stratigraphic development of loess,i.e.,paleosol occurred in the warm climate period in the same location,but loess was deposited in other locations.The initial age of loess deposition tends to become older from west to east and from south to north .In contrast ,the cold cli-matic belt showed an opposite trend.The TL ages of loess provide strong evidence for the Quaternary stratigraphy throughout geological times and the shift tendency of climatic belt.3.The depositing rate of the Malan loess along the middle reaches of the Yellow River varies from place to place but the TL age shows a linear relationship with the depositing thickness.The de-positing rate of loess in the north is higher than that in the south,suggesting that loess materials are derived from desert areas of northern China.  相似文献   

13.
Geochemistry of rare earth elements in oceanic phillipsites   总被引：3，自引：0，他引：3  
The behavior of rare earth elements (REE) was examined in oceanic phillipsites collected from four horizons of eupelagic clay in the Southern Basin of the Pacific. The REE concentrations were determined in the >50-μm-fraction phillipsite samples by the ICP-MS method. The composition of separate phillipsite accretions was studied using the electron microprobe and secondary ion mass-spectrometry. Rare earth elements in phillipsite-only samples are related to the admixture of ferrocalcium hydroxophosphates. The analysis of separate phillipsite accretions reveals low (<0.1–18.1 ppm) REE (III) concentrations. The Ce concentration varies between 2.7 and 140 ppm. The correlation analysis shows that REE (III) are present as an admixture of iron oxyhydroxides in separate phillipsite accretions. Based on the REE (III) concentration in iron oxyhydroxides, we can identify two generations of phillipsite accretions. Massive rounded accretions (phillipsite I) are depleted in REE, while pseudorhombic (phillipsite II) accretions are enriched in REE and marked by a positive Ce anomaly. Oceanic phillipsites do not accumulate REE or inherit the REE signature of the volcaniclastic material and oceanic deep water. Hence, the REE distribution in phillipsites does not depend on the sedimentation rate and host sediment composition.  相似文献   

14.
Rare earth element compositions of Lower Ordovician dolomites in the Central and Northern Tarim Basin are studied. Most dolomite samples are more or less contaminated by clay minerals. Their rare earth element compositions have been consequently changed, showing both seawater-like and non-seawater-like features. The clay contamination should be disposed before the REE data are used. Through ICP-MS and ICP-AES analyses, the REE features are well documented. The clay contamination is quantitatively determined by microscopic investigation, trace elements and REE contents. The dolomites, at least in the Tarim Basin, are thought to be pure when their total LREE contents are less than 3×10^-6. Through comparison, the pure dolomites show similarities in REE patterns but differences in REE contents with co-existing pure limestone, which indicates that dolomitization may slightly change the REE compositions. Nevertheless, whatever the change is, the pure dolomites may act as a potential REE proxy for Ordovician seawater, which would be significant for ancient massive dolomite strata that lack limestone.  相似文献   

15.
The platforms on both sides of the Malangou River （a lateral ditch of the Qingshui River that is a tributary of the Yongding River） where Malan Village in Zhaitang Town of Mentougou District of Beijing is located are the place of China＇s typical section of the Quaternary Malan loess. During the investigation in the eastern suburbs of Beijing City, the authors not only clarified 5 grades of terraces on the Pinggu piedmont plain, but also found a clayey silt section mixed with a small amount of alluvial-diluvial gravel layers at a height of 15-25 m above the river level near a Fishpond in Xinli Village of Nandule Town. Results of the study of grain size of the section document that the loess mostly is silty soil （0.05--0.005 mm）, and that the grain size probability cumulative curves of the section are dominated by single-peak, coarse-grained segment I and coarse-grained segment II types, reflecting that its depositional environment is similar to eolian phase. Identification results of heavy minerals from the section show that their contents account for 0.01%-0.11%, averaging 0.04%. There are 24 kinds of heavy minerals, most of which are stable heavy minerals, and the clay minerals mostly are illite, which is consistent with the Malan loess on the Loess Plateau. The chemical composition data reflect that the source area of the loess is relatively arid. The six grade classification of sporopollen in the section further shows the subdivision of the history of alternating warm and humid phases in this geological period. The thermoluminescence dating results range from 21.0 ka to 59.2 ka, convincingly demonstrating that the section indeed consists of Malan loess. The above studies provide a new basis for overall understanding of the distribution of the Malan loess at the northeast margin of the North China Plain and its environment change in the Late Pleistocene.  相似文献   

16.
Manganese nodules in areas CP and CC of the central Pacific are rich in REE. Comparatively speaking,the REE contents of nodules in area CP are hihger than those in area CC; and the REE contents of nodulesfrom seamounts are higher than those of nodules from sea-floor plains and hills. Within the nodules, the REEshow a zonal distribution. The REE distribution patterns of the nodules are similar to those of the sedimentsand have a mirror image relationship with those of the sea water. Trivalent REE were not obviously differenti-ated when they entered into the nodules from the sea water.A major factor causing the difference of REE abundances between nodules and sediments is the redoxconditions. The redox intensity of the ocean floor of the Pacific is controlled mainly by Antarctic Bottom Wat-er(AABW), The iron-bearing facies in the nodules is the main carrier of REE.  相似文献   

17.
Rare earth element (REE) contents, and Sr and Nd isotopic compositions were measured for three suites of mantle xenoliths from the Kuandian, Hannuoba and Huinan volcanoes in the north of the Sino-Korean Platform. From the correlations of Yb contents with Al/Si and Ca/Si ratios, the peridotites are considered to be the residues of partial melting of the primitive mantle. The chondrite-normalized REE compositions are diverse, varying from strongly LREE-depleted to LREE-enriched, with various types of REE patterns. Metasomatic alteration by small-volume silicate melts, of mantle peridotites previously variably depleted due to fractional melting in the spinel peridotite field, can account for the diversity of REE patterns. The Sr/ Ba versus La/Ba correlation indicates that the metasomatic agent was enriched in Ba over Sr and La, suggestive of its volatile-rich signature and an origin by fluid-triggered melting in an ancient subduction zone. The Sr and Nd isotopic compositions of these xenoliths, even from  相似文献   

18.
The rare earth elements(REE) composition of the polymetallic crusts and nodules obtained from the South China Sea(SCS) were analyzed through inductively coupled plasma mass spectrometry.Results revealed great differences in the REE abundances(∑REE) of the SCS polymetallic crusts and nodules; the crusts show the highest ∑REE, whereas the nodules exhibit the lowest ∑REE. The similarity in their NASC-normalized patterns, the enriched light REE(LREE), the markedly positive Ce anomaly(δCe), and the non-or weakly positive Eu anomaly(δEu), suggest that the polymetallic crusts and nodules are of hydrogenetic origin. Moreover, the REE contents and their relevant parameters are quite different among the various layers of the crusts and nodules, which probably results from the different marginal sea environments and mineral assemblages of the samples. The growth profiles of the SCS polymetallic crusts and nodules reveal the tendency ∑REE and δCe to slightly increase from the outer to the inner layers, suggesting that the growth environments of these samples changed smoothly from an oxidizing to a relatively reducing environment; in addition, the crust ST1 may have experienced a regressive event(sea-level change) during its growth, although the REE composition of the seawater remained relatively stable. On the basis of the regional ∑REE distribution in the SCS crusts and nodules,the samples collected near the northern margin were influenced by terrigenous material more strongly compared with the other samples, and the REE contents are relatively low. Therefore, the special geotectonic environment is a significant factor influencing the abundance of elements, including REE and other trace elements. Compared with the oceanic seamount crusts and deep-sea nodules from other oceans,the SCS polymetallic crusts and nodules exhibit special REE compositions and shale-normalized patterns, implying that the samples are of marginal sea-type Fe-Mn sedimentary deposits, which are strongly affected by the epicontinental environment, and that they grew in a more oxidative seawater environment. This analysis indicates that the oxidized seawater environment and the special nano property of their Fe-Mn minerals enrich the REE adsorption.  相似文献   

19.
This paper deals with the REE geochemical characteristics of Permian-Triassic marine carbonate rocks in Guizhou Province.It is found that there are two broad categories of strati-graphic units in the region studied in accordance with their ΣREE contents and REE distribu-tion patterns: one is characterized by LREE enrichment and slight Ce depletion,with the REE distribution patterns similar to those of North American shales,and the other featrures relative HREE enrichment and relatively remarkable Ce depletion,with the REE distribution patterns close to those of pelagic sediments.In terms of their different ΣREE contents,five types of stratigraphic units can be distinguished.Incorporation of detrital minerals,REE complexing ca-pability,oxidation-reduction conditions of the media are the main factors affecting the REE com-position and REE distribution patterns of marine carbonate rocks in the region studied.In the light of REE geochemical characteristics of carbonate rocks,coupled with sedimentary facies analysis,this paper discusses the characteristics of the Permian-Triassic marine sedimentary environment in Guizhou Province and its evolutional rules.  相似文献   

20.
The Cambrian Gezhongwu Formation in Southwest China is the lowest Cambrian phosphorite unit. The Formation belongs to the Meishucun stage with small shelly fossils. Rare-earth element (REE)data from the Gezhongwu phosphorites of Zhijin documented the depositional conditions. The total REE concentrations are high in the Gezhongwu phosphorites, which are especially rich in yttrium. The PAASnormalized REE patterns of the Gezhongwu phosphorites are characterized by negative Ce anomalies and slight enrichment of MREE, as being hat-shaped. The hat-shaped patterns suggest that the REE originated from depositional environments rather than from subsequent diagenesis. The negative Ce anomalies indicate that the depositional environments are oxic. The positive Eu anomaly, the high total REE and the hatshaped REE pattern revealed contributions from the normal marine environment mixed with hydrothermal water to the REE budget of the Gezhongwu phosphorites.  相似文献   

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