Petrogenesis of Archaean Tonalites

The Archean tonalitic magma series is characterized by a high Al₂O₃ and Na₂O content. Tertiary tonalites with similar major element composition have been generated in subduction zones. It is therefore suggested that the Archean tonalites was generated in relation to subduction zones, the primary magma of the series being of dioritic composition. The generation of the primary magma occurred at about 15 kbar, while the recent generation of andesite occur at about 30 kbar. The higher frequency of generation in the Archean, and the relatively small depth of geneeration is related to the slightly higher temperatures of the mantle in the Archean.

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Zusammenfassung Die tonalitische Magmenfolge des Archäikum wird durch hohe Al₂O₃- und Na₂O-Gehalte gekennzeichnet. Tertiäraltrige Tonalite mit ähnlicher Hauptelement-Zusammensetzung entstanden in Subduktionszonen. Deshalb wird vorgeschlagen, daß die archäischen Tonalite im Zusammenhang mit Subduktionszonen entstanden, wobei das primäre Magma der Folge dioritischer Zusammensetzung war. Das primäre Magma entstand unter einem Druck von etwa 15 kbar; in jüngster Zeit entsteht aber Andesit bei etwa 30 kbar. Die höhere Entstehungsrate im Archäikum wird, so wie auch die verhältnismäßig geringe Entstehungstiefe, zu den etwas höheren Manteltemperaturen im Archäikum in Beziehung gesetzt.

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Résumé La série des magmas tonalitiques de l'Archéen est caractérisée par une haute teneur en Al₂O₃. Les tonalites tertiaires, de même composition quant aux éléments majeurs, ont été engendrées dans des zones de subduction. C'est pourquoi il est suggéré que les tonalites archéennes aient été engendrées en relation avec des zones de subduction, le magma primaire de la série étant de composition dioritique. La genèse du magma primaire se fit sous environ 15 kbar, tandis que la genèse récente des andésites se fait à 30 kbar. La fréquence élevée de la formation dans l'Archéen et la profondeur relativement faible de cette formation est en liaison avec les températures légèrement plus élevées du manteau dans l'Archéen.

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The mobility of the rare earth elements: Evidence and implications from selected terrains affected by burial metamorphism

The mobility of the rare earth element (REE) during hydrous burial metamorphism is described from three localities. Comparison of REE abundances in relict domains and metadomains from flood lavas in the Maddina Volcanics, Fortescue Group, Western Australia shows that, relative to the relict domains, REE may be strongly depleted in certain metadomains. Strong variations in La/Yb, La/Sm and Eu may also occur due to postcrystallization secondary processes. Similar comparisons in flood lavas from Mamainse Point in the Canadian Keweenawan Series show that REE are mobile and increase in abundance in metadomains. Spilites from U.S. Virgin Islands also show evidence for REE mobility during low grade burial metamorphism. In this case light REE (LREE) have been preferentially mobilized with heavy REE (HREE) remaining parallel or sub-parallel on chondrite normalized plots.REE analyses from these locations together with an evaluation of published work suggests that the mobility of REE can be described by: 1. gross REE and selective LREE enrichment; 2. REE movement around a primary mean; 3. gross REE depletion; 4. selective REE mobility. Failure to take into account REE mobility may lead to incorrect conclusions concerning petrogenetic models based on altered basic sequences. The coherence of REE with other key trace elements during alteration is also discussed.     

Concentrations of rare earth elements in topsoil from East China

Fifty topsoil samples collected from 12 different regions of East China have been analyzed for rare earth elements (REEs). The average REE concentrations of the 50 topsoil samples are much higher than world average and are characterized by LREE-enrichment, HREE-depletion, Eu-depletion and Ce-enrichment. However, the REE concentration is not strongly affected by the climate of the sampling site; it is controlled mainly by parent materials. The plot of Ce/Eu against Eu/Sm is proved to be useful to distinguish different parent materials of topsoil. Each element in the 50 topsoil has a good correlation with its neighboring element. Seven of the 13 values are above 0.987.     

深海稀土分布规律与成矿作用

深海稀土是近年发现的一种富集中-重稀土的新型海洋矿产资源,其资源量远超陆地稀土储量,具有重要的潜在应用价值。中国是继日本之后在国际上第二个开展深海稀土调查研究的国家,2011年以来,先后在中印度洋海盆、东南太平洋和西太平洋深海盆地发现了大面积富稀土沉积区,在全球大洋中初步划分出4个深海稀土成矿带：西太平洋深海稀土成矿带、中—东太平洋深海稀土成矿带、东南太平洋深海稀土成矿带和中印度洋海盆-沃顿海盆深海稀土成矿带。深海富稀土沉积主要发育在深海盆地的沸石粘土和远洋粘土中,属于自生成因;部分发育在洋中脊附近的盆地中,受到热液作用的影响。研究发现,深海粘土中稀土元素主要赋存于生物磷灰石中,海水是稀土元素的主要来源;在早期成岩阶段,稀土元素在深海沉积物中发生转移和重新分配,并最终富集于生物磷灰石中;大水深（CCD面之下）、低沉积速率和强底流活动是深海稀土大规模成矿的主要控制因素。今后需要继续加大深海稀土基础调查,加强深海稀土调查探测技术研发,并开展海陆稀土成矿作用对比研究,揭示深海稀土成矿机制和规律。     

Composition and evolution of the eucrite parent body: evidence from rare earth elements

Eucrites are extraterrestrial plagioclase-pigeonite basalts. Experimental studies suggest that they were produced by partial melting of an olivine (Fo₆₅)-pigeonite (Wo₅En₆₅)-plagioclase (An₉₄)-spinel-metal source region. Quantitative modeling of the evolution of REE abundances in the eucrites indicates that the main group of eucrites (e.g. Juvinas) may be produced by approximately 10% equilibrium partial melting of a source region with initial REE abundances which were chondritic relative and absolute. Other eucrites appear to represent greater (e.g. Sioux County—15%) or smaller (e.g. Stannern—4%) degrees of melting. Moore County and Serra de Magé appear to be cumulates of pyroxene and plagioclase produced by fractional crystallization of a Juvinas-like melt. Nuevo Laredo may represent a residual liquid after such fractional crystallization. Our calculations are consistent with the conclusion that the eucrites were derived from a single type of source region. The close correspondence of the age of the eucrites (? 4.6 AE) to the age of the solar system appears to preclude the possibility of extensive chemical differentiation of the eucrite parent body prior to the event which produced the eucritic melts. Thus our calculations have yielded not only the mode of the source region but, assuming homogeneous accretion, the mode and hence the bulk composition of the eucrite parent body as well. We are unable to estimate quantitatively the ratio of metal to olivine in the parent body. If no metal is present, the bulk composition (in oxide wt%) is Na₂O—0.04, MgO—29.7, Al₂O₃—1.8, SiO₂—39.0, CaO—1.2, FeO—28.3. If, in contrast, the parent body contained 30% metal, the bulk composition of the silicate portion of the eucrite parent body is Na₂O—0.06, MgO—28.0, Al₂O₃—2.6, SiO₂—41.3, CaO—1.9, FeO—26.3. Relative abundances of the meteorites suggest that the eucrite parent body is still intact. The solar system object most closely resembling the eucrites is asteroid 4 Vesta. Because Vesta is unique among the asteroids, we have license to conclude that it is the source of the eucrites and its bulk composition is close to the analyses given above.     

Fertiliser characterisation: Major,trace and rare earth elements

In recent years, there has been increasing concern regarding the chemical impact of agricultural activities on the environment so it is necessary to identify contaminants, and/or characterise the sources of contamination. In this study, a comprehensive chemical characterisation of 27 fertilisers of different types used in Spain has been conducted; major, minor and trace elements were determined, including rare earth elements. Results show that compound fertilisers used for fertigation or foliar application have low content of heavy metals, whereas fertilisers used for basal and top dressing have the highest content of both REE and other heavy metals. REE patterns of fertilisers have been determined in order for them to be used as tracers of fertilisers in future environmental studies. Furthermore in this work REE patterns of fertilisers are used as tracers of the source of phosphate in compound fertilisers, distinguishing between phosphorite and carbonatite derived fertilisers. Fertilisers from carbonatites have higher contents of REE, Sr, Ba and Th whereas fertilisers from phosphorites have higher contents of metals of environmental concern, such as Cd, U and As; and the sum of the heavy metals is higher. Some of the analysed fertilisers have Cd concentrations that exceed maximum values established in some countries and can be expected to produce long-term soil accumulation. Furthermore, other elements such as U, As and Cr are 10–50 times higher in concentration than those of Cd, but there is no legislation regarding them, therefore it is necessary to regulate fertiliser compositions in order to achieve environmental protection of soils and waters.     

Kiglapait geochemistry VII: Yttrium and the rare earth elements

Based on 51 wholerock analyses by XRF and summation over the layered group, the Kiglapait Intrusion contains 4.7_?1.6^+1.2 ppm Y, which resides principally in augite and apatite. Using liquid compositions calculated by summation, the partition coefficient D^AUG/L_Y is 0.95 ± 0.12 from 84 to 97 PCS (percent solidified) and 1.5 ± 0.4 above 97 PCS. For feldspar, the most likely value for D is 0.028 ± 0.02 (N = 6).REE analyses for 13 whole rocks were interpreted with the aid of yttrium models to yield trends for wholerocks and liquids vs PCS. Summations over the rocks of the layered group gave La = 2.5, Ce = 5.8, Nd = 3.9, Sm = 1.0, Eu = 0.8, Tb = 0.17, Yb = 0.37, and Lu = 0.06 ppm, with 2 s.d. errors near ± 30%. All these elements are highly incompatible until the arrival of augite, which affects chiefly the HREE, and apatite, which affects all (but more strongly, the LREE). The net result is that after apatite arrival at 94 PCS, the liquid compositions are nearly constant, hence D^WR/L_REE ≈ 1.0. These results are compatible with the mineralogy of the intrusion and the estimated partition coefficients for feldspar, olivine, augite, apatite, and Fe-Ti oxide minerals. For pre-apatite liquids, D^FSP/L_REE vary regularly with the normative di content of the liquid and change by an order of magnitude, hence the bulk liquid composition must be considered in any attempt to invert the compositions of feldspars to parent liquids.The Eu anomaly at first decreases in Kiglapait liquids due to plagioclase fractionation, but then increases due to removal of augite and apatite with negative Eu anomalies. The features dominantly responsible for Eu partitioning are liquid structure and, for monoclinic ternary feldspars, crystal structure. The former is best monitored by the augite or diopside content of the liquid and the latter, by the K content of the feldspar.The chondrite-normalized REE pattern for the intrusion has La_N = 7.4, Lu_N = 1.6, (Ce/Yb)_N = 3.6, and Eu/Eu* = 2.4, indicating its feldspar-rich nature. The chilled margin of the nearby Hettasch Intrusion has a similar but more evolved pattern, corresponding roughly to the Kiglapait liquid at 70 PCS. As with other data, those for the REE suggest source differences for the two intrusions rather than a relationship due to fractionation.     

Chemical effect of pesticide application on soils: evidence from rare earth elements

The main objective of this study is to investigate the distribution of rare earth elements (REEs) in Lolium perenne L. plant species which has been grown on vineyard soils treated with pesticide commonly used in the study area. These plants have been grown on two types of soils: (1) brown calcareous soils developed on loess and (2) brown to calcic brown soils developed on conglomerates. The significant correlation observed between the concentrations of phosphorus and the total amount of REEs, in addition to the enrichment in middle REEs (MREEs), suggests the complexation of REEs with phosphates and organic matter. The soils were enriched in REEs due to pesticide application but the plants were depleted. The ratio of REEs in plant over REEs in soil before application of pesticides is higher than that after application of pesticides. Application of pesticides to crops did not affect the fractionation of REEs neither in leaves nor in roots. No selectivity in uptake of REEs occurred because of pesticides except for Ce and Eu which show a negative anomaly relative to the other REEs.     

相山铀矿田成矿流体特征:来自微量、稀土元素地球化学证据

相山铀矿田的成矿流体性质和来源存在争议,为进一步探讨相山铀矿田成矿流体的性质和来源,本文对相山铀矿田西部的居隆庵铀矿床和北部的沙洲铀矿床中的新鲜围岩、蚀变围岩及矿石的微量、稀土元素含量及其变化进行了研究。结果显示:在含较多热液成因萤石的居隆庵铀矿床中,从新鲜围岩到蚀变围岩到矿石,Zr、Hf含量先降低再升高;而在含少量热液萤石的沙洲铀矿床中,新鲜围岩、蚀变围岩和矿石的Zr、Hf含量基本一致。鉴于富F流体易汲取岩石中的Zr、Hf,因此,这两个矿床中不同类型样品Zr、Hf含量的不同变化趋势,可能与居隆庵铀矿床的成矿流体富F、而沙洲铀矿床的成矿流体相对贫F有关。这两个铀矿床中矿石的稀土配分曲线与其各自的新鲜及蚀变围岩的稀土配分曲线形态相似但又存在差异,说明每个矿床的新鲜围岩、蚀变围岩和矿石之间的稀土元素既具有继承性、又受到不同性质的流体的影响。居隆庵铀矿床中矿石显示Eu负异常,可能主要是继承了围岩的Eu负异常;沙洲铀矿床中矿石Eu显示弱负异常至弱正异常的特征,可能与围岩中斜长石因热液蚀变作用而释放出的Eu的进入流体有关。基于新鲜围岩、蚀变围岩及矿石的U和REE研究,推断居隆庵铀矿床成矿流体中U和REE均以F的络合物形式迁移;但沙洲铀矿床中铀矿石品位较低,可能是与流体中相对贫F有关。     

Ligand extraction of rare earth elements from aquifer sediments: Implications for rare earth element complexation with organic matter in natural waters

The ability of organic matter as well as carbonate ions to extract rare earth elements (REEs) from sandy sediments of a Coastal Plain aquifer was investigated for unpurified organic matter from different sources (i.e., Mississippi River natural organic matter, Aldrich humic acid, Nordic aquatic fulvic acid, Suwannee River fulvic acid, and Suwannee River natural organic matter) and for extraction solutions containing weak (i.e., CH₃COO⁻) or strong (i.e., ) ligands. The experimental results indicate that, in the absence of strong REE complexing ligands in solution, the amount of REEs released from the sand is small and the fractionation pattern of the released REEs appears to be controlled by the surface stability constants for REE sorption with Fe(III) oxides/oxyhydroxides. In the presence of strong solution complexing ligands, however, the amount and the fractionation pattern of the released REEs reflect the strength and variation of the stability constants of the dominant aqueous REE species across the REE series. The varying amount of REEs extracted by the different organic matter employed in the experiments indicates that organic matter from different sources has different complexing capacity for REEs. However, the fractionation pattern of REEs extracted by the various organic matter used in our experiments is remarkable consistent, being independent of the source and the concentration of organic matter used, as well as solution pH. Because natural aquifer sand and unpurified organic matter were used in our experiments, our experimental conditions are more broadly similar to natural systems than many previous laboratory experiments of REE-humic complexation that employed purified humic substances. Our results suggest that the REE loading effect on REE-humic complexation is negligible in natural waters as more abundant metal cations (e.g., Fe, Al) out-compete REEs for strong binding sites on organic matter. More specifically, our results indicate that REE complexation with organic matter in natural waters is dominated by REE binding to weak sites on dissolved organic matter, which subsequently leads to a middle REE (MREE: Sm-Ho)-enriched fractionation pattern. The experiments also indicate that carbonate ions may effectively compete with fulvic acid in binding with dissolved REEs, but cannot out compete humic acids for REEs. Therefore, in natural waters where low molecular weight (LMW) dissolved organic carbon (DOC) is the predominant form of DOC (e.g., lower Mississippi River water), REEs occur as “truly” dissolved species by complexing with carbonate ions as well as FA, resulting in heavy REE (HREE: Er-Lu)-enriched shale-normalized fractionation patterns. Whereas, in natural terrestrial waters where REE speciation is dominated by organic complexes with high molecular weight DOC (e.g., “colloidal” HA), only MREE-enriched fractionation patterns will be observed because the more abundant, weak sites preferentially complex MREEs relative to HREEs and light REEs (LREEs: La-Nd).     

四川稀土精矿的稀土元素和微量元素地球化学特征及开发利用意义

产自广东省梅州市玉水铜矿的景文矿,属于含水、重稀土-矾-铝硅酸盐矿物(简写为HREE-V-铝硅酸盐矿物),其化学结构式为Y₂Al₂V₂⁴⁺(SiO₄)₂O₄(OH)₄,该矿物在全球属首次发现,暂未开展相关研究。相对于含轻稀土矿物,含重稀土矿物在电子探针分析过程中,当被高压电子束轰击时,被激发出来的特征X射线线系繁多,线系之间分布更加密集,彼此之间相互重叠的现象也更为严重,要获得理想数据的难度很大,是亟待解决和突破的技术难题。本文对该矿物进行了精细的电子探针定量分析,获得理想的化学成分数据,为新矿物命名提供了理论数据技术支撑。通过对实验方法的探索和总结获得以下结果：①利用15kV加速电压、100nA束流对试样进行全元素扫描,以此确定出17种元素;②在定量分析过程中,对重叠峰进行了剥离;③利用仪器软件中的Zoom-Peak ID程序,选择出17种元素的分析线系、精确的峰位及上下背景值;④选取合适的标样及测试时间等定量分析条件,最终获得理想的定量分析结果(平均总量97.41wt%)。上述四条也是确保获得理想定量分析数据的关键因素。

     

State of rare earth elements in the rare earth deposits of Northwest Guizhou,China

We studied the states of rare earth elements in ore of the Xianglushan rare earth deposit. Rare earth ore samples were tested and examined by scanning electron microscope, electron probe, and chemical leaching. No independent rare earth minerals were detected by scanning electron microscope. Elements detected by the electronic probe for the in situ micro-zone of the sample included: O, Al, Si, Ca, Mg, Fe, Ti, K, Na, S, Cl, C, Cu, Cr, V, and Pt. Rare earth elements were not detected by electron probe. (NH4)₂SO₄, (NH₄)Cl, NaCl, and H₂SO₄ were used as reagents in chemical leaching experiments that easily leached out rare earth elements under the action of 10% reagent, indicating that the rare earth elements in ore are mainly in the ionic state rather than present as rare earth minerals.     

巴尔哲超大型稀有稀土矿床成矿机制研究

巴尔哲矿床中的矿化和非矿化碱性花岗岩主要造岩矿物均为微斜长石、石英、钠闪石和钠长石,但其相对含量及颗粒大小明显不同,且两类岩石中包裹体的组成特征及锆石的结晶习性也有显著差异.主量元素分析显示,矿化与非矿化碱性花岗岩均以富硅、富碱、贫镁和钙为特征,为较典型的非造山A型花岗岩.尽管矿化碱性花岗岩中K_2O和Na_2O的含量均没有明显的增加,但其Na+K/Al、Na_2O+K_2O/CaO、FeO~*/MgO及K_2O/MgO等岩石化学参数与非矿化碱性花岗岩明显不同.在矿化碱性花岗岩中除了矿化的稀土元素及Nb、Zr强烈富集外,U、Th及Y也明显富集,而Ba、Sr、P、Eu和Ti表现为强烈的亏损.在非矿化碱性花岗岩中除了大离子亲石元素Rb略有富集外,稀土元素、Nb、Zr、U、Th、Ta及Y并无明显富集,虽然Sr、P、Eu和Ti也表现为亏损,但与矿化碱性花岗岩相比其亏损程度明显降低.岩相学、岩石化学及微量元素地球化学特征显示,矿化碱性花岗岩不可能是非矿化碱性花岗岩硅化和钠长石化作用的产物,二者应是同一岩浆体系不同演化阶段熔体固结的产物.K/Rb、Rb/Sr及δEu等地球化学参数显示,矿化碱性花岗岩是高演化A型花岗质熔体固结的产物;而岩石学、包裹体及地球化学特征则显示,这种高演化的A型花岗质熔体已经进入了岩浆一热液过渡阶段.巴尔哲矿床稀有稀土元素的超常富集和成矿与A型花岗岩的高演化过程密切相关.     

Rare earth elements in the early Archaean Isua iron-formation, West Greenland

The rare earth element (REE) patterns in the 3.8 Ga-old Isua iron-formation are generally flat, resembling those of some primitive basalts. Samples with positive, negative or no europium anomaly were found. It is shown that diagenesis and metamorphism did not significantly change the REE patterns. The presence or absence of europium anomalies in iron-formations cannot be used as an indicator of the presence or absence of oxygen in the atmosphere during the Archaean and Precambrian. The REE contents cannot be used to distinguish Algoma-type from Superior-type iron-formations. There appears to be a striking similarity between the Archaean submarine exhalations and modern submarine hydrothermal systems. It is considered likely that Archaean and early Precambrian seawater had a chondritic REE pattern with a slight enrichment of light REE.     

Geochemistry of rare earth elements in oceanic phillipsites

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.     

大青山煤田煤系高岭岩稀土元素地球化学特征

采用中子活化法对采自内蒙古大青山煤田石炭-二叠纪煤系的12个高岭岩样品进行了稀土元素(REE)含量测定。结果表明,样品的稀土元素含量变化很大,ΣREE最低31.98×10^-6,最高616.3×10^-6,平均178.6×10^-6,与NASC的173.21×10^-6相近;ΣLREE/ΣHREE介于6.32~46.14之间,平均17.5,明显高于NASC;中—弱Eu亏损,弱Ce正异常。通过不同对比样品(北美页岩、超基性岩、基性岩、中性岩、酸性岩以及偏碱性岩等)所作的标准化分析结果表明,研究样品不具有典型的沉积型泥岩特征;结合薄片鉴定及前人分析结果推论,高岭岩可能由中—基性或偏碱性火山碎屑物质原地蚀变而成,泥炭化所提供的酸性介质条件对火山灰向高岭岩转化以及稀土元素的分异提供了必要的条件。     

桂岭岩体稀土、微量元素地球化学特征研究

文章运用岩石地球化学方法,对桂岭岩体的构造环境和地球化学特征进行了研究,结果显示：桂岭岩体岩石平均LREE／HREE=7．68,（La／Yb）N-6．77,（La／Sm）N-4．65,（Gd／Yb）N-1．04,平均δEu=0．45〈1,表明轻重稀土轻度分异,轻稀土相对富集,轻稀土内部分馏明显,存在负铕异常;岩体明显亏损Nb、Sr、Ti,显示桂岭岩体的源区可能主要来自地壳,是地壳环境下壳源岩石发生部分熔融的产物;研究表明,桂岭岩体形成于挤压一伸展的大地构造环境。     

Precambrian tholeiitic-dacitic rock-suites and Cambrian ultramafic rocks in the Pennine nappe system of the Alps: Evidence from Sm-Nd isotopes and rare earth elements

Major element, trace element and Sm-Nd isotope analyses were made of polymetamorphic hornblendefelses, plagioclase amphibolites and banded amphibolites from the Berisal complex in the Simplon area (Italy, Switzerland) to determine their age, origin and genetic relationships. In light of major and rare earth element data, the hornblendefelses are inferred to have originally been pyroxene-rich cumulates, the plagioclase amphibolites and the dark layers of the banded amphibolites to have been tholeiitic basalts and the light layers dacites. The Sm-Nd isotope data yield isochron ages of 475±81 Ma for the hornblendefelses, 1,018±59 Ma for the plagioclase amphibolites and 1,071±43 Ma for the banded amphibolites. The 1 Ga magmatic event is the oldest one ever found in the crystalline basement of the Pennine nappes. The Sm -Nd isotope data support the consanguinity of the tholeiitic dark layers and the dacitic light layers of the banded amphibolites with the tholeiitic plagioclase amphibolites and the ultramafic hornblendefelses.The initial _Nd values indicate that all three rock types originated from sources depleted in light rare earth elements. We suggest that plagioclase and banded amphibolites were a Proterozoic tholeiite-dacite sequence that was strongly deformed and flattened during subsequent folding. The hornblendefelses are thought to be Cambrian intrusions of pyroxene-rich material.     

Rare-earth element distribution in basic and ultrabasic rocks from west Norway

Samples of ten eclogites in gneiss, one eclogite in dunite-peridotite, three dunites and four garnet- and dunite-peridotites from the Nordfjord-Molde area, west Norway were analysed for La, Ce, Nd, Sm, Eu, Gd, Tb, Yb and Lu by radiochemical neutron activation analysis.The chondrite normalized REE patterns of eclogites in gneisses show mostly slight enrichment of the heavy REE, which converge towards a value about ten times above the average chondrite. It is suggested that the light REE scatter is due to the original mineralogical composition of the rocks.One garnet-peridotite shows a distribution pattern similar to those reported for high-temperature peridotites while the two others could be compared with that of Lac de Lherz and Still water peridotite.Two of the dunites taken from the same locality show a difference in the individual REE content by a factor of one order of magnitude. This is explained by the higher content of tremolite in the most REE-enriched sample.