Excess europium content in precambrian sedimentary rocks and continental evolution

We propose that the europium excess in Precambrian sedimentary rocks, relative to those of younger age is derived from volcanic rocks of ancient island arcs, which were the source materials for the sediments. Precambrian sedimentary rocks and present-day volcanic rocks of island arcs have similar REE patterns, total REE abundances and excess Eu, relative to the North American shale composite. The present upper crustal REE pattern, as exemplified by that of sediments, is depleted in Eu, relative to chondrites. This depletion is considered to be a consequence of development of a grandioritic upper crust by partial melting in the lower crust, which selectively retains europium.     

Rare earths in Archean graywackes from Wyoming and from the Fig Tree Group,South Africa

Six graywackes from the Archean greenstone belt in the Wind River of Wyoming and 11 graywackes and three shales from the Archean Fig Tree Group, South Africa, were analyzed for the rare earth elements (REE). There are real deviations beyond analytical uncertainty among sediments from the same formation. The absolute abundance of the REE (∑REE) is somewhat lower than that of the North American shale composite (NASC) which is representative of younger sedimentary rocks. Still, the results confirm previous suggestions that the RE pattern in Precambrian sediments is the same as the NASC but that, relative to the heavy REE, graywackes are slightly enriched in the light REE, shales are depleted, and there is a slight enrichment in Eu relative to the NASC. The average abundance of Eu relative to the other REE for all the Precambrian sediments is the same as that in chondritic meteorites. Attesting to the complexity of graywacke genesis, there is no correlation between the variations in the REE parameters and the variations in major or minor element concentrations. In particular, there is no obvious correlation between the excess Eu and Sr abundance. The total amount of REE, the $\text{La}\text{Yb}$ ratio, and the Eu enrichment factor, however, all increase in the graywackes with the amount granite-gneiss detritus in the rocks. In general, the REE distributions in Archean graywackes and shales appear to be related to the relative amounts of clastic feldspar, mica, and minor phases which concentrate the REE.     

Evolution in the provenance of a tectonically controlled Plio–Pleistocene alluvial system between the Variscan Iberian Massif and the Atlantic margin, Portugal

Geochemical and mineralogical data from a Pliocene to Pleistocene alluvial sequence are integrated to access the factors that control rare earth elements (REE) geochemistry and the evolution and spatial differences in provenance. The studied alluvial system is situated in a tectonic active setting at the contact between the Variscan Massif, with several Paleozoic and Precambrian units that support a coastal range, and the Atlantic margin. REE and HREE abundances are generally higher in swamp-lake than in floodplain sediments. The majority of the REE in floodplain sediments is hosted by Y and Th-bearing minerals and illite; in swamp-lake sediments is also probable an association with organic matter. The high Gd/Yb, Eu/Eu* and kaolinite content in older sediments suggest that during the earlier phases provenance was mainly from the hinterland (weathered granitic rocks and its sediment cover). The subsequent illite (Mg-rich) clay assemblages and REE patterns indicate mainly lateral input from the eastern basin edge (Palaeozoic and Precambrian metapelitic rocks). These sediments tend to have lower Gd/Yb and La/Sm than their source rocks. The analysis of the chemical index of alteration (CIA) indicates that although a north-directed fluvial axis existed at that time the “mature” basin edge units found to the south (Silurian) had a limited role in supplying sediments. This shift in provenance is attributed to the uplift of the coastal range. Afterwards, the contribution of recycled Cretaceous and Cenozoic sedimentary units increased progressively. This is demonstrated by the increase is SiO₂/TiO₂, CIA and kaolinite/illite when the climatic conditions are expected to have become less chemically aggressive.     

Rare earth element geochemistry of Archean metasedimentary rocks from Kambalda,Western Australia

Archean sedimentary rocks of very limited lateral extent from horizons within basaltic and ultramafic volcanic sequences at Kambalda, Western Australia, are extremely variable in major elements, LIL and ferromagnesian trace element compositions. The REE patterns are uniform and do not have negative Eu anomalies. Two samples have very low total REE abundances and positive Eu anomalies attributed to a very much greater proportion of chemically deposited siliceous material. Apart from these two samples, the Kambalda data are similar to REE abundances and patterns from Archean sedimentary rocks from Kalgoorlie, Western Australia and to average Archean sedimentary rock REE patterns. These show a fundamental distinction from post-Archean sedimentary rock REE patterns which have higher $\text{La}\text{Yb}$ ratios and a distinct negative Eu anomaly.     

Rare earth element patterns and crustal evolution—II. Archean sedimentary rocks from Kalgoorlie,Australia

REE data, with major element and other trace element data are reported for a suite of Archean sedimentary rocks (2800 million years old) from Kalgoorlie, Western Australia. The REE patterns fall into two groups with ?LREE/?HREE ratios of 6 and 15, respectively. The first group have either no Eu anomaly relative to chondrites, or a positive Eu anomaly, in contrast to the pronounced Eu depletion (Eu/Eu ~ 0.67) shown by younger (Post-Archean) sedimentary rocks.The problem of positive Eu enrichment relative to chondritic patterns, is examined by analysing a suite of Devonian greywackes, derived from calc-alkaline volcanic rocks. Some of these samples also show positive Eu anomalies, attributable to local accumulation of feldspar. This explanation is preferred to models involving an early anorthositic crust. The group of samples showing heavy REE depletion patterns (complementary to those observed in garnet) appear to be derived from adjacent Na-rich granites which display identical REE patterns. Locally abundant K-rich granites do not appear to have made any contribution to the Archean sedimentary rocks.The majority of the sedimentary rocks have REE patterns indistinguishable from those of recent island arc calc-alkaline rocks, and so could constitute evidence that the Archean crust was principally formed by processes analogous to present day island-arc type volcanism. However, similar REE patterns may be produced by an appropriate mixture of the common bimodal tholeiitic-felsic igneous suite commonly observed in Archean terrains. The REE data presented here do not distinguish between these two models.     

Rare earth element patterns and crustal evolution—I. Australian post-Archean sedimentary rocks

A suite of Australian shales, greywackes and subgreywackes ranging in age from Proterozoic to Triassic were analyzed for the rare earth elements (REE) in order to detect any secular changes in rare earth distribution. These post-Archean sediments show remarkably similar relative rare earth patterns. They are characterized by negative Eu anomalies of almost constant magnitude (average Eu/Eu* = 0.67 ± 0.05) relative to chondrites and nearly constant ratios of light to heavy rare earths (average ∑LREE/∑HREE = 9.7 ± 1.8).

The REE abundances are generally higher in the younger sediments which may suggest that the absolute abundances of the rare earths in clastic sediments have gradually increased with time. Since no secular change in relative rare earth distribution was detected in the post-Archean sediments, a uniform process of crustal growth and evolution seems to have operated over the past 1500 million years at least.

Australites show rare earth distributions very similar to that of the average clastic sediment. This suggests that the tektite parent material originated in the upper crust.     

Rare earth element distributions in some Precambrian rocks and their phyllosilicates,Numedal, Norway

Mass spectrometric analyses for rare earth elements (REE) have been carried out on some Precambrian mica schists, gneisses and granites from the Precambrian Numedal area, Norway and on their phyllosilicates. The rocks, which are metamorphosed in the upper greenschist to amphibolite facies, were originally partly sedimentary, partly magmatic.The total REE contents for rocks varies from 145 to 761 ppm. An average of 16 phyllosilicate samples gave 417 ppm REE (max. of 1809 ppm, min. of ca. 50 ppm). Coexisting light and dark phyllosilicates have similar abundances of REE. For the micas of high REE content most of the REE was extractable by rinsing with EDTA. The data thus support the possibility of an extensive adsorption of REE ions on micaceous minerals. The REE distribution patterns do not provide a clear distinction between the sedimentary and magmatic origin for the rocks examined.     

华南热水沉积硅质岩建造及其成矿效应

华南地区热水沉积建造发育。文中介绍该地区热水沉积建造 ,特别是震旦系顶部、泥盆系榴江组和二叠系当冲组 3个重要层位的硅质岩建造 ,分析它们的地质地球化学特征。研究表明 ,华南三层位沉积硅质岩的共同特征是TiO2 、Al2 O3 和K2 O含量一致偏低 ,大部分微量元素含量偏低 (与地壳克拉克值相比 ) ,但Ba、As、Sb富集 ,具有较为典型的热水沉积成因特点。多元统计分析显示 ,大部分微量元素在第一个主因子上均有显著因子载荷 ,与它们在基底的富集或亏损无关 ,代表了古地热系热水循环中的淋滤因子。华南三层位热水成因硅质岩具有相似的REE地球化学特征。REE总量低 ,稀土配分模式落在典型热水沉积物的上、下限之间 ,多数样品呈现δCe和δEu负异常。正常沉积的混入使部分硅质岩的REE配分模式复杂化。最后 ,讨论了与热水沉积建造相关的成矿效应 ,为金属矿床成因和评价提供约束条件     

川西昌台勉戈组沉积岩系稀土特征

川西昌台地区上三叠统勉戈组中酸性火山岩之上主要为一套灰黑色至黑色沉积岩石组合,包括板岩、页岩和泥岩等。这套岩石组合可分为两类:底部为存在热水活动参与形成的沉积岩,厚度较薄;底部之上为无热水活动参与形成的沉积岩,厚度较大。本文取样上述两类岩石测得的稀土元素特征基本相似,无明显区别:两类样品稀土含量普遍偏高,与球粒陨石标准化的的配分曲线呈右倾型,LREE富集,基本无Ce正/负异常,具有明显的Eu负异常。有热水活动参与的沉积岩样品与太平洋SER地区现代海底典型热水沉积物的稀土元素特征明显不一致;与该区域内呷村矿区的典型热水沉积岩重晶石和硅质岩的稀土元素特征也不一致。但与秦岭志留系部分热水沉积岩样品和湘黔寒武系牛蹄塘组底部碳质伊利石页岩样品的稀土特征一致,呈现正常碎屑岩的稀土元素特征。综合分析认为,川西勉戈组碎屑页岩出现Eu负异常特征的主要原因是所测样品中的热液组分含量较少甚至无。     

Geochemical tracers of source rocks in a Cretaceous to Quaternary sedimentary sequence (Eastern Sierras Pampeanas,Argentina)

Metamorphic rocks, granitic rocks, and sediments from the Eastern Sierras Pampanas, Argentina, were analyzed for major and trace element concentrations, including rare earth elements (REE). Parental rocks exhibit distinctive REE normalized diagram patterns and elemental ratios, and some elemental ratios reveal significant differences between rock sources. For example, ratios such as Th/Sc, Cr/Th, and La/Cr have a mean value of 0.7, 8.4 and 0.4 in metamorphic rocks, whereas granitic rocks exhibit means of 1.4, 0.7 and 4.9, respectively. These ratios are also useful in linking detrital materials with the corresponding parental rocks. Metamorphic sources yield sediments with lower Th/Sc and La/Cr, and higher Cr/Th ratios than sediments derived from granitic sources. REE and other elements are enriched in the silt-size fraction, whereas they are diluted by quartz in the sand-size fraction.The size of the Eu/Eu* anomaly can be used as a stratigraphical correlation tool in the sedimentary record: Cretaceous rocks show a mean value of 0.9±0.1, whereas Tertiary rocks have a mean value of 2.9±0.3. The Eu anomaly in Quaternary and modern sediments ranges from 0.5 to 0.8.     

前寒武纪沉积岩地球化学特征及其对地壳演化的指示意义

本文介绍了运用前寒武纪沉积岩地球化学特征推断地球早期地壳的组成、增生历史及太古—元古宙界面构造性质突变问题,这已成为国际前寒武纪地质研究的前沿课题,并已相继在世界典型的前寒武纪低级区及部分高级区开展了这一方面的研究工作,取得了一系列重要进展。     

羌塘盆地那底岗日地区布曲组碳酸盐岩烃源岩稀土元素分布特征及意义

对采自羌塘盆地那底岗日地区布曲组碳酸盐岩烃源岩进行了稀土元素地球化学研究,分析结果表明:海相碳酸盐岩烃源岩稀土总量(∑REE)最大值75.21μg/g,最小值20.58μg/g,平均值为36.67μg/g.稀土元素北美页岩标准化后具有相对富集轻稀土,亏损重稀土的特点.布曲组碳酸盐岩烃源岩Ce/Ce*值为0.83～0.9...     

Sources of stream sediments in the granulite terrain of the Walawe Ganga Basin,Sri Lanka,indicated by rare earth element geochemistry

Thirty-eight samples of stream sediments draining high-grade metamorphic rocks in the Walawe Ganga (river) Basin, Sri Lanka, were analysed for their REE contents, together with samples of metamorphic suites from the source region. The metamorphic rocks are enriched in light REE (LREE) compared to heavy REE (HREE) and are characterised by high La/Lu ratios and negative Eu anomalies. The chondrite-normalised patterns for these granulite-grade rocks are similar to that of the average post-Archaean upper crust, but they are slightly enriched with La and Ce. The REE contents of the <63-μm fraction of the stream sediments are similar to the probable source rocks, but the other grain size fractions show more enriched patterns. The <63-μm stream sediments fraction contains lower total REE, more pronouncd negative Eu anomalies, higher Eu_N/Sm_N and lower La _N/Lu_N ratios relative to other fractions. The lower La _N/Lu_N ratio is related to the depletion of heavy minerals in the <63-μm fraction. The 63–125-μm and 125–177-μm grain size fractions of sediments are particularly enriched in LREE (average ΣLREE=2990 μg/g and 3410 μg/g, respectively). The total HREE contents are surprisingly uniform in all size fractions. However, the REE contents in the Walawe Ganga sediments are not comparable with those of the granulite-grade rocks from the source region of the sediments. The enrichment of REE is accounted for by the presence of REE containing accessory mineral phases such as zircon, monazite, apatite and garnet. These minerals are derived from an unknown source, presumably from scattered bodies of granitic pegmatites.     

Rare earth elements in Huronian (Lower Proterozoic) sedimentary rocks: Composition and evolution of the post-Kenoran upper crust

The Huronian sequence (Lower Proterozoicl. north of Lake Huron, contains tillites and abundant fine-grained sedimentary rocks. Analyses of rare earth elements (REE) in the matrix of tillite samples from the Gowganda Formation (~ 2.3 Gal is considered to be a reasonable estimate of upper crustal REE abundances for the region north of Lake Huron at the time of Gowganda deposition. The average is characterized by a moderately steep pattern (σLREEσHREE = 9.1) and a slight negative europium anomaly ($\text{Eu}\text{Eu1}\text{= 0.89}$). This pattern is similar to estimates of the composition of the surface of the Canadian Shield and is intermediate between estimates of typical Archean and post-Archean sedimentary rocks. REE patterns for framework granitoid clasts from the tillite suggest that K-rich granites, which were apparently unimportant in the formation of Archean sedimentary rocks, were abundant in the source regions of the Gowganda Formation. This may explain the intermediate nature of the Gowganda pattern.Comparison of the tillites and associated Gowganda mudstones suggests that previous estimates of upper crustal REE abundances, which were based on the analyses of fine-grained sedimentary rocks, may be systematically high. Relative distributions, however, are the same.Analyses of mudstones from the McKim. Pecors. Serpent Gowganda Lorrain and Gordon Lake Formations suggest rapid evolution in the composition of the exposed upper crust at the close of the Kenoran orogeny. REE patterns at the base of the Huronian are similar to typical Archean sedimentary rocks. REE characteristics change up section: patterns at the top resemble typical post-Archean sedimentary rocks.It is inferred that an essentially episodic change from an early exposed upper crust dominated by a tonalite-greenstone suite to one approximating granodioritic composition is recorded in Huronian sedimentary rocks. A deviation from the evolutionary trend of the Huronian, documented in the Gowganda Formation, may be related to the glacial origin of the Gowganda.     

Rare earth elements in tektites

Four moldavites and one sample each of an australite, billitonite, indochinite, philippinite, thailandite, Ivory Coast tektite, bediasite and a georgianite were analyzed using neutron activation analysis for La, Ce, Sm, Eu, Tb, Yb and Lu. The REE abundances resemble those of sedimentary rocks. Most of the tektites display a depletion of Eu, a characteristic feature of mature Phanerozoic continental sedimentary rocks. However, the Ivory Coast tektite and georgianite are relatively enriched in Eu, possibly due to the presence of plagioclase-rich source rocks.     

Geochemistry of the early proterozoic metasedimentary rocks of the alligator rivers region,Northern Territory,Australia

The early Proterozoic metasedimentary sequence of the Alligator Rivers Region (a part of the Pine Creek Geosyncline) in the Northern Territory, Australia, overlies an Archaean granitoid basement. Early Proterozoic sedimentary sequences, in general, record important changes in the composition of the upper continental crust about the Archaean-Proterozoic boundary. However, the geochemistry of only a few of these sequences has been documented. The geochemistry of the early Proterozoic succession in the Alligator Rivers Region is reported here and the results are interpreted in terms of differences between the stratigraphic units, their provenance—particularly in relation to crustal evolution, and their subsequent metamorphism and weathering.Clastic metasedimentary rocks throughout the Alligator Rivers Region have a remarkably uniform major and trace element geochemistry. The Kakadu Group and upper member of the Cahill Formation are relatively more enriched in SiO₂ and correspondingly more depleted in Al₂O₃ than the rest of the sequence, reflecting the greater dominance of metapsammitic assemblages. The lower member of the Cahill Formation, which hosts the major U deposits of the Alligator Rivers Region, and the metasedimentary sequence in general, exhibit no significant enrichment in U above normal background values. Rare earth element (REE) concentrations in the metasedimentary units within the Alligator Rivers Region are uniform, though in detail there are some important differences within and between formations.The composition of the early Proterozoic clastic metasediments in the Alligator Rivers Region is consistent with the composition of similar material of the same age from other areas, and supports current ideas on crustal evolution. The Alligator Rivers metasediments are enriched in Si and K, and depleted in Mg, Ca, and Na relative to the Archaean average for clastic sedimentary rocks, and their REE geochemistry resembles typical post-Archaean sedimentary rocks having a light REE enriched pattern and a distinct Eu/Eu1 depletion compared to typical Archaean sediments. However, the REE data indicate that two compositionally distinct sources are involved in the provenance of the Kakadu Group, and possibly the lower member of the Cahill Formation, where two types of REE patterns can be distinguished on their HREE concentration and Eu/Eu1 anomaly.     

Rare earth elements in granitic rocks

The younger granites in Finland contain more REE than the older ones. In the youngest, postorogenic rapakivi granites, the total REE concentration is highest, the light REE are more enriched, and the negative Eu anomaly is more pronounced than in the older granites. The enrichment of the light REE, the anomalous behavior of the extreme elements (La, Ce, and Lu) in normalized graphs, and the depletion of Eu indicate the degree of differentiation the rock has undergone. These features are usually more pronounced in large, homogeneous granites than in metamorphic or volcanogenic rocks. Silicic vein rocks usually contain less REE than the granites proper; the distribution pattern in many is as in granites, but in some the heavy elements are more enriched. The positive Eu anomaly in Precambrian metamorphic rocks is tentatively attributed to metamorphic differentiation and to the secretion of silicic material from the host rock.     

REE and Trace Element Geochemistry of Yinachang Fe-Cu-REE Deposit, Yunnan Province, China

1IntroductionThebehaviorsoftherare earthelements (REE)duringmagmatism ,metamorphismandmeta somationareofgreatgeologicalinterestbecauseoftheirapplicationsingeochronologyandgeochemi caltracing (e .g .reviewsbyFaure ,1 986;LipinandMckay ,1 989) .Becauseoftheirsimilargeo chemicalbehaviorsandlowsolubilitiesinwater,theREEshaveprovedthemselvestobeapowerfultoolforthecharacterizationofprovenanceswhenappliedtosedimentaryrocks (McDanieletal.,1 994) .Althoughtheirbehaviorsunderhydrothermalconditionsar…     

西秦岭造山带徽成盆地早白垩世地层物源综合分析

徽成盆地是西秦岭造山带内一个具有代表性的盆地,保留较完整的地层记录.早白垩世田家坝组、周家湾组和鸡山组为一套砂砾岩沉积组合序列.本文通过对早白垩世砂岩的古水流恢复、砾石成分与含量、重矿物和地球化学分析,对沉积岩物源区特征和原型盆地进行探讨.古水流恢复和砾石成分统计表明,沉积物主要是近源堆积,主要来自于盆地南缘和北部.重矿物研究结果表明,早白垩世砂岩母岩以岩浆岩为主,并有少量变质岩/沉积岩.地球化学分析表明,早白垩世砂岩为成熟度较低的硬砂岩和长石/岩屑砂屑岩.稀土元素标准化配分曲线呈现轻稀土富集、重稀土平坦和弱Eu负异常特征.砂岩物源区组成判别图研究表明,早白垩世砂岩的物源区主要出露长英质火山岩.砂岩源区构造环境判别图解及特征指数分析表明,早白垩世砂岩源区主要形成于大陆岛弧和活动大陆边缘.结合区域资料和前人研究,表明早白垩世徽成地区发育走滑拉分盆地.     

Geochemical Constraints of Sediments on the Provenance, Depositional Environment and Tectonic Setting of the Songliao Prototype Basin

The geochemistry of sediments is primarily controlled by their provenances, and different tectonic settings have distinctive provenance characteristics and sedimentary processes. So, it is possible to discriminate provenances, depositional environments and tectonic settings in the development of a sedimentary basin with the geochemistry of the clastic rocks. The analytical results of the present paper demonstrate that sediments in the Songliao prototype basin are enriched in silica (SiO2=66.48-80.51 %), and their ΣREE are 30-130 dmes of that of chondrite with remarkable Eu anomalies. In discriminating diagrams of Eu/Eu vs eeeeeREE and (La/Yb)N vs ΣREE, most samples locate above the line Eu/ Eu=l, on the right of the line Eu/Eu/ΣREE=1 and under the line La/Yb)N/eeeeeREE=1/8, which indicates that the depositional environment of sediments in the basin was oxidizing. In addition, variations of MgO, TiO2, A12O3, FeO+Fe2O3, Na2O and CaO vs SiO2 reflect a tendency of increasing mineral maturity of sediments