微量元素分布揭示腕足化石壳体原始信息保存现状

以产于四川龙门山地区泥盆系观雾山组的有铰纲腕足化石Ｉｎｄｅｐｅｎｄａｔｒｙｐａ ｌｅｍｍａ Ｃｈｅｎ为研究对象,利用激光熔样等离子质谱（ＬＡ－ＩＣＰ－ＭＳ）对其壳体棱柱层中Ｆｅ、Ｍｇ、Ｍｎ、Ｎａ、Ｂａ和Ｓｒ六种微量元素进行了就位分析。它们在壳体横切面中的对称分布特征总体上与壳体增生方式和过程相一致,表明壳体的绝大部分未经成岩作用的改造。与常用的结构判据、阴极发光判据和微量元素含量判据相比较,微量元     

Trace element distribution in Chilean ignimbrites

The geochemistry of Chilean ignimbrites is discussed in terms of major and trace elements. The variation in the major elements and in the distribution of Ba, Co, Cu, Ga, Pb, Sn, Sr, V, and Zr with the differentiation factor (1/3Si+K)-(Ca+Mg) has been studied. The general trend is that characteristic of calc-alkaline rhyolite-dacite-andesite associations. Exceptionally high values of copper reported and high values of Sn and Zr provide further evidence of the anatectic origin of these ignimbrites.     

Trace element distribution in Central Dabie eclogites

Coesite-bearing eclogites from Dabieshan (central China) have been studied by ion microprobe to provide information on trace element distributions in meta-basaltic mineral assemblages during high-pressure metamorphism. The primary mineralogy (eclogite facies) appears to have been garnet and omphacite, usually with coesite, phengite and dolomite, together with high-alumina titanite or rutile, or both titanite and rutile; kyanite also occurs occasionally as an apparently primary phase. It is probable that there was some development of quartz, epidote and apatite whilst the rock remained in the eclogite facies. A later amphibolite facies overprint led to partial replacement of some minerals and particularly symplectitic development after omphacite. They vary from very fine-grained dusty-looking to coarser grained Am + Di + Pl symplectites. The eclogite facies minerals show consistent trace element compositions and partition coefficients indicative of mutual equilibrium. Titanite, epidote and apatite all show high concentrations of REE relative to clinopyroxene. The compositions of secondary (amphibolite facies) minerals are clearly controlled by local rather than whole-rock equilibrium, with the composition of amphibole in particular depending on whether it is replacing clinopyroxene or garnet. REE partition coefficients for Cpx/Grt show a dependence on the Ca content of the host phases, with D _REE ^Cpx/Grt decreasing with decreasing D _Ca . This behaviour is very similar to that seen in mantle eclogites, despite differences in estimated temperatures of formation of 650–850 °C (Dabieshan) and 1000–1200 °C (mantle eclogites). With the exception of HREE in garnet, trace elements in the eclogites are strongly distributed in favour of minor or accessory phases. In particular, titanite and rutile strongly concentrate Nb and Zr, whilst LREE–MREE go largely into epidote, titanite and apatite. If these minor/accessory minerals behave in a refractory manner during melting or fluid mobilisation events and do not contribute to the melt/fluid, then the resultant melts and fluids will be strongly depleted in LREE–MREE. Received: 11 February 1999 / Accepted: 31 January 2000     

Trace element distribution coefficients in alkaline series

Mineral/groundmass partition coefficients for U, Th, Zr, Hf, Ta, Rb, REE, Co and Sc have been systematically measured in olivine, clinopyroxene, amphibole, biotite, Ti-magnetites, titanite, zircon and feldspars, in basaltic to trachytic lavas from alkaline series (Velay, Chaîne des Puys: Massif Central, France and Fayal: Azores). Average partition coefficients are denned within the experimental uncertainty for limited compositional ranges (basalt-hawaiite, mugearites, benmoreite-trachyte), and are useful for trace element modelling. The new results for U, Th, Ta, Zr and Hf partition coefficients show contrasting behaviour. They can thus be used as “key elements” for identifying fractionating mineral phases in differentiation processes (e.g. Ta and Th for amphibole and mica).Partition coefficient may be calculated using the two-lattice model suggested by Nielsen (1985). Such values show a considerably reduced chemical dependence in natural systems, relative to weight per cent D values. The residual variations may be accounted for by temperature or volatile influence. This calculation greatly enhances modelling possibilities using trace elements for comparing differentiation series as well as for predicting the behaviour of elements during magmatic differentiation.     

Evaluation of cold-water carbonates as a possible paleoclimatic indicator

The common belief currently shared by many geoscientists concerning the climatic interpretation of limestones is that a warm-water environment is essential. This concept is not necessarily true because the rate and extent of terrigenous sediment dilution, rather than water temperature, is the primary factor determining whether or not a limestone forms at nearshore or continental shelf depths. Because carbonate productivity is lowest in cold climates, however, CaCO₃ abundance and the thickness of carbonate accumulations tend to be least at high latitudes. In this regard present-day continental shelves and beaches offer a poor model for comparing cold-water and warm-water carbonates because of the generally emergent continental tectonic framework, recent eustatic sea-level changes, and the presence of ice caps at the modern poles.Typically, the influence of climate on non-reef continental shelf and beach environments cannot be clearly distinguished by the presence or absence of major taxonomic groups. Faunal diversity and equitability are more sensitive in this regard. The absence of shelf-depth inorganic carbonate precipitates, micrite envelopes, and peloids may also point to the cold-water origin of a rock. Skeletal mineralogy and oxygen isotopes of certain unrecrystallized carbonates may be good paleoclimatic indicators; however, trace elements and physical-textural attributes of the carbonate fraction are probably temperature insensitive.Previous studies of high-latitude continental shelves have concentrated merely on the abundance of calcareous material and there is seemingly a disproportionate amount of information with respect to low-latitude carbonate studies. Further research on cold-water carbonates may open up new avenues for alternative paleoenvironmental and paleoclimatic interpretations.     

Trace element and PGE distribution in layered ferromanganese crusts

A collection of layered ferromanganese ores (27 samples) from the Atlantic and Pacific oceans was studied. Trace element and PGE contents were determined layer-by-layer (up to 10 microlayers) in 13 of these samples.The trace, rare earth, and platinum group element distributions, including their layer-to-layer variations, were compared in hydrogenic and hydrothermal crusts from different regions. It was found that the main PGE variations (by a factor of 10–50) are related to their layer-to-layer variations within a given ore field.The distributions of PGE and trace elements are strongly heterogeneous, which is related, first, to different contents of the elements in the layers of different age in ferromanganese crusts (FMC) and, second, to the observed regional heterogeneity and influence of hydrothermal fluids. Geochemical data indicate that CFC formation was mainly caused by the hydrochemical precipitation of material from seawater. This process was accompanied by diagenetic phenomena, water-rock interaction, and influence of volcanic and hydrothermal sources.     

Chemostratigraphy of Neoproterozoic carbonates: implications for 'blind dating'

The δ¹³C_carb and ⁸⁷Sr/⁸⁶Sr secular variations in Neoproteozoic seawater have been used for the purpose of 'isotope stratigraphy' but there are a number of problems that can preclude its routine use. In particular, it cannot be used with confidence for 'blind dating'. The compilation of isotopic data on carbonate rocks reveals a high level of inconsistency between various carbon isotope age curves constructed for Neoproteozoic seawater, caused by a relatively high frequency of both global and local δ¹³C_carb fluctuations combined with few reliable age determinations. Further complication is caused by the unresolved problem as to whether two or four glaciations, and associated negative δ¹³C_carb excursions, can be reliably documented. Carbon isotope stratigraphy cannot be used alone for geological correlation and 'blind dating'. Strontium isotope stratigraphy is a more reliable and precise tool for stratigraphic correlations and indirect age determinations. Combining strontium and carbon isotope stratigraphy, several discrete ages within the 590–544 Myr interval, and two age-groups at 660–610 and 740–690 Myr can be resolved.     

Trace element distribution and risk assessment in South Indian surface waterways

The concentrations of 27 major and trace elements are determined in surface water samples collected from 48 sites of diverse waterways in four states (Tamil Nadu, Kerala, Karnataka, and Telangana) of South India. The aims of this study are to identify the element distribution, comparatively assess the pollution risk, and evaluate human health risks related to diverse waterways in the study area. The results indicate that elements such as Cr, Se, As, Fe, and Mn are the major pollutants, as their concentrations exceeded the acceptable national and international water quality standards in several sites of Ennore, Adyar, Cooum, Periyar, and Vrishabhavathi rivers. Furthermore, statistical analysis reveals that the Ennore, Adyar, Cooum, Periyar, and Kaveri river basins are affected by various anthropogenic activities, leading to moderate-to-high pollution by As, Cr, Mn, Fe, and Se. Potential pollution sources are industrial waste, sewage intrusion, paint industry waste, and automobile runoff. Overall, the investigated sites are categorized into three major groups: highly, moderately, and least polluted. Risk on human health by metals is then evaluated using hazard quotients (HQs) and carcinogenic risk evaluation; the results indicated that As with HQ >1 is the most hazardous pollutant, which could lead to non-carcinogenic and carcinogenic concerns, particularly in children. This study helps in establishing pollutant loading reduction goal and the total maximum daily loads and consequently contributes to preserving public health and developing water conservation strategies.     

Isotope stratigraphy of Neoproterozoic cap carbonates in the Araras Group, Brazil

The Neoproterozoic carbonate sequence on the southeastern border of the Amazon Craton is divided into three lithostratigraphic units: a basal cap dolomite, an intermediate limestone, limestone-mudstone unit, and an upper dolarenite-dolorudite unit. Sections of the cap-carbonate were measured from the inner shelf to the outer shelf. Carbon isotope ratios (relative to PDB) vary between − 10.5 and − 1.7‰ in cap dolomite, and between − 5.4 and + 0.1‰ in laminated limestone and mud-limestone. Limestones and mud-limestones exhibit ⁸⁷Sr/⁸⁶Sr ratios ranging from 0.70740 to 0.70780. A comparative isotope stratigraphy between the inner-shelf and the middle-shelf basin shows differences in carbon isotope ratios: The cap dolomite and limestones have lower δ¹³C ratios on the border of the basin (inner shelf) than in the middle shelf of the basin. These lower values can be related to shallower environmental conditions and to a stronger influence of the continental border. The ⁸⁷Sr/⁸⁶Sr ratios are the same in both areas, and are consistent with seawater composition at around 600 Ma.     

Geochemical signature of the Cenomanian to Eocene rocks in Israel -a palaeoenvironmental indicator

Distinctive trace-metal concentrations characterize Cenomanian to Eocene marine carbonates from Israel. The Cenomanian-Turonian platform carbonates, including clayey formations, exhibit low average values ranging between 2 and 29 ppm for Zn, Cr, V, Ni, Cu, U and Co. The Santonian-Campanian and Early to Middle Eocene marine chalks show higher average concentrations of these trace-metals ranging between 3 and 56 ppm. The highest average concentrations of these metals (5–118 ppm) are found in the Maastrichtian and in the Palaeocene marine chalks and marls. The possible relationship between these metal background levels and the lithology, the biogenic productivity, the organic matter content, the iron oxide concentration, the rate of sedimentation of the studied time-rock units as well as the palaeogeographical changes are discussed. The extent of the exposed palaeo-landmasses due to tectonics, the intensity of weathering conditions and the detritus supply into the basin, control primarily the iron and trace-metal content in the studied sediments.     

Copepod distribution as an indicator of epikarst system connectivity

The distribution of 27 copepod species was determined in 35 drips in four Slovenian caves (Dimnice, Postojna Planina Cave System, Škocjanske Jame, Županova Jama), and of ten species from 13 drips in one US cave (Organ Cave, West Virginia). The dripping water comes from epikarst, the skin of karst. A significant fraction of the copepod species found (nine species in Slovenia and three in West Virginia) occurred over a maximum linear extent of 100 m. These and other localized distributions probably resulted from colonization of epikarst by an ancestral surface population in a single location, with subsequent lateral spread in the direction of epikarst flow. This suggests that the distribution of copepods could potentially be used to trace major flow paths in epikarst without the need for the injection of dyes or other tracers.

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Résumé La distribution de 27 espèces de copépodes a été déterminée dans 35 zones de percolation de quatre grottes slovènes (Dimnice, système de grottes Postojna Planina, Škocjanske Jame, Županova Jama) et grace à dix espèces de 13 zones de percolation d’une grotte des Etats-Unis (Grotte Organ, Ouest de la Virginie). L’eau de percolation provient de l’épikarst, la partie supérieure du karst. Une fraction importante des espèces de copépodes trouvées (9 espèces en Slovénie et 3 dans l’Ouest de la Virginie) s’étendait sur une longueur maximum de 100 m. Ces dernières ainsi que d’autres distributions localisées étaient probablement issues de la colonisation par une population ancienne de surface, de zones localisées de l’épikarst, puis par une dispersion latérale dans la direction de l’écoulement dans l’épikarst. Ceci suggère que la distribution des copépodes pourrait potentiellement être utilisée pour identifier les principales trajectoires d’écoulement dans l’épikarst, sans utiliser l’injection de colorants ou d’autres traceurs.

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Resumen Se determina la distribución de 27 especies de copépodo en 35 gotas de cuatro cavernas de Eslovenia (Dimnice, Sistema de Caverna Planina Postojna, Jame Škocjanske, y Jama Županova), y de diez especies en 13 gotas de una caverna de Estados Unidos (Caverna órgano, Virginia Occidental). El agua que gotea se deriva del epikarst, la piel del karst. Una fracción significativa de las especies de copépodos encontradas (9 especies en Eslovenia y 3 en Virginia Occidental) se presentaron en una extensión linear máxima de 100 m. Estas y otras distribuciones localizadas resultaron probablemente de colonización del epikarst por poblaciones superficiales ancestrales en una sola localización, con una expansión lateral subsiguiente en la dirección de flujo epikárstico. Esto sugiere que la distribución de copépodos podría tener un uso potencial para trazar rutas de flujo principales en epikarst sin tener la necesidad de inyectar colorantes u otros trazadores.

     

Trace element abundances in andesites

Abundance data for Cs, Rb, Tl, Ba, Pb, Sr, the rare earths, Th, U, Zr, Hf, Sn, Nb, Mo, Mn, Cu, Co, Ni, Sc, V, Cr, Ag, Sb and the major elements are reported for two andesites and a dacite from Saipan, nine andesites and a dacite from Bougainville and two andesites from Fiji. The Saipan rocks are low-K varieties and contain notably low abundances of Rb, Ba, Th and U and have rare earth patterns subparallel to chondritic patterns. The Bougainville andesites include low-Si and high-K varieties which have higher concentrations of the large cations. The Fijian samples are close to the average circum-Pacific andesite and have rareearth patterns sub-parallel to those of sedimentary rocks.All the andesites contain characteristically low (< 20 ppm) values for Ni and have Ni/Co ratios < 1, and V/Ni ratios > 10.These data preclude derivation of calc-alkaline rocks by mixing of upper crustal material or by fractional crystallisation from basaltic parents. A two stage model is proposed involving sea-floor spreading and transportation of the oceanic crust down the dipping seismic plane into the mantle where it is remelted to form andesites.     

An evaporitic facies in Neoproterozoic post-glacial carbonates: The Gifberg Group, South Africa

A geological study of the hitherto poorly described Neoproterozoic Gifberg Group, with emphasis on lithogeochemistry and O, C and Sr isotopic composition of the carbonate-dominated Widouw Formation (Vredendal Outlier, westernmost South Africa) revealed that the entire group is an equivalent of the relatively well constrained Port Nolloth Group in the external, paraautochthonous part of the Pan-African Gariep Belt further north. Thus, the Vredendal Outlier can be regarded as the southern extension of the Port Nolloth Zone. Two diamictite units are recognised in the Vredendal Outlier, which can be correlated respectively with the c. 750 Ma Kaigas Formation diamictite and the 583 Ma, syn-Gaskiers Numees Formation diamictite in the Gariep Belt proper. The dominating carbonate unit in the studied area is post-glacial with respect to the older of the two diamictite units. The combined textural, structural and geochemical evidence suggests that parts of the variably dolomitised limestone succession represent former evaporite beds. Sedimentation in a restricted, very shallow and proximal basin led to a wide range in C isotope ratios (δ¹³C_PDB from − 4.2 to + 4.8‰), very high Sr concentrations (derived from original anhydrite) and initial ⁸⁷Sr/⁸⁶Sr ratios that are significantly higher (0.70785) than those of coeval seawater. As C and Sr isotopes are commonly used for chemostratigraphic correlation, and high Sr concentrations in Neoproterozic carbonates are often interpreted as evidence of former aragonite, the findings of this study should be used as warning against uncritical use of geochemical and isotopic parameters for describing ancient seawater composition. Thus C and Sr isotope ratios alone in Neoproterozoic carbonates may be less powerful proxies of ancient seawater composition, and high Sr contents are not necessarily indicative of an “aragonite sea”, as previously inferred.     

Trace element distribution in sphalerites from Pb−Zn-ore occurrences of the Eastern Alps

Summary With secondary ion mass spectrometry as a new analytical method, which grants trace element determination in the microscale at the ppma-level and below, the abundance, distribution, and correlation of Mn, Fe, Cu, Ga, Ge, As, Ag, Cd, In, Sb, Hg, Tl, and Pb in sphalerites from different occurrences of the Eastern Alps were studied. On the whole the trace element characteristics known from average analyses is confirmed also in the microscale, but in different crystallization stages of one and the same deposit considerable variations can be found. Also in the correlation of elements great differences exist. The eminent inhomogeneity in trace element distribution is an indication for the presence of microcrystals. Thus the assumed Tl-content of already mentioned Pb-As-S-microphases has been confirmed in these investigations.

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Mikrobereichs-Spurenelementcharakterisierung von Zinkblenden aus ostalpinen Pb–Zn-Vorkommen

Zusammenfassung Mit der Sekundärionen-Massenspektrometrie als neuer analytischen Methode, die die Spurenbestimmung im Mikrobereich bis in den ppma-Bereich und darunter gestattet, wurde Anwesenheit, Verteilung und Korrelierbarkeit von Mn, Fe, Cu, Ga, Ge, As, Ag, Cd, In, Sb, Hg, Tl und Pb in Zinkblenden aus verschiedenen ostalpinen Vorkommen untersucht. Im großen und ganzen wird die aus Durchschnittsanalysen bekannte generelle Spurenelementcharakteristik auch im Mikrobereich bestätigt, doch sind in verschiedenen Kristallisationsphasen von Proben ein und derselben Lagerstätte beträchtliche Variationen festzustellen. Weiters können auch in der Korrelierbarkeit der Begleitelemente große Unterschiede gefunden werden. Die ausgeprägten Inhomogenitäten in der Elementverteilung können auch Hinweise für das Vorliegen kleinster Mikrokristallausscheidungen liefern. So konnte der vermutete Tl-Gehalt der bereits bekannten Pb-As-S-Mikrophasen bestätigt werden.

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With 7 Figures

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The abbreviations, ppma for atomic parts per million, and ppm for parts per million, will be used throughout.     

Trace element distribution in US groundwaters: a probabilistic assessment using public domain data

A large database of dissolved-fraction groundwater concentrations for Ag, As, Ba, Be, Cd, Co, Cr, Cu, Hg, Ni, Pb, Sb, Se, Tl, Sn, V and Zn was constructed using public domain data. Data analysis techniques for multiply-censored sample populations were used to extract salient information regarding sample populations from the raw data. The results of this work show that trace element concentrations are approximately log-normally distributed. Median values for <90% censored sample populations range from 0.2 to 35 μg l⁻¹. Minimum to maximum concentrations range as high as 7 orders of magnitude for certain elements (e.g. Zn). This work provides a rapid, cost-effective screening tool for evaluating groundwater quality based on observed trace element concentration data.     

Trace element distribution in mineral separates of the Allende inclusions and their genetic implications

Concentrations of the REE, Sc, Co, Fe, Zn, Ir, Na and Cr were determined by instrumental neutron activation and mass spectrometric isotope dilution analysis for mineral separates of the coarseand fine-grained types (group I and II of Martin and Mason's classification) of the Allende inclusions.These data, combined with data on mineral/liquid partition coefficients, oxygen isotope distributions and diffusion calculations, suggest the following: (1) Minerals in the coarse-grained inclusions (group I) crystallized in a closed system with respect to refractory elements. On the other hand, differences in oxygen isotope distributions among minerals preclude a totally molten stage in the history of the inclusion. Group I inclusions were formed by rapid condensation (either to liquid or solid) in a supercooled solar nebula; extrasolar pyroxene and spinel dust were included but not melted in the condensing inclusions, thus preserving their extrasolar oxygen isotope composition. REE were distributed by diffusion during the subsequent heating at subsolidus temperatures; because oxygen diffuses much more slowly at these temperatures, the oxygen isotope anomalies were preserved. (2) The fine-grained (group II) inclusions were also formed by condensation from a super-cooled nebular gas; however, REE-rich clinopyroxene and spinel were formed early and REE-poor sodalite and nepheline were formed later and mechanically mixed with clinopyroxene and spinel to form the inclusions. The REE patterns of the bulk inclusions and the mineral separates are fractionated, indicating that REE abundances in the gaseous phase were already fractionated at the time of condensation of the minerals. (3) Pre-existing Mg isotope anomalies in the coarse-grained inclusions must have been erased during the heating stage thus resetting the ²⁶Al-²⁶Mg chronometer.     

青海省同德县加吾金多金属矿区微量元素在地质体中的分布特征

青海省同德县加吾矿区处在东昆仑-西秦岭衔接部位的青海南山冒地槽带。区内地层以中三叠统隆务河群为主,构造以NNW向压扭性断裂为主,除曲如沟花岗闪长岩体外,其余以花岗斑岩脉产出。区内除Cr、Mo外,大部分元素较为富集,其中Au、As、Sb、Bi、Ag富集程度较高,尤其在破碎带、褐铁矿化石英脉和花岗斑岩脉中,Au、As、Sb、Bi、Pb等元素的含量比其余几种岩性高1-3个数量级。通过因子分析和建立地球化学模式图,客观的反映了区内各地质体中微量元素的分布规律。     

Organotemplate structures in sedimentary manganese carbonates of the Neoproterozoic Penganga Group, Adilabad, India

Manganese carbonates interstratified with bedded chert in the Chanda Limestone of the Neoproterozoic Penganga Group at Adilabad, south India, have been studied for possible evidence that microbiota played a role in the mediation of early diagenetic Mn-carbonate formation in Precambrian marine sedimentary successions. The manganese carbonate and chert beds occur within a below wave base, deep-water distally steepened ramp succession. High resolution SEM petrography of the manganese carbonates revealed two basic morphologies-spherical to oval-cylindrical shaped microconcretions, and tubular to irregular, elongated, film-like microstructures. Infolded filmy to hollow tubular strand-like internal morphologies of the spherical to oval-cylindrical shaped microconcretions suggest their microbial affinity. The tubular and film morphologies with mesh-like interconnections closely resemble architectures of microbial extracellular polymeric substance (EPS). Mineralization took place on these organotemplates by the process of permineralization as well as replacement in an early diagenetic pore-water environment with reduction of higher manganese oxy-hydroxides by organic matter and consequent increase in dissolved carbonate.     

北京十三陵地区中—新元古界碳酸盐岩Pb—Pb年龄研究

对北京十三陵地区中一新元古界碳酸盐岩进行了系统地采样和207pb/204pb-206Pb/204Pb年龄测定.共测定了63个样品(大部分样品采取两种溶解方式),得到中元古界雾迷山组第三段的207Pb/204pb-206Pb/204pb等时线年龄为1373±92Ma(95%置信度误差,下同,MSWD＝4.7),杨庄组为1488±55Ma(MSWD＝14),高于庄组第三段为1608±74Ma(MSWD＝8.1).这些年龄数据与目前已有地质记录相吻合.串岭沟组的碳酸盐相的206Pb/204Pb-207Pb/204Pb未构成等时线,但全岩的206Pb/204pb-207Pb/204Pb比碳酸盐相具有更明显的线性趋势,其原因尚待进一步研究.另外,根据同一个样品用稀盐酸溶解和用氢氟酸加硝酸混合酸溶解的铅同位素比值的接近的现象,显示碳酸盐岩中的硅质没有陆源的特征,是沉积盆地中的产物.     

Trace element distribution patterns and their relationship to the crystallization of granitic melts

The distribution of Ba, Rb and Sr during crystallization of a granitic melt is examined in a number of theoretical models. The modes of crystallization considered are perfect fractional crystallization, perfect equilibrium crystallization, and an intermediate mode, incremental equilibrium crystallization. The effect of the degree of separation of cumulus minerals from melt during crystallization is also considered. Perfect fractional and incremental equilibrium crystallization (with small increments) are broadly similar, but differ in the final stages of crystallization in that the latter mode defines a finite trace element composition for the last solid. The effect of intercumulus melt in both modes of crystallization imparts a ‘liquid’ character to the solids, and suppresses the degree of enrichment of Rb and depletion of Ba and Sr in late solids and melts.Examination of trace element data for the Acid Phase of the Bushveld Igneous Complex in the light of these models suggests that these granites represent a suite of cumulate rocks, containing relatively large amounts of intercumulus melt.