The significance of the Variscan orogeny in the Świętokrzyskie Mountains (Mid Polish Uplands)

The witokrzyski Horst, created during the Laramide phase, is situated in the central part of the Mid Polish Uplands. It is composed of folded Paleozoic rocks partly covered by Mesozoic sediments. In this area two tectonostratigraphic units can be distinguished: the Kielce Unit to the S and the ysogóry Unit to the N.They are separated by the WNW-ESE trending witokrzyski overthrust, along which the rocks of the ysogóry Unit have been transported towards the south over the Kielce Unit. Thrusting took place after the Early Carboniferous, and before the Permian. As it is concluded from the differences of their stratigraphic and tectonic evolution, these two juxtaposed units of the witokrzyskie Mts were originally set at a considerable distance one from another. The present area of these units developed in two blocks of crust differing in structure, thickness and evolution. It is proposed that the important fault situated north of the witokrzyski overthrust and accompanied by magmatic phenomena could be a reactivation of a Variscan suture zone.

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Zusammenfassung Im Zentrum des Polnischen Mittelgebirges entstand während der laramischen Phase der witokrzyski Horst. Er besteht aus gefalteten Gesteinen, die zum Teil mit mesozoischen Ablagerungen bedeckt sind. Es lassen sich in diesem Gebiet zwei geologische Einheiten unterscheiden, die in Bau und Entwicklung wesentliche Unterschiede aufweisen: die Kielce-Einheit im S und die ysogóry-Einheit im N. Diese Einheiten werden von der WNW-OSO vorlaufenden witokrzyski-Überschiebung voneinander getrennt, an der die Gesteine des ysogóry-Einheit nach SW auf die gefalteten Ablagerungen der Kielce-Einheit überschoben worden sind. Dieser Vorgang erfolgte während der variszischen Orogenese, und zwar nach dem Unterkarbon und vor dem Oberen Perm.Die Unterschiede in der stratigraphischen und tektonischen Entwicklung der Kielce-Einheit und der ysogóry-Einheit deuten darauf hin, daß die beiden Einheiten vor der variszischen Gebirgsbildung weit voneinander entfernt gelegen haben: zwischen beiden lag im Unterkarbon ein tiefes Becken. Darauf deuten sowohl die im nördlichen Teil der Kielce-Einheit auftretenden bathypelagischen Ablagerungen aus dem Visé, als auch Spuren vulkanischer Tätigkeit.Die nördlich der witokrzyski-Überschiebung gelegene Störung, an der zahlreiche magmatische und hydrothermale Erscheinungen auftreten, ist wahrscheinlich das Relikt einer während der variszische Orogenese entstandene Suturzone.

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Résumé Le horst de Swietokrzyski, situé dans la partie centrale des «Uplands» de la Pologne moyenne, s'est formé au cours de la phase laramide. Il est constitué de roches paléozoïques plissées partiellement recouvertes de sédiments mésozoïques. Dans cette région, on distingue deux unités tectono-stratigraphiques: l'unité de Kielce au sud et celle de Lysogory au nord. Elles sont séparées par le charriage de Swietokrzyski, d'orientation WNW-ESE, suivant lequel les roches de l'unité de Lysogory ont été transportées vers le SW sur l'unité de Kielce. Ce charriage a eu lieu après le Carbonifère inférieur et avant le Permien. Les différences d'histoires stratigraphiques et tectoniques qui existent entre ces deux unités ainsi juxtaposées indiquent qu'elles devaient se trouver à l'origine à grande distance l'une de l'autre: elles étaient séparées au Carbonifère inférieur par un bassin profond. En témoignent les dépôts bathy-pélagiques viséens, ainsi que des traces d'activité volcanique dans la partie nord de l'unité de Kielce.La faille importante située au nord du charriage, faille jalonée par de multiples manifestations magmatiques et hydrothermales, est probablement la trace d'une zone de suture engendrée au cours de l'orogenèse varisque.

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Pravčice Rock Arch (Bohemian Switzerland National Park, Czech Republic) deterioration due to natural and anthropogenic weathering

The dominant factors affecting the development of weathering forms on the Prav?ice Rock Arch (PRA) (Bohemian Switzerland National Park, Czech Republic) are discussed, based on the in situ monitoring of weathering forms, as well as on laboratory studies of materials taken from this site. The in situ monitoring shows the progressive development of distinct weathering forms (delamination of case-hardened rock surfaces, cyclic efflorescence, and granular disintegration of exposed weakly cemented rock mass) in specific portions of the PRA, whose location is controlled by lithology, jointing/local hydrodynamics, and exposure to climatic factors. From the analysis of efflorescence, the dominance of sulphates is evident; particularly of gypsum and alums. However, the synergistic effects of the several salt species (that also include minor nitrates and chlorides) upon the mechanical disintegration of sandstone can be expected.     

Fluid inclusion and sulfur isotope thermometry of the Inkaya (Simav-Kütahya) Cu-Pb-Zn-(Ag) mineralization, NW TURKEY

The Inkaya Cu-Pb-Zn-(Ag) mineralization, located about 20 km west of the Simav (Kütahya-Turkey), is situated in the northern part of the Menderes Massif Metamorphics. The mineralization is located along an E-W trending fault in the Cambrian Simav metamorphics consisting of quartz-muscovite schist, quartz-biotite schist, muscovite schist, biotite schist and the Ar?kayas? formation composed of marbles. Mineralized veins are 30–35 cm in width. The primary mineralization is represented by abundant galena, sphalerite, chalcopyrite, pyrite, fahlore and minor amounts of cerussite, anglesite, digenite, enargite, chalcocite, covellite, bornite, limonite, hematite and goethite with gangue quartz. Fluid inclusion studies on the quartz samples collected from the mineralized veins indicate that the temperature range of the fluids is 235°C to 340°C and the salinities are 0.7 to 4.49 wt. % NaCl equivalent. The wide range of homogenization temperatures indicates that two different fluid generations were trapped in quartz. Sulfur isotope studies of the sulfide minerals showed that all of the δ ³⁴S values are between ?2.1 and 2.6 per mil. These values are a typical range for hydrothermal sulfide minerals that have sulfur derived from a magmatic source. Pyrite-galena and pyrite-chalcopyrite sulfur isotope fractionation is consistent with an approach to isotopic equilibrium, and calculated temperatures are 254.6 and 277.4°C for pyrite-galena and 274.7°C for pyrite-chalcopyrite. The microthermometric data and sulfur isotope thermometry indicate the existence of a hydrothermal fluid that circulated along the fault crossing the Simav metamorphics and Ar?kayas? formation. Fluid inclusion and sulfur isotope thermometry can be used in combination with ore petrographical and geological information to provide site-specific targets for meso-hypothermal metal concentrations.     

Constraining the marine strontium budget with natural strontium isotope fractionations (Sr/Sr∗, δSr) of carbonates, hydrothermal solutions and river waters

We present strontium (Sr) isotope ratios that, unlike traditional ⁸⁷Sr/⁸⁶Sr data, are not normalized to a fixed ⁸⁸Sr/⁸⁶Sr ratio of 8.375209 (defined as δ^88/86Sr = 0 relative to NIST SRM 987). Instead, we correct for isotope fractionation during mass spectrometry with a ⁸⁷Sr-⁸⁴Sr double spike. This technique yields two independent ratios for ⁸⁷Sr/⁸⁶Sr and ⁸⁸Sr/⁸⁶Sr that are reported as (⁸⁷Sr/⁸⁶Sr∗) and (δ^88/86Sr), respectively. The difference between the traditional radiogenic (⁸⁷Sr/⁸⁶Sr normalized to ⁸⁸Sr/⁸⁶Sr = 8.375209) and the new ⁸⁷Sr/⁸⁶Sr∗ values reflect natural mass-dependent isotope fractionation. In order to constrain glacial/interglacial changes in the marine Sr budget we compare the isotope composition of modern seawater ((⁸⁷Sr/⁸⁶Sr∗, δ^88/86Sr)_Seawater) and modern marine biogenic carbonates ((⁸⁷Sr/⁸⁶Sr∗, δ^88/86Sr)_Carbonates) with the corresponding values of river waters ((⁸⁷Sr/⁸⁶Sr∗, δ^88/86Sr)_River) and hydrothermal solutions ((⁸⁷Sr/⁸⁶Sr∗, δ^88/86Sr)_HydEnd) in a triple isotope plot. The measured (⁸⁷Sr/⁸⁶Sr∗, δ^88/86Sr)_River values of selected rivers that together account for ∼18% of the global Sr discharge yield a Sr flux-weighted mean of (0.7114(8), 0.315(8)‰). The average (⁸⁷Sr/⁸⁶Sr∗, δ^88/86Sr)_HydEnd values for hydrothermal solutions from the Atlantic Ocean are (0.7045(5), 0.27(3)‰). In contrast, the (⁸⁷Sr/⁸⁶Sr∗, δ^88/86Sr)_Carbonates values representing the marine Sr output are (0.70926(2), 0.21(2)‰). We estimate the modern Sr isotope composition of the sources at (0.7106(8), 0.310(8)‰). The difference between the estimated (⁸⁷Sr/⁸⁶Sr∗, δ^88/86Sr)_input and (⁸⁷Sr/⁸⁶Sr∗, δ^88/86Sr)_output values reflects isotope disequilibrium with respect to Sr inputs and outputs. In contrast to the modern ocean, isotope equilibrium between inputs and outputs during the last glacial maximum (10-30 ka before present) can be explained by invoking three times higher Sr inputs from a uniquely “glacial” source: weathering of shelf carbonates exposed at low sea levels. Our data are also consistent with the “weathering peak” hypothesis that invokes enhanced Sr inputs resulting from weathering of post-glacial exposure of abundant fine-grained material.     

The variability of δ34S and sulfur speciation in sediments of the Sulejów dam reservoir (Central Poland)

The study was carried out on the Sulejów dam reservoir (Central Poland). Water and sediment samples were collected between February and October 2006. Sulfur compounds in the sediment were chemically extracted and subjected to isotopic analysis.Large variability of SO₄²⁻ concentration in the water column (from 10.3 to 36.2 mg/dm³) and the isotopic composition of sulfur (δ³⁴S from 2.1 to 5.4‰) was observed. The main identified sources of SO₄²⁻ were watercourses, surface runoff, and phosphorus fertilizers.Both oxidized sulfur species (SO₄²⁻) and its reduced forms were found in sediments. Particular sulfur forms were characterized by large variations in both, concentrations and the isotopic composition of sulfur. SO₄²⁻ in the sediment and in the water column had different genesis. Bacterial oxidation of organic sulfur and its binding in SO₄²⁻ were observed in the sediment. Under reducing conditions, oxidized and organic sulfur is converted to H₂S which reacted with Fe or other metallic ions leading to metal sulfide precipitation. Monosulfides were shown to have a very low concentration, ranging up to 0.07 mg/g of sediment. The transformation of elemental sulfur from sulfides through their chemical oxidation occurred in the sediment.     

Investigating the influence of sulphur dioxide (SO2) on the stable isotope ratios (δC and δO) of tree rings

This study reports the influence of a 20th century pollution signal recorded in the δ¹³C and δ¹⁸O of absolutely dated tree rings from Quercus robur and Pinus sylvestris from southern England. We identify a correspondence between the inter-relationship and climate sensitivity of stable isotope series that appears to be linked to recent trends in local SO₂ emissions. This effect is most clearly exhibited in the broadleaved trees studied but is also observed in the δ¹³C values of the (less polluted) pine site at Windsor. The SO₂ induced stomatal closure leads to a maximum increase of 2.5‰ in the isotope values (δ¹³C). The combined physiological response to high pollution levels is less in δ¹⁸O than δ¹³C. The SO₂ signal also seems to be present as a period of reduced growth in the two ring-width chronologies. Direct, quantitative correction for the SO₂ effect represents a significant challenge owing to the nature of the records and likely local plant response to environmental pollution. Whilst it appears that this signal is both limited to the late industrial period and demonstrates a recovery in line with improvements in air quality, the role of atmospheric pollution during the calibration period should not be underestimated and adequate consideration needs to be taken when calibrating biological environmental proxies in order to avoid development of biased reconstructions.     

First outcomes in the definition of groundwater protection zones at the Viñales National Park (Cuba) and surrounding area

Due to the existence of several pollution hazards in the area and its surroundings, groundwater protection in the Viñales National Park has been defined as a priority task in its management plan for 5 years (2009–2013). Those hazards affect directly the surface waters and the karst nature of the territory allowing the contaminants to enter directly into the aquifers without any or at least small self-depuration processes. In turn, those processes can affect very large areas in a short time. In this paper several results of precedent studies related to the vulnerability, hazards, risk, and the mapping of the spatial variability of natural recharge are integrated in a GIS analysis. The methodology is based on the method of Jimenez-Madrid et al. which is slightly modified in this contribution. The analysis of hydrographs, chemographs, mathematical models and tracer tests is necessary for the definition of a response plan against any contamination events and for model validation, together with the incorporation of data related to the energetic responses from the aquifer systems to external forcing.     

Trace elements in Holocene sediments of the southern Doñana National Park (SW Spain): historical pollution and applications

The multidisciplinary analysis of core sediments from Doñana National Park, south Spain, permits to delimitate both the paleoenvironmental changes and the geochemical evolution of this area during the Holocene. In a first phase (10–6.5 kyr cal), this area was occupied by freshwater/brackish marshes with periodical alternation of dry periods and humid intervals. In a second phase, these marshes were inundated during the Flandrian transgression (~6.5 kyr cal), with the deposition of bioclastic sands. The third phase (6.5–3.6 kyr cal) is characterized by the transition to an old lagoon, with unpolluted, bottom sediments. The geochemical concentrations of these clayey sediments can be used as a geochemical background for present-day and future environmental evaluations of this area. In the following 600 years approximately, two tsunamis caused the partial infilling of this area with bioclastic, marine sediments. In the interval comprised between these two tsunamis, this lagoon was polluted with heavy metals derived from historical mining activities. This environmental contamination represents one of the oldest evidences of mining pollution in the world (>3 kyr cal BP).     

The genesis of the amethyst geodes at Artigas (Uruguay) and the paleohydrology of the Guaraní aquifer: structural, geochemical, oxygen, carbon, strontium isotope and fluid inclusion study

The amethyst-bearing geodes found in the flood basalts of the Arapey formation at Artigas (Uruguay) were formed as protogeodes by bubbles of CO₂-rich basalt-derived fluids. The formation of the celadonite rim and the lining of the geodes by agate followed by quartz and amethyst were driven by the artesian water of the Guaraní aquifer percolating the basalts from below. The temperature of the amethyst formation is estimated from fluid inclusion data to be between 50° and 120°C. Oxygen stable isotope data suggest a crystallization temperature of calcite of about only 24°C. The actual wellhead temperature of the water produced from the Guaraní aquifer in the study area is around 29°C.     

Stable isotope records (δO and δC) of Lower-Middle Jurassic belemnites from the Western Balkan mountains (Bulgaria): Palaeoenvironmental application

Stable O and C isotope data of 110 Upper Pliensbachian-Lower Bajocian belemnites have been obtained and used to attempt a reconstruction of palaeotemperature and its variation in two epicontinental depositional environments from the Western Balkan mountains (Bulgaria). The samples were collected from 3 sections with high-resolution ammonite subdivision. Initially taphonomic, cathodoluminescence and geochemical analyses were used for evidence of diagenetic alteration. Non-luminescent parts of the belemnite rostra have been sampled for isotope analyses and 76 samples, having δ¹⁸O < −4‰ (PDB), δ¹³C > −0.5‰ (PDB), Fe < 250 ppm, Mn < 50 ppm, Sr > 950 ppm and Sr/Mn ratio > 80 were used for palaeotemperature interpretations. The O and C isotope data generally exhibit little stratigraphical variability with minor fluctuations, however, there are prominent positive C isotope excursions and coeval negative O isotope shifts detected in the Lower Toarcian Tenuicostatum, Falciferum and Bifrons Zones. The O isotope data, interpreted in terms of palaeotemperature, revealed relatively high seawater temperatures during the Toarcian, Aalenian and Early Bajocian, with detectable temperature rises during the Early Toarcian (maximum value of 29.6 °C). Both C isotope maxima and O isotope minima are used as evidence of the Early Toarcian anoxic event reported from many localities of the same age and in similar facies in Western Europe. In the study the latter is recognized as 3 episodes, which are closely related with the seawater temperature maxima. This isotope record pattern is considered as a consequence of a global Tethyan transgression during the Early Toarcian.     

The Use of Stable Sulfur, Oxygen and Hydrogen Isotope Ratios as Geochemical Tracers of Sulfates in the Podwiśniówka Acid Drainage Area (South-Central Poland)

The paper presents the results of determinations of stable S and O isotopes of dissolved sulfates and O and H stable isotopes of waters from three ponds, that is, Marczakowe Do?y acid pond, Marczakowe Do?y fish pond and Podwi?niówka acid pit pond, located in the Holy Cross Mountains (south-central Poland). The δ³⁴S_V-CDT and δ¹⁸O_V-SMOW of SO₄ ^2? in waters of three ponds (n = 14) varied from ?16.2 to ?9.5 ‰ (mean of ?13.6 ‰) and from ?8.1 to ?3.2 ‰ (mean of ?4.8 ‰), respectively. The mean δ³⁴S–SO₄ ^2? values were closer to those of pyrite (mean of ?25.4 ‰) and efflorescent sulfate salts (mean of ?25.6 ‰), recorded previously in the Podwi?niówka quarry, than to sulfates derived from other anthropogenic or soil and bedrock sources. The SO₄ ^2? ions formed by bacterially induced pyrite oxidation combined with bacterial (dissimilatory) dissolved sulfate reduction, and presumably with subordinate mineralization of carbon-bonded sulfur compounds, especially in both Marczakowe Do?y ponds. In addition, the comparison of δ¹⁸O–SO₄ ^2? and δ¹⁸O–H₂O values indicated that 75–100 % of sulfate oxygen was derived from water. Due to the largest size, the Podwi?niówka acid pit pond revealed distinct seasonal variations in both δ¹⁸O–H₂O (?9.2 to ?1.6) and δD–H₂O (?29.7 to ?71.3) values. The strong correlation coefficient (r ² = 0.99) was noted between δ¹⁸O–H₂O and δD–H₂O values, which points to atmospheric precipitation as the only source of water. The sediments of both acid ponds display different mineral inventory: the Marczakowe Do?y acid pond sediment consists of schwertmannite and goethite, whereas Podwi?niówka acid pit pond sediment is composed of quartz, illite, chlorite and kaolinite with some admixture of jarosite reflecting a more acidic environment. Geochemical modeling of two acid ponds indicated that the saturation indices of schwertmannite and nanosized ε-Fe₂O₃ (Fe³⁺ oxide polymorph) were closest to thermodynamic equilibrium state with water, varying from ?1.44 to 3.05 and from ?3.42 to 6.04, respectively. This evidence matches well with the obtained mineralogical results.     

Study of the effect of seepage through the body of earth dam on its stability by predicting the affecting hydraulic factors using models of Brooks–Corey and van Genuchten (Case study of Nazluchay and Shahrchay earth dams)

Stability of an earth dam is affected by different factors of which the most important is seepage. One of the factors in defining the seepage rate is hydraulic conductivity coefficients in suctions and various moistures in earth dam body in which different models of soil–water retention curves are used to be defined. In this study, first the soil–water retention curves of van Genuchten and Brooks–Corey models are used to predict the soil–water retention of different body layers of 2 dams. Then, hydraulic conductivity coefficients are calculated through Mualem and Burdine’s models. Water seepage rate and the stability of dams were calculated in two phases: I. construction finalization prior to intaking water and II. rapid drawdown of water. Bishop and Morgenstern–Price methods are used to analyze the stability of dams. The stability and seepage results demonstrate that simultaneous use of Brooks–Corey’s soil–water retention curve with Mualem’s method results in the highest seepage rate in comparison with van Genuchten’s model in case of variable n, m and Burdine hydraulic conductivity. Safety factors achieved from both cases of construction finalization prior to intaking water and rapid drawdown of water demonstrated the accuracy and reliability of hydraulic coefficient prediction.     

In situ trace elements and sulfur isotope analysis of sulfides from the Akiri Cu ± (Ag) deposit,Benue Trough,North-central Nigeria: Implications for ore genesis

The Benue Trough of Nigeria is an intracratonic rift basin hosting several vein-type base metal deposits. The Akiri Cu ± (Ag) deposit represents a distinct sub-class of sediment-hosted Pb-Zn-Cu-Ba mineralization found throughout the Benue Trough. The deposit is hosted in bleached red beds of the Keana Formation and in shale-siltstones and carbonates of the Ezeaku Formation in the Middle Benue Trough, North-Central Nigeria. Mineralization at the Akiri deposit occurs as vein in-fillings in a series of NE-SW and E-W trending faults and fractures in the Early- to Late-Turonian Keana and Eze-Aku sedimentary rocks. To better constrain the sources of ore minerals and structural controls on the formation of this sediment-hosted Cu ± (Ag) mineralization, we report combined geologic, geochemical, mineralogical, and stable isotopic data for the Akiri Cu ± (Ag) deposit. Major ore-stage sulfides at Akiri are chalcopyrite and pyrite, which were accompanied by several types of alteration, including silicification, hematization, limited pyritization, and bleaching of mineralized sandstone bodies. In-situ trace element and sulfur isotopic data distinguishes early-stage pyrite (Py1) from late-stage pyrite (Py2). The late-stage Py2 co-exists with chalcopyrite suggesting coeval precipitation. Early-stage pyrite (Py1) contains lower Ag (avg. 0.04 ppm) but higher Au (avg. 3.03 ppm) than the late-stage pyrite (Py2) (avg. Ag = 2.78 ppm; Au = 0.424 ppm). The δ³⁴S values of the early-stage sulfide (Py1) vary from 19.07‰ to 25.99‰ (avg. 22.20‰), suggesting that sulfur was largely derived from thermochemical reduction (TSR) of seawater sulfate. The δ³⁴S values for co-existing Py2 and chalcopyrite range from 9.83‰ to 11.24‰ (avg. 10.32‰) and from 7.37‰ to 10.69‰ (avg. 8.96‰), respectively, suggesting a derivation of sulfur from TSR of seawater sulfate with contributions from magmatic sulfur. Based on structural features and ore textures, we propose that sulfide precipitation at Akiri was facilitated by sulfur-rich fluids circulating through pre-existing structures (fractures and faults) under fairly high (>200 °C) to moderate (<170 °C) temperature conditions. Geological, mineralogical, geochemical and isotopic data from this study support the classification of the Akiri Cu (+Ag) deposit as an epigenetic sandstone-hosted copper deposit.     

Reclamation or succession—A case study of transformation of soils and vegetation in reclaimed areas or in areas left for succession as exemplified by the sand mine excavation (southern Poland)

The aim of the study was to evaluate the vegetation and initial soils forming in the area of the“Szczakowa”Sand Mine cast(located approx.50km NW away from Krakow in southern Poland)that have either been reclaimed or left for succession.In the course of …     

A study of rare earth element (REE)–SiO2 variations in felsic liquids generated by basalt fractionation and amphibolite melting: a potential test for discriminating between the two different processes

The origin of felsic magmas (>63% SiO₂) in intra-oceanic arc settings is still a matter of debate. Two very different processes are currently invoked to explain their origin. These include fractional crystallization of basaltic magma and partial melting of lower crustal amphibolite. Because both fractionation and melting can lead to similar major element, trace element and isotopic characteristics in felsic magmas, such lines of evidence have been generally unsuccessful in discriminating between the two processes. A commonly under-appreciated aspect of rare earth element (REE) solid–liquid partitioning behavior is that D _REE for most common igneous minerals (especially hornblende) increase significantly with increasing liquid SiO₂ contents. For some minerals (e.g., hornblende and augite), REE partitioning can change from incomptatible (D < 1) at low liquid SiO₂ to compatible (D > 1) at high liquid SiO₂. When this behavior is incorporated into carefully constrained mass-balance models for mafic (basaltic) amphibolite melting, intermediate (andesitic) amphibolite melting, lower or mid to upper crustal hornblende-present basalt fractionation, and mid to upper crustal hornblende-absent basalt fractionation the following general predictions emerge for felsic magmas (e.g., ∼63 to 76% SiO₂). Partial melting of either mafic or intermediate amphibolite should, regardless of the type of melting (equilibrium, fractional, accumulated fractional) yield REE abundances that remain essentially constant and then decrease, or steadily decrease with increasing liquid SiO₂ content. At high liquid SiO₂ contents LREE abundances should be slightly enriched to slightly depleted (i.e., C _l/C _o ∼ 2 to 0.2) while HREE abundances should be slightly depleted (C _l/C _o ∼ 1 to 0.2). Lower crustal hornblende-bearing basalt fractionation should yield roughly constant REE abundances with increasing liquid SiO₂ and exhibit only slight enrichment (C _l/C _o ∼ 1.2). Mid to upper crustal hornblende-bearing basalt fractionation should yield steadily increasing LREE abundances but constant and then decreasing HREE abundances. At high liquid SiO₂ contents LREE abundances may range from non-enriched to highly enriched (C _l/C _o ∼ 1 to 5) while HREE abundances are generally non-enriched to only slightly enriched (C _l/C _o ∼ 1 to 2). Hornblende-absent basalt fractionation should yield steadily increasing REE abundances with increasing liquid SiO₂ contents. At high SiO₂ contents both LREE and HREE are highly enriched (C _l/C _o ∼ 3 to 4). It is proposed that these model predictions constitute a viable test for determining a fractionation or amphibolite melting origin for felsic magmas in intra-oceanic arc environments where continental crust is absent. Electronic supplementary material  The online version of this article (doi:) contains supplementary material, which is available to authorized users.