The fractal properties of geochemical landscapes as an indicator of weathering and transport processes within the Eastern Alps

Variations in surface morphology and lithology provide an opportunity to study lithologic and morphologic influences on the spatial pattern of stream-sediment geochemistry within two contrasting environments of the Eastern Alps (Hohe Tauern Range and Gurktaler Alpen Range). The fractal dimension, a measure of surface roughness over a variety of scales, is used to model the dissipation of erosive products due to climatic controlled denudation and fluvial mass transport. Based on a spatial correlation analysis, specific elemental concentrations are used as indicators for a dominant lithotype. Fractal geometry of these elements has been estimated by sequential Gaussian simulation of the area/perimeter relationship (Dal) and by the estimation of multifractal spectra. It is shown that within a 510–780 km² survey area the spatial variations of Al, Ga, Ni and Ca can be approximated by single fractals but for those of Ag and Sn multifractal models must be used. Fractal properties derived from simulated surfaces are explainable by the process controlling the spatial structure of the data. Climatic and tectonic parameters apparently influences Dal at large scales. At smaller scales rock-type variation exert an additional influence on Dal.     

The TiO2/Ta ratio as an indicator of the degree of differentiation of tin granites

Tin deposits in Eastern Marche (French Massif Central) and North of Viseu (Portugal) are associated with final stages of differentiation of granitoid magmatism. Fractional crystallization causes increase in Sn, W, Ta, Rb, Cs, F and Li, and decrease in Ti, La, U, Th, Ba etc. That trend is very clearly expressed by tantalum, strongly correlated with tin, and by titanium. Hence the TiO₂/Ta ratio is a good indicator of granitic melt differentiation. Its value gradually ranges from 4 900 in the less differentiated granodiorite to <1 in the most differentiated granite from Marche area. That ratio could be a useful guide to suitable areas for tin exploration.     

The geochemistry of arsenic and its use as an indicator element in geochemical prospecting

The geochemistry of arsenic is reviewed, and the use of the element as an indicator in geochemical prospecting for various types of mineral deposits is outlined.Arsenic is a widespread constituent of many types of mineral deposits, particularly those containing sulphides and sulpho-salts. In these and other deposits arsenic commonly accompanies Cu, Ag, Au, Zn, Cd, Hg, U, Sn, Pb, P, Sb, Bi, S, Se, Te, Mo, W, Fe, Ni, Co, and Pt metals. Under most conditions arsenic is a suitable indicator of deposits of these elements, being particularly useful in geochemical surveys utilizing primary halos in rocks, and secondary halos and trains in soils and glacial materials, stream and lake sediments, natural waters, and vegetation. Some of the natural arsenic compounds (e.g., arsine, dimethylarsine) are volatile, but methods utilizing gaseous arsenic halos for geochemical prospecting have not yet been developed.     

The geochemistry of antimony and its use as an indicator element in geochemical prospecting

The geochemistry of antimony is reviewed, and the use of the element as an indicator in geochemical prospecting for various types of mineral deposits is outlined.Antimony is widely diffused in many types of mineral deposits, particularly those containing sulphides and sulphosalts. In these and other deposits, antimony commonly accompanies Cu, Ag, Au, Zn, Cd, Hg, Ba, U, Sn, Pb, P, As, Bi, S, Se, Te, Nb, Ta, Mo, W, Fe, Ni, Co, and Pt metals. Under most conditions antimony is a suitable indicator of deposits of these elements, being particularly useful in geochemical surveys utilizing primary halos in rocks, and secondary halos and trains in soils and glacial materials, stream and lake sediments, natural waters, and to a limited degree vegetation. Some of the natural antimony compounds (e.g. stibine, dimethylstibine) are volatile, but methods utilizing gaseous antimony halos for geochemical prospecting have not yet been developed.     

Partitioning of Nb and Ta between rutile and felsic melt and the fractionation of Nb/Ta during partial melting of hydrous metabasalt

In order to fully assess the role of rutile in fractionation of Nb/Ta during partial melting of hydrous metabasalt, we have measured rutile - felsic melt partition coefficients (D values) for Nb and Ta with tonalitic to trondhjemitic compositions at 1.5-3.5 GPa, 900-1350 °C and ∼5.0-20 wt% H₂O. D_Nb, D_Ta and D_Nb/D_Ta range from 17 ± 1 to 246 ± 13, 34 ± 2 to 232 ± 25 and 0.51 ± 0.04 to 1.06 ± 0.13, respectively. For the compositions investigated, melt composition appears to have no observable effect on the partitioning; the effect of pressure is also slight; whereas temperature and H₂O have marked effects. D_Nb, D_Ta and D_Nb/D_Ta increase with decreasing temperature and H₂O content, showing a reversal of D_Nb/D_Ta from <1.0 to >1.0. Using the data that approached equilibrium and obeyed Henry’s law, expressions describing the dependences of D_Nb, D_Ta and D_Nb/D_Ta on temperature, pressure and melt H₂O content were obtained:

(1)     

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.

     

Plagioclase zoning as an indicator of magma processes at Bezymianny Volcano,Kamchatka

Back-scattered electron (BSE)-derived zoning patterns of plagioclase phenocrysts are used to identify magma processes at Bezymianny Volcano, Kamchatka, based on the 2000–2007 sequence of eruptive products. The erupted magmas are two-pyroxene andesites, which last equilibrated at ~915°C temperature, 77–87 MPa pressure, and a water content of ~1.4 wt%. Textural and compositional zoning of individual plagioclase phenocrysts typically includes a repeated core-to-rim sequence of oscillatory zoning (An_50–60) truncated by a dissolution surface followed by an abrupt increase in An content (up to An₈₅), which then gradually decreases rimward. This zoning pattern is interpreted to be the result of frequent replenishments of the magma chamber which cause both thermal and chemical interaction between resident and recharge magmas. The outermost 70- to 150-μm-wide zoning patterns of plagioclase phenocrysts are composed of dissolution surface with a subsequent increase in An and Fe contents. Zoning patterns of the rims exhibit correlation among plagioclase phenocrysts within one eruption. Rims are interpreted as a result of crystallization of a batch of magma in the conduit after recharge event.     

Nb/Ta fractionation observed in eclogites from the Chinese Continental Scientific Drilling Project

This paper reports detailed analyses of Nb and Ta concentrations of 19 eclogite samples and their principal mineral constituents from the main drill hole of the Chinese Continental Scientific Drilling Project (CCSD) and nearby outcrops. We observe highly fractionated and overall suprachondritic Nb/Ta values in minerals, e.g., rutile (4.8–87), titanite (12–62) and amphibole (2.0–67). Amphiboles in amphibolites (retrograded from eclogite) can be classified into two groups: a low Nb/Ta group that bears higher Al contents and is thus of higher pressure origin, and a high Nb/Ta, lower pressure group. The former group was likely formed during subduction; the latter may have formed during exhumation in the presence of rutile and titanite. The significant Nb/Ta fractionation in rutile and other minerals may reflect early dehydration of the subducted slab at shallow depths before the formation of rutile, which occurs at depths ≥50 km. The dehydration, with amphiboles existing as the main Nb–Ta-bearing phase, would lead to Nb/Ta fractionation, i.e., forming subchondritic Nb/Ta ratios in the released fluids and, complementarily, suprachondritic Nb/Ta ratios in the residual phases. While a large proportion of the fluids may escape from the slab to the mantle wedge, considerable amounts of the fluids can be retained in hydrous minerals within the descending slab, thus forming hydrated cold eclogites with subchondritic Nb/Ta characteristics. As subduction continues to depths over 50 km, rutile appears and consequently controls the Nb–Ta budget. In the presence of rutile, melting of the hydrated cold eclogites with very low Nb/Ta ratios would form magmas with negative Nb, Ta anomalies and subchondritic Nb/Ta. Further dehydration of the continuously descending slab results in even more fractionated Nb/Ta ratios in subsequently released fluids and residues, providing a feasible explanation for the large Nb/Ta variation observed in the modern arc magmas and residual eclogites.     

The use of plagioclase composition as an indicator of magmatic processes in the Upper Zone of the Bushveld Complex

Summary Analytical data on the composition of plagioclase from the lower part of the Upper Zone in the eastern Bushveld Complex is presented. Detailed electron microprobe investigations failed to establish any cyclic variation through that sequence but revealed similar variations in An content, potassium and iron concentrations below and above magnetite layers. These findings can be attributed to the heterogeneous nature of the plagioclase both within individual grains and within a given sample, which would mask any possible trends of cryptic variation. The Sr concentration and Sr/Al₂O₃ ratio of plagioclase, determined by XRF on plagioclase separates, however change slightly at the level of the Main Magnetite Layer, which can possibly be related to the breakdown of density stratified liquid layers within the resident magma. Analyses of plagioclase separates are thus considered to be more suitable to indicate magmatic processes than plagioclase compositions determined by electron microprobe.

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Plagioklaszusammensetzung als Indikator für magmatische Prozesse in der Upper Zone des Bushveld Komplexes

Zusammenfassung Analytische Daten von Plagioklasen aus dem unteren Teil der Upper Zone im östlichen Bushveld Komplex werden präsentiert. Detaillierte Untersuchungen mittels Elektronen-strahl-Mikrosonde ergaben keine Hinweise auf eine zyklische Variation in dieser Abfolge, zeigten aber eine dänliche Variation des An-Gehaltes, Bowie der Kalium- und Eisengehalte im Liegenden und Hangenden von Magnetitlagen. Dies läßt sich mit der heterogenen Natur der Plagioklase, sowohl in Einzelkörnern, als auch innerhalb einer Probe erklären, die jeden möglichen verborgenen Variationstrend verdecken würden. Der mittels XRF Analytik an separierten Plagioklasen bestimmte Gehalt an Sr und das Sr/Al₂O₃ Verhältnis dndern sich allerdings geringfügig im Bereich des Main Magnetite Layer. Dies wird möglicherweise mit derv Zusammenbruch von dichtegeschichteten Schmelzlagen im Magma in Beziehung gebracht. Die Analyse von Plagioklaskonzentraten scheint daher geeigneter zu sein magmatische Prozesse anzuzeigen als Mikrosondenuntersuchungen.

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With 6 Figures     

Flat rare earth element patterns as an indicator of cumulate processes in the Lesser Qinling carbonatites, China

The Lesser Qinling carbonatite dykes are mainly composed of calcites. They are characterized by unusually high heavy rare earth element concentrations (HREE; e.g. Yb > 30 ppm) and flat to weakly light rare earth element (LREE) enriched chondrite-normalized patterns (La/Yb_n = 1.0–5.5), which is in marked contrast with all other published carbonatite data. The trace element contents of calcite crystals were measured in situ by laser ablation inductively coupled plasma mass spectrometry (LA-ICPMS). Some crystals show reduced LREE from core to rim, whereas their HREE compositions are relatively constant. The total REE contents and chondrite-normalized REE patterns from the cores of carbonate crystals are similar to those of the whole rock. The carbon and oxygen isotopic compositions of calcites fall within the range of primary, mantle-derived carbonatites. The initial Sr isotopic compositions (0.70480–0.70557) of calcites are consistent with an EM1 source or mixing between HIMU and EM1 mantle sources. However these sources cannot produce carbonatite parental magmas with a flat or slightly LREE enrichment pattern by low degrees of partial melting. Analyses of carbonates from other carbonatites show that carbonates have nearly flat REE pattern if they crystallize from a LREE enriched carbonatite melt. This implies that when carbonates crystallize from a carbonatite melt the calcite/melt partition coefficients (D) for HREE are much greater than the D for the LREE. The nearly flat REE patterns of the Lesser Qinling carbonatites can be explained if they are carbonate cumulates that contain little trapped carbonatite melt. Strong enrichment of HREE in the carbonatites may require their derivation by small degrees of melting from a garnet-poor source.     

Enzymatic activity as an indicator of regeneration processes in degraded soil reclaimed with various types of waste

Soil material sampled from a reclamation experiment established in a former “Jeziórko” Sulphur Mine was analysed. The reclamation was carried out on a soil-less substrate with a particle size distribution of slightly loamy sand characterised by high acidity and poor sorption capacity. The different variants of the experiment consisted in the addition of post-flotation lime, mineral fertilisation, sewage sludge, and mineral wool to the reclaimed soil-less substrate. Next, the plots prepared in this way were sown with a mixture of grasses. A plot without any reclamation treatments served as a control. The analyses consisted in the determination of soil enzymatic parameters. The results obtained revealed a positive effect of the reclamation treatments on the analysed properties. All wastes and combinations thereof introduced into the degraded substrate stimulated catalase, protease, and urease activity. The activity of the other enzymes, i.e. dehydrogenases and acid phosphatase, as well as the level of fluorescein diacetate hydrolysis increased only in objects treated with sewage sludge. In turn, in objects receiving mineral fertilisation, a decline in the acid phosphatase activity was noted. In objects treated with mineral wool, the level of stimulation was dependent on the mode of application of this additive. In general, a mixture of 500 m³ ha^?1 of mineral wool with the substrate proved more beneficial (with the exception of the acid phosphatase activity and fluorescein diacetate hydrolysis). A higher increase in the analysed enzymatic parameters was also found in objects treated with sewage sludge combined with post-flotation lime than in objects where sewage sludge was used alone.     

太古宙TTG的Nb/Ta变化特征: 对“Nb-Ta悖论”的启示

英云闪长岩-奥长花岗岩-花岗闪长岩（TTG）是地球早期大陆地壳最重要的组成部分。TTG的Nb/Ta比值变化不仅与它的成因相关,而且与早期构造环境和地壳分异过程关系紧密。本文选择阴山地块出露的TTG片麻岩及下地壳斜长角闪岩/麻粒岩包体作为研究对象,开展了寄主花岗闪长岩和同源镁铁质包体中的角闪石和黑云母的原位微区矿物的微量元素分析工作,以及TTG与非同源斜长角闪岩包体的全岩主微量元素分析工作。矿物化学研究结果表明,花岗闪长岩和同源镁铁质包体的角闪石具有相似的Mg^#值,但是两者具有明显不同的Nb/Ta比值。镁铁质包体中的角闪石更富Cr、Ta,Nb/Ta比值为30~50;TTG岩石中的角闪石Cr和Ta含量偏低,但具有更高的Nb/Ta比值（38~70）。TTG和镁铁质包体中的角闪石Cr含量与Nb/Ta具有较好的负相关关系。全岩地球化学分析结果揭示,TTG片麻岩的具有高Nb/Ta比值（13~65,平均值31）,斜长角闪岩和麻粒岩包体具有变化的Nb/Ta比值（10~56）。太古宙绿岩带中玄武质岩石的Nb/Ta平均值为~15,阴山地块斜长角闪岩和麻粒岩包体具有高的Nb/Ta比值,反映了这些代表基性下地壳的岩石经历了部分熔融作用或后期的交代作用,使其Nb/Ta比值发生改变。研究区具有高Nb/Ta比值的TTG可能来源于高Nb/Ta比值基性下地壳部分熔融,并继承了源区高Nb/Ta比值的特征。通过本文研究揭示,高Nb/Ta比值的TTG并非一定形成于俯冲带洋壳榴辉岩相部分熔融,下地壳富角闪石和黑云母的岩石部分熔融是形成高Nb/Ta比值TTG的一种重要途径。

     

华北地区中生代玄武岩高Nb/Ta值对地壳岩石再循环的直接记录

为揭示中国东部中生代大规模岩石圈减薄作用的深部地幔地球化学响应,对华北东部5个地区的中生代玄武岩进行了ICP-MS分析。结果表明,119~125 Ma玄武岩不仅具显著分异的稀土元素组成(La/Yb=35~60)、岛弧玄武岩型微量元素分布特征,且具高Ni(210×10-6~510×10-6)和Cr(510×10-6~1400×10-6)含量、高Mg#(71~78),以及系统高于球粒陨石的Nb/Ta值[19.9±1.0(1σ),n=16];而100 Ma碱锅玄武岩具有与球粒陨石(17.6)接近的Nb/Ta值[17.3±0.2(1σ)]。再循环地壳岩石在金红石稳定域内以榴辉岩为残余的部分熔融体 地幔橄榄岩反应,不仅使地幔岩石熔点降低、获得高Nb/Ta值及石榴子石特征,而且橄榄石向辉石的转变反应使Ni和Cr在交代地幔中的总分配系数显著降低。受熔体交代地幔橄榄岩的部分熔融可合理解释119~125 Ma玄武岩的上述地球化学特征,玄武岩Nb/Ta值应是对岩石圈减薄过程中地壳物质返回地幔后熔融产生硅质熔(流)体对上覆地幔交代的直接地球化学记录。     

Megacryst-bulk rock isotopic disequilibrium as an indicator of contamination processes: The Edgecumbe Volcanic Field,SE Alaska

Sr and Nd isotopic ratios are reported from mineral separates and bulk rock samples from the Edgecumbe Volcanic Field in southeast Alaska, a suite of lavas that has developed by assimilation. Megacrysts in the basaltic unit and the rhyodacites are in isotopic equilibrium with their matrices. Because the rhyodacites developed as the result of assimilation, the assimilate must have been completely dissolved. In contrast, megacrysts in the two andesitic units are in isotopic disequilibrium with their matrix. These megacrysts must be a mixture of those inherited from the contaminant, crystals in equilibrium with the groundmass, and possibly crystals inherited from a mafic liquid.     

Caucasian mineral waters: The modern hydrothermal system of the crust-mantle origin

Doklady Earth Sciences -