中天山地块科马提质超镁铁岩体的发现：新疆峡东岩体

新疆和甘肃交界处的峡东岩体是以纯橄岩为主的超镁铁质杂岩体,经过全岩主量元素分析和橄榄石的探针分析,发现纯橄岩具有很高的MgO含量(36%~39%),橄榄石的镁值（Fo值）在90~96之间。通过反演原始岩浆成分的方法得到原始岩浆中MgO=28%、FeO=9%,属于科马提质岩浆。通过模拟初始岩浆的结晶分异过程,峡东岩体是科马提质岩浆发生高程度结晶分异的产物。利用MELTS软件计算原始岩浆的演化过程,得到初始岩浆的液态温度为1703℃,在1649℃和1555℃时分别开始结晶铬尖晶石和橄榄石,在1093℃开始结晶单斜辉石,这一结晶顺序与峡东岩体的矿物组合是一致的,也说明峡东岩体是科马提质岩浆高度结晶分异的产物。通过计算得到初始岩浆为原始地幔发生24%的高度部分熔融形成,如此高程度的部分熔融是否与地幔柱有关还有待进一步研究。鉴于橄榄石中的Ni含量未发现有与硫化物发生交换反应的证据,因此对于其铜镍硫化物成矿条件是不利因素,其他控制硫化物熔离的因素还需要进一步探讨,但铬尖晶石充分结晶分异为发育铬铁矿矿化提供了有利的条件。     

The Kalka layered intrusion,central Australia

The Kalka Intrusion, central Australia has a 5000 m-thick layered sequence comprising Pyroxenite, Norite and Anorthosite Zones; an Olivine Gabbro Zone is enclosed by, and has a facies relationship with, the Norite Zone. Contamination is evidenced by high initial ⁸⁷Sr/⁸⁶Sr ratios ( 0.708) in the lower four-fifths of the intrusion, and resulted in pyroxenite rather than peridotite as a basal crystal accumulate. After an early phase of erratic buildup in contamination due to assimilation of ragged granulite wall-rock, armouring of the walls and mixing produced an homogeneous Norite Zone (threshold) magma body crystallising opx-cpx-plag. Within the succeeding 3500 m of section plagioclase An values have a general decline up sequence (An_74-60-feldspar threshold) with superimposed short term digressions to more calcic compositions. Initial ⁸⁷Sr/⁸⁶Sr ratios also fall very gradually (0.7081-0.7078 — isotopic threshold) with transient fluctuations to distinctly lower values. Maxima in plagioclase An contents and ⁸⁷Sr/ ⁸⁶Sr minima may be correlated with the spasmodic appearance of olivine and pronounced lithological variation. Such features are explained by the ponding of fresh bodies of uncontaminated magma on the floor of the chamber; these formed a hybrid with threshold magma that temporarily dominated crystallisation thereby perturbing plagioclase and isotopic compositions; eventually, mixing of the hybrid into the overlying threshold magma returned crystallisation to its initial state. The facies-controlled Olivine Gabbro Zone is the physical expression of ponded basal hybrid magmas. The onset of the Anorthosite Zone is marked by a pronounced decline in ⁸⁷Sr/⁸⁶Sr ratios to around 0.705 registering a major influx of new magma. In this instance the new magma dominated the system and a change to plagioclase as the dominant liquidus phase indicates a drastic change in input magma composition. The evolution of Kalka was determined by an interplay of crystal fractionation, fresh magma pulses, and magma mixing, with the latter effects producing both increases and decreases in plagioclase An contents; the complete process can only be revealed by combined mineral composition and isotopic data.     

Tidal intrusion fronts

A tidal intrusion front forms as a dense seawater inflow plunges (subducts) beneath ambient estuarine water during flood tide. The associated foam lines and color changes have been observed on many smaller estuaries with constricted mouths. Internal hydraulic theory and laboratory experiments are reviewed and expressions are obtained for the position of plunging and the amount of associated mixing. The existence of a tidal intrusion front and its structure are discussed in terms of densimetric Froude numbers. These fronts are particularly important in smaller estuaries in which the intrusion process may dominate wind and tidal mixing and thus determine the overall stratification of the estuary. Three classes of three-dimensional plunging flow are identified and discussed. In particular, it is suggested that the peculiar, cursive V-shape plunge line is characteristic of strongly plunging flow.     

新疆北山地区罗东镁铁质-超镁铁质层状岩体岩石成因

罗东镁铁质-超镁铁质岩体位于塔里木板块东北部的新疆北山地区,岩体平面形态为眼球状,出露面积约2.1 km2.由纯橄岩、单辉橄榄岩、斜长二辉橄榄岩、橄榄二辉岩、方辉辉石岩、橄长岩、橄榄辉长岩、辉长岩、苏长辉长岩和淡色辉长岩组成,堆晶结构和堆晶韵律发育,属于层状岩体.岩浆演化过程中主要分离结晶/堆晶相是橄榄石和单斜辉石,此...     

The Somerset Dam Layered basic intrusion,Southeastern Queensland

The Somerset Dam Layered Basic Intrusion is probably a sub‐volcanic magma chamber, and it consists of 20 saucer‐shaped layers composed of troctolites, olivine gabbros, ferrigabbros, and leucogabbros. The layered sequence is 1650 ft (500 m) thick, and comprises several repetitions of a standard pattern termed a zone. Each zone is generally composed of four layers, and successive mineral assemblages from the base upwards are: plagioclase‐olivine, plagioclase‐augite‐olivine, plagioclase‐augite‐magnetite‐ilmenite, and plagioclase‐uralite. Pronounced modal and textural changes define the boundaries between these layers. Within a zone, systematic variation in the proportions and compositions of minerals is thought to be the result of a slight decrease in temperature, and an increase in the partial pressures of water vapour and oxygen from the base to the top.

Repetition of zones is explained by a mechanism involving periodic renewals of magma. Lack of progressive changes in mineral compositions and proportions from the base to the top of the layered sequence is also a consequence of the magma composition, the control of water vapour pressure, and the limited range of crystallisation temperatures. Gravitational settling of early minerals does not explain the variation within a zone, or the small‐scale rhythmic layering that is locally developed, and it is concluded that diffusion has been an important control.     

新疆东天山黄山东岩体岩石地球化学特征与岩石成因

黄山东岩体位于东天山北部的土墩-黄山-图拉尔根镁铁-超镁铁质岩带中段,受康古尔塔格-黄山深大断裂控制,是由辉长闪长岩、角闪辉长岩、橄榄辉长岩、辉长苏长岩及二辉橄榄岩组成的复式岩体。主量元素化学组成部分属拉斑玄武岩系列,也有部分属钙碱性系列。大部分岩石相对富集LREE、适度亏损高场强元素(Nb、Ta、Ti)。元素地球化学和Nd、Sr、Pb同位素体系证明,岩浆遭受了5%～8%的中-上地壳物质的同化混染作用。岩浆源区由被消减板片交代的地幔楔物质和软流圈地幔物质组成。岩石圈根部拆沉和软流圈地幔上涌过程中生成了黄山东岩体。富铁硅酸盐的分离结晶作用对硫化物富集并分凝起到了关键性作用,成矿过程应该是岩浆自身演化过程的有机组成部分。     

Petrology of the Hopen mangerite-charnockite intrusion, Lofoten, north Norway

The Hopen massif, intrusive age 1900 m.y., exposed area 15 km², in the Lofoten-Vesterålen granulite facies province has the mineral assemblages: (1) mesoperthite+plagioclase (An_7–20)+quartz+clinopyroxene (Di_20–25)+orthopyroxene En_15–25+opaques±minor amphibole±minor biotite; (2) mesoperthite+plagioclase (An <2)+quartz+clinopyroxene (Di <10)+olivine Fe lt;5)+opaques. By using mineral and whole rock analyses, the crystallization conditions were estimated to be 1000°C, 12 kb load pressure and an oxygen fugacity approximately corresponding to the WM buffer. Rocks with the assemblage of type (2) contain secondary orthoferrosilite (Fe_0.90–0.95Mn_0.04–0.07Mg_0.01Ca_0.01)₂Si₂O₆, generated by reactions involving fayalite, magnetite and quartz at 800°C, 10kb load pressure and at oxygen fugacities approaching QFM buffer conditions. Subsequent to a crustal thickening, the mangeritic rocks in Lofoten-Vesterålen were emplaced in a tensional environment comparable with modern continental rifts. A ‘gabbro pillow’ magma chamber at the crustal base is proposed as parental magma for the mangeritic rocks, of which the Hopen massif represents a late differentiation.     

Loveringite from the koitelainen layered intrusion,Northern Finland

Summary Conditions favouring the crystallization of loveringite, (Ca, REE) (Ti, Fe, Cr)₂₁ 0₃₈ in Koitelainen were sustained from the base of the lower zone to the upper part of the main zone. Loveringite is most common in rocks with much intercumulus quartz, potassium feldspar, and phlogopite, and is accompanied by accessories such as zircon, chlorapatite, baddeleyite and thorite. It is particularly common among pyroxene cumulates in the upper part of the lower zone. Here, and apparently also in plagioclaseorthopyroxene-clinopyroxene cumulates of the main zone, loveringite occurs as a cumulus phase. The presence of Cr in the intercumulus liquid is not essential to the stability of loveringite; instead, petrographic evidence and the presence of incompatible elements (Zr, Hf, REE, U, Th) contained in loveringite point to the crucial role of crustal contaminants. Loveringite crystallized in parts of the magma chamber heavily contaminated by acid crustal anatectic melt, and eventually settled from density flows loaded with cumulus crystals. Postcumulus reactions produced concentric ilmenitezircon mantles around loveringites and thus contributed to the compositional heterogeneity of the mineral. We suggest that much of the loveringite that once crystallized in layered intrusions may have been consumed through postcumulus reactions. Loveringite is easy to detect under the reflected light microscope and can be readily distinguished from rutile, chromite and ilmenite, but not from some other members of the crichtonite group. The composition of the Koitelainen loveringite is comparable to that of other occurrences. The spectral reflectance values are 2–3% lower as compared to ilmenite. The reflectance data indicate that the mineral is anisotropic. The VHN₁₀₀ values, 792–933, are significantly higher than those published heretofore.[/p]

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Loveringit aus dem Intrusiv-Komplex von Koitelaineen, Nordfinland

Zusammenfassung In der Koitelainen-Intrusion waren während der magmastichen Etwitcklung der Gesteine der älower zone" und ämain zone" die Bedingungen für die Bildung von Loveringit, (Ca, REE) (Ti, Fe, Cr)₂₁ O₃₈, erfüllt, der in Gesteinen mit Quarz, Kalifeldspat und Phlogopit als Interkumulus, häufig auftritt. Sein Vorkommen ist eng verknüpft mit akzessorischen Mineralen wir Zirkon, Chlorapatit, Baddeleyit und Thorit. Ebenso häufig wurde Loveringit in den Pyroxen-Kumulaten der älower zone" und in PlagioklasOrtho-und Klinopyroxen-Kumulaten der ämain zone" als Kumulus-Phase gefunden. Die Anwesenheit von Cr in der Interkumulus-Schmelze ist kein wesentlicher Faktor für die Stabilität des Loveringits. Vielmehr zeigen petrologische Hinweise und die Konzentration der inkompatiblen Elemente (Zr, Hf, seltene Erden, U, Th) in Loveringit die entscheidende Rolle der krustalen Kontamination des Magmas bei seiner Bildung an. Es kristallisierte in Teilbereichen der Magmenkammer, die durch krustale anatektische Schmelze stark kontaminiert war. Reaktionen während der Postkumulusphase führten zur Bildung von konzentrischen Ilmenit-Zirkon-Säumen um Loveringitkristalle und bewirken eine chemische Inhomogenität sowie teilweise Aufläsung des Minerals. Aufgrund dieser Beobachtungen wird vermutet, daß ein großer Teil der in älayered intrusions" einmal kristallisierten Loveringite bei Reaktionen in der Postkumulusphase von der Schmelze wieder konsumiert wurde. Die chemische Zusammensetzung des Loveringits von Koitelainen ist mit der aus anderen Vorkommen vergleichbar. Mikroskopisch läßer sich anhand seiner Reflexionsdaten ohne weiteres von den Begleitmineralen Rutil, Chromit und Ilmenit unterscheiden. Die spektrale Reflexion von Loveringit ist 2–3% niedriger als bei Ilmenit. Die VHN_1OO-Werte mit 792–933 sind im Vergleich zu den bisher publizierten Daten wesentlich höher.

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Pyroxene mineral chemistry of the Jinchuan intrusion,China

Summary Chemical compositions of orthopyroxene and clinopyroxene from the Jinchuan ultramafic intrusion have been obtained by electron microprobe analysis. The Mg number (MgO/(MgO + FeO)) for both pyroxenes falls within narrow ranges, 82–87 for clinopyroxene and 81–85.5 for orthopyroxene, suggesting limited magma differentiation in regard to the present igneous body. The Al₂O₃ content ranges from 2.44 wt.% to 4.43 wt.% and increases with decreasing Mg of the pyroxenes, i.e., with the more evolved magma. This is attributed to the relatively greater effects of Al₂O₃, TiO₂, Cr₂O₃ and Fe₂O₃ than that of SiO₂ on pyroxene crystallization.Negative linear relationships between Ti⁴⁺ and Si⁴⁺, and Al³⁺ and Si⁴⁺ characterize the pyroxenes. In clinopyroxene, regression of Si⁴⁺ versus Al³⁺ results in a straight line with a slope of –1.012, indicating that the decrease of Si⁴⁺ in the crystal structure is matched by an increase only in tetrahedral Al³⁺; octahedral Al³⁺ has remained relatively constant. The negative linear relationship between Ti⁴⁺ and Si⁴⁺ in clinopyroxene reflects either a greater tendency of Ti⁴⁺ to occupy octahedral sites than Al³⁺, or that replacement of Al³⁺ for Si⁴⁺ demands a more efficient charge balance. The scatter in plots of Ti⁴⁺ versus Si⁴⁺ for orthopyroxene indicates that charge balance is not as critical as structure symmetry.The crystallization temperature of pyroxene is calculated to be 1108–1229°C usingWood andBanno's (1973) two pyroxene thermometer, and is within 40°C of that calculated fromWells's (1977) thermometer. The distribution coefficient (Kd) for Mg²⁺ and Fe²⁺ between clinopyroxene and orthopyroxene is estimated to be 0.86, which is higher than that of the other intrusions and lower than that of mantle nodules, but still falls within their Kd-1/T trend. This suggests that the Kd value of pyroxene is controlled mainly by temperature.

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Mineralchemie der Pyroxene der Jinchuan-Intrusion, China

Zusammenfassung Die chemische Zusammensetzung von Orthopyroxenen und Klinopyroxenen aus der ultramafischen Jinchuan Intrusion wurden mit der Mikrosonde bestimmt. Die Mg-Zahl (MgO/(MgO + FeO)) beider Pyroxene liegt innerhalb enger Grenzen, 82–87 für Klinopyroxen und 81–85.5 für Orthopyroxen. Dies weist auf beschränkte magmatische Differentiation der Intrusion hin. Der Al₂O₃-Gehalt liegt zwischen 2.44 Gew.%. und 4.43 Gew.%. und nimmt mit der abnehmenden Mg-Zahl der Pyroxene ab, d.h. mit dem mehr entwickelten Magma. Dies wird damit erklärt, daß Al₂O₃, TiO₂, Cr₂O₃ und Fe₂O₃ einen größeren Einfluß auf die Kristallisation der Pyroxene ausüben als SiO₂.Die Pyroxene werden durch negative lineare Beziehungen zwischen Ti⁴⁺ und Si⁴⁺, sowie Al³⁺ und Si⁴⁺ charakterisiert. In Klinopyroxenen resultiert die Regression von Si⁴⁺ gegen Al³⁺ in einer geraden Linie mit einer Neigung von –1.012. Dies weist darauf hin, daß die Abnahme der Si⁴⁺ Gehalte in die Kristallstruktur durch Zunahme von ausschliesslich tetraedrischem Al³⁺ kompensiert wird; oktaedrisches Al³⁺ ist relativ konstant geblieben. Die negative lineare Beziehung zwischen Ti⁴⁺ und Si⁴⁺ in Klinopyroxenen geht entweder auf eine stärkere Tendenz des Ti₄O₂, oktaedrische Plätze zu besetzen zurück, oder darauf daß ein Ersatz von Al³⁺ für Si⁴⁺ einen effizienteren Ladungsausgleich verlangt. Die unregelmäßige Verteilung der Plots von Ti⁴⁺ gegen Si⁴⁺ in Orthopyroxenen läßt erkennen, daß Ladungsausgleich hier nicht so kritisch ist wie die Symmetrie der Struktur.Die Kristallisationstemperatur der Pyroxene wurde mit dem Zwei Pyroxenthermometer nachWood undBanno (1973) mit 1108–1229°C bestimmt. Diese Werte liegen innerhalb von 40°C des vonWells (1977) berechneten. Der Verteilungskoeffizient (Kd) für Mg²⁺ und Fe²⁺ zwischen Klinopyroxen und Orthopyroxen wird auf 0.86 berechnet; das ist höher als der aus anderen Intrusionen und niedriger als der von Mantelxenolithen, fällt aber immer noch innerhalb des Kd-1/T Trends derselben. Dies legt den Gedanken nahe, daß der Kd Wert der Pyroxene hauptsächlich durch Temperatur bestimmt wird.

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Seawater intrusion in the Salalah plain aquifer,Oman

Salalah is situated on a fresh water aquifer that is replenished during the annual monsoon season. The aquifer is the only source of water in Salalah city. The rainfall and mist precipitation in the Jabal AlQara recharges the plain with significant renewable fresh groundwater that has allowed agricultural and industrial development to occur. In Salalah city where groundwater has been used extensively since the early 1980s for agricultural, industrial and municipal purposes, the groundwater has been withdrawn from the aquifer more rapidly than it can be replenished by natural recharge. The heavy withdrawal of large quantities of the groundwater from the aquifer has led to the intrusion of seawater. Agricultural activities utilize over 70% of the groundwater. For the study of the saltwater intrusion, the area has been divided into four strips, A, B, C and D, on the basis of land-use in the area. Water samples were collected from 18 water wells. Chemical analysis of major ions and pollution parameters in the groundwater was carried out and compared to the previous observed values. The electrical conductivity and chloride concentrations were highest in the agricultural and residential strips and Garziz grass farm. Before 1992 the aquifer was in a steady state, but presently (2005) the groundwater quality in most of the agricultural and residential strips does not meet drinking water standards. In addition, model simulations were developed with the computer code MODFLOW and MT3DMS for solute transport to determine the movement of the freshwater/saltwater interface. The study proposes the protection of the groundwater in Salalah plain aquifer from further encroachment by artificial recharge with reclaimed water, preferably along the Salalah coastal agricultural strip. This scheme can also be applied to other regions with similar conditions.     

Petrology of the Treknattan intrusion in the Fongen-Hyllingen complex, Trondheim region, Norway: a late intrusion into an evolved layered complex

The basic-ultrabasic Treknattan intrusion is an important example of a late intrusion in a solidified, evolved, layered complex and sheds light on possible mechanisms by which such associations may develop. The Treknattan intrusion, emplaced into the basic Fongen-Hyllingen intrusion shortly after the latter had solidified, consists mainly of massive or weakly layered peridotite (olivine ± Cr-spinel cumulate) and troctolite (plagioclase + olivine ± Cr-spinel cumulate). The mineral compositional range partially overlaps the most primitive end of the much larger variation-interval in the Fongen-Hyllingen intrusion. The margin of the Treknattan intrusion is sometimes outlined by massive feldspathic websterite which appears to have formed by reaction between magma and melts of gabbroic country rock. The parental magma appears to have been a relatively water-rich picritic basalt with a possible genetic relationship to the magma parental to the enveloping Fongen-Hyllingen intrusion, both displaying tholeiitic relationship between olivine and Ca-poor pyroxene, and having crystallized from relatively water-rich magmas with an early crystallization order of olivine ± Cr-spinel-plagioclase-Ca-rich pyroxene. The recognition of the Treknattan intrusion as a separate body suggests that the bulk composition of the Fongen-Hyllingen intrusion is dioritic rather than gabbroic as previously thought.     

Methane-bearing,aqueous, saline solutions in the Skaergaard intrusion,east Greenland

Solutions of H₂O–NaCl–CH₄ occur in fluid inclusions enclosed by quartz, apatite and feldspar from gabbroic pegmatitites, anorthositic structures and intercumulus minerals within the Skaergaard intrusion. The majority of the fluid inclusions resemble 10 m diameter sub-to euhedral negative crystals. A vapour phase and a liquid phase are visible at room temperature, solids are normally absent. The salinity of the fluids ranges from 17.5 to 22.8 wt.% NaCl. CH₄, which comprises less than six mole percent of the solution, was detected in the vapour phase of the fluid inclusions with Raman microprobe analysis. Homogenization of the fluid inclusions occurred in the liquid phase in the majority of the fluid inclusions, though 10% of the inclusions homogenized in the gas phase. Thermodynamic consideration of the stability of feldspars + quartz, and the C–O–H system, indicates that the solutions were trapped at temperatures between 655 and 770°C, at oxygen fugacities between 1.5 and 2.0 log units below the QFM oxygen buffer. Textural evidence and the composition of the solutions suggest that the fluids coexisted with late-magmatic intercumulus melts and the melts which formed gabbroic pegmatites. These solutions are thought to have contributed to late-magmatic metasomatism of the primocryst assemblages of the Skaergaard intrusion.     

Numerical investigation of seawater intrusion at Gooburrum,Bundaberg, Queensland,Australia

Seawater intrusion in coastal agricultural areas due to groundwater abstraction is a major environmental problem along the northeastern coast of Australia. Management options are being explored using numerical modelling, however, questions remain concerning the appropriate level of sophistication in models, choice of seaward boundary conditions, and how to accommodate heterogeneity and data uncertainty. The choice of seaward boundary condition is important since it affects the amount of salt transported into the aquifers and forms the focus of the present study. The impact of this boundary condition is illustrated for the seawater-intrusion problem in the Gooburrum aquifers, which occur within Tertiary sedimentary strata. A two-dimensional variable-density groundwater and solute-transport model was constructed using the computer code 2DFEMFAT (Cheng et al. 1998). The code was tested against an experiment for a steady-state freshwater-saltwater interface and against the Elder (Elder 1967) free-convection problem. Numerical simulations show that the imposition of the commonly-used equivalent hydrostatic freshwater heads, combined with a constant salt concentration at the seaward boundary, results in overestimated seawater intrusion in the lower Gooburrum aquifer. Since the imposition of this boundary condition allows water flow across the boundary, which subsequently takes salt into the aquifer, a careful check is essential to estimate whether too much mass of salt is introduced.

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Resumen La intrusión de agua salada en áreas agrícolas costeras a causa de la abstracción de aguas subterráneas es un problema medioambiental mayor a lo largo de la costa noreste de Australia. Se están explorando opciones de manejo mediante el uso de modelos numéricos, sin embargo, quedan pendientes cuestionamientos con respecto al nivel apropiado de sofisticación de los modelos, la elección de condiciones de límites hacia el mar y cómo acomodar la heterogeneidad y la incertidumbre de los datos. La elección de límites hacia el mar es importante ya que afecta la cantidad de sal transportada a los acuíferos y forma el centro de interés del presente estudio. Se ilustra el impacto de esta condición de límites para el problema de la intrusión de agua de mar en los acuíferos de Gooburrum, Queensland, Australia. Se construyó un modelo de transporte de solutos y de densidad variable de aguas subterráneas de dos dimensiones mediante el uso del código de computación 2DFEMFAT. El código se probó contra un experimento para una interfase de agua salada-agua dulce de estado constante y contra el problema de Elder de convexión libre. Las simulaciónes numéricas muestran que las cimas de agua dulce hidrostáticas equivalentes utlizadas comúnmente combinadas con una concentración de sal constante en el límite hacia el mar resultan en una sobreestimación de la intrusión de agua de mar en el acuífero bajo de Gooburrum. Puesto que la imposición de esta condición de límites permite flujo de agua a través de los límites, el cual subsecuentemente transporta sal al acuífero, una verificación cuidadosa es esencial para estimar si se introduce demasiada masa de sal.

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Résumé Investigations numériques de lintrusion deau de mer à Gooburrum, Bundaberg, Queensland. Lintrusion deau salée due au captage deau souterraine dans les régions agricoles situées le long de la côte Nord-Est de lAustralie est un grave problème environnemental. Des solutions à ce problème sont présentement étudiées à laide de la modélisation numérique. Cependant des questions subsistent concernant le niveau de sophistication du modèle, le choix des limites le long de lintrusion salée et la manière daccommoder lhétérogénéité et lincertitude des données. Le choix de la limite le long de lintrusion deau salée est important puisque cette limite détermine la quantité de sel transporté dans laquifère et constitue le sujet de la présente étude. Leffet du choix de cette limite est bien illustré par le problème dintrusion deau salée dans les aquifères de Gooburrum, Queensland, Australie. Un modèle bidimensionnel découlement à densité variable et de transport de solutés a été conçu en utilisant le code 2DFEMFAT. Ce code a été testé avec une expérimentation ayant pour objet lécoulement en régime permanent dune interface eau salée/eau douce. Il a aussi été mis à lépreuve par le problème de convection libre de Elder. Les simulations numériques révèlent que limposition de la limite communément utilisée, quon appelle la «charge hydrostatique équivalente deau douce», conduit, dans le cas o lon a une concentration constante en sels le long de lintrusion deau salée, à une surestimation de lintrusion deau salée dans laquifère inférieur de Gooburrum. Puisque que cest limposition de cette limite qui permet lécoulement de leau au-delà de la frontière de laquifère, ce qui introduit subséquemment du sel dans laquifère, une vérification minutieuse doit tre effectuée afin de contrôler la quantité de sel introduit.

     

The petrogenesis of the Kangerdlugssuaq alkaline intrusion,east Greenland

Evidence of layering and physical conditions of emplacement are discussed for this saucer-shaped, differentiated syenite mass. The intrusion is thought to derive from a magma of quartz trachytic composition,rather than from partial melting of the basement gneiss. The derivation of an undersaturated residual liquid, necessary to produce the pulaskite and the foyaite, is discussed, together with the mechanism whereby the ‘thermal barrier’ is crossed. Possible explanations considered are the depression of the thermal barrier through increased vapour pressure; the formation of iron-bearing feldspar; escape of silica and some potassium with volatile constituents; and crystal ? liquid equilibrium control.     

Low-sulfide PGE mineralization in layered intrusion ring,Vestfold Hills,Antarctica

This paper presents results of the study of norite complex from the Vestfold Hills (East Antarctica) containing a low-sulfide type of mineralization. The ore mineralization occurs in specific rock types and along the contact of norites the host rocks. Three mineralization types: Fe–Ni–Cu sulfide, oxide, and PGE-bearing are known. PGE mineralization is represented by palladium–bismuth tellurides of the michenerite–merenskyite series. A model of ore-formation succession and a concept of the origin of low-sulfide PGE mineralization by means of crystallization and subsequent evolution of monosulfide and intermediate solid solutions have been developed.     

Shape and intrusion style of the Coastal Batholith, Peru

The Coastal Batholith of Peru extends over 1600 km parallel to the coast along the Andean trend. Gravity profiles on three traverses across the batholith indicate the geometry is essentially that of a flat slab with average thickness from 2.0–3.2 km, and a thick root 4–10 km wide to the west. Granitic material does not extend to depths greater than 3 km below sea level datum.This study supports recent gravity work which indicates plutons are commonly thin, 5 km or less in thickness. Detailed mapping in the Lima segment of the Coastal Batholith reveals thin plutons where space was made dominantly by downward displacement via floor depression. However, early roof uplift also created some space. Stoping occurs but is not a major space maker. Floor depression may be modelled by cantilever or piston mechanisms and although the strong marginal deformation with mylonites, tuffisites, microbreccia, faults and shear zones suggests the piston model best describes the mechanism of emplacement of much of the Coastal Batholith some space was probably made by a cantilever mechanism. In brief, space making processes involved early roof uplift and regional doming, then floor depression mainly by piston and probably subsidiary cantilever mechanisms and, finally, local stoping producing the cut-out rectilinear nature of the batholith.The Coastal Batholith formed on shallow partial melting of hydrous basaltic marginal basin rocks between 5 and 10 km. Floor depression occurred as the crustal column foundered into an actively deflating layer of partial melt. This is an efficient space making process and is limited here to shallow levels of the upper crust only. The melts ascended to within 2 or 3 km of the surface, up dyke-like conduits then spread horizontally to form tabular plutons.     

Ni-Co sulphide segregation in the Mamb pyroxenite intrusion, Cameroon

The amphibole metapyroxenite intrusion from Mamb (Cameroon) consists of enstatite, diopside-augite, edenite, and traces of plagioclase, biotite and rutile. It contains notable amounts of sulphides (pyrrhotite, pentlandite, chalcopyrite, pyrite and Co-rich violarite). The sulphide phase segregated during magma crystallization as immiscible droplets (≤ 1 mm) included in growing ferromagnesian minerals or aggregated in the silicate crystal mush to form an interstitial phase. However, observed sulphide assemblages are likely to result from low-T (≤ 300 °C) re-equilibration of high-T monosulphide solid solutions, more particularly during the Pan-African metamorphic event. The Mamb amphibole pyroxenite intrusion is tentatively considered as a potential source for Ni and Co mineralization.     

Numerical simulation of sea water intrusion near Beihai, China

 A leaky aquifer system occurs in the coastal plain near Beihai, China. Seawater intrusion into the confined aquifer took place along the northern coast. Chloride concentrations at some observation wells increased steadily from 1988 and were at their peak in 1993. A quasi-three-dimensional element model has been developed to simulate the spatial and temporal evolution of hydraulic heads and chloride concentrations of the groundwater near the northern coast. The simulation model was based on the transition zone approach, which requires simultaneous solution of the governing water flow and solute transport equations. An irregular grid of a quadrangle was used to discretize the flow domain. Various aquifer parameters were verified with the numerical model in order to obtain satisfactory matches between computed values and observed data from an investigation. Three pumpage schemes were designed to use the calibrated model for prediction of future changes in water levels and chloride concentrations in groundwater in the study area. Results show that seawater intrusion would worsen in the confined aquifer if the current rates of groundwater pumpage continue. The alternative, to eliminate pumpage in the intruded area and to moderate pumpage rates from water supply wells far from the seashore, may limit seawater intrusion significantly and is considered attractive in the area. Received: 27 September 1999 · Accepted: 27 December 1999     

新疆阿尔泰元古代基性岩浆侵入事件

新疆阿尔泰山南缘深变质岩地层中零星出露有一些变质辉长岩,原被认为是晚古生代基性侵入体。对富蕴县乌恰沟基性岩的研究表明,乌恰沟变质基性岩是未受陆壳物质混染的上地幔部分熔融的产物,其Nd模式年龄TDM为945～977Ma,Sm-Nd等时线年龄为(974±63.4)Ma,反映了阿尔泰南缘在青白口纪初期的一次基性岩浆侵入事件。深变质围岩的Nd模式年龄为1435～1580Ma,相当于中元古代长城纪,代表了阿尔泰地区下—中元古界克木齐群形成的时代。     

Garnet-cordierite gneisses near the Egersund-Ogna anorthositic intrusion, southwestern Norway

Graphite-bearing garnet-cordierite rocks from the Sjelset-Vikesá region, south Bogaland, Norway have been analysed by microprobe methods. The garnets belong to the pyropealmandine series and contain 28 mole% pyrope, while the cordierites contain about 71% of the Mg end-member. A regional temperature of about 720–750°C and a lithostatic pressure in the order of 6–7 kb have been inferred from the garnet and cordierite compositions. The petrographic observation suggests that such P---T conditions might reflect a retrograde metamorphic event. A tentative estimation of the fluid phase composition, based on the study of opaque minerals, is presented.