The petrogenesis of the Edough amphibolites, Annaba, NE Algeria: two unrelated basic magmas and the lherzolite-harzburgite residue of a possible magma source

Summary The conditions of metamorphism and petrogenesis of Kef Lakhal amphibolites and associated amphibolite and olivine-rich lenses are discussed. The Kef Lakhal amphibolites contain plagioclase ranging from An₈₅ and An₁₂ and Ca-poor normally zoned garnet (< 9 wt% CaO) and were last metamorphosed to upper amphibolite facies. The amphibolite lenses invariably contain calcic plagioclase (An_97-78) and Ca-rich (up to 14 wt% CaO) doubly zoned garnets. Based on garnet zoning, it is found that the lenses experienced the three metamorphisms recorded elsewhere in the massif whereas the main amphibolites suffered only the last two metamorphisms, the last of which reached conditions of about T= 700 ± 80 °C and P= 8–10 Kb. This agrees with two unrelated igneous suites and is supported by the chemistry of the rocks and quantitative modelling. The Kef Lakhal amphibolites were formed by olivine-dominated fractional crystallisation processes from melts derived by partial melting of a homogeneous source and preserve MORB affinities. The amphibolite lenses were also evolved by fractional processes dominated by olivine but from a less homogeneous source and have island arc characteristics. The associated olivine-rich lenses are lherzolite-harzburgite mantle residua which suffered up to 35% melting. Bearing in mind the lack of isotopic and structural information, the data presented in this study indicate that fractional crystallisation of liquids produced through non model melting of these residua does not reproduce the composition of either of the amphibolites. Fractionation of melts similar to those derived from the Ronda peridotites yield compositions similar to the Edough amphibolites.

---

Die Entstehung der Edough Amphibolite, Annaba, NE Algerien; zwei basische Magmen und das Lherzolit-Harzburgit-Residuum einer möglichen Magmenquelle

Zusammenfassung Die Metamorphosebedingungen und die Petrogenese der Amphibolite von Kef Lakhal und der mit ihnen assoziierten Amphibolit- und Olivin-reichen Linsen werden diskutiert. Die Kef Lakhal-Amphibolite enthalten Plagioklas, dessen Zusammensetzung von An₈₅ bis An₁₂ schwankt, und Ca-armen, normal zonierten Granat (< 9 Gew % CaO). Sie wurden unter Bedingungen der obenen Amphibolitfacies metamorphosiert. Die Amphibolit-Linsen führen stets Ca-reichen (An_97-78) Plagioklas und doppelt zonierten Granat (bis zu 14 Gew % Ca0). Die Granatzonierung läßt erkennen, daß die Linsen drei Metamorphose-Phasen, die auch sonst in dem Massiv nachgewiesen wurden, ausgesetzt waren. Die letzte Phase erreichte Bedingungen von ungefähr T = 700 ± 80 °C und P = 8–10 kb. Dies weist auf zwei, miteinander nicht verwandte magmatische Gesteinsabfolgen hin; dieses Konzept wird durch die chemische Zusammensetzung und durch quantitative Modellierung unterstützt. Die Kef Lakhal-Amphibolite wurden durch Olivin-dominierte fraktionierte Kristallisation aus Schmelzen gebildet, die durch partielle Aufschmelzung einer homogenen Quelle entstanden sind und MORB-Charakteristik haben. Die Amphibolit-Linsen gehen auch auf Olivin-dominierte Fraktionierungs-Prozesse zurück, hatten aber eine weniger homogene Quelle und zeigen Inselbogen-Charakteristika. Die assoziierten Olivin-reichen Linsen sind Lherzolit-Harzburgit Mantel-Residua, die von bis zu 35% Aufschmelzung betroffen waren. Obwohl zu berücksichtigen ist, daß isotopengeologische und strukturelle Daten fehlen, zeigen die Ergebnisse, daß fraktionierte Kristallisation von Schmelzen, die durch Non-Modell Aufschmelzung der Residua entstanden sind, nicht die Zusammensetzung der Amphibolite reproduzieren können. Hingegen liefert Fraktionierung von Schmelzen, die denen des RondaPeridotits ähnlich sind, Zusammensetzungen, die denen der Edough Amphibolite ähnlich sind.

---

---

With 11 Figures     

An examination of the validation of a model of the hydro/thermo/mechanical behaviour of engineered clay barriers

This paper focuses attention on the development of a numerical model of the hydro/thermo/mechanical behaviour of unsaturated clay and its consequent verification and validation. The work presented describes on-going collaboration between the Cardiff School of Engineering and Atomic Energy of Canada. The model development, which was carried out at Cardiff, can be described as being based on a mechanistic approach to coupled heat, moisture and air flow. This is then linked to a deformation analysis of the material within a ‘consolidation’ type of model. The whole is solved via the finite element method to yield a computer software code named COMPASS (COde for Modelling PArtly Saturated Soil). Some aspects of verification and validation of the model have been addressed in-house. However, the purpose of current AECL work is to provide an independent, rigorous, structured programme of validation and the paper will also explore the further validation of COMPASS within this context. © 1998 by John Wiley & Sons, Ltd.     

Experimental determination of argon solubility in silicate melts: An assessment of the effects of liquid composition and temperature

The argon solubility of 38 liquids in the system Na₂O-CaO-MgO-Al₂O₃-SiO₂ (NCMAS) has been determined at 1873 K and 1 bar, the argon concentration of presaturated glasses being measured using a static mass spectrometer. For compositions in the subsystem diopside (CaMgSi₂O₆), nepheline (NaAlSiO₄), albite (NaAlSi₃O₈), anorthite (CaAl₂Si₂O₈), argon solubility is generally a linear function of the relative proportion of each end member, solubility being lowest in diopside melt (1.53 10⁻⁵ cm³ STP · g⁻¹ · bar⁻¹) and highest in albite melt (2.88 10⁻⁴ cm³ STP · g⁻¹ · bar⁻¹). For the tectosilicate joins studied (SiO₂-Na₂Al₂O₄, SiO₂-CaAl₂O₄, SiO₂-MgAl₂O₄) solubility decreases with decreasing silica content in all cases, being highest for Na-bearing liquids and lowest for Mg-bearing liquids at constant molar silica content. Where comparison is possible our results are in good agreement with data from the literature. When our data are considered in isolation we find that argon solubility shows an excellent correlation with calculated ionic porosity. The covariation of argon solubility and liquid density is also reasonable, that with molar volume less convincing and that with polymerization state (as defined by the ratio of the number of nonbridging oxygens and tetrahedral network forming cations; NBO/T) nonexistent. However, when our data are combined with those from the literature no well constrained correlation between argon solubility and ionic porosity is apparent. Based upon this observation and consideration of the temperature dependence of noble gas solubility it is concluded that ionic porosity is not a universally applicable parameter which may be used to predict noble gas solubility as a function of composition, temperature and pressure. Two new models for calculating argon solubility are proposed, both employing the notion of partial molar argon solubilities. The first uses oxide components, for which partial molar argon solubility is directly proportional to partial molar ionic porosity calculated at 1873 K, irrespective of the temperature of experimental equilibration. The second model, which offers the best fit to the available data, employs tetrahedral units rather than oxides as the proposed melt components. This latter model successfully accounts for reported argon solubilities in simple Al-free systems, in simple Al-bearing systems and in natural liquids. This is interpreted to infer that argon is incorporated in large sites in the liquid structure (such as the space within rings of n-tetrahedra) although further work is required to understand the quantitative links between melt structure and noble gas solubility.     

Nature of the small main belt Asteroid 3169 Ostro

We present a set of rotational lightcurve measurements of the small main belt Asteroid 3169 Ostro. Our observations reveal an unambiguous, double-peaked rotational lightcurve with a peak-to-peak variation up to 1.2±0.05 mag and a synodic period of 6.509±0.001 h. From the large flux variation and the overall shape of the lightcurves, we suggest that 3169 Ostro could be a tightly bound binary or a contact binary, similar to the Trojan Asteroid 624 Hektor. A shape model of this system is proposed on the assumption that 3169 Ostro is a Roche binary described by a pair of homogeneous elongated bodies, with a size ratio of 0.87, in hydrostatic equilibrium and in circular synchronous motion around each other. The direction of the spin axis is determined modulo 180° by its J2000 ecliptic coordinates λ₀=50±10°, β₀=±54±5°. The binary interpretation and the pole solution adequately fit the earlier photometric observations made in 1986 and 1988. However, additional supporting lightcurves are highly desirable especially in the next mutual events occurrence of 2008 and 2009 in order to remove the pole ambiguity and to confirm unambiguously the binary nature of 3169 Ostro.     

Occurrence and characteristics of sporadic sodium layer observed by lidar at a mid-latitude location

Na lidar observations of SSL during the past 5 years at a mid-latitude location (Wuhan, China, 31°N, 114°E) are reported in this paper. From 26 SSL events detected in about 230 h of observation, an SSL occurrence rate of 1 event/9 h at our location was obtained. This result, combined with that reported by Nagasawa and Abo (Geophys. Res. Lett. 22 (1995) 263) at Tokyo, Japan, reveals that the SSL occurrence can be relatively frequent at some mid-latitude locations. The statistical analyses of main parameters for the 26 SSL events were made, and the results were compared with those previously reported. By examining the corresponding data from a nearby ionosonde, it was found that there was a fairly good correlation between SSL and Es. Of the 18 pairs of SSL and Es events checked, 15 of SSL were accompanied by Es, and 8 pairs of them were correlated within 1 h in time and within 5 km in altitude. From the analyses of observed perturbations during SSL development, the role of dynamic processes of atmosphere in the SSL formations were emphasized.     

Rock physics template (RPT) analysis of well logs and seismic data for lithology and fluid classification in Cambay Basin

The Cambay Basin is 450-km-long north–south-trending graben with an average width of 50 km, having maximum depth of about 7 km. The origin of the Cambay and other Basins on the western margin of India are related to the break up of the Gondwana super-continent in the Late-Triassic to Early-Jurassic (215 ma). The structural disposition of the Pre-Cambrian basement—a complex of igneous and metamorphic rocks exposed in the vicinity of the Cambay Basin—controls its architecture. The principal lineaments in the Basin are aligned towards NE-SE, ENE-WSW and NNW-SSE, respectively. Rock physics templates (RPTs) are charts and graphs generated by using rock physics models, constrained by local geology, that serve as tools for lithology and fluid differentiation. RPT can act as a powerful tool in validating hydrocarbon anomalies in undrilled areas and assist in seismic interpretation and prospect evaluation. However, the success of RPT analysis depends on the availability of the local geological information and the use of the proper model. RPT analysis has been performed on well logs and seismic data of a particular study area in mid Cambay Basin. Rock physics diagnostic approach is adopted in the study area placed at mid Cambay Basin to estimate the volume in the reservoir sands from 6 wells (namely; A, B, C, D, E and F) where oil was already encountered in one well, D. In the study area, hydrocarbon prospective zone has been marked through compressional (P wave) and shear wave (S wave) impedance only. In the RPT analysis, we have plotted different kinds of graphical responses of Lame’s parameters, which are the function of P-wave velocity, S-wave velocity and density. The discrete thin sand reservoirs have been delineated through the RPT analysis. The reservoir pay sand thickness map of the study area has also been derived from RPT analysis and fluid characterization. Through this fluid characterization, oil-bearing thin sand layers have been found in well E including well D. The sand distribution results prove that this methodology has able to perform reservoir characterization and seismic data interpretation more quantitatively and efficiently.     

Interrelationship between geochemical elements of sediment and groundwater at Samrak Park Delta of Nakdong River Basin in Korea: multivariate statistical analyses and artificial neural network approaches

This research was conducted at Samrak Park Delta of Nakdong River Basin in Busan Metropolitan City, Korea. The main objective of this study was to evaluate the interrelationship of geochemical elements in sediments and groundwater through multivariate statistical analyses and a multilayer perceptron artificial neural network model. The mean concentrations of chemical elements were Si (46%), Fe (16.9%), Al (15.7%), K (7.5%) and Ca (4.5%) in sediments, and Na (8650 mg/L), Mg (999 mg/L), Ca (432 mg/L), K (293 mg/L) and Cl (17,640 mg/L) in groundwater, respectively. The principal component analysis produced 3 kinds of factors with the variances of 63.37, 27.02 and 9.62%, respectively. It is suggested that the chemical components of sediments and groundwater were mainly originated from source rocks and seawater intrusion, with the minor impacts of irrigation and industry. Cluster analysis also showed that chemical elements were mainly controlled by the natural geogenic sources and seawater intrusion. Multilayer perceptron of artificial neural network (ANN) presented the good interrelationship between sediment and groundwater. The determination coefficients (R ²) between ANN predicted values and observed values in groundwater showed the high values of 0.61–0.97 except Mg, Mn and Sr. It is revealed that the chemical components of sediment and groundwater were derived from local geological origin and from the minor impact of anthropogenic sources. Multivariate analyses and ANN contributed to the identification of the mutual relationship between the geochemical elements of sediment and those of groundwater.     

西天山喇嘛苏铜矿成矿斑岩的岩石学、地球化学特征及成因探讨

位于西天山别珍套-科古琴晚古生代岛弧西段的喇嘛苏铜矿床是区内最大的铜矿床,与成矿作用有着密切关系的斑岩体为英云闪长斑岩、花岗闪长斑岩,是同源岩浆分异演化的产物,且花岗闪长斑岩可能属于岩浆演化晚期的产物。本区成矿斑岩的主量、微量元素和Sr-Nd同位素地球化学特征表明,其富集大离子亲石元素,而相对亏损高场强元素,出现了较为明显的Ta、Nb负异常,初始锶同位素ISr和εNd(t=390Ma)值分别为0.7072～0.7076和-0.32～0.17,显示壳幔混合源的特征,利用Sr和Nd同位素估算其源区物质约有50%来源于地壳。岩石地球化学特征指示了其为典型钙碱性火山弧花岗岩,暗示其形成于大陆弧环境。结合区域地质背景,推测本区成矿斑岩是在洋壳俯冲作用下发生部分熔融,交代原先的地幔楔,并混合了部分下地壳的物质,经历分离结晶作用的产物,其形成可能与晚古生代准噶尔洋板块向南的俯冲作用有关。结合东西天山的成矿斑岩的地球化学特征对比研究,岩浆源区的差别可能导致不同类型斑岩型矿床的形成,斑岩型铜矿床的形成较斑岩型钼矿床可能有更少的地壳物质贡献。     

Controlling factors of the δ 11B-pH proxy and its research direction

Significant boron isotope fractionation occurs in nature (?70 ‰ to +75 ‰) due to the high geochemical reactivity of boron and the large relative mass difference between ¹⁰B and ¹¹B. Since the 1990s, reconstruction of ancient seawater pH using the isotopic composition of boron in bio-carbonates (δ ¹¹B_carb), and then calculation of the past pCO₂ have become important issues for the international isotope geochemistry community, and are called the δ ¹¹B-pH proxy. Although many achievements have been made by this proxy, various aspects of boron systematics require rigorous evaluation. Based on the previous researches, mechanism of boron isotope fractionation, variation of boron isotope (δ ¹¹B) in nature (especially in bio-carbonates) and controlling factors of the δ ¹¹B-pH proxy, such as the dissociation constant of B(OH)₃ in seawater (pK_a), the δ ¹¹B of seawater (δ ¹¹B_SW), the boron isotopic fractionation factor between B(OH) ₄ ^? and B(OH)₃ (α _4–3), and the incorporated species of boron into bio-carbonates, are reviewed in detail and the research directions of this proxy are proposed. Generally, the controversy about pK_a, δ ¹¹B_sw, and α _4–3 is relatively less, but whether boron incorporated into bio-carbonates only in the form of B(OH) ₄ ^? remains doubtful. In the future, it is required that the physicochemical processes that control boron incorporation into carbonates be rigorously characterized and that the related chemical and isotopic fractionation be quantified. It is also necessary and important to establish a “best-fit empirically equation” between δ ¹¹B_carb and pH of seawater based on the precipitation experiments of inorganic or culture experiments of corals or foraminifera. In addition, extended application of the δ ¹¹B-pH proxy to the earlier part of the Phanerozoic relying on the Brachiopods is worthy of studying. Like other geochemical indicators, there are limiting factors of δ ¹¹B; however, it remains a very powerful tool in the reconstruction of past seawater pH at present.