Development of rodingite in basaltic rocks in serpentinites,East Liguria,Italy

Hydrogrossular replacement of plagioclase in basaltic rocks enclosed in serpentinite, and relationships between hydrogrossular, pumpellyite, vesuvianite are described. Rogingitic rocks are dominated by mixed layer chlorite-smectite, chlorite, pumpellyite, hydrogrossular and vesuvianite. In these rocks pumpellyite attains maximal Mg contents, and chemical analysis shows extreme removal of Na₂O, K₂O, TiO₂ and SiO₂ from the basalts, and increase in the Fe³⁺/Fe²⁺ ratio. Leaching during serpentinization by extremely alkaline solutions dominated by Ca-Mg(OH) may explain removal of components, but the oxidation may suggest that at an earlier stage dykes may have acted as input aquifers.     

Structural states of Mg-cordierite I: Order parameters from synchrotron X-ray and NMR data

The hexagonal to orthorhombic phase transition in synthetic Mg-cordierite has been studied by (i) measuring the spontaneous strain associated with the transition using Synchrotron X-ray powder diffraction and (ii) measuring the degree of Al, Si order in terms of the number of Al-O-Al bonds per formula unit using solid state NMR spectroscopy. This defines the two order parametersQ andQ _od respectively, and their relationship as a function of annealing temperature and time is used to define the structural states of cordierite during the ordering sequence. The formation of modulated hexagonal cordierite within which a high degree of Al, Si order can be attained, results in a strongly non-linear relationship betweenQ andQ _od .The transition from modulated to orthorhombic cordierite is strongly first-order under all temperature conditions studied and involves a large step inQ, whileQ _od changes continuously throughout the ordering sequence with no marked discontinuity at the phase transition. The lattice distortion, traditionally defined in cordierite by the Δ index provides no full information on the degree of Al, Si order in anhydrous Mg-cordierite, and both order parameters must be used to define its structural state. Transmission electron microscopy has been used to study the mechanism of the transformation from hexagonal to modulated to orthorhombic cordierite.     

On the occurrence of eclogite in Western Norway

Recent experimental data show that eclogites may form in the crust under conditions where total pressure exceeds water pressure. The regional distribution of eclogites in Western Norway and their association with crustal rocks makes their formation in the crust the most attractive hypothesis. Before a mantle origin should be assigned to any rock within this eclogite and garnet peridotite area it should be demonstrated that their country rocks are in a metamorphic state incompatible with the load pressures required for eclogite stability. Criteria for ascertaining eclogite formation in the crust are discussed.Publication no. 8 in the Norwegian geotraverse project.     

Kyanite-andalusite equilibrium

The solubilities of macrocrystalline andalusite and kyanite have been measured in water between 400 and 550 °C and at pressures of 1–3 kilobars. Resulting data indicate that the phases are in equilibrium at 398 °C (1 kb,), 472 °C (2 kb) and 534 °C (3 kb). Due to the inherent difficulty of measuring small solubility differences errors in these temperatures could be as much as ±40 °C although experimental reproducibility suggests greater precision.     

Experimental introduction of excess Ar40 into a granitic melt

Samples of a Precambrian granite were melted in sealed capsules to produce a radiogenic Ar⁴⁰ atmosphere over the melt. The amount of Ar⁴⁰ incorporated in the quenched charge was then determined. Under these experimental conditions the amount of argon dissolved in the quenched melt was appreciable and could be an important source of error in potassiumargon dating.Publication authorized by the Director, U.S. Geological Survey.     

Trace element chemistry of major rivers in Orissa State, India

 Geochemical analyses of surface waters from rivers flowing through Orissa State, India, indicated that trace element concentrations were extremely variable and consistently higher than world river average. The Brahmani River was the most solute-rich river studied, followed by the Baitarani and Mahanadi Rivers. Although all three rivers drain similar geology, the Brahmani River catchment is heavily industrialized, and water samples collected upstream and downstream from industries indicated that anthropogenic activity directly influenced its chemical composition. Samples collected from several towns, in all three river systems, did not invariably show similar patterns, with various elements having higher dissolved concentrations upstream. Because the concentration of total solids increased downstream, this implied that some components of the sewage had effectively sequestered available elements from solution and converted them to particulate material. Although the impact of pollution is clearly recognizable in water samples collected in proximity to the anthropogenic source, there are only slight elemental accumulations in the lower reaches of the Mahanadi River, with no accumulation in the Brahmani River. Apparently for these large rivers, discharged effluent becomes rapidly diluted, while complexation and sedimentation further removes trace elements from the water column. However, in the less voluminous Baitarani River, elementar enrichment near the river's mouth suggests that in this secondary river, where dilution effects are less, the concerns over regional water quality may be more prevalent. Received: 1 April 1995 · Accepted: 30 August 1995     

大洋环流型式转换在冰期旋回中的作用及经典第四纪冰期理论质疑(续)

大洋环流型式转换在冰期旋回中的作用及经典第四纪冰期理论质疑(续)汉景泰Ｗ．Ｓ．Ｆｙｆｅ(加拿大西安大略大学地质系)４问题及讨论大洋环流－气候学说认为从冰期到间冰期海洋－大气系统全球性巨型再组合导致了末次冰期的终止。     

Reappraisal of the metamorphic facies concept

Eskola's concept of metamorphic facies, now 50 years old, is reappraised in the light of current knowledge and usage among petrologists. Facies should be defined solely in terms of observable geologic criteria. LikeEskola, we continue to view each facies as a set of mineral assemblages that approximate equilibrium within a definite range of temperature; but this is inference and must be excluded from the definition of facies. Mutual boundaries between facies are transitional. Division into subfacies has proved unacceptable to many writers, and has led to confusion in the physical interpretation of metamorphic parageneses. We propose henceforth not to recognize subfacies. Eleven facies are recognized in this paper, and their terminology has been adapted as nearly as possible to current general usage:

1. A.
   Low-pressure facies commonly but not exclusively of contact metamorphism. In order of increasing temperature:

   1. (1)
      Albite-epidote-hornfels.     

Pan-African plates: Additional evidence from igneous events in Saudi Arabia

The chemical and geological nature of thec. 600 m.y. igneous complex of the Al-Hadah escarpment of Saudi Arabia is fitting to that of a modern subduction environment. It appears that plate motions were occurring during this Pan-African tectonic event but the scale of both plates and motions was smaller than that of the present time.