Low temperature fluid alteration of oceanic layer 2 basalts, DSDP Leg 37

1977 ◽  
Vol 14 (4) ◽  
pp. 911-926 ◽  
Author(s):  
A. J. Andrews
Keyword(s):  
Low Temperature ◽  
Chemical Nature ◽  
Sea Water ◽  
Significant Rise ◽  
Secondary Phases ◽  
Acoustic Basement ◽  
Layer 2 ◽  
Fluid Alteration ◽  
Fluid Interaction ◽  
Mineralogical Evidence

Penetration of cold seawater into layer 2 of the oceanic crust occurs to at least 600 m, the maximum depth drilled below the sediment-acoustic basement boundary during Leg 37 of the DSDP. The main alteration phases are Mg-saponite, Fe-K rich celadonite, phillipsite, calcite, and hematite. The only exception to this occurs in the form of intensely hydrothermally altered gabbro breccias from an intrusive complex at site 334. There is no mineralogical evidence to suggest an increase in metamorphic grade with depth; however, a variation in mineralogy and alteration intensity, occurs as a function of structure, permeability, and the chemical nature of rock-fluid interaction. On this basis three types of alteration are defined as follows: (A) fracture focussed, oxidative; (B) palagonitic; and (C) non-oxidative, pervasive.Electron microprobe analyses reveal that alteration of fresh glass to palagonite involves the addition of H2O, an increase in total Fe, K2O, TiO2, and possibly SiO2, and the loss of CaO, MgO, Na2O, and MnO.Detailed examination of the mineralogy and chemistry of oxidative alteration suggests that during low temperature sea water–basalt interaction, basalt experiences a net gain in CaO, total Fe and K2O, while SiO2 and MgO appear to have been locally remobilized. These trends are generally consistent with the distribution of secondary phases. The distributions of Mn, Cu, Ni, Zn, Co, and Sr do not appear to have been significantly affected during this process.It is apparent that seawater must have experienced significant Eh lowering during this interaction; however, the occurrence of hematite–magnetite and absence of sulphide in this particular environment requires that seawater was either highly depleted in total sulfur or experienced a significant rise in pH.

Reaction aureoles around uraninites within biotite and plagioclase: evidence of low-temperature sequential fluid alteration and LREE-mobilization from monazite

2016 ◽  
Vol 80 (4) ◽  
pp. 567-584 ◽  
Author(s):  
Manoj K. Ozha ◽  
Biswaji Mishra ◽  
Aiveliagaram V. Jeyagopal
Keyword(s):  
Low Temperature ◽  
Secondary Phases ◽  
Alpha Radiation ◽  
Fluid Infiltration ◽  
The Matrix ◽  
Fluid Alteration ◽  
Simulation Results ◽  
Radial Cracks ◽  
Penetration Depths ◽  
Intense Radiation

AbstractOptical microscopy, Raman spectroscopy and electron probe microanalyses were conducted on a migmatitic metapelite to investigate the effects of alpha radiation and subsequent alteration at the interface between uraninite inclusions and the host minerals biotite, chlorite and albitic plagioclase. The study reveals (1) anomalous colouration under the polarizing microscope; (2) pertinent changes in the characteristic Raman spectra of host phases; (3) reaction aureoles, composed of secondary phases (viz. chlorite and K-feldspar) of various sizes (∼15–45 μm) within biotite and plagioclase, respectively; (iv) K-feldspatization and sericitization of plagioclase at the grain boundaries; (5) agreement between the observed α-penetration depths and the Monte-Carlo simulation results; and (6) dissolution textures within the matrix monazites. Analysis of the compositions of the reaction aureoles in albitic plagioclase reveals a systematic distribution of K-feldspar-, LREE- and clay-rich zones; while the same in biotite is composed of secondary chlorite. The growth sequence of the secondary phases indicates an influx of a K-rich fluid, following intense radiation damage, efficiently superimposed by LREE-metasomatism and later acidic alteration. These changes took place under low-temperature (≤150°C) conditions, wherein radial cracks (within plagioclase) and cleavages/fractures (within biotite) favoured fluid infiltration-circulation into the reaction aureoles. Depletion of the LREEs from the dissolved matrix monazites and their enrichment as a discrete LREE phase within the damaged aureoles in plagioclase demonstrate micrometre-scale LREE mobility.

scholarly journals On the function of chlorocruorin

1940 ◽  
Vol 129 (855) ◽  
pp. 137-153 ◽  
Keyword(s):  
Carbon Monoxide ◽  
Oxygen Consumption ◽  
Dissolved Oxygen ◽  
Sea Water ◽  
Oxygen Carrier ◽  
Significant Rise ◽  
Oxygen Concentrations

1.The oxygen consumption of Sabella decreases soon after the concentration of dissolved oxygen in the sea water falls below the value corresponding to air saturation both at 10 and 17° C. Above air saturation at 17° C there is no significant rise in oxygen consumption. 2. The oxygen consumption of Sabella whose chlorocruorin has been converted to carboxychlorocruorin is lower than that of normal worms. This is the case at air saturation of the water and at oxygen concentrations below air saturation both at 10 and 17° C. 3. The fall in oxygen consumption of the animals after treatment with carbon monoxide is not due to an action of the latter on cell enzymes. 4. It follows that chlorocruorin functions as an oxygen carrier in Sabella at all temperatures and oxygen pressures to which the animals are subjected in nature.

Elba manganese ores and their origin, South-eastern Desert, U.A.R.

1971 ◽  
Vol 38 (294) ◽  
pp. 235-244 ◽  
Author(s):  
E. Z. Basta ◽  
W. S. Saleeb
Keyword(s):  
Low Temperature ◽  
Surface Oxidation ◽  
Eastern Desert ◽  
Oxidation Zone ◽  
Manganese Ores ◽  
South Eastern ◽  
Narrow Belt ◽  
Ore Types ◽  
Mineralogical Evidence ◽  
Very Low Temperature

SummaryThe manganese ores of Elba, South-eastern Desert, occur as numerous veins located within a narrow belt trending N.W.-S.E. Three ore-types were distinguished: hard crystalline ore consisting mainly of pyrolusite or ramsdellite or both, banded colloform ore consisting mainly of psilomelane, and in places cryptomelane, and soft nodular ore consisting of todorokite with minor amounts of psilomelane (or cryptomelane), nsutite, and pyrolusite. Black calcite and baryte occur in some of the veins and increase with depth.Based on the field and mineralogical evidence the origin of the ore is discussed. It is suggested that the ore is a very low-temperature epithermal fissure deposit of black calcite type that occurs near the surface (oxidation zone) in brecciated zones along faults.

scholarly journals The Melting of Free-Drifting Icebergs

1980 ◽  
Vol 1 ◽  
pp. 119-122 ◽  
Author(s):  
D. S. Russell-Head
Keyword(s):  
Low Temperature ◽  
Water Temperature ◽  
Population Studies ◽  
Sea Water ◽  
Surface Shape ◽  
Different Temperatures

Blocks of ice with the proportions of tabular icebergs have been observed melting in water of different temperatures and salinities. The sub-surface shape adopted by the blocks melting in water of the same salinity as sea-water was typically a ‘bath-tub’ one. The basal and mean-side melt rates were of a similar value. The melt rates obtained in the laboratory for icebergs in water of a low temperature match those inferred from population studies of Antarctic icebergs. The melt rate is proportional to the water temperature above the onset of freezing raised to the power 1.5 and melt rates at 18°C are likely to be greater than one metre per day.

Distribution and evolution of uranium in the oceanic lithosphere

1979 ◽  
Vol 291 (1381) ◽  
pp. 423-431 ◽  
Keyword(s):  
Sea Water ◽  
Oceanic Lithosphere ◽  
Uranium Content ◽  
Major And Trace Elements ◽  
Ultramafic Rocks ◽  
Layer 2 ◽  
Secondary Enrichment ◽  
Layer 4 ◽  
Mid Atlantic Ridge ◽  
Fractionation Trend

Induced fission track techniques permit us to determine quantitatively the microscopic distribution of uranium in rocks, in their constituent minerals, and in percolating fluids. Both primary magmatic variations and secondary mobilization of uranium can be discerned. Concentrations of uranium in phenocrysts and fresh glasses of oceanic basalts and gabbros are very low (2-80 parts/10 9 ) and are comparable to concentrations in the same minerals of the associated ultramafic rocks. Variations with depth in D.S.D.P. holes show several distinct cyclic variations of uranium, accompanied by parallel trends in some major and trace elements. In Hole 332B (mid-Atlantic ridge, 36 °N), uranium and other elements can be shown to fall into two distinct groupings, each group following its own characteristic fractionation trend, suggesting that two distinct magmas differentiated independently beneath the median valley, the two magmas alternating in their contribution to the formation of oceanic layer 2. Earlier investigations of the uranium distribution in surface pillows and other dredged rocks exposed to sea water had shown that, owing to halmyrolysis, the uranium concentration increases systematically with distance from the axis of a midoceanic ridge. Subsequent investigations on rocks drilled from horizons deeper into oceanic layer 2 indicate that secondary enrichment or redistribution of uranium is confined to specific zones of altered basalt, near fractures, pillow and flow margins, and especially along horizontal planes of breccias and sediments in between massive flow where convective water circulation is thought to occur. Ultramafic rocks from the base of layer 3 and top of layer 4 are also enriched in uranium when hydrated by sea water during the process of serpentinization. A combination of these processes may double the uranium content of an oceanic lithospheric plate between the time of its formation and its eventual subduction.

scholarly journals The tectono-metamorphic evolution of a dismembered ophiolite (Tinos, Cyclades, Greece)

1996 ◽  
Vol 133 (3) ◽  
pp. 237-254 ◽  
Author(s):  
Yaron Katzir ◽  
Alan Matthews ◽  
Zvi Garfunkel ◽  
Manfred Schliestedt ◽  
Dov Avigad
Keyword(s):  
High Temperature ◽  
Low Temperature ◽  
Subduction Zone ◽  
Sea Water ◽  
Regional Metamorphism ◽  
Greenschist Facies ◽  
Normal Faults ◽  
Model Calculations ◽  
Facies Metamorphism ◽  
Greenschist Facies Metamorphism

AbstractThe six exposures of the Upper tectonic Unit of the Cycladic Massif occurring on the island of Tinos are shown to comprise a metamorphosed dismembered ophiolite complex. The common stratigraphic section consisting of tens-of-metres- thick tectonic slices of mafic phyllites overlain by serpentinites and gabbros is considered to have been derived by a combination of thrusting during obduction and subsequent attenuation by low-angle normal faults. All rock types show evidence of a phase of regional greenschist-facies metamorphism, which in the case of the phyllites is accompanied by penetrative deformation. The greenschist-facies metamorphism in gabbros is preceded by high temperature sea-floor amphibolite-facies alteration, whereas in the serpentinites, the antigorite + forsterite greenschist-facies assemblage overprinted an earlier low temperature lizardite serpentinite. Trace element patterns of the mafic phyllites and a harzburgitic origin of meta-serpentinites suggest a supra subduction zone (SSZ) affinity for the ophiolitic suite. ρ18O values of phyllites, gabbros and serpentinites range from 6 to 15%o. Model calculations indicate that such values are consistent with low temperature (50–200°C) alteration of parent rocks by sea-water at varying water/rock ratios. This would agree with the early low temperature mineralogy of the serpentinites, but the early high temperature alteration of the gabbros would require the presence of 18O-enriched sea-water.The following overall history is suggested for Tinos ophiolitic slices. (1) Oceanic crust was generated at a supra-subduction zone spreading centre with high temperature alteration of gabbros. (2) Tectonic disturbance (its early hot stages recorded in an amphibolitic shear zone at the base of serpentinites) brought the already cooled ultramafics into direct contact with sea-water and caused low-T serpentinization. (3) Tectonism after cooling involved thrusting which caused repetition and inversion of the original order of the oceanic suite. (4) Regional metamorphism of all the ophiolite components at greenschist-facies conditions (−450°C) overprinted the early alteration mineralogy. It was probably induced by continued thrusting and piling up of nappes. The Tinos ophiolite, dated as late Cretaceous and genetically related to other low pressure rock-units of the same age in the Aegean, differs in age and degree of dismemberment and metamorphism from ophiolites in mainland Greece.

scholarly journals Hysteretic magnetoelectric behavior of CoFe2O4–BaTiO3 composites prepared by reductive sintering and reoxidation

2019 ◽  
Author(s):  
Roberto Köferstein
Keyword(s):  
Impedance Spectroscopy ◽  
Low Temperature ◽  
Secondary Phases ◽  
Field Sweep ◽  
Photometric Analysis ◽  
Magnetoelectric Composites ◽  
Synthesis Route

Magnetoelectric composites (CoFe2O4)x–(BaTiO3)1-x with x = 0.1, 0.2, 0.3, 0.4 and 0.5 were prepared bya polyol mediated synthesis route. The densification step was performed in a reducing forming gasatmosphere at 1250 1C. Under these conditions Co2+ and Fe3+ are reduced to the corresponding metalsand thus a reaction of these elements with the BaTiO3 matrix is prevented. Reoxidation in air to CoFe2O4at a rather low temperature of 800 1C leads to samples free of secondary phases. While the course of thesynthesis was monitored by TGA, XRD and photometric analysis, the final composites were characterizedvia SEM, EDX, impedance spectroscopy and magnetic and magnetoelectric (ME) measurements. Allsamples show pronounced ME hystereses and aME maxima dependent on the Hdc field sweep direction.The sample with x = 0.4 exhibits the highest maximum aME of 420 mV Oe-1 cm-1.

scholarly journals Global atmospheric oxygen variations recorded by Th/U systematics of igneous rocks

2019 ◽  
Vol 116 (38) ◽  
pp. 18854-18859 ◽  
Author(s):  
He Liu ◽  
Robert E. Zartman ◽  
Trevor R. Ireland ◽  
Wei-dong Sun
Keyword(s):  
Oceanic Crust ◽  
Sea Water ◽  
Atmospheric Oxygen ◽  
Sharp Decrease ◽  
Temporal Variations ◽  
Global Scale ◽  
Significant Rise ◽  
Water Soluble ◽  
Igneous Rocks ◽  
Major Step

Atmospheric oxygen has evolved from negligible levels in the Archean to the current level of about 21% through 2 major step rises: The Great Oxidation Event (GOE) in the early Proterozoic and the Neoproterozoic Oxygenation Event (NOE) during the late Proterozoic. However, most previous methods for constraining the time of atmospheric oxygenation have relied on evidence from sedimentary rocks. Here, we investigate the temporal variations of the Th/U of arc igneous rocks since 3.0 billion y ago (Ga) and show that 2 major Th/U decreases are recorded at ca. 2.35 Ga and ca. 0.75 Ga, coincident with the beginning of the GOE and NOE. The decoupling of U from Th is predominantly caused by the significant rise of atmospheric oxygen. Under an increasingly oxidized atmosphere condition, more uranium in the surface environment became oxidized from the water-insoluble U4+ to the water-soluble U6+ valance and incorporated in the sea water and altered oceanic crust. Eventually, the subduction of this altered oceanic crust produced the low-Th/U signature of arc igneous rocks. Therefore, the sharp decrease of Th/U in global arc igneous rocks may provide strong evidence for the rise of atmospheric oxygen. We suggest that the secular Th/U evolution of arc igneous rocks could be an effective geochemical indicator recording the global-scale atmospheric oxygen variation.

CLINICAL AND IMMUNOLOGICAL RESPONSE OF INFANTS AND CHILDREN TO ADMINISTRATION OF LOW- TEMPERATURE ADAPTED RESPIRATORY SYNCYTIAL VIRUS

PEDIATRICS ◽  
1971 ◽  
Vol 48 (5) ◽  
pp. 745-755 ◽  
Author(s):  
Hyun Wha Kim ◽  
Julita O. Arrobio ◽  
Gloria Pyles ◽  
Carl D. Brandt ◽  
Ena Camargo ◽  
...  
Keyword(s):  
Low Temperature ◽  
Immune Responses ◽  
Natural Infection ◽  
Serum Antibody ◽  
Immunological Response ◽  
Significant Rise ◽  
Infants And Children ◽  
Older Children ◽  
Respiratory Tract Illness ◽  
Syncytial Virus

Thirty-nine infants and children 6 months to 13 years of age received live 26°C grown respiratory syncytical (RS) virus (strain A2) by the oropharyngeal and nasopharyngeal route. RS virus was recovered from 22 individuals and 17 of these showed a significant rise in CF and/or plaque reduction serum antibody. Twelve of those from whom virus was recovered and an additional three from whom virus was not recovered showed a threefold or greater rise of RS nasal neutralizing activity. Thus 26 of the total showed some evidence of having been infected with the ES strain. The rate of infection was significantly greater in infants and children under 2 years of age than in older children. Infection in individuals older than 8 months of age was asymptomatic. Three infants infected with the vaccine strain had relatively minor respiratory tract illness. The findings from this study indicate that the low-temperature adapted virus retains a low level of virulence which is expressed only in individuals undergoing primary infection. Nonetheless, these studies have shown that it is possible to induce local and systemic immune responses to RS virus by means other than fully virulent natural infection.

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