Showing papers on "Basalt published in 1978"
1,158 citations
TL;DR: The mixing equation applied by Vollmer [1] to Pb and Sr isotope ratios is shown to be a general equation applicable to consideration of element and isotope ratio.
954 citations
TL;DR: In this paper, the authors studied the evolution of Apollo 15 green glass and found that the ICE age of 3.8 + or - 0.4 eons overlaps the range of reported (Ar-39)-(Ar-40) ages and implies a distinct source region for green glass.
940 citations
TL;DR: In this article, the effects of these minerals on the rare earth elements (REE) patterns of granitic melts during partial melting or differentiation are exaggerated as compared to basaltic systems, making detection of residual phases easier.
660 citations
TL;DR: In this paper, Pb isotopic compositions and U, Th, and Pb concentrations of basalts from the island of Hawaii were reported. But the results of the study were limited to the island and not to all the islands of Hawaii.
530 citations
TL;DR: In this paper, the authors regarded the alkalic series as a category in a classification of igneous rock series (rock associations) and not as a class in petrographic systematics.
Abstract: The alkalic rocks are here regarded as a category in a classification of igneous rock series (rock associations) and not as a class in petrographic systematics The alkalic series as a whole are characterized by higher Na2O+K2O content than the subalkalic series in the alkali vs SiO2 diagram At least three different trends (types) of differentiation appear to exist in large-scale alkalic volcanic associations One (here designated as the Kennedy trend) starts from weakly nepheline-normative basalt and shows increasing normative nepheline with advancing fractionation to reach a phonolitic composition Another (here called the Coombs trend) starts from hypersthene-normative basalt and shows increasing normative hypersthene and then normative quartz with advancing fractionation to reach a comenditic composition Besides these two trends, it seems that many alkalic associations exist which show a differentiation trend starting from nepheline-normative basaltic composition and leading to hypersthenenormative, and then to quartz-normative compositions (here designated as the straddle-B type) Alkalic rocks of these three trends are higher not only in Na2O+K2O but also in Rb, Ba, Sr and Zr than subalkalic rocks The alkalic basalts as a whole are characterized by higher contents of such elements and not by any degree of silica undersaturation It is widely believed that alkalic rocks are characterized by the presence of normative nepheline as well as by the absence of orthopyroxene and pigeonite Indeed such a relationship holds for the Kennedy trend, but it is not always valid for other types of alkalic associations Some alkalic rocks of the Coombs trend and straddle-B type have quartz (or other silica minerals) and orthopyroxene and pigeonite
509 citations
TL;DR: In this paper, a series of immobile-element diagrams for metamorphic volcanic suites is presented, based on geochemical data on meta-volcanic suites in the greenschist, amphibolite and granulite facies.
468 citations
TL;DR: In this article, fresh mid-ocean ridge basalt of varying crystallinity has been powdered and reacted with seawater and an artificial Na-K-Ca-Cl solution at 200-500°C and 500-1000 bar in sealed gold capsules.
463 citations
TL;DR: Trace element analyses have been carried out on hydrothermally altered pillow basalts of greenschist facies dredged from the median valley of the Mid-Atlantic Ridge as mentioned in this paper.
425 citations
TL;DR: In this article, the authors found olivine to be the liquidus phase from 1 atm to 10.5 kbar where it is replaced by clinopyroxene.
417 citations
TL;DR: In this article, the authors assess the scale of isotopic heterogeneity in a partially molten asthenosphere and assess the available experimental data on diffusion kinetics in minerals and melts similar to those existing in the mantle, showing that a fluid-free mantle can maintain a state of disequilibrium on a centimeter scale for periods of 108 to 109 years.
TL;DR: In this paper, rare earth element (REE) and major element data are presented on 44 Archaean samples which include spinifex textured ultramagnesian lavas (STPK) spinifeix textured basalts (STB) and low MgO tholeiites.
Abstract: Rare earth element (REE) and major element data are presented on 44 Archaean samples which include spinifex textured ultramagnesian lavas (STPK) spinifex textured basalts (STB) and low MgO tholeiites. The samples come from the Yilgarn and Pilbara Blocks (W. Australia), Barberton (South Africa), Belingwe and Que Que (Rhodesia), Abitibi (Canada) and the 3.7 b.y. Isua Belt of Western Greenland. In addition REE data are given on three near primitive mid-ocean ridge basalts (MORB) and a glassy MORB-type basalt from Taiwan. We suggest that REE patterns, particularly the light REE and Eu, can be affected by metamorphism, but argue that the consistency of pattern from samples both within and between areas enables recognition of primary patterns. La/Sm ratios of 2.7 b.y. STPK are characterised by being lower than those of associated basalts. The 3.5 b.y. STPK Barberton material does not show this feature but instead displays significant heavy REE depletion. The separation of garnet from these liquids is suggested as a possible mechanism for the high CaO/Al2O3 ratios, (Al loss) and the heavy REE and Sc depletion. The REE data on Barberton material is equivocal on the derivation of the so-called basaltic komatiites from the peridotitic komatiites. However, REE analyses on STPK and high magnesian lavas from elsewhere suggests that crystal fractionation is not a viable mechanism to produce one from the other. We suggest instead, that varying amounts of partial melting of different sources is responsible for the spectrum of compositions. The STB appear to be an easily recognised rock type within the Archaean. They are characterised by quench (clinopyroxene) textures and a light REE enriched pattern. It is suggested that these are near primary melts and that their REE patterns mirror their mantle source. We propose a two stage model for the 2.7 b.y. mafic complexes, in which, prior to the generation of ultrabasic magmas, the source underwent a small amount of partial melting which resulted in the removal of a melt enriched in incompatible elements. The depletion process could be achieved either during mantle diapirism or by upward migration of interstitial melts into an Archaean low velocity zone. The spread of La/Sm ratios in STPK and STB is used as an argument that the Archaean mantle was chemically heterogeneous and that the degree of heterogeneity was similar to that observed in modern ocean volcanics. As a result, partial melting of the mantle under different P-T conditions produced a spectrum of magma types. The information presently available on Archaean mafic and silicic magmatism and the incompleteness of geochemical data on present day tectonic environments are two major obstacles in formulating Archaean tectonic models. In addition a comparison of present day and Archaean ultramafic and silicic rocks suggests that plate tectonic models as presently understood may not be suitable analogues for all Archaean tectonic environments.
TL;DR: Anorthosite-quartz mangerite complexes are the chief manifestations of Elsonian magmatic activity of Paleohelikian age (about −1500 to −1400 Ma) in Labrador, Canada as mentioned in this paper.
TL;DR: In this paper, a petrographic and microprobe analysis of the zoning relations in olivine phenocrysts was carried out and the inclusions were inferred to be melts entrapped at the time of extensive corrosion of the host crystals.
Abstract: Compositional relations among natural glasses in basalts recovered by Legs 45 and 46 (DSDP) provide powerful constraints on their differentiation histories. Residual glass compositions in the moderately evolved aphyric and abundantly phyric basalts within each site demonstrate that none of the units is mutually related to any other or to a common parent by simple fractional crystallization. At Site 396, where clinopyroxene phenocrysts are absent, progressively more evolved liquids (lower Mg/ (Mg+Fe) and higher TiO2) are characterized by lower calcium-aluminum ratios, which can only be generated by clinopyroxene fractionation. This paradox is amplified by some melt inclusions in olivine phenocrysts that have higher CaO/Al2O3 and lower TiO2 than any residual glasses. The occurrences of these distinctive compositions are correlated with the highly magnesian character of the host olivines (Fo90−89), and the melts are interpreted as trapped primitive liquids, parental to the more fractionated derivatives. Melt inclusions intermediate in composition between the residual glasses and the most primitive olivine melt inclusions are present in the cores of some plagioclase phenocrysts that have had a history of resorption. On the basis of a petrographic and microprobe analysis of the zoning relations in these phenocrysts, the inclusions are inferred to be melts entrapped at the time of extensive corrosion of the host crystals. Interpreted in conjunction with other mineral and geochemical data, the compositional trends in the glasses indicate that magma mixing has played a major role in the genesis of the Leg 45 and 46 basalts. The reality of mixing is demonstrated by extensive disequilibrium textures in the plagioclase phenocrysts and the presence in evolved lavas of refractory plagioclase and olivine phenocrysts bearing primitive melt inclusions. The chemical imprint of clinopyroxene fractionation despite the absence of clinopyroxene phenocrysts is believed to be accomplished by plating of gabbro on to the upper walls of the subvolcanic magma chamber as it evolves between mixing events. Repeated influxes of primitive magma batches will move the resultant hybrids alway from clinopyroxene saturation and generate olivine-plagioclase cotectic magmas. This model provides a physical buffering mechanism that accounts for the volumetric dominance of moderately evolved basalts among ocean floor tholeiites. Major and trace element models based on the combination of mixing and fractional crystallization also explain heretofore enigmatic geochemical characteristics of MORB.
TL;DR: In this paper, the authors suggest that low-Ti ophiolitic basalts are not formed at mid-ocean ridges but are products of a spreading center close to a subduction zone, for example, in an interarc basin or incipient island-arc site.
Abstract: Al2O3/TiO2 and CaO/TiO2 ratios of primitive mid-ocean ridge basalts increase along with degree of partial melting (TiO2 content decreases) until ratios seen in chondrites (about 20 and 17, respectively) are reached at ?0.8% TiO2. Low-Ti (<0.6%) basalts from ophiolitic complexes (for example, Troodos and Betts Cove), island arcs, and interarc basins are characterized by much higher Al2O3/TiO2 and CaO/TiO2 ratios (up to 60). Such low-Ti ophiolitic basalts could be formed by remelting of a severely depleted source that had experienced a previous episode of magma extraction of the type in mid-ocean ridges. We suggest that these low-Ti basalts are not formed at mid-ocean ridges but are products of a spreading center close to a subduction zone, for example, in an interarc basin or incipient island-arc site. In this model, remelting of the refractory source is induced by the introduction of water from subducted oceanic crust. Geochemical data on high-Mg volcanic rocks from Papua and the Mariana Trench are presented, and an analogy with low-Ti ophiolitic basalts is suggested. “Basaltic komatiites” from ophiolitic complexes are discussed, and it is suggested that there are critical geochemical differences between these and Archean komatiites.
TL;DR: In this paper, the same equations for partial melting and crystallization of trace elements were used to model major elements in a way similar to the quantitative petrogenetic modelling used for trace elements, however, modelling with major elements is constrained by the stoichiometry of the solid phases.
TL;DR: In this article, the authors show that the Azores mantle plume is 10 to 30 times enriched in LIL elements with very small (⪢ 0.1 < D < 1) bulk crystal/melt partition coefficients (Rb, Cs, Ba, La).
TL;DR: Two distinct suites of igneous rocks occur within the San Juan volcanic field: an Oligocene suite of predominantly intermediate-composition lavas and breccias, with associated silicic differentiates erupted mainly as ash-flow tuffs, and Neocene-Pliocene bimodal suite of mafic alkalic lavas as discussed by the authors.
Abstract: Two distinct suites of igneous rocks occur within the San Juan volcanic field: an Oligocene suite of predominantly intermediate-composition lavas and breccias, with associated silicic differentiates erupted mainly as ash-flow tuffs, and Neocene-Pliocene bimodal suite of silicic rhyolites and mafic alkalic lavas. The Oligocene volcanism, probably related to subduction along the western margin of the American plate, has chemical and isotopic characteristics indicative of complex interactions with Precambrian cratonic lithosphere. It also appears to record the rise, differentiation, and crystallization of a large composite batholith beneath the San Juan field. The earliest intermediate-composition lavas and breccias have major- and minor-element compositional patterns indicative of high-pressure fractionation and are relatively nonradiogenic in both Pb and Sr, suggesting significant interaction with lower crust of the American plate. The more silicic ash-flow tuffs show compositional evidence of low-pressure fractional crystallization and are more radiogenic in Pb and Sr — features thought to indicate significant shallow residency for the magmas and interaction with upper crust. Especially radiogenic Pb-isotope compositions of some of these rocks may reflect interactions between the magmas and convecting meteoric water rich in leached Pb, a process thought to have been even more important in forming associated hydrothermal ore deposits. Ore leads tend to be more radiogenic than associated rock leads. Many of the Miocene-Pliocene basaltic lavas seem to be mantle-derived lavas, similar to those of oceanic islands, but some anomalous xenocrystic basaltic andesites, containing relatively nonradiogenic lead, may have been slightly contaminated by lower crustal components. Rhyolitic lavas and intrusions of the bimodal suite are also nonradiogenic in Pb and Sr, in comparison with the Oligocene rhyolites, and do not appear to have interacted with Precambrian upper crust, probably because they erupted largely through the subvolcanic batholith. The Miocene-Pliocene rhyolites are best interpreted as partial melts of lower crust, with the thermal energy to initiate magma generation provided by concurrent basaltic volcanism.
01 Jan 1978
TL;DR: In this paper, a unit map of nearside basalt types has been prepared from all telescopic spectral reflectance data currently available for lunar soils, and four parameters were chosen (UV/VIS ratio, albedo, 1 and 2 micron bands) to distinguish and map each of 13 mare basalt type and three additional volcanic groups.
Abstract: A unit map of nearside basalt types has been prepared from all telescopic spectral reflectance data currently available for lunar soils. Four parameters were chosen (UV/VIS ratio, albedo, 1 micron band strength, 2 micron band strength) to distinguish and map each of 13 mare basalt types and three additional volcanic groups. Multispectral imagery and albedo maps were used to define unit boundaries while spectra were used to examine the 1 and 2 micron bands and calibrate and quantify the multispectral images. Although the volume of each basalt type is not known, it is clear from the unit map that only 1/3 to 1/2 of the surface basalt types are likely to be represented in the returned lunar samples. For mature lunar soils a single parameter alone does not provide chemical information, but when the four are used together, TiO2 and in some cases FeO can be estimated. Further study of the mineralogy of unsampled lunar basalts requires precise spectra to 2.5 microns with higher spectra and spatial resolution.
TL;DR: In this article, the Pb-, Nd-, and Sr-isotope compositions of oceanic ferromanganese deposits, together with the Nd-and Sr-Isotope composition of altered ocean-floor basalts are reported.
Abstract: The Pb-, Nd-, and Sr-isotope compositions of oceanic ferromanganese deposits, together with the Nd-, and Sr-isotope compositions of altered ocean-floor basalts are reported. These data are used to evaluate the sources of these metals in both the oceans and ferromanganese deposits and the extent to which ocean-floor basalts are a source of, or a sink for these metals.
TL;DR: In this paper, mass spectrometric analyses of phenocrysts, containing glass-vapor inclusions quenched in glassy rims of tholeiitic submarine pillow basalts from spreading centers and Hawaii, indicate that water released from the inclusions upon thermal decrepitation is much less than is released from equivalent volumes of the matrix glass enclosing the same phenocryst.
TL;DR: In this article, the chemistry of 33 basaltic rocks dredged from the West Mariana basin and from the Mariana trench during the R/V “Dmitry Mendeleev” 1976 cruise in the western Pacific is described.
Journal Article•
TL;DR: The distribution coefficients of Zr and Nb have been found between armalcolite, ilmenite, clinopyroxene, rutile, plagioclase, and a coexisting high-Ti mare basalt melt in the 1105-1128 C temperature range as mentioned in this paper.
TL;DR: The largest of a series of 20 vulcanian eruptions of Fuego volcano between 1944 and 1976 occurred in four distinct 4-17-hour pulses over a 10-day period as discussed by the authors.
TL;DR: In this article, the trace elements found in ocean ridge basalts are compared to other terrestrial basalts, such as those having La/Yb ratios greater than those of chondrites, and those having L 1 -L 2 -Y 2 - ratios less than the chondrite ratios.
TL;DR: In this paper, the floating tendency of plagioclase in basaltic liquids is at least 0.03 g/cm3 greater than indicated by the calculations, and this correction factor is applied to calculations of PlagiClase buoyancy in the Skaergaard Intrusion, it is found that the plagiclase crystals in the lower and middle zones were less dense than the coexisting liquids.
Abstract: Plagioclase buoyancy experiments have been carried out in a high-temperature centrifuge furnace using seventeen basaltic liquids and plagioclase crystals of three compositions: An89, An76 and An55. The results show that the floating tendency of plagioclase in basaltic liquids is at least 0.03 g/cm3 greater than indicated by the calculations. If this correction factor is applied to calculations of plagioclase buoyancy in the Skaergaard Intrusion, it is found that the plagioclase crystals in the lower and middle zones were less dense than the coexisting liquids. Other phenomena relevant to crystal transport in basaltic liquids were observed in the centrifuge experiments. These included crystal flotation by rising bubbles, plagioclase sinking because of the formation of plagioclase-magnetite composite grains, graded bedding of olivine and magnetite, and more than 60% intercumulus basaltic liquid between settled olivine crystals.
TL;DR: In this article, the K-Ar method was used to sample 30 samples of Upper Tertiary basalts intruding marine and continental sequences and put limits on the age of tectonic events, such as folding in the Syrian arc, faulting in the Central Sinai - Negev Shear Zone and shearing along the Jordan Rift.
Abstract: Thirty samples of Upper Tertiary basalts intruding marine and continental sequences were by the K-Ar method. Four volcanic phases are recorded: (a) 24.8±1.5 Ma of the Raqabat e Na'ame dike in Central Sinai; (b) 20.4±0.7 Ma of basalt intrusions in Central Sinai and the Arava. Some of these are offset by E-W to NE-SW dextral faults of the Central Sinai – Negev Shear Zone; (c) 14.5±0.3 to 4.9±1.3 Ma of basalt flows in the Eastern Galilee and the Coastal Plain; (d) 2.7±0.6 Ma of ‘En Yahav dike. These results contribute to the correlation between Tertiary continental formations from different areas, and put limits on the age of tectonic events, such as folding in the Syrian arc, faulting in the Central Sinai - Negev Shear Zone and shearing along the Jordan Rift.
TL;DR: In this paper, the rare earth elements (REE) LaLu are generally considered to be unaffected by weathering and are thus often used to characterise variations in basalt and magma composition.
Abstract: DREDGED oceanic basalts and those sampled by deep-ocean drilling have commonly undergone some weathering with subsequent changes in their chemical composition1–7. The rare-earth elements (REE) La–Lu are generally considered to be unaffected by weathering and are thus often used to characterise variations in basalt and magma composition. When considered relative to chondritic abundances8, the overall REE distribution is a critical diagnostic tool. In particular, the relative depletion of light-REE is used to discriminate between magma types. We present here new findings which show that REE are affected by low-temperature weathering processes. In particular, the light-REE show enrichments which may result in a basalt with a primary light-REE depleted pattern showing a flat or enriched light-REE pattern.
TL;DR: In this paper, the authors proposed a set of seismic, geochemical, acoustic, thermal, and certain electrical criteria for recognition of active discharge zones of subsea-floor hydrothermal convection systems.
Abstract: Hydrothermal mineral deposits in oceanic crust include metalliferous sediments and encrustations and massive sulfides. The occurrence of these deposits is explained by the hypothesis that they are concentrated at the discharge zones of high intensity subsea-floor hydrothermal convection systems involving the circulation of sea water through oceanic crust and upper mantle at oceanic spreading centers.Criteria that have proven most useful for recognition of hydrothermal deposits in oceanic crust based on known deposits at oceanic spreading centers include petrology of the deposits and surrounding rocks; structural conditions that create exceptionally high permeability and thermal gradients; seismicity in the form of microearthquakes and earthquake swarms; geochemical properties of hydrothermal discharge ( 3 He, 222 Rn, ferric hydroxides, silica); contrasts in acoustic impedence between normal sea water and hydrothermal solutions; anomalous gravity as an indicator of geologic structure; electrical properties of the hydrothermal solutions and deposits; an associated low in residual magnetic intensity attributed to hydrothermal alteration of the magnetic mineral component of basalt; patterns of deposition in early rift and advanced oceanic ridge stages of opening of an ocean basin; and distribution of hydrothermal deposits both parallel and perpendicular to an oceanic spreading center.The seismic, geochemical, acoustic, thermal, and certain electrical criteria are applicable to recognition of active discharge zones of subsea-floor hydrothermal convection systems. The petrologic, structural, gravity, magnetic, and other electrical criteria are applicable to recognition of hydrothermal deposits in all of oceanic crust which underlies ocean basins covering two-thirds of the Earth and is emplaced on land as ophiolites.