The petrology, phase relations and tectonic setting of basalts from the taupo volcanic zone, New Zealand and the Kermadec Island arc - havre trough, SW Pacific     

John A. Gamble  Ian E.M. Smith  Ian J. Graham  B. Peter Kokelaar  James W. Cole  Bruce F. Houghton  Colin J.N. Wilson 《Journal of Volcanology and Geothermal Research》1990,43(1-4)

Volcanism in the Taupo Volcanic Zone (TVZ) and the Kermadec arc-Havre Trough (KAHT) is related to westward subduction of the Pacific Plate beneath the Indo-Australian Plate. The tectonic setting of the TVZ is continental whereas in KAHT it is oceanic and in these two settings the relative volumes of basalt differ markedly. In TVZ, basalts form a minor proportion (< 1%) of a dominant rhyolite (97%)-andesite association while in KAHT, basalts and basaltic andesites are the major rock types. Neither the convergence rate between the Pacific and Indo-Australian Plates nor the extension rates in the back-arc region or the dip of the Pacific Plate Wadati-Benioff zone differ appreciably between the oceanic and continental segments. The distance between the volcanic front and the axis of the back-arc basin decreases from the Kermadec arc to TVZ and the distance between trench and volcanic front increases from around 200 km in the Kermadec arc to 280 km in TVZ. These factors may prove significant in determining the extent to which arc and backarc volcanism in subduction settings are coupled.All basalts from the Kermadec arc are porphyritic (up to 60% phenocrysts) with assemblages generally dominated by plagioclase but with olivine, clinopyroxene and orthopyroxene. A single dredge sample from the Havre Trough back arc contains olivine and plagioclase microphenocrysts in glassy pillow rind and is mildly alkaline (< 1% normative nepheline) contrasting with the tholeiitic nature of the other basalts. Basalts from the TVZ contain phenocryst assemblages of olivine + plagioclase ± clinopyroxene; orthopyroxene phenocrysts occur only in the most evolved basalts and basaltic andesites from both TVZ and the Kermadec Arc.Sparsely porphyritic primitive compositions (Mg/(Mg+Fe²) > 70) are high in Al₂O₃ (>16.5%), and project in the olivine volume of the basalt tetrahedron. They contain olivine (Fo₈₇) phenocrysts and plagioclase (> An₆₀) microphenocrysts. These magmas have ratios of CaO/Al₂O₃, A1₂O₃/TiO₂ and CaO/TiO₂ in the range of MORB and MORB picrites and can evolve to the low-pressure MORB cotectic by crystallisation of olivine±plagiociase. Such rocks may be the parents of other magmas whose evolutionary pathways are complicated by interaction of crystal fractionation, crystal accumulation and mixing processes and the filtering action of crust of variable density and thickness. The interplay of these processes likely accounts for the scatter of data about the cotectic. More evolved rocks from both TVZ and KAHT contain clinopyroxene and orthopyroxene phenocrysts and their compositions merge with basaltic andesites and andesites. Stepwise least-squares modelling using phenocryst assemblages in proportions observed in the rocks suggest that crystal fractionation and accumulation processes can account for much of the diversity observed in the major-element compositions of all lavas.We conclude that the parental basaltic magmas for volcanism in the TVZ and KAHT segments are similar thereby implying grossly similar source mineralogy. We attribute the diversity to secondary processes influencing liquids as they ascended through complex plumbing systems in the sub arc mantle and cross.  相似文献   

Introduction     

Alison Ord  Bruce E. Hobbs  Hans-Bernd Mühlhaus 《Pure and Applied Geophysics》1991,136(4):371-374

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Field-Scale Investigation of Infiltration Into a Compacted Soil Liner     

Samuel V. Panno  Beverly L. Herzog  Keros Cartwright  Kenneth R. Rehfeldt  Ivan G. Krapac  Bruce R. Hensel 《Ground water》1991,29(6):914-921

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On the entropy of glaucophane Na2Mg3Al2Si8O22(OH)2     

Richard A. Robie  Bruce S. Hemingway  Philippe Gillet  B. Reynard 《Contributions to Mineralogy and Petrology》1991,107(4):484-486

The heat capacity of glaucophane from the Sesia-Lanza region of Italy having the approximate composition (Na_1.93Ca_0.05Fe_0.02) (Mg_2.60Fe_0.41) (Al_1.83Fe_0.15Cr_0.01) (Si_7.92Al_0.08)O₂₂(OH)₂ was measured by adiabatic calorimetry between 4.6 and 359.4 K. After correcting the C _p ⁰ data to values for ideal glaucophane, Na₂Mg₃Al₂Si₈O₂₂(OH)₂ the third-law entropy S ₂₉₈ ⁰ -S ₀ ⁰ was calculated to be 541.2±3.0 J·mol^-1·K^-1. Our value for S ₂₉₈ ⁰ -S ₀ ⁰ is 12.0 J·mol^-1·K^-1 (2.2%) smaller than the value of Likhoydov et al. (1982), 553.2±3.0, is within 6.2 J·mol^-1·K^-1 of the value estimated by Holland (1988), and agrees remarkably well with the value calculated by Gillet et al. (1989) from spectroscopic data, 539 J·mol^-1·K^-1.  相似文献   

Mapping the state of fracture around cavities   总被引：3，自引：0，他引：3  

Emery Z. Lajtai  Bruce J. Carter  E.J. Scott Duncan 《Engineering Geology》1991,31(3-4):277-289

The state of stress around cavities is heterogeneous. Consequently, the state of fracture may also vary from point to point. Under compressive loading, cavity may be in one of four possible states: pre-fracture (pre-microfracture initiation), microfracture propagation (initiation to the onset of dilata dilatancy to failure) and post-failure. These four states are separated by the crack initiation stress, the crack damage stress and the failure stress. fracture events with confining pressure is examined with reference to three intact rocks: a brittle granite, a semi-brittle limestone and a ductile sal

The maximum principal stress (σ₁) at crack initiation, crack damage (onset of dilatancy), yielding and failure are established as a function stress (σ₃). For a single intact rock, all four fracture events can be represented using one function (the Rocker function) with a single fac various fracture states.

The proposed fracture criteria, based on the experimental data, are combined with the existing state of stress to prepare a fracture map around an elli intact Lac du Bonnet granite. The state of stability is expressed through a newly defined stability factor, the unconfined strength ratio (USR), wh to the traditional safety factor. In contrast to the conventional safety factor in rock mechanics (SFstrength/σ₁), which is σ₃ 3–σ₁, space of the stability diagram.  相似文献   

The geochemistry of Jurassic dolerites from Portal Peak,Antarctica     

Janet M. Hergt  Bruce W. Chappell  Gunter Faure  Teresa M. Mensing 《Contributions to Mineralogy and Petrology》1989,102(3):298-305

Geochemical and isotopic analyses have been performed on a suite of samples from a Jurassic quartz tholeiite sill of the Ferrar Group at Portal Peak, Queen Alexandra Range, near the Beardmore Glacier in Antarctica. The data include major and trace element (XRF and INAA) concentrations, as well as Sr and Nd isotopic compositions, and are combined with the results of other studies on samples from Antarctica. It is demonstrated that despite differences in the pre-intrusion (or eruption) evolution of the Ferrar Group magmas, the similarity in isotopic and chemical compositions for these rocks supports the existence of a remarkably uniform mantle source with unusual signature over a distance of thousands of kilometres. The favoured origin of this source involves the subduction of terrestrial sedimentary material into a depleted mantle reservoir.  相似文献   

Erratum     

Amy J. G. Jurewicz  E. Bruce Watson 《Contributions to Mineralogy and Petrology》1989,102(2):255-255

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The role of orbit determination in satellite altimeter data analysis     

Bruce C. Douglas  Clyde C. Goad 《Boundary-Layer Meteorology》1978,13(1-4):245-251

The satellite-borne radar altimeters on GEOS 3 and SEASAT produce high-precision measurement of distance from the satellite to the ocean surface. However, the precision of the GEOS 3 altimeter (~50 cm) and especially the forthcoming SEASAT (~10 cm) instrument far exceeds our ability to determine the position of either satellite using conventional electronic or laser-tracking methods. Thus special techniques are required to prevent the uncertainty of the satellite position from degrading the value of the altimeter data. The altimeter data themselves provide a solution to this problem. Using the condition that intersections of passes of altimeter data must measure the same time-invariant part of the sea-surface height, the root-mean-square error of 292 intersections of 47 passes of GEOS 3 altimeter data from the Atlantic Ocean was reduced from 17 m to 44 cm. Simulations of the SEASAT problem also show that altimeter data can aid in determining the satellite orbit, and have their greatest value when radar or laser tracking is sparse.  相似文献   

Partitioning of manganese between forsterite and silicate liquid   总被引：1，自引：0，他引：1  

E. Bruce Watson 《Geochimica et cosmochimica acta》1977,41(9):1363-1374

Partition coefficients for Mn between forsterite and liquid in the system MgO-CaO-Na₂O-Al₂O₃-SiO₂ (+ about 0.2% Mn) were measured by electron microprobe for a variety of melt compositions over the temperature range 1250–1450°C at one atm pressure. The forsterite-liquid partition coefficient of Mn (mole ratio, MnO in Fo/MnO in liquid, designated D_mn^fo?Liq) depends on liquid composition as well as temperature: at 1350°C, D_Mn^Fo?Liqranges from 0.60 (basic melt, SiO₂ = 47wt%) to 1.24 (acidic melt, SiO₂ = 65wt%). At lower temperatures, the partition coefficient is more strongly dependent on melt composition.The effects of melt composition and temperature on D_Mn^fo?Liq can be separately evaluated by use of the Si:O atomic ratio of the melts. A plot of D_mn^Fo?Liq measured at various temperatures vs melt Si:O for numerous liquid compositions reveals discrete, constant-temperature curves that are not well defined by plotting D_Mn^Fo?Liq against other melt composition parameters such as melt basicity or MgO content. For constant Si:O in the melt, In D_Mn^Fo?Liq vs reciprocal absolute temperature is linear; however, the slope of the plot becomes more positive for higher values of Si:O, indicating a higher energy state for Mn²⁺ ions in acidic melts than in basic melts.Comparison of Mn partitioning data for the iron-free system used in this study with data of other workers on iron-bearing compositions suggests that the effect of iron on Mn partitioning between olivine and melt is small over the range of basalt liquidus temperatures.  相似文献   

Trace-Organics Biodegradation in Aquifer Recharge   总被引：1，自引：0，他引：1  

Bruce E. Rittmann  Perry L. McCarty  Paul V. Roberts 《Ground water》1980,18(3):236-243

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