Ground-Water Fluctuations in Response to Arbitrary Pumpage     

Allen Moench 《Ground water》1971,9(2):4-8

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Melting and phase relations in the plane tholeiite-lherzolite-nepheline basanite to 40 kilobars with geological implications     

Keisuke Ito  George C. Kennedy 《Contributions to Mineralogy and Petrology》1968,19(3):177-211

Six crystalline mixtures, picrite, olivine-rich tholeiite, nepheline basanite, alkali picrite, olivine-rich basanite, and olivine-rich alkali basalt were recrystallized at pressures to 40 kb, and the phase equilibria and sequences of phases in natural basaltic and peridotitic rocks were investigated.The picrite was recrystallized along the solidus to the assemblages (1) olivine+orthopyroxene+ clinopyroxene +plagioclase+spinel below 13 kb, (2) olivine+orthopyroxene+clinopyroxene+spinel between 13 kb and 18 kb, (3) olivine+orthopyroxene+clinopyroxene+ garnet+spinel between 18 kb and 26 kb, and (4) olivine+clinopyroxene+garnet above 26 kb. The solidus temperature at 1 atm is slightly below 1,100° and rises to 1,320° at 20 kb and 1,570° at 40 kb. Olivine is the primary phase crystallizing from the melt at all pressures to 40 kb.The olivine-rich tholeiite was recrystallized along the solidus into the assemblages (1) olivine+ clinopyroxene+plagioclase+spinel below 13 kb, (2) clinopyroxene+orthopyroxene+ spinel between 13 kb and 18 kb, (3) clinopyroxene+garnet+spinel above 18 kb. The solidus temperature is slightly below 1,100° at 1 atm, 1,370° at 20 kb, and 1,590° at 40 kb. The primary phase is olivine below 20 kb but is orthopyroxene at 40 kb.In the nepheline basanite, olivine is the primary phase below 14 kb, but clinopyroxene is the first phase to appear above 14 kb. In the alkali-picrite the primary phase is olivine to 40 kb. In the olivine-rich basanite, olivine is the primary phase below 35 kb and garnet is the primary phase above 35 kb. In the olivine-rich alkali basalt the primary phase is olivine below 20 kb and is garnet at 40 kb.Mineral assemblages in a granite-basalt-peridotite join are summarized according to reported experimental data on natural rocks. The solidus of mafic rock is approximately given by T=12.5 P _Kb+1,050°. With increasing pressure along the solidus, olivine disappears by reaction with plagioclase at 9 kb in mafic rocks and plagioclase disappears by reaction with olivine at 13 kb in ultramafic rocks. Plagioclase disappears at around 22 kb in mafic rocks, but it persists to higher pressure in acidic rocks. Garnet appears at somewhat above 18 kb in acidic rocks, at 17 kb in mafic rocks, and at 22 kb in ultramafic rocks.The subsolidus equilibrium curves of the reactions are extrapolated according to equilibrium curves of related reactions in simple systems. The pyroxene-hornfels and sanidinite facies is the lowest pressure mineral facies. The pyroxene-granulite facies is an intermediate low pressure mineral facies in which olivine and plagioclase are incompatible and garnet is absent in mafic rocks. The low pressure boundary is at 7.5 kb at 750° C and at 9.5 kb at 1,150° C. The high pressure boundary is 8.0 kb at 750° C and 15.0 kb at 1,150° C. The garnet-granulite facies is an intermediate high pressure facies and is characterized by coexisting garnet and plagioclase in mafic rocks. The upper boundary is at 10.3 kb at 750° C and 18.0 kb at 1,150° C. The eclogite facies is the highest pressure mineral facies, in which jadeite-rich clinopyroxene is stable.Compositions of minerals in natural rocks of the granulite facies and the eclogite facies are considered. Clinopyroxenes in the granulite-facies rocks have smaller jadeite-Tschermak's molecule ratios and higher amounts of Tschermak's molecule than clinopyroxenes in the eclogite-facies rocks. The distribution coefficients of Mg between orthopyroxene and clinopyroxene are normally in the range of 0.5–0.6 in metamorphic rocks in the granulite facies. The distribution coefficients of Mg between garnet and clinopyroxene suggest increasing crystallization temperature of the rocks in the following order: eclogite in glaucophane schist, eclogite and granulite in gneissic terrain, garnet peridotite, and peridotite nodules in kimberlite.Temperatures near the bottom of the crust in orogenic zones characterized by kyanitesillimanite metamorpbism are estimated from the mineral assemblages of metamorphic rocks in Precambrian shields to be about 700° C at 7 kb and 800° C at 9 kb, although heat-flow data suggest that the bottom of Precambrian shield areas is about 400° C and the eclogite facies is stable.The composition of liquid which is in equilibrium with peridotite is estimated to be close to tholeiite basalt at the surface pressure and to be picrite at around 30 kb. The liquid composition becomes poorer in normative olivine with decreasing pressure and temperature.During crystallization at high pressure, olivine and orthopyroxene react with liquid to form clinopyroxene, and a discontinuous reaction series, olivine orthopyroxene clinopyroxene is suggested. By fractional crystallization of pyroxenes the liquid will become poorer in SiO₂. Therefore, if liquid formed by partial melting of peridotite in the mantle slowly rises maintaining equilibrium with the surrounding peridotite, the liquid will become poorer in MgO by crystallization of olivine, and tholeiite basalt magma will arrive at the surface. On the other hand, if the liquid undergoes fractional crystallization in the mantle, the liquid may change in composition to alkali-basalt magma and alkali-basalt volcanism may be seen at a late stage of volcanic activity.Publication No. 681, Institute of Geophysics and Planetary Physics, University of California, Los Angeles.  相似文献   

The geology of part of an orogenic belt in western Sierra Leone,West Africa     

Peter M. Allen 《International Journal of Earth Sciences》1968,58(2):588-620

Zusammenfassung Die Sierra Leone unterteilt sich in zwei Haupteinheiten. Die östliche ist ein Teil des festen präkambrischen westafrikanischen Kratons und besteht aus hochgradig metamorphem Gestein und Granitgneisen. Die Strukturen verlaufen in vorherrschend NE-Richtung. Der westliche Teil enthält Elemente eines orogenen Gürtels, nämlich der Rokeliden, die entweder im späten Präkambrium oder frühen Paläozoikum entstanden sind und nach NNW streichen. Die Gesteinsserien, die den orogenen Gürtel bilden, setzen sich aus dem Kasila-System, einer unbenannten Gneisgruppe östlich davon, den Rokel River Series und den Marampa Schists zusammen. Die sich an das Kasila-System, umbenannt in Kasila-Gruppe, anschließenden Gneise und wahrscheinlich auch die Kasila-Gruppe selbst können mit dem Gestein des Kratons verglichen werden, sind jedoch während der Entstehung der Rokeliden neu überprägt worden. Sie bilden die Basis der Mulde, die Sedimente und vulkanisches Gestein aus den Rokel River Series und den Marampa Schists enthält. Die Rokel River Series sind neu benannt und unterteilen sich in die Rokel River Gruppe mit sechs Formationen und in die Taban Formation, die aus nach-orogener Molasse besteht. Die Marampa Schists sind neu benannt in Marampa Formation. Das Ausmaß der Metamorphose steigert sich über die Rokeliden nach WSW, und die Marampa Formation ist der am stärksten metamorphisierte Teil der geosynklinalen Ausfüllung.

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Sierra Leone is divisible into two major structural units. The eastern one is part of the stable Precambrian West African craton and consists of high grade metamorphic rocks and granitic gneisses. The foliation has a dominantly NE trend. The western unit contains the elements of an orogenic belt named the Rokelides, which formed in either late Precambrian or early Palaeozoic, and trends NNW. The rock groups which comprise the orogenic belt are the Kasila System, an unnamed group of gneisses on the east of it, the Rokel River Series and the Marampa Schists. The gneisses adjacent to the Kasila System, renamed Kasila Group, and also, probably, the Kasila Group can be correlated with rocks in the craton, but were refoliated during the Rokelide orogenesis. They constituted the basement to the geosyncline which contained sediments and volcanic rocks of the Rokel River Series and Marampa Schists. The Rokel River Series is renamed, and divided into Rokel River Group which contains six formations, and the Taban Formation which is post-orogenic molasse. The Marampa Schists are renamed the Marampa Formation. The intensity of metamorphism and deformation increases across the Rokelides towards the WSW and the Marampa Formation is the most highly metamorphosed part of the geosynclinal infilling.

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Résumé Le Sierra Leone peut se diviser en deux principales sections structurales. La section orientale fait partie du craton stable précambrien de l'Afrique occidentale, formé de roches métamorphiques de haute qualité et de gneiss de granit. La foliation a principalement une direction NE. La section occidentale contient les éléments d'une ceinture orogénique appelée les Rokelides qui ont été formées soit vers la fin de la période précambrienne, soit au début de la période paléozoique et en direction NNW. Les groupes rocheux qui comprennent la ceinture orogénique sont le Kasila System, un groupe de gneiss sans nom situé à son côté est, la Rokel River Series et les Marampa Schists. Les gneiss avoisinant le Kasila System, renommé Kasila Group et en toute probilité le Kasila Group également peuvent être rattachés aux roches du craton mais auraient été refoliés pendant l'orogenèse Rokelide. Ils ont formé la base du géosynclinal qui contient des sédiments et des roches volcaniques de la Rokel River Series et des Marampa Schists. La Rokel River Series a été renommée et divisée en Rokel River Group qui contient six formations et la Taban Formation qui est la mollasse post-orogénique. Les Marampa Schists ont été renommés la Marampa Formation. L'intensité du métamorphisme et de la déformation augmente vers WSW à travers les Rokelides, et la Marampa Formation est la partie la plus métamorphosée de l'accumulation géosynclinale.

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Bacterial Movement Through Fractured Bedrock   总被引：1，自引：0，他引：1  

Martin J. Allen  S. M. Morrison 《Ground water》1973,11(2):6-10

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Constructing the Coronal Magnetic Field By Correlating Parameterized Magnetic Field Lines With Observed Coronal Plasma Structures     

Gary  G. Allen  Alexander  David 《Solar physics》1999,186(1-2):123-139

A method is presented for constructing the coronal magnetic field from photospheric magnetograms and observed coronal loops. A set of magnetic field lines generated from magnetogram data is parameterized and then deformed by varying the parameterized values. The coronal flux tubes associated with this field are adjusted until the correlation between the field lines and the observed coronal loops is maximized. A mathematical formulation is described which ensures that (i) the normal component of the photospheric field remains unchanged, (ii) the field is given in the entire corona over an active region, (iii) the field remains divergence-free, and (iv) electric currents are introduced into the field. It is demonstrated that a parameterization of a potential field, comprising a radial stretching of the field, can provide a match for a simple bipolar active region, AR 7999, which crossed the central meridian on 1996 November 26. The result is a non-force-free magnetic field with the Lorentz force being of the order of 10^–5.5 g cm s^–2 resulting from an electric current density of 0.079 A m^–2. Calculations show that the plasma beta becomes larger than unity at a relatively low height of 0.25 r supporting the non-force-free conclusion. The presence of such strong non-radial currents requires large transverse pressure gradients to maintain a magnetostatic atmosphere, required by the relatively persistent nature of the coronal structures observed in AR 7999. This scheme is an important tool in generating a magnetic field solution consistent with the coronal flux tube observations and the observed photospheric magnetic field.  相似文献   

A need for incentivizing field hydrology,especially in an era of open data: discussion of “The role of experimental work in hydrological sciences – insights from a community survey”*     

Scott T. Allen  Wouter R. Berghuijs 《水文科学杂志》2020,65(Z2):1262-1265

ABSTRACT

The sharing of data and collection of new data are both essential, but they are not inherently complementary. When data are openly available, researchers may be motivated to use those data rather than collect more because field work has costs and risks. The competitive advantage to those who do not put resources towards fieldwork may discourage field hydrology. Allocating efforts towards generating field data, which benefits hydrological sciences, is not necessarily best for individual hydrologists, especially in an era of open data. The objective of this work is to open a conversation on whether individuals’ best interests may contrast with the community’s desire for new observations. If the community wants new field observations, there is a need to consider the shifting balance of incentives and disincentives for pursuing field studies in hydrology.  相似文献   

The location of exploding granules     

Marc S. Allen  Steven Musman 《Solar physics》1973,32(2):311-314

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Preface     

Simon M. Cargill  Allen L. Clark 《Mathematical Geology》1978,10(5):405-406

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Source rocks of the Lower Old Red Sandstone: Exotic Pebbles from the Brownstones,Ross-on-Wye,Hereford and Worcester     

J.R.L. Allen 《Proceedings of the Geologists' Association. Geologists' Association》1974,85(4):493-IN5

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The north liberty radio observatory of the University of Iowa     

J. A. Van Allen  C. D. Wende  S. R. Mosier 《Solar physics》1969,7(1):159-163

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