The lithospheric mantle and lower crust-mantle relationships under Scotland: a xenolithic perspective

In the British Isles the majority of volcanic rocks containing upper mantle and lower crustal xenoliths occur in Scotland. Most of the occurrences are of Carboniferous–Permian age. This paper presents new data on the mineral chemistry of spinel lherzolite xenoliths from the five principal Scottish tectonic terranes. Compositional variations among the minerals emphasize the broad lateral heterogeneity of the subcontinental lithospheric mantle across the region. The remarkable range of Al2O3 v. CaO exhibited by the clinopyroxenes compared with data from other ‘xenolith provinces' emphasizes the extremely complex tectonomagmatic history of the Scottish lithosphere. The generalized age increase from southern and central Scotland to the Northern Highland and Hebridean terranes of the north and NW, with concomitant complexity of geological history, is reflected also by trace element and isotopic studies. Reaction relationships in lherzolites from the Hebridean Terrane, owing to pervasive metasomatism, involve secondary growth of sodic feldspar. This, and light REE enrichment of clinopyroxenes, points to involvement of a natro-carbonatitic melt. Most pyroxenitic xenoliths are inferred to form a basal crustal layer with a generally sharp discontinuity above the underlying (dominantly lherzolitic) mantle. A second discontinuity is inferred to separate these ultramafic cumulates from overlying, broadly cognate metagabbroic cumulates

On resolvent matrices for nondegenerate matricial Schur problems

AbstractFull-rank jpq-elementary factors with a pole of order n + 1 at z = ∞ (or at z = 0) are recognized as left and right resolvent matrices of certain nondegenerate matricial Schur problems

Contact Metamorphism of the Virginia Formation in the Minnamax Deposit St. Louis County, Minnesota

A Thesis submitted to the faculty of the Graduate School of the University of Minnesota by Mark H. Kirstein in partial fulfillment of the requirements for the degree of Master of Science, October 1979. Plate 1 referenced in the thesis is also attached to this record.The Middle Precambrian Virginia Formation, cut by diabase dikes, was intruded and contact metamorphosed by the Late Precambrian Duluth Complex near Babbitt, Minnesota. Sulfide mineralization of magmatic origin, with minor amounts formed by hydrothermal replacement, is concentrated at the irregular contact zone between the Virginia Formation and the Duluth Complex. Five miles south of Babbitt this mineralization constitutes the Minnamax Copper-Nickel Deposit, which is being investigated and evaluated underground by AMAX Exploration, Inc. The Virginia Formation consists of pelitic hornfels, calc-silicate pods, and "reaction" rims around the pods. The pelitic hornfels is dark gray, fine-grained, massive, and composed of plagioclase, hypersthene, and cordierite with local occurrences of orthoclase, biotite, and graphite. The calc-silicate pods are light gray, fine- to coarse grained, are spherical to ellipsoidal and range from 4 inches to 8 feet across. There are three types of pods; homogenous types with no mineral zones developed, layered types with mineral layers developed, and concentric types with mineral zones developed. The primary minerals are diopside, grossular garnet, plagioclase, sphene, wollastonite, and possibly some calcite, and quartz. From strikes and dips of relict bedding in pelitic horn.fels and from the broken, fra.ctured, and jumclad nature of calc-silicate pods deformation of the Virginia Formation appears intense. The "reaction" rims are dark gray, fine-grained, and up to 3 inches wide. They are composed of plagioclase, hypersthene and poikiloblastic clinopyroxene giving a composition intermediate between the pelitic hornfels and calc-silicate pods. The protolith of the pelitic hornfels appears to be a calcareous argillite and the calc-silicates a siliceous dolomitic limestone. The pods are believed to have originally been calcareous concretions in argillite with some being pieces brought up from the calcareous zone at the top of the Biwabik Iron Formation. The "reaction" rims developed after deformation took place, as they surround broken and fractured pods, and formed from diffusion of calcium from the pods into the pelitic hornfels. The metadiaba.se dikes are dark gray, fine-grained, and massive. They are composed of lathy plagioclase, augite, and hypersthene. A relict ophitic texture is evident and relict plagioclase phenocrysts have been resorbed. Sulfides consist of pyrrhotite, exsolved pentlandite, and chalcopyrite in pelitic hornfels and chalcopyrite with exsolved cubanite in calc-silicate pods. Minor ilmenite and magnetite is present in the sulfides. Alteration consists of uralitization of pyroxenes and sericitic and kaolinitic alteration of plagioclase. Quartz, calcite, apophyllite, anhydrite, fluorite, heulandite, laumontite, and prehnite are gangue minerals. This emplacement occurred after the main metamorphic event and formed by hydrothermal replacement. Based on the primary mineral assemblages present, the rocks fall in the pyroxene hornfels facies. The presence of plagioclase and wollastonite in the calc-silicate pods give a minimum temperature of 600 degrees Celsius at 2 kilobars pressure, and a mole fraction of CO2 in the vapor phase less than 0.25. An increase of albite in plagioclase can lower the temperature of the reaction forming plagioclase and wollastonite, and could cause the plagioclase and wollastonite to disappear with quartz and calcite stableo From the presence of laumontite, an upper limit of 350 degrees Celsius at 2 kilobars pressure can be given for the sulfides e:mplaced hydrothermally. A bottom temperature ranging from 250 to 300 degrees Celsius can be given by the presence of exsolved cubanite in chalcopyrite

Influence of Complex Exciton-Phonon Coupling on Optical Absorption and Energy Transfer of Quantum Aggregates

We present a theory that efficiently describes the quantum dynamics of an electronic excitation that is coupled to a continuous, highly structured phonon environment. Based on a stochastic approach to non-Markovian open quantum systems, we develop a dynamical framework that allows us to handle realistic systems where a fully quantum treatment is desired yet the usual approximation schemes fail. The capability of the method is demonstrated by calculating spectra and energy transfer dynamics of mesoscopic molecular aggregates, elucidating the transition from fully coherent to incoherent transfer

Magneto-elastic coupling in La(Fe, Mn, Si)₁₃H<i>y</i> within the Bean-Rodbell model

First order magnetic phase transition materials present a large magnetocaloric effect around the transition temperature, where these materials usually undergo a large volume or structural change. This may lead to some challenges for applications, as the material may break apart during field change, due to high internal stresses. A promising magnetocaloric material is La(Fe, Mn, Si)13Hy, where the transition temperature can be controlled through the Mn amount. In this work we use XRD measurements to evaluate the temperature dependence of the unit cell volume with a varying Mn amount. The system is modelled using the Bean-Rodbell model, which is based on the assumption that the spin-lattice coupling depends linearly on the unit cell volume. This coupling is defined by the model parameter η, where for η > 1 the material undergoes a first order transition and for η  ≤ 1 a second order transition. We superimpose a Gaussian distribution of the transition temperature with a standard deviation σ T 0 , in order to model the chemical inhomogeneity. Good agreement is obtained between measurements and model with values of η  ∼ 1.8 and σ(T0) = 1.0 K

Comparing superconducting and permanent magnets for magnetic refrigeration

We compare the cost of a high temperature superconducting (SC) tape-based solenoid with a permanent magnet (PM) Halbach cylinder for magnetic refrigeration. Assuming a five liter active magnetic regenerator volume, the price of each type of magnet is determined as a function of aspect ratio of the regenerator and desired internal magnetic field. It is shown that to produce a 1 T internal field in the regenerator a permanent magnet of hundreds of kilograms is needed or an area of superconducting tape of tens of square meters. The cost of cooling the SC solenoid is shown to be a small fraction of the cost of the SC tape. Assuming a cost of the SC tape of 6000 $/m2 and a price of the permanent magnet of 100$/kg, the superconducting solenoid is shown to be a factor of 0.3-3 times more expensive than the permanent magnet, for a desired field from 0.5-1.75 T and the geometrical aspect ratio of the regenerator. This factor decreases for increasing field strength, indicating that the superconducting solenoid could be suitable for high field, large cooling power applications