Wyniki wyszukiwania - Biblioteka Nauki

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Continuous magma mixing and cumulate separation in the High Tatra Mountains open system granitoid intrusion, Western Carpathians (Poland/Slovakia): a textural and geochemical study

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Gawęda A. , Szopa K. , Włodyka R. , Burda J. , Crowley Q. , Sikorska M.

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2019

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tom Vol. 69, no. 4

549--570

EN

In this study the formation of the polygenetic High Tatra granitoid magma is discussed. Felsic and mafic magma mixing and mingling processes occurred in all magma batches composing the pluton and are documented by the typical textural assemblages, which include: mafic microgranular enclaves (MME), mafic clots, felsic clots, quartz-plagioclase-titanite ocelli, biotite-quartz ocelli, poikilitic plagioclase crystals, chemically zoned K-feldspar phenocrysts with inclusion zones and calcic spikes in zoned plagioclase. Geochemical modelling indicates the predominance of the felsic component in subsequent magma batches, however, the mantle origin of the admixed magma input is suggested on the basis of geochemical and Rb-Sr, Sm-Nd and Pb isotopic data. Magma mixing is considered to be a first-order magmatic process, causing the magma diversification. The cumulate formation and the squeezing of remnant melt by filter pressing points to fractional crystallization acting as a second-order magmatic process.

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Digital Concentration-Distribution Models - tools for a describing heterogeneity of the hybridized magmatic mass as reflected in elemental concentration of growing crystal

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Śmigielski M. , Słaby E. , Domonik A.

Acta Geologica Polonica

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2012

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tom Vol. 62, no. 1

129-141

EN

Raster digital models (digital concentration-distribution models - DC-DMs) as interpolations of geochemical data are proposed as a new tool to depict the crystal growth mechanism in a magmatic environment. The Natural Neighbour method is proposed for interpolation of Electron Microprobe Analysis (EMPA) data; the Natural Neighbour method and Kriging method are proposed for interpolating data collected by the LA-ICP-MS method. The crystal growth texture was analysed with the application of DC-DM derivatives: 3D surface models, shaded relief images, aspect and slope maps. The magmatic mass properties were depicted with the application of solid models. Correlation between the distributions of two elements on a single crystal transect was made by operations on the obtained raster DC-DMs. The methodology presented is a universal one but it seems to be significant for the depiction of magma mixing processes and the heterogeneity of the magmatic mass.

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Magma mingling textures in granitic rocks of the eastern part of the Strzegom-Sobótka Massif (Polish Sudetes)

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Domańska-Siuda J. , Bagiński B.

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tom Vol. 69, no. 1

143--160

EN

Many granitic intrusions display evidence of magma mixing processes. The interaction of melts of contrasting composition may play a significant role during their generation and evolution. The Strzegom-Sobótka massif (SSM), located in the Sudetes (SW Poland) in the north-eastern part of the Bohemian Massif of the Central European Variscides, exhibits significant evidence of magma mingling on the macro- and micro-scales. The massif is a composite intrusion, with four main varieties: hornblende-biotite granite (with negligible amount of hornblende) and biotite granite in the western part, and two-mica granite and biotite granodiorite in the eastern part. Field evidence for magma mingling is easily found in the biotite granodiorite, where dark enclaves with tonalitic composition occur. Enclaves range from a few centimeters to half a meter in size, and from ellipsoidal to rounded in shape. They occur individually and in homogeneous swarms. The mixing textures in the enclaves include fine-grained texture, acicular apatite, rounded plagioclase xenocrysts, ocellar quartz and blade-shaped biotite. The most interesting feature of the enclaves is the presence of numerous monazite-(Ce) crystals, including unusually large crystals (up to 500 μm) which have grown close to the boundaries between granodiorite and enclaves. The crystallization of numerous monazite grains may therefore be another, previously undescribed, form of textural evidence for interaction between two contrasting magmas. The textures and microtextures may indicate that the enclaves represent globules of hybrid magma formed by mingling with a more felsic host melt. Chemical dating of the monazite yielded an age of 297±11 Ma.

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The Hurst exponent as a tool for the description of magma field heterogeneity reflected in the geochemistry of growing crystals

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Domonik A. , Słaby E. , Śmigielski M.

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tom Vol. 60, no. 3

437-443

EN

Trace element behaviour during crystallization of three alkali feldspar crystals of mixed origin was investigated. The first crystal (gm1) was growing under an intensive magma mixing regime in an active region of an inhomogeneous magmatic field. The second crystal (ref) was growing in a coherent region of this field and the third one (gm2) was growing under moderate progress in magma mixing, with the process being close to completion. The Hurst exponent (H) was used as a tool for the description of the local heterogeneities of the magma field during the mixing process. Values of H were calculated for compatible trace element patterns along each traverse for each crystal. The gm1 crystal is strongly zoned. The value of the Hurst exponent (H) for zones reflecting intensive chemical mixing varies between 0.06 and 0.47. It emphasizes strong anti-persistent behaviour of elements during crystallization. The zones that grew in a slightly contaminated felsic magma exhibit H > 0.5. It means that the process goes over a longer path than a random walk and shows increasing persistence in element behaviour with decreasing hybridization. Similarly, zones crystallized in magma regions compositionally located close to coherent characteristic or in active domains featuring a high homogenization (crystals gm2, ref) show higher H values.