Distribution Of Mineral Inclusions Research Articles

The Belomorian eclogite province (eastern Fennoscandian Shield, Russia): Meso-Neoarchean or Late Paleoproterozoic?

A critical discussion of competing models of the geodynamic nature (oceanic or continental subduction) and age (Meso-Neoarchean or Late Paleoproterozoic) of the eclogite facies metamorphism in the Belomorian eclogite province (BEP) is based on the systematic analysis of the sum of previously known and newly obtained data characterizing the geological structure of the Salma eclogite association and features of zircons from eclogites, including the isotopegeochronological and geochemical characteristics, composition and distribution of mineral inclusions. Regular changes in the REE trends and crystallization-recrystallization temperature of porous zircons in eclogite-metagabbro illustrate the sequence of magmatic and metamorphic events in the Meso-Neoarchean and Paleoproterozoic. The susceptibility to recrystallization of zircons is due to partial metamictness and porous structure. The earliest (~2.9 Ga) zircon zones retain mag-matic-type REE trends. The microinclusions of the prenite-pumpelliite and greenschist facies minerals and the increase in the LREE and MREE concentrations indicate hydrothermal metamorphism in the spreading ridge and on the ocean floor at 2.9–2.82 Ga. Prenite, pumpelliite, albite, actinolite, chlorite, diaspore and saponite also form inclusions in the eclogitic garnet. An increase of LREE and MREE, the disappearance of the Ce positive anomaly, a change from negative to positive Eu anomaly at 2.82–2.78 Ga indicate that plagioclase was removed during the formation of the ‘garnet + omphacite’ eclogite association and the replacement of sphene with rutile. The eclogite facies metamorphism linked with subduction of the oceanic crust is also indicated by the microinclusions of garnet and rutile in zircon. The crystallization temperature in 700–900 °C range of the round-oval zircons from eclogites-metagabbronorites records the Neoarchean granulite facies metamorphism at 2.77–2.70 Ga, the negative Eu anomalies in the cores and rims of zircons indicate the participation of plagioclase in the metamorphic crystallization. Late (2.1–1.7 Ga) rims of porous zircons that occurred at 600–680 °C are distinguished by minimal REE concentrations, a change from a positive Eu anomaly to a negative one, and the appearance of a negative Ce anomaly, which indicates the presence of plagioclase, reducing type of fluids and, accordingly, low water activity that is characteristic of high-temperature metamorphism under stretching condition and mantle-plume activity. The deep Sm-Nd system reworking in the Belomorian tectonic province, including BEP, at ~1.9 Ga was caused by the crustal heating that spread from the Lapland granulite belt border in the west-south-westward direction. The Lu-Hf system in zircon reworking with a significant increase in radiogenic Hf indicates the recrystallization of a long-existing garnet, in which a significant amount of radiogenic 176Hf accumulated by 1.9 Ga as a result of the 176Lu decay. This contradicts the earlier suggestion of the eclogite garnet primary crystallization in the late Paleoproterozoic (1.94–1.89 Ga).

Zircon-Inclusion Mineralogy of a Diamond-Grade Eclogite from the Kokchetav Massif, Northern Kazakhstan

In order to understand the dehydration process related to phengite decomposition during subduction of crust into the deep mantle, we systematically investigated mineral inclusions in zircons from Kokchetav diamond-grade eclogites. In the eclogites, phengite is absent from the matrix but only occurs as inclusions in clinopyroxene. The clinopyroxene is zoned; the core augite contains K2O up to 0.24 wt%, whereas the rim omphacite contains secondary K-feldspar inclusions. Phengite may have been consumed during prograde reactions, and K was fixed in clinopyroxene or in a fluid/melt phase. Inclusions of clinopyroxene and garnet were identified in zircon cores, whereas garnet, rutile, quartz, and composite inclusions are present in the mantles and quartz occurs in the rims. Distribution of mineral inclusions in zoned zircons indicates that zircon cores grew at the peak UHP stage, whereas the rims grew in the quartz stability field during decompression. The composite inclusions have assemblages of albite + glass + epidote, rutile + ilmenite, quartz + rutile, and rutile + albite. The former three-phase composite inclusions have rounded outlines and triple-junction grain boundaries, suggesting crystallization from fluid or melt. During the growth of zircon from core to mantle, phengite was consumed, and new garnet, rutile and fluid/melt were formed.

Improved Sample Preparation and Surface Analysis Methodology for Contact Angle Measurements on Coal ( Heterogeneous) Surfaces

An improved experimental procedure to measure contact angle has been consolidated with coal surface preparation involving polishing with abrasive paper, alumina powder,and a cloth, followed by ultrasonic and mechanical cleaning. Specifically, the captivebubble measuring technique has been compared with the sessile-drop technique and the former has been recommended for the examination of the hydrophobic properties of coal surfaces. Results of the research program, which is currently under way, on the effect of the nature. amount, size, and distribution of mineral inclusions in coal on its wettability are briefly reviewed.

Pressure–temperature evolution of retrogressed kyanite eclogites, Weinschenk Island, North–East Greenland Caledonides

Caledonian eclogites and associated high-pressure rocks are present in a 400×100-km long belt along the coast of North–East Greenland. Kyanite and clinozoisite eclogites on Weinschenk Island (77°54′N, 21°17′W) occur as lenses within amphibolite facies, quartzofeldspathic gneisses. The eclogites have been extensively overprinted by lower pressure assemblages and exhibit a variety of coronitic and symplectitic reaction textures that record the exhumation path of the rocks. Textural relationships and mineral composition data indicate that the initial high-pressure, plagioclase-free assemblage was garnet+omphacite±kyanite±clinozoisite+rutile. Compositional growth zoning in garnet, together with distribution of mineral inclusions within it, record a prograde evolution from epidote–amphibolite facies progressing into the eclogite facies. Post-peak pressure reaction textures include clinopyroxene–plagioclase intergrowths after omphacite; the replacement of kyanite by sapphirine–plagioclase, spinel–plagioclase and corundum–plagioclase symplectites; and resorption of garnet by amphibole–plagioclase kelyphites. The replacement textures indicate that post-eclogite facies decompression took place while the rocks remained at elevated temperatures (upper amphibolite/granulite facies conditions). The metamorphic evolution of the eclogites is in agreement with eclogite formation by thick-skinned crustal imbrication and subhorizontal shortening of the Laurentian margin during Caledonian collision, exhumation to amphibolite facies by emplacement of the eclogite-bearing thrust sheet on the Laurentian margin and accompanying erosion, and final exhumation to the surface by post-Caledonian crustal thinning.

96/05925 The role of carbonization in the evolution of coal char gasification reactivity

The relevance of thermal annealing of coals to the physico-chemical properties of the residual coke or char has been often addressed in the literature. The emphasis is most frequently on the structural modifications induced by carbonization in relation to mechanical properties. More limited and sparse information is available on the influence of the severity of pyrolysis and of carbonization conditions on the reactivity of chars in the context of coal gasification. Thermal annealing affects char gasification along two paths: on one side it induces reordering of the turbostratic structure of coals, on the other side it affects the activity and distribution of mineral inclusions. Both processes lead to char deactivation, their relative importance being dependent on the nature of the parent coal. In this paper the effect of thermal annealing on the reactivity of char from bituminous coal in carbon dioxide atmospheres is investigated. Experimental results are interpreted in the light of a simple reaction model.

OBSERVAÇÃO MICROSCÓPICA DE INCLUSÕES MINERAIS NO XILEMA DE ESPÉCIES TROPICAIS DA AMAZÔNIA

Foi investigada a distribuição de inclusões minerais (cristais e grãos de sílica) no xilema secundário de 53 famílias, representando 250 espécies de madeiras amazônicas. Grãos de silica ocorrem em cerca de 36% das espécies estudadas, frequentemente nas células dos raios. Cristais nas células dos raios são geralmente solitários, enquanto que nas fibras e células do parênquima axial são algumas vezes em cadeias cristalíferas. Os cristais são frequentemente do tipo prismático e somente em uma espécie (Scleronema micranthum)foi encontrado cristal do tipo drusa.

An automatic system for distribution analysis of ore mineral inclusions ? Development and application

An analytical system has been developed which permits the characterization of the distribution of ore mineral inclusions in the matrix. By means of on-line coupling of a computer with the energy- dispersive X-ray spectrometer of an electron microprobe a high degree of automation can be achieved. Information about chemical identity, average concentration and distribution of mineral inclusions can be obtained. This system has been employed in investigations of two sample series from the lead-zinc mining district of Bleiberg-Kreuth (Austria). The results and practicability of this system are discussed.