Search results for "engineering.material"
showing 10 items of 2352 documents
Rhyolitic dykes of Paros Island, Cyclades
2005
Abstract The discovery of rhyolitic dykes from the NE part of the island of Paros is described here for the first time. The dykes that can be mapped for a length of ca. 1.1 km are striking about 6° and 38° NE. The width reaches up to 11m maximum. The rhyolitic rocks are porphyric with a fine-grained matrix of mainly feldspar, quartz, some biotites and opaques. K-feldspar, biotite and plagioclase occur as phenocrysts, and mafic-intermediate enclaves are common. At the chilled margin in contact to the gneissic country rocks the dykes are vitric. There, the enclaves have been preserved from contact reaction with the melt and alteration effects and show primary igneous minerals such as clinopyr…
The Nhlangano gneiss dome in south-west Swaziland – A record of crustal destabilization of the eastern Kaapvaal craton in the Neoarchaean
2015
Abstract The Nhlangano granite-gneiss in south-west Swaziland, dated at 2.98 Ga, forms an elliptical dome of remobilised, migmatitic crust. Strongly deformed supracrustal rocks wrap around or form synformal keels infolded with subdomes of Nhlangano Gneiss and represent Mesoarchaean Pongola Supergroup strata at amphibolite- to granulite-facies metamorphic grade. Amphibolites represent the metamorphosed equivalents of Nsuze Group basalts and andesites on the basis of similar trace element and Nd isotope data. Garnetiferous Mahamba Gneiss, dated at c. 2.96 Ga, represents the metamorphosed equivalents of felsic to intermediate volcanic rocks and minor pelitic interflow sedimentary units of the …
Non-explosive, dome-forming eruptions at Mt. Taranaki, New Zealand
2012
Abstract Volcanic domes may be emplaced rapidly and with few hazardous consequences, even at the summit of large stratovolcanoes. In this study the most recent activity of Mt. Taranaki in New Zealand is shown to have been a passive effusion of a c. 5.9 million m3 lava dome with minor associated explosions and little syn-eruptive hazard. This event, the Sisters eruption, appears to have been unrecorded by local indigenous populations but likely occurred between A.D. 1785 and 1820. The magma erupted is chemically distinct from the preceding A.D. 1755 Tahurangi eruption. Based on breakdown of hornblende crystal rims, the Sisters magma was probably only four days outside the hornblende stabilit…
Nanoparticle-Directed Metal–Organic Framework/Porous Organic Polymer Monolithic Supports for Flow-Based Applications
2017
A two-step nanoparticle-directed route for the preparation of macroporous polymer monoliths for which the pore surface is covered with a metal–organic framework (MOF) coating has been developed to facilitate the use of MOFs in flow-based applications. The flow-through monolithic matrix was prepared in a column format from a polymerization mixture containing ZnO-nanoparticles. These nanoparticles embedded in the precursor monolith were converted to MOF coatings via the dissolution–precipitation equilibrium after filling the pores of the monolith with a solution of the organic linker. Pore surface coverage with the microporous zeolitic imidazolate framework ZIF-8 resulted in an increase in su…
Mediterranean Tertiary lamproites derived from multiple source components in postcollisional geodynamics
2008
Abstract In the Mediterranean area, lamproitic provinces in Spain, Italy, Serbia and Macedonia have uniform geological, geochemical and petrographic characteristics. Mediterranean lamproites are SiO2-rich lamproites, characterized by relatively low CaO, Al2O3 and Na2O, and high K2O/Al2O3 and Mg-number. They are enriched in LILE relative to HFSE and in Pb, and show depletion in Ti, Nb and Ta. Mediterranean lamproites show huge regional variation of Sr, Nd and 207Pb/204Pb isotopic values, with 87Sr/86Sr range of 0.707–0.722, eNd range from −13 to −3, and 207Pb/204Pb range of 15.62–15.79. Lamproitic rocks are derived from melts with three components involved in their origin, characterized by c…
Solution and recrystallisation processes and associated landforms in gypsum outcrops of Sicily
2003
Abstract Four small areas of Messinian (Upper Miocene) age gypsum, outcropping in western Sicily, are described. Messinian age evaporites are found in Sicily over a 1000-km 2 area. Here, gypsum outcrops extensively as a consequence of soil erosion induced by human impact. Geomorphological maps show how the rocky surfaces are characterized by a wide range of forms. There are large, medium, small, and microsized forms, which can be identified as belonging to different morphotypes. The morphotypes can be classified into two main categories: those that originated by solution and those that originated through recrystallisation. Four areas, illustrated by geomorphological maps, were specifically …
Intrusion age of Pan-African augen gneisses in the southern Menderes Massif and the age of cooling after Alpine ductile extensional deformation
1996
AbstractPb–Pb single zircon ages of 546.2 ± 1.2 Ma demonstrate that the augen gneisses in the southern Menderes Massif were generated from Pan-African intrusions. During the Alpine orogenic evolution of the Menderes Massif these granites were metamorphosed and transformed into augen gneiss in an extensional top-to-the-south shear zone, located between augen gneisses and overlying schists. Quartz fabrics suggest a pronounced static recrystallization that post-dates the ductile deformation in the shear zone. Ar–Ar muscovite ages of 43–37 Ma from augen gneisses and schists suggest that ductile deformation and subsequent cooling occurred in the Eocene. These results contradict previous models t…
The Proterozoic P–T–t Evolution of the Kemp Land Coast, East Antarctica; Constraints from Si-saturated and Si-undersaturated Metapelites
2007
Integrated metamorphic and geochronological data place new constraints on the metamorphic evolution of a Neoproterozoic orogen in east Antarctica. Granulite-facies rocks from a 150 km stretch of the Kemp Land coast reflect peak conditions involving T � 870^9908 Ca t P� 7� 4^10 kbar, with pressure increasing westward towards an Archaean craton. Electron microprobe-derived (Th þ U)^Pb monazite ages from metapelitic assemblages indicate that the major mineral textures in these rocks developed during the c. 940 Ma Rayner Orogeny. Complex compositional zoning in monazite suggests high-T recrystallization over c. 25 Myr. Diversity in metapelitic reaction textures reflects silica and ferromagnesia…
Electron Spin Resonance and Thermoluminescence dating of shells and sediments from Sambaqui (shell mound) Santa Marta II, Brazil
2020
In Tupi, the word Sambaqui means “mound of shells”. These archaeological sites are cultural vestiges left by the prehistoric occupation of the Brazilian coast from five to six thousand years ago. Mollusks, fishes, and other marine edible foods were important for the survival of this population. The remains of foods, mainly shells, were heaped up, giving a mound of different proportions, which became part of the landscape of the Brazilian coastal plain. Due to the large number of Sambaquis in Brazil and considering that Sambaqui Santa Marta II, Laguna, SC, has not yet been dated, Electron Spin Resonance (ESR) measurements were performed in aragonite shells collected from different layers of …
The analcime problem and its impact on the geochemistry of ultrapotassic rocks from Serbia
2004
AbstractTertiary ultrapotassic volcanic rocks from Serbia occasionally display low levels of K2O and K2O/ Na2O. In these rocks, analcime regularly appears as pseudomorphs after pre-existing leucite microphenocrysts. The process ofleucite transformation in Serbian ultrapotassic rocks is very thorough: fresh leucite survives only in ugandites from the Koritnik lava flows as well as in rare inclusions in Cpx. This paper focuses on the impact of ‘analcimization’ on the mineralogy and geochemistry ofthe Serbian ultrapotassic rocks, using the samples where leucite survived as a monitor for the process.Analcimization has had a great impact on the geochemistry of the rocks, but affects only a restr…