Search results for "Continent"
showing 10 items of 598 documents
Characterization of an early metamorphic stage through inclusions in zircon of a diamondiferous quartzofeldspathic rock from the Erzgebirge, Germany
2003
About 1000 zircon grains from a diamondiferous quartzofeldspathic rock of the Saxonian Erzgebirge were investigated for inclusions using optical microscopy and confocal laser-Raman spectroscopy. Cathodoluminescence imagery was applied to characterize the growth zone of zircon where the inclusions occurred. The most abundant inclusion minerals are microdiamonds. Coesite was not detected. However, garnet and jadeite occur as rare inclusions in zircon cores where diamonds are lacking. Jadeite was detected for the first time in quartzofeldspathic rocks from the crystalline complex of the Erzgebirge. The compositions of the pristine garnets in the zircons are similar to those of core areas of mi…
Internal Differentiation of the Archean Continental Crust: Fluid-Controlled Partial Melting of Granulites and TTG-Amphibolite Associations in Central…
2009
Fault bound blocks of granulite and enderbite occur within upper amphibolite-facies migmatitic tonalitic-trondhjemitic-granodioritic (TTG) gneisses of the Iisalmi block of Central Finland. These units record reworking and partial melting of different levels of the Archean crust during a major tectonothermal event at 2·6-2·7 Ga. Anhydrous mineral assemblages and tonalitic melts in the granulites formed as a result of hydrous phase breakdown melting reactions involving amphibole at peak metamorphic conditions of 8-11 kbar and 750-900°C. A nominally fluid-absent melting regime in the granulites is supported by the presence of carbonic fluid inclusions. The geochemical signature of light rare e…
Precambrian crustal evolution and continental drift
1981
One of the major questions of Precambrian research is whether present-day plate tectonic models can be applied to the evolution of the ancient continental crust or whether the tectonic style suggests a unidirectional and therefore non-uniformitarian development in response to gradual changes in the global thermal regime through time.
Costruzioni discorsive sull’Europa e sui rapporti tra continenti nell’antichità greca
2019
L’articolo studia le retoriche cui sono state sottoposte le identità rappresentate dai continenti. Viene mostrato così che la mitica parentela originaria ha dato luogo ora ad un legame di solidarietà tra i popoli che occupano l’una o l’altra zona geografica, ora ad una giustificazione delle pretese imperialistiche di un popolo su un altro. Si mostra altresì che i confini tra i continenti vengono presentati, a seconda del punto di vista difensivo o aggressivo da cui se ne parla, ora come segni di una ‘architettura’ naturale di cui si pretende il rispetto, ora come ostacoli da superare in nome dell’amore della conoscenza che vuole esplorare l’ignoto o dell’addomesticamento di ciò che è selvag…
Διαλεκτικές κατασκευές για την Ευρώπη και για τις σχέσεις ανάμεσα σε ηπείρους στην ελληνική αρχαιότητα
2020
L’articolo studia le retoriche cui sono state sottoposte le identità rappresentate dai continenti. Viene mostrato così che la mitica parentela originaria ha dato luogo ora ad un legame di solidarietà tra i popoli che occupano l’una o l’altra zona geografica, ora ad una giustificazione delle pretese imperialistiche di un popolo su un altro. Si mostra altresì che i confini tra i continenti vengono presentati, a seconda del punto di vista difensivo o aggressivo da cui se ne parla, ora come segni di una ‘architettura’ naturale di cui si pretende il rispetto, ora come ostacoli da superare in nome dell’amore della conoscenza che vuole esplorare l’ignoto o dell’addomesticamento di ciò che è selvag…
Improving angle stability by switching shunt reactors in mixed overhead cable lines. An Italian 400 kV case study
2019
Stringent environmental constraints make the construction of new transmission overhead lines more and more difficult. Alternatively, today it is possible to use cable lines for high (HV) and extra-high (EHV) voltage systems. The configuration of the so-called mixed lines can create some problems in the operation of the electrical system, both during steady-state and transient conditions. In particular, the system stability is one of the main concerns when analyzing the dynamic response of power systems. In this paper, the study of angular stability of a system containing a mixed line is presented: a specific control logic applied to the shunt reactors of the mixed line is proposed as improv…
Analysis and simulations of the primary frequency control during a system split in continental europe power system
2021
The occurrence of system separations in the power system of Continental Europe has been observed in recent decades as a critical event which might cause power imbalances higher than the reference incident specified per system design, representing an actual challenge for the stability and safe operation of the system. This work presents an analysis and simulations of the primary frequency control in the Continental Europe synchronous area in conditions of system separation. The adopted approach is based on fundamental aspects of the frequency-containment reserve process. The analysis takes an actual event into consideration, which determined the separation of the system in January 2021. The …
Heat generation associated with collision of two plates: the Himalayan geothermal belt
1998
Abstract An analysis of heat discharged by thermal fluids along the c. 3000-km-long Himalayan geothermal belt (HGB) shows that heat transfer is concentrated along 30- to 50-km-wide `heat bands' which are associated with at least 600 geothermal systems. The bands have been interpreted as segments of major, concentric slip lines caused by plastic deformation of the ductile crust within the Asian plate resulting from plate collision. Assuming that this crust behaves like an ideal plastic medium, the heat transfer within and along a slip line can be estimated. It amounts to c. 55 mW/m2 for a 40-km-wide band. Estimates of present-day heat discharges point to 20–35 mW/m2 for convective, and 10–30…
Forearc carbon sink reduces long-term volatile recycling into the mantle
2019
Carbon and other volatiles in the form of gases, fluids or mineral phases are transported from Earth's surface into the mantle at convergent margins, where the oceanic crust subducts beneath the continental crust. The efficiency of this transfer has profound implications for the nature and scale of geochemical heterogeneities in Earth's deep mantle and shallow crustal reservoirs, as well as Earth's oxidation state. However, the proportions of volatiles released from the forearc and backarc are not well constrained compared to fluxes from the volcanic arc front. Here we use helium and carbon isotope data from deeply sourced springs along two cross-arc transects to show that about 91 per cent…
Age and tectonic setting of Late Archean greenstone-gneiss terrain in Henan Province, China, as revealed by single-grain zircon dating
1988
The authors report precise U-Pb zircon ages for single grains of a metarhyodacite from the Late Archean Dengfeng greenstone belt in Henan Province, China, near the southern margin of the North China craton. Most grains belong to an igneous population whose U-Pb isotopic systematics define a straight line intersecting concordia at 2512 +/- 12 Ma, and this is interpreted as the time of crystallization of the original greenstone volcanics. Several grains are distinctly older, between 2576 +/- 9 and 2945 +/- 44 Ma, and the authors interpret the older grains as xenocrysts of pre-greenstone continental crust that provide evidence for crustal derivation or crustal contamination of the original rhy…