scholarly journals Eocene ultra-high temperature (UHT) metamorphism in the Gruf complex (Central Alps): constraints by LA-ICPMS zircon and monazite dating in petrographic context

2018 ◽  
Vol 175 (5) ◽  
pp. 774-787 ◽  
Author(s):  
Christian Nicollet ◽  
Valérie Bosse ◽  
Maria Iole Spalla ◽  
Federica Schiavi
Keyword(s):  
High Temperature ◽  
Central Alps ◽  
Monazite Dating ◽  
Uht Metamorphism ◽  
Gruf Complex ◽  
Ultra High Temperature

Granulites and charnockites of the Gruf Complex: Evidence for Permian ultra-high temperature metamorphism in the Central Alps

Lithos ◽  
2011 ◽  
Vol 124 (1-2) ◽  
pp. 17-45 ◽  
Author(s):  
A. Galli ◽  
B. Le Bayon ◽  
M.W. Schmidt ◽  
J.-P. Burg ◽  
M.J. Caddick ◽  
...  
Keyword(s):  
High Temperature ◽  
Central Alps ◽  
Gruf Complex ◽  
High Temperature Metamorphism ◽  
Ultra High Temperature

Dating crustal anatexis in UHT granulites with Lu-Hf

2020 ◽  
Author(s):  
Omar Gianola ◽  
Bernardo Cesare ◽  
Omar Bartoli ◽  
Fabio Ferri ◽  
Robert Anczkiewicz
Keyword(s):  
Rare Earth ◽  
Mineral Assemblage ◽  
Melt Inclusions ◽  
Central Alps ◽  
Dehydration Melting ◽  
Crustal Anatexis ◽  
Slab Breakoff ◽  
Uht Metamorphism ◽  
Gruf Complex ◽  
Asthenospheric Upwelling

<p>Ultra-high temperature (UHT) metamorphism is a thermal regime that can be attained by the lower continental crust in exceptional contexts and that is usually accompanied by fluid-absent dehydration melting. Such conditions are observed in the Gruf Complex, a 12 x 10 km migmatitic body located in the Central Alps, which is characterized by the presence of UHT granulitic schlieren and enclaves within migmatitic orthogneisses and charnockites. Two types of granulites, both with a massive and melanocratic texture, were investigated. The first granulite contains sapphirine, garnet, orthopyroxene, K-feldspar and biotite in the peak mineral assemblage, whereas the second type displays garnet, orthopyroxene, sillimanite and biotite. In both granulites, garnets are porphyroblastic and can reach up to 2 cm in size. These garnets are almost pure almandine-pyrope solid solutions and are zoned, showing pyrope-richer rims (Alm<sub>43-54</sub>Prp<sub>43-55</sub>Sps<sub>0-2</sub>Grs<sub>1-6</sub>) compared to cores (Alm<sub>47-62</sub>Prp<sub>32-48</sub>Sps<sub>0-3</sub>Grs<sub>2-9</sub>). A clear zoning is also observed in the rare earth elements (REE), with garnet cores showing the highest REE concentrations. Moreover, the porphyroblastic garnets are characterized by the presence of numerous melt inclusions (MI), which can be noticed both in garnet cores and rims. The MI occur as polycrystalline (nanogranitoids) and glassy inclusions, and dominantly display a peraluminous, rhyolitic composition, suggesting that they were originated, along with the host garnet, by incongruent, fluid-absent melting reactions during crustal anatexis. Lu-Hf ages obtained for the MI-bearing garnet cores of both granulites indicate that they formed at about 41 ± 4 Ma, which therefore can be interpreted as the time that crustal anatexis generated the UHT granulites. Considering the granulites in the context of the alpine framework, it is also inferred that UHT conditions in the lower crust were achieved as a consequence of asthenospheric upwelling, probably related to slab steepening or slab breakoff.</p>

The influence of cordierite on melting and mineral-melt equilibria in ultra-high-temperature metamorphism

2004 ◽  
Vol 95 (1-2) ◽  
pp. 87-98 ◽  
Author(s):  
Simon L. Harley ◽  
P. Thompson
Keyword(s):  
High Temperature ◽  
Invariant Point ◽  
Temperature Sensitive ◽  
Stability Range ◽  
Mineral Equilibria ◽  
The Stability ◽  
Uht Metamorphism ◽  
The Impact ◽  
Napier Complex ◽  
Ultra High Temperature

ABSTRACTExperimentally constrained calibrations of the incorporation of H2 O and CO2 into cordierite as functions of P–T-aH2O-aCO2 are integrated with KFMASH grids which define mineral-melt equilibria in pelites. This is used to explore the impact of the volatile content and composition of cordierite on anatexis and melt-related processes in high-temperature (HT) and ultra-high-temperature (UHT) metamorphism. The strongly temperature-sensitive H2O content of cordierite coexisting with dehydration melts (0·4–1·6 wt.%) causes a 10–25% relative decrease in the amount of melt produced from pelites compared with models which treat cordierite as anhydrous.KFMASH melting grids quantified for aH2O demonstrate consistency between the measured H2O contents in cordierite from granulite-migmatite terrains and mineral equilibria. These indicate anatexis with aH2O in the range 0·26–0·16 at 6–8 kbar and 870–930°C. The pressure-stability of cordierite+garnet with respect to orthopyroxene+sillimanite+quartz in KFMASH is strongly influenced by cordierite H2O content, which decreases from 1·1 to 0·5 wt.% along the melting reaction Grt+CrdH+Kfs=Opx+Sil+Qz+L. The lower-T invariant point involving biotite (8·8 kbar/900°C) that terminates this reaction has aH2O of 0·16±0·03, whereas the higher-T terminating invariant point involving osumilite (7·9 kbar/940°C) occurs at aH2O 0·08±0·02. Osumilite-bearing assemblages in UHT terrains imply aH2O of <0·08, and at 950–1000°C and 8–9 kbar calculated aH2O is only 0·04–0·02. Cordierites stable in osumilite-bearing assemblages or with sapphirine+quartz have maximum predicted H2O contents of ca. 0·2 wt.%, consistent with H2O measured in cordierites from two sapphirine-bearing UHT samples from the Napier Complex.The addition of CO2to the H2O-undersaturated (dehydration-melting) system marginally decreases the temperature of melting because of the stabilisation of cordierite, the solid product of the peritectic melting reactions. The preferential incorporation of CO2 enhances the stability of cordierite, even at fixed aH2O, and causes the stability fields of Grt+Crd+Sil+Kfs+Qz+L and Grt+Opx+Crd+Kfs+Qz+L to expand to higher pressure, and to both higher and lower temperatures. The minimum solubility of H2O in granitic melt is independent of the CO2 content of cordierite, and the distribution of H2O between melt and cordierite is similar at a given melt H2O-content to the H2O-only system. This enhanced stability of CO2-bearing cordierite leads to a reduced stability range for osumilite-bearing assemblages to temperatures of ca. 950–975°C or greater. Cordierites in the Napier Complex UHT gneisses contain 0·5 and 1·05 wt.% CO2, consistent with a role for CO2 in stabilising cordierite with respect to osumilite in these unusual sapphirine-bearing granul

Ultra-high Temperature (UHT) Processing: Technological Significance and Updates

2020 ◽  
Vol 16 (8) ◽  
pp. 1183-1195
Author(s):  
Prasad Rasane ◽  
Nitya Sharma ◽  
Sana Fatma ◽  
Sawinder Kaur ◽  
Alok Jha ◽  
...  
Keyword(s):  
High Temperature ◽  
Shelf Life ◽  
Raw Milk ◽  
Fundamental Principle ◽  
Point Of View ◽  
Cold Chain ◽  
Historical Significance ◽  
Perishable Commodity ◽  
Quality Of Milk ◽  
Ultra High Temperature

Background: Background: Milk forms an integral part of the human diet from the nutritional point of view. Besides nutrition, it has also unique functional properties which are harnessed by the industry for numerous uses. Being highly perishable specific techniques are required to minimize the losses during processing and adequate preservation of this precious commodity. In the U.S. and many other parts of the world, the traditional pasteurization of milk requires a minimum heat treatment of 72ºC for 15 seconds with subsequent refrigeration. However, the advent of Ultra High Temperature (UHT) treatment of milk has added a new dimension to the marketing of liquid milk in urban as well as remote areas without the requirement of cold chain management. The distinctive feature of UHT processed milk is that it is commercially-sterile-not pasteurized and so has long shelf life at room temperature. UHT milk, also known as long-life milk, is emerging as an attractive commercial alternative offering a hygienic product of unmatched quality, which can be bought anywhere, at any time and in any quantity. The present review will discuss numerous aspects of UHT processing of milk with reference to historical significance, fundamental principle, various systems used and prerequisites, type of exchangers used, fouling and other defects in system, chemical and microbiological effect of the treatment, its effect on nutritional components, organoleptic quality of milk and the advantage and involved challenges of the process. Conclusion: Raw milk is easily contaminated with pathogens and microbes and hence its consumption of raw milk is associated with certain ill health effects. Therefore, heating milk before consumption is strongly suggested. Thus, UHT treatment of milk is done to ensure microbial safety and also to extend the shelf life of this highly perishable commodity. Heating milk at such a high temperature is often associated with the change of organoleptic properties like change in flavor or cooked flavor, rancidity due to microbes or acid flavor, etc. But UHT treatment does not substantially decrease the nutritional value or any other benefits of milk.

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