scholarly journals Decompressional equilibration of the Midsund granulite from Otrøy, Western Gneiss Region, Norway

2019 ◽  
Vol 70 (6) ◽  
pp. 471-482
Author(s):  
Johanna Holmberg ◽  
Michał Bukała ◽  
Pauline Jeanneret ◽  
Iwona Klonowska ◽  
Jarosław Majka
Keyword(s):  
High Pressure ◽  
Thermodynamic Model ◽  
Thermodynamic Modelling ◽  
Ultrahigh Pressure ◽  
Stability Field ◽  
Uhp Metamorphism ◽  
Limited Evidence ◽  
Western Gneiss Region ◽  
Widespread Phenomenon ◽  
The Stability

Abstract The Western Gneiss Region (WGR) of the Scandinavian Caledonides is an archetypal terrain for high-pressure (HP) and ultrahigh-pressure (UHP) metamorphism. However, the vast majority of lithologies occurring there bear no, or only limited, evidence for HP or UHP metamorphism. The studied Midsund HP granulite occurs on the island of Otrøy, a locality known for the occurrence of the UHP eclogites and mantle-derived, garnet-bearing ultramafics. The Midsund granulite consists of plagioclase, garnet, clinopyroxene, relict phengitic mica, biotite, rutile, quartz, amphibole, ilmenite and titanite, among the most prominent phases. Applied thermodynamic modelling in the NCKFMMnASHT system resulted in a pressure–temperature (P–T) pseudosection that provides an intersection of compositional isopleths of XMg (Mg/Mg+Fe) in garnet, albite in plagioclase and XNa (Na/Na+Ca) in clinopyroxene in the stability field of melt + plagioclase + garnet + clinopyroxene + amphibole + ilmenite. The obtained thermodynamic model yields P–T conditions of 1.32–1.45 GPa and 875–970 °C. The relatively high P–T recorded by the Midsund granulite may be explained as an effect of equilibration due to exhumation from HP (presumably UHP) conditions followed by a period of stagnation under HT at lower-to-medium crustal level. The latter seems to be a more widespread phenomenon in the WGR than previously thought and may well explain commonly calculated pressure contrasts between neighboring lithologies in the WGR and other HP–UHP terranes worldwide.

Pre-Caledonian granulite and gabbro enclaves in the Western Gneiss Region, Norway: indications of incomplete transition at high pressure

2000 ◽  
Vol 137 (3) ◽  
pp. 235-255 ◽  
Author(s):  
M. KRABBENDAM ◽  
A. WAIN ◽  
T. B. ANDERSEN
Keyword(s):  
High Pressure ◽  
Shear Zones ◽  
Granulite Facies ◽  
Amphibolite Facies ◽  
Ultrahigh Pressure ◽  
Western Gneiss Region ◽  
Ultrahigh Pressure Metamorphism ◽  
Mountain Belts ◽  
Orogenic Cycle ◽  
Highly Strained

The Western Gneiss Region of Norway is a continental terrane that experienced Caledonian high-pressure and ultrahigh-pressure metamorphism. Most rocks in this terrane show either peak-Caledonian eclogite-facies assemblages or are highly strained and equilibrated under late-Caledonian amphibolite-facies conditions. However, three kilometre-size rock bodies (Flatraket, Ulvesund and Kråkenes) in Outer Nordfjord preserve Pre-Caledonian igneous and granulite-facies assemblages and structures. Where these assemblages are preserved, the rocks are consistently unaffected by Caledonian deformation. The three bodies experienced high-pressure conditions (20–23 kbar) but show only very localized (about 5%) eclogitization in felsic and mafic rocks, commonly related to shear zones. The preservation of Pre-Caledonian felsic and mafic igneous and granulite-facies assemblages in these bodies, therefore, indicates widespread (∼ 95%) metastability at pressures higher than other metastable domains in Norway. Late-Caledonian amphibolite-facies retrogression was limited. The degree of reaction is related to the protolith composition and the interaction of fluid and deformation during the orogenic cycle, whereby metastability is associated with a lack of deformation and lack of fluids, either as a catalyst or as a component in hydration reactions. The three bodies appear to have been far less reactive than the external gneisses in this region, even though they followed a similar pressure–temperature evolution. The extent of metastable behaviour has implications for the protolith of the Western Gneiss Region, for the density evolution of high-pressure terranes and hence for the geodynamic evolution of mountain belts.

scholarly journals Study of silica-undersaturated magmas through the Kalsilite- Nepheline-Diopside-Silica system at 4.0 GPa and dry conditions

2018 ◽  
Vol 18 (2) ◽  
pp. 87-102
Author(s):  
Márcio Roberto Wilbert de Souza ◽  
Rommulo Vieira Conceição ◽  
Daniel Grings Cedeño ◽  
Roberto Vicente Schmitz Quinteiro
Keyword(s):  
High Pressure ◽  
Solid Solutions ◽  
Negative Correlation ◽  
Stability Field ◽  
Thermal Barrier ◽  
High Pressure And Temperature ◽  
Alkaline Magma ◽  
Magma Genesis ◽  
Dry Conditions ◽  
The Stability

This study experimentally investigates the Kalsilite-Nepheline-Diopside-Silica system at high pressure and temperature, with emphasis on silica-undersaturated volume (leucite-nepheline-diopside — Lct-Nph-Di; and kalsilite-nepheline-diopside — Kls + Nph + Di — planes), at 4.0 GPa (~120 km deep), temperatures up to 1,400ºC and dry conditions, to better understand the influence of K2O, Na2O, and CaO in alkali-rich silica-undersaturated magma genesis. In the Lct-Nph-Di plane, we determined the stability fields for kalsilite (Klsss), nepheline (Nphss) and clinopyroxene (Cpxss) solid solutions, wollastonite (Wo) and sanidine (Sa); and three piercing points: (i) pseudo-eutectic Kls + Nph + Di + liquid (Lct62Nph29Di9) at 1,000ºC; (ii) Kls + Sa + (Di + Wo) + liquid (Lct75Nph22Di2) at 1,200ºC; and (iii) pseudo-eutectic Kls + Di + Wo + liquid (Lct74Nph17Di9) at 1,000ºC. Kalsilite stability field represents a thermal barrier between ultrapotassic/potassic vs. sodic compositions. In the plane Kls-Nph-Di, we determined the stability fields for Klsss, Nphss and Cpxss and two aluminous phases in smaller proportions: spinel (Spl) and corundum (Crn). This plane has a piercing point in Kls + Nph + Di(± Spl) + liquid (Kls47Nph43Di10) at 1,100ºC. Our data showed that pressure extends K dissolution in Nph (up to 39 mol%) and Na in Kls (up to 27 mol%), and that these solid solutions, if present, determinate how much enriched in K and Na an alkaline magma will be in an alkaline-enriched metasomatic mantle. Additionally, we noted positive correlation between K2O and SiO2 concentration in experimental melts, negative correlation between CaO and SiO2, and no evident correlation between Na2O and SiO2. 

scholarly journals Ultra-High Pressure Metamorphism and Geochronology of Garnet Clinopyroxenite in the Paleozoic Dunhuang Orogenic Belt, Northwestern China

Minerals ◽  
2021 ◽  
Vol 11 (2) ◽  
pp. 117
Author(s):  
Zhen Li ◽  
Hao Wang ◽  
Qian Zhang ◽  
Meng-Yan Shi ◽  
Jun-Sheng Lu ◽  
...  
Keyword(s):  
High Pressure ◽  
Secondary Ion Mass Spectrometry ◽  
Volcanic Rocks ◽  
Orogenic Belt ◽  
Northwestern China ◽  
Stability Field ◽  
Uhp Metamorphism ◽  
Ultra High Pressure ◽  
Metamorphic Facies ◽  
Tectonic Exhumation

Ultra-high pressure (UHP) metamorphism is recorded by garnet clinopyroxenite enclaves enclosed in an undeformed, unmetamorphosed granitic pluton, northeastern Paleozoic Dunhuang orogenic belt, northwestern China. The protoliths of the garnet clinopyroxenite might be basic or ultrabasic volcanic rocks. Three to four stages of metamorphic mineral assemblages have been found in the garnet clinopyroxenite, and clockwise metamorphic pressure–temperature (P-T) paths were retrieved, indicative of metamorphism in a subduction environment. Peak metamorphic P-T conditions (790–920 °C/28–41 kbar) of garnet clinopyroxenite suggest they experienced UHP metamorphism in the coesite- or diamond-stability field. The UHP metamorphic event is also confirmed by the occurrence of high-Al titanite enclosed in the garnet, along with at least three groups of aligned rutile lamellae exsolved from the garnet. Secondary ion mass spectrometry (SIMS) U-Pb dating of metamorphic titanite indicates that the post-peak, subsequent tectonic exhumation of the UHP rocks occurred in the Devonian period (~389–370 Ma). These data suggest that part of the Paleozoic Dunhuang orogenic belt experienced UHP metamorphism, and diverse metamorphic facies series prevailed in this Paleozoic orogen. It can be further inferred that most of the UHP rocks in this orogen remain buried.

scholarly journals New insights on the GeSe x Te1−x phase diagram from theory and experiment

2019 ◽  
Vol 75 (2) ◽  
pp. 246-256 ◽  
Author(s):  
Markus Guido Herrmann ◽  
Ralf Peter Stoffel ◽  
Michael Küpers ◽  
Mohammed Ait Haddouch ◽  
Andreas Eich ◽  
...  
Keyword(s):  
Phase Diagram ◽  
High Pressure ◽  
Low Temperature ◽  
Hexagonal Phase ◽  
Structure Type ◽  
Stability Field ◽  
Temperature Behaviour ◽  
Formation Enthalpies ◽  
The Stability

The high-pressure and low-temperature behaviour of the GeSe x Te1−x system (x = 0, 0.2, 0.5, 0.75, 1) was studied using a combination of powder diffraction measurements and first-principles calculations. Compounds in the stability field of the GeTe structure type (x = 0, 0.2, 0.5) follow the high-pressure transition pathway: GeTe-I (R3m) → GeTe-II (f.c.c.) → GeTe-III (Pnma). The newly determined GeTe-III structure is isostructural to β-GeSe, a high-pressure and high-temperature polymorph of GeSe. Pressure-dependent formation enthalpies and stability regimes of the GeSe x Te1−x polymorphs were studied by DFT calculations. Hexagonal Ge4Se3Te is stable up to at least 25 GPa. Significant differences in the high-pressure and low-temperature behaviour of the GeTe-type structures and the hexagonal phase are highlighted. The role of Ge...Ge interactions is elucidated using the crystal orbital Hamilton population method. Finally, a sketch of the high-pressure phase diagram of the system is provided.

Geochronological evidence for phased volcanic activity in Fife and Caithness necks, Scotland

1981 ◽  
Vol 72 (1) ◽  
pp. 1-7 ◽  
Author(s):  
R. M. Macintyre ◽  
R. A. Cliff ◽  
N. A. Chapman
Keyword(s):  
High Pressure ◽  
Volcanic Activity ◽  
Shallow Depth ◽  
Stability Field ◽  
Early Permian ◽  
Explosive Activity ◽  
Isotopic Studies ◽  
The Stability ◽  
Considerable Depth ◽  
Geochronological Evidence

AbstractIn an attempt to establish a chronology for volcanic neck emplacement and so elucidate petrogenesis, isotopic studies have been carried out on various cumulate inclusions, blocks and megacrysts which occur chiefly in association with tuffs infilling several Scottish vents. K-Ar ages of 13 samples of low-pressure cumulate minerals (biotite, hornblende and pyroxene) from necks in East Fife indicate crystallisation at shallow depth at 314 Ma. U-Pb analyses of zircons are concordant at 318 Ma suggesting they are also members of this suite and their formation is penecontemporaneous with the Namurian volcanic activity which is welldocumented stratigraphically. By 295 Ma crystallisation of anorthoclase megacrysts had been completed, perhaps from the fractionated residuum. An eruption from considerable depth (within the stability field of garnet precipitation) then broke through to the surface bearing high-pressure megacrysts. This penetrated and disrupted the early cumulates carrying them to the surface and producing the diverse vent assemblages. K-Ar dating of basanites suggest that the Duncansby Ness neck in Caithness was emplaced around 270 Ma in the early Permian. For two Fife necks the balance of evidence favours an age of 290 Ma (Stephanian) for this final explosive activity associated with vent formation.

Ultra-high pressure aluminous titanites in carbonate-bearing eclogites at Shuanghe in Dabieshan, central China

1996 ◽  
Vol 60 (400) ◽  
pp. 461-471 ◽  
Author(s):  
D. A. Carswell ◽  
R. N. Wilson ◽  
M. Zhai
Keyword(s):  
High Pressure ◽  
Phase Equilibria ◽  
Amphibolite Facies ◽  
Central China ◽  
Stability Field ◽  
Ultra High Pressure ◽  
Metamorphic Fluids ◽  
Metamorphic Terrane ◽  
The Stability ◽  
Peak Assemblage

AbstractPetrographic features and compositions of titanites in eclogites within the ultra-high pressure metamorphic terrane in central Dabieshan are documented and phase equilibria and thermobarometric implications discussed. Carbonate-bearing eclogite pods in marble at Shuanghe contain primary metamorphic aluminous titanites, with up to 39 mol.% Ca(Al,Fe3+)FSiO4 component. These titanites formed as part of a coesite-bearing eclogite assemblage and thus provide the first direct petrographic evidence that AlFTi−1O−1 substitution extends the stability of titanite, relative to rutile plus carbonate, to pressures within the coesite stability field. However, it is emphasised that A1 and F contents of such titanites do not provide a simple thermobarometric index of P—T conditions but are constrained by the activity of fluorine, relative to CO2, in metamorphic fluids — as signalled by observations of zoning features in these titanites.These ultra-high pressure titanites show unusual breakdown features developed under more H2O-rich amphibolite-facies conditions during exhumation of these rocks. In some samples aluminous titanites have been replaced by ilmenite plus amphibole symplectites, in others by symplectitic intergrowths of secondary, lower Al and F, titanite plus plagioclase. Most other coesite-bearing eclogite samples in the central Dabieshan terrane contain peak assemblage rutile often partly replaced by grain clusters of secondary titanites with customary low Al and F contents.

Effects of pressure and H2O content on the compositions of primary crustal melts

1996 ◽  
Vol 87 (1-2) ◽  
pp. 11-21 ◽  
Author(s):  
Alberto E. Patiño Douce
Keyword(s):  
High Pressure ◽  
Wide Spectrum ◽  
Low Pressure ◽  
Source Material ◽  
Stability Field ◽  
Dehydration Melting ◽  
Isothermal Conditions ◽  
The Stability ◽  
Melting Experiments

ABSTRACT:Melting experiments with and without added H2O on a model metagreywacke and a natural metapelite demonstrate how pressure and H2O content control the compositions of melts and residual assemblages. Several effects are observed under isothermal conditions. Firstly, the stability field of biotite shrinks with decreasing pressure and with increasing H2O content, whereas that of plagioclase shrinks with increasing pressure and H2O content. Secondly, the ferromagnesian content of melts at the source (i.e. coexisting with their residual assemblages) decreases with decreasing H2O activity. Thirdly, with increasing pressure the Ca/Mg and Ca/Fe ratios of melts decrease relative to those of coexisting garnet. As a consequence, a wide spectrum of melts and crystalline residues can be generated from the same source material. For example, H2O-starved dehydration melting of metagreywacke at low pressure (≤10 kbar) generates K-rich (granitic) melts that coexist with pyroxene- and plagioclase-rich residues, whereas melting of the same material at high pressure (≍15 kbar) and with minor H2O infiltration can generate leucocratic Na-rich and Ca-poor (trondhjemitic) melts that coexist with biotite- and garnet-rich residues. An increased H2O content stabilises orthopyroxene at the expense of garnet + biotite + plagioclase, causing melts to shift towards granodioritic or perhaps tonalitic compositions.

scholarly journals First report of ultra-high pressure metamorphism in the Paleozoic Dunhuang orogenic belt (NW China): Constrains from <i>P</i>-<i>T</i> paths of garnet clinopyroxenite and SIMS U-Pb dating of titanite

2020 ◽  
Author(s):  
Zhen M. G. Li ◽  
Hao Y. C. Wang ◽  
Qian W. L. Zhang ◽  
Meng-Yan Shi ◽  
Jun-Sheng Lu ◽  
...  
Keyword(s):  
High Pressure ◽  
Northwest China ◽  
Orogenic Belt ◽  
Stability Field ◽  
Uhp Metamorphism ◽  
High Pressure Metamorphism ◽  
Ultra High Pressure ◽  
Mineral Assemblages ◽  
Metamorphic Facies ◽  
Tectonic Exhumation

Abstract. Ultra-high pressure (UHP) metamorphism is recorded by garnet clinopyroxenite enclaves enclosed in an undeformed, unmetamorphosed granitic pluton, northeastern Paleozoic Dunhuang orogenic belt, northwest China. Three to four stages of metamorphic mineral assemblages have been found in the garnet clinopyroxenite, and clockwise metamorphic pressure-temperature (P-T) paths were retrieved, indicative of metamorphism of a possible subduction environment. Peak metamorphic P-T conditions (790~920 °C/28~41 kbar) of garnet clinopyroxenite suggest that they experienced high pressure to UHP metamorphism, and the UHP metamorphism occurred in the coesite- or diamond-stability field. The UHP metamorphic event is further confirmed by the occurrence of high-Al titanite enclosed in the garnet, along with at least three groups of aligned rutile lamellae exsolved from within the garnet. SIMS U-Pb dating of metamorphic titanite indicates that the post peak, subsequent tectonic exhumation of the UHP rocks occurred in the Devonian (~ 389~370 Ma). These data suggest that part of the Paleozoic Dunhuang orogenic belt experienced UHP metamorphism, and diverse metamorphic facies series prevailed in this orogen in the Paleozoic. It can be further inferred that most of the UHP rocks of this orogen are now buried in the depth.

scholarly journals Unconventional Stoichiometries of Na–O Compounds at High Pressures

Materials ◽  
2021 ◽  
Vol 14 (24) ◽  
pp. 7650
Author(s):  
Lihua Yang ◽  
Yukai Zhang ◽  
Yanli Chen ◽  
Xin Zhong ◽  
Dandan Wang ◽  
...  
Keyword(s):  
High Pressure ◽  
High Pressures ◽  
Stability Field ◽  
First Principles Calculations ◽  
One Dimensional ◽  
Theoretical Investigations ◽  
Systematic Structure ◽  
Pressure Stability ◽  
The Stability ◽  
New Compounds

It has been realized that the stoichiometries of compounds may change under high pressure, which is crucial in the discovery of novel materials. This work uses systematic structure exploration and first-principles calculations to consider the stability of different stoichiometries of Na–O compounds with respect to pressure and, thus, construct a high-pressure stability field and convex hull diagram. Four previously unknown stoichiometries (NaO5, NaO4, Na4O, and Na3O) are predicted to be thermodynamically stable. Four new phases (P2/m and Cmc21 NaO2 and Immm and C2/m NaO3) of known stoichiometries are also found. The O-rich stoichiometries show the remarkable features of all the O atoms existing as quasimolecular O2 units and being metallic. Calculations of the O–O bond lengths and Bader charges are used to explore the electronic properties and chemical bonding of the O-rich compounds. The Na-rich compounds stabilized at extreme pressures (P > 200 GPa) are electrides with strong interstitial electron localization. The C2/c phase of Na3O is found to be a zero-dimensional electride with an insulating character. The Cmca phase of Na4O is a one-dimensional metallic electride. These findings of new compounds with unusual chemistry might stimulate future experimental and theoretical investigations.

Sign in / Sign up

Export Citation Format

Share Document