Influence of ferric iron on phase equilibria in greenschist facies assemblages: the hematite-rich metasedimentary rocks from the Monti Pisani (Northern Apennines)

2014 ◽  
Vol 32 (4) ◽  
pp. 371-387 ◽  
Author(s):  
D. Lo Pò ◽  
R. Braga
Keyword(s):  
Phase Equilibria ◽  
Ferric Iron ◽  
Northern Apennines ◽  
Greenschist Facies ◽  
Metasedimentary Rocks

The Slide Mountain Terrane and the structural evolution of the Finlayson Lake Fault Zone, southeastern Yukon

1997 ◽  
Vol 34 (2) ◽  
pp. 105-126 ◽  
Author(s):  
Heather E. Plint ◽  
Terence M. Gordon
Keyword(s):  
Fault Zone ◽  
Thermal Evolution ◽  
Structural Evolution ◽  
Ocean Basin ◽  
Greenschist Facies ◽  
Reverse Fault ◽  
Metasedimentary Rocks ◽  
Petrologic Study ◽  
Tectonic Boundary ◽  
Finlayson Lake

The Finlayson Lake Fault Zone forms a fundamental, but little studied, tectonic boundary between strata of autochthonous North America and the accreted Slide Mountain and Yukon–Tanana terranes in southeastern Yukon. A structural and petrologic study was undertaken to examine the depositional environment of the Slide Mountain Terrane, its tectono-thermal evolution in the fault zone, and its relationship with the Yukon–Tanana Terrane. The Slide Mountain and Yukon–Tanana terranes are divisible into units dominated by metavolcanic and metasedimentary rocks. Field observations and whole-rock geochemistry indicate that Slide Mountain greenstone is ocean-floor basalt deposited in a deep submarine basin with a proximal terrigenous sediment influx. Either a marginal- or ocean-basin setting is supported by the data. Slide Mountain greenstone is thrust northeastward over metasedimentary rocks of Slide Mountain Terrane and southwestward over rocks of the Yukon–Tanana Terrane. Regional metamorphic grade ranges from subgreenschist to greenschist facies. Pressure–temperature estimates for the subgreenschist–greenschist facies transition are 270–310 °C and 2.1–3.6 kbar (1 kbar = 100 MPa), based on assumed geothermal gradients and the reaction isograd Pmp + Chl = Act + Ep + H2O. Metamorphic peak postdates motion along the westernmost reverse fault that juxtaposes the Slide Mountain and Yukon–Tanana terranes. We interpret the Finlayson Lake Fault Zone as a northeasterly directed thrust sequence disrupted by synmetamorphic back thrusts. The back thrusting may be the consequence of shortening in the upper crust, or larger scale processes such as "tectonic wedging" of Yukon–Tanana Terrane under Slide Mountain Terrane.

scholarly journals Thermodynamic modelling of carbonate-silicate rocks from the Sakar unit, Sakar-Strandzha zone, SE Bulgaria

2021 ◽  
Vol 82 (3) ◽  
pp. 76-78
Author(s):  
Tzvetomila Vladinova ◽  
Milena Georgieva
Keyword(s):  
Metamorphic Grade ◽  
Thermodynamic Modelling ◽  
Greenschist Facies ◽  
Amphibolite Facies ◽  
General Increase ◽  
Metasedimentary Rocks ◽  
Town Area ◽  
East West ◽  
Silicate Rocks

The P-T evolution of carbonate-bearing metasedimentary rocks from the Sakar unit (Sakar-Strandzha Zone, SE Bulgaria) has been obtained using Perple_X modelling and conventional geothermometry. The metamorphic conditions vary from greenschist facies (250–350 °C/2–4 kbar) in the Klokotnitsa village area to amphibolite facies (550–650 °C/4.5–6.5 kbar) in the Topolovgrad town area, confirming a general increase of the metamorphic grade at east-west direction.

scholarly journals Applying Phase Equilibria Modelling to Metamorphic and Geological Processes: Recent Developments and Future Potential

2017 ◽  
Vol 44 (1) ◽  
pp. 27 ◽  
Author(s):  
Chris Yakymchuk
Keyword(s):  
Phase Equilibria ◽  
Phase Diagrams ◽  
Secular Change ◽  
Major Advance ◽  
Accessory Minerals ◽  
Chemical Systems ◽  
Metasedimentary Rocks ◽  
Geological Processes ◽  
Recent Developments ◽  
Future Potential

Phase equilibria modelling has played a key role in enhancing our understanding of metamorphic processes. An important breakthrough in the last three decades has been the ability to construct phase diagrams by integrating internally consistent datasets of the thermodynamic properties of minerals, fluids and melts with activity–composition models for mixed phases that calculate end-member activities from end-member proportions. A major advance in applying phase equilibria modelling to natural rocks is using isochemical phase diagrams to explore the phase assemblages and reaction sequences applicable for a particular sample. The chemical systems used for modelling phase equilibria are continually evolving to provide closer approximations to the natural compositions of rocks and allow wider varieties of compositions to be modelled. Phase diagrams are now routinely applied to metasedimentary rocks, metabasites and intermediate to felsic intrusive rocks and more recently to ultramafic rocks and meteorites.    While the principal application of these phase diagrams is quantifying the pressure and temperature evolution of metamorphic rocks, workers are now applying them to other fields across the geosciences. For example, phase equilibria modelling of hydrothermal alteration and the metamorphism of hydrothermally altered rocks can be used to determine ‘alteration vectors’ to hydrothermal mineral deposits. Combining the results of phase equilibria of rock-forming minerals with solubility equations of accessory minerals has provided new insights into the geological significance of U–Pb ages of accessory minerals commonly used in geochronology (e.g. zircon and monazite). Rheological models based on the results of phase equilibria modelling can be used to evaluate how the strength of the crust and mantle can change through metamorphic and metasomatic processes, which has implications for a range of orogenic processes, including the localization of earthquakes. Finally, phase equilibria modelling of fluid generation and consumption during metamorphism can be used to explore links between metamorphism and global geochemical cycles of carbon and sulphur, which may provide new insights into the secular change of the lithosphere, hydrosphere and atmosphere.RÉSUMÉLa modélisation des équilibres de phases a joué un rôle clé dans l’amélioration de notre compréhension des processus métamorphiques. Une percée importante au cours des trois dernières décennies a été la capacité de construire des diagrammes de phase en y intégrant des ensembles de données cohérentes des propriétés thermodynamiques des minéraux, des fluides et des bains magmatiques avec des modèles d'activité-composition pour des phases mixtes qui déduisent l’activité des membres extrêmes à partir des proportions des membres extrêmes. Une avancée majeure dans l'application de la modélisation d'équilibre de phase aux roches naturelles consiste à utiliser des diagrammes de phases isochimiques pour étudier les assemblages de phase et les séquences de réaction applicables pour un échantillon particulier. Les systèmes chimiques utilisés pour la modélisation des équilibres de phase évoluent continuellement pour fournir des approximations plus proches des compositions naturelles des roches et permettent de modéliser de plus grandes variétés de compositions. Les diagrammes de phase sont maintenant appliqués de façon routinière aux roches métasédimentaires, aux métabasites et aux roches intrusives intermédiaires à felsiques et plus récemment aux roches ultramafiques et aux météorites.   Bien que l'application principale de ces diagrammes de phase consiste à quantifier l'évolution de la pression et de la température des roches métamorphiques, les utilisateurs les appliquent maintenant à d'autres spécialités des géosciences. Par exemple, la modélisation des équilibres de phase de l'altération hydrothermale et du métamorphisme des roches d’altération hydrothermale peut être utilisée pour déterminer les « vecteurs d'altération » des gisements minéraux hydrothermaux. La combinaison des résultats des équilibres de phase des minéraux constitutifs des roches avec des équations de solubilité des minéraux accessoires a permis d’en savoir davantage sur la signification géologique des âges U–Pb des minéraux accessoires couramment utilisés en géochronologie (par exemple zircon et monazite). Les modèles rhéologiques basés sur les résultats de la modélisation des équilibres de phase peuvent être utilisés pour évaluer comment la résistance de la croûte et du manteau peut changer à travers des processus métamorphiques et métasomatiques, ce qui a des implications sur une gamme de processus orogéniques, y compris la localisation des séismes. Enfin, la modélisation des équilibres de phase de la génération et de l’absorption des fluides pendant le métamorphisme peut être utilisée pour explorer les liens entre le métamorphisme et les cycles géochimiques globaux du carbone et du soufre, ce qui peut fournir de nouvelles perspectives sur le changement séculaire de la lithosphère, de l'hydrosphère et de l'atmosphère. 

scholarly journals Fluid-induced breakdown of monazite in medium-grade metasedimentary rocks of the Pontremoli basement (Northern Apennines, Italy)

2015 ◽  
Vol 34 (1) ◽  
pp. 63-84 ◽  
Author(s):  
D. Lo Pò ◽  
R. Braga ◽  
H.-J. Massonne ◽  
G. Molli ◽  
A. Montanini ◽  
...  
Keyword(s):  
Northern Apennines ◽  
Metasedimentary Rocks

scholarly journals The dynamothermal aureole of the Donqiao ophiolite (northern Tibet)

1997 ◽  
Vol 34 (1) ◽  
pp. 59-65 ◽  
Author(s):  
Mei-Fu Zhou ◽  
John Malpas ◽  
Paul T. Robinson ◽  
Peter H. Reynolds
Keyword(s):  
High Pressure ◽  
Subduction Zone ◽  
Greenschist Facies ◽  
Metamorphic Rocks ◽  
High Grade ◽  
Mineral Paragenesis ◽  
Metasedimentary Rocks ◽  
Northern Tibet ◽  
Suprasubduction Zone ◽  
Ar Geochronology

Metamorphic rocks found at the base of the Jurassic Donqiao ophiolite of northern Tibet are interpreted as a basal dynamothermal aureole produced during obduction of the massif. The rocks form a sequence some 8 m thick, varying from high-grade amphibolites at the contact with overlying harzburgites to greenschist facies metasedimentary rocks lower down. The mineral paragenesis is similar to other such aureoles, and indicates that temperatures in excess of 750 °C may have been reached during metamorphism. The lack of high-pressure minerals suggests that the rocks were produced by subcretion in a relatively shallow dipping subduction zone. Ar–Ar geochronology on amphibole separates provides dates of 175–180 Ma for the displacement of the ophiolite, significantly older than the age of emplacement estimated from stratigraphie relationships. The ophiolite was clearly obducted very soon after its formation in a suprasubduction zone environment.

The geological structure of the Emilia-Tuscany Northern Apennines and Alpi Apuane

2019 ◽  
Vol 11 (2.5) ◽  
pp. 1-78 ◽  
Author(s):  
Paolo Conti ◽  
Gianluca Cornamusini ◽  
Luigi Carmignani ◽  
Giancarlo Molli
Keyword(s):  
Geological Structure ◽  
Northern Apennines

Phase equilibria in partially open systems under pressure: the decomposition of stoichiometric GeO2 oxide

2003 ◽  
Vol 173 (12) ◽  
pp. 1359 ◽  
Author(s):  
Vadim V. Brazhkin ◽  
Roman N. Voloshin ◽  
A.G. Lyapin ◽  
Svetlana V. Popova
Keyword(s):  
Phase Equilibria ◽  
Open Systems
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