Autonomic Molecular Transport by Polymer Films Containing Programmed Chemical Potential Gradients

2015 ◽  
Vol 137 (15) ◽  
pp. 5066-5073 ◽  
Author(s):  
Chunjie Zhang ◽  
Amit Sitt ◽  
Hyung-Jun Koo ◽  
Kristopher V. Waynant ◽  
Henry Hess ◽  
...  
Keyword(s):  
Polymer Films ◽  
Chemical Potential ◽  
Molecular Transport ◽  
Potential Gradients ◽  
Chemical Potential Gradients

Genesis of coronae and implications of an early Neoproterozoic thermal event: a case study from SE Chotanagpur Granite Gneissic Complex, India

2020 ◽  
pp. 1-20
Author(s):  
Vedanta Adak ◽  
Upama Dutta
Keyword(s):  
Chemical Potential ◽  
Corona Formation ◽  
Geological Evolution ◽  
Geological Information ◽  
Potential Gradients ◽  
A Minor ◽  
Chemical Potential Gradients ◽  
Early Neoproterozoic ◽  
Extract Information

Abstract Partial equilibrium textures such as corona provide information on changing pressure–temperature (P-T) conditions experienced by a rock during its geological evolution. Coronae layers may form in single or multiple stages; understanding the genesis of each layer is necessary to correctly extract information regarding the physicochemical conditions experienced by the rock. Mafic rocks from SE Chotanagpur Granite Gneissic Complex, India, show the presence of multi-layered coronae at olivine–plagioclase contact with the mineral sequence: olivine | orthopyroxene | amphibole + spinel | plagioclase. Textural studies indicate that the coronae formed during metamorphism in a single stage due to a reaction between olivine and plagioclase. Reaction modelling shows that the corona formation occurred in an open system and experienced a minor volume loss. Pseudosection modelling and thermobarometry suggest that the P-T conditions related to corona formation are 860 ± 50°C and 7 ± 0.5 kbar. A μMgO-μCaO diagram shows that the layers in coronae formed in response to chemical potential gradients between the reactant minerals. A combination of field observations and the P-T conditions of coronae formation suggest a fluid-driven metamorphism. Correlation with extant geological information indicates that the corona-forming event is possibly related to the accretion of India and Antarctica during the assembly of Rodinia.

Demixing of Materials under Chemical Potential Gradients

1985 ◽  
Vol 68 (1) ◽  
pp. 1-6 ◽  
Author(s):  
TAKUMA ISHIKAWA ◽  
HIROSHI SATO ◽  
RYOICHI KIKUCHI ◽  
S. A. AKBAR
Keyword(s):  
Chemical Potential ◽  
Potential Gradients ◽  
Chemical Potential Gradients

scholarly journals Arrested development – a comparative analysis of multilayer corona textures in high-grade metamorphic rocks

Solid Earth ◽  
2017 ◽  
Vol 8 (1) ◽  
pp. 93-135 ◽  
Author(s):  
Paula Ogilvie ◽  
Roger L. Gibson
Keyword(s):  
Steady State ◽  
Reaction Mechanisms ◽  
Chemical Potential ◽  
Layer Growth ◽  
Igneous Rocks ◽  
Diffusion Controlled ◽  
Corona Formation ◽  
Potential Gradients ◽  
T Path ◽  
Chemical Potential Gradients

Abstract. Coronas, including symplectites, provide vital clues to the presence of arrested reaction and preservation of partial equilibrium in metamorphic and igneous rocks. Compositional zonation across such coronas is common, indicating the persistence of chemical potential gradients and incomplete equilibration. Major controls on corona mineralogy include prevailing pressure (P), temperature (T) and water activity (aH2O) during formation, reaction duration (t) single-stage or sequential corona layer growth; reactant bulk compositions (X) and the extent of metasomatic exchange with the surrounding rock; relative diffusion rates for major components; and/or contemporaneous deformation and strain. High-variance local equilibria in a corona and disequilibrium across the corona as a whole preclude the application of conventional thermobarometry when determining P–T conditions of corona formation, and zonation in phase composition across a corona should not be interpreted as a record of discrete P–T conditions during successive layer growth along the P–T path. Rather, the local equilibria between mineral pairs in corona layers more likely reflect compositional partitioning of the corona domain during steady-state growth at constant P and T. Corona formation in pelitic and mafic rocks requires relatively dry, residual bulk rock compositions. Since most melt is lost along the high-T prograde to peak segment of the P–T path, only a small fraction of melt is generally retained in the residual post-peak assemblage. Reduced melt volumes with cooling limit length scales of diffusion to the extent that diffusion-controlled corona growth occurs. On the prograde path, the low melt (or melt-absent) volumes required for diffusion-controlled corona growth are only commonly realized in mafic igneous rocks, owing to their intrinsic anhydrous bulk composition, and in dry, residual pelitic compositions that have lost melt in an earlier metamorphic event. Experimental work characterizing rate-limiting reaction mechanisms and their petrogenetic signatures in increasingly complex, higher-variance systems has facilitated the refinement of chemical fractionation and partial equilibration diffusion models necessary to more fully understand corona development. Through the application of quantitative physical diffusion models of coronas coupled with phase equilibria modelling utilizing calculated chemical potential gradients, it is possible to model the evolution of a corona through P–T–X–t space by continuous, steady-state and/or sequential, episodic reaction mechanisms. Most coronas in granulites form through a combination of these endmember reaction mechanisms, each characterized by distinct textural and chemical potential signatures with very different petrogenetic implications. An understanding of the inherent petrogenetic limitations of a reaction mechanism model is critical if an appropriate interpretation of P–T evolution is to be inferred from a corona. Since corona modelling employing calculated chemical potential gradients assumes nothing about the sequence in which the layers form and is directly constrained by phase compositional variation within a layer, it allows far more nuanced and robust understanding of corona evolution and its implications for the path of a rock in P–T–X space.

scholarly journals The key role of µH2O gradients in deciphering microstructures and mineral assemblages of mylonites: examples from the Calabria polymetamorphic terrane

2021 ◽  
Author(s):  
Fabrizio Tursi
Keyword(s):  
Chemical Potential ◽  
Shear Zones ◽  
Chemical Potentials ◽  
Ductile Shear Zones ◽  
Mineral Assemblages ◽  
Potential Gradients ◽  
Ductile Shear ◽  
Chemical Potential Gradients

AbstractA careful petrologic analysis of mylonites’ mineral assemblages is crucial for a thorough comprehension of the rheologic behaviour of ductile shear zones active during an orogenesis. In this view, understanding the way new minerals form in rocks sheared in a ductile manner and why relict porphyroblasts are preserved in zones where mineral reactions are generally supposed to be deformation-assisted, is essential. To this goal, the role of chemical potential gradients, particularly that of H2O (µH2O), was examined here through phase equilibrium modelling of syn-kinematic mineral assemblages developed in three distinct mylonites from the Calabria polymetamorphic terrane. Results revealed that gradients in chemical potentials have effects on the mineral assemblages of the studied mylonites, and that new syn-kinematic minerals formed in higher-µH2O conditions than the surroundings. In each case study, the banded fabric of the mylonites is related to the fluid availability in the system, with the fluid that was internally generated by the breakdown of OH-bearing minerals. The gradients in µH2O favoured the origin of bands enriched in hydrated minerals alternated with bands where anhydrous minerals were preserved even during exhumation. Thermodynamic modelling highlights that during the prograde stage of metamorphism, high-µH2O was necessary to form new minerals while relict, anhydrous porphyroblasts remained stable in condition of low-µH2O even during exhumation. Hence, the approach used in this contribution is an in-depth investigation of the fluid-present/-deficient conditions that affected mylonites during their activity, and provides a more robust interpretation of their microstructures, finally helping to explain the rheologic behaviour of ductile shear zones.

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