Journal: Petrology

Abbreviation

Petrology

Publisher

Pleiades Publishing

Journal Volumes

ISSN

0869-5911
1556-2085

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Publications 1 - 9 of 9
  • Metamorphic rocks of the Samerberg complex, Eastern Alps
    Item type: Journal Article
    Perchuk, L.L.; Gerya, Taras; Parfenova, O.V.; et al. (2007)
    Petrology
  • Initiation of transform faults at rifted continental margins
    Item type: Journal Article
    Gerya, Taras (2013)
    Petrology
  • A primer in gibbs energy minimization for geophysicists
    Item type: Journal Article
    Connolly, James (2017)
    Petrology
  • Large-scale-long-term Strength of the Lithosphere: New Theory and Applications
    Item type: Journal Article
    Gerya, Taras (2024)
    Petrology
    Abstract: Long-term strength of the lithosphere is often assumed to be equivalent to its average deviatoric stress level. However, this definition is only correct for a homogeneous visco-elastic material, in which no localized (in space and/or time) weakening and deformation processes occur. Here, I instead propose to define the large-scale-long-term strength of the lithosphere as the measure of its mechanical resistance to irreversible deformation, which corresponds to the amount of mechanical energy irreversibly spent (i.e., dissipated) for producing unit irreversible (i.e., inelastic, visco-plastic) deformation. According to this new definition, strength is the ratio of the integrated (through given lithospheric volume and time) mechanical energy dissipation to the integrated irreversible visco-plastic strain. With this new definition, the large-scale-long-term strength of the lithosphere stands as a strain-averaged rather than a volume-time-averaged quantity. As the result, an interesting behavior can occur when, due to localization of irreversible deformation along volumetrically minor weak structures, strength of the lithosphere can be significantly lower than its average long-term deviatoric stress level characteristic for volumetrically dominant strong elastic regions. This definition is applicable for both homogeneous and heterogeneous (i.e., localized in space and/or time) lithospheric deformation and provides a useful framework for analyzing various geodynamic settings on regional and global scale. In particular, I show some implications of this new lithospheric strength theory for better understanding of (i) intense melt-induced weakening of the lithosphere by magmatic processes, (ii) very low strength of plate interface in subduction zones and (iii) low brittle/plastic strength of tectonic plates predicted by global mantle convection models with plate tectonics. Although this work focuses on evaluating the long-term-large-scale brittle/plastic strength and deformation parameters, the proposed approach can also be applied for quantifying the effective ductile (i.e., viscous) strength and respective long-term-large-scale rheological properties.
  • Staurolite in Metabasites: P–T–X Parameters and the Ratios of Major Components as Criteria of Staurolite Stability
    Item type: Journal Article
    Borisova, Evgenia B.; Baltybaev, Sh K.; Connolly, James (2022)
    Petrology
    Abstract: Fe–Mg staurolite is a typical and widespread mineral of medium-temperature high-alumina metapelites, whereas magnesian staurolite is only relatively rarely found in metamorphosed mafic rocks (metabasites). The most significant factors controlling staurolite stability in metabasites were identified by thermodynamic modeling and analysis of the common features of the mineral-forming processes. In contrast to staurolite in low- and medium-pressure metapelites, staurolite in metabasites is stable at medium- and high-pressure metamorphism. An increase in the proportion of carbon dioxide in the water–carbon dioxide fluid shifts the staurolite-forming mineral reactions to lower temperatures and higher pressures. Al, Fe, Mg, and Ca are the major components of rocks that are critically important for the formation of magnesian staurolite in these rocks, and the contents and ratios of these components are of crucial importance for the stability of staurolite in metabasites. To understand the processes forming the mineral in metabasites, it is instrumental to subdivide metabasites into subgroups of predominantly magnesian, ferruginous–magnesian, and ferruginous protoliths. With regard to this subdivision, three petrochemical modules are proposed in the form of ratios of major components: MgO/CaO, CaO/FM, and Al2O3/FM, based on which it is possible to predict the stability of staurolite in mafic rocks at appropriate P–T parameters of metamorphism.
  • The problem of depth in geology
    Item type: Journal Article
    Moulas, E.; Podladchikov, Yuri Y.; Aranovich, L.Y.; et al. (2013)
    Petrology
  • Chlorine Solubility in Silicate Melts: New Experiments and Thermodynamic Mixing Model
    Item type: Journal Article
    Aranovich, Leonid Y.; Golunova, Maria A.; Connolly, James A.D.; et al. (2024)
    Petrology
    We present new experimental data on Cl solubility in model basalt melts of eutectic compositions diopside (Di)–albite (Ab) and Di–anorthite ± quartz (Qtz). The starting glasses were equilibrated with aqueous NaCl–CaCl2 fluid at 4 kbar in the temperature range of 900–1200°C. The experiments show that Cl solubility decreases with increasing NaCl in the fluid. Ca–Na partitioning between melts and fluid is weekly temperature dependent and resembles that of the plagioclase–fluid system. The newly obtained experimental data, along with previously published results on the model granite melting in the presence of (Na,K)Cl brines (Aranovich et al., 2013), are used to calibrate an empirical thermodynamic model for salt species (NaCl, KCl, and CaCl2) in silicate melt. Calculations show that Cl solubility in haplogranite melt decreases with increasing K/Na ratio in the fluid (and correspondingly, melt). The data acquired on Ca and Na partitioning between melt and fluid make it possible to model the evolution of the Ca/Na ratio in the crystallization course of basalt melts. At a high pressure (10 kbar), Cl solubility in model granite increases with increasing Н2О content. The calculated phase diagram for a simple pseudo-ternary system Ab–H2O–NaCl demonstrates complex phase relations and, correspondingly, evolution of the Н2О and NaCl concentrations in the melt. This complex evolution is illustrated by data on the composition of quartz-hosted melt and fluid inclusions from granites in the Verkhneurmisskii massif in the Badzhal volcano-plutonic zone.
  • P-T estimates and timing of the sapphirine-bearing metamorphic overprint in kyanite eclogites from Central Rhodope, northern Greece
    Item type: Journal Article
    Moulas, Evangelos; Kostopoulos, Dimitrios; Connolly, James; et al. (2013)
    Petrology
  • Order/disorder phase transition in cordierite and its possible relationship to the development of symplectite reaction textures in granulites
    Item type: Journal Article
    Vinograd, V.L.; Perchuk, L.L.; Gerya, Taras V.; et al. (2007)
    Petrology
    Based on a consistent set of empirical interatomic potentials, static structure energy calculations of various Al/Si configurations in the supercell of Mg-cordierite and Monte Carlo simulations the phase transition between the orthorhombic and hexagonal modifications of cordierite (Crd) is predicted at 1623 K. The temperature dependences of the enthalpy, entropy, and free energy of the Al/Si disorder were calculated using the method of thermodynamic integration. The simulations suggest that the commonly observed crystallization of cordierite in the disordered hexagonal form could be related to a tendency of Al to occupy T1 site, which is driven by local charge balance. The increase in the Al fraction in the T1 site over the ratio of 2/3(T1): 1/3(T2), that characterizes the ordered state, precludes formation of the domains of the orthorhombic phase. This intrinsic tendency to the crystallization of the metastable hexagonal phase could have significantly postponed the formation of the association of orthorhombic cordierite and orthopyroxene over the association of quartz and garnet in metapelites subjected to granulite facies metamorphism. The textures of local metasomatic replacement (the formation of Crd + Opx Or Spr + Crd symplectites between the grains of garnet and quartz) indicate the thermodynamic instability of the association of Qtz + Grt at the moment of the metasomatic reaction. This instability could have been caused by the difficulty of equilibrium nucleation of orthorhombic cordierite.
Publications 1 - 9 of 9