Metamorphic mineral reactions: Porphyroblast, corona and symplectite growth

Abstract

Much of the Earth's dynamics is related to mineral reactions in the solid-state. Classically, this is referred to as metamorphic crystallization (Kretz, 1994). Based on the chemical compositions of the phases involved in a metamorphic mineral reaction, two basic reaction types may be distinguished. Reactions that involve only structural rearrangements , while the compositions of the reactant and product phases are identical, are referred to as partitionless and 'polymorphic phase transformations'. If, in contrast, one or more reactant phases are replaced by one or more product phases with different compositions, this implies that chemical components are supplied to or removed from the reaction interfaces separating the reactants from the product phases. In the absence of advective transport via a fluid or melt, the necessary chemical mass transport can occur only by diffusion. Accordingly, this reaction type is partitioning and is referred to as 'diffusive phase transformation'. Some treatments of the kinetics of mineral reactions are based on partitionless polymorphic phase transformations and are reviewed only briefly in this chapter. However, because most metamorphic mineral reactions are partitioning diffusive phase transformations, the following discussion will focus mainly on this reaction type. In this chapter, three types of reactions that play a key role in metamorphic crystallization are addressed. During prograde metamorphism continuous supply of aqueous fluid by dehydration reactions may facilitate relatively rapid intercrystalline diffusion so that a state close to chemical equilibrium on the scale of mineral grains and beyond may be attained resulting in 'porphyroblastic mineral growth'. Interface-reaction controlled and diffusion-controlled growth are two endmember models in the kinetics of porphyroblastic growth and differ in terms of the spatial extent of chemical equilibration and its influence on the distribution and compositional zoning of porphyroblasts. The first section of this chapter may serve as a review of some of the key works in metamorphic petrology addressing the factors that control the abundance and size distribution of porphyroblasts and their chemical zoning patterns.

In Situ Hyperspectral Raman Imaging: A New Method to Investigate Sintering Processes of Ceramic Material at High-temperature

“…Reaction rims and corona textures are common non-equilibrium features in many metamorphic rocks [71,72] and ancient ceramics [63]. As the reactant and product phases have different compositions, interlayer growth requires chemical mass-transfer which, in the absence of melts and fluids, can occur by diffusion only.…”

“…As the reactant and product phases have different compositions, interlayer growth requires chemical mass-transfer which, in the absence of melts and fluids, can occur by diffusion only. At the same time, localized reactions must proceed at the 'reaction interfaces', which divide the growing layers on either side [72]. Both processes may be rate limiting and the coupling between the two processes determines the overall reaction kinetics [72].…”

“…At the same time, localized reactions must proceed at the 'reaction interfaces', which divide the growing layers on either side [72]. Both processes may be rate limiting and the coupling between the two processes determines the overall reaction kinetics [72]. Two approaches are possible to identify the rate-limiting step and to identify the direction of the migration front: (i) the rim growth approach and (ii) experiments with isotopically doped reactants [71,73,74].…”

Synthesis of monticellite–forsterite and merwinite–forsterite symplectites in the CaO–MgO–SiO2 model system: influence of temperature and water content on microstructure evolution

“…The underlying process is referred to as cellular segregation reaction (Cahn 1959;Christian 2002). Two types of cellular segregation reactions are discerned (Cahn 1959;Gaidies et al 2017): (1) in cellular precipitation a solid solution, which is supersaturated with respect to some component, segregates out this component through precipitation of a second phase, which forms rods or lamellae in the matrix of the formerly supersaturated solid solution. (2) In eutectoidal decomposition, a homogeneous precursor phase decomposes into two new phases, which both differ in structure and composition from the reactant and form a vermicular or lamellar intergrowth.…”

Conditions and timing of low-pressure – high-temperature metamorphism in the Montresor Belt, Rae Province, Nunavut

“…Whereas the application of the pair correlation function (PCF) indicates that garnet crystal centres are clustered at any test distance, the mark covariance function (MCF) suggests that garnet crystal sizes are randomly distributed. Hence, the MCF results point to garnet growth kinetics independent of nutrient diffusion across the rock matrix but that garnet growth was rather controlled by the rate of interface reactions (e.g., Kretz, 1974;Carlson, 1989Carlson, , 1991Hirsch et al, 2000;Hirsch, 2011;Petley-Ragan et al, 2016;Gaidies et al, 2017). However, given the evidence of significant garnet resorption, results of the MCF statistics may be of limited use.…”