Fluid Exchange between Reacting Bodies of Rock

Greenwood, H. J.

doi:10.1007/978-94-009-4013-0_7

Cited by 1 publication

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“…For instance, in low‐grade metapelites it is assumed that a hydrous fluid wets grain boundaries during prograde garnet crystallization (e.g. Greenwood, 1985). In samples such as these, the breakdown of reactants generates a flux of nutrients into a hydrous fluid.…”

Section: New Conceptual Model For Porphyroblast Crystallizationmentioning

confidence: 99%

Porphyroblast crystallization kinetics: the role of the nutrient production rate

Schwarz

Engi

Berger

2011

Journal of Metamorphic Geology

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The mechanisms that govern porphyroblast crystallization are investigated by comparing quantitative textural data with predictions from different crystallization models. Such numerical models use kinetic formulations of the main crystallization mechanism to predict textural characteristics, such as grain size distributions. In turn, data on porphyroblast textures for natural samples are used to infer which mechanism dominated during their formation. Whereas previous models assume that the rate-limiting step for a porphyroblast producing reaction is either transport or growth, the model advanced in this study considers the production of nutrients for porphyroblasts as a potentially rate-limiting factor. This production reflects the breakdown of (metastable) reactants, which at a specific pressure (P) and temperature (T) depends on the bulk composition of the sample. The production of nutrients that potentially contribute to the formation of porphyroblasts is computed based on thermodynamic models. The conceptual model assumes that these nutrients feed into some intergranular medium, and products form by nutrient consumption from that medium, with rates depending on reaction affinity. For any sequence of P-T conditions along a P-T-t path, the numerical model first computes an effective supersaturation (r eff ) of the product phase(s), then an effective nucleation rate (J), and finally the amount of (porphyroblast) growth. As a result, the model is useful in investigating how the textural characteristics of a sample (of given bulk composition) depend on the P-T-t path followed during porphyroblast crystallization. The numerical model is tested and validated by comparing simulation results with quantitative textural data for garnet porphyroblasts measured in samples from the Swiss Central Alps.

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Section: New Conceptual Model For Porphyroblast Crystallizationmentioning

confidence: 99%