CRYSTAL AGING AND THE FORMATION OF FINE-SCALE IGNEOUS LAYERING

Fine-scale layering in igneous intrusions shows parallels with experimentally produced banding observed in crystallizing salt solutions in which recent advances have demonstrated the importance of crystal aging on the development of banding. These experiments, as well as numerical models of fine-scale layering development during crystal aging, reproduce features observed in fine scale layering that are not readily explained by periodic nucleation and crystal growth models. These include the phenomenon of ''lost segments'', in which the development of a layer may be reversed such that the layer disappears over time but does so without affecting the overall spacing of later-developing layers, and the development of ''doublet'' layers, which results when crystals at the margins of developing layers preferentially grow at the expense of those in the center. While these results suggest that crystal aging is the dominant process in the development of fine-scale layering, crystal aging may enhance the textural and modal features of igneous layering initiated by a variety of other crystal settling, nucleation or growth processes.