Crystal Size Distributions and Scaling Laws in the Quantification of Igneous Textures

This study demonstrates the value of the combined use of scaling of the chemical evolution of cooling magmas have investigated the detailed relationships between temanalysis and crystal size distribution (CSD) measurements in the interpretation of igneous textures and outlines applications of these perature, phase abundance, and phase composition. The reaction series (Bowen, 1922) and the CIPW norm (Cross methods to other fundamentally important problems. Theoretical calculations and measurements of natural samples are used to et al., 1903) have been supplemented by modern thermodynamic models that predict the compositions and abundcharacterize the relationship between igneous texture and cooling history. The total number (NT) and mean length ( L ) of crystals ances of minerals in equilibrium with melt of a given composition and temperature (e.g. Ariskin et al., 1993; in a sample are correlated through a scaling relationship of the form N T ∝ L. This proportionality depends on the mineralogy Ghiorso & Sack, 1995). Although there are a few areas of uncertainty, the chemistry of igneous petrogenesis is of the rock, and so a modal normalization factor (C) is introduced. The CSD slope, S, and intercept, ln(n°), are uniquely related to fairly well understood. But chemical models cannot address the central probeach other through the equation ln(n°) = 4ln(S) − ln(C), where S = L. This overall relationship allows the texture of a rock lem of igneous crystallization, which is the physical process of generating a set of crystals from magma. Two to be related to the local duration of cooling through an arbitrary crystal growth model. Quantification of the link between the texture magmas with the same composition will normally produce the same minerals in the same proportions. However, of a rock and its cooling history makes it possible to predict spatial variations in texture. We show an example of this method using depending on their thermal histories, these two magmas can solidify into rocks with drastically different physical the Sudbury Igneous Complex, Canada. Additional applications include relating the textures of volcanic rocks to spatial and temporal appearances (e.g. basalt and gabbro). The set of minerals is the same, but what distinguishes them is the abundance variations in the magma chamber and extracting kinetic parameters from suites of comagmatic rocks. and size of the constituent crystals. The fine-grained rocks in the chilled margins of most basic intrusions cooled rapidly and the coarse-grained rocks in the interiors of plutons cooled slowly. This has