Constraints on magma mixing and heterogeneity from correlation of compositional zoning in plagioclase.

摘要

Major, trace element, and isotopic zoning in crystals preserves a record of heterogeneity in magmatic systems which is generally accepted to result from mixing, and assimilation processes. Quantitative comparison of crystal zoning data has the potential to mutually constrain the kinematics of magma mixing and previous chemical environments. However, it has been difficult to quantitatively compare micro-analytical data between mineral phases and chemical tracers due to the inherent difficulty of aligning zoning profiles from potentially off-center profiles and lack of an adequate statistical framework.; We submit two methods for correlation and alignment of zoning profiles in an internally consistent, statistically constrained format: Wavelet Based Correlation (WBC) and Shared Characteristic Diagrams (SCD). WBC compares the overall similarity of selected scales of zoning features, while SCD identifies correlative segments of zoning. SCD provides a measure of the degree of shared history in crystal populations, and the spatial heterogeneity of chemical tracers in magmatic systems. Thus, SCD provides a framework to interpret the physical and chemical evolution of chemical reservoirs in magmatic systems. We align profiles with an empirical approach that selects a best fit from a range of possible alignments. A Monte Carlo algorithm is used to evaluate the statistical significance of profile correlations in both techniques.; Application of WBC to granodiorites of the Tuolumne Intrusive Suite reveals complex transport histories for crystals sampled at a gradational contact, consistent with field observations. SCD from dacite domes at Chaos Crags reveal differences in heterogeneity between rhyodacite host and mafic inclusion crystal populations, in addition to differences in the distribution of intensive variables controlling anorthite content and 87Sr/86Sr in plagioclase. Mafic inclusion populations are more heterogeneous than those from the host rhyodacite, and distribution of 87Sr/ 86Sr is homogeneous than the distribution of the indistinguishable thermal or volatile content. These observations are consistent with inclusion and host textures and whole rock analyses. Both WBC and SCD produce reliable results in natural systems indicating that they can be applied to other systems and data sets.*; *This dissertation is a compound document (contains both a paper copy and a CD as part of the dissertation). The CD requires the following system requirements: Adobe Acrobat.