Troy Baggerman and Sue DeBari, at Western Washington University in Bellingham,
have just had a journal paper published. The paper uses the geochemistry of several Mount Baker lava flows to model how andesite might be derived from a more mafic basaltic magma through crystal fractionation or magma mixing. They used three Baker lava flows for their study: the basalt and basaltic andesite of Sulphur Creek, the Mg-rich andesite of Glacier Creek , and the andesite and dacite of Boulder Glacier.
Troy completed his geology Masters at WWU last year, working with Dr. DeBari. After they revised his thesis, it has now been published in Contributions to Mineralogy and Petrology.
Troy and Sue, modeling the chemical composition of the various lavas, conclude the following (paraphrasing the abstract):
The two dominantly andesitic units (Glacier Creek and Boulder Glacier) are different enough from each other that they could not have been derived from the same parent basalt. Nor could either of them have been derived from the Sulphur Creek basalt by crystal fractionation processes. Crystal fractionation also cannot explain the compositional diversity within each unit. Compositional diversity within the Sulphur Creek unit (basalt to basaltic andesite) can, however, be successfully modeled by mixing of basalt with compositions similar to the dacites in the BG unit. Given that the Boulder Glacier dacites erupted at*80–90 ka, and a similar composition was mixed with the Sulphur Creek lavas at 9.8 ka, the process that produced this felsic end-member must have been repeatedly active for at least 70 ka.
The reference is
Baggerman, T. and DeBari, S., 2011, The generation of a diverse suite of Late Pleistocene and Holocene basalt through dacite lavas from the northern Cascade arc at Mount Baker, Washington: Contributions in Mineralogy and Petrology p. 161:75–99 DOI 10.1007/s00410-010-0522-2
The paper’s abstract is available at the journal’s website, and the entire paper may be purchased there as well, if you don’t have access to it via an institutional computer (say, at WWU).