An Eocene (ca 45 million year old) gabbro pluton near House Mountain in southwest Idaho provides an opportunity to explore how the conditions of crystallization are recorded in zircon chemistry. Zircon is a zirconium silicate mineral present in trace amounts in magmas, which is capable of incorporating large, highly charged elements (e.g. transition metals, actinides, lanthanides) that do not easily substitute into other minerals. Variations in these elements can be used to track magma evolution. For example, the titanium concentration is related to the temperature at which zircon crystallizes from the magma; rare earth elements (REE) and the relative proportion of europium (Eu-anomaly) can be used to track the degree of crystallization of the magma.
Trace elements (TE) were measured in situ on 25 micron spots in zoned zircon crystals using laser ablation inductively coupled plasma mass spectrometry. Two samples from the pluton, an equigranular gabbro and a felsic granophyre, were analyzed. The zircons from the gabbro record cooling temperatures, and evolution from a primitive, mafic magma to one enriched in TE with a stronger Eu-anomaly. Residual felsic melt segregated from crystallized minerals and concentrated in the granophyre records evolved compositions in the final stage of crystallization.
Terhaar, Danielle and Schmitz, Mark, "Zircon Chemistry in a Gabbro Pluton at House Mountain, Idaho" (2015). College of Arts and Sciences Presentations. Paper 45.