Speaker: Prof. Beth Ann Bell
Affiliation: UCLA

Abstract:
Zircon continues to grow in importance as a probe of the crust, both its current architecture and the parts of it that have been lost to erosion over deep time. A wide array of applications in the earth sciences, ranging from tectonic reconstructions of modern-day crustal terranes to investigation of Earth’s earliest crust in the Hadean Eon, benefit from being able to fully exploit the information trapped in zircon about its source rocks and the environments in which they formed. One less-explored avenue for reconstructing zircon source rocks is the mineral inclusions trapped in them, whose interpretation is somewhat complicated compared to direct age and isotopic results from the host zircons themselves. This talk presents three projects showing different applications of inclusions in detrital zircon that were derived from igneous rocks. First, the proportion of apatite in a zircon inclusion assemblage can help to predict how felsic the source magma was, and avoids some of the biases that impede this when the prediction is made using the major minerals quartz and feldspar. Second, the Fe-Ti oxides trapped as inclusions in zircon reflect the redox state of the magma from which the zircon grew, and can help to reconstruct the source magma when other indicators such as trace elements in the host zircon are more ambiguous or overprinted. Third, the proportion of inclusion phases made up of highly incompatible trace elements helps to predict whether a detrital population had significant provenance from highly felsic leucogranites, which are significant both in the context of crustal maturation and mineral exploration. Future applications involving inclusions in zircon will be able to exploit the trace element and isotopic information that is available on increasingly smaller spatial scales due to tools like the ion microprobe.

Submitted by: Omar Abuassaf (oabuassaf@epss.ucla.edu)