Using accessory minerals of probes of crustal processes

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The objective of my research program over the next five years (and leading to the longer term ten-year time frame) is to gain a better understanding of the Earth's crustal processes recorded through chemical and isotopic variations in accessory minerals such as zircon, monazite, apatite, and titanite. To work towards that goal, I will utilize results obtained by doing in situ tracer radiogenic isotope measurements, including Lu-Hf in zircon and Sm-Nd in monazite, apatite, and titanite; the trace element compositions of those minerals; and U-Th-Pb geochronology. This comprehensive suite of complimentary geo-analytical techniques will be effectively and efficiently used to address a wide range of diverse geologic problems that collectively were not possible until recently. By studying the mineral-scale processes that have controlled the chemical and isotopic changes in the Earth's crust, we can help with the development of a more robust model for the evolution of the crust over time. As part of the Lu-Hf and Sm-Nd research, synthetic minerals will be grown at high-T, doped with elements and specific isotopes of elements, and then chemically and structurally characterized. These crystals will be used as isotopic standards for Hf in zircon and Nd in monazite, titanite, and apatite for radiogenic tracer isotope studies. The synthetic standards will then be used to obtain more precise and accurate in situ analyses of natural minerals using laser ablation multi collector inductively coupled plasma mass spectrometry. One area to be investigated over the next five years includes the granite-lower crustal xenolith connection using Mesozoic lower crustal xenoliths and granites from the Mojave Desert in SE California. This locality is ideal for studying the granite-source connection, as the source region and possibly related anatectic melts can be directly sampled. The source region of post-Alpine tonalites and related rocks from the Adamello batholith in northern Italy will also be studied as part of a larger collaborative research effort with colleagues in Switzerland. The third focus area will address the origin of iron ore, copper, gold (IOCG) and iron ore apatite (IOA) ore deposits and related rocks from the Norrbotten region (e.g., Kiruna) in northern Sweden.