Origins of textural, compositional, and isotopic complexity in monazite and its petrochronological analysis

Monazite is one of the most versatile accessory minerals for deciphering geologic processes, particularly in rocks with complex geotectonic histories. Its value as a petrochronometer comes from a combination of mechanical and chemical stability, coupled with thermodynamic reactivity to changing intrinsic and extrinsic factors, including temperature, pressure, whole-rock composition, and fluid activity, such that individual monazite grains may consist of multiple discrete compositional, textural, and isotopic sub-domains. Using microbeam techniques, each subdomain may be described and analyzed independently to construct a holistic time-resolved history for the evolution of individual monazite grains. Through acquisition of similar data from a representative number of grains, a geologic history for the mineral population, and by extension, the rocks(s) in which they were, or are, hosted may be constructed. Monazite has additional value because the development of textures is, in part, controlled by the composition of fluids present. Moreover, multiple isotope systems (U-Th-Pb, Sm-Nd, and O) may be exploited to collect information for both geochronological and geochemical purposes. This contribution reviews the mechanisms by which textural complexity develops in monazite, describes some of the analytical methods used to exploit the complexity, and demonstrates the broad range of applications that benefit from the study of texturally complex monazite. In addition, we present new data sets that highlight the power of petrochronology and laser ablation split-stream inductively coupled plasma mass spectrometry in harnessing the unique attributes of monazite.