Unravelling complex geologic histories using U–Pb and trace element systematics of titanite

Abstract

Unravelling the spatio-temporal evolution of orogenic terranes requires a comprehensive understanding of the duration and extent of metamorphic events and hydrothermal alteration. Commonly used minerals such as zircon and monazite may not fully record geological histories in complex tectonic settings because their elemental constituents do not react under many metamorphic and metasomatic conditions. Here, we complement the current geochronological record of the Capricorn Orogen, Western Australia, with titanite U-Pb geochronology and geochemistry of felsic intrusive rocks to draw conclusions about the use of titanite in understanding the evolution of orogenic terranes. Because titanite usually incorporates common-Pb and may be variably reset by multiple metamorphic and hydrothermal events, a workflow is provided here for the systematic and robust interpretation of titanite U-Pb data. The addition of trace element data in titanite is particularly effective for differentiating whether a grain is igneous, recrystallized or metamorphic. We have developed several petrogenetic indices to differentiate these three types of titanite using Zr-in-titanite temperature, Th/U, Th/Pb, Al/(Al+Fe), light to heavy rare earth element ratio, and Eu anomalies. The addition of trace element geochemistry can also highlight anomalously radiogenic 207 Pb/ 206 Pb reservoirs. Utilization of our workflow in the Capricorn Orogen reveals that titanite ages from the same samples as published zircon U-Pb data range from coeval to several hundreds of Myr of age difference between the two minerals. Titanite geochronology and trace element geochemistry indicates ~30 Myr of previously unrecognized prolonged cooling for the Capricorn Orogeny to ca. 1750 Ma. The spatial extent of reworking of the Mutherbukin Tectonic Event is also broadened significantly farther north and south than previously recognized. Incorporating titanite geochronology and trace geochemistry ACCEPTED MANUSCRIPT 2013). This is because the laser ablation method enables rapid, simultaneous acquisition of trace element and isotopic compositions from small volumes. The incorporation of common-Pb in titanite can also pose a significant problem if a sample records more than one geological event. If a single sample records an igneous crystallization and metamorphic recrystallization event, differentiation between the two is usually possible in a mineral with negligible common-Pb (e.g., zircon) because a discordia line will intercept the U-Pb concordia between the first and second event (e.g., Taylor et al., 2014; Zhang et al.,

Natural Titanite Reference Materials forIn SituU‐Pb and Sm‐Nd Isotopic Measurements byLA‐(MC)‐ICP‐MS

“…At the time of writing, the mechanism of common Pb incorporation into different types of titanite crystals has not been extensively explored (Olierook et al 2018). In contrast to zircon, titanite frequently accommodates significant amounts of common Pb in its crystal lattice.…”

Resolving multiple geological events using in situ Rb–Sr geochronology: implications for metallogenesis at Tropicana, Western Australia

“…A small round-robin analytical run consisting of ∼ 20 standards preceded analytical runs to monitor long-term stability and overall data integrity. Data were reduced in Iolite (Paton et al, 2011) and in-house Excel macros. Analyses that crosscut multiple minerals or mineral generations at depth were excluded.…”

Resolving multiple geological events using in situ Rb-Sr geochronology: implications for metallogenesis at Tropicana, Western Australia

“…The U-Pb method has long been employed to date crystallization, metamorphism and hydrothermal events, often by targeting cores and rims in individual grains. Many U-bearing minerals have recorded multiple ages due to their ability to participate in metamorphic/hydrothermal reactions or become (partially) reset by events above mineral closure temperatures, including zircon (Liu et al, 2012), monazite (Rasmussen et al, 2007), titanite (Olierook et al, 2019), rutile (Zack and Kooijman, 2017) and apatite (Kirkland et al, 2018). However, not all geological events are associated with (partial) reset or new growth of U-bearing minerals.…”