INNOVATIVE APPLICATIONS OF U-PB GEOCHRONOLOGY, A TRIBUTE TO SAMUEL A. BOWRING'S LEGACY

Part of Sam Bowring's legacy is his drive to develop, refine and adopt improved methods of U-Pb geochronology. His fierce pursuit of low Pb blank, single zircon, high-precision TIMS methods set the bar and spawned a number of new, high-precision labs founded by his students and post-docs. He improved the U-Pb dating of other accessory minerals, such as titanite, apatite, rutile and monazite, and was an early supporter of James Mattinson's chemical abrasion techniques (Mattinson 2005) that are now widely adopted and produce precisions of better than 0.1%. Sam's Earthtime initiative led to inter-laboratory calibrations among the U-Pb community and cross-calibrations with other systems such as Ar-Ar and Astrochronology, ultimately leading to increased accuracy and enhancing collaborations among disparate disciplines.

As a tribute to Sam's dogged pursuit of innovative applications of U-Pb geochronology, we present two vignettes that combine in-situ SIMS and single zircon CATIMS U-Pb dating with micro- to nano- textural imaging to unravel complex histories in mafic rocks. In the first example we show how shock metamorphic features in magmatic baddeleyites can be spatially correlated with U-Pb dates to establish both the magmatic age of recent martian magmatism and time of ejection of shergottite meteorite NWA 5298 (Moser et al., 2013; Darling et al., 2016). In the second example baddeleyite and several populations of texturally distinct zircons were used to establish the magmatic date and at least two periods of hydrothermal alteration in Caribbean basalts, a tectonic history spanning 40 m.y. These advances in in-situ geochronology ultimately rely on accurate dates for reference baddeleyite and zircon made possible through Sam's contributions to the field. Although Sam was not directly involved in either of these projects, we believe that this integrated approach reflects Sam's vision of the potential for U-Pb geochronology.