Abstract Title: Characteriation of Mantle-Derived, Kimberlitic Zircon Megacrysts

Abstract Submitted to: EDUCATION

Abstract Text:

Mantle-derived zircon have long been used to date the eruption of their host rocks, such as kimberlites. Zircon are useful for geochronology due to their resistance to alteration and their incorporation of large amounts (ppm) of radioactive elements like uranium (U) and thorium (Th). In this study, we characterized 21 mantle zircon from 8 kimberlites spanning the Amazonian, Congo, Kaapvaal, Slave, Siberian, and Tanzanian cratons. The mantle zircon reveal a range of color, size and texture with their kimberlite eruption ages ranging from ~350 to 50 Ma. We acquired uranium-lead (U-Pb) dates and trace element data via Laser Ablation Inductively Coupled Plasma Mass Spectrometry (LA ICP-MS), which allows for the rapid acquisition of U-Pb ages for large numbers of zircon compared to the pioneering TIMs studies of the 1970s. By comparing U-Pb dates, trace element profiles, and Cathodoluminescence (CL) images, we assess if our zircon samples reflect any unique characteristics associated with their kimberlite pipes and respective cratons. In addition to potentially providing improved constraints on kimberlite eruption ages, this study allows the opportunity to look for the presence of pre-eruption zircon that may reveal precursor kimberlite activity that may not be evident in the exposed kimberlites. Initial U-Pb dating results show that some zircon record the timing of kimberlite emplacement whereas others yield older mantle ages (some >2 Ga).