The importance of high precision in the evaluation of U-Pb zircon age spectra

Using Stochastic Point Pattern Analysis to Track Regional Orientations of Magmatism During the Transition to Cenozoic Extension and Rio Grande Rifting, Southern Rocky Mountains

“…Protracted zircon age spectra can be caused by prolonged magmatic zircon growth (autocrysts), inclusions of zircon from previous pulses of a similar magmatic locus (antecrysts) or inclusions of ancient zircon material unrelated to the sampled pulse of magmatism (xenocrysts) (J. S. Miller et al., 2007). The ability to assess the cause of this dispersion is commonly driven by the level of analytical precision used for the U‐Pb analysis (Gaynor et al., 2022).…”

“…However, these young plateaus yield weighted mean ages with MSWD values >1 (1.3–7.8) and are over‐dispersed. The relatively low temporal precision of LA‐ICPMS spot analyses is not sensitive enough to discern between models to explain this dispersion, such as subtle Pb‐loss or antecrystic inheritance (Gaynor et al., 2022). As a result, we calculated weighted mean ages for the younger plateaus with conservative uncertainties expanded by $$\sqrt{\text{MSWD}}$$, which is a simple model for accounting for overdispersion of ages (e.g., Vermeesch, 2018; Table S3 in Supporting Information S1).…”

Supplemental Material: Recommendations for the reporting and interpretation of isotope dilution U-Pb geochronological information

“…3A, 3B, and 5C). Causes may be geological (growth, or a combination of different age components in the same grain; see Gaynor et al, 2022a;Samperton et al, 2015), systemic (Pb-loss through decay damage, variable Th/U of melt, and/or zircon through fractional crystallization), or computational (variation of Pb*/ Pb c amongst analyses, introducing variation of the 206 Pb/ 238 U date). Below, we briefly mention commonly used approaches for assigning ages to data sets argued to be scattered as a result of geological processes.…”

Technical Note: Pb-loss-aware Eruption/Deposition Age Estimation

“…>0.5% relative precision and accuracy versus <0.05% relative (Schoene, 2014)). Since the ability to precisely and accurately recognize discordant analyses is directly dependent on analytical precision and accuracy (Gaynor et al, 2022), the ability to exclude such samples is comparatively limited in most detrital studies. This concern is potentially redoubled if low-temperature aqueous/meteoric alteration and "incipient weathering" is indeed a primary driver of Pb loss in radiation-damaged (e.g.…”