Implications of erosion and bedrock composition on zircon fertility: Examples from South America and Western Australia

Abstract

Isotopic analysis of zircon has been useful in charting our planet's geological history from the Holocene to the Hadean. Zircon is present in a range of lithologies, yet its yield in sedimentary systems is governed by the zircon fertility of the source rocks and their denudation rate. This interplay is illustrated in South America where rocks exposed in the Amazonia craton have higher Zr concentrations (i.e. greater zircon yield) than the Andes; however, the detrital zircon population of the Amazon River catchment shows more zircon from the Andes given the higher erosion rate.Nonetheless, the observed zircon frequency can be corrected for erosional and fertility biases. Additionally, detrital zircon in fluvial sediment in Western Australia, previously interpreted as quantifying differential erosion, can alternatively be explained as an effect of Zr content (therefore zircon fertility) of the sources. Understanding the variables controlling zircon yield will facilitate accurately interpreting detrital zircon signatures through deep time and their application to crustal evolution questions.

Detrital zircons reveal sea-level and hydroclimate controls on Amazon River to deep-sea fan sediment transfer

“…Grainsize variations may influence DZ age populations (Ibañez-Mejia et al, 2018), but amal ga mat ing multiple published river samples should smooth potential grain-size effects, and turbidite deposits sampled from the fan were a consistent grain size (dominantly fine sand). Variable Zr content across source terranes or drainage basins (e.g., zircon fertility; Moecher and Samson, 2006) would affect calculated proportions of erosion versus sediment supply (Amidon et al, 2005;Spencer et al, 2018). However, the temporal variation in our calculated relative sediment loads from distinct source areas in the Amazon system cannot be related to fertility, as source terrane fertility does not change temporally.…”

Resolving the Architecture and Early Evolution of a Forearc Basin (Georgia Basin, Canada) Using Detrital Zircon

“…Our data also show that MDS groups generally correlate with MDA, and samples assigned to the same MDS group are broadly equivalent stratigraphically. However, both MDAs and MDS groups vary as a function of many factors, including depositional environment 35 , source area lithology 36 and magmatic quiescence 6 . These physical aspects of the paleoenvironment impact DZ results and must be taken into consideration prior to their use in stratigraphic analysis.…”

Episodic zircon age spectra mimic fluctuations in subduction

“…Bias may have been introduced by the non-uniform nature of the individual sampling campaigns, by differential erosion, and by the fact that young plutonic bodies have not yet been exhumed, whereas older magmatic units may have already been entirely eroded and either subducted or re-buried in sedimentary basins. Additionally, the relationship of the true zircon age distribution of the margin to magmatic volume fluctuations can be complicated by differential zircon fertility of the arc products through time 31 .…”