Zirconium isotopic composition of the upper continental crust through time

Abstract

The stable isotopic composition of insoluble, refractory elements such as titanium (Ti) or zirconium (Zr), which are modified by magmatic differentiation but, a priori, are poorly affected by weathering or diagenesis, serve as powerful potential proxies to reconstruct the compositional evolution of the continental crust. Here we present the evolution of the Zr stable isotopic compositions (δ 94/90 Zr IPGP-Zr , per mille suggest a Zr-weighted δ 94/90 Zr IPGP-Zr value of 0.077 ± 0.058‰ (2SD, n = 44) for the UCC, which is statistically distinct (t test, p value = 2.88×10 -10 ) and higher than that of the mantle (0.040 ± 0.044‰, n = 72). Combining the δ 94/90 Zr IPGP-Zr values of different terrestrial reservoirs, the δ 94/90 Zr IPGP-Zr of the BSE and bulk Earth is constrained to be 0.041 ± 0.041‰.

Determination of the zirconium isotopic composition of the new isotopic standard NRC ZIRC-1 using MC-ICP-MS

“…Allende ( δ 94/90 Zr IPGP-Zr = −0.041 ± 0.021‰) is isotopically lighter than Earth ( δ 94/90 Zr IPGP-Zr = 0.041 ± 0.041‰). 1 Further work is required to investigate the origin of this difference, but, Allende could be used as a reference material in the future to evaluate the quality of the data.…”

“…More recently, Zr isotope analysis has attracted much interest, owing to its petro-genetic importance and the development of high precision analytical methods on a MC-ICP-MS, using sample decomposition or direct solid sampling analysis. 1,9–11,13–18 The typical reproducibility for the isotopic ratios is 7–10 ppm (part per mil) per u. Several investigations have revealed large Zr isotope fractionation (>0.5‰ for the 94 Zr/ 90 Zr ratio) in magmatic systems and discussed the origin of the isotopic fractionation.…”

“…14 Some studies showed that felsic rock standards have heavier Zr isotopic compositions than mafic reference materials, and the Zr isotope composition of the upper continental crust is heavier than that of the mantle. 1,14–16,19 Zirconium isotopes can provide a new approach to study magmatic differentiation, crustal evolution, or other high temperature processes. This newly emerged field requires additional work to explore isotopic fractionation mechanisms.…”

Zr isotopes reveal long storage timescales of Archean magmas

“…This implies that there is no Zr isotope fractionation during serpentinization. Previous studies also showed that chemical weathering does not affect Zr isotope compositions 14,22 . The metamorphic and inherited zircon domains in this study have identical δ 94 Zr values to the magmatic domains (Extended Fig.…”

“…Among the five stable isotopes of Zr, 94 Zr/ 90 Zr ratios are usually analyzed and reported as δ 94 Zr relative to IPGP-Zr standard (δ 94 Zr = 1000× [( 94 Zr/ 90 ZrSample/ 94 Zr/ 90 ZrIPGP)-1]) 11 . Recent studies report significant variations in the Zr isotope composition of different rocks (-0.13 to 0.63‰) and minerals (-4.24 to 1.01‰), though the mechanisms for these variations are still debated [11][12][13][14][15][16][17][18][19][20][21][22][23][24] .…”