Skip to Main content Skip to Navigation
Journal articles

Understanding preservation of primary signatures in apatite by comparing matrix and zircon-hosted crystals from the Eoarchean Acasta Gneiss Complex (Canada)

Abstract : A novel way to investigate the petrogenesis of ancient poly-metamorphosed terranes is to study zircon-hosted mineral inclusions, which are sensitive to melt evolution such as apatite. Recent contributions on such inclusions in unmetamorphosed granitoids can provide valuable petrogenetic information and, in turn, represent a way to circumvent effects of metamorphism. Yet, the impact of metamorphism on apatite inclusion has never been studied in detail. To address the issue of chemical and isotopic preservation of primary signals in apatite crystals both in the matrix and armored within zircons, we have studied apatite crystals from four 3.6-4.0 Ga TTG granitoids from the Acasta Gneiss Complex (Canada). Our results demonstrate that U-Th-Pb isotope systematics in matrix apatite crystals were reset at 1.8-1.7 Ga (Wopmay orogen) whereas primary REE signatures were preserved in many crystals. In contrast, zircon-hosted apatite inclusions all preserved primary REE signatures despite variable ages between 1.7 and 4.0 Ga. We interpret reset ages to be a consequence of metamorphism that managed to affect U-Th-Pb systematics because of advanced radiation damage accumulation in host-zircon lattices. Only the most pristine zircon crystal has an apatite inclusion with a concordant age consistent with the magmatic age of the zircon (4.0 Ga). In addition, our results show that apatite crystals from TTG have distinct REE composition from post-Archean granitoids apatites, that is preserved even in some apatites with reset ages. This capacity to retain primary information and discriminate granitoid types makes apatite a very valuable tool for reconstructing the nature and evolution of ancient crustal rocks through the use of detrital minerals.
Complete list of metadata

https://hal.archives-ouvertes.fr/hal-02561884
Contributor : Emilie Bruand <>
Submitted on : Wednesday, May 6, 2020 - 1:24:24 PM
Last modification on : Tuesday, April 20, 2021 - 12:12:16 PM

Identifiers

Citation

C. Antoine, Emilie Bruand, Martin Guitreau, Jean-Luc Devidal. Understanding preservation of primary signatures in apatite by comparing matrix and zircon-hosted crystals from the Eoarchean Acasta Gneiss Complex (Canada). Geochemistry, Geophysics, Geosystems, AGU and the Geochemical Society, 2020, ⟨10.1029/2020GC008923⟩. ⟨hal-02561884⟩

Share

Metrics

Record views

169

Files downloads

528