Abstract
Detrital zircons are the only confirmed surviving remnants of >4.03 Ga crust while younger detrital zircons provide a parallel record of more recent crustal evolution to that preserved in crystalline rocks. Zircons often preserve inclusions that may provide clues as to the origins of out-of-context grains in the sedimentary record. Previous studies have established that inclusions of biotite in magmatic zircon are compositionally well-matched to biotite in the source rock matrix, although a direct application to ancient detrital zircons has not been made. A number of studies have documented variations in the Fe, Mg, and Al contents of magmatic biotite from different source rocks and tectonic settings, suggesting that biotite inclusions may indeed serve as provenance indicators for detrital zircons. Consistent with earlier studies, we find that the FeO⁎/MgO ratio of magmatic biotite from continental arcs, collisional, and within-plate settings varies with relative oxidation state as well as whole-rock FeO⁎/MgO, while its Al2O3/(FeO⁎ + MgO) varies with whole-rock A/CNK (molar Al/(2⋅Ca + Na + K)). Biotite from oxidized metaluminous and reduced S-type granitoids can be readily distinguished from each other using FeO⁎/MgO and Al2O3/(FeO⁎ + MgO), while biotite from reduced I-type and oxidized peraluminous granites may in some cases be more ambiguous. Biotite from peralkaline and reduced A-type granites are also distinguishable from all other categories by Al2O3/(FeO⁎ + MgO) and FeO⁎/MgO, respectively. Biotite inclusions in Hadean zircons from Jack Hills, Western Australia indicate a mixture of metaluminous and reduced S-type host rocks, while inclusions in 3.6–3.8 Ga detrital zircons from the Nuvvuagittuq Supracrustal Belt indicate more oxidized peraluminous magmas. These results highlight the diversity of felsic materials on the early Earth and suggest that biotite inclusions are applicable to zircon provenance throughout the sedimentary record.
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