Trace Element and Lu-Hf Systematics in Hadean-Archean Detrital Zircons: Implications for Crustal Evolution

Abstract

AbstractThe very limited Hadean and Eoarchean rock record has greatly affected our understanding of the earliest evolution of the planet but has also spurred a strong interest in using the chemical characteristics of ancient detrital zircons as proxies for this missing record. In the northern Wyoming Province, detrital zircons with U-Pb ages from 3.3 to 4.0 Ga exhibit trace element and U-Pb systematics that suggest minimal, if any, disturbance to the Lu-Hf system since magmatic crystallization. The 207Pb/206Pb ages of these zircons define a continuum of ages within analytical error from 3.5 to 4.0 Ga. Initial Hf isotopic compositions outline a trend that begins at ∼4.1 Ga, with values characteristic of primitive or slightly depleted mantle followed by a steady decrease in minimum initial values to about −9 at 3.5 Ga, characteristic of a reservoir with Lu/Hf of <0.1. Initial Hf compositions are variable, however, and indicate mixing with magmas derived from a primitive or depleted mantle that begins to inc...