Inherited, enriched, heated, or recycled? The Grenville Orogeny: Examining potential causes of Earth's most zircon fertile magmatic episode
An increasing number of tectonic studies rely on U-Pb ages of detrital zircon to identify sediment source regions. Such studies can be confounded if zircon ages reflect original primary sources rather than final, proximal sources. Such is the case with ~ 1 Ga Grenville zircon in North America – detrital grains are found in abundance thousands of kilometres from known exposed sources. This is likely a result of the incredible zircon fertility of Grenville age plutons (i.e. granitoids with very high Zr abundance). There are multiple possible mechanisms that can explain such high zircon abundances including: (1) very significant degrees of inherited xenocrystic zircon in the granitoids; (2) very unusually trace-element enriched source areas of the granitic magmas; (3) massive degrees of crustal recycling during Grenville orogenic events; or (4) extremely high temperatures of granitic magmas that allow for very high quantities of zirconium to be dissolved in the magmas. Each of these possibilities will be discussed in the context of what looks to be the single most zirconium-enriched major magmatic event in Earth history!