Impact of differential zircon fertility of granitoid basement rocks in North America on age populations of detrital zircons and implications for granite petrogenesis

Abstract

Age populations of detrital zircons in sand or sandstone preserve a reliable record of the ages of granitoid source rocks from which most of the zircon grains were ultimately derived, and this provenance signal can be used to infer sediment sources from independent knowledge of the areal distribution of granitoids of different ages provided allowance is made for sedimentary recycling of durable zircon sand grains. A compilation of 1386 whole-rock Zr analyses (ppm) from 72 North American suites of granitoid rock implies that the mean zircon fertility of different types and ages of granitoids ranges over nearly half an order of magnitude. Although Zr enters the lattices of some other igneous minerals sparingly, zircon contents of granitic rocks are inferred to vary with Zr contents. Subduction-related granitoid suites of varying ages (Archean, Paleoproterozoic, accreted peri-Gondwanan Neoproterozoic, Appalachian Paleozoic, Cordilleran Mesozoic) have a mean Zr content of 150 ppm and are assigned an arbitrary zircon fertility factor (ZFF) of 1.0. Mesoproterozoic Grenville granitoid suites associated with collisional orogeny have a mean Zr content of ~ 520 ppm (ZFF ~ 3.5). Anorogenic plutons of a transcontinental Mesoproterozoic igneous belt and of Appalachian pre-Iapetan Neoproterozoic and pre-Atlantic Mesozoic rift belts have a mean Zr content of ~ 375 ppm (ZFF ~ 2.5). Variations in the content of other high field strength elements (HFSE) parallel variations in Zr content. The differential zircon fertility of granitoid basement rocks should be taken into account for estimates of relative contributions of zircon populations from multiple bedrock sources to sediment of mixed provenance, and variations in ZFF suggest that subduction-related, collision-related, and anorogenic granitoid assemblages reflect different modes of crust–mantle evolution.