Oxygen isotope perspective on Precambrian crustal growth and maturation

In this study we contrast insights on Precambrian crustal growth and matura tion from radiogenic and oxygen isotope systematics in the Superior (3.0-2. 7 Ga) and Grenville (1.3-1.0 Ga) Provinces of the Canadian shield. Oxygen i sotope ratios in zircon provide the best evidence of supracrustal input int o ancient orogens. Archean Superior Province zircons have relatively low de lta(18)O values and a limited range (5.7 parts per thousand +/- 0.6 parts p er thousand), while Proterozoic Grenville Province zircons have elevated de lta(18)O values and a wider range (8.2 parts per thousand+/1.7 parts per th ousand). These data reflect fundamental differences in crustal evolution an d maturation between the Superior and the Grenville Provinces. In the Grenv ille Province, radiogenically juvenile supracrustal material with high delt a(18)O values was buried (or subducted) to the base of the crust within 150 m.y. of initial crust production, causing high magmatic delta(18)O values (delta(18)O [zircon] greater than or equal to 8 parts per thousand) in anor thosite suite and subsequent plutons. Information about Large volumes and r apid recycling of Grenville crust is not accessible from radiogenic isotope data alone. The Grenville data contrast with the restricted delta(18)O val ues of Superior Province magmatism, where subtle (similar to 1 parts per th ousand) elevation in delta(18)O occurs only in volumetrically minor, late t o postorogenic (sanukitoid) plutons. Differences in sediment delta(18)O val ues between the Superior and Grenville Provinces are predominantly a functi on of the delta(18)O of source materials, rather than differences in chemic al maturity or erosion styles. This study shows that zircon is a robust ref erence mineral to compare igneous processes in rocks that have undergone ra dically different histories.