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Analysis of [[delta].sup.18]O in igneous zircons of known age traces the evolution of intracrustal recycling and crust-mantle interaction through time. This record is especially sensitive because oxygen isotope ratios of igneous rocks are strongly affected by incorporation of supracrustal materials into melts, which commonly have [[delta].sup.18]O values higher than in primitive mantle magmas. This study summarizes data for [[delta].sup.18]O in zircons that have been analyzed from 1,200 dated rocks ranging over 96% of the age of Earth. Uniformly primitive to mildly evolved magmatic [[delta].sup.18]O values are found from the first half of Earth history, but much more varied values are seen for younger magmas. The similarity of values throughout the Archean, and comparison to the composition of the 'modern' mantle indicate that [[delta].sup.18]O of primitive mantle melts have remained constant ([+ or -] 0.2[per thousand]) for the past 4.4 billion years. The range and variability of [[delta].sup.18]O in all Archean zircon samples is subdued ([[delta].sup.18]O(Zrc)=5-7.5[per thousand]) ranging from values in high temperature equilibrium with the mantle (5.3 [+ or -] 0.3[per thousand]) to slightly higher, more evolved compositions (6.5-7.5[per thousand]) including samples from: the Jack Hills (4.4-3.3 Ga), the Beartooth Mountains (4.0-2.9 Ga), Barberton (3.5-2.7 Ga), the Superior and Slave Provinces (3.0 to 2.7 Ga), and the Lewisian (2.7 Ga). No zircons from the Archean have been analyzed with magmatic [[delta].sup.18]O above 7.5[per thousand]. The mildly evolved, higher Archean values (6.5-7.5[per thousand]) are interpreted to result from exchange of protoliths with surface waters at low temperature followed by melting or contamination to create mildly elevated magmas that host the zircons. During the Proterozoic, the range of [[delta].sup.18]O(Zrc) and the highest values gradually increased in a secular change that documents maturation of the crust. After ~1.5 Ga, high [[delta].sup.18]O zircons (8 to > 10[per thousand]) became common in many Proterozoic and Phanerozoic terranes reflecting [[delta].sup.18]O(whole rock) values from 9 to over 12[per thousand]. The appearance of high [[delta].sup.18]O magmas on Earth reflects non-uniformitarian changes in the composition of sediments, and rate and style of recycling of surface-derived material into magmas within the crust.

Oxygen isotope compositions of mineral separates were determined from two metaluminous granitoids (Emas and Sao Rafael plutons) from northeastern Brazil. The I-type Emas pluton has high [[delta].sup.18]O (WR) values (11.5-11.8[per thousand]), whereas the Sao Rafael pluton has low [[delta].sup.18]O (WR) values (7.5-8.1[per thousand]), but Sr and Nd are characteristics of S-type granitoids. Measured mineral-mineral fractionations suggest continuous sub-solidus inter-mineral isotope exchange among all minerals except zircon. There is a large and consistent quartz-epidote fractionation that gives apparent temperatures that are much lower than anticipated closure temperatures for epidote. Oxygen isotope fractionation between natural zircon and magmatic epidote is opposite to that predicted from theoretical determinations, as [[delta].sup.18]O (epidote)