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Creation of a continent recorded in zircon zoning

¹ Department of Earth Sciences, University of Western Ontario, London, Ontario N6A 5B7, Canada
² Department of Geology and Geophysics, University of Utah, Salt Lake City, Utah 84112, USA
³ U.S. Geological Survey, Menlo Park, California 94305, USA
⁴ Department of Geology and Geophysics, University of Wisconsin, Madison, Wisconsin 53706, USA
⁵ U.S. Geological Survey, Menlo Park, California 94305, USA
⁶ Department of Geology and Geophysics, University of Wisconsin, Madison, Wisconsin 53706, USA

View larger version (40K): [in this window] [in a new window]   Figure 1. Inset: Geology of southern Superior province of the Canadian shield; Kapuskasing uplift is indicated. Bedrock geology map of the Borden Lake belt in southern Kapuskasing uplift is modified after Percival and West (1994) and shows amphibolite-granulite transition (dashed line), paleopressures, and zircon sample location site 32.

View larger version (29K): [in this window] [in a new window]   Figure 2. Summary of spatially correlated U-Pb and O isotopic measurements for 47 detrital cores and 26 metamorphic rims (Table DR1; see footnote 1). Age ranges for events depicted by solid bars are discussed in text. Note small time gap between end of sedimentation in Borden Lake belt and onset of lower crustal metamorphism of same sediments. Note also that previous laser fluorination analyses of Superior province magmatic zircon regionally gave average 18O of 5.7 ± 0.6 and values as high as 6.5 ± 0.4 for late sanukitoid magmas (King et al., 1998).

View larger version (46K): [in this window] [in a new window]   Figure 3. A: Composite cathodoluminescence (CL) image (i.e., gray-scale values of metamorphic rim inverted; see Fig. DR1 [see footnote 1] for original) of grain 4 showing locations and results of U-Pb and oxygen isotopic spot analyses. B: Composite (rim grayscale inverted) CL image of grain 6 showing patchy resetting of U-Pb age to metamorphic values and domainal enrichment of 18O associated with darkening and/or disruption of CL in core (these changes may be due to recrystallization). Note concentric age and oxygen banding in metamorphic rim. Crystal growth spans 150 m.y. C: 18O results from grain 4 indicating that no discernible isotopic exchange has occurred between core and rim (see text). D: Stages of continental plate creation and local destruction corresponding to zircon growth zone sequences and sequence boundaries.