Relationships between zircon U-PbSHRIMP ages and leucosome type in migmatites of the Halls Creek Orogen, western Australia

Field relations, and zircon zoning and SHRIMP U-Pb patterns from an outcrop of deformed pelitic migmatites reveal relationships between leucosome type and the amount of zircon growth during migmatization. Zircons from the old est, stromatic migmatites show several Pb-207/Pb-206 intragrain analyses wi th 1850-1890 Ma anatectic ages and distinctive cathodoluminescence (CL) pat terns, although the sample is dominated by inferred pre-1855 Ma detrital zi rcons. Subsequent thick 'contact-sheath' leucosomes and 'back veins' develo ped at 1845-1830 Ma in response to intrusion of mafic dykes into the stroma tic migmatites. Zircons show CL evidence for substantial anatectic growth a nd overgrowths with post-1850 Ma ages, and a single population age 20 my yo unger than the other migmatites. Zircons from the structurally youngest, sh ear- and vein-hosted leucosomes show few overgrowths and retain a large det rital population. Correlation between shear zones and minimal anatectic zir con growth is inferred to reflect rapid deformation-induced melt extraction from the protolith, and/or rapid quenching. nle earlier contact-sheath and stromatic leucosomes probably had a combination of slow melt segregation, larger interacting melt volume and longer residence times at high temperatu res. Results suggest that rapid melt extraction by deformation will increas e the tendency for preservation of source lock isotopic patterns in some gr anites.