Complex geological histories extending for ≥ 4.0 Ga deciphered from xenocryst zircon microstructures

Zircons older than 3.0 Ga have previously been identified as detrital grains within ca. 3.0 Ga elastic metasedimentary rocks of the Narryer Terrane. In this study, a detailed microstructural investigation of greater than or equal to 4.0 Ga zircons recently discovered as xenocrysts within two late Archaean granitic gneisses from the Narryer and Murchison terranes of the Yilgarn Craton is reported. The microstructures of these ca. 200 mu m long crystals record complex histories of disturbance between ca. 4183 and 3945 Ma that may reflect high-grade thermal events. Younger events recorded within these grains can be related to regional magmatic and metamorphic episodes known from the regional geology of the northwestern part of the Yilgarn Craton. By combining detailed examination of zircon microstructures using backscattered electron and cathodoluminescence imaging with trace element and ion microprobe isotopic microanalytical methods, this study has demonstrated that complex histories can be determined from individual zircons, (C) 2000 Elsevier Science B.V. All rights reserved.