Australian Journal of Earth Sciences (1999) 46, 923–932 INTRODUCTION The Albany–Fraser Orogen (Myers 1990) is an arcuate orogenic belt girdling the southern and southeastern mar- gins of the Archaean Yilgarn Craton in Western Australia (Figure 1). The main tectonic and metamorphic features of the belt were developed during the Mesoproterozoic Albany–Fraser Orogeny, which can be subdivided into two distinct stages of activity (Clark et al. in press): Stage I rep- resenting continental collision (ca 1345–1280 Ma), and Stage II reflecting reactivation in an essentially intracratonic set- ting (ca 1215–1140 Ma). Both thermotectonic stages involved oblique dextral convergence between the orogen and the Yilgarn Craton, and the northwestward transport of thrust slices (Myers 1993, 1995; Nelson et al. 1995; Clark et al. in press). The Fraser Complex (Myers 1985) forms a major com- ponent of the northeastern part of the Albany–Fraser Orogen (Figure 1). It crops out discontinuously for over 185 km along strike and is approximately 32 km wide. On the basis of gravity and magnetic anomalies, the complex is interpreted to extend subsurface for a further 250 km to the northeast under the Cenozoic cover of the Eucla Basin (Bunting et al. 1976). Myers (1985) proposed that the com- plex was a metamorphosed and tectonically dismembered layered basic intrusion, or suite of intrusions; one of the most areally significant in the world (Hess 1989). He identi- fied five tectonostratigraphic units, each ~2–5 km thick, bounded by zones of intense deformation (Figure 1). Subordinate granulite facies paragneiss and orthogneiss cropping out between the mafic units were considered to have been tectonically interleaved with the basic rocks (now mainly pyroxene granulites), and hence bear no intrusive or genetic relationship to them. The term ‘Fraser Complex’ was therefore defined to include only the basic igneous rocks. Herein, we support the interpretation of Myers (1985). However, for ease of reference, the term ‘Fraser Complex’ is applied sensu lato to the entire package of rocks bounded by the Fraser and Coramup Faults (Figure 1). Metasedimentary rocks and gneisses which occur between the mafic units were attributed to the Biranup Complex by Myers (1985, 1995) and are termed the ‘supracrustal rocks’ in this work. Relationships between magmatism, metamorphism and deformation in the Fraser Complex, Western Australia: constraints from new SHRIMP U–Pb zircon geochronology* D. J. CLARK, 1 P. D. KINNY, 2 N. J. POST 1 and B. J. HENSEN 1 1 School of Geology, University of New South Wales, Sydney, NSW 2052, Australia. 2 Tectonics Special Research Centre, School of Applied Geology, Curtin University of Technology, GPO Box U1987, Perth, WA 6845, Australia. SHRIMP U–Pb zircon isotopic data have been obtained for four samples collected from granitoids and paragneisses in the Fraser Complex, a large composite metagabbroic body cropping out in the Mesoproterozoic Albany–Fraser Orogen of Western Australia. The data are combined with the results of field mapping and petrographic analysis to revise a model for the geological evolution of the Fraser Complex. Three main phases of deformation are recognised in the Fraser Complex (D1–3) associated with two metamorphic events (M1–2), which involve four distinguishable episodes of recrystallisation. The first metamorphic event recognised (M1a/D1) reached granulite facies and is characterised by peak T 800°C and P = 600–700 MPa. A syn-M1a/D1 charnockite has a U–Pb SHRIMP zircon age of 1301  6 Ma, which also provides an estimate for the age of intrusion of Fraser Complex gabbroic rocks. Disequilibrium textures comprising randomly oriented minerals (M1b), consistent with approximately isobaric cooling, formed in various lithologies in the interval between D1 and D2. Post-D1, pre-D2 granites intruded at 1293  8 Ma and were foliated during the D2 event, which culminated in the burial of the Fraser Complex to depths equivalent to 800–1000 MPa. Following burial, pyroxene granulites on the western boundary of the complex were pervasively retrogressed to garnet amphibolite (M2a). An igneous crystallisation age of 1288  12 Ma from a syn-M2a aplite dyke suggests that retrogression may have occurred only a few millions of years after the peak of granulite facies metamorphism. Exhumation to depths of less than ~400 MPa occurred within ~20–30 million years of the M2a pressure peak. Associated deformation (D3) is characterised by the devel- opment of mylonite and transitional greenschist/amphibolite facies disequilibrium textures (M2b). Key words: Albany–Fraser Orogen, Fraser Complex, geochronology, Mesoproterozoic. *Tables 2 and 3 [indicated by an asterisk (*) in the text and listed at the end of the paper] are Supplementary Papers lodged with the National Library of Australia (Manuscript Section); copies may be obtained from the Business Manager, Geological Society of Australia.