EVOLUTION OF AN ARCHEAN METAMORPHIC BELT - A CONVENTIONAL AND SHRIMP U-PB STUDY OF ACCESSORY MINERALS FROM THE JIMPERDING METAMORPHIC BELT,YILGARN CRATON, WEST AUSTRALIA

U-Pb TIMS analyses of zircon, monazite, titanite, and apatite combined with SHRIMP U-Th-Pb analyses of zircons from magmatic and metasedimen tary rocks of the Jimperding Metamorphic Belt in the southwestern part of the Yilgarn craton (Western Australia), provide reliable informati on on the evolution of this belt. SHRIMP analyses on single detrital z ircon grains suggest the sediments originated from Archean sources sim ilar in age to the Narryer Gneiss Complex. Deposition of the elastic m etasediments is bracketed by the youngest concordant grain (3055 +/- 1 2 Ma) and the minimum age of a possible amphibolite dike crosscutting the sediments (2711 +/- 7 Ma). SHRIMP and TIMS analyses on zircons fro m a porphyritic granite and an orthogneiss indicate that magmatism occ urred during the prograde stage of a regional metamorphic event (2660- 2670 Ma). Metamorphic monazites from pelitic schists define an age of 2661 +/- 1 Ma that relates to mineral growth, also during the prograde stage of metamorphism. Peak metamorphism was reached at ca. 2650 Ma, as demonstrated by titanite from a deformed orthogneiss (2649 +/- 4 Ma ). This period is coeval with the production of granulitic facies asse mblages farther east and with the age of magmatic zircons from the adj acent Katrine syenite. By combining age estimates for monazite growth in pelitic terranes with closure temperatures for other accessory mine rals, the rates of thermal processes accompanying the late Archean reg ional metamorphism in the southwestern Yilgarn Craton can be assessed. During prograde metamorphism, the heating rate was ca. 15 degrees C M a(-1) followed by a post-metamorphic cooling from approximately -10 de grees C Ma(-1) to -1/-2 degrees C Ma(-1).