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

Abstract

U-Pb TIMS analyses of zircon, monazite, titanite, and apatite combined with SHRIMP U-Th-Pb analyses of zircons from magmatic and metasedimentary rocks of the Jimperding Metamorphic Belt in the southwestern part of the Yilgarn craton (Western Australia), provide reliable information on the evolution of this belt. SHRIMP analyses on single detrital zircon grains suggest the sediments originated from Archean sources similar in age to the Narryer Gneiss Complex. Deposition of the clastic metasediments is bracketed by the youngest concordant grain ($$3055 \pm 12 Ma$$) and the minimum age of a possible amphibolite dike crosscutting the sediments ($$2711 \pm 7 Ma$$). SHRIMP and TIMS analyses on zircons from a porphyritic granite and an orthogneiss indicate that magmatism occurred during the prograde stage of a regional metamorphic event (2660-2670 Ma). Metamorphic monazites from pelitic schists define an age of $$2661 \pm 1 Ma$$ 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 ($$2649 \pm 4 Ma$$). This period is coeval with the production of granulitic facies assemblages farther east and with the age of magmatic zircons from the adjacent Katrine syenite. By combining age estimates for monazite growth in pelitic terranes with closure temperatures for other accessory minerals, the rates of thermal processes accompanying the late Archean regional metamorphism in the southwestern Yilgarn Craton can be assessed. During prograde metamorphism, the heating rate was ca. $$15^{\circ}C Ma^{-1}$$ followed by a post-metamorphic cooling from approximately $$-10^{\circ}C Ma^{-1}$$ to $$-l/-2^{\circ}C Ma^{-1}$$.