Geology and geochemistry of Archaean granites in the Kalgoorlie region of the Eastern Goldfields, Western Australia: a syn-collisional tectonic setting?

Abstract

Granites in the Kalgoorlie region of the Archaean Yilgarn Craton are predominantly biotite granodiorite and monzogranite with some hornblende-bearing varieties. Granites are divided, on the basis of field relationships, petrography and chemical composition, into five supersuites. An older supersuite containing four suites pre-dates regional folding and four supersuites post-date regional folding. The potassic composition of the mainly silica-rich granites (> 68% SiO 2) suggest that the most appropriate source for the majority of supersuites is continental crust with a composition in the range tonalite to granodiorite. Most supersuites evolved by fractional crystallization, mainly of biotite and plagioclase. Some suites contain synplutonic dykes and microgranite xenoliths that crystallized from enriched, mantle-derived magmas. There was only limited and local chemical interaction between granite and mantle-derived magmas. Geometric and temporal relationships between regional structures and granites indicate that the granites were emplaced during a major orogenic event. However, S-type granites which are widespread in some modern syn-collision settings, are absent in the Kalgoorlie region. The predominance of high fO 2, I-type granites in the study area probably reflects the absence of large, graphite-bearing metasedimentary accumulations in the lower crustal source regions. The distribution of suites and supersuites implies a common source region beneath the Kalgoorlie and Gindalbie granite-greenstone terranes suggesting that they shared a common geological history dating back to late greenstone deposition.