Late Archaean granites of the southeastern Yilgarn Block, Western Australia: age, geochemistry, and origin

Abstract

Late Archaean granitic rocks from the southern Yilgarn Craton of Western Australia have a close temporal relationship to the basaltic and komatiitic volcanism which occurs within spatially associated greenstone belts. Greenstone volcanism apparently began ∼2715 Ma ago, whereas voluminous felsic magmatism (both extrusive and intrusive) began about 2690 Ma ago. A brief but voluminous episode of crust-derived magmatism ∼2690-2685 Ma ago resulted in the emplacement of a diverse assemblage of plutons having granodioritic, monzogranitic and tonalitic compositions. This early felsic episode was followed immediately by the emplacement of mafic sills, and, after a further time delay, by a second episode of voluminous crust-derived magmatism dominated by monzogranite but containing plutons covering a wide compositional range, including diorite, granodiorite and tonalite. The products of this 2665–2660 Ma magmatic episode now form a significant fraction of the exposed southern Yilgarn Craton. Later magmatism, which continued to at least 2600 Ma ago, appears largely restricted to rocks having unusually fractionated compositions.The magmatic sequence basalt-voluminous crust-derived magmatism-later diverse magmatism, is interpreted in terms of a dynamically-based model for the ascent of the head of a new mantle plume. In this model basalts and komatiites are derived by decompression melting of rising plume material, and the crust-derived magmas result after conductive transport of heat from the top of the plume head into overlying continental crust. This type of magmatic evolution, the fundamentally bimodal nature of the magmatism, the presence of high-Mg volcanics (komatiites), and the areal extent of the late Archaean magmatic event, are all suggested to be characteristic of crustal reworking above mantle plumes rather than resulting from other processes, such as those related to subduction.

Geochemical and Nd isotope constraints on petrogenesis of granitoids from NW part of the eastern Dharwar craton: Possible implications for late Archaean crustal accretion

“…Models suggested for late Archaean crust formation can be broadly divided into two groups viz. subduction-related accretion (Card, 1990;de Wit, 1998;Dirks and Jelsma, 1998;Kusky, 1989;Stevensen et al, 2009) and mantle plume-related growth (Chardon et al, 1998;Hill et al, 1992;Jayananda et al, 2000;Stein and Hofmann, 1994). Similar divergence of views exists for the late Archaean crust formation of the Dharwar craton, southern India.…”

Proterozoic basement provinces of southern and southwestern Australia, and their correlation with Antarctica

“…It may represent reworked Yilgarn Craton , although its youngest components (2595-2575Ma) are 5-25 Ma younger than any plutons dated in adjacent parts of the craton (e.g. Hill et al 1992;Nelson 1998), and Myers et al (1996) interpreted it as an allochthonous Archaean block accreted to the Yilgarn Craton during the Albany-Fraser event. The Dalyup Gneiss comprises biotite-hornblende granodiorite and monzogranite gneiss with SHRIMP U-Pb zircon crystallization ages of 1695-1634Ma and TD~ Nd model ages of 2.2-2.1 Ga .…”

Constraints on the age of granitoid emplacement, metamorphism, gold mineralization, and subsequent cooling of the Archean greenstone terrane at Big Bell, Western Australia

“…At present, no intrnsions with ages similar to that of the main gold-sulfide-scheelite mineralization have been identified in the Big Bell mine area, and a genetic relationship to a specific calc-alkaline pluton cannot be established. In other parts of the Yilgarn craton, however, large plutons of biotitegranite, dated at 2660 to 2665 Ma and characterized by K feldspar megacrysts, are exposed in several granitoid batholiths (Hill et al, 1992). There is certainly no gap in time between gold mineralization at Big Bell and calc-alkaline magmatic activity in the craton.…”