Crustal evolution in the georgetown inlier, north queensland, Australia: a detrital zircon grain study

The use of in situ Hf-isotope analysis of zircon allows a more detailed evaluation of magma-generation processes than the analysis of whole-rock isotopic systems, and is a powerful tool for studying crustal evolution. Detrital zircon grains have been analysed by ill situ LAM-ICPMS and LAM-MC-ICPMS for U-Pb ages, trace element patterns and Hf-isotope composition to evaluate patterns of magma genesis and crustal evolution in the central part of the Precambrian Georgetown Inlier, North Queensland, Australia. Archean zircons and low epsilon(Hf), in Proterozoic and Phanerozoic magmatic zircons provide direct evidence for the existence of Archean crustal components in the Georgetown Inlier, although the surface geology is dominated by Mesoproterozoic basement rocks and Palaeozoic granitoids. Crustal evolution in the Georgetown Infier has involved at least three stages of heating and granitoid magmatism, possibly associated with basaltic magma underplating and/or overplating (1545-1585 Ma, 420 Ma and 340 Ma). In general, granitoids with high epsilon(Hf) are typical of the Percyvale area, closest to the Phanerozoic Tasman Fold Belt, and may reflect thinner and younger crust. Granitoids with less radiogenic Hf-isotope compositions are typical of the Einasleigh and Mount Surprise areas in the central part of the Inlier, and may reflect the presence of older and thicker crust. The most significant juvenile additions to the crust after Archean time occurred in the Emasleigh and Mount Surprise areas during Mesoproterozoic time and in the Percyvale area during Carboniferous time. In the Mount Surprise area, resorbed zircon cores of Mesoproterozoic age are overgrown by magmatic fints of Siluro-Devonian age. Similarities in the Hf-isotope composition of core-rim pairs suggest that the large range in EHf observed in zircons from SiluroDevonian granitoids reflects remelting of a heterogeneous 1545-1585 Ma old crust, rather than mixing between juvenile and crustal sources. Crustal remelting has been the main process responsible for the production of granitoid magmas in the Georgetown Inlier. However, minor addition of mantle-defived material may have occurred during both Mesoproterozoic and Carboniferous time. Similarities and differences in the crustal evolution of the Mt Isa, Broken Hill and Georgetown blocks suggest that the Proterozoic history of the Australian continental margin involved the accretion and subsequent dispersal of individual, originally Archean, microcomments. (c) 2007 Elsevier B.V. All rights reserved.