<div>Archean crustal evolution, and its tectonic paradigm, can be directly linked to the evolution of the mantle, the hydrosphere-atmosphere, oxygenation of the Earth, and the formation and storage of ore deposits. Hence, it is vital to understand the evolution of the early crust if we are to understand our planet’s evolution as well as transformational events in its history.</div><div> The collection of vast amounts of isotopic data, especially U-Pb, Sm-Nd, Lu-Hf, and δ18O, over the last 30 years, has significantly advanced our understanding of crustal processes and their timing. However, we rarely look at these data in a spatial context. This study aims to constrain the time-space evolution of the south-east Superior Craton, Canada, by mapping the zircon Hf-O isotopes and trace element data from 148 Archean magmatic rocks (6340 total analyses).</div><div> In Lu-Hf space, the dataset demonstrates the highly juvenile nature of this region, with the majority of values between εHfi +6 and +2. When plotted spatially, the most juvenile data (+4 to +6 εHfi) delineate an E-W oriented zone, broadly in-line and sub-parallel to the Cadillac-Larder Lake and Porcupine-Destor structures. Surrounding this juvenile region is less juvenile crust (0 to +3 εHf). Corresponding δ18O values show that light to mantle-like data (3.0-5.6‰) correlate with the most juvenile crust imaged by the εHf, with heavier δ18O (5.8-7.5‰) plotting to the south, east and west of this zone. Zircon trace element proxies for hydration (Eu/Eu*), oxidation (ΔFMQ using Ti, Ce, U), and continental vs. oceanic origin (Ui/Yb) replicate the pattern observed in the Lu-Hf and δ18O. This suggests that, broadly, the SE Superior consists of a central E-W orientated juvenile zone consisting of the most reduced, least hydrated, least continental, and most high-temperature hydrothermally-altered crust. This zone is surrounded by crust which is more hydrated, oxidised, has a greater supracrustal δ18O component, and is slightly less juvenile. The major ore systems of the Abitibi subprovince, including VMS, gold and komatiite-hosted Ni-Cu-PGE systems, fall within the E-W highly-juvenile zone.</div><div> Current tectonic models for this region of the Superior Craton range from (1) long-lived Neoarchean subduction across the whole Abitibi tectono-thermal ‘event’ (2750-<2695 Ma) – ‘horizontal’ tectonics; and (2) a variety of non-arc processes such as plume-related crustal overthickening (i.e., oceanic plateau), sagduction/drip tectonics, and subcretion, amongst others – ‘vertical’ tectonics. Models combining arc and non-arc processes have also been suggested (i.e., plume-arc interaction), and our data broadly support a combined model. We propose the E-W zone delineated by the various geochemical data represents a paleo-rift zone, driven by ambient mantle or mantle plume processes. The dry, reduced, oceanic character of the zone appears to preclude an arc or back-arc setting prior to ca. 2.7 Ga. However, temporal changes in hydration, oxidation, and the increased heavy δ18O component at ca. 2.7 Ga suggest a major geodynamic shift, potentially marking the onset of subduction and associated compression. This is contribution 2020-050 of the Mineral Exploration Research Centre (MERC) Metal Earth project.</div><div> This Abstract was submitted/presented to the 2023 6th International Archean Symposium (6IAS) 25 - 27 July (https://6ias.org/)

<div>The ‘Major crustal boundaries of Australia’ data set synthesises more than 40 years of acquisition of deep seismic reflection data across Australia, where major crustal-scale breaks, often inferred to be relict sutures between different crustal blocks, have been interpreted in the seismic reflection profiles. The widespread coverage of the seismic profiles now provides the opportunity to construct a map of major crustal boundaries across Australia. Starting with the locations of the crustal breaks identified in the seismic profiles, geological (e.g. outcrop mapping, drill hole, geochronology, isotope) and geophysical (e.g. gravity, aeromagnetic, magnetotelluric, passive seismic) data are used to map the crustal boundaries, in map view, away from the seismic profiles. For some of these boundaries, a high level of confidence can be placed on the location, whereas the location of other boundaries can only be considered to have medium or low confidence. In other areas, especially in regions covered by thick sedimentary successions, the locations of some crustal boundaries are essentially unconstrained. </div><div>The ‘Major crustal boundaries of Australia’ map shows the locations of inferred ancient plate boundaries, and will provide constraints on the three dimensional architecture of Australia. It allows a better understanding of how the Australian continent was constructed from the Mesoarchean through to the Phanerozoic, and how this evolution and these boundaries have controlled metallogenesis. It is best viewed as a dynamic dataset, which will need to be refined and updated as new information, such as new seismic reflection data, becomes available.</div><div><br></div>

The Lu-Hf isotopic system, much like the Sm-Nd isotopic system, can be used to understand crustal evolution and growth. Crustal differentiation processes yield reservoirs with differing initial Lu/Hf values, and radioactive decay of 176Lu results in diverging 176Hf/177Hf between reservoirs over time. This chapter outlines the fundamentals of the Lu-Hf isotopic system, and provides several case studies outlining the utility of this system to mineral exploration and understanding formation processes of ore deposits. The current, rapid, evolution of this field of isotope science means that breadth of applications of the Lu-Hf system are increasing, especially in situations where high-precision, detailed analyses are required. <b>Citation:</b> Waltenberg, K. (2023). Application of the Lu–Hf Isotopic System to Ore Geology, Metallogenesis and Mineral Exploration. In: Huston, D., Gutzmer, J. (eds) <i>Isotopes in Economic Geology, Metallogenesis and Exploration</i>. Mineral Resource Reviews. Springer, Cham. https://doi.org/10.1007/978-3-031-27897-6_7