Pinpointing Paleoarchean magmatic-hydrothermal events during the geodynamic and crustal evolution of the East Pilbara Terrane 

<p>The nature of Paleoarchean (>3.2 Ga) crustal accretion continues to be debated, in particular the onset and timing of subduction-like processes. Crust of this age is typically characterised by dome-and-keel geometry that is widely interpreted to be related to &#8220;sagduction&#8221; or the episodic dripping of denser, mafic volcanics into the mantle around buoyant silicic cratonic nuclei. This occurs during regional scale crust-mantle overturn events.</p><p>The exceptional preservation of the East Pilbara Terrane (EPT) has been instrumental in the development of this model and its role in Paleoarchean continental crust formation. The Emu Pool Supersuite (~3324-3290 Ma) represents a phase of voluminous silicic magmatism that has been attributed to overturn and sagduction within the EPT (e.g. Wiemer et al., 2018). However, the widespread occurrence of magmatic-hydrothermal Cu and Mo mineralisation, reported to be linked to this magmatic episode, have received little attention. Comparisons to Phanerozoic porphyry Cu-Mo deposits have been drawn (e.g. Barley & Pickard, 1999), which is intriguing as such porphyry-type deposits have a clear genetic link to arc magmatism and subduction processes as they require hydrous, Cl-rich magmatism (e.g. Tattich et al., 2021).</p><p>To date the chronological relationships of the magmatic-hydrothermal deposits to the major dome forming silicic magmatism is poorly constrained. In one deposit, hydrothermal activity is constrained by ¹⁸⁷Re-¹⁸⁷Os geochronology (Stein et al., 2007) to late to post Emu Pool Supersuite magmatism, yet this interpretation is hampered by issues relating to the &#955;¹⁸⁷Re uncertainty. Furthermore, interpretation of Paleoarchean geodynamics and magmatic evolution generally relies on micro-beam zircon U-Pb geochronological analyses, typically reported at single&#160;²⁰⁷Pb/²⁰⁶Pb date precision at >&#177;10 Myrs (2s), and presents challenges for accurately resolving geological processes and events.</p><p>We demonstrate that high-precision CA-ID-TIMS (Chemical Abrasion-Thermal-Ionisation Mass Spectrometry) zircon U-Pb geochronology, utilising ATONA low-noise detectors, can now routinely obtain precision of&#160; ~<&#177;200 kyrs (2s) on&#160;²⁰⁷Pb/²⁰⁶Pb dates of single zircon or fragments at ~3.3 Ga. By combining detailed field relationships, with unprecedented temporal precision, we show that the Mo-Cu hydrothermal mineralisation can be demonstrably linked to their host plutons and formation timescales can even be constrained to ~1 Myrs, comparable to Phanerozoic porphyry deposits. This study identifies that magmatic-hydrothermal systems were not synchronous across the EPT. Instead they occurred over >7 Myrs during the early phase of Emu Pool Supersuite and silicic magmatism within domes.</p><p>Whilst the geodynamic trigger for Mo and Cu magmatic-hydrothermal mineralisation at ~3.3 Ga remains enigmatic, we highlight their timing and occurrence should be accommodated within Paleoarchean geodynamic models. Furthermore, the results illustrate the potential of modern high-precision U-Pb geochronology to routinely examine Paleoarchean magmatic records at timescales that closely approximate known plutonic accretion rates within the Phanerozoic.</p><p>&#160;</p><p>References</p><p>Barley, & Pickard, (1999) Precambrian Research, 96, 41-62</p><p>Stein et al., (2007) Geochimica et Cosmochimica Acta, 71</p><p>Tattitch et al., (2021) Nature communications, 12, 1-11.</p><p>Wiemer et al., (2018) Nature Geoscience, 11, 357-361.</p>