<p>The Mesoproterozoic Roper Group of the McArthur Basin has excellent petroleum potential, but its poorly constrained post-depositional history has hampered resource exploration and management. The Derim Derim Dolerite occupies an important position in the regional event chronology, having intruded the Roper Group prior to deformation associated with the ‘Post-Roper Inversion’ event. It was assigned a magmatic crystallisation age of 1324 ± 4 Ma (uncertainties are 95% confidence unless otherwise indicated) in 1997, based on unpublished Sensitive High Resolution Ion Micro Probe (SHRIMP) U-Pb analyses of dolerite-hosted baddeleyite from sample 97106010, collected from the Derim Derim Dolerite type locality in outcrop within the northwestern McArthur Basin. Herein, we refine these data via Isotope Dilution-Thermal Ionisation Mass Spectrometry (ID-TIMS) analysis of baddeleyites plucked from the SHRIMP grain-mounts, which yielded a precise mean 207Pb/206Pb date of 1327.5 ± 0.6 Ma. This date is significantly older than a baddeleyite U-Pb ID-TIMS date of 1313.8 ± 1.3 Ma recently obtained from dolerite ALT-05, sampled in Pacific Oil and Gas Ltd drillhole Altree 2, near the northern margin of the Beetaloo Sub-basin, and 200 km south of 97106010. This pair of results indicates that Derim Derim Dolerite magmatism spanned at least 10-15 Ma. Previously documented geochemical variation in Mesoproterozoic mafic rocks across the Northern Territory (such as the 1325 ± 36 Ma (2σ) Galiwinku Dolerite in the northern McArthur Basin, 1316 ± 40 Ma phonolites intruding the eastern Pine Creek Orogen, and 1295 ± 14 Ma gabbro in the Tomkinson Province) may reflect episodic pulses of magmatism hitherto obscured by the low precision of the available isotopic dates. <p><b>Citation:</b> Bodorkos, S., Yang, B., Collins, A.S., Crowley, J., Denyszyn, S.W., Claoue-Long, J.C., Anderson, J.R. and Magee, C., 2020 Precise U–Pb baddeleyite dating of the Derim Derim Dolerite: evidence for episodic mafic magmatism in the greater McArthur Basin. In: Czarnota, K., Roach, I., Abbott, S., Haynes, M., Kositcin, N., Ray, A. and Slatter, E. (eds.) Exploring for the Future: Extended Abstracts, Geoscience Australia, Canberra, 1–4.

The Mesoproterozoic Roper Group of the McArthur Basin has excellent petroleum potential but exploration has been hampered by poor constraints on its post-depositional history that has compromised understanding of the tectonostratigraphic evolution of the basin. The Derim Derim Dolerite occupies an important position in the event chronology of the McArthur Basin, having intruded the Roper Group prior to post-Roper basin inversion, and it is also a major component of Mesoproterozoic intraplate mafic magmatism in northern Australia. Since 1997, the Derim Derim Dolerite has been assigned a magmatic crystallisation age of 1324 ± 4 Ma (all uncertainties are 95% confidence), based on unpublished Sensitive High Resolution Ion Micro Probe (SHRIMP) U–Pb analyses on baddeleyite attributed to a dolerite sample from Bureau of Mineral Resources drill-hole Urapunga 5. Herein, we establish that the SHRIMP sample originated from the type locality of the Derim Derim Dolerite in outcrop 90 km northwest of Urapunga 5 and document the 207Pb/206Pb date interpreted from the 1997 dataset. New U–Pb SHRIMP reanalysis of the same grain-mounts yielded a mean 207Pb/206Pb date of 1320.1 ± 5.3 Ma, confirming the 1997 result, and Isotope Dilution-Thermal Ionisation Mass Spectrometry (ID TIMS) analysis of baddeleyites plucked from the mounts yielded a precise mean 207Pb/206Pb date of 1327.5 ± 0.6 Ma. This date is significantly older than a baddeleyite U–Pb ID-TIMS date of ca 1313 Ma recently reported elsewhere from dolerite in the Beetaloo Sub-basin 200 km to the south, indicating that magmatism attributed to the Derim Derim Dolerite spanned at least 10–15 Ma. Previously documented geochemical variation in Mesoproterozoic intraplate mafic rocks across the Northern Territory (such as the 1325 ± 36 Ma Galiwinku Dolerite in the McArthur Basin, 1316 ± 40 Ma phonolites in the Nimbuwah Domain of the eastern Pine Creek Orogen, and 1295 ± 14 Ma gabbro in the Tomkinson Province) may reflect episodic pulses of magmatism hitherto obscured by the low precision of the available isotopic dates. The timing and geochemistry of Derim Derim-Galiwinku mafic igneous activity is strikingly similar to that of the Yanliao Large Igneous Province (LIP) in the northern North China Craton, and the global paucity of 1330–1300 Ma LIPs suggests that the North Australian Craton and the North China Craton were in relatively close proximity at that time.