| Summary: | The Tonian to Ediacaran geology of Tasmania, Australia preserves an extensive record of continental rifting related to the Neoproterozoic opening of the Pacific Ocean. We integrate new and previously published structural, stratigraphic, sedimentary provenance, age, and geochemical data to establish four tectonostratigraphic stages in Tasmania that formed during three episodes of Neoproterozoic rifting. Rift Event 1 initiated with Tonian (780–750 Ma) intraplate magmatism and clastic sedimentation and was followed by deposition of an eastward thickening and deepening succession of ≤ 780 Ma–730 Ma locally sourced siliciclastic strata and carbonate (tectonostratigraphic stage 1). Cryogenian glaciogenic strata and thick successions of mafic volcaniclastic turbidites (tectonostratigraphic stage 2) contain unimodal 670–640 Ma detrital zircon age populations and may record a second rift event (Rift Event 2). Final rifting (Rift Event 3) involved voluminous ca. 580 Ma basaltic volcanism and active extensional faulting (tectonostratigraphic stage 3) and was followed by latest Ediacaran to early Cambrian sag-phase deposition (tectonostratigraphic stage 4). Neoproterozoic rifting in Tasmania is broadly contemporaneous with punctuated Tonian to Ediacaran rifting along the paleo-margins of the Pacific Ocean in southeast Australia, East Antarctica, and western Laurentia. Rift Event 1 in Tasmania may record the rifting of Australia-Antarctica from western Laurentia to form the nascent Pacific Ocean. Geological correlations are consistent with models in which Tasmania remained attached to either eastern Australia-Antarctica or western Laurentia during the late Tonian and Cryogenian before being isolated as a microcontinent in the late Ediacaran during Rift Event 3.
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