Mafic volcanic rocks on King Island, Tasmania: evidence for 579 Ma break-up in east Gondwana

• Published in: Precambrian Research
• Main Authors: Meffre, S, Direen, N, Crawford, AJ, Kamenetsky, VS
• Format: Article in Journal/Newspaper
• Language: English
• Published: Elsevier Science BV 2004
• Subjects: Earth Sciences; Geology; Igneous and Metamorphic Petrology; King Island; North Atlantic
• Online Access: https://doi.org/10.1016/j.precamres.2004.08.004; http://ecite.utas.edu.au/32658

The eastern coast of King Island in southeastern Australia exposes a thick, well-preserved sequence of latest Neoproterozoic volcanic, and related shallow intrusive rocks. These rocks are associated with shallow marine carbonates and siltstones and pass up into massive conglomerates representing a marine flooding event and unconformity, during continental break-up and subsequent volcanic passive margin formation. Unusual differentiated sills (Grimes Intrusive suite) with extreme internal variation (wehrlite to andesite compositions) intrude deformed Proterozoic metasediments of the Rodinian basement. A thin, basal tholeiitic basaltic volcanic unit (City of Melbourne Volcanics) is less contaminated than the underlying sills, and preceded eruption of a thick sequence of highly depleted picritic pillows, sub-aerial flows and hyaloclastites (Shower Droplet Volcanics). The picrite sequence is overlain by thick tholeiitic basalts and reworked volcanogenic conglomerates (Bold Head Formation) that show a strong compositional similarity to enriched mid ocean ridge basalts. Both the picrites and the upper tholeiitic basalts are not crustally contaminated and have an Nd-Sm isochron age of 579 16 Ma with initial Nd of +4.2. The lithostratigraphy and range of compositions represented are analogous to early magmatism associated with continental break-up and volcanic passive margin formation, including voluminous Seaward Dipping Reflector Sequences, in the Mesozoic North Atlantic volcanic margins. 2004 Elsevier B.V. All rights reserved.