Late Neoproterozoic passive margin of East Gondwana: Geochemical constraints from the Anakie Inlier, central Queensland, Australia

Abstract

Development of the East Gondwana passive margin and when it occurred are constrained by the composition of low grade mafic schists and U-Pb ages of detrital zircons in psammitic schists from the Bathampton Metamorphics in the Anakie Inlier of central Queensland. These rocks show considerable variation in light lithophile elements due to post-magmatic processes. They have flat heavy rare earth element patterns, low-TiO 2 (<2 >wt%) contents and their immobile element Ti, V, Y, La, Nb, Th and Zr values, indicate that they have an NMORB-like magmatic affinity. However, they differ from N-MORB in that they show light rare earth depleted patterns and lower incompatible trace element contents. Their relative low abundance and association with metasediments suggest they formed in a magma-poor rifted margin setting. They are associated with psammitic rocks with detrital zircon ages indicating probable deposition in the late Neoproterozoic at ca 600 Ma. A magma-poor rifted margin in northeastern Australia differs from the volcanic passive setting that occurred in southeastern Australia at this time. These findings support development of the East Gondwana margin at 600 Ma that may have been related to rifting of a microcontinent off East Gondwana well after the breakup of Rodinia at ca 750 Ma.

Orogen-perpendicular structures in the central Tasmanides and implications for the Paleozoic tectonic evolution of eastern Australia

“…19 substrate crust at the central part of the Thomson Orogen could have formed by rifting in the Early Cambrian (Glen, 2005;Fergusson et al, 2009;Glen, 2013;Glen et al, 2013).…”

Crustal architecture of the Thomson Orogen in Queensland inferred from potential field forward modelling

“…Neoproterozoic to early Cambrian deposition in the Thomson Orogen (Murray & Kirkegaard 1978;Murray 1994; Draper 2006;Brown et al 2014;Carr et al 2014) may reflect a Neoproterozoic passive margin setting, which has been interpreted further east in the adjacent Anakie Inlier, Charters Towers and Greenvale provinces and further south in the Koonenberry Belt and Adelaide Fold Belt (Fergusson et al 2001(Fergusson et al , 2007a(Fergusson et al , 2009. Alternatively, Neoproterozoic to early Cambrian deposition in the Thomson Orogen may reflect the interior extensional architecture of the region during the Rodinia break-up, which occurred further east (Spampinato et al 2015a).…”

Early Palaeozoic continental growth in the Tasmanides of northeast Gondwana and its implications for Rodinia assembly and rifting

“…The northeast Gondwana margin in the Late Neoproterozoic to early Paleozoic, as exemplified by the development of the Thomson Orogen, has formed in several discrete phases: (1) a phase of rifting and passive margin development associated with the formation of Late Neoproterozoic sedimentary and mafic igneous units (Direen and Crawford, 2003a, b;Fergusson et al, 2009;Greenfield et al, 2011), (2) Cambrian convergence culminating in the Middle to Late Cambrian Delamerian Orogeny (Foden et al, 2006), an event associated with widespread continental growth in eastern Australia, (3) an Ordovician extensional event associated with backarc sedimentation, deformation and silicic calc-alkaline igneous activity (Fergusson and Henderson, 2013), and (4) compressional deformation and reworking in the Late Ordovician -Early Silurian Benambran Orogeny (Glen, 2005).…”

“…Others have argued, based on the presence of tholeiitic and alkaline mafic volcanic rocks in various parts of the Tasmanides, that rifting and separation of at least small continental fragments occurred at around 580 Ma (Direen and Crawford 2003a, b;Fergusson et al, 2009;Greenfield et al, 2011). Alternatively, breakup at around 560 Ma was favoured by Veevers et al (1997) based on an inferred 400 Ma duration of a Pangean supercycle and further emphasised by Veevers (2000Veevers ( , 2004.…”