Lead isotope systematics of ore systems of the Macquarie Arc — Implications for arc substrate

Spatial variations in lead isotopes, Tasman Element, eastern Australia

“…The zone of low μ associated with the Macquarie Arc is also characterised by Δt values commonly in excess of 150 Myr, suggesting that the melts that produced these rocks were derived either directly from the subducting proto-Pacific plate or from mantle strongly metasomatised by volatiles (including lead) extracted from this plate. This interpretation is compatible with that of Forster et al (2011), who found that deposits in the Macquarie Arc derived lead from a mantle-like lead isotope reservoir (i.e. subducted proto-Pacific oceanic crust) without significant contributions of crustal lead (i.e.…”

Ordovician marginal basin evolution near the palaeo-Pacific east Gondwana margin, Australia

“…Fergusson (2009) devised a different solution whereby the Ordovician arc lay proximal, but oblique to, the continent margin, resulting in simultaneous turbidite deposition in both back-and fore-arc regions prior to rotation of the arc to its present orientation. However, this model does not explain the observed identical stratigraphic transitions and sedimentation patterns in both foreand back-arc basins, nor does it offer satisfactory solutions for the lack of provenance mixing in either fore-or back-arc, or the absence of any trace of subducted sediment in the volcanic geochemistry (Carr et al 1995;Crawford et al 2007b;Forster et al 2011).…”

“…2, columns A and F) (Glen 2005;Glen et al 2009a); and the lack of provenance mixing between the volcanic rocks and flanking turbidites. Despite the proximity of the sediments, there is no trace element or Pb-isotope evidence for the inclusion of subducted sediment (Carr et al 1995;Crawford et al 2007b;Forster et al 2011), nor are there proximal subduction complexes or features indicative of arc facing (Glen 2005). sequences, (3) re-evaluation of contact relationships, and (4) integration of data from a disrupted harzburgite that lies between the western two belts of the 'arc'.…”

Refining accretionary orogen models for the Tasmanides of eastern Australia

“…Although it is not known when the Macquarie volcanics were initiated, Phase 1 predates 480 Ma and is thus coeval with post-kinematic granites intruding the Kanmantoo Group in South Australia. The general lack of continent-derived detritus (Glen et al 1998;Crawford et al 2007;Meffre et al 2007;Quinn et al in press), the primitive nature of Pb isotopes (Carr et al 1995;Forster et al 2011), and the positive whole rock eNd of lavas and intrusive rocks (Wyborn & Sun 1993;Crawford et al 2007), are all consistent with formation on primitive igneous crust.…”