Implications of radiolarian research for analysis of subduction complex terranes in the New England Orogen, NSW, Australia

Abstract

Radiolarians provide important age constraints on geologically complex strata in the New England Orogen of eastern Australia. Several terranes interpreted as subduction complexes were undated prior to radiolarian studies. Radiolarian faunas indicate that the Djungati terrane is significantly younger than the previously inferred Ordovician to Sulurian age range. Basalt-chert successions in the Djungati terrane developed during the Silurian to Late Devonian in an environment which was far from the influence of terrigenous sedimentation. Radiolarians from tuffs within overlying arc-derived volcaniclastic sequences constrain the timing of tectonic assembly of the terrane at a convergent margin to the latest Devonian-Early Carboniferous. The extensive, but previously undated, Anaiwan terrane also contains radiolarians which indicate a latest Devonian to Early Carboniferous age for siliceous oceanic sediments. These sediments were accreted into a subduction complex. Volcaniclastic sediments within this subduction complex contain radiolarians which indicate that it developed during the Early Carboniferous. Radiolarians in the Willowie Creek beds provide the first age constraints (Late Devonian) for another lithotectonic entity, the Yugambal terrane, which is located along the eastern edge of the southern New England orogen. Many of the recently determined radiolarian ages are at variance with age estimates used to develop models for the tectonic development of the orogen. These new age data require major reappraisal of models. Detailed analysis of the geological evolution of individual terranes is required before an integrated model for the entire orogen can be developed.