University of Tasmania
Browse
51617.pdf (3.72 MB)

Re-evaluation of contact relationships between the Ordovician volcanic belts and the quartz-rich turbidites of the Lachlan Orogen

Download (3.72 MB)
journal contribution
posted on 2023-05-16, 21:34 authored by Sebastien MeffreSebastien Meffre, Robert ScottRobert Scott, Glen, RA, Squire, RJ
Some published tectonic reconstructions of the eastern Lachlan Orogen in New South Wales have shown Ordovician volcanic and volcaniclastic rocks of the Macquarie Arc conformably overlying or interfingering with a coeval Ordovician quartz-rich turbidite sequence. Re-examination of key contacts between the volcanic and quartz-rich successions has found no evidence to support this interpretation, and suggests that the two packages are separate tectonostratigraphic terranes. The contacts between these two coeval successions are generally marked by major faults containing mylonites, cataclasites and, at some locations, fragments of mid-ocean ridge-type pillow basalt and chert. The quartz-rich turbidites are generally highly deformed and of higher metamorphic grade than the adjacent volcanics. At Oberon and Mudgee, contacts are faulted but there are no mylonites or significant differences in metamorphic grade. At Palmers Oaky and Black Springs, Silurian quartz-rich sandstones overlying the Ordovician volcanics have been mistakenly assigned to the Ordovician in previous studies. Throughout the Lachlan Orogen, there is no mixing of framework grains. Quartz-rich turbidite successions are dominated by quartz with lesser feldspar and rare tourmaline, zircon and monazite derived from recycled continental sources. In contrast, the volcaniclastic sandstones contain feldspar, clinopyroxene and lithic fragments derived from subduction-related clinopyroxene-phyric basalt and plagioclase-phyric andesite. Detrital-zircon populations also differ, with separate U/Pb age populations and almost no overlap. Comparison of the Ordovician sequences of the Lachlan Orogen with modern turbidites from continental- and arc-related sedimentary basins suggests that complete separation of sedimentary sources is only possible if the sandstones were deposited hundreds of kilometres apart, in separate tectonic environments. The two sequences were juxtaposed along major faults in the Late Ordovician or Early Silurian, probably when the Macquarie Arc collided with a thick Ordovician sedimentary wedge located on the Gondwanan continental margin.

History

Publication title

Australian Journal of Earth Sciences

Volume

54

Issue

2/3

Pagination

363-383

ISSN

0812-0099

Department/School

School of Natural Sciences

Publisher

Taylor & Francis

Place of publication

UK

Repository Status

  • Restricted

Socio-economic Objectives

Other mineral resources (excl. energy resources) not elsewhere classified

Usage metrics

    University Of Tasmania

    Exports

    RefWorks
    BibTeX
    Ref. manager
    Endnote
    DataCite
    NLM
    DC